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Europaisches Patentamt 
European Patent Office 
Office europeen des brevets 



llllflllllrlNltllllllllli; 

(H) EP 0 971 345 A1 



EUROPEAN PATENT APPLICATION 

published in accordance with Art. 158(3) EPC 



(43) Date of publication: 

12.01.2000 Bulletin 2000/02 



(21) Application number: 97949124.8 

(22) Date of filing: 17.12.1997 



(84) Designated Contracting States: 
DE FR GB IT NL 

(30) Priority: 19.12.1996 JP 33930496 
22.01 .1997 JP 931897 
24.09.1997 JP 25911097 

(71) Applicant: 

Matsushita Electric Industrial Co., Ltd. 
Kadoma-shi, Osaka 571-0050 (JP) 

(72) Inventors: 

• OSHIMA.M 

115-3,Katsura Minamitatsumicho 
Kyoto 615-8074 (JP) 

• KONISHI.Shinichi 
Nara 631 (JP) 

• TANAKA,Shin-ichi 
Kyoto 610-03 (JP) 



(51) Int. CI. 7 : G11B 11/10, G11B7/00, 
G06F 12/14 



(86) International application number: 
PCT/JP97/04664 



(87) International publication number: 

WO 98/27553 (25.06.1998 Gazette 1998/25) 



• KOISHI, Kenji 
Hyogo 669-13 (JP) 

• MORIYA, Mitsurou 
Nara 630-01 (JP) 

• GOTOH, Yoshiho 
Rm201, Parkside 22 
Joutou-ku,Osaka-shi Osaka 536 (JP) 

• TAKEMURA, Yoshinari 
Osaka 566 (JP) 

• MIYATAKE, Norio 
Kobe-shi Hyogo 655 (JP) 

• MURAKAMI, Motoyoshi 
Osaka 573 (JP) 

(74) Representative: 

Piesold, Alexander J. 
Frank B. Dehn & Co., 
European Patent Attorneys, 
179 Queen Victoria Street 
London EC4V 4EL (GB) 



(54) OPTICAL DISK, METHOD FOR RECORDING AND REPRODUCING WRITE-ONCE 

INFORMATION ON AND FROM OPTICAL DISK, OPTICAL DISK REPRODUCING DEVICE 
OPTICAL DISK RECORDING AND REPRODUCING DEVICE, DEVICE FOR RECORDING ' 
WRITE-ONCE INFORMATION ON OPTICAL DISK, AND OPTICAL DISK RECORDING DEVICE 

(57) An optical disk storing write-once information 
usable for protecting the copyright of the software by 
preventing the duplication, unauthorized use, etc., of the 
software. In the optical disk, a recording layer (213) is 
formed on a disk substrate (211) with a dielectric layer 
(212) inbetween. Then, an intermediate dielectric layer 
(214) and a reflecting layer (215) are successively lami- 
nated upon the recording layer (213), and an overcoat 
layer (216) is formed on the surface of the reflecting 
layer (215). A plurality of BCA (one of write-once identi- 
fication information systems) sections (220a and 220b) 
are recorded by lowering the vertical magnetic anisot- 
ropy of the recording layer (213). At the time of repro- 
duction, the write-once information is detected from 
differential signals. 




Q. 
UJ 



EP 0 971 345 A1 



Description 

FIELD OF THE INVENTION 

[0001] The present invention relates to an optical disk 
for recording, reproducing and erasing information. In 
particular, the present invention relates to an optical 
disk comprising write-once information that can be used 
for copyright protection, for example for copy-protection 
or protection from unauthorized use of software. 
Throughout this specification, "write-once information" 
refers to information that is recorded after finishing the 
disk manufacturing process. The present invention 
relates further to a method for recording and a method 
for reproducing write-once information on the optical 
disk, an apparatus for reproducing the optical disk, an 
apparatus for recording and reproducing the optical 
disk, an apparatus for recording write-once information 
on the optical disk, and an apparatus for recording on 
the optical disk. 

BACKGROUND OF THE INVENTION 

[0002] In recent years, the speed with which electronic 
calculators and information processing systems can 
process ever greater amounts of information has 
increased sharply. Together with the digitalization of 
audio and video information, this gave rise to the rapid 
dissemination of low-cost, high-volume auxiliary stor- 



the orientation of the magnetic field (this rotation occurs 
mainly due to two magneto-optical effects - the Kerr 
effect and the Faraday effect), is detected by a photode- 
tector though the change in the intensity of the irradi- 
5 ated light. In order to decrease the interference between 
opposite magnetizations and allow high-density record- 
ings, a magnetic material with perpendicular magnetic 
anisotropy is used for the recording layer of the optical 
disk. 

10 [0006] Moreover, when the data is reproduced, the 
reproduction signal level during data reproduction can 
be raised to detect the reproduction signal by using a 
layered structure for the recording layer: Several mag- 
netic thin films comprising an exchange coupling multi- 
15 layer or a magneto-static coupling multilayer. 

[0007] For the recording layer, a material is used that 
can record information by locally raising the tempera- 
ture or inducing a chemical reaction due to absorption 
of the irradiated laser light. The local variations in the 
20 recording layer can be detected by irradiating laser light 
of a different intensity or wavelength than that used for 
the recording and detecting the reproduction signal 
using the reflected or the transmitted light. 
[0008] Regarding such optical disks, there is a need 
25 for a way to protect the data on the disk with write-once 
information (identification data) that allows for copyright 
protection, for example copy protection and protection 
against unauthorized use of software. 
[0009] With the above configuration, it is possible to 



age devices and recording media therefor, especially 30 record disk information in TOC (or control data) areas 

ODIICa disks Wninh nan ho annaeearl »/»k kink •...» .... ' ' 



al disks, which can be accessed with high access 
speeds. 

[0003] The basic configuration of conventional optical 
disks is as follows: A dielectric layer is formed on top of 
a disk substrate, and a recording layer is formed on top 3t 
of the dielectric layer. On top of the recording layer, an 
intermediate dielectric layer and a reflecting layer are 
formed in that order. An overcoat layer is formed on top 
of the reflecting layer. 

[0004] The following is an explanation of how an opti- 40 
cal disk with the above configuration is operated. 
[0005] In the case of an optical disk having, in its 
recording layer, a magneto-optical layer with perpendic- 
ular magnetic anisotropy, the recording and erasing of 
information is performed by locally (a) heating the 45 
recording layer with a laser beam to a temperature with 
small coercive force above the compensation tempera- 
ture or to a temperature near or above the Curie tem- 
perature to decrease the coercive force of the recording 
layer in the irradiated portion, and (b) magnetizing the so 
recording layer in the direction of an external magnetic 
field. (This is also called "thermomagnetic recording" of 
information.). Moreover, for the reproduction of the 
recording signal, a laser beam with less intensity than 
the laser beam for recording or erasing irradiates the 55 
recording layer. The recording state of the recording 
layer, that is, the rotation of the polarization plane of the 
light that is reflected or transmitted in accordance with 



but when disk data is recorded with pre-pits, the disk 
information has to be administered stamper by stamper 
and cannot be administered user by user. 
[0010] Moreover, when information is recorded using 
a magnetic film or a film of a phase-reversible material, 
administrative information easily can be changed, which 
means that it easily can be rewritten (manipulated), so 
that the contents on the optical disk cannot be copyright 
protected. 

SUMMARY OF THE INVENTION 

[0011] It is an object of the present invention to solve 
the problems of the prior art. It is a further object of the 
present invention to provide an optical disk comprising 
write-once information that can be used for copyright 
protection, for example for copy-protection or protection 
from unauthorized use of software, a method for record- 
ing write-once information on an optical disk, a method 
for reproducing write-once information from an optical 
disk, an apparatus for reproducing optical disks, an 
apparatus for recording and reproducing optical disks, 
an apparatus for recording write-once information on 
optical disks, and an apparatus for recording on optical 
disks. 

[0012] In order to attain these objects, a first configu- 
ration of an optical disk in accordance with the present 
invention comprises a disk substrate and a recording 



2 



EP 0 971 345 A1 



layer on the disk substrate. The recording layer includes 
a magnetic film with a magnetic anisotropy in a direction 
perpendicular to a surface of the magnetic film. The 
optical disk stores write-once information formed by first 
recording areas and second recording areas in a pre- 5 
determined portion of the recording layer. A magnetic 
anisotropy in a direction perpendicular to a surface of 
the second recording areas is smaller than a magnetic 
anisotropy in a direction perpendicular to a surface of 
the first recording areas. The second recording areas 10 
are formed as stripe-shaped marks that are oblong in a 
radial direction of the disk. A plurality of the marks is 
arranged in a circumferential direction of the disk, the 
arrangement being based on a modulation signal of the 
write-once information. In accordance with this first con- 15 
figuration, an optical disk can be achieved, which com- 
prises write-once information that can be used for 
copyright protection, for example for copy-protection or 
protection from unauthorized use of software. 
[0013] It is preferable that the optical disk according to 20 
the first configuration further comprises an identifier 
indicating whether there is a row of a plurality of marks 
arranged in a circumferential direction of the disk. With 
this configuration, the system can be started in a short 
time. Moreover, in this configuration, it is preferable that 25 
the identifier indicating the row of marks is stored 
among control data. With this configuration, it is known 
when the control data is reproduced whether write-once 
information is stored, so that the write-once information 
can be reproduced reliably. 30 
[0014] It is preferable that in the optical disk according 
to the first configuration, the pre-determined portion 
comprising write-once information is at an inner perime- 
ter portion of the disk. With this configuration, the posi- 
tion of the optical head with respect to a radial direction 35 
of the disk can be determined with an optical head stop- 
per or address information of a bit signal. 
[0015] It is preferable that in the optical disk according 
to the first configuration, a difference between a lumi- 
nous energy that is reflected from the first recording 40 
areas and a luminous energy that is reflected from the 
second recording areas is below a certain value. It is 
particularly preferable that the difference between lumi- 
nous energy that is reflected from the first recording 
areas and luminous energy that is reflected from the 45 
second recording areas is not more than 10%. With this 
configuration, variations of the reproduction waveform 
accompanying changes of the reflected luminous 
energy can be suppressed. 

[0016] It is preferable that in the optical disk according 50 
to the first configuration, a difference between an aver- 
age refractive index of the first recording areas and an 
average refractive index of the second recording areas 
is not more than 5%, With this configuration, the differ- 
ence between luminous energy that is reflected from the 55 
first recording areas and luminous energy that is 
reflected from the second recording areas can be 
adjusted to not more than 10%. 



[0017] It is preferable that in the optical disk according 
to the first configuration, the magnetic anisotropy of the 
magnetic film of the second recording areas in an in- 
plane direction is dominant. With this configuration, 
using a reading device having a polarizer and a photo- 
detector the reproduction signal of the first recording 
areas, which corresponds to the write-once information, 
can be attained. Thus, the write-once information can 
be obtained rapidly and without using an optical head. 
[0018] It is preferable that in the optical disk according 
to the first configuration, at least a portion of the mag- 
netic film of the second recording areas is crystallized. 
With this configuration, the magnetic anisotropy perpen- 
dicular to the magnetic film of the second recording 
areas can be almost completely eliminated, so that the 
reproduction signal can be reliably detected as the dif- 
ference of the polarization orientation to the first record- 
ing areas. 

[0019] It is preferable that in the optical disk according 
to the first configuration, the recording layer comprises a 
multilayer magnetic film. With this configuration, the 
magnetically induced super resolution method "FAD" 
can be used as the reproduction method. Thus, signal 
reproduction with regions smaller than the laser beam 
spot becomes possible. 

[0020] A second configuration of an optical disk in 
accordance with the present invention comprises a disk 
substrate and a recording layer on the disk substrate. 
The recording layer includes a film that can be reversibly 
changed between two optically detectable states. The 
optical disk stores write-once information formed by first 
recording areas and second recording areas in a pre- 
determined portion of the recording layer. A luminous 
energy that is reflected from the first recording areas dif- 
fers from a luminous energy that is reflected from the 
second recording areas. The second recording areas 
are formed as stripe-shaped marks that are oblong in a 
radial direction of the disk. A plurality of the marks is 
arranged in a circumferential direction of the disk, the 
arrangement being based on a modulation signal for the 
write-once information. In accordance with this second 
configuration, an optical disk can be achieved, which 
comprises write-once information that can be used for 
copyright protection, for example for copy-protection or 
protection from unauthorized use of software. 
[0021] It is preferable that the optical disk according to 
the first configuration further comprises an identifier for 
indicating whether there is a row of a plurality of marks 
arranged in a circumferential direction of the disk. More- 
over, it is preferable that the identifier indicating the row 
of marks is stored among control data. 
[0022] It is preferable that in the optical disk according 
to the first configuration, the pre-determined portion 
comprising write-once information is at an inner perime- 
ter portion of the disk. 

[0023] It is preferable that in the optical disk according 
to the first configuration, the recording layer undergoes 
a reversible phase change between a crystalline phase 



3 



5 



EP 0 971 345 A1 



and an amorphous phase, depending on irradiation 
conditions for irradiated light. With this configuration, 
information can be recorded by utilizing an optical differ- 
ence based on a reversible structural change at the 
atomic level. Moreover, information can be reproduced 5 
as a difference of the reflected luminous energy or the 
transmitted luminous energy at a certain wavelength. 
Moreover, in this case, it is preferable that the difference 
between luminous energy that is reflected from the first 
recording areas and luminous energy that is reflected 10 
from the second recording areas is at least 10%. With 
this configuration, a reproduction signal of the first 
recording area, which corresponds to the write-once 
information, can be obtained reliably. Moreover, in this 
case, it is preferable that a difference between an aver- 15 
age refractive index of the first recording areas and an 
average refractive index of the second recording areas 
is at least 5%. With this configuration, the difference 
between the luminous energy reflected from the first 
recording areas and the luminous energy reflected from 2 o 
the second recording areas can be adjusted to at least 
10%. Moreover, in this case, it is preferable that the sec- 
ond recording areas of the recording layer are in a crys- 
talline phase. With this configuration, recording can be 
performed with excessive laser power. Furthermore, 25 
since the luminous energy reflected from the crystalline 
phase can be large, detection of the reproduction signal 
becomes easy. Moreover, in this case, it is preferable 
that the recording layer comprises a Ge-Sb-Te alloy. 
[0024] In a third configuration of an optical disk in 30 
accordance with the present invention, main information 
and write-once information is recorded, the write-once 
information being different for each disk, and the write- 
once information storing at least watermark production 
parameters for producing a watermark. In accordance 35 
with this third configuration, the following operations can 
be performed: When the watermark production parame- 
ters and the disk ID are recorded in the write-once infor- 
mation with absolutely no correlation between the disk 
ID and the watermark production parameters, it 40 
becomes impossible to guess the watermark from the 
disk ID. Thus, an illegal copier issuing a new ID and 
issuing an improper watermark can be prevented. 
[0025] It is preferable that in the optical disk according 
to the third configuration, the main information is 45 
recorded by providing convex-concave pits in a reflec- 
tive layer, and the write-once information is recorded by 
partially removing the reflective layer. 
[0026] It is preferable that in the optical disk according 
to the third configuration, the main information and the so 
write-once information are recorded by partially chang- 
ing a reflection coefficient of a reflective layer. 
[0027] It is preferable that in the optical disk according 
to the third configuration, a recording layer comprises a 
magnetic layer with a magnetic anisotropy in a direction 55 
perpendicular to a surface of the magnetic layer, the 
main information is recorded by partially changing a 
magnetization direction of the recording layer, and the 



write-once information is recorded by partially changing 
the magnetic anisotropy in the direction perpendicular 
to the surface of the magnetic layer. 
[0028] A first method for recording write-once informa- 
tion onto an optical disk (a) comprising a disk substrate, 
and a recording layer on the disk substrate, including a 
magnetic film with a magnetic anisotropy in a direction 
perpendicular to a surface of the magnetic film; and (b) 
storing write-once information formed by first recording 
areas and second recording areas in a pre-determined 
portion of the recording layer; comprises forming the 
second recording areas as a plurality of stripe-shaped 
marks that are oblong in a radial direction of the disk in 
a circumferential direction of the disk by irradiating laser 
light based on a modulation signal of the write-once 
information in a circumferential disk direction in the pre- 
determined portion of the recording layer in a manner 
that a magnetic anisotropy in a direction perpendicular 
to a surface of the second recording areas becomes 
smaller than a magnetic anisotropy in a direction per- 
pendicular to a surface of the first recording areas. In 
accordance with this first method for recording write- 
once information onto an optical disk, write-once infor- 
mation that can be used for copyright protection, for 
example for copy-protection or protection from unau- 
thorized use of software, can be efficiently recorded 
onto an optical disk. 

[0029] It is preferable that in the first method for 
recording write-once information, when the second 
recording areas are formed, a laser light source is 
pulsed in accordance with a modulation signal of phase- 
encoded write-once information, and the optical disk or 
the laser light is rotated. With this configuration, rotation 
variations can be eliminated, especially when the clock 
of a rotation sensor is used, so that the write-once infor- 
mation can be recorded with little fluctuations of the 
channel clock period. 

[00301 It is preferable that in the first method for 
recording write-once information, the optical diskfurther 
comprises a reflective layer and a protective layer on the 
disk substrate, and an intensity of laser light irradiated 
to form the second recording areas is smaller than an 
intensity of laser light destroying at least one of the disk 
substrate, the reflective layer and the protective layer. 
With this configuration, write-once information can be 
recorded at software companies or retailers. 
[0031] It is preferable that in the first method for 
recording write-once information, an intensity of laser 
light irradiated to form the second recording areas is an 
intensity for crystallizing at least a portion of the record- 
ing layer. With this configuration, the magnetic anisot- 
ropy of the recording layer perpendicular to the surface 
of the recording layer cannot be restored, so that manip- 
ulation of the write-once information can be prevented. 
[0032] It is preferable that in the first method for 
recording write-once information, an intensity of laser 
light irradiated to form the second recording areas is 
larger than an intensity of laser light heating the record- 



4 



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EP 0 971 345 A1 



ing layer to a Curie temperature. With this configuration, 
it is possible to decrease or eliminate the magnetic ani- 
sotropy of the recording layer perpendicular to the sur- 
face of the recording layer, especially when the intensity 
of the laser light is excessive. 

[0033] It is preferable that in the first method for 
recording write-once information, an intensity of laser 
light irradiated to form the second recording areas is an 
intensity for making a magnetic anisotropy of the mag- 
netic layer of the first recording areas in an in-plane 
direction dominant. 

[0034] It is also preferable that in the first method for 
recording write-once information, rectangularly stripe- 
shaped laser light is irradiated with a unidirectional con- 
vergence focusing lens onto the recording layer when 
the second recording areas are formed. 
[0035] It is also preferable that in the first method for 
recording write-once information, a light source of the 
laser light that is irradiated for forming the second 
recording areas is a YAG laser. In this case, it is prefer- 
able that a magnetic field above a certain value is 
applied to the recording layer while irradiating laser light 
from the YAG laser. With this configuration, write-once 
information can be recorded easily by partially changing 
the magnetic anisotropy perpendicular to the surface of 
the recording layer after aligning the magnetic anisot- 
ropy in a direction perpendicular to the surface of the 
recording layer. In this case, it is even more preferable 
that the magnetic field applied to the recording layer is 
at least 5kOe. 

[0036] A second method for recording write-once 
information onto an optical disk (a) comprising a disk 
substrate; and on the disk substrate a recording layer 
comprising a film that can be reversibly changed 
between two optically detectable states; and (b) storing 
write-once information formed by first recording areas 
and second recording areas in a pre-determined portion 
of the recording layer; comprises forming the second 
recording areas as a plurality of stripe-shaped marks 
that are oblong in a radial direction of the disk in a cir- 
cumferential direction of the disk by irradiating laser light 
based on a modulation signal of the write-once informa- 
tion in a circumferential disk direction in the pre-deter- 
mined portion of the recording layer in a manner that a 
luminous energy of light reflected from the first record- 
ing areas differs from a luminous energy of light 
reflected from the second recording areas. In accord- 
ance with this second method for recording write-once 
information onto an optical disk, write-once information 
that can be used for copyright protection, for example 
for copy-protection or protection from unauthorized use 
of software, can be efficiently recorded onto an optical 
disk. 

[0037] It is preferable that in the second method for 
recording write-once information, when the second 
recording areas are formed, a laser light source is 
pulsed in accordance with a modulation signal of phase- 
encoded write-once information, and the optical disk or 



the laser light is rotated. 

[0038] It is also preferable that in the second method 
for recording write-once information, the optical disk fur- 
ther comprises a reflective layer and a protective layer 
5 on the disk substrate, and an intensity of laser light irra- 
diated to form the second recording areas is smaller 
than an intensity of laser light destroying at least one of 
the disk substrate, the reflective layer and the protective 
layer. 

10 [0039] It is also preferable that in the second method 
for recording write-once information, an intensity of 
laser light irradiated to form the second recording areas 
is an intensity for crystallizing at least a portion of the 
recording layer. 

15 [0040] It is also preferable that in the second method 
for recording write-once information, rectangularly 
stripe-shaped laser light is irradiated onto the recording 
layer with a unidirectional convergence focusing lens 
when the second recording areas are formed. In this 

20 case, it is also preferable that a light source of the laser 
light that is irradiated for forming the second recording 
areas is a YAG laser. 

[0041] A third method for recording write-once infor- 
mation onto an optical disk comprises producing a 

25 watermark based on a disk ID; and overlapping the 
watermark on specific data to record it as write-once 
information. In accordance with this third method for 
recording write-once information onto an optical disk, 
the disk ID can be detected from the watermark, so that 

30 the origin of illegal copies can be determined. 

[0042] A first method for reproducing write-once infor- 
mation from an optical disk (a) comprising a disk sub- 
strate, and a recording layer on the disk substrate, the 
recording layer including a magnetic film with a mag- 

35 netic anisotropy in a direction perpendicular to a surface 
of the magnetic film; and (b) storing write-once informa- 
tion formed by first recording areas and second record- 
ing areas in a pre-determined portion of the recording 
layer, the first and second recording layers having differ- 

40 ent magnetic anisotropies in a direction perpendicular 
to a surface of the magnetic layer; comprises irradiating 
linearly polarized laser light onto the pre-determined 
portion; and detecting a change in a polarization orien- 
tation of light reflected from the optical disk or light 

45 transmitted through the optical disk. In accordance with 
this first method for reproducing write-once information 
from an optical disk, the write-once information can be 
reproduced easily. 

[0043] It is preferable that in the first method for repro- 
50 ducing write-once information, the linearly polarized 
laser light is irradiated onto the pre-determined portion 
after magnetizing the recording layer of the pre-deter- 
mined portion in one step by applying a magnetic field 
that is larger than a coercive force of the recording layer 
55 in the pre-determined portion. With this configuration, 
the polarization orientation detected from the first 
recording areas is normally constant, and the reproduc- 
tion signal can be obtained with a stable amplitude from 



5 



EP 0 971 345 A1 



10 



the difference with respect to the polarization orientation 
of the second recording areas. 
[0044] It is also preferable that in the first method for 
reproducing write-once information, the linearly polar- 
ized laser light is irradiated onto the pre-determined por- 
tion after aligning a magnetization of the recording layer 
of the pre-determined portion by applying a unidirec- 
tional magnetic field to the pre-determined portion while 
increasing the temperature of the recording layer in the 
pre-determined portion above the Curie temperature by 
irradiating laser light of constant luminous energy. With 
this configuration, after recording the write-once infor- 
mation, the signal can be reliably reproduced without 
being influenced by outside magnetic fields or the like. 
[0045] A second method for reproducing write-once 
information from an optical disk (a) comprising a disk 
substrate; and a recording layer on the disk substrate, 
the recording layer including a film that can be reversibly 
changed between two optically detectable states; and 
(b) storing write-once information formed by first record- 
ing areas and second recording areas with different 
reflection coefficients in a pre-determined portion of the 
recording layer; comprises irradiating focused laser light 
onto the pre-determined portion; and detecting a 
change in a luminous energy reflected from the disk. In 
accordance with this second method for reproducing 
write-once information from an optical disk, the write- 
once information can be reproduced easily. 
[0046] A first configuration of an apparatus for repro- 
ducing optical disks comprising (a) a main information 
recording area for recording main information; and (b) 
an auxiliary signal recording area overlapping partly 
with the main information recording area for recording a 
phase-encoding modulated auxiliary signal that over- 
laps a signal of main information, comprises means for 
reproducing a main information signal in the main infor- 
mation recording area with an optical head; first decod- 
ing means for decoding a main information signal to 
obtain main information data; means for reproducing a 
mixed signal comprising a main information signal in the 
auxiliary signal recording area and the auxiliary signal 
as a reproduction signal with the optical head; fre- 
quency separation means for suppressing the main 
information signal in the reproduction signal to obtain 
the auxiliary signal; and second decoding means for 
phase-encoding decoding the auxiliary signal to obtain 
the auxiliary data. In accordance with this first configu- 
ration of an apparatus for reproducing optical disks, the 
decoding data of the auxiliary signal can be reproduced 
reliably. 

[0047] It is preferable that in the apparatus for repro- 
ducing optical disks according to the first configuration, 
the frequency separation means is a low-frequency 
component separation means for suppressing high fre- 
quency components in the reproduction signal repro- 
duced with the optical head to obtain a low frequency 
reproduction signal, and that the apparatus further com- 
prises a second-slice-level setting portion for producing 



a second slice level from the low-frequency reproduc- 
tion signal; and a second-level slicer for slicing the low- 
frequency reproduction signal at the second slice level 
to obtain a binarized signal; wherein the apparatus 

5 phase-encoding decodes the binarized signal to obtain 
the auxiliary data. With this configuration, errors due to 
variations of the envelope of the reproduction signal of 
the write-once information can be prevented. In this 
case, it is preferable that the second-slice-level setting 

10 portion comprises auxiliary low-frequency component 
separation means with a time constant that is larger 
than that of the low-frequency component separation 
means; a reproduction signal reproduced with the opti- 
cal head or a low-frequency reproduction signal 

15 obtained with the low-frequency component separation 
means is entered into the auxiliary low-frequency com- 
ponent separation means; and components with fre- 
quencies lower than the low-frequency reproduction 
signal are extracted to obtain a second slice level. With 

20 this configuration, the slice level can be set following the 
level variations of low frequency components, so that 
the signal easily can be reproduced. 
[0048] It is preferable that the apparatus for reproduc- 
ing optical disks according to the first configuration fur- 

25 ther comprises frequency transformation means for 
transforming a main information signal included in a 
reproduction signal reproduced with the optical head 
from a time domain into a frequency domain to produce 
a first transformation signal; means for producing a 

30 mixed signal, wherein auxiliary information has been 
added or superposed to the first transformation signal; 
and frequency inverse-transformation means for trans- 
forming the mixed signal from the frequency domain to 
the time domain to produce a second transformation 

35 signal. With this configuration, the ID signal can be 
spectrally dispersed, so a deterioration of the video sig- 
nal, which corresponds to the main information, can be 
prevented, and the reproduction of the main information 
becomes easier. 

40 [0049] In a second configuration of an apparatus for 
reproducing optical disks, an optical head irradiates lin- 
early polarized light onto an optical disk, and a change 
of a polarization orientation of light that is transmitted or 
reflected from the optical disk is detected in accordance 

45 with a recording signal on the optical disk. The appara- 
tus comprises means for moving, when necessary, the 
optical head into a pre-determined portion of the optical 
disk where write-once information is stored, and means 
for reproducing the write-once information after detect- 
50 ing a change of a polarization orientation of light that is 
transmitted or reflected from the pre-determined por- 
tion. In accordance with this second configuration of an 
apparatus for reproducing optical disks, the reproduc- 
tion signal can be detected easily, because it is not influ- 

55 enced by variations of the reflected luminous energy or 
by noise components included in the addition signal. 
[0050] It is preferable that the apparatus for reproduc- 
ing optical disks according to the second configuration 



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11 



EP 0 971 345 A1 



further comprises means for detecting an identifier indi- 
cating whether write-once information within control 
data of the optical disk is present, the indication being 
based on a detection signal of detection light that is 
received with at least one photo-detector of the optical 5 
head or on an addition signal of detection signals of 
detection light that is received with a plurality of photo- 
detectors of the optical head, wherein to detect the iden- 
tifier and to verify whether write-once information is 
present, the optical head is moved to the pre-deter- , 0 
mined portion of the optical disk where write-once infor- 
mation is stored, when necessary. With this 
configuration, stripes and defects in the write-once 
information easily can be discriminated, so that the 
start-up time for the apparatus can be considerably 15 
shortened. 

[0051] It is preferable that the apparatus for reproduc- 
ing optical disks according to the second configuration 
further comprises decoding means for phase-encoding 
decoding during reproduction of the write-once informa- 20 
tion. This configuration can be used for the reproduction 
of write-once information, such as an ID signal. 
[0052] In a third configuration of an apparatus for 
reproducing optical disks whereon main information is 
stored and write-once information that differs for each 25 
disk is stored, the apparatus comprises a signal repro- 
duction portion for reproducing the main information; a 
write-once information reproduction portion for repro- 
ducing the write-once information; and a watermark 
attaching portion for producing a watermark signal 30 
based on the write-once information, adding the water- 
mark signal to the main information and giving it out. In 
accordance with this third configuration of an apparatus 
for reproducing optical disks, illegal copies being made 
to obtain the main information of, for example, the video 35 
signal can be prevented. 

[0053] It is preferable that in the apparatus for repro- 
ducing optical disks according to the third configuration, 
the write-once information is recorded by partially 
changing a reflection coefficient of a recording layer on 40 
the optical disk. 

[0054] It is also preferable that in the apparatus for 
reproducing optical disks according to the third configu- 
ration, a recording layer of the optical disk comprises a 
magnetic film having a magnetic anisotropy that is per- 45 
pendicular to a film surface; and write-once information 
is stored by partially changing the perpendicular mag- 
netic anisotropy of the magnetic film. 
[0055] It is also preferable that in the apparatus for 
reproducing optical disks according to the third configu- so 
ration, a watermark attaching portion overlaps a signal 
of the main information with auxiliary information com- 
prising a watermark. With this configuration, the auxil- 
iary information being deleted from the main information 
with a normal recording and reproducing system can be 55 
prevented. 

[0056] It is also preferable that the apparatus for 
reproducing optical disks according to the third configu- 



ration further comprises a frequency transformation 
means for producing a first transformation signal by 
transforming a signal of main information from a time 
domain into a frequency domain; means for producing a 
mixed signal by adding or superposing write-once infor- 
mation and the first transformation signal; and fre- 
quency inverse-transformation means for producing a 
second transformation signal by transforming the mixed 
signal from the frequency domain into the time domain. 
[0057] It is also preferable that the apparatus for 
reproducing optical disks according to the third configu- 
ration further comprises an MPEG decoder for expand- 
ing main information into a video signal; and means for 
inputting the video signal into the watermark attaching 
portion. With this configuration, the watermark can be 
spectrally dispersed and added to the main information, 
such as the video signal, without deteriorating the sig- 
nal. In this case, it is preferable that the apparatus fur- 
ther comprises a watermark reproduction portion for 
reproducing watermarks; the MPEG decoder and the 
watermark reproduction portion both comprise a mutual 
authentication portion; and encrypted main information 
is sent and decrypted only if the mutual authentication 
portions authenticate each other. With this configura- 
tion, illegal elimination or manipulation of watermarks 
can be prevented, because the encryption is not can- 
celled when the digital signal is intercepted from an 
intermediate bus. In this case, it is preferable that a 
compound signal of main information that is com- 
pounded with an encryption decoder is input into the 
MPEG decoder. With this configuration, there is no cor- 
relation between information such as the ID and the 
watermark production parameters, so that illegal copies 
with unauthorized watermarks can be prevented. In this 
case, it is even more preferable that the apparatus fur- 
ther comprises a watermark reproduction portion for 
reproducing watermarks; an encryption decoder and 
the watermark reproduction portion both comprise a 
mutual authentication portion; and encrypted main 
information is sent and decrypted only if the mutual 
authentication portions authenticate each other. 
[0058] In a first configuration of an apparatus for 
recording and reproducing optical disks whereon infor- 
mation can be recorded, erased and reproduced and 
whereon main information is stored on a main recording 
area of a recording layer of the optical disks using a 
recording circuit and an optical head, the apparatus 
comprises means for reproducing write-once informa- 
tion that Is recorded onto a pre-determined portion of 
the recording layer using a signal output portion of the 
optical head, which detects the write-once information 
as a change of a polarization orientation; means for 
recording the main information onto the main recording 
area as encrypted information that is encrypted with an 
encryption encoder using the write-once information; 
and means for reproducing the main information by 
reproducing the write-once information with the signal 
output portion of the optical head and composing the 



7 



13 EP 0 971 345 A1 14 



encrypted information as a decryption key in an encryp- 
tion decoder. In accordance with this first configuration 
of an apparatus for recording and reproducing optical 
disks, illegal copies can be prevented, so that the copy- 
right can be protected. 5 
[0059] In a second configuration of an apparatus for 
recording and reproducing optical disks whereon main 
information is recorded onto a main recording area of a 
recording layer of the optical disks using a recording cir- 
cuit and an optical head, the apparatus comprises a w 
watermark attaching portion for adding a watermark to 
the main information. Write-once information that is 
stored in a pre-determined portion of the recording layer 
is reproduced with the optical head. The reproduced 
write-once information is added to the main information w 
as a watermark with the watermark attaching portion. 
The main information including the watermark is 
recorded onto the main recording area. In accordance 
with this second configuration of an apparatus for 
recording and reproducing optical disks, the recording 20 
history can be traced from the watermark recording 
data, so that illegal copies and illegal use can be pre- 
vented. 

[0060] It is preferable that in the apparatus for record- 
ing and reproducing optical disks according to the sec- 25 
ond configuration, the main information is recorded by 
partially changing a reflection coefficient of the record- 
ing layer. 

[0061] It is also preferable that in the apparatus for 
recording and reproducing optical disks according to the 30 
second configuration, the recording layer comprises a 
magnetic film having a magnetic anisotropy that is per- 
pendicular to a film surface; and main information is 
stored by partially changing a magnetization direction of 
the magnetic film. In this case, it is preferable that the 35 
main information and the write-once information are 
reproduced by detecting a change of a magnetization 
orientation of the recording layer or a change of the per- 
pendicular anisotropy of the recording layer with an opti- 
cal head as a change of a polarization orientation. 40 
[0062] It is also preferable that in the apparatus for 
recording and reproducing optical disks according to the 
second configuration, a watermark attaching portion 
overlaps a signal of the main information with auxiliary 
information comprising a watermark. 45 
[0063] It is also preferable that the apparatus for 
recording and reproducing optical disks according to the 
second configuration further comprises a frequency 
transformation means for producing a first transforma- 
tion signal by transforming a signal of main information 50 
from a time domain into a frequency domain; means for 
producing a mixed signal by adding or superposing 
write-once information and the first transformation sig- 
nal; and frequency inverse-transformation means for 
producing a second transformation signal by transform- 55 
ing the mixed signal from the frequency domain into the 
time domain. 

[0064] It is also preferable that the apparatus for 



recording and reproducing optical disks according to the 
second configuration further comprises an MPEG 
decoderfor expanding main information into a video sig- 
nal; and means for inputting the video signal into the 
watermark attaching portion. In this case, it is preferable 
that the apparatus further comprises a watermark 
reproduction portion for reproducing watermarks; the 
MPEG decoder and the watermark reproduction portion 
both comprise a mutual authentication portion; and 
encrypted main information is sent and decrypted only if 
the mutual authentication portions authenticate each 
other. It is also preferable that a compound signal of 
main information that is compounded with an encryption 
decoder is input into the MPEG decoder. It is even more 
preferable that the apparatus further comprises a water- 
mark reproduction portion for reproducing watermarks; 
the encryption decoder and the watermark reproduction 
portion both comprise a mutual authentication portion; 
and encrypted main information is sent and decrypted 
only if the mutual authentication portions authenticate 
each other. 

[0065] In a configuration of an apparatus for recording 
write-once information onto an optical disk storing main 
information, the apparatus comprises means for record- 
ing auxiliary information comprising at least one of a 
disk ID and watermark production parameters. In 
accordance with this configuration of an apparatus for 
recording write-once information onto an optical disk, it 
can be determined from the disk ID or the watermark 
who made an illegal copy or illegal use of the disk, so 
that the copyright can be protected. 
[0066] It is preferable that in the apparatus for record- 
ing write-once information onto an optical disk accord- 
ing to this configuration, the main information is stored 
by providing convex / concave pits in a reflection film of 
the optical disk, and the auxiliary information is stored 
by partially erasing the reflection film. 
[0067] It is also preferable that in the apparatus for 
recording write-once information onto an optical disk 
according to this configuration, the main information is 
stored by partially changing a reflection coefficient of a 
recording layer of the optical disk, and the auxiliary 
information is stored by partially changing a reflection 
coefficient of the recording layer of the optical disk. 
[0068] It is also preferable that in the apparatus for 
recording write-once information onto an optical disk 
according to this configuration, a recording layer of the 
optical disk comprises a magnetic film having a mag- 
netic anisotropy that is perpendicular to a film surface; 
main information is stored by partially changing a mag- 
netization direction of the magnetic film; and auxiliary 
information is stored by partially changing the perpen- 
dicular magnetic anisotropy of the magnetic film. 
[0069] In a configuration of an apparatus for recording 
optical disks storing main information, the apparatus 
comprises means for producing a watermark based on 
auxiliary information comprising a disk ID; and means 
for recording data, which consists of certain data to 



25 



30 



35 



45 



50 



8 



15 



EP 0 971 345 A1 



which the watermark has been superposed. In accord- 
ance with this configuration of an apparatus for record- 
ing optical disks storing main information, the 
watermark can be detected from the recorded data, and 
the contents history can be determined, so that the cop- 5 
yright can be protected. 

BRIEF DESCRIPTION OF THE DRAWINGS 

[0070] 

Fig. 1 is a cross-sectional drawing showing a con- 
figuration of an optical disk in accordance with an 
embodiment of the present invention. 
Fig. 2 is a cross-sectional drawing showing a con- 
figuration of an optical disk in accordance with 
another embodiment of the present invention. 
Fig. 3 is a drawing illustrating the principle of how 
magneto-optical disks are reproduced in accord- 
ance with an embodiment of the present invention. 
Fig. 4 is a graph showing the Kerr hysteresis loop in 
a perpendicular direction to the film surface for a 
BCA portion that has been heated and for a non- 
BCA portion that has not been heated in the record- 
ing layer of the magneto-optical disk in accordance 
with an embodiment of the present invention. 
Fig. 5 is a graph showing the relation between the 
laser recording current for recording identifying 
information on a magneto-optical disk in accord- 
ance with the present invention and the BCA 
recording characteristics. 

Fig. 6(a) is a traced graph showing a differential sig- 
nal waveform of a BCA signal at a recording current 
of 8Afor a magneto-optical disk in accordance with 
an embodiment of the present invention. Fig. 6(b) is 
a traced graph showing its addition signal wave- 
form. 

Fig. 7 is a drawing of the optical structure of an 
apparatus for recording and reproducing magneto- 
optical disks in accordance with an embodiment of 
the present invention. 

Fig. 8 is a process drawing illustrating a method for 
manufacturing a magneto-optical disk in accord- 
ance with an embodiment of the present invention. 
Fig. 9 is a process drawing illustrating a method for 
recording identifying write-once information onto a 
magneto-optical disk in accordance with an embod- 
iment of the present invention. 
Fig. 10 is a drawing showing a apparatus for detect- 
ing BCA identifying write-once information from a 
magneto-optical disk in accordance with an embod- 
iment of the present invention. 
Fig. 11(a) is a schematic drawing illustrating the 
state of the BCA portions when identifying write- 
once information that has been recorded with 
excessive power onto a magneto-optical disk in 
accordance with an embodiment of the present 
invention. Fig. 11(b) is a schematic drawing illus- 



trating the state of the BCA portions when identify- 
ing write-once information that has been recorded 
with adequate power onto a magneto-optical disk in 
accordance with an embodiment of the present 
invention. 

Fig. 12(a) is a schematic drawing showing the result 
of an observation with an optical microscope and a 
polarization microscope of a BCA portion when 
BCA identifying write-once information that has 
been recorded with excessive recording power onto 
a magneto-optical disk in accordance with an 
embodiment of the present invention. Fig. 12(b) is a 
schematic drawing showing the result of an obser- 
vation with an optical microscope and a polarization 
microscope of a BCA portion when BCA identifying 
write-once information that has been recorded with 
adequate recording power onto a magneto-optical 
disk in accordance with an embodiment of the 
present invention. 

Fig. 13(a) is a graph showing the rotation angle of 
the polarization plane in the non-BCA portions of a 
magneto-optical disk in accordance with an embod- 
iment of the present invention. Fig. 13(b) is a graph 
showing the rotation angle of the polarization plane 
in the BCA portions of a magneto-optical disk in 
accordance with an embodiment of the present 
invention. 

Fig. 14 is a block diagram of an apparatus for repro- 
ducing a DVD-ROM and an apparatus for recording 
and reproducing a DVD in accordance with an 
embodiment of the present invention. 
Fig. 15 is a block diagram of a stripe recording 
apparatus in accordance with an embodiment of 
the present invention. 

Fig. 16 is a diagram illustrating the signal waveform 
and the trimming for an RZ recording in accordance 
with an embodiment of the present invention. 
Fig. 17 is a diagram illustrating the signal waveform 
and the trimming for a PE-RZ recording in accord- 
ance with an embodiment of the present invention. 
Fig. 18(a) is a perspective drawing of the focusing 
portion in an embodiment of the present invention. 
Fig. 18(b) is a drawing showing the stripe arrange- 
ment and the emitted pulse signal in an embodi- 
ment of the present invention. 
Fig. 19 is a diagram showing the stripe arrange- 
ment on a magneto-optical disk in accordance with 
an embodiment of the present invention, and the 
contents of the TOC data. 
Fig. 20 is a flowchart illustrating the switching 
between CAV and CLVforthe stripe reproduction in 
an embodiment of the present invention. 
Fig. 21(a) is a diagram illustrating the data structure 
after ECC encoding in accordance with an embodi- 
ment of the present invention. Fig. 21(b) is a dia- 
gram illustrating the data structure for n = 1 after 
ECC encoding. Fig. 21(c) is a diagram illustrating 
the ECC error correction capability in an embodi- 



20 



25 



30 



40 



50 



17 



EP 0 971 345 A1 



18 



ment of the present invention. 
Fig. 22 (a) is a diagram illustrating the data struc- 
ture of the synchronized signal. Fig. 22(b) is a dia- 
gram illustrating the waveform of the fixed pattern. 
Fig. 22(c) is a diagram showing the recording 5 
capacities. 

Fig. 23(a) shows the structure of a low-pass filter. 
Fig. 23(b) is a graph showing the waveform of a sig- 
nal after passing though the low-pass filter. 
Fig. 24(a) shows the waveform of the reproduction 10 
signal in an embodiment of the present invention. 
Fig. 24(b) explains the dimensional accuracy of the 
stripes in an embodiment of the present invention. 
Fig. 25 is a flowchart showing how the TOC data is 
read and reproduced in an embodiment of the 15 
present invention. 

Fig. 26 is a block diagram of the second level slice 
portion in an embodiment of the present invention. 
Fig. 27 shows the waveform of the reproduction sig- 
nal at different elements for binarizing the signal in 20 
an embodiment of the present invention. 
Fig. 28 is a block diagram showing a particular cir- 
cuit structure for the second level slice portion in an 
embodiment of the present invention. 
Fig. 29 is a block diagram showing a circuit struc- 25 
ture for the second level slice portion in an embodi- 
ment of the present invention. 
Fig. 30 is a block diagram showing a circuit struc- 
ture for the second level slice portion in an embodi- 
ment of the present invention. 30 
Fig. 31 is a diagram of the actual signal waveform of 
the reproduction signal at different elements for 
binarizing the signal in an embodiment of the 
present invention. 

Fig. 32 is a block diagram showing a disk manufac- 35 
turing apparatus for a contents provider and a 
reproduction apparatus for a system operator in 
accordance with an embodiment of the present 
invention. 

Fig. 33 is a block diagram showing a disk manufac- 40 
turing portion in a disk manufacturing apparatus in 
accordance with an embodiment of the present 
invention. 

Fig. 34 is a block diagram of an entire broadcasting 
apparatus and a reproduction apparatus on the 45 
system operator side in accordance with an embod- 
iment of the present invention. 
Fig. 35 shows graphs of the waveform in the time- 
domain and the spectrum in the frequency-domain 
of an original signal and a video signal in accord- so 
ance with an embodiment of the present invention. 
Fig. 36 is a block diagram of a receiver on the user 
side and a broadcasting apparatus on the system 
operator side in accordance with an embodiment of 
the present invention. 55 
Fig. 37 is a block diagram of a watermark detection 
apparatus in accordance with an embodiment of 
the present invention. 



Fig. 38 is a cross-sectional drawing showing the 
trimming with a pulsed laser in accordance with an 
embodiment of the present invention. 
Fig. 39 is a diagram showing the signal reproduc- 
tion waveform of the trimmed portions in accord- 
ance with an embodiment of the present invention. 
Fig. 40 is a cross-sectional drawing showing the 
configuration of an optical disk in accordance with 
an embodiment of the present invention. 
Fig. 41 is a block diagram showing an apparatus for 
recording and reproducing optical disks in accord- 
ance with an embodiment of the present invention. 
Fig. 42 is a block diagram showing an apparatus for 
recording and reproducing magneto-optical disks in 
accordance with an embodiment of the present 
invention. 

DESCRIPTION OF THE PREFERRED EMBODI- 
MENTS 

[0071] The following is a more detailed description of 
the present invention, with reference to the preferred 
embodiments. 

First Embodiment 

[0072] First of all, the structure of a magneto-optical 
disk is explained. 

[0073] Fig. 1 is a cross-section showing the structure 
of a magneto-optical disk in a first embodiment of the 
present invention. As is shown in Fig. 1, a dielectric 
layer 212 is formed on top of a disk substrate 21 1 , and 
a recording layer 213 is formed on top of the dielectric 
layer 212. In the recording layer 213, a plurality of BCA 
portions 220a and 220b (BCA is one of the formats for 
write-once identification information) is recorded in a cir- 
cumferential direction of the disk. On top of the record- 
ing layer 213, an intermediate dielectric layer 214 and a 
reflecting layer 21 5 are deposited in that order. An over- 
coat layer 216 is formed on top of the reflecting layer 
215. 

[0074] Referring to Fig. 8, the following is an explana- 
tion of a method for producing a magneto-optical disk in 
accordance with this embodiment. 
[0075] First of all, as shown in Fig. 8 (1), a disk sub- 
strate 21 1 , which has guide grooves or pre-pits for track- 
ing guidance, is produced by injection molding using a 
polycarbonate resin. Then, as is shown in Fig. 8 (2), an 
80nm thick dielectric layer 212 of SiN is formed on the 
disk substrate 21 1 by reactive sputtering with a Si target 
in an atmosphere containing argon gas and nitrogen 
gas. Then, as is shown in Fig. 8 (3), a 30nm thick 
recording layer 213 consisting of a TbFeCo film is 
formed on the dielectric layer 212 by DC sputtering with 
a TbFeCo alloy target in an argon gas atmosphere. 
Then, as is shown in Fig. 8 (4), a 20nm intermediate die- 
lectric layer 214 consisting of a SiN film is formed on the 
recording layer 213 by reactive sputtering with a Si tar- 



10 



EP 0 971 345 A1 



20 



get in an atmosphere containing argon gas and nitrogen 
gas. Then, as is shown in Fig. 8 (5), a 40nm thick reflect- 
ing layer 215 consisting of an AITi film is formed on the 
intermediate dielectric layer 214 by DC sputtering with 
an AITi target in an argon gas atmosphere. Finally, as is 5 
shown in Fig. 8 (6), a 10 urn thick overcoat layer 216 is 
formed on the reflecting layer 21 5 by dropping an UV- 
light curing resin on the reflecting layer 215, coating the 
disk with the UV-light curing resin using a spin-coater at 
2500rpm, and curing the UV-light curing resin by irradi- }0 
ating it with UV light. 

[0076] The following is an explanation of a method for 
recording identifying information (write-once informa- 
tion, which is recorded after finishing the disk manufac- 
turing process), with reference to Fig. 9. 15 
[0077] First of all, as is shown in Fig. 9 (7), the mag- 
netization orientation of the magnetic layer 213 is 
aligned into one direction with a magnetizer 217. The 
recording layer 213 of the magneto-optical disk of this 
embodiment is a vertical magnetization film having a 20 
coercive force of 1 1 kOe. Thus, the magnetization orien- 
tation of the recording layer 213 can be aligned with the 
direction of the magnetic field generated by the magnet- 
izer 217 by setting the strength of the electric field gen- 
erated by the electromagnet of the magnetizer 217 to 25 
15kGauss, and passing the magneto-optical disk 
through this magnetic field. Next, as is shown in Fig. 9 

(8) , using a high-power laser 218, for example a YAG 
laser, and a unidirectional convergence focusing lens 
219 such as a cylindrical lens, the laser light is focused 30 
on the recording layer 213 in the form of oblong stripes. 
BCA portions 220a and 220b are recorded as identify- 
ing information in the circumferential direction of the 
disk. The recording principle, recording method and 
reproduction method are explained in more detail in the 35 
course of this specification. Then, as is shown in Fig. 9 

(9) , a BCA reader 221 is used to detect the BCA por- 
tions 220a and 220b, a PE (phase encode) decoding 
and a comparison with the recorded data is performed 

to verify whether there is a match. If the BCA portions 40 
match the recorded data, the recording of the identifying 
information is completed, and if the BCA portions do not 
match, the magneto-optical disk is removed from the 
process. 

[0078] The following is an explanation of the operation 45 
principle of the BCA reader 221, with reference to Fig. 
10. 

[0079] As is shown in Figs. 10(a) and (c), the BCA 
reader 221 comprises a polarizer 222 and a detector 
223, whose polarizing planes are perpendicular to each so 
other. Consequently, as is shown in Fig. 10(a) and (b), 
when the laser beam is irradiated at the BCA portion 
220a of the recording layer 213, no detection signal is 
output, because the vertical magnetic anisotropy of the 
BCA portion 220a is low (the magnetic anisotropy in the 55 
in-plane direction is dominant). However, when the laser 
beam is irradiated at a portion outside the BCA portions 
(non-BCA portion 224) of the recording layer 213, the 



polarizing plane of the reflected light rotates and a sig- 
nal is output to the photo-detector (PD) 256, because 
this portion is magnetized in a direction perpendicular to 
the film surface. Thus, a BCA regeneration signal as 
shown in Fig. 10(b) can be attained, and the BCA por- 
tions 220 can be detected speedily without using an 
optical head for magneto-optical recording and repro- 
duction. 

[0080] Since the magnetic anisotropy in the vertical 
direction of the film surface of the BCA portions is con- 
siderably lower, a BCA reproduction signal can be 
attained for the BCA portions 220a. The following is a 
more detailed explanation of this: 
[0081] Fig. 4 shows the hysteresis loop 225a of a BCA 
portion 220 of the recording layer 213 that has been 
heated by irradiation with identifying information, that is, 
with laser light, and a Kerr hysteresis loop 225b of a 
non-BCA portion 224, which has not been heated, in a 
direction perpendicular to the film plane. It can be seen 
from Fig. 4, that the Kerr rotation angle and the vertical 
magnetic anisotropy of the heated BCA portion 220 
have been deteriorated considerably. Thus, magneto- 
optical recording cannot be performed in the heated 
BCA portions 220, because the residual magnetism in 
the vertical direction disappears. 
[0082] As is shown in Fig. 9, in this embodiment, after 
the magnetization orientation of the vertical magnetiza- 
tion film in the recording layer 213 has been aligned in 
one direction (that is, after magnetization), the BCA por- 
tions 220 are recorded as the identifying information. 
After the BCA portions 220 have been recorded by lay- 
ering the layers and deteriorating the recording layer 
213, the magnetization orientation of the vertical mag- 
netization film in the recording layer 213 can be aligned 
into one direction while applying a magnetic field that is 
smaller than the field that has to be applied at room tem- 
perature by irradiating the recording layer 213 with, for 
example, a stroboscopic light to raise its temperature. 
[0083] The recording layer 21 3 of the magneto-optical 
disk in the present embodiment has a coercive force of 
11kOe at room temperature. However, when it is irradi- 
ated by, for example, a stroboscopic light or a laser 
beam and its temperature is raised to at least 100°C, 
the coercive force becomes about 4kOe, so that when a 
magnetic field of at least 5kOe is applied, the magneti- 
zation orientation of the recording layer 213 can be 
aligned into one direction. 

[0084] The following is an explanation of the recording 
power for a magneto-optical BCA recording. 
[0085] Fig. 5 shows the BCA recording characteristics 
for a BCA signal that was recorded on a magneto-opti- 
cal disk using a BCA trimming device (BCA recording 
device - CWQ pulse recording with a YAG laser excited 
with a 50W lamp; product by Matsushita Electric Indus- 
trial Co., Ltd). As can be seen from Fig. 5, when the 
recording current of the laser is below 8A, no BCA por- 
tion is recorded. When the recording current of the laser 
is in the optimal range of 8 - 9A, a BCA image 226a can 



11 



21 



EP 0 971 345 A1 



22 



be attained only with a polarization microscope, as is 
shown in Figs. 5 and 12 (b). This BCA image 226a can- 
not be observed with an optical microscope. When the 
recording current of the laser is at least 9A, the BCA 
images 226b and 226c can be attained with both the 5 
optical microscope and the polarization microscope, as 
is shown in Figs. 5 and 12(a). When the recording cur- 
rent of the laser as shown in Fig. 5 is higher than 10A, 
then the protective layer (overcoat layer) is destroyed. 
This situation is illustrated in Fig. 11. In Fig. 11, the 10 
reflecting layer 215 and the overcoat layer 216 have 
been destroyed by excessive laser power. On the other 
hand, when the recording current of the laser is in the 
optimal range of 8 - 9A, only the recording layer 213 is 
deteriorated as shown in Fig. 11(b), and the reflecting 15 
layer 215 and the overcoat layer 216 are left intact. 
[0086] The following explains a recording / reproduc- 
tion apparatus for magneto-optical disks according to 
this embodiment, with reference to Fig. 7. 
[0087] Fig. 7 illustrates the optical configuration of a 20 
recording / reproduction apparatus for magneto-optical 
disks according to the first embodiment of the present 
invention. Fig. 7 illustrates an optical head 255 for mag- 
neto-optical disks, a pulse generator 254, a laser light 
source 241, a collimator lens 242, a polarization beam 25 
splitter 243, an objective lens 244 for focusing the laser 
beam on the magneto-optical disk, a half mirror 246 for 
separating the light reflected from the magneto-optical 
disk into a signal reproduction direction and a focus 
tracking control direction, a X/4-plate 247 for rotating the 30 
polarization plane of the light reflected from the mag- 
neto-optical disk, a polarization beam splitter 248 for 
separating the light reflected from the magneto-optical 
disk according to its polarization plane, photodetectors 
249 and 250, and a receiver/controller 253 for focus 35 
tracking. Further indicated are a magneto-optical disk 
according to the present embodiment, a magnetic head 
251, and a magnetic head modulation driving circuit 
252. 

[0088] As is shown in Fig. 7, a linearly polarized laser 40 
beam emitted from the laser light source 241 is colli- 
mated by the collimator lens 242 into a parallel laser 
beam. Only the P-polarized component of this parallel 
laser beam passes the polarization beam splitter 243, is 
focused by the objective lens 244 and irradiated onto 45 
the recording layer of the magneto-optical disk 240. 
Thus, the information concerning the regular recording 
data (data information) is recorded by partially changing 
the magnetization orientation of the vertical magnetiza- 
tion film (pointing upwards and downwards). Owing to so 
the magneto-optical effect, the orientation of the polari- 
zation plane of the light that is reflected (or transmitted) 
by the magneto-optical disk 240 changes according to 
the magnetization. The reflected light, whose polariza- 
tion plane was thus rotated, is irradiated on the polariza- 55 
tion beam splitter 243, and then separated by the half 
mirror 246 into a signal reproduction direction and a 
focus tracking control direction. The polarization plane 



of the beam of the signal reproduction direction is 
rotated 45° by a W4 plate. Then, the P-polarized compo- 
nent and the S-polarized component are separated by 
the polarization beam splitter 248. The light is thus sep- 
arated into two light beams, whose luminous energy is 
detected by the photodetectors 249 and 250. A change 
in the orientation of the polarization plane is detected as 
a differential signal of the luminous energies detected 
by the two photodetectors 249 and 250. The reproduc- 
tion signal for the data information is obtained from this 
differential signal. The focus tracking controller 253 
uses the light that has been separated by the half mirror 
246 into the focus tracking control direction to control 
the focus of the objective lens 244 and to control track- 
ing. 

[0089] The BCA portions 220, serving as identifying 
information for the magneto-optical disk in his embodi- 
ment, are detected with the same reproduction method 
as the data information. As is shown in Fig. 4, the verti- 
cal magnetic anisotropy of the heated BCA portions 220 
deteriorates considerably (hysteresis loop 225a). When 
the recording layer is produced or when the signal is 
reproduced, the magnetization direction of the vertical 
magnetization layer is aligned in one direction, so that 
the polarization plane of a laser beam that is irradiated 
on the not heated non-BCA portions 224 with greater 
vertical magnetic anisotropy is rotated for an angle 8 k in 
accordance with the magnetization direction. On the 
other hand, the Kerr rotation angle of the BCA portions 
220, which have been heated and whose vertical mag- 
netic anisotropy is considerably deteriorated, has 
become very small, so that the polarization plane of a 
laser beam that is irradiated on the BCA portions 220 
hardly rotates at all when reflecting the laser beam. 
[0090] The following is a method for aligning the mag- 
netization direction of the vertical magnetization film 
into one direction, when the BCA portions are repro- 
duced: A magneto-optical disk recording / reproduction 
apparatus as shown in Fig. 7 irradiates a laser beam of 
at least 4mW onto the magnetic layer 213 of a magneto- 
optical disk 240, so that the magnetic layer 213 is 
heated to at least the Curie temperature. At the same 
time, the magnetic head 251 applies a constant mag- 
netic field of at least 200 Oe, so that the magnetization 
direction of the recording layer of the BCA portions is 
aligned into one direction. 

[0091] Fig. 6(a) shows an actual traced waveform of 
the detected differential signal for the identifying data. 
Fig. 6(b) shows a traced waveform of the detected all- 
sum signal of the identifying signal, which is a summa- 
tion signal detected with several photo-detectors. As 
can be seen from Fig. 6(a), the identifying information 
can be detected as a pulse waveform with a sufficient 
amplitude ratio in the differential signal. Even when the 
magnetic properties of the recording layer change or a 
portion of the recording layer is crystallized, the change 
of the average refractive index will be less than 5%, so 
that the variations in the luminous energy of the light 



35 



40 



45 



50 



12 



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EP 0 971 345 A1 



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reflected from the magneto-optical disk are less than 
10%. Consequently, the variations of the reproduction 
waveform caused by a change of the luminous energy 
of the reflected light are very small. 
[0092] Fig. 13 illustrates the polarization of the 
reflected light compared to that of the incident light. As 
is shown in Fig. 13(b), light reflecting from the heated 
BCA portions 220 has exactly the same polarization 
direction 227b as incident light. On the other hand, light 
reflecting from the non-BCA portions 224 has a polari- 
zation direction 227a that, owing to the Kerr effect in the 
magnetization film having with vertical magnetization 
anisotropy, is rotated by a rotation angle 9 k against the 
polarization direction of the incident light. 
[0093] Moreover, this embodiment detects the identi- 
fying information from a differential signal. Using this 
reproduction method, variations of the luminous energy 
that do not follow the polarized light can be almost com- 
pletely canceled, so that the noise due to these lumi- 
nous energy variations can be reduced. 

Second Embodiment 

[0094] Fig. 2 is a cross-section showing the structure 
of a magneto-optical disk in a second embodiment of 
the present invention. As is shown in Fig. 2, a dielectric 
layer 232 is formed on top of a disk substrate 231 , and 
a tri-layer recording layer comprising a magnetic repro- 
duction film 233, an intermediate magnetic film 234, and 
a magnetic recording film 235 is formed on top of the 
dielectric layer 232. In the recording layer, a plurality of 
BCA portions 220a and 220b is recorded in a circumfer- 
ential direction of the disk. On top of the recording layer, 
an intermediate dielectric layer 236 and a reflecting 
layer 237 are deposited in that order. An overcoat layer 
238 is formed on top of the reflecting layer 237. 
[0095] Referring to Fig. 8 of the first embodiment and 
to Fig. 9, the following is an explanation of a method for 
producing a magneto-optical disk in accordance with 
this embodiment. 

[0096] First of all, a disk substrate 231, which has 
guide grooves or pre-pits for tracking guidance, is pro- 
duced by injection molding using a polycarbonate resin. 
Then, an 80nm thick dielectric layer 232 of SiN is 
formed on the disk substrate 231 by reactive sputtering 
with a Si target in an atmosphere containing argon gas 
and nitrogen gas. The recording layer comprises a mag- 
netic reproduction film 233 of GdFeCo with a Curie tem- 
perature of T c1 and a coercive force of H c i, an 
intermediate magnetic film 234 of TbFe with a Curie 
temperature of T c2 and a coercive force of H c2 , and a 
magnetic recording film 235 of TbFeCo with a Curie 
temperature of T c3 and a coercive force of H^. These 
films are formed on top of the dielectric layer 232 by DC 
sputtering with alloy targets in an Ar gas atmosphere. 
Then, a 20nm intermediate dielectric layer 236 consist- 
ing of a SiN film is formed on the recording layer by 
reactive sputtering with a Si target in an atmosphere 



containing argon gas and nitrogen gas. Then, a 40nm 
thick reflecting layer 237 consisting of an AITi film is 
formed on the intermediate dielectric layer 236 by DC 
sputtering with an AITi target in an argon gas atmos- 

5 phere. Finally, an 8 u.m thick overcoat layer 238 is 
formed on the reflecting layer 237 by dropping an UV- 
light curing resin on the reflecting layer 237, coating the 
disk with the UV-light curing resin using a spin-coater at 
3000rpm, and curing the UV-light curing resin by irradi- 

w ating it with UV light. 

[0097] The reproduction magnetic layer 233 is set to a 
thickness of 40nm, a Curie temperature T c1 of 300°C, 
and a coercive force H c1 of 100 Oe at room tempera- 
ture. The intermediate magnetic film 234 is set to a 

15 thickness of 10nm, a Curie temperature T c2 of 120°C, 
and a coercive force H c2 of 3kOe at room temperature. 
The magnetic recording film 235 is set to a thickness of 
50nm, a Curie temperature T^ of 230°C, and a coercive 
force of 15kOe at room temperature. 

20 [0098] The following explains the reproduction princi- 
ple for the tri-layer recording layer of this embodiment 
with reference to Fig. 3. Fig. 3 shows a reproduction 
magnetic field 228, laser light spots 229a, 229b, and 
229c, recording domains 230, a magnetic reproduction 

25 film 233, an intermediate magnetic film 234, and a mag- 
netic recording film 235. As is shown in Fig. 3, the 
domains 230 containing the information signals are 
recorded into the magnetic recording film 235. At room 
temperature, the magnetization of the magnetic record- 

30 ing film 235 is transferred to the magnetic reproduction 
film by coupling forces between the magnetic recording 
film 235, the intermediate magnetic film 234, and the 
magnetic reproduction film 233. At signal reproduction, 
the regeneration magnetic film 233 retains the signal of 

35 the magnetic recording film 235 in the low temperature 
portion 229b of the laser beam spot 229a. In the high 
temperature portion 229c of the laser beam spot 229a, 
however, the temperature of the intermediate magnetic 
film 234 rises above the Curie temperature, so that the 

40 coupling forces between the recording magnetic layer 
235 and the reproduction magnetic layer 233 are inter- 
rupted and the magnetization direction of the magnetic 
reproduction film 233 is aligned with the magnetization 
direction of the magnetic reproduction film 228, 

45 because the Curie temperature of the intermediate 
magnetic film 234 is lower than that of the other mag- 
netic films. Therefore, the recording domains 230 
become masked by the high temperature portion 229c, 
which is a part of the laser beam spot 229a. Conse- 

50 quently, the signal can be reproduced only from the low 
temperature portion 229b of the laser beam spot 229a. 
This reproduction method is a magnetically induced 
super resolution method called "FAD". Using this repro- 
duction method, a signal reproduction with regions 

55 smaller than the laser beam spot becomes possible. 
[0099] A similar reproduction is also possible when 
the magnetically induced super resolution method 
called "RAD" is used, wherein signal reproduction is 



13 



25 



EP 0 971 345 A1 



26 



possible only in the high temperature portion of the 
laser beam spot. 

[0100] The following explains the recording method for 
identifying information (write-once information) in a 
magneto-optical disk of this embodiment, with reference 
to Fig. 9. 

[0101] First of all, as is shown in Fig. 9 (7), the mag- 
netization orientation of the recording layer is aligned 
into one direction with the magnetizer 217. The mag- 
netic recording film 235 of the recording layer in the 
magneto-optical disk of this embodiment is a vertical 
magnetization film having a coercive force of 15kOe. 
Thus, the magnetization orientation of the recording 
layer can be aligned with the direction of the magnetic 
field generated by the magnetizer 217 by setting the 
strength of the electric field generated by the electro- 
magnet of the magnetizer 217 to 20kGauss, and pass- 
ing the magneto-optical disk through this magnetic field. 
Next, as is shown in Fig. 9 (8), using a high-power laser 
218, for example a YAG laser, and a unidirectional con- 
vergence focusing lens 219 such as a cylindrical lens, 
the laser light, is focused on the recording layer in form 
of oblong stripes. BCA portions 220a and 220b are 
recorded in the circumferential direction of the disk. The 
recording principle, recording method and reproduction 
method are the same as in the first embodiment. As in 
the first embodiment, the recording layer also can be 
magnetized after the BCA recording. When the temper- 
ature of the recording layer is raised for magnetization 
using, for example, a stroboscope light, the magnetiza- 
tion orientation of the recording layer also can be 
aligned into one direction with a magnetic field that is as 
small as 5kOe. 

[0102] The recording layer of this embodiment is a tri- 
layer and comprises the magnetic reproduction film 
233, the intermediate magnetic film 234, and the mag- 
netic recording film 235, The identifying information can 
be recorded by considerably decreasing the magnetic 
anisotropy in a direction perpendicular to the film sur- 
face in at least the portion where the magnetic record- 
ing film 235 has been heated, and letting the magnetic 
anisotropy in substantially in-plane directions dominate. 
[0103] The Curie temperature and the coercive force 
of the magnetic film constituting the recording layer can 
be changed relatively easily by choosing a material with 
different structure or by adding atoms with different ver- 
tical magnetic anisotropy. Therefore, the conditions for 
producing the recording layer of the magneto-optical 
disk and the conditions for recording the identifying 
information can be optimally set. 
[0104] In the first and second embodiments, a poly- 
carbonate resin is used for the disk substrates 21 1 and 

231 , a SiN film is used for the dielectric layers 212, 214, 

232, and 236, and a TbFeCo film, a GdFeCo film, and a 
TbFe film are used for the magnetic films. However, it is 
also possible to use glass or plastic, such as a polyolefin 
or PMMA, for the disk substrates 21 1 and 231 . It is also 
possible to use other nitride films such as AIN, or oxide 



films such as Ta0 2 , or chalcogen composition films 
such as ZnS, or a film of a mixture of at least two of the 
above for the dielectric layers 212, 214, 232, and 236. It 
is also possible to use rare earth metal - transition metal 

5 ferrimagnetic film of a different material or structure, or 
a MnBi film, PtCo film or any other magnetic film with 
vertical magnetic anisotropy for the magnetic film. 
[0105] Moreover, In the second embodiment, the ver- 
tical magnetic anisotropy of the magnetic recording film 

w 235 in the tri-layer recording layer was deteriorated. 
However, the same effect can be attained when the ver- 
tical magnetic anisotropy of either the magnetic repro- 
duction film 233 or the magnetic recording film, or both, 
or the vertical magnetic anisotropy of the magnetic 

15 reproduction film 233, the intermediate magnetic film 
234, and the magnetic recording film 235 is deterio- 
rated. 

Third Embodiment 

20 

[0106] Fig. 40 is a cross-section showing the structure 
of a magneto-optical disk in a third embodiment of the 
present invention. As is shown in Fig. 40, a dielectric 
layer 302 is formed on top of a disk substrate 301, and 

25 a recording layer 303 of a phase-changeable material 
that can reversibly change between a crystal phase and 
an amorphous phase is formed on top of the dielectric 
layer 302. In the recording layer 303, a plurality of BCA 
portions 310 is recorded in a circumferential direction of 

30 the disk. On top of the recording layer 303, an interme- 
diate dielectric layer 304 and a reflecting layer 305 are 
deposited in that order. An overcoat layer 306 is formed 
on top of the reflecting layer 305. Two optical disks, of 
which only the first disk has the overcoat layer 306 are 

35 laminated by adhesion layer 307. It is also possible to 
laminate together two optical disks of the same configu- 
ration by hot-melting. 

[0107] The following is an explanation of a method for 
producing a magneto-optical disk in accordance with 

40 this embodiment. 

[0108] First of all, a disk substrate 301, which has 
guide grooves or pre-pits for tracking guidance, is pro- 
duced by injection molding using a polycarbonate resin. 
Then, an 80nm thick dielectric layer 302 of ZnSSi0 2 is 

45 formed on the disk substrate 301 by high-frequency RF 
sputtering with a ZnSSi0 2 target in an atmosphere con- 
taining argon gas. Then, a 20nm recording layer 303 of 
a GeSbTe alloy is formed on top of the dielectric layer 
302 by RF sputtering with a GeSbTe alloy in an Ar gas 

so atmosphere. Then, a 60nm intermediate dielectric layer 
304 consisting of a ZnSSi0 2 film is formed on the 
recording layer 303 by RF sputtering with a ZnSSi0 2 
target in an atmosphere containing argon gas. Then, a 
40nm thick reflecting layer 305 consisting of an AlCrfilm 

55 is formed on the intermediate dielectric layer 304 by DC 
sputtering with an AlCr target in an argon gas atmos- 
phere. Then, a5p thick overcoat layer 306 is formed 
on the reflecting layer 305 by dropping an UV-light cur- 



14 



27 



EP 0 971 345 A1 



ing resin on the reflecting layer 305, coating the disk 
with the UV-light curing resin using a spin-coater at 
3000rpm, and curing the UV-light curing resin by irradi- 
ating it with UV light. Thus, a first optical disk is 
obtained. Similarly, a second optical disk is obtained, 5 
but without forming the overcoat layer. Finally, the first 
and the second optical disks are laminated to each 
other by hot-melting, and curing an adhesive that forms 
an adhesive layer 307. 

[0109] The recording of information on the recording 10 
layer 303 of the GeSbTe alloy uses local changes in the 
portions where laser light is focused on a microscopic 
spot. In other words, the difference of the optical proper- 
ties between the crystal phase and the amorphous 
phase, which are based on reversible structural 15 
changes on the atomic level, are used. The recorded 
information can be reproduced by detecting the differ- 
ence of the reflected luminous energy or the transmitted 
luminous energy at a certain wavelength. 
[0110] When an optical disk has a recording layer con- 20 
sisting of a thin film that can be reversibly changed 
between these two optically detectable states, it can be 
used as a high-density rewritable exchangeable 
medium, for example a DVD-RAM. 

[0111] The recording method for identifying informa- 25 
tion (write-once information) according to this embodi- 
ment can be almost the same as in the first and the 
second embodiment. That is, using a high-power laser, 
for example a YAG laser, and a unidirectional conver- 
gence focusing lens such as a cylindrical lens, a laser 30 
beam is focused on the recording layer 303 as oblong 
stripes. BCA portions 310 are recorded in the circumfer- 
ential direction of the disk. When a laser beam with 
higher power than for the recording of information in the 
recording layer 303 is irradiated on the optical disk of 35 
this embodiment, an excessive structural change due to 
crystallization by phase transition occurs. Thus, it 
becomes possible to non-reversibly record the BCA por- 
tions 310. It is preferable that the BCA portions 310 are 
recorded as non-reversible crystal phases. By thusly 40 
recording the BCA portions 310 (i.e. the identifying 
information) the luminous energy reflected from the por- 
tions where identifying information is recorded differs 
from the luminous energy reflected from other portions. 
Therefore, as in the first embodiment, the identifying 45 
information can be reproduced with an optical head. It is 
preferable that the difference of the luminous energies 
reflected from the optical disk is at least 10%. By setting 
the difference of the average refractive indices to at 
least 5%, the change of the reflected luminous energies so 
can be set to at least 10%. In the case of DVD-RAMs, as 
in the case of DVD-ROMs, not only an excessive struc- 
tural change of the recording layer can be brought 
about, but it is also possible to raise the difference of the 
reflected luminous energies above a certain value by 55 
partially destroying the protective layer or the reflecting 
layer to reproduce the BCA signal. Moreover, since it is 
a laminated structure, there are no problems with relia- 



bility. 

[0112] The following explains an apparatus and a 
method for recording identifying information (write-once 
information) in accordance with the present invention 
with reference to the drawings. 
[0113] Since the identifying information is compatible 
with disk recording / reproduction apparatuses for 
DVDs, the technology for recording identifying informa- 
tion on a DVD and the format of the recorded signal is 
explained in more detail, whereas explanations on the 
reproduction signal pattern of the magneto-optical disk 
are omitted. However, since the identifying information 
in a high-density magneto-optical disk such as an 
ASMO (Advanced Stage Magneto-Optical Disk) is per- 
formed with an optical head 255 as shown in Fig. 7, and 
the reproduction conditions are different from the detec- 
tion method of the recording signal. 
[0114] Fig. 15 is a block diagram of a laser recording 
apparatus according to an embodiment of the present 
invention. Fig. 16 illustrates the signal waveform and 
trimming shape of an "RZ recording" in an embodiment 
of the present invention. As is shown in Fig. 16 (1), the 
present invention uses an RZ recording for the identify- 
ing information. In an RZ recording, one time unit is 
divided into several timeslots, for example a first times- 
lot 920a, a second timeslot 921a, a third timeslot 922a, 
etc. When the data is "00", a pulse 924a whose width is 
narrower than the timeslot period (that is, the period T of 
the channel clock) in the first timeslot 920a (that is, 
between t=t1 and t = t2), as shown in Fig. 16 (1). 
Influences of rotational instabilities of the motor 915 
shown in Fig. 15 can be removed by letting a clock sig- 
nal generator 913 generate the clock signal in accord- 
ance with a rotational pulse from a rotation sensor 915a 
of the motor 915, and synchronizing the recording 
therewith. The stripe 923a in the first recording area 
925a of the four recording areas on the disk, which indi- 
cates a "00", is trimmed with the laser, as is shown in 16 
(2). 

[0115] When the data is "01", a pulse 924b whose 
width is narrower than the timeslot period (that is, the 
period T of the channel clock) is recorded in the second 
timeslot 921b (that is, between t = t2 and t = t3), as 
shown in Fig. 16 (3). The stripe 923b in the second 
recording area 926b of the four recording areas on the 
disk, which indicates a "01", is trimmed by the laser, as 
is shown in 16 (4). 

[0116] A "10" and a "11", are recorded in the third 
timeslot 922a and the fourth timeslot, respectively. 
[0117] Thus, a circumferential barcode as shown in 
Fig. 39(1) is recorded on the disk. 
[0118] The following explains the "NRZ recording" 
used in a conventional barcode recording. In a NRZ 
recording, a pulse with the same width as the timeslot 
period (that is, the period T of the channel clock) is 
recorded. In the RZ recording of the present invention, 
(1 / n) T is sufficient for the pulse width of one pulse, but 
for a NRZ recording, a broader width T is necessary for 



15 



EP 0 971 345 A1 



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the pulse width. When several T's follow upon each 
other, a double or triple pulse width of 2T or 3T becomes 
necessary. 

[0119] With laser trimming as in the present invention, 
it is necessary to change the configuration of the appa- 5 
ratus itself to change the line width for laser trimming, 
which is difficult to realize and not practical for NRZ 
recording. Consequently, to represent a "00", stripes of 
the temporal width T are formed in the first and third 
recording area taken from the left, and to represent a 
"10", a stripe of the temporal width 21 is formed in the 
second and third recording area taken from the left. 
[0120] In conventional NRZ recording, the pulse width 
is 1T or 2T, so that it is clear that the laser trimming of 
the present invention is not applicable. The stripes (bar- 
code) recorded by the laser trimming of the present 
invention are reproduced as shown in Fig. 6 (a) or Fig. 
31 (1), which show experimental results. However, the 
trimming line width varies from disk to disk, so that a 
precise control is very difficult. The reason for this is that 
when the reflecting film or the recording layer of the opti- 
cal disk is trimmed, the trimming line width varies owing 
to variations of the pulse laser output power, thickness 
and material of the reflecting layer, and thermal conduc- 
tivity and thickness of the disk substrate. Moreover, 
when barcodes with different line widths are provided 
on the same disk, the structure of the recording appara- 
tus becomes complicated. For example, for an NRZ 
recording used for a product barcode, the trimming line 
width has to be matched precisely to the channel clock 
period, that is 1T, 2T, 3T or, generally speaking, nT. It is 
particularly difficult to change the line widths between 
2T, 3T etc. while recording the bars. The barcode format 
for conventional products is NRZ, so that when it is 
applied to the laser barcode of the present invention, it 
is difficult to precisely record different line widths of 2T, 
3T etc. on the same disk, which decreases the yield. 
Moreover, since the laser trimming line width varies, a 
stable recording cannot be achieved and decoding 
becomes difficult. By using RZ recording as in the 
present invention, a stable digital recording can be 
achieved, even when the laser trimming line width var- 
ies. Moreover, there has to be only one laser trimming 
line width for RZ recording, so that it is not necessary to 
modulate the laser power and the structure of the 
recording apparatus can be simple. 
[0121] Thus, by combining several RZ recordings, a 
laser barcode for an optical disk of the present invention 
can achieve a stable digital recording. 
[0122] The following explains the PE modulation of an 
RZ recording. Fig. 17 shows the signal waveform and 
trimming form of the PE-modulated RZ recording in Fig. 
1 6. First of all, if the data is "0", a pulse 924a with a tem- 
poral width that is smaller than the time slot period (that 
is the channel clock period T) is recorded in the left 
timeslot 920a (that is between t = t1 and t = t2 ) of the 
two timeslots 920a and 921a, as shown in Fig. 17 (1). If 
the data is "1", a pulse 924b with a temporal width that 



is smaller than the time slot period (that is the channel 
clock period T) is recorded in the right timeslot 921b 
(that is between t = t2 and t = t3 ) of the two timeslots 
920b and 921b, as shown in Fig. 17 (3). A stripe 923a 
indicating a "0", is recorded in the left recording area 
925a, and a stripe 923b indicating a "1" is recorded in 
the right recording area 926b by laser trimming, as 
shown in Figs. 17 (2) and (4). Thus, in the case of a 
"010", a pulse 924c is recorded in the left timeslot (to 
represent "0"), a pulse 924d is recorded in the right 
timeslot (to represent "1"), and a pulse 924e is recorded 
in the left timeslot (to represent "0"), as shown in Fig. 17 
(5). The stripes are trimmed by a laser in the left, the 
right and again the left recording areas of two recording 
areas each on the disk. Fig. 17 (5) shows the signal for 
the PE-modulated data "010". As is shown in Fig. 17 (5), 
there is a signal for each channel bit. In other words, the 
signal density is usually constant and DC-free. Since 
this PE modulation is DC-free, it is robust against low- 
frequency components, even when the pulse edge is 
detected at reproduction time. Consequently, the 
decoding circuit for the disk reproduction apparatus can 
be simpler. Moreover, since there is at least one pulse 
924 within a channel clock time of 2T, a clock that is syn- 
chronized with the channel clock can be reproduced 
without using a PLL. 

[0123] In this manner, a circular barcode as shown in 
Fig. 39 (1) is recorded on the disk. To record the data 
"01000" of Fig. 39 (4) with the PE-RZ recording of this 
embodiment, a barcode 923 corresponding to the 
recording signal 924 of Fig. 39 (3) is recorded as shown 
in Fig. 39 (2). When the optical pickup of the reproduc- 
tion apparatus reproduces this barcode, a reproduction 
signal with a waveform as shown in Fig. 39 (5) is 
attained, because the reflection signal in a portion of the 
pit modulation signal is lost due to defective portions in 
the reflecting layer of the barcode. After passing the 
regeneration signal though a second-order or third- 
order Tchebychev LPF 943 as shown in Fig. 23 (a), a 
signal with the waveform shown in Fig. 39 (6) is 
attained. This signal is sliced with a level slice portion, 
and the reproduction data "01000" shown in Fig. 39 (7) 
is reconstructed. 

[0124] As is explained with Figs. 1 1 (a) and (b), when 
laser trimming with excessive power is performed on a 
single-substrate magneto-optical disk, the overcoat 
layer (protective layer) is destroyed. Consequently, after 
laser trimming was performed with excessive power, it is 
necessary to reform the protective layer at the factory, 
Therefore, barcode recording cannot be performed at 
software companies or retailers, so that its application 
will be very limited. It is also possible that there will be 
problems with its reliability. 

[0125] Laser trimming recordings of write-once infor- 
mation on single-substrate magneto-optical disks with- 
out destroying the overcoat layer (protective layer) can 
be achieved by heating only the recording layer and 
changing the magnetic anisotropy in the direction per- 



15 



20 



25 



30 



35 



45 



50 



16 



31 EP 0 £ 

pendicular to the film surface. When this was experi- 
mentally verified, there was no change in the magnetic 
properties after 96 hours at 85°C and 95% humidity. 
[0126] On the other hand, when the laser trimming 
recording method of the present invention was applied 
to a laminated disk of two optical disks with transparent 
substrates, the protective layer remains without being 
destroyed, which was experimentally verified with a 
x800 optical microscope. Also in a similar experiment 
with a magneto-optical disk lasting 96 hours at 85°C 
and 95% humidity, no change in the reflection film at the 
trimmed portions could be observed. Thus, by applying 
the laser trimming recording method of the present 
invention to laminated disks, such as DVDs, the protec- 
tive layer does not have to be reformed at the factory, so 
that a barcode laser trimming recording can be per- 
formed at places other than the press factory, for exam- 
ple, at software companies or at retailers. Therefore, it is 
not necessary anymore to give secret keys of software 
company codes to anyone outside the company, so 
when security information, such as a serial number for 
copy protection, is recorded in the barcode, its security 
can be greatly improved. As will be explained further 
below, by setting the trimming line width for DVDs to 14T 
(that is, 1.82 urn), the barcode can be separated from 
the pit signals of the DVD, so that the barcode can be 
recorded superimposed on the pit recording areas of 
the DVD. Thus, by applying the trimming method and 
the modulation recording method of the present inven- 
tion to a laminated disk, such as a DVD, a secondary 
recording can be performed after shipping from the fac- 
tory. A secondary recording also can be performed by 
applying the same recording method to magneto-optical 
disks. 

[0127] The following explains the operation of the 
laser recording apparatus with reference to Fig. 15. As 
is shown in Fig. 15, first, the entered data is merged with 
an ID number issued by a serial number generator 908 
in an input portion 909. An encryption encoder 830 
signs or encrypts with an encryption function such as 
RSA or DES, as necessary. An ECC encoder 907 per- 
forms error correction encoding and adds interleaf. 
Then, a PE-RZ modulation is performed with a PE-RZ 
modulator 910. A clock signal generator 913 generates 
the modulation clock by synchronizing the rotation pulse 
from a motor 915 or a rotation sensor 915a. Based on 
the PE-RZ modulation signal, a laser emission circuit 
91 1 generates a trigger pulse. This trigger pulse is input 
Into a high-power laser 912, for example a YAG laser, 
driven by a laser power circuit 929. Thereby, pulsed 
laser light is emitted, which is focused by a focusing 
member 914 on the recording layer 235 of a single-sub- 
strate magneto-optical disk 240, or on the recording 
layer 303 of a laminated disk 300, or on the reflecting 
film 802 of a laminated disk 800. This produces a bar- 
code-shaped deterioration recording or erasure of the 
recording layers 235, 303 or the reflecting film 802. 
Error correction techniques will be explained in more 



71 345 A1 32 

detail further below. The adopted encryption method is 
to sign the private key of the software company used by 
the public key code as the serial number. Doing so, 
nobody but the software company has the private key, 

5 and since it is not possible to come up with a new serial 
number, the unlawful issuance of serial numbers by par- 
ties other than the software company can be prevented. 
Also, since the public key cannot be read "backwards" 
the security of the system is high. Thus, even when the 

10 public key is recorded on the disk and transmitted with 
the reproduction apparatus, counterfeiting can be pre- 
vented. The magneto-optical disk 240, the DVD-RAM 
disk 300 and the DVD-ROM disk 800 are discriminated 
by the disk discriminator 260, which uses the reflection 

15 coefficient and a means for reading the disk-type identi- 
fying information. In the case of a magneto-optical disk 
240, the recording power is lowered and the lens is 
defocused. Thus, a stable BCA recording can be 
recorded on the magneto-optical disk 240. 

20 [0128] The following paragraph explains the focusing 
member 914 of the laser recording apparatus with refer- 
ence to Fig. 18. 

[0129] As is shown in Fig. 18 (a), the light from the 
laser 912 enters a focusing member 914, and is colli- 

25 mated by a collimator 912a. A cylindrical lens 917 
focuses the laser light only in the circumferential direc- 
tion on the optical disk, so that the light turns into a 
stripe extending in the radial direction. A mask 918 trims 
this light, and a focusing lens 919 focuses the light on 

30 the recording layer 235 of the magneto-optical disk 240, 
or the recording layer 303 of the DVD-RAM disk 300, or 
the reflection film 802 of the DVD-ROM disk 800. The 
recording layers 235, 303 or the reflection film 802 are 
deterioration-recorded or erased in stripe-form. The 

35 mask 918 controls the four sides of the stripe. However, 
in reality, it is sufficient if only one peripheral side in the 
longitudinal direction of the stripe is controlled. Thus, a 
stripe 923 as shown in Fig. 18 (b) can be recorded on 
the disk. In PE modulations, the three stripe intervals 
1T, 2T and 3T are possible. Discrepancies from these 
intervals cause jitter, which brings the error rate up. 
Since in the present invention the clock generator 913 
generates the recording clock in sync with the rotation 
pulse from the motor 915, and passes it on to the mod- 
ulator 910, the stripes 923 can be recorded precisely in 
accordance with the motor 915, or in other words, with 
the rotation of the magneto-optical disk 240, the DVD- 
RAM disk 300, or the DVD-ROM disk 800. Therefore, jit- 
ter can be reduced. It is also possible to scan a continu- 
ously excited laser in a radial direction and form a 
barcode using a scanning means for the laser. 
[0130] Fig. 19 illustrates the characteristics of the disk 
format. As is shown in Fig. 19, on a DVD, all data are 
recorded with CLV However, the stripes 923 of the 
present invention are recorded by CAV, overlapping the 
prepit signals of the read-in data areas (overlap-writing), 
which are recorded with CLV. Thus, the CLV data are 
recorded by a pit pattern on the master record, whereas 



17 



33 EP 0 < 

the CAV data are recorded by deleting the reflective film 
off with the laser. Because of this overlap-writing, pits 
are recorded between 1T, 21, and 3T of the barcode 
stripes. Using this pit information, tracking with an opti- 
cal head becomes possible, and T max and T mjn of the pit 
signal can be detected. Thus, the rotation speed of the 
motor can be controlled by detecting these signals. If 
the relation between the trimming width t of the stripes 
and the pit clock T(pit) is t > 14T(pit), T mjn can be 
detected, and the rotation speed of the motor can be 
controlled by detecting this signal. If t is shorter than 
14T(pit), its pulse width becomes the same, and it is 
impossible to discern the stripes 923a and the pits, so 
that decoding becomes impossible. Moreover, since the 
address information of the pits is read at the same radial 
position as the stripes, the address information can be 
obtained and track jumping performed, because the 
length of the address region 944 contains at least one 
frame of pit information. Moreover, as is shown in Fig. 
24, by providing a ratio, i.e. a duty ratio, between stripes 
and non-stripes of less than 50%, that means T(S) < 
T(NS), the substantial reflection coefficient only drops 
6dB, so that the focus of the optical head can be applied 
steadily. There are players that cannot control tracking 
due to the stripes, but since the stripes 923 are CAV 
data, reproduction by optical pickup is possible, if driv- 
ing is performed using a rotation pulse from, for exam- 
ple, a Hall element of the motor 17 and CAV rotation. 
[0131] In magneto-optical disks, the variation of the 
reflection coefficient is less than 10%, so that it has 
absolutely no influence on the focus control. 
[0132] Fig. 20 is a flowchart showing the order of oper- 
ations when the pit data of the optical tracks in the stripe 
area are not reproduced correctly. When the optical disk 
is inserted (step 930a), first the optical head is moved to 
the inner perimeter of the optical disk (step 930b) and 
accesses the stripes 923 shown in Fig. 19. When the pit 
signals in the area of the stripes 923 are not all correctly 
reproduced, the rotational phase control for CLV cannot 
be applied. Therefore, rotation speed control is applied 
by measuring the frequency or T max or T min the pit sig- 
nals with a rotation sensor of the hole element of the 
motor (step 930c). Then, it is determined whether there 
are stripes or not (step 930i). If there are no stripes the 
optical head moves to the outer perimeter of the optical 
disk (step 930f). If there are stripes, the stripes (bar- 
code) are reproduced (step 930d). Then, it is deter- 
mined whether the reproduction of the barcodes is 
finished (step 930e). If the reproduction of the barcodes 
is finished, the optical head moves to the outer perime- 
ter of the disk (step 930f). Since there are no stripes in 
this area, the pit signals are completely reproduced and 
the focus and tracking servo are applied correctly. More- 
over, since the pit signals are completely reproduced in 
this manner, a regular control of the rotation phase 
becomes possible (step 930g) and CLV rotation is pos- 
sible. Therefore, the pit signal can be correctly repro- 
duced in step 930h. 



71 345 A1 34 

[0133] Thus, by switching between rotation speed 
control and rotation phase control, two different types of 
data, namely data of stripes (barcodes) and data 
recorded in pits, can be reproduced. Because the 

5 stripes (barcodes) are at the innermost perimeter of the 
optical disk, it is possible to switch between the two 
kinds of rotation control, i.e. rotation speed control and 
rotation phase control, by measuring the position of the 
optical head in the radial direction of the disk using an 

,o optical head stopper and the address information of the 
pit signals. 

[0134] The format for high-speed switch recording is 
illustrated by the data structure for synchronized 
encoded data in Fig. 22. 

15 [0135] The fixed pattern in Fig. 22(a) is "01000110". 
Usually, a pattern such as "01000111" with the same 
number 0's and 1's is normal for a fixed pattern, but in 
the present invention, the data rather has this structure. 
The reason for this is as follows: To perform high-speed 

20 switch recording, at least two pulses have to fit into 1t. 
Since the data area is a PE-RZ recording as shown in 
Fig. 21(a), high-speed switch recording is possible. 
However, the synchronized coding in Fig. 22(a) is 
arranged as irregular channel bits, so that in regular 

25 methods there may be two pulses within it, in which 
case high-speed switch recording cannot be performed. 
In the present invention, the fixed pattern is for example 
"01000110". Consequently, as is shown in Fig. 22(b), 
there is one pulse on the right side of T 1t no pulse in T 2 , 

30 one pulse on the right side of T 3 , and one pulse on the 
left side of T 4 , and there is no timeslot with two pulses. 
Therefore, by adopting synchronized coding in the 
present invention, high-speed switch recording 
becomes possible, and the production speed can be 

35 doubled. 

[0136] The following is an explanation of a recording / 
reproduction apparatus. Fig. 14 is a block diagram of a 
recording / reproduction apparatus. The following expla- 
nation concentrates on decoding. A low-pass filter 943 

40 eliminates high-frequency components due to the pits 
from the stripe signal output. In case of a DVD, the sig- 
nal of a maximum of 14T with T = 0.13 u.m may be 
reproduced. In this case, high-frequency components 
can be eliminated by passing the signal through a sec- 

45 ond-order or third-order Tchebychev low-pass filter 943 
as shown in Fig. 23(a), as was experimentally verified. 
In other words, if a low-pass filter of at least second 
order is used, the pit signal and the barcode signal can 
be differentiated, and the barcode can be reliably repro- 

50 duced. Fig. 23(b) shows the waveform for a worst-case 
simulation. 

[0137] Thus by using a low-pass filter 943 of at least 
second order, the pit regeneration signal can be elimi- 
nated almost completely, and the stripe regeneration 
55 signal can be output, so that the strip signal can be reli- 
ably decoded. 

[0138] Returning to Fig. 14, a PE-RZ decoder 930a 
decodes the digital data, and this data is error-corrected 



18 



35 EP 0 971 345 A1 36 



by an ECC decoder 930b. Then, a deinterleaving por- 
tion 930d cancels the interleaf, and an RS decoder 930c 
performs the calculations for decoding the Reed-Solo- 
mon coding, to perform error correction. As is shown by 
the data structure in Fig. 21(a), the interleaf and the 5 
Reed-Solomon error correction encoding are performed 
with an ECC encoder 907, as shown in Fig. 15. Conse- 
quently, by adopting this data structure, if the byte error 
rate before correction is 10" 4 , a disk error will occur in 
only one out of 10 7 disks, as is shown in Fig. 21(c). As 10 
is shown in Fig. 22(a), in this data structure, one sync 
code is assigned for every four synchronized encodings 
to reduce the data length of the code, whereby the sync 
code can be reduced to 1/4 pattern, which increases the 
efficiency. 15 
[0139] The following explains the scalability of this 
data structure with reference to Fig. 22. As is shown in 
Fig. 22(c), in the present invention, the recording capac- 
ity can be between, for example, 12 byte and 188 byte, 
and can be arbitrarily raised by steps of 16 byte. Fig. 20 
21(a) shows that n can change between n = 1 to n = 12. 
If, for example, n = 1, as in Fig. 21(b), there are only four 
data rows 951a, 951b, 951c, and 951 d, and the follow- 
ing rows are the ECC rows 952a, 952b, 952c, and 952d. 
The data row 951 d becomes the 4-byte EDC row. Thus, 25 
the remaining rows 951e to 951z are taken to be filled 
with 0's, and error correction-coding is performed. This 
ECC encoding is performed by the ECC encoder 907 if 
the laser recording apparatus in Fig. 15, and recorded 
as a barcode on the disk. If n = 1 , only 12 bytes can be 30 
recorded over an angular range of 51°. Similarly, if n = 
2, 18 bytes are recorded, and if n = 12, 271 bytes are 
recorded over an angular range of 336°. 
[0140] In the present invention, this scalability has a 
purpose. Moreover, the production tact time is important 35 
for the laser trimming. If the BCA recording areas are 
trimmed one by one, a slow apparatus can take more 
than 10 seconds to record a maximum of several thou- 
sands. Since the production tact time is four seconds, 
this will slow down the production tact time. On the other 40 
hand, the main object for application of the present 
invention is first of all the disk ID, for which about 10 
bytes should suffice. If 271 bytes are written instead of 
10 bytes, the laser processing time will rise six-fold, so 
that the production cost increases. Employing the seal- 45 
ability method of the present invention can reduce pro- 
duction cost and time. 

[0141] The ECC encoder 930b of the recording / 
reproduction apparatus in Fig. 14, can error-correct 
data from 12 bytes to 271 bytes with the same program, 50 
by, for example, filling up the rows 951 e to 951 z with 0's 
if n = 1 as in Fig. 21(b). 

[0142] As is shown in Fig. 24, for 1T, the pulse width 
of 4.4 us becomes about one half of the stripe interval of 
8.92 u.s. For 2T, the pulse width is 4.4 u.s for a stripe 55 
interval of 1 7.84 us, and for 3T, the pulse width is 4.4 u.s 
for a stripe interval of 26.76 u.s, so that, taking the aver- 
age for a PE-RZ modulation, about 1/3 corresponds to 



the pulse portion (reflection coefficient about zero). 
Consequently, in a disk with a standard reflection coeffi- 
cient of 70%, the reflection coefficient drops to about 
2/3, that is, to about 50%, and thus can be reproduced 
with a regular ROM disk player. 
[0143] Moreover, in magneto-optical disks, the aver- 
age refractive index of the recording layer does not 
change, and the average change of the reflection coef- 
ficient is less than 10%, so that level fluctuations of the 
reproduction waveform are small and compatibility with 
DVD players is easy. 

[0144] The following is an explanation of the reproduc- 
tion order with reference to the flowchart in Fig. 25. 
When the disk is inserted, first, the TOC (Control Data) 
is reproduced (step 940a). In optical disks according to 
the present invention, a stripe existence identifier 937 is 
recorded as a pit signal in the TOC of the TOC region 
936, as is shown in Fig. 19. Therefore, when the TOC is 
reproduced, it can be verified whether stripes are 
recorded or not. Then, it is determined whether the 
stripe existence identifier 937 is "0" or "1" (step 940b). If 
the stripe existence identifier 937 is "0", the optical head 
moves towards the outer perimeter of the optical disk, 
switches to rotation phase control and performs a regu- 
lar CLV reproduction (step 940f). If the stripe existence 
identifier 937 is "1 ", it is determined whether the stripes 
are on the opposite side of the reproduction side, that is, 
whether they are recorded on the reverse side of the 
disk (the reverse-side stripe existence identifier 948 is 
"1" or "0") (step 940h). If the reverse-side stripe exist- 
ence identifier 948 is "1", the recording layer on the 
reverse side of the optical disk is reproduced (940i). If 
the reverse side of the optical disk cannot be repro- 
duced automatically, a reverse-side reproduction 
instruction is given out and displayed. If it is known in 
step 940h that stripes are recorded on the side that is 
being reproduced, the optical head is moved to the 
region of the stripes 923 on the inner perimeter of the 
optical disk (step 940c), the rotation speed control is 
switched, and the stripes 923 are reproduced with CAV 
rotation (step 940d). Then, it is determined whether the 
reproduction of the stripes 923 has finished (step 940e). 
If the reproduction of the stripes 923 has finished, the 
optical head moves towards the outer perimeter of the 
optical disk, switches again to rotation phase control, 
and performs regular CLV regeneration (step 940f), to 
regenerate the data of the pit signals (step 940g). 
[0145] Thus, by recording a stripe existence identifier 
937 in the pit region of the TOC, the stripes 923 can be 
reliably reproduced. If the stripe existence identifier on 
the optical disk is not defined, the region of the stripes 
923 cannot be properly tracked, so that time has to be 
spent to discriminate between stripes 923 and defects. 
In other words, even when there are no stripes, an 
attempt is made to read the stripes, and it has to be ver- 
ified in a separate step, whether there are really no 
stripes, or whether they are perhaps located even more 
towards the inner perimeter, so that extra time is needed 



19 



37 



EP 0 971 345 A1 



to start up the reproduction process. Moreover, since 
the reverse-side stripe existence identifier 948 has been 
recorded, it can be determined whether the stripes 923 
are recorded on the reverse side. Therefore, even in the 
case of an optical disk such as a double-sided DVD, the 
barcode stripes 923 can be reliably reproduced. In a 
DVD-ROM, the inventive stripes pass through both 
reflecting layers of a double-sided disk, so that they also 
can be read from the reverse side. Reading the reverse- 
side stripe existence identifier 948, the stripes 923 can 
be reproduced from the reverse side by encoding the 
stripes backwards at recording time. As is shown in Fig. 
22(a) the present invention uses "01000110" for the 
synchronized coding. Consequently, when reproduced 
from the reverse side, the synchronized coding 
"01100010" is detected. Therefore, it can be detected 
whether the barcode stripes 923 are reproduced from 
the reverse side. In that case, a second decoder 930 of 
the recording / reproduction apparatus of Fig. 14 
decodes the code backwards, so that even when a dou- 
ble-sided disk is reproduced from the reverse side, the 
penetrating barcode stripes 923 can be correctly repro- 
duced. Moreover, as is shown in Fig. 19, a write-once 
stripe data existence identifier 939 and the stripe 
recording capacity are recorded in the TOC. Conse- 
quently, when stripes 923 have already been recorded 
in a first trimming, the recordable amount for a second 
trimming of stripes 938 can be calculated. Therefore, 
when the recording apparatus in Fig. 15 performs the 
second trimming, it can be determined from the TOC 
data how much more can be recorded. As a result, it 
can be prevented that the recording exceeds 360° and 
the stripes 923 of the first trimming are destroyed. As is 
shown in Fig. 19, by leaving an empty portion 949 of at 
least one pit signal frame between the stripes 923 of the 
first trimming and the stripes 938 of the second trim- 
ming, it can be prevented that the previous trimming 
data is destroyed. 

[0146] Since a trimming counter identifier 947 is 
recorded in the synchronized coding portion, as shown 
in Fig. 22(b), the stripes 923 of the first trimming and the 
stripes 938 of the second trimming can be discrimi- 
nated. If there were no trimming counter identifier 947, 
the first stripes 923 and the second stripes 938 could 
not be differentiated. 

[0147] The following is an explanation of the proce- 
dure from contents to disk production with reference to 
Fig. 33. As is shown in Fig. 33, first, the original contents 
3 of, for example, a motion picture are encoded in 
blocks with a variable length scheme and turned into a 
compressed video signal, such as image-compressed 
MPEG, in a disk manufacturing portion 19. This signal is 
scrambled by the encryption encoder 14 with the 
encryption key 20 for activation. This scrambled com- 
pressed video signal is recorded as a pit-shaped signal 
on a master disk 6 with the master disk production 
apparatus 5. Using the master disk 6 (or a molding die, 
or a stamper) and a molding apparatus 7, a large-vol- 



ume disk substrate 8 with recorded pits is manufactured 
and a reflecting layer of, for example, aluminum is 
formed with a reflecting layer forming apparatus 15. Two 
disk substrates 8 and 8a are laminated with a laminating 

5 apparatus 9 to finish a laminated disk 10. In case of a 
magneto-optical disk, the compressed video signal is 
recorded as a magneto-optical signal in the recording 
layer In case of a single-sided disk, the disk 240a is fin- 
ished without laminating. In case of a DVD-RAM disk, 

to the compressed video signal is similarly recorded in the 
recording layer, and two disk substrates are laminated 
with a laminating apparatus 9 to finish laminated disk 
300. For DVD-RAMs, there are single-sided disks with a 
recording layer only on one side, and double-sided with 

15 a recording layer on both sides. 

[0148] The following is an explanation of level slicing 
for the BCA with reference to the Figs. 38 and 39. 
[0149] As shown in Fig. 38(1), in a BCA recording with 
a laser, a pulsed laser 808 irradiates laser light on an 

20 aluminum reflection film 809 of a laminated disk 800, so 
that stripe-shaped low-reflection portions 810 are 
recorded as PC modulation signals by trimming the alu- 
minum reflection film 809. Thus, as shown in Fig. 38(2), 
BCA stripes are formed on the disk. When these BCA 

25 stripes are reproduced with a regular optical head, the 
reflection signal from the BCA portion disappears, so 
that the modulation signal is generated from the signal- 
lacking portions 810a, 810b, 810c, which are intermit- 
tently lacking a modulation signal. A modulation signal 

30 with 8-16 modulation of the pits is sliced at a first slice 
level 915 to decode the main signal. On the other hand, 
since the signal level of the signal-lacking portion 810a 
is low, it easily can be sliced at the second slice level 
916. The barcodes 923a and 923b shown in Fig. 39(2) 

35 are sliced at the slice level S 2 shown in Fig. 39(5), so 
that they can be reproduced with a regular optical 
pickup. As is shown in Fig. 39(6), a digital signal can be 
attained by slicing the signal, after suppressing high-fre- 
quent pit signal components with a low-pass filter, at the 

40 second slice level S 2 . By PE-RZ-decoding this digital 
signal, a digital signal as shown in Fig. 39(7) is output. 
The actual appearance of the reproduction signal is 
shown in Fig. 31. 

[01 50] The following is an explanation of the decoding 

45 with reference to Fig. 14. 

[0151] As is shown in Fig. 14, a disk 800 with a BCA 
includes two transparent substrates that are laminated 
together with the recording layer 802a on the inside. 
There may be one recording layer 802a or two recording 

50 layers 802a and 802b. When there are two recording 
layers, a stripe existence identifier 937 (see Fig. 19) 
indicating whether there is a BCA is recorded in the con- 
trol data of the first recording layer 802a near the optical 
head 255. In this case, because the BCA is in the sec- 

55 ond recording layer 802, the focus is on the first record- 
ing layer 802a, and the optical head 255 is moved to the 
radial position of the control data on the innermost 
perimeter of the second recording region 919. Since the 



20 



EP 0 971 345 A1 



40 



control data is main information, it is recorded by EFM, 
8-15, or 8-16 modulation. Only when the stripe exist- 
ence identifier 937 in the control data is "1", the one- 
layer/two-layer switching portion 827 changes the focus 
to the second recording layer 802b to reproduce the 
BCA. Using the first level slice portion 590 and slicing at 
a regular first slice level 915 as shown in Fig. 38(3), the 
BCA is converted into a digital signal. This signal is 
decoded by an EFM decoder 925, an 8-15 modulator- 
decoder 926 or an 8-16 modulator-decoder 927 in the 
first decoder 928. Then it is error-corrected by the ECC 
decoder 36, and output as main information. The BCA is 
only read out when the control data in this main informa- 
tion is reproduced and the stripe existence identifier is 
"1". When the stripe existence identifier 937 is "1", the 
CPU 923 issues an instruction to the one-layer/two- 
layer switching portion 827, and drives the focus adjust- 
ing portion 828 to switch the focus from the first record- 
ing layer 802a to the second recording layer 802b. At 
the same time, the optical head 255 is moved to the 
radial position of the second recording region 920 (in 
the DVD standard, this is the BCA recorded between 
22.3mm and 23.5mm from the inner perimeter of the 
control data), and the BCA is read out. In the BCA 
region, the envelope of the partially missing signal in 
Fig. 38(3) is reproduced. By setting the luminous energy 
for the second slice level 916 of the second level-slice 
portion 929 below the first slice level 915, the reflection 
portions and the missing portions of the BCA can be 
detected, and the digital signal output. This signal is 
decoded in the PE-RZ decoder 930a of the second 
decoder 930 and ECC-decoded in the ECC decoder 
930b to give out the BCA data, which is auxiliary infor- 
mation. Thus, the main information is decoded and 
reproduced by the first decoder 928, and the BCA data, 
which is auxiliary information, is decoded and repro- 
duced by the second decoder. 

[0152] Fig. 24(a) shows the reproduction waveform 
before passing the low-pass filter 943, Fig. 24(b) shows 
the processing precision of the slits in the low-reflection 
portion, and Fig. 23(b) shows the simulated waveform 
after passing the low-pass filter 943. It is difficult to pro- 
vide slits with a width below 5 - 15 urn. Moreover, if a 
recording is performed further than 23.5mm from the 
disk center, the recording data will be destroyed. For 
DVDs, the largest capacity after formatting is limited to 
188 bytes, due to the limitations of the shortest record- 
ing period of 30 u.m, and the largest radius of 23. 5. mm. 
[01 53] The following is a detailed specific example for 
setting the second slice level 916 and the operation of 
the second level slice portion 929. 
[0154] Fig. 26 is a detailed view of the second level 
slice portion 929. The waveform for this explanation is 
shown in Fig. 27. 

[0155] As is shown in Fig. 26, the second level slice 
portion 929 comprises a light-reference-value setting 
portion 588 feeding the second slice level 916 to the 
second level slicer 587, and a frequency divider 587d 



for frequency-dividing the output signal of the second 
level slicer 587. Moreover, the light-reference-value set- 
ting portion 588 comprises a low-pass filter 588a and a 
level converter 588b. 

5 [0156] The following explains its operation. In the BCA 
region, the envelope of the partially missing signal as 
shown in Fig. 27(1) is reproduced due to the BCA. In 
this reproduction signal, high-frequency components 
due to the signal and low-frequency components due to 

10 the BCA signal are mixed. However, the high-frequency 
components of the 8-16 modulation can be suppressed 
with the low-pass filter 943, and only the low-frequency 
signal 932 of the BCA signal as shown in Fig. 27(2) is 
entered into the second level slicer 929. 

15 [0157] When the low-frequency signal 932 is entered 
into the second level slice portion 929, the light-refer- 
ence-value setting portion 588 filters out even lower fre- 
quency components (almost DC) of the low-frequency 
signal 932 with a low-pass filter 588a with a time con- 

20 stant that is larger than the time constant of the low- 
pass filter 943 (in other words, the low-pass filter 588a 
extracts low-frequency components). The level con- 
verter 588b adjusts the signal to a suitable level, so that 
a second slice level 916 as illustrated by the fat line in 

25 Fig. 27(2) is output. As is shown in Fig. 27(2), the sec- 
ond slice level 916 tracks the envelope. 
[0158] In the present invention, when the BCA is read, 
a rotation phase control cannot be performed, and 
tracking control is also not possible. Consequently, the 

30 envelope incessantly fluctuates as in Fig. 27(1). If the 
slice level were constant, the fluctuating reproduction 
signal could be mistaken, causing the error rate to go 
up. Therefore, it would not be appropriate to carry data. 
However, with the circuit in Fig. 26 of the present inven- 

35 tion, the second slice level is constantly corrected and 
fitted to the envelope, so that wrong slicing can be sig- 
nificantly reduced. 

[0159] Thus, the present invention is not affected by a 
fluctuating envelope, and the second level slicer 587 

40 slices the low-frequency signal 932 at the second slice 
level 916, before outputting a binarized digital signal 
such as the one shown in Fig. 27(3). At the start of the 
binarized digital signal output from the second level 
slicer 587, the signal is reversed, and a digital signal as 

45 shown in Fig. 27(4) is output. Accordingly, Fig. 28 shows 
the specific circuits for a frequency dividing means 934 
and a second level slice portion 929. 
[0160] Thus, by setting the second slice level 916, dif- 
ferences in the reflection coefficient of different disks, 

50 variations in the luminous energy due to aging of the 
reproduction laser, and low-frequency level (DC level) 
variations of the 8-16 modulation signal due to track- 
crossing at reproduction time can be absorbed, and a 
reproduction apparatus for optical disks can be provided 

55 that can reliably slice the BCA signal. 

[0161] The following explains another method for slic- 
ing the second slice level 916. Fig. 29 shows another 
circuit diagram for the frequency dividing means 934 



21 



41 EP 0 971 345 A1 42 



and the second level slice portion 929. As is shown in 
Fig. 29, the low-pass filter 943 of the frequency dividing 
means 934 comprises a first low-pass filter 943a with a 
small time constant and a second low-pass filter 943b 
with a large time constant. The second level slicer 587 5 
of the second level slice portion 929 comprises an 
inverting amplifier 687a, a DC reproduction circuit 587b, 
a converter 587c, and a frequency half-divider 587d. 
The waveform for this example is shown in Fig. 31 . 
[0162] The following explains its operation. In the BCA 10 
region, the envelope of the partially missing signal as 
shown in Fig. 31(1) is reproduced due to the BCA. This 
reproduction signal is entered into a first low-pass filter 
943a and a second low-pass filter 943b of the low-pass 
filter 943. The first low-pass filter 943a with the smaller w 
time constant eliminates the high-frequency signal com- 
ponents of the 8-16 modulation from the reproduction 
signal, and outputs the BCA signal. The first low-pass 
filter 943b with the larger time constant passes the DC 
components of the reproduction signal, and outputs the 20 
DC component of the reproduction signal. When the 
first low-pass filter 943a suppresses the high-frequency 
components of the 8-16 modulation and enters this sig- 
nal into the inverting amplifier 587a, the inverting ampli- 
fier 587a amplifies the amplitude, which has been 25 
reduced by passing though the first low-pass filter 943a. 
The amplified signal is DC-reproduced at GND level in 
the DC reproduction circuit 587b, and a signal as shown 
in Fig. 31(3) is entered into the comparator 587c. On the 
other hand, when the second low-pass filter 943b enters 30 
the DC component of the reproduction signal into the 
light-reference-value setting portion 588, the light-refer- 
ence-value setting portion 588 adjusts the signal with a 
resistive divider to an appropriate level and enters the 
second slice level 916 into the comparator 587c, as 35 
shown in Fig. 31(2). The comparator 587c slices the 
output signal of the CD reproduction circuit 587b at the 
second slice level 916 and outputs a binarized digital 
signal as shown in Fig. 31(4). At the start of the digital 
signal, which has been binarized by the comparator 40 
587c, the frequency half-divider 587d reverses the sig- 
nal, and a digital signal is output. Accordingly, Fig. 28 
shows the specific circuits for a frequency dividing 
means 934 and a second level slice portion 929. 
[0163] Fig. 30 shows a specific circuit of the frequency 45 
dividing means 934 and the second level slice portion 
929 to accomplish this. 

[0164] Thus, by setting the second slice level 916 to 
reproduce the BCA signal, differences in the reflection 
coefficient of different disks, variations in the luminous 50 
energy due to aging of the reproduction laser, and low- 
frequency level (DC level) variations of the 8-16 modu- 
lation signal due to track-crossing at reproduction time 
can be absorbed, and reproduction apparatus for opti- 
cal disks can be provided that can slice the BCA signal 55 
reliably. Moreover, when the circuits are discrete, the 
number of elements can be minimized, and a reliable 
BCA reproduction circuit can be achieved. 



[0165] Moreover, if this signal can be loaded into the 
CPU and decoded by software, the clock frequency of 
the PE modulation signal can be reduced to one half 
with the frequency half-divider 587d. Therefore, even 
when a CPU with a slow sample frequency is used, the 
threshold of the signal can be detected reliably. 
[0166] This effect also can be attained by slowing 
down the rotation frequency of the motor at reproduc- 
tion time. This will be explained with Fig. 14. When the 
command has been issued to reproduce the BCA, the 
CPU sends a rotation speed deceleration signal 923b to 
the rotation controller 26. Then, the rotation controller 
26 decelerates the rotation frequency of the motor 17 to 
one half or one quarter. Therefore, the frequency of the 
reproduction signal decreases, and can be decoded by 
software even when a CPU with a slower sample fre- 
quency is used, and a BCA with a small linewidth can be 
reproduced. Sometimes, production facilities manufac- 
ture BCA stripes with a small linewidth, but by slowing 
down the rotation frequency they can be handled with 
slow CPUs. This improves the error rate and the reliabil- 
ity at BCA reproduction time. 

[0167] When the BCA is read at a regular speed (such 
as single speed), the CPU 923 sends a deceleration 
command to the rotation controller 26 to halve the rota- 
tion frequency of the motor 17 only when an error 
occurred in the BCA reproduction. Adopting this 
method, the actual read-out speed for a BCA with an 
average linewidth does not decrease at all. Only when 
the linewidth is narrow and errors occur, the errors can 
be correctly detected by reading the BCA at half the 
speed. Thus, by slowing down the read-out speed for 
narrow BCA linewidths, a slowdown of the BCA repro- 
duction speed can be prevented. 
[0168] In Fig. 14, a low-pass filter 943 is used as the 
frequency dividing means 934 but an envelope-tracking 
circuit or a peak-hold also can be used as long as it is a 
means for suppressing high-frequency signals of the 8- 
16 modulation from the reproduction signal of the BCA 
region. 

[0169] The frequency dividing means 934 and the 
second level slicer 929 also can be means for directly 
binarizing the reproduction signal of the BCA region, 
then entering the reproduction signal into a microproc- 
essor, discriminating the 8-16 signal and the BCA signal 
on the time axis by digitally processing using points with 
difference of edge intervals, and substantially suppress- 
ing the high-frequency signal of the 8-16 modulation. 
[0170] The modulation signal is recorded with pits by 
8-16 modulation to obtain the high-frequency signal 933 
in Fig. 14. On the other hand, the BCA signal becomes 
the low-frequency signal 932. Thus, since in the DVD 
standard, the main information is a high-frequency sig- 
nal 933 of a maximum of 4.5MHz, and the auxiliary 
information is a low-frequency signal 932 with a period 
of 8.92 u.s, that is, about 100kHz, the auxiliary informa- 
tion easily can be frequency-divided with the low-pass 
filter 943. Using a frequency dividing means 934 com- 



43 EP 0 9 

prising a low-pass filter 943 as shown in Fig. 14, the two 
signals easily can be divided. In this case, the low-pass 
filter 943 can be of a simple configuration. 
[0171] The preceding was an outline of the BCA. 
[0172] Fig. 32 is a block drawing of a disk manufactur- 
ing apparatus and a reproduction apparatus. As is 
shown in Fig. 32, the disk manufacturing portion 19 
manufactures laminated ROM or RAM disks or single- 
substrate disks 10 with the same contents. Using a BCA 
recorder 13, the disk manufacturing apparatus 21 PE- 
modulates BCA data 16a, 16b, 16c including the identi- 
fication codes 12a, 12b, 12c, such as IDs that are differ- 
ent for each disk, and forms barcode-shaped BCAs 
18a, 18b, 18c on the disks 10a, 10b, 10c by trimming 
with a YAG-laser. In the following, the disks whereon a 
BCA 18 has been recorded are referred to as BCA disk 
1 1 a, 1 1 b, and 1 1c. As is shown in Fig. 32, the pit portion 
and the recording signal on the BCA disks 11a, 11b, 
and 1 1 c are completely the same. However, a different 
(for example, incrementally numbered) ID is recorded 
into the BCA 1 8 of each disk. Contents providers, such 
as film studios, can record these IDs into an ID data 
base 22. When the disks are shipped, the BCA data is 
read with a barcode reader 24 that can read BCA, and it 
is recorded which disk with which ID has been distrib- 
uted at what time to which system operator 23, that is, 
CATV studio, broadcasting station or airline. 
[0173] A record about which disk ID has been distrib- 
uted to which system operator at what time is recorded 
in the ID data base 22. Therefore, if a large number of 
illegal copies of a certain BCA disk is put into circula- 
tion, it can be traced by checking the real watermark to 
which system operator the illegally copied disk had 
been originally distributed. This feature will be detailed 
further below. Since this ID numbering based on the 
BCA performs virtually the same role as a watermark for 
the entire system, it is called "prewatermarking". 
[0174] The following is an explanation of the data to be 
recorded in the BCA. An ID generator 26 generates IDs. 
Moreover, a watermark-production parameter generator 
27 generates watermark-production parameters based 
on these IDs or on random numbers. Then, the ID and 
the watermark-production parameters are mixed signed 
by a digital signature portion 28 using the private key of 
a public key cryptography. The BCA recorder 13 records 
the ID, the watermark-production parameters and the 
signature data onto each disk 10a, 10b, and 10c. Thus, 
the BCAs 18a, 18b, and 18c are formed. 
[0175] If main information, such as a video signal, is 
recorded on the BCA disks 11a, 11b, or 11c, the BCA 
reproduction portion 39 first reads out the BCA signal 
including the different IDs, as shown in Fig. 41. Then, a 
watermark recording portion 264 converts the video sig- 
nal by superimposing the BCA signal and a recording 
circuit 272 records the converted video signal on the 
BCA disks 1 1a, 1 1 b, and 1 1 c (300 (240, 800) in Fig. 41). 
When the video signal onto which the BCA signal has 
been superimposed is reproduced from the BCA disk 



M 345 A1 44 

300 (240, 800), the BCA reproduction portion 39 reads 
out the BCA signal of the disk, and detects it as the ID1 
of the disk. A watermark reproduction portion detects 
the video signal onto which the watermark has been 

5 superimposed as disk ID2. A comparator compares the 
ID1 read out from the BCA signal with the disk ID2 read 
out from the watermark of the video signal, and when 
the two IDs do not match, the reproduction of the video 
signal is stopped. As a result, the video signal of an ille- 

10 gal disk onto which a watermark that is different from 
the BCA signal has been superimposed cannot be 
replayed. On the other hand, if both IDs match, a 
descrambler 31 descrambles the video signal with the 
superimposed watermark using a compound key com- 

15 prising ID information read out from the BCA signal, and 
the video signal is output. 

[0176] The BCA disks 10a, 10b, and 10c that have 
been "pre-watermarked" with such a disk manufacturing 
apparatus 21 are then sent to the system operators 23a, 
20 23b, and 23c with the reproduction apparatuses 25a, 
25b, and 25c. In Fig. 32, elements of the broadcasting 
apparatus 28 have been partially left out for the sake of 
convenience. 

[0177] Figs. 34 and 35 illustrate the operation per- 

25 formed by the system operators. Fig. 34 is a block dia- 
gram showing the broadcasting apparatus 28 in detail. 
Fig. 35 is a graph showing the waveform of the original 
signal and the video signals on the time axis and their 
waveforms on the frequency axis. 

30 [0178] As is shown in Fig. 34, the broadcasting appa- 
ratus 28 set up in a CATV station comprises a reproduc- 
tion apparatus 25a for system operators, and the disk 
11a with BCA supplied by, for example, the film studio, 
is inserted into this reproduction apparatus 25a. The 

35 main information of the signal that is reproduced with 
the optical head 29 is reproduced with the data repro- 
duction portion 30, descrambled with the descrambler 
31, expanded to the original movie signal with the 
MPEG decoder 33, and sent to the watermark portion 

40 34. The original signal as shown in Fig. 35(1) is first 
entered into the watermark portion 34, and transformed 
by, for example, FFT from the time domain into the fre- 
quency domain by a frequency converter 34a. Thus, the 
frequency spectrum 35a shown in Fig. 35(2) is attained. 

45 A spectrum mixer 36 mixes the frequency spectrum 35a 
with the ID signal having the spectrum shown in Fig. 
35(3). As shown in Fig. 35(4), the spectrum 35b of the 
mixed signal is the same as the frequency spectrum 
35a of the original signal shown in Fig. 35(2). In other 

so words, the ID signal is spectrally dispersed. This signal 
is transformed from the frequency domain to the time 
domain by, for example, inverse FFT with an inverse fre- 
quency converter 37, and a signal as in Fig. 35(5), 
which is almost the same as the original signal (Fig. 

55 35(1)) is obtained. Because the ID signal is spectrally 
dispersed in the frequency domain, the deterioration of 
the video signal is negligible. 

[0179] The following explains how the ID signal 38 is 



23 



45 



EP 0 971 345 A1 



46 



produced. 

[0180] A digital signature verification portion 40 veri- 
fies the signature of the BCA data reproduced from the 
BCA disk 11a by the BCA reproduction portion 39 with, 
for example, the public key sent from, for example, an IC 
card 41. If the signature is invalid, the operation is 
halted. If the signature is valid, this shows that the data 
has not been manipulated and the ID is sent unchanged 
to a watermark-data production portion 41a. Using the 
watermark-production parameters contained in the 
BCA data, a watermark signal corresponding to the ID 
signal shown in Fig. 35(3) can be generated. The water- 
mark signal also can be generated by calculating the 
watermark from the ID data or the card ID of the IC card 
41. 

[0181] In that case, the ID has absolutely nothing to do 
with the watermark-production parameters, so that if the 
watermark-production parameters and the ID are 
recorded in the BCA, the watermark can not be 
deducted from the ID. In other words, only the copyright 
owner knows the relation between ID and watermark. 
Therefore, watermarks being illegally issued to make 
illegal copies and issue new IDs can be prevented. 
[0182] On the other hand, a spectral signal can be 
generated by a certain calculation from the card ID of 
the IC card 41 to bury the card ID of the IC card 41 as a 
watermark in the video output signal by adding it to the 
ID signal 38. In this case, both the circulated (that is, 
supplied by sales) ID of the software and the ID of the 
reproduction apparatus can be verified so that the trac- 
ing of illegal copies becomes easy. 
[0183] The video output signal of the watermark por- 
tion 34 is sent to the output portion 42. If the broadcast- 
ing apparatus 28 broadcasts a compressed video 
signal, the video output signal is compressed with an 
MPEG encoder 43, scrambled with a scrambler 45 
using the system operator's own encryption key 44 and 
broadcast from the broadcasting portion 46 to the audi- 
ence via a network or radio waves. In this case, the 
compression parameter information, such as the trans- 
fer rate after the original MPEG signal has been com- 
pressed, is sent from the MPEG decoder 33 to the 
MPEG encoder 43, so that the compression ratio can be 
increased even with real-time encoding. Moreover, the 
compressed audio signal 48 can bypass the watermark 
portion 34 to avoid expansion and compression, so that 
a deterioration of the audio quality can be avoided. 
[01 84] Then , if no compressed signal is broadcast, the 
video output signal 49 is scrambled unchanged and 
broadcast from the broadcasting portion 46a to the 
audience via a network or radio waves. In video sys- 
tems on board airplanes, scrambling is unnecessary. 
Thus, a video signal with a watermark is broadcast from 
the disk 11a with BCA. 

[0185] An illegal copier could intercept the signal from 
an intermediate bus between two components in Fig. 34 
to obtain the video signal bypassing the watermark por- 
tion 34. To avoid this, the buses between the descram- 



bler 31 and the MPEG decoder 33 and the watermark 
portion 34 are encrypted by handshake between the 
mutual authentication portions 32a and 32b, as well as 
between the mutual authentication portions 32c and 

5 32d. When an encrypted signal is transmitted by the 
mutual authentication portion 32c on the sender side to 
the mutual authentication portion 32c on the receiver 
side, the mutual authentication portion 32c and the 
mutual authentication portion 32d contact each other, 

10 that is, they perform a handshake. Only if the result of 
the handshake is correct, does the mutual authentica- 
tion portion 32d on the sender side cancel the encryp- 
tion. This is the same with the mutual authentication 
portion 32a and the mutual authentication portion 32b. 

15 Thus, with the method of the present invention, the 
encryption is canceled only in the case of mutual 
authentication. Therefore, even when the digital signal 
is taken from an intermediate bus, the encryption has 
not been canceled and since the watermark portion 34 

20 cannot be bypassed in the end, an unlawful elimination 
or manipulation of the watermark can be prevented. 
[0186] Thus, the receiver 50 on the user side receives 
the watermarked video signal 49 transmitted with a 
transmitter 46 of the broadcasting apparatus 28 on the 

25 system-operator side, as is shown in Fig. 36. In the 
receiver, a second descrambler 51 cancels the scram- 
bling, and if the signal is compressed, an MPEG 
decoder 52 expands the signal, which is then output 
from an output portion 53 as a video signal 49a to a 

30 monitor 54. 

[0187] The following discusses the illegal copying. 
The video signal 49a can be intercepted and recorded 
on a tape 56 with a VTR 55, and a large number of ille- 
gal copies of the tape 56 thus can be multiplied and cir- 

35 culated (by sales), resulting in an infringement of the 
rights of the copyright holder. However, if the BCA of the 
present invention is used, there is a watermark in the 
video signal 49a and in the video signal 49b (see Fig. 
37) that is reproduced from a video tape 56. Because 

40 the watermark has been added in the frequency 
domain, it cannot be easily eliminated. Also, it cannot be 
eliminated by passing the signal through a regular 
recording / reproduction system. 
[0188] The following is an explanation of how the 

45 watermark can be detected, with reference to Fig. 37. 
[0189] An illegally copied recording medium 56, for 
example a video tape or a DVD laser disk is reproduced 
with a reproduction apparatus 55a, such as a VTR or a 
DVD player. The reproduced video signal 49b is fed into 

50 a first input portion of a watermark detection apparatus 
57. A first spectrum 60, which is a spectrum of the ille- 
gally copied signal, as shown in Fig. 35 (7) is obtained 
with a first frequency converter 59a by, for example, 
FFG or DCT The original contents are fed into a second 

55 input portion 58a, and a second spectrum 35a is 
obtained by transformation into the frequency domain 
with a second frequency converter 59a. Such a spec- 
trum is shown in Fig. 35 (2). When the difference 



24 



47 EP 0 9 

between the first spectrum 60 and the second spectrum 
35a is taken with a subtracter 62, a differential spectrum 
signal 63 as shown in Fig. 35 (8) can be obtained. This 
differential spectrum signal 63 is given into an ID detec- 
tor 64. The ID detector 64 retrieves the watermark 
parameters for the n-th ID from an ID database 22 (step 
65), inputs them (step 65a), and compares the spec- 
trum signal based on the watermark parameters with 
the differential spectrum signal 63 (step 65b). Then, it is 
determined whether the spectrum signal based on the 
watermark parameters and the differential spectrum 
signal 63 match. If the two match, this means the ID cor- 
responds to the n-th watermark, so that ID = n (step 
65d). If the two do not match, ID is renewed to n + 1, and 
the watermark for the (n + 1)th watermark is retrieved 
from the ID database. These steps are repeated to 
detect the ID of the watermark. If the ID matches, the 
spectrums in Figs. 35 (3) and (8) match. The ID of the 
watermark is output from an output portion 66, and it 
can be seen from where the unauthorized copy came. 
[0190] Thus, because the ID of the watermark can be 
determined as described above, the origin of the pirated 
disks or unauthorized copies can be traced, so that the 
copyright can be protected. 

[0191] If a system that combines the BCA of the 
present invention with a watermark records the same 
video signal on a ROM disk or a RAM disk, and records 
watermark information in the BCA, it can realize a vir- 
tual watermark. The system operator can bury water- 
marks corresponding to the IDs that are issued to the 
contents providers in the video signal that is eventually 
output from the reproduction apparatus. Compared with 
conventional methods for recording video signals with 
watermarks that differ for each disk, the disks' cost and 
production time can be reduced significantly. A water- 
mark circuit is needed in the reproduction apparatus, 
but since FFT and IFFT are staple techniques, this will 
not place an undue burden upon the broadcasting 
devices. 

[0192] In this example, a spectrum-dispersion water- 
mark portion was used, but the same effect can be 
obtained with other types of watermark portions as well. 
[0193] For a DVD-RAM disk 300 or a magneto-optical 
disk 240, a contents provider having, for example, a 
CATV station with the DVD recording / reproduction 
apparatus shown in Fig. 14 or the magneto-optical 
recording / reproduction apparatus shown in Fig. 42 
sends the scrambled data, which has been encrypted 
with the ID number in the BCA as one key, to another 
recording/ reproduction apparatus on the user side via a 
communication line, and the scrambled data is tempo- 
rarily recorded on the DVD-RAM disk 300a or magneto- 
optical disk 240a of, for example, the CATV station. To 
reproduce the scrambled signal from the same mag- 
neto-optical disk 240a is authorized use, so that the 
BCA is read, and the signal is descrambled in a 
descrambling portion, that is, the encryption decoder 
534a, using the BCA data obtained from the BCA output 



n 345 A1 48 

portion 750 as the decryption key, as shown in Fig. 42. 
Then, the MPEG decoder 261 expands the MPEG sig- 
nal to obtain the video signal. If, however, the scrambled 
data, that is recorded on the magneto-optical disk 240a 

5 for authorized use, is copied onto a magneto-optical 
disk 240b, that is, unauthorized use is made, the correct 
decryption key for descrambling the scrambled data 
cannot be obtained during reproduction, because the 
BCA data of the disks are different, so that the encryp- 

10 tion decoder 534a cannot descramble the signal. There- 
fore, the video signal cannot be output. Therefore, a 
signal that is illegally copied onto another magneto-opti- 
cal disk 240b cannot be reproduced, so that the copy- 
right can be protected. In effect, the contents can be 

15 recorded on and reproduced from only one magneto- 
optical disk 240a. The same is true for the DVD-RAM 
disk 300a shown in Fig. 14, where the contents also can 
be recorded on and reproduced from only one disk. 
[0194] The following is an explanation of an even 

20 tougher protection method. First, the BCA data of the 
magneto-optical disk 240 on the user side are sent via 
communication line to the contents provider. Then, on 
the contents provider side, the video signal is transmit- 
ted with the BCA data buried inside the video signal as 

26 a watermark by the watermark recording portion 264. 
On the user side, this signal is recorded onto a mag- 
neto-optical disk 240a. During reproduction, a water- 
mark reproduction verification portion 262 verifies the 
BCA data of the recording permission identifier and the 

30 watermark against the BCA data obtained by the BCA 
output portion 750, and authorizes compound reproduc- 
tion only if they match. This makes the protection of 
copyrights even stronger. Since with this method the 
watermark can be detected by the watermark reproduc- 

35 tion portion 263 even if a digital/analog copy is taken 
directly to video tape from the magneto-optical disk 
240a, the production of illegal digital copies can be pre- 
vented or detected. As in the case of the DVD-RAM disk 
shown in Fig. 14, the production of illegal digital copies 

40 can be prevented or detected. 

[0195] In this case, by providing the magneto-optical 
recording / reproduction apparatus or the DVD record- 
ing / reproduction apparatus with a watermark repro- 
duction portion 263, a recording prevention portion 265 

45 authorizes the recording only if there is a watermark 
indicating a "first recording possible identifier" in the sig- 
nal received from the contents provider. The recording 
prevention portion 265 and a "first recording completion 
identifier, which is discussed below, prevent a second 

so recording of the disk, that is, illegal copying. Moreover, 
an identifier showing "first recording completed" and an 
individual disk number of the magneto-optical disk 240a 
pre-recorded in the BCA recording portion 220 are over- 
lapped by the watermark recording portion 264 with the 

55 recording signal with the primary watermark and buried 
and recorded on the magneto-optical disk 240a as the 
second watermark. If the data from this magneto-optical 
240a are descrambled or converted to analog and 



25 



49 EP 0 9 

recorded onto other media, for example, a video tape or 
a DVD-RAM, then the "first recording completion identi- 
fier" can be detected if the VTR or the like comprises a 
watermark reproduction portion 263. Thus, the record- 
ing prevention portion 265 impedes the recording of a 
second tape or disk, so that illegal copies are prevented. 
If the VTR is not equipped with a watermark production 
portion 263, an illegal copy can be produced. However, 
by examining the watermark of the illegally copied video 
tape, the recording history, for example, the name of the 
contents provider can be reproduced from the recording 
data of the primary watermark, and the BCA disk ID of 
the first, legal recording can be reproduced from the 
buried secondary watermark, so that a follow-up check 
can be made from which contents provider which (or 
whose) disk has been provided on which date. Conse- 
quently, the individual who broke the law can be identi- 
fied and tried for copyright infringement, so that illegal 
copies and plans for similar actions by the same 
infringer can be indirectly impeded. Since the water- 
mark does not disappear even when converting the sig- 
nal to analog, this is also useful for analog VTRs. 
[0196] The following is an explanation of a recording 
apparatus that can record or transmit illegally by circum- 
venting the copy protection even though a watermark 
indicating "first recording complete" or "recording forbid- 
den" is detected and by adding a circuit producing a 
scrambling key. This case cannot be prevented directly, 
but the circumvention circuit becomes extremely com- 
plicated. Moreover, as has been explained above, the 
recording history can be ascertained from the primary 
and the secondary watermark, so that illegal copies and 
illegal use can be prevented indirectly, similar to the 
case explained above. 

[0197] The following is an explanation of the particular 
effects of the BCA. The BCA data specify the disk, and 
with the BCA data the primary user of the contents, who 
is recorded in data base of the contents provider, can be 
specified. Therefore, by adding the BCA, the tracing of 
illegal users becomes easy when watermarks are used. 
[0198] Moreover, as is shown by the recording circuit 
266 in Figs. 14 and 42, BCA data are used for a portion 
of the encryption key for scrambling, and for the primary 
watermark or the secondary watermark, so that when 
both are checked for by the watermark reproduction 
portion 263 of the reproduction apparatus, an even 
stronger copy protection can be realized. 
[0199] Moreover, a watermark or scrambling key, to 
which a time information input portion 269 has added 
the authorization dates from system operators such as 
rental stores, is input into a scrambling portion 271, and 
synthesized into a password 271a. When the reproduc- 
tion device performs a verification of the date informa- 
tion using the password 271a or the BCA data or the 
watermark, a period wherein the scrambling key can be 
cancelled can be specified, for example as "3 days use 
possible", in the encryption decoder 534a. This also can 
be used for a rental disk system, which can be protected 



M 345 A1 50 

with the copy prevention technology of the present 
invention, resulting in strong copyright protection and 
making illegal use very difficult. 
[0200] As explained above, when the BCA is used for 
5 a rewritable optical disk, such as a magneto-optical disk 
used for an ASMO, the copyright protection through 
watermarks or scrambling can be strengthened even 
further. 

[0201] Moreover, the above embodiments have been 

10 explained for a DVD ROM disk of two laminated disks, a 
RAM disk and a single-substrate optical disk. However, 
the present invention can be applied regardless of the 
disk structure to any kind of disk with the same effect. In 
other words, recording the BCA on other types of ROM 

15 disks or RAM disks, on DVD-R disks, or magneto-opti- 
cal disks, the same recording properties and reliability 
can be attained. The above explanations are equally 
applicable to DVD-R disks, DVD-RAM disks and mag- 
neto-optical disks, with the same results, but these 

20 explanations have been omitted. 

[0202] Moreover, the BCA identifying information in 
the above embodiments have the same information sig- 
nal format for DVDs and for magneto-optical disks, so 
that using an optical head for magneto-optical disks with 

25 the structure in Fig. 7, the BCA identifying information 
for DVDs can be reproduced. And, in this case, an 
excellent reproduction signal of the BCA identifying 
information with a small error rate can be attained with 
a reproduction filter and by adjusting the decoding con- 

30 ditions during reproduction. 

[0203] Moreover, since in the magneto-optical disk of 
the above embodiments, only the magnetic properties 
of the recording layer are changed, excellent reliability 
can be achieved in environmental tests, with no deterio- 

35 ration of the recording layer due to oxidation and no 
change of the mechanical properties of the recording 
layer. 

[0204] Furthermore, the above embodiments, have 
been explained by way of examples of a magneto-opti- 

40 cal disk wherein the recording layer has a three-layer 
FAD structure. However, identifying information just as 
easily can be recorded on a RAD type, a CAD type, or a 
double mask type magneto-optical disk that can be 
reproduced with magnetically induced super resolution, 

45 with a recording method of the above embodiments, so 
that the copying of contents can be prevented, while 
maintaining excellent detection signal properties. 

INDUSTRIAL APPLICABILITY 

50 

[0205] In accordance with the present invention iden- 
tifying information (write-once information) easily can be 
recorded onto or reproduced from optical disks, the cop- 
ying of contents can be prevented, which is useful for an 
55 apparatus for recording and reproducing optical disks 
with an accent on copyright protection. 



26 



51 



EP 0 971 345 A1 



52 



Claims 

1 . An optical disk comprising: 

a disk substrate; and 

a recording layer on the disk substrate, the 
recording layer including a magnetic film with 
magnetic anisotropy in a direction perpendicu- 
lar to a surface of the magnetic film; wherein 
the optical disk stores write-once information 
formed by first recording areas and second 
recording areas in a pre-determined portion of 
said recording layer; 

a magnetic anisotropy in a direction perpendic- 
ular to a surface of the second recording areas 
is smaller than a magnetic anisotropy in a 
direction perpendicular to a surface of the first 
recording areas; 

the second recording areas are formed as 
stripe-shaped marks that are oblong in a radial 
direction of the disk; and 
a plurality of the marks is arranged in a circum- 
ferential direction of the disk, the arrangement 
being based on a modulation signal of the 
write-once information. 

2. The optical disk according to Claim 1 , further com- 
prising an identifier for indication whether there is a 
row of a plurality of marks arranged in a circumfer- 
ential direction of the disk. 

3. The optical disk according to Claim 2, wherein the 
identifier indicating the row of marks is stored 
among control data. 

4. The optical disk according to Claim 1 , wherein the 
pre-determined portion comprising write-once infor- 
mation is at an inner perimeter portion of the disk. 

5. The optical disk according to Claim 1 , wherein a dif- 
ference between a luminous energy that is reflected 
from the first recording areas and a luminous 
energy that is reflected from the second recording 
areas is below a certain value. 

6. The optical disk according to Claim 5, wherein the 
difference between luminous energy that is 
reflected from the first recording areas and lumi- 
nous energy that is reflected from the second 
recording areas is not more than 10%. 

7. The optical disk according to Claim 1 , wherein a dif- 
ference between an average refractive index of the 
first recording areas and an average refractive 
index of the second recording areas is not more 
than 5%. 

8. The optical disk according to Claim 1, wherein the 



magnetic anisotropy of the magnetic film of the sec- 
ond recording areas in an in-plane direction is dom- 
inant. 

5 9. The optical disk according to Claim 1, wherein at 
least a portion of the magnetic film of the second 
recording areas is crystallized. 

10. The optical disk according to Claim 1 , wherein said 
10 recording layer comprises a multilayer magnetic 

film. 

11. An optical disk comprising: 

15 a disk substrate; and 

a recording layer on the disk substrate, the 
recording layer including a film that can be 
reversibly changed between two optically 
detectable states; 
20 wherein 

the optical disk stores write-once information 
formed by first recording areas and second 
recording areas in a pre-determined portion of 
said recording layer; 
25 a luminous energy that is reflected from the first 

recording areas differs from a luminous energy 
that is reflected from the second recording 
areas; 

the second recording areas are formed as 
30 stripe-shaped marks that are oblong in a radial 

direction of the disk; and 
a plurality of the marks is arranged in a circum- 
ferential direction of the disk, the arrangement 
being based on a modulation signal for the 
35 write-once information. 

12. The optical disk according to Claim 1 1 , further com- 
prising an identifier for indication whether there is a 
row of a plurality of marks arranged in a circumfer- 

40 ential direction of the disk. 

13. The optical disk according to Claim 12, wherein the 
identifier indicating the row of marks is stored 
among control data. 

45 

14. The optical disk according to Claim 1 1 , wherein the 
pre-determined portion comprising write-once infor- 
mation is at an inner perimeter portion of the disk. 

so 15. The optical disk according to Claim 11, wherein the 
recording layer undergoes a reversible phase 
change between a crystalline phase and an amor- 
phous phase, depending on irradiation conditions 
for irradiated light. 

16. The optical disk according to Claim 15, wherein the 
difference between luminous energy that is 
reflected from the first recording areas and lumi- 



20 



27 



53 EP 0 S 

nous energy that is reflected from the second 
recording areas is at least 10%. 

17. The optical disk according to Claim 15, wherein a 
difference between an average refractive index of 
the first recording areas and an average refractive 
index of the second recording areas is at least 5%. 

18. The optical disk according to Claim 15, wherein the 
second recording areas of said recording layer are 
in a crystalline phase. 

19. The optical disk according to Claim 15, wherein 
said recording layer comprises a Ge-Sb-Te alloy. 

20. An optical disk whereon main information and write- 
once information is recorded, the write-once infor- 
mation being different for each disk, and the write- 
once information storing at least watermark produc- 
tion parameters for producing a watermark. 

21. The optical disk according to Claim 20, wherein the 
main information is recorded by providing convex- 
concave pits in a reflective layer, and the write-once 
information is recorded by partially removing the 
reflective layer. 

22. The optical disk according to Claim 20, wherein the 
main information and the write-once information are 
recorded by partially changing a reflection coeffi- 
cient of a reflective layer. 

23. The optical disk according to Claim 20, wherein a 
recording layer comprises a magnetic layer with a 
magnetic anisotropy in a direction perpendicular to 
a surface of the magnetic layer, the main informa- 
tion is recorded by partially changing a magnetiza- 
tion direction of the recording layer, and the write- 
once information is recorded by partially changing 
the magnetic anisotropy in the direction perpendic- 
ular to the surface of the magnetic layer. 

24. A method for recording write-once information onto 
an optical disk (a) comprising a disk substrate, and 
a recording layer on the disk substrate, including a 
magnetic film with a magnetic anisotropy in a direc- 
tion perpendicular to a surface of the magnetic film; 
and (b) storing write-once information formed by 
first recording areas and second recording areas in 
a pre-determined portion of said recording layer; 
the method comprising forming the second record- 
ing areas as a plurality of stripe-shaped marks that 
are oblong in a radial direction of the disk in a cir- 
cumferential direction of the disk by irradiating laser 
light based on a modulation signal of the write-once 
information in a circumferential disk direction in the 
pre-determined portion of said recording layer in a 
manner that a magnetic anisotropy in a direction 



n 345 A1 54 

perpendicular to a surface of the second recording 
areas becomes smaller than a magnetic anisotropy 
in a direction perpendicular to a surface of the first 
recording areas. 

5 

25. The recording method according to Claim 24, 
wherein, when the second recording areas are 
formed, a laser light source is pulsed in accordance 
with a modulation signal of phase-encoded write- 

10 once information, and the optical disk or the laser 
light is rotated. 

26. The recording method according to Claim 24, 
wherein the optical disk further comprises a reflec- 
ts tive layer and a protective layer on the disk sub- 
strate, and an intensity of laser light irradiated to 
form the second recording areas is smaller than an 
intensity of laser light destroying at least one of the 
disk substrate, the reflective layer and the protec- 

20 tive layer. 

27. The recording method according to Claim 24, 
wherein an intensity of laser light irradiated to form 
the second recording areas is an intensity for crys- 

25 tallizing at least a portion of said recording layer. 

28. The recording method according to Claim 24, 
wherein an intensity of laser light irradiated to form 
the second recording areas is larger than an inten- 

30 sity of laser light for heating said recording layer to 
a Curie temperature. 

29. The recording method according to Claim 24, 
wherein an intensity of laser light irradiated to form 

35 the second recording areas is an intensity for mak- 
ing a magnetic anisotropy of the magnetic layer of 
the first recording areas in an in-plane direction 
dominant. 

40 30. The recording method according to Claim 24, 
wherein, with a unidirectional convergence focusing 
lens, rectangularly stripe-shaped laser light is irradi- 
ated onto said recording layer when the second 
recording areas are formed. 

45 

31. The recording method according to Claim 24, 
wherein a light source of the laser light that is irradi- 
ated for forming the second recording areas is a 
YAG laser. 

50 

32. The recording method according to Claim 31, 
wherein a magnetic field above a certain value is 
applied to said recording layer while irradiating 
laser light from the YAG laser. 

55 

33. The recording method according to Claim 32, 
wherein the magnetic field applied to said recording 
layer is at least 5kOe. 



28 



55 



EP 0 971 345 A1 



56 



34. A method for recording write-once information onto 
an optical disk (a) comprising a disk substrate; and 
on the disk substrate a recording layer comprising a 
film that can be reversibly changed between two 
optically detectable states; and (b) storing write- 
once information formed by first recording areas 
and second recording areas in a pre-determined 
portion of said recording layer; the method compris- 
ing forming the second recording areas as a plural- 
ity of stripe-shaped marks that are oblong in a radial 
direction of the disk in a circumferential direction of 
the disk by irradiating laser light based on a modu- 
lation signal of the write-once information in a cir- 
cumferential disk direction in the pre-determined 
portion of said recording layer in a manner that a 
luminous energy of light reflected from the first 
recording areas differs from a luminous energy of 
light reflected from the second recording areas. 



41. A method for reproducing write-once information 
from an optical disk (a) comprising a disk substrate, 
and a recording layer on the disk substrate, the 
recording layer including a magnetic film with a 

5 magnetic anisotropy in a direction perpendicular to 
a surface of the magnetic film; and (b) storing write- 
once information formed by first recording areas 
and second recording areas in a pre-determined 
portion of said recording layer, the first and second 

10 recording layers having different magnetic ani- 
sotropies in a direction perpendicular to a surface of 
the magnetic layer; the method comprising: 

irradiating linearly polarized laser light onto 
15 said pre-determined portion; and 

detecting a change in a polarization orientation 
of light reflected from the optical disk or light 
transmitted through the optical disk. 



35. The recording method according to Claim 34, 
wherein, when the second recording areas are 
formed, a laser light source is pulsed in accordance 
with a modulation signal of phase-encoded write- 
once information, and the optical disk or the laser 
light is rotated. 

36. The recording method according to Claim 34, 
wherein the optical disk further comprises a reflec- 
tive layer and a protective layer on the disk sub- 
strate, and an intensity of laser light irradiated to 
form the second recording areas is smaller than an 
intensity of laser light destroying at least one of the 
disk substrate, the reflective layer and the protec- 
tive layer. 

37. The recording method according to Claim 34, 
wherein an intensity of laser light irradiated to form 
the second recording areas is an intensity for crys- 
tallizing at least a portion of said recording layer. 

38. The recording method according to Claim 34, 
wherein, with a unidirectional convergence focusing 
lens, rectangularly stripe-shaped laser light is irradi- 
ated onto said recording layer when the second 
recording areas are formed. 

39. The recording method according to Claim 35, 
wherein a light source of the laser light that is irradi- 
ated for forming the second recording areas is a 
YAG laser. 

40. A method for recording write-once information onto 
an optical disk, comprising: 

producing a watermark based on a disk ID; and 
overlapping the watermark on specific data to 
record it as write-once information. 



20 42. The reproducing method according to Claim 41, 
wherein the linearly polarized laser light is irradi- 
ated onto said pre-determined portion after mag- 
netizing the recording layer of said pre-determined 
portion in one step by applying a magnetic field that 

25 is larger than a coercive force of the recording layer 
in said pre-determined portion. 

43. The reproducing method according to Claim 41, 
wherein the linearly polarized laser light is irradi- 

30 ated onto said pre-determined portion after aligning 
a magnetization of said recording layer of said pre- 
determined portion by applying a unidirectional 
magnetic field to said pre-determined portion while 
increasing the temperature of said recording layer 

35 in said pre-determined portion above the Curie 
temperature by irradiating laser light of constant 
luminous energy. 

44. A method for reproducing write-once information 
40 from an optical disk (a) comprising a disk substrate; 

and a recording layer on the disk substrate, the 
recording layer including a film that can be reversi- 
bly changed between two optically detectable 
states; and (b) storing write-once information 
45 formed by first recording areas and second record- 
ing areas with different reflection coefficients in a 
pre-determined portion of said recording layer; the 
method comprising: 

so irradiating focused laser light onto said pre- 

determined portion; and detecting a change in 
a luminous energy reflected from the disk. 

45. An apparatus for reproducing optical disks compris- 
55 ing (a) a main information recording area for record- 
ing main information; and (b) an auxiliary signal 
recording area overlapping partly with the main 
information recording area for recording a phase- 



EP 0 971 345 A1 



encoding modulated auxiliary signal that overlaps a 
signal of main information, the apparatus compris- 
ing: 

means for reproducing a main information sig- 
nal in the main information recording area with 
an optical head; 

first decoding means for decoding a main infor- 
mation signal to obtain main information data; 
means for reproducing a mixed signal compris- 
ing a main information signal in said auxiliary 
signal recording area and the auxiliary signal 
as a reproduction signal with the optical head; 
frequency separation means for suppressing 
the main information signal in the reproduction 
signal to obtain the auxiliary signal; and 
second decoding means for phase-encoding 
decoding the auxiliary signal to obtain the aux- 
iliary data. 

46. The apparatus according to Claim 45, wherein the 
frequency separation means is a low-frequency 
component separation means for suppressing high 
frequency components in the reproduction signal 
reproduced with the optical head to obtain a low fre- 
quency reproduction signal, the apparatus further 



a second-slice-level setting portion for produc- 
ing a second slice level from said low-fre- 
quency reproduction signal; and 
a second-level slicer for slicing the low-fre- 
quency reproduction signal at the second slice 
level to obtain a binarized signal; 
wherein the apparatus phase-encoding 
decodes the binarized signal to obtain the aux- 
iliary data. 

47. The apparatus according to Claim 46, wherein 

the second-slice-level setting portion com- 
prises auxiliary low-frequency component sep- 
aration means with a time constant that is 
larger than that of the low-frequency compo- 
nent separation means; 
a reproduction signal reproduced with the opti- 
cal head or a low-frequency reproduction sig- 
nal obtained with the low-frequency component 
separation means is entered into the auxiliary 
low-frequency component separation means; 
and 

components with frequencies lower than the 
low-frequency reproduction signal are 
extracted to obtain a second slice level. 

48. The apparatus according to Claim 45, further com- 
prising: 



58 

frequency transformation means for transform- 
ing a main information signal included in a 
reproduction signal reproduced with the optical 
head from a time domain into a frequency 
domain to produce a first transformation signal; 
means for producing a mixed signal, wherein 
auxiliary information has been added or super- 
posed to the first transformation signal; 
frequency inverse-transformation means for 
transforming the mixed signal from the fre- 
quency domain to the time domain to produce 
a second transformation signal. 

49. An apparatus for reproducing optical disks, wherein 
an optical head irradiates linearly polarized light 
onto an optical disk, and a change of a polarization 
orientation of light that is transmitted or reflected 
from the optical disk is detected in accordance with 
a recording signal on the optical disk; and the appa- 
ratus comprises: 

means for moving, when necessary, the optical 
head into a pre-determined portion of the opti- 
cal disk where write-once information is stored, 
and 

means for reproducing the write-once informa- 
tion after detecting a change of a polarization 
orientation of light that is transmitted or 
reflected from the pre-determined portion. 

50. The apparatus according to Claim 49, further com- 
prising means for detecting an identifier indicating 
whether write-once information within control data 
of the optical disk is present, the indication being 
based on a detection signal of detection light that is 
received with at least one photo-detector of the 
optical head or on an all-sum signal of detection 
signals of detection light that is received with a plu- 
rality of photo-detectors of the optical head, 

wherein to detect the identifier and to verify 
whether write-once information is present, the opti- 
cal head is moved to the pre-determined portion of 
the optical disk where write-once information is 
stored, when necessary. 

51. The apparatus according to Claim 49, further com- 
prising decoding means for phase-encoding decod- 
ing during reproduction of the write-once 
information. 

52. An apparatus for reproducing optical disks whereon 
main information is stored and write-once informa- 
tion that differs for each disk is stored, the appara- 
tus comprising: 

a signal reproduction portion for reproducing 
the main information; 

a write-once information reproduction portion 



30 



EP 0 971 345 A1 



for reproducing the write-once information; and 
a watermark attaching portion for producing a 
watermark signal based on the write-once 
information, adding the watermark signal to the 
main information and giving it out. 

53. The apparatus according to Claim 52, wherein the 
write-once information is recorded by partially 
changing a reflection coefficient of a recording layer 
on the optical disk. 

54. The apparatus according to Claim 52 wherein a 
recording layer of the optical disk comprises a mag- 
netic film having a magnetic anisotropy that is per- 
pendicular to a film surface; and 

write-once information is stored by partially 
changing the perpendicular magnetic anisot- 
ropy of the magnetic film. 

55. The apparatus according to Claim 52 wherein a 
watermark attaching portion overlaps a signal of 
the main information with auxiliary information com- 
prising a watermark. 

56. The apparatus according to Claim 52, further com- 
prising: 

a frequency transformation means for produc- 
ing a first transformation signal by transforming 
a signal of main information from a time domain 
into a frequency domain; 
means for producing a mixed signal by adding 
or superposing write-once information and the 
first transformation signal; and 
frequency inverse-transformation means for 
producing a second transformation signal by 
transforming the mixed signal from the fre- 
quency domain into the time domain. 

57. The apparatus according to Claim 52, further com- 
prising: 

an MPEG decoder for expanding main informa- 
tion into a video signal; and 
means for inputting the video signal into the 
watermark attaching portion. 

58. The apparatus according to Claim 57, further com- 
prising a watermark reproduction portion for repro- 
ducing watermarks; 

wherein 

said MPEG decoder and said watermark repro- 
duction portion both comprise a mutual authen- 
tication portion; and 

encrypted main information is sent and 
decrypted only if the mutual authentication por- 



tions authenticate each other. 

59. The apparatus according to Claim 57 wherein a 
decoded signal of main information that is com- 

5 pounded with an encryption decoder is input into 
the MPEG decoder. 

60. The apparatus according to Claim 59, further com- 
prising a watermark reproduction portion for repro- 

10 ducing watermarks; 
wherein 

an encryption decoder and said watermark 
reproduction portion both comprise a mutual 
15 authentication portion; and 

encrypted main information is sent and 
decrypted only if the mutual authentication por- 
tions authenticate each other. 

20 61. An apparatus for recording and reproducing optical 
disks whereon information can be recorded, erased 
and reproduced and whereon main information is 
stored on a main recording area of a recording layer 
of the optical disks using a recording circuit and an 

25 optical head, the apparatus comprising: 

means for reproducing write-once information, 
that is recorded onto a pre-determined portion 
of the recording layer, using a signal output 
30 portion of the optical head, which detects the 

write-once information as a change of a polari- 
zation orientation; 

means for recording the main information onto 
the main recording area as encrypted informa- 

35 tion that is encrypted with an encryption 

encoder using the write-once information; and 
means for reproducing the main information by 
reproducing the write-once information with the 
signal output portion of the optical head and 

40 decoding the encrypted information as a 

decryption key in an encryption decoder. 

62. An apparatus for recording and reproducing optical 
disks whereon main information is recorded onto a 
45 main recording area of a recording layer of the opti- 
cal disks using a recording circuit and an optical 
head, the apparatus comprising: 

a watermark attaching portion for adding a 
so watermark to the main information; 

wherein 

write-once information that is stored in a pre- 
determined portion of the recording layer is 
reproduced with the optical head; 
55 the reproduced write-once information is 

added to the main information as a watermark 
with said watermark attaching portion; 
the main information including the watermark is 



31 



EP 0 971 345 A1 



recorded onto the main recording area. 

63. The apparatus according to Claim 62, wherein the 
main information is recorded by partially changing a 
reflection coefficient of the recording layer. 

64. The apparatus according to Claim 62 wherein the 
recording layer comprises a magnetic film having a 
magnetic anisotropy that is perpendicular to a film 
surface; and 

main information is stored by partially changing 
a magnetization direction of the magnetic film. 



encrypted main information is sent and 
decrypted only if the mutual authentication por- 
tions authenticate each other. 

5 70. The apparatus according to Claim 68 wherein a 
decoded signal of main information that is com- 
pounded with an encryption decoder is input into 
the MPEG decoder. 

w 71. The apparatus according to Claim 70, further com- 
prising a watermark reproduction portion for repro- 
ducing watermarks; 
wherein 



65. The apparatus according to Claim 64 wherein the 15 
main information and the write-once information are 
reproduced by detecting a change of a magnetiza- 
tion orientation of the recording layer or a change of 
the perpendicular anisotropy of the recording layer 
with an optical head as a change of a polarization 20 
orientation. 

66. The apparatus according to Claim 62 wherein a 
watermark attaching portion overlaps a signal of 
the main information with auxiliary information com- 
prising a watermark. 

67. The apparatus according to Claim 62, further com- 
prising: 

a frequency transformation means for produc- 
ing a first transformation signal by transforming 
a signal of main information from a time domain 
into a frequency domain; 
means for producing a mixed signal by adding 
or superposing write-once information and the 
first transformation signal; and 
frequency inverse-transformation means for 
producing a second transformation signal by 
transforming the mixed signal from the fre- 
quency domain into the time domain. 

68. The apparatus according to Claim 62, further com- 
prising: 



an MPEG decoder for expanding main in 
tion into a video signal; and 
means for inputting the video signal into the 
watermark attaching portion. 

69. The apparatus according to Claim 68, further com- 
prising a watermark reproduction portion for repro- 
ducing watermarks; 
wherein 

said MPEG decoder and said watermark repro- 
duction portion both comprise a mutual authen- 
tication portion; and 



said encryption decoder and said watermark 
reproduction portion both comprise a mutual 
authentication portion; and 
encrypted main information is sent and 
decrypted only if the mutual authentication por- 
tions authenticate each other. 

72. An apparatus for recording write-once information 
onto an optical disk storing main information, the 
apparatus comprising means for recording auxiliary 
information comprising at least one of a disk ID and 
watermark production parameters. 

73. The apparatus according to Claim 72, wherein the 
main information is stored by providing convex-con- 
cave pits in a reflection film of the optical disk, and 
the auxiliary information is stored by partially eras- 
ing the reflection film. 

74. The apparatus according to Claim 72, wherein the 
main information is stored by partially changing a 
reflection coefficient of a recording layer of the opti- 
cal disk, and the auxiliary information is stored by 
partially changing a reflection coefficient of the 
recording layer of the optical disk. 

75. The apparatus according to Claim 72 wherein a 
recording layer of the optical disk comprises a mag- 
netic film having a magnetic anisotropy that is per- 
pendicular to a film surface; 

main information is stored by partially changing 
a magnetization direction of the magnetic film; 
and 

auxiliary information is stored by partially 
changing the perpendicular magnetic anisot- 
ropy of the magnetic film. 

76. An apparatus for recording optical disks storing 
main information, comprising: 

means for producing a watermark based on 
auxiliary information comprising a disk ID; and 
means for recording data, which consists of 



32 



EP 0 971 345 A1 



certain data to which the watermark has been 
superposed. 



5 



10 



15 



20 



30 



35 



40 



45 



SO 



33 



EP 0 971 345 A1 




22Da 220b 



FIG. 1 



34 




FIG. 2 



EP 0 971 345 A1 



, Movement of rec ording medium 



• 229b 



229c 

\ 




\ 229a 


......... • ..... . -. 


Hf 
II 

■t 


mr 
ii 

mt 


: ;: ' : : .:-'-.-.v. : 



-230 



> 233 
/ 234 

> 235 



FIG. 3 



36 



EP 0 971 345 A1 



0K(° ) 



1 T 

/ / 
// 
// 

- -4^ „„ 



7" 



' X 

// 
// 
// 

J/ 5 



He (KOe) 



FIG. 4 



37 



EP 0 971 345 A1 




38 



EP 0 971 345 A1 



(a) Differential signal waveform of BCA signal 

for 8 A recording current 273 




■(b) Addition signal waveform of BCA signal 
for 8 A recording current 




FIG. 6 

39 



EP 0 971 345 A1 




EP 0 971 345 A1 



( 1 ) Formation of substrate 



( 2 ) Formation of dielectric layer 

o 

// \\ 



WWWWWM 



( 3 ) Formation of magnetic 
recording layer 



o 




( 5 ) Formation of reflection layer^_^ 




FIG. 8 



41 



EP 0 971 345 A1 



7 ) Magnetization of magnetic layer 2 17 

| Q3L0IQZ0IJ magneti2er 



- ^213 




42 



EP 0 971 345 A1 




(a) recording power )) 



EP 0 971 345 A1 

optimum power 




FIG. 11 



EP 0 971 345 A1 



(a) BCA for large recording power 

1-1 optical microscope 1-2 polarization microscope 




(b) BCA for optimum recording power 

2-1 optical microscope 2-2 polarization microscope 




FIG. 12 



45 



EP 0 971 345 A1 



(a) Rotation angle for polarization plane of 
light reflected from non-BCA portions 

I light reflected from non-BCA portions 

P D 2 

incident light 




>PD1 

( b ) Rotation angle for polarization plane of 
light reflected from BCA portions 

light reflected from BCA portions 
incident light 




>■ P D 1 



FIG. 13 



46 



EP 0 971 345 A1 

replaced sheet (rule 26) 




FIG. 14 



47 



EP 0 971 345 A1 




48 



EP0 971 345 A1 



RZ recording 
recording blocks based 
on rotation pulse _l 



(1) recording signal "00" 



<A /920a ,^f 21a ^9223 
T1 I T2 I T3 I T4 



/934a 



j — I 



(2) trimming pattern for "00" 



925a / 926a 



(4) trimming pattern for "pi" 

^/925b 



j^/926b ^9 27b 



FIG. 16 



(3) recording signal "01" 921b 

| T1 I T2 \ T3 I T4 I T1 I 



49 



EP 0 971 345 A1 



PE-RZ recording 
recording 
blocks 



J_ 



( 1 ) recording signal "0" 



J/ 921a / 922a 



H i r^t 



(2) trimming shape for "0" 

925n ^ 926a 



(3) recording signal "1 " 



I J/ 8Z1D 



1 r>» 



H t2 t3 

(4 ) trimming shape for "1 " 

,r< 825b ^ 





? 1 f 1 


I — ^— 






/ 


✓ 924c 




r 


'9j24e 


r 


' 924e i 



12 13 t 

FIG. 17 



b te t7 



EP 0 971 345 A1 





52 



EP 0 971 345 A1 



move optical head to 
inner perimeter 



rotation speed 
control 



stripes? 




930f 



data reproduction 



'930g 



-930h 



FIG. 20 



53 



EP 0 971 345 A1 



(a) data structure 
\< £ 



(b) data structure for n=1 



Preamble (All OOh) 




EDC(4B) 



Postamble (Ait 55h) 



RS15 

random error correctability 



1 row 



951a- 
951b- 



4n rows 
0£ng12) 



SB 




RS 1 


"o 




*4 


RS 1 




RS 


EDC 


RS ,3 


C ,oo 


RS 13 


! ECC 


RS 13 




RS 1 3 








RS 14 




RS 1. 





Byte error rate 
before correction 


Number of disks not 
readable after correction 


10 - 5 


1 :10<° 


10 ^ 


1 : 10 7 


10 "3 


1 : 10 4 


burst error correctability=5.7mm 



FIG. 21 

54 



EP 0 971 345 A1 



(a) data structure for synchronized coding 



synchronized coding 



Sync 
Byte 
/ Resync 


Bit Pattern 


Fixed Pattern 


Sync Code 


( Channel bit ) 

C 15 C 14 C 13 ^2 C 11 C 1C 


C 9 C 8 


(Data bit) 
b 3 b 2 b, b 0 


SB 


0 1 SO 0 ! 0 1 


1 0 


0 0 0 0 


RSi 


0 1 j 0 0 | 0 1 


1 0 


0 0 0 1 


RS 2 


0 1 | 0 0 j 0 1 


1 0 


0 0 10 










RSi 


0 1 I 0 0 i 0 1 


1 0 


i 










RSis 


0 1 j 0 0 i 0 1 


1 0 


1111 


(b) fixed 








jynch 
0 

J 


rorjzing pattern 
1 | 0 0 | 0 


1 


1 0 

(0 1) 


trimming counter identifier ^ ^ 

first trimming recording 
^-second trimming recording 




i 


n 








> t 




I T 9 | TV 







(c) maximum capacity 





recording 
capacity 


total number 
of bytes 


efficiency 


recorded 
angular range 


unrecorded 
angular range 


minimum 


12B 


41 B 


29.3% 


51° 


309° 


maximum 


188B 


271 B 


69.4% 


336° 


24° 



FIG. 22 



55 



EP 0 971 345 A1 



(a) low-pass filter g43 



Zout 




(500) 







8200pF 



T 



8200pF 



Zin 
(50 Q) 



(b) simulated waveform after pass through low-pass filter for 1 14L = I s= o.1 



" pit regeneration 
_ signal 

(continues for 14T) 



FIG. 23 



56 



EP 0 971 345 A1 



(a) reproduction signal waveform 
T (S) 



T (NS) 



T (S) ST (NS) orT (S) T (NS) 




Il4H 



n=1,2, 3, or 4 



reflectivity requirement : I s /Ii4H ^0.1 



(b) processing precision of slits (atr=22.2mm) 
30Xniam « 



SOXn^m 




FIG. 24 



57 



EP 0 971 345 A1 




reproduce recording layer 
on reverse side or output 
" instruction to reproduce 
reverse side " 



move optical head to 
inner periphery 



reproduce stripes 
(after switching to CAV 
rotation control 




finished? 



■>! Yes 



move optical head to outer 
periphery (after switching to 
rotation phase control) 



-940f 



data reproduction " 



-940g 



FIG. 25 



58 



EP0 971 345 A1 




X » 








5 








ency 
ng m 


j 






i g-1 


i 













CO 
CVJ 

d 

UL 



59 



EP 0 971 345 A1 



( 1 ) BCA region 
reproduction 
signal 



GND - 



(2) low-pass 
filter output 



GND - 



916 : second slice level 



(3) binary output 
GND _ 



"innnnnnn ... 



(4) output of 
frequency 
half-divider 

GND ~ 



FIG. 27 



EP 0 971 345 A1 




61 



EP 0 971 345 A1 




CM 

d 





L 


T 
C 




1 1 










> q= 







62 



EP 0 971 345 A1 




EP 0 971 345 A1 



(1) 

reproduction 
signal 



(2) 
second 
slice level 

(3) 
comparator 
input signal 



I J..1 £ ill ill Iiii^l .»! l. lufiy.ii J Li ill i til J 



MUM 


m 


m 


mm 




lllllltlU.I 


\J 








u 








U 





























































i 






Y 




vA 



























(4) 
binary 
signal 



FIG. 31 



EP 0 971 345 A1 




EP 0 971 345 A1 




FIG. 33 



66 



EP 0 971 345 A1 



passejduJOD psssejduiooun 

I ^ UOjjL I I UOflJOd ( 




67 



EP 0 971 345 A1 



(1) original signal 



( 2 ) spectrum of original signal 



(3) spectrum of ID signal 



(4) signal after spectral dispersion 



( 5 ) signal after inverse frequency conversion 



(6) illegally 



copied signal 



( 7 ) frequency spectrum of illegal copy 



(8) spectrum ( 7 ) minus spectrum ( 2 ) 



J L 



FIG. 35 



EP 0 971 345 A1 



11 


1 


8 i 




73 




D) 
<D 












to 1 , 1 









uojuod 
"i yidjno 



japooap 03dW 

r 



5? ^9 



CD 
CO 

d 

Ll 



<D co 

'« S 


|ja»!UJ8U84| 

is t 




O 


"^j ^ uoipod 5jJBUJjajeM| 




2 

<D 


1 ? 




a 
o 






systen 


1 <6c ) 









EP 0 971 345 A1 




70 



EP 0 971 345 A1 




EP0 971 345 A1 




( 4 ) recording data i 0 j 1 i 0 i 0 i 0 
reproduction signal 

( 5 ) reproduction 
signal 

(6) after filtering 

(7) reproduction data j 0 j 1 j 0 j 0 i 0 

FIG. 39 



72 



EP 0 971 345 A1 




EP 0 971 345 A1 




74 



EP 0 971 345 A1 




FIG. 42 



75 



EP 0 971 345 A1 



INTERNATIONAL SEARCH REPORT 



CLASSIFICATION OF SUBJECT MATTER 
Int. CI 6 G11B11/10, 7/00, G06F12/14 
According to International Patent Classification (IPC) or to both national 



itional application No. 
PCT/JP97/04664 



B. FIELDS SEARCHED 



Int. CI 6 G11B11/10, 7/00, 20/10, G06F12/14 



icumentation searched otner man minimum a 

Jitsuvo Shinan Koho 
Kokax Jitsuyo Shinan Koho 
Toroku Jitsuvo Shinan Koho 



that such documents are ini 

UK - ill? 



C. DOCUMENTS CONSIDERED TO BE RELEVANT 



Citation of document, with indication, where appropriate, of the relevant passages 



Relevant to claim No. 



JP, 4-105218, A (Seiko Epson Corp.), 
April 7, 1992 (07. 04. 92) (Family: none) 

JP, 5-50531, U (Hitachi Maxell, Ltd.), 
July 2, 1993 (02. 07. 93) (Family: none) 

JP, 63-308756, A (Matsushita Electric Industria 
Co. , Ltd.) , 

December 16, 1988 (16. 12. 88) (Family: none) 

JP, 63-100632, A (Sony Corp.), 

May 2, 1988 (02. 05. 88) (Family: none) 

JP, 7-85574, A (Victor Co. of Japan, Ltd.), 
March 31, 1995 (31. 03. 95) (Family: none) 



49 
1, 4 

11, 15 
19 



j~| Further documents are listed in the continuation of Bo*C. Q See patent family at 



Special categories of died . 



, U ,pu H U^.a.r.f te ra- i ^«..f l U^ r "X" S^I^'SSM^ * ievoive .. 
au^a»mwuicBmaytlm>wdoubuoBpnoriry^«^)orwhlA^ Hep when tbi ' 



smber of the same patent family 



Date of the actual completion of the ii 

January 21, 1998 (21. 01. 98) 



Date of mailing of the international search report 

February 3, 1998 (03. 02. 98) 



Name and mailing address of the ISA/ 

Japanese Patent Office 
Facsimile No. 

Form PCT/ISA/210 (second sheet) (July 1992) 



76