Magneto-optical disk having write-once identification marks and method for recording thereof

An optical disk and a method for storing write-once information usable for preventing the illegal copies. The optical disk comprises a disk substrate, and a recording layer having a magnetic film disposed on the disk substrate. The optical disk stores write-once information formed by first recording areas and second recording areas and the write-once information being different for each disk. The second recording areas are formed as a plurality of stripe-shaped marks that are oblong in a radial direction of the disk by irradiating laser light based on a modulation signal of the write-once information 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 is smaller than a magnetic anisotropy in a direction perpendicular to a surface of the first recording areas.

FIELD OF THE INVENTION
 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
 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 storage devices and recording media
 therefor, especially optical disks, which can be accessed with high access
 speeds.
 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 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.
 The following is an explanation of how an optical disk with the above
 configuration is operated.
 In the case of an optical disk having, in its recording layer, a
 magneto-optical layer with perpendicular magnetic anisotropy, the
 recording and erasing of information is performed by locally (a) heating
 the recording layer with a laser beam to a temperature with small coercive
 force above the compensation temperature or to a temperature near or above
 the Curie temperature to decrease the coercive force of the recording
 layer in the irradiated portion, and (b) magnetizing the 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 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 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 photodetector through the change in the
 intensity of the irradiated light. In order to decrease the interference
 between opposite magnetizations and allow high-density recordings, a
 magnetic material with perpendicular magnetic anisotropy is used for the
 recording layer of the optical disk.
 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 magnetic thin films
 comprising an exchange coupling multilayer or a magneto-static coupling
 multilayer.
 For the recording layer, a material is used that can record information by
 locally raising the temperature or inducing a chemical reaction due to
 absorption of the irradiated laser light. The local variations in the
 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.
 Regarding such optical disks, there is a need 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.
 With the above configuration, it is possible to record disk information in
 TOC (or control data) areas, 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.
 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
 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 recording 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.
 In order to attain these objects, a first 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
 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-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 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 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.
 It is preferable that the optical disk according to 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 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.
 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 perimeter portion of the disk. With this
 configuration, the position of the optical head with respect to a radial
 direction of the disk can be determined with an optical head stopper or
 address information of a bit signal.
 It is preferable that in the optical disk according to the first
 configuration, a difference 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. It is
 particularly preferable that the difference between luminous energy that
 is reflected from the first recording areas and luminous energy that is
 reflected from the 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.
 It is preferable that in the optical disk according to the first
 configuration, a difference 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%. With this configuration, the
 difference between luminous energy that is reflected from the first
 recording areas and luminous energy that is reflected from the second
 recording areas can be adjusted to not more than 10%.
 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.
 It is preferable that in the optical disk according to the first
 configuration, at least a portion of the magnetic film of the second
 recording areas is crystallized. With this configuration, the magnetic
 anisotropy perpendicular 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 difference of the polarization orientation
 to the first recording areas.
 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.
 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 differs
 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.
 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.
 Moreover, it is preferable that the identifier indicating the row of marks
 is stored among control data.
 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 perimeter portion of the disk.
 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 and an amorphous phase, depending on
 irradiation conditions for irradiated light. With this configuration,
 information can be recorded by utilizing an optical difference based on a
 reversible structural change at the atomic level. Moreover, information
 can be reproduced 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 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
 average 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 the
 second recording areas can be adjusted to at least 10%. Moreover, in this
 case, it is preferable that the second recording areas of the recording
 layer are in a crystalline phase. With this configuration, recording can
 be performed with excessive laser power. Furthermore, 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.
 In a third configuration of an optical disk in 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 with this third configuration, the following
 operations can be performed: When the watermark production parameters and
 the disk ID are recorded in the write-once information with absolutely no
 correlation between the disk ID and the watermark production parameters,
 it 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.
 It is preferable that in the optical disk according to the third
 configuration, 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.
 It is preferable that in the optical disk according to the third
 configuration, the main information and the write-once information are
 recorded by partially changing a reflection coefficient of a reflective
 layer.
 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 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.
 A first 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
 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 perpendicular 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 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.
 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 information can be recorded with little fluctuations of the
 channel clock period.
 It is preferable that in the first method for recording write-once
 information, the optical disk further 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.
 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 recording layer. With this configuration, the magnetic anisotropy of
 the recording layer perpendicular to the surface of the recording layer
 cannot be restored, so that manipulation of the write-once information can
 be prevented.
 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
 recording layer to a Curie temperature. With this configuration, it is
 possible to decrease or eliminate the magnetic anisotropy of the recording
 layer perpendicular to the surface of the recording layer, especially when
 the intensity of the laser light is excessive.
 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
 magnetic layer of the first recording areas in an in-plane direction
 dominant.
 It is also preferable that in the first method for recording write-once
 information, rectangularly stripe-shaped laser light is irradiated with a
 unidirectional convergence focusing lens onto the recording layer when the
 second recording areas are formed.
 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
 preferable 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 anisotropy 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 5 kOe.
 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 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 luminous energy of light
 reflected from the first recording areas differs from a luminous energy of
 light reflected from the second recording areas. In accordance 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.
 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.
 It is also preferable that in the second method for recording write-once
 information, the optical disk further 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.
 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.
 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 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.
 A third method for recording write-once information onto an optical disk
 comprises producing a 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 the origin of illegal copies can be determined.
 A first 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 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,
 the first and second recording layers having different 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
 orientation of light reflected from the optical disk or light 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.
 It is preferable that in the first method for reproducing write-once
 information, the linearly polarized laser light is irradiated onto the
 pre-determined portion after magnetizing the recording layer of the
 pre-determined portion in one step by applying a magnetic field that is
 larger than a coercive force of the recording layer in the pre-determined
 portion. With this configuration, the polarization orientation detected
 from the first recording areas is normally constant, and the reproduction
 signal can be obtained with a stable amplitude from the difference with
 respect to the polarization orientation of the second recording areas.
 It is also preferable that in the first method for reproducing write-once
 information, the linearly polarized laser light is irradiated onto the
 pre-determined portion after aligning a magnetization of the recording
 layer of the pre-determined portion by applying a unidirectional 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 information, the signal
 can be reliably reproduced without being influenced by outside magnetic
 fields or the like.
 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 recording 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.
 A first configuration of an apparatus for reproducing 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 overlaps a signal of main information,
 comprises means for reproducing a main information signal in the main
 information recording area with an optical head; first decoding 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; 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 auxiliary data. In accordance with this
 first configuration of an apparatus for reproducing optical disks, the
 decoding data of the auxiliary signal can be reproduced reliably.
 It is preferable that in the apparatus for reproducing optical disks
 according to the first configuration, 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 frequency reproduction signal, and that the apparatus further
 comprises a second-slice-level setting portion for producing a second
 slice level from the low-frequency reproduction 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
 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 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 optical head
 or a low-frequency reproduction signal 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. With this configuration, the slice level can be set following the
 level variations of low frequency components, so that the signal easily
 can be reproduced.
 It is preferable that the apparatus for reproducing optical disks according
 to the first configuration further 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 mixed signal, wherein auxiliary information has been added
 or superposed to the first transformation signal; and frequency
 inverse-transformation means for transforming the mixed signal from the
 frequency domain to the time domain to produce a second transformation
 signal. With this configuration, the ID signal can be spectrally
 dispersed, so a deterioration of the video signal, which corresponds to
 the main information, can be prevented, and the reproduction of the main
 information becomes easier.
 In a second configuration of an apparatus for reproducing optical disks, 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. The apparatus 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 detecting a change of a polarization
 orientation of light that is transmitted or reflected from the
 pre-determined portion. In accordance with this second configuration of an
 apparatus for reproducing optical disks, the reproduction signal can be
 detected easily, because it is not influenced by variations of the
 reflected luminous energy or by noise components included in the addition
 signal.
 It is preferable that the apparatus for reproducing optical disks according
 to the second configuration further comprises 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 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 identifier and
 to verify whether write-once information is present, the optical head is
 moved to the pre-determined portion of the optical disk where write-once
 information 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 shortened.
 It is preferable that the apparatus for reproducing optical disks according
 to the second configuration further comprises decoding means for
 phase-encoding decoding during reproduction of the write-once information.
 This configuration can be used for the reproduction of write-once
 information, such as an ID signal.
 In a third configuration of an apparatus for reproducing optical disks
 whereon main information is stored and write-once information that differs
 for each disk is stored, the apparatus comprises a signal reproduction
 portion for reproducing the main information; a write-once information
 reproduction portion 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. 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 signal can be
 prevented.
 It is preferable that in the apparatus for reproducing optical disks
 according to the third configuration, the write-once information is
 recorded by partially changing a reflection coefficient of a recording
 layer on the optical disk.
 It is also preferable that in the apparatus for reproducing optical disks
 according to the third configuration, a recording layer of the optical
 disk comprises a magnetic film having a magnetic anisotropy that is
 perpendicular to a film surface; and write-once information is stored by
 partially changing the perpendicular magnetic anisotropy of the magnetic
 film.
 It is also preferable that in the apparatus for reproducing optical disks
 according to the third configuration, a watermark attaching portion
 overlaps a signal of the main information with auxiliary information
 comprising a watermark. With this configuration, the auxiliary information
 being deleted from the main information with a normal recording and
 reproducing system can be prevented.
 It is also preferable that the apparatus for reproducing optical disks
 according to the third configuration 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 information and the first transformation signal;
 and frequency inverse-transformation means for producing a second
 transformation signal by transforming the mixed signal from the frequency
 domain into the time domain.
 It is also preferable that the apparatus for reproducing optical disks
 according to the third configuration further comprises an MPEG decoder for
 expanding 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
 signal. 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. With this configuration, illegal elimination or manipulation of
 watermarks can be prevented, because the encryption is not cancelled 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
 compounded with an encryption decoder is input into the MPEG decoder. With
 this configuration, there is no correlation 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 further 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.
 In a first configuration of 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
 optical head, the apparatus comprises means for reproducing write-once
 information 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
 encrypted information as a decryption key in an encryption decoder. In
 accordance with this first configuration of an apparatus for recording and
 reproducing optical disks, illegal copies can be prevented, so that the
 copyright can be protected.
 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 circuit
 and an optical head, the apparatus comprises a 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 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
 history can be traced from the watermark recording data, so that illegal
 copies and illegal use can be prevented.
 It is preferable that in the apparatus for recording and reproducing
 optical disks according to the second configuration, the main information
 is recorded by partially changing a reflection coefficient of the
 recording layer.
 It is also preferable that in the apparatus for recording and reproducing
 optical disks according to the second configuration, 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. In this
 case, it is preferable that the 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 perpendicular
 anisotropy of the recording layer with an optical head as a change of a
 polarization orientation.
 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.
 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 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 frequency
 domain into the time domain.
 It is also preferable that the apparatus for recording and reproducing
 optical disks according to the second configuration further comprises an
 MPEG decoder for expanding main information into a video signal; 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
 watermark 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.
 In a configuration of an apparatus for recording write-once information
 onto an optical disk storing main information, the apparatus comprises
 means for recording 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.
 It is preferable that in the apparatus for recording write-once information
 onto an optical disk according 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.
 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.
 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
 magnetic anisotropy that is perpendicular 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 anisotropy of the magnetic film.
 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 which the watermark has been
 superposed. In accordance with this configuration of an apparatus for
 recording optical disks storing main information, the watermark can be
 detected from the recorded data, and the contents history can be
 determined, so that the copyright can be protected.

DESCRIPTION OF THE PREFERRED EMBODIMENTS
 The following is a more detailed description of the present invention, with
 reference to the preferred embodiments.
 First Embodiment
 First of all, the structure of a magneto-optical disk is explained.
 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 211, 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
 circumferential direction of the disk. On top of the recording layer 213,
 an intermediate dielectric layer 214 and a reflecting layer 215 are
 deposited in that order. An overcoat layer 216 is formed on top of the
 reflecting layer 215.
 Referring to FIG. 8, the following is an explanation of a method for
 producing a magneto-optical disk in accordance with this embodiment.
 First of all, as shown in FIG. 8(a), a disk substrate 211, which has guide
 grooves or pre-pits for tracking guidance, is produced by injection
 molding using a polycarbonate resin. Then, as is shown in FIG. 8(b), an 80
 nm thick dielectric layer 212 of SiN is formed on the disk substrate 211
 by reactive sputtering with a Si target in an atmosphere containing argon
 gas and nitrogen gas. Then, as is shown in FIG. 8(c), a 30 nm 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(d), a 20 nm intermediate
 dielectric layer 214 consisting of a SiN film is formed on the recording
 layer 213 by reactive sputtering with a Si target in an atmosphere
 containing argon gas and nitrogen gas. Then, as is shown in FIG. 8(e), a
 40 nm thick reflecting layer 215 consisting of an AlTi film is formed on
 the intermediate dielectric layer 214 by DC sputtering with an AlTi target
 in an argon gas atmosphere. Finally, as is shown in FIG. 8(f), a 10 .mu.m
 thick overcoat layer 216 is formed on the reflecting layer 215 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 2500 rpm, and curing
 the Uw-light curing resin by irradiating it with UV light.
 The following is an explanation of a method for recording identifying
 information (write-once information, which is recorded after finishing the
 disk manufacturing process), with reference to FIG. 9.
 First of all, as is shown in FIG. 9(a), the magnetization 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 coercive force of 11
 kOe. Thus, the magnetization orientation of the recording layer 213 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 electromagnet of the magnetizer 217 to 15 kGauss, and passing the
 magneto-optical disk through this magnetic field. Next, as is shown in
 FIG. 9(b), 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 on the recording layer 213 in the form of
 oblong stripes. BCA portions 220a and 220b are recorded as identifying
 information in the circumferential direction of the disk. The recording
 principle, recording method and reproduction method are explained in more
 detail in the course of this specification. Then, as is shown in FIG.
 9(c), a BCA reader 221 is used to detect the BCA portions 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 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.
 The following is an explanation of the operation principle of the BCA
 reader 221, with reference to FIG. 10.
 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 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 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 signal 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 portions 220 can be detected speedily without
 using an optical head for magneto-optical recording and reproduction.
 Since the magnetic anisotropy in the vertical direction of the film surface
 of the BCA portions is considerably lower, a BCA reproduction signal can
 be attained for the BCA portions 220a. The following is a more detailed
 explanation of this:
 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.
 As is shown in FIG. 9, in this embodiment, after the magnetization
 orientation of the vertical magnetization film in the recording layer 213
 has been aligned in one direction (that is, after magnetization), the BCA
 portions 220 are recorded as the identifying information. After the BCA
 portions 220 have been recorded by layering the layers and deteriorating
 the recording layer 213, the magnetization orientation of the vertical
 magnetization 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 temperature by irradiating the recording
 layer 213 with, for example, a stroboscopic light to raise its
 temperature.
 The recording layer 213 of the magneto-optical disk in the present
 embodiment has a coercive force of 11 kOe at room temperature. However,
 when it is irradiated by, for example, a stroboscopic light or a laser
 beam and its temperature is raised to at least 100.degree. C., the
 coercive force becomes about 4 kOe, so that when a magnetic field of at
 least 5 kOe is applied, the magnetization orientation of the recording
 layer 213 can be aligned into one direction.
 The following is an explanation of the recording power for a
 magneto-optical BCA recording.
 FIG. 5 shows the BCA recording characteristics for a BCA signal that was
 recorded on a magneto-optical disk using a BCA trimming device (BCA
 recording device--CWQ pulse recording with a YAG laser excited with a 50 W
 lamp; product by Matsushita Electric Industrial Co., Ltd). As can be seen
 from FIG. 5, when the recording current of the laser is below 8 A, no BCA
 portion is recorded. When the recording current of the laser is in the
 optimal range of 8-9 A, a BCA image 226a can be attained only with a
 polarization microscope, as is shown in FIGS. 5 and 12(b). This BCA image
 226a cannot be observed with an optical microscope. When the recording
 current of the laser is at least 9 A, the BCA images 226b and 226c can be
 attained with both the optical microscope and the polarization microscope,
 as is shown in FIGS. 5 and 12(a). When the recording current of the laser
 as shown in FIG. 5 is higher than 10 A, then the protective layer
 (overcoat layer) is destroyed. This situation is illustrated in FIG. 11.
 In FIG. 11, the 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 8-9 A, only the recording
 layer 213 is deteriorated as shown in FIG. 11(b), and the reflecting layer
 215 and the overcoat layer 216 are left intact.
 The following explains a recording/reproduction apparatus for
 magneto-optical disks according to this embodiment, with reference to FIG.
 7.
 FIG. 7 illustrates the optical configuration of a recording/reproduction
 apparatus for magneto-optical disks according to the first embodiment of
 the present invention. FIG. 7 illustrates an optical head 255 for
 magneto-optical disks, a pulse generator 254, a laser light source 241, a
 collimator lens 242, a polarization beam 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
 .lambda./4-plate 247 for rotating the polarization plane of the light
 reflected from the magneto-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 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.
 As is shown in FIG. 7, a linearly polarized laser beam emitted from the
 laser light source 241 is collimated 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 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 magnetization film (pointing
 upwards and downwards). Owing to the magneto-optical effect, the
 orientation of the polarization plane of the light that is reflected (or
 transmitted) by the magneto-optical disk 240 changes according to the
 magnetization. The reflected light, whose polarization plane was thus
 rotated, is irradiated on the polarization 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.degree. by a .lambda./4
 plate. Then, the P-polarized component and the S-polarized component are
 separated by the polarization beam splitter 248. The light is thus
 separated 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 reproduction
 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 tracking.
 The BCA portions 220, serving as identifying information for the
 magneto-optical disk in his embodiment, are detected with the same
 reproduction method as the data information. As is shown in FIG. 4, the
 vertical 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 .theta..sub.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 magnetic 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.
 The following is a method for aligning the magnetization direction of the
 vertical magnetization film into one direction, when the BCA portions are
 reproduced: A magneto-optical disk recording/reproduction apparatus as
 shown in FIG. 7 irradiates a laser beam of at least 4 mW 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 magnetic field of at least 200 Oe, so that the
 magnetization direction of the recording layer of the BCA portions is
 aligned into one direction.
 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 summation
 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 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.
 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 polarization direction 227a that, owing to
 the Kerr effect in the magnetization film having with vertical
 magnetization anisotropy, is rotated by a rotation angle .theta..sub.k
 against the polarization direction of the incident light.
 Moreover, this embodiment detects the identifying information from a
 differential signal. Using this reproduction method, variations of the
 luminous energy that do not follow the polarized light can be almost
 completely canceled, so that the noise due to these luminous energy
 variations can be reduced.
 Second Embodiment
 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 reproduction 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 circumferential
 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.
 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.
 First of all, a disk substrate 231, which has guide grooves or pre-pits for
 tracking guidance, is produced by injection molding using a polycarbonate
 resin. Then, an 80 nm 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 magnetic reproduction film 233 of GdFeCo with a Curie
 temperature of T.sub.c1 and a coercive force of H.sub.c1, an intermediate
 magnetic film 234 of TbFe with a Curie temperature of T.sub.c2 and a
 coercive force of H.sub.c2, and a magnetic recording film 235 of TbFeCo
 with a Curie temperature of T.sub.c3 and a coercive force of H.sub.3.
 These films are formed on top of the dielectric layer 232 by DC sputtering
 with alloy targets in anAr gas atmosphere. Then, a 20 nm intermediate
 dielectric layer 236 consisting 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 40 nm thick reflecting layer 237
 consisting of an AlTi film is formed on the intermediate dielectric layer
 236 by DC sputtering with an AlTi target in an argon gas atmosphere.
 Finally, an 8 .mu.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 300 rpm, and curing the UV-light curing resin by irradiating it with UV
 light.
 The reproduction magnetic layer 233 is set to a thickness of 40nm, a Curie
 temperature T.sub.c1 of 300.degree. C., and a coercive force H.sub.c1 of
 100 Oe at room temperature. The intermediate magnetic film 234 is set to a
 thickness of 10 nm, a Curie temperature T.sub.c2 of 120.degree. C., and a
 coercive force H.sub.c2 of 3 kOe at room temperature. The magnetic
 recording film 235 is set to a thickness of 50 nm, a Curie temperature
 T.sub.c3 of 230.degree. C., and a coercive force H.sub.c3 of 15 kOe at
 room temperature.
 The following explains the reproduction principle 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 film 233, an intermediate
 magnetic film 234, and a magnetic 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 recording 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 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 coupling forces between the recording magnetic
 layer 235 and the reproduction magnetic layer 233 are interrupted and the
 magnetization direction of the magnetic reproduction film 233 is aligned
 with the magnetization direction of the magnetic reproduction film 228,
 because the Curie temperature of the intermediate magnetic film 234 is
 lower than that of the other magnetic films. Therefore, the recording
 domains 230 become masked by the high temperature portion 229c, which is a
 part of the laser beam spot 229a. Consequently, 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 reproduction method, a signal
 reproduction with regions smaller than the laser beam spot becomes
 possible.
 A similar reproduction is also possible when the magnetically induced super
 resolution method called "RAD" is used, wherein signal reproduction is
 possible only in the high temperature portion of the laser beam spot.
 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.
 First of all, as is shown in FIG. 9(a), the magnetization orientation of
 the recording layer is aligned into one direction with the magnetizer 217.
 The magnetic 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 15 kOe. 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 electromagnet of the magnetizer 217 to 20
 kGauss, and passing the magneto-optical disk through this magnetic field.
 Next, as is shown in FIG. 9(b), 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 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 temperature of the recording layer is raised
 for magnetization using, for example, a stroboscopic light, the
 magnetization orientation of the recording layer also can be aligned into
 one direction with a magnetic field that is as small as 5 kOe.
 The recording layer of this embodiment is a tri-layer and comprises the
 magnetic reproduction film 233, the intermediate magnetic film 234, and
 the magnetic recording film 235, The identifying information can be
 recorded by considerably decreasing the magnetic anisotropy in a direction
 perpendicular to the film surface in at least the portion where the
 magnetic recording film 235 has been heated, and letting the magnetic
 anisotropy in substantially in-plane directions dominate.
 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 vertical 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.
 In the first and second embodiments, a polycarbonate resin is used for the
 disk substrates 211 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 211 and
 231. It is also possible to use other nitride films such as AIN, or oxide
 films such as TaO.sub.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 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.
 Moreover, In the second embodiment, the vertical magnetic anisotropy of the
 magnetic recording film 235 in the tri-layer recording layer was
 deteriorated. However, the same effect can be attained when the vertical
 magnetic anisotropy of either the magnetic reproduction film 233 or the
 magnetic recording film, or both, or the vertical magnetic anisotropy of
 the magnetic reproduction film 233, the intermediate magnetic film 234,
 and the magnetic recording film 235 is deteriorated.
 Third Embodiment
 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 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 the disk. On
 top of the recording layer 303, an intermediate 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 laminated by adhesion
 layer 307. It is also possible to laminate together two optical disks of
 the same configuration by hot-melting.
 The following is an explanation of a method for producing a magneto-optical
 disk in accordance with this embodiment.
 First of all, a disk substrate 301, which has guide grooves or pre-pits for
 tracking guidance, is produced by injection molding using a polycarbonate
 resin. Then, an 80 nm thick dielectric layer 302 of ZnSSiO.sub.2 is formed
 on the disk substrate 301 by high-frequency RF sputtering with a
 ZnSSiO.sub.2 target in an atmosphere containing argon gas. Then, a 20 nm
 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 atmosphere.
 Then, a 60 nm intermediate dielectric layer 304 consisting of a
 ZnSSiO.sub.2 film is formed on the recording layer 303 by RF sputtering
 with a ZnSSiO.sub.2 target in an atmosphere containing argon gas. Then, a
 40 nm thick reflecting layer 305 consisting of an AlCr film is formed on
 the intermediate dielectric layer 304 by DC sputtering with an AlCr target
 in an argon gas atmosphere. Then, a 5 .mu.m thick overcoat layer 306 is
 formed on the reflecting layer 305 by dropping an UV-light curing resin on
 the reflecting layer 305, coating the disk with the UV-light curing resin
 using a spin-coater at 300 rpm, and curing the UV-light curing resin by
 irradiating it with UV light. Thus, a first optical disk is obtained.
 Similarly, a second optical disk is obtained, 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.
 The recording of information on the recording 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 properties
 between the crystal phase and the amorphous phase, which are based on
 reversible structural changes on the atomic level, are used. The recorded
 information can be reproduced by detecting the difference of the reflected
 luminous energy or the transmitted luminous energy at a certain
 wavelength.
 When an optical disk has a recording layer consisting 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.
 The recording method for identifying information (write-once information)
 according to this embodiment 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 convergence focusing lens such as a
 cylindrical lens, a laser beam is focused on the recording layer 303 as
 oblong stripes. BCA portions 310 are recorded in the circumferential
 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 this embodiment, an excessive structural change due to
 crystallization by phase transition occurs. Thus, it becomes possible to
 non-reversibly record the BCA portions 310. It is preferable that the BCA
 portions 310 are recorded as non-reversible crystal phases. By thusly
 recording the BCA portions 310 (i.e. the identifying information) the
 luminous energy reflected from the portions where identifying information
 is recorded differs from the luminous energy reflected from other
 portions. Therefore, as in the first embodiment, the identifying
 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 can be set
 to at least 10%. In the case of DVD-RAMs, as in the case of DVD-ROMs, not
 only an excessive structural 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 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
 reliability.
 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.
 Since the identifying information is compatible with disk
 recording/reproduction apparatuses for DVDs, the technology for recording
 identifying information 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 performed with an optical
 head 255 as shown in FIG. 7, and the reproduction conditions are different
 from the detection method of the recording signal.
 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(a), the present invention uses
 an RZ recording for the identifying information. In an RZ recording, one
 time unit is divided into several timeslots, for example a first timeslot
 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(a). Influences of
 rotational instabilities of the motor 915 shown in FIG. 15 can be removed
 by letting a clock signal generator 913 generate the clock signal in
 accordance 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 indicates a "00", is trimmed with the laser, as is shown in 16(b).
 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(c). 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(d).
 A "10" and a "11" are recorded in the third timeslot 922a and the fourth
 timeslot, respectively.
 Thus, a circumferential barcode as shown in FIG. 39(a) is recorded on the
 disk.
 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 the pulse width. When several T's follow upon each other, a
 double or triple pulse width of 2 T or 3 T becomes necessary.
 With laser trimming as in the present invention, it is necessary to change
 the configuration of the apparatus 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 2 T is
 formed in the second and third recording area taken from the left.
 In conventional NRZ recording, the pulse width is 1 T or 2 T, so that it is
 clear that the laser trimming of the present invention is not applicable.
 The stripes (barcode) recorded by the laser trimming of the present
 invention are reproduced as shown in FIG. 6(a) or FIG. 31(a), 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 optical 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 conductivity and thickness of the disk substrate. Moreover,
 when barcodes with different line widths are provided on the same disk,
 the structure of the recording apparatus 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 1 T, 2 T,
 3 T or, generally speaking, nT. It is particularly difficult to change the
 line widths between 2 T, 3 T 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 2 T, 3 T 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 varies. 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.
 Thus, by combining several RZ recordings, a laser barcode for an optical
 disk of the present invention can achieve a stable digital recording.
 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. 16. First of all, if the data is "0", a pulse 924a with a temporal
 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(a). 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(c). 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(b) and (d). 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(e).
 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(e)
 shows the signal for the PE-modulated data "010". As is shown in FIG.
 17(e), 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 2 T,
 a clock that is synchronized with the channel clock can be reproduced
 without using a PLL.
 In this manner, a circular barcode as shown in FIG. 39(a) is recorded on
 the disk. To record the data "01000" of FIG. 39(d) with the PE-RZ
 recording of this embodiment, a barcode 923 corresponding to the recording
 signal 924 of FIG. 39(c) is recorded as shown in FIG. 39(b). When the
 optical pickup of the reproduction apparatus reproduces this barcode, a
 reproduction signal with a waveform as shown in FIG. 39(e) 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 through a second-order or
 third-order Tchebychev LPF 943 as shown in FIG. 23(a), a signal with the
 waveform shown in FIG. 39 (f) is attained. This signal is sliced with a
 level slice portion, and the reproduction data "01000" shown in FIG. 39(a)
 is reconstructed.
 As is explained with FIGS. 11(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.
 Laser trimming recordings of write-once information on single-substrate
 magneto-optical disks without destroying the overcoat layer (protective
 layer) can be achieved by heating only the recording layer and changing
 the magnetic anisotropy in the direction perpendicular to the film
 surface. When this was experimentally verified, there was no change in the
 magnetic properties after 96 hours at 85.degree. C. and 95% humidity.
 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 .times.800 optical
 microscope. Also in a similar experiment with a magneto-optical disk
 lasting 96 hours at 85.degree. 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 protective layer does not have to be
 reformed at the factory, so that a barcode laser trimming recording can be
 performed at places other than the press factory, for example, 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 14
 T (that is, 1.82 .mu.m), 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 invention to a laminated disk,
 such as a DVD, a secondary recording can be performed after shipping from
 the factory. A secondary recording also can be performed by applying the
 same recording method to magneto-optical disks.
 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
 performs 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 911 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-substrate 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 barcode-shaped deterioration recording
 or erasure of the recording layers 235, 303 or the reflecting film 802.
 Error correction techniques will be explained in more 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, and since it is
 not possible to come up with a new serial number, the unlawful issuance of
 serial numbers by parties 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 public key is recorded
 on the disk and transmitted with the reproduction apparatus,
 counterfeiting can be prevented. 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 coefficient and a means for
 reading the disk-type identifying 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.
 The following paragraph explains the focusing member 914 of the laser
 recording apparatus with reference to FIG. 18.
 As is shown in FIG. 18(a), the light from the laser 912 enters a focusing
 member 914, and is collimated by a collimator 912a. A cylindrical lens 917
 focuses the laser light only in the circumferential direction 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 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 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 1
 T, 2 T and 3 T 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 modulator 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-IROM disk 800. Therefore, jitter can be
 reduced. It is also possible to scan a continuously excited laser in a
 radial direction and form a barcode using a scanning means for the laser.
 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 the CAV data are recorded by deleting the reflective film
 off with the laser. Because of this overlap-writing, pits are recorded
 between 1 T, 2 T, and 3 T of the barcode stripes. Using this pit
 information, tracking with an optical head becomes possible, and T.sub.max
 and T.sub.min 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&gt;14 T(pit), T.sub.min can be detected, and the rotation speed of the
 motor can be controlled by detecting this signal. If t is shorter than 14
 T(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)&lt;T(NS), the substantial
 reflection coefficient only drops 6 dB, 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 driving is performed using
 a rotation pulse from, for example, a Hall element of the motor 17 and CAV
 rotation.
 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.
 FIG. 20 is a flowchart showing the order of operations 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.sub.max or T.sub.min of the pit signals with
 a rotation sensor of the hole element of the motor (step 930c). Then, it
 is determined whether there are stripes or not (step 930d). 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 (barcode) are
 reproduced (step 930d). Then, it is determined 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 perimeter 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. Moreover, 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 possible. Therefore, the pit signal can be
 correctly reproduced in step 930h.
 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 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
 optical head stopper and the address information of the pit signals.
 The format for high-speed switch recording is illustrated by the data
 structure for synchronized encoded data in FIG. 22.
 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 switch recording, at
 least two pulses have to fit into it. 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 methods there may be two pulses within 1
 t, 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.sub.1, no pulse in T.sub.2, one pulse on the right side of
 T.sub.3, and one pulse on the left side of T.sub.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 doubled.
 The following is an explanation of a recording/reproduction apparatus. FIG.
 14 is a block diagram of a recording/reproduction apparatus. The following
 explanation concentrates on decoding. A low-pass filter 943 eliminates
 high-frequency components due to the pits from the stripe signal output.
 In case of a DVD, the signal of a maximum of 14 T with T=0.13 .mu.m may be
 reproduced. In this case, high-frequency components can be eliminated by
 passing the signal through a second-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 reproduced. FIG. 23(b) shows the waveform for a
 worst-case simulation.
 Thus by using a low-pass filter 943 of at least second order, the pit
 regeneration signal can be eliminated almost completely, and the stripe
 regeneration signal can be output, so that the strip signal can be
 reliably decoded.
 Returning to FIG. 14, a PE-RZ decoder 930a decodes the digital data, and
 this data is error-corrected by an ECC decoder 930b. Then, a
 deinterleaving portion 930d cancels the interleaf, and an RS decoder 930c
 performs the calculations for decoding the Reed-Solomon coding, to perform
 error correction. As is shown by the data structure in FIG. 21(a), the
 interleaf and the Reed-Solomon error correction encoding are performed
 with an ECC encoder 907, as shown in FIG. 15. Consequently, by adopting
 this data structure, if the byte error rate before correction is
 10.sup.-4, a disk error will occur in only one out of 10.sup.7 disks, as
 is shown in FIG. 21(c). As 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.
 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 capacity can be between, for example, 12 byte and 188 byte,
 and can be arbitrarily raised by steps of 16 byte. FIG. 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 951d, and the
 following rows are the ECC rows 952a, 952b, 952c, and 952d. The data row
 951d becomes the 4-byte EDC row. Thus, 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 recorded over an angular range of 51.degree..
 Similarly, if n=2, 18 bytes are recorded, and if n=12, 271 bytes are
 recorded over an angular range of 336.degree..
 In the present invention, this scalability has a purpose. Moreover, the
 production tact time is important 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 thousands. Since the
 production tact time is four seconds, this will slow down the production
 tact time. On the other 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 scalability method of the present invention can reduce
 production cost and time.
 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,
 by, for example, filling up the rows 951e to 951z with 0's if n=1 as in
 FIG. 21(b).
 As is shown in FIG. 24, for 1 T, the pulse width of 4.4 .mu.s becomes about
 one half of the stripe interval of 8.92 .mu.s. For 2 T, the pulse width is
 4.4 .mu.s for a stripe interval of 17.84 .mu.s, and for 3 T, the pulse
 width is 4.4 .mu.s for a stripe interval of 26.76 .mu.s, so that, taking
 the average 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 coefficient 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.
 Moreover, in magneto-optical disks, the average refractive index of the
 recording layer does not change, and the average change of the reflection
 coefficient is less than 10%, so that level fluctuations of the
 reproduction waveform are small and compatibility with DVD players is
 easy.
 The following is an explanation of the reproduction 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
 regular 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 existence
 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 reproduced 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).
 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 verified 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 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
 "0100011" for the synchronized coding. Consequently, when reproduced from
 the reverse side, the synchronized coding "0110001" 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 double-sided disk is reproduced from the
 reverse side, the penetrating barcode stripes 923 can be correctly
 reproduced. 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. Consequently, 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.degree. 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 trimming, it can be prevented
 that the previous trimming data is destroyed.
 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 discriminated.
 If there were no trimming counter identifier 947, the first stripes 923
 and the second stripes 938 could not be differentiated.
 The following is an explanation of the procedure 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 compressed 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-volume 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 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 finished without laminating. In case
 of a DVD-RAM disk, 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 a recording layer on both sides.
 The following is an explanation of level slicing for the BCA with reference
 to the FIGS. 38 and 39.
 As shown in FIG. 38(a), in a BCA recording with a laser, a pulsed laser 808
 irradiates laser light on an 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 aluminum reflection film 809.
 Thus, as shown in FIG. 38(b), BCA stripes are formed on the disk. When
 these BCA 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 intermittently lacking a modulation signal. A modulation signal
 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(b) are sliced
 at the slice level S.sub.2 shown in FIG. 39(e), so that they can be
 reproduced with a regular optical pickup. As is shown in FIG. 39(f), a
 digital signal can be attained by slicing the signal, after suppressing
 high-frequent pit signal components with a low-pass filter, at the second
 slice level S.sub.2. By PE-RZ-decoding this digital signal, a digital
 signal as shown in FIG. 39(a) is output. The actual appearance of the
 reproduction signal is shown in FIG. 31.
 The following is an explanation of the decoding with reference to FIG. 14.
 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 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 control data of the first recording layer 802a near the optical
 head 255. In this case, because the BCA is in the second recording layer
 802, the focus is on the first recording 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 control data is
 main information, it is recorded by EFM, 8-15, or 8-16 modulation. Only
 when the stripe existence 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(c), the BCA is converted intog 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 information 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 adjusting
 portion 828 to switch the focus from the first recording 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 22.3 mm and 23.5 mm 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(c) 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 information. Thus, the main
 information is decoded and reproduced by the first decoder 928, and the
 BCA data, which is auxiliary information, is decoded and reproduced by the
 second decoder.
 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 provide slits with a
 width below 5-15 .mu.m. Moreover, if a recording is performed further than
 23.5 mm 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 recording period of 30 .mu.m, and the
 largest radius of 23.5. mm.
 The following is a detailed specific example for setting the second slice
 level 916 and the operation of the second level slice portion 929.
 FIG. 26 is a detailed view of the second level slice portion 929. The
 waveform for this explanation is shown in FIG. 27.
 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 setting portion 588 comprises a
 low-pass filter 588a and a level converter 588b.
 The following explains its operation. In the BCA region, the envelope of
 the partially missing signal as shown in FIG. 27(a) is reproduced due to
 the BCA. In this reproduction signal, high-frequency components due to the
 signal and low-frequency components due to 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(b) is entered into the second
 level slicer 929.
 When the low-frequency signal 932 is entered into the second level slice
 portion 929, the light-reference-value setting portion 588 filters out
 even lower frequency components (almost DC) of the low-frequency signal
 932 with a low-pass filter 588a with a time constant 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 converter 588b
 adjusts the signal to a suitable level, so that a second slice level 916
 as illustrated by the fat line in FIG. 27(b) is output. As is shown in
 FIG. 27(b), the second slice level 916 tracks the envelope.
 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 envelope incessantly fluctuates as in FIG. 27(a). 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 invention, the second slice level is constantly corrected and
 fitted to the envelope, so that wrong slicing can be significantly
 reduced.
 Thus, the present invention is not affected by a fluctuating envelope, and
 the second level slicer 587 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(c). At the start of the binarized digital
 signal output from the second level slicer 587, the signal is reversed,
 and a digital signal as shown in FIG. 27(d) is output. Accordingly, FIG.
 28 shows the specific circuits for a frequency dividing means 934 and a
 second level slice portion 929.
 Thus, by setting the second slice level 916, differences in the reflection
 coefficient of different disks, 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 that can reliably slice the BCA signal.
 The following explains another method for slicing the second slice level
 916. FIG. 29 shows another circuit diagram for the frequency dividing
 means 934 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 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.
 The following explains its operation. In the BCA region, the envelope of
 the partially missing signal as shown in FIG. 31(a) 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 time constant eliminates the
 high-frequency signal components 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 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 signal into the
 inverting amplifier 587a, the inverting amplifier 587a amplifies the
 amplitude, which has been reduced by passing through 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(c) is entered
 into the comparator 587c. On the other hand, when the second low-pass
 filter 943b enters the DC component of the reproduction signal into the
 light-reference-value setting portion 588, the light-reference-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 shown in FIG. 31(b). 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(d).
 At the start of the digital signal, which has been binarized by the
 comparator 587c, the frequency half-divider 587d reverses the signal, 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.
 FIG. 30 shows a specific circuit of the frequency dividing means 934 and
 the second level slice portion 929 to accomplish this.
 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 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
 reproduction apparatus for optical disks can be provided that can slice
 the BCA signal reliably. Moreover, when the circuits are discrete, the
 number of elements can be minimized, and a reliable BCA reproduction
 circuit can be achieved.
 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.
 This effect also can be attained by slowing down the rotation frequency of
 the motor at reproduction 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 frequency is used, and a BCA with a small linewidth can be
 reproduced. Sometimes, production facilities manufacture 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 reliability
 at BCA reproduction time.
 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
 rotation 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 reproduction speed
 can be prevented.
 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.
 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 microprocessor,
 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 suppressing the high-frequency signal of the 8-16
 modulation.
 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 signal 933 of a maximum
 of 4.5 MHz, and the auxiliary information is a low-frequency signal 932
 with a period of 8.92 .mu.s, that is, about 100 kHz, the auxiliary
 information easily can be frequency-divided with the low-pass filter 943.
 Using a frequency dividing means 934 comprising 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.
 The preceding was an outline of the BCA.
 FIG. 32 is a block drawing of a disk manufacturing 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 identification codes 12a, 12b, 12c, such as IDs that are different 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 11a, 11b, and 11c.
 As is shown in FIG. 32, the pit portion and the recording signal on the
 BCA disks 11a, 11b, and 11c are completely the same. However, a different
 (for example, incrementally numbered) ID is recorded into the BCA 18 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 distributed at what time to which system operator
 23, that is, CATV studio, broadcasting station or airline.
 A record about which disk ID has been distributed 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 circulation, 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".
 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.
 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 signal by superimposing the BCA
 signal and a recording circuit 272 records the converted video signal on
 the BCA disks 11a, 11b, and 11c (300 (240, 800) in FIG. 41). When the
 video signal onto which the BCA signal has been superimposed is reproduced
 from the BCA disk 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 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
 illegal 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 comprising ID information read out from the
 BCA signal, and the video signal is output.
 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, 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.
 FIGS. 34 and 35 illustrate the operation performed by the system operators.
 FIG. 34 is a block diagram 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.
 As is shown in FIG. 34, the broadcasting apparatus 28 set up in a CATV
 station comprises a reproduction 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 main information of the
 signal that is reproduced with the optical head 29 is reproduced with the
 data reproduction portion 30, descrambled with the descrambler 31,
 expanded to the original movie signal with the MPEG decoder 33, and sent
 to the watermark portion 34. The original signal as shown in FIG. 35(a) is
 first entered into the watermark portion 34, and transformed by, for
 example, FFT from the time domain into the frequency domain by a frequency
 converter 34a. Thus, the frequency spectrum 35a shown in FIG. 35(b) is
 attained. A spectrum mixer 36 mixes the frequency spectrum 35a with the ID
 signal having the spectrum shown in FIG. 35(c). As shown in FIG. 35(d),
 the spectrum 35b of the mixed signal is the same as the frequency spectrum
 35a of the original signal shown in FIG. 35(b). In other 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 frequency converter 37, and a signal as in FIG. 35(e), which is
 almost the same as the original signal (FIG. 35(a)) is obtained. Because
 the ID signal is spectrally dispersed in the frequency domain, the
 deterioration of the video signal is negligible.
 The following explains how the ID signal 38 is produced.
 A digital signature verification portion 40 verifies 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(c) can be
 generated. The watermark signal also can be generated by calculating the
 watermark from the ID data or the card ID of the IC card 41.
 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.
 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 tracing of illegal copies becomes easy.
 The video output signal of the watermark portion 34 is sent to the output
 portion 42. If the broadcasting 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 audience via
 a network or radio waves. In this case, the compression parameter
 information, such as the transfer rate after the original MPEG signal has
 been compressed, 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.
 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 systems on board
 airplanes, scrambling is unnecessary. Thus, a video signal with a
 watermark is broadcast from the disk 11a with BCA.
 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 portion 34. To avoid this, the buses between the descrambler 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 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, that is, they perform a
 handshake. Only if the result of the handshake is correct, does the mutual
 authentication portion 32d on the sender side cancel the encryption. This
 is the same with the mutual authentication portion 32a and the mutual
 authentication portion 32b. 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 cannot be bypassed in the end, an unlawful
 elimination or manipulation of the watermark can be prevented.
 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 system-operator side, as is shown in FIG. 36. In the receiver, a
 second descrambler 51 cancels the scrambling, 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 monitor 54.
 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
 illegal copies of the tape 56 thus can be multiplied and circulated (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 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.
 The following is an explanation of how the watermark can be detected, with
 reference to FIG. 37.
 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 a first input
 portion of a watermark detection apparatus 57. A first spectrum 60, which
 is a spectrum of the illegally copied signal, as shown in FIG. 35(a) is
 obtained with a first frequency converter 59a by, for example, FFG or DCT.
 The original contents are fed into a second input portion 58a, and a
 second spectrum 35a is obtained by transformation into the frequency
 domain with a second frequency converter 59a. Such a spectrum is shown in
 FIG. 35(b). When the difference between the first spectrum 60 and the
 second spectrum 35a is taken with a subtractor 62, a differential spectrum
 signal 63 as shown in FIG. 35(h) can be obtained. This differential
 spectrum signal 63 is given into an ID detector 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 spectrum 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 corresponds 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(c) and (h) match. The ID of the
 watermark is output from an output portion 66, and it can be seen from
 where the unauthorized copy came.
 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.
 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 virtual watermark. The
 system operator can bury watermarks 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 watermark
 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.
 In this example, a spectrum-dispersion watermark portion was used, but the
 same effect can be obtained with other types of watermark portions as
 well.
 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 temporarily 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 magneto-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 portion 750 as the decryption key,
 as shown in FIG. 42. Then, the MPEG decoder 261 expands the MPEG signal to
 obtain the video signal. If, however, the scrambled data, that is recorded
 on the magneto-optical disk 240a 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 encryption decoder 534a cannot descramble the signal. Therefore,
 the video signal cannot be output. Therefore, a signal that is illegally
 copied onto another magneto-optical disk 240b cannot be reproduced, so
 that the copyright can be protected. In effect, the contents can be
 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.
 The following is an explanation of an even 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 transmitted with the BCA data
 buried inside the video signal as a watermark by the watermark recording
 portion 264. On the user side, this signal is recorded onto a
 magneto-optical disk 240a. During reproduction, a watermark reproduction
 verification portion 262 verifies the BCA data of the recording permission
 identifier and the watermark against the BCA data obtained by the BCA
 output portion 750, and authorizes compound reproduction only if they
 match. This makes the protection of copyrights even stronger. Since with
 this method the watermark can be detected by the watermark reproduction
 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 prevented or detected. As in the case of the DVD-RAM disk
 shown in FIG. 14, the production of illegal digital copies can be
 prevented or detected.
 In this case, by providing the magneto-optical recording/reproduction
 apparatus or the DVD recording/reproduction apparatus with a watermark
 reproduction portion 263, a recording prevention portion 265 authorizes
 the recording only if there is a watermark indicating a "first recording
 possible identifier" in the signal received from the contents provider.
 The recording prevention portion 265 and a "first recording completion
 identifier", which is discussed below, prevent a second 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 overlapped by
 the watermark recording portion 264 with the 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 recorded onto other media, for
 example, a video tape or a DVD-RAM, then the "first recording completion
 identifier" can be detected if the VTR or the like comprises a watermark
 reproduction portion 263. Thus, the recording 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. Consequently, the individual who
 broke the law can be identified and tried for copyright infringement, so
 that illegal copies and plans for similar actions by the same infringer
 can be indirectly impeded. Since the watermark does not disappear even
 when converting the signal to analog, this is also useful for analog VTRs.
 The following is an explanation of a recording apparatus that can record or
 transmit illegally by circumventing the copy protection even though a
 watermark indicating "first recording complete" or "recording forbidden"
 is detected and by adding a circuit producing a scrambling key. This case
 cannot be prevented directly, but the circumvention circuit becomes
 extremely complicated. 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.
 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.
 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.
 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 reproduction device performs a verification
 of the date information 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 with the copy prevention technology of the present invention,
 resulting in strong copyright protection and making illegal use very
 difficult.
 As explained above, when the BCA is used for 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.
 Moreover, the above embodiments have been 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 disks or RAM disks, on DVD-R
 disks, or magneto-optical disks, the same recording properties and
 reliability can be attained. The above explanations are equally applicable
 to DVD-R disks, DVD-RAM disks and magneto-optical disks, with the same
 results, but these explanations have been omitted.
 Moreover, the BCA identifying information in the above embodiments have the
 same information signal format for DVDs and for magneto-optical disks, so
 that using an optical head for magneto-optical disks with 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 conditions during reproduction.
 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 deterioration
 of the recording layer due to oxidation and no change of the mechanical
 properties of the recording layer.
 Furthermore, the above embodiments, have been explained by way of examples
 of a magneto-optical 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,
 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
 In accordance with the present invention identifying information
 (write-once information) easily can be recorded onto or reproduced from
 optical disks, the copying of contents can be prevented, which is useful
 for an apparatus for recording and reproducing optical disks with an
 accent on copyright protection.