CA2187602A1 - Optical disc recording medium - Google Patents
Optical disc recording mediumInfo
- Publication number
- CA2187602A1 CA2187602A1 CA002187602A CA2187602A CA2187602A1 CA 2187602 A1 CA2187602 A1 CA 2187602A1 CA 002187602 A CA002187602 A CA 002187602A CA 2187602 A CA2187602 A CA 2187602A CA 2187602 A1 CA2187602 A1 CA 2187602A1
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- Prior art keywords
- layer
- optical disc
- recording
- information
- writing information
- Prior art date
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- Optical Record Carriers And Manufacture Thereof (AREA)
- Optical Recording Or Reproduction (AREA)
Abstract
An read-only information plane 11A consisting of irregular pits is formed on the upper surface of a substrate 11 made of a transparent material such as plastic by a method such as injection molding; a transparent spacer layer 12 having a higher refractive index than that of the substrate 11 is provided thereon; a tracking guide groove 12A is formed on the upper surface of the transparent spacer layer 12; a writing information recording layer 13 and a protective layer 14 consisting of phase-change material or magneto-optical material are successively superimposed thereon.
Description
-SPECIFICATION
Optical Disc Recording Medium BACKGROUND OF THE INVENTION
1. Field of the Invention:
The present invention relates to an optical disc recording medium, and more particularly to a multilayer film type optical disc recording medium having two or more recording layers, such as a DVD (digital video disc).
Optical Disc Recording Medium BACKGROUND OF THE INVENTION
1. Field of the Invention:
The present invention relates to an optical disc recording medium, and more particularly to a multilayer film type optical disc recording medium having two or more recording layers, such as a DVD (digital video disc).
2. Description of the Related Art:
As the need for processing large amounts of data such as found in digital moving pictures on personal computers has increased in recent years, the capacity of storage devices must be enlarged.
When an optical disc is used as a medium of storage for digital video, it is superior to a magnetic tape medium in recording density and access speed but is inferior to magnetic tape in storage capacity, and thus is inferior to magnetic tape in the amount of digital video it is capable of storing.
In the field of optical laser discs there exists a double-sided disc produced by laminating two one-sided discs back to back to increase storage capacity or reproduction time. This double-sided disc is not a desirable solution when using a single optical head for reading information, because the disc must be taken out and flipped over to be again inserted into the optical disc readout device after playback of the information on one side is completed.
Therefore, as a method for increasing the recording capacity when reproducing (reading) information on only one side of the disc, multiple recording layers on the disc can be employed.
Although conventional multilayer discs are exclusively used for reading data, a system by which two recording layers are used to double the reproduction time has been considered for digital video discs (DVD) which have been proposed as the next generation of optical discs.
Fig. 1 shows an example of a cross-sectional structure of such a double-layer medium for reading information on one side thereof. Information is recorded by means of pits on the surface of a substrate 51 consisting of a transparent material such as plastic, formed by an injection molding. A transparent spacer layer 52 is provided on the substrate, the spacer layer 53 having a refractive index larger than that of the substrate so that a second recording layer is disposed in accordance with either a photo-polymer method (G. Bouwhuis et al., ~Principles of Optical Disk Systems", Adam Hilger Ltd., Bristol and Boston, P. 204-206) or a thin-sheet laminating method. Then, a reflective layer 53 having a high reflectance, e.g., aluminum, is formed thereon by a sputtering method or the like.
A laser beam for reading information is incident through the above-mentioned substrate 51 and focused on a first recording layer K1 or a second recording layer K2. The information is recorded as a series of pits of variable length on the recording layers K1 and K2. When the pits are exposed to the laser beam, the amount of the reflected light is decreased by scattering or diffraction of the light. Then, the reflected light is received by a photodetector on the optical head to be converted into electric signals of variable amplitudes.
In case of an optical disc which is exclusively used for reproducing (reading) data, such as a compact disc or a laser disc, there is no problem in applications in which the user only receives information, as in e.g., music or movies. However, when such an optical disc is used as a medium of storage device for a personal computer, it is not well suited to highly-interactive applications which require writing/reading operations, unless information can be recorded on that medium.
For example, when the score of a computer game still in progress is saved, a hard disc or a semiconductor memory in which information can be recorded must be used instead of the optical disc, and the operation of the medium becomes complicated.
For the above-mentioned application, a recording medium in which a read-only area is provided can be used, as using a medium such as a partial ROM magneto-optical disc enables a user to record any desired information (for example, the score of a computer game still in progress) on the same disc during reproduction of the previously-recorded information.
However, even if the information is recorded on the same disc, since the read only area is separate from the recordable area on the disc such as is the case with partial ROM discs, a track jump or a seek of an optical head must be performed to switch from one area to the other (e.g., changing from the recordable area to the read-only area or changing from the read-only area to the recordable area), which disadvantageously takes a few tens or hundreds of milliseconds.
In order to eliminate these problems in the prior art, an object of the present invention is to provide an optical disc - 21 û7602 -recording medium having overlying recordable and read-only layers and being capable of selectively recording predetermined information on the same optical disc containing the read-only information.
SUMM~Y OF THE INVENTION
To achieve this aim, the invention is an optical disc comprising a substrate of transparent member such as plastic material, the substrate comprising a read-only information plane having pits on a surface thereof; a transparent spacer layer formed on the substrate, the transparent spacer layer having a refractive index larger than that of the substrate; a tracking guide groove formed on the upper surface of the transparent spacer layer; a writing information recording layer formed above the tracking guide groove, and a protective layer formed on the writing information recording layer.
When reproducing the information which is previously recorded on the read-only plane of the optical disc having the above-mentioned structure, the light is first focused on the read-only information plane of the first layer. Irradiation of a laser beam onto the pits provided on the read-only information plane decreases an amount of light reflected by scattering or diffracting it, and when the laser beam is irradiated on a part where no pit is formed, an amount of light equal to the product of the incident light and the reflectance ratio of the first layer and second layer is returned to the optical head side.
When this reflected light is converted into electric signals, information concerning a length of the pits is - 21~76~
derived from the amplitude of the electric signals. If information must be recorded during a playback session in which information is reproduced from the read-only information plane, the laser beam spot is first moved to another plane.
This is achieved by temporarily turning off a focus servo and operating a focusing actuator to forcibly move a focusing position of the laser beam in a focusing direction. When the focusing position has reached the writing information recording layer, a focus jump is carried out by again turning on the focus servo. As a result, a shift from a read-only area to a recording area or from a recording area to a read-only area can be attained in a short period of time.
According to another aspect of the invention, a threshold value of the recording level in the above-mentioned writing information recording layer is set to a sufficiently-high value as compared to a value of a laser power needed to reproduce information stored in the read-only information plane.
This configuration effectively prevents the information from being deteriorated or erased by the application of heat to the writing information recording layer which is apt to be caused when the focusing point of the laser beam is moved from the read-only information plane.
According to another aspect of the invention, an interference layer and a reflection layer are provided between the above-described writing information recording layer and the protective layer.
This structure improves the quality of ~1 ~7~02 recording/reproduction by the Faraday effect for transmission.
- BRIEF DESCRIPTION OF THE DRAWINGS
The novel features believed characteristic of the invention are set forth in the appended claims. The invention itself, however, as well as other features and advantages thereof, will be best understood by reference to the detailed description which follows, read in conjunction with the accompanying drawings, wherein:
Fig. 1 is an explanatory view showing a cross section of a conventional two-layer read-only disc and a reflective path for a laser beam;
Fig. 2 is a partial cross-sectional view showing an embodiment according to the present invention; and Fig. 3 is a partial cross-sectional view showing a modification of Fig. 1.
DETAILED DESCRIPTION OF THE PREFERRED EM~ODIMENTS
A first embodiment according to the present invention will now be described with reference to Fig. 2.
In Fig. 2, reference numeral 11 denotes a substrate made of transparent plastic or the like. This substrate 11 is formed by a technique such as injection molding and is provided with an read-only information plane llA having pits on the upper side.
The pits formed on the substrate material reduce the reflection of an emitted laser beam by scattering or diffraction of light. The amount of the reflected light thus increases or decreases depending on existence/ahsence of the pits at the portion of the substrate material on which the laser beam is focused. Therefore, when the reflected light is received by a photodetector to be converted into electric signals, information concerning the length of the pits can be derived from the amplitude of the electric signals.
A transparent spacer layer 12 having a refractive index higher than that of the substrate 11 is provided on the read-only information plane llA. Further, a tracking guide groove 12A (a pregroove) is formed on the upper surface of the spacer layer 12; a writing information recording layer 13 consisting of phase-change material or magneto-optical material is superimposed thereon; and a protective layer 14 is further superimposed on the phase-change of magneto-optical material.
Here, the transparent spacer layer 12 having a higher refractive index than that of the substrate 11 enables the laser beam to be reflected on the read-only information plane.
Also, the tracking guide groove 12A formed on the upper surface of the transparent spacer layer 12 is used for tracking the laser beam when recording to or reading information from the writing information recording layer 13.
The writing information recording layer 13 has a recording level threshold value which is set to be a sufficiently-high value as compared with the reproduction laser power of the above read-only information plane llA. In such a case, the threshold value of the recording level in the writing information recording layer 13 can be set to a value which is sufficiently high as compared with the reproduction laser power of the above-mentioned read-only information plane llA by setting a refractive index of the transparent spacer ~1 87602 -layer 12, a composition ratio of the recording layer, film thickness and other variables to appropriate values. As a result, the information can be prevented from being erased, even if the writing information recording layer 13 is heated when a focus point of the laser beam is moved away from the read-only information plane.
More specifically, the read-only information plane llA
having phase pits is formed on the substrate 11 made of plastic or the like by a technique such as injection molding.
The transparent spacer layer 12 having a higher refractive index than that of the substrate 11 is formed on the read-only information plane llA and the tracking guide groove 12A is further formed on the upper surface of the transparent spacer layer 12 by the photo-polymer method or the like.
In general, light is reflected at the interface between materials having different refractive indices. Assuming that the refractive index of the material on the light incident side is n1 and the refractive index of the other material is n2, a reflectance ratio R of the reflected light can be expressed as follows:
R = (n2 - n1) / (n2 + n1) ............. (1) Since the refractive index of polycarbonate which is often used as substrate material is approximately 1.58, use of a transparent material (i.e., a material having an extinction coefficient which is substantially zero), which has a refractive index of approximately 3.0, as the transparent spacer layer 12 can yield a reflectance of approximately 30 at the interface and form a practical reflective plane, 21 876~2 .
although the material of the transparent space layer 12 is not restricted to a particular type.
The tracking guide groove (pregroove) 12A formed on the upper surface of the transparent spacer layer 12 is required for tracking the laser beam when recording to or reading information from the writing information recording layer 13.
The tracking guide groove 12A is formed by, e.g., the photo-polymer manufacturing method. The writing information recording layer 13, which is made of a phase-change recording material or magneto-optical recording material and which is formed on the upper surface of the transparent spacer layer 12, has a recording threshold value that is sufficiently high as compared with the laser power used for reading information from the read-only information plane llA by adequately determining the refractive index of the transparent spacer layer 12, the recording layer composition ratio, a film thickness and other variables. This consequently prevents the information from being deteriorated or erased when, e.g., the writing information recording layer 13 is heated when the focusing point of the laser beam is moved from the read-only information plane llA to the writing information recording layer 13.
In Fig. 2, although the material used for the writing information recording layer 13 is not restricted to a particular type in the present invention, it is effective to use phase-change recording material (e.g. GeSbTe system), magneto-optical recording material (e.g. TbFeCo system), dye type write once material (e.g. cyanine dye) or other - 21 876~2 _ materials. The film thickness for these is 200-1000 Angstrom.
As for the material used for the transparent spacer layer 12, it is effective to use poly-crystal SiO2 or amorphous SiN
(film thickness is 500-1500 Angstrom). As for the material used for the protective layer 14, it is effective to use the same material as the material used for the transparent space layer 12. However, the film thickness for the protective layer 14 is preferably more than 500 Angstrom.
Here, when the phase-change recording material or the magneto-optical recording material is used, it may be possible to incorporate the structure shown in Fig. 3 in order to enhance signals or adjust the sensitivity. The structure shown in Fig. 3 is obtained by further providing an interference layer 17 and a reflective layer 18 between the writing information recording layer 13 and the protective layer 14 shown in Fig. 1. In such a case, the film thickness of the writing information recording layer 13 is set to be relatively thin so that the incident light can pass through the interference layer 17 and can be reflected by the reflection layer 18 to return to the incident side.
The structure using an interference layer 17 and a reflective layer 18 is described in S. Tanaka et al., ~Design Concept of Magneto-Optical Disk", Japanese Journal of Applied Physics, Vol. 28, 1989 September 28-3, pp. 67-70.
In case of the magneto-optical disc, since the angle of polar rotation generally becomes larger by the Faraday effect for transmission rather than the Kerr effect for reflection, the embodiment shown in Fig. 3 is more advantageous.
2~ ~7~
-Moreover, the protective layer 14, at the topmost position, effectively functions as an element for mechanically or chemically protecting each of the above-mentioned layers.
Although the material used for each layer in Fig. 3 is not restricted to a particular type in this invention, it is effective to use, as the transparent spacer layer 12, poly-crystal SiO2 or amorphous SiN (film thickness is 500-1500 Angstrom).
Also, it is effective to use, as writing information recording layer 13, magneto-optical material such as TbFeCo system or phase-change material such as GeSbTe system (film thickness is less than 600 Angstroms).
Moreover, it is effective to use as the interference layer 17, poly-crystal SiO2 or amorphous SiN (film thickness is less than 1000 Angstrom), to use as the reflective layer 18, aluminum (film thickness is more than 300 Angstrom), and to use W resin as the protective layer 14.
The functioning of the optical disc during reproduction in the above embodiment will now be described.
When reproducing (reading) information previously recorded on the read-only information plane llA of the optical disc, the light is focused on the read-only information plane llA of the first layer. The information is recorded on the read-only information plane llA as a series of variable length pits (irregularities on the recording plane). When the pits are exposed to the laser beam, the amount of the light reflected by scattering or diffraction of the light is decreased. On the other hand, when the laser beam is ~ 1 87~2 -irradiated on a part of the substrate where no pit is formed, the amount of the light reflected and returned to the optical head side is equal to the product of the incident light and the reflectance ratio of the first layer 11 and second layer 12.
When the reflected light is received by a photodetector to be converted into electric signals, information concerning a length of the pits can be derived from the amplitude of the electric signals. If information must be recorded during a playback session during which information is reproduced from the read-only information plane llA, it is first required to move the laser beam spot to another plane.
In order to move the laser beam spot to another plane, a focus servo is temporarily turned off, and a control current flows to a focusing actuator to forcibly move a focusing position of the laser beam in a focusing direction. When the focusing position has reached the writing information recording layer 13, the focus servo is again turned on, thereby performing the focus jump. The focus jump takes a few milliseconds and switches from a reproduction area to a recording area (or from a recording area to a reproduction area) within a shorter time compared to the time taken for the regional movement on the disc plane.
By the above-described structure, predetermined information can be immediately recorded onto the same optical disc being used for reproduction without adopting any other recording means. Further, when the present invention is incorporated into a personal computer or a game machine, it is -possible to provide an excellent novel optical disc medium which is suitable for highly interactive applications (for example, computerized game applications).
While this invention has been described with reference to an illustrative embodiment, this description is not intended to be construed in a limiting sense. Various modifications of the illustrative embodiment, as well as other embodiments of the invention, will be apparent to persons skilled in the art upon reference to this description. It is, therefore, contemplated that the appended claims will cover any such modifications or embodiments as fall within the true scope of the invention.
As the need for processing large amounts of data such as found in digital moving pictures on personal computers has increased in recent years, the capacity of storage devices must be enlarged.
When an optical disc is used as a medium of storage for digital video, it is superior to a magnetic tape medium in recording density and access speed but is inferior to magnetic tape in storage capacity, and thus is inferior to magnetic tape in the amount of digital video it is capable of storing.
In the field of optical laser discs there exists a double-sided disc produced by laminating two one-sided discs back to back to increase storage capacity or reproduction time. This double-sided disc is not a desirable solution when using a single optical head for reading information, because the disc must be taken out and flipped over to be again inserted into the optical disc readout device after playback of the information on one side is completed.
Therefore, as a method for increasing the recording capacity when reproducing (reading) information on only one side of the disc, multiple recording layers on the disc can be employed.
Although conventional multilayer discs are exclusively used for reading data, a system by which two recording layers are used to double the reproduction time has been considered for digital video discs (DVD) which have been proposed as the next generation of optical discs.
Fig. 1 shows an example of a cross-sectional structure of such a double-layer medium for reading information on one side thereof. Information is recorded by means of pits on the surface of a substrate 51 consisting of a transparent material such as plastic, formed by an injection molding. A transparent spacer layer 52 is provided on the substrate, the spacer layer 53 having a refractive index larger than that of the substrate so that a second recording layer is disposed in accordance with either a photo-polymer method (G. Bouwhuis et al., ~Principles of Optical Disk Systems", Adam Hilger Ltd., Bristol and Boston, P. 204-206) or a thin-sheet laminating method. Then, a reflective layer 53 having a high reflectance, e.g., aluminum, is formed thereon by a sputtering method or the like.
A laser beam for reading information is incident through the above-mentioned substrate 51 and focused on a first recording layer K1 or a second recording layer K2. The information is recorded as a series of pits of variable length on the recording layers K1 and K2. When the pits are exposed to the laser beam, the amount of the reflected light is decreased by scattering or diffraction of the light. Then, the reflected light is received by a photodetector on the optical head to be converted into electric signals of variable amplitudes.
In case of an optical disc which is exclusively used for reproducing (reading) data, such as a compact disc or a laser disc, there is no problem in applications in which the user only receives information, as in e.g., music or movies. However, when such an optical disc is used as a medium of storage device for a personal computer, it is not well suited to highly-interactive applications which require writing/reading operations, unless information can be recorded on that medium.
For example, when the score of a computer game still in progress is saved, a hard disc or a semiconductor memory in which information can be recorded must be used instead of the optical disc, and the operation of the medium becomes complicated.
For the above-mentioned application, a recording medium in which a read-only area is provided can be used, as using a medium such as a partial ROM magneto-optical disc enables a user to record any desired information (for example, the score of a computer game still in progress) on the same disc during reproduction of the previously-recorded information.
However, even if the information is recorded on the same disc, since the read only area is separate from the recordable area on the disc such as is the case with partial ROM discs, a track jump or a seek of an optical head must be performed to switch from one area to the other (e.g., changing from the recordable area to the read-only area or changing from the read-only area to the recordable area), which disadvantageously takes a few tens or hundreds of milliseconds.
In order to eliminate these problems in the prior art, an object of the present invention is to provide an optical disc - 21 û7602 -recording medium having overlying recordable and read-only layers and being capable of selectively recording predetermined information on the same optical disc containing the read-only information.
SUMM~Y OF THE INVENTION
To achieve this aim, the invention is an optical disc comprising a substrate of transparent member such as plastic material, the substrate comprising a read-only information plane having pits on a surface thereof; a transparent spacer layer formed on the substrate, the transparent spacer layer having a refractive index larger than that of the substrate; a tracking guide groove formed on the upper surface of the transparent spacer layer; a writing information recording layer formed above the tracking guide groove, and a protective layer formed on the writing information recording layer.
When reproducing the information which is previously recorded on the read-only plane of the optical disc having the above-mentioned structure, the light is first focused on the read-only information plane of the first layer. Irradiation of a laser beam onto the pits provided on the read-only information plane decreases an amount of light reflected by scattering or diffracting it, and when the laser beam is irradiated on a part where no pit is formed, an amount of light equal to the product of the incident light and the reflectance ratio of the first layer and second layer is returned to the optical head side.
When this reflected light is converted into electric signals, information concerning a length of the pits is - 21~76~
derived from the amplitude of the electric signals. If information must be recorded during a playback session in which information is reproduced from the read-only information plane, the laser beam spot is first moved to another plane.
This is achieved by temporarily turning off a focus servo and operating a focusing actuator to forcibly move a focusing position of the laser beam in a focusing direction. When the focusing position has reached the writing information recording layer, a focus jump is carried out by again turning on the focus servo. As a result, a shift from a read-only area to a recording area or from a recording area to a read-only area can be attained in a short period of time.
According to another aspect of the invention, a threshold value of the recording level in the above-mentioned writing information recording layer is set to a sufficiently-high value as compared to a value of a laser power needed to reproduce information stored in the read-only information plane.
This configuration effectively prevents the information from being deteriorated or erased by the application of heat to the writing information recording layer which is apt to be caused when the focusing point of the laser beam is moved from the read-only information plane.
According to another aspect of the invention, an interference layer and a reflection layer are provided between the above-described writing information recording layer and the protective layer.
This structure improves the quality of ~1 ~7~02 recording/reproduction by the Faraday effect for transmission.
- BRIEF DESCRIPTION OF THE DRAWINGS
The novel features believed characteristic of the invention are set forth in the appended claims. The invention itself, however, as well as other features and advantages thereof, will be best understood by reference to the detailed description which follows, read in conjunction with the accompanying drawings, wherein:
Fig. 1 is an explanatory view showing a cross section of a conventional two-layer read-only disc and a reflective path for a laser beam;
Fig. 2 is a partial cross-sectional view showing an embodiment according to the present invention; and Fig. 3 is a partial cross-sectional view showing a modification of Fig. 1.
DETAILED DESCRIPTION OF THE PREFERRED EM~ODIMENTS
A first embodiment according to the present invention will now be described with reference to Fig. 2.
In Fig. 2, reference numeral 11 denotes a substrate made of transparent plastic or the like. This substrate 11 is formed by a technique such as injection molding and is provided with an read-only information plane llA having pits on the upper side.
The pits formed on the substrate material reduce the reflection of an emitted laser beam by scattering or diffraction of light. The amount of the reflected light thus increases or decreases depending on existence/ahsence of the pits at the portion of the substrate material on which the laser beam is focused. Therefore, when the reflected light is received by a photodetector to be converted into electric signals, information concerning the length of the pits can be derived from the amplitude of the electric signals.
A transparent spacer layer 12 having a refractive index higher than that of the substrate 11 is provided on the read-only information plane llA. Further, a tracking guide groove 12A (a pregroove) is formed on the upper surface of the spacer layer 12; a writing information recording layer 13 consisting of phase-change material or magneto-optical material is superimposed thereon; and a protective layer 14 is further superimposed on the phase-change of magneto-optical material.
Here, the transparent spacer layer 12 having a higher refractive index than that of the substrate 11 enables the laser beam to be reflected on the read-only information plane.
Also, the tracking guide groove 12A formed on the upper surface of the transparent spacer layer 12 is used for tracking the laser beam when recording to or reading information from the writing information recording layer 13.
The writing information recording layer 13 has a recording level threshold value which is set to be a sufficiently-high value as compared with the reproduction laser power of the above read-only information plane llA. In such a case, the threshold value of the recording level in the writing information recording layer 13 can be set to a value which is sufficiently high as compared with the reproduction laser power of the above-mentioned read-only information plane llA by setting a refractive index of the transparent spacer ~1 87602 -layer 12, a composition ratio of the recording layer, film thickness and other variables to appropriate values. As a result, the information can be prevented from being erased, even if the writing information recording layer 13 is heated when a focus point of the laser beam is moved away from the read-only information plane.
More specifically, the read-only information plane llA
having phase pits is formed on the substrate 11 made of plastic or the like by a technique such as injection molding.
The transparent spacer layer 12 having a higher refractive index than that of the substrate 11 is formed on the read-only information plane llA and the tracking guide groove 12A is further formed on the upper surface of the transparent spacer layer 12 by the photo-polymer method or the like.
In general, light is reflected at the interface between materials having different refractive indices. Assuming that the refractive index of the material on the light incident side is n1 and the refractive index of the other material is n2, a reflectance ratio R of the reflected light can be expressed as follows:
R = (n2 - n1) / (n2 + n1) ............. (1) Since the refractive index of polycarbonate which is often used as substrate material is approximately 1.58, use of a transparent material (i.e., a material having an extinction coefficient which is substantially zero), which has a refractive index of approximately 3.0, as the transparent spacer layer 12 can yield a reflectance of approximately 30 at the interface and form a practical reflective plane, 21 876~2 .
although the material of the transparent space layer 12 is not restricted to a particular type.
The tracking guide groove (pregroove) 12A formed on the upper surface of the transparent spacer layer 12 is required for tracking the laser beam when recording to or reading information from the writing information recording layer 13.
The tracking guide groove 12A is formed by, e.g., the photo-polymer manufacturing method. The writing information recording layer 13, which is made of a phase-change recording material or magneto-optical recording material and which is formed on the upper surface of the transparent spacer layer 12, has a recording threshold value that is sufficiently high as compared with the laser power used for reading information from the read-only information plane llA by adequately determining the refractive index of the transparent spacer layer 12, the recording layer composition ratio, a film thickness and other variables. This consequently prevents the information from being deteriorated or erased when, e.g., the writing information recording layer 13 is heated when the focusing point of the laser beam is moved from the read-only information plane llA to the writing information recording layer 13.
In Fig. 2, although the material used for the writing information recording layer 13 is not restricted to a particular type in the present invention, it is effective to use phase-change recording material (e.g. GeSbTe system), magneto-optical recording material (e.g. TbFeCo system), dye type write once material (e.g. cyanine dye) or other - 21 876~2 _ materials. The film thickness for these is 200-1000 Angstrom.
As for the material used for the transparent spacer layer 12, it is effective to use poly-crystal SiO2 or amorphous SiN
(film thickness is 500-1500 Angstrom). As for the material used for the protective layer 14, it is effective to use the same material as the material used for the transparent space layer 12. However, the film thickness for the protective layer 14 is preferably more than 500 Angstrom.
Here, when the phase-change recording material or the magneto-optical recording material is used, it may be possible to incorporate the structure shown in Fig. 3 in order to enhance signals or adjust the sensitivity. The structure shown in Fig. 3 is obtained by further providing an interference layer 17 and a reflective layer 18 between the writing information recording layer 13 and the protective layer 14 shown in Fig. 1. In such a case, the film thickness of the writing information recording layer 13 is set to be relatively thin so that the incident light can pass through the interference layer 17 and can be reflected by the reflection layer 18 to return to the incident side.
The structure using an interference layer 17 and a reflective layer 18 is described in S. Tanaka et al., ~Design Concept of Magneto-Optical Disk", Japanese Journal of Applied Physics, Vol. 28, 1989 September 28-3, pp. 67-70.
In case of the magneto-optical disc, since the angle of polar rotation generally becomes larger by the Faraday effect for transmission rather than the Kerr effect for reflection, the embodiment shown in Fig. 3 is more advantageous.
2~ ~7~
-Moreover, the protective layer 14, at the topmost position, effectively functions as an element for mechanically or chemically protecting each of the above-mentioned layers.
Although the material used for each layer in Fig. 3 is not restricted to a particular type in this invention, it is effective to use, as the transparent spacer layer 12, poly-crystal SiO2 or amorphous SiN (film thickness is 500-1500 Angstrom).
Also, it is effective to use, as writing information recording layer 13, magneto-optical material such as TbFeCo system or phase-change material such as GeSbTe system (film thickness is less than 600 Angstroms).
Moreover, it is effective to use as the interference layer 17, poly-crystal SiO2 or amorphous SiN (film thickness is less than 1000 Angstrom), to use as the reflective layer 18, aluminum (film thickness is more than 300 Angstrom), and to use W resin as the protective layer 14.
The functioning of the optical disc during reproduction in the above embodiment will now be described.
When reproducing (reading) information previously recorded on the read-only information plane llA of the optical disc, the light is focused on the read-only information plane llA of the first layer. The information is recorded on the read-only information plane llA as a series of variable length pits (irregularities on the recording plane). When the pits are exposed to the laser beam, the amount of the light reflected by scattering or diffraction of the light is decreased. On the other hand, when the laser beam is ~ 1 87~2 -irradiated on a part of the substrate where no pit is formed, the amount of the light reflected and returned to the optical head side is equal to the product of the incident light and the reflectance ratio of the first layer 11 and second layer 12.
When the reflected light is received by a photodetector to be converted into electric signals, information concerning a length of the pits can be derived from the amplitude of the electric signals. If information must be recorded during a playback session during which information is reproduced from the read-only information plane llA, it is first required to move the laser beam spot to another plane.
In order to move the laser beam spot to another plane, a focus servo is temporarily turned off, and a control current flows to a focusing actuator to forcibly move a focusing position of the laser beam in a focusing direction. When the focusing position has reached the writing information recording layer 13, the focus servo is again turned on, thereby performing the focus jump. The focus jump takes a few milliseconds and switches from a reproduction area to a recording area (or from a recording area to a reproduction area) within a shorter time compared to the time taken for the regional movement on the disc plane.
By the above-described structure, predetermined information can be immediately recorded onto the same optical disc being used for reproduction without adopting any other recording means. Further, when the present invention is incorporated into a personal computer or a game machine, it is -possible to provide an excellent novel optical disc medium which is suitable for highly interactive applications (for example, computerized game applications).
While this invention has been described with reference to an illustrative embodiment, this description is not intended to be construed in a limiting sense. Various modifications of the illustrative embodiment, as well as other embodiments of the invention, will be apparent to persons skilled in the art upon reference to this description. It is, therefore, contemplated that the appended claims will cover any such modifications or embodiments as fall within the true scope of the invention.
Claims (6)
1. An optical disc, comprising:
a substrate of transparent material, said substrate comprising a read-only information plane having pits on an upper surface thereof;
a transparent spacer layer formed on said substrate, said transparent spacer layer having a higher refractive index than that of said substrate, a tracking guide groove being formed on an upper surface of said transparent spacer layer;
a writing information recording layer formed above said tracking guide groove; and a protective layer formed on said writing information recording layer.
a substrate of transparent material, said substrate comprising a read-only information plane having pits on an upper surface thereof;
a transparent spacer layer formed on said substrate, said transparent spacer layer having a higher refractive index than that of said substrate, a tracking guide groove being formed on an upper surface of said transparent spacer layer;
a writing information recording layer formed above said tracking guide groove; and a protective layer formed on said writing information recording layer.
2. An optical disc as defined in claim 1, wherein the writing information recording layer has a recording level threshold value set to a value that is sufficiently high as compared to a laser power needed to reproduce information stored on said read-only information plane to avoid deteriorating or erasing previously recorded data.
3. An optical disc as defined in claim 1, further comprising:
an interference layer through which incident light passes;
and a reflective layer from which incident light is reflected so that it can return to an incident side, wherein said interference layer and said reflection layer are provided between said writing information recording layer and said protective layer.
an interference layer through which incident light passes;
and a reflective layer from which incident light is reflected so that it can return to an incident side, wherein said interference layer and said reflection layer are provided between said writing information recording layer and said protective layer.
4. An optical disc as defined in claim 3, wherein said interference layer is provided on said writing information recording layer and said reflection layer is provided on said interference layer.
5. An optical disc as defined in claim 1, wherein a material of said writing information layer comprises one of a phase-change recording material, a magneto-optical recording material and a dye-type write-once material.
6. An optical disc as defined in claim 3, wherein a material of said writing information layer comprises one of a phase-change recording material, a magneto-optical recording material and a dye-type write-once material.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP7281824A JP2671878B2 (en) | 1995-10-30 | 1995-10-30 | Optical disc recording medium |
| JP281824/1995 | 1995-10-30 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA2187602A1 true CA2187602A1 (en) | 1997-05-01 |
Family
ID=17644515
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA002187602A Abandoned CA2187602A1 (en) | 1995-10-30 | 1996-10-10 | Optical disc recording medium |
Country Status (2)
| Country | Link |
|---|---|
| JP (1) | JP2671878B2 (en) |
| CA (1) | CA2187602A1 (en) |
Families Citing this family (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| AU5566200A (en) | 1999-06-22 | 2001-01-09 | Matsushita Electric Industrial Co., Ltd. | Optical disk, optical disk device, and reproducing method for optical disk |
| JP5073632B2 (en) * | 2008-10-10 | 2012-11-14 | シャープ株式会社 | Optical information recording medium and optical information recording medium driving device |
-
1995
- 1995-10-30 JP JP7281824A patent/JP2671878B2/en not_active Expired - Lifetime
-
1996
- 1996-10-10 CA CA002187602A patent/CA2187602A1/en not_active Abandoned
Also Published As
| Publication number | Publication date |
|---|---|
| JP2671878B2 (en) | 1997-11-05 |
| JPH09128804A (en) | 1997-05-16 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| FZDE | Discontinued |
Effective date: 20000731 |