JPH0721587A - Optical disk dedicated for reproducing - Google Patents

Abstract

PURPOSE:To provide a optical disk which can identify the unit of information smaller than a spot diameter without changing a light source or an optical system and further can improve a C/N. CONSTITUTION:Light emitting layers 3 are made to scatter along a track T on a substrate 2 so as to emit light 5 of a wavelength different from that of read light 14 with intensity depending on the temperature by irradiating it with the read light. With this light emitting layer 3 as the unit of information, information is expressed by the presence/absence or length of this unit of information.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a novel read-only optical disk capable of accommodating high density information.

[0002]

2. Description of the Related Art As information devices such as computers, communications, and video devices have become more sophisticated and personalized, the amount of information to be processed has increased, and therefore the performance of recording devices and media has become higher in recent years. Has become a major development target. In particular, it can be said that high density recording and high capacity recording are very demanding in view of the coming digital age of image information. The method of reproducing (reading) the record information from the recording medium (optical disk) by the optical recording / reading method is a promising reproducing method for a high-density and large-capacity recording medium.

An optical disc based on the optical recording and reading system is
At present, it is already commercially available as a music CD, CD-ROM, LD, magneto-optical disk, or the like. To reproduce information from these discs, the reading light from the light source is first focused on the spinning disc. The condensed light is reflected on the disc. The reflected light is modulated according to the recorded information on the disc. A reproduction signal is obtained by photoelectrically converting the modulated light. A semiconductor laser is often used as the light source for downsizing of the reading device.

The record information is represented by the presence or absence of a small information unit or the length. The information unit is an optical disc such as a CD.
Concavities and convexities (called pits) provided on the disc.
The pits are scattered on a flat track, and the reflected light is modulated by tracing the focused read light (hereinafter abbreviated as read light) on the track. The track may be provided in a spiral shape or in a concentric shape.

In a magneto-optical disk, an area (called a mark) whose magnetization direction is opposite to that of a track portion serves as an information unit. Linearly polarized light (readout light) for this information unit
Is irradiated, the polarization plane of the reflected light rotates in the direction opposite to the track portion. Therefore, when the reflected light is passed through a polarizer and photoelectrically converted, a reproduction signal is obtained. In this way, the optical disc that reproduces information by the optical recording and reading system is
By condensing the read light on the disk into small pieces,
Since the information unit can be reduced to that size, it has a relatively large recording density (about 10 ⁸ marks / cm ² in the present magneto-optical disk).

The optical head used for such optical recording / reading is composed of a light source such as a semiconductor laser and a condensing optical system such as a lens and a mirror, and a servo for focusing (condensing) and tracking. It has a mechanism.

[0007]

In the conventional optical disk, the degree of condensing the read light (spot diameter) determines the size of the information unit, that is, the recording density. Since the minimum value of the spot diameter is limited by the wavelength of the light source and the numerical aperture of the condensing optical system, it cannot be made smaller than the diffraction limit. In other words, it has hitherto been impossible to reproduce an information unit smaller than the spot diameter.

The recording density of the current light source and the condensing optical system is almost at its limit. As a method of increasing the recording density, a method of improving the optical system to obtain a large numerical aperture or a light source of a short wavelength can be considered as a method for increasing the recording density, but both of them are accompanied by an increase in the size and cost of the device. There is a problem. In optical recording and reading, in order to obtain a reproduction signal from reflected light, it is necessary to divide the optical paths of read light and reflected light. Since laser light having coherency is often used as a light source, there is a problem that if there is light returning to the light source, the intensity of the reproduction signal is affected and the C / N (carrier / noise) ratio is lowered.

Further, in general, in addition to the change (AC component) in the amount of light (the amount of light of the polarization component when reading the magneto-optical recording medium) to be converted into a reproduction signal, a DC component of the amount of light is superimposed on the reflected light. This DC component is the C / N of the reproduced signal.
There is a problem that it causes a reduction in the ratio. A first object of the present invention is to make it possible to identify an information unit smaller than the spot diameter without changing the light source or the optical system. Thereby, the recording density can be increased without increasing the size and cost of the device. The second purpose is to improve the C / N ratio of the reproduced signal.

[0010]

Therefore, the first aspect of the present invention is to provide "a light emitting layer which emits light having a wavelength different from that of the reading light by irradiation of the reading light along the track on the substrate with intensity depending on temperature. Is provided and the light emitting layer is used as an information unit, and information is represented by the presence or absence of the information unit or the length thereof.

The second aspect of the present invention is that "a light emitting layer which emits light having a wavelength different from that of the reading light with intensity depending on temperature upon irradiation of the reading light is entirely provided on the substrate. On the reading light irradiation side, a light reflection layer or a light absorption layer is scattered along the track, and these light reflection layers or light absorption layers are used as information units, and information is represented by the presence or absence of this information unit or the length. And a read-only optical disc (claim 2).

The third aspect of the present invention is the optical disc according to claim 1 or 2, wherein a heat reflection layer is provided on the side of the light emitting layer on which the reading light is irradiated and / or on the side opposite thereto or on the periphery thereof. (Claim 3) "is provided. A fourth aspect of the present invention is an optical disk according to claim 1 or 2, wherein a heat insulating layer is provided on the side of the light emitting layer on which the reading light is irradiated and / or on the side opposite thereto or on the periphery thereof. )" I will provide a.

In a fifth aspect of the present invention, "the optical disk according to any one of claims 1 to 4 is characterized in that a light reflecting layer is provided on the side of the light emitting layer opposite to the side where the reading light is irradiated."
I will provide a. According to a sixth aspect of the present invention, the optical disc according to claim 3 or 4, wherein the heat reflection layer or the heat insulation layer provided on the side opposite to the reading light irradiation side also functions as the light reflection layer. Item 6) ”is provided.

[0014]

In the optical disk according to the present invention, the change of the emission intensity from the light emitting layer 3 which emits the light 5 having a wavelength different from that of the readout light 14 with the intensity depending on the temperature by the irradiation of the readout light is detected and converted. To be a reproduction signal. for that reason,
It is provided on the substrate 2 of the optical disk so as to face the light emitting layer 3 scattered along the track T or the light emitting layer 3 provided on the entire surface of the substrate 2 and to be scattered on the irradiation side of the reading light 14. The light reflecting layer 11 or the light absorbing layer 11 '(which shields the light emitting layer) serves as an information unit. The presence or absence or length of this information unit represents information.

This information unit has the same function as a conventional pit or mark. The disc has spiral or concentric explicit or implicit tracks, on which information units are scattered. The light emitting layer 3 is a layer that emits the light 5 having a wavelength range different from that of the reading light 14 when the reading light 14 is irradiated (this phenomenon is called photoluminescence). The light emitting layer 3 includes a layer that emits light having a wavelength longer than the irradiation light (for example, a semiconductor layer) and a layer that emits light having a short wavelength (for example, an up-converter layer).

Many of the materials for the light emitting layer 3 emit light when irradiated with light having a short wavelength of 600 nm or less, but the material for the up converter layer is in the infrared region (1000 n
It also emits light when irradiated with light (around m). Examples of the material of the light emitting layer 3 include semiconductors such as amorphous silicon, GaAs, and InP, those obtained by doping the semiconductor with ions, phosphors, infrared-visible conversion materials (fluoride to which Er ³⁺ or Y ³⁺ is added, or Chloride, ZnS, CaS-Eu mixture, Zn
O, the above compounds doped with ions, etc.) and organic materials are preferred.

If the thickness of the light emitting layer 3 is too thin, light emission does not sufficiently occur, which makes it difficult to identify the information unit. Further, if the thickness of the light emitting layer 3 is too thick, it takes time to form the layer, resulting in poor productivity. Therefore, it is preferable that the thickness be appropriate. For example, a thickness of 50 to 500 nm is preferable, but the thickness is not limited to this. In addition, the light emitting layer 3 is
It is preferable to form a porous film having a lower density in terms of luminous efficiency.

The material of the light reflecting layer 11 is, for example, Al, A
g, Au, In-Sb alloy, CuO, etc. are preferable. As the material of the light absorption layer 11 ′, for example, graphite carbon, a lower oxide of metal, or the like is preferable. If the thickness of the light-reflecting layer 11 or the light-absorbing layer 11 ′ is too thin, the shielding of light emission due to reflection or absorption becomes insufficient, and if it is too thick, it takes time to form the layer and productivity deteriorates. It should be thick. For example, a thickness of 50 to 500 nm is preferable, but the thickness is not limited to this.

FIG. 1 is a schematic vertical sectional view showing the reading principle of an optical disk according to the present invention. Among the light emitting materials used for the light emitting layer, there are some light emitting materials whose emission intensity largely depends on temperature. In the present invention, a light emitting material whose emission intensity largely depends on temperature is selected from among the light emitting materials and used for the light emitting layer 3. For example, in the case of a light emitting layer made of amorphous Si, the emission intensity decreases as the temperature rises from room temperature to about 300 ° C, and the emission peak wavelength shifts to the long wavelength side (see Fig. 2). . In many upconverter layers (light emitting layers), the light emission intensity is significantly reduced at a certain temperature or higher. Therefore, by appropriately selecting the light emitting material and the wavelength range of the emitted light to be detected, it is possible to make a large difference in the emission intensity due to the temperature difference.

In the reading of information, the intensity of the read light spot 4 focused to the diffraction limit exhibits a Gaussian distribution, and has a temperature (high temperature) distribution corresponding to this intensity distribution. The region showing the distribution is slightly shifted backward because the disc is rotating (see distribution 7 in FIG. 1). Therefore, the inside of the spot is divided into a high temperature region corresponding to the high temperature distribution region and a low temperature region other than the high temperature region.

When a material whose light intensity in the wavelength range to be detected greatly decreases due to temperature rise is used as the light emitting material of the light emitting layer, the light emission from the light emitting layer (information unit) 3a in the high temperature region within the spot upon irradiation of the reading light. Becomes extremely small. On the other hand, the light emission 5 from the light emitting layer (information unit) 3b in the low temperature region in the spot is much larger than the light emission 5 from the light emitting layer (information unit) 3a in the high temperature region.

Therefore, even if there are two information units (light emitting layers) 3a and 3b in the spot, only the information unit 3b in the low temperature region in the spot can be identified and read. In addition, the light emitting layer (information unit) in the high temperature region
Light emission from 3a and light emitting layer in low temperature region (information unit)
Since there is a big difference between the light emission 5 from 3b, a large C /
Reading can be done with N ratio.

On the contrary, when a material whose light intensity in the wavelength range to be detected greatly increases due to temperature rise is used as the light emitting material of the light emitting layer, the light emitting layer (information unit) from the light emitting layer in the high temperature area within the spot is used. The light emission is much larger than the light emission from the light emitting layer (information unit) in the low temperature region. In this case, of the two information units (light emitting layers) 3a and 3b in the spot, only the information unit 3a in the high temperature region can be identified and read with a large C / N ratio.

The light 5 emitted from the light emitting layer 3 has a wavelength range greatly different from that of the reading light 14, so that the beam splitter 5
17 and the optical filter 22 are used to separate only the emitted light, which is detected by the photodetector 23. As a result, C / is obtained by detecting the reflected light 12 of the read light 14 and the scattered light (not shown).
It is possible to prevent a decrease in N ratio. Further, since the direct current component is not easily superimposed on the light emission signal, it is advantageous in preventing the decrease of the C / N ratio.

The optical system that collects the emitted light 5 may also be used as the optical system that collects the read light 14. In this case, strict light collection is difficult because the wavelengths of the emitted light 5 and the read light 14 are different, but strict light collection is not necessary because the light emission intensity can be detected. In the reading of a conventional optical disc, the split photosensor 18 detects the intensity distribution of the reflected light 12 of the read light 14 to perform focusing and tracking optimization controls 20 and 21. Such control is also possible in the reading of the optical disk according to the present invention, but in addition, the light emission 5 from the light emitting layer 3 is used for focusing by the light emission intensity, and tracking is performed by the low frequency component of the light emission. (Envelope detection) is also possible.

In order to efficiently heat the light emitting layer 3 by irradiating the reading light 14, the heat reflecting layer 10 or the heat insulating layer 10 'is provided on the side of the light emitting layer 3 on which the reading light is irradiated and / or on the opposite side thereof or on the periphery thereof. Is preferably provided (see FIG. 3). Heat reflective layer
For ITO, ITO, ZnO, TiO ₂ or the like used for the infrared reflective film is preferable. The heat insulating layer 10 'is made of SiO ₂ , Z
nS-SiO ₂ or SiN is preferable.

If the thickness of the heat reflection layer 10 or the heat insulation layer 10 'is too thin, the heat reflection or heat insulation effect will be insufficient, and if it is too thick, it will take time to form the layer and productivity will be deteriorated. It should be thick. For example, a thickness of 10 to 500 nm is preferable, but the thickness is not limited to this. In addition to the read light 14, the reflected light 12 is used to heat the light emitting layer 3 to increase the detected light emission intensity, and the light emitted from the light emitting layer 3 to the side opposite to the light emission detection side is reflected. In order to increase the emitted light intensity detected (reflected light 13),
It is preferable to provide the light reflection layer 11 on one side of the light emitting layer 3 (on the side opposite to the irradiation of the reading light) (see FIG. 4). Light reflection layer 11
For example, Al, Ag, Au, In—Sb alloy, CuO and the like are preferable as the material.

If the thickness of the light-reflecting layer 11 is too thin, the reflection will be insufficient, and if it is too thick, it will take time to form the layer and the productivity will be deteriorated. For example, 50
A thickness of ~ 500 nm is preferred, but not limited to this thickness. Further, it is preferable to use the light reflecting layer also as the heat reflecting layer or the heat insulating layer from the viewpoint of shortening the optical disc manufacturing process. As a material for such a dual-purpose layer, for example, an In-Sb alloy is preferable.

The substrate 2 of the optical disc according to the present invention comprises:
For example, glass material or polymethylmethacrylate,
Plastic materials such as polycarbonate, polymethylpentene, polyolefin and epoxy resin are preferred. If a disc having the light emitting layer 3, the heat reflecting layer 10 or the heat insulating layer 10 'formed on the substrate 2 (hereinafter referred to as a single disc) is used as an optical disc as it is, deterioration of each layer or the substrate 2 ( In order to prevent such deformation (in the case of a plastic substrate), it is common to bond the veneer disk with a protective (sealing) substrate or another veneer disk with an adhesive. The protective layer (for example, epoxy resin layer) 15 may be simply formed on the single disk.

An optical disk having a structure in which a protective substrate is bonded to a single plate disk is called a single-sided disk, and an optical disk in which two single plate disks are bonded to each other is called a double-sided disk. The protective substrate is preferably made of the same material as the substrate 2. The adhesive is preferably a photocurable adhesive for a single-sided disc and a hot melt adhesive or a thermosetting adhesive for a double-sided disc.

Hereinafter, the present invention will be described in detail with reference to Examples, but the present invention is not limited thereto.

[0032]

Example 1 Glass substrate 2 having a diameter of 5 inches and a thickness of 1 mm
A heat insulating layer made of ZnS-SiO ₂ was formed thereon by sputtering to a thickness of about 50 nm, and a light emitting layer made of amorphous Si, which is a photoluminescent material, was also formed thereon at a thickness of about 50 nm. In order to improve the luminous efficiency, the light emitting layer is preferably a porous layer having a lower density.

Next, a photoresist is applied on this and prebaked, and then a KrF excimer laser (wavelength 2) is applied.
By using an exposure device having a light source of 49 nm) and a signal original plate, “1” and “0” of information to be recorded (mark length 0.25 μm
m, the mark interval is 0.25 μm).
The signal original plate was produced using a laser (wavelength 400 to 500 nm) cutting machine.

After that, the heat insulating layer and the light emitting layer were patterned by Ar gas dry etching to form the heat insulating layer 10 'and the light emitting layer 3 which were scattered. Further, a heat insulating layer 10 'made of ZnS-SiO ₂ on the approximately 100n
It was formed with a thickness of m. Finally, an epoxy resin was applied onto this by a roll coater and cured to form a protective layer 15, and an optical disk was manufactured (see FIG. 5).

The light emission from the light emitting layer 3 made of amorphous Si (the material of the light emitting layer) showed the temperature characteristics as shown in FIG. This optical disk reproducing apparatus comprises a rotating system, a reproducing laser light source, a reproducing system and their optical systems. The light source 16 comprises an optical system such as a second harmonic laser with λ = 532 nm and a condenser lens with an aperture ratio (NA) = 0.5.

The reproducing system comprises a photodetector 23 and an optical system for sending light to the photodetector. The optical disk is rotated by a rotating system, the reading light 14 from the light source 16 is condensed by the condenser lens 1, and the optical disk 2
The upper light emitting layer 3 was irradiated. At this time, the light 5 emitted from the light emitting layer 3 showed a broad dispersion in the wavelength range of about 700 to about 1000 nm. By disposing a short wavelength cut filter (an example of the optical filter 22) in front of the photodetector 23, the read light 14 can be separated from the reflected light 12, and only the long wavelength light emission 5 can be detected. An outline of the reading optical system is shown in FIG.

Focusing of the reading light 14 is performed by optimization control based on the beam shape of the reflected light, and tracking is performed by diffracted light (push-pull signal) from the mark row. The diameter of the spot 4 of the readout light 14 was determined from the diffraction limit and was about 1 μm. The optical disk was rotated so that the spot 4 moved on the disk at a constant linear velocity of 7 m / sec, and reading was performed.

In the reading of information, the intensity of the spot 4 of the read light 14 focused to the diffraction limit has a Gaussian distribution and has a temperature (high temperature) distribution corresponding to this intensity distribution, but on the rotating disk, Since the disk is rotating, the region showing the high temperature distribution is slightly shifted backward (see distribution 7 in FIG. 1). Therefore, the spot was divided into a high temperature region corresponding to the high temperature distribution region and a low temperature region other than the high temperature region.

As the light emitting material of the light emitting layer 3, a material (amorphous Si) whose light intensity in the wavelength range to be detected greatly decreases due to temperature rise is used. The light emission from the information unit 3a was extremely small. On the other hand, the light emission 5 from the light emitting layer (information unit) 3b in the low temperature region in the spot was much larger than the light emission from the light emitting layer (information unit) 3a in the high temperature region.

Therefore, only the information unit 3b in the low temperature region within the spot could be identified and read. Further, since there is a large difference in intensity between the light emission from the light emitting layer (information unit) 3a in the high temperature region and the light emission 5 from the light emitting layer (information unit) 3b in the low temperature region, a large C / N ratio is obtained. I was able to read it. In this way, an information unit smaller than the diameter of the spot 4 of the reading light 14 (mark length 0.25 μm
m, the mark interval was 0.25 μm). The C / N ratio during reading is 50d at a laser power of 6mW.
It was B or more. In the reading with the laser power of 2 mW, the C / N ratio was about 40 dB, and it was confirmed that the C / N ratio changed due to the temperature difference of the light emitting layer 3 due to the difference in the reading light power.

[0041]

On the Example 2 Example 1 and the same type of substrate 2 by sputtering, the insulating layer 10 made of ZnS-SiO ₂ '
Was formed to a thickness of about 50 nm, and then an Al layer having a thickness of about 50 nm was similarly formed. After applying a photoresist on this and pre-baking, an exposure apparatus using a KrF excimer laser (wavelength 249 nm) as a light source and a signal original plate are used to record "1" and "0" (marks) of information to be recorded. Exposure was performed so as to correspond to a length of 0.25 μm and a mark interval of 0.25 μm). After that, only the Al layer was patterned by Ar gas dry etching to form an interspersed Al layer (an example of the light reflection layer 11).

[0042] By sputtering a light emitting layer 3 of amorphous Si on the about to 100nm form, about the heat insulating layer 10 'made of ZnS-SiO ₂ thereon similarly 1
Was formed to a thickness of 00 nm. Finally, an epoxy resin was applied by a roll coater and then cured to form a protective layer 15, thus completing an optical disc (see FIG. 7).

Also in this optical disc, as in the first embodiment,
An information unit (mark length 0.25 μm, mark interval 0.25 μm) smaller than the diameter of the spot 4 of the reading light 14 could be read. The C / N ratio at the time of reading was 50 dB or more at a laser power of 6 mW.

[0044]

[Embodiment 3] A heat insulating layer 10 ′ made of ZnS—SiO _{2 is formed} on a substrate 2 of the same type as in Embodiment 1 by sputtering.
Was formed to a thickness of about 50 nm, and then an Al layer having a thickness of about 50 nm was similarly formed. After applying a photoresist on this and pre-baking, an exposure apparatus using a KrF excimer laser (wavelength 249 nm) as a light source and a signal original plate are used to record "1" and "0" (marks) of information to be recorded. Exposure was performed so that the length was 0.4 μm and the mark spacing was 0.4 μm. After that, only the Al layer was patterned by Ar gas dry etching to form an interspersed Al layer ((one example of the light reflection layer 11)).

On this, a light emitting layer 3 made of ZnS doped with Te (1 atom%), which is a phosphor, was formed to a thickness of about 100 nm by sputtering. This light emitting layer 3 showed light emission having a peak at 400 to 500 nm with Te as a blue light emission center when irradiated with a semiconductor laser (780 nm). Further, when heated, the emission intensity drastically decreased around 100 ° C.

[0046] Furthermore, to form a heat insulating layer 10 'made of ZnS-SiO ₂ on the 100 nm, also (an example of a light reflecting layer 11) 60 nm Al layer by sputtering. Finally, an epoxy resin was applied by a roll coater and then cured to form a protective layer 15, thus completing an optical disc (see FIG. 8). This optical disc is irradiated with the reading light 16 condensed using an optical system having a wavelength of 780 nm and a numerical aperture of 0.5 with a semiconductor laser as a light source, and the spot is 7 m / s.
Reading was performed by rotating the optical disk so as to move at a constant linear velocity of ec.

The light around 500 nm emitted from the light emitting layer 3 by the irradiation of the reading light was detected by the photodetector 28 having a long wavelength cut filter (an example of the optical filter 23) arranged in front. The focusing and tracking optimization controls were performed in the same manner as in Example 1. In this way, an information unit smaller than the diameter of the spot 4 of the reading light 14 (mark length 0.4 μm, mark interval
0.4 μm) could be read. C / when reading
The N ratio was 55 dB or more at a laser power of 4 mW. When reading with a laser power of 2 mW, C /
The N ratio was about 45 dB, and it was confirmed that the C / N ratio changed due to the temperature difference of the light emitting layer 3 due to the difference in the read light power.

[0048]

As described above in detail, according to the present invention, an information unit smaller than the spot diameter can be identified without changing the light source or the optical system. Thereby, the recording density can be increased without increasing the size and cost of the device. Further, according to the present invention, the C / N ratio of the reproduced signal can be improved.

[Brief description of drawings]

FIG. 1 is an explanatory diagram showing the reading principle of an optical disc according to the present invention (when the light emitting layer 3 is partially provided) (top:
FIG. 1 is a schematic cross-sectional view of an optical disc, middle: a schematic plan view of the optical disc, and bottom: a temperature distribution diagram on the optical disc).

FIG. 2 is a data diagram showing an example of temperature characteristics of light emission intensity from the light emitting layer 3 of the optical disc according to the present invention.

FIG. 3 is a schematic cross-sectional view showing an example of an optical disc according to the present invention (when the heat reflection layer 10 or the heat insulation layer 10 ′ is provided around the light emitting layer 3).

FIG. 4 is a schematic cross-sectional view showing an example of an optical disc according to the present invention (in the case where a light reflection layer 11 is provided on the side opposite to the reading light irradiation side of the light emitting layer 3).

5 is a schematic cross-sectional view showing an optical disc of Example 1. FIG.

FIG. 6 is a schematic sectional view showing a reading optical system according to the optical disc of the present invention.

FIG. 7 is a schematic sectional view showing an optical disc of Example 2.

FIG. 8 is a schematic sectional view showing an optical disc of Example 3.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Condensing lens 2 ... Optical disc substrate 3 ... Emitting layer 3a ... Emitting layer that becomes hot in spot 4 3b ... Emitting layer that does not become hot in spot 4 4 ... Readout light spot 5 ... Emission from light emitting layer 6 ... Moving direction of read-out light spot 7 ... Temperature distribution on optical disc 8 ... Spectral intensity of light emission from light emitting layer made of amorphous Si (25 ° C.) 9 ... Spectral intensity of light emitted from light emitting layer made of amorphous Si (200 ° C) 10 ... Heat reflection layer 10 '... Heat insulation layer 11 ... Light reflection layer 12 ... Reflected light of readout light 13・ ・ ・ Reflected light of emitted light 14 ・ ・ ・ Read light 15 ・ ・ ・ Protective layer (eg epoxy resin) 16 ・ ・ ・ Light source of read light (eg semiconductor laser) 17 ・ ・ ・ Beam splitter 18 ・ ・・ Split photo sensor (for optimized drive) 1 9 ・ ・ ・ Optimization drive circuit 20 ・ ・ ・ Optimization drive for focusing 21 ・ ・ ・ Optimization drive for tracking 22 ・ ・ ・ Optical filter (for example, short wavelength cut filter) 23 ・ ・ ・ Photo detector (Emission detection) 24) Disc movement direction T ... Track or above

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Tatsuo Niwa 3 2-3 Marunouchi, Chiyoda-ku, Tokyo Inside Nikon

Claims (6)

[Claims] 1. A light emitting layer, which emits light having a wavelength different from that of the reading light at a temperature-dependent intensity upon irradiation of the reading light, is scattered along a track on a substrate, and the light emitting layer is used as an information unit. A read-only optical disc characterized in that information is represented by the presence or absence or length of this information unit. 2. A light emitting layer, which emits light having a wavelength different from that of the read light at a temperature-dependent intensity when the read light is irradiated, is entirely provided on the substrate, and the track is provided on the read light irradiated side of the light emitting layer. A read-only optical disc characterized in that a light-reflecting layer or a light-absorbing layer is scattered along a line, and these light-reflecting layers or light-absorbing layers are used as information units to represent information by the presence or absence or length of the information units . 3. The optical disk according to claim 1, wherein a heat reflection layer is provided on the read light irradiation side of the light emitting layer and / or on the side opposite thereto or on the periphery thereof. 4. The optical disk according to claim 1, wherein a heat insulating layer is provided on the side of the light emitting layer on which the reading light is irradiated and / or on the side opposite thereto or on the periphery thereof. 5. A light reflecting layer is provided on the side of the light emitting layer opposite to the side on which the readout light is irradiated.
The described optical disc. 6. The optical disk according to claim 3, wherein the heat reflecting layer or the heat insulating layer provided on the side opposite to the side where the reading light is irradiated also serves as a light reflecting layer.