JPH08235636A - Optical recording medium and reproducing method thereof - Google Patents

Abstract

(57) [Abstract] [Purpose] It is an object to provide an optical recording medium capable of reproducing higher density information by enhancing a super-resolution effect and a reproducing method thereof. A recording layer 5 provided on the reflective layer 7 and capable of transmitting reproduction light; a mask layer 3 provided on the recording layer 5 for improving reproduction light transmittance by a reaction due to absorption of reproduction light; The recording layer 5 is characterized in that the recording portion has a higher transmittance for reproducing light than the non-recording portion.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical recording medium capable of reproducing high density recorded information and a reproducing method thereof.

[0002]

2. Description of the Related Art Recently, in order to improve a reproducible recording density, a super-resolution technique using an optical recording medium having a mask layer made of a dye material has been studied. This technique is intended to form an effective spot smaller than a read-out spot by increasing the transmittance of a part of the mask layer, thereby reproducing information recorded at high density.

JP-A-5-242524 (G11B 7
/ 24) and JP-A-5-266478 (G11
B 7/00) describes using, for example, an inverse photochromic spiropyran in such a mask layer. In this case, at the time of reproduction, the light absorption of a part of the spot forming portion of the mask layer is reduced, the effective spot becomes small, and the light absorption increases after passing through the reproduction light spot. The decrease in the light absorption of the mask layer having the reverse photochromic property is based on the photoreaction of the reverse photochromic material generated by the irradiation of the reproducing light, and the increase in the light absorption of the mask layer after passing the reproducing light spot is After passing, it is mainly due to thermal reaction at room temperature.

Further, Japanese Patent Laid-Open No. 5-242524 (G11
B 7/24) discloses a mask layer using a thermochromic dye material in which the magnitude of light absorption changes depending on the temperature.

[0005]

However, in response to the demand for higher density of information, the super-resolution effect is further improved over that of the conventional optical recording medium having the super-resolution mask layer. Things are desired.

Therefore, the present invention has been made in view of the above problems, and an object of the present invention is to provide an optical recording medium and a reproducing method thereof capable of reproducing higher density information by enhancing the super-resolution effect. And

[0007]

The optical recording medium of the present invention comprises:
The recording layer, which is provided on the reflecting surface and can transmit the reproducing light, and the reaction by absorbing the reproducing light, which is provided on the recording layer or between the recording layer and the reflecting surface, improves the transmittance for the reproducing light. And a mask layer for controlling the recording layer. The recording layer has a higher transmittance for reproducing light than a non-recording portion.

In particular, the recording layer is characterized in that a recording portion having a higher transmittance for reproducing light than that of a non-recording portion is formed by irradiation of recording light.

Further, the recording layer is characterized by containing a phase change type recording material which changes from an amorphous state to a crystalline state by irradiation with recording light.

Another optical recording medium of the present invention comprises a recording layer and a mask layer which is provided on the recording layer and whose transmittance for reproducing light is improved by a reaction due to absorption of reproducing light. It is characterized in that the recorded portion has a higher reflectance to the reproduction light than the non-recorded portion.

In particular, the recording layer is characterized in that a recording portion having a higher reflectance with respect to the reproducing light than that of the non-recording portion is formed by the irradiation of the recording light.

Further, the recording layer is characterized by containing a phase change type recording material which changes from a crystalline state to an amorphous state upon irradiation with recording light.

In particular, the mask layer is characterized by containing a photon-mode material whose transmittance with respect to reproduction light is increased by a photon-mode reaction caused by absorption of reproduction light.

Furthermore, the portion of the mask layer irradiated with the reproduction light has an optical density of 0.4 or more before the irradiation.

According to the reproducing method of the optical recording medium of the present invention, the reproducing light is irradiated onto the optical recording medium provided with the recording layer and the mask layer whose transmittance for the reproducing light is improved by the reaction due to the absorption of the reproducing light. The information of the recording layer is reproduced such that the reproduction light from the recording portion of the recording layer has a higher light intensity than the reproduction light from the non-recording portion of the recording layer.

[0016]

The recording layer, which is provided on the reflecting surface (for example, the reflecting layer or the reflective substrate) and is capable of transmitting the reproducing light, and the reaction by absorbing the reproducing light, which is provided on the recording layer, have a transmittance for the reproducing light. With an improved mask layer, an optical recording medium having a recording portion of the recording layer having a higher transmittance for reproducing light than a non-recording portion is irradiated with reproducing light from the mask layer side toward the recording layer, The reproduction light improves the transmittance of the mask layer and a part of the reproduction light reaches the recording layer. After that, the reproduction light reaching the recording layer is further transmitted through the recording portion having a higher transmittance than the non-recording portion, and then is reflected by the reflecting surface, and the reflected light corresponding to the recording portion is remarkably reflected on the mask layer. Incident. As a result, the mask layer significantly improves the transmittance of the portion corresponding to the recording portion, so that the difference between the recording portion and the non-recording portion becomes sufficiently clear, and the track density and linear recording density of the optical recording medium are improved. It can be fully achieved. In addition, a recording layer that is provided on a reflective surface (for example, a reflective layer or a reflective substrate) and that can transmit reproduction light,
A mask layer which is provided between the recording layer and the reflecting surface and has a transmittance for reproducing light improved by a reaction due to absorption of the reproducing light; When an optical recording medium having a high transmittance to the recording layer is irradiated with reproducing light from the recording layer side toward the mask layer, the reproducing light is transmitted through a recording portion having a higher transmittance than a non-recording portion, and the recording portion After improving the transmittance of the mask layer corresponding to (1), the reflected light corresponding to the recording portion is re-incident on the mask layer. As a result, the mask layer remarkably improves the transmittance of the portion corresponding to the recording portion, so that the difference between the recording portion and the non-recording portion becomes sufficiently clear,
The track density and linear recording density of the optical recording medium can be sufficiently improved.

Further, a mask layer is provided on the recording layer, the transmittance of which with respect to the reproducing light is improved by the reaction due to the absorption of the reproducing light, and the recording portion of the recording layer has a higher reflectance with respect to the reproducing light than the non-recording portion. When the optical recording medium is irradiated with reproduction light from the mask layer side to the recording layer, the reproduction light improves the transmittance of the mask layer and part of the reproduction light reaches the recording layer. After that, the reproduction light reaching the recording layer is more reflected by the recording portion having a higher reflectance than the non-recording portion, and the reflected light corresponding to the recording portion re-enters the mask layer remarkably. As a result,
Since the transmittance of the mask layer corresponding to the recording portion is remarkably improved, the difference between the recording portion and the non-recording portion is sufficiently clarified, and the track density and the linear recording density of the optical recording medium can be sufficiently improved. .

In particular, when the mask layer contains a photon mode material whose transmittance to the reproduction light is increased by a photon mode reaction caused by absorption of the reproduction light, the reflection surface is formed after the reproduction light is incident on the mask layer. Alternatively, if the configuration is such that the light is reflected by the recording layer and is incident on the mask layer again, the nonlinearity of the transmittance change becomes remarkable and the transmittance increases remarkably, so that the track density and the linear recording density can be significantly improved. .

This non-linear increase will be described by taking the optical recording medium of FIG. 5 as an example.

In FIG. 5, 11 is a translucent substrate and 12 is the substrate 1.
A recording layer formed on 1 and capable of transmitting reproducing light, 13 contains a photon mode material such as a photon mode photochromic material or a photon mode saturable absorptive dye material formed on the recording layer 12. , A mask layer having a layer thickness L (cm) having a property of increasing the transmittance of reproduction light by a photon mode reaction caused by absorption of reproduction light by the photon mode material, and 14 is formed on the mask layer 13. , A reflective layer having a reflectance R _rec that reflects the reproduction light.

The transmittance T of the mask layer 13 for reproducing light is expressed by the following equation.

T = exp (−2.3εCL) where ε is the molecular extinction coefficient [l / (mol.multidot.m) of the photon mode material in a state where the above photon mode reaction can occur.
cm)], C is the concentration [mol / l] of the photon mode material in the above state, and the optical density OD of the mask layer 13 is εCL.

The inventor of the present application theoretically found that the transmittance T of the mask layer 13 changes according to the following differential equation with respect to time t [sec].

[0024]

[Equation 1]

Here, φ represents the probability that the absorption of the molecule disappears due to the photon mode reaction, which corresponds to the quantum yield of the reaction in the case of the photochromic molecule and 1 in the case of the saturable absorptive dye molecule. τ represents the time [second] during which the molecule in the above material absorbs light and disappears due to the photon mode reaction. In the case of a photochromic molecule, it is substantially infinite, and in the case of a saturable absorptive dye molecule, It corresponds to the excitation lifetime. Further, P generally indicates the irradiation intensity of the reproducing light, but in this case, it indicates the intensity [W] after passing through the recording layer,
S is the irradiation area [cm ² ] of the reproduction light on the mask layer 13, λ
Is the wavelength [m] of the reproduction light, T ₀ is the transmittance before irradiation of the reproduction light, and the constant α is expressed by the following equation.

[0026] ^{α = 2.3 × 10 3 / (} hcN A) = 1.9
× 10 ⁴ [Jm / mol] where h is Planck's constant, c is light velocity in vacuum, and N _A is Avogadro's number.

The results of solving the above differential equation by numerical calculation are shown below. Here, P = 4 mW, S = 1 × 1
It was set to 0 ⁻⁸ cm ² and λ = 680 × 10 ⁻⁹ m.

FIG. 6 shows a case where the mask layer 13 contains a photon-mode photochromic material, and the above-mentioned differential when the reflectance R _rec of the reflective layer 14 is 0.2, 0.5 and 0.8. The relationship between the square of the transmittance T obtained by solving the equation by numerical calculation and the irradiation time (time) of the reproduction light is shown.
Since τ of this photon-mode photochromic material is substantially infinite, the first term on the right side of the equation can be ignored. Further, the sensitivity εφ represented by the product of the quantum yield φ and the molecular extinction coefficient ε uses a value of 1000 l / (mol · cm), and the initial optical density (optical density before reproduction light irradiation) OD of the mask layer 13 is 1 (T ₀ = 0.1) was used.

FIG. 7 shows a case where the mask layer 13 contains a saturable absorptive dye material, and the reflectance R _rec of the reflective layer 14 is 0.2, 0.5 and 0.8. The above differential equation is solved by numerical calculation to represent the relationship between the square of the transmittance T and the irradiation time (time) of the reproduction light. The excitation lifetime τ
Is 100 ns which is a typical value of such a material, the molecular extinction coefficient ε is 20000 l / (mol / cm), and the initial optical density (optical density before irradiation of reproducing light) OD of the mask layer 13 is 0.7. (T ₀ = 0.2) was used.

From these figures, the larger the reflectance R _rec is,
It can be seen that the nonlinearity of the change in the transmittance of the mask layer 13 with respect to the light irradiation amount becomes significantly large, and the increase in the transmittance becomes remarkable.

Moreover, the photon-mode material, like the reverse photochromic material, has a lower absorption due to a photoreaction upon irradiation with reproducing light, and also has a thermal reaction (heat-mode reaction) due to a temperature rise at the spot center. Does not occur, the improvement of the transmittance at the center of the spot does not become insufficient, and the super-resolution effect can be sufficiently obtained. Further, unlike the thermochromic material, the photon-mode material is not a reaction that occurs with an increase in temperature, so that it is not necessary to apply sufficient heat to the mask layer to cause a reaction. As a result, even when the recording layer has a heat mode property such as a phase change layer, there is no fear that the information in the recording layer is destroyed by the heat.

Further, when the optical density of the mask layer is 0.4 or more, the nonlinear increase of the transmittance becomes remarkable,
The track density and linear recording density can be further improved.

[0033]

The first embodiment of the present invention will be described in detail. FIG.
FIG. 2 is a schematic cross-sectional view of the reflective optical recording medium of this embodiment, and FIG. 2 is a diagram showing a recording mark portion (recording portion) and a land portion (non-recording portion) of the optical recording medium.

In FIG. 1, 1 is a diameter 12c having a spiral groove with a pitch of 0.8 μm and a depth of 600 Å on the surface.
m is a transparent substrate made of polycarbonate, 2 is a transparent dielectric layer made of SiN or the like having a layer thickness of 500 Å formed on the surface of the substrate 1 having the above group by a sputtering method, and 3 is a diarylethene-based substrate or the like. Mask layer having a layer thickness of 0.2 μm, which is formed by applying a cyclohexanone solution containing the photon-mode photochromic material and polystyrene as a binder by spin coating.
Is a translucent dielectric layer made of ZnS-SiO ₂ having a layer thickness of 1000 Å formed on the mask layer 3 by sputtering or the like, and 5 is reproduction light formed on the translucent dielectric layer 4 by sputtering or the like. Is a phase change type recording layer made of Ge ₂ Sb ₂ Te ₅ having a thickness of 300 Å, and 6 is a transparent layer made of ZnS-SiO ₂ having a layer thickness of 1000 Å formed on the recording layer 5 by a sputtering method or the like. An optical dielectric layer, 7 is a reflective layer made of gold with a layer thickness of 300 Å formed on the transparent dielectric layer 6 by a sputtering method, and 8 is a layer formed on the reflective layer 7 by a spin coating method. Thickness 10
It is a protective layer made of a UV curable resin of μm.

FIG. 2 shows a part of the recording mark portion and the land portion which are not shown in FIG.

The photochromic material of this embodiment is
The following structural formula was used.

[0037]

Embedded image

This material has a wavelength of 60 when irradiated with blue light.
Light absorption in the vicinity of 0 to 700 nm increases (colors), and irradiation with red light decreases light absorption in the same wavelength range (discoloration). This material is a photon-mode photochromic material, both phenomena occur in the photon mode, and the reaction by heat does not substantially occur.

The transparent dielectric layer 2 and the mask layer 3 are used.
If not, as described on page 39 of the Optical Memory Symposium '88, the above optical recording medium, the phase-change recording layer 5 is amorphized by irradiation with high-power laser light, and the amorphous portion is formed. Wavelength of 600
Since the transmittance for light in the region of about 700 nm is reduced, the reflection of light from the medium for light in the region is about 20.
%, And the phase-change recording layer 5 in the amorphous state is changed to the crystalline state by the irradiation of the laser beam with the medium power, and the transmittance of the crystallized portion for the light of the same wavelength region is improved. As a result, the reflectance of the medium for the light in the same region is improved to about 50%.

The recording / reproducing method for the optical recording medium of this embodiment is as follows.
This is different from the recording / reproducing method of an optical recording medium having a normal phase change recording layer.

That is, in this embodiment, as the initial state (erased state), the entire surface of the recording layer 5 of the optical recording medium is previously irradiated with high-power laser irradiation to be in an amorphous state, and information is recorded at a medium power. This is performed by irradiating the laser beam of No. 1 to form a recording mark portion that is partially crystallized on the recording layer 5. Therefore, in this embodiment, the reflectance for the reproduction light is higher in the recording mark portion than in the land portion.

On the other hand, conventionally, in the initial state, the entire surface of the recording layer 5 of the optical recording medium is previously irradiated with medium power laser light to be in a crystalline state, and information recording is irradiated with high power laser light. Then, a recording mark portion (recording portion) which is partially amorphized is formed in the recording layer 5. Therefore, conventionally, the reflectance for the reproduction light is higher in the land portion (non-recording portion) than in the recording mark portion (recording portion).

Hereinafter, as described above, the optical recording medium of the present example in which the initial state of the optical recording medium provided with the mask layer is an amorphous state, and the comparative example in which the initial state of the optical recording medium is a crystalline state After recording information on the optical recording medium at various frequencies at a relative speed of 5 m / s, reproduction is performed at the same relative speed, and the ratio of the leak signal output from the adjacent track to the output signal from the track being reproduced is measured. It was measured as crosstalk between adjacent tracks.

In this measurement, the optical recording medium of this embodiment has a wavelength of 680 nm output from a semiconductor laser and an optical output of 8 m.
The initial state is set by irradiating the laser beam of W, and the optical recording medium of the comparative example is set to the initial state by irradiating the laser beam from the semiconductor laser having a wavelength of 680 nm and an optical output of 5 mW. Both optical recording media have a wavelength of 680n output from a semiconductor laser.
The spot diameter on the medium surface is 1.2 due to the m band laser light.
Recording / reproduction was performed by setting to be about μm.
In this example, the optical power during recording and reproduction was 5 mw and 2 mW, respectively, and in the comparative example, during reproduction, the optical power was 2 mW as in the case of this example, and the power during recording made the crystalline state amorphous. Therefore, it is set to 8 mW, which is larger than that of this embodiment.

The mask layers of both optical recording media have a wavelength of 680 nm and 2
All tracks are irradiated with an mW semiconductor laser so as to be erased, and a halogen lamp is provided on the entire mask layer 3 of the optical recording medium through a filter that selectively transmits blue light in advance so that the recording layer 5 does not change phase during reproduction. Light output from 4mW /
The mask layer 3 was irradiated with cm ² of light so that the initial optical density OD of the mask layer 3 was 0.4 or more, preferably 0.4 to 1. In this embodiment, the mask layer 3 may be erased and the recording layer 5 may be initially erased at the same time by irradiation with laser light from a semiconductor laser with a wavelength of 680 nm of 8 mW or more.

In this experiment, the width of the recording mark portion is about 0.6 μm and the track pitch of the track composed of the recording mark portion is constant at 1.3 μm in both the present embodiment and the comparative example.

As a result of the measurement, the crosstalk of this embodiment is
While the crosstalk of the comparative example is -32 dB,
A significant improvement of -34 dB and 2 dB was achieved.

As shown in FIG. 3A, the reproducing light spot has the same light intensity distribution as the conventional one, but FIG.
As shown in FIG. 3, in the optical recording medium of the present embodiment, the reflectance corresponding to the recording mark portion is large and the reflectance corresponding to the land portion is small. Therefore, when the reproduction light spot is located on the recording mark portion, Corresponding mask layer 3 as shown in (b)
This is because the non-linear transmittance change becomes large in the portion, and the transmittance at the center of the track becomes significantly large.

On the other hand, also in the comparative example, the reproducing light spot has the same light intensity distribution as in the conventional case, as shown in FIG. However, as shown in FIG. 4C, in the optical recording medium of the comparative example, the reflectance corresponding to the recording mark portion is small and the reflectance corresponding to the land portion is large, contrary to the present embodiment, so that the reproduction light When the spot is located on the recording mark portion, the reflectance corresponding to the vicinity of the center of the spot is small, so the transmittance of the corresponding portion of the mask layer 3 is small, and the reflectance corresponding to the periphery is large, so that the corresponding portion. The transmittance of the mask layer is significantly increased. As a result, in the case of this comparative example, since the transmittance distribution of the mask layer 3 is widened as shown in FIG. 4B, even if the mask layer 3 is provided, the crosstalk is remarkably improved as in the present embodiment. Can't get

Next, the second embodiment of the present invention will be described in detail. The optical recording medium of the present example and the optical recording medium of Comparative Example 2 are the optical recording medium of the first example and Comparative example 1, respectively.
The optical recording medium is different from the above optical recording medium in that the recording layer 5 is a layer having a layer thickness of 1000 Å, which contains a phthalocyanine dye shown below, which is a saturable absorptive dye.

[0051]

Embedded image

R is, for example, a methyl group or an ethyl group.

In the saturable absorptive dye of this embodiment, it takes about 10 to 100 ns (= excited state lifetime) for the dye molecule to be excited by light irradiation in the red wavelength region to return to the ground state. , During this period, the dye molecule does not absorb light. That is, this dye causes a temporary decrease in absorption in the red wavelength region. Incidentally, this reaction also occurs in a so-called photon mode, which is a reaction between photons and molecules, and substantially does not occur by a reaction due to heat.

Moreover, since this material returns to a favorable coloring state after the above-mentioned period, unlike the first embodiment, in order to set the initial optical density, a step of irradiating light of another wavelength before irradiating the reproducing light is carried out. Is not necessary, and the setting is set according to the material concentration of the saturable light absorbing dye material and the layer thickness of the mask layer at the time of producing the medium. In this embodiment, the initial optical density OD of the mask layer 3 is 0.8.

Hereinafter, similar to the first embodiment, the optical recording medium of the present embodiment in which the initial state of the optical recording medium provided with the mask layer is an amorphous state, and the initial state of the optical recording medium is a crystalline state. After recording information on the optical recording medium of Comparative Example 2 at various frequencies at a relative speed of 5 m / s, crosstalk between adjacent tracks was measured.

In this measurement, the optical recording medium of this embodiment has a wavelength of 680 nm output from a semiconductor laser and an optical output of 9 m.
The optical recording medium of the comparative example was set to the initial state by irradiation with the laser beam of W, and the optical recording medium of the comparative example was set to the initial state by irradiation of the laser beam from the semiconductor laser having a wavelength of 680 nm and an optical output of 6 mW. The spot diameter on the medium surface is 1.2 μm due to the laser light of wavelength 680 nm band.
Recording / playback was performed with the settings set to approximately the same level. In this embodiment, the optical power during recording and reproduction is 6 m, respectively.
In the comparative example, the reproducing power was set to 4 mW as in the present embodiment, and the recording power was set to 9 mW, which is higher than that in the present embodiment, to make the crystalline state amorphous.

Also in this experiment, the width of the recording mark portion is about 0.6 μm and the track pitch of the track composed of the recording mark portion is 1.3 μm in both the present embodiment and the comparative example.
And is constant.

As a result of the measurement, the crosstalk of this embodiment is
While the crosstalk of the comparative example is −31 dB,
Significant improvements of -33 dB and 2 dB were achieved.

As described above, the optical recording medium of the present example can obtain a remarkable crosstalk improvement as compared with the optical recording medium of the comparative example 2 for the same reason as in the first example.

In the above-mentioned embodiment, the phase change type recording medium provided with the phase change type layer and the reflection layer which are set to the layer thickness capable of transmitting the reproducing light is described, but the reflection layer is not provided and the phase change type layer is not provided. The reflective layer itself may be used, and the present invention can be appropriately applied to other optical recording media.

Further, in the above description, the mask layer, the transparent recording layer, and the reflective layer are provided in this order on the transparent substrate.
A translucent recording layer, a mask layer, and a reflective layer may be provided in this order, and the mask layer and the translucent recording are provided on a reflective substrate (a substrate having a reflective layer, a substrate whose surface is a reflective surface). The layers, the translucent recording layer, and the mask layer may be provided in this order.

Further, the material contained in the mask layer is not limited to the material of the above-mentioned embodiment, but if it is a photon mode material, a remarkable effect is produced, and its initial optical density is preferably 0.4 or more, further preferably. Is 0.45 or more.

Although the reduction of crosstalk has been described above, it is needless to say that it is also effective for improving the linear recording density.

[0064]

According to the structure of the present invention, the recording layer is provided on the reflecting surface (for example, the reflecting layer or the reflecting substrate) and can transmit the reproducing light, and the reproducing light is provided on the recording layer. A mask layer whose transmittance to the reproduction light is improved by a reaction, and the reproduction light is recorded from the mask layer side onto an optical recording medium in which the recording portion of the recording layer has a higher transmittance to the reproduction light than the non-recording portion. When irradiated toward the layer, the reproduction light improves the transmittance of the mask layer and a part of the reproduction light reaches the recording layer. After that, the reproduction light reaching the recording layer is further transmitted through the recording portion having a higher transmittance than the non-recording portion, and then is reflected by the reflecting surface, and the reflected light corresponding to the recording portion is remarkably reflected on the mask layer. Incident. As a result, the mask layer significantly improves the transmittance of the portion corresponding to the recording portion, so that the difference between the recording portion and the non-recording portion becomes sufficiently clear, and the track density and linear recording density of the optical recording medium are improved. It can be fully achieved.

A recording layer provided on a reflective surface (eg, a reflective layer or a reflective substrate) and capable of transmitting reproducing light, and a reaction due to absorption of the reproducing light provided between the recording layer and the reflective surface. A mask layer for improving the transmittance for reproducing light by means of a mask layer for reproducing light from the recording layer side to an optical recording medium in which the recording portion of the recording layer has a higher transmittance for reproducing light than the non-recording portion. When irradiated toward, the reproduction light is more transmitted through the recorded portion having a higher transmittance than the non-recorded portion, and after being improved in the transmittance of the mask layer corresponding to the recorded portion, it is reflected by the reflecting surface. The reflected light corresponding to the recording portion re-enters the mask layer remarkably. As a result, the mask layer remarkably improves the transmittance of the portion corresponding to the recording portion, so that the difference between the recording portion and the non-recording portion becomes sufficiently clear,
The track density and linear recording density of the optical recording medium can be sufficiently improved.

Further, in another structure of the present invention, a mask layer provided on the recording layer for improving the transmittance for the reproduction light by the reaction due to the absorption of the reproduction light is provided, and the recording portion of the recording layer is compared with the non-recording portion. When an optical recording medium having a high reflectance for reproducing light is irradiated with the reproducing light from the mask layer side to the recording layer, the reproducing light improves the transmittance of the mask layer and a part of the reproducing light reaches the recording layer. After that, the reproduction light reaching the recording layer is more reflected by the recording portion having a higher reflectance than the non-recording portion, and the reflected light corresponding to the recording portion is re-incident on the mask layer. As a result, the transmittance of the mask layer corresponding to the recording portion is remarkably improved, so that the difference between the recording portion and the non-recording portion becomes sufficiently clear, and the track density of the optical recording medium,
The linear recording density can be sufficiently improved.

In particular, when the mask layer contains a photon mode material whose transmittance to the reproduction light is increased by the photon mode reaction caused by absorption of the reproduction light, the reflection surface is formed after the reproduction light is incident on the mask layer. Alternatively, when the light is reflected by the recording layer and is incident on the mask layer again, the transmittance increases remarkably in a non-linear manner,
It is possible to significantly improve the track density and the linear recording density.

Moreover, the photon mode material, like the reverse photochromic material, has a lower absorption due to the photoreaction upon irradiation with the reproducing light, and also has a thermal reaction (heat mode reaction) due to the temperature rise at the spot center. Does not occur, the improvement of the transmittance at the center of the spot does not become insufficient, and the super-resolution effect can be sufficiently obtained. Further, unlike the thermochromic material, the photon-mode material is not a reaction that occurs with an increase in temperature, so that it is not necessary to apply sufficient heat to the mask layer to cause a reaction. As a result, even when the recording layer has a heat mode property such as a phase change layer, there is no fear that the information in the recording layer is destroyed by the heat.

Further, when the optical density of the mask layer is 0.4 or more, the nonlinear increase of the transmittance becomes remarkable,
The track density and linear recording density can be further improved.

[Brief description of drawings]

FIG. 1 is a schematic cross-sectional view of an optical recording medium according to a first embodiment of the invention.

FIG. 2 is a schematic view showing a recording mark portion and a land portion of the optical recording medium.

FIG. 3 is a diagram for explaining the first embodiment.

FIG. 4 is a diagram for explaining a comparative example 1.

FIG. 5 is a schematic cross-sectional view of an optical recording medium used to investigate the relationship between reflectance and (transmittance T) ^{2 of a} mask layer made of a photon-mode photochromic material and irradiation time of reproduction light.

FIG. 6 is a diagram showing a relationship between (transmittance T) ² of a mask layer of the above-mentioned optical recording medium provided with a mask layer made of a photon mode photochromic material and irradiation time of reproduction light.

FIG. 7 is a diagram showing the relationship between (transmittance T) ² of the mask layer of the optical recording medium having a mask layer made of a photon mode saturable absorptive dye material and the irradiation time of the reproduction light.

[Explanation of symbols]

 1 translucent substrate 3 mask layer 5 recording layer 7 reflective layer

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Kazuhiko Kuroki 2-5-5 Keihan Hondori, Moriguchi City, Osaka Sanyo Electric Co., Ltd.

Claims (9)

[Claims] 1. A reproducing layer provided on a reflecting surface and capable of transmitting reproducing light, and a reproducing layer absorbing reaction on the recording layer or between the recording layer and the reflecting surface. And a mask layer having an improved transmissivity with respect to the recording layer, wherein the recording layer has a higher transmissivity with respect to reproducing light than a non-recording portion. 2. The optical recording medium according to claim 1, wherein the recording layer is formed with a recording portion having a higher transmittance with respect to a reproducing light than a non-recording portion when the recording light is irradiated. 3. The optical recording medium according to claim 1, wherein the recording layer contains a phase change recording material that changes from an amorphous state to a crystalline state by irradiation with recording light. 4. A recording layer, and a mask layer which is provided on the recording layer and whose transmittance for reproducing light is improved by a reaction due to absorption of reproducing light. An optical recording medium having a high reflectance for reproducing light. 5. The optical recording medium according to claim 4, wherein the recording layer is formed with a recording portion having a higher reflectance with respect to the reproducing light than the non-recording portion when the recording light is irradiated. 6. The optical recording medium according to claim 4, wherein the recording layer contains a phase-change recording material that changes from a crystalline state to an amorphous state by irradiation with recording light. 7. The mask layer contains a photon-mode material whose transmittance with respect to reproduction light is increased by a photon-mode reaction caused by absorption of reproduction light. 5. The optical recording medium according to 5 or 6. 8. The optical recording medium according to claim 7, wherein the portion of the mask layer irradiated with the reproduction light has an optical density of 0.4 or more before the irradiation. 9. An optical recording medium provided with a recording layer and a mask layer whose transmittance for reproducing light is improved by a reaction due to absorption of reproducing light is irradiated with reproducing light, and the optical recording medium from the recording portion of the recording layer is irradiated. A method of reproducing information from an optical recording medium, characterized in that the reproduction light has a higher light intensity than the reproduction light from the non-recording portion of the recording layer to reproduce information on the recording layer.