JPH08147757A - Information recording medium and its reproducing method - Google Patents

Abstract

PURPOSE: To obtain an information recording medium which is lessened in the influence of a side lobe component at the time of reproducing on a main lobe component and is free from a change in light quantity between the center and peripheral part of reflected light. CONSTITUTION: This information recording medium 10 is constituted by providing the medium with a light adjusting film 11 between a transparent substrate 2 and a recording medium 12. This light adjusting film 11 has a nonlinear refractive index characteristic lower change the refractive index to a low-illuminance laser beam than change in the refractive index to a high-illuminance laser beam. Since the change in the refractive index is hardly generated in the peripheral part irradiated with the low-illuminance laser beam, the phase differences between the recorded parts and the un-recorded parts are eliminated by adjusting the thickness of the light adjusting film 11 and are no longer detected as reproduced signals. Only the light adjusting film 11 irradiated with the high- illuminance laser beam in the central part generates the large change in the refractive index, thereby generating the reflectivity and phase differences between the recorded parts and the un-recorded parts and enabling the detection as the reproduced signals.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an information recording medium and a reproducing method thereof, and more particularly to a rewritable, write-once or read-only information recording medium for reproducing information using a laser beam and a reproducing method thereof.

[0002]

2. Description of the Related Art FIG. 9 is a diagram for explaining an example of a conventional information recording medium and a reproducing method thereof. As shown in FIG. 1B, this conventional information recording medium 1 has a structure in which a resist 3, a reflective film 4 and an ultraviolet curable resin 5 are sequentially laminated on a disk-shaped transparent substrate 2, 3 is a read-only type optical disc such as a compact disc-read only memory (CD-ROM) in which a row of pits intermittently formed in accordance with the recorded information, that is, a concave portion and a convex portion are formed repeatedly.

At the time of reproducing already recorded information on the conventional information recording medium 1, as shown in FIG. 9B, a laser beam 8 from a laser light source (not shown) is emitted by an objective lens 7 in an optical head 6. The resist 3 is focused through the transparent substrate 2. As a result, a light spot having a diameter D and a light intensity having a Gaussian distribution is formed on the surface perpendicular to the optical axis on the reflective film 4 as shown in FIG. 9A. Since the light intensity of the reflected light of this light spot changes between the concave portion and the convex portion of the resist 3, by detecting the change of the light intensity of this reflected light,
The recorded information can be reproduced.

In the information recording medium 1 as described above, higher density has been demanded in recent years, and as one of the techniques therefor, a technique for reducing the diameter (spot diameter) D of the light spot has been conventionally known. There is. For example, if the light from the light source is collimated and then a shield plate or a V-shaped prism is placed in this optical path, a diffraction pattern appears on the optical disc, and the spot diameter appearing in the center is a spot determined by the wavelength of the light source. 20% smaller than the diameter, recording density 1.5
There is double the super-resolution head technology.

As an information recording medium using this super-resolution head technology, optical discs for magneto-optical discs and MUSE type laser discs are described in the following documents 1 to 3. Here Document 1: "High Density Optical Recordi
ng by Superresolution ", International Symposium on
Optical Memory 1989 Technical Digest, 27D-17, pp.99-
100, Sept. 1989. Reference 2: “Reproduction C / N Characteristics of High Density Magneto-Optical Disk with Super-Resolution Optical Head”, Proceedings of the 39th Joint Lecture in Applied Physics, No. 3 ”, 31p-L-6,
p.1002, March 1992. Reference 3: "High Density Video Disc Us
ing Superresolution and Green Laser ", International
Symposium on Optical Memory and Optical Data Stor
age '93, Tul.4, July 1993.

In addition, there is an optical medium in which already recorded information is reproduced by utilizing a phase difference as a conventional information recording medium, and a Pb-Te-Se film (M. Terao,
et al .: J. Appl. Phys., 62 (3), 1029 (1987)., Te-T.
i-Ag-Se film, Te-C film (Katsutaro Ichihara, Hideki Okawa: Electronic Ceramics, November issue, p.5 (19)
87) .M / Mashita, N.Yasuda: Proc.SPIE, 329, p190 (198
2).), CS2-Te film (H. Yamazaki, et al .: Rev. Elect
r.Commun.Lab., 32, 260 (1984)) is known. Also,
As the organic recording film, the technology disclosed in Japanese Patent Laid-Open No. 62-119755 has already been commercialized.

Further, as a conventional information recording medium for increasing the recording density by reducing the light spot diameter,
A transparent substrate and a recording film or a reflective film having a light control film having a light transmittance characteristic that the light transmittance is low for a light beam of low illuminance and high for a light beam of high illuminance. An information recording medium provided between the two is also conventionally known (JP-A-6-44609).

[0008]

However, in the conventional information recording medium for obtaining a reproduction signal by utilizing the above-mentioned phase difference, the main lobe component of the reproduction beam center of the reproduction beam of the super-resolution optical system and the diffraction The side lobe component of the pattern circumference is subjected to phase modulation by the pit (recording part) on the medium surface, and the main lobe component and side lobe component interfere with each other, and the beam profile at the re-imaging point changes. Then, the reproduced signal after passing through the pinhole or the slit undergoes an edge shift having a phase pattern dependence, so that the reproduced signal is distorted and the jitter value increases.

Further, in the conventional information recording medium provided with the above-mentioned light control film, the light control film changes the light transmittance according to the illuminance of the light beam, so that the light amount of the reflected light is reduced and the reproduction signal is reproduced. Is deteriorated and the track servo is hard to be applied.

The present invention has been made in view of the above points,
An object of the present invention is to provide an information recording medium which reduces the influence of the side lobe component on the main lobe component at the time of reproduction and has no change in the light amount between the center of the reflected light and the peripheral portion and a reproducing method thereof.

[0011]

In order to achieve the above object, the information recording medium of the present invention records information by a laser beam by utilizing the shape change or the characteristic change of the recording film above the transparent substrate, In a rewritable or write-once type optical information recording medium for reproduction, or a reproduction-only type optical information recording medium for reproducing information recorded on a recording film due to a change in shape, a transparent substrate and a recording film are used. In the meantime, the change in the refractive index with respect to the laser beam having a light intensity higher than the predetermined light intensity is large, and the change in the refractive index with respect to the laser beam having the light intensity less than or equal to the predetermined light intensity is large. Is provided with a light adjusting film.

The light control film of the present invention has the following formula:

[0013]

Embedded image The use of poly- (2,5-chenylene vinylene) represented by the following has a wide wavelength range to be used and has high-speed response,
Moreover, since the operation input light intensity is low, it is desirable for practical use.

Further, in the reproducing method of the information recording medium of the present invention, the rewritable type, the additional recording in which the information recorded by utilizing the shape change or the characteristic change of the recording film on the information surface above the transparent substrate is reproduced by the laser beam. Type optical information recording medium or a read-only type optical information recording medium for reproducing information recorded on a recording film by a shape change by a laser beam, the method is provided between a transparent substrate and a recording film. The above-mentioned light adjusting film adjusts the reflectance, the absorptance, the transmittance, and the phase difference between the recorded portion and the unrecorded portion, which are caused by the shape change or the characteristic change of the recording film during reproduction, and The above-mentioned object is achieved by reproducing the image data so as to be positioned within the depth of focus of the surface.

[0015]

In the present invention, the spot diameter of the recording laser beam is substantially reduced by providing the light adjusting film having the nonlinear refractive index effect, which is one of the nonlinear optical effects, between the transparent substrate and the recording film. Further, it is possible to significantly reduce the influence of the side lobe component on the main lobe component at the time of reproduction by the super-resolution optical system.

Here, the above-mentioned nonlinear optical effect means the electric polarization of a substance when light is incident on the substance, which is expressed by the following general formula χ ⁽¹⁾ E + χ ⁽²⁾ E ² + χ ⁽³⁾ E ³ + When expressed by ..., it means the effect expressed by the second and subsequent terms. Here, χ ⁽ⁱ⁾ is the i-th order electric susceptibility, and E is the electric field intensity of light. In particular, second harmonic generation (SHG) according to the second term
The third harmonic generation (THG) by the third term and the third term is well known as the conversion effect, but the third term also changes the optical constant according to the light intensity, such as the nonlinear refractive index effect and the nonlinear absorption effect. Is important as giving. For example, the nonlinear refractive index effect is such that the refractive index n of a substance changes in proportion to the incident light intensity, and is described by n = n ₀ + n ₂ I. Here, n ₀ is a constant and n ₂ is a non-refractive index coefficient.

Next, the function of the light adjusting film will be described.
A laser beam is generally used as the recording / reproducing light beam applied to the information recording medium. As described above, the light intensity distribution of the laser beam is a Gaussian distribution with respect to the plane perpendicular to the optical axis, and the central portion is strong and becomes weaker toward the peripheral portion. When the laser beam having such a light intensity distribution is irradiated from the transparent substrate side to the information recording medium provided with the light adjusting film having the nonlinear refractive index effect within the depth of focus of the information surface of the information recording medium, the predetermined light intensity is obtained. Since the peripheral part irradiated with the following low illuminance laser beam hardly changes the refractive index, the phase difference between the recorded part and the unrecorded part is eliminated by adjusting the film thickness of the light adjustment film, and it is no longer detected as a reproduction signal. , A refractive index change occurs only in the light adjustment film irradiated with a laser beam having a high illuminance higher than the predetermined light intensity in the central portion, and a reflectance and a phase difference occur between a recorded portion and an unrecorded portion, and a reproduction signal Can be detected as. Such an action is applicable to all information recording media that are reproduced by using the reflectance difference or the phase difference.

Next, the operation when the information recording medium having the light adjusting film is reproduced by the super-resolution optical system will be described.
If the central part of the objective lens in the optical head is shielded or the phase of the light passing through the central part of the objective lens is made earlier than the phase of the light passing through the peripheral part of the objective lens, the recording film or the reflective film will be The half-width diameter of the focused laser beam can be reduced.

By irradiating the information recording medium of the present invention having the above-mentioned light adjusting film with the laser beam thus reduced in diameter, the spot diameter irradiated on the recording film or the reflective film can be further reduced. Can be achieved. If the center of the objective lens is shielded or the phase of the light passing through the center of the objective lens is made earlier than the phase of the light passing through the peripheral part of the objective lens, side lobes will appear around the reduced main lobe. Although generated, the light intensity of the side lobes is much smaller than the light intensity of the main lobes, so that the refractive index change does not substantially occur in the light adjustment film.

[0020]

EXAMPLES Next, examples of the present invention will be described.
FIG. 1 shows an explanatory diagram of a first embodiment of an information recording medium and a reproducing method thereof according to the present invention. In the figure, the same components as those in FIG. 9 are designated by the same reference numerals. As shown in the cross-sectional view of FIG. 1B, in the information recording medium 10 of this embodiment, a light adjusting film 11, a recording film 12, a reflecting film 4 and an ultraviolet curable resin 5 are sequentially laminated on a transparent substrate 2. And the resist 3
Is a read-only type optical disc in which a row of pits intermittently formed according to the recording information, that is, a concave portion and a convex portion are formed on the recording film 12 corresponding to the above.

The transparent substrate 2 is formed in a desired shape such as a disk shape or a card shape by using a transparent ceramic material such as glass or a transparent resin material such as polycarbonate, polymethylmethacrylate, polynetylpentene or epoxy. However, here, as an example, it is assumed that it is disk-shaped.

As shown in FIG. 2, the light adjusting film 11 has a change in the refractive index with respect to a laser beam with a low illuminance equal to or lower than the light intensity Ib from a change in the refractive index with respect to a laser beam with a high illuminance greater than the light intensity Ib. Also has a low nonlinear refractive index characteristic. Light adjusting film 11 having such a nonlinear refractive index characteristic
Is a poly-represented by the formula shown in Chemical Formula 1 above.
(2,5-Chenylene vinylene) (abbreviated as PTV) and two types of non-linear optical liquids whose working principle is a molecular rotation non-linear effect (refractive index shows light intensity dependence due to rotational arrangement of molecules according to optical electric field). There are glass cells filled with carbon sulfide (CS ₂ ), polydiacetylene bis- (paratoluene sulfonate) (abbreviated as PTS) whose nonlinear refractive index effect is purely derived from electronic polarization, and the like.

In particular, PTV is already known as a conductive polymer material having an amorphous structure, has a wide wavelength range to be used, has a high-speed response, and has a small operating input light intensity, and is a high-performance nonlinear material that can be put to practical use. It is an optical material and is suitable for the light adjusting film 11.

Next, a method of forming the light adjusting film 11 by PTV will be described. First, 2,5-chenylene bis (dimethylsulfonium) dichloride was treated with an alkaline aqueous solution at 0 ° C., then 0.3 mol of tetramethyl ammonium hydroxide was added in a methanol-water mixed solution, and the mixture was heated at −30 ° C. Polymerization was performed by stirring with. After collecting the obtained yellow precipitate and dissolving it in dichloromethane,
This was formed into a film on a quartz glass substrate by a spin coating method and air dried. Finally this is 200-250
The PTV light adjusting film 11 having excellent optical quality can be obtained by heating at a temperature of 5 ° C. for 5 hours under a vacuum of 10 ⁻² Torr.

Next, the recording film 12 shown in FIG. 1 (B) is formed as an information recording layer of a rewritable, write-once, or read-only type information recording medium, and is any known one. A material made of a material can be used. on the other hand,
The reflection film 4 is laminated on the recording film surface of a rewritable, write-once, and read-only information recording medium, and may be made of any known material.

To reproduce already recorded information on the information recording medium 10, a laser beam 8 from a laser light source (not shown) is made transparent by an objective lens 7 in the optical head 6 as shown in FIG. 1 (B). The recording film 12 or the reflective film 4 is focused via the substrate 2. The optical head 6 includes a semiconductor laser as a laser light source and has a conventionally known configuration including an actuator for autofocusing, and is applied as it is.

Next, the reproducing operation of the recorded information on the information recording medium 10 will be described. The laser beam 8 narrowed down to the diffraction limit by the objective lens 7 passes through the transparent substrate 2 and is focused on the recording film 12 or the reflective film 4 via the light adjusting film 11. As a result, as shown in FIG. 1A, a light spot having a light intensity showing a Gaussian distribution is formed on the surface perpendicular to the optical axis on the reflective film 4. Since the light intensity of the reflected light of the light spot changes between the concave portion and the convex portion of the recording film 12, by detecting the change of the light intensity of the reflected light,
The recorded information can be reproduced.

As described above, since the light adjusting film 11 has a small change in the refractive index with respect to the low illuminance laser beam having the light intensity of Ib or less, the light intensity of the peripheral portion of the laser beam 8 is Ib or less. The portion does not substantially affect the refractive index of the light adjustment film 11. On the other hand, the portion of the central portion of the laser beam 8 where the light intensity is higher than Ib reaches the recording film 12 or the reflecting film 4 after increasing the refractive index of the light adjusting film 11.

Due to the change in the refractive index of the light adjusting film 11, the optical characteristics (reflectance, absorptance, transmittance, phase) of the information recording medium 10 change with the light intensity Ib as a boundary. Therefore, the optical characteristics (reflectance, absorptivity, etc.) of the recorded portion (for example, the concave portion) and the unrecorded portion (for example, the convex portion) are set in advance in the optical design condition of the information recording medium 10 in a state where the refractive index of the light adjustment film 11 does not change. The optical characteristics (reflectance, absorptance, transmittance, phase) may be different under the condition that the transmittance and the phase are set to be almost equal and the refractive index of the light adjusting film 11 is changed. By setting to 1, the reproduction signal can be detected by the light that has passed through the light adjustment film 11 in the range having the light intensity Ib higher.

Therefore, the light spot portion having a light intensity higher than Ib at which the reproduction signal can be detected has a spot diameter D2 as shown in FIG. 1A, and the actual light spot diameter D1. It is possible to detect the reproduced signal in the range of smaller diameter than
An effect equivalent to that of reducing the spot diameter can be obtained. As a result, it is possible to reproduce already recorded information even on an information recording medium that is recorded at a higher density than before.

Next, a second embodiment of the present invention will be described. FIG. 3 shows an explanatory diagram of a first embodiment of an information recording medium and a reproducing method thereof according to the present invention. In the figure, the same components as those in FIG. 1 are designated by the same reference numerals, and their description will be omitted. FIG.
As shown in the sectional view of (B), the information recording medium 10 of the present embodiment is a read-only type optical disc having the same structure as the information recording medium 10 shown in FIG. 1 (B).

The reproducing method of this embodiment is different from that of the first embodiment. That is, the present embodiment is characterized in that the optical head 13 has a configuration in which the opaque light shielding plate 14 is arranged at the center of the objective lens 7 on the light incident side. In this way, when the light shield plate 14 is attached to the center of the objective lens 7 on the light incident side to shield the laser beam 8, the light intensity distribution of the laser beam 8 focused on the recording film 12 or the reflective film 4 becomes As shown by the solid line in FIG. 3A, the main lobe 8a having a smaller spot diameter D3 than the light intensity distribution shown by the broken line in FIG. Side lobes 8b and 8c, which are formed on the optical axis passing through the center of the lens 7 and have a light intensity smaller than that of the main lobe 8a, are generated in the peripheral portion.

Therefore, a light adjusting film 11 having a threshold Ib which is lower than the peak value of the main lobe 8a and higher than the peak values of the side lobes 8b and 8c is provided between the transparent substrate 2 and the recording film 12. By using the information recording medium 10 provided in the recording film 12, the recording film 12 can be formed by the non-linear refractive index effect of the light adjusting film 11 and the optical design effect of the information recording medium.
Alternatively, the diameter of the spot irradiated on the reflection film 4 can be further reduced, and the density can be further increased as compared with the first embodiment.

Next, a second embodiment of the information recording medium of the present invention will be described. FIG. 4 is a sectional view showing a second embodiment of the information recording medium according to the present invention in comparison with an example of a conventional information recording medium. FIG. 1A is a sectional view of the second embodiment of the information recording medium of the present invention, in which the information recording medium 20 is a transparent substrate 21.
It has a structure in which a light adjustment film 22, a base protection film 23, a recording film 24, a light interference protection film 25, a reflection film 26, and an ultraviolet curable resin 27 are sequentially laminated on top.

The present embodiment is characterized in that the light adjusting film 22 is provided between the transparent substrate 21 and the base protective film 23 as compared with the conventional information recording medium shown in FIG. 4B.
The present embodiment is an example of a rewritable phase change type information recording medium that records information on the recording film 23 as a change in phase state. For example, the transparent substrate 21 is made of polycarbonate and has a thickness of 1.2 mm.
The thickness of the light adjusting film 22 is 50 nm by PTV, and the base protection film 23 is 140 n by ZnS—SiO ₂ .
The recording film 24 is made of Ge ₂ Sb ₂ Te ₅ with a thickness of m.
A film thickness of 0 nm, light interference protective layer 25 is ZnS-SiO ₂
And the reflective film 26 is made of Al.
The film thickness is 0 nm, and the ultraviolet curable resin 27 is formed with a film thickness of 50 μm.

The light adjusting film 22 has the light intensity-refractive index characteristic shown in FIG. 2 similarly to the light adjusting film 11 shown in FIGS. The conventional ZnS-S shown in FIG.
The film thickness of the iO ₂ light interference protection film 25 is 20 nm.

Next, examples of changes in the reflectance and the phase difference between the recorded portion and the unrecorded portion with respect to the change in the film thickness of the light adjustment film 22 of the information recording medium 20 shown in FIG. 4A will be described. . First, FIG. 5 shows a PTV in a state in which the information recording medium 20 has a low refractive index change due to irradiation with a laser beam of low illuminance
The optical calculation result at the wavelength of the laser beam of 680 nm is shown about the change of the reflectance and phase difference of the recording part (amorphous) and the unrecorded part (crystal) of the recording film 24 with respect to the film thickness change of the light adjusting film 22.

In FIG. 5, the broken line I indicates the reflectance of the unrecorded portion, the solid line II indicates the reflectance of the recorded portion, and + indicates the phase difference between the recorded portion and the unrecorded portion. As can be seen from the figure, in the present embodiment, there is no difference in the reflectance of the recorded portion and the unrecorded portion with respect to the laser beam of low illuminance, that is, 45%, regardless of the film thickness of the light adjustment film 22, and there is no phase difference. Can be as low as about 10 °.

FIG. 6 shows a PT in which the information recording medium 20 has a high refractive index change due to irradiation with a laser beam of high illuminance.
The optical calculation result at the wavelength of the laser beam of 680 nm is shown about the change of the reflectance and the phase difference of the recorded part (amorphous) and the unrecorded part (crystal) of the recording film 24 with respect to the change of the film thickness of the V light adjusting film 22.

In FIG. 6, the broken line III indicates the reflectance of the unrecorded portion, the solid line IV indicates the reflectance of the recorded portion, and + indicates the phase difference between the recorded portion and the unrecorded portion. As can be seen from the figure, in this embodiment, the thickness of the light adjusting film 22 is 3 with respect to the laser beam of high illuminance.
When 0 [nm] ≦ d (PTV) ≦ 60 [nm], the reflectance difference between the recorded portion and the unrecorded portion is about 20%, the phase difference can be reduced to about 10 °, and it can be detected as a reproduced signal. is there.

FIG. 7 shows the information recording medium 20 with ZnS.
When the film thickness of the -SiO ₂ light interference protection film 25 is set to 150 nm, the recording portion of the recording film 24 with respect to the film thickness change of the PTV light adjusting film 22 in a state where the refractive index change is low due to the irradiation of the laser beam of low illuminance ( Amorphous) and unrecorded area (crystal)
The optical calculation results of the change in the reflectance and the phase difference at the wavelength of the laser beam of 680 nm are shown.

In FIG. 7, the broken line V indicates the reflectance of the unrecorded portion, the solid line VI indicates the reflectance of the recorded portion, and + indicates the phase difference between the recorded portion and the unrecorded portion. As can be seen from the figure, in the present embodiment, the reflectance of the recorded portion and the unrecorded portion is about 60% with respect to the laser beam of low illuminance, regardless of the film thickness of the light adjustment film 22, and there is no difference. The phase difference can be as low as about 6 °.

FIG. 8 shows the information recording medium 20 with ZnS
When the film thickness of the —SiO ₂ light interference protection film 25 is set to 150 nm, the recording portion of the recording film 24 (for the film thickness change of the PTV light adjusting film 22 in the state where the refractive index change is high due to the irradiation of the laser beam with high illuminance) ( Amorphous) and unrecorded area (crystal)
The optical calculation results of the change in the reflectance and the phase difference at the wavelength of the laser beam of 680 nm are shown.

In FIG. 8, the broken line VII indicates the reflectance of the unrecorded portion, the solid line VIII indicates the reflectance of the recorded portion, and + indicates the phase difference between the recorded portion and the unrecorded portion. As can be seen from the figure, in the present embodiment, with respect to the laser beam of high illuminance, the film thickness of the light adjustment film 22 is set to 70 [nm] ≦ d (PTV) ≦ 90 [nm],
The reflectance difference between the recorded portion and the unrecorded portion is about 20%, the phase difference can be reduced to about 6 °, and it can be detected as a reproduced signal.

The present invention is not limited to the above embodiments, but it is possible to record information only once, and to reproduce information, which is an example of a write-once type information recording medium or rewritable type information recording medium. It can also be applied to a magneto-optical recording medium for recording as a change in the direction of. Further, the light adjustment films 11 and 22 may have a structure of two or more layers.

[0046]

As described above, according to the present invention,
The light adjustment film causes almost no phase difference between the recorded portion and the unrecorded portion in the peripheral portion irradiated with the low illuminance laser beam having the predetermined light intensity or less, so that it is detected as a reproduction signal. However, the central part irradiated with the laser beam of high illuminance higher than the predetermined light intensity changes the refractive index, and the reflectivity and the phase difference occur between the recorded part and the unrecorded part. Therefore, by irradiating the laser beam, the spot diameter on the recording film can be substantially reduced, and the recording density can be increased.

Further, according to the present invention, the central portion of the objective lens in the optical head is shielded or the phase of the light transmitted through the central portion of the objective lens is determined from the phase of the light transmitted through the peripheral portion of the objective lens. As soon as possible, by reducing the full width at half maximum of the laser beam focused on the recording film or the reflective film,
It is possible to further reduce the diameter of the spot irradiated on the recording film or the reflective film.

Further, according to the present invention, when the center of the objective lens is shielded or the phase of the light passing through the central part of the objective lens is made earlier than the phase of the light passing through the peripheral part of the objective lens, a small diameter is obtained. The side lobe generated around the converted main lobe can significantly reduce the influence on the main lobe because the phase difference between the recorded portion and the unrecorded portion is reduced by the light adjustment film, and thus the recording density can be reduced. Higher density can be realized.

Further, according to the present invention, the light adjusting film has a structure in which the refractive index is changed according to the illuminance, and a light control film such as a conventional information recording medium is used for adjusting the light according to the illuminance of the light beam. Since the transmittance does not change, the amount of reflected light does not decrease, which causes deterioration of the reproduction signal,
It is possible to prevent the problem that the track servo is hard to be applied.

[Brief description of drawings]

FIG. 1 is an explanatory diagram of a first embodiment of an information recording medium and a reproducing method of the present invention.

FIG. 2 is a characteristic diagram of an example of a light adjustment film of a main part of the present invention.

FIG. 3 is an explanatory diagram of a first embodiment of an information recording medium of the present invention and a second embodiment of a reproducing method.

FIG. 4 is a sectional view showing a second embodiment of the information recording medium of the present invention and a conventional information recording medium in comparison.

FIG. 5 is a characteristic diagram showing an example of the relationship between the film thickness of the PTV light adjusting film with respect to a low illuminance laser beam, and the reflectance and phase difference.

FIG. 6 is a characteristic diagram showing an example of the relationship between the film thickness of the PTV light adjusting film with respect to a high illuminance laser beam, and the reflectance and phase difference.

FIG. 7 is a characteristic diagram showing another example of the relationship between the film thickness of the PTV light adjusting film with respect to a laser beam of low illuminance and the reflectance and the phase difference.

FIG. 8 is a characteristic diagram showing another example of the relationship between the film thickness of the PTV light adjusting film with respect to a high-illuminance laser beam, and the reflectance and phase difference.

FIG. 9 is an explanatory diagram of an example of a conventional information recording medium and a reproducing method.

[Explanation of symbols]

 2, 21 Transparent substrate 4, 26 Reflective film 5, 27 UV curable resin 6, 13 Optical head 7 Objective lens 8 Laser beam 8a Main lobe 8b, 8c Side lobe 10 Information recording medium of the first embodiment 11, 22 Light adjusting film 12, 23 recording film 20 information recording medium of the second embodiment 23 underlayer protective film 25 optical interference protective film

Claims (4)

[Claims] 1. A rewritable or write-once type optical information recording medium for recording information by a laser beam by utilizing a shape change or a characteristic change of a recording film above a transparent substrate, or recording by a shape change. In a read-only optical information recording medium for reproducing information recorded on a film by a laser beam, a refractive index for the laser beam having a light intensity higher than a predetermined light intensity is provided between the transparent substrate and the recording film. Change in the refractive index with respect to the laser beam having a light intensity less than or equal to the predetermined light intensity is large, and an information recording medium having at least one or more non-linear refractive index characteristics is provided. . 2. The light control film has the following formula: The information recording medium according to claim 1, wherein poly- (2,5-chenylene vinylene) represented by the following is used. 3. A rewritable or write-once type optical information recording medium for reproducing information recorded by a laser beam by utilizing a shape change or a characteristic change of a recording film on an information surface above a transparent substrate, or a shape change. In a reproducing method of a reproduction-only type optical information recording medium for reproducing information recorded on a recording film by a laser beam, a light having a intensity higher than a predetermined light intensity provided between the transparent substrate and the recording film. The shape of the recording film at the time of reproduction by at least one or more light adjusting films, in which the change in the refractive index with respect to the laser beam with respect to the intensity is largely changed with respect to the laser beam with the light intensity equal to or lower than the predetermined light intensity. The reflectance, the absorptance, the transmittance, and the phase difference between the recorded portion and the unrecorded portion, which are caused by the change or the characteristic change, are adjusted, and the light adjustment film is positioned within the depth of focus of the information surface. The method of reproducing the information recording medium, characterized in that to play manner. 4. The objective lens center in an optical head for making the laser beam incident from a transparent substrate to focus on the recording film is shielded, or the phase of light transmitted through the central portion of the objective lens is set to the objective. 4. The reproducing method for an information recording medium according to claim 3, wherein the reproducing is performed earlier than the phase of the light transmitted through the peripheral portion of the lens.