JP2001266404A - Optical information medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical information medium capable of higher density recording. SOLUTION: In an optical information medium 10 on which optically readable information is recorded, a liquid crystal layer 2 in which the alignment of a liquid crystal phase having double refraction is fixed is disposed and an information carrying part in which the retardation of the liquid crystal layer 2 is changed corresponding to the depth of pits 4a-4c is provided, respectively on the surface of a substrate 1 having the plural pits 4a-4c carrying information and having depth different from one another.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an optical information medium having a high recording density, such as a digital video disk (DVD).

[0002]

2. Description of the Related Art Optical information media such as DVDs can generally record at higher densities than magnetic recording media. ing. As a method of increasing the recording density of an optical information medium, a method of narrowing a track pitch or a pit interval and increasing a linear density is known. However, if the track pitch or pit interval is narrow with respect to the beam spot of the reproduction light, signal reproduction becomes impossible.
The resolution of the reproducing apparatus is limited by the beam spot of the reproducing light, and the reproducing limit is generally a spatial frequency of 2 NA / λ. Here, NA is the numerical aperture of the optical system of the reproducing apparatus, and λ is the wavelength of the reproducing light. Therefore, in the method of narrowing the track pitch and the pit interval, an increase in the numerical aperture of the optical system of the reproducing apparatus and a reduction in the wavelength of the reproducing light have been studied. There is a problem, and shortening the wavelength of the reproduction light has many technical problems in obtaining a stable light source. On the other hand, as a method of increasing the recording density without being restricted by the numerical aperture and the wavelength of the reproduction light, a super-resolution recording medium using a material whose optical characteristics change non-linearly with respect to the light intensity has been proposed. This recording medium requires a high-powered reproduction light in order to cause a non-linear effect at the time of reproduction.
The design of the device is not easy.

[0003]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a conventional reproducing apparatus without increasing the numerical aperture of an optical system or reducing the wavelength of reproduced light, and without using the super-resolution phenomenon. It is an object of the present invention to provide an optical information medium having a high recording density capable of performing reproduction even with low-power reproduction light by using a reproduction optical system and a reproduction light source used from the same.

[0004]

According to the present invention, there is provided an optical information medium comprising a liquid crystal layer in which the orientation of a birefringent liquid crystal phase is fixed on a substrate surface having a plurality of pits having different depths for carrying information. Wherein the thickness of the liquid crystal layer changes according to the depth of the pit. In the present invention, “pit” means not only a concave part but also a convex part, and when the “pit” is a convex part, “depth” means a height. Further, the “liquid crystal layer” in the optical information medium of the present invention means a liquid crystal region appearing in an arbitrary cross section of the optical information medium, and the liquid crystal region is continuous in the cross-sectional direction (see FIG. 8) or It does not matter whether it is discontinuous in the direction (see FIG. 7). In the optical information medium of the present invention,
When polarized light having a component in the birefringent principal axis direction of each information carrying part and a direction orthogonal thereto is incident on a plurality of information carrying parts consisting of pits on the substrate surface and the liquid crystal layer, the birefringent principal axes in each information carrying part. A phase difference is generated between the polarized light in the direction and the polarized light in the direction orthogonal thereto, and the phase difference differs depending on the thickness of the liquid crystal layer in the information carrying portion. Therefore, when the signal light is detected by the light receiving device having the optical system that converts the phase difference into the light intensity, the transmitted light intensity or the reflected light intensity is different for each information carrying unit, and accordingly, the optical information medium of the present invention. Then, multi-value recording becomes possible. The liquid crystal layer provided on the substrate is preferably a nematic phase because an alignment structure can be easily formed.

[0005]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, an optical information medium according to the present invention will be described with reference to the drawings. In all the drawings, the same or equivalent components are denoted by the same reference numerals. FIG.
FIG. 1 is a cross-sectional view illustrating a basic configuration example of a first optical information medium according to the present invention. The optical information medium 10 shown in FIG. 1 is a read-only recording medium, and has pits 4a, 4a,
A liquid crystal layer 2 having a birefringent liquid crystal phase having a fixed orientation is provided on the surface of a support substrate 1 having the liquid crystal layers 4b and 4c, and the liquid crystal layer has a thickness corresponding to the depth of the pits 4a to 4c. Is changing. In the optical information medium shown in FIG. 1, reproduction light may be irradiated from either side of the support substrate 1 or the liquid crystal layer 2, and signal detection may be performed using either reflected light or transmitted light. When the reproduction light is irradiated from the support substrate 1 side to detect a signal by reflected light or transmitted light, and when the reproduction light is irradiated from the liquid crystal layer 2 side and the signal is detected by transmitted light, the support substrate 1 is reproduced. It is necessary to be substantially transparent to light, and for this type of support substrate, for example, glass or transparent resin can be used as a material. Of these, transparent resins are preferred because they are easy to handle and inexpensive, and examples of the transparent resin include resins such as acrylic resin, polycarbonate, polyester, polyimide, polyamide, polyetherimide, epoxy resin, and polyolefin. Can be. The reproduction light is irradiated from the liquid crystal layer 2 side,
When the reflected light is used for signal detection, the material of the support substrate 1 does not need to be particularly transparent, and may be glass, acrylic resin, polycarbonate, polyester, polyimide, polyamide, polyetherimide, epoxy resin, polyolefin, or the like. Resins, metals such as aluminum, copper, gold, platinum and silver, and semiconductors such as silicon can be used arbitrarily. Here, the shape and dimensions of the support substrate 1 are not particularly limited, but are generally preferably disk-shaped, the diameter is about 10 to 300 mm, and the thickness is 25 μm to 5 m.
m. FIG. 2 is a sectional view showing a basic configuration example of the second optical information medium according to the present invention. The optical information medium 20 shown in FIG. 2 is a read-only recording medium.
The optical information medium shown in FIG. 1 has a structure in which a second support substrate 3 is provided on the liquid crystal layer side, and the liquid crystal layer 2 is sandwiched between the support substrates 1 and 3. Also in this recording medium, each pit 4a to 4c
Are different from each other in thickness. In the optical information medium 20 shown in FIG. 2, the reproduction light may be emitted from either side of the support substrate 1 or the support substrate 3, and the signal may be detected using either reflected light or transmitted light. The support substrate on the side irradiated with the reproduction light needs to be substantially transparent to the reproduction light, and for example, glass or a transparent resin can be used as the material of the support substrate. Of these, transparent resin is preferred as the material of the support substrate on the side that irradiates the reproduction light because it is easy to handle and inexpensive.Specific examples of the transparent resin include acrylic resin, polycarbonate, polyester, polyimide, polyamide, There are resins such as polyetherimide, epoxy resin and polyolefin. In the case of using reflected light for signal detection, there is no particular limitation on the substrate material on the side not irradiated with reproduction light. Resins such as glass, acrylic resin, polycarbonate, polyester, polyimide, polyamide, polyetherimide, epoxy resin, and polyolefin; metals such as aluminum, copper, gold, platinum, and silver; and semiconductors such as silicon can be used. On the other hand, when the transmitted light is used for signal detection, the material of the support substrate on which the reproduction light is not irradiated is also substantially transparent to the reproduction light similarly to the support substrate on which the reproduction light is irradiated. There is a need.
As a material for the transparent support substrate, for example, glass or a transparent resin can be used, and among them, the use of a transparent resin is preferable because it is easy to handle and inexpensive. As transparent resin, acrylic resin, polycarbonate, polyester,
Resins such as polyimide, polyamide, polyetherimide, epoxy resin, and polyolefin can be used. Here, the shapes and dimensions of the support substrates 1 and 3 are arbitrary, but generally, a disk shape is preferable, the diameter is about 10 to 300 mm, and the thickness is 25 μm to
It is about 5 mm. The support substrate 1 and the support substrate 3 may be in close contact with each other via the liquid crystal layer 2 as shown in FIG. 2, or, as in the optical information medium 30 shown in FIG.
And another intermediate layer 5 may be interposed between them. The intermediate layer 5 may be an air layer, a vacuum layer, or a resin layer. When a resin layer is used, it is preferable to use an acrylic resin, a polycarbonate resin, an epoxy resin, a polyolefin resin, or the like. Pits 4a to 4c on the surface of the support substrate 1
Are convex portions or concave portions for changing the film thickness of the liquid crystal layer 2. When two support substrates are used, pits may be formed only on one of the support substrates. Like the optical information medium 40 shown, a pitch may be formed on each of the opposing surfaces of the two support substrates 1 and 3 with the liquid crystal layer 2 interposed therebetween. The support substrates 1 and 3 can be provided with grooves or the like for tracking, addressing, and the like. Further, each support substrate can be provided with an anti-reflection layer, a reflection layer, a protection layer, and the like as necessary. May be added. Pit 4a on substrate surface
The width of 4c to 4c (width of the bottom or top) depends on the material used for the substrate, the recording density of the optical information media 10 to 40, the resolution of the reproducing optical system, and the like, but cannot be unconditionally specified. It is preferably in the range of 2 to 10 μm. If the width of the pits 4a to 4c is smaller than 0.2 μm, it may be difficult to detect information due to the problem of the resolution of the reproducing optical system. If the width of the pits 4a to 4c is larger than 10 μm, high recording may be performed. Inability to obtain density. The depth of the pits 4a to 4c cannot be unconditionally specified because it depends on the material properties of the liquid crystal layer 2 to be used, the wavelength of the reproducing light source, and the like, but is generally preferably in the range of 0.01 to 10 μm. The depth of the pits 4a to 4c is 0.01 μm
If it is smaller than m, the change in the detected signal strength is small, and the signal may not be detected. When the depth of the pits 4a to 4c is larger than 10 μm, it is difficult to form the pits 4a to 4c, which may cause a problem in mass production in industrial production. Pit 4 on the substrate surface
Although there is no particular limitation on the method of forming the grooves 4a to 4c and the pits 4a to 4c at the same time as the substrate is formed by etching the substrate surface, press molding, injection molding, or the like.
Can be produced.

Next, the liquid crystal layer 2 used in the present invention will be described. Generally, when a liquid crystal layer made of a single material transmits polarized light having a component in the birefringent principal axis direction and a direction perpendicular thereto, a phase difference is generated in the other polarized light component with respect to one polarized light component, The magnitude of the generated phase difference depends on the retardation defined by the product of the refractive index anisotropy (birefringence) of the liquid crystal layer and the thickness of the liquid crystal layer, and the wavelength of incident light. FIG. 5 is a graph showing the relationship between the phase difference generated in light incident on the three types of liquid crystal layers having different birefringences and the thickness of the liquid crystal layer. FIG. 6 is a graph showing the relationship between the phase difference and the thickness of the liquid crystal layer when light of different wavelengths enters the liquid crystal layer having a single birefringence. In the optical information medium of the present invention, a change in phase difference with respect to the thickness of the liquid crystal layer shown in FIGS. 5 and 6 is used for recording information, and a signal is transmitted using an optical system that converts the change in phase difference into light intensity. By recording light, it is possible to perform multi-level recording on the information carrying portion formed by the convex portions of the liquid crystal layer. Therefore, it is desirable to set the height of the projections 4a to 4c of the liquid crystal layer 2 to a desired value in accordance with the liquid crystal material used and the light source used. In the optical information medium of the present invention, a reproducing apparatus is used to irradiate it with reproducing light, and the change in the intensity of the reflected light or transmitted light is used for reading information. If the light absorption of the liquid crystal layer with respect to the reproduction light is large, the reproduction light may be absorbed and a sufficient reproduction light intensity may not be obtained. Therefore, it is preferable that the light absorption rate of the liquid crystal layer 2 with respect to the reproduction light is small. However, since the reproduction light intensity also depends on the intensity of the light source used, the upper limit of the light absorptivity of the liquid crystal layer 2 with respect to the reproduction light cannot be determined unconditionally. Generally, its value is 5
0% or less, preferably 5% or less, more preferably 1% or less.
% Is desirable. When the light absorption of the liquid crystal layer 2 is for light having a wavelength other than the reproduction light, there is no such concern.

Although the liquid crystal material forming the liquid crystal layer 2 of the present invention is not particularly limited, a material having a nematic phase as a liquid crystal phase is preferable from the viewpoint of easy alignment control. Although there is no particular limitation on the method of fixing the liquid crystal alignment, a preferable method is to use a polymer liquid crystal composition as a liquid crystal material, bring the polymer liquid crystal composition into a liquid crystal state, and form an alignment structure. A method of fixing the orientation of the liquid crystal phase to glass by cooling the polymer liquid crystal composition, using a photocurable low molecular liquid crystal composition as a liquid crystal material, and converting the photocurable low molecular liquid crystal composition into a liquid crystal state. A method of forming an alignment structure and then irradiating the photocurable liquid crystal composition with light to fix the alignment of the liquid crystal phase can be exemplified. The above-mentioned polymer liquid crystal composition means a composition containing a polymer liquid crystal as a main component, and the polymer liquid crystal is not particularly limited as long as a desired alignment structure can be fixed. Any of chain type and side chain type polymer liquid crystals can be used. Specific examples of such polymer liquid crystals include:
Main-chain liquid crystal polymers such as polyester, polyamide, polycarbonate, and polyesterimide; and side-chain liquid crystal polymers such as polyacrylate, polymethacrylate, polymalonate, and polysiloxane. Among them, a liquid crystalline polyester, which has good orientation in forming a liquid crystal alignment structure and is relatively easy to synthesize, is desirable. Preferable examples of the constituent units of the polyester include aromatic or aliphatic diol units, aromatic or aliphatic dicarboxylic acid units, and aromatic or aliphatic hydroxycarboxylic acid units. Further, the photocurable low-molecular liquid crystal composition means a composition containing a low-molecular liquid crystal as a main component, and as the low-molecular liquid crystal,
For example, those having a basic skeleton of a biphenyl derivative, a phenylbenzoate derivative, a stilbene derivative, or the like into which a functional group such as an acryloyl group, a vinyl group, or an epoxy group is introduced may be used. Either lyotropic or thermotropic liquid crystal can be used for the photocurable low-molecular liquid crystal, but use of the thermotropic low-molecular liquid crystal is more preferable from the viewpoint of workability, process, and the like. The photocurable low-molecular liquid crystal composition may contain a photopolymerization initiator, a sensitizer, and the like, if necessary. Even when using a polymer liquid crystal composition for forming a liquid crystal layer, or when using a photocurable low-molecular liquid crystal composition, each of the above compositions is used for the purpose of improving the heat resistance of the finally obtained liquid crystal layer. The product may contain a cross-linking agent such as a bisazide compound or glycidyl methacrylate within a range that does not hinder the development of the liquid crystal phase. Use of a crosslinking agent promotes crosslinking of liquid crystal constituent molecules in a state where a liquid crystal phase is developed. Furthermore, various additives such as dichroic dyes, dyes, pigments, antioxidants, and ultraviolet absorbers impair the effects of the present invention in the above-described polymer liquid crystal composition and photocurable low-molecular liquid crystal composition. It can be appropriately contained within the range not present. The incorporation of the above-mentioned crosslinking agent or additive increases the stability of the liquid crystal layer, and thus has the effect of improving the long-term storage stability of optical information.
There is no particular limitation on the method of forming the liquid crystal layer, but the melt or solution of the liquid crystal layer forming composition is roll-coated, die-coated, bar-coated, gravure roll-coated, spray-coated, dip-coated, spin-coated. A method of applying the composition for liquid crystal formation on the alignment substrate by a coating method or the like, and a method of press-forming the composition for forming a liquid crystal on the alignment substrate are common. Then, by removing the alignment substrate from the liquid crystal layer in which the orientation of the liquid crystal phase is fixed, an optical information medium without a support substrate can be obtained, and the liquid crystal layer in which the orientation of the liquid crystal phase is fixed is supported. By transferring the image onto the substrate, an optical information medium with a supporting substrate can be obtained. In this case, if the supporting substrate itself can also be used as the alignment substrate, the transfer step can be omitted and the liquid crystal layer can be directly provided on the supporting substrate. The optical information medium of the present invention shown in the drawings is a single-sided optical information medium in which the information carrying part, that is, the pits having different depths and the liquid crystal layer adjacent thereto are present only on one side of the substrate. Alternatively, a single-sided optical information medium can be bonded together to form a double-sided optical information medium. There is no limitation on the number of information carrying units, whether single-sided or double-sided, as long as the number is plural.

[0008]

The present invention will be described in more detail with reference to the following Examples, which do not limit the present invention. Example 1 Glass having a diameter of 130 mm and a thickness of 1.1 mm was used as a support substrate, and three types of pits 4 a to 4 c having a pit width of 2 μm and different depths were formed by etching (support substrate 1). The depths of the pits 4a to 4c formed by the etching were determined to be 1.
4 μm, pit 4b 2.2 μm, pit 4c 3.0
μm. As an acrylic monomer showing liquid crystal properties,
Methylhydroquinone bis (4- (6-acrylyloxyoxyhexyloxy) benzoic acid) ester (compound 1)
2.9 g of 4-cyanophenol 4- (6-acryloyloxyoxyhexyloxy) benzoate (Compound 2) was weighed and dissolved in 90 g of N-methyl-2-pyrrolidone to obtain a solution. This solution was applied to the supporting substrate 1 by a spin coater, placed in a clean oven set at 60 ° C., and dried for 15 minutes.
The liquid crystal layer 2 was subjected to a heat treatment in an oven set at a temperature of 5 ° C. for 5 minutes, and cooled from that temperature to 50 ° C. at a rate of about 1 ° C./min to complete the nematic alignment of the liquid crystal layer 2. After the heat treatment, the film supporting substrate 1 was taken out of the oven, cooled to room temperature, and irradiated with an electron beam (EB) at room temperature. The EB irradiation was performed at an acceleration voltage of 30 kV in an atmosphere having an oxygen concentration of 0.20% at room temperature. After the irradiation, the liquid crystal layer 2 was cured, had a birefringence Δn of 0.10, and had a surface hardness of about H to 2H in terms of pencil hardness. According to the electron microscope observation of the cross section (see FIG. 7) of the optical disk sample (optical disk 50) thus obtained, the material constituting the liquid crystal layer 2 is filled in the pits 4a to 4c of the support substrate 1, and the pits 4a to 4c are filled. The thickness was in accordance with the depth of 4c. The optical disc 50 is placed between the orthogonal polarizing plates so that the main axis of birefringence of the liquid crystal layer 2 and the absorption axis of the polarizing plate are at 45 degrees, and a reproduction laser beam (wavelength 780 nm) is irradiated from the support substrate 1 side. When the transmitted light intensity for each of the pits 4a to 4c was detected and the transmittance was determined, the pit 4a
Is 26%, pit 4b is 55%, pit 4c is 79%, and different values are obtained for each of the pits 4a to 4c.
In the pits 4a to 4c of the optical disk 50, multi-value recording of information is possible. Example 2 Two types of pits 4a and 4b having a pit width of 1.6 μm and different depths were formed on a glass substrate having a diameter of 130 mm and a thickness of 0.6 mm (support substrate 1). The depth of the formed pits 4a and 4b is 0.5 μm for the pit 4a and 0.8 μm for the pit 4b by electron microscopic observation of the cross section of the substrate.
m. The following formula is used as a side-chain polymer liquid crystal exhibiting liquid crystallinity.

Embedded image (R = —CH ₃ , the number average molecular weight Mn by GPC and the weight average molecular weight Mw are each M
n = 2,500, Mw = 10,000) and 12 g with the following formula

Embedded image (R = —CH ₃ , the number average molecular weight Mn by GPC and the weight average molecular weight Mw are respectively Mn = 3, 0
00, Mw = 11,000), weigh 8 g, 130 g
Was dissolved in chloroform to prepare a solution. This solution was applied to the support substrate 1 by a spin coater, placed in a clean oven set at 60 ° C., and dried for 15 minutes.
Further heat treatment in an oven set at 160 ° C for 5 minutes,
The cholesteric alignment of the liquid crystal layer 2 was completed, and the nematic alignment was fixed by cooling from the temperature. The birefringence Δn of the liquid crystal layer was 0.13. By observing the cross section (see FIG. 8) of the optical disk sample (optical disk 60) obtained in this way with an electron microscope, the liquid crystal material is filled in the pits 4a and 4b of the support substrate 1, and the pits 4a and 4b are filled.
The thickness of the liquid crystal layer 2 changed according to the depth of 4b. Further, the liquid crystal layer 2 was also present in a portion having no pits 4a and 4b, and the film thickness in that portion was 1 μm. The optical disk 60 is placed between orthogonal polarizing plates such that the birefringent main axis of the liquid crystal layer 2 and the absorption axis of the polarizing plate are at 45 degrees, and a reproducing laser beam (780 nm wavelength) is irradiated from the liquid crystal layer 2 side. The transmitted light intensity for each of the pits 4a and 4b was detected, and the transmittance was determined. As a result, the pit 4a was 45% and the pit 4b was 5%.
9%, and a different value is obtained for each of the pits 4a and 4b. Multi-value recording of information is possible in the pits 4a and 4b of the optical disc 60. Example 3 Polycarbonate resin was injection-molded to obtain a pit width of 1.
Pits 4a, 4b, 4c of three different depths of 6 μm
Was produced. The support substrate 1 has a diameter of 13
0 mm, 0.6 mm thick, and formed pits 4 a to 4
The depth of the pit 4c was determined by observing the cross section of the substrate with an electron microscope.
a is 0.7 μm, pit 4b is 1.0 μm, pit 4c
Was 1.2 μm. The following formula is used as the main chain type polymer liquid crystal exhibiting liquid crystallinity.

Embedded image The liquid crystalline polyester having the structure shown in (logarithmic viscosity 0.21,
Having a nematic phase as a liquid crystal phase, an isotropic phase-nematic phase transition temperature of 300 ° C. or higher, and a glass transition point of 115 ° C.

Embedded image 10 g of a liquid crystalline polyester (logarithmic viscosity: 0.18, having a smectic phase as a liquid crystal phase, and having an isotropic phase-smectic phase transition temperature of 150 to 160 ° C.) shown in (1), and crushed and mixed to obtain a liquid crystal composition Was prepared. This composition is sandwiched between supporting substrates 3 made of polycarbonate resin having the same size as the supporting substrate 1 and having no pits 4a to 4c.
After heating to ° C., both substrates 1 and 3 were pressed together by press working. At 200 ° C., the two supporting substrates 1 and 3
After heat treatment for 0 minutes, the substrate was cooled and fixed at room temperature to fix the nematic alignment structure between the supporting substrates 1 and 3. The birefringence Δn of the liquid crystal layer was 0.20. By observing the cross section (see FIG. 9) of the optical disk sample (optical disk 70) obtained in this way with an electron microscope, the liquid crystal material is filled in the pits 4a to 4c of the support substrate 1, and the pits 4a to 4c are filled.
The thickness was in accordance with the depth of 4c. The optical disk 70 is placed between orthogonal polarizing plates such that the birefringent main axis of the liquid crystal layer 2 and the absorption axis of the polarizing plate are at 45 degrees, and a reproduction laser beam (wavelength 780 nm) is irradiated from the support substrate 3 side. ,
The transmitted light intensity for each of the pits 4a to 4c was detected, and the transmittance was determined. The pit 4a was 26%, the pit 4b was 47%, and the pit 4c was 62%.
Different values are obtained for c, and multi-value recording of information is possible in the pits 4a to 4c of the optical disk 70. Example 4 The depths of the pits 4a, 4b, 4c were 0.8 μm, 1.2 μm.
An optical disk was manufactured in the same manner as in Example 1 except that the thickness was set to m, 1.6 μm. Further, aluminum was deposited on the liquid crystal layer 2 side of the obtained disk to provide a reflective layer (reflective layer 9). ) Was obtained (see FIG. 10). According to the electron microscope observation of the cross section (FIG. 10) of the optical disk 80, convex portions 4a to 4c are formed on the liquid crystal layer 2 corresponding to the pits A to C of the master, respectively, and the liquid crystal layer 2 has convex portions 4a to 4c. Had a thickness corresponding to the height of the building. The optical disk 60 is irradiated with a reproducing laser beam (wavelength 780 nm), which is linearly polarized by a polarizing plate, from the support substrate 1 side so that the birefringent main axis and the polarization axis of the liquid crystal layer 2 become 45 degrees. After separating the reflected light with a polarizing beam splitter, it was led to a light receiving element, and the reflected light intensity was detected.
The reflectance of each part is 33% for the convex part 4a and 62% for the convex part 4b.
% And the convex portion 4c are 84%, and different values are obtained for the respective convex portions 4a to 4c.
Allows multi-value recording of information. Comparative Example 1 An optical disc was produced in the same manner as in Example 1 except that the non-liquid crystal layer 13 was formed using the support substrate 1 used in Example 1 and an acrylic monomer having no liquid crystallinity as a material applied to the support substrate 1. A sample (optical disk 90) was prepared (see FIG. 11), and the transmittance of each of the pits 4a to 4c was determined. As a result, there was no difference in transmittance between the pits 4a to 4c. Cannot record multi-valued information.

[0009]

As described above, the optical information medium of the present invention has a liquid crystal layer in which the orientation of a birefringent liquid crystal phase is fixed on a substrate surface having a plurality of pits having different depths for carrying information. By changing the retardation of the liquid crystal layer according to the depth of the pits, it is possible to increase the numerical aperture of the optical system of the reproducing apparatus, shorten the wavelength of the reproducing light and use the super-resolution phenomenon. Thus, an optical information medium having a high recording density and capable of performing reproduction even with low-power reproduction light using a reproduction optical system and a reproduction light source developed so far can be realized.

[Brief description of the drawings]

FIG. 1 is a sectional view showing a first basic configuration example of an optical information medium of the present invention.

FIG. 2 is a sectional view showing a second basic configuration example of the optical information medium of the present invention.

FIG. 3 is a sectional view showing a third basic configuration example of the optical information medium of the present invention.

FIG. 4 is a sectional view showing a fourth basic configuration example of the optical information medium of the present invention.

FIG. 5 is a graph showing a change in phase difference with respect to the thickness of a liquid crystal layer when a light source is fixed.

FIG. 6 is a graph showing a change in phase difference with respect to the thickness of a liquid crystal layer when a liquid crystal material is fixed.

FIG. 7 is a cross-sectional view illustrating the optical disc in the first embodiment.

FIG. 8 is a cross-sectional view illustrating an optical disc according to a second embodiment.

FIG. 9 is a cross-sectional view illustrating an optical disc according to a third embodiment.

FIG. 10 is a cross-sectional view illustrating an optical disc according to a fourth embodiment.

FIG. 11 is a sectional view showing an optical disc in Comparative Example 1.

[Explanation of symbols]

1,3 Supporting substrate (substrate) 2 Liquid crystal layer 4a-4c Pits on substrate surface 5 Intermediate layer 9 Reflective layer 13 Non-liquid crystal layer 10,20,30,40 Optical information medium 50,60,70,80,90 Optical disk (optical Information media)

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) G02F 1/13 505 G02F 1/13 505

Claims (2)

[Claims] 1. An optical information medium on which optically readable information is recorded, wherein the orientation of a birefringent liquid crystal phase is fixed on the surface of a substrate having a plurality of pits having different depths for carrying information. An optical information medium having a liquid crystal layer, wherein the thickness of the liquid crystal layer changes according to the depth of the pit. 2. The optical information medium according to claim 1, wherein the liquid crystal phase is a nematic phase.