JPH01184641A - Information recording medium - Google Patents

Abstract

PURPOSE:To enhance C/N (carrier wave/noise) at the time of reproduction by incorporating a nonlinear optical material into another layer adjacent to the recording layer of an information recording medium or another layer. CONSTITUTION:This recording medium is constituted of a substrate 1, a nonlinear optical layer 2 provided on one face thereof and the recording layer 3. The recording medium is constituted of the substrate 1 and the recording layer 3'. The nonlinear optical material is incorporated into the layer 3'. The layer 2 of the information recording medium provided with the layer 2 as the separate layer is larger in the refractive index of light than the layer 3 and the wavelength-converted light progresses from the layer of the larger refractive index to the layer of the smaller refractive index and is then detected; therefore, the influence of scattering is decreased and the high C/N is obtd. even if there are ridges around the bits. The wavelength conversion of the laser light for reproduction with the medium having the layer 3' is executed only in the part where the bits are not formed and the information can be read in accordance with the presence or absence of the wavelength-converted light. The high C/N is, therefore, obtd.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of the Invention] The present invention relates to an information recording medium having a recording layer on which information is written and/or read by a high energy density laser beam.

[Technical Background of the Invention] In recent years, information recording media that use high energy density beams such as laser light have been developed and put into practical use. This information recording medium is called an optical disk, and includes video disks, audio disks, large-capacity still image files, large-capacity computer disk memories,
It is also applied to optical cards, micro image recording media, super micro image recording media, micro facsimiles, original plates for phototypesetting, etc.

An information recording medium basically consists of a transparent substrate made of plastic, glass, etc., and a recording layer provided thereon. As a material for the recording layer.

Metals or semimetals such as Bi, Sn, In, and Te; and dyes such as cyanine, metal complex, and quinone are known.

Information is written on an information recording medium by, for example, irradiating the recording medium with a laser beam, and the irradiated portion of the recording layer absorbs the light and locally increases in temperature, causing physical or chemical damage. Information is recorded by causing changes in the optical properties of the optical fiber. Reading information from a recording medium is also performed by irradiating the recording medium with a laser beam, and the information is reproduced by detecting reflected or transmitted light according to changes in the optical characteristics of the recording layer. .

Normally, physical changes in the recording layer are made by creating holes (pits), but some of the recording layer material that is melted at this time remains around the pits and forms a ridge, making it difficult to read. There is a drawback that the laser beam is sometimes scattered at this ridge portion, reducing the C/N ratio (carrier/noise ratio).

In addition, information is read based on the difference in reflectance or transmittance between pit-formed areas and non-pit-formed areas.
If the difference is not sufficient, the C/N ratio will decrease.

[Summary of the Invention] An object of the present invention is to provide an information recording medium with improved C/N ratio during information reproduction.

Further, another object of the present invention is to provide an information recording medium in which information can be reproduced by detecting light at the wavelength (second harmonic) of the irradiated laser light.

[11] An information recording medium in which a recording layer on which information can be written and/or read by a laser is provided on a substrate, adjacent to the recording layer.

The information recording medium of the present invention, characterized in that the contacting layer contains a nonlinear optical material; and [21 on the substrate,
Achieved by the information recording medium of the present invention, which is provided with a recording layer on which information can be written and/or read by a laser, wherein the recording layer contains a nonlinear optical material; can do.

Preferred embodiments of the information recording medium of the present invention are as follows.

(1) The information recording medium of [11] above, wherein the nonlinear optical material is capable of generating a second harmonic.

(2) The information recording medium according to [1] above, wherein the nonlinear optical material has a light transmittance of 10% or more to the second harmonic of the reading laser beam.

(3) The information recording medium according to [1] above, wherein the recording layer is made of a light-absorbing substance.

(4) The information recording medium of [11] above, wherein a layer substantially made of a nonlinear optical material is provided between the substrate and the recording layer.

(5) The information recording medium according to [2] above, wherein the nonlinear optical material is capable of generating a second harmonic.

(6) The information recording medium of [21] above, wherein the nonlinear optical material has a light transmittance of 10% or more to the second harmonic of the reading laser beam.

(7) The information recording medium of [21] above, wherein the recording layer contains a light-absorbing substance.

The present invention converts the wavelength of laser light for reproduction using the nonlinear optical material by mixing and containing a nonlinear optical material in the recording layer of an information recording medium or in a separate layer adjacent to the recording layer, and converts the wavelength of the laser beam for reproduction. By reading the signal based on this, the C/N ratio during reproduction can be significantly increased.

In the present invention, a nonlinear optical material refers to a material that can exhibit nonlinearity (IP linear optical effect) between the electric field of light and polarization when a strong optical electric field such as a laser beam is applied.
Nonlinear optical effects are caused by the interaction of matter and light, and are mainly caused by deviations from the linearity of electrical polarization at optical frequencies;
In other words, nonlinear polarization becomes a problem. Specifically, nonlinear optical effects include second-order effects (second-order nonlinear polarization) such as second harmonic generation, optical mixing, parametric oscillation, optical rectification, and Pockels effect, and third-order effects (third-order nonlinear polarization). ) include third harmonic generation, Kerr effect, optical bistability, optical mixing, etc., and there are also higher-order effects.In the present invention, among these effects exhibited by nonlinear optical materials, the second one related to wavelength conversion is Harmonic generation, optical mixing, parametric oscillation and third harmonic generation are important, and the material is used, for example, for the purpose of converting semiconductor laser light having a wavelength in the infrared region to a wavelength in the visible region.

That is, in the first information recording medium in which a layer containing a nonlinear optical material (this is referred to as 1 nonlinear optical layer 1) is provided as a separate layer, the reproduction laser beam is transmitted to the second harmonic ( 34 wavelengths), and information is read based on the fact that the amount of the wavelength-converted light differs between the pit-formed portion and the non-pit-formed portion of the recording layer. At this time, the nonlinear optical layer has a higher refractive index than the recording layer, and since the wavelength-converted light is detected after traveling from a layer with a high refractive index to a layer with a low refractive index, there are ridges around the pits. Also, the influence of scattering is reduced, and a high C/N ratio can be obtained.

In addition, in the second information recording medium, since a nonlinear optical material is mixed and contained in the recording layer, the wavelength conversion of the reproduction laser beam is performed only in the area where no pits are formed, and the presence or absence of the wavelength-converted light (detection , not detected).

Therefore, based on the difference in the reflectance of the reproducing laser beam, information can be read at a higher C/N ratio than in conventional reading.

[41m of the invention] Representative examples of the information recording medium of the invention are shown in FIGS. 1 and 2.
Each of FIGS. 1 and 2 is a cross-sectional view showing an example of the layer structure of an information recording medium.

In FIG. 1, the recording medium is formed from a substrate l, a nonlinear optical layer 2 provided on one side thereof, and a recording layer 3, and in FIG. 2, a recording medium is formed from a substrate l and a recording layer 3°. configured. The recording layer 3° contains a nonlinear optical material.

However, the information recording medium of the present invention is not limited to these embodiments, and as long as the nonlinear optical material is mixed and contained in the recording layer or is adjoined to the recording layer as an independent layer, it can be implemented in any manner. can be configured.

The information recording medium having the above structure can be manufactured, for example, by the method described below.

The substrate used in the present invention can be arbitrarily selected from various materials used as substrates for conventional information recording media. Optical properties, flatness, processability of the substrate,
In terms of ease of handling, stability over time, and manufacturing cost,
Examples of substrate materials include glass such as soda lime glass; acrylic resins such as cell cast polymethyl methacrylate and injection molded polymethyl methacrylate; vinyl chloride resins such as polyvinyl chloride and vinyl chloride copolymers; epoxy resins; and polycarbonate. can be mentioned.

Among these, polymethyl methacrylate, polycarbonate, epoxy resin, and glass are preferred from the viewpoint of dimensional stability, transparency, and flatness.

The surface of the substrate on which the recording layer is provided has improved flatness,
An undercoat layer may be provided for the purpose of improving adhesive strength and preventing deterioration of the recording layer. Examples of materials for the undercoat layer include polymethyl methacrylate, acrylic acid/methacrylic acid copolymer, and nitro. cellulose, polyethylene,
Polymer substances such as pyrene and polycarbonate; organic substances such as silane coupling agents; and inorganic oxides (SiO2, A-203, etc.), inorganic fluorides (MgF2)
Inorganic substances such as

In the case of a glass substrate, in order to prevent adverse effects on the recording layer due to alkali metal ions and alkaline earth metal ions liberated from the substrate, wood-philic groups such as styrene-maleic anhydride copolymer and/or maleic anhydride are added. Preferably, a subbing layer made of a polymer having acid groups is provided.

The undercoat layer can be formed by, for example, dissolving or dispersing the above-mentioned substance in a suitable solvent, and then applying this coating solution to the substrate surface by a coating method such as spin cording, dip coating, or extrusion coating.

Further, a pre-groove layer may be provided on the substrate for the purpose of forming tracking grooves or unevenness representing information such as address signals. Materials for the pre-groove layer include:
A mixture of at least one monomer (or oligomer) of acrylic acid monoester, diester, triester, and tetraester and a photopolymerization initiator can be used.

The pre-groove layer is formed by first coating a mixture of the above acrylic ester and polymerization initiator on a precisely made matrix (stamper), then placing the substrate on top of this coating solution layer. , the substrate and the liquid phase are fixed by curing the liquid layer by irradiating ultraviolet rays through the substrate or the matrix.
Next, by peeling the substrate from the mother mold, a substrate provided with a pregroove layer is obtained. The layer thickness of the pregroove layer is generally in the range of 0.05 to 1100 IL,
It is preferably in the range of 0.1 to 50 #Lm.

Furthermore, in the case of a plastic substrate, pregrooves may be provided directly on the substrate surface.

Next, a recording layer is formed on the substrate (or undercoat layer, pregroove layer).

As the material for the recording layer, a substance capable of absorbing laser light, such as a dye, is used, and any dye conventionally known as a recording material for information recording media can be used. As an example.

Seven thalocyanine pigments such as copper phthalocyanine.

Cyanine pigments, pyrylium/thiopyrylium pigments, azulenium pigments, squarylium pigments, Ni,
Examples include metal complex dyes such as Or, naphthoquinone-based anthraquinone-based dyes, indophenol-based dyes, indoaniline-based dyes, triphenylmethane-based dyes, triallylmethane-based dyes, aminium-based diimmonium-based dyes, and nitroso compounds. can. Among these, semiconductor lasers that emit near-infrared light have been put into practical use as recording and reproducing lasers, and light-absorbing materials have a high absorption rate for light in the near-infrared region of 700 to 900 nm. Dyes are preferred.

In addition, metals or metalloids may be used as the light-absorbing substance; these may be used alone or in combination as a composition; metals or metalloids, their oxides, halogens, etc. A compound or a sulfide may be used in combination.

Examples of metals and metalloids include Mg, Se, Y, Ti,
Zr, Hf, ■, Nb, Ta, Cr.

Mo, W, Mn, Re, Fe, Co, Ni.

Ru, Rh, Pd, Ir, Pt, Cu, Ag, Au,
Zn, Cd, A1. Ga, In, Si, Ge, Te
, Pb, Po, Sn, Bi, and metalloid metals. Among these, preferred is Sn
, Bi and In. These substances may be used alone, or in combination of two or more or as an alloy.

When the recording layer contains a nonlinear optical material, which is a characteristic requirement of the present invention, examples of the nonlinear optical material include:
Lithium niobate (LiNbO), potassium dihydrogen phosphate (K H2P Oa, abbreviated as KDP), lithium iodate (LiIO3), barium metaborate (Ba
B 20 m ); and urea derivatives, nitroaniline derivatives [e.g., 2-methyl-4-nitroaniline (MNA), 2-N,N-dimethylamino-5-nitroacetanilide (DAN)] , metanitroaniline, L-N-(4-nitrophenyl)-
Examples include organic compounds such as 2-(hydroxymethyl)pyrrolidine 1 and nitropyridine-N-oxide derivatives [for example, 3-methyl-4-nitropyridine-1-oxide (POM)].

Nitroaniline derivatives include i) Compounds represented by the general formula (I) described in Japanese Patent Application No. 61-29999 filed by the present applicant. A hydrogen atom or an optionally substituted alkyl group, which may be the same as each other, or 1lil and R2 may form a ring; R3 is a hydrogen atom or an optionally substituted alkyl group or an optionally substituted aryl group) In the above general formula (I), examples of the alkyl group are:
Methyl group, ethyl group, propyl group, butyl group, pentyl group, octyl group, dodecyl group, hexadecyl group, tocosyl group, 2-hydroxyethyl group, methoxycarbonylmethyl group, 2-methanesulfonylaminoethyl group, 2-methoxyethyl group 2-7 cetyloxyethyl group, benzyl group, 2-phenylethyl group and tetrahydrofurfuryl group. Examples of the ring formed by R1 and R2 include a pyrrolidino ring, a 2-hydroxymethylpyrrolidino ring, a morpholino ring, and a piperidino ring. Furthermore, examples of aryl groups include phenyl group, 4
-methylphenyl group.

Examples include l-naphthyl group and 2-naphthyl group.

Specific examples include compounds having the following structural formula.

The following margins ii) Compound represented by the general formula (■) and its acid adduct described in the specification of Japanese Patent Application No. 61-53462: \ NO? (However, Zl and Z2 are each nitrogen atom or C
R5 groups, which may be the same or different, at least one of which is a nitrogen atom; X is an alkyl group, aryl group, halogen atom, alkoxy group, aryloxy group, acylamino group, carbamoyl group, sulfamoyl group, Acyloxy group, alkoxycarbonyl group, aryloxycarbonyl group, alkoxysulfonyl group, aryloxysulfonyl group, alkylthio group, arylthio group, hydroxy group, thiol group, carboxy group, ureido group, cyano group, alkylsulfonyl group, arylsulfonyl group, an alkylsulfinyl group, an arylsulfinyl group, or a nitro group, in which the alkyl group and the aryl group may be substituted; R4 is a hydrogen atom;
an optionally substituted alkyl group, an optionally substituted aryl group, or an acyl group; R5 is a hydrogen atom, an optionally substituted alkyl group, or an optionally substituted aryl group; n is an integer in the range of 0 to 3) In the above general formula (■), examples of the alkyl group are:
Methyl group, ethyl group, isopropyl group, butyl group, t-
Butyl group, octyl group, t-octyl group, decyl group, hexadecyl group, tocosyl group, 2-hydroxyethyl group,
Examples include carboxymethyl group, cyanomethyl group, 2-methoxyethyl group, benzyl group, 2-phenylethyl group, trifluoromethyl group and 3-(2-benzimidazolyl)propyl group. Examples of 7-aryl groups include phenyl, 4-methylphenyl, 3-methoxyphenyl and 4-chlorophenyl. Examples of the halogen atom include a fluorine atom, a chlorine atom, a bromine atom, and an iodine atom.

Examples of alkoxy groups include methoxy group, butoxy group,
2-methoxyethoxy group, benzyloxy group and 2-
Examples include phenylethoxy group.

Examples of aryloxy groups include phenoxy group, 4-t
-butylphenoxy group and 4-chlorophenoxy group. Examples of acylamino groups include acetylamino, methanesulfonylamino, benzoylamino and 4-methylbenzenesulfonylamino groups. Examples of carbamoyl groups include carbamoyl, N-methylcarbamoyl and N-phenylcarbamoyl. Examples of sulfamoyl groups include sulfamoyl, N-methylsulfamoyl and N-phenylsulfamoyl groups. Examples of acyloxy groups include acetyloxy, pivaloyloxy, benzoyloxy and benzenesulfonyloxy groups. Examples of ureido groups include methylureido, ethylureido, and phenylureido.

Further, among the compounds represented by the general formula (n), compounds represented by the general formula (■): \O2 (wherein Z3 and Z4 are synonymous with Zl and Zl, and R6 is synonymous with R4) are preferred. and its acid adducts.

Further, among the compounds represented by the general formula (m), the general formula (■): O2 (wherein, R1 has the same meaning as R4; R8 has the same meaning as R5; and the NO2 group is at the 5-position or substituted at the 6-position), general formula (V): \N(h (wherein R9 has the same meaning as R4; R10 has the same meaning as R5; and the NO2 group is substituted at the 5- or 6-position Compounds represented by and acid adducts thereof include compounds represented by and acid adducts thereof.

The above acid adducts have general formulas (n), (m), and (IV).
And the compound represented by (V) is an organic acid such as carboxylic acid or sulfonic acid; or sulfuric acid.

It is a compound to which an inorganic acid such as hydrochloric acid, nitric acid, or phosphoric acid is added (usually one molecule).

Specific examples include compounds having the following structural formula.

Space below 1ii) Compounds represented by the general formula (Vl) and acid adducts thereof described in Japanese Patent Application No. 1984-53884: ・Z6, (However, Z5 has at least one nitro group substituted with 1) is an atomic group necessary to form a five- to six-membered aromatic ring having as; 26 may be substituted or fused,
Examples of the five- to six-membered aromatic ring formed by Z5 in the above general formula (Vl), which is an atomic group necessary to form a virole ring, imidazole ring, pyrazole ring, triazole ring, or tetrazole ring, include: Thiazoles, oxazoles, imidazoles, pyridines,
Examples of the 22-substituent group include pyrimidines and benzenes, and these rings may be substituted or condensed with the following groups. Examples of the 22 substituents include alkyl groups, aryl groups, halogen atoms, alkoxy groups, Aryloxy group, acylamino group, carbamoyl group, sulfamoyl group, acyloxy group, alkyloxycarbonyl group, aryloxycarbonyl group, alkyloxysulfonyl group, aryloxysulfonyl group, alkylthio group, arylthio group, hydroxy group, thiol group, carboxy group , ureido group, cyano group, alkylsulfonyl group, arylsulfonyl group, alkylsulfinyl group, arylsulfinyl group and nitro group. Examples of alkyl groups include methyl group, ethyl group, isopropyl group,
butyl group, t-butyl group, octyl group, t-octyl group, tesyl group, hexadecyl group, tocosyl group, 2-hydroxyethyl group, carboxymethyl group, cyanomethyl group,
Examples include 2-methoxyethyl group, benzyl group, 2-phenylethyl group, trifluoromethyl group and 3-(2-benzimidazolyl)propyl group. Examples of aryl groups include phenyl, 4-methylphenyl, 3-methoxydiphenyl and 4-chlorophenyl. Examples of the halogen atom include a fluorine atom, a chlorine atom, a bromine atom, and an iodine atom. Examples of alkoxy groups include methoxy, butoxy, 2-methoxyethoxy, benzyloxy and 2-phenylethoxy groups. Examples of aryloxy groups include phenoxy, 4-t-butylphenoxy and 4-chlorophenoxy. Examples of the acylamino group include an acetylamino group, a methanesulfonylamino group, a benzoylamino group, and a 4-methylbenzenesulfonylamino group. Examples of carbamoyl groups are:
Examples include carbamoyl group, N-methylcarbamoyl group, N-ethylcarbamoyl group and N-phenylcarbamoyl group.

Examples of sulfamoyl groups include sulfamoyl group, N
-methylsulfamoyl group and N-phenylsulfamoyl group. Examples of acyloxy groups include:
Examples include acetyloxy, piparoyloxy, benzoyloxy and benzenesulfonyloxy groups. Examples of ureido groups include methylureido, ethylureido, and phenylureido.

Examples of pyrrole rings formed by Z6 include pyrrole, indole, 2-methylindole, 5-methoxyindole, 5-hydroxyindole, L-)liptophan, rubazole, 3-carboxindole and 2,5-dimethylbindole. Roles can be mentioned. Examples of imidazole rings include imidazole, 2-methylimidazole, 2-ethylimidazole, 2-undecylimidazole, 2-phenylimidazole, 2,4-dimethylimidazole, 2-ethyl-4-methylimidazole,
L-histidine, 4,5-diphenylimidazole, 2
, 4.5-) ryenylimidazole, benzimidazole, 2-methylbenzimidazole, 2-methyl-5
-chlorobenzimidazole, 2-methyl-5,6-dichlorobenzimidazole, 2-methyl-5-chloro-
Mention may be made of 6-diatubenzimidazole and 2-mercaptobenzimidazole. Examples of pyrazole rings include pyrazole, 3,5-dimethylpyrazole, 3.
Mention may be made of 5-diphenylpyrazole, 4-bromo-3,5-dimethylpyrazole, 3-methylpyrazole and indazole. Examples of triazole rings include 1,
3.4-triazole, 1,2.4-)lyazole, 2
-Chloro-1,3,4-)riazole, 2,5-dimethyl-1,3,4-)riazole, 3,5-diphenyl-
1,2,4-) riazoles and benzotriazoles. Examples of tetrazole rings include tetrazole and 5-phenyltetrazole.

Furthermore, the ring formed by Z6 may contain a substituent that forms a dimer, such as -S-.

Specific examples include compounds having the following structural formula.

Furthermore, diacetylene derivatives described in JP-A-56-43220, diolefin compounds described in JP-A-61-78748, JP-A-61-1
Diazo compounds described in JP-A No. 52647, and JP-A-61-60638 and JP-A-61-13713
No. 6, JP-A-61-147238, JP-A-61-14
Organic compounds described in JP-A No. 8433 and JP-A-61-167930, as well as “Non1inear
Optical Properties of
Organic and PolymericMa
terials″ACS SYMPOSIUM 5ER
IES 233. DavidJ, William
s edition (American Chemical
5ociety.

(Published in 1983) and "Organic Nonlinear Optical Materials" supervised by Masao Kato and He Nakanishi (CMC Co., Ltd., Published in 1985)
Organic compounds described in can be used.

Among these compounds, K has a high transmittance to blue light.
DP, lithium niobate, lithium iodate, barium metaborate, urea, POM, the compound represented by the above general formula (II) (described in Japanese Patent Application No. 61-53462) and the compound represented by the above general formula (Vl) ( #Gansho61
-53884) is preferable, and the transmittance for the second harmonic of the reading laser beam, for example, blue light in the wavelength range of 400 to 500 nm, is preferably 105 or more.

In particular, the wavelength is generally 700 to 900 nm as a reproduction laser.
A semiconductor laser with an oscillation wavelength in the near-infrared region of POM with high general formula (II) and (V
φ compounds represented by l) are preferred.

Note that these nonlinear optical materials can be used alone or in combination of two or more.

The recording layer is prepared by, for example, preparing a coating solution by dissolving or dispersing the above-mentioned light-absorbing substance, optionally a nonlinear optical material, and optionally a binder in a suitable solvent, and then applying this coating solution to the surface of the substrate. It can be formed by forming a coating film and then drying it.

Examples of such solvents include fluorine-substituted organic compounds such as fluorinated alcohols, toluene, xylene, ethyl acetate, butyl acetate, cellosolve acetate, methyl ethyl ketone, dichloromethane, 1,2-dichloroethane, chloroform, dimethylformamide, methyl isobutyl Examples include solvents that can dissolve dyes, such as ketones, cyclohexanone, cyclohexane, tetrahydrofuran, ethyl ether, dioxane, ethanol, n-propanol, isopropanol, and n-butanol.

Examples of binders include natural organic polymer substances such as gelatin, cellulose derivatives, dextran, rosin, and rubber; and hydrocarbon resins such as polyethylene, polypropylene, polystyrene, and polyisobutylene, polyvinyl chloride, polyvinylidene chloride, and polychloride. Vinyl resins such as vinyl/polyvinyl acetate copolymers, acrylic resins such as polymethyl acrylate and polymethyl methacrylate, polyvinyl alcohol, chlorinated polyethylene, epoxy resins,
Examples include synthetic organic polymeric substances such as butyral resins, rubber derivatives, and initial condensates of thermosetting resins such as phenol-formaldehyde resins.

The coating solution further contains antioxidants, UV absorbers, plasticizers,
Various additives such as lubricants may be added depending on the purpose.

Examples of the coating method include a spray method, a spin code method, a dip method, a roll coat method, a blade coat method, a doctor roll method, and a screen printing method.

When the recording layer contains a nonlinear optical material, the mixing ratio of the light absorbing substance and the nonlinear optical material in the coating liquid is as follows:
Generally, lO:o is in the range of 5 to 1:10 (weight ratio), preferably in the range of 10:1 to 2:5. Also,
When a binder is used in combination, the ratio of dye to binder generally ranges from 0.01 to 99% (by weight), preferably from 1.0 to 95% (by weight).

The recording layer may be a single layer or a multilayer, but the layer thickness is generally o.
, in the range of oi to 10pm, preferably 0.02 to
It is in the lpm range. Furthermore, the recording layer may be provided not only on one side of the substrate but also on both sides.

The recording layer can also be formed by vapor depositing, sputtering or ion blasting a light absorbing substance and optionally a nonlinear optical material onto the surface of the substrate. The thickness of the recording layer is generally in the range of 100 to 1,500 OX, preferably in the range of 150 to 100 OX, in view of the optical density required for optical information recording.

Alternatively, the nonlinear optical material may be contained in a layer adjacent to the recording layer, and in that case, the layer containing the nonlinear optical material (nonlinear optical layer) may be a layer consisting essentially only of the material. Alternatively, it may be a layer consisting of a binder containing the material dispersed therein.

The nonlinear optical layer is prepared by preparing a coating solution by dissolving or dispersing the nonlinear optical material, materials, and optionally a binder in an appropriate solvent, and then applying this coating solution to the surface of the substrate or the recording layer to form a coating film. It can be formed by drying after forming. This nonlinear optical layer may be provided on either side of the recording layer as long as it is in contact with the recording layer.

The solvent and binder can be selected from among the solvents and binders that can be used in the recording layer described above. In addition, when a binder is used in combination, the ratio of the nonlinear optical material to the binder is generally 10 to 500% (weight ratio).
It is preferably in the range of 50 to 300% (weight ratio).

The layer thickness of the nonlinear optical layer is generally in the range of 0.01 to 30 pm, preferably in the range of 0.02 to 5 pm.

Note that the nonlinear optical material may be contained in both the recording layer and the nonlinear optical layer.

A protective layer may be provided on the recording layer (or nonlinear optical layer) for the purpose of physically and chemically protecting the recording layer, etc. This protective layer is provided on the substrate where the recording layer is not provided. It may also be provided on the sides for the purpose of increasing scratch resistance and moisture resistance.

Examples of materials used for the protective layer include 5iO1S i
Examples include inorganic substances such as O2 and MgF2.5n02; organic substances such as thermoplastic resins, thermosetting resins, and UV curable resins. The protective layer can be formed, for example, by laminating a film obtained by extrusion of plastic onto the recording layer (or silver salt layer or reflective layer) and/or onto the substrate via an adhesive layer. Alternatively, it may be applied by methods such as vacuum evaporation, sputtering, and coating. In the case of thermoplastic resins and thermosetting resins, the coating solution is prepared by dissolving these in an appropriate solvent, and then the coating is applied. It can also be formed by applying a liquid and drying it. In the case of a UV curable resin, it can also be formed by preparing a coating liquid as it is or by dissolving it in an appropriate solvent, applying this coating liquid, and curing it by irradiating it with UV light. These coating solutions further contain antistatic agents, antioxidants, and UV
Various additives such as absorbents may be added depending on the purpose.

The thickness of the protective layer is generally in the range 0.11-100p.

In the present invention, the information recording medium may be a single board having the above-mentioned structure, or alternatively, two substrates having the above-mentioned structure are placed facing each other so that the recording layer is on the inside, and bonded together using an adhesive or the like. Alternatively, a substrate having the above structure may be used as at least one of the two disc-shaped substrates, and a ring-shaped inner spacer and a ring-shaped outer spacer may be formed. It may also be an air sandwich type recording medium obtained by bonding through the.

Note that writing of information to the information recording medium of the present invention is performed using G.
This can be done by irradiating the surface of the recording layer with a beam of a semiconductor laser emitting near-infrared light, such as an a-As laser, to form pits in the recording layer. If a nonlinear optical layer is provided, the irradiation with the laser beam can take place from the opposite side.

When reading information from a recording medium, first a similar laser beam is irradiated onto the surface of the recording layer. If a nonlinear optical layer is provided, the irradiation with the laser beam can take place from the opposite side. The irradiated laser beam is wavelength-converted into a second harmonic (34 wavelengths) etc. by the nonlinear optical material in the recording layer or nonlinear optical layer.Then, this wavelength-converted light is detected by a detector. Can read information.

Note that it is equally effective to make the laser beam enter, record, and reproduce from the same side as the nonlinear optical layer.

At this time, if the nonlinear optical material is included as a separate layer, an information signal can be obtained based on the difference in the amount of light detected in the pit-formed portion and the pit-unformed portion. Furthermore, when a nonlinear optical material is included in the recording layer, an information signal can be obtained based on whether wavelength-converted light is detected in the pit-formed portion and the pit-unformed portion. That is, in the latter case, unlike conventional reproduction methods, information can be reproduced depending on the presence or absence (on-off) of detection light.

Examples and comparative examples of the present invention are described below. However, each of these aspects does not limit the invention.

[Example 1] Disc-shaped glass substrate (outer diameter: 130 mm, inner diameter: 15 m
A layer of A nonlinear optical layer having a thickness of 2#Lm was formed.

Next, copper phthalocyanine was vacuum deposited on the nonlinear optical layer to form a recording layer having a layer thickness of 250 Å.

In this way, an information recording medium consisting of a substrate, a nonlinear optical layer, and a recording layer was manufactured in this order (FIG. 1).

[Comparative Example 1] An information recording medium consisting of a substrate and a recording layer was manufactured by performing the same operations as in Example 1 except that the nonlinear optical layer was not provided.

[Example 2] Disc-shaped glass substrate (outer diameter: 130 mm, inner diameter: 15 m
Co-deposited copper phthalocyanine and a nonlinear optical material (structural formula: 1:5 (pigment: nonlinear optical material, weight ratio) by vacuum evaporation method on a layer with a thickness of 1.2 mm). formed a recording layer of 100 OA.

In this way, an information recording medium consisting of a substrate and a recording layer containing a nonlinear optical material was manufactured (FIG. 2).

[Comparative Example 2] An information recording medium consisting of a substrate and a recording layer was manufactured by performing the same operation as in Example 2 except that only copper phthalocyanine was used.

[Evaluation of information recording media] Each of the obtained information recording media was irradiated with semiconductor laser light (wavelength:
830nm, irradiation power: 8mW, beam diameter: 1#Lm
) was irradiated from the recording layer side under the conditions of 0 rotation speed of 180 Orpm and recording radius of 30 mm, the laser beam was modulated and a 2 MHz recording signal was used.

A duty ratio of 50 and 50% was recorded.

Next, the semiconductor laser light (irradiation power = 1 m W
) was irradiated onto the recording medium from the recording layer side to read information. At this time, for the recording medium of the example, an optical filter was provided in front of the reading light receiver to cut off light with a wavelength of 500 nm or more, and was set so that only the second harmonic reached the light receiver. In addition, for the recording medium of the comparative example, no optical filter was installed in front of the light receiver.
The reflected light of the laser light was detected by a light receiver. The ratio of carrier to noise output levels (C/N ratio) was measured.

The results obtained are shown in Table 1.

Table 1 Examples! Comparative example 1 C/N ratio (dB) 54 47 Example 2
Comparative Example 2 C/N ratio (dB) 51 46 As is clear from the results shown in Table 1, the information recording medium of the present invention (Example 1) having a nonlinear optical layer and the recording layer containing a nonlinear optical material The included information recording media of the present invention (examples?) all have a C/N during reading compared to conventional information recording media that do not include nonlinear optical materials (Comparative Example 1.2). The ratio was significantly high.

[Brief explanation of the drawing]

FIG. 1 and FIG. 2 are sectional views each showing an example of the structure of an information recording medium according to the present invention. 2: a nonlinear optical layer; 3: a recording layer; 3': a recording layer containing a nonlinear optical material;

Claims (1)

[Claims] 1. Writing information on the substrate by laser and/or
Alternatively, an information recording medium provided with a readable recording layer, characterized in that a layer adjacent to the recording layer contains a nonlinear optical material. 2. Writing information on the board using a laser and/or
Alternatively, an information recording medium provided with a readable recording layer, characterized in that the recording layer contains a nonlinear optical material.