1. Field of the Invention
The present invention relates to media suitable for use in optical information recording by using holography, a method for recording optical information in the medium and/or playing back optical information from the medium by using holography, and a method for manufacturing the optical information recording media.
2. Description of Related Art
Optical information recording media have been known as one of large-capacity recording media available for recording a mass of data such as high density image data. While rewritable optical mediums such as a magnetic optical disk and a phase change optical disk and recordable optical mediums such as CD recordable (CD-R) have been in practical use, there is a strong demand for large-capacity optical information recording mediums Conventional optical information recording media are used for two-dimensional recording, and there is a definite ceiling to a capacity increase. Therefore, in recent years, holographic recording media are remarked as a three-dimensional recording medium.
Holographic recording for recording optical information in an optical information recording medium by using holography utilizes interference fringes generated inside the recording medium by superposition of information light carrying image information that has a two-dimensional intensity distribution and reference light that is uniform in intensity so as to cause an optical characteristic distribution, thereby recording the information in the form of the interference fringes. In order to reproduce or play back the information, reference light is applied to the optical information recording medium so as to be diffracted by the interference fringes and outgoes as reproducing light having an intensity distribution corresponding to the optical characteristic distribution.
The holographic recording medium is capable of recording optical characteristic distributions three-dimensionally therein and, in consequence, capacitated for multiplex recording, i.e. to partly superpose areas where information are recorded by separate information light When employing the multiplex recording in the digital volume holography, it is possible to reproduce original information with a high degree of fidelity despite of an inferior signal to sound ratio (SN ratio). This is because an SN ratio for one spot is considerably enhanced. Consequentially, it is possible to perform hundreds of times of multiple recording, so that a greater storage capacity can be obtained in the optical information recording medium.
The optical information recording disk made by such an infusion method possibly encounters shrinkage of the holographic recording layer during curing, so that the holographic recording layer becomes uneven in thickness. More specifically, the holographic recording layer, that has a thickness of approximately 600 μm, thins down at a central part as compared with a marginal part.
There has been proposed a holographic optical information recording disk such as described in, for example, Publication of Japanese Patent Application No. 2004-29476. This optical information recording disk has a structure having a holographic recording layer held between two disk-shaped holding substrates which contains a photo able organic material and has an outer marginal part not involved in holographic recording is previously cured with ultraviolet light. However, since the cured holographic recording layer is in a gel resin state, it is uneven in thickness between an inner marginal part and the outer marginal due to resin contraction and external stress. Consequentially, the holographic optical information recording medium encounters uneven recording performance and deterioration in the degree of multiplexing. In addition, it is unclear where a boundary between areas available and unavailable for recording of the holographic recording layer is, so that it is impossible to figure out an accurate storage capacity of the optical information recording medium
It is an object of the present invention to provide a holographic optical information recording medium having a holographic recording layer that has a uniform and most appropriate thickness in which high density image information is recorded.
It is another object of the present invention to provide a holographic optical information recording medium having a holographic recording layer that is cured without air holes left therein.
It is still another object of the present invention to provide a method for manufacturing a holographic optical information recording medium at a high manufacturing efficiency.
It is a further object of the present invention to provide an optical information recording method, as well as an optical information reproducing method.
In accordance with one aspect of the present invention, the foregoing objects are accomplished by a method for manufacturing an optical information recording medium having a recording layer between a transparent top substrate and a bottom substrates in which optical information is recorded by the use of holography, which comprises the steps of forming a retention recess having a specified depth by either one of the transparent top substrate and the bottom substrate and spacer means secured thereto for receiving a holographic recording material there filling the retention recess with the holographic recording material, curing the holographic recording material in the retention recess with, for example, heat to form the holographic recording layer, preferably having a thickness greater than 100 μm, and bonding the other of the transparent top substrate and the bottom substrate to the holographic recording layer and the spacer means. The retention recess is preferably filled with the holographic recording material as much as the cured holographic recording layer is flush with the spacer means.
In the case where the optical information recording medium is in the shape of a disk having a spindle hole, the spacer means may comprise an annular inner spacer provided around the spindle hole of the optical information recording medium and an annular outer spacer provided along a periphery of the optical information recording medium. Further, the retention recess may be formed by the transparent top substrate and the annular inner spacer and the annular outer spacer. Otherwise, the retention recess may be formed by the bottom substrate and the annular inner spacer and the annular outer spacer.
In accordance with anther aspect of the present invention, the foregoing objects are accomplished by an optical information recording medium for recording optical information in a holographic recording layer thereof by the use of holography, which comprises a transparent top substrate, a bottom substrates and spacer means secured to either one of the transparent top substrate and the bottom substrate and spacer means for forming a retention recess having a specified depth on the one substrate, wherein a holographic recording material is filled and cured so as to form a holographic recording layer and subsequently the other of the transparent top substrate and the bottom substrate is secured to the holographic recording layer and the spacer means. The retention recess is filled with the holographic recording material as much as the cured holographic recording layer is flush with the spacer means.
In the case where the optical information recording medium is in the shape of a disk having a spindle hole, the spacer means may comprise an annular inner spacer provided around the spindle hole of the optical information recording medium and an annular outer spacer provided along a periphery of the optical information recording medium. Further, the retention recess may be formed by the transparent top substrate and the inner and the outer annular spacer, or otherwise by the bottom substrate and the inner and the outer annular spacer.
For recording information in the optical information recording medium, the optical information recording medium is irradiated with information-bearing light and reference light coaxial with each other so as thereby to generate interference fringes in the holographic recording layer by superposition between the information-bearing light and the reference light.
The information having been recorded in the holographic recording layer is reproduced by irradiating the optical information recording medium with reference light so as to regenerate information bearing-reproduction light from the holographic recording layer.
The foregoing and other objects and features of the present invention will be clearly understood from the following detailed description when read with reference to the accompanying drawing, in which:
The following detailed description will be directed to a method for manufacturing an optical information recording medium. Though the optical information recording medium is not described with specific embodiments thereof separately but will be intelligible from the description of the optical information recording medium manufacturing method.
A method for manufacturing an optical information recording medium comprises the steps of curing process, a bonding process and, if necessary, other processes.
The curing process is a process for curing a holographic recording layer in a retention recess defined by one of a top and a bottom substrate and inner and outer annular spacers.
The substrate, top or bottom, is not bounded by shape, structure and size and may be designed appropriately according to applications of the optical information recording medium. The substrate is preferably made in the shape of a disc or a card. It is preferred for the substrate to be made of a material capable of providing sufficient mechanical strength for the optical information recording medium. At least one of the substrates at an incident side through which a beam enters and impinges the holographic recording layer is to have sufficiently high transmittance for wavelengths of recording and reproducing or playback light
Examples of the substrate material include glass, ceramics, resins, etc. Among them, resins are preferred in terms of moldability and cost. The resins are not bounded by type and may be selected appropriately according to purposes or applications of the optical information recording medium. Examples of the resins include acetate resins such as triaccetylcellulose, polyester resins, polyethersulfone resins, polysulfone resins, polycarbonate resins, polyamide resins, polyimide resins, polyolefin resins, acryl resins, polynorbomen resins, cellulosic resins, polyallylate resins, polystyrene resins, polyvinyl alcohol resins, polyvinyl chloride resins, polyvinyliden chloride resins, polyacrylic resins, etc. These resins may be synthesized or products on the market and may be used individually or in any combination of two or more.
The substrate is provided with a plurality of radial linear address servo areas, which serve as locating regions, arranged at regular angular intervals so as to form a sector-shaped data area between each circumferentially adjacent radial linear address servo areas. Each address servo area has focusing/tracking servo information and address information previously formed by emboss pits (servo pits) which enables focusing and tracking servo control operation in a sampled servo method. In this instance, the focusing servo may be performed by using a reflective surface of the reflection layer. It is possible to employ, for example, wobble pits for the tracking servo information. When the optical information recording medium takes the shape of a card, the substrate is not always necessary to have patterned servo pits.
The substrate is not bounded by molding process and may be molded by various processes known in the art such as film molding, extrusion molding, injection molding, blow molding, compression molding, transfer molding, calender forming, thermoforming, flow molding, laminate molding, and compression molding using a metalic mold according to purposes or applications of the optical information recording medium. Among them, it is especially preferred to employ extrusion molding or injection molding in terms of superior manufacturing efficiency. The substrate is not bounded by thickness and may have an appropriate thickness, preferably in a range from 0.3 to 2 mm, according to purposes or applications of the optical information recording medium. The substrate possibly causes uncontrollable deformation during storage if having a thickness less than 0.1 mm and makes the whole optical information medium too heavy to load a drive motor in excess if having a thickness greater than 5 mm.
The annular spacers are provided on outer and inner rims of the substrate so as to retain a desired thickness of the holographic recording layer. One of the inner and outer annular spacers, especially the inner annular spacer, may not be provided if it is convenient. The annular spacer, inner or outer, is not bounded by shape, size and material and may be designed appropriately according to applications of the optical information recording medium. Specifically, the annular spacer may have a cross section shaped such as, for example, square, rectangular, trapezoidal or elliptical and a thickness preferably in a range from 100 to 100 μm in a general way, and may be preferably made of the same material as the substrate.
These annular spacers may be provided on either one or both of the top and bottom substrates. In the case where the annular spacers are provided on the bottom substrate, there is a problem encountered by the optical information recording medium that a gap layer and a filter layer or selective reflection layer crinkle due to a strain of an adhesive layer caused by stress produced by cure shrinkage of the holographic recording layer. This results from such a structure that the selective reflection layer is coated on a polycarbonate sheet bonded as the gap layer of the bottom substrate by means of the adhesive layer and the holographic recording layer is formed and cured on the selective reflection layer. However, because the top substrate is not provided with both of a gap layer and a selective reflection layer, it is preferred to provide the annular spacers on the top substrate so as to form a retention recess for a holographic recording material. The annular spacers may be previously prepared and then bonded to the substrate or may be integrally molded as a single-piece substrate. When the annular spacers are made of a resin, they may be formed by the same molding method as the substrate.
The retention recess, formed on the top substrate or the bottom substrate, is filled with a holographic recording material. It is preferred to load an amount of holographic recording material sufficient enough to form a uniform and appropriate thickness of a cured holographic recording layer on the same level as the annular spacers. This is synonymous with that the loading amount of a holographic recording material should be determined counting in cure contraction of the holographic recording material.
The holographic recording material is not bounded by type and may be selected appropriately according to purposes or applications of the optical information recording medium. Examples of the holographic recording material include photopolymers which are polymerized by irradiated light, photorefractive materials which are modulated in refractive index by a space charge distribution caused by irradiated light, photochromic materials which are modulated in refractive index due to isomerization of molecules caused by irradiated light, inorganic materials such as a lithium niobate and a barium titanate, and chalcogen materials. Among them, it is especially preferred to use a photopolymer.
The photopolymer is not bounded by type and may be selected appropriately according to purposes or applications of the optical information recording medium. For example, the photopolymer may contain monomers and a photoinitiator, and, if necessary, a sensitizer, oligomers and other components.
Examples of the photopolymers include those described in “Photopolymer Handbook” (Kogyo Chosakai Publishing: 1989); “Photopolymer Technology” (Daily Industrial Newspapers: 1989); SPIE proceedings Vol. 3010 (1997) and Vol. 3291 (1998) of Society of Photo-Optical Instrumentation Engineers (SPIE); U.S. Pat. Nos. 4,942,112, 4,959,284, 5,759,721 and 6,221,536; Publication of International Application Nos. 97/13183, 97/44714 and 99/26112; Japanese Patent Nos. 2849021, 2873126, 2880342, 3057082 and 3161230; and Publication of Japanese Patent Application Nos. 2000-275859 and 2001-316416.
Examples of a method for changing optical characteristics of the holographic recording layer with information light include a method using diffusion of a low molecular weight component. The holographic recording layer may be added with a component that diffuses in a direction opposite to a polymerizing component in order to alleviate a volume change during polymerization or may be added with a compound having an acid cleavage structure in addition to a polymer. In the case where a photopolymer containing the low molecular weight component is used for the holographic recording layer, some holographic recording layers are required to have a liquid retention substrate therein. Further, when adding a compound having an acid cleavage substrate, a volume change can be controlled by compensating expansion due to cleavage and concentration due to polymerization of monomers.
The monomers are not bounded by type and may be selected appropriately according to purposes or applications of the optical information recording medium. Examples of the monomers include radical polymerization type monomers having an unsaturated bond such as an acryl group or a methacryl group and cationic polymerization type monomers having an ether structure such as an epoxy ring or an oxetane ring. These monomers may be monofunctional or multifunctional. Further, they may be of a type utilizing a bridging reaction Examples of the radical polymerization type monomers include acryloyl morpholine, phnoxyethyl acrylate, isobornyl acrylate, 2-hydroxypropyl acrylate, 2-ethylhexyl acrylate, 1,6-hexanediol diacrylate, tripropylene glycol diacrylate, diacrylate of propylene modified neopentyl glycol 1,9-nonandiol diacrylate, hydroxypivalate neopentyl glycol diacrylate, diacrylate of ethylene oxide modified bisphenol A, polyethylene glycol diacrylate, pentaerythritol triacrylate, pentaerythritol tetraacrylate, pentaerythritol hexaacrylate, triacrylate of ethylene modified glycerol, trimethylolpropane acrylate, triacrylate of ethylene modified trimethylolpropane, 2-naphtol-1-oxyethyl acrylate, 2 carbazole-9-iy lethyl acrylate, (trimethysilyloxyl) dimethylsilyl propyle acrylate, vinyl-1-naphthoate, N-vinylcatbazole, etc. Examples of the cationic polymerization type monomers include bisphenol A epoxy resins, phenol novolac epoxy resins, grycerol triglycidyl ethers, 1,6-hexanglycidyl ethers, vinyl trimethoxy shiran, 4-vinylphenyl trimethoxyshiran, γ-methacryloxy-propyl triethoxyshiran, and compounds expressed by the following constitutional formulas (A) to (E). These monomers may be used individually or in any combination of two or more.
The photoinitiator is not bounded by type as long as it has a sensitivity to information light and may be of a type causing radical polymerization, cationic polymerization, bridging reason. Examples of the photoinitiator include 2,2′-bis(o-chlorophenyl)-4,4′,5,5′-tetraphenyl-1,1′-tetrafluoroborate; diphenyliodunium hexafluorophosphate, 4,4′-di-t-butyl diphenyl iodonium tetrafluoroborate; 4-diethyl aminofenylbenzene diazonium hexafluorophosphate; benzoin, 2-hydroxy-2-methyl-1-phenylpropan-2-on; benzophenone; thioxanthene; 2,4,6-trimethylbenzoil diphenylacyl phosphine oxide; triphenylbutyl borate tetraethyl ammonium; and compounds expressed by the following constitutional formula (F).
The photorefractive materials are not bounded by type as long as it shows a photorefractive effect and may be selected appropriately according to purposes or applications of the optical information recording medium. For example, the photorefractive material may comprise a charge generating material and transportation material and, if necessary, other components.
Examples of the charge generating material include phthalocyanine pigments/dyes such as metallic phthalocyanine, nonmetallic phthalocyanine and derivatives of them; naphthlocyanine pigments/dyes; azo pigments/dyes such as monoazo, disazoand trisazo; perylene pigments/dyes indigo pigments/dyes; quinacridone pigments/dyes; polycyclic quinone pigments/dyes such as anthraquinone and anthanthrone; cyanine pigments/dyes; charge transfer complexes as typified by TTF-TCNQ comprising an electron receptive material and an electron releasing material; azulenium salts; fullerene as typified by C60 and C70; and methanofullerene that is a derivative of fullerene. These charge generating materials may be used individually or in any combination of two or more.
The charge transport material, that is a material for transporting holes or electrons and may comprise a low molecular compound or a low molecular compound, is not bounded by type. Examples of the charge transport material include nitrogen-bearing cyclic compounds such as indole, carbazole, oxazole, inoxazole, thiazole, imidazole, pyrazole, oxadiazole, pyrazoline, thia-thiazole, triazole; derivatives of the nitrogen-bearing cyclic compounds; hydrazone compounds; triphenylamine; triphenylmethane; butadiene; stilbene; quinine compounds such as anthraquinone diphenoquinone; derivatives of the quinine compounds; fullerene such as C60 and C70; derivatives of the fullerene; π-conjugated polymers or oligomers such as polyacetylene, polypyrrole, polythiophene and polyaniline; conjugated polymers or oligomers such as polysilane and polygermane; and polycyclic aromatic compounds such as anthracene, phenanthrene and coronene. These charge transport materials may be used individually or in any combination of two or more.
The photochromic material is not bounded by type as long as it causes photochromic reaction and may be selected appropriately from various materials such as azobenzene compounds, stilbene compounds, indigo compounds, thioindigo compounds, spiropyran compounds, spirooxazin compounds, fulgide compounds, anthracene compounds, hydrazone compounds and cinnamic acid compounds according to purposes or applications of the optical information recording medium. Among them, it is preferred to use azobenzene derivatives or stilbene derivatives which cause a structure change due to this-trans isomerization by irradiated light, or spiropyran derivatives or spirooxazin derivatives which cause ring opening-ring closing structure change by irradiated light.
Examples of the chalcogen materials include materials comprising chalcogenide glass containing a chalcogen element sand metal particles dispersed in the chalcoenide glass which are able to be diffused in it by irradiated light. The chalcogenide glass is not bounded by type as long as it is made of a nonoxide amorphous material containing a chalcogen element such as S, Te or Se and capable of being photo-doped with metal particles. Examples of the amorphous material containing a chalcogen element include Ge—S glass, As—S glass, As—Se glass, As—Se—Ce glass. Among them, it is preferred to use Ge—S glass. When using a Ge—S chalcogenide glass, although the composition ratio of Ge and S can be varied according to a wavelength of irradiated light it is preferred for Ge—S chalcogenide glass to have a chemical composition represented by GeS2.
The metal particles are not bounded by type as long as they are capable of being photo-doped in the chalcogenide glass and may be selected appropriately from particles of various metals such as Al, Au, Cu Cr. Ni, Pt, Sr, In, Pd, Ti, Fe, Ta, W, Zn and Ag according to purposes or applications of the optical information recording medium. Among them, it is preferred to use Ag, Au or Cu in terms of photodoping adaptability and, especially, Ag in terms of distinguished photo-doping adaptability. The metal particle content of the chalcogenide glass is preferably in a range of from 0.1 to 2% by volume, and more preferably in a range of from 0.1 to 1.0% by volume, with respect to the whole holographic recording layer. If the metal particle content is less than 0.1% by volume, the holographic recording layer possibly encounters deterioration of recording accuracy due to insufficiency of a change in transmittance by photo-doping. If the metal particle content is beyond 2% by volume, the holographic recording layer has photo transmittance too low to cause photo-doping sufficiently.
The holographic recording layer can be formed by various methods known in the art such as an injection method, a deposition method, a wet coating method; a molecular beam epitaxy (MBE) method, a cluster ion beam method, a molecular lamination method, a laser beam method, a printing method and a transfer method. Among them, it is preferred to form the holographic recording layer by the injection method or the wet coating method. The injection method is performed by using a dispenser. The wet coating method is well performed by using a coating liquid with a holographic recording material dissolved or dispersed therein. The wet coating method is not bounded by type and may be selected from among, for example, an inkjet coating method, a spin coating method, a kneader coating method, a bar coating method, a blade coating method, a cast coating method, a dip coating method and a curtain coating method.
Curing of the holographic recording layer is not bounded by type and may be performed by various methods known in the art such as ultraviolet curing and heat curing. It is preferred to cure the holographic recording layer at a temperature of from 60 to 200° C. for from one to 24 hours. According to the method for manufacturing the optical information recording medium of the present invention in which the holographic recording layer formed on one of the top and bottom substrates is cured before it is covered by the other substrate, bubbles are efficiently removed from the holographic recording material during curing and no air holes remains in the holographic recording layer.
The bonding process is performed to bond one of top and bottom substrates (for example the top substrate) to the other substrate (i.e. the bottom substrate) with the holographic recording layer formed thereon after the holographic recording layer has been cured. The top substrate is bonded to the inner and outer annular spacers and the cured holographic recording layer with an adhesive taking care not to allow bubbles to enter inside the top substrate. The adhesive is not bounded by type and may be selected appropriately various adhesives known in the art such as rubber-base adhesives, silicone adhesives, acrylic adhesives, urethane adhesives, vinyl alkyl ether adhesives, polyvinyl alcohol adhesives, polyvinyl prrolidone adhesives, polyacrylamide adhesives and cellulosic adhesives according to purposes or applications of the optical information recording medium.
The other process performed as needed include a reflection layer forming process. A filter layer forming process, a first gap layer forming process and a second gap layer forming process.
The optical information recording medium manufactured as described above is adapted to have the holographic recording layer adjusted uniformly and appropriately in thickness, more specifically, preferably greater than 100 μm and more preferably in a range from 100 to 900 μin in thickness. The holographic recording layer provides a sufficient SN ratio even 10 to 300 multiple shift recording is performed when having the preferred thickness and a more enhanced SN ratio when having the more preferred thickness.
The method for manufacturing the optical information recording medium, taking the form of a disk, will be specifically described with reference to FIGS. 4 to 8.
As shown in
In this embodiment just described above, the terms “top” and “bottom” can be transposed each other. In other words, the retention recess 106 may be formed on the top substrate 101. In this case, the gap layer and the filter layer provided on the bottom substrate 102 are prevented from causing crinkles due to cure contraction of a holographic recording material.
The optical information recording medium of the present invention will be described in detail below. The optical information recording medium comprises a holographic recording layer, a filter layer, a reflection layer, first and second gap layers, and, additionally, other layers as appropriate, formed between a top and a bottom substrates.
The holographic recording layer is made of a material capable of varying optical characteristics such as optical absorptivity, refractive index or the like according to intensity of specified electromagnetic wave lengths and formed in a uniform and appropriate thickness by the method just described above.
The filter layer, that is provided between the bottom substrate and the holographic recording layer, is adapted to transmit a specified wavelength of fight, for example red light, (which is hereafter referred to as first light) and to reflect a specified wavelength of light different from the first light, for example green light, (which is hereafter referred to as second light). The filter layer has a thickness preferably in a range of from 1 to 30 μm and more preferably in a range of from 3 to 10 μm. Preferred examples of the filter layer is a dichroic mirror layer or a cholesteric liquid crystal layer. The cholesteric liquid crystal layer comprises at least a nematic liquid crystal compound and a chiral compound and, if necessary, a polymerizable monomer and other components. A preferred cholesteric liquid crystal layer has a function of circular polarized light separation. Such the cholesteric liquid crystal layer selectively reflects a circular polarized light component that the circular polarized light has a polarization direction coincide with a rotative direction of spiral of the liquid crystal and a wavelength coincide with the pitch of spiral of the liquid cal. Therefore, the cholesteric liquid crystal layer is constructed such that it transmits circular polarize light having a specified wavelength (red light in this case) and reflects the remaining circular polarized light (green light), thereby separating two beams of circular polarized light from available light in a specified band of wavelength utilizing the selective reflection feature.
It is preferred to set a cholesteric crystal liquid layer-bearing film on the bottom substrate. The cholesteric crystal liquid layer-bearing film is prepared by coating a cholesteric crystal liquid over a backing, orienting and solidifying the coated cholesteric crystal liquid and then punching out the backing into the same disk-shape as the retention recess of the bottom substrate. It is of course allowed to coat a cholesteric crystal liquid directly on the bottom substrate
The reflection layer, that is formed over patterned servo pits on the bottom substrate, is made of a material having a high reflectivity for both information light and reference light. It is preferred to use Al, an Al alloy, Ag or an Ag alloy when employing information and reference light having wavelengths in a range of from 400 to 780 nm, or Al, an Al alloy, Ag, an Ag alloy, Au, A Cu alloy or TiN when employing information and reference light having wavelengths longer than 650 nm.
The reflection layer may be composed of a dye type recording layer such as used for DVD-R so that the optical information recording medium is made capable of writing or rewriting directory information such as a hologram recorded area, a rewritten time, an error location, an alteration proceeding and the like in the reflection layer and erasing them using red laser light without having an effect on hologram in the holographic recording layer, beside reflecting red laser light.
Formation of the reflection layer is not bounded by forming process and may be performed by various vapor-phase growth known in the art such as vacuum deposition, spattering, plasma chemical vapor deposition (CVD), photo chemical vapor deposition (CVD), ion plating and electronic beam vapor deposition according to applications of the optical information recording medium. Among them, it is preferred to employ spattering in terms of commercial production adaptability and coating quality. The reflection layer has a thickness preferably greater than 50 nm and more preferably greater than 100 nm in terms of satisfactory reflectivity.
The first gap layer is formed between the filter layer and the reflection layer as appropriate in order to smooth out the top surface of the bottom substrate, and besides to adjust a size of a hologram produced in the holographic recording layer. Because it is required for the holographic recording layer to have a region where information and reference light interfere adjusted to a certain extent, it is effective to provide a gap between the holographic recording layer and the patterned servo pits. The first gap layer is not bounded by thickness and may have a thickness preferably in a range of from 1 to 200 μm according to purposes or applications of the optical information recording medium.
The second gap layer is formed between the filter layer and the holographic recording layer as appropriate. The first gap layer is not bounded by material and may be made of a transport resin film or a norbomen resin film. Examples of such a film material include triacetylcellulose (TAC), polycarbonate (PC), polyethylene terephthalate (PE), polystyrene (ES), polysulfone (PSF), polyvinyl alcohol (PVA), methyl polymethacrylate-polymethylmethacrylate (PMMA), ARTON (trade name) which is produced by JSR and Zeonoa (trade name) which is produced by Nihon Zeon Co., Ltd. according to purposes or applications of the optical information recording medium. The second gap layer is not bounded by thickness and may have a thickness preferably in a range of from 1 to 200 μm according to purposes or applications of the optical information recording medium.
The optical information recording medium may be disk-sed or card-shaped. A card-shaped optical information recording medium may not be provided with patterned servo pit clusters. When the optical information recording medium 21 is 1.9 mm in thickness, the bottom substrate 1, the gap layer 8, the filter layer 6, the holographic recording layer 4 and the top substrate 5 are 0.6 mm, 100 μm, 2 to 3 μm, 0.6 mm and 0.6 mm in thickness, respectively.
Referring to
Recording information in the optical information recording medium 22 or reproducing the information from the optical information recording medium 22 is performed using the optical information recording/reproducing apparatus shown in
As is apparent from the above description, recording information in the optical information recording medium 21 or 22 is performed by generating interference fringes inside the holographic recording layer 4 by superposition of information-bearing light on a two dimensional intensity distribution and reference light having a nearly uniform intensity so as to record the information in the form of a distribution of optical characteristic. In order to reproduce the information, the optical information recording medium 21 or 22 is irradiated with reference light so as to be distributed by the interference fringes. Consequently, the information is reproduced in the form of the distribution of optical characteristic.
Referring to
In order to assess the optical information recording medium of the present invention, practical and comparative examples of the optical information recording medium were made by the method of the present invention illustrated in
An optical information recording medium, taking the form of a disc having a construction such as shown in
Subsequently, a holographic recording layer 4 was formed over the filter layer 6 by applying a photopolymer liquid using a dispenser (see
The cured holographic recording layer 4 was 600 μm in thickness and was flush with the inner and outer annular spacers 103 and 104 (see
An optical information recording medium, having a shell construction similar to the prior art optical information recording medium such as shown in
The optical information recording media of the practical and comparative examples were assessed on their properties including storage stability of recorded information and uniformity of thickness of the holographic recording layer. The result of assessment is shown in Table.
The storage ability was estimated on whether a problem of information reproduction was encountered by the optical information recording media of the practical and comparative examples that were subjected to an accelerated preservation test at a temperature of 60° C. and a relative humidity of 90% for one week and graded according to the following standards.
⊚: Very good in storage ability
∘: Good in storage ability
Δ: Poor in storage ability (practically acceptable)
X: Very poor in storage ability (practically unacceptable)
The uniformity of thickness of the holographic recording layer was estimated on circumferential and radial distributions of thickness of the holographic recording layer peeled off from the base substrate determined using a non-contact laser film thickness meter and graded according to the following standards.
◯: Thickness is uniform at both inner and outer parts
X: Thickness varies
As apparent from the description, the optical information recording medium of the present invention has the holographic recording layer uniform and appropriate in thickness and is capable of recording information at a significant high density by coaxial irradiation of information-bearing light and reference light. Furthermore, the optical information recording medium of the present invention is manufactured at a high efficiency.
While the exemplary embodiments described above are presently preferred, it should be understood that the embodiments are offered by way of example only. Accordingly, the present invention is not limited to a particular embodiment, but extends to various modifications that nevertheless fall within the scope of the appended claims.
Number | Date | Country | Kind |
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2005-120341 | Apr 2005 | JP | national |