JP7310316B2 - volume hologram, retinal scanning display, head-mounted display - Google Patents

Description

The present invention relates to volume holograms, retinal scanning display devices, and head-mounted display devices.

2. Description of the Related Art A retinal scanning display device that scans a laser beam from a laser light source and draws images directly on the retina is known (for example, Patent Document 1). Patent Literature 1 discloses an example of using a volume hologram as a deflection section that deflects the direction of laser light toward the eye. By using a volume hologram, it is possible to reduce the size of the apparatus as compared with the case of using a concave mirror. In addition, since the laser light has an extremely narrow wavelength band and is substantially single wavelength light, and the volume hologram also has wavelength selectivity, only the wavelength of the laser light is diffracted and reflected by the volume hologram. of light can be easily transmitted.

However, when the volume hologram expands or shrinks due to temperature changes, the peak wavelength of the light diffracted and reflected by the volume hologram changes, making it impossible to obtain the desired diffraction efficiency. There is a risk that the color balance of the image may be out of alignment.

JP 2010-117542 A

SUMMARY OF THE INVENTION An object of the present invention is to provide a volume hologram and a retinal scanning display device capable of suppressing changes in diffraction efficiency caused by temperature changes.

The present invention solves the above problems by means of the following solutions. In order to facilitate understanding, reference numerals corresponding to the embodiments of the present invention will be used for explanation, but the present invention is not limited thereto.

A first invention is a volume hologram (30) used as a deflector (30) for deflecting image light of an optical engine using a laser light source (10), wherein the spectral distribution curve has a half width of 5 nm or more. Volume hologram (30).

The second invention is used in a retinal scanning display device that scans laser light from a laser light source (10) and directly draws images on the retina, and as a deflector (30) that deflects the direction of the scanned laser light. A volume hologram (30) to be used, the volume hologram (30) having a half width of 5 nm or more in a spectral distribution curve.

A third invention is the volume hologram (30) according to the first invention or the second invention, wherein when the film thickness of the volume hologram (30) is t (μm) and the refractive index modulation amount is Δn, , Δn≧−5×10 ⁻⁶ t ² +0.003t+0.0007, provided that when t≧30 μm, the relationship Δn≧0.005 is satisfied.

A fourth invention is the volume hologram (30) according to any one of the first invention to the third invention, wherein the film thickness of the volume hologram (30) is t (μm) and the refractive index modulation amount is Δn A volume hologram (30) characterized by satisfying the relationship Δn≦0.0641t ^(−1.049) when .

A fifth invention is the volume hologram (30) according to any one of the first invention to the fourth invention, wherein the emission angle of the laser beam incident on the volume hologram (30) at the incident angle θ ₁ is θ ₂ , θ 2 ≤ 0.3214 θ ₁ +234.75 and θ ₂ ≥ -θ _{1 +118 within the range of 0° ≤ θ 1 ≤ 85° and 100° ≤ θ 2 ≤ 260 °} A volume hologram (30) characterized in that it satisfies both relations of .33.

A sixth invention is the volume hologram (30) according to the fifth invention, characterized in that when θ ₂ ≧160°, the relationship θ ₂ ≦82.436 θ1 ^(0.2278) is satisfied. Volume hologram (30).

A seventh invention is a volume hologram (30) according to the fifth invention, characterized in that when θ ₂ <160°, the relationship θ ₁ ≧40° is satisfied. be.

An eighth invention is the volume hologram (30) according to any one of the first invention to the seventh invention, wherein the emission angle of the laser beam incident on the volume hologram (30) at the incident angle θ ₁ is θ ₂ , satisfying the relationship θ ₂ ≥ 65.549ln(θ ₁ )-170.32 within the ranges of 0° ≤ θ ₁ ≤ 85° and 100° ≤ θ ₂ ≤ 260°; A volume hologram (30) characterized by

A ninth invention is a retinal scanning display device (1) including the volume hologram (30) according to any one of the first to eighth inventions in a deflection section (30).

A tenth invention includes the volume hologram according to any one of the first invention to the eighth invention in a deflection section (30), and the deflection section (30) is provided on a transparent member to provide a see-through hologram. A head-mounted display device that allows observation by superimposing a display on the field of view.

According to the present invention, it is possible to provide a volume hologram and a retinal scanning display device capable of suppressing changes in diffraction efficiency due to temperature changes.

1 is a diagram showing an overview of a retinal scanning display device 1, which is a first embodiment of a head-mounted display device using a volume hologram according to the present invention; FIG. FIG. 4 is a diagram showing a distribution of diffraction efficiency with respect to wavelength when the volume hologram 30 has extremely high wavelength selectivity; 3 is a diagram showing an example of diffraction efficiency distribution at 20° C. of the volume hologram 30 used in the deflection unit 30 in this embodiment. FIG. 4 is a diagram showing the diffraction efficiency distribution at 40° C. of the volume hologram 30 used in the deflector 30 in this embodiment. FIG. 3 is a diagram showing the distribution of diffraction efficiency at 0° C. of the volume hologram 30 used in the deflector 30 in this embodiment. FIG. FIG. 4 is a diagram showing diffraction efficiency distribution curves with half-value widths of 5 nm, 10 nm, and 20 nm; It is a figure which shows simulation conditions. FIG. 10 is a diagram summarizing the results of a simulation in which the half-value width was obtained by changing the film thickness t and Δn; 5 is a graph of an approximation formula showing a preferable combination range of the film thickness t and Δn obtained from the half-value width; FIG. 10 is a diagram summarizing the results of a simulation in which the maximum value of diffraction efficiency was obtained by changing the film thickness t and Δn; 4 is a graph of an approximation formula showing a preferable combination range of film thickness t and Δn obtained from the maximum value of diffraction efficiency; It is a figure which shows the simulation conditions which paid its attention to an incident angle and an output angle. FIG. 10 is a diagram summarizing the results of a simulation in which the half-value width was obtained by changing the incident angle θ ₁ and the output angle θ ₂ ; 5 is a graph of an approximation formula showing a preferable combination range of the film thickness t and Δn obtained from the half-value width; FIG. 10 is a diagram summarizing the results of a simulation in which the maximum value of diffraction efficiency was obtained by changing the incident angle θ ₁ and the output angle θ ₂ ; 3 is a graph of an approximation formula showing a preferable combination range of the incident angle θ ₁ and the output angle θ ₂ obtained from the maximum value of diffraction efficiency. FIG. 10 is a diagram showing a head-mounted display device 2 according to a second embodiment; FIG. FIG. 11 is a diagram showing a head-mounted display device 3 according to a third embodiment;

BEST MODE FOR CARRYING OUT THE INVENTION The best mode for carrying out the present invention will be described below with reference to the drawings.

(First embodiment)
FIG. 1 is a diagram showing an outline of a retinal scanning display device 1, which is a first embodiment of a head-mounted display device using a volume hologram according to the present invention.
Each figure shown below including FIG. 1 is a schematic diagram, and the size and shape of each part are shown exaggerated or omitted as appropriate for easy understanding.
Also, in the following description, specific numerical values, shapes, materials, and the like are shown and described, but these can be changed as appropriate.
It should be noted that the specific numerical values defined in the specification and claims should be treated as including a general error range. That is, the difference of about ±10% is substantially no difference, and the numerical value set in a range slightly exceeding the numerical range of the present invention is substantially the difference of the present invention. should be interpreted as being within range.

The retinal scanning display device 1 includes a laser light source 10, a scanning unit 20, and a deflecting unit 30. The scanning unit 20 scans the laser light from the laser light source 10 in two directions perpendicular to each other, thereby scanning the image of the observer. Draw directly onto the retina of eye E.

The laser light source 10 is an optical engine that emits laser light toward the scanning unit 20 . In FIG. 1, the laser light source 10 is shown as a single unit. Alternatively, an optical member that forms an optical path may be arranged as necessary. The laser light source 10 is controlled by a control unit (not shown), and is scanned by a scanning unit 20 to be described later to emit laser light having an intensity and a color corresponding to pixels of an image drawn on the retina.

The scanning unit 20 is controlled by a control unit (not shown) to scan laser light in two orthogonal directions corresponding to an image to be drawn on the retina. The scanning unit 20 can be composed of, for example, a MEMS (Micro Electro Mechanical Systems) mirror.

The deflection unit 30 diffracts and deflects the laser light scanned by the scanning unit 20 and directs it to the retina of the eye E of the observer. The laser light deflected by the deflection unit 30 is set to converge and pass through the center of the pupil, and reaches the retina for observation without being deflected by the crystalline lens (lens) of the eye E. visible by a person.
The deflection unit 30 of this embodiment is configured using a volume hologram 30 . The deflector 30 is arranged over a support (not shown) such as a glass plate. In addition, instead of using a glass plate as a substrate, a substrate made of PET (polyethylene terephthalate) resin, PC (polycarbonate) resin, COP (cycloolefin polymer) resin, PVA (polyvinyl alcohol) resin, thiourethane resin, etc. is used. may be used. By constructing the retinal scanning display device 1 in the form of, for example, glasses, the deflector 30 can be arranged at a position corresponding to the lens portion of the glasses. The deflection unit 30, which is composed of the volume hologram 30, has a deflection effect similar to that of an aspherical concave mirror, but is small and lightweight because it is a thin film. In this embodiment, the deflection unit 30 is entirely composed of the volume hologram 30, so the same reference numeral 30 is used in the following description.

As the hologram-forming photosensitive material for forming the volume hologram 30, for example, a known photosensitive material for the volume hologram 30 such as a silver salt material, a dichromate gelatin emulsion, a photopolymerizable resin, or a photocrosslinkable resin is used. can do.

[Photosensitive composition for volume hologram recording]
A photosensitive composition for volume hologram recording according to the present invention contains a photopolymerizable monomer, a photopolymerization initiator, a sensitizing dye that sensitizes the photopolymerization initiator, and a binder resin, The polymerizable monomers include at least photoradical polymerizable monomers and photocationically polymerizable monomers.

<Photopolymerizable Monomer>
The photopolymerizable monomer in the present invention is a compound that undergoes polymerization or dimerization reaction upon irradiation with light and that can diffuse and move in the hologram recording layer.
Examples of the photopolymerizable monomer in the present invention include photoradical polymerizable monomers, photocationically polymerizable monomers, photodimerizable compounds, and the like, including at least photoradical polymerizable monomers and photocationically polymerizable monomers .
The radical photopolymerizable monomer and the cationic photopolymerizable monomer are described below.

(Photoradical polymerizable monomer)
As the photoradical polymerizable monomer used in the present invention, when the volume hologram recording photosensitive composition of the present invention is used to form a hologram recording layer, a photoradical polymerization initiator described later may be added by, for example, laser irradiation. The compound is not particularly limited as long as it is a compound that polymerizes by the action of the generated active radical, but it is preferable to use a compound having at least one ethylenically unsaturated double bond in the molecule. Examples include unsaturated carboxylic acids, unsaturated carboxylic acid salts, esters of unsaturated carboxylic acids and aliphatic polyhydric alcohol compounds, and amide bonds of unsaturated carboxylic acids and aliphatic polyvalent amine compounds. .

Examples of the photoradical polymerizable monomers include methyl methacrylate, hydroxyethyl methacrylate, lauryl acrylate, N-acryloylmorpholine, 2-ethylhexyl carbitol acrylate, isobornyl acrylate, methoxypropylene glycol acrylate, and 1,6-hexanediol diacrylate. , tetraethylene glycol diacrylate, trimethylolpropane triacrylate, pentaerythritol triacrylate, pentaerythritol tetraacrylate, acrylamide, methacrylamide, styrene, 2-bromostyrene, phenyl acrylate, 2-phenoxyethyl acrylate, 2,3-naphthalene dicarboxylic acid Acid (acryloxyethyl) monoester, methylphenoxyethyl acrylate, nonylphenoxyethyl acrylate, β-acryloxyethyl hydrogen phthalate, phenoxypolyethylene glycol acrylate, 2,4,6-tribromophenyl acrylate, diphenic acid (2-methacryloxy ethyl) monoester, benzyl acrylate, 2,3-dibromopropyl acrylate, 2-hydroxy-3-phenoxypropyl acrylate, 2-naphthyl acrylate, N-vinylcarbazole, 2-(9-carbazolyl)ethyl acrylate, triphenylmethylthio Acrylates, 2-(tricyclo[5,2,102.6]dibromodecylthio)ethyl acrylate, S-(1-naphthylmethyl)thioacrylate, dicyclopentanyl acrylate, methylenebisacrylamide, polyethylene glycol diacrylate, trimethylol Propane triacrylate, pentaerythritol triacrylate, diphenic acid (2-acryloxyethyl) (3-acryloxypropyl-2-hydroxy) diester, 2,3-naphthalenedicarboxylic acid (2-acryloxyethyl) (3-acryloxy) propyl-2-hydroxy) diester, 4,5-phenanthenedicarboxylic acid (2-acryloxyethyl)(3-acryloxypropyl-2-hydroxy) diester, dibromo neopentyl glycol diacrylate, dipentaerythritol hexaacrylate, 1 , 3-bis[2-acryloxy-3-(2,4,6-tribromophenoxy)propoxy]benzene, diethylenedithioglycol diacrylate, 2,2-bis(4-acryloxyethoxyphenyl)propane, bis(4 -acryloxydiethoxyphenyl)methane, bis(4-acryloxyethoxy-3,5-dibromophenyl)methane, 2,2-bis(4-acryloxyethoxyphenyl)propane, 2,2-bis(4-acryloxyphenyl)methane oxydiethoxyphenyl)propane, 2,2-bis(4-acryloxyethoxy-3,5-dibromophenyl)propane, bis(4-acryloxyethoxyphenyl)sulfone, bis(4-acryloxydiethoxyphenyl)sulfone , bis(4-acryloxypropoxyphenyl)sulfone, bis(4-acryloxyethoxy-3,5-dibromophenyl)sulfone, and compounds in which acrylate is changed to methacrylate, and JP-A-2-247205. and an ethylenically unsaturated double bond-containing compound containing at least two S atoms in the molecule as described in JP-A-2-261808. They can be mixed and used.

Moreover, the average refractive index of the radically photopolymerizable monomer is preferably larger than the average refractive index of the cationic photopolymerizable monomer described later, and is preferably larger by 0.02 or more. This is because if the difference in average refractive index between the radically photopolymerizable monomer and the cationic photopolymerizable monomer is lower than the above value, the desired refractive index modulation amount (Δn) may not be obtained. .

(Photo cationic polymerizable monomer)
The cationic photopolymerizable monomer used in the present invention is a compound that undergoes cationic polymerization with a Bronsted acid or a Lewis acid generated by decomposition of a cationic photopolymerization initiator, which will be described later, when irradiated with energy. Examples include cyclic ethers such as epoxy groups and oxetane groups, thioethers, and vinyl ethers.
Further, when a radically photopolymerizable monomer and a cationic photopolymerizable monomer are used in combination, the polymerization of the radically photopolymerizable monomer is preferably carried out in a composition having a relatively low viscosity. The photo-cationically polymerizable monomer is preferably liquid at room temperature.

Examples of the photocationically polymerizable monomer include diglycerol diether, pentaerythritol polydiglycidyl ether, 1,4-bis(2,3-epoxypropoxyperfluoroisopropyl)cyclohexane, sorbitol polyglycidyl ether, and 1,6-hexane. Diol glycidyl ether, polyethylene glycol diglycidyl ether, phenyl glycidyl ether and the like can be mentioned.

In the present invention, only one of the photocationically polymerizable monomers described above may be used, or two or more of them may be used in combination.

In the photosensitive composition for volume hologram recording of the present invention, the content of the total amount of photopolymerizable monomers is 8.5 to 85 parts by mass with respect to 100 parts by mass of the total solid content of the photosensitive composition for volume hologram recording. and more preferably 8.5 to 70 parts by mass. Here, the solid content refers to components other than the solvent, and the monomers that are liquid at room temperature are also included in the solid content.
If the total content of the photopolymerizable monomers is less than the above range, a high refractive index modulation amount (Δn) cannot be obtained, and there is a possibility that a high-luminance volume hologram recording material cannot be obtained. is. On the other hand, if the content of the photopolymerizable monomer is larger than the above range, the content of the binder resin is relatively decreased, and the hologram recording layer may not be retained.

Further, in the photopolymerizable monomer in the volume hologram recording photosensitive composition of the present invention, the content ratio of the photoradical polymerizable monomer and the photocationically polymerizable monomer is The photo cationic polymerizable monomer is preferably in the range of 30 to 90 parts by mass, more preferably in the range of 50 to 80 parts by mass.

<Photoinitiator>
As the photopolymerization initiator constituting the volume hologram recording photosensitive composition of the present invention, a photoradical polymerization initiator and a photocationic polymerization initiator can be used.

(Photoradical polymerization initiator)
Photoradical polymerization initiators used in the present invention include imidazole derivatives, bisimidazole derivatives, N-arylglycine derivatives, organic azide compounds, titanocenes, aluminate complexes, organic peroxides, N-alkoxypyridinium salts, thioxanthone derivatives. and the like, and more specifically, 1,3-di(t-butyldioxycarbonyl)benzophenone, 3,3′,4,4′-tetrakis(t-butyldioxycarbonyl)benzophenone, 3-phenyl -5-isoxazolone, 2-mercaptobenzimidazole, bis(2,4,5-triphenyl)imidazole, 2,2-dimethoxy-1,2-diphenylethan-1-one (trade name Irgacure 651, manufactured by BASF) ), 1-hydroxy-cyclohexyl-phenyl-ketone (trade name Irgacure 184, manufactured by BASF), 2-benzyl-2-dimethylamino-1-(4-morpholinophenyl)-butanone-1 (trade name Irgacure 369, BASF), bis(η5-2,4-cyclopentadien-1-yl)-bis(2,6-difluoro-3-(1H-pyrrol-1-yl)-phenyl) titanium (trade name Irgacure 784, BASF Corporation), etc., but are not limited to these.

Examples of photocationic polymerization initiators include sulfonic acid esters, imidosulfonates, dialkyl-4-hydroxysulfonium salts, arylsulfonic acid-p-nitrobenzyl esters, silanol-aluminum complexes, (η6-benzene)(η5-cyclopentadienyl ) Iron (II) and the like, more specifically benzoin tosylate, 2,5-dinitrobenzyl tosylate, N-tosiphthalimide and the like, but are not limited to these.

Aromatic iodonium salts, aromatic sulfonium salts, aromatic diazonium salts, aromatic phosphonium salts, triazine compounds, iron arene complexes, etc. are exemplified as photoradical polymerization initiators and photocationic polymerization initiators. and more specifically, chlorides, bromides, borofluorides, hexafluorophosphate salts of iodonium such as diphenyliodonium, ditolyliodonium, bis(p-tert-butylphenyl)iodonium, bis(p-chlorophenyl)iodonium, Iodonium salts such as hexafluoroantimonate salts, sulfonium chlorides such as triphenylsulfonium, 4-tert-butyltriphenylsulfonium, tris(4-methylphenyl)sulfonium, bromides, borofluorides, hexafluorophosphate salts, hexafluoro sulfonium salts such as antimonate salts, 2,4,6-tris(trichloromethyl)-1,3,5-triazine, 2-phenyl-4,6-bis(trichloromethyl)-1,3,5-triazine, 2,4,6-substituted-1,3,5-triazine compounds such as 2-methyl-4,6-bis(trichloromethyl)-1,3,5-triazine, including but not limited to isn't it.

From the viewpoint of stabilizing the recorded hologram, the photopolymerization initiator is preferably one that is decomposed after hologram recording.

The content of the photopolymerization initiator in the photosensitive composition for volume hologram recording of the present invention is 0.04 to 6.5 parts by mass with respect to 100 parts by mass of the total solid content of the photosensitive composition for volume hologram recording. is preferred, and 1.8 to 5.0 parts by mass is more preferred.
This is because if the content of the photopolymerization initiator is less than the above range, the photopolymerizable monomer described above may not be sufficiently polymerized, and the desired refractive index modulation amount (Δn) may not be obtained. . On the other hand, if the amount is more than the above range, the unreacted photopolymerization initiator may deteriorate the hologram properties.

<Sensitizing dye>
The sensitizing dye in the present invention is generally a component that absorbs light and has the function of increasing the sensitivity of the photopolymerization initiator to recording light. This is because the use of a sensitizing dye makes it active even with visible light, making it possible to record a hologram using visible laser light.

Sensitizing dyes used in the present invention include thiopyrylium salt dyes, merocyanine dyes, quinoline dyes, styrylquinoline dyes, coumarin dyes, ketocoumarin dyes, thioxanthene dyes, xanthene dyes, oxonol dyes, Cyanine dyes, rhodamine dyes, pyrylium ion dyes, cyclopentanone dyes, cyclohexanone dyes, diphenyliodonium ion dyes and the like can be mentioned. Specific examples of cyanine dyes and merocyanine dyes include 3,3′-dicarboxyethyl-2,2′-thiocyanine bromide and 1-carboxymethyl-1′-carboxyethyl-2,2′-quinocyanine bromide. , 1,3′-diethyl-2,2′-quinothiacyanine iodide, 3-ethyl-5-[(3-ethyl-2(3H)-benzothiazolylidene)ethylidene]-2-thioxo-4- oxazolidine, 3,9-diethyl-3′-carboxymethyl-2,2′-thiacarbocyanine iodine salt, and specific examples of coumarin-based dyes and ketocoumarin-based dyes include 3-(2′-benzo imidazole)-7-diethylaminocoumarin, 3,3′-carbonylbis(7-diethylaminocoumarin), 3,3′-carbonylbiscoumarin, 3,3′-carbonylbis(5,7-dimethoxycoumarin), 3,3 '-Carbonylbis(7-acetoxycoumarin) and the like, but are not limited thereto.

When high transparency is required for the volume hologram recording material described later, it is preferable to use a material that is easily decolorized due to decomposition or the like during the heating process or the light irradiation process after the interference exposure process. In general, dyes that are easily decomposed by light are preferred. By leaving it under room light or sunlight for several hours to several days, the pigment in the volume hologram recording material is decomposed and no longer absorbs in the visible region, so that a highly transparent volume hologram recording material can be obtained. is.

The content of the sensitizing dye is preferably 0.001 to 2.0 parts by mass, more preferably 0.001 to 1.2 parts by mass, with respect to 100 parts by mass of the total solid content of the photosensitive composition for volume hologram recording. Part is more preferred.
If the content of the sensitizing dye is more than the above range, when high transparency is required, the dye may not be sufficiently decomposed by light irradiation, resulting in a colored hologram recording layer. If the amount is less than the above range, the sensitivity of the photopolymerization initiator cannot be sufficiently sensitized, and the photopolymerization initiator may become inactive to visible light.

<Binder resin>
The binder resin has the function of improving the film-forming property and the uniformity of the film thickness of the hologram recording layer, and stabilizing the hologram formed by polymerization by light irradiation. It contributes to an increase in the heat resistance and the improvement of mechanical properties.
As the binder resin used in the present invention, one or more selected from thermoplastic resins and thermosetting resins are preferably used. Among them, it is preferable to use at least a thermoplastic resin, and it is preferable to use a thermoplastic resin and a thermosetting resin together from the viewpoint of increasing the refractive index modulation amount (Δn) and improving heat resistance and mechanical properties.

(Thermoplastic resin)
Examples of thermoplastic resins include polyvinyl acetate, polyvinyl butyrate, polyvinyl formal, polyvinyl carbazole, polyacrylic acid, polymethacrylic acid, polymethyl acrylate, polymethyl methacrylate, polyethyl acrylate, polybutyl acrylate, polymethacrylonitrile, Polyethyl methacrylate, polybutyl methacrylate, polyacrylonitrile, poly-1,2-dichloroethylene, ethylene-vinyl acetate copolymer, syndiotactic polymethyl methacrylate, poly-α-vinyl naphthalate, polycarbonate, cellulose acetate, cellulose triacetate , cellulose acetate butyrate, polystyrene, poly-α-methylstyrene, poly-o-methylstyrene, poly-p-methylstyrene, poly-p-phenylstyrene, poly-2,5-dichlorostyrene, poly-p-chloro Styrene, poly-2,5-dichlorostyrene, polyarylate, polysulfone, polyethersulfone, styrene-acrylonitrile copolymer, styrene-divinylbenzene copolymer, styrene-butadiene copolymer, styrene-maleic anhydride copolymer Polymer, ABS resin, polyethylene, polyvinyl chloride, polypropylene, polyethylene terephthalate, polyvinylpyrrolidone, polyvinylidene chloride, hydrogenated styrene-butadiene-styrene copolymer, transparent polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, (meth) Copolymers of acrylic acid cycloaliphatic esters and methyl (meth)acrylate, and the like are included.
A thermoplastic resin can be used individually by 1 type or in combination of 2 or more types.

Among the thermoplastic resins used in the binder resin of the present invention, it is preferable to contain a polyacrylic acid ester from the viewpoint of increasing the amount of refractive index modulation (Δn).

Polyacrylic acid esters used in the present invention include, for example, polymethyl acrylate, polyethyl acrylate, poly n-propyl acrylate, poly n-butyl acrylate, polybenzyl acrylate, poly n-hexyl acrylate, polyisopropyl acrylate, polyisobutyl Acrylates, poly-t-butyl acrylate, polycyclohexyl acrylate, polyphenyl acrylate, poly-1-phenylethyl acrylate, poly-2-phenylethyl acrylate, polyfurfuryl acrylate, polydiphenylmethyl acrylate, polypentachlorophenyl acrylate, polynaphthyl acrylate, etc. are mentioned. The poly(meth)acrylic acid ester may further contain a hydrolyzate of the poly(meth)acrylic acid ester. The thermoplastic resin used for the binder resin in the present invention is, among others, polymethyl methacrylate, and polymethyl methacrylate and poly(meth)acrylic acid in terms of increasing the amount of refractive index modulation (Δn) and storage stability. Copolymers of esters are preferred.

The weight-average molecular weight of the thermoplastic resin used for the binder resin in the present invention is in the range of 20,000 to 150,000 in terms of diffusion mobility of the photopolymerizable monomer during hologram recording and high-temperature storage stability. is preferably in the range of 80,000 to 150,000, and more preferably in the range of 120,000 to 140,000.
The weight-average molecular weight in the present invention refers to the polystyrene-equivalent value of gel permeation chromatography (GPC) measurement.

The glass transition temperature (Tg) of the thermoplastic resin used for the binder resin in the present invention is preferably within the range of 60°C to 150°C, more preferably within the range of 70°C to 120°C.
If the glass transition temperature (Tg) is higher than the above range, the diffusion mobility of the photopolymerizable monomer is poor, the desired refractive index modulation amount (Δn) cannot be obtained, and a volume hologram recording material with high brightness cannot be obtained. Because it is possible. On the other hand, if the glass transition temperature (Tg) is lower than the above range, the binder resin softens and the interference fringes are disturbed under high-temperature storage, and the desired refractive index modulation amount (Δn) may not be obtained. Because there is
The glass transition temperature (Tg) can be measured using a differential thermal analyzer (DSC) or the like.

(Thermosetting resin)
When a thermosetting resin is used as the binder resin in the present invention, the strength of the hologram recording layer can be increased, the volume hologram recording characteristics can be improved, and a stable layer structure can be formed by curing in the heating process. Also, some of the functional groups of the thermosetting resin can interact with some of the photopolymerizable monomers and form bonds upon irradiation with light. In this case, since the photopolymerizable monomer is fixed by the light irradiation step after the volume hologram recording, the strength of the volume hologram recording material can be increased.

The thermosetting resin used for the binder resin in the present invention is not particularly limited, and monomers, oligomers and polymers having thermosetting groups can be preferably used.
Examples of the thermosetting resin include compounds containing hydroxyl groups, mercapto groups, carboxyl groups, amino groups, epoxy groups, oxetane groups, isocyanate groups, carbodiimide groups, oxazine groups, metal alkoxides, and the like. can. In the present invention, among others, it is more preferable to use a compound containing an epoxy group and an oxetane group, and more preferably to use an epoxy group-containing compound. The epoxy group-containing compound used in the present invention is not particularly limited as long as it is a resin containing one or more epoxy groups in one molecule.

Among the above compounds having epoxy groups, examples of monofunctional epoxy compounds having one epoxy group include phenyl glycidyl ether, p-tert-butylphenyl glycidyl ether, butyl glycidyl ether, 2-ethylhexyl glycidyl ether, and allyl glycidyl ether. Ether, 1,2-butylene oxide, 1,3-butadiene monoxide, 1,2-epoxidedecane, epichlorohydrin, 1,2-epoxydecane, styrene oxide, cyclohexene oxide, especially containing polymerizable unsaturated bonds Examples thereof include 3-methacryloyloxymethylcyclohexene oxide, 3-acryloyloxymethylcyclohexene oxide, 3-vinylcyclohexene oxide, glycidyl (meth)acrylate and the like.

Examples of polyfunctional epoxy compounds having two or more epoxy groups include bisphenol A diglycidyl ether, bisphenol F diglycidyl ether, bisphenol S diglycidyl ether, brominated bisphenol A diglycidyl ether, and brominated bisphenol F diglycidyl. Ether, brominated bisphenol S diglycidyl ether, epoxy novolak resin, hydrogenated bisphenol A diglycidyl ether, hydrogenated bisphenol F diglycidyl ether, hydrogenated bisphenol S diglycidyl ether, 3,4-epoxycyclohexylmethyl-3′,4 '-epoxycyclohexanecarboxylate, 2-(3,4-epoxycyclohexyl-5,5-spiro-3,4-epoxy)cyclohexane-meta-dioxane, bis(3,4-epoxycyclohexylmethyl)adipate, vinylcyclohexene oxide , 4-vinylepoxycyclohexane, bis(3,4-epoxy-6-methylcyclohexylmethyl)adipate, 3,4-epoxy-6-methylcyclohexyl-3′,4′-epoxy-6′-methylcyclohexanecarboxylate, Methylenebis(3,4-epoxycyclohexane), dicyclopentadiene diepoxide, di(3,4-epoxycyclohexylmethyl)ether of ethylene glycol, ethylenebis(3,4-epoxycyclohexanecarboxylate), dioctyl epoxyhexahydrophthalate , di-2-ethylhexyl epoxyhexahydrophthalate, 1,4-butanediol diglycidyl ether, 1,6-hexanediol diglycidyl ether, glycerin triglycidyl ether, trimethylolpropane triglycidyl ether, polyethylene glycol diglycidyl ether, polypropylene glycol diglycidyl ethers, 1,1,3-tetradecadiene dioxide, limonene dioxide, 1,2,7,8-diepoxyoctane, 1,2,5,6-diepoxycyclooctane and the like. be done.
In addition, epoxy group-containing polymers are also preferably used. The epoxy group-containing polymer includes, for example, a copolymer using a monomer having an epoxy group or a glycidyl group as a copolymerization component. Examples of the monomer having an epoxy group or a glycidyl group include glycidyl (meth)acrylate and glycidyl esters of α,β-unsaturated carboxylic acids such as glycidyl maleate.
These epoxy compounds may be used individually by 1 type, and may use 2 or more types together.

The weight average molecular weight of the thermosetting resin used for the binder resin in the present invention is preferably in the range of 5000 to 100000, and being in the range of 10000 to 50000 improves the refractive index modulation amount (Δn). It is more preferable from the viewpoint of performance and the film strength of the hologram recording layer.

When a thermoplastic resin and a thermosetting resin are used together as a binder resin, the compounding ratio of the thermoplastic resin and the thermosetting resin is determined from the viewpoint of improving the refractive index modulation amount (Δn) and strength of the volume hologram recording medium. , The thermoplastic resin / thermosetting resin in mass ratio is preferably in the range of 50/50 to 90/10, more preferably in the range of 60/40 to 90/10, 70/30 to More preferably, it is in the range of 80/20.

In the photosensitive composition for volume hologram recording of the present invention, the content of the binder resin is the same as that of the photosensitive composition for volume hologram recording, from the viewpoint of improvement in the amount of refractive index modulation (Δn) and strength of the volume hologram recording material. It is preferably 1 to 40 parts by mass, more preferably 25 to 35 parts by mass, based on 100 parts by mass of the total solid content.

<Other ingredients>
The volume hologram recording photosensitive composition of the present invention may optionally contain fine particles, a thermal polymerization inhibitor, a silane coupling agent, a coloring agent, and the like, as long as the effects of the present invention are not impaired.
For example, fine particles are preferably used to impart good foil tearability.
Examples of fine particles that can be used include organic fine particles containing low-density polyethylene, high-density polyethylene, polypropylene, poly(meth)acryl as a resin skeleton, and inorganic particles such as silica, mica, talc, and titania. You may use 1 type or in mixture of 2 or more types of microparticles|fine-particles. Among the above, fluorine-containing fine particles, which are fine particles of a fluorine-containing resin in which some or all of the hydrogen atoms in the resin skeleton or side chains of the organic fine particles are substituted with fluorine atoms, or titania fine particles are preferable. .

When the volume hologram recording photosensitive composition of the present invention is applied, a solvent may be used as necessary. When the photosensitive composition for volume hologram recording contains a component that is liquid at room temperature, the coating solvent may not be necessary at all.
Examples of the solvent include ketone solvents such as methyl ethyl ketone, acetone and cyclohexanone; ester solvents such as ethyl acetate, butyl acetate and ethylene glycol diacetate; aromatic solvents such as toluene and xylene; alcohol solvents such as methanol, ethanol and propanol; ether solvents such as tetrahydrofuran and dioxane; halogen solvents such as dichloromethane and chloroform;

The materials described above are merely examples of materials used as materials for forming a volume hologram, and the materials are not limited to these.
Further, the formation of the volume hologram 30 using such a hologram-forming photosensitive material can be performed in the same manner as a conventionally known method of forming a reflection hologram.

In addition, the laser light has an extremely narrow wavelength band and is substantially single wavelength light, and the volume hologram 30 also has wavelength selectivity. It can be configured so that the volume hologram 30 of the deflection section 30 has almost no optical effect. Therefore, the retinal scanning display device 1 of the present embodiment can be reduced in size and weight, and can perform display corresponding to the laser light scanned by the scanning unit 20 while observing the deflecting unit 30 through. Visible.

As described above, in the retinal scanning display device 1 of the present embodiment, by using the volume hologram 30 in the deflector 30, it is possible to obtain the excellent effects described above. By narrowing the band of the laser light emitted by the laser light source 10 and using the volume hologram 30 capable of selectively diffracting and reflecting only the light in this band, the transparency is high and the hologram is drawn on the retina. It is considered that the display contents can be appropriately visually recognized.

However, when the volume hologram 30 is used for deflection of laser light in a retinal scanning display device, it has been found that a change in diffraction efficiency due to a change in temperature poses a problem. More specifically, if the wavelength selectivity of the volume hologram 30 is too high, the desired diffraction efficiency cannot be obtained due to changes in temperature, and only a dark image can be observed, or the color balance of the observed image is shifted. I used to relax.

FIG. 2 is a diagram showing the distribution of diffraction efficiency with respect to wavelength when the volume hologram 30 has very high wavelength selectivity. The horizontal axis of FIG. 2 indicates the wavelength, and the vertical axis indicates the diffraction efficiency of the volume hologram 30 . In FIG. 2, the distribution of the diffraction efficiency at room temperature is indicated by a solid line, the time at high temperature is indicated by a dashed line, and the time at low temperature is indicated by a one-dot chain line.
The volume hologram 30, which has extremely high wavelength selectivity as indicated by the solid line in FIG. 2, hardly diffracts light outside the laser light band, and at first glance seems ideal. However, when the temperature of the volume hologram 30 changes, the selectively diffracted wavelength changes. As shown in FIG. 2, the diffraction wavelength shifts to the long wavelength side at high temperatures, and the diffraction wavelength shifts to the short wavelength side at low temperatures. It is considered that this is due to expansion or contraction of the volume hologram 30 due to temperature change. As shown in FIG. 2, the wavelength band diffracted by the volume hologram 30 greatly deviates from the band of the laser beam at both high and low temperatures, and a sufficient amount of diffracted light cannot be obtained. Under such circumstances, the volume hologram 30 cannot be used as the deflecting section 30 .

Therefore, we have developed a volume hologram 30 that can reduce the influence of temperature changes, and made it possible to use the volume hologram 30 as the deflection unit 30 .
FIG. 3 is a diagram showing an example of the diffraction efficiency distribution at 20° C. of the volume hologram 30 used in the deflector 30 in this embodiment.
The volume hologram 30 used in the deflection unit 30 of the present embodiment illustrated in FIG. 3 has a half width of 5 nm in the spectral distribution curve. In this specification, the half-value width of the spectral distribution curve is the width of the curve (wavelength range, also referred to as full width at half maximum) at half the peak value of the spectral distribution curve. The vertical axis of the spectral distribution curve may be the amount of light itself or the diffraction efficiency. In this embodiment, the spectral distribution curve is used as the diffraction efficiency distribution curve.

The spectral distribution curve may be obtained by measuring the laser beam that is actually diffracted and reflected, or by measuring the laser beam that is transmitted through the volume hologram 30 without being diffracted and reflected.

3 also shows the band of the laser light emitted by the laser light source 10, as in FIG. The band of the laser light emitted by the laser light source 10 of this embodiment has a wavelength width of 1 nm centered at 530 nm. As shown in FIG. 3, at 20° C., the peak position of the diffraction efficiency substantially coincides with the band of the laser light emitted from the laser light source 10, and the laser light can be efficiently diffracted and reflected.

FIG. 4 is a diagram showing the diffraction efficiency distribution at 40° C. of the volume hologram 30 used in the deflection unit 30 in this embodiment.
At 40° C., the diffraction efficiency distribution curve (spectral distribution curve) shifts to the longer wavelength side by approximately 2 nm. Therefore, the decrease in diffraction efficiency is suppressed to approximately half, and images can be displayed satisfactorily.

FIG. 5 is a diagram showing the distribution of the diffraction efficiency at 0° C. of the volume hologram 30 used in the deflection section 30 in this embodiment.
Even at 0° C., the diffraction efficiency distribution curve (spectral distribution curve) shifts to the short wavelength side by approximately 2 nm. Therefore, the decrease in diffraction efficiency is suppressed to approximately half, and image display is sufficiently possible.

Therefore, it is desirable that the volume hologram 30 has a half width of 5 nm or more in the spectral distribution curve.
More preferably, the volume hologram 30 has a half width of 10 nm or more in the spectral distribution curve.
More preferably, the volume hologram 30 has a half width of 20 nm or more in the spectral distribution curve.
FIG. 6 is a diagram showing diffraction efficiency distribution curves with half widths of 5 nm, 10 nm, and 20 nm.
As shown in FIG. 6, the wider the half-value width, the less likely it is to be affected by temperature changes.
Further, the wavelength width at 90% of the maximum efficiency is preferably 5 nm or more, more preferably 10 nm or more. This is because even if the center wavelength shifts, the efficiency hardly changes, so the effect of temperature change can be further reduced.

Next, a more specific configuration of the volume hologram 30 having a wide half width in the spectral distribution curve as described above will be described.
Since the half-value width of the diffracted light of the volume hologram 30 is considered to be greatly affected by the film thickness and the refractive index modulation amount Δn, these optimum ranges are defined first.
FIG. 7 is a diagram showing simulation conditions. FIG. 7(a) shows a list of simulation conditions, and FIG. 7(b) shows the conditions of the incident angle and the outgoing angle.
Here, the volume hologram 30 was simulated under the conditions shown in FIG. 7, and the effects of the film thickness and the refractive index modulation amount Δn on the half-value width were investigated. The amount of refractive index modulation Δn varies greatly depending on the selection and composition of materials before exposure, but can be changed depending on the exposure conditions, so it is possible to obtain a desired value. Note that the simulation results shown below use the average values of the P-polarized light and the S-polarized light.

The reflection hologram was simulated based on Kogelnik's Coupled Wave theory (The Bell System Technical Journal Vol.48, No.9, pp.2909-2947 (Nov.1969)).
The diffraction efficiency η of the reflection hologram is given by the following equation (A) when the absorption in the medium can be ignored.

η=1/[1+(1−ξ ² /ν ² )/sinh ² {√(ν ² −ξ ² )}] (A)
where ν and ξ are given by

ν=πtΔn/{λ√(cos θ _R ·cos θ _S )}
ξ=t/2×( _kRz +Kz _{-kSz )}
however,
t: Thickness of photosensitive material λ: Wavelength in vacuum θ _R : Angle between incident light and hologram surface normal vector θ _S : Angle between diffracted light and hologram surface normal vector k _Rz : Wave vector hologram of incident light Component in the direction normal to the surface k _Sz : Component of the wave vector of the diffracted light in the direction normal to the hologram surface K _z : Component of the diffraction grating vector in the direction normal to the hologram surface Δn : Amplitude of refractive index modulation of the hologram medium n : Hologram medium is the average refractive index of

Here, the wave vector k of the light is given by |k|=2πn/λ, and the diffraction grating vector K is a vector perpendicular to the interference fringe plane of the volume hologram. , |K|=2π/Λ.

(Half width simulation with film thickness t and Δn as variables)
FIG. 8 is a diagram summarizing the results of a simulation in which the half-value width was obtained by changing the film thickness t and Δn. FIG. 8 summarizes the results of a total of 300 simulations performed by combining 15 types of film thickness t and 20 types of Δn.
As can be seen from FIG. 8, a thinner film thickness t is desirable, and a higher Δn value is desirable, but it is difficult to quantitatively grasp them. Therefore, from the results shown in FIG. 8, a preferable range of the combination of the film thickness t and .DELTA.n was formulated.
Specifically, the half-value width shown in FIG. 8 can be divided into a plurality of regions within the numerical range. We collected the data and found an approximation that represents the data group. As the boundaries, boundaries with half widths of 5 nm, 10 nm, 15 nm, 20 nm, and 30 nm were set.

FIG. 9 is a graph of an approximation formula showing a preferable combination range of the film thickness t and Δn obtained from the half width.
FIG. 9 also shows the results of polynomial approximation performed for each of the half-value widths of 5 nm, 10 nm, 15 nm, 20 nm, and 30 nm, which are the boundary values described above.

From the approximation result with a half width of 5 nm,
Δn≧−5×10 ⁻⁶ t ² +0.003t+0.0007
However, when t≧30 μm, Δn≧0.005
It can be said that it is desirable to satisfy the relationship of By satisfying this relationship, the half width can be 5 nm or more. Since the polynomial is used for approximation, the accuracy of the approximation is lowered in the range where the film thickness t exceeds 30 μm. Considering that the approximation curve is almost flat when the film thickness t is around 30 μm, when t≧30 μm, Δn≧0.005 (Δn=0.005 is t = Δn when 30 µm) (the same applies to other conditions below).

More desirably, from the approximation result with a half width of 10 nm,
Δn≧−5×10 ⁻⁸ t ⁴ +3×10 ⁻⁶ t ³ −6×10 ⁻⁵ t ² +0.001 t+4×10 ⁻⁵
However, when t≧30 μm, Δn≧0.015
It can be said that it is desirable to satisfy the relationship of By satisfying this relationship, the half width can be 10 nm or more.

More desirably, from the approximation result with a half width of 15 nm,
Δn≧1×10 ⁻⁷ t ⁴ −6×10 ⁻⁶ t ³ +5×10 ⁻⁵ t ² +0.0021 t−0.0012
However, when t≧30 μm, Δn≧0.03
It can be said that it is desirable to satisfy the relationship of By satisfying this relationship, the half width can be 15 nm or more.

More desirably, from the approximation result with a half width of 20 nm,
Δn≧1×10 ⁻⁸ t ⁴ +4×10 ⁻⁶ t ³ −0.0002t ² +0.0056t−0.0045
However, when t≧30 μm, Δn≧0.04
It can be said that it is desirable to satisfy the relationship of By satisfying this relationship, the half width can be 20 nm or more.

More desirably, from the approximation result with a half width of 30 nm,
Δn≧2×10 ⁻⁸ t ⁵ −2×10 ⁻⁶ t ⁴ +9×10 ⁻⁵ t ³ −0.0019 t ² +0.0195 t−0.0169
However, when t≧30 μm, Δn≧0.06
It can be said that it is desirable to satisfy the relationship of By satisfying this relationship, the half width can be 30 nm or more.

(Diffraction efficiency simulation with film thickness t and Δn as variables)
When the film thickness t and Δn are changed, not only the half-value width described above but also the diffraction efficiency is affected. Therefore, considering the diffraction efficiency, the appropriate range of the film thickness t and Δn is further limited.
FIG. 10 is a diagram summarizing the results of a simulation in which the maximum value of diffraction efficiency was obtained by changing the film thickness t and Δn. As in the case of FIG. 8, FIG. 10 summarizes the results of a total of 300 simulations performed by combining 15 types of film thickness t and 20 types of Δn.
As can be seen from FIG. 10, a thicker film thickness t is desirable, and a higher Δn value is desirable, but it is difficult to grasp them quantitatively. Therefore, as in the case of FIG. 8, a preferable range of the combination of the film thickness t and Δn was formulated from the results shown in FIG.
Specifically, the boundaries were set such that the maximum value of the diffraction efficiency was 0.2, 0.4, 0.6, and 0.8.

FIG. 11 is a graph of an approximation formula showing a preferable combination range of the film thickness t and Δn obtained from the maximum value of the diffraction efficiency.
FIG. 11 also shows the results of polynomial approximation for each of the maximum diffraction efficiency values of 0.2, 0.4, 0.6, and 0.8, which are the boundary values described above.

From the approximation result of the maximum diffraction efficiency of 0.2,
Δn ≧ 0.0641t ^(−1.049)
It can be said that it is desirable to satisfy the relationship of By satisfying this relationship, the maximum diffraction efficiency can be 0.2 or more.

More preferably, from the approximation result of the maximum diffraction efficiency of 0.4,
Δn ≧ 0.1297t ^(−1.065)
It can be said that it is desirable to satisfy the relationship of By satisfying this relationship, the maximum value of the diffraction efficiency can be 0.4 or more.

More preferably, from the approximation result of the maximum diffraction efficiency of 0.6,
Δn ≧ 0.1768t ^(−1.07)
It can be said that it is desirable to satisfy the relationship of By satisfying this relationship, the maximum diffraction efficiency can be 0.6 or more.

More preferably, from the approximation result of the maximum diffraction efficiency of 0.8,
Δn ≧ 0.257t ^(−1.051)
It can be said that it is desirable to satisfy the relationship of By satisfying this relationship, the maximum value of diffraction efficiency can be 0.8 or more.

(Half width simulation with the incident angle θ ₁ and the output angle θ ₂ as variables)
In the simulations described above, the incident and exit angles were fixed at 50° and 180°, respectively. This 50° incident angle and 180° outgoing angle are the most suitable combination, assuming the head-mounted retinal scanning display device 1 . However, of course, the combination of the incident angle and the outgoing angle is not limited to this, and can be appropriately changed in design. Therefore, a simulation was performed assuming that the incident angle and the output angle are changed.

FIG. 12 is a diagram showing simulation conditions focusing on the incident angle and the outgoing angle. FIG. 12(a) shows a list of simulation conditions, and FIG. 12(b) shows a state in which the incident angle _θ1 and the outgoing angle _θ2 are changed.
Here, the volume hologram 30 was simulated under the conditions shown in FIG. 12, and the effects of the incident angle θ ₁ and the output angle θ ₂ on the half-value width were investigated.

FIG. 13 is a diagram summarizing the results of a simulation in which the half-value width was obtained by changing the incident angle _θ1 and the output angle _θ2 . FIG. 13 summarizes the results of a total of 306 simulations performed by combining 18 types of incident angle θ ₁ from 0° to 85° and 17 types of output angle θ ₂ from 100° to 260°.
Looking at FIG. 13, the larger the incident angle θ ₁ (closer to 85°), the wider the half-value width, and the smaller the output angle θ ₂ (closer to 100°), the wider the half-value width. I understand that it can be done, but it is difficult to grasp it quantitatively. Therefore, from the results shown in FIG. 13, a preferable range for the combination of the incident angle _.theta.1 and the outgoing angle _.theta.2 was mathematically expressed in the same manner as the case of the film thickness t and .DELTA.n described above. As the boundaries, the boundaries with half-value widths of 15 nm and 18 nm were set, but as can be seen from _FIG . are doing. Therefore, there are two approximation formulas with the half-value width of 15 nm as the boundary.

FIG. 14 is a graph of an approximation formula showing a preferable combination range of the film thickness t and Δn obtained from the half width.
FIG. 14 also shows the results of polynomial approximation for two half-value widths of 15 nm (15 nm-A and 15 nm-B) and 18 nm, which are the boundary values described above.

From the result of the half width of 15 nm, within the ranges of 0° ≤ θ ₁ ≤ 85° and 100° ≤ θ ₂ ≤ 260°,
θ ₂ ≦0.3214 θ ₁ +234.75
and θ ₂ ≧−θ ₁ +118.33
It can be said that it is desirable to satisfy both relationships. By satisfying this relationship, the half width can be 15 nm or more.

Also, from the result of the half width of 18 nm,
If θ ₂ ≧160°,
θ ₂ ≤ 82.436 θ ₁ ^(0.2278)
It is desirable to satisfy
Moreover, when θ ₂ <160°,
θ ₁ ≧40°
It is desirable to satisfy the relationship of
By satisfying these relationships, the half width can be 18 nm or more.

(Diffraction Efficiency Simulation with Incident Angle _θ1 and Output Angle _θ2 as Variables)
When the incident angle θ ₁ and the exit angle θ ₂ change, not only the half-value width mentioned above but also the diffraction efficiency is affected. Therefore, considering the diffraction efficiency, the appropriate range of the incident angle _θ1 and the output angle _θ2 is further limited.
FIG. 15 is a diagram summarizing the results of a simulation in which the maximum value of the diffraction efficiency was obtained by changing the incident angle _θ1 and the output angle _θ2 . 15, 18 types of incident angle _θ1 from 0° to 85° and 17 types of output angle _θ2 from 100° to 260° were combined in the same manner as in FIG. 13, for a total of 306 types of simulations. I am summarizing the results.
Looking at FIG. 15, it can be seen that a smaller incident angle _θ1 (closer to 0°) is desirable, and a larger outgoing angle _θ2 (closer to 260°) is desirable. difficult to do Therefore, as in the case of FIG. 13, from the results shown in FIG. 15, a preferable range of the combination of the incident angle _θ1 and the output angle _θ2 was mathematically expressed.
Specifically, the boundaries were set such that the maximum values of the diffraction efficiency were 0.6 and 0.8.

FIG. 16 is a graph of an approximation formula showing a preferable combination range of the incident angle θ ₁ and the output angle θ ₂ obtained from the maximum value of the diffraction efficiency.
FIG. 16 also shows the result of performing polynomial approximation on the maximum diffraction efficiency values of 0.6 and 0.8, which are the boundary values described above.

From the approximation result of the maximum diffraction efficiency value of 0.6, within the ranges of 0° ≤ θ ₁ ≤ 85° and 100° ≤ θ ₂ ≤ 260°,
θ ₂ ≧65.549ln(θ ₁ )−170.32
It can be said that it is desirable to satisfy the relationship of By satisfying this relationship, the maximum diffraction efficiency can be 0.6 or more.

More preferably, within the ranges of 0° ≤ θ ₁ ≤ 85° and 100° ≤ θ ₂ ≤ 260° from the approximation result of the maximum diffraction efficiency value of 0.8,
θ ₂ ≧41.648ln(θ ₁ )−28.802
It can be said that it is desirable to satisfy the relationship of By satisfying this relationship, the maximum value of diffraction efficiency can be 0.8 or more.

As for the volume hologram 30 used in the deflection unit 30 in this embodiment, the preferable range of the film thickness t and Δn and the preferable range of the incident angle θ ₁ and the output angle θ ₂ are appropriately combined to obtain an optimal volume hologram 30 for the usage conditions. A volume hologram 30 can be used.
In order to measure the film thickness of an actually produced volume hologram, it is preferable to observe the cross section with an SEM. As a method for measuring Δn, simulation calculation of diffraction efficiency is performed based on measurement results of film thickness, diffraction angle, and wavelength, and Δn is calculated from fitting with the measurement result of diffraction efficiency.

As described above, the retinal scanning display device 1 of the present embodiment uses the volume hologram 30 in the deflection unit 30, and the half width of the diffracted light is 5 nm or more. can suppress the decrease in Further, since the volume hologram 30 used in the deflection unit 30 of the present embodiment is within the preferable ranges of the film thickness t and Δn and the preferable ranges of the incident angle θ ₁ and the output angle θ ₂ described above, the half width is A wide volume hologram 30 with good diffraction efficiency can be realized, and an appropriate display can be realized regardless of temperature changes.
Although the simulation was performed with respect to the green wavelength of 530 nm, the same consideration can be applied to red and blue light.

(Second embodiment)
FIG. 17 is a diagram showing the head-mounted display device 2 of the second embodiment.
The volume hologram 30 of the present invention can be used not only in the retinal scanning display device 1 shown in the first embodiment, but also in other types of head-mounted display devices.
In the head-mounted display device 2 shown in FIG. 17, the image light projected from the microdisplay 40 is deflected by the volume hologram 30 and diffracted and reflected toward the eye E of the observer. The microdisplay 40 is an optical engine using a laser light source.
The volume hologram 30 can have the same configuration as the volume hologram 30 of the first embodiment. Note that the volume hologram 30 of the second embodiment has an effect of deflecting light equivalent to that of a curved half mirror. is.

(Third embodiment)
FIG. 18 is a diagram showing the head-mounted display device 3 of the third embodiment.
The head-mounted display device 3 of the third embodiment is a retinal projection type display device that does not scan laser light.
The laser light emitted from the laser light source 50 is collimated by a collimator lens 60, transmitted through a liquid crystal display (LCD) 70, and furthermore unnecessary diffracted light is removed by a high-order diffraction removal optical system 80. The volume hologram 30 is reached.
The volume hologram 30 of the third embodiment can also have the same configuration as the volume hologram 30 of the first embodiment, and has the same effect of deflecting light as a curved half mirror, and diffracts and reflects image light. It is a deflecting portion that not only allows the background to pass through, but also enables observation.

(deformed form)
Various modifications and changes are possible without being limited to the embodiments described above, and they are also within the scope of the present invention.

(1) In each embodiment, a single wavelength has been described, but the present invention can also be applied when there are multiple wavelengths, such as using laser light corresponding to the three colors of RGB. In that case, separate hologram layers may be formed and stacked for each of the RGB wavelengths, or interference fringes for each of the RGB wavelengths may be formed in the same layer.

(2) In each embodiment, each numerical range defined as a desirable range may not be satisfied in the entire area of the volume hologram. For example, the angle of incidence and the angle of emergence with respect to the volume hologram may not satisfy the desired numerical range over the entire area of the volume hologram. For example, it is preferable that the center of the line of sight (the center of the volume hologram) satisfies the conditions of the angle range defined this time.

(3) In each embodiment, an example in which the volume hologram 30 is applied to a head-mounted display device has been described. For example, the volume hologram of the present invention may be used in a display device that is not worn on the head.

Although the embodiments and modifications can be used in combination as appropriate, detailed description thereof will be omitted. Moreover, the present invention is not limited to each embodiment described above.

1 retinal scanning display device 10 laser light source 20 scanning unit 30 deflection unit, volume hologram

Claims (8)

A volume hologram used as a deflection unit for deflecting image light of an optical engine using a laser light source,
The spectral distribution curve has a half width of 20 nm or more ,
When the film thickness of the volume hologram is t (μm) and the refractive index modulation amount is Δn,
Δn≧1×10 ⁻⁸ t ⁴ +4×10 ⁻⁶ t ³ −0.0002t ² +0.0056t−0.0045
However, when t≧30 μm, Δn≧0.04
satisfy the relationship of
Δn≧0.1297t ^(−1.065)
A volume hologram that satisfies the relationship of A volume hologram used as a deflection unit for deflecting the direction of the scanned laser light used in a retinal scanning display device that scans the laser light from the laser light source and directly draws on the retina,
The spectral distribution curve has a half width of 20 nm or more ,
When the film thickness of the volume hologram is t (μm) and the refractive index modulation amount is Δn,
Δn≧1×10 ⁻⁸ t ⁴ +4×10 ⁻⁶ t ³ −0.0002t ² +0.0056t−0.0045
However, when t≧30 μm, Δn≧0.04
satisfy the relationship of
Δn≧0.1297t ^(−1.065)
A volume hologram that satisfies the relationship of In the volume hologram according to claim 1 or claim 2 ,
When the emission angle of the laser beam incident on the volume hologram at the incident angle θ ₁ is θ ₂ ,
Within the ranges of 0° ≤ θ ₁ ≤ 85° and 100° ≤ θ ₂ ≤ 260°,
θ ₂ ≦0.3214 θ ₁ +234.75
,and,
θ ₂ ≧−θ ₁ +118.33
satisfying the relationship between
A volume hologram characterized by In the volume hologram according to claim 3 ,
If θ ₂ ≧160°,
θ ₂ ≤ 82.436 θ 1 ^(0.2278)
satisfying the relationship of
A volume hologram characterized by In the volume hologram according to claim 3 ,
If θ ₂ <160°, then
θ ₁ ≧40°
satisfying the relationship of
A volume hologram characterized by In the volume hologram according to any one of claims 1 to 5 ,
When the emission angle of the laser beam incident on the volume hologram at the incident angle θ ₁ is θ ₂ ,
Within the ranges of 0° ≤ θ ₁ ≤ 85° and 100° ≤ θ ₂ ≤ 260°,
θ ₂ ≧65.549ln(θ ₁ )−170.32
satisfying the relationship of
A volume hologram characterized by A retinal scanning display device comprising the volume hologram according to any one of claims 1 to 6 in a deflection section. including the volume hologram according to any one of claims 1 to 6 in a deflection unit,
The head-mounted display device, wherein the deflection unit is provided on a transparent member so that the display can be superimposed on a see-through field of view and observed.

Images