Photopolymer-based holographic recording medium, grating and preparation method therefor, and device

Abstract

The present application discloses a photopolymer-based holographic recording medium, a volume holographic grating and a preparation method therefor, and a holographic device. The photopolymer-based holographic recording medium at least comprises a compound having a plurality of isocyanate reactive functional groups and a polyisocyanate-based compound, wherein the number of the isocyanate reactive functional groups is different from the number of isocyanate groups. The volume holographic grating prepared in the present application has a relatively high refractive index modulation for red, green and blue light.

Description

Photopolymer-based holographic recording media, gratings, their fabrication methods and equipment

[0001] This application claims priority to Chinese Patent Application No. 2024118960269, filed on December 20, 2024, entitled "Photopolymer-type holographic recording medium, grating and preparation method and apparatus thereof", the entire contents of which are incorporated herein by reference. Technical Field

[0002] This application relates to the field of holographic materials technology, and in particular to a photopolymer-type holographic recording medium, a volume holographic grating, a method for preparing the same, and a holographic device. Background Technology

[0003] Augmented Reality (AR) technology based on holographic waveguide systems has enormous application potential. The core optical component of a holographic waveguide system is a volume holographic grating. To achieve color display, the volume holographic grating needs to be sensitive to red, green, and blue light.

[0004] In related technologies, three gratings sensitive to red, green, and blue light respectively are first fabricated using photopolymers, and then the three gratings are bonded together to achieve color display. However, the bonding precision requirements for the three gratings are high, which increases the complexity of the process and results in low fabrication efficiency and yield of photopolymers. Summary of the Invention

[0005] Based on this, this application provides a photopolymer-type holographic recording medium, a volume holographic grating, a method for preparing the same, and a holographic device, which can achieve high refractive index modulation for red, green, and blue light while avoiding the use of bonding processes.

[0006] In a first aspect, this application provides a photopolymer-type holographic recording medium, which includes a compound having multiple isocyanate reactive functional groups, a polyisocyanate-based compound, a polymerizable monomer, a photoinitiating system, a chain transfer agent, a catalyst, and additives.

[0007] The number of isocyanate reactive functional groups is different from the number of isocyanate groups in the polyisocyanate compound.

[0008] Secondly, this application provides a volume holographic grating, wherein the photopolymer holographic recording medium used in the volume holographic grating includes the photopolymer holographic recording medium as described above.

[0009] Thirdly, this application provides a volume holographic grating, the volume holographic grating comprising a red light photosensitive photopolymer film, a green light photosensitive photopolymer film and a blue light photosensitive photopolymer film;

[0010] The red light photosensitive polymer film, the green light photosensitive polymer film, and the blue light photosensitive polymer film are stacked together, and adjacent film layers are connected by covalent bonds formed by isocyanate reactive functional groups or isocyanate groups.

[0011] Fourthly, this application provides a method for fabricating a volume holographic grating, the method comprising:

[0012] A mixed solution of three photopolymer holographic recording media is provided, wherein the photopolymer holographic recording media is the photopolymer holographic recording media described above, and the photosensitive initiation systems of the three photopolymer holographic recording media are red light photosensitive initiation system, green light photosensitive initiation system and blue light photosensitive initiation system, respectively;

[0013] A substrate is provided, and a mixed solution of a first photopolymer holographic recording medium is uniformly distributed on the surface of the substrate, so that the first photopolymer holographic recording medium forms a first photopolymer film on the surface of the substrate.

[0014] A mixed solution of a second type of photopolymer holographic recording medium is uniformly distributed on the surface of the first photopolymer film, so that the second type of photopolymer holographic recording medium forms a second photopolymer film on the surface of the first photopolymer film. The residual isocyanate reactive functional groups or isocyanate groups in the first photopolymer film and the second photopolymer film react to connect the first photopolymer film to the second photopolymer film in a covalent manner.

[0015] A mixed solution of a third type of photopolymer holographic recording medium is uniformly distributed on the surface of the second photopolymer film, so that the third type of photopolymer holographic recording medium forms a third photopolymer film on the surface of the second photopolymer film. The residual isocyanate reactive functional groups or isocyanate groups in the second and third photopolymer films react to connect the second photopolymer film to the third photopolymer film in a covalent manner.

[0016] A volume holographic grating was fabricated by exposing a multilayer photopolymer film.

[0017] Fifthly, this application provides a holographic device, which includes a volume holographic grating as described above.

[0018] This application provides a photopolymer-type holographic recording medium, a volume holographic grating, a method for preparing the same, and a holographic device. The photopolymer-type holographic recording medium includes a compound having multiple isocyanate reactive functional groups, a polyisocyanate-based compound, a polymerizable monomer, a photoinitiator system, a chain transfer agent, a catalyst, and additives; wherein the number of isocyanate reactive functional groups is different from the number of isocyanate groups in the polyisocyanate-based compound. Because the number of reactive isocyanate functional groups differs from the number of isocyanate groups, residual reactive isocyanate functional groups or isocyanate groups remain after the reactive isocyanate functional groups in the photopolymer holographic recording medium react with the isocyanate groups. These residual functional groups can react with residual functional groups in other photopolymer holographic recording media, thereby connecting the photopolymer films through covalent bonds. This avoids the need for lamination processes to bond the gratings. Furthermore, since each layer of photopolymer film is independent, each layer can use the refractive index modulation of the corresponding layer of photopolymer, without sharing the refractive index modulation of a single layer. This results in a volume holographic grating with high refractive index modulation and diffraction efficiency for red, green, and blue light, thereby improving the display brightness of AR devices. Attached Figure Description

[0019] Figure 1 is a schematic flowchart of the fabrication method of a volume holographic grating provided in this application.

[0020] Figure 2 is a schematic diagram of the UV-Vis transmittance curves of sample 1 after recording three types of gratings. Detailed Implementation

[0021] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of this application.

[0022] The flowchart shown in the attached diagram is for illustrative purposes only and does not necessarily include all content and operations / steps, nor does it necessarily have to be performed in the order described. For example, some operations / steps can be broken down, combined, or partially merged, so the actual execution order may change depending on the actual situation.

[0023] In the following description, the use of suffixes such as "module," "part," or "unit" to denote elements is solely for the purpose of illustration and has no inherent meaning. Therefore, "module," "part," or "unit" may be used interchangeably.

[0024] Augmented reality (AR) is a technology that overlays virtual information onto the real world and is currently widely used in various fields such as gaming, education, retail, and industrial manufacturing. Among them, AR devices with color display capabilities (AR glasses, head-up displays (HUDs)) can provide users with a more realistic and richer interactive experience.

[0025] Holographic waveguide technology is one of the development directions for AR devices, offering significant advantages such as simple fabrication processes and low cost. Furthermore, its high transparency and high diffraction efficiency allow it to easily achieve a large field of view while maintaining a thin and lightweight structure. The core optical component of a holographic waveguide system is a volume holographic grating. To achieve color display, the volume holographic grating needs to be sensitive to red, green, and blue light.

[0026] In related technologies, a method is also provided for fabricating three types of gratings sensitive to red, green, and blue light in the same layer of photopolymer. However, this method requires these three gratings to share the refractive index modulation of a single layer of photopolymer, which results in low diffraction efficiency for all three gratings, leading to low display brightness in the final AR device.

[0027] To address the aforementioned challenges, this application provides a photopolymer-based holographic recording medium, a volume holographic grating, a method for fabricating the grating, and a holographic device. This avoids the need for bonding processes to attach the grating, and the resulting volume holographic grating exhibits high refractive index modulation and diffraction efficiency for red, green, and blue light. It also enhances the display brightness of AR devices.

[0028] The embodiments of this application will now be described in detail with reference to the accompanying drawings.

[0029] This application provides a photopolymer-type holographic recording medium, which includes a compound having multiple isocyanate reactive functional groups, a polyisocyanate-based compound, a polymerizable monomer, a photoinitiator system, a chain transfer agent, a catalyst, and additives; wherein the number of isocyanate reactive functional groups is different from the number of isocyanate groups in the polyisocyanate-based compound.

[0030] It should be noted that photopolymer holographic recording media materials typically contain a low-refractive-index film-forming resin and a high-refractive-index writing monomer. In the embodiments of this application, compounds with multiple isocyanate reactive functional groups and polyisocyanate group compounds can form film-forming resins, while polymerizable monomers are equivalent to writing monomers.

[0031] In this embodiment, by controlling the number of isocyanate reactive functional groups to differ from the number of isocyanate groups, residual unreacted isocyanate reactive functional groups or isocyanate groups remain after the isocyanate reactive functional groups in each photopolymer holographic recording medium react with the isocyanate groups. The residual unreacted functional groups in one photopolymer holographic recording medium react with those in another, resulting in covalent bonds between the photopolymer films. This avoids the need for lamination processes for grating bonding. Furthermore, since each photopolymer film layer is independent, each layer can use the refractive index modulation of its corresponding layer, without sharing the refractive index modulation of a single layer. This results in a volume holographic grating with high refractive index modulation and diffraction efficiency for red, green, and blue light, thereby improving the display brightness of the AR device.

[0032] In some embodiments, the ratio of the number of isocyanate reactive functional groups to the number of isocyanate groups is 1:(1.01 to 1.5) or (1.01 to 1.5):1. This allows control over the number of residual unreacted functional groups in the photopolymer-type holographic recording medium, avoiding the presence of a large number of unreacted functional groups that could affect the holographic recording performance.

[0033] For example, the ratio of the number of isocyanate reactive functional groups to the number of isocyanate groups can be 1:1.01, 1:1.35, 1:1.5, 1.01:1, 1.35:1, or 1.5:1, and no specific limitation is made here.

[0034] In some embodiments, the ratio of the number of isocyanate reactive functional groups to the number of isocyanate groups is 1:(1.01 to 1.3) or (1.01 to 1.3):1. This allows control over the number of residual unreacted functional groups in the photopolymer holographic recording medium, resulting in good bonding between the layers of photopolymer films and good holographic recording performance.

[0035] For example, the ratio of the number of isocyanate reactive functional groups to the number of isocyanate groups can be 1:1.01, 1:1.2, 1:1.3, 1.01:1, 1.2:1, or 1.3:1, and no specific limitation is made here.

[0036] In some embodiments, the mass ratio of the compound having multiple isocyanate reactive functional groups, the polyisocyanate group compound, the polymerizable monomer, the photoinitiator system, the chain transfer agent, the catalyst and the additive is (30-70):(10-50):(0.1-60):(0.1-4):(0.1-3):(0.1-3):(0.1-7).

[0037] The following describes the raw materials of each component in the photopolymer holographic recording medium, using parts by weight as an example.

[0038] For example, the compound having multiple isocyanate reactive functional groups can be 30 to 70 parts, such as 30 parts, 40 parts, 50 parts, 60 parts, or 70 parts.

[0039] For example, the polyisocyanate compound can be 10 to 50 parts, such as 10 parts, 20 parts, 30 parts, 40 parts, or 50 parts.

[0040] For example, the polymerizable monomer can be 0.1 parts to 60 parts, such as 0.1 parts, 10 parts, 30 parts, 50 parts, or 60 parts.

[0041] For example, the photoinitiator system can be 0.1 to 4 parts, such as 0.1, 1, 2.5, 3, or 4 parts.

[0042] For example, the chain transfer agent can be 0.1 to 3 parts, such as 0.1 parts, 1 part, 2 parts, 2.5 parts, or 3 parts.

[0043] For example, the catalyst can be 0.1 parts to 3 parts, such as 0.1 parts, 1 part, 2 parts, 2.5 parts, or 3 parts.

[0044] For example, the additive can be 0.1 parts to 7 parts, such as 0.1 parts, 1 part, 3 parts, 5.5 parts, or 7 parts.

[0045] It is understood that by reasonably controlling the amount of each component added, this application can achieve full synergy among the components, and prevent the holographic performance of the final photopolymer holographic recording medium from deteriorating due to too much or too little of a certain component, thus ensuring that the final photopolymer holographic recording medium has better overall holographic performance.

[0046] For example, by controlling the amount of multiple isocyanate reactive functional groups to 30 to 70 parts and the amount of polyisocyanate group compound to 10 to 50 parts, the multiple isocyanate reactive functional groups and the polyisocyanate group compound can react together to form a film-forming resin, thereby providing support for other components.

[0047] For example, by controlling the polymerizable monomer content to between 0.1 and 60 parts, the polymerizable monomer can form a writing monomer with a high refractive index. This provides a material basis for forming a volume holographic grating with refractive index modulation.

[0048] For example, by controlling the photosensitive initiation system to 0.1 to 4 parts, an appropriate number of photons can be absorbed during exposure, and the polymerization reaction can be controlled at a certain speed, so that the grating can be formed quickly and obtain a high diffraction efficiency. In addition, it can also ensure that the final holographic recording medium has the required light transmittance and that the grating has a certain diffraction efficiency.

[0049] For example, by controlling the chain transfer agent to 0.1 to 3 parts, the polymer chain length can be controlled within a reasonable range, and the excessive polymerization can be effectively prevented, ensuring that the final holographic recording medium has the required optical properties and diffraction efficiency.

[0050] For example, controlling the catalyst to 0.1 to 3 parts can effectively increase the reaction rate of related components and the consumption rate of related components after exposure, thereby quickly forming a concentration difference of monomers in the bright and dark areas and realizing a phase-type volume holographic grating with refractive index modulation.

[0051] For example, by controlling the additive to 0.1 to 7 parts, and taking the additive as a leveling agent, the uniformity of the mixture can be effectively improved, the fluidity can be enhanced, and the cost can be reasonably controlled.

[0052] In some embodiments, the photosensitizing system includes a photosensitizer and / or a photoinitiator. Photosensitizers are also known as dyes or photosensitive dyes.

[0053] In some embodiments, the mass ratio of photosensitizer to photoinitiator is (0.001–1):(0.1–3). By controlling the mass ratio of photosensitizer to photoinitiator within the above range, the concentration of photosensitizer can be effectively controlled, ensuring that the number of absorbed photons during holographic exposure is controlled within a suitable range, the polymerization reaction rate is controlled within a reasonable range, and the grating formation rate is controlled within a certain range, thus guaranteeing the transmittance of the photopolymer holographic recording medium and obtaining excellent diffraction efficiency. In more specific examples, the mass of photosensitizer is 1 / 10 to 1 / 3 of the mass of photoinitiator, such as 1 / 10, 1 / 9, 1 / 8, 1 / 7, 1 / 6, 1 / 5, 1 / 4, or 1 / 3.

[0054] For example, a photoinitiating system can consist of a photosensitizer, a photoinitiator, and a co-initiator. For photoinitiating systems of different wavelengths, the system can consist of a photosensitizer and a photoinitiator, or it can consist of a photosensitizer and a co-initiator. Different broadband responses can also be achieved by adjusting the type of photosensitizer. It should be noted that when a photoinitiator with an appropriate wavelength is selected in the photopolymer-type holographic recording medium material, the photosensitizer may not be added.

[0055] For example, the photosensitizer is a dye that has a high electron transfer efficiency under light irradiation, including but not limited to cyanine dyes, fluorescein dyes, coumarin ketone dyes, nitrogen-containing aromatic heterocyclic compounds, aromatic amine compounds, benzylidene cycloalkane ketone compounds, or any mixture of these compounds in any proportion.

[0056] For example, a photoinitiator is an initiator that can be activated by photochemical radiation and initiate a polymerization reaction of the corresponding polymerizable groups, including but not limited to aromatic ketones, benzoin and its derivatives, benzoyl ketals, acylphosphine oxides, ammonium arylboronate, chromium salts, aryl diazonium salts, onium salts, organometallic compounds, or any mixture of these compounds in any proportion.

[0057] For example, photoinitiators include one or more of the following: benzophenone, alkylbenzophenone, 4,4'-bis(dimethylamino)benzophenone, anthrone and halogenated benzophenone, 2,4,6-trimethylbenzoyldiphenylphosphine oxide, diacylphosphine oxide, phenyl dihydroxyacetate, camphorquinone, α-aminoalkylphenyl ketone, α,α-dialkoxyacetophenone, α-hydroxyalkylphenyl ketone, tetrabutylammonium triphenylhexylborate, tetrabutylammonium tri-(3-fluorophenyl)hexylborate, tetrabutylammonium tri-(3-chloro-4-methylphenyl)hexylborate, ferrocene compounds, iodonium salts, thiodonium salts, and hexaaryldiimidazole.

[0058] For example, the co-initiators are mainly amine substances, including but not limited to ethylenediamine, propylenediamine, isopropylenediamine, epoxide urea, triethanolamine, triisopropanolamine, N-methyldiethanolamine, N,N-dimethylaniline and its variants, N-phenylglycine, and L-cysteine.

[0059] In some embodiments, the photosensitizing initiation system includes a red light photosensitizing initiation system, a green light photosensitizing initiation system, or a blue light photosensitizing initiation system. The photosensitizer of the red light photosensitizing initiation system includes a red light photosensitizing dye, the photosensitizer of the green light photosensitizing initiation system includes a green light photosensitizing dye, and the photosensitizer of the blue light photosensitizing initiation system includes a blue light photosensitizing dye.

[0060] In the embodiments of this application, if the prepared photopolymer holographic recording medium needs to be sensitive to red light, then a red light photoinitiating system is used; if the prepared photopolymer holographic recording medium needs to be sensitive to green light, then a green light photoinitiating system is used; and if the prepared photopolymer holographic recording medium needs to be sensitive to blue light, then a blue light photoinitiating system is used.

[0061] In some embodiments, the red light photosensitive dye may be selected from one or more of methylene blue, cyanine dye, squaric acid cyanine dye, porphyrin dye, and porphyrin dye; the green light photosensitive dye may be selected from one or more of benzylidene cycloalkane ketone compounds, erythrosine, rose red, eosin, and rhodamine B; and the blue light photosensitive dye may be selected from one or more of benzylidene cycloalkane ketone compounds, 3,3′-carbonylbis(7-diethylaminocoumarin), and 5′-riboflavin monophosphate sodium salt.

[0062] It should be noted that, under certain specific circumstances, the photosensitizer of the green light photoinitiating system may not include the green light photosensitive dye, and the photosensitizer of the blue light photoinitiating system may not include the blue light photosensitive dye, thus enabling the prepared photopolymer holographic recording medium to be sensitive to green and blue light.

[0063] In some embodiments, the isocyanate reactive functional group is a hydroxyl or a mercapto group, and compounds having multiple isocyanate reactive functional groups include compounds with a refractive index less than that of the polymerizable monomer and having two or more isocyanate reactive functional groups.

[0064] For example, compounds having multiple isocyanate reactive functional groups generally have a refractive index of less than or equal to 1.55.

[0065] In some embodiments, compounds having multiple isocyanate reactive functional groups may be selected from 2-ethyl-1,3-hexanediol, 1,2,4-butanetriol, 1,6-hexanediol, 2,5-hexanediol, 1,4-cyclohexanediol, 1,8-octanediol, 1,7-heptanediol, 1,3-butanediol, 1,5-pentanediol, 1,4-cyclohexanediol, 1,3-cyclopentanediol, tetraethylene glycol, trimethylolpropane, trimethylolpropane, etc. One or more of the following: propane, glycerol, triethanolamine, polyester polyols with a molecular weight of 100 to 2000, polycarbonate polyols, polyether polyols, 2,3-dithio(2-mercapto)-1-propanethiol, 1,2-octanedithiol, 2,5-dimethylmercapto-1,4-dithiane, 1,2-butanedithiol, 1,3-butanedithiol, 3,7-dithia-1,9-nonanedithiol, and 2,3-butanedithiol.

[0066] In some embodiments, the polyisocyanate-based compound includes a compound with a refractive index less than that of the polymerizable monomer and having two or more isocyanate groups.

[0067] For example, the refractive index of polyisocyanate-based compounds is generally less than or equal to 1.55.

[0068] In some embodiments, the polyisocyanate compound may be selected from one or more of hexamethylene diisocyanate, trimethylhexamethylene diisocyanate, (2,4,6-trioxotriazine-1,3,5(2H,4H,6H)-triyl)tri(hexamethylene)isocyanate, butane-1,4-diisocyanate, isophorone diisocyanate, and dicyclohexylmethane diisocyanate.

[0069] In some embodiments, the polymerizable monomer may be selected from at least one of alkenylnaphthalene compounds, alkenylanthracene compounds, alkenylbenzene compounds, acrylic compounds, methacrylic acid compounds, acrylate compounds, methacrylate compounds, N-vinylpyrrole, N-vinylcarbazole, N-vinylimidazol, N-vinylindole, N-vinylpyrrolidone, and trans-N-3-yntynebutenylcarbazole.

[0070] For example, alkenyl naphthalene compounds can be selected from 1-vinylnaphthalene, 2-vinylnaphthalene, etc.

[0071] For example, alkenyl anthracene compounds may be selected from 2-vinylanthracene, 9-vinylanthracene, etc.

[0072] For example, alkenylbenzene compounds can be selected from styrene, 2-chlorostyrene, 2-bromostyrene, 3-chlorostyrene, 3-bromostyrene, 4-chlorostyrene, 4-bromostyrene, p-(chloromethyl)styrene, p-(bromomethyl)styrene, etc.

[0073] For example, methacrylic acid compounds may be selected from methacrylic acid and its derivatives; for example, acrylate compounds may be selected from pentabromophenyl acrylate, pentachlorophenyl acrylate, phenoxyethyl acrylate, pentabromobenzyl acrylate, 2-naphthyl acrylate, 1,4-di(2-thionaphthyl)2-butyl acrylate, phenoxyethoxyethyl acrylate, bisphenol A diacrylate, tetrabromobisphenol A diacrylate, 2-phenoxyethyl acrylate, benzyl acrylate, p-chlorophenyl acrylate, 2,4,6-trichlorophenyl acrylate, p-bromophenyl acrylate, 2,4,6-tribromophenyl acrylate, propane-2,2-diylbis[(2,6-dibromo-4,1-phenylene)oxy(2-{[3,3,3-tris(4-chlorophenyl)propionyl]oxy}propane-3,1-diyl)oxyethane-2,1-diyl]diacrylate, etc.

[0074] For example, methacrylate compounds may be selected from 2-phenoxyethyl methacrylate, benzyl methacrylate, p-bromophenyl methacrylate, p-chlorophenyl methacrylate, 2,4,6-trichlorophenyl methacrylate, pentabromophenyl methacrylate, pentachlorophenyl methacrylate, phenoxyethyl methacrylate, phenoxyethoxyethyl methacrylate, 1,4-di(2-thionaphthyl)2-butyl methacrylate, pentabromobenzyl methacrylate, 2-naphthyl methacrylate, bisphenol A dimethacrylate, tetrabromobisphenol A dimethacrylate, etc.

[0075] In some embodiments, the chain transfer agent is a thiol compound, including but not limited to one or more of dodecyl mercaptan, mercaptoethanol, hexamethylene mercaptan, phenylethyl mercaptan, 5-(4-pyridyl)-1,3,4-oxadiazole-2-thiol, and 4-methyl-4H-1,2,4-triazole-3-thiol. Controlling the amount of chain transfer agent allows the polymer chain length to be kept within a reasonable range and effectively prevents excessive polymerization, ensuring that the final holographic recording medium has the required optical properties and diffraction efficiency.

[0076] In some embodiments, the catalyst is a tertiary amine catalyst or an organometallic catalyst, including but not limited to triethylenediamine, bis(dimethylaminoethyl) ether, dimethylethanolamine, 2-(2-dimethylaminoethoxy)ethanol, trimethylhydroxyethylpropanediamine, N,N-bis(dimethylaminopropyl)isopropanolamine, dibutyltin dilaurate, stannous octoate, potassium carboxylate catalysts, and bismuth carboxylate catalysts. Controlling a certain amount of catalyst can effectively increase the reaction rate of the relevant components and the consumption rate of the relevant components after exposure, thereby rapidly forming a concentration difference of monomers in the bright and dark areas to obtain photopolymers.

[0077] In some embodiments, the additives include one or more of defoamers, leveling agents, plasticizers, and dehydrating agents.

[0078] For example, when the additive includes a defoamer, the content of the defoamer does not exceed 3% based on the total mass of the photopolymer holographic recording medium.

[0079] For example, when the additive includes a leveling agent, the leveling agent content does not exceed 3% based on the total mass of the photopolymer holographic recording medium.

[0080] For example, when the additive includes a plasticizer, the plasticizer content does not exceed 3% based on the total mass of the photopolymer-type holographic recording medium.

[0081] For example, the defoamer is a silicone defoamer, such as BYK-011, BYK-012, BYK-014, BYK-023, BYK-051N, BYK-085, BYK-1610, BYK-1707, BYK-1740, BYK-1760 manufactured by BYK Corporation, DC65, AFE-7820 manufactured by Dow Corning Corporation, or any mixture of these defoamers in any proportion.

[0082] For example, the leveling agent is a silicone surface additive, such as BYK-302, BYK-306, BYK-307, BYK-327, BYK-329, BYK-333, BYK-356, BYK-358, BYK-378, BYK-3455, BYK-3566, or any mixture of these surface additives manufactured by BYK Corporation.

[0083] For example, the plasticizer is toluene, xylene, dimethylformamide, dimethylacetamide, glycerol, phthalates, or any mixture of these compounds in any proportion.

[0084] Examples of dehydrating agents include, but are not limited to, p-toluenesulfonyl isocyanate, triethyl orthoformate, CUWR-WB20 dehydrating agent from Guangzhou Yourun Synthetic Materials Co., Ltd., ALT-201 dehydrating agent from Anxiang Elite Chemical Co., Ltd., and PCCI dehydrating agent from Shanghai Luer Chemical Trading Co., Ltd.

[0085] The following describes a method for preparing a photopolymer-type holographic recording medium comprising the aforementioned components.

[0086] As shown in Figure 1, this application embodiment also provides a method for fabricating a volume holographic grating, including the following steps:

[0087] S101. Provides a mixed solution of three photopolymer holographic recording media, wherein the photoinitiation systems of the three photopolymer holographic recording media are red light photoinitiation system, green light photoinitiation system and blue light photoinitiation system, respectively;

[0088] S102. Provide a substrate and uniformly distribute a mixed solution of a first photopolymer type holographic recording medium on the surface of the substrate to generate a first photopolymer film on the surface of the substrate.

[0089] S103. The mixed solution of the second type of photopolymer holographic recording medium is uniformly distributed on the surface of the first photopolymer film to generate a second photopolymer film on the surface of the first photopolymer film. The residual isocyanate reactive functional groups or isocyanate groups in the first and second photopolymer films react to connect the first photopolymer film to the second photopolymer film in a covalent manner.

[0090] S104. A mixed solution of a third type of photopolymer holographic recording medium is uniformly distributed on the surface of a second photopolymer film to generate a third photopolymer film on the surface of the second photopolymer film. The residual isocyanate reactive functional groups or isocyanate groups in the second and third photopolymer films react to connect the second photopolymer film to the third photopolymer film in a covalent manner.

[0091] S105. Expose the multilayer photopolymer film to obtain a volume holographic grating.

[0092] In the embodiments of this application, the photosensitive initiation systems of the first, second, and third photopolymer holographic recording media are different. The composition of the photopolymer holographic recording media can be referred to the above embodiments, and will not be repeated here.

[0093] For example, the photosensitive initiation systems of the first, second, and third photopolymer-type holographic recording media can be red light photosensitive initiation system, green light photosensitive initiation system, and blue light photosensitive initiation system, respectively, or they can be blue light photosensitive initiation system, red light photosensitive initiation system, and green light photosensitive initiation system, respectively. That is, the order in which the photopolymer thin film is formed on the substrate and the stacking order can be determined according to the coating order, and no specific limitation is made here.

[0094] For example, two beams of light are coherently exposed, and after the exposure is completed, they are polymerized by ultraviolet light. After the polymerization is completed, a volume holographic grating can be produced.

[0095] It should be noted that residual isocyanate reactive functional groups or isocyanate groups are present in the first, second, and third photopolymer films.

[0096] As can be seen from the above, the method for fabricating volume holographic gratings proposed in this application has few fabrication steps, is simple to operate, and is easy to implement, making it easy to obtain volume holographic gratings with high refractive index modulation and diffraction efficiency for red, green, and blue light.

[0097] This application provides a volume holographic grating, wherein the photopolymer holographic recording medium used in the volume holographic grating includes the photopolymer holographic recording medium described in any of the above embodiments or is prepared by the volume holographic grating preparation method described in any of the above embodiments.

[0098] This application also provides a volume holographic grating, which includes a red light photosensitive photopolymer film, a green light photosensitive photopolymer film, and a blue light photosensitive photopolymer film.

[0099] The red light photosensitive polymer film, the green light photosensitive polymer film, and the blue light photosensitive polymer film are stacked together, and adjacent films are connected by covalent bonds formed by isocyanate reactive functional groups or isocyanate groups.

[0100] For example, the stacking order of the red light photosensitive photopolymer film, the green light photosensitive photopolymer film, and the blue light photosensitive photopolymer film can be determined according to the coating order. For example, the stacking order from bottom to top can be: substrate—red light photosensitive photopolymer film—green light photosensitive photopolymer film—blue light photosensitive photopolymer film, or substrate—blue light photosensitive photopolymer film—red light photosensitive photopolymer film—green light photosensitive photopolymer film. No specific limitation is made here.

[0101] In some embodiments, the red light photosensitive photopolymer film, the green light photosensitive photopolymer film, and the blue light photosensitive photopolymer film all include varying numbers of isocyanate reactive functional groups and isocyanate groups.

[0102] In some embodiments, the ratio of the number of isocyanate reactive functional groups to the number of isocyanate groups is 1:(1.01 to 1.5) or (1.01 to 1.5):1. This allows control over the number of residual unreacted functional groups in the photopolymer-type holographic recording medium, avoiding the presence of a large number of unreacted functional groups that could affect the holographic recording performance.

[0103] For example, the ratio of the number of isocyanate reactive functional groups to the number of isocyanate groups can be 1:1.01, 1:1.35, 1:1.5, 1.01:1, 1.35:1, or 1.5:1, and no specific limitation is made here.

[0104] In some embodiments, the ratio of the number of isocyanate reactive functional groups to the number of isocyanate groups is 1:(1.01 to 1.3) or (1.01 to 1.3):1. This allows control over the number of residual unreacted functional groups in the photopolymer holographic recording medium, resulting in good bonding between the layers of photopolymer films and good holographic recording performance.

[0105] For example, the ratio of the number of isocyanate reactive functional groups to the number of isocyanate groups can be 1:1.01, 1:1.2, 1:1.3, 1.01:1, 1.2:1, or 1.3:1, and no specific limitation is made here.

[0106] As can be seen from the above, the volume holographic grating proposed in this application has a structure of three layers of photosensitive photopolymer thin films, and the photopolymer thin films are connected by covalent bonds. At the same time, the volume holographic grating has high refractive index modulation and diffraction efficiency for red, green and blue light.

[0107] This application also provides a holographic device, which includes the volume holographic grating described in any of the above embodiments.

[0108] The embodiments of this application will be described below through specific examples.

[0109] Example 1: Six photopolymer-type holographic recording media 1-6 are provided. The preparation method of the photopolymer-type holographic recording media is to mix all the components provided above evenly. The raw material components are detailed in Tables 1-6.

[0110] Table 1

[0111] Table 2

[0112] Table 3

[0113] Table 4

[0114] Table 5

[0115] Table 6

[0116] It should be noted that in Tables 1-6, the components of the photopolymer holographic recording media include: a) compounds and components with multiple isocyanate reactive functional groups; and b) polyisocyanate compounds, where the number of isocyanate reactive functional groups differs from the number of isocyanate groups. Furthermore, the photoinitiation systems for the photopolymer holographic recording media in Tables 1 and 2 are red light photoinitiation systems, those in Tables 3 and 4 are green light photoinitiation systems, and those in Tables 5 and 6 are blue light photoinitiation systems.

[0117] Example 2: Samples 1-8 were prepared using photopolymer holographic recording media 1-6. The photopolymers included a first photopolymer film, a second photopolymer film, and a third photopolymer film, which were formed by mixing a solution of any one of the above-mentioned photopolymer holographic recording media 1-6.

[0118] The first photopolymer film is disposed on the substrate, and the first photopolymer film, the second photopolymer film and the third photopolymer film are stacked in sequence. Adjacent films are connected by covalent bonds. Please refer to Table 7 for details.

[0119] Table 7

[0120] Comparative example:

[0121] Comparative samples 9-16 were prepared using photopolymer holographic recording media 7-12, as detailed in Table 8.

[0122] Among them, the components used in the photopolymer holographic recording medium 7-12 are basically one-to-one with those used in the photopolymer holographic recording medium 1-6. The difference is that in component a) compounds with multiple isocyanate reactive functional groups and component b) polyisocyanate group compounds, the number of isocyanate reactive functional groups is the same as the number of isocyanate groups. That is, the photopolymer films formed by the photopolymer holographic recording medium 7-12 do not have any residual isocyanate reactive functional groups and isocyanate groups.

[0123] Table 8

[0124] Since the photopolymer films formed by the photopolymer holographic recording media 7-12 do not have residual isocyanate reactive functional groups and isocyanate groups, the first, second and third photopolymer films formed by the photopolymers 9-16 are all connected by a bonding process.

[0125] Experimental example:

[0126] The holographic performance parameters of samples 1 to 6 in Example 2 were tested, and the results are shown in Table 9 and Figure 2. The adhesion between adjacent photopolymer films in samples 1-16 was tested, and the results are shown in Table 10.

[0127] (1) The test method for the performance of holographic recording media includes the following steps:

[0128] Solid-state lasers with wavelengths of 633 nm, 532 nm, and 457 nm were used as light sources. After passing through a beam expander, beam splitter, and half-wave plate, two beams with the same intensity and a diameter of 8 mm were obtained. The two beams were intersected and exposed within the prepared holographic recording medium, with a light intensity of 2.91 mW / cm². 2 For each group of samples, exposure was performed sequentially at 633nm, 532nm, and 457nm. After exposure, the UV-Vis transmittance curve of the sample was measured by photobleaching, and the single-grating diffraction efficiency (η) of the photopolymer sample at different wavelengths was calculated by formula (1).

[0129] In the formula, η is the diffraction efficiency, and I d For diffracted light, I t This is transmitted light.

[0130] (2) The adhesion between adjacent photopolymer films in the photopolymer was tested using a cross-cut adhesion test.

[0131] The cross-cut adhesion test (CBT) is the most common method for testing paint film adhesion. According to international standards, it is divided into six levels: 0B, 1B, 2B, 3B, 4B, and 5B. The higher the level, the stricter the requirements. Level 5B indicates smooth edges with no paint peeling at the edges and intersections. Level 4B indicates small areas of paint peeling at the intersections, with the total peeling area less than 5%. Level 3B indicates small areas of paint peeling at the edges and intersections, with the total peeling area between 5% and 15%. Level 2B indicates large areas of paint peeling at the edges and intersections, with the total peeling area between 15% and 35%. Level 1B indicates large areas of paint peeling at the edges and intersections, with the total peeling area between 35% and 65%. Level 0B indicates that the peeling area exceeds the 1B standard.

[0132] The 100-point test method includes the following steps:

[0133] Use a crisscross cutter to cut a cross grid pattern on the coating, cutting down to the photopolymer film; brush five times diagonally with a brush, then stick tape to the cut and pull it off (the instructions are to use 3M 600 or 610 tape to stick in the grid, and quickly pull up the 3M tape); observe the grid area, and use a magnifying glass to observe the number of times the tape has been pulled up.

[0134] Table 9

[0135] Table 10

[0136] The photopolymer-type holographic recording medium provided in this application embodiment has high sensitivity. Specifically, the diffraction efficiency of the holographic recording medium can be adjusted between 10% and 100% according to actual needs, and the exposure dose is less than 30 mJ / cm. 2 Furthermore, in the volume holographic grating provided in this application embodiment, each layer of photopolymer film is connected by covalent bonds, and each photopolymer film is independent of the others. Each layer of photopolymer film can use the refractive index modulation of the corresponding layer of photopolymer, as shown in Figure 2. The volume holographic grating provided in this application has high refractive index modulation and diffraction efficiency for red, green and blue light.

[0137] It should be understood that the terminology used in this application specification is for the purpose of describing particular embodiments only and is not intended to limit the application.

[0138] It should also be understood that the term “and / or” as used in this application specification and the appended claims means any combination of one or more of the associated listed items and all possible combinations, and includes such combinations.

[0139] The above description is merely a specific embodiment of this application, but the scope of protection of this application is not limited thereto. Any person skilled in the art can easily conceive of various equivalent modifications or substitutions within the technical scope disclosed in this application, and such modifications or substitutions should all be covered within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.

Claims

1. A photopolymer-type holographic recording medium, the photopolymer-type holographic recording medium comprising a compound having multiple isocyanate reactive functional groups, a polyisocyanate group compound, a polymerizable monomer, a photoinitiator system, a chain transfer agent, a catalyst, and additives; in, The number of isocyanate reactive functional groups differs from the number of isocyanate groups in the polyisocyanate compound.

2. The photopolymer-type holographic recording medium according to claim 1, wherein, The ratio of the number of isocyanate reactive functional groups to the number of isocyanate groups is 1:(1.01~1.5) or (1.01~1.5):

1.

3. The photopolymer-type holographic recording medium according to claim 2, wherein, The ratio of the number of isocyanate reactive functional groups to the number of isocyanate groups is 1:(1.01~1.3) or (1.01~1.3):

1.

4. The photopolymer-type holographic recording medium according to claim 1, wherein, The mass ratio of the compound having multiple isocyanate reactive functional groups, the polyisocyanate group compound, the polymerizable monomer, the photoinitiator system, the chain transfer agent, the catalyst, and the additive is (30-70):(10-50):(0.1-60):(0.1-4):(0.1-3):(0.1-3):(0.1-7).

5. The photopolymer-type holographic recording medium according to claim 1, wherein, The photosensitive initiation system includes a photosensitizer and / or a photoinitiator; When the photoinitiation system includes a photosensitizer and a photoinitiator, the mass ratio of the photosensitizer to the photoinitiator is (0.001~1):(0.1~3).

6. The photopolymer-type holographic recording medium according to claim 5, wherein, The photosensitive initiation system includes a red light photosensitive initiation system, a green light photosensitive initiation system, or a blue light photosensitive initiation system. The photosensitizer of the red light photosensitive initiation system includes a red light photosensitive dye, the photosensitizer of the green light photosensitive initiation system includes a green light photosensitive dye, and the photosensitizer of the blue light photosensitive initiation system includes a blue light photosensitive dye. The red light-sensitive dye is at least one of methylene blue, anthocyanin dye, squaric acid cyanin dye, porphyrin dye, and porphyrin dye. The green photosensitive dye is at least one of benzylidene cycloalkane ketone compounds, erythrosine, rose red, eosin, and rhodamine B; The blue light-sensitive dye is at least one of a benzylidene cycloalkane ketone compound, 3,3′-carbonylbis(7-diethylaminocoumarin), or sodium 5'-riboflavin monophosphate.

7. The photopolymer-type holographic recording medium according to claim 5, wherein, The photoinitiation system consists of a photosensitizer, a photoinitiator, and a co-initiator.

8. The photopolymer-type holographic recording medium according to claim 1, wherein, The isocyanate reactive functional group is a hydroxyl or a mercapto group, and the compound having multiple isocyanate reactive functional groups includes compounds with a refractive index less than that of the polymerizable monomer and having two or more isocyanate reactive functional groups.

9. The photopolymer-type holographic recording medium according to claim 8, wherein, The compound having multiple isocyanate reactive functional groups has a refractive index of less than or equal to 1.

55.

10. The photopolymer-type holographic recording medium according to claim 8, wherein, The compounds having multiple isocyanate reactive functional groups are 2-ethyl-1,3-hexanediol, 1,2,4-butanetriol, 1,6-hexanediol, 2,5-hexanediol, 1,4-cyclohexanediol, 1,8-octanediol, 1,7-heptanediol, 1,3-butanediol, 1,5-pentanediol, 1,4-cyclohexanediol, 1,3-cyclopentanediol, tetraethylene glycol, trimethylolethane, and trimethylolpropane. At least one of the following: glycerol, triethanolamine, polyester polyol with a molecular weight of 100 to 2000, polycarbonate polyol, polyether polyol, 2,3-dithio(2-mercapto)-1-propanethiol, 1,2-octanedithiol, 2,5-dimethylmercapto-1,4-dithiane, 1,2-butanedithiol, 1,3-butanedithiol, 3,7-dithia-1,9-nonanedithiol, and 2,3-butanedithiol.

11. The photopolymer-type holographic recording medium according to claim 1, wherein, The polyisocyanate-based compounds include compounds with a refractive index less than that of the polymerizable monomer and containing two or more isocyanate groups.

12. The photopolymer-type holographic recording medium according to claim 11, wherein, The refractive index of the polyisocyanate-based compound is less than or equal to 1.

55.

13. The photopolymer-type holographic recording medium according to claim 11, wherein, The polyisocyanate group compound is at least one of hexamethylene diisocyanate, trimethylhexamethylene diisocyanate, (2,4,6-trioxotriazine-1,3,5(2H,4H,6H)-triyl)tri(hexamethylene)isocyanate, butane-1,4-diisocyanate, isophorone diisocyanate, and dicyclohexylmethane diisocyanate.

14. The photopolymer-type holographic recording medium according to claim 1, wherein, The polymerizable monomer is at least one of the following: alkenylnaphthalene compounds, alkenylanthracene compounds, alkenylbenzene compounds, acrylic acid compounds, methacrylic acid compounds, acrylate compounds, methacrylate compounds, N-vinylpyrrole, N-vinylcarbazole, N-vinylimidazol, N-vinylindole, N-vinylpyrrolidone, and trans-N-3-yntynebutenylcarbazole.

15. A volume holographic grating, the volume holographic grating comprising a red light photosensitive photopolymer film, a green light photosensitive photopolymer film, and a blue light photosensitive photopolymer film; in, The red light photosensitive polymer film, the green light photosensitive polymer film, and the blue light photosensitive polymer film are stacked together, and adjacent films are connected by covalent bonds formed by isocyanate reactive functional groups or isocyanate groups.

16. The volume holographic grating according to claim 15, wherein, The red light photosensitive polymer film, the green light photosensitive polymer film, and the blue light photosensitive polymer film all include varying numbers of isocyanate reactive functional groups and isocyanate groups.

17. The volume holographic grating according to claim 15, wherein, The ratio of the number of isocyanate reactive functional groups to the number of isocyanate groups is 1:(1.01~1.5) or (1.01~1.5):

1.

18. The volume holographic grating according to claim 17, wherein, The ratio of the number of isocyanate reactive functional groups to the number of isocyanate groups is 1:(1.01~1.3) or (1.01~1.3):

1.

19. The volume holographic grating according to claim 15, wherein, The volume holographic grating is prepared by the following method: A mixed solution of three photopolymer holographic recording media is provided, wherein the photoinitiation systems of the three photopolymer holographic recording media are red light photoinitiation system, green light photoinitiation system and blue light photoinitiation system, respectively; A substrate is provided, and a mixed solution of a first photopolymer type holographic recording medium is uniformly distributed on the surface of the substrate to generate a first photopolymer film on the surface of the substrate; A mixed solution of a second type of photopolymer holographic recording medium is uniformly distributed on the surface of the first photopolymer film to generate a second photopolymer film on the surface of the first photopolymer film. The residual isocyanate reactive functional groups or isocyanate groups in the first and second photopolymer films react to connect the first photopolymer film to the second photopolymer film in a covalent manner. A mixed solution of a third type of photopolymer holographic recording medium is uniformly distributed on the surface of the second photopolymer film to generate a third photopolymer film on the surface of the second photopolymer film. The residual isocyanate reactive functional groups or isocyanate groups in the second and third photopolymer films react to connect the second photopolymer film to the third photopolymer film in a covalent manner. The volume holographic grating is prepared by exposing a multilayer photopolymer film.

20. A holographic device comprising a volume holographic grating as described in any one of claims 15-19.

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