Holographic gratings and augmented / mixed reality devices

Abstract

The present disclosure relates to a holographic grating including a holographic photopolymer, and to an augmented reality / virtual reality device including the holographic grating. The holographic grating can include at least one nanoparticle, a bright portion, a dark portion, and a holographic photopolymer. The holographic photopolymer can also include a polymer matrix, a writing monomer, and a dye system. The holographic photopolymer can be dispersed throughout the bright portion and the dark portion of the holographic grating. In some forms, the bright portion can include a first concentration of the nanoparticle and / or the dark portion can include a second concentration of the nanoparticle. The first concentration of the nanoparticle can be greater than the second concentration of the nanoparticle.

Description

[0001] Inventors: Nan Hu, Peng Wang, Sergey Simavoryan, Hongxi Zhang

[0002] Cross-reference to related applications

[0003] This application claims the benefit of U.S. Provisional Application No. 63 / 568,416, filed March 21, 2024, which is incorporated herein by reference in its entirety. Technical Field

[0004] This disclosure relates to a holographic grating comprising a holographic optical polymer, which can be used in augmented reality / mixed reality (AR / MR) glasses, optical displays, and other holographic applications. Background Technology

[0005] As the use of augmented reality glasses and optical displays becomes increasingly prevalent, the demand for improved holographic media is growing. Holographic media or materials can be generated by holographic gratings (e.g., volumetric holographic gratings). For example, as taught in U.S. Patent Nos. 9,281,000 B2 and 8,771,904 B2, photopolymer formulations comprise a chemically crosslinked matrix polymer, a writing monomer, and a photoinitiator system for generating holographic media via a volumetric holographic grating. However, methods for generating such photopolymer formulations require nitrogen purging to remove oxygen, which presents an economically viable requirement. Furthermore, if oxygen is not completely removed, free radicals can oxidize the polymer, thus leading to defective polymerization of the polymer.

[0006] Furthermore, the combination of a high refractive index and low thickness is crucial for achieving a highly visible hologram. Most volumetric grating hologram films used in AR / MR glasses achieve only 50% reflectivity but have a thickness greater than 12 µm, resulting in low refractive index modulation. By increasing this refractive index modulation to greater than 0.03, thin hologram films with a thickness between 5 and 12 µm can be produced without compromising the wider field of view of AR / MR glasses.

[0007] Therefore, there is a need for further contributions in this technical field. More specifically, but not exclusively, there is a need for thin holographic polymers / films and methods for their preparation, exhibiting refractive index modulation greater than 0.03, low levels of scattering, transmittance greater than 90%, and haze less than 1.5%. Summary of the Invention

[0008] This disclosure generally relates to a holographic grating comprising a holographic photopolymer, and to an augmented reality / virtual reality device comprising the holographic grating.

[0009] In one embodiment, a holographic grating includes at least one nanoparticle, a bright portion, a dark portion, and a holographic photopolymer. In some forms, the holographic grating may include at least one photocurable nanoparticle. In some forms, the holographic photopolymer may be dispersed throughout the bright and dark portions of the holographic grating. In some forms, the bright portion may include a first concentration of the nanoparticles, and the dark portion may include a second concentration of the nanoparticles. In some forms, the first concentration of the nanoparticles is greater than the second concentration of the nanoparticles.

[0010] In some forms, the at least one nanoparticle may comprise an inorganic nanocrystal core and an organic surface-modified shell. In some forms, the at least one nanoparticle may have a diameter of about 1 nm to about 25 nm. In some forms, the at least one nanoparticle may be present in about 5 wt% to about 90 wt% of the total weight of the holographic photopolymer. In some embodiments, the inorganic nanocrystal core may comprise at least one of ZrO2, TiO2, TiO2 core-ZrO2 shell materials, ZnO, CeO2, Ta2O5 / SiO2, and ITO. In some forms, the organic surface-modified shell comprises at least one reactive portion.

[0011] In some forms, the holographic photopolymer may include a polymer matrix. In some forms, the polymer matrix includes a grid size that may be larger than the size of the nanocrystal core of the photocurable nanoparticles. In some forms, the holographic photopolymer may include a writing monomer, which in some forms may be a photocurable writing monomer. In some forms, the holographic photopolymer may include a dye system.

[0012] In some forms, the polymer matrix may exhibit a low refractive index (RI), for example, less than about 1.6, although variations in this value are possible and expected. In some forms where the polymer matrix exhibits a low RI, the polymer matrix may comprise aliphatic polyurethane. Alternatively, in some forms where the polymer matrix exhibits a low RI, it may comprise one or more of polypropylene glycol, NCO-terminated aliphatic prepolymers, and organotin catalysts. For example, the NCO-terminated aliphatic prepolymer may comprise one or more ether groups, polyether polyols, or combinations thereof.

[0013] In some forms, the writing monomer may exhibit a high RI, for example, greater than about 1.45, resulting in a refractive index modulation (Δn) greater than about 0.04, although variations in both values ​​are possible and expected. In some forms of the liquid writing monomer exhibiting a high RI, it may include at least one crosslinkable monomer. For example, the at least one crosslinkable monomer may include at least one crosslinkable portion and at least one polymerizable monomer comprising at least one polymerizable portion, or a combination thereof. In some forms of the liquid writing monomer exhibiting a high RI, it may include ethoxylated fluorene diacrylate, m-phenoxybenzyl acrylate, 2-hydroxy-3-phenoxypropyl acrylate, biphenyl methyl acrylate, ethoxylated bisphenol A diacrylate, N-vinylpyrrolidone, and said at least one nanoparticle.

[0014] In some forms, the holographic grating may further comprise a solvent, such as 1-ethyl-2-pyrrolidone.

[0015] In some forms of the holographic photopolymer comprising a dye system, the dye system may include a dye and a co-initiator. The dye may include at least one of Safranin O, neomethylene blue, and ethyl violet. In some forms, the co-initiator may include at least one of tetrabutylammonium tri(3-chloro-4-methylphenyl)(hexyl)borate and tetrabutylammonium butyltriphenylborate. In some forms, the ratio of the dye to the co-initiator may be from about 1:10 to about 1:14.

[0016] In one implementation, the augmented reality / mixed reality (AR / MR) device includes the hologram described herein.

[0017] In another embodiment, the film comprises the holographic grating described herein.

[0018] These and other implementation methods are described in more detail below. Attached Figure Description

[0019] Figure 1 Explain the holographic grating.

[0020] Figure 2A and Figure 2B Explanation of nanoparticles.

[0021] Figure 3 A schematic diagram of the experimental setup for measuring the characteristics of holographic photopolymers.

[0022] Figure 4 A graphical illustration showing the reflectivity efficiency from 400 to 700 nm.

[0023] Figure 5 A graphical illustration to show the measurement data of transmittance.

[0024] Figure 6 A graphical illustration showing the measurement data of total transmittance.

[0025] Figure 7 A graphical illustration of measurement data showing the stability of reflection efficiency over time.

[0026] Figure 8 A graphical illustration to show the measurement data of transmittance. Detailed Implementation

[0027] In one embodiment, a holographic medium is provided for use in augmented reality / mixed reality (AR / MR) devices and / or optical displays. Other embodiments involve holographic gratings and / or holographic photopolymers.

[0028] In one embodiment, the holographic grating includes at least one nanoparticle, a bright portion, a dark portion, and a holographic photopolymer. In some forms, the holographic photopolymer may include a polymer matrix. In some forms, the holographic photopolymer may include a writing monomer. In some forms, the holographic photopolymer may include a dye system. For example, the holographic photopolymer can provide a highly visible hologram for use in AR / MR 3D glasses, thus improving the user's viewing experience. In another embodiment, a film (e.g., a photopolymer film) is prepared according to the methods described herein. In some forms, the film may include the holographic grating described herein.

[0029] As used in this article, the term "bond" or "bonded" refers to a chemical bond between two atoms or two parts when the atoms connected by the bond are considered to be part of a larger structure.

[0030] As used herein, the term "moiety" refers to a specific segment or functional group of a molecule. For example, a chemical moiety can be a recognizable chemical entity embedded in or attached to a molecule.

[0031] This disclosure relates to a holographic grating comprising a holographic photopolymer and an augmented reality / virtual reality device comprising the holographic grating. In one embodiment, the holographic grating comprises at least one nanoparticle, a bright portion, a dark portion, and a holographic photopolymer. In some forms, the holographic photopolymer may comprise a polymer matrix, a writing monomer, and a dye system. In some forms, the holographic photopolymer may further comprise a solvent.

[0032] like Figure 1As shown, for example, the holographic photopolymer can be dispersed throughout the bright portion 103 and dark portion 105 of the holographic grating 101. In some forms, the bright portion 103 may include a first concentration of the nanoparticles, the dark portion 105 may include a second concentration of the nanoparticles, and the first concentration of the nanoparticles may be greater than the second concentration of the nanoparticles. In some forms, the higher concentration of the nanoparticles in the bright portion 103 relative to the dark portion 105 in the holographic grating 101 can be achieved by exposure to a light pattern. In some forms, exposure to the light pattern used to form the holographic grating 101 can deplete the reactive portions in the bright portion 103, which drives the diffusion of writing monomers including the nanoparticles from the dark portion 105 to the bright portion 103. Therefore, the diffraction efficiency of the holographic grating 101 can be enhanced. Figure 1 As depicted, the holographic grating 101 may include more than one bright portion 103 and more than one dark portion 105.

[0033] In some forms, the holographic polymer may include a polymer matrix exhibiting a low RI (e.g., less than about 1.6). In some embodiments where the polymer matrix exhibits a low RI, the polymer matrix may include an aliphatic polyurethane, and / or may include a siloxane or epoxy. In some forms where the polymer matrix exhibits a low RI, the polymer matrix may include a polar mixing precursor for high compatibility with the nanoparticles. The polar mixing precursor may include a prepolymer comprising a high concentration of polar moieties, such as hydroxyl, urethane, mercapto, or sulfonic acid groups, or combinations thereof. In some forms where the polymer matrix exhibits a low RI, the polymer matrix may include polypropylene glycol, an NCO-terminated aliphatic prepolymer, and an organotin catalyst. Some more specific, but not limiting, examples of the polymer matrix include Arcol PPG-725 (polypropylene glycol, Covestro, Germany), Arcol LHT-112 (polypropylene glycol, Covestro, Germany), Desmodur WP 260 (NCO-terminated aliphatic prepolymer, Covestro, Germany), or Fomorez UL-28 (organotin catalyst, Galata Chemicals, USA).

[0034] In some forms, the polymer matrix may include a grid size greater than about 5 nm, greater than about 10 nm, greater than about 20 nm, greater than about 30 nm, or greater than about 40 nm. As used herein, grid size refers to the average distance between the two crosslinking agents within the polymer matrix. In some forms, the polymer matrix includes a grid size greater than the size of the nanocrystal nucleus of the at least one nanoparticle. Without being bound by any particular theory, it is believed that a polymer matrix having a grid size greater than the nanocrystal nucleus allows the nanoparticles to diffuse across the polymer matrix. In some forms, the polymer matrix may be non-photocurable to prevent the polymer matrix from curing upon exposure to light. In some forms, the polymer matrix may be about 25% by weight to about 50% by weight, about 25% by weight, about 30% by weight, about 35% by weight, about 40% by weight, about 45% by weight, or about 50% by weight, or any weight percentage within this range (e.g., 36%) of the holographic photopolymer. In some forms where the polymer matrix includes aliphatic polyurethane, it may improve compatibility with the present polypropylene glycol. The polymer matrix may also include a tin catalyst (e.g., an organotin catalyst). For example, the organotin catalyst may include 1-ethyl-2-pyrrolidone.

[0035] In some forms, the holographic polymer may include a writing monomer. In some forms, the writing monomer may exhibit high RI (Residual Intensity). In some forms, the writing monomer may include a high-RI liquid writing monomer that is photosensitive and curable upon exposure to ultraviolet or visible light. In some forms, the high-RI liquid writing monomer may include at least one crosslinkable monomer comprising at least one crosslinkable portion and at least one polymerizable monomer comprising at least one polymerizable portion, or a combination thereof. In some forms, the high-RI liquid writing monomer may include ethoxylated fluorene diacrylate, m-phenoxybenzyl acrylate, 2-hydroxy-3-phenoxypropyl acrylate (CAS No.: 16969-10-1), biphenyl methyl acrylate (CAS No.: 54140-58-8), ethoxylated bisphenol A diacrylate, and at least one of the nanoparticles. In some forms, the writing monomer may be photocurable because it cures upon exposure to light. In some forms, the photocurable writing monomer can be cured upon exposure to light having wavelengths of about 190 nm to about 980 nm, about 190 nm, about 200 nm, about 250 nm, about 300 nm, about 400 nm, about 500 nm, about 600 nm, about 700 nm, about 800 nm, about 900 nm, about 980 nm, or any wavelength (e.g., 515 nm) within this range. Some non-limiting examples of writing monomers that can be used in the holographic photopolymer include EA-F5710 (a mixture of ethoxylated fluorene diacrylate and m-phenoxybenzyl acrylate) (OSAKA GAS Chemicals, Japan), 2-hydroxy-3-phenoxypropyl acrylate (Sigma-Aldrich, Germany), SR349 (Sartomer Americas, USA), biphenyl methyl acrylate (MiwonSpecialty Chemical Co., South Korea), and N-vinylpyrrolidone (BASF, Germany). It is believed that writing monomers and polymer matrices with similar structures can achieve increased miscibility. Furthermore, the specific writing monomers used can unexpectedly result in improved diffusion of nanoparticles from the dark portion to the bright portion of the holographic grating.

[0036] As will be discussed in more detail below, in some forms, the at least one nanoparticle of the holographic grating may comprise one or more organically surface-modified nanoparticles. In these forms, and without being bound by any particular theory, it is believed that for organically surface-modified nanoparticles, depending on the number of functional groups on the organic end-capping agent per nanoparticle, there exists the possibility that any given reactive acrylate / methacrylate or other functional group on the surface of the nanoparticle will react with the reactive groups of the writing monomer. The possibility of crosslinking the nanoparticle with the writing monomer can increase with the higher the number of functional groups on the organic end-capping agent per nanoparticle. Therefore, in the case of nanoparticles having functional groups capped at one end, the nanoparticles can act as crosslinking agents for the writing monomer. The organic end-capping agent on the nanoparticle can be customized in terms of surface coverage, end-capping agent length, and the density of functional groups on the organic end-capping agent.

[0037] In some forms, the writing monomer may be about 25% by weight to about 50% by weight, about 25% by weight, about 30% by weight, about 35% by weight, about 40% by weight, about 45% by weight, about 50% by weight, or any weight percentage within this range (e.g., 34%) of the holographic photopolymer. In some forms, the writing monomer may include the at least one nanoparticle. In some forms, the writing monomer and the at least one nanoparticle included therein may be about 40% by weight to about 65% by weight, about 40% by weight, about 45% by weight, about 50% by weight, about 55% by weight, about 60% by weight, about 65% by weight, or any weight percentage within this range (e.g., 56% by weight) of the holographic photopolymer.

[0038] Examples of the at least one nanoparticle included in the holographic grating are illustrated in Figure 2A and Figure 2BIn some forms, the at least one nanoparticle may comprise an inorganic nanocrystal core 201 and an organic surface-modified shell. In some forms, the size of the inorganic nanocrystal core may be from about 5 nm to about 50, about 5, about 10 nm, about 20 nm, about 30 nm, about 40 nm, or any size within this range (e.g., about 27 nm). In some forms, the nanoparticle may be photocurable such that it cures upon exposure to light. In some forms, the photocurable nanoparticle may cure upon exposure to light having a wavelength of about 190 nm to about 980 nm, about 190 nm, about 200 nm, about 250 nm, about 300 nm, about 400 nm, about 500 nm, about 600 nm, about 700 nm, about 800 nm, about 900 nm, about 980 nm, or any wavelength within this range (e.g., 515 nm). In some forms, the at least one nanoparticle may have a diameter from about 1 nm to about 25 nm. In some forms, the average diameter of the nanoparticles is less than 20 nm. In some forms, the average diameter of the nanoparticles is less than 10 nm. In some embodiments, the at least one nanoparticle may be from about 5% to about 90% by weight of the holographic photopolymer. In some forms, the at least one nanoparticle may be about 5%, about 15%, about 20%, about 30%, about 40%, about 50%, about 60%, about 70%, about 80%, about 90% by weight of the holographic photopolymer, or any weight percentage within this range (e.g., 22% by weight).

[0039] The inorganic nanocrystal core 201 may include one or more of ZrO2, TiO2, TiO2 core-ZrO2 shell materials, ZnO, CeO2, Ta2O5 / SiO2, and ITO. The organic surface-modified shell may include at least one organic end-capping agent 205, the organic end-capping agent 205 comprising a first end bonded to the surface 207 of the inorganic nanocrystal core 201 and a second end optionally bonded to at least one reactive portion 203. In some forms, the length of one or more of the organic end-capping agents 205 may be variable. For example, the organic end-capping agent 205 may be a long organic end-capping agent 209 or a short organic end-capping agent 211. Figure 2B In some forms, the reactive portion 203 may include functional groups, such as acrylates, methacrylates, or combinations thereof.

[0040] In some embodiments, the nanoparticles including the surface-modified organic shell can be selected based on the ability of the surface-modified organic shell to react with the writing monomer. This reaction can have unexpected results of producing refractive index modulation after laser exposure. The organic end-capping agent on the nanoparticles is beneficial for compatibility with organic precursors and also facilitates the diffusion of the nanoparticles. A non-limiting example of a writing monomer that can be used in holographic photopolymers includes acrylate-terminated zirconium oxide in ethyl acetate (48.5 wt%) (Pixelligent Technologies, Maryland). In some forms, the nanoparticles can exhibit, for example, a high RI greater than about 1.6. In some forms, the nanoparticles can have a refractive index of about 1.6 to about 2.03, about 1.6, about 1.65, about 1.7, about 1.8, about 1.9, about 2.0, about 2.03, or any refractive index within this range (e.g., 1.73). While not intended to be bound by any particular theory, it is believed that the particle size of the nanoparticles can have improved diffusion of the nanoparticles from the bright portion to the dark portion of the holographic grating, and the unexpected results of optionally improving transparency to greater than 90% and reducing haze to less than 1.5% across all visible light wavelengths.

[0041] In some forms, the polymer matrix may have a refractive index less than about 1.6. In some forms, the polymer matrix may have a refractive index of about 1.5 to about 1.65, about 1.5, about 1.55, about 1.56, about 1.57, about 1.58, about 1.59, about 1.60, about 1.61, about 1.62, about 1.63, about 1.64, about 1.65, or any value within this range (e.g., 1.608). In some forms, the writing monomer may have a refractive index greater than about 1.45. In some forms, the writing monomer may have a refractive index of about 1.45 to about 2.0, about 1.45, about 1.5, about 1.6, about 1.7, about 1.8, about 1.9, about 2.0, or any refractive index within this range (e.g., 1.81). In some forms, the liquid writing monomer may have a refractive index of about 1.45 to about 1.80, about 1.45, about 1.5, about 1.6, about 1.7, about 1.8, or any refractive index within this range (e.g., 1.63). It is believed that selecting writing monomers and polymer matrices with similar polymer chains can provide holographic optical polymers with a refractive index modulation (Δn) greater than about 0.04. In some forms, the refractive index modulation of the holographic polymer may be greater than about 0.03, about 0.035, about 0.036, about 0.037, about 0.038, about 0.039, about 0.040, about 0.041, about 0.042, about 0.043, about 0.044, about 0.045, about 0.046, about 0.047, about 0.048, about 0.049, about 0.050, or any refractive index modulation within this range (e.g., 0.0453). Figure 3 An experimental setup is schematically illustrated for measuring the refractive index modulation of the holographic polymer.

[0042] In some forms, the holographic photopolymer may further include a solvent, which may, for example, be a high-boiling-point solvent. For instance, the boiling point of the solvent may be greater than about 140 °C. In some forms, the solvent may include 1-ethyl-2-pyrrolidone. A particular, non-limiting example of a solvent that can be used in the holographic photopolymer includes product no. 146358 (Sigma-Aldrich, Germany). In some forms, the solvent may be about 1% by weight to about 10% by weight, about 1% by weight, about 2% by weight, about 3% by weight, about 4% by weight, about 5% by weight, about 6% by weight, about 7% by weight, about 8% by weight, about 9% by weight, about 10% by weight, or any weight percentage within this range (e.g., 6.2% by weight).

[0043] In some forms, the holographic photopolymer may include a dye system. In one form, the dye system may include a dye and a co-initiator. For example, the dye may include Safranin O, neomethylene blue, ethyl violet, or combinations thereof. As another example, the co-initiator may include tetrabutylammonium tri(3-chloro-4-methylphenyl)(hexyl)borate (CAS No.: 1147315), tetrabutylammonium butyltriphenylborate, or combinations thereof. Some non-limiting examples of dyes that can be used in holographic photopolymers include product no. B21674.09 (ThermoFisher Scientific, USA) (CAS no. 477-73-6) and product no. 330469 (Sigma-Aldrich, Germany) (CAS no. 103-01-5). Some non-limiting examples of co-initiators that can be used in holographic photopolymers include tetrabutylammonium tri(3-chloro-4-methylphenyl)(hexyl)borate (CAS No. 1147315-11-4, Chang Zhou Qi Di Chemical Co., Ltd) and tetrabutylammonium butyltriphenylborate (CAS No. 120307-06-4, Angene International Limited / A2B CHEM LLC).

[0044] For example, the dye system may be about 0.5 wt% to about 3 wt%, about 0.5 wt%, about 0.75 wt%, about 1 wt%, about 1.25 wt%, about 1.5 wt%, about 1.75 wt%, about 2 wt%, about 2.25 wt%, about 2.5 wt%, about 2.75 wt%, or about 3% by weight of the holographic polymer, or any weight percentage within this range (e.g., 1.8 wt%). The polymerization rate and degree of polymerization can be adjusted (e.g., increased) by controlling / modifying the ratio of dye to co-initiator. In some forms, the weight ratio of the dye to the co-initiator may be about 1:2 to about 1:20, about 1:2, about 1:5, about 1:10, about 1:15, about 1:20, or any ratio within this range.

[0045] In some forms, the holographic photopolymer may have a reflectance greater than about 70%, about 75%, about 80%, about 85%, about 90%, or any reflectance above these values ​​(e.g., 87%).

[0046] In some forms, the holographic photopolymer may have a thickness of about 3 µm to about 12 µm, about 3 µm, about 4 µm, about 5 µm, about 6 µm, about 7 µm, about 8 µm, about 9 µm, about 10 µm, about 11 µm, about 12 µm, or any thickness within this range.

[0047] In one embodiment, a method for preparing a holographic photopolymer includes providing a polymer matrix comprising an aliphatic polyurethane; providing a writing monomer comprising at least one nanoparticle; providing a dye system; mixing the polymer matrix, the writing monomer, and the dye system; and drying the mixture at room temperature. In some forms, the method may further include applying a vacuum to the mixture for about 1 hour. In other forms, a vacuum may be applied to the mixture for about 30 minutes. During application, the vacuum may be at a pressure of about -0.09 MPa to about 0.09 MPa. The vacuum may be applied to remove defects in the mixture and may be performed prior to polymerization. In some forms, the method may further include polymerizing the mixture to form a photopolymer film or adhesive system. The method may also further include exposing the photopolymer film to a laser and bleaching the photopolymer film.

[0048] In another embodiment, a method for preparing a holographic polymer includes preparing a dye system; preparing a writing monomer comprising nanoparticles dispersed throughout the writing monomer; preparing a polymer matrix; mixing the dye system, the writing monomer, and the polymer matrix to form a mixture; and applying a vacuum to the mixture. In some forms, preparing the dye system may include mixing tetrabutylammonium borate tris(3-chloro-4-methylphenyl)(hexyl)borate, Safranin O, and 1-ethyl-2-pyrrolidone at a temperature of about 40°C to about 70°C for about 1 to about 3 hours. In some forms, preparing the writing monomer may include mixing ethoxylated fluorene diacrylate, m-phenoxybenzyl acrylate, 2-hydroxy-3-phenoxypropyl acrylate, SR349, biphenyl methyl acrylate, N-vinylpyrrolidone, and nanoparticles at ambient temperature for about 10 minutes to about 1 hour. In some forms, the dispersion solvent of the nanoparticles (e.g., ethyl acetate) may be rotary evaporated. For example, preparing the polymer matrix may include mixing polypropylene glycol, the writing monomer, and the dye system to form a second mixture. The preparation of the polymer matrix may further include mixing the second mixture with an NCO-terminated polyether prepolymer to form a third mixture. The preparation of the polymer matrix may also further include mixing the third mixture with an organotin catalyst solution to form the resulting mixture. The preparation of the catalyst solution may include mixing the organotin catalyst with 1-ethyl-2-pyrrolidone at a ratio of about 1:9 (organotin catalyst: 1-ethyl-2-pyrrolidone). In some forms, the ratio of the organotin catalyst to 1-ethyl-2-pyrrolidone may be about 1:2 to about 1:20, about 1:2, about 1:5, about 1:10, about 1:15, about 1:20, or any ratio within this range (e.g., 1:9).

[0049] In some forms, the resulting mixture may be subjected to a vacuum at a temperature of about 20°C to about 50°C for about 5 minutes to about 1 hour. In some forms, the third mixture may be subjected to a vacuum for about 30 minutes. For example, the vacuum may be applied at a pressure of about 0.01 MPa to about 0.09 MPa.

[0050] In another embodiment, the method for preparing the holographic photopolymer may further include a two-stage chemical pathway. For example, the first stage may include polymerizing the third mixture to form a photopolymer film. The second stage may include exposing the photopolymer film to an atmosphere at approximately 1 mW / cm². 2 Approximately 20 mW / cm 2The power density of the laser has a wavelength of about 532 nm for about 1 second to about 30 seconds. Exposing the photopolymer film to the laser may further include polymerizing the writing monomers dispersed in the polymer matrix. In some forms, the second stage may further include bleaching the photopolymer film. Bleaching the photopolymer film may include exposing the photopolymer to a combination of ultraviolet light having a wavelength of about 340 nm to about 400 nm and visible light having a wavelength of about 400 nm to about 750 nm.

[0051] While not intended to be bound by any particular theory, it is believed that a two-stage chemical approach can improve holographic photopolymers because the two-stage chemical process provides the ability to precisely control the sequence, timing, and selectivity of different chemical transformations, enabling the synthesis of complex molecules or materials with high efficiency and precision. In some forms, a solid host matrix comprising a polyurethane matrix and additives can be formed to produce a first photopolymer, which is then subsequently recorded into a second photopolymer comprising the dye system and the writing monomer. Furthermore, the writing monomer and the polymer matrix can be selected for ether-like groups to increase the transparency of the holographic photopolymer. In some forms, the holographic photopolymer can have a transmittance greater than about 80%, about 85%, about 90%, about 95%, or any transparency within these limits (e.g., 91%).

[0052] In one embodiment, the film is prepared according to the method described herein. For example, the film may be a photopolymer film. In some forms, the photopolymer film may include a holographic grating as described herein. In some forms, the photopolymer film may be prepared in an atmosphere comprising an oxygen percentage of about 25% to about 0% oxygen, less than about 25% oxygen, less than about 20% oxygen, less than about 15% oxygen, less than about 10% oxygen, less than about 5% oxygen, less than about 1% oxygen, or any oxygen percentage within this range.

[0053] In some embodiments, the holographic polymer may be a film or coating applied to a glass or plastic substrate. In some forms, the coating may be applied to the glass substrate via a vacuum lamination coating method, while in others, the coating may be applied to the plastic substrate via a roll-to-roll coating method.

[0054] In one embodiment, the augmented reality / mixed reality (AR / MR) device includes a holographic grating as described herein. The AR / MR device may include AR / MR headphones. Alternatively, the AR / MR device may include a holographic display.

[0055] Example

[0056] It has been found that implementations of holographic gratings as described herein can exhibit improved performance. These benefits are further demonstrated by the following examples, which are intended to be illustrative only and not to limit the scope or fundamental principles in any way.

[0057] Preparation of photopolymer solutions

[0058] Example 1 - ZrO2 hybrid formulations and formulations containing ZrO2

[0059] Preparation of nanoparticle-dispersed writing monomer mixtures

[0060] 1.03 g of EA-F5710 (a mixture of ethoxylated fluorene diacrylate and m-phenoxybenzyl acrylate) (OSAKA GAS Chemicals, Japan), 0.10 g of 2-hydroxy-3-phenoxypropyl acrylate (CAS No.: 16969-10-1), 0.41 g of Sartomer SR349, 0.50 g of biphenyl methyl acrylate (CAS No.: 54140-58-8), and acrylate-terminated zirconium oxide (48.5 wt%) in ethyl acetate (PCPC-1-50-ETA, Pixelligent) were mixed in the dark at ambient temperature for 0.5 hours. Subsequently, the ethyl acetate was removed by rotary evaporation, and the mixture was completely dried under vacuum.

[0061] Preparation of photo-initiated mixture solutions

[0062] 200 mg of tetrabutylammonium tri(3-chloro-4-methylphenyl)(hexyl)borate (CAS No.: 1147315, co-initiator) and 20.0 mg of safranin O (photosensitizer or dye) were dissolved in the dark at 55°C and mixed in 0.35 g of 1-ethyl-2-pyrrolidone (CAS No.: 2687-91-4) for 2 hours.

[0063] Preparation of tin catalyst solution (for urethane polymerization)

[0064] One part of organotin catalyst (FOMREZ UL-28, dimethyltin dinedecanoate) was mixed with nine parts of 1-ethyl-2-pyrrolidone (CAS NO.: 2687-91-4) at room temperature to form a 10% catalyst stock solution.

[0065] Preparation of ZrO2 hybrid formulations for photopolymerization.

[0066] The writing monomer mixture, 1.4 g of Arcol PPG-725 (polypropylene glycol, Covestro), and 0.46 g of the photoinitiator mixture solution were mixed overnight in the dark at 60°C. The mixture was then cooled to 35°C. Next, 0.69 g of isocyanate (Desmodur WP 260, Covestro) was added. The mixture was vigorously mixed at 35°C for 3 minutes. Subsequently, 0.026 g of tin catalyst solution was added to the resulting mixture, and it was mixed at 35°C for 3 minutes. The resulting liquid solution was then placed under vacuum at 35°C for 15 minutes to remove bubbles caused by mixing.

[0067] Example 1-REF – Photopolymer formulations without ZrO2 for comparison

[0068] Preparation of writing monomer mixtures

[0069] 1.04 g of EA-F5710 (a mixture of ethoxylated fluorene diacrylate and m-phenoxybenzyl acrylate) (OSAKA GAS Chemicals, Japan), 0.11 g of 2-hydroxy-3-phenoxypropyl acrylate (CAS No.: 16969-10-1), 0.43 g of Sartomer SR349 and 0.52 g of biphenyl acrylate (CAS No.: 54140-58-8) were mixed in the dark at 60°C for 1 hour.

[0070] Preparation of photo-initiated mixture solutions

[0071] 200 mg of tetrabutylammonium tri(3-chloro-4-methylphenyl)(hexyl)borate (CAS No.: 1147315, co-initiator) and 20.0 mg of safranin O (photosensitizer or dye) were dissolved in the dark at 55°C and mixed in 0.35 g of 1-ethyl-2-pyrrolidone (CAS No.: 2687-91-4) for 2 hours.

[0072] Preparation of tin catalyst solution (for urethane polymerization)

[0073] One part of organotin catalyst (FOMREZ UL-28, dimethyltin dinedecanoate) was mixed with nine parts of 1-ethyl-2-pyrrolidone (CAS NO.: 2687-91-4) at room temperature to form a 10% catalyst stock solution.

[0074] Preparation of photopolymer formulations without ZrO2 for comparison

[0075] The writing monomer mixture prepared as described above, 1.21 g of Arcol PPG-725 (polypropylene glycol, Covestro), and 0.46 g of the photoinitiator mixture solution were mixed overnight in the dark at 60°C. The mixture was then cooled to 35°C. Next, 0.64 g of isocyanate (Desmodur WP 260, Covestro) was added. The mixture was vigorously mixed at 35°C for 3 minutes. Subsequently, 0.026 g of tin catalyst solution was added to the resulting mixture, and it was mixed at 35°C for 3 minutes. The resulting liquid solution was then placed under vacuum at 35°C for 15 minutes to remove bubbles caused by mixing.

[0076] Example 2 - ZrO2 hybrid formulations and formulations containing ZrO2

[0077] Preparation of nanoparticle-dispersed writing monomer mixtures

[0078] 0.80 g of EA-F5710 (a mixture of ethoxylated fluorene diacrylate and m-phenoxybenzyl acrylate) (OSAKA GAS Chemicals, Japan), 0.10 g of 2-hydroxy-3-phenoxypropyl acrylate (CAS NO.: 16969-10-1), 0.40 g of Sartomer SR349, 0.50 g of biphenyl methyl acrylate (CAS NO.: 54140-58-8), 0.20 g of N-vinylpyrrolidone (CAS NO.: 88-12-0), and acrylate-terminated zirconium oxide (48.5 wt%) in ethyl acetate (PCPC-1-50-ETA, Pixelligent) were mixed in the dark at ambient temperature for 0.5 hours. The ethyl acetate was then removed by rotary evaporation and the mixture was completely dried under vacuum.

[0079] Preparation of photo-initiated mixture solutions

[0080] 200 mg of tetrabutylammonium tri(3-chloro-4-methylphenyl)(hexyl)borate (CAS NO.: 1147315, co-initiator) and 20.0 mg of safranin O (photosensitizer or dye) were dissolved in the dark at 55°C and mixed in 0.35 g of 1-ethyl-2-pyrrolidone (CAS NO.: 2687-91-4) for 2 hours.

[0081] Preparation of tin catalyst solution (for urethane polymerization)

[0082] One part of organotin catalyst (FOMREZ UL-28, dimethyltin dinedecanoate) was mixed with nine parts of 1-ethyl-2-pyrrolidone (CAS NO.: 2687-91-4) at room temperature to form a 10% catalyst stock solution.

[0083] Preparation of photopolymer ZrO2 hybrid formulation

[0084] The writing monomer prepared as described above, 1.4 g of Arcol PPG-725 (polypropylene glycol, Covestro), 0.5 g of Arcol LHT-112 (polypropylene glycol, Covestro), and 0.46 g of the photoinitiator mixture solution were mixed overnight in the dark at 60°C. The mixture was then cooled to 35°C. Next, 0.97 g of isocyanate (Desmodur WP 260, Covestro) was added. The mixture was vigorously mixed at 35°C for 3 minutes. Subsequently, 0.026 g of tin catalyst solution was added to the resulting mixture, and it was mixed at 35°C for 3 minutes. The resulting liquid solution was then placed under vacuum at 35°C for 15 minutes to remove bubbles caused by mixing.

[0085] Glass substrate coating (for exposed sample preparation)

[0086] The glass substrate was cleaned and dried in a light-controlled environment (safety red light). The glass substrate was cut into approximately 2” x 2” cubes. The cut glass substrate was cleaned with soap (detergent) and water, and then dried with nitrogen (N2) at room temperature for approximately 30 seconds followed by heating to approximately 60°C. A drop of synthetic photopolymer material was then applied to the glass plate, and subsequently covered with a second glass plate held at a controlled thickness distance by applying silica microspheres. The glass laminated sample was vacuum-treated and laminated using an NPC vacuum chamber bonding machine (https: / / www.npcgroup.net / eng / solarcell / vacuum-bonding). After lamination, the sample specimens were placed overnight at 35°C.

[0087] Holographic-mirror recording

[0088] The polymerized photopolymer film was exposed to a Denisyuk (mirror hologram) configuration with a laser at 532 nm and at a speed of 5 to 10 mW / cm. 2The power density was adjusted and the exposure time was 2 to 10 seconds. After exposure, the hologram was visually inspected and a bleaching step was applied under UV light. The laminated hologram between two glass slides was exposed to a UVASPOT 1000 RF2 lamp from Honle UV Technology, Germany. The UVASPOT is a modular, high-intensity UV unit and system that achieves extremely high uniformity throughout the irradiation field. Different spectra can be generated for applications in the UVA (340 nm to 400 nm) range through various lamp and filter configurations.

[0089] Reflection efficiency measurement

[0090] Reflectance efficiency was calculated from the transmittance of the holographic recording area (HOE) and the non-recording area (non-HOE area). The transmittance of the HOE and non-HOE areas of the sample was measured after the bleaching step. Transmission spectra were measured from 350 to 700 nm using a Shimadzu UV-VIS-NIR spectrophotometer (model UV-3600 i Plus). The sample was placed vertically on a sample holder. The measurement area (HOE or non-HOE area) was aligned with the opening of the sample holder, allowing the beam to pass through the measurement area. Transmittance measurements from 350 to 700 nm were performed using a slow scan at 0.5 nm data intervals. The reflectance efficiency was calculated using the following formula: [(non-HOE transmittance – HOE transmittance) / non-HOE transmittance]. Figures 5 to 8 A graphical illustration is provided to depict the various optical properties of Examples 1 and 2. The table below provides data relating to the haze properties measured in Example 1.

[0091]

[0092] The use of the terms “may”, “may be”, or “can” should be understood as shorthand for “is” or “is not”, or alternatively, “does” or “does not”, “will” or “will not”. For example, the statement “the thermally conductive composite material may further include a backing layer” should be interpreted as, for example, “in some embodiments, the thermally conductive composite material further includes a backing layer” or “in some embodiments, the thermally conductive composite material does not further include a backing layer”.

[0093] Unless otherwise specified, all figures representing quantities of components, properties (e.g., molecular weight, reaction conditions, etc.) used in this specification and embodiments should be understood to be modified in all cases by the term "about". As used herein, the term "about" can include any numerical value that may vary without altering the essential function of the value. When used with ranges, "about" also discloses a range defined by the absolute values ​​of its two endpoints. The term "about" may refer to plus or minus 10% of the indicated number.

[0094] Therefore, unless otherwise indicated, the numerical parameters set forth in this specification and the appended embodiments are approximate values ​​and may vary depending on the desired properties sought to be obtained. This is at least not an attempt to limit the application of equivalence theory. Within the scope of the embodiments, each numerical parameter should be understood at least according to the number of significant figures reported and by applying ordinary rounding techniques.

[0095] For the disclosed processes and / or methods, the functions performed in the processes and / or methods may be implemented in different orders, as may be indicated by the context. Furthermore, the outlined steps and operations are provided only as examples, and some of the steps and operations may be optional, combined into fewer steps and operations, or extended to additional steps and operations.

[0096] This disclosure may sometimes describe different components contained within or connected to different other components. The architectures depicted are merely examples, and many other architectures can be implemented to achieve the same or similar functionality.

[0097] The terminology used in this invention and in the appended embodiments is generally intended to be "open-ended" (e.g., the term "including" should be interpreted as "including, but not limited to," the term "having" should be interpreted as "having at least," the term "includes" should be interpreted as "including, but not limited to," etc.). Furthermore, if a specific number of elements is introduced, it can be interpreted as including at least the number cited, as indicated by the context (e.g., a bare citation of "two citations" without other modifiers includes at least two citations or two or more citations). As used in this disclosure, any extractive words and / or phrases presenting two or more alternative terms should be understood to cover the possibility of including one, any, or both of the stated terms. For example, the phrase "A or B" should be understood to include the possibility of "A" or "B" or "A and B."

[0098] The terminology and words used are not limited to their bibliographical meaning, but are used solely to achieve a clear and consistent understanding of the invention. Unless otherwise indicated herein or in obvious contradiction, the terms “a,” “an,” “the,” and similar references used in this context to describe the disclosure (particularly in the context of the following embodiments) should be understood to cover both the singular and plural. The use of any and all embodiments or representative language (e.g., “such as”) provided herein is intended only to better illustrate the disclosure and does not limit the scope of any implementation. No language in this specification should be construed as indicating any unrepresented element essential to the practice of the disclosure.

[0099] The grouping of alternative elements or embodiments disclosed herein should not be construed as limiting. Members of each group may be mentioned and embodied independently or in any combination with other members of that group or other elements found herein. It is contemplated that one or more members of a group may be included in or removed from a group for convenience and / or patentability reasons. In the event of any such inclusion or removal, the specification is considered to contain the groups as modified, thus satisfying the written description of all Markush groups used in the appended embodiments.

[0100] The specific embodiments described herein include the best modes known to the inventors for carrying out this disclosure. Of course, variations of these described embodiments will become apparent to those skilled in the art upon reading the foregoing description. The inventors expect those skilled in the art to appropriately employ such variations, and the inventors intend to practice this disclosure in ways other than those specifically described herein. Therefore, the embodiments include all modifications and equivalents of the subject matter cited in embodiments permitted by applicable law. Furthermore, unless otherwise indicated herein or explicitly contradicted by the context, any combination of the foregoing elements in all possible variations is contemplated. In summary, it should be understood that the embodiments disclosed herein illustrate the principles of the embodiments. Other modifications may be employed within the scope of the embodiments. Therefore, alternative embodiments may be used, by way of example and not by way of limitation, in accordance with the teachings herein. Therefore, the embodiments are not limited to those exactly as shown and described.

[0101] The term "substantially" means that the cited feature, parameter, or value does not need to be precisely achieved, but deviations or variations (including, for example, tolerances, measurement errors, measurement accuracy limitations, and other suitable factors) may not prevent the quantity of the effect that the feature is intended to provide from occurring.

[0102] Aspects of this disclosure may be embodied in other forms without departing from the spirit or essential characteristics of this disclosure. The described aspects should be considered in all illustrative and not restrictive respect to the extent necessary. The subject matter embodied is indicated by the appended embodiments rather than by the foregoing description. All variations within the equivalent meaning and scope of the embodiments should be adopted within their scope.

Claims

1. A holographic grating, comprising: At least one photocurable nanoparticle; The bright portion of the at least one photocurable nanoparticle, comprising a first concentration, is included. The dark portion comprising the at least one photocurable nanoparticle at a second concentration, wherein the first concentration of the at least one photocurable nanoparticle is greater than the second concentration of the at least one photocurable nanoparticle; and Holographic photopolymers comprise a polymer matrix, photocurable writing monomers, and a dye system. The holographic polymer is dispersed throughout the bright and dark portions of the holographic grating.

2. The holographic grating of claim 1, wherein the at least one photocurable nanoparticle comprises an inorganic nanocrystal core and an organic surface-modified shell.

3. The holographic grating of claim 2, wherein the inorganic nanocrystal core comprises at least one of ZrO2, TiO2, TiO2 core-ZrO2 shell material, ZnO, CeO2, Ta2O5 / SiO2 and ITO.

4. The holographic grating of claim 2, wherein the organic surface-modified shell comprises at least one reactive portion.

5. The holographic grating of claim 4, wherein the reactive portion comprises at least one of acrylate and methacrylate.

6. The holographic grating of claim 1, wherein the at least one photocurable nanoparticle is about 5% to about 90% by weight of the holographic photopolymer.

7. The holographic grating of claim 1, wherein the at least one photocurable nanoparticle comprises a diameter of about 1 nm to about 25 nm.

8. The holographic grating of claim 1, wherein the polymer matrix exhibits a refractive index of less than about 1.

6.

9. The holographic grating of claim 1, wherein the polymer matrix comprises aliphatic polyurethane.

10. The holographic grating of claim 1, wherein the polymer matrix comprises polypropylene glycol, one or more NCO-terminated aliphatic prepolymers, and an organotin catalyst.

11. The holographic grating of claim 1, wherein the photocurable writing monomer exhibits a refractive index greater than about 1.

45.

12. The holographic grating of claim 1, wherein the liquid writing monomer comprises at least one of a crosslinkable monomer and a polymerizable monomer, the crosslinkable monomer comprising at least one crosslinkable portion, and the polymerizable monomer comprising at least one polymerizable portion.

13. The holographic grating of claim 1, wherein the liquid writing monomer comprises ethoxylated fluorene diacrylate, m-phenoxybenzyl acrylate, 2-hydroxy-3-phenoxypropyl acrylate, biphenyl methyl acrylate, ethoxylated bisphenol A diacrylate, and at least one of the nanoparticles.

14. The holographic grating of claim 1, wherein the dye system comprises a dye and a co-initiator.

15. The holographic grating of claim 14, wherein the dye comprises at least one of safranin O, neomethylene blue, and ethyl violet.

16. The holographic grating of claim 14, wherein the co-initiator comprises at least one of tetrabutylammonium tri(3-chloro-4-methylphenyl)(hexyl)borate and tetrabutylammonium butyltriphenylborate.

17. The holographic grating of claim 1, wherein the polymer matrix comprises a grid size larger than the size of the nanocrystal core of the photocurable nanoparticles.

18. An augmented reality / virtual reality device comprising a holographic grating according to any one of claims 1 to 18.

19. A film comprising a holographic grating according to any one of claims 1 to 18.

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