WO2025199375A1

WO2025199375A1 - Holographic grating and augmented reality/mixed reality apparatus

Info

Publication number: WO2025199375A1
Application number: PCT/US2025/020779
Authority: WO
Inventors: Nan HU; Peng Wang; Sergey Simavoryan; Hongxi Zhang
Original assignee: Nitto Denko Corp
Current assignee: Nitto Denko Corp
Priority date: 2024-03-21
Filing date: 2025-03-20
Publication date: 2025-09-25
Anticipated expiration: 2026-09-21

Abstract

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

Description

HOLOGRAPHIC GRATING AND AUGMENTED REALITY/MIXED REALITY APPARATUS

Inventors: Nan Hu, Peng Wang, Sergey Simavoryan, and Hongxi Zhang

CROSS-REFERENCE TO RELATED APPLICATIONS

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

FIELD

The present disclosure is related to a holographic grating including a holographic photopolymer which may be used in augmented reality/mixed reality (AR/MR) glasses, optical displays, and other holographic applications.

BACKGROUND

As the use of augmented reality glasses and optical displays becomes more common, the demand for improved holographic media has increased. Holographic media or materials can be produced from holographic gratings such as a volume holographic grating. As taught in U.S. Patent Nos. 9,281 ,000 B2 and 8,771 ,904 B2 for example, a photopolymer formulation includes chemically crosslinked matrix polymers, writing monomers, and a photoinitiator system for producing holographic media via volume holographic gratings. However, the process to produce this photopolymer formulation requires a nitrogen purge to remove oxygen, which may present economic feasibility. Further, if the oxygen is not completely removed, radicals may be oxidized thus resulting in deficient polymerization of the polymers.

Furthermore, a high refractive index in combination with a low thickness of the film is essential to achieve highly visible holograms. Most volume grating hologram films for AR/MR glasses can only achieve 50% reflection efficiency but have a thickness greater than 12 pm, resulting in a low refractive index modulation. By increasing the refractive index modulation to greater than 0.03, thin holographic films having a thickness between 5-12 pm may be produced without inhibiting a wider field of view for AR/MR glasses.

As such, there is a need for further contributions in this area of technology. More particularly, but not exclusively, thin holographic photopolymers/films with a refractive index modulation greater than 0.03, a low level of scattering, transmittance greater than 90%, and a haze of less than 1.5% and methods for making same are needed. SUMMARY

The present disclosure generally relates to a holographic grating including a holographic photopolymer, and to an augmented reality/virtual reality apparatus including the same.

In one embodiment, a holographic grating includes at least one nanoparticle; a light 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 light portion and the dark portion of the holographic grating. In some forms, the light 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.

In some forms, the at least one nanoparticle may include 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 at about 5 wt. % to about 90 wt. % of the total weight of the holographic photopolymer. In some embodiments, the inorganic nanocrystal core may include at least one of ZrC>2, TiC>2, TiC>2 a core-ZrCh shell material, ZnO, CeC>2, Ta2Os/SiO2, and ITO. In some forms, the organic surface modified shell includes at least one reactive moiety.

In some forms, the holographic photopolymer may include a polymer matrix. In some forms, the polymer matrix includes a mesh size which may be greater than the size of the nanocrystal core of the photocurable nanoparticle. 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.

In some forms, the polymer matrix may exhibit a low refractive index (Rl), such as a refractive index which is less than about 1.6, although variations in this value are possible and contemplated. In some forms where the polymer matrix exhibits a low Rl, the polymer matrix may include an aliphatic polyurethane. Additionally or alternatively, in some forms where the polymer matrix exhibits a low Rl, it may include one or more of polypropylene glycol, NCO-terminated aliphatic prepolymers, and an organotin catalyst. By way of example, the NCO-terminated aliphatic prepolymers may include one or more ether groups, a polyether polyol, or a combination thereof.

In some forms, the writing monomer may exhibit a high Rl such as greater than about 1.45, resulting in a refractive index modulation (An) greater than about 0.04, although variations in both values are possible and contemplated. In some forms where the liquid writing monomer exhibits a high Rl, it may include at least one crosslinkable monomer. By way of example, the at least one crosslinkable monomer may include at least one crosslinkable moiety, and at least one polymerizable monomer including at least one polymerizable moiety, or a combination thereof. In some forms where the liquid writing monomer exhibits a high Rl, it may include ethoxylated fluorene diacrylate, m- phenoxybenzyl acrylate, 2-hydroxy-3-phenoxypropylacrylate, biphenylmethyl acrylate, ethoxylated bisphenol a diacrylate, N-vinyl pyrrolidinone and the at least one nanoparticle.

In some forms, the holographic grating may further include a solvent such as 1- ethyl-2-pyrrolidone.

In some forms where the holographic photopolymer includes a dye system, the dye system may include a dye and a co-initiator. The dye may include at least one of safranine O, new methylene blue, and ethyl violet. In some forms, the co-initiator may include at least one of borate salt tetrabutylammonium tris(3-chloro-4-methylphenyl) (hexyl)borate and borate salt tetrabutylammonium butyltriphenylborate. In some forms, the ratio of the dye and the co-initiator can be about 1 :10 to about 1 :14

In one embodiment, an augmented reality/mixed reality (AR/MR) apparatus includes a holographic described herein.

In another embodiment, a film includes a holographic grating described herein. These and other embodiments are described in greater detail below.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a holographic grating.

FIGs. 2A & 2B are illustrations of nanoparticles.

FIG. 3 is a schematic illustration of an experimental setup to measure characteristics of a holographic photopolymer.

FIG. 4 is a graphical illustration showing reflectance efficiency from 400-700 nm.

FIG. 5 is a graphical illustration showing measured data of transmittance.

FIG. 6 is a graphical illustration showing measured data of total transmission.

FIG. 7 is a graphical illustration showing measured data of stability of refraction efficiency over time.

FIG. 8 is a graphical illustration showing measured data of transmittance. DETAILED DESCRIPTION

In one embodiment, a holographic media for use in augmented reality/mixed reality (AR/MR) apparatus and/or optical displays is provided. Other embodiments relate to a holographic grating and/or a holographic photopolymer.

In one embodiment, a holographic grating includes at least one nanoparticle, a light 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. By way of example, the holographic photopolymer may provide for highly visible holograms for use in AR/MR 3-dimensional glasses, thus improving the viewing experience of the user. In another embodiment, a film (such as a photopolymer film) is made according to methods described herein. In some forms, the film may include a holographic grating described herein.

The term “bond” or “bonded” as used herein means a chemical bond between two atoms or to two moieties when the atoms joined by the bond are considered to be part of a larger structure.

The term “moiety” as used herein refers to a specific segment or functional group of a molecule. By way of example, chemical moieties may be recognized chemical entities embedded in or appended to a molecule.

The present disclosure relates to a holographic grating including a holographic photopolymer and an augmented reality/virtual reality apparatus including the same. In one embodiment, the holographic grating includes at least one nanoparticle, a light portion, a dark portion, and a holographic photopolymer. In some forms, the holographic photopolymer may include a polymer matrix, a writing monomer, and a dye system. In some forms, the holographic photopolymer may further include a solvent.

As shown in FIG. 1 for example, the holographic photopolymer may be dispersed throughout the light portion 103 and the dark portion 105 of the holographic grating 101. In some forms, the light 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 greater concentration of the nanoparticles in the light portion 103 relative to the dark portion 105 in the holographic grating 101 may be produced by exposure to a light pattern. In some forms, exposure to the light pattern for the formation of the holographic grating 101 may deplete reactive moieties in the light portion 103, which drives diffusion of writing monomers including the nanoparticles from the dark portion 105 to the light portion 103. As a result, the diffraction efficiency of the holographic grating 101 may be enhanced. As depicted in FIG 1., the holographic grating 101 may include more than one light portion 103 and more than one dark portion 105.

In some forms, the holographic photopolymer may include a polymer matrix which exhibits a low Rl, such as less than about 1.6. In some embodiments where the polymer matrix exhibits a low Rl, the polymer matrix may include an aliphatic polyurethane, and/or it may include a siloxane or an epoxy. In some forms where the polymer matrix exhibits a low Rl, the polymer matrix may include a polar mixing precursor for high compatibility with the nanoparticles. The polar mixing precursors may include prepolymers including a high concentration of polar moieties, such as hydroxyl, carbamate, mercapto, or sulfonic groups, or a combination thereof. In some forms where the polymer matrix exhibits a low Rl, the polymer matrix may include polypropylene glycol, NCO-terminated aliphatic prepolymers, and an organotin catalyst. Some more particular but non-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 prepolymers, Covestro, Germany), or Fomrez UL-28 (organotin catalyst, Galata Chemicals, USA).

In some forms, the polymer matrix may include a mesh size which is 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, mesh size refers to the average distance between two crosslinkers within the polymer matrix. In some forms, the polymer matrix includes a mesh size which is greater than the size of a nanocrystal core of the at least one nanoparticle. Without intending to be limited by any particular theory, it is believed that the polymer matrix having a mesh size greater than the nanocrystal core allows for the nanoparticles to diffuse across the polymer matrix. In some forms, the polymer matrix may be non-photocurable to prevent polymer matrix from solidifying upon exposure to light. In some forms, the polymer matrix may be about 25% to about 50%, about 25%, about 30%, about 35%, about 40%, about 45%, or about 50%, by weight, or any weight percent bounded by this range (e.g. 36%), of the holographic photopolymer. In some forms where the polymer matrix includes an aliphatic polyurethane, it may improve compatibility with polypropylene polyol present. Forms in which the polymer matrix includes a tin catalyst, such as an organotin catalyst, are also possible. By way of example, the organotin catalyst may include 1-Ethyl-2-Pyrrolidone.

In some forms, the holographic photopolymer may include a writing monomer. In some forms, the writing monomer may exhibit a high Rl. In some forms, the writing monomer may include a high Rl liquid writing monomer which may be light sensitive and curable when exposed to ultraviolet light or visible light. In some forms, the high Rl liquid writing monomer may include at least one crosslinkable monomer that includes at least one crosslinkable moiety, and at least one polymerizable monomer including at least one polymerizable moiety, or a combination thereof. In some forms, the high Rl liquid writing monomer may include ethoxylated fluorene diacrylate, m-phenoxybenzyl acrylate, 2- hydroxy-3-phenoxypropylacrylate (CAS No.: 16969-10-1), biphenylmethyl acrylate (CAS No.: 54140-58-8), ethoxylated bisphenol a diacrylate, and the at least one nanoparticle. In some forms, the writing monomer may be photocurable due to the writing monomer solidifying upon exposure to light. In some forms, the photocurable writing monomer may solidify when exposed 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 bounded by this range, e.g. 515 nm. Some non-limiting examples of a writing monomer that can be used in the holographic photopolymer include EA-F5710 (mixture of ethoxylated fluorene diacrylate and m-phenoxybenzyl acrylate) (OSAKA GAS Chemicals, Japan, 2-hydroxy-3-phenoxypropylacrylate (Sigma-Aldrich, Germany), SR349 (Sartomer Americas, USA), biphenylmethyl acrylate (Miwon Specialty Chemical Co., South Korea), and N-vinyl pyrrolidinone (BASF, Germany). It is believed a writing monomer and a polymer matrix with similar structures may achieve increased miscibility. In addition, the particular writing monomer used may have the unexpected result of improving diffusion of nanoparticles from the dark portion of the holographic grating to the light portion of the holographic grating.

As will be discussed in greater detail below, in some forms the at least one nanoparticle of the holographic grating may include one or more organic surface modified nanoparticles. In these forms, and without intending to be bound by any particular theory, it is believed that for organic surface modified nanoparticles, depending on the number of functional groups on organic capping agents per nanoparticle, there is a probability of any given reactive acrylate/methacrylate or other functional group on the surface of the nanoparticle reacting with reactive groups of writing monomers. The probability of nanoparticle crosslinking with writing monomers may be higher as the number of functional groups on organic capping agents per nanoparticle is higher. Thus, for the case of nanoparticles having functional groups capped on one end, the nanoparticles could act as crosslinking agents of writing monomers. The organic capping agents on the nanoparticles can be tailored in terms of surface coverage, capping agent length, and the density of functional groups on the organic capping agents.

In some forms, writing monomer may be about 25% to about 50%, about 25%, about 30%, about 35%, about 40%, about 45%, about 50%, by weight, or any weight percent bounded by 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% to about 65%, about 40%, about 45%, about 50%, about 55%, about 60%, about 65%, by weight, or any weight percent bounded by this range (e.g. 56%) of the holographic photopolymer.

Examples of the at least one nanoparticle included in the holographic grating are illustrated in FIGs. 2A and 2B. In some forms, the at least one nanoparticle may include an inorganic nanocrystal core 201 and an organic surface modified shell. In some forms, the size of the inorganic nanocrystal core may be about 5 nm to about 50, about 5, about 10 nm, about 20 nm, about 30 nm, about 40 nm, or any size bounded by this range, e.g. about 27 nm. In some forms, the nanoparticle may be photo curable such that it solidifies upon exposure to light. In some forms, the photocurable nanoparticle may solidify when exposed 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 bounded by this range, e.g. 515 nm. In some forms, the at least one nanoparticle may have a diameter of about 1 nm to about 25 nm. In some forms, the mean diameter of the nanoparticle is less than 20 nm. In some forms, the mean diameter of the nanoparticle is less than 10nm. In some embodiments, the at least one nanoparticle may be 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, or any weight percent bounded by this range (e.g. 22%), of the holographic photopolymer.

The inorganic nanocrystal core 201 may include one or more of ZrC>2, TiC>2, TiC>2, a core-ZrC>2 shell material, ZnO, CeC>2, Ta2Os/SiO2, and ITO. The organic surface modified shell may include at least one organic capping agent 205 including a first end which is bonded to a surface 207 of the inorganic nanocrystal core 201 , and a second end to which at least one reactive moiety 203 is optionally bonded. In some forms, the length of one or more of the organic capping agents 205 may vary. For example, the organic capping agent 205 may be a long organic capping agent 209 or a short organic capping agent 211 (FIG. 2B). In some forms, the reactive moiety 203 may include a functional group such as an acrylate, a methacrylate, or a combination thereof.

In some embodiments, the nanoparticle including the surface modified organic shell may be selected for the ability of the surface modified organic shell to react with the writing monomer. This reaction may have the unexpected result of generating reflective index modulation upon laser exposure. The organic capping agents on the nanoparticle benefit compatibility with organic precursors, which also favors diffusion of the nanoparticles. One non-limiting example of a writing monomer that can be used in the holographic photopolymer includes Zirconia oxide capped with acrylates (48.5 wt%) in ethyl acetate (Pixelligent Technologies, Maryland). In some forms, the nanoparticle may exhibit a high Rl which, for example, may be greater than about 1.6. In some forms, the nanoparticle may 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 bounded by this range, e.g., 1.73. While not intending to be bound by any particular theory, it is believed the particle size of the nanoparticle may have the unexpected result of improving diffusion of nanoparticles from the light portion of the holographic grating to the dark portion of the holographic grating, as well as optically improving transparency to greater than 90% across all visible wavelengths and decreasing haze to below 1.5%.

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 bounded by 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 bounded by 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 bounded by this range, e.g., 1.63. It is believed that the selection of a writing monomer and a polymer matrix with similar polymer chains may provide the holographic photopolymer with a refractive index modulation (An) of greater than about 0.04. In some forms, the refractive index modulation of the holographic photopolymer 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 bounded by this range, e.g., 0.0453. FIG. 3 schematically illustrates the experimental setup with which the refractive index modulation of the holographic photopolymer may be measured.

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

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. By way of example, the dye may include safranine O, new methylene blue, ethyl violet, or a combination thereof. By way of further example, the co-initiator may include borate salt tetrabutylammonium tris(3- chloro-4-methylphenyl) (hexyl)borate (CAS No.: 1147315), borate salt tetrabutylammonium butyltriphenylborate, or a combination thereof. Some non-limiting examples of the dye that may be used in the holographic photopolymer 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 the co-initiator that may be used in the holographic photopolymer include borate salt tetrabutylammonium tris(3-chloro-4-methylphenyl) (hexyl)borate (CAS No. 1147315-11- 4, Chang Zhou Qi Di Chemical Co., Ltd) and borate salt tetrabutylammonium butyltriphenylborate (CAS No. 120307-06-4, Angene International Limited/A2B CHEM LLC).

By way of example, the dye system may be about 0.5% to about 3%, about 0.5%, about 0.75%, about 1%, about 1.25%, about 1.5%, about 1.75%, about 2%, about 2.25%, about 2.5%, about 2.75%, or about 3%, by weight, or any weight percent bounded by this range (e.g. 1.8%), of the holographic photopolymer. The polymerization rate and degree of polymerization may be adjusted (e.g., increased) by controlling/modifying the ratio of the dye to the co-initiator. In some forms, the ratio by weight 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 bounded by this range.

In some forms, the holographic photopolymer may have a reflection efficiency greater than about 70%, about 75%, about 80%, about 85%, about 90%, or any reflection efficiency bounded by these values, e.g., 87%.

In some forms, the holographic photopolymer may have a thickness of about 3 pm to about 12 pm, about 3 pm, about 4 pm, about 5 pm, about 6 pm, about 7 pm, about 8 pm, about 9 pm, about 10 pm, about 11 pm, about 12 pm, or any thickness bounded by this range.

In one embodiment, a method for making a holographic photopolymer includes providing a polymer matrix including an aliphatic polyurethane; providing a writing monomer) including 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, the vacuum may be applied to the mixture for about 30 minutes. When applied, the vacuum may be at a pressure of about -0.09 MPa to about 0.09 MPa. The vacuum may be applied to remove imperfections in the mixture and performed prior to polymerization. In some forms, the method may further include polymerizing the mixture to form a photopolymer film or binder system. The method may also further include exposing the photopolymer film to a laser and bleaching the photopolymer film.

In another embodiment, a method for making a holographic photopolymer includes preparing a dye system; preparing a writing monomer including nanoparticles dispersed throughout the writing monomer; preparing a polymer matrix; mixing the dye system, writing monomer, and polymer matrix to form a mixture; and applying a vacuum to the mixture. In some forms, preparing the dye system may include mixing Borate salt tetrabutylammonium tris(3-chloro-4-methylphenyl) (hexyl)borate, safranine 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-phenoxypropylacrylate, SR349, biphenylmethyl acrylate, N-vinyl pyrrolidone and nanoparticles at ambient temperature for about 10 minutes to about 1 hour. In some forms, a dispersion solvent (such as ethyl acetate) of the nanoparticles, may be rotary evaporated. By way of example, preparing the polymer matrix may include mixing polypropylene glycol, the writing monomer, and the dye system to form a second mixture. Preparation of the polymer matrix may further include mixing the second mixture with an NCO-terminated polyether prepolymer to form a third mixture. Preparation of the polymer matrix may also further include mixing the third mixture with an organotin catalyst solution to form a resultant mixture. Preparation of the catalyst solution may include mixing an 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 can 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 bounded by this range, e.g., 1 :9.

In some forms, a vacuum may be applied to the resultant mixture for about 5 minutes to about 1 hour at a temperature of about 20 °C to about 50 °C. In some forms, a vacuum may be applied to the third mixture for about 30 minutes. By way of example, the vacuum may be applied at a pressure of about 0.01 MPa to about 0.09 MPa. In a further embodiment, a method for making a holographic photopolymer may further include performing a two-stage chemistry approach. For example, a first a stage may include polymerizing the third mixture to form a photopolymer film The second stage may include exposing the photopolymer film to a laser having a wavelength of about 532 nm at a power density of about 1 mW/cm² to about 20 mW/cm² for about 1 second to about 30 seconds. Exposing the photopolymer film to a laser may further include polymerizing the writing monomer dispersed within the polymerized polymer matrix. In some forms, the second stage may further include bleaching the photopolymer film. The 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 from about 400nm to about 750nm.

While not intending to be bound by any particular theory, it is believed that utilizing a two-stage chemistry approach may improve upon the holographic photopolymer because the two-stage chemistry process provides the ability to achieve precise control over the sequence, timing, and selectivity of different chemical transformations, enabling the synthesis of complex molecules or materials with high efficiency and accuracy. In some forms, a solid host matrix including a polyurethane matrix and additives can be formed to produce a first photopolymer, and then followed by recording into a second photopolymer including the dye system and the writing monomer. Additionally, the writing monomer and the polymer matrix may be selected for similar ether groups to increase the transparency of the holographic photopolymer. In some forms, the holographic photopolymer may have a transmittance greater than about 80%, about 85%, about 90% about 95%, or any transparency bounded by these values, e.g., 91%.

In one embodiment, a film is made according to a method described herein. By way of 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 made in an atmosphere including about 25% oxygen 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 percent of oxygen bounded by this range.

In some embodiments, the holographic photopolymer may be a film or coating applied to a glass substrate or to a plastic substrate. In some forms, the coating may be applied to a glass substrate via a vacuum lamination coating method while in other forms, the coating may be applied to a plastic substrate via a roll-to-roll coating method.

In one embodiment, an augmented reality/mixed reality (AR/MR) apparatus includes a holographic grating as described herein. The AR/MR apparatus may include an AR/MR headset. Additionally or alternatively, the AR/MR apparatus may include a holographic display.

EXAMPLES

It has been discovered that embodiments of the holographic grating as described herein may exhibit improved performance. These benefits are further demonstrated by the following examples, which are intended to be illustrative of the disclosure only and are not intended to limit the scope or underlying principles in any way.

Preparation of photopolymer solution

Example 1 - ZrC>2 hybridized formulation and formulation with ZrC>2 Preparation of nanoparticles dispersed writing monomers mixture

1.03 g of EA-F5710 (mixture of ethoxylated fluorene diacrylate and m- phenoxybenzyl acrylate) (OSAKA GAS Chemicals, Japan), 0.10 g of 2-Hydroxy-3- phenoxypropylacrylate (CAS No.: 16969-10-1), 0.41 g of Sartomer SR349, 0.50 g of biphenylmethyl acrylate (CAS No.: 54140-58-8), and Zirconia oxide capped with acrylates (48.5 wt%) in ethyl acetate (PCPC-1-50-ETA, Pixelligent) were mixed in the dark for 0.5 hours at ambient temperature. Ethyl acetate was then removed by rotary evaporation, and fully dried under vacuum.

Preparation of photoinitiation mixture solution

200 mg of Borate salt tetrabutylammonium tris(3-chloro-4-methylphenyl) (hexyl)borate (CAS No.: 1147315, coinitiator) and 20.0 mg of Safranine O (Photosensitizer or dye) were dissolved and mixed in 0.35 g of 1-ethyl-2-pyrrolidone (CAS No.: 2687-91-4) at 55 °C for 2 hours in the dark.

Preparation of Tin catalyst solution (for urethane polymerization)

1 part of an organotin catalyst (FOMREZ UL-28, Dimethyltin dineodecanoate) was mixed with 9 parts of 1-ethyl-2-pyrrolidone (CAS No.: 2687-91-4) at room temperature to form a 10% catalyst stock solution.

Preparation of photopolymer ZrC hybridized formulation.

The writing monomers mixture as prepared step, 1.4 g of Arcol PPG-725 (Polypropylene glycol, Covestro), and 0.46 g of a photoinitiation mixture solution were mixed in the dark at 60 °C overnight. The mixture was cooled down to 35 °C. This was followed by the addition of 0.69 g of isocyanate (Desmodur WP 260, Covestro). The mixture was mixed vigorously for 3 minutes at 35 °C. Then 0.026 g of Tin catalyst solution was added into the resulting mixture, and mixed for 3 minutes at 35 °C. The resulting liquid solution was ready to place under a vacuum at 35 °C for 15 minutes to remove air bubbles caused by mixing.

Example 1-REF - Photopolymer formulation without ZrC^for comparison Preparation of writing monomers mixture

1.04 g of EA-F5710 (mixture of ethoxylated fluorene diacrylate and m- phenoxybenzyl acrylate) (OSAKA GAS Chemicals, Japan), 0.11 g of 2-Hydroxy-3- phenoxypropylacrylate (CAS No.: 16969-10-1), 0.43 g of Sartomer SR349, and 0.52 g of biphenylmethyl acrylate (CAS No.: 54140-58-8) were mixed in the dark for 1 hour at 60°C. Preparation of photoinitiation mixture solution

Preparation of Tin catalyst solution (for urethane polymerization)

Preparation of photopolymer formulation without ZrO2 for comparison

The writing monomers mixture as prepared above, 1.21 g of Arcol PPG-725 (Polypropylene glycol, Covestro), and 0.46 g of a photoinitiation mixture solution were mixed in the dark at 60 °C overnight. The mixture was cooled down to 35 °C. This was followed by the addition of 0.64 g of isocyanate (Desmodur WP 260, Covestro). The mixture was mixed vigorously for 3 minutes at 35 °C. Then 0.026 g of Tin catalyst solution was added into the resulting mixture, and mixed for 3 minutes at 35 °C. The resulting liquid solution was ready to place under a vacuum at 35 °C for 15 minutes to remove air bubbles caused by mixing.

Example 2 - ZrO2 hybridized formulation and formulation with ZrC>2 Preparation of nanoparticles dispersed writing monomers mixture

0.80 g of EA-F5710 (mixture of ethoxylated fluorene diacrylate and m- phenoxybenzyl acrylate) (OSAKA GAS Chemicals, Japan), 0.10 g of 2-Hydroxy-3- phenoxypropylacrylate (CAS No.: 16969-10-1), 0.40 g of Sartomer SR349, 0.50 g of biphenylmethyl acrylate (CAS No.: 54140-58-8), 0.20 g of N-vinyl pyrrolidinone CAS No.: 88-12-0) and Zirconia oxide capped with acrylates (48.5 wt%) in ethyl acetate (PCPC-1- 50-ETA, Pixelligent) were mixed in the dark for 0.5 hours at ambient temperature. Ethyl acetate was then removed by rotary evaporation, and fully dried under vacuum.

Preparation of photoinitiation mixture solution

Preparation of Tin catalyst solution (for urethane polymerization)

Preparation of photopolymer ZrC hybridized formulation.

The writing monomers mixture as prepared 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 photoinitiation mixture solution were mixed in the dark at 60 °C overnight. The mixture was cooled down to 35 °C. This was followed by the addition of 0.97 g of isocyanate (Desmodur WP 260, Covestro). The mixture was mixed vigorously for 3 minutes at 35 °C. 0.026 g of Tin catalyst solution was then added into the resulting mixture, and mixed for 3 minutes at 35 °C. The resulting liquid solution was ready to place under a vacuum at 35 °C for 15 minutes to remove air bubbles caused by mixing.

Glass substrate coating (Sample preparation for exposure)

In a light controlled (safe red-light lamp) environment, a glass substrate was cleaned and dried. The glass substrate was cut to about 2” x 2” square. The cut glass substrate was cleaned with soap (washing detergent) and water, and then dried by nitrogen gas (N2) at room temperature for about 30 seconds and then heated to about 60 °C. A drop of synthesized photopolymer material was then applied to the glass plate, and then covered with a second glass plate, which was kept at a distance of a controlled thickness by applying silica microsphere beads. The glass sandwiched samples were vacuumed and laminated using an NPC vacuum chamber bonding machine (https://www.npcgroup.net/eng/solarcell/vacuum-bonding). After lamination, the sample specimens were left at 35 °C overnight.

Hologram-mirror recording

The polymerized photopolymer film was exposed to a Denisyuk (mirror type hologram) arrangement with a laser at 532 nm and exposed with a power density of 5-10 mW/cm2 with an exposure time of 2-10 seconds. After exposure, holograms were examined visually and a bleaching step under UV light was applied. The hologram laminated between two glass slides was exposed under a lamp UVASPOT 1000 RF2 from Honle UV Technology, Germany. The UVASPOT is a modular, high-intensity UV unit and system that can achieve very high uniformity throughout the irradiation field. Through various lamp and filter configurations, different spectra can be produced for applications in the ranges of UVA (340 nm - 400 nm).

Reflection efficiency measurement

Reflection efficiency was calculated from transmittance of a hologram recorded area (HOE) and a non-recorded area (Non-HOE area). The transmittance of the HOE area and the Non-HOE area of a sample were measured after a bleaching step. The transmittance spectrum was measured from 350-700nm with a Shimadzu UV-VIS-NIR spectrophotometer, model UV-3600 i Plus. A 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 which allowed beams to pass the measurement area. The transmittance measurement from 350-700 nm was scanned with slow speed with data interval of 0.5 nm. The reflection efficiency was calculated from the formula: [(Transmittance of Non-HOE-Transmittance of HOE)/Transmittance of Non-HOE], FIGS. 5-8 are graphical illustrations depicting various optical properties of Examples 1 and 2. The following table provides data relating to measured haze properties of Example 1 .

Use of the term “may” or “may be” or “can” should be construed as shorthand for “is” or “is not” or, alternatively, “does” or “does not” or “will” or “will not,” etc. For example, the statement “a thermally conductive composite may further comprise a backing layer” should be interpreted as, for example, “In some embodiments, a thermally conductive composite further comprises a backing layer,” or “In some embodiments, a thermally conductive composite does not further comprise a backing layer.”

Unless otherwise indicated, all numbers expressing quantities of ingredients, properties, such as, molecular weight, reaction conditions, and so forth used in the specification and embodiments are to be understood as being modified in all instances by the term “about.” The term “about” as used herein, can include any numerical value that can vary without changing the basic function of that value. When used with a range, “about” also discloses the range defined by the absolute values of the two endpoints. The term “about” may refer to plus or minus 10% of the indicated number.

Accordingly, unless indicated to the contrary, the numerical parameters set forth in the specification and attached embodiments are approximations that may vary depending upon the desired properties sought to be obtained. At the very least, and not as an attempt to limit the application of the doctrine of equivalents. To the scope of the embodiments, each numerical parameter should at least be construed in light of the number of reported significant digits and by applying ordinary rounding techniques.

For the processes and/or methods disclosed, the functions performed in the processes and methods may be implemented in differing order, as may be indicated by context. Furthermore, the outlined steps and operations are only provided as examples, and some of the steps and operations may be optional, combined into fewer steps and operations, or expanded into additional steps and operations.

This disclosure may sometimes illustrate different components contained within, or connected with, different other components. Such depicted architectures are merely examples, and many other architectures can be implemented which achieve the same or similar functionality.

The terms used in this disclosure, and in the appended embodiments, are generally intended as “open” terms (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 “includes, but is not limited to,” etc.). In addition, if a specific number of elements is introduced, this may be interpreted to include at least the recited number, as may be indicated by context (e.g., the bare recitation of "two recitations," without other modifiers, includes at least two recitations, or two or more recitations). As used in this disclosure, any disjunctive word and/or phrase presenting two or more alternative terms should be understood to contemplate the possibilities of including one of the terms, either of the terms, or both terms. For example, the phrase “A or B” will be understood to include the possibilities of “A” or “B” or “A and B.”

The terms and words used are not limited to the bibliographical meanings but are merely used to enable a clear and consistent understanding of the disclosure. The terms “a,” “an,” “the” and similar referents used in the context of describing the present disclosure (especially in the context of the following embodiments) are to be construed to cover both the singular and the plural, unless otherwise indicated herein or clearly contradicted by context. The use of any and all examples, or representative language (e.g., “such as”) provided herein is intended merely to better illuminate the present disclosure and does not pose a limitation on the scope of any embodiments. No language in the specification should be construed as indicating any non-embodied element essential to the practice of the present disclosure.

Groupings of alternative elements or embodiments disclosed herein are not to be construed as limitations. Each group member may be referred to and embodied individually or in any combination with other members of the group or other elements found herein. It is anticipated that one or more members of a group may be included in, or deleted from, a group for reasons of convenience and/or patentability. When any such inclusion or deletion occurs, the specification is deemed to contain the group as modified thus fulfilling the written description of all Markush groups used in the appended embodiments.

Certain embodiments are described herein, including the best mode known to the inventors for carrying out the present disclosure. Of course, variations on these described embodiments, will become apparent to those of ordinary skill in the art upon reading the foregoing description. The inventor expects skilled artisans to employ such variations as appropriate, and the inventors intend for the present disclosure to be practiced otherwise than specifically described herein. Accordingly, the embodiments include all modifications and equivalents of the subject matter recited in the embodiments as permitted by applicable law. Moreover, any combination of the above-described elements in all possible variations thereof is contemplated unless otherwise indicated herein or otherwise clearly contradicted by context. In closing, it is to be understood that the embodiments disclosed herein are illustrative of the principles of the embodiments. Other modifications that may be employed are within the scope of the embodiments. Thus, byway of example, but not of limitation, alternative embodiments may be utilized in accordance with the teachings herein. Accordingly, the embodiments are not limited to the embodiments precisely as shown and described.

By the term "substantially" it is meant that the recited characteristic, parameter, or value need not be achieved exactly, but that deviations or variations, including for example, tolerances, measurement error, measurement accuracy limitations and other suitable factors may occur in amounts that do not preclude the effect the characteristic was intended to provide.

Aspects of the present disclosure may be embodied in other forms without departing from its spirit or essential characteristics. The described aspects are to be considered in all respects illustrative and not restrictive. The embodied subject matter is indicated by the appended embodiments rather than by the foregoing description. All changes, which come within the meaning and range of equivalency of the embodiments, are to be embraced within their scope.

Claims

CLAIMS What is claimed is:

1. A holographic grating, comprising: at least one photocurable nanoparticle; a light portion comprising a first concentration of the at least one photocurable nanoparticle, a dark portion comprising a second concentration of the at least one photocurable nanoparticle, 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 a holographic photopolymer comprising a polymer matrix, a photocurable writing monomer, and a dye system; wherein the holographic photopolymer is dispersed throughout the light portion and the dark portion 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 ZrC>2, TiC>2, TiC>2 a core-ZrCh shell material, ZnO, CeC>2, Ta2Os/SiO2, and ITO.

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

5. The holographic grating of claim 4, wherein the reactive moiety comprises at least one of an acrylate and a 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 includes 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 less than about 1.6.

9. The holographic grating of claim 1 , wherein the polymer matrix comprises an 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 comprising at least one crosslinkable moiety and a polymerizable monomer comprising at least one polymerizable moiety.

13. The holographic grating of claim 1 , wherein the liquid writing monomer comprises ethoxylated fluorene diacrylate, m-phenoxybenzyl acrylate, 2-hydroxy-3- phenoxypropylacrylate, biphenylmethyl acrylate, ethoxylated bisphenol a diacrylate, and the at least one nanoparticle.

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 safranine O, new methylene blue, and ethyl violet.

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

17. The holographic grating of claim 1 , wherein the polymer matrix includes a mesh size which is greater than the size of the nanocrystal core of the photocurable nanoparticle.

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

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