Backfill emptying periodic structure and manufacturing method

Abstract

Methods for recording grating structures and the resulting grating structures are disclosed herein. In one example, a method includes depositing a holographic mixture onto a first substrate, the holographic mixture containing a mixture of a monomer and an inert material; exposing the holographic mixture using a holographic exposure phase separation process to form a nanostructure comprising a polymer-rich region and an inert material-rich region; removing inert material from the inert material-rich region to form a grating comprising a polymer-rich region and a region containing a residual polymer network; applying an ashing process to the regions containing the residual polymer network to form an ashed grating comprising polymer-rich regions and air regions; a coating material is deposited onto the ashed grating to form a coated grating, wherein the coating material backfills the air regions and coats the polymer-rich regions.

Description

[0001] Cross-referenced applications

[0002] This application claims priority to U.S. Provisional Application No. 63 / 385,863, filed December 2, 2022, the disclosure of which is incorporated by reference in its entirety. Technical Field

[0003] The present invention generally relates to backfilling surface relief gratings and more particularly to backfilling empty periodic structures. Background Art

[0004] Waveguides can be described as structures that have the ability to confine and guide waves (i.e., limit the spatial region in which waves can propagate). A subclass includes optical waveguides, which are structures that can guide electromagnetic waves, typically those in the visible spectrum. Waveguide structures can be designed to control the propagation path of waves using a variety of different mechanisms. For example, planar waveguides can be designed to utilize a diffraction grating to diffract and couple incident light into the waveguide structure, allowing the in-coupled light to travel within the planar structure via total internal reflection (TIR).

[0005] The fabrication of waveguides can include the use of material systems that allow for the recording of holographic optical elements within or on the surface of the waveguide. One class of such materials includes polymer dispersed liquid crystal (PDLC) mixtures, which are mixtures containing photopolymerizable monomers and liquid crystals. Another subclass of such mixtures includes holographic polymer dispersed liquid crystal (HPDLC) mixtures. Holographic optical elements, such as volume phase gratings, can be recorded in such liquid mixtures by irradiating the material with two or more mutually coherent laser beams. During the recording process, the monomers polymerize and the mixture undergoes photopolymerization-induced phase separation, resulting in regions densely populated by liquid crystal (LC) droplets, interspersed with regions of transparent polymer. Alternating liquid crystal-rich and liquid crystal-poor regions form the fringe surface of the grating.

[0006] Waveguide optical elements, such as those described above, are contemplated for use in a range of display systems and sensor applications. In many applications, various waveguide structures and material systems can be used to implement waveguides containing one or more grating layers expressing a variety of optical functions, enabling new innovations in near-eye displays for augmented reality (AR) and virtual reality (VR), compact head-up displays (HUDs) for aviation and road transportation, and sensors for biometrics and laser radar (LIDAR) applications. Because many of these applications involve consumer products, there is an increasing need for efficient, low-cost methods for mass-producing holographic waveguides. Summary of the Invention

[0007] In some aspects, the technology described herein relates to a method for recording a grating structure, the method comprising: depositing a holographic mixture onto a first substrate, the holographic mixture comprising a mixture of a monomer and an inert material; exposing the holographic mixture to a holographic recording beam to form a volume grating comprising polymer-rich regions and inert material-rich regions; removing the inert material from the inert material-rich regions to form a depleted periodic structure comprising polymer-rich regions and regions containing a residual polymer network; applying an ashing process to the regions containing the residual polymer network to form an ashed grating comprising polymer-rich regions and air regions; and depositing a coating material onto the ashed grating to form a final grating, wherein the coating material backfills the air regions and overcoats the polymer-rich regions.

[0008] In some aspects, the technology described herein relates to methods wherein the coating material is a chemical compound of silicon and nitrogen.

[0009] In some aspects, the technology described herein relates to methods wherein the coating material is silicon nitride (Si3N4) applied with a minimum thickness greater than 200 nm.

[0010] In some aspects, the technology described herein relates to methods wherein the coating material has a refractive index greater than the refractive index of the polymer.

[0011] In some aspects, the technology described herein relates to methods wherein the coating material has a lower refractive index than the polymer.

[0012] In some aspects, the technology described herein relates to methods in which the coating material is a composite of more than one material.

[0013] In some aspects, the techniques described herein relate to methods in which depositing a coating material includes more than one coating step.

[0014] In some aspects, the technology described herein relates to methods wherein the coating material includes nanoparticles.

[0015] In some aspects, the techniques described herein relate to methods wherein the final grating is a tilted grating.

[0016] In some aspects, the techniques described herein relate to methods where the final grating is a photonic crystal.

[0017] In some aspects, the techniques described herein relate to methods further comprising depositing an anti-reflective coating onto the final grating.

[0018] In some aspects, the techniques described herein relate to methods wherein depositing a coating material comprises a plasma enhanced chemical vapor deposition (PECVD) process.

[0019] In some aspects, the technology described herein relates to a method further comprising covering the coating material with a second substrate, wherein an upper surface is in contact with air and a lower surface supports a release layer positioned in contact with the coating material.

[0020] In some aspects, the techniques described herein relate to methods wherein depositing a coating material comprises an atomic layer deposition (ALD) process.

[0021] In some aspects, the technology described herein relates to methods wherein depositing a coating material includes spreading a portion of the coating material into pores contained within the polymer-rich region.

[0022] In some aspects, the technology described herein relates to methods wherein the final grating comprises a volume phase grating (VPG) comprising alternating polymer-rich regions and coating material-rich regions, covered by a surface relief grating (SRG) formed from the coating material, wherein the maxima of the SRG cover the polymer-rich regions of the VPG, and wherein the minima of the SRG cover the coating material-rich regions of the VPG.

[0023] In some aspects, the techniques described herein relate to methods wherein the VPG is a volume Bragg grating (VBG).

[0024] In some aspects, the technology described herein relates to methods in which a holographic mixture contacting a surface of a first substrate is modified by at least one selected from the group consisting of nanostructuring, chemical functionalization, and coating.

[0025] In some aspects, the technology described herein relates to methods in which the coating partially backfills the air region such that a portion of the air region remains between adjacent portions of the coating covering adjacent polymer-rich regions.

[0026] In some aspects, the technology described herein relates to methods in which the coating contacts the first substrate in sections between adjacent polymer-rich regions.

[0027] In some aspects, the technology described herein relates to methods that also include depositing a backfill material onto the coating contacting the first substrate in sections between adjacent polymer-rich regions to backfill air regions between adjacent portions of the coating.

[0028] In some aspects, the technology described herein relates to methods in which a backfill material partially backfills air regions between adjacent portions of a coating layer such that air regions remain between adjacent portions of the coating layer above the backfill material.

[0029] In some aspects, the technology described herein relates to methods wherein the backfill material comprises a high refractive index resin.

[0030] In some aspects, the techniques described herein relate to methods wherein depositing the backfill material comprises dropcasting, spin coating, slot-die coating, or spray coating.

[0031] In some aspects, the techniques described herein relate to methods further comprising curing the deposited backfill material.

[0032] In some aspects, the technology described herein relates to methods wherein the coating comprises an inorganic material.

[0033] In some aspects, the technology described herein relates to methods wherein the coating comprises Al2O3, TiO2, and / or HfO2.

[0034] In some aspects, the techniques described herein relate to methods wherein depositing a coating material comprises an atomic layer deposition technique.

[0035] In some aspects, the technology described herein relates to a grating structure comprising: a substrate; a repeating pattern of polymer regions located on the substrate; a coating conformally coating exposed surfaces of the substrate and the polymer regions; and a backfill material occupying areas between adjacent portions of the coating.

[0036] In some aspects, the technology described herein relates to grating structures in which the coating contacts the substrate in segments between adjacent polymer regions.

[0037] In some aspects, the technology described herein relates to grating structures in which a backfill material partially backfills regions between adjacent portions of the coating layer such that air regions exist between the adjacent portions of the coating layer above the backfill material.

[0038] In some aspects, the technology described herein relates to grating structures wherein the backfill material comprises a high refractive index resin.

[0039] In some aspects, the technology described herein relates to a grating structure comprising: a substrate; a repeating pattern of polymer regions located on the substrate; a coating that conformally coats the exposed surfaces of the substrate and the polymer regions, wherein the coating completely fills the segments between the polymer regions and extends beyond the tops of the polymer regions so as to form a final grating comprising a volume phase grating (VPG), wherein the volume phase grating comprises alternating polymer-rich regions and coating material-rich regions, covered by a surface relief grating (SRG) formed from the coating material, wherein the maxima of the SRG cover the polymer-rich regions of the VPG, and wherein the minima of the SRG cover the coating material-rich regions of the VPG.

[0040] In some aspects, the technology described herein relates to grating structures in which the coating is a chemical compound of silicon and nitrogen.

[0041] In some aspects, the techniques described herein relate to grating structures in which the coating material is silicon nitride (Si3N4) applied with a minimum thickness greater than 200 nm.

[0042] In some aspects, the technology described herein relates to grating structures in which the refractive index of the coating is greater than the refractive index of the polymer region.

[0043] In some aspects, the technology described herein relates to grating structures in which the refractive index of the coating is lower than the refractive index of the polymer region.

[0044] In some aspects, the technology described herein relates to grating structures in which the coating is a composite of more than one material.

[0045] In some aspects, the technology described herein relates to grating structures in which the coating includes nanoparticles.

[0046] In some aspects, the technology described herein relates to grating structures in which polymer regions are tilted to produce tilted gratings.

[0047] In some aspects, the technology described herein relates to grating structures and also includes anti-reflection of the cover coating.

[0048] In some aspects, the technology described herein relates to a grating structure further comprising a second substrate, wherein an upper surface is in contact with air and a lower surface supports a release layer positioned in contact with the coating material.

[0049] In some aspects, the technology described herein involves grating structures in which a coating is applied to holes contained within a polymer region.

[0050] In some aspects, the technology described herein relates to a method for manufacturing a diffraction waveguide, comprising the steps of: coating a holographic mixture onto a first substrate, the holographic mixture comprising an inert component and a monomer component; exposing the holographic mixture to a holographic recording beam to form a volume grating comprising polymer-rich regions separated by regions of the inert component; removing at least a portion of the inert component from the volume grating to form an empty periodic structure comprising polymer-rich regions separated by air regions; depositing a first high refractive index material onto the polymer structure using a dry deposition process; and depositing a second high refractive index material onto the first high refractive index material using a liquid deposition process.

[0051] In some aspects, the technology described herein relates to methods wherein the polymer structure is a surface relief diffractive structure.

[0052] In some aspects, the technology described herein relates to methods wherein the inert component comprises liquid crystals, inert fluids, and / or nanoparticles.

[0053] In some aspects, the technology described herein relates to methods wherein the first high refractive index material is inorganic.

[0054] In some aspects, the technology described herein relates to methods wherein the first high refractive index material comprises a plurality of layers.

[0055] In some aspects, the techniques described herein relate to methods in which multiple layers comprise different materials.

[0056] In some aspects, the techniques described herein relate to methods in which multiple layers comprise different thicknesses.

[0057] In some aspects, the techniques described herein relate to methods wherein the dry deposition process is selected from one of atomic layer deposition (ALD), chemical vapor deposition (CVD), plasma enhanced chemical vapor deposition (PECVD), and metal-organic chemical vapor deposition (MOCVD).

[0058] In some aspects, the technology described herein relates to methods wherein the second high refractive index material is a resin.

[0059] In some aspects, the technology described herein relates to methods wherein the liquid deposition process is selected from the group consisting of drop coating, spin coating, slot coating, and spray coating.

[0060] In some aspects, the techniques described herein relate to methods wherein depositing the second high refractive index material includes using a solution including a solvent.

[0061] In some aspects, the technology described herein relates to methods in which a second high refractive index material is applied to a structure created by applying a dry deposition process to a polymer material to provide air space above the second high refractive index material surrounded by adjacent portions of a first high refractive index material.

[0062] In some aspects, the technology described herein relates to methods in which a second high refractive index material at least partially fills air gaps between adjacent regions of a first high refractive index material that exist after applying a dry deposition process to a polymer structure.

[0063] In some aspects, the technology described herein relates to methods in which a second high refractive index material completely immerses a structure resulting from applying a dry deposition process to a polymer structure.

[0064] In some aspects, the technology described herein relates to methods in which a second high refractive index material planarizes a structure resulting from applying a dry deposition process to a polymer structure.

[0065] In some aspects, the technology described herein relates to methods further comprising positioning a second substrate on a second high refractive index material, wherein the second high refractive index material bonds the second substrate to the structure resulting from applying the dry deposition and liquid deposition processes to the polymer structure.

[0066] In some aspects, the technology described herein relates to a method further comprising covering a second substrate over the structure resulting from applying the dry deposition and liquid deposition processes to the polymeric structure.

[0067] In some aspects, the technology described herein relates to methods further comprising depositing a release layer onto the second substrate, which facilitates removal of the second substrate.

[0068] In some aspects, the technology described herein relates to a method further comprising applying a thermal reflow process to a polymer structure.

[0069] In some aspects, the technology described herein relates to a diffractive waveguide comprising: a first substrate; a polymer structure comprising polymer stripes formed on the first substrate; a first layer of high refractive index material conformally coating the polymer stripes; and a second layer of high refractive index material occupying spaces between adjacent portions of the first layer of high refractive index material.

[0070] In some aspects, the technology described herein relates to diffractive waveguides in which a second high refractive index material completely fills segments between adjacent portions of a first high refractive index material layer and includes a planarization layer above the height of the first high refractive index material to planarize the polymer structure.

[0071] In some aspects, the technology described herein relates to a diffractive waveguide further comprising a second substrate covering a planar surface of a second high refractive index material.

[0072] In some aspects, the technology described herein relates to a diffractive waveguide in which a first high refractive index material layer comprises an inorganic material and a second high refractive index material layer comprises an organic material.

[0073] In some aspects, the technology described herein relates to diffractive waveguides in which a first high refractive index material and a second high refractive index material have a higher diffraction index than the polymer structure.

[0074] In some aspects, the technology described herein relates to diffractive waveguides in which polymer stripes are tilted.

[0075] In some aspects, the technology described herein relates to diffractive waveguides in which the depth of the polymer stripes is in the range of 1-3 microns, and the stripe spacing is in the range of 0.35 to 0.80 microns.

[0076] In some aspects, the technology described herein relates to diffractive waveguides in which the ratio of the depth of the polymer fringes to the fringe spacing is in the range of 1:1 to 5:1.

[0077] In some aspects, the technology described herein relates to a diffractive waveguide comprising: a first substrate; a polymer structure comprising polymer stripes formed on the first substrate; a first layer of high refractive index material occupying spaces between adjacent polymer stripes; and a second layer of high refractive index material conformally coating the first layer of high refractive index material and exposed portions of the polymer stripes.

[0078] In some aspects, the technology described herein relates to a diffractive waveguide in which the first high refractive index material layer comprises an organic material and the second high refractive index material layer comprises an inorganic material.

[0079] In some aspects, the technology described herein relates to a method for manufacturing a diffraction waveguide, comprising the steps of: coating a holographic mixture onto a first substrate, the holographic mixture comprising an inert component and a monomer component; exposing the holographic mixture to a holographic recording beam to form a volume grating comprising polymer-rich regions separated by regions of the inert component; removing at least a portion of the inert component from the volume grating to form an empty periodic structure comprising polymer-rich regions separated by air regions; depositing a first high refractive index material onto the polymer structure using a liquid deposition process; and depositing a second high refractive index material onto the first high refractive index material using a dry deposition process. BRIEF DESCRIPTION OF THE DRAWINGS

[0080] The specification will be more fully understood with reference to the following figures and data graphs, which are presented as various embodiments of the disclosure and should not be construed as a complete recitation of the scope of the disclosure, wherein:

[0081] Figure 1 is a schematic cross-sectional view of a backfilled EPS structure according to an embodiment of the present invention.

[0082] Figure 2 is a flow chart of a method of fabricating a backfilled nanostructure according to an embodiment of the present invention.

[0083] Figures 3A-3E An example process flow for fabricating deep SRGs according to an embodiment of the present invention is described.

[0084] Figure 4 is a method for producing a Figure 3E Schematic illustration of the backfill method of the polymer-air SRG described in .

[0085] Figure 5A is a SEM image of an example EPS grating after ashing.

[0086] Figure 5B is a plot of diffraction efficiency (DE) versus angle for S-polarized light.

[0087] Figure 5C This is a graph of DE versus angle for P-polarized light.

[0088] Figure 6A is a SEM image of an example EPS grating after ashing.

[0089] Figure 6B This is a graph of DE versus angle for S-polarized light.

[0090] Figure 6C This is a graph of DE versus angle for P-polarized light.

[0091] Figure 7A is the image of the instance raster.

[0092] Figure 7B yes Figure 7A Graph of DE versus angle of the grating for S-polarized light.

[0093] Figure 7C yes Figure 7A Graph of DE versus angle of the grating for P-polarized light.

[0094] Figure 8A Shown is the DE percentage versus angle for ALD coated gratings with ALD coating thickness ranging from 0-50 nm.

[0095] Figure 8B Shown is the DE percentage versus angle for PECVD SiN coated gratings with ALD coating thickness ranging from 0-500 nm.

[0096] Figure 8C is a graph summarizing the coating thickness versus angle characteristics of fully backfilled gratings in ALD and SiN PECVD conditions.

[0097] Figure 9 An example nanostructure fabrication process according to an embodiment of the present invention is described.

[0098] Figure 10 is a cross-sectional view of a surface relief grating structure according to an embodiment of the present invention.

[0099] Figure 11 After applying the high refractive index coating 1011 according to an embodiment of the present invention Figure 10 Cross-section of the grating.

[0100] Figure 12 After partially backfilling with high refractive index material Figure 11 Cross-section of the grating.

[0101] Figure 13 After being completely immersed in a high refractive index material Figure 11 Cross-section of the grating.

[0102] Figure 14 yes Figure 11 Cross-sectional view of a grating in which a polymer structure is conformally coated with a first high refractive index material and conformally coated with a second high refractive index material.

[0103] Figure 15-17 illustrate Figure 14 Another configuration of a second high refractive index material.

[0104] Figure 18 is partially backfilled with a third refractive index material according to an embodiment of the present invention. Figure 14 Cross-sectional view of the grating structure.

[0105] Figure 19 is to provide a planar top surface that is completely immersed in a third index material Figure 14 Cross-sectional view of the grating structure.

[0106] Figure 20 yes Figure 19 A cross-sectional view of a grating structure in which a second substrate is bonded to a planar surface of a third refractive index material.

[0107] Figure 21 yes Figure 14 Cross-sectional view of a grating structure in which a third refractive index material is conformally coated on a second high refractive index material.

[0108] Figure 22-24 The three stages of diffractive waveguide fabrication using a dry immersion process are described.

[0109] Figure 25 A liquid deposition process performed on a grating structure according to an embodiment of the present invention is described.

[0110] Figure 26 is a flow chart conceptually illustrating a method of fabricating a submerged surface relief polymer structure according to an embodiment of the present invention. DETAILED DESCRIPTION

[0111] Various disclosed embodiments relate to backfilled empty periodic structures (EPS) and methods for manufacturing backfilled gratings, which are described by way of example with reference to the accompanying drawings. EPS is described in U.S. Patent No. 11,442,222, entitled “Evacuated gratings and methods of manufacturing,” filed on August 28, 2020, which is incorporated herein by reference in its entirety.

[0112] The field of view (FOV) and spectral information that can be carried by the waveguide are determined by the lowest refractive index in the structure. The polymer materials currently used in the manufacture of surface relief gratings (SRGs) cannot achieve the high refractive index required for both high angular bandwidth and full color. Disclosed herein are methods for introducing high refractive index materials (resins) into polymer waveguide structures, including liquid deposition of resins and / or dry deposition of inorganic materials (e.g., using ALD or other processes). These "immersion" processes can achieve a wider FOV and / or improved RGB coverage, wherein the number of waveguides per AR display eyepiece is reduced. Depending on the recording geometry and the releasable substrate, a release coating can be applied to any substrate used in the waveguide to process the initially recorded volume diffraction structure (e.g., VBG) into a surface relief structure. The substrate can have any thickness depending on the design, but typically they are <1 mm. The various fabrication steps described in the references can be applied to form well-defined surface relief gratings using phase separation. These processes may include cleaning the phase separation material with a solvent and dry etching to remove any organic residual grooves. Various methods can be used for applying the resin, such as drop coating, spin coating, slot coating, spray coating, and the like.

[0113] While the description addresses immersion of gratings formed by a phase separation process, this is exemplary only. The various methods disclosed can also be applied to gratings formed using nanolithographic processes, which can form surface relief gratings. Therefore, after a grating structure is created by any process, a backfill process has been found to produce advantageous results. The grating structure can be a deep surface relief grating. Examples of deep SRGs are described in U.S. Patent No. 11,442,222, which is incorporated by reference above. Deep SRGs can have a thickness in the range of 1-3 microns, with a Bragg fringe spacing of 0.35 to 0.80 microns. In some embodiments, the ratio of grating depth (thickness) to Bragg fringe spacing can be from 1:1 to 5:1.

[0114] In some examples, a backfill method can be used after the EPS is generated. The backfill method can include depositing a silicon nitride (Si3N4) layer on top of the EPS to form a backfill nanostructure. Figure 1 1 is a schematic cross-sectional view of a backfilled EPS structure according to an embodiment of the present invention. EPS structure 154 may be located on substrate 152. The substrate may have a refractive index of n=1.5-2.0. EPS structure 154 may include alternating polymer segments having a refractive index of n=1.5. A conformal coating 156 may be formed on EPS structure 154. EPS structure 154 may be 400 nm thick. Conformal coating 156 may be Si x N yThe conformal coating 156 may extend 200 nm above the EPS structures 154. The refractive index of the conformal coating 156 may be n=2.0. The conformal coating 156 may completely fill the segments between the EPS structures 154. In some examples, the conformal coating 156 may not completely fill the segments between the EPS structures 154, such that air exists between adjacent segments of the conformal coating 156.

[0115] The grating may include a volume phase grating (VPG) 158a including polymer segments and coating regions. The VPG 158a may be covered by a surface relief grating (SRG) 158b formed by a conformal coating 156. The minimum of the SRG covers the polymer segments of the VPG, and the maximum of the SRG covers the coating regions of the VPG.

[0116] Figure 2 1 is a flow chart of a method for fabricating backfilled nanostructures according to an embodiment of the present invention. Method 100 includes depositing 102 a layer comprising a holographic mixture of a monomer and an inert material on a substrate. Method 100 also includes exposing 104 the holographic mixture to a holographic recording beam. The holographic recording beam can produce a nanostructure comprising polymer-rich regions and inert material-rich regions. The holographic recording beam can produce phase separation within the holographic mixture. Method 100 also includes removing 106 the inert material from the inert material-rich regions. The remaining nanostructure can include polymer-rich regions and regions containing a residual polymer network. Method 100 also includes etching 108 the remaining nanostructure. Etching 108 can be a plasma etching step (e.g., ashing). Some of the residual polymer network can be removed to form a grating comprising polymer-rich regions and air regions. Etching 108 can better define the polymer-rich regions to produce a polymer grating structure. Method 100 also includes coating 110 the grating with a backfill material. The backfill material can be deposited on the polymer-rich regions and on the sidewalls of the polymer-rich regions. The backfill material may also displace air regions, resulting in a raster of alternating polymer-rich regions and backfill material. Figure 1 Description: Example backfill EPS structure.

[0117] In many embodiments, the inert material used in the holographic mixture is a liquid crystal.

[0118] In many embodiments, the backfill material may be a chemical compound of elemental silicon and nitrogen. In many embodiments, the coating material may be SiN, applied with a minimum thickness greater than 200 nm.

[0119] In some embodiments, the backfill material may be zirconium oxide and / or titanium oxide (eg, titanium dioxide).

[0120] In various embodiments, the coating material can have a refractive index greater than that of the polymer-rich region, or a refractive index lower than that of the polymer-rich region.

[0121] In many embodiments, the coating material may be a composite material of more than one material. In many embodiments, the coating material may include nanoparticles. In many embodiments, more than one material is deposited in more than one coating step. In many embodiments, the coating material may be deposited using a PECVD process. In many embodiments, the coating material may be deposited using an ALD process. In many embodiments, depositing the coating material includes filling a portion of the coating material into the pores contained in the polymer-rich region. Filling of the pores with the coating material may occur during the deposition of the coating material. However, in some cases, exposing the polymer region to another material (e.g., by immersing the structure in a material bath) or thermal stimulation may be used to adjust the pores to facilitate filling.

[0122] In many embodiments, the holographic mixture contacting side of the substrate may include at least one of: nanostructuring, chemical functionalization, and / or coating.The surface of the substrate in contact with the holographic mixture layer may include at least one of: nanostructuring, chemical functionalization, and / or coating.

[0123] In some embodiments, the coating can be applied to any type of surface relief nanostructure, generally including non-tilted gratings, tilted gratings, and photonic crystals. In many embodiments, the unit is formed by covering the coating material with a second substrate, wherein a release layer is applied to its lower surface in contact with the coating material. Many embodiments may include the additional step of applying an anti-reflective coating.

[0124] In some embodiments, the grating structure can be recorded without sandwiching the holographic material between the first and second substrates. In such embodiments, the second substrate can be applied on top of the nanostructures after the coating material is deposited. In such embodiments, the second substrate can also support a release layer. The second substrate can be applied as a protective layer on top of the previously recorded nanostructures. In some embodiments, where the protective layer is for temporary use, the second substrate can support a release layer to allow removal after the holographic exposure process.

[0125] In many embodiments, the nanostructure formed after deposition of the coating material comprises a volume phase grating (VPG) having alternating polymer-rich and coating material-rich regions, covered by a surface relief grating (SRG) formed from the coating material. The VPG can be a volume Bragg grating (VBG). The SRG's minima overlie the polymer-rich regions of the VBG, and the SRG's maxima overlie the coating material-rich regions of the VBG. In many embodiments, the combination of the SRG's diffraction properties (e.g., wide angular response) and the VPG's diffraction properties (e.g., high diffraction efficiency around the Bragg condition) can provide a hybrid grating with enhanced angular, polarization, and spectral response characteristics that can be tuned for a range of applications.

[0126] Figures 3A-3E An example process flow for fabricating deep SRGs according to an embodiment of the present invention is described. Figure 3A In the embodiment of the present invention, a pair of substrates 212, 1502 sandwich an unexposed holographic mixture layer 211. The pair of substrates 212, 1502 may include a base substrate 212 and a cover substrate 1502. The cover substrate 1502 may have different properties from the base substrate 212 so that the cover substrate adheres to the unexposed holographic mixture layer 211 while being removable from the formed volume grating after exposure. The holographic mixture layer 211 may include a monomer and an inert material.

[0127] exist Figure 3B In the embodiment, the holographic mixture layer 211 is exposed by a pair of holographic recording beams 213, 214. Figure 3C As illustrated in FIG, holographic recording beams 213, 214 expose the holographic mixture layer 211 to form a volume grating 215. The monomer and the inert material may phase separate, and the monomer may be converted into a polymer, so that the volume grating 215 is formed. The volume grating 215 may include alternating polymer-rich regions and inert material-rich regions. Figure 3D In the embodiment of the present invention, the cover substrate 1502 can be removed to expose the volume grating 215. The cover substrate 1502 can be removed to allow the volume grating 215 to remain on the base substrate without damaging the volume grating 215 during the removal process.

[0128] As in Figure 3E As described in , inert material can be removed or evacuated from the inert material-rich regions between the polymer-rich regions, thereby leaving air regions. The polymer-rich regions and the air regions form a polymer-air SRG 216.

[0129] Figure 4 is a method for producing a Figure 3E Schematic illustration of the backfill method on the polymer-air SRG 216 described in FIG. The first stage 202 illustrates the nanostructure configured as a non-tilted grating in the initial stage. Figures 3A-3E The steps described are used to fabricate the grating of the first stage 202. The grating in the first stage 202 may correspond to the grating of the first stage 202. Figure 3EA polymer-air SRG 216 is depicted. The nanostructure includes polymer-rich regions separated by regions containing residual polymer. The residual polymer may be a weak polymer network immersed in air. The refractive index of the polymer-rich region may have an average refractive index of 1.5, while the residual polymer regions may have an average refractive index of 1.2-1.3. The substrate may have a refractive index in the range of 1.5-2.0. The thickness of the nanostructure may be 400 nm. The second stage 204 illustrates the nanostructure after an etching step in which the residual polymer network is removed. The etching step may be a plasma etching step. The third stage 206 illustrates the nanostructure after backfilling. Backfilling may be a coating process that may involve the deposition of silicon nitride (Si3N4). Deposition may be performed via ALD or PECVD. The SiN layer coats the polymer grating and may have a refractive index of 2.0. The SiN layer may be deposited to a thickness of 200 nm over the polymer grating at 90°C. The deposition time may be approximately 100 seconds.

[0130] Backfilling grating structures with SiN offers several key advantages for waveguide displays, including EPS gratings. For example, the effective refractive index of the EPS structure can be increased to support FoVs of 50 degrees and above. The SiN backfill forms a diffusion barrier to oxygen and moisture, which protects the grating. The SiN backfill material acts as a hard, solvent-resistant coating that withstands scratching and cleaning. SiN also has high thermal conductivity, providing high heat and thermal shock resistance.

[0131] Figure 5A is a SEM image of an example EPS grating after ashing. The EPS grating was originally recorded using a holographic mixture containing 42% LC. Figure 5B is a plot of diffraction efficiency (DE) versus angle for S-polarized light. Figure 5C is a graph of DE versus angle for P polarized light. Each DE graph provides Figure 5A DE curves after ashing and after SiN deposition as illustrated in . As illustrated, the diffraction efficiency is significantly improved due to the SiN deposition.

[0132] Figure 6A is a SEM image of an example EPS grating after ashing. The EPS grating was originally recorded using a holographic mixture containing 35% LC. Figure 6B This is the DE and angle diagram of S-polarized light.

[0133] Figure 6C It is the DE and angle diagram of P polarized light. Each DE diagram provides Figure 6A DE curves after ashing and after SiN deposition on the ashed grating as illustrated in As illustrated, the diffraction efficiency is significantly improved due to the SiN deposition.

[0134] Figures 5A-5C and Figures 6A-6CEPS gratings made with different LC concentrations (42 wt% vs. 35 wt%) were compared. As illustrated, Figures 5A-5C The high LC concentration of the grating leads to a higher P-polarization DE after PECVD deposition of SiN.

[0135] Figure 7A is the image of the instance raster. This raster is combined with Figure 1 In addition, a post-processing acetone clean was performed after the coating step. Figure 7B yes Figure 7A DE vs. angle diagram of the grating for S-polarized light. Figure 7C yes Figure 7A As shown, the DE of the grating with P-polarized light is slightly affected by the acetone cleaning after the coating process.

[0136] DE diagrams are provided as Figure 7A DE curve after ashing as described in , after PECVD deposition of SiN and then after subsequent acetone cleaning. Acetone cleaning can be performed with a soft wipe. Figures 7B-7C , there is no significant change in DE after cleaning the nanostructures using acetone applied with a soft wipe.

[0137] Figures 8A-8B These graphs show DE versus angle for tilted grating backfill EPS designs. The backfill can be SiN. Different graphs correspond to different coating thicknesses. Coating thicknesses are expressed in nanometers. DE is calculated for an LED source operating in the green band. Figure 8A Shown is the DE percentage versus angle for ALD-coated gratings with ALD coating thickness ranging from 0-50 nm. Figure 8B Shown is the DE percentage versus angle for PECVD SiN coated gratings with ALD coating thickness ranging from 0-500 nm. Figure 8C The following is a graph summarizing the coating thickness versus angle characteristics of fully backfilled gratings in ALD and SiN PECVD conditions. The structure may include a substrate refractive index of 2.0; a fill factor of 0.5; a tilt angle of 25 degrees; a polymer thickness of 0.5 micron, a grating period of 0.38 micron, a polymer refractive index of 1.5, and a coating refractive index of 2.0. Note that in Figures 8A-8C In the example of , when the coating thickness is greater than or equal to 95nm, complete backfill occurs (at Figure 4 (described in the third stage 206 of FIG. 1 ).

[0138] While the SiN backfill method disclosed herein offers potentially significant advantages, including increasing the effective refractive index of the grating structure and, in the case of displays, increasing the field of view. PECVD deposited SiN enhances and improves the environmental robustness of the grating structure. PECVD can be faster and more economical than ALD deposition. There are some significant but potentially controllable risks associated with the use of PECVD. Thick layers of SiN (e.g., >100 nm) may not cause significant haze. Thick layers of SiN (e.g., >100 nm) may not cause significant transmission losses. Thick layers of SiN may potentially cause strong reflections (and therefore losses). However, the effects of any reflections can be ameliorated by a well-designed AR coating. Because the proposed method relies on backfill, uniformity of PECVD may not be a major issue compared to conformality of ALD.

[0139] In many embodiments, the top substrate can act as a release layer. In many embodiments, an additional step of removing the release layer can be performed after the nanostructures are cured. The release layer can be used in a multilayer manufacturing process, as discussed in International Publication No. WO2022 / 187870 (entitled "Evacuated periotic structures and methods of manufacturing" and filed on March 7, 2022), which is incorporated herein by reference in its entirety. WO2022 / 187870 further discloses different release layers. In many embodiments, the release layer can serve a dual function: a removable adhesion layer and a layer comprising a modified surface configured to affect aspects of the formation of the nanostructures.

[0140] Figure 9 An example nanostructure fabrication process according to an embodiment of the present invention is described. In a first step, an exposure process 702 is performed. During the exposure process 702, a cell assembly 702a is produced, comprising a holographic mixture layer sandwiched between a bottom substrate and a top substrate. The top substrate may include a release surface that may be coated with a release layer. The release surface contacts the holographic mixture layer. The cell assembly 702a may be exposed 702b via a holographic exposure process to form a holographic grating. Following the exposure process 702, an evacuation process 704 may be performed to form an EPS. After exposure, polymer-rich regions and inert material-rich regions exist. In this process, the top substrate is peeled 704a from the holographic mixture. The release layer may facilitate removal of the top substrate from the holographic mixture. The grating may be subjected to a solvent soak 704b. The solvent soak may remove residual inert material from the inert material-rich region and the polymer-rich region. The cell assembly may be dried from the solvent. In some embodiments, a nitrogen drying process may be used to dry the cell assembly.

[0141] After the evacuation process 704, the EPS may be subjected to various EPS enhancement processes 706. An ashing process 706a may be used to clean weak polymer networks, which may enhance performance. In a further step, thermal reflow (not shown) may be used to modify the geometry and surface quality of the etched features (e.g., modifying the tilt angle). The thermal reflow process may include heating the polymer above its glass transition temperature. When heated above its glass transition temperature, the polymer transitions to a viscous state. A surface of minimum energy (e.g., a surface of minimum area) is formed under surface tension. This process typically occurs at high temperatures, but may also occur at moderate temperatures if the polymer melt is sufficiently viscous. In many embodiments, reflow may result in curvature of the surface of the polymer structure. The resulting curved diffraction element may extend the angular response of the grating structure.

[0142] Additionally, coating process 706b can be used to coat the ashed grating with a coating. Coating process 706b can be an ALD process. Coating process 706b can deposit a coating such as a SiN coating. Coating process 706b can enhance the effective refractive index and strength.

[0143] The coating process may include depositing at least one layer of a high refractive index material onto the polymer structure using a dry deposition process. Different inorganic materials may be deposited at different layer thicknesses. The coating process may include a liquid deposition process. Using a liquid deposition process, a resin-based high refractive index material may be deposited onto a structure formed by the dry deposition process. Different configurations of high refractive index materials may be formed by applying dry and liquid deposition in different sequences. The manufacture of a given waveguide design may utilize different deposition schemes based on different dry and liquid deposition schemes and different high refractive index materials to meet different grating recipe requirements for input, fold, and output gratings. In many embodiments, immersion / coating with a high refractive index material will result in at least one of reduced surface roughness, a higher effective refractive index, and planarization. Waveguides containing immersed gratings may benefit from reduced eyeglow. In many cases, the diffractive structure produced by immersion may benefit from a high contrast between the high refractive index material and the polymer stripes, which may have a lower refractive index.

[0144] Figure 10-21 A conceptual illustration of the cross-sectional configuration of an immersion grating. Coating thicknesses may be exaggerated for illustrative purposes. The roughened surface of the polymer grating structure is illustrative and may not accurately represent actual roughness, which will depend on the holographic recording material, the degree of phase separation, the efficiency of the etching process, and additional processes such as thermal reflow. As previously discussed, the high-refractive-index material layer can be deposited on the polymer grating structure using either a dry deposition process or a liquid deposition process.

[0145] Figure 10 is a cross-sectional view of a surface relief grating 1000 according to an embodiment of the present invention. Figures 3A-3E or Figure 9 The SRG 1000 is fabricated using the techniques described herein, without an end-coating process. The SRG 1000 comprises polymer stripes 1001 supported by a substrate 1002. The polymer stripes 1001 are separated from each other by air gaps 1004. The illustrated polymer structure can be fabricated by exposing a holographic material, removing inert components from inert material-rich regions, etching to remove unreacted material, and cleaning. The SRG 1000 can also be fabricated using other methods, such as nanoimprint lithography. The SRG 1000 can be a deep SRG, with a thickness in the range of 1-3 microns and a Bragg fringe spacing of 0.35 to 0.80 microns. In some embodiments, the ratio of grating depth (thickness) to Bragg fringe spacing can be 1:1 to 5:1. The polymer stripes 1001 are a well-defined alternating pattern of polymer and air regions. As illustrated, the polymer stripes 1001 can be tilted or non-tilted.

[0146] Figure 11 After applying the high refractive index coating 1011 according to an embodiment of the present invention Figure 10 In many embodiments, the high refractive index coating 1011 can be an inorganic material applied using a dry deposition process, and the coating thickness can be in the range of 1.5 nm to 100 nm.

[0147] The dry deposition process can be atomic layer deposition (ALD), chemical vapor deposition (CVD), plasma-enhanced chemical vapor deposition (PECVD), or metal-organic chemical vapor deposition (MOCVD). The coating process can produce a high-refractive-index coating 1011 that conformally coats the polymer stripes 1001. The polymer stripes 1001 form a polymer grating. The coating 1011 can be an ALD-deposited layer of Al2O3, TiO2, or HfO2. The grating grooves of the polymer stripes 1001 can be partially immersed in the coating 1011. As a result, air portions 1102 can still exist between the coatings 1011. In some examples, the high-refractive-index coating 1011 can completely fill the grating grooves of the polymer stripes 1001. This can result in a flat coating extending above the polymer stripes 1001, with the air portions 1102 completely filled with the high-refractive-index coating 1011.

[0148] Figure 12 After partially backfilling with filler 1021 Figure 11 The backfill material may be another inorganic material deposited using a dry deposition process. Alternatively, the backfill material may be a resin deposited using a liquid deposition process.

[0149] Combine Figure 11A polymer stripe 1001 is depicted coated with a high-refractive index coating 1011. Additional high-refractive index material may be placed on top of the high-refractive index coating 1011. The additional material may create a filler 1021 that fills the bottoms of the gaps in the high-refractive index coating 1011. Filler 1021 may be a high-refractive index resin. The high-refractive index resin may be applied in a solvent or without a solvent. A variety of methods may be used to produce filler 1021. For example, drop coating may be utilized, where a volume of liquid is dropped onto the surface of the high-refractive index coating 1011. Additionally, spin coating, slot coating, or spray coating processes may be employed. Following the spin coating and baking process, filler 1021 may fill the grating grooves. As illustrated, filler 1021 and coating 1011 may be used together. In some instances, filler 1021 may be applied without coating 1011, such that filler 1021 directly contacts polymer stripes 1001. Additionally, a coating 1011 may be applied over the filler 1021 such that the high refractive index coating 1011 contacts the top of the filler 1021 and the exposed surfaces of the polymer stripes 1001 .

[0150] Figure 13 After being completely immersed in the high refractive index material 1031 Figure 11 In many embodiments, the upper surface 1032 of the second high refractive index material can provide planarization of the grating structure. This planarization can occur as a separate planarization step after the deposition of the high refractive index material 1031, or it can occur naturally due to the deposition process.

[0151] The high refractive index coating 1011 and / or filler 1021 may have a refractive index and thickness to produce smooth sidewalls of the polymer stripes 1001. The high refractive index coating 1011 and / or filler 1021 may have a refractive index and thickness to reduce haze when light is diffracted by the polymer stripes 1001. The high refractive index coating 1011 and / or filler 1021 may have a refractive index and thickness to provide an effective refractive index when compared to air gaps between the polymer stripes 1001 alone.

[0152] Figure 14 yes Figure 11 Figure 1 shows a cross-sectional view of a grating in which polymer stripes 1001 are conformally coated with a first high refractive index coating 1011 and conformally coated with a second high refractive index material 1041. The resulting structure includes air gaps 1042 between adjacent polymer structures. In many embodiments, the second high refractive index material 1041 can be a resin (or a resin mixed with a solvent) deposited using a liquid deposition process. The air gaps 1042 can extend down to the grating structure base 1043.

[0153] Figure 15-17 illustrate Figure 14Another configuration of the second high refractive index material 1041. Figure 15 In the embodiment of the present invention, the second high refractive index material region 1051 may include a reduced air volume 1052. Figure 16 In , the air volume between the polymer stripes is filled with a second high refractive index material 1061, resulting in a surface modulation 1062 of only the grating structure. Figure 17 In the embodiment of the present invention, the second high refractive index material 1071 can have a planar surface 1072, which can be bonded to a substrate 1073 or can provide a surface for an optical coating (such as an AR coating).

[0154] In other embodiments, for example Figure 18-19 In the embodiment described in

[0015] , a third high refractive index material can be deposited after the first and second high refractive index materials are deposited. The refractive indices of the three materials can be selected so that the refractive indices are in any ratio. In some cases, the highest refractive index material can be located between the other two lower refractive index materials. Figure 18 It is partially backfilled with the third refractive index material 1081 Figure 14 Cross-sectional view of the grating structure. Figure 19 is to provide a planar top surface 1092 completely immersed in the third refractive index material 1091 according to an embodiment of the present invention Figure 14 Cross-sectional view of the grating structure.

[0155] The second substrate 2002 can be positioned on top of the planar top surface 1092 of the third refractive index material 1091 . Figure 20 yes Figure 19 1091 , wherein the second substrate 2002 is bonded to the planar surface 1092 of the third refractive index material 1091 .

[0156] Figure 21 yes Figure 14 FIG1 is a cross-sectional view of a grating structure, wherein the third refractive index material 2102 is conformally coated on the second high refractive index material 1041. An air gap 2104 exists between adjacent portions of the third refractive index material 2102.

[0157] Examples include one or more dry deposition processes

[0158] Combine Figure 11 The high refractive index coating 1011 may include one or more layers of a high refractive index material, each ranging from 1 nm to 100 nm. The high refractive index material may be an inorganic material, including Al2O3, TiO2, or HfO2. In some examples, the high refractive index material is HfO2. The material may be deposited in more than one deposition cycle.

[0159] High refractive index materials can be deposited using various dry deposition processes, such as atomic layer deposition (ALD), chemical vapor deposition (CVD), plasma-enhanced chemical vapor deposition (PECVD), and metal-organic chemical vapor deposition (MOCVD). In various embodiments, ALD can employ plasma-enhanced spatial ALD, which provides a faster process than conventional (pulsed / purged) ALD systems.

[0160] In various embodiments, nearly complete immersion can be achieved by thick ALD coating structures. For example, in some embodiments, layers of an inorganic high refractive index material can be deposited to form a thick ALD structure comprising a first refractive index layer positioned between two lower refractive index layers. Such a structure can be used to increase the effective refractive index of the immersion layer. Such a configuration can also be used to smooth the roughness of a polymer structure. In some embodiments, layers of different high refractive index inorganic materials can be deposited to form a thick ALD, in the form of a mixed oxide nanolaminate (comprising alternating layers of different materials).

[0161] Dry deposition can deposit multiple layers of inorganic material onto a polymer structure with a refractive index of 1.53 on a glass substrate with a refractive index of 1.5, where each layer has a thickness ranging from 1 nm to 100 nm and a refractive index between 2.0 and 2.2. The multiple layers can include alternating high and low refractive indices, which can provide refractive index optimization and / or surface roughness smoothing. Smoothing can occur on the sidewalls of the polymer structure stripes.

[0162] A liquid deposition process (discussed further below) can deposit a high index resin layer with a refractive index in the range of 1.9-2.0 to planarize the grating structure and bond it to a high index cover with a refractive index of 1.9. Either the substrate or the cover can include a release layer.

[0163] Figure 22-24 The three stages of diffractive waveguide fabrication using a dry immersion process are described. Figure 22The first stage is described. A first substrate 2222 includes a holographic mixture 2224 and a boundary region 2226. A second substrate 2228 including a release layer 2230 can be positioned above the first substrate 2222 such that the holographic mixture 2224 is positioned between the first substrate 2222 and the second substrate 2228. A holographic recording beam 2232 is passed through the first substrate to expose the holographic mixture 2224. The holographic mixture 2224 can form a grating during a phase separation process. The holographic mixture 2224 includes an inert component (e.g., a liquid crystal, an inert fluid, or nanoparticles) and a monomer component. The holographic recording beam 2232 holographically polymerizes and phase separates the mixture to form a volume grating including polymer-rich regions separated by inert component-rich regions. Different exposure techniques can be applied to each region of the holographic mixture to produce different types of gratings. For example, exposure can be performed using a holographic master having different grating regions and different patterns. The release layer 2230 allows the second substrate 2228 to be removed after the grating is recorded. The release coating can be applied to either substrate depending on the record geometry and the substrate that needs to be released. The substrates can be of any thickness depending on the design, but typically they are <1 mm.

[0164] Figure 23 The second stage is described. The second substrate 2228 is released to allow the method of converting the volume grating into an SRG as discussed above to proceed. A set of standard manufacturing steps are applied to form a well-defined surface relief grating 2302 by removing at least a portion of the inert component from the volume grating to form a surface relief grating 2302 comprising polymer-rich regions separated by air regions. Further processing may include solvent cleaning of the phase separation material and dry etching to clean the grooves of any organic residue.

[0165] Figure 24 The third stage is described, which involves conformally coating the high refractive index material onto the polymer structure. A conformal coating process 2404 can be performed, which coats the polymer structure to form a coated polymer structure 2402. The high refractive index coating of the coated polymer structure 2402 can be deposited using any of the process steps described above.

[0166] Examples include one or more liquid deposition processes

[0167] Liquid deposition processes can be performed on polymer structures. Figure 22 and 23 Described are the steps to produce polymer structures. Figure 25 The liquid deposition process performed on the grating structure according to an embodiment of the present invention is described. Figure 23 Surface relief grating 2302 or combined Figure 24 A liquid deposition process 2504 is performed on the coated polymer structure 2402 to form the grating structure 2502 .

[0168] The liquid deposition process can be drop coating (dropping a certain volume of liquid on the surface), spin coating, slit coating or spray coating. The liquid deposition process can apply the high refractive index material over the entire surface of the grating structure. The coated structure can be encapsulated by bonding to an additional substrate including a release layer. The grating structure is subjected to a curing process (e.g., UV curing). After UV curing, the additional substrate can be released. The flatness of the final structure can be improved by including spacers and / or an autoclave. In some embodiments, the resin used for deposition can have a reduced viscosity by including a solvent that can improve the uniformity of spin coating. The liquid deposition process can be performed before or after the dry deposition process. In some embodiments, the liquid deposition process can be performed without a dry deposition process.

[0169] The polymer structure can be at least partially filled with a high-refractive index resin. A dry deposition process can be used after the liquid deposition process to fill gaps in the high-refractive index resin. This can reduce dry deposition run times. The dry-deposited material can fill cracks created by using a solution-based high-refractive index resin.

[0170] In some embodiments, a layer of high refractive index resin can be applied to bond the grating structure to the high refractive index substrate. A thin layer of liquid high refractive index resin can be applied to the dry deposition coated polymer structure to planarize the grating surface and bond the grating to the high refractive index substrate. In many embodiments, thick dry deposition immersion structures can be achieved by at least partially filling the polymer structure via dry deposition and then backfilling the structure with a high refractive index resin.

[0171] In some embodiments, the substrates (the first and second substrates described above) may be glass and / or plastic substrates. Figure 24 and 25 Following the dry and / or wet deposition process described, a second (covering) substrate can be added to position the grating structure between the substrates. The second substrate can provide protection for both the grating structure and the user's eyes. The second substrate can increase the effective refractive index of the overall structure by adding a substrate with a higher refractive index than the substrate forming the grating.

[0172] Figure 26is a flow chart conceptually illustrating a method for manufacturing an immersed surface relief polymer structure according to an embodiment of the present invention. Method 2600 includes coating (2602) a holographic mixture onto a first substrate. The holographic mixture includes an inert component and a monomer. Method 2600 also includes holographically exposing (2604) the holographic mixture with a holographic recording beam. The holographic recording beam holographically polymerizes and phase separates the mixture to form a volume grating including polymer-rich regions separated by inert component-rich regions. Method 2600 also includes removing (2606) at least a portion of the inert component from the volume grating. The resulting grating is a depleted periodic structure that includes a polymer structure. The polymer structure can be a repeating structure of polymer regions separated by air regions. Method 2600 also includes depositing (2608) a first high refractive index material on the polymer structure using a dry deposition process.

[0173] The method 2600 also includes depositing (2610) a second high refractive index material over the structure resulting from the deposition of the first high refractive index material using a liquid deposition process.

[0174] The first high refractive index material may be deposited on the polymer structure using a dry deposition process.The second high refractive index material may be deposited on the structure resulting from the deposition of the first high refractive index material using a liquid deposition process.

[0175] In many embodiments, the second high refractive index material can planarize the structure resulting from depositing the first high refractive index material onto the polymer structure. In some embodiments, a release cover can be applied to the planarized second high refractive index material. Advantageously, the planarized second high refractive index material can flatten the top surface of the grating structure, which allows the release cover to sit flush on the grating structure.

[0176] In many embodiments, the second high refractive index material is an organic material comprising one or more resins. The resins may be mixed with a solvent. The second high refractive index material may be more than one layer of different organic materials of varying thickness and / or refractive index formed in a stacked or nano-laminated structure.

[0177] In some embodiments, the release cover can include a release layer. Example release layers are disclosed in detail in U.S. Patent Publication No. 2022 / 0283376, filed on March 7, 2022, and entitled “Evacuated Periodic Structures and Methods of Manufacturing,” which is incorporated herein by reference in its entirety for all purposes.

[0178] Principle of Equivalence

[0179] Although the above description contains many specific embodiments of the present invention, these should not be construed as limiting the scope of the present invention, but rather as examples of one embodiment of the present invention. It is therefore understood that the present invention may be practiced in ways other than the specific description without departing from the scope and spirit of the present invention. Therefore, the embodiments of the present invention should be considered in all respects to be illustrative and not restrictive. Therefore, the scope of the invention should not be determined by the embodiments described, but by the appended claims and their equivalents.

Claims

1. A method for recording a grating structure, the method comprising: depositing a holographic mixture onto a first substrate, the holographic mixture comprising a mixture of a monomer and an inert material; exposing the holographic mixture to a holographic recording beam to form a volume grating comprising polymer-rich regions and inert material-rich regions; removing the inert material from the inert material-rich regions to form a depleted periodic structure comprising polymer-rich regions and regions containing a residual polymer network; applying an ashing process to the region containing the residual polymer network to form an ashed grating comprising polymer-rich regions and air regions; and A coating material is deposited onto the ashed grating to form a coated grating, wherein the coating material at least partially backfills the air regions and coats the polymer-rich regions.

2. The method of claim 1, wherein the coating material has a refractive index greater than the refractive index of the polymer.

3. The method of claim 1, wherein the coating material is a composite of more than one material. The method of claim 1 , wherein depositing the coating material comprises more than one coating step. The method of claim 1 , wherein the coating material comprises nanoparticles. The method of claim 1 , wherein the coated grating is a tilted grating.

7. The method of claim 1 further comprising depositing an anti-reflective coating onto the coated grating. The method of claim 1 , wherein depositing the coating material comprises an atomic layer deposition (ALD) process.

9. The method of claim 1, wherein depositing the coating material comprises spreading a portion of the coating material into pores contained within the polymer-rich region.

10. The method of claim 1 , wherein the coated grating comprises a volume phase grating (VPG) comprising alternating polymer-rich regions and coating material-rich regions, covered by a surface relief grating (SRG) formed from the coating material, wherein the maximum values ​​of the SRG cover the polymer-rich regions of the VPG, and wherein the minimum values ​​of the SRG cover the coating material-rich regions of the VPG.

11. The method of claim 1 , wherein the surface of the first substrate contacting the holographic mixture is modified by at least one selected from the group consisting of nanostructuring, chemical functionalization, and coating.

12. The method of claim 1, wherein the coating partially backfills the air region such that a portion of the air region remains between adjacent portions of the coating covering adjacent polymer-rich regions.

13. The method of claim 12, wherein the coating contacts the first substrate in sections between adjacent polymer-rich regions.

14. The method of claim 13, further comprising depositing a backfill material onto the coating contacting the first substrate in sections between adjacent polymer-rich regions to backfill air regions between adjacent portions of the coating.

15. The method of claim 14, wherein the backfill material partially backfills the air regions between adjacent portions of the coating layer such that air regions still exist between adjacent portions of the coating layer above the backfill material. The method of claim 15 , wherein the backfill material comprises a high refractive index resin. The method of claim 16 , wherein depositing the backfill material comprises drop coating, spin coating, slot coating, or spray coating.

18. The method of claim 17, further comprising curing the deposited backfill material.

19. The method of claim 12, wherein the coating comprises an inorganic material.

20. The method of claim 19, wherein the coating comprises Al2O3, TiO2 and / or HfO2.

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