Vacuum periodic structures and methods of manufacture

Abstract

Described herein are improvements to gratings for use in waveguides and methods of fabricating those gratings. Deep surface relief gratings (SRGs) can offer many advantages over conventional SRGs, a key advantage being higher S-diffraction efficiency. In one embodiment, deep SRGs can be implemented as polymer surface relief gratings or vacuum periodic structures (EPS). EPSs can be formed by first recording a holographic polymer dispersed liquid crystal (HPDLC) periodic structure. The liquid crystal is removed from the hardened periodic structure to provide a polymer surface relief grating. Polymer surface relief gratings have many applications, including use in waveguide-based displays.

Description

[Technical field]

[0001] Cross-Referenced Applications This application claims priority to U.S. Provisional Patent Application No. 63 / 157467, filed March 5, 2021, U.S. Provisional Patent Application No. 63 / 174401, filed April 13, 2021, and U.S. Provisional Patent Application No. 63 / 223311, filed July 19, 2021, the disclosures of which are incorporated by reference in their entireties.

[0002] The present invention relates generally to waveguides and methods for making waveguides, and more particularly to a waveguide display including a grating formed in a multi-component mixture from which one material component is removed, and a method for making said grating. [Background technology]

[0003] A waveguide can be referred to as a structure with the ability to confine and guide waves (i.e., regulate the spatial region through which waves can propagate). One subclass includes optical waveguides, which are structures that can guide electromagnetic waves, typically in the visible spectrum. Waveguide structures can be designed to control the wave propagation path using several different mechanisms. For example, planar waveguides can be designed to utilize diffraction gratings to diffract and couple light incident on the waveguide structure so that the light can proceed to propagate within the planar structure via Total Internal Reflection (TIR).

[0004] Fabrication of a waveguide may involve 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 that include a photopolymerizable monomer and a liquid crystal. A further 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 illuminating the material with two mutually coherent laser beams. During the recording process, the monomer polymerizes and the mixture undergoes photopolymerization-induced phase separation, creating regions that are packed with liquid crystal (LC) microdroplets and interspersed with regions of transparent polymer. The alternating liquid crystal-rich and liquid crystal-depleted regions form a plane of grating stripes.

[0005] Waveguide optics such as those described above may be considered for a range of display and sensor applications. In many applications, waveguides containing one or more grating layers encoding multiple optical functions can be realized using a variety of waveguide architectures and material systems, 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. Many of these applications are directed to consumer products, and there is a growing demand for efficient, low-cost means of manufacturing holographic waveguides in large quantities. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] International Publication No. 2022 / 015878 [Patent Document 2] International Publication No. 2021 / 242898 [Patent Document 3] U.S. Patent No. 9,632,226 [Patent Document 4] U.S. Pat. No. 4,133,152 [Non-patent literature]

[0007] [Non-Patent Document 1] Pekka Ayras, Pasi Saarikko, Tapani Levola, “Exit pupil expander with a large field of view based on diffractive optics”, Journal of the SID 17 / 8, (2009), pp 659-664 [Non-Patent Document 2] Kiyoshi Yokomori, “Dielectric surface-relief gratings with high diffraction efficiency”, Applied Optics; Vol. 23; Issue 14; (1984); pp. 2303-2310 [Non-Patent Document 3] MA Golub, AA Friesem, L. Eisen, “Bragg properties of efficient surface relief gratings in the resonance domain”, Optics Communications; 235; (2004); pp261-267 [Non-Patent Document 4] Gerritsen HJ, Thornton DK, Bolton SR; “Application of Kogelnik's two-wave theory to deep, slanted, highly efficient, relief transmission gratings”, Applied Optics; Vol. 30; Issue 7; (1991); pp 807-814 [Non-Patent Document 5] O. Sakhno, LM Goldenberg, M. Wegener, J. Stumpe, “Deep surface relief grating in azobenzene-containing materials using a low intensity 532 nm laser”, Optical Materials: X, 1, (2019), 100006, pp 3-7 [Non-Patent Document 6] Moharam MG et al., “Diffraction characteristics of photoresist surface -relief gratings”, Applied Optics, Vol. 23, page 3214, Sep 15, 1984 [Non-Patent Document 7] Fries F. et al, “Real-time beam shaping without additional optical elements”, Light Science & Applications, 7(1), 18, (2018) Summary of the Invention [Means for solving the problem]

[0008] Many embodiments are directed to polymer lattice structures, their designs, methods of manufacture, and materials.

[0009] Various embodiments are directed to a method for making a periodic structure comprising the steps of providing a holographic mixture to a base substrate; sandwiching the holographic mixture between the base substrate and a cover substrate, where the holographic mixture forms a holographic mixture layer on the base substrate; applying a holographic recording beam to the holographic mixture layer to form a holographic polymer dispersed liquid crystal periodic structure comprising alternating polymer rich and liquid crystal rich regions; and removing the cover substrate from the holographic polymer dispersed liquid crystal periodic structure, the cover substrate having different properties than the base substrate such that it can be removed from the formed holographic polymer dispersed liquid crystal periodic structure after exposure while still adhering to the unexposed holographic mixture layer.

[0010] Various embodiments further include a method for fabricating a periodic structure, comprising the steps of providing a first holographic mixture on a first base substrate; sandwiching the first holographic mixture between the first base substrate and a cover substrate, the first holographic mixture forming a first holographic mixture layer on the first base substrate; applying a holographic recording beam to the first holographic mixture layer to form a first holographic polymer dispersed liquid crystal periodic structure comprising alternating polymer rich and liquid crystal rich regions; and insulating the cover substrate from the first holographic mixture. the second holographic mixture being sandwiched between the second base substrate and a cover substrate, the second holographic mixture forming a second holographic mixture layer on the second base substrate; and applying a holographic recording beam to the second holographic mixture layer to form a second holographic polymer dispersed liquid crystal periodic structure comprising alternating polymer rich and liquid crystal rich regions.

[0011] Additionally, various embodiments are directed to a device for making deep surface relief gratings (SRGs), comprising a holographic mixture sandwiched between a base substrate and a cover substrate, the holographic mixture configured to form a holographic polymer dispersed liquid crystal grating comprising alternating polymer rich and liquid crystal rich regions when exposed to a holographic recording beam, the base substrate and the cover substrate having different properties such that the cover substrate can be removed from the formed holographic polymer dispersed liquid crystal grating after exposure, while adhering to the unexposed holographic mixture layer.

[0012] Additionally, various embodiments are directed to a waveguide device comprising a waveguide supporting a polymer grating structure for diffracting light propagating therethrough by total internal reflection, the polymer grating structure comprising a polymer region, an air gap between adjacent portions of the polymer region, and a coating disposed on top of the polymer region and on top of the waveguide.

[0013] Additionally, various embodiments are directed to a waveguide device comprising a waveguide supporting a polymer grating structure for diffracting light propagating therethrough by total internal reflection, the polymer grating structure comprising a polymer region, an air gap between adjacent portions of the polymer region, an optical layer disposed between the polymer region and the waveguide, and a coating disposed on top of the polymer region and on top of the optical layer.

[0014] Additionally, various embodiments are directed to a waveguide device comprising a waveguide supporting a polymer grating structure for diffracting light propagating therethrough by total internal reflection, the polymer grating structure comprising a polymer region, an air gap between adjacent portions of the polymer region, and an optical layer disposed between the polymer region and the waveguide.

[0015] Additionally, various embodiments are directed to a waveguide device comprising a waveguide supporting a polymer grating structure for diffracting light propagating therethrough by total internal reflection, the polymer grating structure comprising a polymer region and an air gap between adjacent portions of the polymer region, the polymer region and the air gap being in direct contact with the waveguide.

[0016] Additionally, various embodiments are directed to a method for making a grating comprising providing a mixture of a monomer and a non-reactive material, coating a layer of the mixture on a surface of a substrate, applying a holographic recording beam to the layer to form a holographic polymer dispersion grating comprising alternating polymer-rich regions and non-reactive material-rich regions, removing at least a portion of the non-reactive material in the non-reactive material-rich regions to form a polymer surface relief grating comprising alternating polymer regions and air regions, and applying a coating on top of the polymer regions and on top of the substrate in the air regions.

[0017] Further, various embodiments are directed to a method for making a grating comprising providing a mixture of a monomer and a non-reactive material; coating a layer of the mixture on a surface of a substrate; applying a holographic recording beam to the layer to form a holographic polymer dispersion grating comprising alternating polymer-rich regions and non-reactive material-rich regions; removing at least a portion of the non-reactive material in the non-reactive material-rich regions to form a polymer surface relief grating comprising alternating polymer regions and air regions, wherein the optical layer is disposed between the polymer regions and the substrate; and applying a coating to a top surface of the polymer regions and to a top surface of the optical layer in the air regions.

[0018] Additionally, various embodiments are directed to a method for making a grating comprising providing a mixture of a monomer and a non-reactive material; coating a layer of the mixture on a surface of a substrate; applying a holographic recording beam to the layer to form a holographic polymer dispersion grating comprising alternating polymer-rich and non-reactive material-rich regions; removing at least a portion of the non-reactive material in the non-reactive material-rich regions to form a polymer surface relief grating comprising alternating polymer and air regions; and performing a plasma ashing process to remove at least a portion of the polymer from the polymer regions.

[0019] This description will be more fully understood with reference to the following figures and data graphs, which are presented as illustrative embodiments of the invention and should not be construed as a complete description of the scope of the invention. [Brief description of the drawings]

[0020] [Figure 1] Figure 1A conceptually illustrates method steps for making a surface relief grating in which a mixture of monomer and liquid crystal deposited on a transparent substrate is exposed to a holographic exposure beam according to an embodiment of the invention. Figure 1B conceptually illustrates method steps for making a surface relief grating from an HPDLC grating formed on a transparent substrate according to an embodiment of the invention. Figure 1C conceptually illustrates method steps for making a surface relief grating in which liquid crystal is removed from an HPDLC grating to form a polymer surface relief grating according to an embodiment of the invention. Figure 1D conceptually illustrates method steps for covering a surface relief grating with a protective layer according to an embodiment of the invention. [Diagram 2] 1 is a flow diagram conceptually illustrating a method for fabricating a polymer surface relief grating from an HPDLC grating formed on a transparent substrate, in accordance with an embodiment of the present invention. [Figure 3A] 1A-1C are diagrams of example implementations of polymer surface relief gratings or vacuum periodic structures. [Figure 3B] FIG. 3 is a cross-sectional schematic diagram of a polymer air periodic structure 3000a according to an embodiment of the present invention. [Figure 3C] 1 is a graph showing the effect of optical layer thickness on diffraction efficiency versus incidence angle. [Figure 4] FIG. 4A conceptually illustrates method steps for making a surface relief grating in which a mixture of monomer and liquid crystal deposited on a transparent substrate is exposed to a holographic exposure beam according to an embodiment of the present invention. FIG. 4B conceptually illustrates method steps for making a surface relief grating from an HPDLC periodic structure formed on a transparent substrate according to an embodiment of the present invention. FIG. 4C conceptually illustrates method steps for making a surface relief grating in which liquid crystal is removed from an HPDLC periodic structure to form a polymer surface relief grating according to an embodiment of the present invention. FIG. 4D conceptually illustrates method steps for making a surface relief grating in which the surface relief grating is partially refilled with liquid crystal to form a hybrid surface relief periodic structure according to an embodiment of the present invention. FIG. 4E conceptually illustrates method steps for making a surface relief grating in which a hybrid surface relief periodic structure is covered with a protective layer according to an embodiment of the present invention. [Diagram 5] 1 is a flow diagram conceptually illustrating a method for fabricating hybrid surface relief periodic structures in accordance with an embodiment of the present invention. [Figure 6] 1 is a graph showing calculated P-polarized and S-polarized diffraction efficiency versus incidence angle for a 1 micrometer thick depth surface relief grating in accordance with an embodiment of the present invention. [Figure 7] 1 is a graph showing calculated P-polarized and S-polarized diffraction efficiency versus incidence angle for a 2 micrometer thick depth surface relief grating in accordance with an embodiment of the present invention. [Figure 8] 1 is a graph showing calculated P-polarized and S-polarized diffraction efficiency versus incidence angle for a 3 micrometer thick depth surface relief grating in accordance with an embodiment of the present invention. [Figure 9]9A and 9B are scanning electron microscope images of several embodiments containing different thiol concentrations. [Figure 10] 10A and 10B are images comparing HPDLC periodic structures with polymer surface relief gratings or vacuum periodic structures. [Figure 11] 11A and 11B are plots comparing HPDLC periodic structures with polymer surface relief gratings or vacuum periodic structures. [Figure 12] 12A and 12B are two plots of the S and P diffraction efficiencies of two example polymer surface relief gratings with different depths. [Figure 13] 13A and 13B are two different plots of the S and P diffraction efficiencies of various example polymer surface relief gratings fabricated with different initial liquid crystal concentrations. [Figure 14] 14A and 14B are two different plots of the S and P diffraction efficiencies of various example polymer surface relief gratings fabricated with different initial liquid crystal concentrations. [Figure 15] 1 is a graph of diffraction efficiency versus grating layer thickness showing the dependence of evanescent coupling on grating layer thickness. [Figure 16] FIG. 16A is a diagram of various stages of manufacture of a surface relief grating mounting a cover substrate according to an embodiment of the present invention. FIG. 16B is a diagram of various stages of manufacture of a surface relief grating mounting a cover substrate according to an embodiment of the present invention. FIG. 16C is a diagram of various stages of manufacture of a surface relief grating mounting a cover substrate according to an embodiment of the present invention. FIG. 16D is a diagram of various stages of manufacture of a surface relief grating mounting a cover substrate according to an embodiment of the present invention. FIG. 16E is a diagram of various stages of manufacture of a surface relief grating mounting a cover substrate according to an embodiment of the present invention. FIG. 16F is a diagram of various stages of manufacture of a surface relief grating mounting a cover substrate according to an embodiment of the present invention. FIG. 16G is a diagram of various stages of manufacture of a surface relief grating mounting a cover substrate according to an embodiment of the present invention. [Figure 17]FIG. 1 shows example reactions for forming a holographic mixture layer, according to an embodiment of the present invention. [Figure 18] FIG. 2 illustrates a reaction between a reagent and a base substrate according to an embodiment of the present invention. [Figure 19] 1 illustrates a reaction between a release material and a cover substrate according to an embodiment of the present invention. [Figure 20A] 1A-1D are diagrams of various gratings according to embodiments of the present invention. [Figure 20B] 1A-1D are diagrams of various gratings according to embodiments of the present invention. [Figure 20C] FIG. 2 is a diagram of a grating according to an embodiment of the present invention. [Figure 21A] FIG. 1 conceptually illustrates an embodiment of a waveguide in which evanescent coupling to a grating can occur. [Figure 21B] FIG. 1 conceptually illustrates an embodiment of a waveguide in which evanescent coupling to a grating can occur. [Figure 21C] FIG. 1 conceptually illustrates an embodiment of a waveguide in which evanescent coupling to a grating can occur. [Figure 22A] 1A-1D are diagrams of various stages in fabricating a reciprocal lattice, according to an embodiment of the present invention. [Figure 22B] 1A-1D are diagrams of various stages in fabricating a reciprocal lattice, according to an embodiment of the present invention. [Figure 22C] 1A-1D are diagrams of various stages in fabricating a reciprocal lattice, according to an embodiment of the present invention. [Figure 22D] 1A-1D are diagrams of various stages in fabricating a reciprocal lattice, according to an embodiment of the present invention. [Figure 23A] FIG. 2 is a schematic diagram of a grating according to an embodiment of the present invention. [Figure 23B] FIG. 2 is a schematic diagram of a grating according to an embodiment of the present invention. [Figure 23C] FIG. 2 is a schematic diagram of a grating according to an embodiment of the present invention. [Figure 24] FIG. 2 illustrates an example process flow for making an SRG, in accordance with an embodiment of the present invention. [Figure 25A] FIG. 1 illustrates the principle of a dual interaction grating for implementation in a waveguide. [Figure 25B] FIG. 1 illustrates the principle of a dual interaction grating for implementation in a waveguide. [Figure 26] FIG. 2 conceptually illustrates a cross section of a grating according to an embodiment of the present invention. [Figure 27] FIG. 27 is a conceptual diagram of beam propagation in the grating of FIG. 26. [Figure 28] FIG. 1 is a diagram of an example of a partially backfilled grid, according to an embodiment of the present invention. [Figure 29] FIG. 13 shows a schematic of the beam-grating interaction geometry of a TIR surface grating. [Diagram 30] FIG. 1 conceptually illustrates a waveguide display according to an embodiment of the present invention. [Diagram 31] FIG. 2 conceptually illustrates a waveguide display having two air-spaced waveguide layers in accordance with an embodiment of the present invention. [Diagram 32] FIG. 2 conceptually illustrates typical light ray paths for a waveguide display according to an embodiment of the present invention. [Diagram 33] FIG. 1 conceptually illustrates a waveguide display in which a waveguide supports a curved optical surface, according to an embodiment of the present invention. [Diagram 34] FIG. 2 conceptually illustrates a waveguide display in which a waveguide supports upper and lower curved optical surfaces, according to an embodiment of the present invention. [Diagram 35] FIG. 1 conceptually illustrates a waveguide display in accordance with an embodiment of the present invention, in which a waveguide supports a curved optical surface and an input image is provided using a pixel array that is pre-distorted to compensate for aberrations induced by the curved optical surface. [Diagram 36] FIG. 1 conceptually illustrates a waveguide display in accordance with an embodiment of the present invention, in which a waveguide supports a curved optical surface and an input image is provided using a pixel array supported by a curved substrate and pre-distorted to compensate for aberrations induced by the curved optical surface. [Figure 37]4 is a flow diagram conceptually illustrating a method for projecting image light for viewing using a waveguide including an S grating and a P grating, in accordance with an embodiment of the present invention. [Figure 38] 1 is a flow diagram conceptually illustrating a method for projecting image light for viewing using a waveguide that supports an optically prescribed surface and includes an S grating and a P grating, in accordance with an embodiment of the present invention. [Figure 39A] 1A-1D conceptually illustrate portions of pixel patterns having rectangular elements of different sizes and aspect ratios for use in an emissive display panel, according to an embodiment of the present invention. [Figure 39B] FIG. 2 conceptually illustrates a portion of a pixel pattern having Penrose tiles for use in an emissive display panel according to an embodiment of the present invention. [Figure 39C] FIG. 2 conceptually illustrates a portion of a pixel pattern having hexagonal elements for use in an emissive display panel, according to an embodiment of the present invention. [Figure 39D] FIG. 2 conceptually illustrates a portion of a pixel pattern having square elements for use in an emissive display panel, according to an embodiment of the present invention. [Figure 39E] FIG. 2 conceptually illustrates a portion of a pixel pattern having diamond-shaped elements for use in an emissive display panel, according to an embodiment of the present invention. [Figure 39F] FIG. 2 conceptually illustrates a portion of a pixel pattern having isosceles triangular elements for use in an emissive display panel, according to an embodiment of the present invention. [Figure 39G] FIG. 2 conceptually illustrates a portion of a pixel pattern having hexagonal elements with a horizontally offset aspect ratio for use in an emissive display panel, according to an embodiment of the invention. [Fig. 39H] FIG. 2 conceptually illustrates a portion of a pixel pattern having rectangular elements with a horizontally offset aspect ratio for use in an emissive display panel, according to an embodiment of the invention. [Figure 39I]FIG. 2 conceptually illustrates a portion of a pixel pattern having diamond-shaped elements with a horizontally offset aspect ratio for use in an emissive display panel, according to an embodiment of the invention. [Figure 39J] FIG. 2 conceptually illustrates a portion of a pixel pattern having triangles with a horizontally offset aspect ratio for use in an emissive display panel, according to an embodiment of the present invention. [Diagram 40] FIG. 1 conceptually illustrates a portion of a pixel pattern having diamond-shaped elements where different pixels may have different emissive characteristics, in accordance with an embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0021] There is growing interest in the use of various periodic structures (e.g., gratings) in waveguides to provide various functions. These periodic structures can include angle-multiplexed gratings, color-multiplexed gratings, folded gratings, double-interaction gratings, rolled K-vector gratings, cross-folded gratings, mosaic gratings, chirped gratings, gratings with spatially varying refractive index modulation, gratings with spatially varying grating thickness, gratings with spatially varying average refractive index, gratings with spatially varying refractive index modulation tensor, and gratings with spatially varying average refractive index tensor. In certain instances, gratings for diffraction of various polarizations of light (e.g., S-polarized and P-polarized) can be beneficial. It is particularly advantageous to have a grating that diffracts either S-polarized or P-polarized light. Particular applications for this technology include waveguide-based displays, such as augmented and virtual reality displays. One example is an input grating that can be used to input either S-polarized or P-polarized light or both into a waveguide. However, in many cases, it is advantageous to have a grating that diffracts either S-polarized or P-polarized light. For example, a waveguide display that uses an unpolarized light source, such as an OLED light source, produces both S and P polarized light, and therefore it is advantageous to have a grating that can diffract both S and P polarized light.

[0022] One particular class of gratings includes surface relief gratings (SRGs) that can be used to diffract either P-polarized or S-polarized light. Another class of gratings is surface relief gratings (SRGs) that are typically selective for P-polarized light, resulting in a 50% efficiency loss with unpolarized light sources such as organic light-emitting diodes (OLEDs) and light-emitting diodes (LEDs). Combining a mixture of S-polarized and P-polarized gratings can theoretically provide a factor of two improvement over a waveguide that uses only P-polarized gratings. It is therefore advantageous to have a highly efficient S-polarized grating. In many embodiments, the S-polarized grating can be provided by a periodic structure formed in a holographic photopolymer. One periodic structure includes a grating such as a Bragg grating. In one embodiment, the S-polarized grating can be provided by a periodic structure formed in a holographic polymer dispersed liquid crystal (HPDLC) with the birefringence altered using an alignment layer or other process to reorient the liquid crystal (LC) director. In some embodiments, S-polarized diffractive periodic structures can be formed using liquid crystals, monomers, and other additives that spontaneously organize into S-diffractive periodic structures under phase separation. In certain embodiments, these HPDLC periodic structures can form deep SRGs with excellent S-polarized diffraction efficiency.

[0023] One class of deep SRGs is the polymer air SRG or evacuated periodic structure (EPS) that can exhibit high S diffraction efficiency (up to 99%) and low P diffraction efficiency and can be implemented as an input grating for a waveguide. The EPS can be a vacuum Bragg grating (EBG). Such periodic structures can be formed by removing liquid crystal from a HPDLC periodic structure formed from holographic phase separation of a mixture of liquid crystal and monomer. Deep SRGs formed by such a process typically have thicknesses in the range of 1-3 micrometers with a fringe spacing of 0.35-0.80 micrometers. In certain embodiments, the ratio of grating depth to fringe spacing can be from 1:1 to 5:1. As can be readily appreciated, such gratings can be formed with different dimensions depending on the specific requirements of a given application. Examples of how the thickness of an SRG can produce different resulting diffraction efficiencies are described in conjunction with FIGS. 6-8.

[0024] In many embodiments, the condition for deep SRG is characterized by a high ratio of grating depth to fringe spacing. In some embodiments, the condition for the formation of deep SRG is that the grating depth is roughly twice the grating period. Modeling such deep SRG using Kogelnik theory can give a reasonably accurate estimate of the diffraction efficiency and avoid the need for more advanced modeling that typically requires numerical solution of Maxwell's equations. The grating depth that can be achieved using removal of liquid crystal from HPDLC periodic structures significantly exceeds the grating depth possible using conventional nanoimprint lithography methods that cannot achieve the condition for deep SRG (typically providing only 250-300 nm depth for a grating period of 350-460 nm). (Non-Patent Document 1). Here, while S-polarized diffraction deep SRG is emphasized in this application, it should be emphasized that deep SRG can provide a range of polarization response characteristics depending on the thickness of the grating formulation, specifically, depending on the grating depth, as discussed later. Thereby, deep SRG can be implemented in a variety of different applications.

[0025] The literature supports the equivalence of deep SRGs with periodic structures. One reference (Non-Patent Document 2) discloses a study of the diffractive properties of dielectric surface relief gratings by numerically solving Maxwell's equations. The diffraction efficiency of gratings with grooves about twice the depth of the grating period is found to be comparable to that of volume phase gratings. Modeling by Yokomori predicts that dielectric surface relief gratings recorded interferometrically in photoresist can have high diffraction efficiencies up to 94% (throughput efficiency 85%). The equivalence of deep SRGs with periodic structures is also discussed in another article by Golub (Non-Patent Document 3). A further article by Gerritsen considers the formation of Bragg-like SRGs in photoresist (Non-Patent Document 4).

[0026] Many embodiments of the present disclosure provide methods for making SRGs, including deep SRGs, that can provide significant advantages over nanoimprint lithography processes, especially for tilted gratings. Periodic structures of arbitrary complexity can be made using interference or master and contact print replicas. In an embodiment, after removing the LC, the SRG can be backfilled with a material with different properties than the LC. This allows for periodic structures with modulated properties that are not limited by the grating chemistry required for grating formation.

[0027] In an embodiment, the backfilling material may not be an LC material. In an embodiment, the backfilling material may have a refractive index greater than air, which may increase the angular bandwidth of the waveguide. In some embodiments, the deep SRG may be partially backfilled with LC to provide a hybrid SRG / periodic structure. Alternatively, in an embodiment, the refilling step may be avoided by removing only a portion of the LC from the LC-rich regions of the HPDLC to provide a hybrid SRG / periodic structure. The refilling approach has the advantage that a different LC can be used to form the hybrid periodic structure. The material may be deposited using an inkjet deposition process.

[0028] In an embodiment, the methods described herein may be used to create photonic crystals. Photonic crystals may be implemented to create a wide variety of diffractive structures, including periodic structures such as Bragg gratings. Periodic structures may be used as diffractive gratings to provide functionality, including but not limited to input gratings, output gratings, beam expansion gratings, and diffraction of two or more primary colors. Photonic crystals may be three-dimensional lattice structures that may have diffractive capabilities not achievable with basic periodic structures. Photonic crystals may include many structures, including two- and three-dimensional Bravais lattices. Recording of such structures may benefit from three or more recording beams.

[0029] In some embodiments, waveguides incorporating photonic crystals can be arranged in a stack of waveguides, each with a grating recipe for diffracting a unique spectral bandwidth. In many embodiments, photonic crystals formed by liquid crystal extraction provide deep SRGs. In many embodiments, deep SRGs formed using liquid crystal extraction processes can typically have thicknesses in the range of 1 to 3 micrometers with a fringe spacing of 0.35 micrometers to 0.80 micrometers. The fringe spacing can be the Bragg fringe spacing. In many embodiments, the condition for deep SRGs is characterized by a high ratio of grating depth to fringe spacing. In some embodiments, the condition for the formation of deep SRGs is that the grating depth can be approximately twice the grating period. It should be emphasized that while S-polarized diffracting deep SRGs are described herein, deep SRGs can provide a range of polarization response characteristics depending on the thickness of the grating recipe, specifically the grating depth, as discussed later. Deep SRGs can also be used in conjunction with conventional Bragg gratings to enhance the color, uniformity, and other properties of waveguide displays.

[0030] Deep SRGs have been fabricated in glassy monomeric azobenzene materials using laser holographic exposure (Non-Patent Document 5), which also discloses how SRGs can be recorded in holographic photopolymers using two linearly orthogonally polarized laser beams.

[0031] The present disclosure provides a method for making surface relief gratings that can provide significant advantages over nanoimprint lithography processes, especially for tilted gratings. Periodic structures of arbitrary complexity can be made using interference or master and contact print replicas. In an embodiment, after removing the LC, the SRG can be backfilled with a material with different properties than the LC. This allows for periodic structures with modulated properties that are not limited by the grating chemistry required for grating formation. In an embodiment, the SRG can be partially backfilled with LC to provide a hybrid SRG / periodic structure. Alternatively, in an embodiment, the refilling step can be avoided by removing only a portion of the LC from the LC-rich regions of the HPDLC to provide a hybrid SRG / periodic structure. The refilling approach has the advantage that a different LC can be used to form the hybrid grating. The material can be deposited using an inkjet process. In an embodiment, the refilling material can have a refractive index greater than air, which can increase the diffraction efficiency of the periodic structure.

[0032] Although this disclosure is made in the context of fabricating deep SRGs, it will be understood that many other grating structures can be fabricated using the techniques described herein, for example, any type of SRG (e.g., Raman-Nath grating) can also be fabricated, including SRGs where the grating depth is less than the grating frequency.

[0033] 1A-1D show processing equipment that can be used in a method for making deep SRG or EPS according to an embodiment. FIG. 1A conceptually shows an apparatus 190A that can be used in a step of a method for making a surface relief grating according to an embodiment of the present invention, in which a mixture 191 of monomers and liquid crystals deposited on a transparent substrate 192 is exposed to a holographic exposure beam 193, 194. The holographic exposure beam 193, 194 can be an ultraviolet light beam. In an example, the mixture 191 can also include at least one of a photoinitiator, a co-initiator, a multifunctional thiol, an adhesion promoter, a surfactant, and / or additional additives.

[0034] The mixture 191 may include nanoparticles. The mixture 191 may include photoacid. The mixture 191 may be a monomer diluted with a non-reactive polymer. The mixture 191 may include two or more monomers. In an embodiment, the monomer may be isocyanacrylate-based or thiolene-based. In an embodiment, the liquid crystal may be a complete liquid crystal mixture or a liquid crystal single. The liquid crystal single may include only a portion of the complete liquid crystal mixture. Various example liquid crystal singles may include one or all of cyanobiphenyl, alkyl, alkoxy, cyanobiphenyl, and / or terphenyl derivatives. The liquid crystal mixture may be a cholesteric liquid crystal. The liquid crystal mixture may include a chiral dopant that can control the lattice period. The liquid crystal mixture may include photoresponsive and / or halogen-bonded liquid crystals. In an embodiment, the liquid crystal may be replaced with other materials that phase separate from the monomer during exposure to create polymer-rich and material-rich regions. Advantageously, the material and liquid crystal single can be a cost-effective substitute for the complete liquid crystal mixture that is removed in a later step, as described below.

[0035] In some embodiments, the liquid crystal in mixture 191 has a difference between the extraordinary refractive index and the ordinary refractive index of less than 0.01. In some embodiments, the liquid crystal in mixture 191 has a difference between the extraordinary refractive index and the ordinary refractive index of less than 0.025. In some embodiments, the liquid crystal in mixture 191 has a difference between the extraordinary refractive index and the ordinary refractive index of less than 0.05.

[0036] FIG. 1B conceptually illustrates an apparatus 190B that may be used in a method step for fabricating a surface relief grating from an HPDLC Bragg grating 195 formed in a transparent substrate using a holographic exposure beam according to an embodiment of the present invention. The holographic exposure beam may convert monomers to polymer in the same regions. The holographic exposure beam may include crossed recording beams and may include alternating light and dark illuminated regions. A polymerization-driven diffusion process may cause the monomer and LC to diffuse in opposite directions, with the monomer gelling to form polymer-rich regions (in the light regions) and the liquid crystal becoming trapped in the polymer matrix to form liquid crystal-rich regions (in the dark regions).

[0037] FIG. 1C conceptually illustrates an apparatus 190C that may be used in a step of a method for making a deep polymer surface relief grating 196 or EPS, in which liquid crystal is removed from the HPDLC periodic structure of FIG. 1B to form a polymer surface relief grating, according to an embodiment of the present invention. Advantageously, the polymer surface relief grating 196 may include a large depth with a relatively small grating period to form a deep SRG. The liquid crystal may be removed by washing with a solvent such as isopropyl alcohol (IPA). The solvent may be strong enough to wash off the liquid crystal, but weak enough to preserve the polymer. In an embodiment, the solvent may be cooled below room temperature before washing the grating. FIG. 1D conceptually illustrates an apparatus 190D that may be used in a step of a method for making a polymer surface relief grating, in which the polymer surface relief grating is covered with a protective layer 197, according to an embodiment of the present invention.

[0038] FIG. 2 conceptually illustrates a method for forming deep SRGs from HPDLC periodic structures formed on a transparent substrate, according to an embodiment of the present invention. As shown, a method 200 for forming deep SRGs or EPSs is provided. Referring to the flow diagram, the method 200 includes providing a mixture of at least one monomer and at least one liquid crystal (201). The at least one monomer may include an isocyanacrylate monomer or a thiolene. For example, the mixture may include a liquid crystal and a thiolene-based photosensitive resin. In an embodiment, the mixture may include a liquid crystal and an acrylate-based photosensitive resin. In an embodiment, the at least one liquid crystal may be a complete liquid crystal mixture or a liquid crystal single that may include only a portion of the liquid crystal mixture, such as a single component of the liquid crystal mixture. In an embodiment, the at least one liquid crystal may be substituted for a solution that phase separates from the monomer during exposure. Criteria for such a solution may include the ability to phase separate from the monomer during exposure, ease of removal after exposure and during cleaning, and ease of handling. Example surrogate solutions include solvents, non-reactive monomers, inorganics, and nanoparticles.

[0039] Providing a mixture of monomers and liquid crystals may also include mixing one or more of the following with at least one monomer and liquid crystal: an initiator such as a photoinitiator or co-initiator, a multifunctional thiol, a dye, an adhesion promoter, a surfactant, and / or additional additives such as other crosslinkers. The mixture may be allowed to rest to allow the co-initiator to catalyze the reaction between the monomer and the thiol. The resting period may be performed for a period of approximately 8 hours at low temperature (e.g., 20° C.) in a dark space or a space with red light (e.g., infrared light). After resting, additional monomer may be mixed with the monomer. The mixture may then be strained or filtered through a filter with a small pore size (e.g., 0.45 μm pore size). After straining, the mixture may be stored at room temperature in a dark space or a space with red light before coating.

[0040] A transparent substrate can then be provided (202). In certain embodiments, the transparent substrate can be a glass substrate or a plastic substrate. In some embodiments, the transparent substrate can be a flexible substrate to facilitate roll-to-roll processing. In some embodiments, the EPS can be manufactured on a flexible substrate through a roll-to-roll process and then peeled off and attached to a rigid substrate. In some embodiments, the EPS can be manufactured on a flexible substrate and a second flexible release layer can be peeled off and discarded, leaving the EPS on the flexible layer. The flexible layer can then be bonded to another rigid substrate.

[0041] A layer of the mixture can be deposited or coated on the surface of the substrate (203). The layer of the mixture can be deposited using inkjet printing. In an embodiment, the mixture is sandwiched between a transparent substrate and another substrate using glass spacers to maintain the internal dimensions. An anti-adhesion coating can be applied to the other substrate before the mixture is sandwiched. The anti-adhesion coating can include fluoropolymers such as OPTOOL UD509 (manufactured by Daikin Chemicals), Dow Corning 2634, Fluoropel (manufactured by Cytonix), and EC200 (manufactured by PPG Industries, Inc). A holographic recording beam can be applied to the mixture layer (204), the holographic recording beam can be an interference pattern of two beams that can cause phase separation of the LC and the polymer. In response to the holographic recording beam, the liquid monomer changes to a solid polymer, and the neutral non-reactive material (e.g., LC) diffuses during the holographic exposure in response to the change in chemical potential driven by the polymerization. LC can be one implementation of the neutral non-reactive material, but other materials can be used. The material and monomer may form a miscible mixture prior to holographic exposure and may become immiscible upon holographic exposure.

[0042] After applying the holographic recording beam, the mixture may be cured. The curing process may include leaving the mixture under low intensity white light for a period of time until the mixture is fully cured. The low intensity white light may cause a photobleaching dye process to occur. Thus, HPDLC periodic structures having alternating polymer-rich and liquid crystal-rich regions may be formed (205). In an embodiment, the curing process may take 2 hours or less. After curing, one of the substrates may be removed to expose the HPDLC periodic structures. Advantageously, the anti-adhesion coating allows the other substrate to be removed while the HPDLC periodic structures remain.

[0043] The HPDLC periodic structure may include alternating areas of liquid crystal rich regions and areas of polymer regions. The liquid crystal in the liquid crystal rich regions may be removed (206) to form a polymer surface relief grating or EPS that can be used as a deep SRG. The liquid crystal may be removed by gently immersing the grating into a solvent such as IPA. The IPA may be cooled and maintained at a temperature below room temperature while the grating is immersed in IPA. The periodic structure may then be removed from the solvent and dried. In an embodiment, the periodic structure is dried using a high flow air source such as compressed air. After the LC is removed from the periodic structure, a polymer air surface relief grating is formed.

[0044] As shown in Figures 1A-1D, the formed surface relief grating may be further covered with a protective layer. In one example, the protective layer may be a barrier to moisture and oxygen with anti-scratch capabilities. In one example, the protective layer may be a coating that does not fill the void areas where the removed LC once was. The coating may be deposited using a low-temperature process. In one implementation, the protective layer may have anti-reflective (AR) properties. The coating may be a silicate or silicon nitride. The coating process may be performed by a plasma-assisted chemical vapor deposition (CVD) process, such as a nanocoating process. The coating may be a parylene coating. The protective layer may be a glass layer. A vacuum or an inert gas may fill the gaps where the removed LC once was before the protective layer is applied. In one embodiment, the coating process may be integrated with the LC removal process (206). For example, the coating material may be mixed with a solvent used to wash the LC from the periodic structure.

[0045] FIG. 3A shows a cross-sectional schematic diagram of an exemplary embodiment of a polymer-air periodic structure 3000 implemented in a waveguide 3002. The polymer-air surface relief grating 3000 includes periodic polymer sections 3004a. Adjacent polymer sections 3004a sandwich air sections 3004b. The air sections 3004b are sandwiched by polymer sections 3004a. The air sections 3004b have different refractive indices than the polymer sections 3004a. Advantageously, the polymer-air surface relief Bragg grating 3000 can be formed with a high ratio of grating depth 3006a to Bragg fringe spacing 3006b that can create deep SRG. As shown, the polymer sections 3004a and air sections 3004b extend all the way into the waveguide 3002 to directly contact the waveguide 3002. As shown, there may be no bias layers between the polymer sections 3004a and air sections 3004b and the waveguide 3002. As discussed above, deep SRGs can exhibit many beneficial qualities, such as high S diffraction efficiency, that may not be present in typical SRGs.

[0046] In one example, the polymer air surface relief Bragg grating 3000 can have a Bragg fringe spacing 3006b of 0.35 μm to 0.8 μm and a grating depth of 1 μm to 3 μm. In an embodiment, a grating depth of 1 μm to 3 μm may be too thick for most EPS (with ashing and ALD) for folded and output gratings for waveguide applications where leaky structures are required. Values ​​in the range of 0.1 μm to 0.5 μm may be more suitable for leaky structures, especially when modulation is increased with ashing and ALD. For example, input structures may include depths in the range of 0.4 μm up to 1 μm. Structures with depths of 1 μm to 3 μm may be advantageous for displays, and even higher structures may be advantageous for non-display applications. Structures with semiperiod (e.g., critical dimension) to height ratios of 7:1 or even 8:1 have been demonstrated with advantageous effects.

[0047] In some embodiments, the polymer regions 3004a may contain at least some residual liquid crystal when the liquid crystal is not completely removed during step 206 described in connection with FIG. 2. In some embodiments, the presence of residual LC in the polymer rich regions may increase the refractive index modulation of the final polymer SRG. In some embodiments, the air regions 3004b may contain some residual liquid crystal when the liquid crystal is not completely removed from these air regions 3004b during step 206. In some embodiments, by leaving some residual liquid crystal in the air regions 3004b, a hybrid grating as described in connection with FIG. 4-5 may be created.

[0048] In an embodiment, an optical layer 3008 may be present between the polymeric and air regions 3004a and the waveguide 3002. The optical layer 3008 may be a bias layer between the polymeric and air regions 3004a and the waveguide 3002. FIG. 3B shows a cross-sectional schematic diagram of a polymeric air periodic structure 3000a according to an embodiment of the present invention. The polymeric air periodic structure 3000a includes many identically numbered components as the polymeric air periodic structure 3000 of FIG. 3A. The description of these components is applicable to the polymeric air periodic structure 3000a described in connection with FIG. 3B, and this description will not be repeated in detail. As shown, the optical layer 3008 is positioned between the polymeric and air regions 3004a and the waveguide 3002. The waveguide can include a substrate 3002 and an optical layer 3008 (e.g., a bias layer) sandwiched between the substrate 3002 and a polymer grating structure, with the polymer periodic structure extending all the way to the optical layer for direct contact with the optical layer. The polymer periodic structure includes polymer regions 3004a and air regions 3004b.

[0049] In one example, the optical layer 3008 may be formed when the grating is formed using nanoimprint lithography (NIL). The grating pattern may be imprinted into a resin leaving a thin layer under the periodic structure that is a few micrometers thick. This optical layer 3008, which may be a few micrometers thick, may be between the waveguide (e.g., glass) substrate and the periodic grating layer and may not be removable without damaging the NIL grating structure. When the bias index is smaller than the bias index of the waveguide substrate, the bias layer may restrict the light for some angle of view (furthest from the TIR in the waveguide) to the high index substrate, which may be similar to the cladding in an optical fiber core. This may cause the supported area in the waveguide to be clipped and thereby not supported by the waveguide. Elimination of the bias layer may provide grating coupling from the high index substrate to the grating structure with a smaller index than the substrate, which may not be possible if the bias layer is present.

[0050] In the formation of EPS, the phase separation process leading to grating formation can occur throughout the entire holographic recording material layer, so that the grating can form throughout the volume of the cell gap, resulting in the elimination of the optical layer 3008. The elimination of the optical layer 3008 can achieve a wider field of view when using a high refractive index waveguide substrate. The wide viewing angle content can be propagated with a lower refractive index grating structure. EPS can deliver similar optical performance characteristics to nanoimprinted SRG, albeit with a smaller peak refractive index. This can open up the possibility of low-cost fabrication of diffractive structures for efficient waveguides.

[0051] While elimination of the optical layer 3008 from a waveguide grating device can provide viewing benefits as discussed above, in some embodiments the optical layer 3008 may be present in the EPS. The present disclosure allows for waveguide grating devices with or without the optical layer 3008.

[0052] In an embodiment, having an optical layer 3008 can be advantageous because the evanescent coupling between the waveguide and the grating is a function of the refractive index of the grating structure (e.g., grating depth, the angle of the faces that make up the structure, and grating depth), the waveguide core, and the optical layer 3008 (if present). In an embodiment, the optical layer 3008 can be used as a tuning parameter to optimize the overall waveguide design for better efficiency and bandwidth. Unlike nano-grating SRGs, the bias layer used with EPS may not be of the same refractive index as the grating structure.

[0053] FIG. 3C is a graph showing the effect of the thickness of the optical layer 3008 on the diffraction efficiency versus the angle of incidence. The dotted line 3052 represents an angle of incidence of +6 degrees. Evanescent coupling may begin at an angle of approximately +6 degrees (towards negative angles). The various plots represent different thicknesses of the optical layer 3008. The plots show that the thickness of the optical layer 3008 can be used to increase the diffractive coupling (for example, for an optical layer thickness of 300 nm) over an approximate angular range of +6 degrees to +16 degrees. Over an approximate angular range of 0 degrees to +6 degrees, there may be less coupling. The S-shaped characteristics may be altered by replacing the 300 nm optical layer with a thicker or thinner bias layer, as shown in FIG. 3C. In an embodiment, the thickness of the optical layer may be from 2 μm to 3 μm, from 1 μm to 2 μm, or from 0.5 μm to 1 μm.

[0054] In some embodiments, the EPS can be fabricated as part of a stacked grating structure. Examples of stacked grating structures are discussed in U.S. Patent Application Publication No. 2020 / 0133999, entitled "Nanoparticle-based holographic photopolymer materials and related applications," filed July 14, 2021, which is hereby incorporated by reference in its entirety for all purposes. In some embodiments, the EPS can include a multi-layer structure including a release layer. The release layer can be used in the grating stacking process, which can reduce the number of glass layers. The release layer can be applied at each exposure step to allow the deposition of a new layer of recording material. A similar process can also be used to stack multiple gratings at different tilt angles to increase the angular bandwidth.

[0055] As discussed above, in many embodiments, the present invention also provides methods for making hybrid surface relief / periodic structures. Figure 4A conceptually illustrates an apparatus 210A that can be used in a method step for making a hybrid surface relief grating (hybrid SRG) in which a mixture of monomer and liquid crystal 211 deposited on a transparent substrate 212 is exposed to a holographic exposure beam 213, 214, according to an embodiment of the present invention. Figure 4B conceptually illustrates an apparatus 210B that can be used in a method step for making a hybrid SRG from an HPDLC periodic structure 215 formed on a transparent substrate using a holographic exposure beam, according to an embodiment of the present invention. Figure 4C conceptually illustrates an apparatus 210C that can be used in a method step for making a surface relief grating in which liquid crystal is removed from the HPDLC periodic structure 215 to form a polymer air SRG 216, according to an embodiment of the present invention. These polymer air SRGs 216 or EPS can be deep SRGs. The steps shown and described in connection with Figures 4A-4C broadly correspond to the steps shown and described in connection with Figures 2A-2C in the process for creating a polymer air SRG, and therefore the foregoing description is applicable to Figures 4A-4C.

[0056] FIG. 4D also conceptually illustrates additional steps that may be performed to create a hybrid grating. The apparatus 210D may be used in a step of a method for making a surface relief grating in which the surface relief grating is at least partially refilled with liquid crystal to form a hybrid SRG 217 according to an embodiment of the present invention. The refilled liquid crystal may be of a different consistency than the previously removed liquid crystal previously removed in FIG. 4C. It is further understood that the liquid crystal removed in FIG. 3C may only be partially removed in an alternative method to forming a hybrid SRG 217. FIG. 4E also conceptually illustrates an apparatus 210E that may be used in a step of a method for making a surface relief grating in which the hybrid SRG 217 formed in the step shown in FIG. 4D is covered with a protective layer 218 according to an embodiment of the present invention. In a hybrid EPS, the air area 3004b of FIG. 3A and FIG. 3B may be replaced with a backfill material as discussed above.

[0057] FIG. 5 is a flow diagram illustrating an exemplary method for forming a hybrid surface relief periodic structure from an HPDLC periodic structure formed on a transparent substrate according to an embodiment of the present invention. As shown, a method 220 for forming a hybrid surface relief periodic structure is provided. Referring to the flow diagram, the method 220 includes providing a mixture of at least one monomer and at least one liquid crystal (221). The at least one monomer may include an isocyanacrylate monomer. Providing the mixture of monomer and liquid crystal may also include mixing one or more of the following with the at least one monomer and liquid crystal: a photoinitiator, a co-initiator, a multifunctional thiol, and / or additional additives. The mixture may be allowed to rest to allow the co-initiator to catalyze the reaction between the monomer and the thiol. The rest period may be performed for a period of approximately 8 hours at a low temperature (e.g., 20° C.) in a dark space or a space with red light (e.g., infrared light). After resting, additional monomer may be mixed with the monomer. The mixture may then be strained or filtered through a filter with a small pore size (e.g., 0.45 μm pore size). After straining, the mixture may be stored at room temperature in a dark space or with red light before coating.

[0058] Next, a transparent substrate may be provided (222). In certain embodiments, the transparent substrate may be a glass substrate or a plastic substrate. An anti-adhesion coating may be applied to the transparent substrate before the mixture is coated on the substrate. The anti-adhesion coating may be a release layer that allows the transparent substrate to be easily released from the exposed periodic structure. Various examples of release layers are discussed below. A layer of the mixture may be deposited on the surface of the substrate (223). In some embodiments, the mixture is sandwiched between the transparent substrate and another substrate using glass spacers to maintain the internal dimensions. A holographic recording beam may be applied to the mixture layer (224). The holographic recording beam may be an interference pattern of two beams that may cause phase separation of the LC and the polymer. After applying the holographic recording beam, the mixture may be cured. The curing process may include keeping the mixture under low intensity white light for a period of time until the mixture is fully cured. The low intensity white light may cause a photobleaching dye process to take place. Thus, a HPDLC periodic structure having alternating polymer-rich and liquid crystal-rich regions may be formed (225). In some embodiments, the curing process can take place in 2 hours or less. After curing, one of the substrates can be removed to expose the HPDLC periodic structure. The release layer can help keep one of the substrates from adhering to the exposed periodic structure.

[0059] The HPDLC grating may include alternating sections of liquid crystal rich regions and sections of polymer regions. The liquid crystal in the liquid crystal rich regions may be removed (226) to form a polymer surface relief grating or EPS, which is a form of deep SRG. The liquid crystal may be removed by gently immersing the exposed periodic structure into a solvent such as isopropyl alcohol (IPA). The IPA may be maintained at a lower temperature while the periodic structure is immersed in IPA. The periodic structure is then removed from the solvent and dried. In an embodiment, the periodic structure is dried using a high flow air source such as compressed air. After the LC is removed from the grating, a polymer air surface relief periodic structure is formed. The resulting periodic structure may be the periodic structure described in connection with FIG. 3A and FIG. 3B. A bias layer as shown in FIG. 3A or FIG. 3B may or may not be present. Steps 221-226 of FIG. 5 roughly correspond to the steps described in connection with FIG. 2 when creating a polymer air SRG, and therefore these descriptions are applicable to FIG. 5.

[0060] Additionally, method 220 includes at least partially refilling the deflated liquid crystal rich region with liquid crystal (227) to form a hybrid SRG. The refilled liquid crystal may be of a different consistency than the previously removed liquid crystal previously removed in step 226. Additionally, it is understood that the liquid crystal removed in step 226 may only be partially removed in an alternative approach to forming a hybrid SRG. Advantageously, a hybrid SRG may provide the ability to tailor certain beneficial properties of the SRG. One specific property that may be improved by including at least some liquid crystal within the SRG is a reduction in haze. In an embodiment, the deflated liquid crystal rich region may be backfilled with a refractive material different from the liquid crystal. The backfill material may have a different refractive index than the remaining polymer rich region.

[0061] As shown in FIG. 4E, the formed surface relief grating may be further covered with a protective layer. In one example, the protective layer may be a barrier to moisture and oxygen with anti-scratch capabilities. In one example, the protective layer may be a coating that does not fill the void areas where the removed LC once was. The coating may be deposited using a low-temperature process. In one implementation, the protective layer may have anti-reflective (AR) properties. The coating may be a silicate or silicon nitride. The coating process may be performed by a plasma-assisted chemical vapor deposition (CVD) process, such as a plasma-treated nanocoating process. The coating may be a parylene coating. The protective layer may be a glass layer. A vacuum or an inert gas may fill the gaps where the removed LC once was before the protective layer is implemented. In one embodiment, the coating process may be integrated with the LC removal process (226). For example, the coating material may be mixed with a solvent used to wash the LC from the grating. In one implementation, the coating material may be a material with a refractive index smaller or larger than the polymer and may fill the spaces between adjacent polymer portions. The difference in refractive index between the polymer and the coating material can cause the polymer SRG to continue to diffract.

[0062] While Figures 1-5 show particular methods and apparatus for forming deep SRG and hybrid surface relief / Bragg gratings, a variety of fabrication methods implementing different steps or variations of such steps may be utilized. As can be readily appreciated, the particular process utilized may depend on the particular requirements of a given application. For example, many embodiments utilize other periodic structures as protective layers.

[0063] A hybrid SRG / periodic structure with a shallow SRG structure may result in low SRG diffraction efficiency. The methods disclosed in this disclosure can form a more effective SRG structure by optimizing the liquid crystal depth in the liquid crystal rich regions such that the SRG has a high ratio of depth to grating pitch while making the periodic structure thick enough for efficient diffraction. In many embodiments, the periodic structure components of the hybrid grating can have a thickness in the range of 1 to 3 micrometers. In some embodiments, the SRG components of the hybrid grating can have a thickness in the range of 0.25 to 3 micrometers. The initial HPDLC periodic structure has a thickness equal to the sum of the final SRG and periodic structure components. As can be easily understood, the thickness ratio of the two periodic structure components can depend on the application of the waveguide. In some embodiments, the combination of SRG with the periodic structure can be used to fine-tune the angular bandwidth of the periodic structure. In some cases, the SRG can increase the angular bandwidth of the periodic structure.

[0064] In many embodiments, in the hybrid SRGs shown in Figures 4A-4E, the refill depth of the liquid crystal regions of the periodic structure may be varied across the periodic structure to provide spatially varying relative SRG / periodic structure strength. In some embodiments, during liquid crystal removal and refilling as defined in steps 206, 226, and 227, the liquid crystal in the liquid crystal-rich grating regions may be fully or partially removed. In some embodiments, the liquid crystal used to refill or partially refill the regions where liquid crystal has disappeared may have a different chemical composition than the liquid crystal used to form the initial HPDLC periodic structure. In various embodiments, a first liquid crystal with phase separation properties compatible with the monomer may be specified to provide optimal modulation and grating definition for the HPDLC grating, while a second refill liquid crystal may be specified to provide desired refractive index modulation properties for the final hybrid grating. In some embodiments, the polymer portion of the hybrid grating may be switchable with electrodes applied to the surface of the substrate and the cover layer. In many embodiments, the refill liquid crystal may include additives, which may include, but are not limited to, features that enhance switching voltage, switching time, polarization, transparency, and other parameters. Hybrid gratings formed using the refilling process have the added advantage that the LC forms a continuum (rather than a collection of LC droplets), thereby reducing haze. In some embodiments, the backfilling material can be a material with a different refractive index than the polymer region. The backfilling material does not have to be a liquid crystal material.

[0065] Although deep SRGs, EPSs, and / or hybrid SRGs may be described in the context of S and P gratings, these periodic structures have applicability in many other periodic structure types. These periodic structures may include, but are not limited to, angle multiplexed gratings, color multiplexed gratings, folded gratings, dual interaction gratings, rolled K-vector gratings, cross folded gratings, mosaic gratings, chirped gratings, gratings with spatially varying refractive index modulation, gratings with spatially varying grating thickness, gratings with spatially varying average refractive index, gratings with spatially varying refractive index modulation tensor, and gratings with spatially varying average refractive index tensor. Furthermore, deep SRGs, EPSs, and / or hybrid SRGs may be switchable or non-switchable periodic structures depending on their particular implementation. Deep SRGs, EPSs, and / or hybrid SRGs may be fabricated in plastic or glass substrates. These periodic structures may be fabricated in one substrate and transferred to another substrate.

[0066] In some embodiments, the EPS can be either ungraded or graded, or it can be a spatially varying graded structure (e.g., a rolled K-vector formula with a very large aspect ratio of height to period, typically ranging from 2 to 12). Graded EPS is shown below in various examples. The EPS can include a height of 2.0 μm with a period of 0.400 μm (e.g., aspect ratio=5). The combination of a controlled and repeatable tilt angle and a high aspect ratio can provide the EPS structure Bragg properties that enable high efficiency waveguide design. Furthermore, the EPS can be fabricated with or without bias layers. The EPS can be made using a phase separation process that can be implemented using an inkjet printing process, which offers a significant economic advantage in mass production over the complex wafer etching and nanoimprint lithography used to produce some SRG display waveguides.

[0067] In an embodiment, the EPS may be configured as at least one of a multiplexed grating, a tilted grating, a photonic crystal, a mixed modulated grating, a hybrid polymer grating structure, a sinusoidal grating (e.g., formed by plasma ashing of an isotropic photopolymer grating), a metasurface, or a grating structure combining a tilted volume grating overlaid by a surface relief grating. A tilted volume grating overlaid by a surface relief grating may include a grating structure that is essentially a volume grating with a grating thickness in the region of low refractive index having a grating thickness slightly smaller than the high refractive index region. The variation in grating thickness is tens of nanometers, while the average volume grating thickness may be 1-10 micrometers, depending on the application. The configuration is equivalent to an SRG layer located on top of the volume grating layer. In an embodiment, the SRG and volume grating may combine the benefits of the wider angular bandwidth of the SRG with the higher efficiency of the volume grating. This is more likely when the volume grating is thinner. The surface relief structure may arise naturally as a result of nonlinearities in the diffusion process at the tips of the grating. The effect can be controlled using plasma ashing or some other type of etching applied to the grating and processed. A combined SRG and volumetric grating may be formed by fabricating an EPS and then partially backfilling the EPS with another material. Such configurations are discussed throughout this disclosure as hybrid gratings.

[0068] In an embodiment, the EPS is formed using different diffusion regimes with different diffusion constants in at least two different directions. In complex lattice structures such as photonic crystals, the spacing of the diffraction nodes can result in non-uniformity in the modulation of the completed lattice. Material components with different diffusion time constants can allow for more efficient lattice formation along different directions. In an embodiment, the EPS is formed to provide a photonic structure incorporating tilted lattice structures and tilted lattice structures and photonic crystal structures with diffraction nodes. The lattice configurations include regions where the lattice includes planar stripes that are tilted (or not tilted) and photonic crystal regions where the diffractive structures with diffraction nodes can include elongated elements such as cylinders that can be tilted. The photonic crystal regions can include three-dimensional diffraction node structures. In an embodiment, the EPS is formed to provide a photonic crystal that includes tilted diffraction features where the principle nodes of the photonic crystal are formed by multiplexed lattices where plasma ashing is applied along a path parallel to the main crystal direction. Photonic crystals can be formed by multiplexing two or more lattices such that the intersecting regions of the bright fringes form modulation peaks. The regions around these peaks may be marred using plasma ashing applied along low modulation paths that are parallel to the principle crystal direction. The cross-sectional shape of the node may depend on the number of lattices and their relative orientation. For example, intersecting two lattices at 90 degrees can result in a square cross-sectional node. Tilted photonic crystal nodes can be formed using tilted lattices. This principle can be extended to three-dimensional photonic crystals.

[0069] In an embodiment, the polymer grating structure can be formed to provide photonic crystals formed by Bravais lattices and other structures recorded with three beams, the process including plasma ashing. All five two-dimensional Bravais lattices (e.g., squares, triangles, diamonds) can be recorded using a three-beam exposure system. The techniques for making two-dimensional photonic crystals may be applied to more complex three-dimensional structures, including three-dimensional Bravais lattices and other structures. All fourteen Bravais lattices can be recorded using three beams, or even two beams using more multiplexed exposure techniques. The two-beam multiplexed exposure scheme can be used with recording media that undergo a single axis rotation between each exposure.

[0070] Consideration of various implementations of deep SRG or EPS In many embodiments, deep SRGs can provide a means to control the polarization in the waveguide. SBGs are typically P-polarization selective, resulting in a 50% efficiency loss with unpolarized light sources such as OLEDs and LEDs. Thus, combining S-polarized and P-polarized diffractive periodic structures can theoretically provide a 2x improvement over a waveguide using only P-polarized diffractive periodic structures. In some embodiments, S-polarized diffractive periodic structures can be provided by periodic structures formed in conventional holographic photopolymers. In some embodiments, S-polarized diffractive periodic structures can be provided by periodic structures formed in HPDLC with birefringence altered using alignment layers or other processes to reorient the liquid crystal directors. In some embodiments, S-polarized diffractive periodic structures can be formed using liquid crystals, monomers, and other additives that naturally organize into S-diffractive periodic structures under phase separation. In many embodiments, S-polarized diffractive periodic structures can be provided by SRGs. Using the process described previously, deep SRGs exhibiting high S diffraction efficiency (up to 99%) and low P diffraction efficiency can be formed by removing liquid crystal from an SBG formed from holographic phase separation of a mixture of liquid crystal and monomer.

[0071] Deep SRGs can also provide other polarization response characteristics. Some prior art theoretical studies, such as "Deep SRGs with both S and P sensitivity with S dominating," have presented deep surface relief gratings with both S and P sensitivity with S dominating. In some embodiments, deep SRGs have demonstrated the ability to provide S polarization response. However, deep SRGs may provide other polarization response characteristics. In many embodiments, deep surface relief gratings with both S and P sensitivity with S dominating are implemented. In some embodiments, the thickness of the SRG can be adjusted to provide various S and P diffraction characteristics. In some embodiments, the diffraction efficiency can be high for P over a spectral and angular bandwidth and low for S over the same spectral and angular bandwidth. In some embodiments, the diffraction efficiency can be high for S over a spectral and angular bandwidth and low for P over the same spectral and angular bandwidth. In some embodiments, high efficiency can be provided for both S and P polarization. A theoretical analysis of a 1.6 index SRG immersed in air with a period of 0.48 micrometers (thus providing an average grating index of 1.3) at 0 degree incidence and 45 degree diffraction angles for a wavelength of 0.532 micrometers is shown in Figures 6-8. Figure 6 is a graph showing the calculated P and S polarization diffraction efficiency versus incidence angle for a 1 micrometer thick deep surface relief grating, demonstrating that in this case high S and P responses can be achieved. Figure 7 is a graph showing the calculated P and S polarization diffraction efficiency versus incidence angle for a 2 micrometer thick deep surface relief grating, demonstrating that in this case the S polarization response dominates over most of the grating's angular range. Figure 8 is a graph showing the calculated P and S polarization diffraction efficiency versus incidence angle for a 3 micrometer thick deep surface relief grating, demonstrating that in this case the P polarization response dominates over a substantial portion of the grating's angular range.

[0072] In many embodiments, the photonic crystal can be a reflective periodic structure or a deep SRG formed by the LC extraction process. A reflective deep SRG made using phase separation followed by LC stripping can enable wide angular and spatial bandwidth. In many embodiments, replacing the current input SBG with a reflective photonic crystal can be used to reduce the optical path from the Picture Generation Unit (PGU) to the waveguide. In some embodiments, the pupil of the PGU and the waveguide can be in contact. In many embodiments, the reflective deep SRG can be approximately 3 micrometers thick. The diffractive nature of the LC extracted periodic structure arises primarily from the refractive index gap between the polymer and air (and not from the depth of the periodic structure as in the case of a typical SRG).

[0073] Consideration of thiol additives in the initial mixture 9A and 9B show comparative scattering electron microscopy (SEM) images of example mixtures used to make polymer air SRGs. As discussed above, the monomers in the initial mixture are acrylate or thiolene based. It was discovered that for some monomers, such as acrylate based monomers, during washing after holographic exposure, the solvent not only removes the liquid crystal material but also washes the polymer away, which is not ideal. It was discovered that a multifunctional thiol additive can solve this problem by strengthening the polymer, making it strong enough to withstand solvent washing. Without being limited to any particular theory, the thiol additive can improve the mechanical strength of formulations consisting of low functionality acrylate monomers that would otherwise form mechanically weak polymers due to reduced cross-linking. Acrylate monomer formulations can be advantageous because they can exhibit high diffraction efficiency with less haze. Thus, adding thiols can make the formation of acrylate monomers a visible option in the creation of polymer SRGs.

[0074] There may be a trade-off between phase separation, periodic structure formation, and mechanical strength between different formulations. Periodic structure formation may benefit from mixtures containing low functionality monomers that react slower during holographic exposure, form less crosslinks, and allow greater diffusion of non-reactive components (e.g., LC). Conversely, mixtures consisting of high functionality monomers may exhibit better phase separation and polymer mechanical strength due to greater crosslinks, but may not have enough time for non-reactive components to diffuse, resulting in lower diffraction efficiency.

[0075] Without being limited to any particular theory, thiol additives can circumvent these limitations by reacting with acrylates or isocyanacrylates to form a non-rigid scaffold prior to holographic exposure. This scaffold can improve the mechanical strength and uniformity of the cured polymer. Thus, mechanical strength can be tuned through slight adjustments in thiol functionality and concentration without appreciably increasing the average functionality of the monomer mixture and without interfering with lattice formation.

[0076] FIG. 9A shows the initial mixture and FIG. 9B shows a comparative mixture containing 1.5 wt% thiol. However, other weight percentages of thiol additive are contemplated. For example, the weight percentage of thiol additive can be 1% to 4%, or 1.5% to 3%. In an embodiment, the multifunctional thiol can be trimethylolpropane tris(3-mercaptopropionate). Both FIG. 9A and FIG. 9B include polymer dense regions 902a / 902b and air regions 904a / 904b. As shown, the added thiol can create a higher density polymer in the polymer dense region 902b of FIG. 9B than in the polymer dense region 902a of FIG. 9A, which can enhance the performance of the grating. It has been found that the weight percentage of thiol additive should be balanced to provide stability in the polymer structure to withstand solvent washout but to ensure that the liquid crystal is not released during solvent washout.

[0077] Comparison between the performance of HPDLC periodic structures and polymer air SRGs 10A and 10B show comparative images of HPDLC gratings and polymer SRG or EPS. FIG. 10A shows the performance for an example HPDLC periodic structure where the liquid crystal has not been removed. The periodic structure of FIG. 10A exhibits nominal or nearly 0% S diffraction efficiency while including a P diffraction efficiency of 20-30%. FIG. 10B shows the performance of an example polymer air SRG where the LC has been removed. The periodic structure of FIG. 10B exhibits an S diffraction efficiency of 51-77% while including a P diffraction efficiency of 18-28%. Thus, the polymer air SRG where the LC has been removed demonstrates a relatively high S diffraction efficiency while maintaining a comparable P diffraction efficiency. Additionally, the grating of FIG. 10B includes a P diffraction haze of 0.11-0.15% and an S diffraction haze of 0.12-0.16%.

[0078] 11A and 11B show plots of a comparison between HPDLC periodic structures with the liquid crystal removed and polymer SRG or EPS with the liquid crystal removed. FIG. 11A shows the P and S diffraction efficiencies for the HPDLC periodic structures with the liquid crystal remaining. The first line 1102a corresponds to the P diffraction efficiency and the second line 1104a corresponds to the S diffraction efficiency. FIG. 11B shows the P and S diffraction efficiencies for polymer SRG or EPS with the liquid crystal removed. The first line 1102b corresponds to the P diffraction efficiency and the second line 1104b corresponds to the S diffraction efficiency. As shown, the S diffraction efficiency increases dramatically after the liquid crystal is removed, while the P diffraction efficiency remains relatively similar. In an embodiment, the ratio of the S diffraction efficiency to the P diffraction efficiency can be adjusted by using different grating periods, grating tilt angles, and grating thicknesses.

[0079] Various examples of deep SRG depth 12A and 12B show various comparative examples of P and S diffraction efficiency with deep SRGs of various depths. Each of these plots shows the diffraction efficiency versus angle. In FIG. 12A, the deep SRG has a depth of approximately 1.1 μm. The first line 1102a represents the S diffraction efficiency and the second line 1104a represents the P diffraction efficiency. As shown, the S diffraction efficiency at the peak is approximately 58% and the P diffraction efficiency at the peak is 23%. It is noted that for this example, the haze for S diffraction is 0.12% and the haze for P diffraction is 0.11%. Such high diffraction efficiency with low haze can make the deep SRG with a depth of approximately 1.1 μm particularly suitable for multiplexed gratings.

[0080] In FIG. 12B, the deep SRG has a depth of approximately 1.8 μm. The first line 1102b represents the S diffraction efficiency and the second line 1104b represents the P diffraction efficiency. As shown, the S diffraction efficiency at the peak is approximately 92% and the P diffraction efficiency at the peak is 63%. It is noted that for this example, the haze for S diffraction is 0.34% and the haze for P diffraction is 0.40%. Thus, both the S diffraction efficiency and the P diffraction efficiency increase dramatically with increasing grating depth. It is noted that the haze appears to increase with increasing grating depth.

[0081] In some embodiments, the EPS can be spatially variable depth for a single EPS grating. In some embodiments, different EPS on the same substrate can have different depths from each other, and do not perform the above-mentioned modulation change in one or more of the various EPS gratings on a single substrate. In some embodiments, one or more EPS can be positioned on each side of the same substrate. In some embodiments, a mixture of planar multiplexed EPS can be positioned on the same waveguide.

[0082] In some embodiments, multiple EPSs can be positioned on a substrate with spatially varying duty cycles, grating shapes, tilts, and / or ALD coating properties. Different ALD coating properties can spatially affect modulation.

[0083] Initial LC concentrations of various examples in the mixture 13A and 13B show the results of a comparative study of different EPS with different initial LC concentrations in the initial mixture. FIG. 13A shows the S diffraction efficiency versus angle. FIG. 13B shows the P diffraction efficiency versus angle. In FIG. 13A, the first line 1202a corresponds to an initial LC content of 20%, the second line 1204a corresponds to an initial LC content of 30%, and the third line 1206a corresponds to an initial LC content of 40%. In FIG. 13B, the first line 1202b corresponds to an initial LC content of 20%, the second line 1204b corresponds to an initial LC content of 30%, and the third line 1206b corresponds to an initial LC content of 40%. Table 1 shows a summary of the different results of the comparative study.

[0084] [Table 1]

[0085] As shown in Figures 13A and 13B and reported in Table 1, both maximum S diffraction and maximum P diffraction increase with increasing initial LC content, while S diffraction haze and P diffraction haze remain roughly constant.

[0086] 14A and 14B show additional example S and P diffraction for various initial LC concentrations. FIG. 14A shows the S diffraction efficiency for various example EPS with various initial LC contents. FIG. 14B shows the P diffraction efficiency for various example EPS with various LC contents. For both FIG. 14A and FIG. 14B, successively from top to bottom, the lines represent 32% LC content, 30% LC content, 28% LC content, 26% LC content, 24% LC content, 22% LC content, and 20% LC content. As shown, the S and P diffraction efficiencies are directly related to the magnitude of the LC content (e.g., higher LC content produces higher S and P diffraction efficiencies).

[0087] Without being limited to any particular theory, the initial LC content is related to the amount of phase separation between LC and monomer that occurs during the holographic exposure and polymerization processes. Thus, a higher LC content will increase the size of the LC-rich regions that are removed to create more air regions after washing. The increased air regions increase the refractive index difference (Δn) between the air regions (previously liquid crystal rich regions) and the polymer rich regions increasing both S and P diffraction efficiencies. In certain embodiments, the average refractive index of the polymer SRG can be adjusted by adjusting the initial neutral (e.g., LC) content, thereby either increasing or decreasing the volume of the polymer after neutral removal. Additionally, increasing the initial neutral content can affect the mechanical strength. Thus, an increase or decrease in mechanical strengthening agents such as thiol additives may be used to offset the increase or decrease in mechanical strength.

[0088] Various example grating thicknesses Figure 15 is a graph of diffraction efficiency versus grating layer thickness showing the dependence of evanescent coupling on grating layer thickness. Duty cycle refers to the ratio of the width of the polymer stripes to the width of the air gap between adjacent polymer stripes. In other words, a 90% duty cycle means that 90% of the grating is polymer and 10% is air.

[0089] It should be noted that increased grating thickness can result in increased coupling when the index of refraction of the stripes and the index of refraction of the substrate are matched. For poor index matching to the substrate (e.g., 1.6 index stripes into a 1.8 index substrate), there may be only one evanescent coupling, so increased stripe depth may not significantly affect coupling. The plot in FIG. 15 shows that a grating structure with index 1.6 with a 90% duty cycle provides an average index of 1.54. Increasing the index of refraction of the grating to 1.65 at the same duty cycle results in an average index of 1.59. There is no diffraction efficiency in either case. Increasing the index of refraction of the grating can result in diffraction efficiency. For example, for grating structures with indexes of 1.7 and 1.8 at a 90% duty cycle resulting in average indexes of 1.63 and 1.72, respectively, both provide diffraction efficiency. In one embodiment, there may be a grating structure into a substrate with index of refraction of 1.8, with the input light incident at 0 degrees to the grating normal.

[0090] Embodiments manufactured using various substrate configurations In various embodiments, a pair of substrates can sandwich the unexposed holographic mixture. The pair of substrates can include a base substrate and a cover substrate. Advantageously, the cover substrate can have different properties than the base substrate to allow it to adhere to the unexposed holographic mixture layer while allowing the cover substrate to be removed from the formed holographic polymer dispersed liquid crystal periodic structure after exposure. The formed holographic polymer dispersed liquid crystal grating can remain on the base substrate after the cover substrate is removed.

[0091] Figures 16A-16G show an example process flow for making a deep SRG, according to an embodiment of the invention. This process flow is similar to the process flow described in connection with Figures 1A-1D and 4A-4E, and includes many of the same reference numbers whose descriptions are applicable to the description of Figures 16A-16G. Additionally, Figures 16A-16G also include a cover substrate 1502, the function of which will be described in more detail below.

[0092] 16A, 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 than the base substrate 212 to allow it to adhere to the unexposed holographic mixture layer 211 while allowing the cover substrate to be removed from the formed holographic polymer dispersed liquid crystal grating after exposure.

[0093] In Fig. 16B, the holographic mixture layer 211 is exposed by a pair of holographic recording beams 213, 214. As shown in Fig. 16C, the holographic recording beams 213, 214 expose the holographic mixture layer 211 to form a holographic polymer dispersed liquid crystal grating 215. The holographic polymer dispersed liquid crystal grating 215 may include alternating polymer-rich and liquid crystal-rich regions. In Fig. 16D, the cover substrate 1502 may be removed to expose the holographic polymer dispersed liquid crystal grating 215.

[0094] Advantageously, the cover substrate 1502 may have different properties than the base substrate 212, such as a different material or different surface properties. For example, the base substrate 212 may be made of plastic and the cover substrate 1502 may be made of glass. The cover substrate 1502 may be removed, leaving the holographic polymer dispersed liquid crystal grating 215 on the base substrate without damaging the holographic polymer dispersed liquid crystal grating 215 during removal.

[0095] In some embodiments, the base substrate 212 may be treated at its surface to contact the holographic mixture layer 211 with an adhesion promoting layer, such as a reagent.

[0096] As shown in FIG. 16E, liquid crystal may be removed or evacuated from the liquid crystal rich regions between the polymer rich regions, leaving air regions. The polymer rich regions and air regions form a polymer-air SRG 216. In FIG. 16F, a material of a different refractive index than the polymer rich regions may be refilled into the air regions to form a hybrid SRG 217. In an embodiment, the material may be a liquid crystal material. The liquid crystal material may be different from the liquid crystal material removed or evacuated from the liquid crystal rich regions. In an embodiment, a portion of the liquid crystal in the liquid crystal rich regions may be left between the polymer rich regions to form a hybrid SRG 217.

[0097] 16G, a protection substrate 218 may be positioned between the base substrate 212 and the hybrid SRG 217. The protection substrate 218 may be used to protect the hybrid SRG 217. The protection substrate 218 may be omitted in some examples. The protection substrate 218 and the cover substrate 1502 may have different properties that allow the protection substrate 218 to add greater protection than the cover substrate 1502 when the grating is implemented into an enabled device.

[0098] In some embodiments, the polymer air SRG 216 may be fabricated as described in connection with Figures 1A-1D. In these embodiments, a protective substrate 218 may be used to protect the polymer air SRG 216.

[0099] In some embodiments, the base substrate 212 can be a glass, quartz, or silica substrate that includes a glass surface. In some embodiments, the base substrate 212 can be a plastic substrate and can have a silicon oxide coating (e.g., SiO 2) The silicon oxide coating or glass surface may include hydroxyl groups on the top surface. An adhesion promoting material may be coated over the silicon oxide coating. The hydroxyl groups may be beneficial in adhering the adhesion promoting material to the base substrate 212.

[0100] In one embodiment, the base substrate 212 can include a glass surface that includes hydroxyl groups and can be reacted with a reagent such that the reagent reacts with the hydroxyl groups. FIG. 17 shows an example reaction in which the base substrate 212 is exposed to a reagent 1604 according to an embodiment of the present invention. The base substrate 212 can include hydroxyl groups 1608 on the surface. The base substrate 212 is exposed to the reagent 1604 and a holographic composite material 1602 that includes a polymer. The reagent 1604 can be a silane coupling agent. In one example, the reagent 1604 is (R′O) 3 The holographic mixture material 1602 includes -Si-R, where R'O- is an alkoxy group and -R is an organic functional group. The alkoxy group can condense with the available hydroxyl groups 1608 at the surface, resulting in a surface decorated with organic functional -R groups, which can facilitate covalent bonding of the coupling agent with the polymer network in the holographic polymer dispersed liquid crystal grating 215. The reagent 1604 can attach to the hydroxyl groups 1608 and the holographic mixture material 1602, creating improved attachment when compared to attachment of the holographic mixture material 1602 without the reagent 1604. The holographic mixture material 1602 can form a holographic mixture layer 1610 on the surface of the base substrate 212.

[0101] 18 illustrates an example reaction in which a reagent 1704 is exposed to the base substrate 212. The reagent 1704 can include a silane coupling agent as shown, and can bond to hydroxyl groups on the surface of the glass surface of the base substrate 212.

[0102] In some embodiments, the cover substrate 1502 can be a glass, quartz, or silica substrate, including a glass surface. In some embodiments, the cover substrate 1502 can be a plastic substrate, and can have a silicon oxide coating (e.g., SiO ) that can act similarly to a glass surface.2 ) A release layer can be coated on the glass surface. In an embodiment, similar to the base substrate 212 discussed above, the cover substrate 1502 can include a glass surface that includes hydroxyl groups and can be reacted with a reactant such that the reactant bonds with the hydroxyl groups to form the release layer.

[0103] FIG. 19 illustrates an example process for forming a release layer. The cover substrate 1502 can be exposed to a release material 1804. The release material 1804 can include a silane-based fluoropolymer or fluoromonomer reactant as shown. The release material 1804 can include a fluoropolymer or fluoromonomer, such as OPTOOL UD509 (manufactured by Daikin Chemicals), Dow Corning 2634, Fluoropel (manufactured by Cytonix), and EC200 (manufactured by PPG Industries, Inc). In an embodiment, the release material 1804 can include a polysiloxane coating. Polysiloxane coatings can adhere better to materials such as plastics that do not have hydroxyl groups on their surfaces. Polysiloxane coatings can be more robust, amenable to processing, and more environmentally friendly to fabricate than fluoropolymers. The release material 1804 can be applied via deposition, spin coating, or spraying. In an embodiment, the cover substrate 1502 can be reusable, so that after removal after holographic exposure, the cover substrate 1502 can be placed onto another holographic mixture layer that can be exposed with a holographic beam.

[0104] In one embodiment, the cover substrate 1502 and / or the base substrate 212 are made of SiO 2 as previously discussed. 2 In these examples, the substrate may be one that does not contain SiO 2 A very thin layer of SiO may be applied to the surface to facilitate adhesion / attachment of applied reagents. 2When the substrate does not contain SiO 2 , surface modification following bonding can provide adhesion. Surface modification can include treatment with a reagent to introduce reactive functional groups, including but not limited to hydroxyl groups. In an embodiment, the cover substrate 1502 and / or the base substrate 212 may not be a glass substrate, but may still contain hydroxyl groups on the surface. For example, the cover substrate 1502 and / or the base substrate 212 may be a sapphire or silicate, which may contain hydroxyl groups on the surface. In this example, the hydroxyl groups can help facilitate attachment of the reagent, and thus, SiO 2 . 2 Examples of silicate substrates are manufactured by Corning Inc. of Corning, NY, Schott AG of Mainz, Germany, Ohara Corporation, Chuo-ku, Sagamihara-shi, Kanagawa-ken, HOYA Corporation, AGC Corporation, Marunouchi, Chiyoda-ku, Tokyo, and CDGM Glass of Central Islip, NY.

[0105] In an embodiment, the cover substrate 1502 and / or the base substrate 212 may include Cleartran, which is a form of chemical vapor deposition (CVD) zinc sulfide. SiO 2 A thin layer of SiO may be applied to the Cleartran substrate to facilitate adhesion / attachment of applied reagents. In an embodiment, the cover substrate 1502 and / or the base substrate 212 may be a transparent ceramic, such as aluminum oxynitride or magnesium aluminate. 2 A thin layer of SiO may be applied to the transparent ceramic substrate to facilitate adhesion / attachment of applied reagents. In an embodiment, the cover substrate 1502 and / or the base substrate 212 may comprise a plastic such as PMMA, acrylic, polystyrene, polycarbonate, cyclic olefin copolymer, cycloolefin polymer, polyester, etc. 2 A thin layer of may be applied to the plastic substrate to facilitate adhesion / attachment of the applied reagents.

[0106] Application of Ashing and / or Atomic Layer Deposition in EPS FabricationIn some embodiments, further post-treatment of the EPS may be used to remove more of the weak polymer network regions. Post-treatment may include using plasma ashing to reduce or eliminate this trace polymer network. Plasma ashing may be similar to plasma ashing in semiconductor manufacturing to remove photoresist from etched wafers. Example equipment and processes are provided by Plasma Etch, Inc., incorporated in California, USA. In plasma ashing, monoatomic (only one atom) substances known as reactive species may be generated from a plasma source and introduced into a vacuum chamber used to oxidize or plasma ash the material to be removed. Reactive species may include oxygen or fluorine during plasma ashing. Advantageously, the plasma beam may be directional to treat tilted lattices. In some embodiments, the plasma ashing may be inductively coupled plasma ashing, a process that allows independent control of chemical and physical contributions to the ashing process by forming reactive species and ions. RF bias at the substrate electrode may be used to control the acceleration of ions to meet the requirements of different surface structures. Electrons and ions in the plasma have different mobilities that result in a direct current (DC) bias. Electrons with small mass can respond quickly to the RF field, resulting in a fast charge to the surface, which further imparts a net negative DC bias to the (wafer) surface in contact with the plasma. The voltage difference between the plasma and the wafer surface accelerates the positive ions to the surface. The negative DC bias can be used to fine-tune many characteristics of the ashing process, such as ashing rate, anisotropy, angular / spatial selectivity, and others. In an embodiment, a surface treatment of chemical additives may be applied to the EPS prior to plasma ashing, which can enhance the DC bias application. In an embodiment, the EPS can be placed in the presence of a gas, such as a noble gas, during plasma ashing. The noble gas can be argon.In an embodiment, plasma ashing may be used to tailor at least one of the shape and spatial variation of the fringes of the polymer grating structure. In an embodiment, the plasma ashing beam intensity may be variable to provide a spatially varying modulation depth. Angular variation of the intensity of the plasma ashing beam may be used for fringe shaping. In an embodiment, plasma ashing may be applied along two or more intersecting directions to form a photonic crystal. In an embodiment, high functionality acrylates around the edges of the diffractive features may modify the density of the EPS diffractive features, with the plasma ashing rate being controlled with a spatial resolution comparable to the EPS spatial frequency. The morphology of the EPS may be altered to improve the performance of the grating and increase the efficiency of processes such as ashing, to improve the grating definition, to modify the surface structure to reduce haze adding material to increase chemical affinity with gases present during the plasma ashing process, and / or to modify the effective refractive index of the grating. In an embodiment, the modulation depth of the EPS may be determined by the plasma ashing time, since more material is removed as the plasma ashing increases.

[0107] In some embodiments, oxygen and / or fluorine may be used as reactive species in the plasma ashing process. In some embodiments, a hydrogen plasma may be used in the plasma cleaning process. In some embodiments, the ashing rate in an oxygen plasma may be controlled by additives in the HPDLC mixture, such as nitrogen. In some embodiments, the plasma ashing process for ashing organic materials uses oxygen and NH 3 A gas mixture of oxygen may be used. Oxygen-based processes may be subject to substrate surface oxidation. In some embodiments, the plasma ashing process may include a plasma without oxygen, which may include a mixture of nitrogen and hydrogen, to overcome surface oxidation. Such plasma mixtures may further include fluorine.

[0108] In certain embodiments, post-coating the EPS with a very thin atomic layer of a high refractive index material can enhance the diffractive properties (e.g., refractive index modulation) of the grating. The coating can be a metal layer or a dielectric layer. One such process, atomic layer deposition (ALD), is a process that uses a TiO 2 , ZnO 2 , or the like. Coating can provide a grating structure that is more robust against temperature changes and various other environmental conditions. The ALD process can provide a large effective refractive index even when the grating structure is made from a material with a smaller refractive index. This technique can be similarly applied to the creation of nanoimprinted SRGs, where a few nanometers of ALD can protect the resin in which the SRG is punched and can also improve the effective refractive index modulation. The use of atomic layer deposition (ALD) on top of the EPS can produce further performance improvements. In many embodiments, the duty cycle of the EPS may not be optimal for a weak polymer network. In one embodiment, the duty cycle of the EPS can be 30% polymer.

[0109] Various EPS manufacturing processes are described above in Figures 1A-1D. Figures 3A and 3B show various EPS after manufacturing. Figures 20A and 20B show various lattices according to embodiments of the present invention. The lattices include many elements numbered the same as those in Figures 3A and 3B. The descriptions of these elements in Figures 3A and 3B are applicable to the lattices of Figures 19A and 19B and will not be repeated in detail. The lattices may be EPS manufactured using the processes described in connection with Figures 1A-1D and 2. The lattices may be hybrid lattices manufactured using the processes described in connection with Figures 4A-4E and 5. As shown in Figures 19A and 19B, the lattices may include a coating 1902. The coating 1902 may be present on horizontal surfaces, such as on the polymer region 3004a and the substrate 3002. As shown, FIG. 19B includes an optical layer 3008 in direct contact with the substrate 3002 such that the optical layer 3008 is positioned between the polymeric region 3004a and the substrate 3002. A coating 1902 may be positioned on the optical layer 3008. The coating 1902 may be deposited using a process such as ALD. The coating 1902 may not have step coverage and thus may only be deposited on horizontal surfaces such as on top of the polymeric region 3004a and the substrate 3002 or the optical layer 3008. In an embodiment, the coating 1902 may be deposited using a process that includes step coverage such that the coating 1902 is present on the sidewalls of the polymeric region 3004a. In an embodiment, the coating 1902 is a TiO 2 or ZnO 2 The coating 1902 may be multi-layered to include multiple different layered materials. In some embodiments, an additional passivation coating may be applied to the surface of the polymer lattice structure over the coating 1902. The additional passivation coating may provide protection from the environment (e.g., protection from moisture and / or contamination).

[0110] In some embodiments, the coating 1902 may be present on the substrate 3002 or the optical layer 3008, and not on the polymer region 3004a. FIG. 20C shows a grating according to an embodiment of the present invention. The grating includes many elements numbered the same as those in FIG. 3A and FIG. 3B. The description of these elements in FIG. 3A and FIG. 3B is applicable to the grating of FIG. 20C and will not be repeated in detail. As shown, the grating of FIG. 20C includes a coating 1902 similar to FIG. 20A and FIG. 20B. However, the coating 1902 is only present on the substrate 3002, and not on the polymer region 3004a as in FIG. 20A and FIG. 20B. In an embodiment with an optical layer 3008, the coating 1902 may only be present on the optical layer 3008, and not on the polymer region 3004a. In an embodiment, the coating 1902 may be removed from over the polymer region 3004a, or the coating 1902 may be selectively deposited on the substrate 3002. The coating 1902 can function as a biasing layer similar to the optical layer 3008.

[0111] Embodiments Including a Tilted EPS In some embodiments, the grating includes tilted EPS to create a tilted grating. The tilted grating can be configured as a binary grating, a blazed grating, and / or a multi-level grating, as well as other structures. The tilted grating can couple monochromatic angular light into the waveguide with high diffraction efficiency. The tilted grating can also maintain the angular content with greater efficiency once the light is inside the waveguide. When configured with a stepped or continuous spatially varying K vector, the angular bandwidth that can be coupled into the waveguide can be increased.

[0112] Embodiments Including Eye Glow Suppression In a waveguide-based display, light is diffracted toward the user and also diffracted away from the user. Eye glow emerges from the front surface of the display waveguide (e.g., the waveguide surface furthest from the eye) and can include unwanted light (due to leakage, stray light diffraction, scattering, and other effects) originating from the reflective surfaces of the eye, the waveguide reflective surfaces, and the surfaces of the grating. The light diffracted away is commonly referred to as "eye glow" and raises concerns about safety, privacy, and social acceptability. "Eye glow" appears as if the user's eyes are glowing or shining through the eye display caused by light leakage from the display, which creates an aesthetic that may be unsettling to some people. In addition to concerns about social acceptability in fashion sense, eye glow can present a different problem: when there is sufficient clarity in the eye glow, people looking at the user may be able to see the projected image that is intended only for the user. Thereby, eye glow may pose serious safety concerns for many users. Various eye glow suppression systems are discussed in detail in U.S. Patent Application Publication No. 2020 / 0133636, entitled “Eye Glow Suppression in Waveguide Based Displays,” filed May 26, 2021, which is hereby incorporated by reference in its entirety for all purposes.

[0113] 21A-21C conceptually illustrate three embodiments of a waveguide in which evanescent coupling to a grating can occur. In these embodiments, a grating layer 2004 is positioned on a substrate 2002. In FIG. 21A, two identical substrates 2002, 2006 sandwich the grating layer 2004. In FIG. 21B, a thin substrate 2006a and a thick substrate 2006 sandwich the grating layer 2004. In FIG. 21C, a thick substrate 2002 supports the grating layer 2004 without the presence of a top substrate. The top substrate 2006, 2006a can be a cover substrate or coating. In other embodiments, a thin protective coating can be applied to the grating layer 2004. The top surface of each waveguide embodiment faces the user's eye. The grating layer 2004 can emit light 2010 from the waveguide towards the user's eye. Undesirable eye glow light 2008 may be radiated into the environment, as shown in the case of Figures 21A and 21B.

[0114] Eye glow and / or light leakage can be reduced from the opposite outer surface by eliminating the top substrate as shown in FIG. 21C. Eliminating the top substrate can result in less eye glow / light leakage than the other two embodiments. In each embodiment shown, all light rays shown undergoing TIR are at a TIR angle that can be evanescently coupled into the grating layer 2004. Zero order rays are indicated by dashed lines. In an embodiment, evanescent grating coupling can result in eye side output light substantially perpendicular to the waveguide as shown.

[0115] If the average refractive index of the grating is less than the substrate, for large angles (far from TIR) where only evanescent coupling can occur, the zero-order TIR light cannot leave both air interfaces and pass through the grating layer 2004 to the TIR. Therefore, light propagation in the TIR can be trapped on one side of the grating or the other. The grating depth in the thickness of the waveguide can affect the amount of light coupled to the desired eye side and the undesired non-eye side where light is lost as eye glow / light leakage. In an embodiment, evanescent coupling can result in the coupled light being converted to a guided mode in at least one of the grating and the eye-side waveguide substrate 2006, 2006a. The evanescent coupling behavior can be a function of the TIR angle, grating thickness, modulation, average refractive index, and the refractive index and thickness of the eye-side substrate 2006, 2006a.

[0116] In certain embodiments, the graded EPS can also provide eye glow suppression. One advantage to the use of EPS in the context of eye glow suppression and other stray light control applications such as glitter suppression is that various grating types can be implemented on the waveguide substrate to provide different types of beam angle selectivity to address stray light present in various regions of the waveguide. In some regions of the waveguide where wide angle capability is desired, the EPS can be configured as a Raman-Nath grating that can have a modulation depth less than the grating pitch over at least a portion of the polymer grating structure. In other regions where high diffraction efficiency for a particular beam angle is required, the EPS can operate in the Bragg regime.

[0117] Embodiments Including Reciprocal Lattice In an embodiment, the gratings disclosed in connection with Figures 20A and 20B can be used to create reciprocal gratings. These reciprocal gratings can be thin film gratings. Figures 22A-22D show various stages of fabricating a reciprocal grating according to an embodiment of the invention. The various stages of fabrication include many elements numbered identically to those in Figures 3A, 3B, 20A, and 20B. The descriptions of these elements in Figures 3A, 3B, 20A, and 20B are applicable to the grating of Figure 20C and will not be repeated in detail. Figure 22A corresponds to the structure created in Figure 1B, which includes polymer regions 3004a separated by phase separated material 2102. The phase separated grating can be formed from a mixture of a monomer and a second component deposited on a substrate 3002 using the recording process described previously. The second component can include a liquid crystal, or a suspension of nanoparticles. Other materials capable of phase separation can be used. After exposure, a grating containing alternating stripes rich in the polymer and stripes rich in the second component can be created.

[0118] In Figure 22B, the phase separated material 2102 is removed to create void regions 3004b to create the EPS. The EPS structure created in Figure 22B corresponds to the EPS structure in Figure 3A. In this step, the second component can be removed to form a polymeric surface relief lattice that includes polymeric regions separated by air spaces.

[0119] In FIG. 22C, a coating 1902 is applied to the surface of the substrate 3002 and on top of the polymeric regions 3004a. In an embodiment, the coating 1902 can be applied through an ALD process. The structure created in FIG. 22C corresponds to the structure in FIG. 19A. In an embodiment, the air regions 3004b can be at least partially backfilled with a material of a different refractive index than that of the polymeric regions 3004a. The backfilling can be performed by applying an ALD coating similar to that described above. In an embodiment, the ALD coating can be thicker than the thin coating described in connection with FIGS. 20A-C. Other methods of backfilling the grating can be used depending on the type and thickness of the backfill layer material. The backfill material can have a higher or lower refractive index than that of the polymeric regions 3004a depending on the intended grating application. At the end of this step, the polymeric surface relief grating can be partially filled with the backfill material, as shown in FIG. 22C. As shown, a portion of the backfill material can be attached to the top surface of the polymeric regions 3004a. Some of the backfill material may also adhere to the upper portion of polymer region 3004a.

[0120] In FIG. 22D, the polymer regions 3004a are removed. The coating 1902 on top of the polymer regions 3004a is also removed. The remaining coating 1902 disposed on the substrate 3002 can be used as a reciprocal lattice. The remaining coating 1902 alternates with air regions 2104. In this step, the polymer regions 3004a and the unwanted coating 1902 can be removed using an etching process, such as a plasma ashing process, to reveal the tilted Bragg surface relief grating of the coating 1902 supported by the substrate 3002. In some embodiments, the polymer regions 3004a can be removed through a plasma ashing technique. The reciprocal lattice can be a thin film Bragg surface relief grating.

[0121] Embodiments for Producing Surface Relief Gratings with Improved Grating Definition One strategy to reduce haze is to reduce the surface roughness of the SRG. In many embodiments, the grating is a composite grating with improved surface definition, such as low surface roughness. FIG. 23A shows a schematic diagram of a grating according to an embodiment of the invention. In a first step, the grating can be formed using phase separation of a raw material mixture including material A and material B, using the procedure discussed above. Material A can be a polymer. After curing of the grating, component B can be extracted to leave a grating including high refractive index regions including voids 2301 embedded in polymer 2302, low refractive index regions including weak polymer structures, and other residues resulting from incomplete phase separation. The polymer structures and other residues can be further removed using a process such as plasma ashing to leave air regions 2303.

[0122] Figure 23B shows a schematic diagram of a grating according to an embodiment of the invention. The grating can be manufactured using a process beginning with that described in connection with Figure 23A. In a next step, the grating is immersed in material C, which fills the voids 2304 and air regions 2305. Material C can be cured using a process such as UV exposure.

[0123] FIG. 23C shows a schematic diagram of a grating according to an embodiment of the invention. The grating can be fabricated by a process beginning with that described in connection with FIG. 23B. In a next step, material C can be removed from the gap regions by a process such as plasma ashing to leave composite regions 2306 of polymer and material C separated by voids 2307. The plasma ashing step can be separate from the plasma ashing step described in connection with FIG. 30A. After plasma ashing, the composite material can have a smoother surface than the polymer 2302 described in connection with FIG. 23A. Material A and material C can provide a refractive index contrast that is low enough to minimize scattering while providing the desired refractive index modulation.

[0124] In many embodiments, bulk scattering may be strongly influenced by the refractive index contrast in the high refractive index regions, while surface scattering may depend on the surface texture. In many embodiments, filling the surface voids, such as in the process discussed in Figures 23A-23C in combination with ashing, can result in a smoother surface structure. In many embodiments, the above process can be used to eliminate bulk scattering contributions that may arise from voids 2304 in the polymer regions.

[0125] FIG. 24 shows an example process flow for fabricating an SRG, according to an embodiment of the invention. In a first step, a grating structure can be formed using a phase separation process that utilizes a feedstock mixture including material A and material B (2410). After phase separation, there can be regions rich in material A and regions rich in material B. In a second step, including a first ashing step, material B can be extracted (2411) to leave a grating structure including high refractive index regions with voids embedded in the polymer and refractive index regions with a residual polymer matrix. The material B rich regions can become air regions after the first ashing step. In a third step, the grating structure can be immersed in material C (2412) to fill the voids in the polymer rich regions and air regions. In a fourth step, material C can be extracted (2413) using a second ashing step to remove material C from the former air regions to leave regions of composite polymer and material C separated by voids. As described previously, this can result in less surface roughness on the fabricated SRG. In one embodiment, the SRG may be a deep SRG as discussed above.

[0126] Surface relief gratings configured as dual interaction gratings In a conventional Bragg grating, the double interaction can be understood using basic ray optics by considering the interaction of the upward and downward TIR rays with the folded grating. The upward and downward rays occur when the guided light is reflected at the lower and upper waveguide TIR surfaces. The two ray paths give rise to two offset diffraction efficiencies versus angular profile, which combine to extend the angular bandwidth. An example of an optical waveguide includes a grating of a first prescription including at least two TIR surfaces, configured such that input TIR light with a first angular range along a first propagation direction undergoes at least two diffractions within the grating and a change in propagation direction from the first propagation direction to a second propagation direction, each ray from the first angular range and its corresponding diffracted ray being located in a diffraction cone of the grating, each diffraction providing a unique TIR angular range along the second propagation direction, which is disclosed in U.S. Patent Application Publication No. 2015 / 0133634, entitled "Waveguide Grating Device," filed on February 12, 2015, which is hereby incorporated by reference in its entirety for all purposes.

[0127] 25A and 25B show the principle of a dual interaction grating for implementation in a waveguide. A waveguide 30 includes a lattice pattern 31 tilted with respect to the waveguide TIR plane and aligned at a clocking angle in the waveguide plane. In many embodiments, the clocking angle may be 45 degrees to provide a 90 degree beam deflection. In FIG. 25A, the first TIR path is located in the input propagation plane 2020 and, after diffraction, is located in the output propagation plane 2021. The grating has a k-vector 2022, which is also labeled with the symbol k. The tilt angle 2023 of the lattice pattern with respect to the waveguide surface normal 2024 is also indicated. TIR light 2025 in the propagation plane 2001 with a TIR angle 2026 with respect to the waveguide plane normal 2027 hits the lattice pattern as an upward traveling ray 2028 that is diffracted into a TIR direction 2029 located inside the propagation plane 2021. In Figure 25B, a second TIR path in the input propagation plane 2001, indicated by reference numeral 2030, has a TIR angle 2031 with respect to the waveguide plane normal 2027 and hits the checkerboard pattern as a downward traveling ray 2033 that is diffracted into a TIR direction 2034 that is inside the output propagation plane 2021. Because the upward and downward traveling TIR rays are asymmetric in this case, there may be two peaks in the output diffraction efficiency versus angle profile.

[0128] FIG. 26 conceptually illustrates a cross section of a grating according to an embodiment of the invention. The grating can be an SRG 2100 including tilted stripes 2101 separated by air volumes 2103. In many embodiments, the grating can be clocked or tilted in the waveguide plane. FIG. 27 is a conceptual diagram of beam propagation in the grating of FIG. 26. The grating can be split for conceptual purposes into a deep grating section 2111 including alternating high and low index stripes 2113 and 2114, and is represented as a configuration 2110 operating in the Bragg regime overlaid by a thin grating section 2112 including alternating high index regions 2115 and low index regions 2116 operating in the Raman-Nath regime. In many embodiments, the high index regions 2115 are polymer and the low index regions 2116 are air. The grating configuration 2110 supports TIR beam propagation including ray paths such as 2117. To simplify the description of the embodiment, guided ray reflections, as represented by rays 2118, 2119, are represented as occurring at the interface between the volume grating portion 2111 and the thin grating portion 2112. A reasonable approximation of the TIR at the thin grating portion 2112 can be considered as being separated from the coupled wave propagation through the volume grating portion 2111.

[0129] In an embodiment, the thin grating portion 2112 may be partially backfilled with a different refractive index material up to the level of the interface between the thin grating portion 2112 and the thick grating portion 2111. FIG. 28 is a diagram of an example of a partially backfilled grating 2121, according to an embodiment of the present invention. This partially backfilled grating 2121 may be considered a hybrid surface relief grating / volume Bragg grating. The backfilled grating 2121 is a grating described in connection with FIG. 27 backfilled with a material of different refractive index. The backfilled grating 2121 may be considered a volume grating. In many embodiments, the unbackfilled regions remaining after partial backfilling of the air regions may provide a polymeric Raman-Nath surface relief grating 2802 comprising alternating polymer and air regions overlying a Bragg grating 2804 comprising alternating polymer and backfilled material regions. In a waveguide implementation, upward and downward TIR propagation directions may be generated by TIR in the waveguide to air interface.

[0130] The double interaction shown in Figures 25A-25B may include TIR rays propagating upward and downward. In the SRG, one of the TIR propagation directions results from reflection diffraction in the SRG occurring at an angle equal to the TIR angle. The SRG can cause diffracted TIR to occur with high efficiency subject to some constraints on the range of incidence angles, K-vector direction, grating clock angle, grating period, and / or grating thickness. In an embodiment, the SRG can be a folded grating. Thus, a first TIR propagation direction 2119 generated by the surface grating and an opposite TIR propagation direction 2120 generated by reflection from the opposite face of the grating substrate can interact within the volume grating portion shown in Figure 28. In many embodiments, this ray-grating can result in a double interaction according to the embodiments and teachings of US Patent No. 5,999,333, which is hereby incorporated by reference in its entirety for all purposes. The diffraction efficiency of the grating may depend on at least one of the guided beam angular bandwidth, the grating vector, the grating thickness, and / or the grating fringe spacing. In an embodiment, the thick grating portions 2111 may be eliminated to provide only the thin substrate relief grating portions 2112 supported by the transparent substrate.

[0131] The hybrid surface relief grating / volume Bragg grating structure can provide several advantages in many embodiments, including a wider cumulative angular response that allows thicker gratings to be used to improve the DE without compromising the angular bandwidth. Coating the hybrid grating with an ALD coating to increase the effective refractive index can further enhance the angular bandwidth. In many embodiments, the hybrid surface relief grating / volume Bragg grating structure can improve the diffraction efficiency for P-polarized light. In some embodiments, the hybrid surface relief grating / volume Bragg grating structure formed by a phase separating mixture of inorganic components and monomers can include a completely inorganic SRG after the final complete removal of the polymer component from the cured grating. In many embodiments, the inorganic component can be nanoparticles. In many embodiments, the hybrid surface relief grating / volume Bragg grating structure can be used in at least one of the folding gratings and / or the output grating to reduce haze and to reduce coupling losses in the folding grating. Reducing haze can increase contrast. Reducing coupling losses in the folding grating can equate to increasing the diffraction efficiency in the folding grating. In many embodiments, a polymer / air SRG can be used as the input grating with high diffraction efficiency.

[0132] As previously illustrated, hybrid surface relief grating / volume Bragg grating structures may be formed by partial backfilling of a grating structure to form a structure comprising a volume Bragg grating with an overlapping surface relief grating. Hybrid surface relief grating / volume Bragg grating structures may exhibit improved angular response after additional plasma ashing or reactive ion etching.

[0133] In many embodiments, a hybrid surface relief grating / volume Bragg grating structure can be formed during holographic phase separation and curing. In many embodiments, the grating can be formed in cells where the grating material is sandwiched between a base substrate and a release layer. The surface structure can be revealed when the release layer is removed. Without being limited to any particular theory, the surface grating can be formed due to polymerization-induced shrinkage during mass transfer and phase separation. The relative depth of the high and low refractive index regions can be adjusted by utilizing an additional plasma ashing step. An ALD deposited layer can be added to the grating surface to increase the effective refractive index. In many embodiments, the grating thickness can be 1.1 micrometers with a grating period of 375 nm and a tilt angle (relative to the cell optical surface normal) of 22 degrees. The completed grating can be isotropic or anisotropic depending on the system components in the initial mixture.

[0134] Figure 29 shows a schematic of the beam-grating interaction geometry 2130 of a TIR surface grating. Such a configuration is commonly referred to as a conical diffraction configuration. The relationship n S >n 0 The refractive index can be any medium that satisfies n 0 is immersed in a low refractive index medium (which in most embodiments will be air) with refractive index n S For a TIR grating recorded on a transparent substrate, the only reflected diffraction order is related to n S / n 0 ≦|sin(u inc )|≦1. With reference to the xyz orthogonal reference frame in FIG. 28, the equation for the incident and diffracted ray angles with respect to the grating vector is: x direction: -kn S sin(u inc )+K S cos(φ s )=-kn S sin(u diff )cos(φ diff ), y direction: K S sin(φ s )=kn Ssin(u diff )sin(φ diff ), and z direction: kn S cos(u inc )=kn S cos(u diff )+K S / tan(φ s ) It can be expressed as: Here, u inc is the incident light vector r inc is the polar angle of φ s is the azimuth angle of the incident ray, and u diff is the diffracted light vector r diff is the polar angle of φ s is the azimuth angle of the lattice vector, and u S is the polar angle of the lattice vector K.

[0135] The wave number k of the incident light can be given by k=2π / λ, where λ is the wavelength of the guided light. The coefficient of the surface component of the lattice vector is K S =k=2π / Λ S where Λ S is the surface grating pitch. A solution to the above equation can be obtained by setting the angle of incidence equal to the angle of diffraction.

[0136] In many embodiments, the dual interaction grating is implemented in a polymer grating structure that includes alternating polymer-rich and air regions. In many embodiments, the grating depth of the polymer grating structure is less than the Bragg fringe spacing. In many embodiments, the grating depth of the polymer grating structure is greater than the Bragg fringe spacing. In many embodiments, total internal reflection from the polymer grating structure occurs when the first order diffraction from the polymer grating structure has a diffraction angle equal to the TIR angle of the waveguide. In many embodiments, the polymer grating structure does not provide a transmitted diffraction order. In many embodiments, the polymer grating structure is a photonic crystal. In many embodiments, the polymer grating structure is configured as a Raman-Nath grating having a first grating period overlapping a Bragg grating having the same grating period, with the minimum of the Raman-Nath grating overlapping the minimum of the Bragg grating. In many embodiments, the polymer grating structure is a tilted grating. In many embodiments, the air regions of the polymer grating structure can be at least partially backfilled with a material having a refractive index different from that of the polymer-rich regions.

[0137] Embodiments Including an OLED Array as an Image Generator There is growing interest in the use of organic light emitting diode (OLED) arrays as image generating devices in waveguide displays. OLEDs have many advantages in waveguide display applications. As an emissive technology, OLEDs do not require a light source. OLEDs can be cost-effectively printed over large areas. Non-rectangular pixel array patterns can be printed on curved or flexible substrates. As discussed later, the ability to pre-deform pixel arrays and create curved focal planes adds new design dimensions that can allow compensation for wavefront distortions of guided beams caused by curved waveguides and prescription lenses supported by the waveguide. Resolutions with 4K x 4K pixel resolutions are currently available with good prospects for higher resolutions in the near term, providing a quicker path to higher resolution, wide FOV AR displays than can be provided by technologies such as liquid crystal in silicon (LCoS) and microelectromechanical system (MEMS) devices such as digital light processing (DLP) devices. Another considerable advantage over LCoS is that it can be switched in microseconds (compared to milliseconds for LC devices).

[0138] OLEDs have certain advantages. In their basic form, OLEDs are Lambertian emitters, which makes efficient light collection much more difficult than in LCoS and DLP microdisplays. The red, green, and blue spectral bandwidths of OLEDs are wider than those of light-emitting diodes (LEDs), which poses additional light management problems in holographic waveguides. The most significant drawback of OLEDs is that half of the available light from an OLED is wasted in a waveguide that uses HPDLC periodic structures, such as switchable periodic structures that tend to select P-polarized light. Therefore, many embodiments of the present invention are directed to a waveguide display for an emissive non-polarized image source that can provide high light efficiency for non-polarized light, and to related methods of manufacturing such a waveguide display.

[0139] For the purposes of describing the embodiments, some well-known features of optical technology familiar to those skilled in the art of optical design and visual display have been omitted or simplified so as not to obscure the basic principles of the present invention. Unless otherwise stated, the term "on-axis" with respect to a ray or beam direction refers to propagation parallel to an axis perpendicular to the surface of the optical component described with respect to the present invention. In the following description, the terms light, ray, beam, and direction may be used interchangeably and in conjunction with one another to indicate the direction of propagation of electromagnetic radiation along a linear trajectory. The terms light and illumination may be used in conjunction with the visible and infrared regions of the electromagnetic spectrum. Some of the following description is presented using terms commonly used by those skilled in the art of optical design. As used herein, the term grating may encompass a grating consisting of a set of gratings in some embodiments. For purposes of illustration, unless otherwise stated, it is understood that the drawings are not to scale.

[0140] Turning now to the drawings, methods and apparatus for providing a waveguide display using an emissive input image panel are illustrated in accordance with various embodiments of the present invention. Figure 30 conceptually illustrates a waveguide display in accordance with an embodiment of the present invention. As shown, apparatus 100 comprises a waveguide 101 supporting input and output gratings 102, 103 with high diffraction efficiency for P-polarized light in a first wavelength range, and input and output gratings 104, 105 with high diffraction efficiency for S-polarized light in the first wavelength range.

[0141] The device 100 further comprises an OLED microdisplay 106 that emits unpolarized light with an emission spectral bandwidth that includes a first wavelength range, and a collimation lens 107 for projecting the light from the OLED microdisplay 106 to a field of view. In the illustrated embodiment, the S and P gratings 102-105 may be layered with no air gap required. In other embodiments, the gratings may be separated by an air gap or a transparent layer. The S and P gratings 102-105 may be deep SRG or EPS as previously described.

[0142] 31 conceptually illustrates a waveguide display according to an embodiment of the invention, in which P and S gratings are disposed in separate air-spaced waveguide layers. As shown, device 110 comprises upper and lower waveguide layers 111 and 112 (supporting gratings 102, 103 and 104, 105, respectively) separated by an air gap 113. Gratings 102, 103 and 104, 105 may be deep SRG or EPS as previously described.

[0143] FIG. 32 conceptually illustrates a typical ray path in a waveguide display according to an embodiment of the present invention. In the embodiment 120 shown in FIG. 32, a microdisplay 106 is configured to emit unpolarized light 121 in a first wavelength range, which is collimated by a collimator lens 107 and projected into the field of view. S-polarized radiation from the microdisplay 106 can be coupled into the waveguide 101 by an S-diffractive input grating 104 into total internal reflection and extracted from the waveguide 101 by an S-diffractive output grating 105. P-polarized light from the microdisplay 106 can be injected and extracted in a similar manner using a P-diffractive input grating 102 and a P-diffractive output grating 103. Dispersion can be corrected for both S and P light, provided that the spatial frequencies of the input and output gratings are matched. The input and output gratings 102, 103 can be deep SRGs or EPSs as previously described.

[0144] 23-25 ​​show particular waveguide display configurations, various configurations, including variations on the illustrated configurations, can be implemented, the particular implementation of which may depend on the particular requirements of a given application. Moreover, such displays can be manufactured using a number of different methods. For example, in many embodiments, the two grating layers are formed using an inkjet printing process.

[0145] In many embodiments, the waveguide operates in a single color range. In many embodiments, the waveguide operates in a green range. In some embodiments, waveguide layers operating in different spectral ranges, such as red, green, and blue (RGB), can be stacked to provide a three-layer waveguide structure. In further embodiments, the layers are stacked with an air gap between the waveguide layers. In various embodiments, the waveguide layers operate in a broader band, such as blue-green and green-red, to provide a two-waveguide-layer solution. In other embodiments, the gratings are color multiplexed to reduce the number of grating layers. Various types of gratings can be implemented. In some embodiments, at least one grating in each layer is a switchable periodic structure.

[0146] The present invention can be applied using a variety of waveguide architectures, including those disclosed in the literature. In many embodiments, the waveguide can incorporate at least one of angle multiplexed gratings, color multiplexed gratings, folded gratings, double interaction gratings, rolled K-vector gratings, cross folded gratings, mosaic gratings, chirped gratings, gratings with spatially varying refractive index modulation, gratings with spatially varying grating thickness, gratings with spatially varying average refractive index, gratings with spatially varying refractive index modulation tensor, and gratings with spatially varying average refractive index tensor. In some embodiments, the waveguide can incorporate at least one of a half wave plate, a quarter wave plate, an anti-reflective coating, a beam splitting layer, an alignment layer, a photochromic backing layer for glare reduction, and a louver film for glare reduction. In some embodiments, the waveguide can support a grating that provides separate light paths for different polarizations. In various embodiments, the waveguide can support a grating that provides separate light paths for different spectral bandwidths. In some embodiments, gratings for use in the present invention may be HPDLC gratings, switching gratings recorded in HPDLC (such switchable Bragg gratings), Bragg gratings recorded in holographic photopolymer, or surface relief gratings.

[0147] In an embodiment, the EPS can be a dual-axis expansion grating for use in a display waveguide. In a Bragg grating, the dual interaction can be understood using basic ray optics by considering the interaction of the upward and downward TIR rays with the folded grating, where the upward and downward rays occur when the guided light is reflected at the lower and upper waveguide TIR surfaces. In an EPS, one of the TIR interfaces is replaced by a grating. When using diffraction grating theory, it can be shown that the SRG (and specifically the SRG folding) can make the diffraction angle equal to the first order of the incidence angle, so that TIR can occur with some constraints on the range of incidence angles, K-vector direction, grating clock angle, grating depth, and grating period. Thus, there are upward and downward TIR paths through the grating for the SRG. By increasing the SRG thickness to the Bragg region, the dual interaction can occur in the EPS in the same way as in a volume Bragg grating. Thus, various embodiments of the present invention relate to a dual interaction EPS.

[0148] In many embodiments, the waveguide display can provide a diagonal image field of at least 50°. In further embodiments, the waveguide display can provide a diagonal image field of at least 70°. In some embodiments, the OLED display can have a brightness of greater than 4000 nits and a resolution of 4k×4k pixels. In some embodiments, the waveguide can have an optical efficiency of greater than 10%, such that an image brightness of greater than 400 nits can be provided using a 4000 nit OLED display. Waveguide displays implementing P gratings typically have a waveguide efficiency of 5% to 6.2%. Providing an S grating as previously discussed can increase the efficiency of the waveguide by a factor of two. In various embodiments, an eyebox of greater than 10 mm with a pupil distance of greater than 25 mm can be provided. In many embodiments, the thickness of the waveguide can be between 2.0 and 5.0 mm.

[0149] FIG. 33 conceptually illustrates a waveguide display according to an embodiment of the invention in which at least a portion of at least one of the waveguide optical surfaces is curved, and the effect of the curved surface portion on the guided beam wavefront. As shown, the device 130 includes a waveguide 131 supporting a curved surface portion 132. In the illustrated embodiment, the waveguide 131 supports input and output gratings 102 and 103 with high diffraction efficiency for P-polarized light in a first wavelength range, and input and output gratings 104 and 105 with high diffraction efficiency for S-polarized light in the first wavelength range. A microdisplay 106 displaying a rectangular array of pixels 133 emits unpolarized light 134 in the first wavelength range, which is collimated and projected by a collimator lens 107 into the field of view. The P-polarized radiation from the microdisplay 106 can be coupled into the waveguide by a P-diffractive input grating 102 into a total internal reflection path, and extracted from the waveguide by a P-diffractive output grating 103. The presence of any non-planar surfaces in the waveguide can distort the wavefront of the guided light such that the output light when viewed from the eyebox exhibits defocus, geometric distortion, and other aberrations. For example, in FIG. 33, light projected by collimator lens 107 from a single pixel has a planar wavefront 135 that, after propagating through waveguide 131 along TIR path 136, forms non-parallel output rays 137-139 that are perpendicular to curved output wavefront 139A. On the other hand, a perfectly planar waveguide would instead provide a parallel beam expanded light. FIG. 34 conceptually illustrates a waveguide configuration 140 in which a waveguide substrate 141 supports two overlapping upper curved surfaces 142 and lower curved surfaces 143.

[0150] FIG. 35 conceptually illustrates a waveguide display according to an embodiment of the invention, in which aberrations introduced by curved surface portions can be corrected by pre-distorting the pixel pattern of an OLED microdisplay. In the illustrated embodiment, the waveguide device 150 is similar to that shown in FIG. 25. As shown, the device 150 includes a microdisplay 151 supporting a pre-distorted pixel pattern 152. Unpolarized first wavelength light 153 emitted by the microdisplay is focused by a lens 107, which substantially collimates the beam entering the waveguide while forming a slightly pre-distorted wavefront 154. After entry and propagation 155 through the waveguide 131, the pre-distorted wavefront is focused by the curved surface 132 to form parallel output rays 156-158 that are perpendicular to a planar output wavefront 159.

[0151] FIG. 36 conceptually illustrates a waveguide display according to an embodiment of the invention, in which aberrations introduced by curved surface portions can be corrected by pre-distorting the pixel pattern of an OLED microdisplay formed on a curved substrate. The curved microdisplay substrate can help correct focus errors, field curvature, distortion, and other aberrations in conjunction with the distorted pixel pattern. In the illustrated embodiment, the waveguide device 160 is similar to that shown in FIG. 32. As shown, a curved substrate microdisplay 161 supports a pre-distorted pixel pattern 164. Unpolarized first wavelength light 163 emitted from the microdisplay is focused by lens 107 to form a substantially collimated and guided beam at the slightly pre-distorted pixel pattern 164, which after input and propagation 165 through the waveguide 131 forms parallel output rays 166-168 that are perpendicular to a planar output wavefront 169.

[0152] While Figures 32-36 show a particular configuration of a waveguide having a curved surface, many other different configurations and modifications can be implemented. For example, the techniques and underlying theory shown in such embodiments may be applied to a waveguide supporting a prescription optical surface of the eye. In many embodiments, a prescription waveguide substrate can be custom manufactured using processes similar to those used in the manufacture of prescription eyeglasses for the eye, with a standard base prescription finely tailored to the requirements of the individual user. In some embodiments, the waveguide grating can be inkjet printed with a standard base prescription. In some embodiments, the OLED display can be custom printed with a pre-distorted pixel pattern formed. In various embodiments, the OLED display can be printed on a curved backplane substrate. In some embodiments, additional refractive or diffractive pre-correction elements can be supported by the waveguide. In many embodiments, additional correction features can be encoded on at least one of the input and output gratings. The input and output gratings can be deep SRG, EPS, or hybrid gratings as described above, and can be manufactured with the methods described in connection with Figures 1-5. The input and output gratings may also have thicknesses as described in connection with FIGS.

[0153] FIG. 37 is a flow diagram conceptually illustrating a method for projecting image light for viewing using a waveguide including an S-diffraction grating and a P-diffraction grating, according to an embodiment of the present invention. As shown, a method 170 for forming an image is provided. Referring to the flow diagram, the method 170 includes providing an OLED array emitting light in a first wavelength range, a collimation lens, and a waveguide supporting input and output gratings with high diffraction efficiency for S-polarized light in the first wavelength range and input and output gratings with high diffraction efficiency for P-polarized light in the first wavelength range (171). In an embodiment, the input and output gratings can be deep SRG, EPS, or hybrid gratings as previously discussed. The image light emitted by the OLED array can be collimated (172) using a collimation lens. S-polarized light can be coupled into a total internal reflection path in the waveguide using an S-diffraction input grating (173). P-polarized light can be coupled into a total internal reflection path in the waveguide using a P-diffraction input grating (174). The S-polarized light can be beam expanded and extracted from the waveguide for viewing (175). The P-polarized light can be beam expanded and extracted from the waveguide for viewing (176).

[0154] FIG. 38 is a flow chart conceptually illustrating a method for projecting image light for viewing using a waveguide that supports an optical prescription surface and includes S and P gratings, according to an embodiment of the present invention. As shown, a method 180 for forming an image is provided. Referring to the flow chart, the method 180 includes providing an OLED array with a pre-distorted pixel pattern that emits light in a first wavelength range, a collimation lens, and a waveguide that supports input and output gratings with high diffraction efficiency for S-polarized light into a first wavelength range and input and output gratings with high diffraction efficiency for P-polarized light in the first wavelength range (181), and further includes providing a prescription optical surface supported by the waveguide (182). In an embodiment, the input and output gratings can be deep SRG, EPS, or hybrid gratings as discussed above. The image light emitted by the OLED array can be collimated using a collimation lens (183). S-polarized light can be coupled into a waveguide using an S-diffraction input grating (184). P-polarized light can be coupled into a waveguide using a P-diffraction input grating (185). The pre-distorted wavefront can be reflected at the prescription surface (186). A planar wavefront can be formed from the pre-distorted wavefront using the optical intensity at the prescription surface (187). The S-polarized light can be beam expanded and extracted from the waveguide for viewing (188). The P-polarized light can be beam expanded and extracted from the waveguide for viewing (189).

[0155] Considerations for embodiments including various pixel shapes The various devices contemplated in this disclosure may be applied using emissive displays with input pixel arrays of many different shapes, limited only by geometric constraints and practical issues in implementing the array. In many embodiments, the pixel array may include pixels that are aperiodic (non-repeating). In such embodiments, asymmetries in pixel shape and distribution may be used to create non-uniformity in the output illumination from the waveguide. Optimal pixel size and shape may be determined using inverse vector ray tracing from the output and input grids (and folded grids, if used) to the pixel array. A variety of asymmetric pixel patterns may be used with the present invention. For example, FIG. 39A conceptually illustrates a portion 230 of a pixel pattern comprising rectangular elements 230A-230F of different sizes and aspect ratios for use in an emissive display panel, according to an embodiment of the present invention. In an embodiment, the pixel array may be based on a non-repeating pattern based on a finite set of polygonal building blocks. For example, Figure 39B conceptually illustrates a portion 240 of a pixel pattern having Penrose tiles 240A-240J for use in an emissive display panel, according to an embodiment of the invention. The tiles may be based on the principles disclosed in US Patent No. 5,399,633 to Penrose, entitled "Set of tiles for covering a surface," which is hereby incorporated by reference in its entirety. Patterns occurring in nature, of which honeycomb is a well-known example, may also be used in many embodiments.

[0156] In many embodiments, the pixels may include an arrangement of identical regular polygons. For example, FIG. 39C conceptually illustrates a portion 250 of a pixel pattern having hexagonal elements, in accordance with an embodiment of the invention. FIG. 39D conceptually illustrates a portion 260 of a pixel pattern having square elements 260A-260D, in accordance with an embodiment of the invention. FIG. 39E conceptually illustrates a portion 270 of a pixel pattern having diamond-shaped elements 270A-270D, in accordance with an embodiment of the invention. FIG. 39F conceptually illustrates a portion 280 of a pixel pattern having isosceles triangular elements 280A-280H, in accordance with an embodiment of the invention.

[0157] In many embodiments, pixels have vertically or horizontally biased aspect ratios. FIG. 39G conceptually illustrates a portion 290 of a pixel pattern having hexagonal elements 290A-290C with horizontally biased aspect ratios. FIG. 39H conceptually illustrates a portion 300 of a pixel pattern having rectangular elements 300A-300D with horizontally biased aspect ratios, in accordance with an embodiment of the invention. FIG. 39I conceptually illustrates a portion 310 of a pixel pattern having diamond-shaped elements 310A-310D with horizontally biased aspect ratios, in accordance with an embodiment of the invention. FIG. 39J conceptually illustrates a portion 320 of a pixel pattern having triangular elements 320A-320H with horizontally biased aspect ratios, in accordance with an embodiment of the invention.

[0158] In many embodiments, OLEDs can be made in cavity shapes and multi-layer structures to shape the spectral emission characteristics of the OLED. In some embodiments, microcavity OLEDs optimized to provide narrow spectral bandwidths can be used. In some embodiments, the spectral bandwidth can be less than 40 nm. In some embodiments, a spectral bandwidth of 20 nm or less can be provided. In some embodiments, OLEDs can be made from materials that provide electroluminescent emission in a relatively narrow band near-selective spectral region corresponding to one of the three primary colors. FIG. 40 conceptually illustrates a pixel pattern in which different pixels can have different emission characteristics. In some embodiments, pixels can have different spectral emission characteristics depending on their position in the pixel array. In some embodiments, pixels can have different angular emission characteristics depending on their position in the pixel array. In some embodiments, pixels can have both spectral and angular emission characteristics that vary spatially across the pixel array. The pixel pattern can be based on any of the patterns shown in FIGS. 39A-39J. In many embodiments, pixels of different sizes and shapes can be arranged to provide spatial emission variations to control uniformity in the final image.

[0159] In many embodiments, OLEDs can have cavity structures designed to transform a given light distribution into a special shape. This can typically be achieved by secondary optical elements, which can be bulky for wearable display applications. Such designs also suffer from the problem of limiting the final light source to a single permanent mode of operation, which can be overcome only by using mechanically adjustable optical elements. In some embodiments, OLEDs can allow real-time regulation of the beam shape without relying on secondary optical elements and without mechanical adjustments. In some embodiments, OLEDs can be continuously tuned between on-axis and off-axis primary emission directions while maintaining high quantum efficiency in any setting, as disclosed in Non-Patent Document 7.

[0160] An important OLED development, "microcavity OLED", can provide potential for more controlled spectral bandwidth and emission angle in some embodiments. However, microcavity OLED is not yet ready for commercial use. In one embodiment (corresponding to a 2 micrometer grating with a refractive index modulation of 0.1, an average refractive index of 1.65, and an incidence angle in the waveguide of 45 degrees), the diffraction efficiency of the SBG is greater than 75% (between 25% of the peak point) for the OLED emission spectrum. Narrower bandwidth OLEDs using deeper cavity structures reduce the bandwidth to 40 nm or less.

[0161] Advantageously, the present invention can use OLEDs optimized for use in the blue at 460 nm, which provide better blue contrast in daylight AR display applications as well as better reliability and lifetime versus the more commonly used 440 nm OLEDs.

[0162] In one embodiment, the emissive display can be an OLED full-color silicon-backplane microdisplay similar to those developed by Kopin Corporation (Westborough, MA). Kopin's microdisplay offers an image diagonal of 0.99 inches and a pixel density of 2490 pixels per inch. The microdisplay uses Kopin's patented Pantile™ magnifying lens to enable a compact form factor.

[0163] Although the present invention has been discussed in terms of an embodiment using an OLED microdisplay as the input image source, in many other embodiments, the present invention can be applied with any other type of emissive microdisplay technology. In an embodiment, the emissive microdisplay can be a microLED. MicroLEDs benefit from reduced power consumption and can operate efficiently at higher brightness than that of OLED displays. However, microLEDs are inherently monochromatic. Phosphors typically used to convert color in LEDs do not fit well into small dimensions, resulting in more complex device architectures that are difficult to scale for microdisplay applications.

[0164] Although polymer periodic structures have been discussed in terms of use in OLED arrays based on waveguide displays, polymer periodic structures have advantageous synergistic applications with other classes of displays. Examples of these displays include image generating devices that use non-emissive display technologies, such as LCoS and MEMS-based displays. While LCoS-based displays typically emit polarized light, which may make the advantages of polymer grating structures less applicable to polarized light, polymer grating structures can provide advantageous efficiency and manufacturing cost savings over conventional imprinted gratings. Furthermore, polymer grating structures can be applicable to a variety of other non-display waveguide-based implementations, such as waveguide sensors and / or waveguide lighting devices.

[0165] Example Embodiments Although a number of embodiments of the invention have been described in detail, it should be understood that the invention can be embodied in many other forms without departing from the spirit or scope of the invention. For example, embodiments such as those listed below are contemplated.

[0166] Item 1: A method for producing a periodic structure, comprising: providing a holographic mixture on a base substrate; sandwiching the holographic mixture between a base substrate and a cover substrate, the holographic mixture forming a holographic mixture layer on the base substrate; applying a holographic recording beam to the holographic mixture layer to form a holographic polymer dispersed liquid crystal periodic structure comprising alternating polymer rich and liquid crystal rich regions; removing the cover substrate from the holographic polymer dispersed liquid crystal periodic structure, the cover substrate having different properties from the base substrate such that it can be removed from the formed holographic polymer dispersed liquid crystal periodic structure after exposure while still being able to adhere to the unexposed holographic mixture layer; The method includes:

[0167] Item 2: The method of item 1, further comprising removing at least a portion of the liquid crystal in the liquid crystal rich regions to form a polymer periodic structure.

[0168] Clause 3: The method of clause 2, further comprising the step of refilling the liquid crystal rich regions with a backfill material.

[0169] Clause 4: The method of clause 3, wherein the backfill material has a refractive index different from that of the remaining polymer-rich region.

[0170] Clause 5: The method of clause 3, wherein the backfill material comprises a liquid crystal material.

[0171] Item 6: The method of item 5, wherein the liquid crystal material is different from the liquid crystal that is removed from the liquid crystal rich region.

[0172] Clause 7: The method of clause 2, wherein the step of removing at least a portion of the liquid crystal comprises removing substantially all of the liquid crystal in the liquid crystal rich regions.

[0173] Clause 8: The method of clause 2, wherein the step of removing at least a portion of the liquid crystal further comprises leaving at least a portion of the liquid crystal in the liquid crystal rich regions.

[0174] Clause 9: The method of clause 2, wherein the step of removing at least a portion of the liquid crystal comprises washing the holographic polymer dispersed liquid crystal grating with a solvent.

[0175] Clause 10: The method of any one of clauses 1 to 9, wherein the base substrate comprises plastic.

[0176] Item 11: The method of item 1, wherein a silicon oxide layer is deposited on a base substrate.

[0177] Item 12: The method of any one of items 1 to 6, wherein the base substrate comprises glass, quartz, or silica.

[0178] Clause 13: The method of any one of clauses 1 to 6, wherein the cover substrate comprises plastic.

[0179] Item 14: The method of item 10, wherein a silicon oxide layer is deposited on the cover substrate.

[0180] Item 15: The method of any one of items 1 to 6, wherein the cover substrate comprises glass, quartz, or silica.

[0181] Item 16: The method of any one of items 1 to 15, wherein an adhesion promoting layer is coated on top of the base substrate, which promotes adhesion between the base substrate and the holographic polymer dispersed liquid crystal periodic structure.

[0182] Item 17: The method of item 16, wherein the base substrate comprises a glass surface containing hydroxyl groups, and the silane-based reagent bonds with the hydroxyl groups and the adhesion promoting layer.

[0183] Item 18: The method of any one of items 1 to 17, wherein a release layer is coated on top of the cover substrate, which releases the cover substrate easily from the holographic polymer dispersed liquid crystal periodic structure.

[0184] Item 19: The method of item 18, wherein the cover substrate comprises a glass surface containing hydroxyl groups and the release layer is a silane-based fluoro reactant that bonds with the hydroxyl groups.

[0185] Item 20: The method of any one of items 1 to 19, further comprising the step of applying a protective substrate to the holographic polymer dispersed liquid crystal periodic structure, the holographic polymer dispersed liquid crystal periodic structure being positioned between the protective substrate and the base substrate.

[0186] Item 21: A method for producing a periodic structure, comprising: providing a first holographic mixture on a first base substrate; sandwiching the first holographic mixture between a first base substrate and a cover substrate, the first holographic mixture forming a first holographic mixture layer on the first base substrate; applying a holographic recording beam to the first holographic mixture layer to form a first holographic polymer dispersed liquid crystal periodic structure comprising alternating polymer rich and liquid crystal rich regions; removing the cover substrate from the holographic polymer dispersed liquid crystal periodic structure; providing a second holographic mixture on a second base substrate; sandwiching the second holographic mixture between a second base substrate and a cover substrate, the second holographic mixture forming a second holographic mixture layer on the second base substrate; applying a holographic recording beam to the second holographic mixture layer to form a second holographic polymer dispersed liquid crystal periodic structure comprising alternating polymer rich and liquid crystal rich regions; The method includes:

[0187] Item 22: The method of item 21, wherein the cover substrate has different properties from the first base substrate and the second base substrate such that after exposure, the cover substrate can be removed from the formed first and second holographic polymer dispersed liquid crystal periodic structures while adhering to the unexposed first and second holographic mixture layers.

[0188] Item 23: The method of any one of items 21 or 22, further comprising removing the cover substrate from the second holographic polymer dispersed liquid crystal periodic structure.

[0189] Item 24: The method of any one of items 21 to 23, further comprising removing at least a portion of the liquid crystal in the liquid crystal rich regions of the first or second holographic polymer dispersed liquid crystal periodic structures to form a polymer surface relief grating.

[0190] Clause 25: The method of clause 24, further comprising the step of refilling liquid crystal rich regions of the first or second holographic polymer dispersed liquid crystal periodic structures with a backfill material.

[0191] Clause 26: The method of clause 25, wherein the backfill material has a refractive index different from that of the remaining polymer-rich region.

[0192] Item 27: The method of item 25, wherein the backfill material includes a liquid crystal material.

[0193] Item 28: The method of item 27, wherein the liquid crystal material is different from the liquid crystal that is removed from the liquid crystal rich region.

[0194] Item 29: The method of item 24, wherein the step of removing at least a portion of the liquid crystal comprises removing substantially all of the liquid crystal in the liquid crystal rich regions.

[0195] Item 30: The method of item 24, wherein the step of removing at least a portion of the liquid crystal further comprises leaving at least a portion of the liquid crystal in the liquid crystal rich regions.

[0196] Item 31: The method of item 24, wherein the step of removing at least a portion of the liquid crystal comprises washing the holographic polymer dispersed liquid crystal grating with a solvent.

[0197] Clause 32: The method of any one of clauses 21 to 31, wherein the first base substrate and / or the second base substrate comprises plastic.

[0198] Item 33: The method of any one of items 21 to 32, wherein a silicon oxide layer is deposited on the first base substrate and / or the second base substrate.

[0199] Clause 34: The method of any one of clauses 21 to 31, wherein the first base substrate and / or the second base substrate comprises glass, quartz, or silica.

[0200] Clause 35: The method of any one of clauses 21 to 31, wherein the cover substrate comprises plastic.

[0201] Item 36: The method of item 35, wherein a silicon oxide layer is deposited on the cover substrate.

[0202] Clause 37: The method of any one of clauses 21 to 31, wherein the cover substrate comprises glass, quartz, or silica.

[0203] Item 38: The method of any one of items 21 to 31, wherein an adhesion promoting layer that promotes adhesion between the first base substrate and the first holographic polymer dispersed liquid crystal grating is coated on top of the first base substrate.

[0204] Item 39: The method of item 38, wherein the first base substrate comprises a glass surface containing hydroxyl groups, and the silane-based reagent bonds with the hydroxyl groups and the adhesion promoting layer.

[0205] Item 40: The method of any one of items 21 to 39, wherein a release layer is coated on top of the cover substrate that allows the cover substrate to be easily released from the holographic polymer dispersed liquid crystal grating.

[0206] Item 41: The method of item 40, wherein the cover substrate comprises a glass surface containing hydroxyl groups and the release layer is a silane-based fluoro reactant that bonds with the hydroxyl groups.

[0207] Item 42: A device for producing deep surface relief gratings (SRGs), comprising: a holographic mixture sandwiched between a base substrate and a cover substrate; the holographic mixture is configured, when exposed to a holographic recording beam, to form a holographic polymer dispersed liquid crystal grating comprising alternating polymer rich and liquid crystal rich regions; The base substrate and the cover substrate have different properties such that the cover substrate can be removed from the formed holographic polymer dispersed liquid crystal grating after exposure, while it can adhere to the unexposed holographic mixture layer.

[0208] Clause 43: The device of Clause 42, wherein the base substrate comprises plastic.

[0209] Clause 44: The device of clause 43, wherein a silicon oxide layer is disposed on the base substrate.

[0210] Clause 45: The device of clause 42, wherein the base substrate comprises glass, quartz, or silica.

[0211] Clause 46: The device of clause 45, wherein the cover substrate comprises plastic.

[0212] Item 47: The device of item 46, wherein a silicon oxide layer is disposed on the cover substrate.

[0213] Clause 48: The device of clause 42, wherein the cover substrate comprises glass, quartz, or silica.

[0214] Item 49: The device of any one of items 42 to 48, wherein an adhesion promoting layer that promotes adhesion between the first base substrate and the first holographic polymer dispersed liquid crystal grating is coated on top of the first base substrate.

[0215] Item 50: The device of item 49, wherein the first base substrate comprises a glass surface containing hydroxyl groups, and the silane-based reagent bonds with the hydroxyl groups and the adhesion promoting layer.

[0216] Item 51: The device of any one of items 42 to 50, wherein a release layer is coated on top of the cover substrate that allows the cover substrate to be easily released from the holographic polymer dispersed liquid crystal grating.

[0217] Item 52: The device of item 51, wherein the cover substrate comprises a glass surface containing hydroxyl groups and the release layer is a silane-based fluoro-reactive material that bonds with the hydroxyl groups.

[0218] Item 53: A method for manufacturing a semiconductor laser, comprising: a waveguide supporting a polymer grating structure for diffracting light propagating therethrough by total internal reflection; The polymer lattice structure is A polymer region; a void between adjacent portions of the polymer region; and a cladding disposed on top of the polymer region and on top of the waveguide; A waveguide device comprising:

[0219] Clause 54: The waveguide device of clause 53, wherein the coating comprises a metal or dielectric layer deposited by atomic layer deposition (ALD) to enhance evanescent coupling between the waveguide and the polymer grating structure.

[0220] Clause 55: The waveguide device of clause 53, wherein the coating comprises a metal or dielectric layer deposited by atomic layer deposition (ALD) to increase the effective refractive index of the polymer grating structure.

[0221] Clause 56: The waveguide device of clause 53, wherein the coating comprises a metal or dielectric layer deposited by atomic layer deposition (ALD) to enhance adhesion and / or to act as a bias layer.

[0222] Clause 57: The waveguide device of clause 53, wherein the coating comprises a conformally deposited metal or dielectric layer by atomic layer deposition (ALD) disposed over the entire polymer region and over the top of the waveguide.

[0223] Clause 58. The waveguide device of clause 53, wherein the coating comprises an atomic layer deposition (ALD) deposited metal or dielectric layer disposed over one or more surfaces of the polymer region, including one or more of an upper surface, a lower surface, or a sidewall surface of the polymer region.

[0224] Clause 59: The waveguide device of clause 53, wherein a passivation coating is applied to a surface of the polymer grating structure and / or coating.

[0225] Item 60: The waveguide device of Item 53, wherein the polymer region includes a tilt angle relative to the waveguide.

[0226] Item 61: The waveguide device of item 53, wherein the polymer grating structure further comprises an isotropic material between adjacent portions of the polymer network, the isotropic material having a refractive index higher or lower than the refractive index of the polymer network.

[0227] Item 62: The waveguide device of item 61, wherein the isotropic material occupies a bottom portion of the space between adjacent portions of the polymer network and air occupies a space above a top surface of the isotropic material to the modulation depth.

[0228] Item 63: The waveguide device of Item 61, wherein the isotropic material includes a birefringent crystalline material.

[0229] Item 64: The waveguide device of Item 63, wherein the birefringent crystal material comprises a liquid crystal material.

[0230] Item 65: The waveguide device of item 53, wherein the polymer grating structure has a modulation depth greater than the wavelength of visible light.

[0231] Item 66: The waveguide device of item 53, wherein the polymer grating structure has a modulation depth and a grating pitch, the modulation depth being greater than the grating pitch.

[0232] Item 67: The waveguide device of item 53, wherein the waveguide comprises two substrates and the polymer grating structure is either sandwiched between the two substrates or positioned on an outer surface of either substrate.

[0233] Item 68: The waveguide device of item 53, wherein the Bragg fringe spacing of the polymer network is from 0.35 μm to 0.8 μm and the grating depth of the polymer network is from 1 μm to 3 μm.

[0234] Item 69: The waveguide device of item 53, wherein the ratio of the grating depth of the polymer network to the Bragg fringe spacing is from 1:1 to 5:1.

[0235] Item 70: The waveguide device of item 53, further comprising an image generating unit, wherein the polymer grating structure comprises a waveguide diffraction grating.

[0236] Item 71: The waveguide device of Item 70, wherein the waveguide grating is configured as a multiplexed grating.

[0237] Item 72: The waveguide device of item 71, wherein the waveguide grating is configured to receive light from an image generating unit that includes a plurality of images.

[0238] Item 73: The waveguide device of item 70, wherein the waveguide grating is configured to extract light from the waveguide.

[0239] Item 74: The waveguide device of Item 70, wherein the waveguide grating is configured as a beam expander.

[0240] Item 75: The waveguide device of item 70, wherein the waveguide grating is configured to receive light containing image data generated from the image generating unit.

[0241] Item 76: The waveguide device of item 75, wherein the waveguide grating is further configured to couple S-polarized light with a high degree of efficiency.

[0242] Item 77: The waveguide device of Item 76, wherein the diffraction grating is further configured to couple S-polarized light at the Bragg angle with an efficiency of between 70% and 95%.

[0243] Item 78: The waveguide device of Item 76, wherein the diffraction grating is further configured to harvest P-polarized light with an efficiency of between 25% and 50% at the Bragg angle.

[0244] Item 79: The waveguide device of item 53, wherein the difference in refractive index between the polymer network and the air gap is from 0.25 to 0.4.

[0245] Item 80: The waveguide device of item 63, wherein the difference in refractive index between the polymer network and the birefringent crystal material is from 0.05 to 0.2.

[0246] Item 81: The waveguide device of item 53, wherein the polymer grating structure comprises a two-dimensional grating structure or a three-dimensional grating structure.

[0247] Item 82: The waveguide device of item 53, further comprising another grating structure.

[0248] Clause 83: The waveguide device of clause 82, wherein the polymer grating structure comprises an intake grating and the other grating structure comprises a beam expander or extraction grating.

[0249] Item 84: A method according to claim 8, comprising: a waveguide supporting a polymer grating structure for diffracting light propagating therein by total internal reflection; The polymer lattice structure is A polymer region; a void between adjacent portions of the polymer region; and an optical layer disposed between the polymer region and the waveguide; a coating disposed over the polymer region and over the optical layer; A waveguide device comprising:

[0250] Clause 85: The waveguide device of clause 84, wherein the coating comprises a metal or dielectric layer deposited by atomic layer deposition (ALD) to enhance evanescent coupling between the waveguide and the polymer grating structure.

[0251] Clause 86: The waveguide device of clause 84, wherein the coating comprises a metal or dielectric layer deposited by atomic layer deposition (ALD) to increase the effective refractive index of the polymer grating structure.

[0252] Clause 87: The waveguide device of clause 84, wherein the coating comprises a metal or dielectric layer deposited by atomic layer deposition (ALD) to enhance adhesion and / or to act as a bias layer.

[0253] Clause 88: The waveguide device of clause 84, wherein the coating comprises a metal or dielectric layer conformally deposited by atomic layer deposition (ALD) disposed over the entire polymer region and the exposed top portion of the optical layer.

[0254] Clause 89: The waveguide device of clause 84, wherein the coating comprises an atomic layer deposition (ALD) deposited metal or dielectric layer disposed over one or more surfaces of the polymer region, including one or more of an upper surface, a lower surface, or a sidewall surface of the polymer region.

[0255] Item 90: The waveguide device of item 84, wherein a passivation coating is applied to a surface of the polymer grating structure.

[0256] Item 91: The waveguide device of Item 84, wherein the polymer region includes a tilt angle relative to the waveguide.

[0257] Item 92: The waveguide device of item 84, wherein the thicknesses of the optical layers are designed to selectively vary the diffraction efficiency versus angular profile within a predetermined range of angles.

[0258] Item 93: The waveguide device of item 84, wherein the polymer grating structure further comprises an isotropic material between adjacent portions of the polymer network, the isotropic material having a refractive index higher or lower than the refractive index of the polymer network.

[0259] Item 94: The waveguide device of item 93, wherein the isotropic material occupies a bottom portion of the space between adjacent portions of the polymer network and air occupies a space above a top surface of the isotropic material to the modulation depth.

[0260] Item 95: The waveguide device of Item 93, wherein the isotropic material includes a birefringent crystalline material.

[0261] Item 96: The waveguide device of item 95, wherein the birefringent crystal material comprises a liquid crystal material.

[0262] Item 97: The waveguide device of item 84, wherein the polymer grating structure has a modulation depth greater than the wavelength of visible light.

[0263] Item 98: The waveguide device of item 84, wherein the polymer grating structure has a modulation depth and a grating pitch, the modulation depth being greater than the grating pitch.

[0264] Item 99: The waveguide device of item 84, wherein the waveguide comprises two substrates and the polymer grating structure is either sandwiched between the two substrates or positioned on an outer surface of either substrate.

[0265] Item 100: The waveguide device of item 84, wherein the Bragg fringe spacing of the polymer network is from 0.35 μm to 0.8 μm, and the grating depth of the polymer network is from 1 μm to 3 μm.

[0266] Item 101: The waveguide device of item 84, wherein the ratio of the grating depth of the polymer network to the Bragg fringe spacing is from 1:1 to 5:1.

[0267] Item 102: The waveguide device of item 84, further comprising an image generating unit, wherein the polymer grating structure comprises a waveguide diffraction grating.

[0268] Item 103: The waveguide device of Item 102, wherein the waveguide grating is configured as a multiplexed grating.

[0269] Item 104: The waveguide device of item 103, wherein the waveguide grating is configured to receive light from an image generating unit that includes a plurality of images.

[0270] Item 105: The waveguide device of item 104, wherein the waveguide grating is configured to extract light from the waveguide.

[0271] Item 106: The waveguide device of Item 102, wherein the waveguide grating is configured as a beam expander.

[0272] Item 107: The waveguide device of item 102, wherein the waveguide grating is configured to receive light containing image data generated from the image generating unit.

[0273] Item 108: The waveguide device of Item 107, wherein the waveguide grating is further configured to couple S-polarized light with a high degree of efficiency.

[0274] Item 109: The waveguide device of Item 108, wherein the diffraction grating is further configured to couple S-polarized light at the Bragg angle with an efficiency of between 70% and 95%.

[0275] Item 110: The waveguide device of Item 108, wherein the diffraction grating is further configured to harvest P-polarized light with an efficiency of between 25% and 50% at the Bragg angle.

[0276] Item 111: The waveguide device of item 84, wherein the difference in refractive index between the polymer network and the air gap is from 0.25 to 0.4.

[0277] Item 112: The waveguide device of item 95, wherein the difference in refractive index between the polymer network and the birefringent crystal material is from 0.05 to 0.2.

[0278] Item 113: The waveguide device of item 84, wherein the polymer grating structure comprises a two-dimensional grating structure or a three-dimensional grating structure.

[0279] Item 114: The waveguide device of item 84, further comprising another grating structure.

[0280] Item 115: The waveguide device of item 114, wherein the polymer grating structure comprises an intake grating and the other grating structure comprises a beam expander or extraction grating.

[0281] Item 116: A method for manufacturing a semiconductor laser, comprising: a waveguide supporting a polymer grating structure for diffracting light propagating therethrough by total internal reflection; The polymer lattice structure is A polymer region; a void between adjacent portions of the polymer region; and an optical layer disposed between the polymer region and the waveguide; A waveguide device comprising:

[0282] Item 117: The waveguide device of item 116, wherein the thicknesses of the optical layers are designed to selectively vary the diffraction efficiency versus angular profile within a predetermined range of angles.

[0283] Item 118: The waveguide device of item 116, wherein the polymer grating structure further comprises an isotropic material between adjacent portions of the polymer network, the isotropic material having a refractive index higher or lower than the refractive index of the polymer network.

[0284] Item 119: The waveguide device of item 118, wherein the isotropic material occupies a bottom portion of the space between adjacent portions of the polymer network and air occupies a space above a top surface of the isotropic material to the modulation depth.

[0285] Item 120: The waveguide device of Item 118, wherein the isotropic material comprises a birefringent crystalline material.

[0286] Item 121: The waveguide device of item 120, wherein the birefringent crystal material comprises a liquid crystal material.

[0287] Item 122: The waveguide device of item 118, wherein the polymer grating structure has a modulation depth greater than the wavelength of visible light.

[0288] Item 123: The waveguide device of item 118, wherein the polymer grating structure has a modulation depth and a grating pitch, the modulation depth being greater than the grating pitch.

[0289] Item 124: The waveguide device of item 118, wherein the waveguide comprises two substrates and the polymer grating structure is either sandwiched between the two substrates or positioned on an outer surface of either substrate.

[0290] Item 125. The waveguide device of item 118, wherein the Bragg fringe spacing of the polymer network is from 0.35 μm to 0.8 μm, and the grating depth of the polymer network is from 1 μm to 3 μm.

[0291] Item 126: The waveguide device of item 118, wherein the ratio of grating depth of the polymer network to Bragg fringe spacing is from 1:1 to 5:1.

[0292] Item 127: The waveguide device of item 118, further comprising an image generating unit, wherein the polymer grating structure comprises a waveguide diffraction grating.

[0293] Item 128: The waveguide device of Item 127, wherein the waveguide grating is configured as a multiplexed grating.

[0294] Item 129: The waveguide device of item 128, wherein the waveguide grating is configured to accept light from an image generating unit that includes a plurality of images.

[0295] Item 130: The waveguide device of item 127, wherein the waveguide grating is configured to extract light from the waveguide.

[0296] Item 131: The waveguide device of Item 130, wherein the waveguide grating is configured as a beam expander.

[0297] Item 132: The waveguide device of item 127, wherein the waveguide grating is configured to receive light containing image data generated from the image generating unit.

[0298] Item 133: The waveguide device of Item 132, wherein the waveguide grating is further configured to couple S-polarized light with a high degree of efficiency.

[0299] Item 134: The waveguide device of Item 133, wherein the diffraction grating is further configured to couple S-polarized light with an efficiency of between 70% and 95% at the Bragg angle.

[0300] Item 135: The waveguide device of Item 133, wherein the diffraction grating is further configured to harvest P-polarized light with an efficiency of between 25% and 50% at the Bragg angle.

[0301] Item 136: The waveguide device of item 116, wherein the difference in refractive index between the polymer network and the void is from 0.25 to 0.4.

[0302] Item 137: The waveguide device of item 120, wherein the difference in refractive index between the polymer network and the birefringent crystal material is from 0.05 to 0.2.

[0303] Item 138: The waveguide device of item 116, wherein the polymer grating structure comprises a two-dimensional grating structure or a three-dimensional grating structure.

[0304] Item 139: The waveguide device of item 116, further comprising another grating structure.

[0305] Item 140: The waveguide device of item 139, wherein the polymer grating structure comprises an intake grating and the other grating structure comprises a beam expander or extraction grating.

[0306] Item 141: The waveguide device of item 116, wherein the optical layer is sandwiched between the waveguide and the polymer grating structure, and the polymer grating structure extends all the way to the optical layer for direct contact with the optical layer.

[0307] Item 142: A method for manufacturing a semiconductor laser, comprising: a waveguide supporting a polymer grating structure for diffracting light propagating therethrough by total internal reflection; The polymer lattice structure is A polymer region; Voids between adjacent portions of the polymer domain; Equipped with A waveguide device, wherein the polymer region and the void are in direct contact with the waveguide.

[0308] Item 143: The waveguide device of item 142, wherein the thicknesses of the optical layers are designed to selectively vary the diffraction efficiency versus angular profile within a predetermined range of angles.

[0309] Item 144: The waveguide device of item 142, wherein the polymer surface relief grating extends all the way to directly contact the waveguide.

[0310] Item 145: The waveguide device of item 142, wherein there is no bias layer between the polymer surface relief grating and the substrate.

[0311] Item 146: The waveguide device of item 142, wherein the polymer grating structure further comprises an isotropic material between adjacent portions of the polymer network, the isotropic material having a refractive index higher or lower than the refractive index of the polymer network.

[0312] Item 147: The waveguide device of item 146, wherein the isotropic material occupies a bottom portion of the space between adjacent portions of the polymer network and air occupies a space above a top surface of the isotropic material to the modulation depth.

[0313] Item 148: The waveguide device of Item 146, wherein the isotropic material comprises a birefringent crystalline material.

[0314] Item 149: The waveguide device of item 148, wherein the birefringent crystal material comprises a liquid crystal material.

[0315] Item 150: The waveguide device of item 142, wherein the polymer grating structure has a modulation depth greater than the wavelength of visible light.

[0316] Item 151: The waveguide device of item 142, wherein the polymer grating structure has a modulation depth and a grating pitch, the modulation depth being greater than the grating pitch.

[0317] Item 152: The waveguide device of item 142, wherein the waveguide comprises two substrates and the polymer grating structure is either sandwiched between the two substrates or positioned on an outer surface of either substrate.

[0318] Item 153. The waveguide device of item 142, wherein the Bragg fringe spacing of the polymer network is from 0.35 μm to 0.8 μm, and the grating depth of the polymer network is from 1 μm to 3 μm.

[0319] Item 154: The waveguide device of item 142, wherein the ratio of grating depth of the polymer network to the Bragg fringe spacing is from 1:1 to 5:1.

[0320] Item 155: The waveguide device of item 142, further comprising an image generating unit, wherein the polymer grating structure comprises a waveguide diffraction grating.

[0321] Item 156: The waveguide device of Item 155, wherein the waveguide grating is configured as a multiplexed grating.

[0322] Item 157: The waveguide device of item 156, wherein the waveguide grating is configured to accept light from an image generating unit that includes a plurality of images.

[0323] Item 158: The waveguide device of item 155, wherein the waveguide grating is configured to extract light from the waveguide.

[0324] Item 159: The waveguide device of Item 155, wherein the waveguide grating is configured as a beam expander.

[0325] Item 160: The waveguide device of item 155, wherein the waveguide grating is configured to receive light containing image data generated from the image generating unit.

[0326] Item 161: The waveguide device of Item 160, wherein the waveguide grating is further configured to couple S-polarized light with a high degree of efficiency.

[0327] Item 162: The waveguide device of Item 160, wherein the waveguide grating is further configured to couple S-polarized light with an efficiency of between 70% and 95% at the Bragg angle.

[0328] Item 163: The waveguide device of Item 160, wherein the diffraction grating is further configured to harvest P-polarized light with an efficiency of between 25% and 50% at the Bragg angle.

[0329] Item 164: The waveguide device of item 142, wherein the difference in refractive index between the polymer network and the air gap is from 0.25 to 0.4.

[0330] Item 165: The waveguide device of item 164, wherein the difference in refractive index between the polymer network and the birefringent crystal material is from 0.05 to 0.2.

[0331] Item 166: The waveguide device of item 142, wherein the polymer grating structure comprises a two-dimensional grating structure or a three-dimensional grating structure.

[0332] Item 167: The waveguide device of item 142, further comprising another grating structure.

[0333] Item 168: The waveguide device of item 167, wherein the polymer grating structure comprises an intake grating and the other grating structure comprises a beam expander or extraction grating.

[0334] Item 169: A method for making a lattice, comprising the steps of: Providing a mixture of monomer and non-reactive material; Providing a substrate; depositing a layer of the mixture onto a surface of a substrate; applying a holographic recording beam to the layer to form a holographic polymer dispersion grating comprising alternating polymer-rich regions and non-reactive material-rich regions; removing at least a portion of the non-reactive material in the non-reactive material-rich regions to form a polymeric surface relief grating comprising alternating polymer and air regions; applying a coating to an upper surface of the polymer region and to an upper surface of the substrate in the air region; The method includes:

[0335] Item 170: The method of item 169, wherein the step of applying the coating comprises an atomic layer deposition (ALD) process.

[0336] Item 171: Coating is TiO 2 or ZnO 2 The method of claim 169,

[0337] Item 172: The method of item 169, wherein the monomer comprises an acrylate, a methacrylate, a vinyl, an isocyanate, a thiol, an isocyanacrylate, and / or a thiolene.

[0338] Item 173: The method of item 172, wherein the mixture further comprises at least one of a photoinitiator, a coinitiator, or an additional additive.

[0339] Item 174: The method of item 172, wherein the thiol comprises a thiol vinyl acrylate.

[0340] Item 175: The method of item 173, wherein the photoinitiator comprises a photosensitive component.

[0341] Item 176: The method of item 175, wherein the photosensitive component comprises a dye and / or a radical generator.

[0342] Item 177: The step of providing a mixture of monomers and liquid crystals comprises: mixing a monomer, a liquid crystal, and at least one of a photoinitiator, a coinitiator, a multifunctional thiol, or an additional additive; storing the mixture in the dark at a temperature not exceeding 22°C; adding additional monomer; filtering the mixture through a 0.6 μm or smaller filter; Store the filtered mixture in a dark place. The method of claim 169,

[0343] Item 178: The method of item 169, wherein the substrate comprises a glass substrate or a plastic substrate.

[0344] Item 179: The method of item 169, wherein the substrate comprises a transparent substrate.

[0345] Item 180: The method of item 169, further comprising sandwiching the mixture between the substrate and another substrate with one or more spacers to maintain internal dimensions.

[0346] Item 181: The method of item 180, further comprising applying an anti-adhesion release layer to a surface of the other substrate.

[0347] Item 182: The method of item 181, wherein the anti-adhesive release layer comprises a fluoropolymer.

[0348] Item 183: The method of item 169, further comprising the step of refilling the liquid crystal rich region with liquid crystal material.

[0349] Item 184: The method of item 183, wherein the liquid crystal material has a different molecular structure than the previously removed liquid crystal.

[0350] Item 185: The method of item 169, wherein removing at least a portion of the liquid crystal comprises removing substantially all of the liquid crystal in the liquid crystal rich regions.

[0351] Item 186: The method of item 169, wherein the step of removing at least a portion of the liquid crystal further comprises leaving at least a portion of the liquid crystal in the polymer-rich regions.

[0352] Item 187: The method of item 169, further comprising applying a protective layer over the deep SRG.

[0353] Item 188: The method of item 187, wherein the protective layer comprises an anti-reflective layer.

[0354] Item 189: The method of item 187, wherein the protective layer comprises a silicate or silicon nitride.

[0355] Item 190: The method of item 187, wherein the step of applying the protective layer includes depositing the protective layer in the deep SRG.

[0356] Item 191: The method of item 190, wherein depositing the protective layer comprises chemical vapor deposition.

[0357] Item 192: The method of item 191, wherein the chemical vapor deposition is a nanocoating process.

[0358] Clause 193: The method of clause 190, wherein the protective layer comprises a parylene coating.

[0359] Item 194: The method of item 169, wherein the liquid crystal rich region comprises an air gap after removing at least a portion of the liquid crystal in the liquid crystal rich region.

[0360] Clause 195: The method of clause 194, further comprising creating a vacuum in the gap or filling the gap with an inert gas.

[0361] Item 196: The method of item 169, wherein the step of removing at least a portion of the liquid crystal comprises washing the holographic polymer dispersed liquid crystal grating with a solvent.

[0362] Item 197: The method of item 196, wherein washing the holographic polymer dispersed liquid crystal grating comprises immersing the holographic polymer dispersed liquid crystal grating in a solvent.

[0363] Item 198: The method of item 196, wherein the solvent comprises isopropyl alcohol.

[0364] Item 199: The method of item 196, wherein the solvent is maintained at a temperature below room temperature while washing the holographic polymer dispersed liquid crystal grating.

[0365] Item 200: The method of item 196, wherein the step of removing at least a portion of the liquid crystal further comprises drying the holographic polymer dispersed liquid crystal grating with a high flow air source.

[0366] Item 201: The method of item 169, further comprising the step of curing the holographic polymer dispersed liquid crystal grating.

[0367] Item 202: The method of item 201, wherein the step of curing the holographic polymer dispersed liquid crystal grating includes exposing the holographic polymer dispersed liquid crystal grating to low intensity white light for a period of about one hour.

[0368] Item 203: The method of item 169, wherein the polymer surface relief grating is configured to capture S-polarized light with an efficiency of between 70% and 95%.

[0369] Item 204: The method of item 203, wherein the polymer surface relief grating is further configured to harvest P-polarized light with an efficiency of between 25% and 50%.

[0370] Item 205: The method of item 169, wherein the difference in refractive index between the polymer network and the voids is from 0.25 to 0.4.

[0371] Item 206: The method of item 183, wherein the difference in refractive index between the polymer network and the liquid crystal material is from 0.05 to 0.2.

[0372] Item 207: The method of item 169, wherein the polymer surface relief grating has a Bragg fringe spacing of 0.35 μm to 0.8 μm and a grating depth of 1 μm to 3 μm.

[0373] Item 208: The method of item 169, wherein the polymer surface relief grating has a ratio of Bragg fringe spacing to grating depth of from 1:1 to 5:1.

[0374] Item 209: The method of item 169, wherein the liquid crystal content in the mixture of monomer and liquid crystal is approximately 20% to 50%.

[0375] Item 210: The method of item 169, wherein the liquid crystal in the mixture of monomer and liquid crystal comprises a liquid crystal single.

[0376] Item 211: The method of item 210, wherein the liquid crystal singlet comprises cyanobiphenyl and / or pentylcyanobiphenyl.

[0377] Item 212: A method for making a lattice, comprising the steps of: Providing a mixture of monomer and non-reactive material; Providing a substrate; depositing a layer of the mixture onto a surface of a substrate; applying a holographic recording beam to the layer to form a holographic polymer dispersion grating comprising alternating polymer-rich regions and non-reactive material-rich regions; removing at least a portion of the non-reactive material in the non-reactive material-rich regions to form a polymeric surface relief grating comprising alternating polymer regions and air regions, the optical layer being disposed between the polymer regions and the substrate; applying a coating to the top surface of the polymer region and to the top surface of the optical layer in the air region; The method includes:

[0378] Item 213: The method of item 212, wherein the step of applying the coating includes an atomic layer deposition (ALD) process.

[0379] Item 214: Coating is TiO 2 or ZnO 2 The method of claim 212,

[0380] Item 215: The method of item 212, wherein the monomer comprises an acrylate, a methacrylate, a vinyl, an isocyanate, a thiol, an isocyanacrylate, and / or a thiolene.

[0381] Item 216: The method of item 215, wherein the mixture further comprises at least one of a photoinitiator, a coinitiator, or an additional additive.

[0382] Item 217: The method of item 215, wherein the thiol comprises a thiol vinyl acrylate.

[0383] Item 218: The method of item 216, wherein the photoinitiator comprises a photosensitive component.

[0384] Item 219: The method of item 218, wherein the photosensitive component comprises a dye and / or a radical generator.

[0385] Item 220: The step of providing a mixture of monomers and liquid crystals includes: mixing a monomer, a liquid crystal, and at least one of a photoinitiator, a coinitiator, a multifunctional thiol, or an additional additive; storing the mixture in the dark at a temperature not exceeding 22°C; adding additional monomer; filtering the mixture through a 0.6 μm or smaller filter; Store the filtered mixture in a dark place. The method of claim 212,

[0386] Item 221: The method of item 212, wherein the substrate comprises a glass substrate or a plastic substrate.

[0387] Item 222: The method of item 212, wherein the substrate comprises a transparent substrate.

[0388] Item 223: The method of item 212, further comprising sandwiching the mixture between the substrate and another substrate with one or more spacers to maintain internal dimensions.

[0389] Item 224: The method of item 223, further comprising applying an anti-adhesion release layer to a surface of the other substrate.

[0390] Item 225: The method of item 224, wherein the anti-adhesive release layer comprises a fluoropolymer.

[0391] Item 226: The method of item 212, further comprising the step of refilling the liquid crystal rich region with liquid crystal material.

[0392] Item 227: The method of item 226, wherein the liquid crystal material has a different molecular structure than the previously removed liquid crystal.

[0393] Item 228: The method of item 212, wherein removing at least a portion of the liquid crystal comprises removing substantially all of the liquid crystal in the liquid crystal rich regions.

[0394] Item 229: The method of item 212, wherein the step of removing at least a portion of the liquid crystal further comprises leaving at least a portion of the liquid crystal in the polymer-rich regions.

[0395] Item 230: The method of item 212, further comprising applying a protective layer over the deep SRG.

[0396] Item 231: The method of item 230, wherein the protective layer comprises an anti-reflective layer.

[0397] Item 232: The method of item 230, wherein the protective layer comprises a silicate or silicon nitride.

[0398] Item 233: The method of item 230, wherein the step of applying the protective layer includes depositing the protective layer in the deep SRG.

[0399] Item 234: The method of item 233, wherein depositing the protective layer comprises chemical vapor deposition.

[0400] Item 235: The method of item 234, wherein the chemical vapor deposition is a nanocoating process.

[0401] Item 236: The method of item 230, wherein the protective layer comprises a parylene coating.

[0402] Item 237: The method of item 212, wherein the liquid crystal rich region comprises an air gap after removing at least a portion of the liquid crystal in the liquid crystal rich region.

[0403] Item 238: The method of item 237, further comprising creating a vacuum in the void or filling the void with an inert gas.

[0404] Item 239: The method of item 212, wherein the step of removing at least a portion of the liquid crystal comprises washing the holographic polymer dispersed liquid crystal grating with a solvent.

[0405] Item 240: The method of item 239, wherein washing the holographic polymer dispersed liquid crystal grating comprises immersing the holographic polymer dispersed liquid crystal grating in a solvent.

[0406] Item 241: The method of item 239, wherein the solvent comprises isopropyl alcohol.

[0407] Item 242: The method of item 239, wherein the solvent is maintained at a temperature below room temperature while washing the holographic polymer dispersed liquid crystal grating.

[0408] Item 243: The method of item 239, wherein the step of removing at least a portion of the liquid crystal further comprises drying the holographic polymer dispersed liquid crystal grating with a high flow air source.

[0409] Item 244: The method of item 212, further comprising the step of curing the holographic polymer dispersed liquid crystal grating.

[0410] Item 245: The method of item 244, wherein the step of curing the holographic polymer dispersed liquid crystal grating includes exposing the holographic polymer dispersed liquid crystal grating to low intensity white light for a period of about one hour.

[0411] Item 246: The method of item 212, wherein the polymer surface relief grating is configured to capture S-polarized light with an efficiency of between 70% and 95%.

[0412] Item 247: The method of item 246, wherein the polymer surface relief grating is further configured to harvest P-polarized light with an efficiency of between 25% and 50%.

[0413] Item 248: The method of item 212, wherein the difference in refractive index between the polymer network and the voids is from 0.25 to 0.4.

[0414] Item 249: The method of item 226, wherein the difference in refractive index between the polymer network and the liquid crystal material is from 0.05 to 0.2.

[0415] Item 250: The method of item 212, wherein the polymer surface relief grating has a Bragg fringe spacing of 0.35 μm to 0.8 μm and a grating depth of 1 μm to 3 μm.

[0416] Item 251 : The method of item 212, wherein the polymeric surface relief grating has a ratio of Bragg fringe spacing to grating depth of from 1:1 to 5:1.

[0417] Item 252: The method of item 212, wherein the liquid crystal content in the mixture of monomer and liquid crystal is approximately 20% to 50%.

[0418] Item 253: The method of item 212, wherein the liquid crystal in the mixture of the monomer and the liquid crystal comprises a liquid crystal single.

[0419] Item 254: The method of item 253, wherein the liquid crystal single comprises cyanobiphenyl and / or pentylcyanobiphenyl.

[0420] Item 255: A method for making a lattice, comprising the steps of: Providing a mixture of monomer and non-reactive material; Providing a substrate; depositing a layer of the mixture onto a surface of a substrate; applying a holographic recording beam to the layer to form a holographic polymer dispersion grating comprising alternating polymer-rich regions and non-reactive material-rich regions; removing at least a portion of the non-reactive material in the non-reactive material-rich regions to form a polymeric surface relief grating comprising alternating polymer and air regions; performing a plasma ashing process to remove at least a portion of the polymer from the polymer region; The method includes:

[0421] Item 256: The method of item 255, wherein the mixture includes a chemical additive to enhance the effectiveness of the plasma ashing process.

[0422] Item 257: The method of item 256, wherein the plasma ashing process includes a reactive species that includes oxygen and the mixture includes nitrogen to control the plasma ashing rate.

[0423] Item 258: The method of item 256, wherein the plasma ashing process includes reactive species including oxygen, fluorine, and / or hydrogen.

[0424] Item 259: The method of item 258, wherein the plasma ashing process includes a plasma mixture of nitrogen and hydrogen.

[0425] Item 260: The method of item 259, wherein the plasma mixture further comprises fluorine.

[0426] Item 261: The method of item 255, wherein the monomer comprises an acrylate, a methacrylate, a vinyl, an isocyanate, a thiol, an isocyanacrylate, and / or a thiolene.

[0427] Item 262: The method of item 261, wherein the mixture further comprises at least one of a photoinitiator, a coinitiator, or an additional additive.

[0428] Item 263: The method of item 261, wherein the thiol comprises a thiol vinyl acrylate.

[0429] Item 264: The method of item 262, wherein the photoinitiator comprises a photosensitive component.

[0430] Item 265: The method of item 264, wherein the photosensitive component comprises a dye and / or a radical generator.

[0431] Item 266: The step of providing a mixture of monomers and liquid crystals comprises: mixing a monomer, a liquid crystal, and at least one of a photoinitiator, a coinitiator, a multifunctional thiol, or an additional additive; storing the mixture in the dark at a temperature not exceeding 22°C; adding additional monomer; filtering the mixture through a 0.6 μm or smaller filter; Store the filtered mixture in a dark place. The method of claim 255, including:

[0432] Item 267: The method of item 255, wherein the substrate comprises a glass substrate or a plastic substrate.

[0433] Item 268: The method of item 255, wherein the substrate comprises a transparent substrate.

[0434] Item 269: The method of item 255, further comprising sandwiching the mixture between the substrate and another substrate with one or more spacers to maintain internal dimensions.

[0435] Item 270: The method of item 265, further comprising applying an anti-adhesion release layer to a surface of the other substrate.

[0436] Item 271: The method of item 270, wherein the anti-adhesive release layer comprises a fluoropolymer.

[0437] Item 272: The method of item 255, further comprising the step of refilling the liquid crystal rich region with liquid crystal material.

[0438] Item 273: The method of item 272, wherein the liquid crystal material has a different molecular structure than the previously removed liquid crystal.

[0439] Item 274: The method of item 255, wherein removing at least a portion of the liquid crystal comprises removing substantially all of the liquid crystal in the liquid crystal rich regions.

[0440] Item 275: The method of item 255, wherein the step of removing at least a portion of the liquid crystal further comprises leaving at least a portion of the liquid crystal in the polymer-rich regions.

[0441] Item 276: The method of item 255, further comprising applying a protection layer over the deep SRG.

[0442] Item 277: The method of item 276, wherein the protective layer comprises an anti-reflective layer.

[0443] Item 278: The method of item 276, wherein the protective layer comprises a silicate or silicon nitride.

[0444] Item 279: The method of item 276, wherein the step of applying the protective layer includes depositing the protective layer in the deep SRG.

[0445] Item 280: The method of item 279, wherein depositing the protective layer comprises chemical vapor deposition.

[0446] Item 281: The method of item 280, wherein the chemical vapor deposition is a nanocoating process.

[0447] Item 282: The method of item 276, wherein the protective layer comprises a parylene coating.

[0448] Item 283: The method of item 255, wherein the liquid crystal rich region comprises an air gap after removing at least a portion of the liquid crystal in the liquid crystal rich region.

[0449] Item 284: The method of item 283, further comprising creating a vacuum in the void or filling the void with an inert gas.

[0450] Item 285: The method of item 254, wherein the step of removing at least a portion of the liquid crystal comprises washing the holographic polymer dispersed liquid crystal grating with a solvent.

[0451] Item 286: The method of item 285, wherein washing the holographic polymer dispersed liquid crystal grating comprises immersing the holographic polymer dispersed liquid crystal grating in a solvent.

[0452] Item 287: The method of item 285, wherein the solvent comprises isopropyl alcohol.

[0453] Item 288: The method of item 285, wherein the solvent is maintained at a temperature below room temperature while washing the holographic polymer dispersed liquid crystal grating.

[0454] Item 289: The method of item 285, wherein the step of removing at least a portion of the liquid crystal further comprises drying the holographic polymer dispersed liquid crystal grating with a high flow air source.

[0455] Item 290: The method of item 255, further comprising the step of curing the holographic polymer dispersed liquid crystal grating.

[0456] Item 291: The method of item 290, wherein the step of curing the holographic polymer dispersed liquid crystal grating includes exposing the holographic polymer dispersed liquid crystal grating to low intensity white light for a period of about one hour.

[0457] Item 292: The method of item 255, wherein the polymer surface relief grating is configured to capture S-polarized light with an efficiency of between 70% and 95%.

[0458] Item 293: The method of item 292, wherein the polymer surface relief grating is further configured to harvest P-polarized light with an efficiency of between 25% and 50%.

[0459] Item 294: The method of item 255, wherein the difference in refractive index between the polymer network and the voids is from 0.25 to 0.4.

[0460] Item 295: The method of item 272, wherein the difference in refractive index between the polymer network and the liquid crystal material is from 0.05 to 0.2.

[0461] Item 296: The method of item 255, wherein the polymer surface relief grating has a Bragg fringe spacing of 0.35 μm to 0.8 μm and a grating depth of 1 μm to 3 μm.

[0462] Item 297: The method of item 255, wherein the polymeric surface relief grating has a ratio of Bragg fringe spacing to grating depth of from 1:1 to 5:1.

[0463] Item 298: The method of item 255, wherein the liquid crystal content in the mixture of monomer and liquid crystal is approximately 20% to 50%.

[0464] Item 299: The method of item 255, wherein the liquid crystal in the mixture of the monomer and the liquid crystal comprises a liquid crystal single.

[0465] Item 300: The method of item 299, wherein the liquid crystal single includes cyanobiphenyl and / or pentylcyanobiphenyl.

[0466] Item 301: Immersing the grating in a refractive material to fill air regions and voids in the polymer rich regions formed by removal of non-reactive material to form alternating polymer and refractive material regions; removing the refractive material in the refractive material regions to leave regions of alternating composite polymer and second non-reactive material and air regions; 255. The method of claim 255 for producing a lattice, further comprising:

[0467] Item 302: The method of item 301, wherein the step of removing the refractive material in the refractive material region is performed using a plasma ashing process.

[0468] Item 303: A waveguide, an optical substrate supporting a polymer grating structure for diffracting light propagating in the waveguide by total internal reflection; The polymer lattice structure is A polymer region; a void between adjacent portions of the polymer region, where a portion of the polymer region at the same height as the void forms, together with the void, a surface relief grating; a backfill material region below the void, wherein a portion of the polymer region at the same height as the backfill material region forms a volume lattice with the backfill material region; Equipped with The polymer grating structure comprises a dual interaction grating, where total internally reflected light from a surface relief grating formed by the polymer grating structure interacts with a volume grating formed by the polymer grating structure to provide a first diffraction efficiency for an angular characteristic, and total internally reflected light from an opposite surface of the optical substrate interacts with the volume grating formed by the polymer grating structure to provide a second diffraction efficiency for an angular characteristic.

[0469] Item 304: The waveguide of item 303, wherein the polymer grating structure is a folded grating.

[0470] Item 305: The waveguide of item 303, wherein the grating depth of the polymer grating structure is less than the fringe spacing of the polymer grating structure.

[0471] Item 306: The waveguide of item 303, wherein the grating depth of the polymer grating structure is greater than the fringe spacing of the polymer grating structure.

[0472] Item 307: The waveguide of item 303, wherein total internal reflection from the surface relief grating formed by the polymer grating structure occurs when the reflected first order diffraction from the surface relief grating formed by the polymer grating structure has a diffraction angle equal to the TIR angle of the waveguide.

[0473] Term 308: The waveguide of term 303, wherein the polymer grating structure does not provide a transmitted diffraction order.

[0474] Item 309: The waveguide of item 303, wherein the polymer grating structure is a photonic crystal.

[0475] Term 310: The waveguide of term 303, wherein the polymer grating structure comprises a Raman-Nath grating overlying the Bragg grating, the Raman-Nath grating having the same grating period as the Bragg grating, and a minimum of the Raman-Nath grating overlying a minimum of the Bragg grating.

[0476] Item 311: The waveguide of item 303, wherein the polymer grating structure is a tilted grating.

[0477] Item 312: The waveguide of item 303, wherein the polymer grating structure is a non-tilted grating.

[0478] Term 313: The waveguide of term 303, wherein the backfilled material region has a refractive index different from the refractive index of the polymer rich region.

[0479] Item 314: The waveguide of item 313, wherein the air region and the polymer rich region at the same height as the air region comprise a Raman-Nath grating.

[0480] Item 315: The waveguide of item 314, wherein the region of backfilled material and the polymer-rich region at the same height as the region of backfilled material comprise a volume Bragg grating.

[0481] Doctrine of Equivalents Although the above description contains many specific embodiments of the present invention, these should not be construed as limitations on 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 can be practiced otherwise than as specifically described without departing from the scope and spirit of the present invention. The present embodiments are therefore to be considered in all respects as illustrative and not restrictive. The scope of the present invention should therefore be determined not by the embodiments exemplified, but by the appended claims and their equivalents. [Explanation of symbols]

[0482] 31 Checkered pattern 100 devices 101 Waveguide 102 P diffraction input grating 103P diffraction output grating 104 S diffraction input grating 105 S diffraction output grating 106 OLED Microdisplays 107 Collimation Lens 110 Equipment 111 Upper waveguide layer 112 Lower waveguide layer 113 void 120 Embodiments 121 Unpolarized 130 Equipment 131 Waveguide 132 Curved Surfaces 134 Unpolarized 135 Planar Wavefront 136 TIR road 137, 138, 139 Output rays 139A Curved Output Wavefront 141 Waveguide Substrate 142 Upward curved surface 143 Downward curved surface 140 Waveguide 150 Waveguide device 151 Microdisplay 152 pixel pattern 153 Unpolarized first wavelength light 154 Pre-distorted Wavefront 155 Propagation 156, 157, 158 Output rays 159 Planar output wavefront 160 Waveguide device 161 Curved Substrate Microdisplay 164 Pre-distorted Pixel Patterns 190A, 190B, 190C, 190D, 190 equipment 191 Mixture 192 Transparent Substrate 193, 194 Holographic exposure beam 195 HPDLC Bragg grating 196 Deep Polymer Surface Relief Grating 197 Protective layer 210A, 210B, 210C, 210D, 210E equipment 211 Mixtures, holographic mixture layers 212 Transparent Substrate 213, 214 Holographic exposure beam 215 HPDLC periodic structures, holographic polymer dispersed liquid crystal gratings 216 Polymer Air SRG 217 Hybrid SRG 218 Protective layer, protective substrate Part of a pixel pattern 230A, 230B, 230C, 230D, 230E, 230F Rectangular elements Part of a 240 pixel pattern 240A, 240B, 240C, 240D, 240E, 240F, 240G, 240H, 240I, 240J Penrose tiles Part of a 250 pixel pattern Part of a 260 pixel pattern 260A, 260B, 260C, 260D square elements Part of a pixel pattern 270A, 270B, 270C, 270D Diamond shaped elements Part of a 280 pixel pattern 280A, 280B, 280C, 280D, 280E, 280F, 280G, 280H Isosceles triangle elements 290 Part of a pixel pattern 290A, 290B, 290C hexagonal elements Part of a 300 pixel pattern 300A, 300B, 300C, 300D rectangular elements 310 Part of a pixel pattern 310A, 310B, 310C, 310D Diamond shaped elements Part of a 320 pixel pattern 320A, 320B, 320C, 320D, 320E, 320F, 320G, 320H triangular elements 902a, 902b Polymer high density area 904a, 904b Air region 1502 Cover Board 1602 Holographic composite material 1604 Reagents 1608 Hydroxyl group 1610 Holographic Mixture Layer 1704 Reagents 1902 Covering 2001 Propagation Plane 2002, 2006, 2006a Board 2004 Lattice layer 2008 Eyeglow Light 2010 light 2020 Input Propagation Plane 2021 Output Propagation Plane 2022 k vector 2023 Checkerboard pattern inclination angle 2024 Waveguide surface normal 2025 TIR light 2026 TIR angle 2027 Waveguide plane normal 2028 Ray of light 2029 TIR direction 2030 Second TIR route 2031 TIR angle 2033 Ray of light 2034 TIR direction 2102 Phase separated material 2104 Air Region 2111 Volume lattice part, thick lattice part 2112 Thin grating part, thin substrate relief grating part 2115 High refractive index area 2116 Low refractive index region 2117 Ray Path 2119 First TIR propagation region 2120 Opposite TIR Propagation Direction 2121 Backfilled lattice 2130 Beam-grating interaction geometry 2301 Vacant 2302 Polymer 2303 Air Region 2304 Vacant 2305 Air Region 2306 Polymer and Materials C 2307 void 2802 Raman-Nath surface relief grating 2804 Bragg grating 3000 Polymer-air periodic structures, polymer-air surface relief gratings, polymer-air surface relief Bragg gratings 3002 Waveguide, substrate 3004a Periodic polymer region, polymer domain 3004b void area 3006a Lattice depth 3006b Bragg fringe spacing 3008 Optical layer

Claims

1. 1. A method for fabricating a periodic structure, comprising: providing a holographic mixture on a base substrate; sandwiching the holographic mixture between the base substrate and a cover substrate, the holographic mixture forming a holographic mixture layer on the base substrate; applying a holographic recording beam to the holographic mixture layer to form a holographic polymer dispersed periodic structure comprising alternating polymer-rich and non-reactive material-rich regions; removing the cover substrate from the holographic polymer dispersed periodic structure, the cover substrate having different properties than the base substrate such that after exposure, the cover substrate is removed from the formed holographic polymer dispersed periodic structure and adheres to the unexposed holographic mixture layer; A release layer is coated on top of the cover substrate, which allows the cover substrate to be easily released from the holographic polymer dispersed periodic structures.

2. The method of claim 1 , further comprising removing at least a portion of the non-reactive material in the non-reactive material rich regions to form the holographic polymer dispersed periodic structures.

3. The method of claim 2 further comprising the step of refilling the non-reactive material-rich region with a backfill material.

4. The method of claim 3 , wherein the backfill material has a refractive index different than the refractive index of the remaining polymer-rich region.

5. The method of claim 3 , wherein the backfill material comprises a liquid crystal material.

6. The method of claim 5 , wherein the liquid crystal material is different from the non-reactive material that is removed from the non-reactive material-rich regions.

7. The method of claim 2 , wherein removing at least a portion of the non-reactive material comprises removing substantially all of the non-reactive material in the non-reactive material-rich region.

8. The method of claim 2 , wherein removing at least a portion of the non-reactive material further comprises leaving at least a portion of the non-reactive material in the non-reactive material-rich region.

9. The method of claim 2 , wherein removing at least a portion of the non-reactive material comprises washing the holographic polymer dispersed periodic structure with a solvent.

10. The method of claim 1 , wherein the base substrate comprises plastic.

11. The method of claim 1 , wherein a silicon oxide layer is deposited on the base substrate.

12. The method of claim 1 , wherein the base substrate comprises glass, quartz, or silica.

13. The method of claim 1 , wherein the cover substrate comprises plastic.

14. The method of claim 10 , wherein a silicon oxide layer is deposited on the cover substrate.

15. The method of claim 1 , wherein the cover substrate comprises glass, quartz, or silica.

16. The method of claim 1 , wherein an adhesion promoting layer is coated on top of the base substrate to promote adhesion between the base substrate and the holographic polymer dispersed periodic structures.

17. 17. The method of claim 16, wherein the base substrate comprises a glass surface containing hydroxyl groups, and a silane-based reagent bonds with the hydroxyl groups and the adhesion promoting layer.

18. The method of claim 1 , wherein the cover substrate comprises a glass surface containing hydroxyl groups and the release layer is a silane-based fluoro reactant that bonds with the hydroxyl groups.

19. The method of claim 1 , further comprising applying a protection substrate to the holographic polymer dispersed periodic structure to position the holographic polymer dispersed periodic structure between the protection substrate and the base substrate.

20. The method of claim 1 , wherein the non-reactive material comprises a liquid crystal material.

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