Optical eyepiece using single-sided patterning of grating couplers

Abstract

To provide an optical eyepiece using single-sided patterning of grating couplers.SOLUTION: An eyepiece includes a substrate and an in-coupling grating patterned on a single side of the substrate. A first grating coupler is patterned on the single side of the substrate, and has a first grating pattern. The first grating coupler is optically coupled to the in-coupling grating. A second grating coupler is patterned on the single side of the substrate adjacent to the first grating coupler. The second grating coupler has a second grating pattern different from the first grating pattern. The second grating coupler is optically coupled to the in-coupling grating.SELECTED DRAWING: None

Description

Technical Field

[0001] (Cross - Reference to Related Applications) This application claims the benefit of U.S. Provisional Application No. 62 / 861,646, filed on June 14, 2019, which is incorporated herein by reference in its entirety.

[0002] This disclosure relates to an optical eyepiece lens using one - side patterning of a grating coupler.

Background Art

[0003] Imprint lithography can be used to fabricate nanometer - scale patterns on a wafer. Imprint lithography creates patterns by mechanical deformation of an imprint resist and subsequent processes. However, an eyepiece lens fabricated using imprint lithography may have a limited field of view. Light generally has to travel a long distance to reach the exit pupil expander of the eyepiece lens. As light travels along a long distance, coherent artifacts deteriorate. Also, the conventional two - side lithography used to manufacture eyepiece lenses can increase processing complexity and reduce manufacturing yield and throughput.

Summary of the Invention

Means for Solving the Problems

[0004] The innovative aspects of the subject matter described herein include an optical eyepiece lens using patterning of a grating coupler. The eyepiece lens includes a substrate and an internal coupling grating patterned on one side of the substrate. A first grating coupler is patterned on one side of the substrate and has a first grating pattern. The first grating coupler is optically coupled to the internal coupling grating. A second grating coupler is patterned on one side of the substrate adjacent to the first grating coupler. The second grating coupler has a second grating pattern different from the first grating pattern. The second grating coupler is optically coupled to the internal coupling grating.

[0005] The innovative aspects of the subject matter described herein further include an eyepiece lens including an internal coupling grating that is patterned on one side of a substrate. The internal coupling grating is configured to diffract light received from a projector into a first portion of light and a second portion of light. The first portion of light has a first orientation with respect to the light received from the projector. The second portion of light has a second orientation with respect to the light received from the projector. The second orientation is different from the first orientation. A diffraction grating is patterned on one side of the substrate. The diffraction grating is configured to receive the first portion of light and the second portion of light from the internal coupling grating. The first portion of light and the second portion of light are each diffracted. The diffracted first portion of light and the diffracted second portion of light are combined.

[0006] The innovative aspects of the subject matter described herein further include an eyepiece lens including an internal coupling grating that is imprinted on one side of a substrate. A grating coupler is imprinted on one side of the substrate. The grating coupler is optically coupled to the internal coupling grating. The grating coupler includes a plurality of tiles that define an exit pupil expander (EPE) of the eyepiece lens. Each tile of the plurality of tiles has a first grating pattern. A grating region is interspersed between the tiles. The grating region has a second grating pattern that is different from the first grating pattern. The grating region defines an orthogonal pupil expander (OPE) of the eyepiece lens.

[0007] The innovative aspects of the subject matter described herein further include an eyepiece lens including a substrate having a refractive index greater than a certain threshold. An internal coupling grating is patterned on one side of the substrate. Three or more grating couplers are patterned on one side of the substrate. The three or more grating couplers are optically coupled to the internal coupling grating. Each of the three or more grating couplers has a different grating pattern.

[0008] The innovative aspects of the subject matter described in this specification further include an eyepiece lens including an internal coupling grating that is patterned on a first side of a substrate having a refractive index above a certain threshold or on a second side of the substrate. A first grating coupler is patterned on the first side of the substrate. The first grating coupler has a first grating pattern. The first grating coupler is optically coupled to the internal coupling grating. A second grating coupler is patterned on the second side of the substrate. The second grating coupler has a second grating pattern different from the first grating pattern. The second grating coupler is optically coupled to the internal coupling grating.

[0009] Among other benefits and advantages, the embodiments disclosed herein increase the field of view, efficiency, and uniformity of optical eyepieces for virtual reality and augmented reality applications. Each eyepiece lens can include two or more diffraction gratings that are patterned on the same side of the substrate. The two or more diffraction gratings can be tiled in a layout. The shape, size, density, and distribution of the tiles can be selected to achieve higher optical performance. Also, the embodiments reduce the amount of Mach-Zehnder interference. Since the tiles can be as small as a few hundred microns, the far-field virtual image quality is not affected. The one-sided manufacturing of the eyepiece lens increases the user-to-world ratio of the eyepiece lens. The nano-gratings are blazed or made from a high refractive index material such as a polymer having a refractive index above 1.6, so that a greater amount of light is directed towards the user's eye. In some embodiments, the grating is etched in a high refractive index glass including TiO 2 , ZrO 2 , or ZnO. In some embodiments, the grating is etched in a synthetic high refractive index substrate such as LiNbO 3 , LiTaO 3 , or SiC. In some embodiments, the grating is TiO 2It is etched in a thin film coating or other inorganic material. The layout of the tiles within the grating coupler can be modified to achieve a higher uniformity of the far-field virtual image. The sharpness of the resulting image is also increased. In some embodiments, the size of each tile can be kept the same while the tile density decreases from a higher density to a sparser one. The eyepiece can thereby be designed to have a preferred diffraction direction. The diffracted light that is directly coupled to the user's eyeball of the eyepiece is reduced while increasing the efficiency of diffraction in other directions. The diffractive properties of the grating can be further improved using the tilt of the protrusions and the blazed or multi-step protrusions or depressions. The different design options provided by the embodiments disclosed herein thus provide higher optical efficiency and quality.

[0010] Details of one or more embodiments of the subject matter described herein are set forth in the accompanying drawings and the description below. Other potential features, aspects, and advantages of the subject matter will become apparent from the description, the drawings, and the claims. The present invention provides, for example, the following. (Item 1) An eyepiece, a substrate, an internal coupling grating patterned on one side of the substrate, a first grating coupler, the first grating coupler being patterned on one side of the substrate, having a first grating pattern, and the first grating coupler being optically coupled to the internal coupling grating, a second grating coupler, the second grating coupler being patterned on one side of the substrate, adjacent to the first grating coupler, the second grating coupler having a second grating pattern different from the first grating pattern, and the second grating coupler being optically coupled to the internal coupling grating and comprising. (Item 2) The first grating coupler includes a plurality of protrusions, each of the plurality of protrusions has one or more side walls, and each of the one or more side walls is oriented at a different angle with respect to the substrate. The eyepiece lens according to item 1. (Item 3) Each of the plurality of protrusions includes at least two intersecting ridges oriented in two different directions, and the angle between the two different directions is within the range of 55 degrees to 65 degrees. The eyepiece lens according to item 2. (Item 4) Each of the plurality of protrusions has at least one of a cylindrical shape, an elliptical shape, at least one rectangular surface, at least one circular surface, at least one triangular surface, or at least one polygonal surface. The eyepiece lens according to item 2. (Item 5) The filling rate of the volume of each of the plurality of protrusions measured along the direction of light incident from the internal coupling grating to the plurality of protrusions is within the range of 10% to 90%. The eyepiece lens according to item 2. (Item 6) The pitch of the axes of the plurality of protrusions is within the range of 300 nm to 450 nm. The eyepiece lens according to item 2. (Item 7) The diagonal pitch of the plurality of protrusions is within the range of 300 nm to 900 nm. The eyepiece lens according to item 2. (Item 8) The height of each of the plurality of protrusions is within the range of 5 nm to 500 nm. The eyepiece lens according to item 2. (Item 9) At least one of the width or length of each of the plurality of protrusions is within the range of 5 nm to 800 nm. The eyepiece lens according to item 2. (Item 10) The cross-section of each of the plurality of protrusions has at least one of a triangular shape, a serrated shape, or a stepped shape. The eyepiece lens according to item 2. (Item 11) Each of the plurality of protrusions includes a plurality of rectangular parallelepipeds, and each of the plurality of rectangular parallelepipeds has a different height. The eyepiece according to item 2. (Item 12) The first grating coupler includes a plurality of depressions, each of the plurality of depressions has one or more side walls, and each of the one or more side walls is oriented at a different angle with respect to the substrate. The eyepiece according to item 1. (Item 13) A method for manufacturing an eyepiece, the method comprising: Providing a substrate; Patternizing an internal coupling grating on one side of the substrate; Patternizing a first grating coupler on one side of the substrate, the first grating coupler being optically coupled to the internal coupling grating and having a first grating pattern; Patternizing a second grating coupler on one side of the substrate and adjacent to the first grating coupler, the second grating coupler being optically coupled to the internal coupling grating and having a second grating pattern different from the first grating pattern; A method comprising. (Item 14) The patternizing of the first grating coupler includes patternizing a plurality of protrusions on one side of the substrate, each of the plurality of protrusions has one or more side walls, and each of the one or more side walls is oriented at a different angle with respect to the substrate. The method according to item 13. (Item 15) The patternizing of the first grating coupler further includes patternizing at least two intersecting ridges oriented in two different directions for each protrusion of the plurality of protrusions, and the angle between the two different directions is in the range of 55 degrees to 65 degrees. The method according to item 14. (Item 16) An eyepiece, An internal coupling grating, wherein the internal coupling grating is patterned on one side of a substrate and configured to diffract light received from a projector into a first portion of the light and a second portion of the light, the first portion having a first orientation with respect to the light received from the projector, the second portion having a second orientation with respect to the light received from the projector, and the second orientation being different from the first orientation; an internal coupling grating A diffraction grating, wherein the diffraction grating is patterned on one side of the substrate Receiving the first portion of the light and the second portion of the light from the internal coupling grating Diffracting the first portion of the light and the second portion of the light Combining the diffracted first portion of the light and the diffracted second portion of the light A diffraction grating configured to perform the above; a diffraction grating An eyepiece lens comprising the above (Item 17) The diffraction grating A first grating coupler A second grating coupler, wherein the first grating coupler is configured to direct the diffracted first portion of the light to the second grating coupler, and the second grating coupler is configured to direct the diffracted first portion of the light to the first grating coupler; a second grating coupler The eyepiece lens according to item 16, comprising the above (Item 18) The first grating coupler defines an orthogonal pupil expander (OPE) of the eyepiece lens, and the second grating coupler defines an exit pupil expander (EPE) of the eyepiece lens; the eyepiece lens according to item 17 (Item 19) The first grating coupler includes a first plurality of ridges oriented in a first direction, and the second grating coupler includes a second plurality of ridges oriented in a second direction; the eyepiece lens according to item 17 (Item 20) The eyepiece according to item 19, wherein the angle between the first direction and the second direction is within a range of 55 degrees to 65 degrees.

Brief Description of the Drawings

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DETAILED DESCRIPTION OF THE INVENTION

[0035] This document describes the design and manufacture of an eyepiece lens using the patterning of internal coupling gratings and grating couplers. The eyepiece lens can be an optical eyepiece lens for use in virtual reality or augmented reality applications. The eyepiece lens includes a substrate and an internal coupling grating patterned on one side of the substrate. The internal coupling grating receives light from a projector. A first grating coupler is patterned on one side of the substrate. The first grating coupler has a first grating pattern. The first grating coupler is optically coupled to the internal coupling grating. A second grating coupler is patterned on one side of the substrate adjacent to the first grating coupler. The second grating coupler has a second grating pattern different from the first grating pattern. The second grating coupler is optically coupled to the internal coupling grating.

[0036] In particular, the benefits and advantages of the embodiments disclosed herein include patterning a diffraction grating on one side of a substrate such that the eyepiece reduces the need for light to travel a longer distance to reach the EPE. The efficiency of the light exiting the eyepiece towards the user is improved, coherent artifacts are thereby reduced, and a larger field of view with improved uniformity is realized within the small area form factor that would otherwise be achieved. Also, the processing complexity is reduced by maintaining a relief pattern on one side of the eyepiece, and the manufacturing yield and throughput are increased.

[0037] Imprint lithography system FIG. 1A illustrates an imprint lithography system 100 that forms a relief pattern on a substrate 102. The substrate 102 may be coupled to a substrate chuck 104. In some embodiments, the substrate chuck 104 includes a vacuum chuck, a pin type chuck, a groove type chuck, an electromagnetic chuck, and / or the like. In some embodiments, the substrate 102 and the substrate chuck 104 are further positioned on an air bearing 106. The air bearing 106 provides movement centered about the x, y, and / or z axes. In some embodiments, the substrate 102 and the substrate chuck 104 are positioned on a base. The air bearing 106, the substrate 102, and the substrate chuck 104 can also be positioned on a stage 108. In some embodiments, a robot system 110 positions the substrate 102 on the substrate chuck 104.

[0038] The imprint lithography system 100 further includes a resist template 112 with an imprint lithography flexible coating coupled to one or more rollers 114, depending on design considerations. The roller 114 provides movement of at least a portion of the resist template 112 with the flexible coating. Such movement can selectively provide different portions of the resist template 112 with the flexible coating to overlap the substrate 102. In some embodiments, the resist template 112 with the flexible coating includes a patterned surface that includes a plurality of features, such as spaced-apart indentations and protrusions. Other configurations of the features are also conceivable. The patterned surface may define any original pattern that defines the basis of the pattern to be formed on the substrate 102. In some embodiments, the resist template 112 with the flexible coating is coupled to a template chuck, such as a vacuum chuck, a pin type chuck, a groove type chuck, or an electromagnetic chuck.

[0039] The imprint lithography system 100 may further include a fluid dispenser 120. The fluid dispenser 120 may be used to deposit a polymerizable material on the substrate 102. The polymerizable material may be positioned on the substrate 102 using techniques such as droplet dispensing, spin coating, immersion coating, chemical vapor deposition, physical vapor deposition, thin film deposition, or thick film deposition. In some embodiments, the polymerizable material is positioned on the substrate 102 as a plurality of curable resist droplets.

[0040] A substrate having a patterned layer positioned thereon FIG. 1B illustrates a side view of a substrate 102 having a patterned layer 150 positioned thereon. Referring to FIGS. 1A and 1B, imprint lithography system 100 may further include an energy source 122 coupled to direct energy (e.g., broadband ultraviolet radiation) toward substrate 102. In some embodiments, roller 114 and air bearing 106 are configured to position a flexible-coated resist template 112 and a desired portion of substrate 102 in a desired alignment. Imprint lithography system 100 may be adjusted by a controller in communication with air bearing 106, roller 114, fluid dispenser 120, and / or energy source 122, and may operate on a computer-readable program stored in memory.

[0041] In some embodiments, roller 114, air bearing 106, or both vary the distance between flexible-coated resist template 112 and substrate 102, defining a desired volume therebetween to be filled with a polymerizable material. For example, flexible-coated resist template 112 contacts the polymerizable material. After the desired volume is filled with the polymerizable material, energy source 122 generates energy, e.g., broadband ultraviolet radiation, to solidify and / or crosslink the polymerizable material, conforming it to a portion of the surface of substrate 102 and the patterned surface of flexible-coated resist template 122, thus defining patterned layer 150 on substrate 102. In some embodiments, patterned layer 150 includes a residual layer 152 and a plurality of features shown as protrusions 154 and depressions 156.

[0042] System for manufacturing an optical waveguide on a substrate FIG. 2 illustrates a system 200 for manufacturing optical waveguides on a substrate. The system 200 includes a deposition system 226, a controller 224, a fluid dispenser 120, a laser source 228, and an energy source 122. The system 200 is used to manufacture a multi-waveguide optical structure that includes a plurality of waveguides stacked to block light passing sequentially through each waveguide, and each waveguide may be associated with a different color and a different depth in a plane.

[0043] The deposition system 226 is configured to deposit an adhesion promoting layer on a substrate (e.g., 102). The adhesion promoting layer is intended to improve the adhesion of curable resist droplets to the substrate 102. For example, the adhesion promoting layer may be applied by spin coating a diluted solution on the substrate 102 and allowing the layer to spin dry.

[0044] The imprint lithography system 200 may be adjusted by a controller 224 that communicates with the deposition system 226, the fluid dispenser 120, the laser source 228, and / or the energy source 122, and may operate on a computer-readable program stored in memory. The controller 224 may be implemented in software or hardware. For example, the controller 224 may be part of a PC, a tablet PC, a smartphone, an Internet of Things (IoT) appliance, or any machine capable of executing instructions that define actions to be performed by the machine.

[0045] The controller 224 may instantiate a gap reference within the optical structure being manufactured to monitor the dispensing of curable resist droplets within the optical eyepiece layer. The gap reference or reference marker is a marker that can be placed within the field of view of the generated optical structure for use as a reference point or measurement. The gap reference may be placed within or on a mark or set of marks within the imaging target or optical instrument.

[0046] The controller 224 may overlay a coated resist template (e.g., 112) on the curable resist droplet to contact the curable resist droplet and pattern it. The coated resist template 112 includes a patterned surface that includes a plurality of recesses and protrusions. The coated resist template 112 may further include a deep lattice structure or dam configured to prevent the curable resist droplet from flowing into the zero RLT region. The controller 224 may further direct broadband ultraviolet radiation from the energy source 122 to cure the curable resist droplet. The controller 224 may further remove the coated resist template 112 and expose the patterned resist, which then conforms to a portion of the patterned surface of the coated resist template 112.

[0047] The controller 224 may etch a diffraction grating formed on the optical structure to define an optical eyepiece layer. In some embodiments, the need to dry etch the substrate 102 (e.g., dry etch a high refractive index glass or sapphire) is eliminated. In some embodiments, the substrate 102 is partially etched (e.g., a plasma process under atmospheric or low pressure conditions) to remove the residual layer and / or transfer the pattern into the substrate 102 while maintaining a portion of the residual layer on the surface of the substrate 102.

[0048] The diffraction grating diffracts light traveling through the optical waveguide. The controller 224 may further direct a laser beam from the laser source 228 onto a portion of the adhesion promoting layer to etch the substrate 102. The controller 224 may etch the optical eye lens layer from the substrate 102 by pulse irradiating a laser beam onto a portion of the adhesion promoting layer to generate nanopores within the substrate 102. The laser beam is applied to the generated nanopores to expand the nanopores and separate the optical eye lens layer from the substrate 102. The resist may be removed by laser ablation in some embodiments, but in other embodiments, this may simply not be placed below (e.g., by masking) or not removed by etching (e.g., by plasma), or any combination thereof. The controller 224 may further bond the optical eye lens layer to another optical eye lens layer imprinted on another substrate to define the optical waveguide.

[0049] The fluid dispenser 120 dispenses a thin layer of imprint resist (e.g., a thermoplastic polymer) in the form of curable droplets onto the substrate 102. In some embodiments, the fluid dispenser 120 dispenses curable resist droplets onto the adhesion promoting layer and is configured to define a diffraction grating. The adhesion promoting layer is disposed between and in contact with the substrate 102 and the dispensed curable resist droplets. The region defining the optical eye lens layer has an edge and there are no curable resist droplets at the edge of the optical eye lens layer.

[0050] In some embodiments, the fluid dispenser 120 is configured to dispense curable resist droplets onto the adhesion promoting layer by injecting curable resist droplets onto the adhesion promoting layer at predetermined coordinates and at a predetermined frequency. Adjacent droplets of the curable resist are spaced a predetermined distance apart on the adhesion promoting layer. For example, the fluid dispenser 120 may be programmed to indicate an area where resist is to be dispensed or where resist is not to be dispensed. A very high resolution resist droplet pattern may be created that includes the predetermined coordinates for the individual resist droplets and a predetermined XY pitch between adjacent droplets. The fluid dispenser 120 operates at a very high frequency while dispensing resist droplets as the substrate 102 passes under the inkjet head. Ultra-high resolution and accuracy (X, Y, volume) are achieved by the inkjet dispensing frequency, head voltage, and stage movement control. The curable resist droplets may be deposited onto the adhesion promoting layer by moving the inkjet head of the fluid dispenser 120, moving the substrate across the inkjet head of the fluid dispenser 120, or moving the inkjet head and the substrate across each other of the fluid dispenser 120.

[0051] In some embodiments, the fluid dispenser 120 is further configured to maintain a zero RLT region corresponding to the edge of the optical eyepiece layer that is free of curable resist droplets. This configuration increases the optical performance of the optical waveguide by reducing light scattering at the edge of the optical eyepiece layer and reducing the number of particle defects on the zero RLT region of the optical waveguide.

[0052] The laser source 228 provides a laser beam for engraving the substrate 102. In some embodiments, the laser source 228 includes a gain medium, an energizing mechanism, and an optical feedback mechanism. The gain medium is a material with properties that allow it to amplify light using stimulated emission. Energy may be supplied as an electric current or as light at a different wavelength. The laser source 228 may use feedback from the optical cavity and can affect the properties of the emitted light such as the polarization, wavelength, and shape of the beam.

[0053] The energy source 122 provides radiation for enhancing (e.g., polymerizing or cross-linking) the resist droplets and leaves a resist coating on the substrate. In some embodiments, the energy source 122 reduces the wavelength of the radiation to achieve higher resolution. For example, the energy source 122 may provide energy at wavelengths in the ultraviolet spectrum or in a shorter (<400 nm) deep ultraviolet spectrum. In some embodiments, the energy source 122 generates an electron beam and achieves the same result as optical exposure.

[0054] Environment of an eyepiece using patterning of a grating coupler FIG. 3A illustrates the operating environment of an optical eyepiece. The eyepiece shown in FIG. 3A includes a substrate (e.g., substrate 400 illustrated and described below with reference to FIG. 4). The substrate can have a refractive index above a certain threshold. In some embodiments, the refractive index of the substrate is above 1.4. The refractive index of the substrate is a dimensionless number that describes the degree of the speed at which light propagates through the substrate. The substrate can be made from a high refractive index polymer or glass. In some embodiments, the grating is patterned over a high refractive index substrate or etched in a thin layer of a low refractive index material included in a high refractive index glass containing TiO 2 , ZrO 2 , or ZnO. In some embodiments, the grating is etched in a synthetic high refractive index substrate such as LiNbO 3 , LiTaO 3 , or SiC. In some embodiments, the grating is etched in a TiO 2 thin film coating or other inorganic material to provide additional optical benefits.

[0055] The eyepiece shown in FIG. 3A includes an internal coupling grating 304 that is patterned on one side of a substrate. The internal coupling grating 304 of FIG. 3A is located at the user's eyebrow or temple when using the eyepiece. The internal coupling grating 304 uses a combination of total internal reflection and diffraction to couple the light rays of light 332 from the light source projector 300 to the first grating coupler 308 and the second grating coupler 320.

[0056] The internal coupling grating 304 is configured to diffract the light 332 received from the projector 300. The light 332 is diffracted and coupled into a first portion 336 of the light and a second portion 312 of the light. The first portion 336 has a first orientation with respect to the light 332 received from the projector 300, and the second portion 312 has a second orientation with respect to the light 332 received from the projector 300. The second orientation is different from the first orientation. For example, the first portion 336 can be oriented in a first direction, and the second portion 312 can be oriented in a second direction. The internal coupling grating 304 is further configured to direct the first portion 336 to the first grating coupler 308. The internal coupling grating 304 is further configured to direct the second portion 312 to the second grating coupler 320. When the internal coupling grating 304 is located at the user's eyebrow or cheek, the eyepiece is vertically divided into the first grating coupler 308 and the second grating coupler 320 as shown in FIG. 3A. The vertical reference frame is in the direction from the user's forehead to the chin of the eyepiece. When the internal coupling grating 304 is located at the user's temple or nostril, the eyepiece can be horizontally divided. The horizontal reference frame is in the direction from ear to ear of the user of the eyepiece.

[0057] The first grating coupler 308 is optically coupled to the internal coupling grating 304 to receive the portion 336 of the light diffracted by the internal coupling grating 304. The first grating coupler 308 is patterned on one side of the substrate and has a first grating pattern. The first grating pattern can include ridges, grooves, linear grating segments, protrusions, depressions, or combinations thereof, as will be illustrated and described in detail below with reference to FIGS. 6A-D, 7A-B, 8A-B, 9A-B, 10, and 11A-B. The first grating coupler 308 is configured to diffract the first portion 336 of the light received from the internal coupling grating 304. The first grating coupler 308 has a periodic structure or pattern that splits the portion 336 of the light into several beams traveling in different directions and further diffracts them. The different directions of the beams depend on the grating pitch and the wavelength of the light such that the grating acts as a dispersive element. The first grating coupler 308 directs the diffracted first portion 340 of the light to the second grating coupler 320. In some embodiments, the first grating coupler 308 defines the OPE of the eyepiece. The OPE uses total internal reflection (TIR) in different directions to spread the diffracted light rays of the light.

[0058] The second grating coupler 320 is optically coupled to the internal coupling grating 304. In some embodiments, the second grating coupler 320 defines the EPE of the eyepiece. The EPE couples the light exiting the OPE towards the user or the world of the eyepiece. In some embodiments, the combination of the OPE and the EPE that function in cooperation is referred to as a combined pupil expander (CPE).

[0059] The second grating coupler 320 is patterned on one side of the substrate and adjacent to the first grating coupler 308. The second grating coupler 320 has a second grating pattern that is different from the first grating pattern. The second grating pattern can include protrusions, grooves, linear grating segments, protrusions, depressions, or combinations thereof, as will be illustrated and described in detail below with reference to FIGS. 6A-D, 7A-B, 8A-B, 9A-B, 10, and 11A-B. The second grating coupler 320 is configured to diffract a second portion 312 of the light. The diffracted second portion 316 of the light is directed to the first grating coupler 308. The eyepiece is configured to combine the diffracted first portion 340 and the diffracted second portion 316. The eyepiece is further configured to direct the combined light 324 to the eyeball 328 of the user of the eyepiece. The first grating coupler 308 and the second grating coupler 320 illustrated in FIG. 3A are sometimes referred to as having a split honeycomb pattern or a split honeycomb configuration.

[0060] In some embodiments, the internal coupling grating 304 includes a first set of parallel protrusions or grooves oriented in a first direction as shown in FIG. 3A. The first set of protrusions, grooves, or linear grating segments can be spaced apart by a first pitch distance. The first grating coupler 308 includes a second set of parallel protrusions or grooves oriented in a second direction different from the first direction. The second set of protrusions, grooves, or linear grating segments can be spaced apart by a second pitch distance. The second grating coupler 320 can include a third set of parallel protrusions or grooves oriented in a third direction different from the first and second directions. The third set of protrusions, grooves, or linear grating segments can be spaced apart by a third pitch distance. The angle between the second direction and the third direction is in the range of 55 degrees to 65 degrees.

[0061] The path lengths of portions of the light 336 and 312 shown in FIG. 3A can be designed such that the two portions 336 and 312 are either in-phase or out-of-phase. Similarly, the path lengths of portions of the light 316 and 340 can be designed such that the two portions 336 and 312 are either in-phase or out-of-phase. Embodiments thus modulate the phase of the OPE and EPE light fields. The modulation of the phase of the light field reduces Mach-Zehnder interference and improves the uniformity of the resulting image. The sharpness of the resulting image is also increased. Also, the embodiment illustrated in FIG. 3A provides increased optical efficiency. In a conventional eyepiece, a large amount of light is diffracted into the air, thus reducing efficiency. In contrast, in the eyepiece of FIG. 3A, the portion of the light 312 in the second grating coupler does not diffract out of the eyepiece and instead reaches the first grating coupler 308. Thus, more light is conserved and the optical efficiency is increased. The eyepiece illustrated in FIG. 3A also improves the diffusion of light in a single-layer architecture. By including specific nano-features in the design, the eyepiece can combine two or more wavelengths of light in a single layer and improve image quality.

[0062] Patterning of Internal Coupling Gratings and Grating Couplers in an Optical Eyepiece Figure 3B illustrates the patterning of the internal coupling grating 348 and grating couplers 356 and 368 in the optical eyepiece. In other embodiments, the eyepiece includes additional or fewer features than those described herein. The eyepiece shown in Figure 3B includes a substrate (e.g., substrate 400 illustrated and described below with reference to Figure 4) and an internal coupling grating 348 imprinted on one side of the substrate and similar to the internal coupling grating 304 shown in Figure 3A. A first grating coupler 356 is imprinted on one side of the substrate and optically coupled to the internal coupling grating 348. The first grating coupler 356 includes a plurality of tiles that define the EPE of the eyepiece. Each tile 352 of the first grating coupler 356 has a first grating pattern. The first grating pattern can include ridges, grooves, linear grating segments, protrusions, indentations, or combinations thereof. The first grating coupler 356 is configured to receive a portion of the light diffracted by the internal coupling grating 348 and further diffract the portion of the light using the tiles.

[0063] A second grating coupler (grating region 368) is interspersed among the tiles. The grating region 368 has a second grating pattern (parallel ridges or grooves) that is different from the first grating pattern. The grating region 368 defines the OPE of the eyepiece. In some embodiments, the internal coupling grating 348 includes a first set of parallel ridges as shown in Figure 3B. The grating region 368 includes a second set of parallel ridges that are orthogonal to the first set of parallel ridges. The grating region 368 is configured to receive another portion of the light diffracted by the internal coupling grating 348 and further diffract the other portion of the light. The first grating coupler 356 is thereby configured to reduce the luminance of the light emitted by the central region 364 of the grating region 368. The grating couplers in Figure 3B receive the light diffracted by the internal coupling grating 348 and diffuse the light emitted by the central region 364 of the grating region 368.

[0064] The single-sided eyepiece lens, in which the internal coupling grating 348, the first grating coupler 356, and the grating region 368 are imprinted on one side of the substrate, provides a larger field of view and reduced coherent artifacts. Coherent artifacts refer to the interfering and reinforcing interference of diffracted light rays emerging from the eyepiece lens. Such artifacts can cause areas of dark and bright patches in the image projected onto the user's field of view. Coherent artifacts can cause a reduction in image and color uniformity. The embodiments disclosed herein improve image and color uniformity by reducing coherent artifacts. The configuration illustrated in FIG. 3B is sometimes referred to as a tiled snowflake grating pattern or a tiled snowflake grating configuration.

[0065] In some embodiments, the area or size of each tile 352 of the plurality of tiles decreases as the position of the tile 352 changes from the central region 364 of the grating coupler 356 to the boundary 360 of the grating coupler 364. The change in the area or size of each tile 352 reduces the luminance of the light emitted by the central region 364. Since the tiles are as small as a few hundred microns, the far-field virtual image quality is not affected. Also, the single-sided nature of the eyepiece lens increases the user-to-world ratio of the eyepiece lens. The nanogratings are blazed or made of a high refractive index material such as a polymer having a refractive index greater than 1.6, so that a greater amount of light is directed towards the user's eyeball 328. Further, the grating can be etched in a high refractive index glass containing TiO 2 、ZrO 2 、or ZnO. In some embodiments, the grating can be etched in a synthetic high refractive index substrate such as LiNbO 3 、LiTaO 3 、or SiC. In some embodiments, the grating is etched in a ZrO 2 、TiO 2 、or SiC thin film coating.

[0066] In some embodiments, the tiles of the grating coupler 356 have a rectangular shape. The size of each tile 352 and the length of the sides of the tile 352 can vary from the boundary 360 to the central region 364. In some embodiments, the tiles of the grating coupler 356 have a circular shape. The diameter of each tile 352 can vary from the boundary 360 to the central region 364. In some embodiments, the tiles of the grating coupler 356 have an elliptical shape. The dimensions of each tile 352 can vary from the boundary 360 to the central region 364. In some embodiments, the tiles of the grating coupler 356 have a polygonal shape. The polygon can be a regular polygon or an irregular polygon. For example, the tile can have a hexagonal shape.

[0067] In some embodiments, each tile 352 of the plurality of tiles shown in FIG. 3B includes a plurality of protrusions, as will be illustrated and described in detail below with reference to FIGS. 6A-D. The protrusions are sometimes referred to as struts, grating struts, or strut gratings. The grating coupler 356 is sometimes referred to as a strut diffraction grating. Each protrusion of the plurality of protrusions has one or more sidewalls, as will be illustrated and described below with reference to FIG. 6A. Each sidewall of the one or more sidewalls can be oriented at a different angle with respect to the substrate. For example, the gradient of each sidewall with respect to the substrate can be different. In some embodiments, each protrusion of the plurality of protrusions includes two intersecting ridges that are oriented in two different directions. The location where the two intersecting ridges meet defines the protrusion.

[0068] Patterning of Internal Coupling Gratings and Grating Couplers in Optical Eyepieces Figure 4 illustrates the internal coupling grating 404 and the patterning of the grating coupler in the optical eyepiece lens. The eyepiece lens shown in Figure 4 includes a substrate 400 that may have a refractive index above a certain threshold. In some embodiments, the refractive index of the substrate is above 1.4. The substrate 400 is described in more detail above with reference to Figures 1A, 1B, 2, and 3A. The internal coupling grating 404 can be patterned on the first side of the substrate 400, the second side of the substrate 400, or both sides of the substrate 400. A first grating coupler 420 is patterned on the first side of the substrate 400. The first grating coupler 420 has a first grating pattern 408. For example, the first grating pattern 408 can include a periodic arrangement of ridges, grooves, linear grating segments, protrusions, recesses, or combinations thereof. In some embodiments, the first grating coupler 420 includes a first set of ridges that are oriented in a first direction. The first grating coupler 420 is optically coupled to the internal coupling grating 404 to receive a first portion of light from the internal coupling grating 404.

[0069] In some embodiments, a second grating coupler 424 is patterned on the first side of the substrate 400. Both the first grating coupler 420 and the second grating coupler 424 are thus patterned on the same side of the substrate 400. The second grating coupler 424 has a second grating pattern 412 that is different from the first grating pattern 408. For example, the second grating pattern 412 can include a periodic arrangement of ridges, grooves, linear grating segments, protrusions, recesses, or combinations thereof. In some embodiments, the second grating coupler 424 includes a second set of ridges that are oriented in a second direction that is different from the first direction. In some embodiments, the angle between the first direction and the second direction is in the range of 55 degrees to 65 degrees. The second grating coupler 424 is optically coupled to the internal coupling grating 404 such that the second grating coupler 424 is configured to receive a second portion of light from the internal coupling grating 404.

[0070] In some embodiments, the second grating coupler 424 is patterned on a second side of the substrate 400. The first grating coupler 420 and the second grating coupler 424 are thus patterned on different sides of the substrate 400. The second grating coupler 424 has a second grating pattern 412 that is different from the first grating pattern 408. For example, the second grating pattern 412 can include a periodic arrangement of ridges, grooves, linear grating segments, protrusions, depressions, or combinations thereof. In some embodiments, the second grating coupler 424 includes a second set of ridges that are oriented in a second direction that is different from the first direction. In some embodiments, the angle between the first direction and the second direction is in the range of 55 degrees to 65 degrees. The second grating coupler 424 is optically coupled to the internal grating 404 such that the second grating coupler 424 is configured to receive a second portion of the light from the internal grating 404.

[0071] In some embodiments, the area 416 or region of the first grating coupler 420 overlaps with the area or region of the second grating coupler 424. The overlapping area 416 diffracts light into the eye ball 328 of the user of the eyepiece. In some embodiments, the area 416 of the first grating coupler 420 overlaps with the second grating coupler 424 such that the overlapping area 416 is configured to diffract a portion of the light into the eye ball 328 of the user of the eyepiece. The overlapping area 416 reduces the luminance of the light directly diffracted into the user's eye ball 328 so that the user does not see a bright central band in the image displayed by the eyepiece. In some embodiments, the size of the area 416 of the first grating coupler is in the range of 10% to 60% of the total area of the first grating coupler 420. In some embodiments, the width 424 of the overlapping area 416 (corresponding to the width of the eye box of the eyepiece) is in the range of 5 mm to 20 mm. In some embodiments, the dimensions of the eye box are 15 mm in the horizontal direction and 18 mm in the vertical direction. The vertical reference frame is in the direction from the forehead to the chin of the user of the eyepiece. The horizontal reference frame is in the direction from ear to ear of the user of the eyepiece. The eye box is an area within the eyepiece (EPE / CPE) that means through which the emitted light rays capture the range of movement and positioning of the eye ball 328 within the field of view of one or more users such that the eyepiece is defined by the eyepiece fixed at a specific distance from the user's eye.

[0072] Grating Pattern in Optical Eyepiece FIG. 5A illustrates an interlocking lattice pattern 500 in an optical eyepiece lens. The eyepiece lens includes a first grating coupler (e.g., the first grating coupler 308 illustrated and described above with reference to FIG. 3A) patterned on one side of a substrate. The first grating coupler has a first grating pattern. For example, the first grating coupler can include a first set of ridges oriented in a first direction, as shown above in FIG. 3A. A second grating coupler (e.g., the second grating coupler 320 illustrated and described above with reference to FIG. 3A) is patterned on one side of the substrate. The second grating coupler has a second pattern different from the first pattern. For example, the second grating coupler can include a second set of ridges oriented in a second direction, as shown above in FIG. 3A. Referring now to FIG. 5A, the first grating coupler contacts the second grating coupler and defines an interlocking alternating pattern 500 at the location of contact. The interlocking alternating pattern 500 diffuses light that is directly diffracted into the eye ball 328 of a user of the eyepiece lens. In some embodiments, the interlocking alternating pattern 500 includes a plurality of parallel ridges 504 oriented in a particular direction. In other embodiments, the interlocking alternating pattern 500 includes alternating bands of the first pattern and the second pattern.

[0073] FIG. 5B illustrates a sawtooth grating pattern 508 in an optical eyepiece lens. In the embodiment illustrated in FIG. 5B, the interlocking alternating pattern is defined to include a plurality of ridges arranged in a sawtooth pattern 508. The sawtooth pattern 508 reduces the brightness of light that is directly diffracted into the eye ball 328 of the user. Accordingly, the user does not see a bright central band in the image displayed by the eyepiece lens.

[0074] FIG. 5C illustrates a chevron grating pattern 512 in an optical eyepiece lens. The pattern illustrated in FIG. 5C includes a plurality of ridges arranged in the chevron grating pattern 512. The chevron grating pattern is a V-shaped pattern that includes a substantially equal area or region of a first grating pattern of a first grating coupler (e.g., the first grating coupler 308 illustrated and described above with reference to FIG. 3A) and a second grating pattern of a second grating coupler (e.g., the second grating coupler 320). The angle between the ridges of the first grating pattern and the ridges of the second grating pattern is in the range of 55 degrees to 65 degrees.

[0075] FIG. 5D illustrates a stencil 516 used in an optical eyepiece lens. The stencil 516 defines an interlocking alternating pattern between a first grating coupler 520 and a second grating coupler 524. The first grating coupler 520 is patterned using a first set of parallel ridges 528 oriented in a first direction. The second grating coupler 524 is patterned using a second set of parallel ridges 532 oriented in a second direction different from the first direction. The stencil 516 thereby mates a first boundary of the first grating coupler 520 with a second boundary of the second grating coupler 524.

[0076] In some embodiments, the interlocking alternating grating pattern in the stencil 516 includes a plurality of protrusions 536. Each protrusion is defined by two intersecting ridges, one from each of the ridges 528 and 532. Each protrusion of the plurality of protrusions 536 can have one or more sidewalls. Each sidewall of the one or more sidewalls can be oriented at a different angle with respect to a substrate (e.g., the substrate 400 illustrated and described above with reference to FIG. 4). In some embodiments, the plurality of protrusions 536 have a refractive index greater than 1.4.

[0077] Diamond-Patterned Protrusions in a Grating Coupler FIG. 6A illustrates a rhombic patterned protrusion in a grating coupler 600 in an optical eyepiece lens. The grating couplers 600, 624, 648, and 674 illustrated in FIGS. 6A-D are also sometimes referred to as having a blazed pillar pattern, a blazed pillar configuration, a blazed protrusion pattern, or a blazed protrusion configuration. Referring now to FIG. 6A, the grating coupler 600 can be blazed to achieve a higher grating efficiency at a given diffraction order. The refractive power thus concentrates at the desired diffraction order while the residual refractive power at other orders is reduced. The shape and pattern of the protrusions of the grating coupler 600 define the blaze wavelength at which the grating coupler 600 is blazed. The direction in which the optical efficiency is increased is called the blaze angle and is a characteristic of the blazed grating coupler 600. The blaze angle depends on the blaze wavelength and the selected diffraction order.

[0078] The blazed grating coupler 600 can have a specific line spacing or pitch that determines the magnitude of the wavelength division caused by the grating coupler 600. In some embodiments, illustrated and described below with reference to FIG. 6D, the grating coupler can have a triangular or sawtooth cross-section that defines a stepped structure. The steps can be inclined at the blaze angle with respect to the grating surface. The blaze angle can be designed to increase the efficiency with respect to the wavelength of light. In some embodiments, the blaze angle is designed such that the diffraction angle and the incident angle correspond. In some embodiments, a larger blaze angle is selected such that the light impinges on the shorter side of the triangular grating lines instead of the longer side. In such embodiments, the grating coupler 600 has a larger line spacing and a higher diffraction order.

[0079] The grating coupler 600 of the eyepiece lens illustrated in FIG. 6A is patterned on one side of a substrate (e.g., the substrate 400 illustrated and described above with reference to FIG. 4) having a refractive index above a certain threshold. In some embodiments, the refractive index of the substrate is above 1.4. The grating coupler 600 is optically coupled to the internal coupling grating of the eyepiece lens, similar to the illustration above in FIG. 3A. The grating coupler 600 includes a plurality of protrusions, e.g., protrusion 612. Each protrusion 612 has one or more sidewalls, e.g., sidewall 604. Each sidewall 604 of the one or more sidewalls can be oriented at a different angle with respect to the substrate. In some embodiments, the grating coupler 600 illustrated in FIG. 6A is referred to as having a diamond pillar pattern or a diamond protrusion configuration.

[0080] In some embodiments, each protrusion 612 of the plurality of protrusions includes at least two intersecting raised portions that are oriented in two different directions. The position where the at least two intersecting ridges meet defines the protrusion 612. In some embodiments, each protrusion has a cylindrical shape. In some embodiments, each protrusion of the grating coupler 600 has an elliptical shape. The dimensions of each ellipsoid interact with light and diffract light. In some embodiments, each protrusion has at least one circular surface, e.g., when the protrusion has a cylindrical shape. In some embodiments, each protrusion 612 has at least one triangular surface 608. In other embodiments, each protrusion 612 has at least one polygonal surface. The polygonal surface can correspond to a regular or non-regular polygon.

[0081] In some embodiments, the fill factor (or duty cycle) of the volume of each protrusion 612 when measured along the direction of light incident from the internal coupling grating to the plurality of protrusions is in the range of 10% to 90%. The fill factor refers to the ratio of the volume of the protrusion 612 to the volume of the recess (empty space) between consecutive protrusions. In some embodiments, the pitch of the axes of the protrusions is in the range of 300 nm to 450 nm. The pitch refers to the measured distance from the center of gravity of the first protrusion to the center of gravity of the adjacent protrusion located in the same row or column as the first protrusion. The center of gravity refers to the geometric center of the mass of the protrusion. In some embodiments, the diagonal pitch of the protrusions is in the range of 300 nm to 900 nm. The diagonal pitch refers to the measured distance from the center of gravity of the first protrusion to the center of gravity of the nearest diagonally adjacent protrusion, i.e., the distance between the center of gravity of the protrusions in one row and that of the nearest protrusion in the next row and the next column.

[0082] In some embodiments, the height of one or more of the protrusions is in the range of 5 nm to 500 nm. In other embodiments, the width or length of the protrusions is in the range of 5 nm to 800 nm. The protrusions can be fabricated in several shapes. For example, the cross-section of the protrusion can have a triangular shape. The plurality of protrusions can have a refractive index greater than 1.4. In some embodiments, the grating coupler 600 includes a plurality of recesses or cavities for diffracting light. Each recess or cavity can have one or more sidewalls, similar to the protrusions discussed above with reference to FIG. 6A. Each sidewall of the one or more sidewalls can be oriented at a different angle with respect to the substrate.

[0083] Patterned Protrusions in a Grating Coupler FIG. 6B illustrates a cuboid patterned protrusion in a grating coupler 624 in an eyepiece lens. The grating coupler 624 includes a plurality of protrusions (e.g., protrusion 632). Each protrusion includes a plurality of cuboids 628. Each cuboid can have different heights, lengths, and depths. Thus, each cuboid can have a different volume of grating material. Each protrusion 632 has one or more sidewalls. Each protrusion has at least one rectangular surface. The grating coupler 624 illustrated in FIG. 6B is sometimes referred to as having a stepped inclined strut pattern or a stepped inclined protrusion configuration.

[0084] In some embodiments, an eyepiece lens manufactured using the grating coupler 624 includes a substrate (e.g., substrate 400 illustrated and described above with reference to FIG. 4) and an internal coupling grating imprinted on one side of the substrate. The grating coupler 624 is also imprinted on one side of the substrate and optically coupled to the internal coupling grating. The grating coupler 624 can include a plurality of tiles that define the EPE of the eyepiece lens, as illustrated and described above with reference to FIG. 3B. A grating region (e.g., grating region 368) can be interspersed between the tiles and define the OPE of the eyepiece lens. Each tile of the grating coupler 624 can include a plurality of cuboids 628, and each cuboid 628 can have a different height. In some embodiments, the height of each cuboid is in the range of 5 nm to 500 nm. In other embodiments, the width or length of each cuboid is in the range of 5 nm to 800 nm. The cross-section of each cuboid has a rectangular shape. In some embodiments, the cross-section of each protrusion 632 has a stepped shape.

[0085] FIG. 6C illustrates the protrusions in the grating coupler 648 in the optical eyepiece lens. The grating coupler 648 may be blazed as described and illustrated above with reference to FIG. 6A. In some embodiments, each protrusion 652 has at least one rectangular surface. For example, the upper surface 656 may be rectangular. In some embodiments, each protrusion has at least one circular surface, for example, when the protrusion has a cylindrical shape. In some embodiments, each protrusion has at least one triangular surface. In other embodiments, each protrusion has at least one polygonal surface.

[0086] FIG. 6D illustrates the serrated patterned protrusions 678 in the grating coupler 674 in the optical eyepiece lens. The cross-sections of the plurality of protrusions have a serrated shape. In some embodiments, the portion of the grating coupler 674 illustrated in FIG. 6D may be part of an interlocking alternating grating pattern that includes a plurality of ridges or protrusions arranged in a serrated grating pattern.

[0087] Patterning of the Grating Coupler FIG. 7A illustrates the patterning of the grating coupler in the optical eyepiece lens. The eyepiece lens illustrated in FIG. 7A includes an internal coupling grating 724 that is patterned on one side of a substrate (e.g., the substrate 400 illustrated and described above with reference to FIG. 4). The configuration illustrated in FIG. 7A is sometimes referred to as a winged grating configuration or a winged grating pattern. In the winged grating configuration, three or more grating couplers are patterned on one side of the substrate. The three or more grating couplers are optically coupled to the internal coupling grating 724. Each of the three or more grating couplers has a different grating pattern, as illustrated in FIG. 7A.

[0088] The internal coupling grating 724 is configured to diffract light received from a projector (e.g., projector 300) into three or more portions of the light. Each portion of the light has a different orientation with respect to the light received from projector 300. The internal coupling grating 724 is further configured to direct the corresponding portions of the light to each grating coupler. Each grating coupler is configured to further diffract the corresponding portion of the light. The eyepiece is configured to combine three or more diffracted portions of the light for transmission to a user's eyeball (e.g., eyeball 328).

[0089] The first grating coupler 700 includes a first linear grating section 704 that is oriented in a first direction. The second grating coupler 712 includes a second linear grating section 716 that is oriented in a second direction different from the first direction. In some embodiments, the angle between the first direction and the second direction is in the range of 55 to 65 degrees. At least one grating coupler is located between two other grating couplers in the eyepiece. For example, in FIG. 7A, a third grating coupler 728 having tiles 720 is located between the first grating coupler 700 and the second grating coupler 712. In some embodiments, the width 708 of the third grating coupler 728 (corresponding to the width of the eye box of the eyepiece) located between the first grating coupler 700 and the second grating coupler 712 is in the range of 5 mm to 20 mm. The grating coupler 728 located between the two other grating couplers 700 and 712 includes a plurality of tiles 720 having a specific grating pattern. The tiles 720 can include protrusions, cavities or indentations, or ridges. In some embodiments, each tile of the plurality of tiles 720 has a polygonal shape.

[0090] FIG. 7B illustrates the patterning of the grating couplers in the optical eyepiece lens. The eyepiece lens illustrated in FIG. 7B includes an internal coupling grating 748 and three or more grating couplers (including a first grating coupler 756, a second grating coupler 772, and a third grating coupler 776). The configuration of FIG. 7B is sometimes referred to as a winged grating configuration or a winged grating pattern. In the winged grating configuration or winged grating pattern, at least one grating coupler is positioned between two other grating couplers. For example, in FIG. 7B, the third grating coupler 776, which includes the linear section 752, is positioned between the first grating coupler 756 and the second grating coupler 772. In some embodiments, the width 764 of the grating coupler that includes the plurality of linear grating sections 752 (which corresponds to the width of the eye box of the eyepiece lens) is in the range of 5 mm to 20 mm.

[0091] The first grating coupler 756 includes a first linear grating section 760 that is oriented in a first direction. The second grating coupler 772 includes a second linear grating section 768 that is oriented in a second direction different from the first direction. In some embodiments, the angle between the first direction and the second direction is in the range of 55 degrees to 65 degrees. In some embodiments, as illustrated in FIG. 7B, the pitch spacing of the features of the third two-dimensional (2D) grating coupler 776 can be determined from the pitch spacing defined by the intersections of the features that define the first one-dimensional (1D) grating coupler 756 and the second 1D grating coupler 772. The difference between the pitch spacing of the features of the grating coupler 776 and the pitch spacing of the intersections of the features of the grating couplers 756 and 772 can cause a virtual image shift or virtual image float that is visible when moving from one grating region to another. Such image float is undesirable, for example, when there is a change in eye position across the CPE area during viewing of the virtual image or when the interpupillary distance (IPD) for a large population is different. The embodiment illustrated in FIG. 7B reduces image float for a single-sided full field of view (FOV) waveguide by generating a distortion-free virtual image. The embodiments illustrated with reference to FIGS. 7A and 7B can be implemented to achieve a preferred diffraction order. The preferred diffraction order reduces the occurrence of a central bright band in the resulting image and increases the eyepiece uniformity. The sharpness of the resulting image is also increased.

[0092] Patterning of the Grating Coupler FIG. 8A illustrates the patterning of grating couplers 816 and 820 in an optical eyepiece lens. The eyepiece lens illustrated in FIG. 8A includes a substrate (e.g., substrate 400 illustrated and described above with reference to FIG. 4A) and an internal coupling grating 800 imprinted on one side of the substrate. The internal coupling grating 800 includes a first set of parallel ridges. A first grating coupler 816 is imprinted on one side of the substrate and optically coupled to the internal coupling grating 800. The configuration shown in FIG. 8A is sometimes referred to as a tiled snowflake grating configuration or a tiled snowflake grating pattern. The first grating coupler 816 includes a plurality of tiles 824 that define the EPE of the eyepiece lens. The tiles 824 have a first grating pattern, e.g., ridges, protrusions, indentations, etc.

[0093] In some embodiments, each tile 824 includes a plurality of protrusions. Each protrusion has one or more sidewalls. Each sidewall is oriented at a different angle with respect to the substrate. In other embodiments, each protrusion includes two intersecting ridges that are oriented in two different directions. In other embodiments, each tile 824 includes a plurality of rectangular parallelepipeds. Each rectangular parallelepiped has a different height. In some embodiments, the area of each tile decreases as the position of the tile varies from the central region 812 of the grating coupler 816 to the boundary 804 of the grating coupler 816. Tiles proximal to the boundary 804 are smaller in area than tiles proximal to the central region 812.

[0094] A second grating coupler (grating region 820) is interspersed among a plurality of tiles 824. The grating region 820 has a second grating pattern that is different from the first grating pattern. The grating region 820 includes a second set of parallel ridges that are orthogonal to a first set of parallel ridges of the internal coupling grating 800. The grating region 820 defines the OPE of the eyepiece. The layout of the tiles 824 can be modified to achieve a higher uniformity of the far-field virtual image. By varying the shape, size, distribution, and density of the tiles, a higher uniformity of the far-field virtual image is obtained. In some embodiments, the size of each tile can be kept the same while the tile density decreases from a higher density to a sparser one. The distribution of the tiles 824 can be either periodic or random. The sharpness of the resulting image is also increased. The different design options provided by the embodiments disclosed herein provide higher optical efficiency and quality.

[0095] In some embodiments, the grating couplers 816 and 820 are configured to receive light diffracted by the internal coupling grating 800. The grating couplers 816 and 820 are configured to reduce the luminance of the light emitted by the central regions 812 of the grating couplers 816 and 820. In some embodiments, the grating couplers 816 and 820 are configured to diffuse the light emitted by the central regions 812.

[0096] Patterning of the Grating Coupler FIG. 8B illustrates the patterning of the grating couplers 868 and 860 in an optical eyepiece. The eyepiece illustrated in FIG. 8B includes a substrate (e.g., substrate 400 illustrated and described above with reference to FIG. 4) and an internal coupling grating 848 imprinted on one side of the substrate. A first grating coupler 868 is imprinted on one side of the substrate and optically coupled to the internal coupling grating 848. The first grating coupler 868 includes a plurality of tiles that define the EPE of the eyepiece.

[0097] Each tile 864 has a first grating pattern (e.g., parallel ridges, protrusions, indentations, etc.). In some embodiments, each tile 864 includes a plurality of indentations. Each indentation of the plurality of indentations has one or more sidewalls. In some embodiments, the plurality of indentations have a refractive index greater than 1.4. In some embodiments, at least one of the width or length of each indentation is in the range of 5 nm to 800 nm. In some embodiments, the cross-section of each indentation has a triangular, serrated, stepped, or multi-step shape. A second grating coupler (grating region 860) is interspersed between the tiles. The grating region 860 has a second grating pattern different from the first grating pattern. The grating region 860 defines the OPE of the eyepiece. As shown in FIG. 8B, the area of each tile 864 increases as the position of the tile 864 changes from the first boundary 852 to the second boundary 856 of the grating region 860. The configuration of FIG. 8B is sometimes referred to as a tiled honeycomb lattice configuration or a tiled honeycomb lattice pattern.

[0098] In some embodiments, the internal coupling grating 848 is configured to receive light from a projector (e.g., projector 300 illustrated and described above with reference to FIG. 3A). The internal coupling grating 848 is configured to diffract light (e.g., light 332 shown in FIG. 3A) into a first portion of the light (e.g., portion 336) and a second portion of the light (e.g., portion 312). The first portion 336 has a first orientation with respect to the light 332 received from the projector 300. The second portion 312 has a second orientation with respect to the light 332 received from the projector 300. The second orientation is different from the first orientation. The diffraction grating is patterned on one side of the substrate. The diffraction grating is configured to receive the first portion 336 of the light and the second portion 312 of the light from the internal coupling grating 848. The diffraction grating includes a first grating coupler 868 and a second grating coupler 860. The first grating coupler 868 includes a plurality of tiles (e.g., tile 864). The second grating coupler 860 includes a grating region 860. The first grating coupler 868 receives the first portion 336 of the light from the internal coupling grating 848. The first grating coupler 868 diffracts the first portion 336 of the light. The first grating coupler 868 directs the diffracted first portion of the light (e.g., portion 340) to the second grating coupler 860. The second grating coupler 860 receives the second portion 312 of the light from the internal coupling grating 848. The second grating coupler 860 further diffracts the second portion 312 of the light. The second grating coupler 860 directs the diffracted second portion of the light (e.g., portion 316) to the first grating coupler 868. The diffraction grating is further configured to combine the diffracted first portion 340 of the light and the diffracted second portion 316 of the light.

[0099] Patterning of the Grating Coupler FIG. 9A illustrates the patterning of the grating coupler 912 in an optical eyepiece lens. The eyepiece lens shown in FIG. 9A includes an internal coupling grating 900 and a grating coupler 912. The grating coupler 912 includes a plurality of intersecting linear grating segments. For example, the linear grating segment 904 intersects the linear grating segment 908. The plurality of intersecting linear grating segments are arranged in a hexagonal packed grating pattern. The grating coupler 912 is sometimes referred to as having a fine line one-sided honeycomb grating pattern or configuration. Each polygon defined by the grating coupler 912 defines at least one angle between two linear grating segments (e.g., 904 and 908) that is in the range of 55 degrees to 65 degrees. Each polygon defined by the grating coupler 912 defines at least one other angle between two linear grating segments 904 and 908 that is in the range of 115 degrees to 125 degrees. In some embodiments, the eyepiece lens shown in FIG. 9A further includes a second grating coupler. The second grating coupler includes a grating area adjacent to the plurality of linear grating segments of the grating coupler 912. The grating coupler 912 functions in the same manner as the grating coupler illustrated and described above with reference to FIGS. 3A, 3B, 4, 7A, 7B, 8A, and 8B.

[0100] FIG. 9B illustrates the patterning of the grating coupler 972 in an optical eyepiece lens. The eyepiece lens illustrated in FIG. 9B includes an internal coupling grating 948 and a grating coupler 972 optically coupled to the internal coupling grating 948. The grating coupler 972 includes a plurality of linear grating segments arranged in a honeycomb grating pattern. For example, the grating coupler 972 includes the linear grating segment 952. In some embodiments, the eyepiece lens includes a second grating coupler. The second grating coupler can include a grating area adjacent to the plurality of linear grating segments of the grating coupler 972. The grating coupler 972 is sometimes referred to as having a fine line one-sided honeycomb grating pattern or configuration.

[0101] In some embodiments, the grating coupler 972 further includes a plurality of protrusions. In some embodiments, the pitch 968 of the axes of the protrusions is in the range of 300 nm to 450 nm. In some embodiments, the diagonal pitch 964 of the plurality of protrusions is in the range of 300 nm to 900 nm. In some embodiments, the grating coupler 972 includes a first set of protrusions having a first pitch axis 956, and the second grating coupler includes a second set of protrusions having a second pitch axis 960. In some embodiments, the angle between the first pitch axis 956 and the second pitch axis 960 is about 90 degrees, regardless of the presence or absence of feature overlap in each of the pitch axis directions. In some embodiments, the angle between the first pitch axis 956 and the second pitch axis 960 is in the range of 55 degrees to 65 degrees, regardless of the presence or absence of feature overlap in each of the pitch axis directions. The feature overlap can be about 30% of the length or width of the protrusion.

[0102] Patterning of Grating Couplers FIG. 10 illustrates the patterning of the grating coupler 1008 in an optical eyepiece. The grating coupler 1008 includes a first set of linear grating segments 1000 that define the OPE of the eyepiece. The grating coupler 1008 includes a second set of linear grating segments 1004 that define the EPE of the eyepiece. The second set of linear grating segments 1004 is sandwiched between the first set of linear grating segments 1000. The grating coupler 1008 is sometimes referred to as having a snowflake grating pattern or configuration.

[0103] In the eyepiece embodiments illustrated with reference to FIGS. 9A, 9B, and 10 above, the geometries of the internal coupling grating (e.g., internal coupling grating 900), OPE (e.g., OPE 1000), and EPE (e.g., EPE 1004) are adjusted such that the internal coupling grating 900 and the eyepiece have a preferred diffraction order. The portion of the light that is directly coupled or diffracted into the user's eyeball 328 is reduced, thus reducing unwanted artifacts. The eyepiece embodiments illustrated with reference to FIGS. 9A, 9B, and 10 above thus prevent the occurrence of artifacts in the bright central band in the resulting image. The diffractive properties of the OPE and EPE gratings can be further improved using the tilt of the protrusions and the blaze or multi-step protrusions or depressions. Patterning of a grating coupler in an optical eyepiece

[0104] FIG. 11A illustrates the patterning of a grating coupler in an optical eyepiece. The eyepiece shown in FIG. 11A includes a substrate (e.g., substrate 400 illustrated and described above with reference to FIG. 4) having a refractive index above a certain threshold. In some embodiments, the threshold is 1.4. The eyepiece further includes an internal coupling grating 1100 patterned on one side of the substrate. A first grating coupler 1120 is patterned on one side of the substrate. The first grating coupler 1120 is optically coupled to the internal coupling grating 1100 to receive a portion of the light from the internal coupling grating 1100. The first grating coupler 1120 has a first grating pattern 1104.

[0105] The second grating coupler 1124 is also patterned on one side of the substrate. The second grating coupler 1124 is optically coupled to the internal coupling grating 1100. The second grating coupler 1124 is adjacent to the first grating coupler 1120. The second grating coupler 1124 has a second grating pattern 1108 that is different from the first grating pattern 1104. In some embodiments, the first grating coupler 1120 or the first grating pattern 1104 includes a first set of ridges that are oriented in a first direction. The second grating coupler 1124 or the second grating pattern 1108 includes a second set of ridges that are oriented in a second direction as shown in FIG. 11A. In some embodiments, the angle between the first direction and the second direction is in the range of 55 degrees to 65 degrees.

[0106] In some embodiments, the internal coupling grating 1100 includes a first set of parallel ridges that are oriented in a first direction. The first grating coupler 1120 includes a second set of parallel ridges that are oriented in a second direction that is different from the first direction. The second grating coupler 1124 includes a third set of parallel ridges that are oriented in a third direction that is different from the first direction and the second direction. In some embodiments, the angle between the second direction and the third direction is in the range of 55 to 65 degrees.

[0107] In some embodiments, the first grating coupler 1120 contacts the second grating coupler 1124. Tiles (e.g., tile 1116) patterned using the second grating pattern 1108 are inserted into the first grating coupler 1120. Other tiles (e.g., tile 1112) patterned using the first grating pattern 1104 are inserted into the second grating coupler 1124. A tiled pattern (e.g., including tiles 1112 and 1116) is thus defined at the location where the first grating coupler 1120 contacts the second grating coupler 1124. Tile 1112 has the first grating pattern 1104. Tile 1116 has the second grating pattern 1108. Thus, the tiled region is configured to diffuse light that is directly coupled into the eye ball 328 of the user of the eyepiece. A sharp transition from the left visual field to the right visual field becomes blurred. The tile size, density, shape, and distribution can be varied to achieve higher virtual image resolution, uniformity, and brightness. The sharpness of the resulting image is also increased.

[0108] In some embodiments, the location where the first grating coupler 1120 contacts the second grating coupler 1124 includes an interlocking alternating grating pattern similar to the interlocking grating pattern 500 illustrated and described above with reference to FIG. 5A. In some embodiments, the location where the first grating coupler 1120 contacts the second grating coupler 1124 includes a stencil that mates a first boundary of the first grating coupler 1120 with a second boundary of the second grating coupler 1124.

[0109] Mated patterning of grating couplers in an optical eyepiece FIG. 11B illustrates the combined patterned grating couplers in an optical eyepiece lens. The eyepiece lens illustrated in FIG. 11B includes an internal grating 1168 configured to diffract light received from a projector (e.g., projector 300 illustrated and described above with reference to FIG. 3). The internal grating 1168 diffracts the light into a first portion of light and a second portion of light. A first grating coupler 1160 is optically coupled to the internal grating 1168. The internal grating 1168 is configured to direct the first portion of light to the first grating coupler 1160. The first grating coupler 1160 has a first grating pattern 1148. A second grating coupler 1164 is also optically coupled to the internal grating 1168. The internal grating 1168 is further configured to direct the second portion of light to the second grating coupler 1164. The second grating coupler 1164 has a second grating pattern 1152 that is different from the first grating pattern 1148.

[0110] A first boundary 1172 of the first grating coupler 1160 mates with a second boundary 1176 of the second grating coupler to define a mated grating area 1156. In some embodiments, the mated grating area 1156 includes an interlocking alternating pattern of the first grating pattern 1148 and the second grating pattern 1152. In some embodiments, the mated grating area 1156 includes a stencil that mates the first boundary 1172 of the first grating coupler 1160 with the second boundary 1176 of the second grating coupler 1164. In some embodiments, a merged grating region including stepped nano features is created to avoid a bright band at the center of the image. The grating features separate into two distinctly different grating patterns from the center of the grating towards each edge.

[0111] Diffraction and coupling of light using grating couplers in an optical eyepiece lens FIG. 12 illustrates the diffraction and coupling of light using a grating coupler in an optical eyepiece lens. FIG. 12 depicts the k-space of the light rays that are enabled to propagate within the waveguide in a manner that can be visualized. The gratings in FIG. 12 enable the light 1224 to diffract (spread and exit) in a particular direction, and thus the angled light is angled so as to reach the user's field of view.

[0112] The outer circle 1200 corresponds to the angular condition for light to propagate within the high refractive index substrate. The inner circle 1204 represents the condition for light to propagate in air. The annular region between the two concentric circles 1200 and 1204 corresponds to the total internal reflection (TIR) condition for light to propagate within the planar waveguide. The rectangle 1208 represents the field of view in air.

[0113] Additional embodiments In some embodiments, the eyepiece lens includes an internal coupling grating that is patterned on one side of the substrate and configured to diffract light received from the projector into a first portion of light and a second portion of light. The first portion has a first orientation with respect to the light received from the projector, and the second portion has a second orientation with respect to the light received from the projector. The second orientation is different from the first orientation. The diffraction grating is patterned on one side of the substrate and configured to receive the first portion of light and the second portion of light from the internal coupling grating. The first portion of light and the second portion of light are diffracted. The diffracted first portion of light and the diffracted second portion of light are combined.

[0114] In some embodiments, the first grating coupler includes a first set of protrusions having a first pitch axis. The second grating coupler includes a second set of protrusions having a second pitch axis.

[0115] In some embodiments, the angle between the first pitch axis and the second pitch axis is in the range of 55 degrees to 65 degrees.

[0116] In some embodiments, the first region of the first grating coupler overlaps with the second region of the second grating coupler. The overlapping first region and the overlapping second region each have an interlocking alternating grating pattern.

[0117] In some embodiments, the interlocking alternating grating pattern is configured to diffuse a third portion of light. The third portion of light is diffracted directly into the eye of the user of the eyepiece by the eyepiece.

[0118] In some embodiments, the interlocking alternating grating pattern includes a stencil that aligns the first boundary of the first grating coupler with the second boundary of the second grating coupler.

[0119] In some embodiments, the interlocking alternating grating pattern includes at least one of a plurality of parallel ridges oriented in a particular direction, a plurality of ridges arranged in a chevron grating pattern, or a plurality of ridges arranged in a sawtooth grating pattern.

[0120] In some embodiments, the interlocking alternating grating pattern includes a plurality of protrusions. Each protrusion of the plurality of protrusions has one or more sidewalls. Each sidewall of the one or more sidewalls is oriented at a different angle with respect to the substrate.

[0121] In some embodiments, the protrusion has a refractive index greater than 1.4.

[0122] In some embodiments, the first grating coupler includes tiles having a first grating pattern. The second grating coupler includes a grating area adjacent to the tiles and having a second grating pattern different from the first grating pattern.

[0123] In some embodiments, the internal coupling lattice includes a first set of parallel ridges oriented in a first direction. The first grating coupler includes a second set of parallel ridges oriented in a second direction different from the first direction. The second grating coupler includes a third set of parallel ridges oriented in a third direction different from the first and second directions.

[0124] In some embodiments, the angle between the second direction and the third direction is in the range of 55 degrees to 65 degrees.

[0125] In some embodiments, the first grating coupler includes a plurality of parallel grating sections oriented in a specific direction and having a first grating pattern. The second grating coupler includes a grating area adjacent to the plurality of parallel grating sections and having a second grating pattern different from the first grating pattern.

[0126] In some embodiments, the first grating coupler includes a plurality of linear grating sections arranged in a honeycomb grating pattern. The second grating coupler includes a grating area adjacent to the plurality of linear grating sections.

[0127] In some embodiments, the eyepiece includes an internal coupling lattice imprinted on one side of a substrate, and a grating coupler imprinted on one side of the substrate and optically coupled to the internal coupling lattice. The grating coupler includes a plurality of tiles that define an exit pupil expander (EPE) of the eyepiece. Each tile of the plurality of tiles has a first grating pattern. Grating regions are interspersed between the plurality of tiles and have a second grating pattern different from the first grating pattern. The grating regions define an orthogonal pupil expander (OPE) of the eyepiece.

[0128] In some embodiments, the grating coupler is configured to receive light diffracted by the internal coupling lattice and reduce the luminance of the light emitted by the central region of the grating coupler.

[0129] In some embodiments, the grating coupler is configured to receive light diffracted by an internal coupling grating and to diffuse the light emitted by a central region of the grating coupler.

[0130] In some embodiments, each tile of a plurality of tiles includes a plurality of protrusions. Each protrusion of the plurality of protrusions has one or more sidewalls. Each sidewall of the one or more sidewalls is oriented at a different angle with respect to the substrate.

[0131] In some embodiments, each protrusion of the plurality of protrusions includes two intersecting ridges that are oriented in two different directions.

[0132] In some embodiments, each protrusion of the plurality of protrusions has a cylindrical or elliptical shape.

[0133] In some embodiments, each protrusion of the plurality of protrusions has at least one rectangular, circular, triangular, or polygonal surface.

[0134] In some embodiments, each tile of a plurality of tiles includes a plurality of rectangular parallelepipeds. Each rectangular parallelepiped of the plurality of rectangular parallelepipeds has a different height.

[0135] In some embodiments, the internal coupling grating includes a first set of parallel ridges. The grating region includes a second set of parallel ridges that are orthogonal to the first set of parallel ridges.

[0136] In some embodiments, the area of each tile of a plurality of tiles decreases as the position of the tile changes from the center of the grating coupler to the boundary of the grating coupler.

[0137] In some embodiments, the area of each tile of a plurality of tiles increases as the position of the tile changes from a first boundary of the grating coupler to a second boundary of the grating coupler.

[0138] In some embodiments, each of the plurality of tiles has at least one of a rectangular shape, a circular shape, an oval shape, a polygonal shape, or a hexagonal shape.

[0139] In some embodiments, each of the plurality of tiles includes a plurality of depressions. Each of the plurality of depressions has one or more sidewalls.

[0140] In some embodiments, the plurality of depressions have a refractive index greater than 1.4.

[0141] In some embodiments, at least one of the width or length of each of the plurality of depressions is in the range of 5 nm to 800 nm.

[0142] In some embodiments, the cross-section of each of the plurality of depressions has a triangular, serrated, or stepped shape.

[0143] In some embodiments, the eyepiece includes a substrate having a refractive index greater than a certain threshold, and an internal coupling grating patterned on one side of the substrate. Three or more grating couplers are patterned on one side of the substrate and optically coupled to the internal coupling grating. Each of the three or more grating couplers has a different grating pattern.

[0144] In some embodiments, the internal coupling grating is configured to diffract light received from a projector into three or more portions of light.

[0145] In some embodiments, each of the three or more portions of light has a different orientation with respect to the light received from the projector.

[0146] In some embodiments, the internal coupling grating is further configured to direct the corresponding portions of the three or more portions of light to each of the three or more grating couplers.

[0147] In some embodiments, each of the three or more grating couplers is configured to diffract corresponding portions of three or more portions of light.

[0148] In some embodiments, the eyepiece is configured to combine the three or more diffracted portions of light.

[0149] In some embodiments, at least one of the three or more grating couplers is positioned between two other grating couplers of the three or more grating couplers.

[0150] In some embodiments, the first other grating coupler of the two other grating couplers includes a first linear grating section oriented in a first direction.

[0151] In some embodiments, the second other grating coupler of the two other grating couplers includes a second linear grating section oriented in a second direction different from the first direction.

[0152] In some embodiments, the angle between the first direction and the second direction is in the range of 55 degrees to 65 degrees.

[0153] In some embodiments, at least one of the three or more grating couplers includes a plurality of linear grating sections oriented in a third direction different from the first direction and different from the second direction.

[0154] In some embodiments, the pitch of at least one of the three or more grating couplers is defined by the intersection of the first other grating coupler of the two other grating couplers and the second other grating coupler of the two other grating couplers.

[0155] In some embodiments, the width of at least one of the three or more grating couplers is in the range of 5 mm to 20 mm.

[0156] In some embodiments, at least one of the three or more grating couplers includes a plurality of tiles.

[0157] In some embodiments, each tile of the set of tiles has a polygonal shape.

[0158] In some embodiments, each tile of the plurality of tiles includes a plurality of protrusions. Each protrusion of the plurality of protrusions has one or more sidewalls.

[0159] In some embodiments, the filling rate of the volume of each protrusion of the plurality of protrusions, measured along the direction of light incident from the internal coupling grating to the plurality of protrusions, is in the range of 10% to 90%.

[0160] In some embodiments, the pitch of the axes of the plurality of protrusions is in the range of 300 nm to 450 nm.

[0161] In some embodiments, the diagonal pitch of the plurality of protrusions is in the range of 300 nm to 900 nm.

[0162] In some embodiments, at least one of the three or more grating couplers is configured to diffuse a portion of the light received from the internal coupling grating.

[0163] In some embodiments, at least one of the three or more grating couplers is configured to reduce the intensity of the light emitted into the user's eyeball of the eyepiece by at least one of the grating couplers.

[0164] In some embodiments, the eyepiece includes an internal coupling grating that is patterned on at least one of a first side having a refractive index above a certain threshold or a second side of the substrate. A first grating coupler is patterned on the first side of the substrate and has a first grating pattern. The first grating coupler is optically coupled to the internal coupling grating. A second grating coupler is patterned on the second side of the substrate and has a second grating pattern different from the first grating pattern. The second grating coupler is optically coupled to the internal coupling grating.

[0165] In some embodiments, the first grating coupler and the second grating coupler are configured to receive light from an internal grating lattice.

[0166] In some embodiments, the area of the first grating coupler overlaps with the second grating coupler such that the overlapping area is configured to diffract a portion of the light into the eye of the user of the eyepiece.

[0167] In some embodiments, the area is in the range of 10% to 60% of the total area of the first grating coupler.

[0168] In some embodiments, at least one of the first grating coupler or the second grating coupler includes a plurality of protrusions. Each protrusion of the plurality of protrusions has one or more sidewalls. Each sidewall of the one or more sidewalls is oriented at a different angle with respect to the substrate.

[0169] In some embodiments, each protrusion of the plurality of protrusions includes at least two intersecting ridges that are oriented in two different directions.

[0170] In some embodiments, the filling ratio of the volume of each protrusion of the plurality of protrusions, measured along the direction of the light incident on the plurality of protrusions from the internal grating lattice, is in the range of 10% to 90%.

[0171] In some embodiments, the pitch of the axes of the plurality of protrusions is in the range of 300 nm to 450 nm.

[0172] In some embodiments, the diagonal pitch of the plurality of protrusions is in the range of 300 nm to 900 nm.

[0173] In some embodiments, the height of each protrusion of the plurality of protrusions is in the range of 5 nm to 500 nm.

[0174] In some embodiments, at least one of the width or length of each protrusion of the plurality of protrusions is in the range of 5 nm to 800 nm.

[0175] In some embodiments, the cross-section of each of the plurality of protrusions has a triangular, serrated, or stepped shape.

[0176] In some embodiments, each of the plurality of protrusions includes a plurality of rectangular parallelepipeds. Each of the plurality of rectangular parallelepipeds has a different height.

[0177] In some embodiments, the plurality of protrusions have a refractive index greater than 1.4.

[0178] In some embodiments, the first grating coupler includes tiles having a first grating pattern. The second grating coupler includes a grating area adjacent to the tiles and having a second grating pattern.

[0179] In some embodiments, the first grating coupler includes a plurality of depressions. Each of the plurality of depressions has one or more sidewalls. Each of the one or more sidewalls is oriented at a different angle with respect to the substrate.

[0180] In some embodiments, the first grating coupler includes a first set of ridges oriented in a first direction. The second grating coupler includes a second set of ridges oriented in a second direction.

[0181] In some embodiments, the angle between the first direction and the second direction is in the range of 55 degrees to 65 degrees.

[0182] In some embodiments, the first grating coupler includes a first set of protrusions having a first pitch axis. The second grating coupler includes a second set of protrusions having a second pitch axis.

[0183] In some embodiments, the angle between the first pitch axis and the second pitch axis is in the range of 55 degrees to 65 degrees.

[0184] In the foregoing description, embodiments have been described with reference to numerous specific details that may vary from implementation to implementation. The description and drawings are, therefore, to be regarded in an illustrative rather than a restrictive sense.

Claims

1. An eyepiece comprising: a substrate, the substrate having a refractive index greater than a threshold; an internal bonding grating on a single face of the substrate; a first grating coupler on the single surface of the substrate, the first grating coupler configured to be optically coupled to the internal coupling grating, the first grating coupler having a first grating pattern; and a second grating coupler on the single face on the substrate, the second grating coupler configured to be optically coupled to the internal coupling grating, the second grating coupler having a second grating pattern, the second grating pattern being oriented in a direction different from a direction in which the first grating pattern is oriented; and a first set of tiles positioned within the first grating coupler, the first set of tiles comprising the second grating pattern; a second set of tiles positioned within the second grating coupler, the second set of tiles comprising the first grating pattern; An eyepiece comprising:

2. An eyepiece lens as described in claim 1, wherein the first grating coupler is adjacent to the second grating coupler.

3. An eyepiece lens as described in claim 1, wherein the first grating pattern has a first set of ridges oriented in a first direction, and the second grating pattern has a second set of ridges oriented in a second direction.

4. An eyepiece lens as described in claim 3, wherein the angle between the first direction and the second direction is within the range of 55 degrees to 65 degrees.

5. An eyepiece as described in claim 1, wherein the internal bonding grating has a first set of parallel ridges oriented in a first direction, the first grating pattern has a second set of parallel ridges oriented in a second direction different from the first direction, and the second grating pattern has a third set of parallel ridges oriented in a third direction different from the first direction and the second direction.

6. An eyepiece lens as described in claim 5, wherein the angle between the second direction and the third direction is within the range of 55 degrees to 65 degrees.

7. An eyepiece as described in claim 1, wherein the first grating coupler contacts the second grating coupler.

8. An eyepiece as described in claim 1, wherein the first set of tiles and the second set of tiles are positioned at a location where the first grating coupler contacts the second grating coupler.

9. An eyepiece as described in claim 8, wherein the first set of tiles are offset relative to the second set of tiles along a direction parallel to the interface between the first grating coupler and the second grating coupler.

10. An eyepiece comprising: a substrate, the substrate having a refractive index greater than a threshold; an internal bonding grating on a single face of the substrate; a first grating coupler on the single surface of the substrate, the first grating coupler configured to be optically coupled to the internal coupling grating, the first grating coupler having a first grating pattern; and a second grating coupler on the single surface on the substrate, the second grating coupler configured to be optically coupled to the internal coupling grating, the second grating coupler having a second grating pattern, the second grating pattern being oriented in a direction different from a direction in which the first grating pattern is oriented; and Equipped with An eyepiece lens, wherein a first boundary of the first grating coupler blends with a second boundary of the second grating coupler to define a blended grating area.

11. An eyepiece lens as described in claim 10, wherein the blended grating area comprises an interdigitated alternating pattern of the first grating pattern and the second grating pattern.

12. The eyepiece of claim 10, wherein the blended grating area comprises a stencil that blends the first boundary of the first grating coupler and the second boundary of the second grating coupler.

13. An eyepiece lens as described in claim 10, wherein the combined lattice areas of the blended lattice areas have graduated nano-features.

14. The eyepiece of claim 10, wherein the internal coupling grating is configured to diffract input light into a first portion and a second portion, the first portion being directed toward the first grating coupler and the second portion being directed toward the second grating coupler.

Images