Method and apparatus for providing holographic waveguide displays using integrated gratings

Abstract

Systems and methods for providing a holographic waveguide display using integrated gratings according to various embodiments of the present invention are illustrated. One embodiment includes a waveguide display including a light source; and a first waveguide including a grating structure including a first grating and a second grating; and an input coupler configured to couple a first field of view portion of the light and to couple a second field of view portion of the light, wherein the first grating is configured to provide beam expansion in a first direction for the first field of view portion of the light, and to provide beam expansion in the first direction and beam extraction toward an observer for the second field of view portion of the light, and the second grating is configured to provide beam expansion in a second direction for the second field of view portion of the light, and to provide beam expansion in the second direction and beam extraction toward an observer for the first field of view portion of the light.

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims the benefit of and priority under 35 U.S.C. §119(e) to U.S. Provisional Patent Application No. 62 / 806,665, filed on February 15, 2019, entitled “Methods and Apparatuses for Providing a Color Holographic Waveguide Display Using Overlapping Bragg Gratings” and U.S. Provisional Patent Application No. 62 / 813,373, filed on March 4, 2019, entitled “Improvements to Methods and Apparatuses for Providing a Color Holographic Waveguide Display Using Overlapping Bragg Gratings”. The disclosures of U.S. Provisional Patent Application Nos. 62 / 806,665 and 62 / 813,373 are incorporated herein by reference in their entirety for all purposes. Technical Field

[0003] The present invention relates generally to waveguide devices and, more particularly, to holographic waveguide displays. Background Art

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

[0005] Fabrication of waveguides may include the use of material systems that allow for the recording of holographic optical elements within the waveguide. One class of such materials includes polymer dispersed liquid crystal (PDLC) mixtures, which are mixtures comprising photopolymerizable monomers and liquid crystals. Another subclass of such mixtures includes holographic polymer dispersed liquid crystal (HPDLC) mixtures. Holographic optical elements, such as volume phase gratings, can be recorded in such liquid mixtures by illuminating the material with two mutually coherent laser beams. During the recording process, the monomers polymerize and the mixture undergoes photopolymerization-induced phase separation, creating regions densely populated by liquid crystal droplets, interspersed with regions of transparent polymer. Alternating liquid crystal-rich and liquid crystal-poor regions form the edge planes of the grating. The resulting grating, which is often referred to as a switchable Bragg grating (SBG), has all the properties typically associated with volume or Bragg gratings, but with a much higher range of refractive index modulation and the ability to electrically tune the grating over a continuous range of diffraction efficiencies (the proportion of incident light diffracted into a desired direction). The latter can be extended from non-diffracting (transparent) to diffracting, with efficiencies approaching 100%.

[0006] Waveguide optics, such as those described above, may be considered for a range of display and sensor applications. In many applications, waveguides containing one or more grating layers encoding a variety of optical functions may be implemented using a variety of waveguide architectures and material systems, leading to new innovations in near-eye displays for augmented reality (AR) and virtual reality (VR), compact head-up displays (HUD) and helmet-mounted displays or head-mounted displays (HMD) for road transport, aviation, and military applications, and sensors for biometrics and laser radar (LIDAR) applications. Summary of the invention

[0007] Systems and methods for providing a holographic waveguide display using integrated gratings according to various embodiments of the present invention are illustrated. One embodiment includes a waveguide display comprising a light source; a first waveguide comprising a grating structure comprising first and second gratings; and an input coupler configured to couple a first field of view portion of light from the light source into the first waveguide and toward the first grating, and to couple a second field of view portion of light from the light source into the first waveguide and toward the second grating, wherein the first grating is configured to provide beam expansion in a first direction for the first field of view portion of the light, and to provide beam expansion in the first direction and beam extraction toward an observer for the second field of view portion of the light, the second grating is configured to provide beam expansion in a second direction for the second field of view portion of the light, and to provide beam expansion in the second direction and beam extraction toward an observer for the first field of view portion of the light, the input coupler, the first grating, and the second grating each include a grating vector, and the grating vectors of the input coupler, the first grating, and the second grating provide a result vector having a magnitude substantially zero.

[0008] In another embodiment, the first grating includes first and second grating prescriptions, and the second grating includes third and fourth grating prescriptions, wherein the first grating prescription is configured to provide beam expansion in a first direction for a first field of view portion of light, the second grating prescription is configured to provide beam expansion in the first direction and beam extraction toward an observer for a second field of view portion of light, the third grating prescription is configured to provide beam expansion in a second direction for the second field of view portion of light, and the fourth grating prescription is configured to provide beam expansion in the second direction and beam extraction toward an observer for the first field of view portion of light.

[0009] In a further embodiment, the first and second grating specifications are at least partially multiplexed and the third and fourth grating specifications are at least partially multiplexed.

[0010] In yet another embodiment, the first grating at least partially overlaps the second grating.

[0011] In yet another embodiment, the first waveguide includes first and second grating layers, the first grating being disposed within the first grating layer and the second grating being disposed within the second grating layer.

[0012] In yet another embodiment, the first waveguide further includes a transparent layer disposed between and adjacent to the first and second grating layers.

[0013] In yet another embodiment, the waveguide display further includes a second waveguide, wherein the first waveguide is configured to couple in a first spectral band and the second waveguide is configured to couple in a second spectral band.

[0014] In another additional embodiment, the input coupler includes an input configuration selected from at least one of an input prism, an input grating, a first and a second input grating, and an input grating including two multiplexed grating specifications.

[0015] In a further additional embodiment, the grating vector of the input coupler has a different magnitude than the grating vector of the first grating.

[0016] In another embodiment, the light source provides light of at least two different wavelengths.

[0017] In yet another embodiment, a method of displaying an image includes providing a waveguide display including a first waveguide supporting an input coupler and a grating structure including first and second gratings, wherein the input coupler, the first grating, and the second grating each include a grating vector, wherein the grating vectors of the input coupler, the first grating, and the second grating provide a result vector having a magnitude substantially zero, coupling a first field of view portion into the waveguide via the input coupler, coupling a second field of view portion into the waveguide via the input coupler, expanding the first field of view portion of light in a first direction using the first grating, expanding the first field of view portion of light in a second direction using the second grating and extracting it from the waveguide, expanding the second field of view portion of light in the second direction using the second grating, and expanding the second field of view portion of light in the first direction and extracting it from the waveguide using the first grating.

[0018] In yet another embodiment, the first grating includes first and second grating specifications, and the second grating includes third and fourth grating specifications, wherein the first grating specification is used to expand the first field portion of light in the first direction, the second grating specification is used to expand the second field portion of light in the first direction and extract it from the waveguide, the third grating specification is used to expand the second field portion of light in the second direction, and the fourth grating specification is used to expand the first field portion of light in the second direction and extract it from the waveguide.

[0019] In yet another embodiment, the first and second grating specifications are at least partially multiplexed, and the third and fourth grating specifications are at least partially multiplexed.

[0020] In yet another additional embodiment, the first grating at least partially overlaps the second grating.

[0021] In yet another additional embodiment, the first waveguide includes first and second grating layers, the first grating being disposed within the first grating layer and the second grating being disposed within the second grating layer.

[0022] In yet another embodiment, the first waveguide further includes a transparent layer disposed between and adjacent to the first and second grating layers.

[0023] In yet another embodiment, the waveguide display further includes a second waveguide, wherein the first waveguide is configured to couple in a first spectral band and the second waveguide is configured to couple in a second spectral band.

[0024] In yet another additional embodiment, the input coupler includes an input configuration selected from at least one of an input prism, an input grating, first and second input gratings, and an input grating including two multiplexed grating specifications.

[0025] In yet another additional embodiment, the grating vector of the input coupler has a different magnitude than the grating vector of the first grating.

[0026] In yet another embodiment, the light source provides light of at least two different wavelengths.

[0027] Additional embodiments and features are partially set forth in the following description, and in part will become apparent to those skilled in the art after examining the specification, or may be learned through practice of the invention. The nature and advantages of the invention may be further understood by reference to the remainder of the specification and the accompanying drawings, which constitute a part of this disclosure. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] The description herein will be more fully understood with reference to the following drawings and data graphs, which are presented as exemplary embodiments of the invention and should not be construed as a complete recitation of the scope of the invention.

[0029] Figure 1 A waveguide display according to an embodiment of the present invention is conceptually illustrated.

[0030] Figure 2 A color waveguide display having two blue-green diffractive waveguides and two green-red diffractive waveguides is conceptually illustrated in accordance with an embodiment of the present invention.

[0031] Figures 3A-3C Integrated gratings according to various embodiments of the present invention are conceptually illustrated.

[0032] Figures 4A-4C The propagation of rays through a grating structure having an input grating and two integrating gratings according to an embodiment of the present invention is schematically illustrated.

[0033] Figures 5A-5E Various raster vector configurations are conceptually illustrated according to various embodiments of the invention.

[0034] Figure 6 A schematic plan view of a grating architecture having an input grating and an integrated grating according to an embodiment of the present invention is conceptually illustrated.

[0035] Figure 7 A flowchart conceptually illustrating a method of displaying an image according to an embodiment of the present invention is shown.

[0036] Figure 8 A flow chart conceptually illustrating a method of displaying an image using an integrated grating including a plurality of gratings according to an embodiment of the present invention is shown.

[0037] Fig. 9 A cross-sectional view of two overlapping waveguide sections implementing an integrated grating in accordance with an embodiment of the present invention is conceptually illustrated.

[0038] Fig.10A schematic plan view of a grating architecture having two sets of integrated gratings according to an embodiment of the present invention is conceptually illustrated.

[0039] Fig.11 A conceptual diagram illustrates the relationship between diffraction efficiency and angle of a waveguide for diffraction occurring at different field angles according to an embodiment of the present invention.

[0040] Fig.12 The viewing geometry provided by a waveguide according to an embodiment of the present invention is shown.

[0041] Fig.13 Conceptually illustrates the field of view geometry of a binocular display with binocular overlap between left-eye and right-eye images provided by a waveguide in accordance with an embodiment of the present invention. DETAILED DESCRIPTION

[0042] For the purpose of describing the embodiments, some well-known features of optical technology known to those skilled in the art of optical design and visual display have been omitted or simplified so as not to confuse the basic principles of the present invention. Unless otherwise stated, the term "on axis" related to the direction of a ray or beam refers to propagation parallel to an axis perpendicular to the surface of the optical component described with respect to the present invention. In the following description, the terms light, ray, beam and direction can be used interchangeably and are associated with each other to indicate the direction of propagation of electromagnetic radiation along a straight line trajectory. The terms light and illumination can be used with respect to the visible and infrared bands of the electromagnetic spectrum. Parts of the following description will be presented using terms commonly used by those skilled in the art of optical design. As used herein, in some embodiments, the term grating can cover a grating consisting of a set of gratings. For the purpose of illustration, it should be understood that the drawings are not drawn to scale unless otherwise stated.

[0043] Waveguide displays according to various embodiments of the present invention can be implemented using many different technologies. Waveguide technology can provide low-cost, efficient and versatile diffractive optical solutions for many different applications. A commonly used waveguide architecture includes an input grating for coupling light from an image source into a TIR path in a waveguide, a folded grating for providing a beam expansion in a first direction, and an output grating for providing a second beam expansion in a direction orthogonal to the first direction and extracting a pupil-expanded beam from the waveguide for observation from an exit pupil or eyebox. Although effective in two-dimensional beam expansion and extraction, this arrangement typically requires a large grating area. When used with a birefringent grating, this architecture also suffers from the effects of turbidity caused by the interaction of millions of gratings in the fold. Another problem is image non-uniformity caused by more beams interacting with the substrate of the waveguide due to a longer optical path. As such, many embodiments of the present invention are directed to wide-angle, low-cost, efficient and compact waveguide displays.

[0044] In many embodiments, the waveguide display includes at least one input grating and at least two integrated gratings, each integrated grating being capable of performing the functions of a conventional folding and output grating. In further embodiments, a single multiplexed input grating is implemented to provide an input light having two bifurcated paths. In other embodiments, two input gratings are implemented to provide a bifurcated light path. In addition to different configurations of the (one or more) input gratings, the integrated gratings can also be configured in various ways. In some embodiments, the integrated gratings contain crossed grating vectors and can be configured to provide beam expansion in two directions and beam extraction for light from the (one or more) input gratings. In several embodiments, the integrated gratings are configured as overlapping gratings with crossed grating vectors. The integrated nature of the grating architecture can allow for compact waveguide displays suitable for a variety of applications, including but not limited to AR, VR, HUD, and LIDAR applications. As can be easily appreciated, the specific architecture and implementation of the waveguide display can depend on the specific requirements of a given application. For example, in some embodiments, a waveguide display is implemented with an integrated grating to provide a binocular field of view of at least 50° diagonal. In further embodiments, the waveguide display is implemented with an integrated grating to provide a binocular field of view of at least -100° diagonal.Waveguide displays, grating architectures, HPDLC materials and manufacturing processes according to various embodiments of the present invention are discussed in further detail below.

[0045] Optical waveguide and grating structures

[0046] The optical structure recorded in the waveguide can include many different types of optical elements, such as but not limited to diffraction gratings. Gratings can be implemented to perform various optical functions, including but not limited to coupling light, directing light, and preventing transmission of light. In many embodiments, the grating is a surface relief grating located on the outer surface of the waveguide. In other embodiments, the implemented grating is a Bragg grating (also known as a volume grating), which is a structure with a periodic refractive index modulation. Bragg gratings can be manufactured using a variety of different methods. One process includes interference exposure of a holographic photopolymer material to form a periodic structure. Bragg gratings can have high efficiency, with little light being diffracted into higher orders. The relative amount of diffracted orders and zero-order light can be changed by controlling the refractive index modulation of the grating, which is a property used to manufacture lossy waveguide gratings to extract light over a large pupil.

[0047] One type of Bragg grating used in holographic waveguide devices is a switchable Bragg grating (SBG). An SBG can be fabricated by first placing a thin film of a mixture of a photopolymerizable monomer and a liquid crystal material between substrates. The substrates can be made of various types of materials, such as glass and plastic. In many cases, the substrates are in a parallel configuration. In other embodiments, the substrates are formed into a wedge shape. One or both substrates can support electrodes, typically transparent tin oxide films, for applying an electric field across the film. The grating structure in the SBG can be recorded in a liquid material (commonly referred to as a slurry) by photopolymerization-induced phase separation using interferometric exposure with spatially periodic intensity modulation. Factors such as, but not limited to, controlling the radiation intensity, the component volume fractions of the materials in the mixture, and the exposure temperature can determine the resulting grating morphology and performance. It can be readily appreciated that a variety of materials and mixtures can be used, depending on the specific requirements of a given application. In many embodiments, HPDLC materials are used. During the recording process, the monomers polymerize and the mixture undergoes phase separation. The LC molecules aggregate to form discrete or coalesced droplets that are periodically distributed in the polymer network within the optical wavelength range. The alternating liquid crystal-rich and liquid crystal-poor regions form the fringe planes of the grating, which can produce Bragg diffraction with strong optical polarization caused by the orientation order of the LC molecules in the droplets.

[0048] The resulting volume phase grating can exhibit very high diffraction efficiency, which can be controlled by the strength of the electric field applied to the film. In the case where an electric field is applied to the grating via a transparent electrode, the natural orientation of the LC droplets may change, resulting in a reduced refractive index modulation of the fringes and a reduction in the hologram diffraction efficiency to a very low level. Typically, the electrodes are configured so that the applied electric field is perpendicular to the substrate. In many embodiments, the electrodes are made of indium tin oxide (ITO). In the OFF state, where no electric field is applied, the extraordinary axis of the liquid crystal is typically aligned perpendicular to the fringes. Therefore, the grating has a higher refractive index modulation for P-polarized light and a higher diffraction efficiency. In the case of an electric field applied to the HPDLC, the grating switches to the ON state, where the extraordinary axes of the liquid crystal molecules are aligned parallel to the applied electric field and therefore aligned perpendicular to the substrate. In the ON state, the grating exhibits a lower refractive index modulation and a lower diffraction efficiency for both S-polarized light and P-polarized light. Therefore, the grating area no longer diffracts light. Depending on the function of the HPDLC device, each grating area can be divided into a plurality of grating elements, such as, for example, a pixel matrix. Typically, the electrodes on one substrate surface are uniform and continuous, while the electrodes on the opposing substrate surface are patterned according to a plurality of selectively switchable grating elements.

[0049] Typically, an SBG element is zeroed within 30 μs and switched on with a longer relaxation time. The diffraction efficiency of the device can be adjusted over a continuous range with the aid of the applied voltage. In many cases, the device exhibits close to 100% efficiency without applied voltage and essentially zero efficiency when a sufficiently high voltage is applied. In some types of HPDLC devices, a magnetic field can be used to control the LC orientation. In some HPDLC applications, the phase separation of the LC material from the polymer can be such that no discernible droplet structure is produced. SBGs can also be used as passive gratings. In this mode, its main advantage is the unique high refractive index modulation. SBGs can be used to provide transmission or reflection gratings for free-space applications. SBGs can be implemented as waveguide devices, where the HPDLC forms a waveguide core or an evanescent coupling layer near the waveguide. The substrate used to form the HPDLC unit cell provides a total internal reflection (TIR) ​​lightguide structure. When the switchable grating diffracts light at an angle exceeding the TIR condition, light can be coupled out of the SBG.

[0050] In some embodiments, the LC can be extracted or drained from the SBG to provide a surface relief grating (SRG) that has properties very similar to a Bragg grating due to the depth of the SRG structure (which is much greater than can be practically achieved using surface etching and other conventional processes typically used to make SRGs). The LC can be extracted using a variety of different methods, including but not limited to washing with isopropyl alcohol and solvents. In many embodiments, one of the transparent substrates of the SBG is removed and the LC is extracted. In further embodiments, the removed substrate is replaced. The SRG can be at least partially backfilled with a material of higher or lower refractive index. Such gratings provide scope for tailoring efficiency, angular / spectral response, polarization, and other properties to suit a variety of waveguide applications.

[0051] Waveguides according to various embodiments of the present invention may include various grating configurations designed for specific purposes and functions. In many embodiments, the waveguide is designed to achieve a grating configuration that can maintain the eye box size while reducing the lens size by effectively expanding the exit pupil of the collimating optical system. The exit pupil can be defined as a virtual aperture, and only light that passes through this virtual aperture can enter the user's eye. In some embodiments, the waveguide includes an input grating optically coupled to a light source, a folded grating for providing beam expansion in a first direction, and an output grating for providing beam expansion in a second direction generally orthogonal to the first direction and beam extraction toward the eye box. As can be easily recognized, the waveguide architecture implemented by the grating configuration can depend on the specific requirements of a given application. In some embodiments, the grating configuration includes a plurality of folded gratings. In several embodiments, the grating configuration includes an input grating and a second grating for performing beam expansion and beam extraction simultaneously. The second grating may include gratings of different specifications for propagating different parts of the field of view, arranged in separate overlapping grating layers or multiplexed in a single grating layer. In addition, various types of grating and waveguide structures can also be used.

[0052] In several embodiments, the gratings within each layer are designed to have different spectral and / or angular responses. For example, in many embodiments, different gratings across different grating layers are overlapped or multiplexed to provide an increase in spectral bandwidth. In some embodiments, three grating layers are used to implement a full-color waveguide, each grating layer is designed to operate in a different spectral band (red, green and blue). In other embodiments, two grating layers, a red-green grating layer and a green-blue grating layer, are used to implement a full-color waveguide. As can be easily recognized, such techniques can be similarly implemented to increase the angular bandwidth operation of the waveguide. In addition to the multiplexing of gratings across different grating layers, multiple gratings can be multiplexed within a single grating layer - that is, multiple gratings can be superimposed within the same volume. In several embodiments, the waveguide includes at least one grating layer having two or more grating specifications multiplexed in the same volume. In a further embodiment, the waveguide includes two grating layers, each layer having two grating specifications multiplexed in the same volume. Multiplexing two or more grating specifications within the same volume may be achieved using various manufacturing techniques. In multiple embodiments, a multiplexed master grating is used with an exposure configuration to form a multiplexed grating. In many embodiments, the multiplexed grating is manufactured by sequentially exposing a layer of optical recording material with two or more configurations of exposure light, where each configuration is designed to form a grating specification. In some embodiments, the multiplexed grating is manufactured by alternating exposure of a layer of optical recording material between two or more configurations of exposure light, where each configuration is designed to form a grating specification. As can be readily appreciated, a variety of techniques, including techniques well known in the art, may be used as appropriate to manufacture the multiplexed grating.

[0053] In many embodiments, the waveguide may incorporate at least one of: angle multiplexed gratings, color multiplexed gratings, folded gratings, dual alternating gratings, scrolled K-vector gratings, cross-folded gratings, mosaic gratings, chirped gratings, gratings with spatially varying refractive index modulation, gratings with spatially varying grating thickness, gratings with spatially varying average refractive index, gratings with spatially varying refractive index modulation tensors, and gratings with spatially varying average refractive index tensors. In some embodiments, the waveguide may incorporate at least one of: half-wave plates, quarter-wave plates, anti-reflection coatings, beam splitters, alignment layers, photochromic backing layers for glare reduction, and shutter films for glare reduction. In several embodiments, the waveguide may support gratings that provide separate optical paths for different polarizations. In various embodiments, the waveguide may support gratings that provide separate optical paths for different spectral bandwidths. In a number of embodiments, the grating may be a HPDLC grating, a switch grating recorded in the HPDLC (such as a switchable Bragg grating), a Bragg grating recorded in a holographic photopolymer, or a surface relief grating. In many embodiments, the waveguide operates in a monochrome band. In some embodiments, the waveguide operates in a green band. In several embodiments, waveguide layers operating in different spectral bands, such as red, green, and blue (RGB), may be stacked to provide a three-layer waveguide structure. In further embodiments, the layers are stacked with air gaps between the waveguide layers. In various embodiments, the waveguide layers operate in a wider band, such as blue-green and green-red, to provide a dual waveguide layer solution. In other embodiments, the gratings are color multiplexed to reduce the number of grating layers. Various types of gratings may be implemented. In some embodiments, at least one grating in each layer is a switchable grating.

[0054] Waveguides in combination with optical structures such as those discussed above can be implemented in a variety of different applications, including but not limited to waveguide displays. In various embodiments, the waveguide display is implemented with an eye box greater than 10 mm and an eye distance greater than 25 mm. In some embodiments, the waveguide display includes a waveguide with a thickness between 2.0-5.0 mm. In many embodiments, the waveguide display can provide an image field of view of at least 50° diagonal. In further embodiments, the waveguide display can provide an image field of view of at least 70° diagonal. The waveguide display can employ many different types of picture generation units (PGUs). In several embodiments, the PGU can be a reflective or transmissive spatial light modulator, such as a liquid crystal on silicon (LCoS) panel or a microelectromechanical system (MEMS) panel. In multiple embodiments, the PGU can be an emissive device such as an organic light emitting diode (OLED) panel. In some embodiments, the OLED display can have a luminance greater than 4000 nits and a resolution of 4k×4k pixels. In several embodiments, the waveguide can have an optical efficiency greater than 10%, so that an image luminance greater than 400 nits can be provided using an OLED display with a luminance of 4000 nits. Waveguides implementing P diffraction gratings (i.e., gratings with high efficiency for P polarized light) typically have a waveguide efficiency of 5%-6.2%. Since P diffraction or S diffraction gratings waste half of the light from a non-polarized source (such as an OLED panel), many embodiments are directed to waveguides that can provide S diffraction and P diffraction gratings to allow the efficiency of the waveguide to be increased by a factor of two. In some embodiments, the S diffraction and P diffraction gratings are implemented in separate overlapping grating layers. Alternatively, under certain conditions, a single grating can provide high efficiency for both p-polarized light and s-polarized light. In several embodiments, the waveguide includes a Bragg-like grating produced by extracting LC from an HPDLC grating (such as those described above) to achieve high S and P diffraction efficiencies over certain wavelength and angle ranges for appropriately selected grating thickness values ​​(typically in the range of 2-5 μm).

[0055] Optical recording material system

[0056] HPDLC mixtures typically include LC, monomers, photoinitiator dyes and coinitiators. The mixture (commonly referred to as a slurry) also typically includes a surfactant. For the purposes of describing the present invention, a surfactant is defined as any chemical agent that reduces the surface tension of the total liquid mixture. The use of surfactants in PDLC mixtures is known and can be traced back to the earliest studies of PDLC. For example, RL Sutherland et al., SPIE, Vol. 2689, pp. 158-169, 1996, describes a PDLC mixture comprising monomers, photoinitiators, coinitiators, chain extenders, and LCs to which surfactants can be added, the disclosure of which is incorporated herein by reference. Natarajan et al., Journal of Nonlinear Optical Physics and Materials, Vol. 5, No. 1, pp. 89-98, 1996, also mention surfactants, the disclosure of which is incorporated herein by reference. In addition, U.S. Patent No. 7,018,563 to Sutherland et al. discusses a polymer dispersed liquid crystal material for forming a polymer dispersed liquid crystal optical element having: at least one acrylic monomer; at least one type of liquid crystal material; a photoinitiator dye; a co-initiator; and a surfactant. The disclosure of U.S. Patent No. 7,018,563 is incorporated herein by reference in its entirety.

[0057] The patent and scientific literature contains many examples of material systems and processes that can be used to make SBGs, including studies of formulating such material systems to achieve high diffraction efficiency, fast response time, low drive voltage, etc. U.S. Patent No. 5,942,157 to Sutherland and U.S. Patent No. 5,751,452 to Tanaka et al. both describe combinations of monomers and liquid crystal materials suitable for making SBG devices. Examples of recipes can also be found in papers from the early 1990s. Many of these materials use acrylate monomers, including:

[0058] RL Sutherland et al., Chem. Mater., Vol. 5, p. 1533 (1993), describes the use of acrylate polymers and surfactants, the disclosure of which is incorporated herein by reference. Specifically, the formulation includes a crosslinking multifunctional acrylate monomer; a chain extender N-vinyl pyrrolidone, LC E7, a photoinitiator Bengal red, and a co-initiator N-phenylglycine. In some variations, a surfactant, octanoic acid, is added.

[0059] Fontecchio et al., SID 00 Digest, pp. 774-776, 2000, describe UV-curable HPDLCs for reflective display applications comprising multifunctional acrylate monomers, LC, photoinitiators, co-initiators and chain terminators, the disclosure of which is incorporated herein by reference.

[0060] YH Cho et al., Polymer International, Vol. 48, pp. 1085-1090, 1999, disclose HPDLC formulations including acrylates, the disclosure of which is incorporated herein by reference.

[0061] • Karasawa et al., Japanese Journal of Applied Physics, Vol. 36, pp. 6388-6392, 1997, describe acrylates of various functional sequences, the disclosure of which is incorporated herein by reference.

[0062] • TJ Bunning et al., Polymer Science: Part B: Polymer Physics, Vol. 35, pp. 2825-2833, 1997, also describe multifunctional acrylate monomers, the disclosure of which is incorporated herein by reference.

[0063] G. Slannacchione et al., Europhysics Letters, Vol. 36(6), pp. 425-430, 1996, describe PDLC mixtures comprising a pentaacrylate monomer, LC, a chain extender, a co-initiator, and a photoinitiator, the disclosure of which is incorporated herein by reference.

[0064] Acrylates have the advantages of fast kinetics, good mixing with other materials, and good compatibility with film-forming processes. Since acrylates are cross-linked, they tend to be mechanically robust and flexible. For example, urethane acrylates with functions of 2 (di) and 3 (tri) have been widely used in HPDLC technology. Higher functional materials such as pentagonal and hexagonal functional rods have also been used.

[0065] Modulation of material composition

[0066] High brightness and excellent color fidelity are important factors in AR waveguide displays. In each case, a high degree of uniformity across the FOV is required. However, the basic optics of the waveguide can lead to non-uniformities due to gaps or overlaps of beams bouncing along the waveguide. Further non-uniformities can be caused by imperfections in the grating and non-planarity of the waveguide substrate. In SBGs, there are further issues of polarization rotation due to birefringent gratings. Where applicable, the biggest challenge is usually with folded gratings, where the multiple intersections of the beam with the grating stripes result in millions of light paths. Careful management of the grating properties, especially the refractive index modulation, can be used to overcome non-uniformities.

[0067] Of the many possible beam interactions (diffraction or zero-order transmission), only a subset contributes to the signal presented at the eyebox. By tracing back from the eyebox, the folded regions contributing to a given field point can be precisely located. The precise correction to the modulation required to send more dark regions to the output illumination can then be calculated. After restoring the output illumination uniformity for one color to the target, the process can be repeated for the other colors. Once the refractive index modulation pattern is established, the design can be exported to a deposition setup, with each target refractive index modulation being translated into a unique deposition setup for each spatial resolution cell on the substrate to be coated / deposited. The resolution of the deposition mechanism depends on the technical limitations of the system used. In many embodiments, spatial patterns can be achieved to a resolution of 30 microns with complete repeatability.

[0068] Compared to waveguides utilizing surface relief gratings (SRGs), SBG waveguides implementing fabrication techniques according to various embodiments of the present invention can allow grating design parameters that affect efficiency and uniformity, such as but not limited to refractive index modulation and grating thickness, to be dynamically adjusted during the deposition process without the need for different masters. For SRGs where modulation is controlled by etch depth, such schemes are impractical because each change in the grating requires repeating a complex and expensive machining process. In addition, achieving the required etch depth accuracy and resist imaging complexity can be very difficult.

[0069] The deposition process according to various embodiments of the present invention can provide adjustment of grating design parameters by controlling the type of material to be deposited. Various embodiments of the present invention can be configured to deposit different materials or different material compositions in different areas on the substrate. For example, the deposition process can be configured to deposit HPDLC material on the substrate area intended to be the grating area and deposit the monomer on the substrate area intended to be the non-grating area. In several embodiments, the deposition process is configured to deposit a layer of optical recording material that varies spatially in component composition, thereby allowing various aspects of the deposited material to be modulated. The deposition of materials with different compositions can be achieved in several different ways. In many embodiments, more than one deposition head can be used to deposit different materials and mixtures. Each deposition head can be coupled to a different material / mixture reservoir. Such implementations can be used for various applications. For example, different materials can be deposited for the grating and non-grating areas of a waveguide unit cell. In some embodiments, the HPDLC material is deposited on the grating area, while only the monomer is deposited on the non-grating area. In several embodiments, the deposition mechanism can be configured to deposit mixtures with different component compositions.

[0070] In some embodiments, nozzles can be implemented to deposit multiple types of materials onto a single substrate. In waveguide applications, nozzles can be used to deposit different materials for grating and non-grating regions of the waveguide. In many embodiments, the jetting mechanism is configured to print gratings, where a deposition device with at least two selectable nozzles can be used to control at least one of material composition, birefringence, and / or thickness. In some embodiments, the manufacturing system provides a device for depositing a grating recording material that is optimized for controlling laser bands. In several embodiments, the manufacturing system provides an apparatus for depositing a grating recording material that is optimized for control of polarization non-uniformity. In several embodiments, the manufacturing system provides a device for depositing a grating recording material that is optimized for control of polarization non-uniformity associated with an alignment control layer. In multiple embodiments, the deposition work cell can be configured for deposition of additional layers, such as beam splitting coatings and environmental protection layers. Inkjet print heads can also be implemented to print different materials on different regions of a substrate.

[0071] As discussed above, the deposition process can be configured to deposit an optical recording material with a spatially varying composition. Modulation of the material composition can be achieved in many different ways. In multiple embodiments, an inkjet printhead can be configured to modulate the material composition by utilizing various inkjet nozzles within the printhead. By changing the composition on a "point-by-point" basis, a layer of optical recording material can be deposited so that it has a varying composition on the planar surface of the layer. Such a system can be implemented using a variety of devices, including but not limited to inkjet printheads. Similar to how a color system uses a palette of only a few colors to produce a spectrum of millions of discrete color values, such as a CMYK system in a printer or an additive RGB system in a display application, an inkjet printhead according to various embodiments of the present invention can be configured to print optical recording materials with different compositions using only a few containers of different materials. Different types of inkjet printheads can have different levels of precision and can print at different resolutions. In many embodiments, a 300 DPI ("dots per inch") inkjet printhead is used. Depending on the level of precision, the discretization of different compositions of a given amount of material can be determined across a given area. For example, given two types of materials to be printed and an inkjet printhead with a precision level of 300 DPI, for a given volume of printed material, if each dot position can contain one of the two types of materials, then there are 90,001 possible discrete values ​​for the composition ratio of the two types of materials across 1 square inch. In some embodiments, each dot position can contain either or both types of materials. In several embodiments, more than one inkjet printhead is configured to print an optical recording material layer with a spatially varying composition. Although the printing of dots in dual-material applications is essentially a binary system, averaging the printed dots across the region can allow the sliding ratio of the ratio of the two materials to be printed to be discretized. For example, the number of discrete levels of possible concentrations / ratios within a unit square is given by the number of dot positions that can be printed within a unit square. As such, there can be a range of different concentration combinations, ranging from 100% of the first material to 100% of the second material. As can be easily appreciated, these concepts apply to actual units and can be determined by the precision level of the inkjet printhead. While a specific example of modulating the material composition of a printed layer is discussed, the concept of modulating the material composition using an inkjet printhead can be extended to using more than two different material reservoirs, and the level of precision can vary, depending largely on the type of printhead used.

[0072] Changing the composition of the printed material can be advantageous for several reasons. For example, in many embodiments, changing the composition of the material during deposition can allow the formation of a waveguide with a grating having a spatially varying diffraction efficiency across different regions of the grating. In embodiments using an HPDLC mixture, this can be achieved by modulating the relative concentration of liquid crystals in the HPDLC mixture during the printing process, which produces a composition that can produce gratings with different diffraction efficiencies when the material is exposed. In several embodiments, a first HPDLC mixture with a certain liquid crystal concentration and a second HPDLC mixture without liquid crystals are used as a printing palette in an inkjet printhead to modulate the diffraction efficiency of the grating that can be formed in the printed material. In such embodiments, the discretization can be determined based on the accuracy of the inkjet printhead. The discrete level can be given by the concentration / ratio of the material printed across a specific area. In this example, the discrete levels range from no liquid crystal in the first PDLC mixture to the maximum concentration of liquid crystals.

[0073] The ability to vary the diffraction efficiency across a waveguide can be used for a variety of purposes. Waveguides are typically designed to guide light internally by reflecting light multiple times between two planar surfaces of the waveguide. These multiple reflections can allow the light path to interact with the grating multiple times. In many embodiments, the material layers can be printed with different material compositions so that the formed grating has a spatially varying diffraction efficiency to compensate for light loss during interaction with the grating, thereby allowing for uniform output intensity. For example, in some waveguide applications, the output grating is configured to provide exit pupil expansion in one direction while also coupling light out of the waveguide. The output grating can be designed so that when light within the waveguide interacts with the grating, only a portion of the light is refracted out of the waveguide. The rest continues in the same optical path, remains within the TIR and continues to reflect within the waveguide. After interacting again with the same output grating for a second time, another portion of the light is refracted out of the waveguide. During each refraction, the amount of light still traveling within the waveguide is reduced by the amount refracted out of the waveguide. As such, the portion refracted at each interaction is gradually reduced in terms of total intensity. By varying the diffraction efficiency of the grating so that it increases with increasing propagation distance, the decrease in output intensity along each interaction can be compensated, allowing for a uniform output intensity.

[0074] Changing the diffraction efficiency can also be used to compensate for other attenuation of light within the waveguide. All objects reflect and absorb to some extent. Light trapped by TIR within a waveguide is constantly reflected between the two surfaces of the waveguide. Depending on the materials that make up the surfaces, part of the light may be absorbed by the material during each interaction. In many cases, this attenuation is small, but can be large across a large area where many reflections occur. In many embodiments, the waveguide unit cells can be printed with different compositions so that the gratings formed by the optical recording material layers have different diffraction efficiencies to compensate for the absorption of light from the substrate. Depending on the substrate, certain wavelengths may be more easily absorbed by the substrate. In a multilayer waveguide design, each layer may be designed to couple a specific range of wavelengths of light. Thus, the light coupled by these individual layers may be absorbed by the substrate of the layer in different amounts. For example, in many embodiments, the waveguide is made of a three-layer stack to achieve a full-color display, where each layer is designed for one of red, green, and blue. In such embodiments, the gratings within each waveguide layer can be formed to have different diffraction efficiencies to perform color balance optimization by compensating for color imbalances caused by transmission losses of certain wavelengths of light.

[0075] In addition to changing the liquid crystal concentration within the material to change the diffraction efficiency, another technique includes changing the thickness of the waveguide unit cell. This can be achieved by using spacers. In many embodiments, spacers are dispersed throughout the optical recording material for structural support during the construction of the waveguide unit. In some embodiments, spacers of different sizes are dispersed throughout the optical recording material. The spacers can be dispersed in ascending order of size in one direction of the optical recording material layer. When the waveguide unit cell is constructed by lamination, the substrate sandwiches the optical recording material in the middle and forms a wedge-shaped optical recording material layer under the structural support of spacers of different sizes. Similar to the above-mentioned modulation process, spacers of different sizes can be dispersed. In addition, modulating the spacer size can be combined with the modulation of the material composition. In several embodiments, a reservoir of HPDLC material, each of which has spacers of different sizes suspended, is used to print a layer of HPDLC material with spacers of different sizes, which are strategically dispersed to form a wedge-shaped waveguide unit cell. In multiple embodiments, the spacer size modulation is combined with the material composition modulation by providing a number of reservoirs equal to the product of the number of spacers of different sizes and the number of different materials used. For example, in one embodiment, the inkjet printhead is configured to print different concentrations of liquid crystals with two different spacer sizes. In such an embodiment, four reservoirs can be prepared: a liquid crystal-free hybrid suspension with a spacer of a first size, a liquid crystal-free hybrid suspension with a spacer of a second size, a liquid crystal-rich hybrid suspension with a spacer of a first size, and a liquid crystal-rich hybrid suspension with a spacer of a second size. Further discussion of material modulation can be found in U.S. Application No. 16 / 203,071, filed on November 18, 2018, entitled “SYSTEMS AND METHODS FOR MANUFACTURING WAVEGUIDE CELLS.” The disclosure of U.S. Application No. 16 / 203,491 is incorporated herein by reference in its entirety for all purposes.

[0076] Multilayer waveguide fabrication

[0077] Waveguide fabrication according to various embodiments of the present invention may be implemented to fabricate multilayer waveguides. Multilayer waveguides refer to a class of waveguides that utilize two or more layers with gratings or other optical structures. Although the following discussion may be related to gratings, any type of holographic optical structure may be appropriately implemented and substituted. Multilayer waveguides may be implemented for a variety of purposes, including but not limited to improving spectral and / or angular bandwidth. Traditionally, multilayer waveguides are formed by stacking and aligning waveguides having a single grating layer. In such cases, each grating layer is typically defined by a pair of transparent substrates. In order to maintain the desired total internal reflection characteristics, spacers are typically used to stack the waveguides to form air gaps between the individual waveguides.

[0078] Many embodiments of the present invention are directed to fabricating multilayer waveguides having alternating substrate layers and grating layers, as compared to conventional stacked waveguides. Such waveguides can be fabricated using an iterative process that is capable of sequentially forming grating layers for a single waveguide. In several embodiments, multilayer waveguides are fabricated with two grating layers. In multiple embodiments, multilayer waveguides are fabricated with three grating layers. Any number of grating layers can be formed, subject to the limitations of the tooling and / or waveguide design used. This allows for a reduction in thickness, material, and cost, as fewer substrates are required, as compared to conventional multilayer waveguides. Additionally, the fabrication process for such waveguides allows for higher throughput, as alignment and substrate matching requirements are simplified.

[0079] The manufacturing process of a multilayer waveguide having alternating transparent substrate layers and grating layers according to various embodiments of the present invention can be implemented using a variety of techniques. In many embodiments, the manufacturing process includes depositing a first layer of optical recording material onto a first transparent substrate. The optical recording material can include a variety of materials and mixtures, including but not limited to HPDLC mixtures and any of the material formulations discussed in the above subsections. Similarly, any of a variety of deposition techniques can be used, such as but not limited to spraying, spin coating, inkjet printing, and any of the techniques described in the above subsections. Transparent substrates of various shapes, thicknesses, and materials can be used. The transparent substrates can include but are not limited to glass substrates and plastic substrates. Depending on the application, the transparent substrates can be coated with different types of thin films for various uses. Once the deposition process is completed, a second transparent substrate can be placed on the deposited first layer of optical recording material. In some embodiments, the process includes a lamination step to form the three-layer composite material to the desired height / thickness. An exposure process can be implemented to form a set of gratings within the first layer of the optical recording material. An exposure process can be used, such as but not limited to single beam interference exposure and any other exposure process described in the above subsections. In essence, a single layer waveguide is now formed. The process can then be repeated to add additional layers to the waveguide. In several embodiments, a second layer of optical recording material is deposited onto a second transparent substrate. A third transparent substrate can be placed onto the second layer of optical recording material. Similar to the previous steps, the composite material can be laminated to a desired height / thickness. A second exposure process can then be performed to form a set of gratings within the second layer of optical recording material. The result is a waveguide with two grating layers. As can be easily appreciated, the process can be iteratively continued to add additional layers. Additional optical recording layers can be added to either side of the current laminate. For example, a third layer of optical recording material can be deposited onto the outer surface of either the first transparent substrate or the third transparent substrate.

[0080] In many embodiments, the manufacturing process includes one or more post-processing steps. Post-processing steps, such as but not limited to planarization, cleaning, application of protective coatings, thermal annealing, alignment of LC directors to achieve a desired birefringence state, extraction of LC from recorded SBGs and refilling with another material, etc., can be performed at any stage of the manufacturing process. Some processes, such as but not limited to waveguide cutting (producing multiple elements), edge finishing, AR coating deposition, final protective coating application, etc., are typically performed at the end of the manufacturing process.

[0081] In many embodiments, spacers (such as but not limited to beads and other particles) are dispersed throughout the optical recording material to help control and maintain the thickness of the optical recording material layer. The spacers can also help prevent the two substrates from collapsing into each other. In some embodiments, the waveguide unit cell is composed of an optical recording layer sandwiched between two planar substrates. Depending on the type of optical recording material used, thickness control may be difficult to achieve due to the viscosity of some optical recording materials and the lack of boundaries of the optical recording layer. In multiple embodiments, the spacer is a relatively incompressible solid, which can allow the construction of a waveguide unit cell with a consistent thickness. The spacer can take any suitable geometric shape, including but not limited to rods and spheres. The size of the spacer can determine the local minimum thickness of the area around the individual spacer. As such, the dimensions of the spacer can be selected to help obtain the desired optical recording layer thickness. The spacer can take any suitable size. In many cases, the size of the spacer ranges from 1 to 30 μm. The spacer can be made of any of a variety of materials, including but not limited to plastics (e.g., divinylbenzene), silicon dioxide, and conductive materials. In several embodiments, the material of the spacer is selected so that its refractive index does not substantially affect the propagation of light in the waveguide unit cell.

[0082] In many embodiments, a first layer of optical recording material is bonded between the first and second transparent substrates using a vacuum filling method. In multiple embodiments, the optical recording material layer is separated in different sections and can be appropriately filled or deposited depending on the specific requirements of a given application. In some embodiments, the manufacturing system is configured to expose the optical recording material from below. In such embodiments, the iterative multi-layer manufacturing process can include flipping the current device so that the exposure light is incident on the newly deposited optical recording layer before being incident on any formed grating layer.

[0083] In many embodiments, the exposure process may include temporarily "erasing" or rendering transparent previously formed grating layers so that they do not interfere with the recording process of the newly deposited optical recording layer. The temporarily "erased" gratings or other optical structures behave like a transparent material, allowing light to pass through without affecting the ray paths. Methods of recording gratings into optical recording material layers using such techniques may include fabricating a stack of optical structures, wherein a first optical recording material layer deposited on a substrate is exposed to form a first set of gratings, which first set of gratings may be temporarily erased so that a second set of gratings may be recorded into a second optical recording material layer using an optical recording beam passing through the first optical recording material layer. Although the recording methods are primarily discussed for waveguides having two grating layers, the underlying principles may also be applied to waveguides having more than two grating layers.

[0084] The multilayer waveguide manufacturing process in conjunction with the step of temporarily erasing the grating structure can be implemented in a variety of ways. Typically, the first layer is formed using conventional methods. The recording material used may include a material system capable of supporting an optical structure that can be erased in response to a stimulus. In embodiments where the optical structure is a holographic grating, the exposure process may utilize a cross-beam holographic recording device. In multiple embodiments, the optical recording process uses a beam provided by a master grating, which may be a Bragg hologram recorded in a photopolymer or an amplitude grating. In some embodiments, the exposure process utilizes a single recording beam in conjunction with the master grating to form an interfering exposure beam. In addition to the processes described, other industrial processes and devices currently used in the field to manufacture holograms may also be used.

[0085] Once the first set of gratings is recorded, additional material layers may be added similar to the above process. During the exposure process of any material layer after the first material layer, an external stimulus may be applied to any previously formed grating to make it effectively transparent. An effectively transparent grating layer may allow light to pass through to expose a new material layer. One or more external stimuli may include optical, thermal, chemical, mechanical, electrical, and / or magnetic stimuli. In many embodiments, the external stimulus is applied at an intensity below a predefined threshold to produce optical noise below a predefined level. The specific predefined threshold may depend on the type of material used to form the grating. In some embodiments, a sacrificial alignment layer applied to the first material layer may be used to temporarily erase the first set of gratings. In some embodiments, the intensity of the external stimulus applied to the first set of gratings is controlled to reduce optical noise in the optical device during normal operation. In several embodiments, the optical recording material also includes an additive for facilitating the process of erasing the gratings, which may include any of the methods described above. In multiple embodiments, the stimulus is applied to restore the erased layer.

[0086] Many different methods can be used to achieve the clearing and recovery of the recorded layer in the above process. In many embodiments, the first layer is cleared by continuously applying a stimulus during the recording of the second layer. In other embodiments, the stimulus is initially applied, and the grating in the cleared layer can naturally recover to its recorded state within a time scale that allows the second grating to be recorded. In other embodiments, the layer remains cleared after the external stimulus is applied and recovers in response to another external stimulus. In several embodiments, an alignment layer or an external stimulus can be used to restore the first optical structure to its recorded state. The external stimulus used for such recovery can be any of a variety of different stimuli, including but not limited to one or more stimuli for clearing the optical structure. Depending on the constituent materials of the optical structure and layer to be cleared, the clearing process may be different. Further discussion of multilayer waveguide fabrication using external stimuli can be found in U.S. application No. 16 / 522,491, entitled "Systems and Methods for Fabricating a Multilayer Optical Structure", filed on July 25, 2019. The disclosure of U.S. application No. 16 / 522,491 is incorporated herein by reference in its entirety for all purposes.

[0087] Waveguides combined with integrated gratings

[0088] Waveguides according to various embodiments of the present invention may include different grating configurations. In many embodiments, the waveguide includes at least one input coupler and at least two integrated gratings. In some embodiments, at least two integrated gratings may be implemented to work in combination to provide beam expansion and beam extraction for light coupled into the waveguide by the input coupler. Multiple integrated gratings may be implemented by overlapping integrated gratings across different grating layers or by multiplexing integrated gratings. In multiple embodiments, the integrated gratings are partially overlapped or multiplexed. The multiplexed grating may include at least two gratings having different grating specifications superimposed in the same volume. Gratings with different grating specifications may have different grating vectors and / or grating tilts relative to the waveguide surface. The magnitude of the grating vector of the grating may be defined as the inverse of the grating period, while its direction may be defined as a direction orthogonal to the grating stripes.

[0089] In several embodiments, an integrated grating may be implemented to perform beam expansion and beam extraction. The integrated grating may be implemented with one or more grating specifications. In multiple embodiments, the integrated grating is implemented with at least two grating specifications. In further embodiments, the integrated grating is implemented with at least three grating specifications. In many embodiments, two grating specifications within the integrated grating have similar clock angles. In some embodiments, the two grating specifications have different tilt angles. The integrated grating according to various embodiments of the present invention may be implemented using a variety of types of gratings, such as but not limited to SRGs, SBGs, holographic gratings, and other types of gratings, including those described in the above subsections. In multiple embodiments, the integrated grating includes two surface relief gratings. In other embodiments, the integrated grating includes two holographic gratings.

[0090] The integrated grating may include at least two grating specifications that are at least partially overlapped or multiplexed. In further embodiments, the integrated grating includes at least two grating specifications that are fully overlapped or multiplexed. In multiple embodiments, the integrated grating includes multiplexed or overlapping gratings having different sizes and / or shapes - that is, one grating may be larger than the other, resulting in only partial multiplexing of the larger grating. As can be readily appreciated, a variety of multiplexing and overlapping configurations may be appropriately implemented depending on the specific requirements of a given application. Although the following discussion may describe configurations as implementing multiplexed or overlapping gratings, such gratings may be appropriately substituted for one another depending on the application. In several embodiments, the integrated grating is implemented by a combination of multiplexed gratings and overlapping gratings. For example, two or more sets of multiplexed gratings may overlap across two or more grating layers.

[0091] Integrated gratings according to various embodiments of the present invention can be used for various purposes, including but not limited to realizing full-color waveguides and solving some key problems in conventional waveguide architectures. Other advantages include reduced material and waveguide refractive index requirements and reduced waveguide dimensions due to the overlapping and / or multiplexing nature of the integrated gratings. Such configurations can allow large field of view waveguides, which usually result in an unacceptable increase in waveguide form factor and refractive index requirements. In many embodiments, the waveguide is implemented with at least one substrate having a low refractive index. In some embodiments, the waveguide is implemented with a substrate having a refractive index lower than 1.8. In a further embodiment, the waveguide is implemented with a substrate having a refractive index not exceeding ~1.5.

[0092] Integrated gratings that can provide both beam expansion and beam extraction - i.e., the functionality of conventional fold and output gratings - can produce a much smaller grating area, thereby achieving a small form factor and lower manufacturing cost. By integrating the functions of beam expansion and extraction, rather than performing them serially as in conventional waveguides, beam expansion and extraction can be accomplished with ~50% of the grating interactions typically required, reducing haze by the same proportion in the case of birefringent gratings. Another advantage is that because the optical path is greatly shortened, the number of beam bounces at the (one or more) glass / air interfaces is reduced, making the output image less sensitive to substrate non-uniformities. This can achieve higher quality images and potentially use cheaper, lower specification substrates.

[0093] In many embodiments, the grating vectors of the input coupler and the integrated grating are arranged to provide a substantially zero result vector. The grating vectors of the input coupler and the integrated grating may be arranged to form a triangular configuration. In several embodiments, the grating vectors may be arranged in an equilateral triangle configuration. In some embodiments, the grating vectors may be arranged in an isosceles triangle configuration, wherein at least two grating vectors have equal magnitudes. In further embodiments, the grating vectors are arranged in an isosceles right triangle configuration. In several embodiments, the grating vectors are arranged in a scalene triangle configuration. Another waveguide architecture includes an integrated diffractive element whose grating vectors are aligned in the same direction to provide horizontal expansion for a set of angles and extraction for a set of separate angles. In several embodiments, one or more of the integrated gratings are asymmetric in their overall shape. In some embodiments, one or more of the integrated gratings have at least one axis of symmetry in their overall shape. In several embodiments, the grating is designed to be sandwiched between electroactive materials, enabling switching between clear and diffraction states of certain types of gratings such as, but not limited to, HPDLC gratings. The grating may be a surface relief or holographic type.

[0094] In many embodiments, a waveguide supporting at least one input coupler and a first and a second integrated grating is implemented. The grating structure can be implemented in a single layer or a multilayer waveguide design. In a single layer design, the integrated gratings can be multiplexed. In an embodiment where each integrated grating includes at least two multiplexed gratings, the multiplexed integrated gratings can include at least four multiplexed gratings. As described above, any individual multiplexed grating can be partially or completely multiplexed with other gratings. In some embodiments, a multilayer waveguide is implemented with overlapping integrated gratings. In a further embodiment, the integrated gratings are partially overlapping. Each integrated grating can be a separate grating or a multiplexed grating.

[0095] In many embodiments, the waveguide architecture is designed to couple the input light into two bifurcated paths using an input coupler. Such a configuration can be implemented in various ways. In some embodiments, a multiplexed input grating is implemented to couple the input light into the two bifurcated paths. In other embodiments, two input gratings are implemented to couple the input light into the two bifurcated paths, respectively. The two input gratings can be implemented in the same layer, or can be implemented separately in two layers. In multiple embodiments, two overlapping or partially overlapping input gratings are implemented to couple the input light into the two bifurcated paths. In many embodiments, the input coupler includes a prism. In further embodiments, the input coupler includes a prism and any of the above-described input grating configurations.

[0096] In addition to various input coupler architectures, the first and second integrated gratings can also be implemented in various configurations. The integrated gratings according to various embodiments of the present invention can be incorporated into a waveguide to perform the dual functions of two-dimensional beam expansion and beam extraction. In several embodiments, the first and second integrated gratings are cross gratings. As described above, some waveguide architectures include designs in which the input light is coupled into two bifurcated paths. In such designs, the two bifurcated paths each point to a different integrated grating. As can be easily recognized, such configurations can be designed to bifurcate the input light based on various light characteristics (including but not limited to angle and spectral bandwidth). In some embodiments, the light can be bifurcated based on the polarization state-for example, the input non-polarized light can be bifurcated into S and P polarization paths. In many embodiments, each of the integrated gratings performs beam expansion in a first direction or in a second direction different from the first direction according to the field of view portion propagating through the waveguide. The first and second directions can be orthogonal to each other. In other embodiments, the first and second directions are not orthogonal to each other. Each integrated grating can provide expansion of light in a first dimension while directing the light toward another integrated grating, which provides expansion and extraction of light in a second dimension. For example, many grating architectures according to various embodiments of the present invention include an input configuration for bifurcating input light into first and second portions of light. The first integrated grating can be configured to provide beam expansion for the first and second portions of light in a first direction and provide beam extraction for the second portion of light. Conversely, the second integrated grating can be configured to provide beam expansion for the first and second portions of light in a second direction and provide beam extraction for the first portion of light.

[0097] In a number of embodiments, the first integrated grating includes a multiplexed first and second grating specifications, and the second integrated grating includes a multiplexed third and fourth grating specifications. In such embodiments, the first grating specification can be configured to provide a beam expansion for a first portion of light in a first direction and redirect the expanded light to a fourth grating specification. The second grating specification can be configured to provide a beam expansion for a second portion of light in a first direction and extract the light out of the waveguide. The third grating specification can be configured to provide a beam expansion for a second portion of light in a second direction and redirect the expanded light to the second grating specification. The fourth grating specification can be configured to provide a beam expansion for a first portion of light in a second direction and extract the light out of the waveguide. As can be easily appreciated, the integrated grating can be implemented with overlapping grating specifications rather than multiplexed grating specifications. In many embodiments, the first and second grating specifications have the same clock angle but different grating tilts. In some embodiments, the third and fourth grating specifications have the same clock angle, which is different from the clock angle of the first and second grating specifications. In a number of embodiments, the first, second, third and fourth grating specifications all have different clock angles. In several embodiments, the first, second, third and fourth grating specifications all have different grating periods. In a number of embodiments, the first and third grating specifications have the same grating period, and the second and fourth grating specifications have the same grating period.

[0098] Figure 1 A waveguide display according to an embodiment of the present invention is conceptually illustrated. As shown, the device 100 includes a waveguide 101 supporting an input grating 102 and a grating structure 103. Each grating can be characterized by a grating vector, which defines the direction of the grating stripes in the plane of the waveguide. The grating can also be characterized by a K vector in 3D space, which in the case of a Bragg grating is defined as a vector perpendicular to the grating stripes. The waveguide reflective surface is parallel to the XY plane of the Cartesian reference frame inset in the figure. In some embodiments, the X and Y axes can correspond to the global horizontal and vertical axes in the reference frame of the user of the display.

[0099] exist Figure 1In an illustrative embodiment of the present invention, the input grating 102 includes a Bragg grating 104. In other embodiments, the input grating 102 is a surface relief grating. The input grating 102 can be implemented to split the input light into two different parts. In a further embodiment, the input grating 102 includes two multiplexed gratings with different grating specifications. In other embodiments, the input grating 102 includes two overlaid surface relief gratings. The grating structure 103 includes two effective gratings 105, 106 with different grating vectors. The gratings 105, 106 can be integrated gratings implemented as surface relief gratings or volume gratings. In many embodiments, the gratings 105, 106 are multiplexed in a single layer. In several embodiments, the waveguide 101 provides two effective gratings across all points of the grating structure 103 by overlaying more than two separate gratings in the grating structure. For clarity, the gratings 105, 106 forming the grating structure 103 will be referred to as first and second integrated gratings because their roles in the grating structure include providing beam expansion by changing the direction of the guided beam in the waveguide plane, and beam extraction. In various embodiments, the integrated gratings 105, 106 perform two-dimensional beam expansion and extract light from the waveguide 101. The field of view coupled into the waveguide can be partitioned into first and second parts, which can be bifurcated by the input grating 102. In many embodiments, the first and second parts correspond to positive and negative angles vertically or horizontally. In some embodiments, the first and second parts can overlap in angular space. In multiple embodiments, the first part of the field of view is expanded in a first direction by the first integrated grating, and in parallel operation, is expanded and extracted in a second direction by the second integrated grating. When the ray interacts with the grating stripes, some of the light that meets the Bragg condition is diffracted, while the non-diffracted light proceeds along its TIR path to the next stripe, continuing the expansion and extraction process. Considering next the second portion of the field of view, the action of the gratings is reversed so that the second portion of the field of view is expanded in the second direction by the second integrated grating and expanded and extracted in the first direction by the first integrated grating.

[0100] In many embodiments, the integrated gratings 105, 106 in the grating structure 103 may be deployed asymmetrically. In some embodiments, the integrated gratings 105, 106 have grating vectors of different magnitudes. In several embodiments, the input grating 102 may have a grating vector that is offset from the Y axis. In a number of embodiments, it is expected that the vector combination of the grating vector of the input grating 102 and the integrated gratings 105, 106 in the grating structure 103 gives a result vector of substantially zero magnitude. As described above, the grating vectors may be arranged in an equilateral, isosceles, or scalene triangle configuration. Depending on the application, certain configurations may be more desirable.

[0101] In many embodiments, at least one grating parameter selected from the group consisting of grating vector orientation, K-vector orientation, grating refractive index modulation, and grating spatial frequency can be spatially varied across at least one grating implemented in a waveguide with the goal of optimizing angular bandwidth, waveguide efficiency, and output uniformity to increase angular response and / or efficiency. In some embodiments, at least one of the gratings implemented in a waveguide can employ a rolling K-vector - i.e., a spatially varying K-vector. In several embodiments, the spatial frequency of the grating(s) is matched to overcome dispersion.

[0102] Figure 1 The device 100 also includes an input image generator. In an illustrative embodiment, the input image generator includes a laser scanning projector 107, which provides a scanning beam 107A on a field of view coupled to a total internal reflection path (TIR path) (e.g., 108A, 108B) in a waveguide through an input grating 102, and is directed toward the integrated gratings 105, 106 to be expanded and extracted (e.g., as shown by rays 109A, 109B). In some embodiments, the laser projector 107 is configured to inject the scanned beam into the waveguide. In several embodiments, the laser projector 107 may have a scanning pattern modified to compensate for optical deformations in the waveguide. In multiple embodiments, the laser scanning pattern and / or grating specifications in the input grating 102 and the grating structure 103 may be modified to overcome illumination striping. In various embodiments, the laser scanning projector 107 may be replaced by an input image generator based on a microdisplay illuminated by a laser or LED. In many embodiments, the input image may be provided by an emissive display. Laser projectors can provide advantages such as improved color gamut, higher brightness, wider field of view, high resolution, and a very compact form factor. In some embodiments, the apparatus 100 may also include a despeckler. In further embodiments, the despeckler may be implemented as a waveguide device. Although Figure 1 A specific waveguide application implementing an integrated grating is shown, but such structures and grating architectures can be used for a variety of applications. In multiple embodiments, a waveguide with an integrated grating can be implemented in a single grating layer for full-color applications. In many embodiments, more than one grating layer implementing an integrated grating is implemented. Such configurations can be implemented to provide wider angular or spectral bandwidth operation. In some embodiments, multi-layer waveguides are implemented to provide full-color applications. In several embodiments, multi-layer waveguides are implemented to provide a wider field of view. In many embodiments, a full-color waveguide with a diagonal field of view of at least ~50° is implemented using an integrated grating. In some embodiments, a full-color waveguide with a diagonal field of view of at least ~100° is implemented using an integrated grating.

[0103] Figure 2 A color waveguide display having two blue-green diffractive waveguides and two green-red diffractive waveguides is conceptually illustrated in accordance with an embodiment of the present invention. Figure 2Schematically illustrates a Figure 1 The system architecture of the present invention but includes a device 200 using four stacked waveguides 201A-201D, including two blue-green diffractive waveguides and two green-red diffractive waveguides. As shown, the device 200 includes a laser scanning projector 202 that provides scanning beams 202A-202D. In an illustrative embodiment, the waveguides providing each color band can be configured to propagate different portions of the field of view. For example, in some embodiments, when the two fields of view are combined, each waveguide operating in a given color band provides a field of view of 35°h×35°v (50° diagonal), thereby producing a 70°h×35°v (78° diagonal) field of view for each color band. In many embodiments, the scanning beam can be generated using red, green and blue laser emitters, where each of the two laser wavelengths selected from red, green and blue is injected into each waveguide according to the color band to be propagated by the waveguide. The intensity of the shock beam can be modulated, the purpose of which is color balancing. The stacked waveguides can be arranged in any order. In several embodiments, considerations such as, but not limited to, color crosstalk may influence the stacking order. In several embodiments, the integrated grating of one waveguide partially or completely overlaps the integrated grating of another waveguide. As described above, the integrated gratings may be implemented in various configurations. In some embodiments, the integrated gratings are implemented across more than one grating layer. In several embodiments, each integrated grating includes two multiplexed grating specifications.

[0104] In many embodiments, the optical geometry requirements for combining waveguide paths for more than one field of view or color band may dictate an asymmetric arrangement of the gratings used in the input grating(s) and the integrated grating. In other words, the grating vectors of the input grating and the integrated grating are neither equilaterally disposed nor symmetrically disposed about the Y axis.

[0105] Although Figure 1 and 2 A specific configuration of the waveguide architecture is shown, but various structures can be appropriately implemented depending on the specific requirements of a given application. In some embodiments, a six-layer waveguide is implemented for full-color applications. The six-layer waveguide can be implemented with three pairs of layers, which are configured for red, green, and blue color bands, respectively. In such embodiments, the waveguides in each pair can be configured for different portions of the field of view.

[0106] In some embodiments, to perform beam expansion and extraction, the waveguide is designed so that each point of interaction of a ray with the grating structure occurs in a region of overlapping effective gratings. In a non-fully overlapping grating configuration, the grating structure will have a region where the first and second effective gratings only partially overlap, so that some rays interact with only one of the effective gratings. In many embodiments, the grating structure is formed of two multiplexed gratings. Figure 3AThe first of the multiplexed gratings 300 shown in FIG. 1 multiplexes a first effective grating 301 with a grating 302 having a different effective grating vector (or clock angle). Figure 3B The second multiplexed grating 310 shown in FIG. 1 multiplexes a second effective grating 311 with a grating 312 having a different effective grating vector. Figure 3A-3B The relative orientation of the multiplexed gratings is intended to illustrate and does not represent the implemented grating shapes. In some embodiments, the shapes of the gratings 301, 302 and 311, 312 may be different from each other. Figure 3A-3B In an embodiment of the invention, the grating vector (clock angle) of the second multiplexed grating is identical to the first grating vector of the first multiplexed grating. Likewise, the grating vector of the first multiplexed grating is identical to the second grating vector of the second multiplexed grating. Now turning to Figure 3C Obviously, when the gratings overlap 320, any point in the grating structure of the effective grating (e.g., in the partially overlapping area - in Figure 3C In the complete overlap region of the effective grating (in Figure 3C 1), there will be four gratings overlapping at any point in the grating structure. However, in such regions, each pair of gratings with the same clock angle results in only two overlapping effective gratings. It should be appreciated from the above description that in many embodiments, two pairs of multiplexed gratings can be implemented as one multiplexed grating consisting of four gratings 301, 302 and 311, 312.

[0107] Figures 4A-4C Schematically illustrates ray propagation through a grating structure 400 having an input grating 401 and two integrated gratings 402, 403 according to an embodiment of the present invention. The ray propagation is illustrated using unrolled ray paths to clarify the interaction between the rays and the gratings. Figure 4A As shown in the schematic diagram of FIG. 4 , light from a first portion of the FOV shows ray 404A coupled into the TIR path in the waveguide through the input grating 401, TIR ray 405A passing to the first integrating grating 402, TIR ray 406A diffracted by the first integrating grating 403 (which also provides beam expansion in the first direction), and ray 407A diffracted out of the waveguide by the second integrating grating 403 (which also provides beam expansion in the second direction). Turning now to the propagation of the second portion of the FOV, as shown in FIG. Figure 4BAs shown in the figure, the ray path includes ray 404B in the TIR path coupled into the waveguide through the input grating 401, TIR ray 405B passing to the second integrated grating 403, TIR ray 406B diffracted by the second integrated grating 403 (which also provides beam expansion in the second direction), and TIR ray 407B diffracted out of the waveguide by the first integrated grating 402 (which also provides beam expansion in the first direction). Figure 4C Shows Figure 4A-4B A combined path of which is covered with an integrated grating. Figure 4C Also shown is the partially overlapping nature of the integrated gratings along the path of the ray. As can be readily appreciated, such configurations can be appropriately modified according to the specific requirements of a given application. Gratings of various shapes can be used. The integrated grating can include two multiplexed gratings, one providing the functionality of a traditional folded grating and the other similar to a traditional output grating for extracting light. Each of the two multiplexed gratings within a single integrated grating can be configured to serve a different portion of the light bifurcated by the input configuration. In multiple embodiments, the two multiplexed gratings within a single integrated grating can have different shapes - that is, certain areas of one or both gratings are not multiplexed. In some embodiments, for a single integrated grating, more than two gratings are multiplexed. In many embodiments, the integrated gratings are multiplexed in a single grating layer. In several embodiments, the integrated gratings are fully multiplexed or overlapped. In other embodiments, only portions of the integrated gratings are multiplexed overlapped.

[0108] As described above, grating vectors can be used to describe and visualize grating architectures, including those implementing integrated gratings. In many embodiments, three grating vectors that can represent traditional input, fold, and output functions can be implemented with substantially zero result vectors. Figure 5A A grating vector configuration with substantially zero result vectors according to an embodiment of the present invention is conceptually illustrated. As shown, configuration 500 includes three grating vectors 501-503, respectively denoted as k1, k2, and k3. For three grating vectors, the configuration with substantially zero result vectors can provide various triangle configurations, such as but not limited to equilateral triangles, isosceles triangles, and scalene triangles. In the case of an architecture using an integrated grating, more than one triangle configuration can be visualized. Figure 5B One such embodiment is conceptually illustrated. As shown, configuration 510 illustrates two triangular configurations. One triangular configuration is formed by grating vectors k1, k2, and k3 (511-513), and the second configuration is formed by grating vectors k1, k4, and k5 (511, 514, and 515). In the illustrative embodiment, grating vector k1 represents the function of an input coupler, grating vectors k2 and k5 represent the function of a first integrated grating, and grating vectors k4 and k3 represent the function of a second integrated grating.

[0109] In many embodiments, the implemented grating vector configurations may include various triangle configurations. In general, the magnitude of the grating vectors may dictate the resulting triangle configuration. In some embodiments, an equilateral triangle configuration is implemented, where all grating vectors have similar or substantially similar magnitudes. Where an integrated grating is implemented, the configuration may include two triangle configurations. In a number of embodiments, the grating vector configuration includes at least one isosceles triangle, where at least two of the grating vectors have similar or substantially similar magnitudes. Figure 5C A grating vector configuration with two isosceles triangles according to an embodiment of the present invention is conceptually illustrated. As shown, since grating vectors k2-k5 have similar magnitudes, configuration 520 forms two isosceles triangles. In several embodiments, the grating configuration includes at least one scalene triangle. Figure 5D A grating vector configuration with two scalene triangles is conceptually illustrated in accordance with an embodiment of the present invention. As shown, configuration 530 forms two scalene triangles. In the illustrative embodiment, the two scalene triangles are mirror images - that is, the magnitude of grating vectors k2 and k4 are equal, and the magnitude of grating vectors k3 and k5 are equal. Figure 5E A grating vector configuration with two different scalene triangles is conceptually illustrated according to an embodiment of the present invention. As shown, configuration 540 includes two different scalene triangles whose grating vectors k2-k5 have different magnitudes.

[0110] Although Figures 5A-5E A specific grating vector configuration is illustrated, but various other configurations may be implemented as appropriate depending on the specific requirements of a given application. For example, in some embodiments, the input coupler is implemented with two different grating vectors. This configuration utilizes an input grating with two different grating specifications, which may be implemented using overlapping or multiplexed grating specifications. Figure 5B-5E In the illustrated embodiment, the illustrated configuration may be implemented as an integrated grating. In many embodiments, grating vectors k2 and k5 represent the function of a first integrated grating, while grating vectors k4 and k3 represent the function of a second integrated grating. In several embodiments, each grating vector k i Represents different grating specifications. For example, many grating architectures according to various embodiments of the present invention can implement integrated gratings, each grating comprising two different grating specifications. In such cases, grating vectors k2 and k5 can respectively represent two different grating specifications of the first integrated grating, and grating vectors k4 and k3 can respectively represent two different grating specifications of the second integrated grating.

[0111] Figure 6A schematic plan view of a grating architecture 600 with an input grating and an integrated grating according to an embodiment of the present invention is conceptually illustrated. As shown, the grating architecture 600 includes an input coupler 601. The input coupler 601 can be a Bragg grating or a surface relief grating. In many embodiments, the input coupler 601 includes at least two gratings. In such embodiments, each input grating can be configured to couple different portions of the input light, which can be based on an angle or spectral characteristic. In some embodiments, the input coupler 601 includes two overlapping gratings. In other embodiments, the input coupler 601 includes two multiplexed gratings. The grating architecture 600 also includes a first (bold line) and a second (dashed line) integrated grating. In an illustrative embodiment, the first integrated grating includes a first grating 602 having a first grating specification and a second grating 603 having a second grating specification. As shown, the second grating 603 is smaller than the first grating 602 and can be fully multiplexed within the volume of the first grating 602. In some embodiments, the first and second gratings 602, 603 overlap across different grating layers. In several embodiments, the first and second gratings 602, 603 are adjacent or nearly adjacent to each other and are neither overlapped nor multiplexed. In a number of embodiments, the first and second gratings 602, 603 have the same clock angle but different grating specifications.

[0112] In many embodiments, the configuration of the first integrated grating is applied in a manner similar to the second integrated grating but flipped about the axis. Figure 6 The illustrative embodiment in FIG. 1 shows a second integrated grating having third 604 and fourth 605 gratings with shapes corresponding to the first and second gratings 602, 603, respectively. The third grating 604 has a third grating specification, while the fourth grating 605 has a fourth grating specification. Similar to the first integrated grating, the third and fourth gratings 604, 605 can have the same clock angle but different grating specifications. In various embodiments, the first and second gratings 602, 603 are clocked at a different angle than the third and fourth gratings 604, 605. Again, the overlapping and multiplexing properties of the third and fourth gratings 604, 605 can be achieved in a similar manner as the first and second gratings 602, 603.

[0113] exist Figure 6In the illustrative embodiment of the present invention, the first and third integrated gratings partially overlap each other, so that the second and fourth gratings 603, 605 also partially overlap. In the illustrative embodiment, the second and fourth gratings 603, 605 are multiplexed within the first and third gratings 602, 604, as such, the waveguide architecture includes a region 606 where all four grating specifications are active. In embodiments where the first and second integrated gratings are implemented in a single layer, the region 606 will contain four multiplexed gratings. In other embodiments, the first and second integrated gratings are implemented across different grating layers.

[0114] During operation, input light incident on the input grating 601 can be bifurcated into two portions of light traveling in a TIR path within the waveguide. One portion can be directed toward the first grating 602, while the other portion can be directed toward the third grating 604. The first grating 602 can be configured to provide beam expansion for the incident light in a first direction and redirect the incident light to the fourth grating 605. The fourth grating 605 can be configured to provide beam expansion for the incident light in a second direction and extract the light out of the waveguide. On the other hand, the third grating 604 can be configured to provide beam expansion for the incident light in the second direction and redirect the incident light to the second grating 603. The second grating 603 can be configured to provide beam expansion for the incident light in the first direction and extract the light out of the waveguide.

[0115] Figure 7 A flow chart conceptually illustrating a method of displaying an image according to an embodiment of the present invention is shown. Referring to the flow chart, method 700 includes providing (701) a waveguide supporting an input grating, a first integrated grating, and a second integrated grating. In many embodiments, the first integrated grating partially overlaps the second integrated grating. In some embodiments, the integrated gratings completely overlap. The first and second integrated gratings may include a multiplexed pair of different K-vector gratings. A first field of view portion may be coupled (702) into the waveguide via the input grating and directed toward the first integrated grating. A second field of view portion may be coupled (703) into the waveguide via the input grating and directed toward the second integrated grating. A first field of view portion of light may be expanded (704) in a first direction using the first integrated grating. The first field of view portion of light may be expanded in a second direction using the second integrated grating and extracted from the waveguide (705). A second field of view portion of light may be expanded in a second direction (706) using the second integrated grating. A second field of view portion of light may be expanded in a first direction using the first integrated grating and extracted from the waveguide (707).

[0116] As described in the above subsections, the integrated grating can be implemented in a number of different ways. In many embodiments, the integrated grating is implemented by two gratings with the same clock angle but different grating specifications. In further embodiments, the two gratings are multiplexed. Figure 8A flow chart conceptually illustrating a method for displaying an image using an integrated grating including a plurality of gratings according to an embodiment of the present invention is shown. Referring to the flow chart, method 800 includes providing (801) a waveguide supporting an input grating, first and second gratings having a first clock angle, and third and fourth gratings having a second clock angle, wherein the first and third gratings at least partially overlap. In many embodiments, the first integrated grating partially overlaps the second integrated grating. In some embodiments, the integrated gratings completely overlap. The first and second integrated gratings may include a multiplexed pair of different K-vector gratings. A first field of view portion may be coupled (802) into the waveguide via the input grating and directed toward the first grating. A second field of view portion may be coupled (803) into the waveguide via the input grating and directed toward the third grating. The first field of view portion of light may be expanded (804) in a first direction using the first grating and redirected toward the fourth grating. The first field of view portion of light may be expanded (805) in a second direction using the fourth grating and extracted (806) from the waveguide. The second field of view portion of light may be expanded (806) in a second direction using the third grating and redirected toward the second grating. A second field of view portion of the light may be expanded in the first direction and extracted from the waveguide using a second grating (807).

[0117] Although Figure 6-8A specific waveguide configuration and method for displaying an image is illustrated, but many different methods may be implemented according to various embodiments of the present invention. For example, in some embodiments, more than one input grating is used. In other embodiments, the input configuration includes a prism. Such methods and implemented waveguides may also be configured to improve performance and / or provide a variety of different functions. In many embodiments, the waveguide device includes at least one grating with a spatially varying pitch. In some embodiments, each grating has a fixed K vector. In multiple embodiments, at least one of the gratings is a rolling k-vector grating according to the embodiments and teachings disclosed in the cited references. The rolling K-vector may allow the angular bandwidth of the grating to be extended without reducing the grating thickness or using multiple grating layers. In some embodiments, the rolling K-vector grating includes a waveguide portion that includes discrete grating elements with differently aligned K-vectors. In some embodiments, the rolling K-vector grating includes a waveguide portion that includes a single grating element, and the K-vector undergoes a smooth monotonic change in direction within the single grating element. In some of the embodiments described, the rolling K-vector grating is used to input light into the waveguide. In some embodiments, a waveguide with two integrated gratings can be implemented as a single layer or multilayer waveguide. In several embodiments, a multilayer waveguide is implemented with more than two integrated gratings. As can be easily appreciated, the specific architecture and configuration implemented can depend on a number of different factors. In some embodiments, the position of the input grating relative to the integrated grating can be dictated by various factors, including but not limited to projector fluctuations and input pupil diameter and convergence. In many applications, it is desirable to minimize the distance between the input grating and the integrated grating to provide a waveguide with a small form factor. The field ray angular path required to fill the eye box typically determines the waveguide height. In many cases, the height of the waveguide grows nonlinearly with projector fluctuations. In some embodiments, the pupil diameter has no significant effect on the footprint of the waveguide. Converging or diverging pupils can be used to reduce the local angular response at any position on the input grating.

[0118] In some embodiments, the waveguide configuration implemented may depend on the configuration of the input image generator / projector. Fig. 9A cross-sectional view 900 of two overlapping waveguide portions implementing integrated gratings according to an embodiment of the present invention is conceptually illustrated. In an illustrative embodiment, the two-layer waveguide is designed for high field of view applications implemented with a converging projector pupil input beam (indicated by ray 901). As shown, the device includes a first waveguide 902 including a first grating layer 903 having a first set of two integrated gratings and a second waveguide 904 including a second grating layer 905 having a second set of two integrated gratings, the second set of two integrated gratings partially overlapping the first set of two integrated gratings. The grating layers 903, 905 with integrated gratings can operate according to the principles discussed in the above subsections. The output beam from the waveguide is generally indicated by a ray 906 intersecting an eye box 907. In the illustrated embodiment, the eye box has dimensions of 10.5 mm x 9.5 mm, an eye distance of 13.5 mm, and a laser projector-waveguide separation of 12 mm. As can be readily appreciated, such dimensions and specifications can be specifically tailored to the requirements of a given application.

[0119] Fig.10 A schematic plan view 1000 of a grating architecture having two sets of integrated gratings in accordance with an embodiment of the present invention is conceptually illustrated. As shown, the grating configuration includes first and second input gratings 1001, 1002, forming a combined input grating region 1003 indicated by the shaded area. In some embodiments, each input grating includes a set of multiplexed or overlapping gratings. The grating configuration also includes a first set of grating structures having first and second integrated gratings 1004, 1005 and a second set of grating structures having third and fourth integrated gratings 1006, 1007. In the illustrative embodiment, the shape and deployment of each set of integrated gratings is asymmetric. Such a configuration may be appropriately implemented depending on a number of factors. In Fig.10 In embodiments of the present invention, an asymmetric grating architecture may be implemented for operation in a converging projector pupil configuration, such as Fig. 9 Furthermore, different grating characteristics can be implemented and tuned for different applications. Fig.11 A conceptual illustration of a diffraction efficiency versus angle graph 1100 of a waveguide for diffraction occurring at different field angles in accordance with an embodiment of the present invention. As shown, the waveguide is tuned to have three different peak diffraction efficiencies, two different peaks 1101, 1102 for the "fold" interaction and one 1103 for the "output". In some embodiments, light undergoes a double interaction within the grating. Such gratings can be designed to have high diffraction efficiency for two different angles of incidence. Return to Fig.10 , the first and second sets of grating structures can be implemented as partially overlapping structures, forming a combined output grating region 1008 as indicated by the shaded area. An eyebox 1009 is overlaid on the drawing and indicated by the dark shaded area. In the illustrative embodiment, the waveguide device is configured to provide a FOV of 120 degrees diagonal. Figure 9-10 As shown in , in some embodiments, a display providing a 120 degree diagonal FOV can be configured with a 12 mm projector to waveguide distance and a 13.5 mm eye relief, which is compatible with many eyeglass inserts. In some embodiments, the display provides a 10.5 mm x 9.5 mm eye box, which can provide easy wearability. Fig.12 The viewing geometry of such a waveguide is shown. As can be readily appreciated, Fig.10 The grating configurations shown can be implemented in various waveguide architectures. In some embodiments, both sets of input gratings and both sets of grating structures are implemented in a single grating layer, with the overlapping portions multiplexed. In several embodiments, the first input grating and the first set of grating structures are implemented in a first grating layer, while the second input grating and the second set of grating structures are implemented in a second grating layer. In multiple embodiments, the first, second, third, and fourth integrated gratings are implemented across four grating layers.

[0120] Fig.13 Conceptually illustrates the field of view geometry of a binocular display with binocular overlap between left-eye and right-eye images provided by a waveguide according to an embodiment of the present invention. Figure 9-10 . In the illustrated embodiment, the waveguide is a stacked color waveguide comprising four waveguides: two blue-green layers and two green-red layers. Each of the waveguides can provide a field of view of 35°h×35°v (~50° diagonal) for a single color band, thereby producing a field of view of 70°h×35°v (~78° diagonal) for each color band. Each waveguide set for the left eye and the right eye can overlap horizontally by 50° to achieve a binocular field of view of ~100° diagonal. As can be easily recognized, various binocular configurations can be appropriately implemented according to the specific requirements of a given application. In many embodiments, the waveguides are tilted at an angle of at least 5°, which can facilitate the implementation of some binocular overlapping field of view applications. In a further embodiment, the waveguides are tilted at an angle of at least 10°. In some embodiments, the fields of view of the left eye and the right eye overlap completely.

[0121] Other Waveguide Embodiments

[0122] In some embodiments, a prism may be used as a substitute for an input grating. In many embodiments, this may require providing an external grating for grating vector closure purposes. In several embodiments, the external grating may be disposed on the surface of the prism. In some embodiments, the external grating may form part of a laser despeckler disposed in an optical system between the laser projector and the input prism. The advantage of using a prism to couple light into a waveguide is that the significant light losses and limited angular bandwidth caused by the use of a rolled K-vector grating are avoided. Practical rolled K-vector input gratings are generally unable to match the much larger angular bandwidth of a folded grating, which may be on the order of 40 degrees or more.

[0123] While the drawings may indicate a high degree of symmetry of grating geometry and grating layout in different wavelength channels, the grating specifications and footprint may be asymmetric. The shape of the input, folded or output gratings may depend on the waveguide application and may be any polygonal geometry influenced by factors such as desired beam spread, output beam geometry, beam uniformity and ergonomic considerations.

[0124] In some embodiments, for displays using unpolarized light sources, the input gratings may be combined with gratings oriented such that each grating diffracts a specific polarization of incident unpolarized light into a waveguide path. Such embodiments may be combined with some of the embodiments and teachings disclosed in PCT application PCT / GB2017 / 000040, “METHOD AND APPARATUS FOR PROVIDING APOLARIZATION SELECTIVE HOLOGRAPHIC WAVGUIDE DEVICE” by Waldern et al., the disclosure of which is incorporated herein by reference in its entirety. The output gratings may be configured in a similar manner such that light from the waveguide paths is combined and coupled out of the waveguide as unpolarized light. For example, in some embodiments, the input gratings and the output gratings each combine a crossed grating having peak diffraction efficiency for orthogonal polarization states. In multiple embodiments, the polarization states are S polarization and P polarization. In several embodiments, the polarization states are in the opposite sense to circular polarization. Gratings recorded in liquid crystal polymer systems (such as SBGs) have an advantage in this regard in that they exhibit strong polarization selectivity due to their inherent birefringence. However, other grating technologies that can be configured to provide unique polarization states may also be used.

[0125] In some embodiments using gratings recorded in a liquid crystal polymer material system, at least one polarization control layer can be provided overlapping at least one of the folded gratings, input gratings or output gratings, the purpose of which is to compensate for polarization rotation in any grating (particularly folded gratings that cause polarization rotation). In many embodiments, all gratings are covered by polarization control layers. In multiple embodiments, the polarization control layer is applied only to the folded gratings or to any other subset of the gratings. The polarization control layer may include an optical delay film. In some embodiments based on HPDLC materials, the birefringence of the grating can be used to control the polarization characteristics of the waveguide device. Using the birefringence tensor, K vector and grating footprint of the HPDLC grating as design variables opens up a design space for optimizing the angular capability and optical efficiency of the waveguide device. In some embodiments, a quarter wave plate can be deployed at the glass-air interface of the waveguide to rotate the polarization of the light to maintain efficient coupling with the grating. In further embodiments, the quarter wave plate is a coating applied to the substrate waveguide. In some waveguide display embodiments, applying a quarter wavelength coating to the substrate of the waveguide can help the light stay aligned with the intended visual axis by compensating for skew waves in the waveguide. In some embodiments, the quarter wave plate may be provided as a multi-layer coating.

[0126] As used in connection with any embodiment described herein, the term grating may encompass a grating comprising a set of gratings. For example, in some embodiments, the input grating and the output grating each comprise two or more gratings multiplexed into a single layer. It is well established in the holographic literature that more than one holographic format can be recorded into a single holographic layer. Methods for recording such multiplexed holograms are well known to those skilled in the art. In some embodiments, the input grating and the output grating may each comprise two overlapping grating layers that contact or are vertically separated by one or more thin optical substrates. In several embodiments, the grating layers are sandwiched between glass or plastic substrates. In a number of embodiments, two or more such grating layers may form a stack in which total internal reflection occurs at the external substrate and air interface. In some embodiments, the waveguide may comprise only one grating layer. In many embodiments, electrodes may be applied to the face of the substrate to switch the grating between diffraction and transparent states. The stack may also include additional layers, such as beam splitting coatings and environmental protection layers.

[0127] In some embodiments, the folded grating angular bandwidth can be enhanced by designing the grating specifications to promote dual interaction of the guided light with the grating.Exemplary embodiments of dual-interaction folded gratings are disclosed in US Patent Application No.: 14 / 620,969, entitled "WAVEGUIDE GRATING DEVICE".

[0128] Advantageously, to improve color uniformity, gratings for use with the present invention can be designed using reverse ray tracing from the eyebox via the output grating and fold grating to the input grating. This process allows identification of the physical extent required for the grating, particularly the fold grating. Unnecessary grating real states that cause haze can be eliminated. The ray paths can be optimized for red, green, and blue, each following a slightly different path due to the dispersion effects between the input and output gratings via the fold grating.

[0129] In many embodiments, the grating is a holographic grating, such as a switchable or non-switchable Bragg grating. In some embodiments, the grating implemented as an SBG can be a Bragg grating recorded in a holographic polymer dispersed liquid crystal (e.g., a matrix of liquid crystal droplets), but SBGs can also be recorded in other materials. In several embodiments, the SBG is recorded in a uniformly modulated material, such as POLICRYPS or POLIPHEM having a matrix of solid liquid crystals dispersed in a liquid polymer. The SBG can be switching or non-switching in nature. In some embodiments, at least one of the input, fold, and output gratings can be electrically switchable. In many embodiments, it is desired that all three grating types are passive, i.e., non-switching. In its non-switching form, SBGs have an advantage over conventional holographic photopolymer materials because their liquid crystal composition is able to provide high refractive index modulation. Exemplary homogeneously modulated liquid crystal-polymer material systems are disclosed in U.S. Patent Application Publication No.: US2007 / 0019152 to Caputo et al. and PCT Application No.: PCT / EP2005 / 006950 to Stumpe et al., both of which are incorporated herein by reference in their entirety. The homogeneously modulated grating is characterized by high refractive index modulation (and therefore high diffraction efficiency) and low scattering. In some embodiments, the input coupler, folded grating, and output grating are recorded in a reverse mode HPDLC material. Reverse mode HPDLC differs from conventional HPDLC in that the grating is passive when no electric field is applied and becomes diffractive when an electric field is present. Reverse mode HPDLC can be based on any of the formulations and processes disclosed in PCT Application No.: PCT / GB2012 / 000680, entitled "IMPROVEMENTS TO HOLOGRAPHIC POLYMER DISPERSEDLIQUID CRYSTAL MATERIALS AND DEVICES." The grating can be recorded in any of the above material systems, but used in a passive (non-switching) mode. The advantage of recording a passive grating in a liquid crystal polymer material is that the final hologram benefits from the high refractive index modulation provided by the liquid crystal. The higher refractive index modulation translates into high diffraction efficiency and wide angular bandwidth. The manufacturing process is exactly the same as that used for the switching mode, but the electrode coating stage is omitted. Liquid crystal polymer material systems are very desirable given their high refractive index modulation. In some embodiments, the grating is recorded in HPDLC but not switched.

[0130] In many embodiments, two spatially separated input couplers can be used to provide two separate waveguide input pupils. In some embodiments, the input couplers are gratings. In several embodiments, the input couplers are prisms. In embodiments using only prism-based input couplers, the pitch and clock angle of the fold and output gratings can be used to address the grating reciprocity condition.

[0131] In many embodiments, the source of data modulated light used with the above-described waveguide embodiments includes an input image node ("IIN") in combination with a microdisplay. The input grating can be configured to receive collimated light from the IIN and cause the light to travel within the waveguide to the folded grating via total internal reflection between the first surface and the second surface. Typically, in addition to the microdisplay panel, the IIN also integrates the light source and the optical components required to illuminate the display panel, separate the reflected light and collimate it into the desired FOV. Each image pixel on the microdisplay can be converted into a unique angular direction within the first waveguide. The present disclosure does not assume any particular microdisplay technology. In some embodiments, the microdisplay panel can be a liquid crystal device or a MEMS device. In several embodiments, the microdisplay can be based on organic light emitting diode (OLED) technology. Such emissive devices do not require separate light sources, thus providing the benefit of a smaller form factor. In some embodiments, the IIN can be based on a scanned modulated laser. According to some embodiments, the IIN projects an image displayed on the microdisplay panel so that each display pixel is converted into a unique angular direction within the substrate waveguide. The collimating optical device included in the IIN can include a lens and a reflector, which can be a diffractive lens and a reflector. In some embodiments, the IIN may be based on the embodiments and teachings disclosed in U.S. Patent Application No. 13 / 869,866, entitled “HOLOGRAPHIC WIDE-ANGLE DISPLAY” and U.S. Patent Application No. 13 / 844,456, entitled “TRANSPARENT WAVEGUIDEDISPLAY”. In several embodiments, the IIN includes a beam splitter for directing light onto a microdisplay and transmitting reflected light to a waveguide. In many embodiments, the beam splitter is a grating recorded in an HPDLC and uses the inherent polarization selectivity of such a grating to separate the light illuminating the display and the image modulated light reflected from the display. In some embodiments, the beam splitter is a polarizing beam splitter cube. In multiple embodiments, the IIN incorporates a despeckler. The despeckler may be a holographic waveguide device based on the embodiments and teachings of U.S. Patent No. 8,565,560, entitled “LASER ILLUMINATION DEVICE”. The light source may be a laser or an LED and may include one or more lenses for modifying the angular characteristics of the illumination beam. The image source may be a microdisplay or a laser-based display. LEDs can provide better uniformity than lasers. If laser illumination is used, there is a risk of illumination striping at the waveguide output.In some embodiments, laser illumination striping in a waveguide can be overcome using techniques and teachings disclosed in U.S. Provisional Patent Application No.: 62 / 071,277, entitled "METHOD AND APPARATUS FOR GENERATING INPUT IMAGES FOR HOLOGRAPHIC WAVEGUIDEDISPLAYS." In some embodiments, the light from the light source is polarized. In one or more embodiments, the image source is a liquid crystal display (LCD) microdisplay or a liquid crystal on silicon (LCoS) microdisplay.

[0132] The principles and teachings of the present invention, in combination with the inventor's other waveguide inventions as disclosed in the references incorporated herein by reference, can be applied to many different displays and sensor devices. In some embodiments directed to displays, a waveguide display according to the principles of the present invention can be combined with an eye tracker. In some embodiments, the eye tracker is a waveguide device overlaying a display waveguide and is based on the embodiments and teachings of PCT / GB2014 / 000197 entitled "HOLOGRAPHIC WAVEGUIDE EYE TRACKER", PCT / GB2015 / 000274 entitled "HOLOGRAPHIC WAVEGUIDE OPTICALTRACKER", and PCT Application No.: GB2013 / 000210 entitled "APPARATUS FOR EYE TRACKING".

[0133] In some embodiments of the present invention directed to displays, a waveguide display according to the principles of the present invention further includes a dynamic focus element. The dynamic focus element may be based on the embodiments and teachings of U.S. Provisional Patent Application No.: 62 / 176,572, entitled "ELECTRICALLY FOCUS TUNABLE LENS". In some embodiments, a waveguide display according to the principles of the present invention may further include a dynamic focus element and an eye tracker that may provide a light field display based on the embodiments and teachings disclosed in U.S. Provisional Patent Application No.: 62 / 125,089, entitled "HOLOGRAPHIC WAVEGUIDE LIGHT FIELD DISPLAYS".

[0134] In some embodiments of the present invention directed to a display, a waveguide in accordance with the principles of the present invention may be based on some embodiments of U.S. Patent Application No.: 13 / 869,866, entitled “HOLOGRAPHIC WIDEANGLE DISPLAY” and U.S. Patent Application No.: 13 / 844,456, entitled “TRANSPARENT WAVEGUIDE DISPLAY”. In some embodiments, a waveguide device in accordance with the principles of the present invention may be integrated within a window, such as a windshield integrated HUD for road vehicle applications. In some embodiments, the window integrated display may be based on the embodiments and teachings disclosed in U.S. Provisional Patent Application No.: PCT Application No.: PCT / GB2016 / 000005, entitled “ENVIRONMENTALLY ISOLATED WAVEGUIDE DISPLAY”. In some embodiments, the waveguide device may include a gradient index (GRIN) waveguide component for relaying image content between the IIN and the waveguide. Exemplary embodiments are disclosed in PCT Application No.: PCT / GB2016 / 000005, entitled “ENVIRONMENTALLYISOLATED WAVEGUIDE DISPLAY”. In some embodiments, based on the embodiments disclosed in U.S. Provisional Patent Application No.: 62 / 177,494, entitled “WAVEGUIDE DEVICE INCORPORATING A LIGHT PIPE”, the waveguide device may incorporate a light pipe for providing beam expansion in one direction.

[0135] In many embodiments, a waveguide according to the principles of the present invention provides an image at infinity. In some embodiments, the image may be at some intermediate distance. In some embodiments, the image may be at a distance compatible with the relaxed viewing range of the human eye. In many embodiments, this may cover a viewing range from about 2 meters to about 10 meters.

[0136] The construction and arrangement of the systems and methods as shown in the various exemplary embodiments are illustrative only. Although only a few embodiments are described in detail in the present disclosure, many modifications are possible (e.g., changes in the size, dimensions, structure, shape and proportion of various elements, the values ​​of parameters, mounting arrangements, the use of materials, colors, orientations, etc.). For example, the position of elements can be reversed or otherwise changed, and the nature or number of discrete elements or positions can be altered or changed. The present invention may be combined with the embodiments and teachings disclosed in U.S. Provisional Patent Application No. 62 / 778,239, entitled "METHODS AND APPARATUSES FOR PROVIDING A SINGLE GRATING LAYER COLOR HOLOGRAPHIC WAVEGUIDE DISPLAY," and the following U.S. applications written by Popovich et al.: US14 / 620,969 "WAVEGUIDE GRATING DEVICE"; US15 / 468,536 "Waveguide Grating Device"; US15 / 807,149 "WAVEGUIDE GRATING DEVICE"; and US16 / 178,104 "WAVEGUIDE GRATING DEVICE," all of which are incorporated herein by reference in their entirety. Therefore, all such modifications are intended to be included within the scope of the present disclosure. The order or sequence of any process or method steps may be changed or re-sequenced according to alternative embodiments. Other substitutions, modifications, changes and omissions may be made in the design, operating conditions and arrangement of the exemplary embodiments without departing from the scope of the present disclosure.

[0137] Principle of Equivalence

[0138] Although the above description contains many specific embodiments of the present invention, these should not be interpreted as limiting the scope of the present invention, but should be regarded as examples of one embodiment thereof. It should therefore be understood that, without departing from the scope and spirit of the present invention, the present invention may be practiced in a manner different from that specifically described. Therefore, the embodiments of the present invention should be regarded as illustrative and non-restrictive in all aspects. Thus, the scope of the present invention should not be determined by the embodiments shown, but by the appended claims and their equivalents.

Claims

1. A waveguide display, comprising: light source; as well as The first waveguide, including: a grating structure comprising a first grating and a second grating multiplexed into a single layer; and Input coupler, configured as: coupling a first field of view portion of light from the light source into the first waveguide and toward the first grating; and coupling a second field portion of light from the light source into the first waveguide and toward the second grating; in: The first grating is configured as: providing beam expansion in a first direction for said first field of view portion of light; and providing beam expansion in the first direction and beam extraction toward an observer for the second field of view portion of light; The second grating is configured as: providing beam expansion in a second direction for said second field of view portion of light; and providing beam expansion in the second direction and beam extraction toward an observer for the first field of view portion of light; The input coupler, the first grating, and the second grating each include a grating vector; and The grating vector of the input coupler, the first grating and the second grating provides a result vector having a magnitude of substantially zero.

2. A waveguide display as claimed in claim 1, wherein: The first grating includes a first grating specification and a second grating specification; and The second grating includes a third grating specification and a fourth grating specification; wherein: The first grating specification is configured to provide the beam expansion in the first direction for the first field of view portion of light; The second grating specification is configured to provide beam expansion in the first direction and beam extraction toward an observer for the second field of view portion of light; The third grating format is configured to provide the beam expansion in the second direction for the second field of view portion of light; and The fourth grating format is configured to provide the beam expansion in the second direction and beam extraction towards an observer for the first field of view portion of light.

3. A waveguide display as described in claim 2, wherein the first grating specification and the second grating specification are at least partially multiplexed; and the third grating specification and the fourth grating specification are at least partially multiplexed.

4. A waveguide display as claimed in claim 3, wherein the first grating at least partially overlaps the second grating.

5. The waveguide display of claim 1, further comprising a second waveguide; wherein the first waveguide is configured to couple in a first spectral band; and the second waveguide is configured to couple in a second spectral band.

6. A waveguide display as described in claim 1, wherein the input coupler includes an input configuration selected from the group consisting of: an input prism; an input grating; a first input grating and a second input grating; and an additional input grating including two multiplexed grating specifications.

7. A waveguide display as claimed in claim 1, wherein the grating vector of the input coupler has a different magnitude than the grating vector of the first grating.

8. The waveguide display of claim 1, wherein the light source provides light of at least two different wavelengths.

9. A method for displaying an image, the method comprising: providing a waveguide display comprising a first waveguide supporting an input coupler and a grating structure comprising a first grating and a second grating multiplexed into a single layer, wherein the input coupler, the first grating and the second grating each comprise a grating vector, wherein the grating vectors of the input coupler, the first grating and the second grating provide a result vector having a magnitude substantially zero; coupling a first field of view portion of light from a light source into the first waveguide via the input coupler; coupling a second field of view portion of light from a light source into the first waveguide via the input coupler; expanding the first field portion of light in a first direction using the first grating; using the second grating to expand the first field portion of light in a second direction and extract it from the first waveguide; expanding the second field portion of light in the second direction using the second grating; as well as The second field portion of light is expanded in the first direction using the first grating and extracted from the first waveguide.

10. The method of claim 9, wherein: The first grating includes a first grating specification and a second grating specification; and The second grating includes a third grating specification and a fourth grating specification; wherein: expanding the first field portion of light in the first direction using the first grating specification; expanding the second field portion of light in the first direction using the second grating specification and extracting it from the first waveguide; expanding the second field portion of light in the second direction using the third grating specification; and The first field of view portion of light is expanded in the second direction using the fourth grating specification and extracted from the first waveguide.

11. The method of claim 10, wherein the first grating specification and the second grating specification are at least partially multiplexed, and the third grating specification and the fourth grating specification are at least partially multiplexed.

12. The method of claim 11, wherein the first grating at least partially overlaps the second grating.

13. The method of claim 9, wherein the waveguide display further comprises a second waveguide; wherein the first waveguide is configured to couple in a first spectral band; and the second waveguide is configured to couple in a second spectral band.

14. The method of claim 9, wherein the input coupler comprises an input configuration selected from the group consisting of: an input prism; an input grating; a first input grating and a second input grating; and an additional input grating comprising two multiplexed grating specifications.

15. The method of claim 9, wherein the grating vector of the input coupler has a different magnitude than the grating vector of the first grating.

16. The method of claim 9, wherein the light source provides light of at least two different wavelengths.

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