Method and apparatus for providing holographic waveguide display using integrated grating

文档序号：292323 发布日期：2021-11-23 浏览：10次中文

阅读说明：本技术 使用集成光栅提供全息波导显示的方法和装置 (Method and apparatus for providing holographic waveguide display using integrated grating ) 是由 A·J·格兰特 J·D·沃德恩 M·M·波波维奇何斯慧 E·劳 R·C·史密斯于 2020-02-18 设计创作，主要内容包括：图示了根据本发明各种实施例的用于使用集成光栅提供全息波导显示器的系统和方法。一个实施例包括一种波导显示器,包括光源；以及第一波导,包括光栅结构,该光栅结构包括第一光栅和第二光栅；以及输入耦合器,被配置为耦合光的第一视场部分并耦合光的第二视场部分,其中第一光栅被配置为为光的第一视场部分提供第一方向上的波束扩展,并为光的第二视场部分提供第一方向上的波束扩展和朝着观察者的波束提取,第二光栅被配置为为光的第二视场部分提供第二方向上的波束扩展,并为光的第一视场部分提供第二方向上的波束扩展和朝着观察者的波束提取。(Systems and methods for providing holographic waveguide displays using integrated gratings according to various embodiments of the present invention are illustrated. One embodiment includes a waveguide display comprising a light source; and a first waveguide comprising a grating structure comprising 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 towards the viewer 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 towards the viewer for the first field of view portion of the light.)

1. A waveguide display, comprising:

a light source; and

a first waveguide comprising:

a grating structure comprising a first grating and a second grating; and

an input coupler configured to:

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 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:

providing a beam expansion in a first direction for the first field of view portion of light; and

providing the second field of view portion of light with beam expansion in the first direction and beam extraction toward a viewer;

the second grating is configured to:

providing a beam expansion in a second direction for the second field of view portion of light; and

providing the first field of view portion of light with beam expansion in the second direction and beam extraction toward a viewer;

the input-coupler, the first grating, and the second grating each comprise a grating vector; and

the grating vectors of the input-coupler, the first grating and the second grating provide a resultant vector having a magnitude of substantially zero.

2. The waveguide display of claim 1, wherein:

the first grating comprises a first grating specification and a second grating specification; and

the second grating comprises 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 a viewer for the second field of view portion of light;

the third grating specification is configured to provide the beam expansion in the second direction for the second field of view portion of light; and

the fourth grating specification is configured to provide the beam expansion in the second direction and beam extraction towards a viewer for the first field of view portion of light.

3. The waveguide display of claim 2, wherein the first and second grating specifications are at least partially multiplexed; and the third and fourth grating specifications are at least partially multiplexed.

4. The waveguide display of claim 3, wherein the first grating at least partially overlaps the second grating.

5. The waveguide display of claim 4, wherein:

the first waveguide comprises a first grating layer and a second grating layer;

the first grating is disposed within the first grating layer; and

the second grating is disposed within the second grating layer.

6. The waveguide display of claim 5, wherein the first waveguide further comprises a transparent layer disposed between and adjacent to the first and second grating layers.

7. The waveguide display of claim 6, further comprising a second waveguide; wherein the first waveguide is configured to be coupled in a first spectral band; and the second waveguide is configured to be coupled in a second spectral band.

8. The waveguide display of claim 1, wherein the input coupler comprises an input configuration selected from the group consisting of: an input prism; inputting a grating; a first input grating and a second input grating; and an input raster comprising two multiplexed raster specifications.

9. The waveguide display of claim 1, wherein the grating vector of the input-coupler has a different magnitude than the grating vector of the first grating.

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

11. A method of 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, 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 resultant vector having a magnitude of 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 and extracting it from the waveguide using the second grating;

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 using the first grating and extracting it from the waveguide.

12. The method of claim 11, wherein:

the first grating comprises a first grating specification and a second grating specification; and

the second grating comprises a third grating specification and a fourth grating specification; wherein:

expanding the first field of view portion of light in the first direction using the first grating specification;

expanding the second field of view portion of light in the first direction and extracting from the waveguide using the second grating specification;

expanding the second field of view portion of light in the second direction using the third grating specification; and

expanding the first field of view portion of light in the second direction and extracting from the waveguide using the fourth grating specification.

13. The method of claim 12, wherein the first and second grating specifications are at least partially multiplexed, and the third and fourth grating specifications are at least partially multiplexed.

14. The method of claim 13, wherein the first grating at least partially overlaps the second grating.

15. The method of claim 14, wherein:

the first waveguide comprises a first grating layer and a second grating layer;

the first grating is disposed within the first grating layer; and

the second grating is disposed within the second grating layer.

16. The method of claim 15 wherein the first waveguide further comprises a transparent layer disposed between and adjacent to the first and second grating layers.

17. The method of claim 16, wherein the waveguide display further comprises a second waveguide; wherein the first waveguide is configured to be coupled in a first spectral band; and the second waveguide is configured to be coupled in a second spectral band.

18. The method of claim 11, wherein the input coupler comprises an input configuration selected from the group consisting of: an input prism; inputting a grating; a first input grating and a second input grating; and an input raster comprising two multiplexed raster specifications.

19. The method of claim 11, wherein the grating vector of the input coupler has a different magnitude than the grating vector of the first grating.

20. The method of claim 11, wherein the light source provides light at least two different wavelengths.

Technical Field

The present invention relates generally to waveguide devices, and more particularly to holographic waveguide displays.

Background

Waveguides may be referred to as structures having the ability to confine and guide waves (i.e., limit the spatial region in which waves may propagate). One subclass includes optical waveguides, which are structures that can guide electromagnetic waves, typically in the visible spectrum. Waveguide structures can be designed to control the propagation path of the wave using a variety of different mechanisms. For example, planar waveguides may be designed to diffract and couple incident light into the waveguide structure using a diffraction grating, such that the coupled-in light may continue to travel within the planar structure via Total Internal Reflection (TIR).

Fabrication of the waveguide may include the use of a material system that allows the holographic optical element to be recorded 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. A holographic optical element, such as a volume phase grating, may be recorded in such a liquid mixture by illuminating the material with two mutually coherent laser beams. During the recording process, the monomers polymerize and the mixture undergoes phase separation by photopolymerization, creating areas densely filled with liquid crystal droplets, interspersed with areas of transparent polymer. The alternating rich and lean liquid crystal regions form an edge plane of the grating. The resulting grating, commonly referred to as a Switchable Bragg Grating (SBG), has all of the characteristics typically associated with volume or Bragg gratings, but has a higher range of refractive index modulation and the ability to electrically tune the grating (the proportion of incident light diffracted into the desired direction) over a continuous range of diffraction efficiencies. The latter can extend from non-diffractive (transparent) to diffractive with efficiencies approaching 100%.

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 can be implemented using various waveguide architectures and material systems, leading to new innovations in near-eye displays for Augmented Reality (AR) and Virtual Reality (VR), compact overhead displays (HUD) and head-mounted or head-mounted displays (HMD) for road transportation, aviation, and military applications, and sensors for biometric identification and LIDAR (LIDAR) applications.

Disclosure of Invention

Systems and methods for providing holographic waveguide displays 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 towards the first grating, and a second field of view portion of the light from the light source is coupled into the first waveguide and towards the second grating, wherein the first grating is configured to provide a beam expansion in a first direction for a first field of view portion of the light, and providing a beam expansion in a first direction and a beam extraction (extraction) towards a viewer for the second field of view portion of the light, the second grating being configured to provide a beam expansion in a second direction for the second field of view portion of the light, and provides beam expansion in a second direction and beam extraction toward a viewer for the first field of view portion of light, the input-coupler, the first grating and the second grating each comprising a grating vector, and the grating vectors of the input coupler, the first grating and the second grating provide a resultant vector having a magnitude of substantially zero.

In another embodiment, the first grating comprises a first and a second grating specification (description), the second grating comprises a third and a fourth grating specification, wherein the first grating rule is configured to provide beam expansion in a first direction for the first field of view portion of the light, the second grating specification is configured to provide beam expansion in the first direction and beam extraction towards the viewer for the second field of view portion of the light, the third grating specification is configured to provide beam expansion in a second direction for the second field of view portion of the light, and the fourth grating specification is configured to provide beam expansion in the second direction and beam extraction towards the viewer for the first field of view portion of the light.

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.

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

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.

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

In yet another embodiment, the waveguide display further comprises a second waveguide, wherein the first waveguide is configured to be coupled in a first spectral band and the second waveguide is configured to be coupled in a second spectral band.

In another additional embodiment, wherein the input coupler comprises an input configuration selected from at least one of an input prism, an input grating, first and second input gratings, and an input grating comprising two multiplexed grating specifications.

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

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

In yet another embodiment, a method of displaying an image, the method includes providing a waveguide display, the waveguide display comprises a first waveguide supporting an input-coupler and a grating structure comprising first and second gratings, 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 of 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 the light in a first direction using the first grating, expanding the first field of view portion of the light in a second direction using the second grating and extracting it from the waveguide, expanding the second field of view portion of the light in the second direction using the second grating, and using the first grating to expand the second field of view portion of the light in the first direction and extract it from the waveguide.

In yet another embodiment, the first grating comprises first and second grating specifications, and the second grating comprises third and fourth grating specifications, wherein a first field of view portion of the light is expanded in a first direction using the first grating specification, a second field of view portion of the light is expanded in the first direction using the second grating specification and extracted from the waveguide, a second field of view portion of the light is expanded in a second direction using the third grating specification, and the first field of view portion of the light is expanded in the second direction using the fourth grating specification and extracted from the waveguide.

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.

In yet an additional embodiment, the first grating at least partially overlaps the second grating.

In yet an 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.

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

In yet an 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.

In yet an additional embodiment, the grating vector of the input coupler has a different magnitude than the grating vector of the first grating.

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

Additional embodiments and features are set forth in part in the description which follows and in part will become apparent to those having ordinary skill in the art upon examination of the specification or may be learned by practice of the invention. A further understanding of the nature and advantages of the present invention may be realized by reference to the remaining portions of the specification and the drawings, which form a part of this disclosure.

Drawings

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

FIG. 1 conceptually illustrates a waveguide display, in accordance with an embodiment of the present invention.

Figures 3A-3C conceptually illustrate integrated gratings according to various embodiments of the invention.

Figures 4A-4C schematically illustrate ray propagation through a grating structure having an input grating and two integrated gratings, in accordance with embodiments of the present invention.

Figures 5A-5E conceptually illustrate various raster vector configurations in accordance with various embodiments of the invention.

Figure 6 conceptually illustrates a schematic plan view of a grating architecture having an input grating and an integrated grating, in accordance with embodiments of the present invention.

Fig. 7 shows a flowchart conceptually illustrating a method of displaying an image according to an embodiment of the present invention.

FIG. 8 shows a flow diagram conceptually illustrating a method of displaying an image with an integrated raster comprising multiple rasters, in accordance with an embodiment of the invention.

Figure 9 conceptually illustrates a cross-sectional view of two overlapping waveguide portions implementing an integrated grating, in accordance with embodiments of the present invention.

Figure 10 conceptually illustrates a schematic plan view of a grating architecture with two sets of integrated gratings, in accordance with embodiments of the present invention.

Figure 11 conceptually illustrates a plot of diffraction efficiency versus angle for a waveguide diffracting at different angles of view, in accordance with an embodiment of the present invention.

FIG. 12 illustrates a viewing geometry provided by a waveguide according to an embodiment of the present invention.

Fig. 13 conceptually illustrates field of view geometries for a binocular display of binocular overlap between left and right eye images provided by a waveguide, in accordance with an embodiment of the present invention.

Detailed Description

For purposes 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 in order not to obscure the underlying principles of the invention. Unless otherwise indicated, the term "on-axis" in relation to the ray or beam direction refers to propagation parallel to an axis perpendicular to the surface of the optical component described in relation to the present invention. In the following description, the terms light, ray, beam and direction may be used interchangeably and are associated with each other to indicate the direction of propagation of electromagnetic radiation along a straight trajectory. The terms light and illumination may be used with respect to the visible and infrared bands of the electromagnetic spectrum. Portions of the following description will be presented using terminology commonly employed by those skilled in the art of optical design. As used herein, the term grating may encompass, in some embodiments, a grating consisting of a set of gratings. For purposes of illustration, it should be understood that the drawings are not drawn to scale unless otherwise indicated.

Waveguide displays according to various embodiments of the present invention may be implemented using a number of different technologies. Waveguide technology can provide a low cost, efficient and versatile diffractive optical solution for many different applications. One commonly used waveguide architecture includes an input grating for coupling light from an image source into a TIR path in a waveguide, a fold grating for providing 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 viewing from an exit pupil or eye box (eyebox). While effective in two-dimensional beam expansion and extraction, such an arrangement typically requires a large grating area. When used with birefringent gratings, this architecture also suffers from haze due to millions of grating interactions in the fold. Another problem is image non-uniformity due to longer optical paths resulting in more beams interacting with the substrate of the waveguide. As such, many embodiments of the present invention are directed to wide-angle, low-cost, efficient, and compact waveguide displays.

In many embodiments, the waveguide display includes at least one input grating and at least two integrated gratings, each capable of performing the functions of a conventional fold and output grating. In a further embodiment, a single multiplexed input grating is implemented to provide input light having two divergent paths. In other embodiments, two input gratings are implemented to provide bifurcated optical paths. In addition to different configurations of the input grating(s), the integrated grating may be configured in various ways. In some embodiments, the integrated grating contains intersecting grating vectors and may be configured to provide beam expansion in both directions and beam extraction for light from the input grating(s). In several embodiments, the integrated grating is configured as an overlapping grating with intersecting grating vectors. The integrated nature of the grating architecture may 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 readily appreciated, the specific architecture and implementation of the waveguide display may depend on the specific requirements of a given application. For example, in some embodiments, the waveguide display is implemented with integrated gratings to provide a binocular field of view of at least 50 ° diagonal. In a further embodiment, the waveguide display is implemented with integrated gratings to provide a binocular field of view of at least 100 ° diagonal. Waveguide displays, grating architectures, HPDLC materials and fabrication processes according to various embodiments of the present invention are discussed in further detail below.

Optical waveguide and grating structure

The optical structure recorded in the waveguide may include many different types of optical elements, such as, but not limited to, diffraction gratings. The grating may 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 grating implemented is a Bragg grating (also referred to as a bulk grating), which is a structure with periodic refractive index modulation. Bragg gratings can be manufactured using a number of different methods. One process includes interference exposure of a holographic photopolymer material to form periodic structures. Bragg gratings can have high efficiency, with little light being diffracted into higher orders. The relative amounts of diffracted order and zeroth order light can be varied by controlling the index modulation of the grating, which is a characteristic used to fabricate lossy waveguide gratings to extract light over a large pupil.

One type of Bragg grating used in holographic waveguide devices is a Switchable Bragg Grating (SBG). SBGs can be manufactured by first placing a thin film of a mixture of photopolymerizable monomers and liquid crystal material between substrates. The substrate may 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 substrate forms a wedge shape. One or both substrates may support electrodes, typically transparent tin oxide films, for applying an electric field across the film. The grating structure in SBG can be recorded in a liquid material (commonly referred to as a slurry) by photopolymerization-induced phase separation with interferometric exposure with spatially periodic intensity modulation. Factors such as, but not limited to, controlling the radiation intensity, the volume fraction of the components of the materials in the mixture, and the exposure temperature, can determine the resulting grating morphology and performance. It will be readily understood that a wide variety of materials and mixtures may 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 over 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 a high optical polarization caused by the order of orientation of the LC molecules in the droplets.

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 thin film. In the case where an electric field is applied to the grating via the transparent electrode, the natural orientation of the LC droplet may change, resulting in a reduction in the refractive index modulation of the fringes and a reduction in hologram diffraction efficiency to a very low level. Typically, the electrodes are configured such 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 generally aligned perpendicular to the fringes. Therefore, the grating has higher refractive index modulation and higher diffraction efficiency for P-polarized light. In the case of an applied electric field to the HPDLC, the grating switches to the ON state, where the extraordinary axis of the liquid crystal molecules is aligned parallel to the applied electric field and thus aligned perpendicular to the substrate. In the ON state, the grating exhibits lower refractive index modulation and lower diffraction efficiency for both S-polarized light and P-polarized light. Thus, the grating regions no longer diffract light. Depending on the function of the HPDLC device, each grating area may 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 opposite substrate surface are patterned according to a plurality of selectively switchable grating elements.

Typically, SBG elements are cleared within 30 μ s and turned on with a longer relaxation time. The diffraction efficiency of the device can be adjusted over a continuous range by means of the applied voltage. In many cases, the device exhibits near 100% efficiency without applied voltage, and substantially zero efficiency with sufficiently high applied voltage. In certain 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 may be to the extent that no discernable droplet structure is produced. SBGs may also be used as passive gratings. In this mode, the main advantage is the unique high index modulation. SBGs may be used to provide transmission or reflection gratings for free space applications. The SBG may be implemented as a waveguide device, where the HPDLC forms a waveguide core or evanescent coupling layer near the waveguide. The substrate used to form the HPDLC cell provides a Total Internal Reflection (TIR) light guide structure. When the switchable grating diffracts light at an angle exceeding the TIR condition, light may be coupled out of the SBG.

In some embodiments, the LC may be extracted or drained from the SBG to provide a Surface Relief Grating (SRG), which has very similar characteristics to a Bragg grating due to the depth of the SRG structure (which is much greater than can actually be achieved using surface etching and other conventional processes commonly used to fabricate SRGs). LC can be extracted using a number of different methods, including but not limited to rinsing with isopropanol and solvent. In many embodiments, one of the transparent substrates of the SBG is removed and the LC is extracted. In a further embodiment, the removed substrate is replaced. The SRG may be at least partially backfilled with a material having a higher or lower index of refraction. Such gratings provide a range for tailoring efficiency, angular/spectral response, polarization, and other characteristics to accommodate various waveguide applications.

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 may be defined as a virtual aperture through which only light rays that pass enter the user's eye. In some embodiments, the waveguide includes an input grating optically coupled to the 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 eyebox. As can be readily appreciated, the waveguide architecture that the grating configuration implements may depend on the specific requirements of a given application. In some embodiments, the grating configuration comprises 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 comprise gratings of different specifications for propagating different portions 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 may also be used.

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, a full-color waveguide is implemented using three grating layers, each designed to operate in a different spectral band (red, green, and blue). In other embodiments, a full color waveguide is implemented using two grating layers, a red-green grating layer and a green-blue grating layer. As can be readily appreciated, such techniques may similarly be implemented to increase the angular bandwidth operation of the waveguide. In addition to multiplexing of gratings across different grating layers, multiple gratings may be multiplexed within a single grating layer-i.e., multiple gratings may 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 comprises two grating layers, each layer having two grating specifications multiplexed in the same volume. Multiplexing two or more grating specifications within the same volume can be accomplished using various fabrication techniques. In various embodiments, a multiplexed master grating is used with an exposure configuration to form a multiplexed grating. In many embodiments, the multiplexed grating is fabricated by sequentially exposing the layer of optical recording material with exposure light (exposure light) in two or more configurations, each configured to form a grating specification. In some embodiments, a multiplexed grating is fabricated by alternately exposing a layer of optical recording material between two or more configurations of exposure light (exposure light), where each configuration is designed to form a grating specification. As can be readily appreciated, the multiplexed grating may be fabricated using a variety of techniques, including those well known in the art, as appropriate.

In many embodiments, the waveguide may incorporate at least one of: angle multiplexed gratings, color multiplexed gratings, folded gratings, double-interaction gratings, rolling K-vector gratings, cross-folded gratings, mosaic gratings, chirped gratings, gratings with spatially varying refractive index modulation, gratings with spatially varying grating thickness, gratings with spatially varying average refractive index, gratings with spatially varying refractive index modulation tensor, and gratings with spatially varying average refractive index tensor. In some embodiments, the waveguide may incorporate at least one of: a half-wave plate, a quarter-wave plate, an anti-reflection coating, a beam splitting layer, an alignment layer, a photochromic backing layer for reducing glare and a louver film for reducing glare. In several embodiments, the waveguide may support a grating that provides separate optical paths for different polarizations. In various embodiments, the waveguide may support a grating that provides separate optical paths for different spectral bandwidths. In various embodiments, the grating may be an HPDLC grating, a switched grating (such as a switchable Bragg grating) recorded in an HPDLC, a Bragg grating recorded in a holographic photopolymer, or a surface relief grating. In many embodiments, the waveguide operates in a monochromatic frequency band. In some embodiments, the waveguide operates in the 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 a further embodiment, the layers are stacked with an air gap between the waveguide layers. In various embodiments, the waveguide layer operates in a wider frequency band (such as blue-green and green-red) to provide a dual waveguide layer solution. In other embodiments, the grating is 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.

Waveguides incorporating optical structures such as those discussed above may 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 of greater than 10mm, and an eye distance of greater than 25 mm. In some embodiments, the waveguide display comprises a waveguide having a thickness between 2.0-5.0 mm. In many embodiments, the waveguide display may provide an image field of view of at least 50 ° diagonal. In a further embodiment, the waveguide display may provide an image field of view of at least 70 ° diagonal. Waveguide displays may employ many different types of Picture Generation Units (PGUs). In several embodiments, the PGU may be a reflective or transmissive spatial light modulator, such as a liquid crystal on silicon (LCoS) panel or a micro-electro-mechanical system (MEMS) panel. In various embodiments, the PGU may be an emissive device such as an Organic Light Emitting Diode (OLED) panel. In some embodiments, the OLED display may have a luminance greater than 4000 nits and a resolution of 4k × 4k pixels. In several embodiments, the waveguide can have an optical efficiency of greater than 10%, such that an OLED display with a luminance of 4000 nits can be used to provide an image luminance of greater than 400 nits. Waveguides implementing P-diffraction gratings (i.e., gratings with high efficiency for P-polarized light) typically have waveguide efficiencies of 5% -6.2%. Since P-diffraction or S-diffraction gratings can 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 a two-fold increase in the efficiency of the waveguide. In some embodiments, the S-diffraction and P-diffraction gratings are implemented in separate overlapping grating layers. Alternatively, under certain conditions, a single grating may provide high efficiency for both p-polarized light and s-polarized light. In several embodiments, the waveguide comprises 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 angular ranges for appropriately selected values of grating thickness (typically in the range of 2-5 μm).

Optical recording material system

HPDLC mixtures typically include LC, monomers, photoinitiator (photoinitiator) dyes and coinitiators (coinitiators). The mixture (often 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 dates back to the earliest studies of PDLC. For example, a PDLC mixture comprising monomers, photoinitiators, co-initiators, chain extenders and LC to which surfactants can be added is described in a paper by r.l. sutherland et al SPIE, volume 2689, page 158-169, 1996, the disclosure of which is incorporated herein by reference. Surfactants are also mentioned in Journal of Nonlinear optical physics and Materials, volume 5, phase 1, pages 89-98, 1996 paper, the disclosure of which is incorporated herein by reference. Furthermore, 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, the material 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.

The patent and scientific literature contains many examples of material systems and processes that may be used to fabricate SBGs, including research into formulating such material systems to achieve high diffraction efficiencies, fast response times, low drive voltages, and the like. Both U.S. patent No.5,942,157 to Sutherland and U.S. patent No.5,751,452 to Tanaka et al describe combinations of monomers and liquid crystal materials suitable for making SBG devices. Examples of formulations (recipe) can also be found in papers in the early 90 s of the 20 th century. Many of these materials use acrylate monomers including:

r.l. sutherland et al, chem.mater, volume 5, page 1533 (1993), describes the use of acrylate polymers and surfactants, the disclosure of which is incorporated herein by reference. Specifically, the formulation includes a cross-linked multifunctional acrylate monomer; the chain extender N-vinyl pyrrolidone, LC E7, the photoinitiator Bengal red and the co-initiator N-phenylglycine. In some variants the surfactant octanoic acid is added.

Fontechio et al SID 00Digest, page 774 and 776, 2000, describes a UV curable HPDLC for reflective display applications comprising multifunctional acrylate monomers, LC, photoinitiators, co-initiators and chain terminators, the disclosure of which is incorporated herein by reference.

Y.H.Cho et al, Polymer International, No. 48, pp.1085-1090, 1999, discloses HPDLC formulations comprising acrylates, the disclosure of which is incorporated herein by reference.

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

T.J.Bunning et al, Polymer Science: Part B: Polymer Physics, Vol.35, p.2825-2833, 1997, also describe multifunctional acrylate monomers, the disclosure of which is incorporated herein by reference.

Lannacchiane et al, Europhysics Letters, Vol 36(6), p 425-430, 1996, describe PDLC mixtures comprising pentaacrylate monomers, LC, chain extenders, co-initiators and photoinitiators, the disclosure of which is incorporated herein by reference.

Acrylates have the advantages of fast kinetics, good mixing with other materials and good compatibility with the film forming process. Since acrylates are crosslinked, 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.

Preparation of Material composition

High luminance 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 fundamental optics of the waveguide can cause non-uniformity due to gaps or overlaps of the beams bouncing along the waveguide. Further non-uniformities may be caused by imperfections in the grating and non-planarity of the waveguide substrate. In SBGs, there is a further problem of polarization rotation due to the birefringent grating. Where applicable, the greatest challenge is typically to fold the grating, where the multiple intersections of the beam with the grating fringes result in millions of optical paths. Careful management of the grating properties, particularly the refractive index modulation, can be used to overcome the non-uniformity.

Of the many possible beam interactions (diffraction or zero-order transmission), only a subset contributes to the signal present at the eye-frame. By back-tracking from the eyebox, the fold region contributing to a given field point can be precisely located. An accurate correction to the modulation can then be calculated, which correction is needed to send more to the dark areas of the output illumination. After the output illumination uniformity for one color is restored to the target, the process can be repeated for the other colors. Once the index modulation pattern is established, the design can be exported to the deposition settings, with each target index modulation translated into a unique deposition setting for each spatial resolution cell on the substrate to be coated/deposited. The resolution of the deposition mechanism depends on the technical limits of the system used. In many embodiments, the spatial pattern can be achieved with complete repeatability to a resolution of 30 microns.

In contrast to waveguides utilizing Surface Relief Gratings (SRGs), SBG waveguides implementing fabrication techniques according to various embodiments of the present invention may 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 deposition without the need for a different master. Such a scheme is impractical for modulating an SRG controlled by etch depth, since each change in the grating requires a complex and expensive process to be repeated. Furthermore, achieving the required etch depth accuracy and resist imaging complexity can be very difficult.

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

In some embodiments, the nozzles may be implemented to deposit multiple types of materials onto a single substrate. In waveguide applications, the nozzle may be used to deposit different materials for the grating and non-grating regions of the waveguide. In many embodiments, the jetting mechanism is configured for printing a raster, wherein at least one of material composition, birefringence, and/or thickness can be controlled using a deposition apparatus having at least two selectable jets. In some embodiments, a manufacturing system provides an apparatus for depositing a grating recording material optimized for controlling a laser band. In several embodiments, a manufacturing system provides an apparatus for depositing a grating recording material optimized for polarization non-uniformity control. In several embodiments, a manufacturing system provides an apparatus for depositing a grating recording material optimized for control of polarization non-uniformity associated with an alignment control layer. In various embodiments, the deposition work cell may be configured for deposition of additional layers, such as a beam splitting coating and an environmental protection layer. An inkjet printhead may also be implemented to print different materials on different areas of a substrate.

As discussed above, the deposition process may be configured to deposit an optical recording material that spatially varies in composition. Modulation of the material composition can be achieved in many different ways. In various embodiments, an inkjet printhead may be configured to modulate material composition by utilizing various inkjet nozzles within the printhead. By altering the composition on a "point-by-point" basis, a layer of optical recording material can be deposited such that it has a varying composition over the planar surface of the layer. Such a system may be implemented using a variety of devices, including but not limited to an inkjet printhead. Similar to how color systems use a palette of only a few colors to produce a spectrum of millions of discrete color values, such as the CMYK system in a printer or the additive RGB system in display applications, an inkjet printhead according to various embodiments of the present invention may be configured to print optical recording materials having different compositions using only a few containers of different materials. In many embodiments, a 300DPI ("dots per inch") inkjet printhead is used. Depending on the level of accuracy, discretization of different compositions of a given quantity of material can be determined across a given region. For example, given two types of material to be printed and an inkjet printhead with an accuracy level of 300DPI, for a given volume of printed material, if each dot location can contain one of the two types of material, there are 90,001 possible discrete values for the composition ratio of the two types of material across 1 square inch. In some embodiments, each dot location may contain either or both types of materials. In several embodiments, more than one ink jet print head is configured to print a layer of optical recording material having a spatially varying composition. While dot printing in bi-material applications is essentially a binary system, averaging printed dots across regions can allow discretization of the sliding scale of the ratio of the two materials to be printed. For example, the number of discrete levels of density/ratio possible within a unit square is given by the number of dot locations that can be printed within the unit square. As such, there may be a range of different combinations of concentrations ranging from 100% of the first material to 100% of the second material. As can be readily appreciated, these concepts apply to actual units and may be determined by the level of accuracy of the inkjet printhead. Although specific examples of modulating the material composition of printed layers are discussed, the concept of modulating the material composition using an inkjet printhead can be extended to the use of more than two different material reservoirs, and the level of accuracy can be different, depending largely on the type of printhead used.

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

The ability to vary the diffraction efficiency across the waveguide can be used for various purposes. Waveguides are typically designed to guide light internally by reflecting the light multiple times between two planar surfaces of the waveguide. These multiple reflections may allow the optical path to interact with the grating multiple times. In many embodiments, the layers of material may be printed with different material compositions such that the resulting 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 may be designed such that only a portion of the light is refracted out of the waveguide when the light within the waveguide interacts with the grating. The remaining portion continues in the same optical path, remains within TIR and continues to reflect within the waveguide. After a second interaction with the same output grating again, another portion of the light is refracted out of the waveguide. During each refraction, the amount of light still traveling within the waveguide reduces the amount of refraction out of the waveguide. As such, the refracted portion gradually decreases in total intensity at each interaction. 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 for, allowing for a uniform output intensity.

Varying the diffraction efficiency can also be used to compensate for other attenuations of the light within the waveguide. All objects have a certain degree of reflection and absorption. Light trapped by TIR within the waveguide is constantly reflected between the two surfaces of the waveguide. Depending on the material constituting the surface, 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 cells may be printed with different compositions such that gratings formed from the layer of optical recording material have different diffraction efficiencies to compensate for absorption of light from the substrate. Depending on the substrate, certain wavelengths may be more readily absorbed by the substrate. In a multilayer waveguide design, each layer may be designed to couple a specific range of light wavelengths. Thus, light coupled by these separate layers may be absorbed by the substrate of the layer in different amounts. For example, in various embodiments, the waveguide is made of a three layer stack, where each layer is designed for one of red, green, and blue colors, to achieve a full color display. In such embodiments, the gratings within each waveguide layer may be formed to have different diffraction efficiencies to perform color balance optimization by compensating for color imbalance due to transmission loss of certain wavelengths of light.

In addition to varying the concentration of liquid crystal within the material to vary the diffraction efficiency, another technique involves varying the thickness of the waveguide cells. This may be achieved by using spacers. In many embodiments, spacers are dispersed throughout the optical recording material for structural support during construction of the waveguide unit. In some embodiments, spacers of different sizes are dispersed throughout the optical recording material. The spacers may be dispersed in ascending order of size in one direction of the optical recording material layer. When constructing a waveguide cell by lamination, the substrate sandwiches the optical recording material and forms a wedge-shaped layer of optical recording material under structural support of spacers of different sizes. Similar to the modulation process described above, spacers of different sizes may be dispersed. Furthermore, modulation of spacer size may be combined with modulation of material composition. In several embodiments, reservoirs of HPDLC material each suspended with differently sized spacers are used to print layers of HPDLC material with differently sized spacers strategically dispersed to form wedge-shaped waveguide cells. In various embodiments, spacer size modulation is combined with material composition modulation by providing a number of reservoirs equal to the product of the number of differently sized spacers and the number of different materials used. For example, in one embodiment, an inkjet printhead is configured to print different concentrations of liquid crystal with two different spacer sizes. In such an embodiment, four reservoirs may be prepared: a liquid crystal-free mixed suspension with spacers of a first size, a liquid crystal-free mixed suspension with spacers of a second size, a liquid crystal-rich mixed suspension with spacers of a first size, and a liquid crystal-rich mixed suspension with spacers of a second size. Further discussion regarding material modulation may be found in U.S. application No.16/203,071 entitled "SYSTEMS AND METHODS FOR manual cooling dough CELLS" filed on 18.11.2018. The disclosure of U.S. application No.16/203,491 is incorporated by reference herein in its entirety for all purposes.

Multilayer waveguide fabrication

Waveguide fabrication according to various embodiments of the present invention may be implemented for fabricating multilayer waveguides. Multilayer waveguides refer to a class that utilizes two or more layer waveguides having gratings or other optical structures. Although the following discussion may be in relation to a grating, any type of holographic optical structure may be suitably implemented and substituted. Multilayer waveguides can be implemented for various 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. To maintain the desired total internal reflection characteristics, waveguides are typically stacked using spacers to form air gaps between individual waveguides.

In contrast to conventional stacked waveguides, many embodiments of the present invention are directed to fabricating multilayer waveguides having alternating substrate and grating layers. Such waveguides may be fabricated in an iterative process that enables the sequential formation of grating layers for a single waveguide. In several embodiments, the multilayer waveguide is fabricated with two grating layers. In many embodiments, the multilayer waveguide is fabricated with three grating layers. Any number of grating layers may be formed, limited by the tool and/or waveguide design used. This allows for reduced thickness, materials and cost compared to conventional multilayer waveguides, since less substrate is required. Furthermore, the fabrication process of such waveguides allows for higher throughput due to simplified alignment and substrate matching requirements.

The fabrication of a multilayer waveguide having alternating transparent substrate layers and grating layers according to various embodiments of the present invention may be accomplished 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 may comprise a variety of materials and mixtures including, but not limited to, HPDLC mixtures and any of the material formulations discussed in the sections above. Similarly, any of a variety of deposition techniques may be used, such as, but not limited to, spray coating, spin coating, ink jet printing, and any of the techniques described in the preceding subsections. Transparent substrates of various shapes, thicknesses and materials may be used. The transparent substrate may include, but is not limited to, a glass substrate and a plastic substrate. Depending on the application, the transparent substrate may be coated with different types of thin films for various purposes. Once the deposition process is complete, a second transparent substrate may be placed over the deposited first layer of optical recording material. In some embodiments, the process includes a lamination step to form the three-layer composite to a desired height/thickness. An exposure process may be carried out to form a set of gratings within the first layer of optical recording material. Exposure processes such as, but not limited to, single beam interference exposure and any other exposure process described in the preceding subsections may be used. Essentially, a single layer waveguide is now formed. The process may 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 may be placed onto the second layer of optical recording material. Similar to the previous steps, the composite material may be laminated to a desired height/thickness. A second exposure process may 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 readily appreciated, the process may continue iteratively to add additional layers. Additional optical recording layers may be added to either side of the current laminate. For example, a third layer of optical recording material may be deposited onto the outer surface of either the first or third transparent substrate.

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 a protective coating, thermal annealing, alignment of the LC director to achieve the desired birefringence state, extraction of the LC from the recorded SBG and refilling with another material, etc., may be performed at any stage of the manufacturing process. Some processes, such as, but not limited to, waveguide dicing (creating multiple elements), edge finishing, AR coating deposition, final protective coating application, etc., are typically performed at the end of the manufacturing process.

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 layer of optical recording material. The spacers may also help prevent the two substrates from collapsing against each other. In some embodiments, the waveguide cell is comprised 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 various embodiments, the spacers are relatively incompressible solids, which may allow the construction of waveguide cells having a consistent thickness. The spacers may take any suitable geometry including, but not limited to, rod-like and spherical. The size of the spacers may determine the local minimum thickness of the area around the individual spacers. As such, the dimensions of the spacers may be selected to help achieve a desired optical recording layer thickness. The spacers may be of any suitable size. In many cases, the size of the spacers ranges from 1 to 30 μm. The spacers may be made of any of a variety of materials, including but not limited to plastics (e.g., divinylbenzene), silica, and conductive materials. In several embodiments, the material of the spacer is selected such that its refractive index does not substantially affect the propagation of light within the waveguide cell.

In many embodiments, the first layer of optical recording material is bonded between the first and second transparent substrates using a vacuum filling process. In various embodiments, the layer of optical recording material is separated in different sections, which may be filled or deposited as appropriate 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 multilayer fabrication process may include flipping the current apparatus so that the exposure light is incident on the newly deposited optical recording layer before being incident on any formed grating layer.

In many embodiments, the exposure process may include temporarily "erasing" or making the previously formed grating layers transparent so that they do not interfere with the recording process of the newly deposited optical recording layer. The temporarily "erased" grating or other optical structure behaves like a transparent material, allowing light to pass without affecting the ray path. Methods of recording gratings into layers of optical recording material using such techniques may include fabricating a stack of optical structures in which a first layer of optical recording material deposited on a substrate is exposed to form a first set of gratings, which may be temporarily erased so that a second set of gratings may be recorded into a second layer of optical recording material using an optical recording beam that passes through the first layer of optical recording material. Although the recording method is mainly discussed for a waveguide having two grating layers, the basic principles can also be applied to waveguides having more than two grating layers.

The multilayer waveguide fabrication process incorporating the step of temporarily erasing the grating structure can be implemented in various ways. Typically, the first layer is formed using conventional methods. The recording material used may comprise a material system capable of supporting optical structures 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 various embodiments, the optical recording process uses a beam provided by a master grating, which may be a Bragg hologram recorded in a photopolymer or amplitude grating. In some embodiments, the exposure process utilizes a single recording beam in conjunction with a master grating to form an interference exposure beam. Other industrial processes and devices currently used in the art for producing holograms can be used in addition to the described processes.

Once the first set of gratings is recorded, additional layers of material may be added similar to the process described above. During the exposure process of any material layer subsequent to 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 layer of material. The 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, the first set of gratings may be temporarily erased using a sacrificial alignment layer applied to the first layer of material. 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 further comprises an additive for facilitating the process of erasing the grating, which may include any of the methods described above. In many embodiments, a stimulus is applied to restore the erased layer.

The removal and recovery of the recording layer in the above-described process can be achieved using many different methods. In many embodiments, the first layer is removed by applying the stimulus continuously during recording of the second layer. In other embodiments, the stimulus is applied initially, and the gratings in the ablated layer may naturally revert to their recorded state within a time scale that allows the second grating to be recorded. In other embodiments, the layer remains cleared after application of an external stimulus and recovers in response to another external stimulus. In several embodiments, the first optical structure may be restored to its recorded state using an alignment layer or external stimuli. The external stimulus for such restoration may be any of a number of different stimuli, including but not limited to one or more stimuli for clearing the optical structure. The removal process may vary depending on the optical structure to be removed and the constituent materials of the layers. Further discussion of Multilayer waveguide fabrication with external stimuli may be found in U.S. application No.16/522,491 entitled "Systems and Methods for waveguide a Multilayer Optical Structure" filed on 25.7.2019. The disclosure of U.S. application No.16/522,491 is incorporated by reference herein in its entirety for all purposes.

Waveguide incorporating integrated grating

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 various embodiments, the integrated gratings are partially overlapped or multiplexed. The multiplexed grating may comprise superimposing at least two gratings with different grating specifications within the same volume. Gratings with different grating specifications may have different grating vectors and/or grating tilts with respect 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 the direction orthogonal to the grating stripes.

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 various embodiments, the integrated grating is implemented with at least two grating specifications. In a further embodiment, the integrated grating is implemented with at least three grating specifications. In many embodiments, the two raster specifications within the integrated raster have similar clock angles. In some embodiments, the two grating specifications have different tilt angles. Integrated gratings according to various embodiments of the present invention may be implemented using various types of gratings, such as, but not limited to, SRG, SBG, holographic gratings, and other types of gratings, including those described in the sections above. In various embodiments, the integrated grating includes two surface relief gratings. In other embodiments, the integrated grating comprises two holographic gratings.

The integrated grating may comprise at least two grating specifications that at least partially overlap or multiplex. In a further embodiment, the integrated grating comprises at least two grating specifications that are completely overlapping or multiplexed. In various embodiments, the integrated grating includes multiplexed or overlapping gratings having different sizes and/or shapes-i.e., one grating may be larger than the other, resulting in only partial multiplexing of the larger grating. As can be readily appreciated, various multiplexing and overlapping configurations may be implemented as appropriate to the specific requirements of a given application. Although the following discussion may describe configurations as implementing multiplexed or overlapping gratings, such gratings may be substituted for each other as appropriate, depending on the application. In several embodiments, the integrated grating is implemented by a combination of a multiplexed grating and an overlapping grating. For example, two or more sets of multiplexed gratings may overlap across two or more grating layers.

Integrated gratings according to various embodiments of the present invention may be used for a variety of purposes including, but not limited to, implementing full-color waveguides and addressing some of the key issues in conventional waveguide architectures. Other advantages include reduced material and waveguide index requirements and reduced waveguide dimensions due to the overlapping and/or multiplexing properties of the integrated grating. Such configurations may allow for a large field of view waveguide, which typically incurs unacceptable increases 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 below 1.8. In a further embodiment, the waveguide is realized with a substrate having a refractive index not exceeding-1.5.

An integrated grating that can provide beam expansion and beam extraction-i.e., the functionality of a conventional folding and output grating-can produce a much smaller grating area, thereby achieving a small form factor and lower manufacturing costs. By integrating the functions of beam expansion and extraction, rather than performing them serially as with conventional waveguides, beam expansion and extraction can be accomplished at-50% of the grating interaction that is typically required, reducing the haze grating at the same rate in the case of birefringence. Another advantage is that the output image is less sensitive to substrate non-uniformities due to the reduced number of beam bounces at the glass/air interface(s) due to the greatly shortened optical path. This may enable higher quality images and may allow the use of cheaper, lower gauge substrates.

In many embodiments, the grating vectors of the input coupler and the integrated grating are arranged to provide a result vector of substantially zero. 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 a further embodiment, the grating vectors are arranged in an isosceles right triangle configuration. In many embodiments, the raster vectors are arranged in a scalene triangle configuration. Another waveguide architecture includes integrated diffractive elements with grating vectors aligned in the same direction to provide horizontal expansion for a set of angles and extraction for a separate set of 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 various embodiments, the grating is designed to be sandwiched between electroactive materials, enabling switching between the clear and diffractive states of certain types of gratings, such as, but not limited to, HPDLC gratings. The grating may be of the surface relief or holographic type.

In many embodiments, a waveguide is implemented that supports at least one input-coupler and first and second integrated gratings. The grating structure may be implemented in a single or multilayer waveguide design. In a single layer design, the integrated grating may be multiplexed. In embodiments where each integrated grating comprises at least two multiplexed gratings, the multiplexed integrated grating may comprise at least four multiplexed gratings. As described above, any individual multiplexed grating may be partially or fully multiplexed with other gratings. In some embodiments, the multilayer waveguide is implemented with overlapping integrated gratings. In a further embodiment, the integrated gratings are partially overlapping. Each integrated grating may be a separate grating or a multiplexed grating.

In many embodiments, the waveguide architecture is designed to couple input light into two divergent paths using an input coupler. Such a configuration may be implemented in various ways. In some embodiments, a multiplexed input grating is implemented to couple input light into two diverging paths. In other embodiments, two input gratings are implemented to couple input light into two diverging paths, respectively. The two input gratings may be implemented in the same layer or may be implemented separately in two layers. In many embodiments, two overlapping or partially overlapping input gratings are implemented to couple input light into two diverging paths. In many embodiments, the input coupler comprises a prism. In a further embodiment, the input coupler comprises a prism and any of the input grating configurations described above.

The first and second integrated gratings may be implemented in various configurations in addition to various input-coupler architecture. Integrated gratings according to various embodiments of the present invention may be incorporated into waveguides to perform the dual functions of two-dimensional beam expansion and beam extraction. In several embodiments, the first and second integrated gratings are crossed gratings. As described above, some waveguide architectures include designs in which input light is coupled into two divergent paths. In such designs, the two divergent paths each point to a different integrated grating. As can be readily appreciated, such configurations may be designed to bifurcate input light based on various light characteristics (including, but not limited to, angle and spectral bandwidth). In some embodiments, the light may be split based on polarization state-for example, the input unpolarized light may be split into S and P polarization paths. In many embodiments, each of the integrated gratings performs beam expansion either in a first direction or in a second direction different from the first direction depending on the portion of the field of view propagating through the waveguide. The first and second directions may be orthogonal to each other. In other embodiments, the first and second directions are not orthogonal to each other. Each integrated grating may provide expansion of light in a first dimension while directing light towards 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 splitting an input light into first and second portions of light. The first integrated grating may be configured to provide beam expansion for the first and second portions of light and beam extraction for the second portion of light in a first direction. In contrast, the second integrated grating may be configured to provide beam expansion for the first and second portions of light and beam extraction for the first portion of light in the second direction.

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

FIG. 1 conceptually illustrates a waveguide display, in accordance with an embodiment of the present invention. As shown, the apparatus 100 includes a waveguide 101 supporting an input grating 102 and a grating structure 103. Each grating may be characterized by a grating vector that defines the direction of the grating fringes in the waveguide plane. The grating can also be characterized by a K vector in 3D space, which in the case of a Bragg grating is defined as the vector perpendicular to the grating fringes. The waveguide reflective surface is parallel to the XY plane of the cartesian reference system in the inset. In some embodiments, the X and Y axes may correspond to global horizontal and vertical axes in a frame of reference of a user of the display.

In the illustrative embodiment of FIG. 1, input grating 102 includes a Bragg grating 104. In other embodiments, input grating 102 is a surface relief grating. The input grating 102 may be implemented to split the input light into two different portions. In a further embodiment, the input grating 102 comprises two multiplexed gratings having different grating specifications. In other embodiments, input grating 102 comprises two overlaid surface relief gratings. The grating structure 103 comprises two active gratings 105, 106 with different grating vectors. The gratings 105, 106 may 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 covering 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, as their role in the grating structure includes 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 extraction of light from the waveguide 101. The field of view coupled into the waveguide may be partitioned into first and second portions, which may be bifurcated as such by the input grating 102. In many embodiments, the first and second portions correspond vertically or horizontally to positive and negative angles. In some embodiments, the first and second portions may overlap in angular space. In various embodiments, a first portion of the field of view is expanded in a first direction by a first integrated grating and, in parallel operation, expanded and extracted in a second direction by a second integrated grating. When a ray interacts with a grating stripe, some of the light that satisfies the Bragg condition is diffracted, while the undiffracted light proceeds along its TIR path to the next stripe, continuing the expansion and extraction process. Next, considering a second portion of the field of view, the effect of the grating is reversed, such 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.

In many embodiments, the integrated gratings 105, 106 in the grating structure 103 may be asymmetrically disposed. 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 various embodiments, it is desirable that the combination of the grating vector of the input grating 102 and the vectors of the integrated gratings 105, 106 in the grating structure 103 give a resulting vector with a magnitude of substantially zero. 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.

In many embodiments, at least one grating parameter selected from the group consisting of grating vector direction, K-vector direction, grating refractive index modulation, and grating spatial frequency may be varied spatially across at least one grating implemented in the waveguide for the purpose 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 the waveguide may 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.

The apparatus 100 of fig. 1 further comprises an input image generator. In the illustrative embodiment, the input image generator includes a laser scanning projector 107 that provides a scanned beam 107A over a field of view coupled through the input grating 102 to total internal reflection paths (TIR paths) (e.g., 108A, 108B) in the waveguide and 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 that is modified to compensate for optical distortions in the waveguide. In various embodiments, the laser scan pattern and/or raster specifications in the input raster 102 and raster structure 103 may be modified to overcome illumination banding. In various embodiments, the laser scanning projector 107 may be replaced by an input image generator based on a micro-display illuminated by a laser or LED. In many embodiments, the input image may be provided by an emissive display. Laser projectors may offer the advantages of improved color gamut, higher brightness, wider field of view, high resolution, and very compact form factor. In some embodiments, the apparatus 100 may also include a despecker. In a further embodiment, the despecker may be implemented as a waveguide device. Although fig. 1 illustrates a particular waveguide application implementing integrated gratings, such structures and grating architectures may be used in a variety of applications. In various embodiments, a waveguide with an integrated grating may 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 may be implemented to provide wider angular or spectral bandwidth operation. In some embodiments, a multilayer waveguide is implemented to provide full color applications. In several embodiments, a multilayer waveguide is implemented to provide a wider field of view. In many embodiments, a panchromatic waveguide having a diagonal field of view of at least-50 ° is implemented using an integrated grating. In some embodiments, a panchromatic waveguide having a diagonal field of view of at least-100 ° is implemented using an integrated grating.

Figure 2 conceptually illustrates a color waveguide display having two blue-green diffractive waveguides and two green-red diffractive waveguides, in accordance with an embodiment of the present invention. Fig. 2 schematically illustrates an apparatus 200 having an architecture similar to that of fig. 1 but including the use of four stacked waveguides 201A-201D, including two blue-green diffractive waveguides and two green-red diffractive waveguides. As shown, the apparatus 200 includes a laser scanning projector 202 that provides scanned beams 202A-202D. In an illustrative embodiment, the waveguides providing each color band may 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 ° hx 35 ° v (50 ° diagonal), resulting in a 70 ° hx 35 ° v (78 ° diagonal) field of view for each color band. In many embodiments, the scanned beam may be generated using red, green and blue laser emitters, wherein each light of 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 shock beam intensity can be modulated for color balance purposes. The stacked waveguides may be arranged in any order. In several embodiments, considerations such as, but not limited to, color crosstalk, may affect the stacking order. In various embodiments, the integrated grating of one waveguide partially or completely overlaps the integrated grating of another waveguide. As described above, the integrated grating may be implemented in various configurations. In some embodiments, the integrated grating is implemented across more than one grating layer. In several embodiments, each integrated grating includes two multiplexed grating specifications.

In many embodiments, the optical geometry requirements for combining waveguide paths for more than one field of view or color band may dictate the asymmetric arrangement of 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 not disposed equilateral nor symmetrically about the Y-axis.

Although fig. 1 and 2 show a particular configuration of waveguide architecture, various structures may be implemented as appropriate to the particular requirements of a given application. In some embodiments, a six-layer waveguide is implemented for full color applications. A six-layer waveguide may be implemented with three pairs of layers configured for the red, green, and blue color bands, respectively. In such embodiments, the waveguides in each pair may be configured for different portions of the field of view.

In some embodiments, to perform beam expansion and extraction, the waveguide is designed such that each point of interaction of a ray with the grating structure occurs in a region that overlaps the active grating. In a non-fully overlapping grating configuration, the grating structure will have a region in which the first and second active gratings only partially overlap, such that some rays interact with only one of the active gratings. In many embodiments, the grating structure is formed of two multiplexed gratings. A first one of the multiplexed gratings 300 shown in fig. 3A multiplexes a first active grating 301 with a grating 302 having a different active grating vector (or clock angle). The second multiplexed grating 310 shown in fig. 3B multiplexes the second active grating 311 with a grating 312 having a different active grating vector. Fig. 3A-3B are intended to illustrate the relative orientation of the multiplexed grating and do not represent the grating shape implemented. In some embodiments, the shapes of gratings 301, 302 and 311, 312 may be different from each other. In the embodiment of fig. 3A-3B, the raster vector (clock angle) of the second multiplexed raster is the same as the first raster vector of the first multiplexed raster. Likewise, the grating vector of the first multiplexed grating is identical to the second grating vector of the second multiplexed grating. Turning now to fig. 3C, it is apparent that when the gratings overlap 320, there are two gratings of different clock angles at any point in the grating structure of the active grating (e.g., in the partially overlapping region — labeled with reference numerals 2-4 in fig. 3C). In the full overlap region of the active gratings (marked with reference number 1 in fig. 3C), 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 will be appreciated from the above description that in many embodiments, two pairs of multiplexed gratings may be implemented as one multiplexed grating consisting of four gratings 301, 302 and 311, 312.

Figures 4A-4C schematically illustrate 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. Ray propagation is illustrated using the unfolded ray paths to clarify the interaction between the rays and the grating. As shown in the schematic diagram of fig. 4A, light from the first portion of the FOV shows ray 404A coupled through input grating 401 into the TIR path in the waveguide, TIR ray 405A leading to first integrated grating 402, TIR ray 406A diffracted by first integrated grating 403 (which also provides beam expansion in the first direction), and ray 407A diffracted out of the waveguide by second integrated 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. 4B, the ray path includes ray 404B coupled into the TIR path in the waveguide through input grating 401, TIR ray 405B leading to second integrated grating 403, TIR ray 406B diffracted by second integrated grating 403 (which also provides beam expansion in the second direction), and TIR ray 407B diffracted out of the waveguide by first integrated grating 402 (which also provides beam expansion in the first direction). Fig. 4C shows the combined path of fig. 4A-4B, overlaid with an integrated grating. Fig. 4C also shows the partially overlapping nature of the integrated grating along the path of the ray. As can be readily appreciated, such configurations may be modified as appropriate to the specific requirements of a given application. Various shapes of gratings may be used. The integrated grating may comprise two multiplexed gratings, one providing the function of a conventional folded grating and the other for extracting light similar to a conventional output grating. Each of the two multiplexed gratings within a single integrated grating may be configured to act as a different portion of the light that is branched off by the input configuration. In various embodiments, two multiplexed gratings within a single integrated grating may have different shapes-i.e., certain regions of one or both gratings are not multiplexed. In some embodiments, more than two gratings are multiplexed for a single integrated grating. 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 grating are multiplexed overlapping.

As described above, raster architectures, including those implementing integrated rasters, may be described and visualized using raster vectors. In many embodiments, three raster vectors that may represent conventional input, folding, and output functions may be implemented with substantially zero result vectors. Figure 5A conceptually illustrates a raster vector configuration having a result vector that is substantially zero, in accordance with embodiments of the present invention. As shown, configuration 500 includes elements denoted as k₁、k₂And k₃Three raster vectors 501-503. For three grating vectors, configurations with substantially zero result vectors may provide various triangular configurations, such as, but not limited to, equilateral triangles, isosceles triangles, and scalene triangles. In the case of an architecture using integrated gratings, more than one triangle configuration may be visualized. Figure 5B conceptually illustrates one such embodiment. As shown, configuration 510 illustrates two triangular configurations. Triangular configuration is by grating vector k₁、k₂And k₃(511-513), the second configuration being formed by a raster vector k₁、k₄And k₅(511, 514 and 515). In an illustrative embodiment, raster vector k₁Representing the function of the input coupler, the raster vector k₂And k₅Representing the function of the first integrated grating, and the grating vector k₄And k₃Representing the function of the second integrated grating.

In many embodiments, the grating vector configuration implemented may include various triangle configurations. In general, the magnitude of the raster vector may dictate the resulting triangular configuration. In some embodiments, an equilateral triangle configuration is implemented in which all grating vectors have similar or substantially similar magnitudes. In the case of an integrated grating implementation, the configuration may include two triangular configurations. In various embodiments, the grating vector configuration comprises at least one isosceles triangle, wherein at least two of the grating vectors have similar or substantially similar magnitudes. Figure 5C conceptually illustrates a grating vector configuration having two isosceles triangles, in accordance with an embodiment of the present invention. As shown, due to the raster vector k₂-k₅Of similar magnitude, so configuration 520 forms two isosceles triangles. In several embodiments, the grating configuration comprises at least one scalene triangle. Figure 5D conceptually illustrates a raster vector configuration having two scalene triangles, in accordance with embodiments of the invention. As shown, configuration 530 forms two scalene triangles. In the illustrative embodiment, the two scalene triangles are mirror images-i.e., the raster vector k₂And k is₄Are equal in magnitude and a raster vector k₃And k is₅Are equal in magnitude. Figure 5E conceptually illustrates a raster vector configuration having two different scalene triangles, in accordance with embodiments of the invention. As shown, configuration 540 includes two different scalene triangles whose raster vector k₂-k₅With different magnitudes.

While fig. 5A-5E illustrate particular raster vector configurations, various other configurations may be implemented as appropriate for the particular requirements of a given application. For example, in some embodiments, the input coupler is implemented with two different raster vectors. This configuration utilizes an input grating having two different grating specifications, which can be implemented using overlapping or multiplexed grating specifications. In the embodiments shown in fig. 5B-5E, the configuration shown may be due to the implementation of an integrated grating. In many embodiments, raster vector k₂And k₅Representing the function of the first integrated grating, and the grating vector k₄And k₃Representing the function of the second integrated grating. In several embodiments, each raster vector k_iRepresenting different grating specifications. For example, many grating architectures according to various embodiments of the present invention may implement integrated gratings, each grating containing two different grating specifications. In such cases, raster vector k₂And k₅Two different grating specifications, grating vector k, of the first integrated grating can be represented separately₄And k₃Two different grating specifications of the second integrated grating may be represented separately.

Figure 6 conceptually illustrates a schematic plan view of a grating architecture 600 having an input grating and an integrated grating, in accordance with embodiments of the present invention. As shown, the grating architecture 600 includes an input coupler 601. The input coupler 601 may be a Bragg grating or a surface relief grating. In many embodiments, input coupler 601 includes at least two gratings. In such embodiments, the respective input gratings may be configured to couple different portions of the light in, which may be based on angular or spectral characteristics. In some embodiments, input coupler 601 includes two overlapping gratings. In other embodiments, input coupler 601 includes two multiplexed gratings. The grating architecture 600 also includes first (bold lines) and second (dashed lines) integrated gratings. In the 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 may 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 neither overlap nor multiplex. In various embodiments, the first and second rasters 602, 603 have the same clock angle but different raster specifications.

In many embodiments, the configuration of the first integrated grating is applied in a similar manner to the second integrated grating but flipped around the axis. For example, the illustrative embodiment in fig. 6 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 and the fourth grating 605 has a fourth grating specification. Similar to the first integrated grating, the third and fourth gratings 604, 605 may 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 may be achieved in a similar manner as the first and second gratings 602, 603.

In the illustrative embodiment of fig. 6, the first and third integrated gratings partially overlap each other such 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, and as such, the waveguide architecture includes a region 606 in which all four grating specifications are active. In embodiments where the first and second integrated gratings are implemented in a single layer, region 606 would contain four multiplexed gratings. In other embodiments, the first and second integrated gratings are implemented across different grating layers.

During operation, input light incident on the input grating 601 may be split into two portions of light traveling in TIR paths within the waveguide. One portion may be directed towards the first grating 602 and another portion may be directed towards the third grating 604. The first grating 602 may be configured to provide beam expansion for incident light in a first direction and redirect the incident light to the fourth grating 605. The fourth grating 605 may be configured to provide beam expansion for incident light in the second direction and extract the light out of the waveguide. On the other hand, the third grating 604 may be configured to provide beam expansion for incident light in a second direction and redirect the incident light to the second grating 603. The second grating 603 may be configured to provide beam expansion for incident light in a first direction and extract light out of the waveguide.

Fig. 7 shows a flowchart conceptually illustrating a method of displaying an image according to an embodiment of the present invention. Referring to the flow diagram, the 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 comprise multiplexed pairs of different K vector gratings. The first field of view portion may be coupled (702) into the waveguide via the input grating and directed towards the first integrated grating. The second field of view portion may be coupled (703) into the waveguide via the input grating and directed towards the second integrated grating. A first field of view portion of the light may be expanded (704) in a first direction using a first integrated grating. The first field of view portion of the light may be expanded in a second direction and extracted from the waveguide using a second integrated grating (705). A second field of view portion of the light may be expanded in a second direction (706) using a second integrated grating. A second field of view portion of the light may be expanded in the first direction and extracted from the waveguide using a first integrated grating (707).

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 having the same clock angle but different grating specifications. In a further embodiment, two gratings are multiplexed. FIG. 8 shows a flow diagram conceptually illustrating a method of displaying an image with an integrated raster comprising multiple rasters, in accordance with an embodiment of the invention. Referring to the flow diagram, 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 comprise multiplexed pairs of different K vector gratings. The first field of view portion may be coupled (802) into the waveguide via the input grating and directed towards the first grating. The second field of view portion may be coupled (803) into the waveguide via the input grating and directed towards the third grating. The first grating may be used to expand (804) a portion of the light in the first field of view in a first direction and redirect towards the fourth grating. The first field of view portion of the light may be expanded in the second direction and extracted from the waveguide using a fourth grating (805). A third grating may be used to expand (806) a portion of the light in the second field of view in a second direction and redirect towards 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).

6-8 illustrate particular waveguide configurations and methods of displaying images, many different methods may be implemented according to various embodiments of the invention. For example, in some embodiments, more than one input grating is used. In other embodiments, the input arrangement comprises 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 arrangement includes at least one grating having a spatially varying pitch. In some embodiments, each grating has a fixed K vector. In various 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, a rolling K-vector grating includes a waveguide portion containing discrete grating elements having differently aligned K-vectors. In some embodiments, a rolling K-vector grating includes a waveguide portion that includes a single grating element within which the K-vector undergoes a smooth monotonic change in direction. In some of the described embodiments, a rolling K-vector grating is used to input light into the waveguide. In some embodiments, the waveguide with two integrated gratings may be implemented as a single layer or multilayer waveguide. In several embodiments, the multilayer waveguide is implemented with more than two integrated gratings. As can be readily appreciated, the particular architecture and configuration implemented may depend on a number of different factors. In some embodiments, the position of the input grating relative to the integrated grating may be dictated by various factors, including but not limited to projector relief and input pupil diameter and vergence. 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 angular path of the field rays required to fill the eyebox typically determines the waveguide height. In many cases, the height of the waveguide grows non-linearly with the projector relief. In some embodiments, the pupil diameter has no significant effect on the footprint of the waveguide. A converging or diverging pupil may be used to reduce the local angular response anywhere on the input grating.

In some embodiments, the waveguide configuration implemented may depend on the configuration of the input image generator/projector. Figure 9 conceptually illustrates a cross-sectional view 900 of two overlapping waveguide portions implementing an integrated grating, in accordance with an embodiment of the present invention. In the illustrative embodiment, the two-layer waveguide is designed for high field-of-view applications implemented with converging projector pupil input beams (indicated by ray 901). As shown, the apparatus 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 that partially overlap the first set of two integrated gratings. Grating layers 903, 905 with integrated gratings may operate according to the principles discussed in the sections above. The output beam from the waveguide is generally indicated by ray 906 intersecting eye box 907. In the illustrated embodiment, the eyebox has dimensions of 10.5mmx9.5mm, an eye distance of 13.5mm, and a 12mm laser projector is separated from the waveguide. As can be readily appreciated, such dimensions and specifications may be specifically tailored to the requirements of a given application.

Figure 10 conceptually illustrates a schematic plan view 1000 of a grating architecture with two sets of integrated gratings, in accordance with embodiments of the present invention. As shown, the grating configuration includes first and second input gratings 1001, 1002 forming a combined input grating area 1003 indicated by the shaded area. In some embodiments, each input grating comprises a set of multiplexed or overlapping gratings. The grating arrangement further comprises a first set of grating structures with first and second integrated gratings 1004, 1005 and a second set of grating structures with third and fourth integrated gratings 1006, 1007. In an illustrative embodiment, the shape and disposition of each set of integrated gratings is asymmetric. Such a configuration may be suitably implemented according to several factors. In the embodiment of FIG. 10, an asymmetric grating architecture may be implemented for operation in converging projector pupil configurations, such as the configuration shown in FIG. 9. In addition, different grating features can be implemented and tuned for different applications. Figure 11 conceptually illustrates a plot 1100 of diffraction efficiency versus angle for a waveguide that diffracts at different field angles, in accordance with embodiments of the present invention. As shown, the waveguide is tuned to have three different peak diffraction efficiencies, two different peaks 1101, 1102 for "folded" interaction, and one 1103 for "output". In some embodiments, the light undergoes a double interaction within the grating. Such gratings can be designed to have high diffraction efficiency for two different angles of incidence. Returning to fig. 10, the first and second sets of grating structures may be implemented as partially overlapping structures, forming a combined output grating region 1008 as indicated by the shaded region. An eye box 1009 is overlaid on the drawing and indicated by the dark shaded area. In an illustrative embodiment, the waveguide device is configured to provide a 120 degree diagonal FOV. As shown in fig. 9-10, in some embodiments, a display providing a 120 degree diagonal FOV may be configured with a projector-to-waveguide distance of 12mm and an eye distance of 13.5mm, which is compatible with many eyewear inserts. In some embodiments, the display provides a 10.5mmx9.5mm eyebox, which may provide easy wear resistance. Fig. 12 shows the viewing geometry of such a waveguide. As can be readily appreciated, the grating configuration shown in fig. 10 can be implemented in a variety of waveguide architectures. In some embodiments, both sets of input gratings and both sets of grating structures are implemented in a single grating layer, with overlapping portions being multiplexed. In several embodiments, the first input grating and the first set of grating structures are implemented in a first grating layer, and the second input grating and the second set of grating structures are implemented in a second grating layer. In various embodiments, the first, second, third, and fourth integrated gratings are implemented across four grating layers.

Fig. 13 conceptually illustrates field of view geometry for a binocular display having binocular overlap between left and right eye images provided by a waveguide, in accordance with an embodiment of the present invention. Binocular displays using various grating architectures, such as those described in fig. 9-10, may be implemented. In the illustrated embodiment, the waveguide is a stacked color waveguide including four waveguides: two blue-green layers and two green-red layers. Each of the waveguides may provide a 35 ° hx 35 ° v (-50 ° diagonal) field of view for a single color band, resulting in a 70 ° hx 35 ° v (-78 ° diagonal) field of view for each color band. Each of the waveguides provided for the left and right eyes may be horizontally overlapped by 50 deg. to achieve a 100 deg. diagonal binocular field of view. As can be readily appreciated, various binocular configurations may be implemented as appropriate to the specific requirements of a given application. In many embodiments, the waveguide is tilted at an angle of at least 5 °, which may facilitate implementation of some binocular overlapping field of view applications. In a further embodiment, the waveguide is tilted at an angle of at least 10 °. In some embodiments, the fields of view of the left and right eyes completely overlap.

Other waveguide embodiments

In some embodiments, a prism may be used as an alternative to the input grating. In many embodiments, this may require the provision of an external grating for grating vector closure purposes. In several embodiments, the external grating may be disposed on a surface of the prism. In some embodiments, the external grating may form part of a laser despecker disposed in the optical system between the laser projector and the input prism. The advantage of using a prism to couple light into the waveguide is that significant light loss and limited angular bandwidth due to the use of a rolling K-vector grating are avoided. Practical rolling K-vector input gratings typically cannot match the much larger angular bandwidth of folded gratings (which may be about 40 degrees or more).

While the figures may indicate a high degree of symmetry in grating geometry and grating layout in different wavelength channels, the grating specifications and footprints may be asymmetric. The shape of the input, folded or output grating may depend on the waveguide application and may be any polygonal geometry that is affected by factors such as desired beam expansion, output beam geometry, beam uniformity and ergonomic factors.

In some embodiments, for displays using unpolarized light sources, the input gratings may be combined into gratings oriented such that each grating diffracts a particular polarization of incident unpolarized light into the waveguide path. Such embodiments may incorporate some of the embodiments AND teachings disclosed in Waldern et al, PCT application PCT/GB2017/000040 "METHOD AND APPARATUS FOR PROVIDING A POLARIZATION SELECTIVE HOLOGRAPHIC WAVGUIDE DEVICE", 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 grating and the output grating each combine crossed gratings with peak diffraction efficiencies for orthogonal polarization states. In many embodiments, the polarization states are S-polarization and P-polarization. In several embodiments, the polarization state is in the opposite sense of circular polarization. The advantage in this respect of gratings recorded in liquid crystal polymer systems, such as SBGs, is that they exhibit strong polarization selectivity due to their intrinsic birefringence. However, other grating techniques that can be configured to provide unique polarization states can also be used.

In some embodiments using gratings recorded in a liquid crystal polymer material system, at least one polarization control layer may be provided overlapping at least one of the folded grating, the input grating or the output grating, with the purpose of compensating for polarization rotation in any grating, in particular the folded grating that would result in polarization rotation. In many embodiments, all of the gratings are covered by a polarization control layer. In various embodiments, the polarization control layer is applied to only the folded grating or to any other subset of the gratings. The polarization control layer may include an optical retardation film. In some embodiments based on HPDLC materials, the birefringence of the grating may 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 design space for optimizing the angular capability and optical efficiency of the waveguide device. In some embodiments, a quarter-wave plate may be disposed at the glass-air interface of the waveguide, rotating the polarization of the light to maintain efficient coupling with the grating. In a further embodiment, the quarter wave plate is a coating applied to the substrate waveguide. In some waveguide display embodiments, applying a quarter-wave coating to the substrate of the waveguide may help the light rays remain aligned with the intended viewing axis by compensating for skew waves in the waveguide. In some embodiments, the quarter wave plate may be provided as a multilayer coating.

As used in relation to any of the embodiments 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 specification 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 layer is sandwiched between glass or plastic substrates. In various embodiments, two or more such grating layers may form a stack, where total internal reflection occurs at the external substrate and air interface. In some embodiments, the waveguide may include only one grating layer. In many embodiments, electrodes may be applied to the face of the substrate to switch the grating between the diffractive and transparent states. The stack may also include additional layers, such as a beam splitting coating and an environmental protection layer.

In some embodiments, the folded grating angular bandwidth may be enhanced by designing the grating specification to facilitate dual interaction of the guided light with the grating. Exemplary embodiments of double-interleaved folded gratings are described in U.S. patent application No.: 14/620,969, respectively.

Advantageously, to improve color uniformity, the gratings used in the present invention can be designed using back ray tracing from the eyebox via the output grating and the folded grating to the input grating. This process allows the identification of the physical extent required by the grating, particularly a folded 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 dispersive effect between the input and output gratings via the folded grating.

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 may be a Bragg grating recorded in a holographic polymer dispersed liquid crystal (e.g., a matrix of liquid crystal droplets), although SBGs may also be recorded in other materials. In several embodiments, the SBG is recorded in a uniformly modulated material, such as policrypts or POLIPHEM with a matrix of solid liquid crystals dispersed in a liquid polymer. SBGs may be switching or non-switching in nature. In some embodiments, at least one of the input, fold and output gratings may be electrically switchable. In many embodiments, it is desirable that all three grating types be passive, i.e., non-switching. In its non-switching form, SBG has advantages over conventional holographic photopolymer materials because its liquid crystal composition can provide high refractive index modulation. U.S. patent application publication No. to Caputo et al: US2007/0019152 and PCT application No. by Stumpe et al: exemplary homogeneously modulated liquid crystal-polymer material systems are disclosed in PCT/EP2005/006950, both of which are incorporated herein by reference in their entirety. A uniformly modulated grating is characterized by high refractive index modulation (and hence high diffraction efficiency) and low scattering. In some embodiments, the input-coupler, the folded grating, and the 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 in the presence of an electric field. The reverse mode HPDLC may be based on a program code recorded in PCT application No. entitled "IMPROVEMENTS TO HOLOGRAPHIC POLYMER DISPERSED LIQUID CRYSTAL MATERIALS AND DEVICES": any of the formulations and processes disclosed in PCT/GB 2012/000680. The grating may be recorded in any of the above material systems, but used in a passive (non-switching) mode. An advantage of recording a passive grating in a liquid crystal polymer material is that the resulting hologram benefits from the high refractive index modulation provided by the liquid crystal. Higher refractive index modulation translates into high diffraction efficiency and wide angular bandwidth. The manufacturing process is exactly the same as for the switching mode, but the electrode coating stage is omitted. Liquid crystal polymer material systems are highly desirable in view of their high refractive index modulation. In some embodiments, the grating is recorded in the HPDLC but is not switched.

In many embodiments, two spatially separated input couplers may be used to provide two separate waveguide input pupils. In some embodiments, the input coupler is a grating. In several embodiments, the input coupler is a prism. In embodiments using prism-only based input-coupler prisms, the pitch and clock angle of the folded and output gratings may be used to address the conditions for grating reciprocity.

In many embodiments, the source of data modulated light used with the waveguide embodiments described above includes an input image node ("IIN") incorporating a microdisplay. The input grating may be configured to receive collimated light from the IIN and to cause the light to travel within the waveguide to the folded grating via total internal reflection between the first and second surfaces. Typically, the IIN integrates, in addition to the microdisplay panel, a light source and the optical components required to illuminate the display panel, separate and collimate the reflected light into the desired FOV. Each image pixel on the microdisplay may be switched into a unique angular direction within the first waveguide. This disclosure does not assume any particular microdisplay technology. In some embodiments, the microdisplay plane can be a liquid crystal device or a MEMS device. In several embodiments, the microdisplay may be based on Organic Light Emitting Diode (OLED) technology. Such emissive devices do not require a separate light source, thus providing the benefit of a smaller form factor. In some embodiments, the IIN may be based on the modulated laser light being scanned. According to some embodiments, the IIN projects an image displayed on the microdisplay panel such that each display pixel is converted into a unique angular direction within the substrate waveguide. The collimating optics included in the IIN may include lenses and mirrors, which may be diffractive lenses and mirrors. In some embodiments, the IIN may be based on a signal obtained in U.S. patent application Ser. No.: 13/869,866 and U.S. patent application No. entitled "TRANSPARENT WAVEGUIDEDISPLAY": 13/844,456, the examples and teachings disclosed in the specification. In several embodiments, the IIN includes a beam splitter for directing light onto the microdisplay and transmitting the reflected light to the waveguide. In many embodiments, the beam splitter is a grating recorded in the HPDLC and the inherent polarization selectivity of such gratings is used to separate the image modulated light that illuminates the display and that is reflected from the display. In some embodiments, the beam splitter is a polarizing beam splitter cube. In various embodiments, the IIN incorporates a despeckle. The despecker 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 banding at the waveguide output. In some embodiments, U.S. provisional patent application No.: 62/071,277 to overcome laser illumination banding in a waveguide. 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.

The principles and teachings of the present invention, in conjunction with other waveguide inventions of the present inventor as disclosed in the references incorporated by reference herein, can be applied to many different display and sensor devices. In some embodiments directed to a display, a waveguide display in accordance with the principles of the present invention may be combined with an eye tracker. In some embodiments, the eye tracker is a WAVEGUIDE device covering a display WAVEGUIDE and is based on PCT/GB2014/000197 entitled "HOLOGRAPHIC WAVEGUIDE EYE TRACKER", PCT/GB2015/000274 entitled "HOLOGRAPHIC WAVEGUIDE optical coupler", and PCT application No.: examples and teachings of GB 2013/000210.

In some embodiments of the invention directed to a display, a waveguide display in accordance with the principles of the invention also includes a dynamic focusing element. The dynamic focusing element may be based on U.S. provisional patent application No.: 62/176,572. In some embodiments, a WAVEGUIDE display according to principles of the present invention may also include a dynamic focusing element and an eye tracker, which may provide a dynamic focusing element based on the U.S. provisional patent application No.: 62/125,089.

In some embodiments of the present invention for displays, a waveguide according to principles of the present invention may be based on U.S. patent application No.: 13/869,866 and U.S. patent application No. entitled "TRANSPARENT WAVEGUIDE DISPLAY": 13/844,456. In some embodiments, a waveguide device according to 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 DISPLAY device described in U.S. provisional patent application No.: PCT application No.: examples and teachings disclosed in PCT/GB 2016/000005. In some embodiments, the waveguide device may include a gradient index (GRIN) waveguide assembly for relaying image content between the IIN and the waveguide. In PCT application No.: exemplary embodiments are disclosed in PCT/GB 2016/000005. In some embodiments, the system is based on U.S. provisional patent application No. entitled "WAVEGUIDE DEVICE INCORPORATING A LIGHT PIPE": 62/177,494, the waveguide arrangement may incorporate a light pipe for providing beam expansion in one direction.

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.

The construction and arrangement of the systems and methods as shown in the various exemplary embodiments are illustrative only. Although only a few embodiments have been described in detail in this disclosure, many modifications are possible (e.g., variations in sizes, dimensions, structures, shapes and proportions of the various elements, values of parameters, mounting arrangements, use of materials, colors, orientations, etc.). For example, the positions of elements may be reversed or otherwise varied, and the nature or number of discrete elements or positions may be altered or varied. The present invention may incorporate the embodiments AND teachings disclosed in U.S. provisional patent application No.62/778,239 entitled METHODS AND apparatus FOR PROVIDING A SINGLE GRATING LAYER COLOR AND method FOR PROVIDING wavegide 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 "wavegide GRATING DEVICE", all of which are incorporated herein by reference in their entirety. Accordingly, all such modifications are intended to be included within the scope of this disclosure. The order or sequence of any process or method steps may be varied 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.

Principle of equivalence

While the above description contains many specificities of the invention, these should not be construed as limitations on the scope of the invention, but rather as an exemplification of one embodiment thereof. It is therefore to be understood that the invention may be practiced otherwise than as specifically described without departing from the scope and spirit of the present invention. The present embodiments are, therefore, to be considered in all respects as illustrative and not restrictive. Thus, the scope of the invention should be determined not by the embodiments illustrated, but by the appended claims and their equivalents.

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Method and apparatus for providing holographic waveguide display using integrated grating

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