Multiple wavelength range imaging light guide system

Abstract

An image light guide system for conveying a virtual image comprising a first waveguide and a second waveguide operable to propagate an image-bearing light beam, the first waveguide including a first in-coupling diffractive optical element formed along the first waveguide, the first in-coupling diffractive optical element operable to diffract a first portion of the image-bearing light beam from a first image source into the first waveguide in an angularly coded fashion, and a first out-coupling diffractive optical element formed along the first waveguide, the first out-coupling diffractive optical element operable to replicate the first portion of the image-bearing light beam and direct the replicated image-bearing light beam out of the first waveguide in an angularly decoded fashion.

Description

[Technical field]

[0001] This disclosure relates generally to electronic display devices, and more particularly to displays that utilize image light guides having diffractive optical elements for conveying image-bearing light to a viewer. [Background technology]

[0002] Head mounted displays (HMDs) and virtual image near-eye displays are being developed for a wide range of applications, including military, commercial, industrial, firefighting, and entertainment applications. In many of these applications, there is value in creating a virtual image that can be visually superimposed over a real-world image in the HMD user's field of view. Optical image light guides can deliver image-bearing light to the viewer in a small space to target the virtual image to the viewer's pupil and enable this superimposition function.

[0003] Although conventional image light guide arrangements have provided significant reductions in the bulk, weight, and overall cost of near-eye display optics, further improvements are needed. In some instances, image resolution is constrained by the reduction in bulk and cost of conventional image light guide arrangements. Similarly, diffraction and propagation of certain wavelengths of light may underperform in conventional image light guide arrangements. Thus, there is a need for an image light guide system that is operable to generate desired virtual image brightness and resolution while managing the volume and cost of the system. Summary of the Invention

[0004] In a first exemplary embodiment, the present disclosure provides an image light guide for carrying a virtual image, comprising: a first waveguide operable to propagate an image-bearing light beam; a first in-coupling diffractive optical element formed along the first waveguide, the first in-coupling diffractive optical element operable to diffract a first portion of the image-bearing light beam from a first image source into the first waveguide in an angularly coded manner; a first out-coupling diffractive optical element formed along the first waveguide, the first out-coupling diffractive optical element operable to replicate the first portion of the image-bearing light beam and direct the replicated first portion of the image-bearing light beam out of the first waveguide in an angularly decoded manner; and a second in-coupling diffractive optical element formed along the first waveguide, the second in-coupling diffractive optical element operable to diffract a first portion of the image-bearing light beam from a second image source into the first waveguide in an angularly coded manner. a coupling diffractive optical element; a second outcoupling diffractive optical element formed along the first waveguide, the second outcoupling diffractive optical element operable to replicate a first portion of the image-bearing light beam and direct the replicated first portion of the image-bearing light beam from the first waveguide in an angularly decoded manner; a second waveguide operable to propagate the image-bearing light beam; a third incoupling diffractive optical element formed along the second waveguide, the third incoupling diffractive optical element operable to diffract a second portion of the image-bearing light beam from the first image source into the second waveguide in an angularly coded manner; and a third outcoupling diffractive optical element formed along the second waveguide, the second outcoupling diffractive optical element operable to replicate a second portion of the image-bearing light beam and direct the second portion of the replicated image-bearing light beam from the second waveguide in an angularly decoded manner.a fourth incoupling diffractive optical element formed along the second waveguide, the fourth incoupling diffractive optical element operable to diffract a second portion of the image-bearing light beam from the second image source into the second waveguide in an angularly coded fashion; and a fourth outcoupling diffractive optical element formed along the second waveguide, the fourth outcoupling diffractive optical element operable to replicate the second portion of the image-bearing light beam and direct the replicated second portion of the image-bearing light beam out of the second waveguide in an angularly decoded fashion.

[0005] In a second exemplary embodiment, the present disclosure provides an image light guide for carrying a virtual image, comprising: a first waveguide operable to propagate an image-bearing light beam; a first in-coupling diffractive optical element formed along the first waveguide, the first in-coupling diffractive optical element operable to diffract a first portion of the image-bearing light beam from a first image source into the first waveguide in an angularly coded manner; and a first out-coupling diffractive optical element formed along the first waveguide, the first in-coupling diffractive optical element operable to diffract a first portion of the image-bearing light beam from a first image source into the first waveguide in an angularly coded manner. a first outcoupling diffractive optical element operable to replicate a first portion of an image-bearing light beam and direct the replicated first portion of the image-bearing light beam from the first waveguide in an angularly decoded manner; a second waveguide operable to propagate the image-bearing light beam; and a second incoupling diffractive optical element formed along the second waveguide, the second incoupling diffractive optical element directing a first portion of the image-bearing light beam from a second image source in an angularly coded manner to the second waveguide. a second incoupling diffractive optical element formed along the second waveguide, the second outcoupling diffractive optical element operable to replicate a first portion of the image-bearing light beam and direct the replicated first portion of the image-bearing light beam from the second waveguide in an angularly decoded manner; a third waveguide operable to propagate the image-bearing light beam; a third incoupling diffractive optical element formed along the third waveguide, the third incoupling diffractive optical element operable to diffract the first portion of the image-bearing light beam from the third image source into the third waveguide in an angularly coded manner; and a third outcoupling diffractive optical element formed along the third waveguide, the third outcoupling diffractive optical element operable to replicate a first portion of the image-bearing light beam and direct the replicated first portion of the image-bearing light beam from the third waveguide in an angularly decoded manner.and a third outcoupling diffractive optical element.

[0006] In a third exemplary embodiment, the present disclosure provides an image light guide for carrying a virtual image, comprising: a first waveguide operable to propagate an image-bearing light beam; a first in-coupling diffractive optical element formed along the first waveguide, the first in-coupling diffractive optical element operable to diffract a first portion of the image-bearing light beam from a first image source into the first waveguide in an angularly coded manner; and a first out-coupling diffractive optical element formed along the first waveguide. a first outcoupling diffractive optical element operable to replicate a first portion of an image-bearing light beam and direct the replicated first portion of the image-bearing light beam from the first waveguide in an angularly decoded form; a second waveguide operable to propagate the image-bearing light beam; and a second incoupling diffractive optical element formed along the second waveguide, the second incoupling diffractive optical element operable to direct a first portion of the image-bearing light beam from a second image source in an angularly decoded form. a second incoupling diffractive optical element formed along the second waveguide, the second outcoupling diffractive optical element operable to replicate a first portion of the image-bearing light beam and direct the replicated first portion of the image-bearing light beam from the second waveguide in an angularly decoded manner; a third incoupling diffractive optical element formed along the second waveguide, the third incoupling diffractive optical element operable to diffract a first portion of the image-bearing light beam from a third image source into the second waveguide in an angularly decoded manner; and a third outcoupling diffractive optical element formed along the second waveguide, the third outcoupling diffractive optical element operable to replicate a first portion of the image-bearing light beam and direct the replicated first portion of the image-bearing light beam from the second waveguide in an angularly decoded manner.

[0007] In a fourth exemplary embodiment, the present disclosure provides an image light guide for carrying a virtual image, comprising: a first waveguide operable to propagate an image-bearing light beam; a first in-coupling diffractive optical element formed along the first waveguide, the first in-coupling diffractive optical element operable to diffract a first portion of the image-bearing light beam from a first image source into the first waveguide in an angularly coded manner; and a first out-coupling diffractive optical element formed along the first waveguide, the first out-coupling diffractive optical element replicating the first portion of the image-bearing light beam and diffracting the replicated first portion of the image-bearing light beam out of the first waveguide in an angularly decoded manner. a first outcoupling diffractive optical element operable to diffract a first portion of the image-bearing light beam from a first image source into the first waveguide in an angularly coded manner; a second incoupling diffractive optical element formed along the first waveguide, the second incoupling diffractive optical element operable to diffract a first portion of the image-bearing light beam from a first image source into the first waveguide in an angularly coded manner; and a second outcoupling diffractive optical element formed along the first waveguide, the second outcoupling diffractive optical element operable to replicate the first portion of the image-bearing light beam and direct the replicated first portion of the image-bearing light beam out of the first waveguide in an angularly decoded manner.

[0008] The accompanying drawings are incorporated herein as part of this specification. The drawings described herein illustrate embodiments of the subject matter of the present disclosure and illustrate selected principles and teachings of the present disclosure. However, the drawings do not illustrate every possible implementation of the subject matter of the present disclosure and are not intended to limit the scope of the present disclosure in any way. [Brief description of the drawings]

[0009] [Figure 1]FIG. 1 shows a simplified cross-sectional view of an image light guide showing the replication of an image-bearing beam along the propagation direction to extend one direction of the eyebox. [Diagram 2] FIG. 2 shows a perspective view of an image light guide with a rotating grating illustrating the expansion of the image-bearing beam perpendicular to the propagation direction to expand in a second direction in the eyebox. [Diagram 3] FIG. 3 shows a schematic side view of a stacked waveguide having multiple incoupling diffractive optical elements, according to an exemplary embodiment of the disclosed subject matter. [Figure 4] FIG. 4 shows a schematic top view of the first waveguide according to FIG. [Diagram 5] FIG. 5 shows a schematic bottom view of the first waveguide according to FIG. [Figure 6] FIG. 6 shows a schematic top view of the second waveguide according to FIG. [Figure 7] FIG. 7 shows a schematic bottom view of the second waveguide according to FIG. [Figure 8] FIG. 8 shows a schematic end view of the laminated waveguide according to FIG. [Figure 9] FIG. 9 shows a schematic end view of the laminated waveguide according to FIG. [Figure 10] FIG. 10 shows a schematic diagram of stacked waveguide incoupling diffractive optical elements and birefringent polarization control elements according to FIGS. [Figure 11] FIG. 11 shows a schematic perspective view of stacked waveguides according to FIG. [Figure 12] FIG. 12 shows a schematic perspective view of stacked waveguides according to FIG. [Figure 13] FIG. 13 shows a schematic side view of a portion of a reflective incoupling diffractive optical element. [Figure 14] FIG. 14 shows a schematic side view of a portion of a transmissive incoupling diffractive optical element. [Figure 15] FIG. 15 is a schematic side view illustrating a stacked waveguide having multiple incoupling diffractive optical elements, according to another exemplary embodiment of the disclosed subject matter. [Figure 16]FIG. 16 shows a schematic side view of a stacked waveguide with multiple incoupling diffractive optical elements according to FIG. 15, except with the waveguides increasing in length from bottom to top. [Figure 17] FIG. 17 shows a schematic side view of a laminated waveguide having a plurality of incoupling diffractive optical elements according to FIG. 15 and also having an optical element. [Figure 18] FIG. 18 is a schematic plan view illustrating a stacked waveguide having multiple incoupling diffractive optical elements, according to yet another exemplary embodiment of the disclosed subject matter. [Figure 19A] FIG. 19A shows a schematic side view of a stacked waveguide having multiple incoupling diffractive optical elements, according to another exemplary embodiment of the disclosed subject matter. [Figure 19B] FIG. 19B shows a schematic end view of a stacked waveguide with multiple incoupling diffractive optical elements according to FIG. 19A. [Figure 20A] FIG. 20A shows a schematic plan view of a double-sided waveguide having multiple incoupling diffractive optical elements, according to another exemplary embodiment of the disclosed subject matter. [Figure 20B] FIG. 20B is a schematic side view of a double-sided waveguide having multiple incoupling diffractive optical elements according to FIG. 20A. [Figure 20C] FIG. 20C is a schematic end view of a waveguide having multiple incoupling diffractive optical elements according to FIG. 20A. [Figure 20D] FIG. 20D is a schematic end view of a waveguide having multiple incoupling diffractive optical elements according to FIG. 20A. [Figure 21A] FIG. 21A shows a schematic side view of a double-sided waveguide with multiple incoupling diffractive optical elements according to FIG. 20A. [Figure 21B] FIG. 21B shows a schematic side view of a double-sided waveguide with multiple incoupling diffractive optical elements according to FIG. 20A. [Figure 22A] FIG. 22A is a schematic plan view of a double-sided waveguide having multiple incoupling diffractive optical elements, according to another exemplary embodiment of the disclosed subject matter. [Figure 22B]FIG. 22B is a schematic side view of a double-sided waveguide according to FIG. 22A. [Figure 22C] FIG. 22C shows a schematic partial view of a composite grating pattern operable to expand and outcouple an image-bearing light beam, according to an exemplary embodiment of the presently disclosed subject matter. [Figure 22D] FIG. 22D is a diagram of a grating vector for a first optical path of image-bearing light at a first wavelength through the double-sided waveguide of FIG. 22A. [Figure 22E] FIG. 22E is a diagram of a grating vector for a second optical path of image-bearing light at a second wavelength through the double-sided waveguide of FIG. 22A. [Figure 22F] FIG. 22F is a diagram of a grating vector for a third optical path of image-bearing light at a third wavelength through the double-sided waveguide of FIG. 22A. [Figure 23] FIG. 23 shows a perspective view of a display system for an augmented reality display using an image light guide, according to an exemplary embodiment of the subject matter of this disclosure. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] It should be understood that the present invention may assume various alternative orientations and step arrangements unless expressly specified to the contrary. It should also be understood that the specific assemblies and systems illustrated in the attached drawings and described in the following specification are merely exemplary embodiments of the inventive concepts defined herein. Thus, specific dimensions, orientations, or other physical characteristics relating to the disclosed embodiments are not to be considered as limiting unless expressly stated otherwise. Also, although not applicable, similar elements in the various embodiments described herein may be generally referred to by similar reference numerals within this section of the specification.

[0011] Those skilled in the relevant art will recognize that the elements and techniques described herein can be practiced without one or more of the specific details, or with other methods, components, materials, etc. In some instances, well-known structures, materials, or operations have not been shown or described in detail to avoid obscuring certain aspects of the disclosure. Throughout this specification, references to "one embodiment" or "embodiment" mean that a particular feature, structure, or characteristic described in connection with an embodiment is included in at least one embodiment of the disclosure. Thus, appearances of the phrase "one embodiment" or "an embodiment" throughout this specification do not necessarily refer to the same embodiment. However, certain features, structures, or characteristics described may be combined in any suitable manner in one or more embodiments.

[0012] As used herein, the terms "first," "second," and the like do not necessarily denote any order, sequential, or priority relationship, but are merely used to more clearly distinguish one element or set of elements from another, unless otherwise specified.

[0013] As used herein, the terms "viewer," "operator," "observer," and "user" are considered equivalent and refer to a person or machine that wears a device having an imaging light guide and / or uses a device having an imaging light guide to view an image.

[0014] As used herein, the term "set" refers to a non-empty set, as the concept of a collection of elements or members of a set is broadly understood in elementary mathematics. As used herein, the term "subset", unless expressly stated otherwise, is used to refer to a non-empty proper subset, i.e., a subset of a larger set having one or more members. For a set S, a subset may include the complete set S. However, a "proper subset" of set S is strictly contained in set S and excludes at least one member of set S.

[0015] As used herein, the terms "coupled" and "coupled" in the optical context refer to a connection in which light travels from one optical medium or device to another optical medium or device.

[0016] As used herein, the terms "wavelength band" and "wavelength range" are equivalent and have the standard meaning used by those skilled in the art of color imaging and refer to a continuous range of light wavelengths used to represent a multicolor image.

[0017] As used herein, the term "beam expansion" is intended to mean the duplication of a beam through multiple encounters with optical elements to provide an exit pupil expansion in one or more directions. Similarly, as used herein, "expanding" a beam or a portion of a beam is intended to mean the duplication of a beam through multiple encounters with optical elements to provide an exit pupil expansion in one or more directions.

[0018] Optical systems such as HMDs can generate a display of a virtual image. Unlike the method of forming a real image, the virtual image is not formed on the display surface. That is, when the display surface is positioned at the perceived location of the virtual image, no image is formed on the surface. Display of a virtual image has a number of unique advantages in the presentation of augmented reality. For example, the apparent size of the virtual image is not limited by the size or location of the display surface. Furthermore, the source object of the virtual image can be small, for example, a magnifying glass provides a virtual image of the object. Compared to a system that projects a real image, a more realistic viewing experience can be provided by forming a virtual image that appears to be at some distance. Providing a virtual image also eliminates the need to correct screen artifacts that may be required when projecting a real image.

[0019] The image light guide may display a virtual image using image-bearing light from a light source such as a projector. For example, a collimated, relative angle encoded light beam from the projector is coupled into the planar waveguide by an input coupling such as an in-coupling diffractive optical element, which may be attached or formed on a surface of the planar waveguide, or embedded within the waveguide. Such a diffractive optical element may be formed as a diffraction grating, a holographic optical element (HOE), or in other known manner. For example, a diffraction grating may be formed by a surface relief. After propagating along the waveguide, the diffracted light may be redirected out of the waveguide by a similar output coupling such as an out-coupling diffractive optical element, which may be arranged to provide pupil dilation along at least one direction of the virtual image. Additionally, a rotating grating may be positioned on / in the waveguide to provide pupil dilation in the orthogonal direction of the virtual image. The image-bearing light output from the waveguide provides an expanded eyebox for the viewer.

[0020] As shown in FIG. 1, the image light guide 10 may include a planar waveguide 22 having plane-parallel surfaces. The waveguide 22 comprises a transparent substrate S having an outer surface 12 and an inner surface 14 opposite the outer surface 12. In this example, an incoupling diffractive optical element IDO and an outcoupling diffractive optical element ODO are disposed on the inner surface 14, the incoupling diffractive optical element IDO being a reflective diffraction grating through which the image-bearing light WI is coupled into the planar waveguide 22. However, the incoupling diffractive optical element IDO may alternatively be a volume hologram or other holographic diffractive element or other type of optical component that provides diffraction for the incident image-bearing light WI. The incoupling diffractive optical element IDO may be located on the outer surface 12 or on the inner surface 14 of the planar waveguide 22 and may be a transmissive or reflective optical element depending on the direction from which the image-bearing light WI approaches the planar waveguide 22.

[0021] When used as part of a virtual image display system, the incoupling diffractive optical element IDO couples image-bearing light WI from a real image source into the substrate S of the planar waveguide 22. Any real image or image dimension is first converted into an array of overlapping angle-related beams that code different locations within the image for presentation to the incoupling diffractive optical element IDO. The image-bearing light WI is diffracted (generally through a first diffraction order) and thereby redirected by the incoupling diffractive optical element IDO into the planar waveguide 22 as an image-bearing light beam WG by total internal reflection ("TIR") for further propagation along the planar waveguide 22. Although diffracted along the boundaries set by the TIR into a generally more condensed range of angle-related beams, the image-bearing light WG preserves the image information in coded form. The outcoupling diffractive optical element ODO receives the encoded image-bearing light WG and diffracts the image-bearing light WG from the planar waveguide 22 (usually also as the first diffracted light) and emits it as image-bearing light WO towards the intended eye position of the viewer, e.g., the eye box E. Typically, the outcoupling diffractive optical element ODO is designed symmetrically with respect to the incoupling diffractive optical element IDO to restore the original angular relationship of the image-bearing light WI between the emitted angularly related beams. However, by increasing the overlap of the angularly related beams present in the eye box E in one dimension, a virtual image can be seen. For this reason, the outcoupling diffractive optical element ODO is arranged with a limited thickness of the image light guide 12 to encounter the image-bearing light WG multiple times and diffract only a portion of the image-bearing light WG at each encounter. The multiple encounters along the length of the outcoupling diffractive optical element ODO have the effect of duplicating the image-bearing light beam WG and magnifying or expanding at least one dimension of the eye box E where the duplicated beams overlap. The expanded eyebox E reduces the sensitivity to the position of the viewer's eyes for viewing the virtual image.

[0022] An outcoupling diffractive optical element having a refractive index change along a single direction can expand one dimension of the eyebox by duplicating each angle-related beam into a direction of propagation along the waveguide during an encounter with the outcoupling diffractive optical element. Additionally, an outcoupling diffractive optical element having a refractive index change along a second direction can expand a second dimension of the eyebox, providing a two-dimensional expansion of the eyebox. The refractive index change along the first direction of the outcoupling diffractive optical element can be arranged to diffract a portion of the energy of each beam exiting the waveguide upon each encounter through a desired first diffraction, while another portion of the beam's energy is preserved for further propagation in the original direction through a zeroth diffraction order. The refractive index change along the second direction of the outcoupling diffractive optical element can be arranged to diffract a portion of the energy of each beam upon each encounter through a desired first diffraction into a direction angled relative to the beam's original direction of propagation, while another portion of the beam's energy is preserved for further propagation in the original direction through a zeroth diffraction order.

[0023] 1, the outcoupling diffractive optical element ODO is shown as a transmissive diffraction grating disposed on the inner surface 14 of the planar waveguide 22. However, like the incoupling diffractive optical element IDO, the outcoupling diffractive optical element ODO may be located on the outer surface 12 or the inner surface 14 of the planar waveguide 22 and may be transmissive, reflective, or a combination depending on the intended direction in which the image-bearing light WG exits the planar waveguide 22.

[0024] As shown in FIG. 2, the image light guide 20 may be arranged to expand the eyebox 74 in two directions, i.e., along both the x-axis and the y-axis of the intended image. To achieve the second direction of beam duplication, the incoupling diffractive optical element IDO with grating vector k0 is oriented to diffract a portion of the image-bearing light WI towards the intermediate rotating grating TG with grating vector k1, which is oriented to diffract a portion of the image-bearing light WG in a reflection mode towards the outcoupling diffractive optical element ODO. Only a portion of the image-bearing light WG is diffracted by each of the multiple encounters with the intermediate rotating grating TG, thereby laterally replicating each of the angle-related beams of the image-bearing light WG approaching the outcoupling diffractive optical element ODO. The image-bearing light WO exits the planar waveguide 22 after the rotating grating TG redirects the image-bearing light WG towards the outcoupling diffractive optical element ODO to longitudinally replicate the angle-related beams of the image-bearing light WG in a second direction. The grating vectors, such as the depicted grating vectors k0, k1, k2, extend in a direction perpendicular to the diffractive features (e.g., grooves, lines, or rulings) of the diffractive optical elements and have a magnitude that is the reciprocal of the period or pitch d (i.e., the center-to-center distance between the grooves) of the diffractive optical elements IDO, TG, ODO. The incoupling diffractive optical element IDO, the rotating grating TG, and the outcoupling diffractive optical element ODO may each have a different period or pitch d.

[0025] As shown in FIG. 2, the incoupling diffractive optical element IDO receives the incident image-bearing light WI, which includes a series of angle-related beams corresponding to individual pixels or equivalent locations in the image generated by the image source 16. The image source 16 operable to generate a full range of angle-coded beams to generate a virtual image may be a combination of, but is not limited to, a real display device combined with focusing optics, a beam scanner to set the angle of the beam more directly, or a one-dimensional real display device used with a scanner. The image light guide 20 provides an extended eyebox by providing multiple encounters of the image-bearing light WG at different orientations, both by the intermediate rotating grating TG and the outcoupling diffractive optical element ODO. In the original orientation of the planar waveguide 22, the intermediate grating TG provides a copy of the beam in the y-axis direction, and the outcoupling diffractive optical element ODO provides a similar copy of the beam in the x-axis direction. The reflective properties of the diffractive optical elements IDO, ODO, TG and their respective periods d, together with the orientation of their respective grating vectors, provide eyebox expansion in two directions while maintaining the intended relationship between the angularly related beams of image-bearing light WI that are output from the image light guide 20 as image-bearing light WO.

[0026] Although the image-bearing light WI input to the image light guide 20 is coded by the incoupling diffractive optical element IDO into a series of different angle-related beams, the information required to reconstruct the image is preserved by considering the systematic effects of the incoupling diffractive optical element IDO. The rotating grating TG, located at an intermediate position between the incoupling diffractive optical element IDO and the outcoupling diffractive optical element ODO, is typically positioned so as not to induce any significant changes to the coding of the image-bearing light WG. The outcoupling diffractive optical element ODO is typically positioned symmetrically with respect to the incoupling diffractive optical element IDO, including, for example, diffractive features that share the same period. Similarly, the period of the rotating grating TG typically matches the common period of the incoupling diffractive optical element IDO and the outcoupling diffractive optical element ODO. As shown in FIG. 2, the grating vector k1 of the rotating grating TG may be oriented at 45 degrees with respect to the other grating vectors k0, k2 (all as undirected line segments). However, in an exemplary embodiment, the grating vector k1 of the rotating grating TG is oriented at 60 degrees relative to the grating vectors k0, k2 of the incoupling diffractive optical element IDO and the outcoupling diffractive optical element ODO in such a way that the image-bearing light WG is rotated by 120 degrees. By orienting the grating vector k1 of the intermediate rotating grating TG at 60 degrees relative to the grating vector k0 of the incoupling diffractive optical element IDO and the grating vector k2 of the outcoupling diffractive optical element ODO, the grating vectors k0, k2 are also oriented at 60 degrees relative to each other (again, considered as undirected lines). Taking the common pitch of the rotating grating TG, the incoupling diffractive optical element IDO and the outcoupling diffractive optical element ODO as the basis for the magnitude of the grating vectors, the three grating vectors k0, k1, k2 (as directed lines) form an equilateral triangle, summing to the magnitude of a zero vector, thereby avoiding asymmetric effects that may result in undesirable aberrations, including chromatic dispersion.

[0027] The image-bearing light WI diffracted into the planar waveguide 22 is effectively coded by the incoupling diffractive optical element IDO, regardless of whether the incoupling diffractive optical element IDO uses a grating, a hologram, a prism, a mirror, or some other mechanism. The reflection, refraction, and / or diffraction of light occurring at the incoupling diffractive optical element IDO must be decoded accordingly by the outcoupling diffractive optical element ODO to recreate the virtual image presented to the viewer. The rotating grating TG, located at an intermediate position between the incoupling diffractive optical element IDO and the outcoupling diffractive optical element ODO, is typically designed and oriented so as not to induce any changes to the coded light. The outcoupling diffractive optical element ODO decodes the image-bearing light WG into the original or desired form of angularly related beams that are replicated in the output beam array that fills the eyebox 74.

[0028] It is relevant whether any symmetry is maintained between the rotating grating TG and the incoupling diffractive optical element IDO and the outcoupling diffractive optical element ODO, or whether changes to the angle-related beam coding of the image-bearing light WI occur along the planar waveguide 22, the rotating grating TG, the incoupling diffractive optical element IDO and the outcoupling diffractive optical element ODO, so that the image-bearing light WO output from the planar waveguide 22 retains or otherwise maintains the original or desired form of the image-bearing light WI for generating the intended virtual image.

[0029] The letter "R" represents the orientation of the virtual image as seen by a viewer whose eyes are in the glasses 74. As shown, the orientation of the letter "R" in the represented virtual image coincides with the orientation of the letter "R" encoded by the image-bearing light WI. A change in rotation about the z-axis or angular orientation of the incident image-bearing light WI with respect to the xy-plane causes a corresponding symmetric change in the rotation or angular orientation of the output light from the outcoupling diffractive optical element ODO. From the aspect of image orientation, the rotating grating TG simply acts as a kind of optical relay, providing a duplication of the angle-coded beam of the image-bearing light WG along one axis of the image (e.g., along the y-axis). The outcoupling diffractive optical element ODO further replicates the angle-coded beam of the image-bearing light WG along another axis of the image (e.g., along the x-axis) while maintaining the original orientation of the virtual image encoded by the image-bearing light WI. As shown in FIG. 2, the rotating grating TG may be a tilted or square diffraction grating placed on the front or back surface of the planar waveguide 22. Alternatively, the rotating grating TG may be a blazed grating.

[0030] The present disclosure provides image light guide arrangements having improved output intensity of image-bearing light across an output aperture, more specifically, the present disclosure provides a waveguide having two or more incoupling and outcoupling diffractive optical elements operable to replicate an image-bearing light beam in two directions and output the replicated image-bearing light beam towards the eyebox.

[0031] As shown in FIGS. 3-11, in an exemplary embodiment, the image light guide system 50 includes a first planar waveguide 100 having a first surface 102 and a second surface 104. The first surface 102 of the waveguide is positioned generally parallel to the second surface 104 of the waveguide. A first incoupling diffractive optical element IDO1 is located on, within, or engaged with the first surface 102, and a second incoupling diffractive optical element IDO2 is located on, within, or engaged with the second surface 104. Further, a first outcoupling diffractive optical element ODO1 is formed on, within, or engaged with the first surface 102, and a second outcoupling diffractive optical element ODO2 is formed on, within, or engaged with the second surface 104. In an exemplary embodiment, the outcoupling diffractive optical elements ODO1, ODO2 are each a diffraction grating. In another exemplary embodiment, the outcoupling diffractive optical elements ODO1, ODO2 are each holographic diffractive elements.

[0032] Now, referring to FIG. 4 showing a plan view of an exemplary embodiment of the first planar waveguide 100, the first incoupling diffractive optical element IDO1 includes a first plurality of periodic diffractive structures 106. For example, the first incoupling diffractive optical element IDO1 may include a first set of periodic linear grating structures 106 positioned generally parallel to the y-axis. The first outcoupling diffractive optical element ODO1 includes a second plurality of periodic diffractive structures 108 and a third plurality of periodic diffractive structures 110. For example, the second plurality of periodic diffractive structures 108 may be composed of a second set of periodic linear grating structures 108 rotated or angularly offset with respect to the x-axis 115 by a polar angle (measured from the x-axis 115) less than 30 degrees (e.g., 25 degrees), and the third plurality of periodic diffractive structures 110 may be composed of a third set of periodic linear grating structures 110 rotated or angularly offset with respect to the x-axis 115 by a polar angle greater than 60 degrees (e.g., 65 degrees). In one exemplary embodiment, the second set of periodic linear grating structures 108 are rotated or angularly offset by a polar angle of about 30 degrees relative to the x-axis 115, and the third set of periodic linear grating structures 110 are rotated or angularly offset by a polar angle of about 150 degrees relative to the x-axis 115. In another embodiment (not shown), the first set of periodic linear grating structures 106 are arranged generally parallel to an alternate axis other than the y-axis, and the second set of periodic linear grating structures 108 are rotated or angularly offset by a polar angle (measured from the vertical axis) of less than 30 degrees (e.g., 25 degrees) relative to an axis perpendicular to the alternate axis, while the third set of periodic linear grating structures 110 are rotated or angularly offset by a polar angle (measured from the vertical axis) of more than 60 degrees (e.g., 65 degrees). The second and third sets of periodic diffractive structures 108, 110 intersect and / or define different grating vectors. The second set of periodic diffractive structures 108 and the third set of periodic diffractive structures 110 form a composite diffractive optical element operable to replicate and outcouple the image-bearing light incoupled by the first incoupling diffractive optical element IDO1.The first set of periodic diffractive structures 106 includes a first period, the second set of periodic diffractive structures 108 includes a second period, and the third set of periodic diffractive structures 110 includes a third period. In an exemplary embodiment, the third period is equal to the second period and the second period is equal to the first period. In an exemplary embodiment, the first period, the second period, and the third period are each less than 50 nm.

[0033] Now, referring to FIG. 5 showing a bottom view of the first planar waveguide 100, the second incoupling diffractive optical element IDO2 includes a fourth plurality of periodic diffractive structures 112. For example, the second incoupling diffractive optical element IDO2 may include a fourth set of periodic linear grating structures 112 rotated or angularly offset by about thirty degrees (30°), e.g., within five degrees (5°) of thirty degrees (30°), relative to the first set of periodic linear grating structures 106. For example, the second incoupling diffractive optical element IDO2 may include a fourth set of periodic linear grating structures 112 rotated or angularly offset by twenty-five degrees (25°) to thirty-five degrees (35°) relative to the first set of periodic linear grating structures 106. The second outcoupling diffractive optical element ODO2 includes a fifth plurality of periodic diffractive structures 114 and a sixth plurality of periodic diffractive structures 116. For example, the fifth plurality of periodic diffractive structures 114 may comprise a fifth set of periodic linear grating structures 114 rotated or angularly offset by approximately thirty degrees (30°) or thirty degrees (30°) relative to the second set of periodic linear grating structures 108, and the sixth plurality of periodic diffractive structures 116 may comprise a sixth set of periodic linear grating structures 116 rotated or angularly offset by approximately thirty degrees (30°) or within five degrees (5°) of thirty degrees (30°) relative to the third set of periodic linear grating structures 110. In an exemplary embodiment, the fifth set of periodic linear grating structures 114 is substantially parallel to an x-axis 115 having a polar angle of approximately 0°, and the sixth set of periodic linear grating structures 116 is rotated or angularly offset by approximately 120° polar angle relative to the x-axis 115. The fifth and sixth sets of periodic diffractive structures 114, 116 intersect and / or define different grating vectors. The fifth and sixth sets of periodic diffractive structures 114, 116 form a composite diffractive optical element operable to replicate and pressure-couple image-bearing light from the second in-coupling diffractive optical element IDO2. The fourth set of periodic diffractive structures 112 includes a fourth period, the fifth set of periodic diffractive structures 114 includes a fifth period, and the sixth set of periodic diffractive structures 116 includes a sixth period. In an exemplary embodiment, the sixth period is equal to the fifth period and the fifth period is equal to the sixth period.In one exemplary embodiment, the first period, the second period, and the third period are each less than 50 nm, and the fourth period, the fifth period, and the sixth period are each greater than 50 nm.

[0034] As shown in FIGS. 3-12, in an exemplary embodiment, the image light guide system 50 includes a second planar waveguide 200 having a first surface 202 and a second surface 204. The first surface 202 of the waveguide is positioned generally parallel to the second surface 204 of the waveguide. A third incoupling diffractive optical element IDO3 is located on, within, or engaged with the first surface 202, and a fourth incoupling diffractive optical element IDO4 is located on, within, or engaged with the second surface 204. The third outcoupling diffractive optical element ODO3 is formed on / within the first surface 202, and the fourth outcoupling diffractive optical element ODO4 is formed on, within, or engaged with the second surface 204. In an exemplary embodiment, the first incoupling diffractive optical element IDO1 is located substantially coaxially with the third incoupling diffractive optical element IDO3 with respect to an axis that is disposed through the first and second surfaces 102, 104 of the first planar waveguide 100 and through the first and second surfaces 202, 204 of the second planar waveguide 200. Similarly, the second incoupling diffractive optical element IDO2 is located substantially coaxially with the fourth incoupling diffractive optical element IDO4 with respect to an axis that is disposed through the first and second surfaces 102, 104 of the first planar waveguide 100 and through the first and second surfaces 102, 104 of the second planar waveguide 200.

[0035] Now, referring to FIG. 6 showing a plan view of an exemplary embodiment of the second planar waveguide 200, the third incoupling diffractive optical element IDO3 includes a seventh plurality of periodic diffractive structures 206. For example, the third incoupling diffractive optical element IDO3 may include a seventh set of periodic linear grating structures 206 positioned generally parallel to the y-axis. The third outcoupling diffractive optical element ODO3 includes an eighth plurality of periodic diffractive structures 208 and a ninth plurality of periodic diffractive structures 210. For example, the eighth plurality of periodic diffractive structures 208 may include an eighth set of periodic linear grating structures 208 rotated or angularly offset with respect to the x-axis by a polar angle (measured from the x-axis) of less than 30 degrees (e.g., 25°), and the ninth plurality of periodic diffractive structures 210 may include a ninth set of periodic linear grating structures 210 rotated or angularly offset with respect to the x-axis by a polar angle (measured from the x-axis) of more than 60° (e.g., 65°). In another embodiment (not shown), the seventh set of periodic linear grating structures 206 are generally arranged parallel to an alternate axis other than the y-axis, and the eighth set of periodic linear grating structures 208 are rotated or angularly offset relative to an axis perpendicular to the alternate axis by a polar angle (measured from the vertical axis) of less than 30 degrees (e.g., 25°), while the ninth set of periodic linear grating structures 210 are rotated or angularly offset relative to the alternate axis by a polar angle (measured from the vertical axis) of more than 60 degrees (e.g., 65°). In an exemplary embodiment, the eighth set of periodic linear grating structures 208 are rotated or angularly offset relative to the x-axis 115 by a polar angle of about 30 degrees, and the ninth set of periodic linear grating structures 210 are rotated or angularly offset relative to the x-axis 115 by a polar angle of about 150 degrees. The eighth and ninth sets of periodic diffractive structures 208, 210 intersect and / or define different grating vectors. The eighth and ninth sets of periodic diffractive structures 208, 210 form a composite diffractive optical element operable to replicate and outcouple image-bearing light from the third incoupling diffractive optical element IDO3. The seventh set of periodic diffractive structures 206 includes a seventh period, the eighth set of periodic diffractive structures 208 includes an eighth period, and the ninth set of periodic diffractive structures 210 includes a ninth period.In one exemplary embodiment, the ninth period is equal to the eighth period, and the eighth period is equal to the seventh period, In one exemplary embodiment, the seventh period, the eighth period, and the ninth period are each less than 50 nm.

[0036] Now, referring to FIG. 7 showing a bottom view of the second planar waveguide 200, the fourth incoupling diffractive optical element IDO4 includes a tenth plurality of periodic diffractive structures 212. For example, the fourth incoupling diffractive optical element IDO4 may comprise a tenth set of periodic linear grating structures 212 rotated or angularly offset by about thirty degrees (30°), e.g., within five degrees (5°) of thirty degrees (30°), relative to the seventh set of periodic linear grating structures 206. For example, the fourth incoupling diffractive optical element IDO4 may include a tenth set of periodic linear grating structures 212 rotated or angularly offset by twenty-five degrees (25°) to thirty-five degrees (30°) relative to the seventh set of periodic linear grating structures 206. The fourth outcoupling diffractive optical element ODO4 includes an eleventh plurality of periodic diffractive structures 214 and a twelfth plurality of periodic diffractive structures 216. For example, the eleventh plurality of periodic diffractive structures 214 may comprise an eleventh set of periodic linear grating structures 214 rotated or angularly offset by approximately thirty degrees (30°), e.g., within five degrees (5°) of thirty degrees (30°), relative to the eighth set of periodic linear grating structures 208, and the twelfth plurality of periodic diffractive structures 216 may comprise a twelfth set of periodic linear grating structures 216 rotated or angularly offset by approximately thirty degrees (30°), e.g., within five degrees (5°) to thirty degrees (30°), relative to the ninth set of periodic linear grating structures 210. In one exemplary embodiment, the eleventh set of periodic linear grating structures 214 are substantially parallel to the x-axis 115 with a polar angle of approximately 0°, and the twelfth set of periodic linear grating structures 216 are rotated or angularly offset relative to the x-axis 115 by a polar angle of approximately 120°. The eleventh and twelfth sets of periodic diffractive structures 214, 216 intersect and / or define different grating vectors. The eleventh and twelfth sets of periodic diffractive structures 214, 216 form a composite diffractive optical element operable to replicate and outcouple image-bearing light from the fourth incoupling diffractive optical element IDO4. The tenth set of periodic diffractive structures 212 includes a tenth period, the eleventh set of periodic diffractive structures 214 includes an eleventh period, and the twelfth set of periodic diffractive structures 216 includes a twelfth period.In an exemplary embodiment, the twelfth period is equal to the eleventh period, and the eleventh period is equal to the tenth period. In an exemplary embodiment, the tenth period, the eleventh period, and the twelfth period are each less than 50 nm, and the tenth period, the eleventh period, and the twelfth period are each greater than 50 nm.

[0037] The first planar waveguide 100 includes a first wavelength range light path and a second wavelength range light path. The first wavelength range light path includes at least a first incoupling diffractive optical element IDO1 and a first outcoupling diffractive optical element ODO1. The first wavelength range light path is operable to incouple, propagate, replicate, and outcouple image-bearing light in a first wavelength range. For example, the first wavelength range light path is operable to direct image-bearing light in a blue wavelength range (e.g., in the range of 440-470 nm or in the range of 450-495 nm) through the waveguide 100. The second wavelength range light path includes at least a second incoupling diffractive optical element IDO2 and a second outcoupling diffractive optical element ODO2. The second wavelength range light path is operable to incoupling, propagate, replicate, and outcouple image-bearing light in a second wavelength range. For example, the second wavelength range light path is operable to direct image-bearing light in the red wavelength range (eg, in the range of 630-660 nm or in the range of 620-750 nm) through the waveguide 100 .

[0038] The second planar waveguide 200 includes a third wavelength range light path and a fourth wavelength range light path. The third wavelength range light path includes at least a third incoupling diffractive optical element IDO3 and a third outcoupling diffractive optical element ODO3. The third wavelength range light path is operable to incouple, propagate through TIR, replicate, and outcouple image-bearing light in the third wavelength range. For example, the third wavelength range light path is operable to direct image-bearing light in a green wavelength range (e.g., in the range of 520-560 nm or the range of 495-570 nm) through the waveguide 200. The fourth wavelength range light path includes at least a fourth incoupling diffractive optical element IDO4 and a fourth outcoupling diffractive optical element ODO4. The fourth wavelength range light path is also operable to incouple, propagate through TIR, replicate, and outcouple image-bearing light in the second wavelength range. For example, the fourth wavelength range light path is operable to direct image-bearing light in the red wavelength range (eg, in the range of 630-660 nm or in the range of 620-750 nm) through the waveguide 200 .

[0039] With respect to the first planar waveguide 100, by rotating the fourth plurality of periodic diffractive structures 112 by approximately thirty degrees (30°) relative to the first plurality of periodic diffractive structures 106, and by rotating the fifth and sixth plurality of periodic diffractive structures 114, 116 by approximately thirty degrees (30°) relative to the second and third plurality of periodic diffractive structures 108, 110, respectively, crosstalk (e.g., interference between incoupled light of different wavelength ranges) between the first wavelength range light path and the second wavelength range light path is reduced. In other words, the diffractive elements of the second incoupling diffractive optical element IDO2 are rotated by approximately thirty degrees (30°) relative to the diffractive elements of the first incoupling diffractive optical element IDO1, and the diffractive elements of the second outcoupling diffractive optical element ODO2 are rotated by approximately thirty degrees (30°) relative to the diffractive elements of the first outcoupling diffractive optical element ODO1.

[0040] Crosstalk may also be reduced between the third and fourth wavelength range optical paths by rotating the tenth plurality of periodic diffractive structures 212 approximately thirty degrees (30°) relative to the seventh plurality of periodic diffractive structures 206, and by rotating the eleventh plurality of grating structures 214, 216 approximately thirty degrees (30°) relative to the eighth plurality of periodic diffractive structures 208 and the ninth plurality of periodic diffractive structures 210, respectively. In other words, the fourth incoupling diffractive optical element IDO4 is rotated approximately thirty degrees (30°) relative to the third incoupling diffractive optical element IDO3, and the fourth outcoupling diffractive optical element ODO4 is rotated approximately thirty degrees (30°) relative to the third outcoupling diffractive optical element ODO3. As shown in Figures 4-7, in an exemplary embodiment, the first, second, and third sets of periodic linear grating structures 106, 108, 110 and the seventh, eighth, and ninth sets of periodic linear grating structures 206, 208, 210 on the first surface 102 of the first waveguide 100 and the first surface 202 of the second waveguide 200, respectively, have generally the same period. In an exemplary embodiment, the first, second, third, seventh, eighth, and ninth sets of periodic linear grating structures have a period of greater than 50 nm. Similarly, the fourth, fifth, and sixth sets of periodic linear grating structures 112, 114, 116 and the tenth, eleventh, and twelfth sets of periodic linear grating structures 212, 214, 216 on the second surface 104 of the first waveguide 100 and the second surface 204 of the second waveguide 200, respectively, have generally the same period. In one exemplary embodiment, the first, second, third, seventh, eighth, and ninth periodic linear grating structures 106, 108, 110, 206, 208, 210 each have a period greater than 50 nm, and the fourth, fifth and sixth, tenth, eleventh and twelfth periodic linear grating structures 112, 114, 116, 212, 214, 216 each have a period less than 50 nm.In another exemplary embodiment, the first, second, third, seventh, eighth, and ninth periodic linear grating structures 106, 108, 110, 206, 208, 210 each have a period less than 50 nm, and the fourth, fifth, sixth, tenth, eleventh, and twelfth periodic linear grating structures 112, 114, 116, 212, 214, 216 each have a period greater than 50 nm. Furthermore, the orientation of the first, second, and third sets of periodic linear grating structures 106, 108, 110 are arranged in substantially the same orientation as the seventh, eighth, and ninth sets of periodic linear grating structures 206, 208, 210, respectively. Similarly, the orientation of the fourth, fifth, and sixth sets of periodic linear grating structures 112, 114, 116 are disposed in substantially the same orientation as the tenth, eleventh, and twelfth sets of periodic linear grating structures 212, 214, 216, respectively. As used herein, and in addition to its ordinary meaning to those in the art, the term “orientation” is meant to refer to the position and / or angle of a set of periodic linear grating structures relative to the x-axis 115.

[0041] In an exemplary embodiment, as shown in Figures 3, 8 and 9, the image-bearing light WI1 from the projector 16A is incident on the first incoupling diffractive optical element IDO1, and a first portion of the image-bearing light WI1 is diffracted by the first incoupling diffractive optical element IDO1 and propagates generally as image-bearing light WG1 through the TIR toward the outcoupling diffractive optical element ODO1. In one embodiment, the periodic linear grating structure (i.e., the first set of periodic linear grating structures 106) of the first incoupling diffractive optical element IDO1 is arranged to optimize coupling of light in a first wavelength range of the image-bearing light WI1, e.g., in the blue wavelength range of the electromagnetic spectrum. The second portion of the image-bearing light WI1 transmits through the first incoupling diffractive optical element IDO1 and the planar waveguide 100 and is incident on the third incoupling diffractive optical element IDO3. At least a portion of the image-bearing light WI1 is diffracted by the third incoupling diffractive optical element IDO3 and propagates toward the second outcoupling diffractive optical element ODO2 via TIR generally as WG2. In one embodiment, the periodic linear grating structures of the third incoupling diffractive optical element IDO3 (i.e., the seventh set of periodic linear grating structures 206) are arranged for optimized coupling of light in a second range of wavelengths of the image-bearing light WI1, e.g., in the green wavelength range.

[0042] The image-bearing light WI2 from the projector 16B is incident on the second incoupling diffractive optical element IDO2, and a first portion of the image-bearing light WI2 is diffracted by the second incoupling diffractive optical element IDO2 and propagates toward the outcoupling diffractive optical element ODO2 via the TIR generally as WG3. In one embodiment, the periodic linear grating structure of the second incoupling diffractive optical element IDO2 (i.e., the fourth set of periodic linear grating structures 112) is arranged to optimize coupling of a wavelength range of the image-bearing light WI2 in the red wavelength range. The second portion of the image-bearing light WI2 transmits through the second incoupling diffractive optical element IDO2 and the planar waveguide 200 and is incident on the fourth incoupling diffractive optical element IDO4. In one embodiment, the periodic linear grating structure of the fourth incoupling diffractive optical element IDO4 (i.e., the tenth set of periodic linear grating structures 210) is arranged to optimize coupling of light in a third range of wavelengths of the image-bearing light WI2, e.g., in the red wavelength range of the electromagnetic spectrum. At least a portion of the image-bearing light WI2 is diffracted by the fourth in-coupling diffractive optical element IDO4 and propagates toward the second out-coupling diffractive optical element ODO2 via TIR generally as WG4. The birefringent polarization control element 130 may be located between the waveguide 100 and the waveguide 200. In an exemplary embodiment, the birefringent polarization control element 130 is substantially coaxial with IDO2 and IDO4 along an axis passing through the first surface 102 and the second surface 104 of the first planar waveguide 100 and the first surface 202 and the second surface 204 of the second planar waveguide 200. The birefringent polarization control element 130 may be operable to rotate the polarization direction of the image-bearing light by ninety degrees (90°). Furthermore, it should be understood that a transmissive diffraction grating has a lower polarization sensitivity than a reflective diffraction grating. If the second incoupling diffractive optical element IDO2 is a reflective diffraction grating, polarization of the image-bearing light via the birefringent polarization control element 130 allows for higher diffraction efficiency.As shown in FIG. 10, in an exemplary embodiment, the image-bearing light WI2 from the projector 16B is incident on the second incoupling diffractive optical element IDO2, which is optimized to diffract or couple a first portion WI2a of the image-bearing light WI2 into the first planar waveguide 100. For example, the second incoupling diffractive optical element IDO2 can be configured to incouple the first portion WI2a of the image-bearing light WI2, where the first portion WI2a is composed of light having an electric field parallel to the periodic diffractive structure of the second incoupling diffractive optical element IDO2 (hereinafter, "parallel electric field light") and light having an electric field perpendicular to the direction of the periodic diffractive structure of the second incoupling diffractive optical element IDO2 (hereinafter, "perpendicular electric field light"). In some exemplary embodiments, the ratio of the parallel electric field light to the perpendicular electric field light coupled to the waveguide 100 is selected from a range of ratios between 8:1 and 6:1. In an exemplary embodiment, 85% of the parallel electric field light diffracted from the second incoupling diffractive optical element IDO2 is coupled into the waveguide 100, and about 15% of the perpendicular electric field light diffracted from the second incoupling diffractive optical element IDO2 is coupled into the waveguide 100. A second portion WI2b of the image-bearing light WI2 is transmitted through the second incoupling diffractive optical element IDO2. The second portion WI2b of the image-bearing light WI2 encounters a birefringent polarization control element 130, which is operable to change the polarization state of the light in the second portion WI2b of the image-bearing light WI2 transmitted through the second incoupling diffractive optical element IDO2. In one embodiment, the birefringent polarization control element 130 is selected from one or more of a half-wave plate, a quarter-wave plate, or a retardation film. In one embodiment, the birefringent polarization control element 130 is a half-wave plate configured to rotate the polarization state of light in the second portion WI2b of the image-bearing light WI2 to WI2c, e.g., 90 degrees, to provide a third portion WI2c of the image-bearing light WI2. The third portion WI2c of the image-bearing light WI2 is diffracted by a fourth incoupling diffractive optical element IDO4 to provide a fourth portion WI2d of the image-bearing light WI2, the fourth portion WI2d including light having a ratio of parallel electric field light to perpendicular electric field light selected from a range of ratios between 1:8 and 1:6.In other words, in an exemplary embodiment, 15% of the parallel electric field light diffracting from the fourth incoupling diffractive optical element IDO4 is coupled into the waveguide 200, and about 85% of the perpendicular electric field light diffracting from the fourth incoupling diffractive optical element IDO4 is coupled into the waveguide 200. A fourth portion WI2d of the image-bearing light WI2 is incoupled into the planar waveguide 200 and generally propagates as incoupled image-bearing light WG4 via TIR towards the fourth outcoupling diffractive optical element ODO4.

[0043] In an exemplary embodiment, as shown in FIGS. 13 and 14, the first incoupling diffractive optical element IDO1 and the third incoupling diffractive optical element IDO3 are configured to optimize the diffraction efficiency for the image-bearing light WI1. For example, the first incoupling diffractive optical element IDO1 and the third incoupling diffractive optical element IDO3 may be configured as transmission type diffraction gratings, and the second incoupling diffractive optical element IDO2 and the fourth incoupling diffractive optical element IDO4 may be configured as reflection type diffraction gratings. In an exemplary embodiment, the first plurality of periodic diffractive structures 106 of the first incoupling diffractive optical element IDO1 may have a tilt angle φ1, and the fourth plurality of periodic diffractive structures 112 of the second incoupling diffractive optical element IDO2 may have a tilt angle φ2. Similarly, the seventh plurality of periodic diffractive structures 206 of the third incoupling diffractive optical element IDO3 may have a tilt angle φ1, and the tenth plurality of periodic diffractive structures 212 of the fourth incoupling diffractive optical element IDO4 may have a tilt angle φ2. The periodic diffractive structures 106, 112 of the first and second incoupling diffractive optical elements IDO1, IDO2 may have a tilt angle φ that is rotated 180 degrees relative to each other.

[0044] As shown in FIG. 15, in an exemplary embodiment, the image light guide system 300A includes a first planar waveguide 320, a second planar waveguide 322, and a third planar waveguide 324. The first planar waveguide 320 has an upper planar surface 330 and a lower planar surface 332 generally parallel to the upper planar surface 330. The first planar waveguide 320 includes an incoupling diffractive optical element 350 located on the lower planar surface 332. The first planar waveguide 320 may also include an intermediate diffractive optical element 352 oriented to diffract a portion of the image-bearing light in a reflective mode toward the outcoupling diffractive optical element 354. The intermediate diffractive optical element 352 may also be referred to herein as a rotating grating. In an exemplary embodiment, the rotating grating 352 is a diffraction grating. In another exemplary embodiment, the rotating grating 352 is a holographic optical element. The rotating grating 352 is operable to replicate the exit pupil through multiple encounters of an image-bearing light beam traveling in one or more directions within the first planar waveguide 320, providing pupil dilation, i.e., eyebox dilation, in one or more directions.

[0045] The outcoupling diffractive optical element 354 is operable to diffract a portion of the image-bearing light beam propagating within the first planar waveguide 320 out of the first planar waveguide 320. In one exemplary embodiment, the outcoupling diffractive optical element 354 is a diffraction grating. In another exemplary embodiment, the outcoupling diffractive optical element 354 is a holographic diffractive element. The outcoupling diffractive optical element 354 is positioned to encounter the image-bearing light beam multiple times to provide an eyebox (E) expansion in one or more directions. For example, a change in refractive index along a single direction can expand one direction of the eyebox (E) by multiple encounters of individual angle-related beams with the outcoupling diffractive optical element 354 in the direction of propagation along the first planar waveguide 320.

[0046] The image light guide system 300A also includes an image beam source 400 that generates an image-bearing light beam 402. In an exemplary embodiment, the image beam source 400 is a picoprojector. For example, the image beam source 400 may be a picoprojector that generates a single primary color band (red, green, or blue wavelengths) of an image that is presented to a viewer looking generally along the z-axis direction through the image light guide system 300A. The image beam source 400 may be positioned such that the central ray of the projected image-bearing light beam 402 is generally perpendicular to the bottom surface 340 of the third planar waveguide 324 within five degrees (5°) of normal. The image beam source 400 may also be positioned such that the central ray of the projected image-bearing light beam 402 is not generally perpendicular to the bottom surface 340 of the third planar waveguide 324.

[0047] 15, in an exemplary embodiment, the image-bearing light beam 402 passes through the third planar waveguide 324 and the second planar waveguide 322 to the incoupling diffractive optical element 350 of the first planar waveguide 320, where a portion of the image-bearing light beam 402 is diffracted into the first planar waveguide 320 as an incoupling image-bearing light beam 404. The incoupling image-bearing light beam 404 propagates through the first planar waveguide 320 by total internal reflection (TIR) ​​between the upper planar surface 330 and the lower planar surface 332. The incoupling image-bearing light beam 404 may be redirected by the rotating grating 352 and may be replicated in at least one direction. The incoupled image-bearing light beam 404 may be replicated through multiple encounters with the outcoupling diffractive optical element 354 along a first direction, and the replicated image-bearing light beams may be directed from the first planar waveguide 320 by the outcoupling diffractive optical element 354 as outcoupling image-bearing light beams 406a, 406b, 406c, 406d, 406e (representing central rays of the outcoupling image-bearing light beams). This replication of the image-bearing light beam results in an expansion of the eyebox E in at least one dimension, reducing sensitivity to the viewer's eye position.

[0048] 15 , in one exemplary embodiment, the incoupling diffractive optical element 350 is a transmissive grating element. In another exemplary embodiment, the incoupling diffractive optical element 350 is positioned on the top planar surface 330 and is a reflective grating element. In one exemplary embodiment, a rotating grating 352 is positioned on the top planar surface 330. In one exemplary embodiment, an outcoupling diffractive optical element 354 is positioned on the top planar surface 330.

[0049] The second planar waveguide 322 includes an upper planar surface 334 and a parallel lower planar surface 336. The second planar waveguide 322 includes an incoupling diffractive optical element 360 located on the lower planar surface 336. The incoupling diffractive optical element 360 may be a surface relief grating. In another exemplary embodiment, the incoupling diffractive optical element 360 is a holographic grating. The second planar waveguide 322 may further include an intermediate optical element 362 operable to redirect and replicate the image-bearing light 394 along a first direction. The intermediate optical element 362 may also be referred to herein as a rotating optical element. In an exemplary embodiment, the rotating optical element 362 is a grating. The rotating optical element 362 may also be a holographic diffractive element. The second planar waveguide 322 may further include an outcoupling diffractive optical element 364. The outcoupling diffractive optical element 364 allows the light beam propagating within the second planar waveguide 322 to exit the second planar waveguide 322. For example, the outcoupling diffractive optical element 364 may be a diffraction grating or a hologram. The outcoupling diffractive optical element 364 may provide an expansion of the eyebox in one or more dimensions by providing one or more sets of periodic diffraction gratings of the outcoupling diffractive optical element 364 along one or more directions upon multiple encounters of the light beam 394.

[0050] The image light guide system 300A includes an image beam source 390 that generates an image-bearing light beam 392. For example, the image beam source 390 may be a picoprojector. In one exemplary embodiment, the image beam source 390 is a picoprojector that generates a single primary color band (red, green, or blue) of an image presented to a viewer looking through the planar waveguides 320, 322, 324 along an optical axis substantially parallel to the z-axis (e.g., along an optical axis substantially parallel to the z-axis). The image beam source 390 may be positioned such that a central ray of the projected image-bearing light beam 392 is substantially perpendicular (e.g., within five degrees (5°) of perpendicular) to the bottom surface 340 of the third planar waveguide 324. In another exemplary embodiment, the image beam source 390 is positioned such that a central ray of the projected image-bearing light beam 392 is not substantially perpendicular to the bottom surface 340 of the third planar waveguide 324.

[0051] The image-bearing light beam 392 passes through the third planar waveguide 324 to the lower planar surface 336 of the second planar waveguide 322, where the image-bearing light beam 392 is incoupled into the second planar waveguide 322 by the incoupling diffractive optical element 360 to become an incoupled light beam 394. The incoupled light beam 394 propagates through the second planar waveguide 322 by TIR between the upper planar surface 334 and the lower planar surface 336. The incoupled light beam 394 may be reoriented by the rotating grating 362 and replicated into multiple beams along at least one direction. The incoupled light beam 394 may be directed out of the planar waveguide 322 by outcoupling the outcoupling diffractive optical element 364 and replicated along at least one direction to become output beams 396a, 396b, 396c, 396d (representing the central ray of the outcoupled image-bearing light beam).

[0052] The incoupling diffractive optical element 360 may be a transmissive grating element. In another exemplary embodiment, the incoupling diffractive optical element 360 may be positioned on the top planar surface 334 and may be a reflective grating element. In one exemplary embodiment, the rotating grating 362 may be positioned on the top planar surface 334. In one exemplary embodiment, the outcoupling diffractive optical element 364 may be positioned on the top planar surface 334.

[0053] The third planar waveguide 324 has a parallel upper planar surface 338 and a parallel lower planar surface 340. The third planar waveguide 324 may further comprise an incoupling diffractive optical element 370 on the surface 340. For example, the incoupling diffractive optical element 370 may be a surface-relaxed diffraction grating or a holographic diffraction grating. The third planar waveguide 324 may include an intermediate diffractive optical element 372, also referred to herein as a rotating grating 372. For example, the rotating grating 372 may be a diffraction grating or a volume hologram. The rotating grating 372 may replicate the light beam traveling in the third planar waveguide 324 along one or more directions providing a dilation of the pupil or eyebox in one or more dimensions. The third planar waveguide 324 further comprises an outcoupling diffractive optical element 374. The outcoupling diffractive optical element 374 allows the light beam 384 propagating in the third planar waveguide 324 to exit the planar waveguide 324. For example, the outcoupling diffractive optical element 374 may be a diffraction grating or a volume hologram. The outcoupling diffractive optical element 374 may further provide eyebox expansion by replicating the light beam 384 as it propagates within the third planar waveguide 324 along one or more directions that provide pupil or eyebox expansion in one or more dimensions.

[0054] The image light guide system 300A further includes an image beam source 380 that generates an image-bearing light beam 382. For example, the image beam source 380 may be a picoprojector. In one exemplary embodiment, the image beam source 380 is a picoprojector that generates a single primary color band (red, green, or blue) of an image presented to an observer looking substantially along the z-axis direction through the planar waveguides 320, 322, 324. The image beam source 380 may also be positioned such that the central ray of the projected image-bearing light beam 382 is substantially perpendicular to the bottom surface 340 of the third planar waveguide 324. In another exemplary embodiment, the image beam source 380 may also be positioned such that the central ray of the projected image-bearing light beam 382 is not perpendicular to the bottom surface 340 of the third planar waveguide 324.

[0055] An image-bearing light beam 382 is incident on the bottom surface 340 of the third planar waveguide 324, and the image-bearing light beam 382 is incoupled by the incoupling diffractive optical element 370 to become an incoupled light beam 384. The incoupled light beam 384 propagates through the third planar waveguide 324 by TIR between the top planar surface 338 and the bottom planar surface 340. The incoupled light beam 384 may be reoriented by the rotating grating 372 and replicated along at least one direction. The incoupled light beam 384 may be directed out of the third planar waveguide 324 by the outcoupling diffractive optical element 374 and replicated along at least one direction to become output beams 386a, 386b, 386c, 386d, 386e (representing the central ray of the outcoupling image-bearing light beam).

[0056] In one exemplary embodiment, the incoupling diffractive optical element 370 may be a transmissive grating element. In another exemplary embodiment, the incoupling diffractive optical element 370 may be positioned on the top planar surface 338 and may be a reflective grating element. In one exemplary embodiment, a rotating grating 372 may be positioned on the top planar surface 338. In one exemplary embodiment, an outcoupling diffractive optical element 374 may be positioned on the top planar surface 338.

[0057] In some embodiments, the single primary wavelength band (red) may have a wavelength range from approximately 625 nm to approximately 740 nm, the single primary wavelength band (green) may have a wavelength range from approximately 500 nm to approximately 565 nm, and the single primary wavelength band (blue) may have a wavelength range from approximately 450 nm to approximately 485 nm.

[0058] In one exemplary embodiment of the image light guide system 300A, a first spacing 326 separates the first planar waveguide 320 from the second planar waveguide 322, and a second spacing 328 separates the second planar waveguide 322 from the third planar waveguide 324. In one exemplary embodiment, the spacings 326, 328 comprise substantially air. In another exemplary embodiment, the spacings 326, 328 comprise nitrogen. In another exemplary embodiment, the spacings 326, 328 comprise an inert gas. In yet another exemplary embodiment, the spacings 326, 328 comprise a material with a low refractive index, e.g., a material having a refractive index substantially equal to one.

[0059] FIG. 16 is a side view of an exemplary embodiment of an image light guide system 300B including a first planar waveguide 320, a second planar waveguide 322b, and a third planar waveguide 324b. Where elements of FIG. 16 correspond to similar elements of FIG. 15, such elements are generally referred to by similar reference numerals. The third planar waveguide 324b is positioned such that an image-bearing light beam 392 from an image beam source 390 does not pass through the third planar waveguide 324b. The second planar waveguide 322b is positioned such that an image-bearing light beam 402 from an image beam source 400 does not pass through the second planar waveguide 322b or the third planar waveguide 324b. In an exemplary embodiment, the length of the third planar waveguide 324b in the x-axis direction is less than the length of the second planar waveguide 322b in the x-axis direction. In an exemplary embodiment, the length of the second planar waveguide 322b in the x-axis direction is shorter than the length of the first planar waveguide 320 in the x-axis direction. Although not shown, in an exemplary embodiment, the planar waveguides 320, 322b, 324b are approximately the same length in the x-axis direction, and the second planar waveguide 322b and the third planar waveguide 324b include cutoffs that allow the image-bearing light beams 392, 402 to engage the incoupling optical elements 360, 350, respectively, without passing through the second planar waveguide 322b and the third planar waveguide 324b.

[0060] Figure 17 is a side view of an example embodiment of an image light guide system 300C including a first planar waveguide 320, a second planar waveguide 322, and a third planar waveguide 324. Where elements in Figure 17 correspond to similar elements in Figures 15 and 16, such elements are generally referred to by like reference numbers.

[0061] The image light guide system 300C includes an optical element 410 operable to redirect the image-bearing light beam 382 to the incoupling diffractive optical element 370 such that the image-bearing light beam 382 is directed towards the incoupling diffractive optical element 370 at a predetermined angle of incidence. In some embodiments, the image-bearing light beam 382 is directed towards the incoupling diffractive optical element 370 at a predetermined angle of incidence between 0 and 20 degrees with respect to an imaginary line along the path of the image-bearing light beam 382 between the projector 380 and the optical element 410.

[0062] In one exemplary embodiment, the redirection optics 410 comprises a prism. For example, the redirection optics 410 may be a prism assembly made up of one or more prisms. In one exemplary embodiment, the redirection optics 410 comprises a specular reflective surface, such as a mirror. For example, the redirection optics 410 may be a mirror assembly made up of one or more mirrors. In another embodiment, the redirection optics 410 may be an assembly of one or more prisms and one or more mirrors.

[0063] In an exemplary embodiment, the image light guide system 300C also includes an optical element 412 operable to redirect the image-bearing light beam 392 to the incoupling diffractive optical element 360 such that the image-bearing light beam 392 is directed toward the incoupling diffractive optical element 360 at a preferred angle of incidence. As shown in FIG. 17, the image-bearing light beam 392 must pass through or transmit through the waveguide 324 in its propagation toward the incoupling diffractive optical element 360. Because the refractive index of the waveguide 324 substrate is higher than the refractive index of the surroundings, the image-bearing light beam 392 refracts when transmitted through the waveguide 324. In an exemplary embodiment, the image-bearing light beam 392 has an angle of incidence on the incoupling diffractive optical element 360 of approximately 0°-20° relative to an imaginary line along the path of the image-bearing light beam 392 between the projector 390 and the optical element 412. In an exemplary embodiment, the image-bearing light beam 392 has an angle of incidence at an angle of approximately 5°. In another exemplary embodiment, the image-bearing light beam 392 has an angle of incidence of approximately 10°. In yet another exemplary embodiment, the image-bearing light beam 392 has an angle of incidence at an angle of approximately 15°.

[0064] In one exemplary embodiment, the redirection optics 412 comprises a prism. For example, the redirection optics 412 may be a prism assembly made up of one or more prisms. In one exemplary embodiment, the redirection optics 412 comprises a mirror. For example, the redirection optics 412 may be a mirror assembly made up of one or more mirrors. In another exemplary embodiment, the redirection optics 412 may be an assembly of one or more prisms and one or more mirrors.

[0065] In an exemplary embodiment, the image light guide system 300C also includes a redirection optical element 414 operable to redirect the image-bearing light beam 402 to the incoupling diffractive optical element 350 such that the image-bearing light beam 402 is directed toward the incoupling diffractive optical element 350 at a preferred angle of incidence. In an exemplary embodiment, the redirection optical element 414 comprises a prism. As shown in FIG. 17, the image-bearing light beam 402 must pass through or transmit through the waveguides 324 and 322 in its propagation toward the incoupling diffractive optical element 350. Because the refractive index of the waveguides 324 and 322 is higher than the refractive index of the surroundings, the image-bearing light beam 402 is refracted when transmitted through both waveguides 322, 324. In one exemplary embodiment, the image-bearing light beam 402 has an angle of incidence on the incoupling diffractive optical element 350 of approximately 0°-20° with respect to an imaginary line along the path of the image-bearing light beam 402 between the projector 400 and the optical element 414. In one exemplary embodiment, the image-bearing light beam 402 has an angle of incidence at an angle of approximately 5°. In another exemplary embodiment, the image-bearing light beam 402 has an angle of incidence at an angle of approximately 10°. In yet another exemplary embodiment, the image-bearing light beam 402 has an angle of incidence at an angle of approximately 15°. Furthermore, in some embodiments, the redirection optical element 414 may be a prism assembly comprised of one or more prisms. In one exemplary embodiment, the redirection optical element 414 comprises a mirror. For example, the redirection optical element 414 may be a mirror assembly comprised of one or more mirrors. In another exemplary embodiment, the redirection optical element 414 may be an assembly of one or more prisms and one or more mirrors.

[0066] In one exemplary embodiment, the redirection optical elements 410, 412, 414 are positioned so as not to be in direct mechanical contact with the surface 340 of the third planar waveguide 324. In another exemplary embodiment, the redirection optical elements 410, 412, and 414 indirectly contact the surface 340 of the third planar waveguide 324, for example, through one or more layers of index-matched or index-non-matched transparent or semi-transparent material.

[0067] In an exemplary embodiment, as shown in Figures 18-19B, the image light guide system 300D includes a first planar waveguide 320 and a second planar waveguide 322d disposed behind the second planar waveguide 320 in Figure 18. Where elements in Figure 18 correspond to similar elements in Figure 15, such elements are generally referred to by similar reference numerals. In an exemplary embodiment, the incoupling diffractive optical element 350 includes a grating feature 420 located on a surface 332 of the first planar waveguide 320. The grating feature 420 has a grating vector k3. The image light guide system 300D also includes an incoupling diffractive optical element 360 having a grating feature 422 located on a surface 336 of the second planar waveguide 322d. The grating feature 422 has a grating vector k2. The image light guide system 300D further includes an incoupling diffractive optical element 370 having a grating feature 424 located on a surface 336 of the second planar waveguide 322d. The grating feature 424 has a grating vector k1. In an exemplary embodiment, the incoupling diffractive optical element 370 is located on a surface 334 of the second planar waveguide 322d. The incoupling diffractive optical element 360 and the incoupling diffractive optical element 370 may be offset along the x-axis direction as shown in FIG. 19A, or may be substantially non-offset along the x-axis direction as shown in FIG. 18.

[0068] In an exemplary embodiment, the first planar waveguide 320 includes a first outcoupling diffractive optical element 354 having a grating vector k6 and operable to outcouple a portion of the image-bearing light beam propagating in the first planar waveguide 320. The second planar waveguide 322d includes a second outcoupling diffractive optical element 364 located on / in the surface 336 and having a grating vector k4. The second planar waveguide 322d also includes a third outcoupling diffractive optical element 374 located on / in the surface 334 and having a grating vector k5. In an exemplary embodiment, the combination of grating vectors ±k3, ±k4, ±k5 forms a triangle when placed tip to tail in a vector diagram. In an exemplary embodiment, the triangle is an equilateral triangle. In another exemplary embodiment, the triangle is an isosceles triangle. In yet another exemplary embodiment, the triangle is a scalene triangle. In an exemplary embodiment, the incoupling diffractive optical elements 350, 360, 370 are not aligned. For example, the incoupling diffractive optical elements 350, 360, 370 may not be aligned along the z-axis direction. In an exemplary embodiment, one or more of the grating vectors ±k1, ±k2, ±k3 are not parallel to each other.

[0069] 19A-19B, in-coupling diffractive optical element 350 is a transmissive grating element. In another exemplary embodiment, in-coupling diffractive optical element 350 is disposed on surface 330 and is a reflective grating element. In an exemplary embodiment, out-coupling diffractive optical element 354 is disposed on surface 330 and is a reflective grating element.

[0070] 20A-21B, in an exemplary embodiment, an image light guide system 600 includes a waveguide 602 having planar parallel surfaces 604, 606. The planar waveguide 602 includes a first incoupling diffractive optical element 610 located on, within, or engaged with the top planar surface 604, and a second incoupling diffractive optical element 612 located on, within, or engaged with the bottom planar surface 606. In an exemplary embodiment, the first incoupling diffractive optical element 610 is optimized to incoupling approximately a first half of the field of view (FOV - not shown) from the single color band pico projector 380, and the second incoupling diffractive optical element 612 is optimized to incoupling approximately a second half of the field of view from the single color band pico projector 380. In one exemplary embodiment, the angle between light beam 620 and light beam 622 after redirection by intermediate diffractive optical elements 614, 616, labeled α, is approximately thirty degrees (30°).

[0071] In FIG. 21A, image-bearing light 640a, 640b from projector 380 is incident on a first incoupling diffractive optical element 610 and a second incoupling diffractive optical element 612. The first incoupling diffractive optical element 610 is optimized to incoupling image-bearing light 640a corresponding to approximately a first half of the FOV of projector 380, and the second incoupling diffractive optical element 612 is optimized to incoupling image-bearing light 640b corresponding to approximately a second half of the FOV of projector 380. In some embodiments, each incoupling diffractive optical element 610, 612 may be optimized to incoupling image-bearing light representing more than half of the total FOV of the projector. For example, the first incoupling diffractive optical element 610 can be optimized for 60% of the FOV measured from a first side of the FOV of the projector 380, while the second incoupling diffractive optical element 612 can be optimized with a 20% overlap for 60% of the FOV measured from a second side of the FOV of the projector 380. This is one non-limiting example, but it should be understood that other amounts of overlap are acceptable, e.g., 10%, 15%, 20%, 25%, etc. Because the angular bandwidth and therefore the FOV supported by a given waveguide is a function of the pitch of the incoupling optics (as well as other factors such as, but not limited to, TIR conditions, waveguide thickness, and over-angle), the FOV cannot be increased by changing the area or footprint of the incoupling optics alone. Thus, by optimizing each incoupling diffractive optical element 610, 612 to support diffraction of image-bearing light corresponding to half the angular bandwidth of the full FOV, the waveguide 602 can support a wide FOV without increasing the thickness of the waveguide or modifying other factors of the waveguide.

[0072] As shown in FIGS. 21A-21B, a portion of the single-color band image-bearing light beam 640a from the wide-field pico-projector 380 is incoupled into the waveguide 602 by the first incoupling diffractive optical element 610 to become the first incoupled light 620. The first incoupled light 620 represents the image-bearing light in approximately half the field of view of the pico-projector 380. The waveguide 602 may include an intermediate diffractive optical element 614, also referred to herein as a rotating grating 614. For example, the rotating grating 614 may be a surface relief grating or a holographic optical element. The first incoupled light 620 is rotated by the first intermediate optical element 614. The first intermediate optical element 614 is positioned on, within, or otherwise engaged with the top surface 604 of the waveguide 602. The first intermediate optical element 614 may replicate the light beam traveling in the waveguide 602 along one or more directions providing pupil (eyebox) dilation in one or more dimensions. In an exemplary embodiment, the first intermediate optical element 614 does not provide any pupil dilation. Instead, the first intermediate optical element 614 may be utilized to redirect light from the first incoupling diffractive optical element 610 toward the first outcoupling diffractive optical element 630. In another exemplary embodiment, the first intermediate optical element 614 provides at least a minimal amount of pupil dilation in at least one dimension. The light beam 620 propagates in the waveguide 602 by TIR between the top planar surface 604 and the bottom planar surface 606 toward the first outcoupling diffractive optical element 630. The first outcoupling diffractive optical element 630 allows the light beam 620 to exit the planar waveguide 602. A first outcoupling diffractive optical element 630 may be positioned on, within, or otherwise engaged with the top surface 604 of the waveguide 602 .

[0073] Another portion of the single color band image-bearing light beam 640b from the wide field pico projector 380 is incoupled into the waveguide 602 by the second incoupling diffractive optical element 612 to become a second incoupled light 622. The second incoupled light 622 represents the image-bearing light of approximately the remaining half of the field of view of the pico projector 380. The waveguide 602 may include a second intermediate diffractive optical element 616, also referred to herein as a rotating grating 616. For example, the rotating grating 616 may be a surface relief grating or a holographic optical element. The second incoupled light 622 is rotated by the second intermediate optical element 616. The second intermediate optical element 616 is positioned on, within, or otherwise engaged with the bottom surface 606 of the waveguide 602. The second intermediate optical element 616 may replicate the light beam traveling within the waveguide 602 along one or more directions to provide pupil dilation in one or more dimensions.

[0074] In one exemplary embodiment, the second intermediate optical element 616 does not provide any pupil dilation. Instead, the second intermediate optical element 616 can be utilized to redirect light from the second incoupling diffractive optical element 612 toward the second outcoupling diffractive optical element 632. In another exemplary embodiment, the second intermediate optical element 616 provides a minimal amount of pupil dilation in at least one dimension. The light beam 622 propagates within the waveguide 602 by TIR between the top planar surface 604 and the bottom planar surface 606 toward the second outcoupling diffractive optical element 632. The second outcoupling diffractive optical element 632 allows the light beam 622 to exit the planar waveguide 602. The second outcoupling diffractive optical element 632 may be positioned on, within, or otherwise engaged with the bottom surface 606 of the waveguide 602. Importantly, as shown in FIG. 20A, the propagation direction of the first incoupled light 620 is orthogonal, i.e., rotated 90 degrees relative to the propagation direction of the second incoupled light 622. This configuration reduces crosstalk between the incoupled lights. Furthermore, in some examples, the intermediate rotating optical elements 614, 616 are configured to redirect these orthogonal portions of light 620, 622 without duplicating them, such that the incoupled portions of light 620, 622 are directed to the respective outcoupling diffractive optical elements 630, 632.

[0075] Furthermore, in an exemplary embodiment, neither the first intermediate optical element 614 nor the second intermediate optical element 616 provides pupil dilation. Rather, the first intermediate optical element 614 and the second intermediate optical element 616 direct diffracted image-bearing light towards the centers of the first outcoupling optical element 630 and the second outcoupling optical element 632. In such an embodiment, the first and second intermediate optical elements 614, 616 may be in close proximity to the first and second incoupling optical elements 610, 612, such that substantially all image-bearing light diffracted by either the first or second incoupling optical elements 610, 612 encounters either the first or second intermediate optical element 614, 616.

[0076] 20A and 21A, in an exemplary embodiment, the first incoupling optical element 610 includes a periodic linear grating structure 650 and the second incoupling optical element 612 includes a periodic linear grating structure 652 that is orthogonal to the periodic linear grating structure 650 and may have a different pitch compared to the periodic linear grating structure 650 of the first incoupling optical element 610. In an exemplary embodiment, to optimize the first incoupling optical element 610 and the second incoupling optical element 612 for incoupling image-bearing light representing respective halves of the projector's FOV, the pitch of the periodic linear grating structure 650 of the first incoupling optical element 610 is about 450 nm and the pitch of the periodic linear grating structure 652 of the second incoupling optical element 612 is about 350 nm. 20B and 20C, the periodic linear grating structure 650 of the first incoupling optical element 610 has the same pitch as the periodic linear grating structure 652 of the second incoupling optical element 612, and the periodic linear grating structure 650 is orthogonal (e.g., rotated 90 degrees) to the periodic linear grating structure 652. In other words, the first and second incoupling diffractive optical elements 610, 612 may have diffractive features with the same pitch, and the direction of periodicity of the diffractive features of the second incoupling diffractive optical element 612 is oriented at about 90 degrees (90 degrees) to the direction of periodicity of the diffractive structure of the first incoupling diffractive optical element 610 to reduce crosstalk.

[0077] The grating features of the first and second outcoupling optical elements 630, 632 may include compound grating features 634. In one exemplary embodiment, the compound grating features 634 of the first and second outcoupling optical elements 630, 632 include a plurality of posts having a regular variation in at least one of two or more directions. In another exemplary embodiment, the grating features 634 of the first and second outcoupling optical elements 630, 632 include diamond shaped posts.

[0078] As mentioned above, the pico projector 380 may have a wide field of view. In an exemplary embodiment, the pico projector 380 generates an image in a single waveband (e.g., red, green, or blue waveband) with a field of view of more than 30 degrees. In an exemplary embodiment, the pico projector 380 may have a field of view of greater than about 45 degrees. In an exemplary embodiment, the image light guide system 600 includes two pico projectors 380a, 380b, each providing about half of the field of view, as shown in FIG. 21B. As shown in FIG. 21B, the image-bearing light 640a from the projector 380a is incident on a first in-coupling diffractive optical element 610, providing image-bearing light representing a first half of the total field of view, and the image-bearing light 640b from the projector 380b is incident on a second in-coupling diffractive optical element 612, providing image-bearing light representing a second half of the total field of view.

[0079] The first outcoupling diffractive optical element 630 may be a surface relief grating or a holographic optical element and may provide pupil dilation in at least one dimension. The first outcoupling diffractive optical element 630 may provide pupil dilation in two orthogonal dimensions. In an exemplary embodiment, the first outcoupling diffractive optical element 630 may include crossed grating features. In another exemplary embodiment, the first outcoupling diffractive optical element 630 may include a first set of posts forming a 2D photonic crystal. For example, the first set of posts may be circular, elliptical, diamond, rectangular, hexagonal, octagonal, or other shapes. In another exemplary embodiment, the first outcoupling diffractive optical element 630 may include a grating structure having nonlinear and / or nonlinear grating features.

[0080] The second outcoupling diffractive optical element 632 may be a surface relief grating or a holographic optical element and may provide pupil dilation in at least one dimension. The second outcoupling diffractive optical element 632 may provide pupil dilation in two orthogonal dimensions. In an exemplary embodiment, the second outcoupling diffractive optical element 632 may include crossed grating features. In another embodiment, the second outcoupling diffractive optical element 632 may include a second set of posts forming a 2D photonic crystal. For example, the second set of posts may be circular, elliptical, diamond, rectangular, hexagonal, octagonal, or other shapes. In an exemplary embodiment, the second outcoupling diffractive optical element 632 may include a grating structure having nonlinear, nonlinear grating features.

[0081] 22A and 22B, in an exemplary embodiment, an image light guide system 700 includes a planar waveguide 702 having a first surface 704 and a second surface 706. The first surface 704 of the waveguide is positioned generally parallel to the second surface 706 of the waveguide. A first incoupling diffractive optical element 708 is located on, within, or otherwise engaged with the first surface 704, a second incoupling diffractive optical element 710 is located on, within, or otherwise engaged with the second surface 706, and a third incoupling diffractive optical element 712 is located on, within, or otherwise engaged with the second surface 706. The first, second, and third incoupling diffractive optical elements 708, 710, 712 are offset relative to one another along the y-axis direction.

[0082] A first intermediate diffractive optical element 714, also referred to herein as a rotating grating, is located on, within, or otherwise engaged with the first surface 704, and a second intermediate diffractive optical element 716 is located on, within, or otherwise engaged with the second surface 706, the second intermediate diffractive optical element being offset from the first intermediate diffractive optical element 714 at least along the y-axis. For example, the rotating grating 714 may be a surface relief grating or a holographic optical element.

[0083] The outcoupling diffractive optical element 730 is formed on, formed in, or otherwise engaged with the first surface 704. In an exemplary embodiment, the outcoupling diffractive optical element 730 is formed on, formed in, or otherwise engaged with the second surface 706. In an exemplary embodiment, the outcoupling diffractive optical element 730 is a surface relief grating. In another exemplary embodiment, the outcoupling diffractive optical element 730 is a holographic optical element. As shown in FIG. 22A, in an exemplary embodiment, the outcoupling diffractive optical element 730 includes a complex grating pattern having periodicity in more than one direction. For example, the outcoupling diffractive optical element 730 includes wavy diffractive features that generate periodicity in the k5 and k6 grating vector directions by a systematic deformation of the diffractive features in the y coordinate direction. In an exemplary embodiment, the systematic deformation of the diffractive features generates a sawtooth pattern. In another exemplary embodiment, the systematic variation of the diffractive features generates a sinusoidal pattern. In another exemplary embodiment, the diffractive features include a plurality of posts having a regular variation in at least one of two or more directions, as shown in FIG. 22C.

[0084] In one exemplary embodiment shown in Figures 22A-22B, a first wavelength range of image-bearing light 740A is incoupled by the first incoupling diffractive optical element 708 and propagates to the outcoupling diffractive optical element 730, where the image-bearing light 740A is diffracted via multiple encounters with composite diffraction grating patterns along two directions, expanding the eyebox in two dimensions (e.g., along the x and y directions) and outcoupling the image-bearing light 740A. The optical path of the first wavelength range of image-bearing light 740A is shown in the vector diagram in Figure 22D, where the sum of the grating vectors k0, k5, and k6 is approximately zero.

[0085] In an exemplary embodiment, the second wavelength range of image-bearing light 740B is incoupled by the second incoupling diffractive optical element 710 and propagates to the first intermediate diffractive optical element 714 where the image-bearing light 740B is directed to the outcoupling diffractive optical element 730. The optical path of the second wavelength range of image-bearing light 740B is shown in the vector diagram in Figure 22E, where the sum of the grating vectors k1, k3, and k6 is approximately zero.

[0086] Similarly, a third wavelength range of image-bearing light 740C is incoupled by the third incoupling diffractive optical element 712 and propagates to the second intermediate diffractive optical element 716 where image-bearing light 740B is directed to the outcoupling diffractive optical element 730. The optical path of the third wavelength range of image-bearing light 740C is shown in the vector diagram in Figure 22F, where the sum of grating vectors k2, k4, and k5 is approximately zero.

[0087] This arrangement allows the waveguide 702 to support three optical paths for three wavelength ranges or angular ranges of image-bearing light.

[0088] As the wavy pattern approaches from the direction of rotation, it appears to the approaching image-bearing light as a generally rectilinear grid pattern.

[0089] The perspective view shown in FIG. 23 illustrates an example of an image light guide system 50, 300A-D, 600, 700 in a display system 1000 for augmented reality display of virtual images. The image light guide system 50, 300A-D, 600, 700 uses one or more image light guides as described above. The display system 1000 is illustrated as an HMD having a right eye rim section 1012 with the image light guide system 50, 300A-D, 600, 700 proximate to a user's right eye. The display system 1000 includes an image source 16A, 16B, 380, 390, 400, such as a picoprojector or similar device, energizable to generate one or more virtual images that are communicated to the image light guide system 50, 300A-D, 600, 700. In an exemplary embodiment, the display system 1000 includes a left-eye rim section having an image light guide system 50, 300A-D, 600, 700 proximate to a user's left eye, and a second image source 16A, 16B, 380, 390, 400 energizable to generate one or more virtual images that are transmitted to the image light guide system 50, 300A-D, 600, 700 of the left-eye rim section. In an example using image light guide systems 50, 300A-D, 600, 700 in both the right-eye rim section 1012 and the left-eye rim section 700, the virtual images generated can be a stereoscopic image pair for a 3D display. During operation by a user or viewer, the virtual images formed by the display system 1000 can be seen superimposed or overlaid on real-world scene content viewed by the viewer through the image light guide systems 50, 300A-D, 600, 700 of the right-eye rim section 1012 and / or the left-eye rim section 1012. Additional components familiar to those skilled in the art of augmented reality visualization may also be provided, such as mounting one or more cameras on the frame of the display system 1000 for viewing scene content or tracking the viewer's gaze.

[0090] One or more features of the embodiments described herein may be combined to create additional embodiments not shown. Although various embodiments have been described in detail above, it should be understood that they are presented for illustrative purposes and not for limiting purposes. It will be apparent to those skilled in the relevant art that the subject matter of the present disclosure may be embodied in other specific forms, variations, and modifications without departing from its scope, spirit, or essential characteristics. The above-described embodiments are therefore to be considered in all respects as illustrative and not restrictive. The scope of the present invention is indicated by the appended claims, and all changes that come within the meaning and range of equivalents thereof are intended to be embraced therein.

Claims

1. 1. An image light guide system for conveying a virtual image, comprising: a first waveguide operable to propagate an image-bearing light beam; a first incoupling diffractive optical element formed along the first waveguide, the first incoupling diffractive optical element operable to diffract a first portion of the image-bearing light beam from the image source into the first waveguide in an angularly coded manner; a first outcoupling diffractive optical element formed along the first waveguide, the first outcoupling diffractive optical element operable to replicate the first portion of an image-bearing light beam in two directions and to direct the replicated first portion of the image-bearing light beam out of the first waveguide in an angularly decoded manner; a second incoupling diffractive optical element formed along the first waveguide, the second incoupling diffractive optical element operable to diffract a second portion of the image-bearing light beam from the image source into the first waveguide in an angularly coded manner; a second outcoupling diffractive optical element formed along the first waveguide, the second outcoupling diffractive optical element operable to replicate the second portion of the image-bearing light beam and direct the replicated image-bearing light beam out of the first waveguide in an angularly decoded manner; a second waveguide operable to propagate an image-bearing light beam; a third incoupling diffractive optical element formed along the second waveguide, the third incoupling diffractive optical element operable to diffract a third portion of the image-bearing light beam into the second waveguide in an angularly coded manner; and a third outcoupling diffractive optical element formed along the second waveguide, the third outcoupling diffractive optical element operable to replicate the third portion of the image-bearing light beam and direct the replicated image-bearing light beam out of the second waveguide in an angularly decoded manner; a fourth incoupling diffractive optical element formed along the second waveguide, the fourth incoupling diffractive optical element operable to diffract a fourth portion of the image-bearing light beam into the second waveguide in an angularly coded manner; and a fourth outcoupling diffractive optical element formed along the second waveguide, the fourth outcoupling diffractive optical element operable to replicate the fourth portion of an image-bearing light beam in two directions and direct the replicated image-bearing light beam out of the second waveguide in an angularly decoded manner.

2. 2. The image light guide system of claim 1, wherein the first waveguide is substantially parallel to the second waveguide along a first axis, and the first incoupling diffractive optical element and the third incoupling diffractive optical element are substantially coaxially positioned along a second axis that is substantially perpendicular to the first axis.

3. 3. The image light guide system of claim 2, wherein the second incoupling diffractive optical element and the fourth incoupling diffractive optical element are positioned substantially coaxially along the second axis that is substantially perpendicular to the first axis.

4. 2. The image light guide system of claim 1, wherein the first portion of the image-bearing light beam comprises image-bearing light of a first wavelength range and the second portion of the image-bearing light beam comprises image-bearing light of a second wavelength range, the second wavelength range being different from the first wavelength range.

5. 2. The image light guide system of claim 1, wherein a third portion of the image-bearing light beam comprises an image-bearing light in a third wavelength range, and a fourth portion of the image-bearing light beam comprises an image-bearing light in the second wavelength range.

6. 10. The image light guide system of claim 1, further comprising: a first image source operable to emit the first and third portions of an image-bearing light beam; and a second image source operable to emit the second and fourth portions of an image-bearing light beam.

7. 2. The image light guide system of claim 1, wherein the first incoupling diffractive optical element includes a first plurality of periodic diffractive structures, and the first outcoupling diffractive optical element includes a second plurality of periodic diffractive structures and a third plurality of periodic diffractive structures, the orientations of the second plurality of periodic diffractive structures being angularly offset by a polar angle of less than 30 degrees with respect to an axis perpendicular to the first plurality of periodic diffractive structures, and the orientations of the third plurality of periodic diffractive structures being angularly offset by a polar angle of more than 60 degrees with respect to the axis.

8. 8. The image light guide system of claim 7, wherein the first plurality of periodic diffractive structures comprises a first period, the second plurality of periodic diffractive structures comprises a second period, and the third plurality of periodic diffractive structures comprises a third period, the third period being substantially equal to the second period, and the second period being substantially equal to the first period.

9. The image light guide system of claim 8 , wherein the first period, the second period, and the third period are each greater than 50 nm.

10. 8. The image light guide system of claim 7, wherein the second incoupling diffractive optical element includes a fourth plurality of periodic diffractive structures, and the second outcoupling diffractive optical element includes a fifth plurality of periodic diffractive structures and a sixth plurality of periodic diffractive structures, the orientations of the fifth plurality of periodic diffractive structures being angularly offset by approximately thirty degrees (30°) relative to the second plurality of periodic diffractive structures, and the orientations of the sixth plurality of periodic diffractive structures being angularly offset by approximately thirty degrees (30°) relative to the third plurality of periodic diffractive structures.

11. 11. The image light guide system of claim 10, wherein the fourth plurality of periodic diffractive structures comprises a first period, the fifth plurality of periodic diffractive structures comprises a second period, and the sixth plurality of periodic diffractive structures comprises a third period, the third period being equal to the second period, and the second period being equal to the first period.

12. 12. The image light guide system of claim 11, wherein the first period, the second period, and the third period are each less than 50 nm.

13. 11. The image light guide system of claim 10, wherein the third incoupling diffractive optical element includes a seventh plurality of periodic diffractive structures and the third outcoupling diffractive optical element includes an eighth plurality of periodic diffractive structures and a ninth plurality of periodic diffractive structures, the orientations of the eighth plurality of periodic diffractive structures being angularly offset by a polar angle of less than 30 degrees with respect to an axis perpendicular to the seventh plurality of periodic diffractive structures and the orientations of the ninth plurality of periodic diffractive structures being angularly offset by a polar angle of more than 60 degrees with respect to an axis perpendicular to the seventh plurality of periodic diffractive structures.

14. 14. The image light guide system of claim 13, wherein the seventh plurality of periodic diffractive structures comprises a first period, the eighth plurality of periodic diffractive structures comprises a second period, and the ninth plurality of periodic diffractive structures comprises a third period, the third period being equal to the second period, and the second period being equal to the first period.

15. The image light guide system of claim 14 , wherein the first period, the second period, and the third period are each greater than 50 nm.

16. 14. The image light guide system of claim 13, wherein the fourth incoupling diffractive optical element includes a tenth plurality of periodic diffractive structures and the fourth outcoupling diffractive optical element includes an eleventh plurality of periodic diffractive structures and a twelfth plurality of periodic diffractive structures, the orientation of the eleventh plurality of periodic diffractive structures being angularly offset by approximately 30 degrees relative to the eighth plurality of periodic diffractive structures and the orientation of the twelfth plurality of periodic diffractive structures being angularly offset by approximately 30 degrees relative to the ninth plurality of periodic diffractive structures.

17. 17. The image light guide system of claim 16, wherein the tenth plurality of periodic diffractive structures comprises a first period, the eleventh plurality of periodic diffractive structures comprises a second period, and the twelfth plurality of periodic diffractive structures comprises a third period, the third period being equal to the second period, and the second period being equal to the first period.

18. 20. The image light guide system of claim 17, wherein the first period, the second period, and the third period are each less than 50 nm.

19. 10. The image light guide system of claim 1, further comprising a birefringent polarization control element located between the second incoupling diffractive optical element and the fourth incoupling diffractive optical element.

20. 7. The image light guide system of claim 6, wherein the first image source comprises a first projector operable to emit the first portion of an image-bearing light beam comprising image-bearing light in a first wavelength range and the third portion of an image-bearing light beam comprising image-bearing light in a second wavelength range different from the first wavelength range, and the second image source comprises a second projector operable to emit the second and fourth portions of image-bearing light comprising image-bearing light in a third wavelength range.

21. 21. The image light guide system of claim 20, wherein one of the first wavelength range and the second wavelength range includes wavelengths from 440 to 470 nm, the other of the first wavelength range and the second wavelength range includes wavelengths from 560 to 520 nm, and the third wavelength range includes wavelengths from 630 to 660 nm.

22. 1. An image light guide system for conveying a virtual image, comprising: a first waveguide operable to propagate an image-bearing light beam; a first incoupling diffractive optical element formed along the first waveguide, the first incoupling diffractive optical element operable to diffract a first portion of the image-bearing light beam from the image source into the first waveguide in an angularly coded manner; a first outcoupling diffractive optical element formed along the waveguide, the first outcoupling diffractive optical element operable to replicate the first portion of an image-bearing light beam in at least one direction and direct the replicated image-bearing light beam out of the first waveguide in an angularly decoded manner; a second waveguide operable to propagate an image-bearing light beam; a second incoupling diffractive optical element formed along the second waveguide, the second incoupling diffractive optical element operable to diffract a second portion of the image-bearing light beam into the second waveguide in an angularly coded manner; and a second outcoupling diffractive optical element formed along the second waveguide, the second outcoupling diffractive optical element operable to replicate the second portion of the image-bearing light beam in at least one direction and direct the replicated image-bearing light beam out of the second waveguide in an angularly decoded fashion; a third waveguide operable to propagate said image-bearing light beam; a third incoupling diffractive optical element formed along the third waveguide, the third incoupling diffractive optical element operable to diffract a third portion of the image-bearing light beam into the third waveguide in an angularly coded manner; and a third outcoupling diffractive optical element formed along the third waveguide, the third outcoupling diffractive optical element operable to replicate a third portion of an image-bearing light beam in at least one direction and direct the replicated image-bearing light beam out of the third waveguide in an angularly decoded manner.

23. a first intermediate diffractive optical element is located in the optical path between the first incoupling diffractive optical element and the first outcoupling diffractive optical element; a second intermediate diffractive optical element is located in the optical path between the second incoupling diffractive optical element and the second outcoupling diffractive optical element; 23. The image light guide system of claim 22, wherein a third intermediate diffractive optical element is disposed in the optical path between the third incoupling diffractive optical element and the third outcoupling diffractive optical element.

24. 23. The image light guide system of claim 22, wherein the third waveguide has a length shorter than both the second waveguide and the first waveguide, and the first portion of the image-bearing light beam does not pass through the second waveguide and the first waveguide to reach the first incoupling diffractive optical element.

25. 23. The image light guide system of claim 22, wherein the second waveguide has a length smaller than the first waveguide and greater than the third waveguide, and the second portion of the image-bearing light beam does not pass through the first waveguide or the third waveguide to reach the second incoupling diffractive optical element.

26. 23. The image light guide system of claim 22, further comprising a first optical element operable to redirect the first portion of an image-bearing light beam so that it strikes the first incoupling diffractive optical element at a predetermined angle of incidence.

27. 27. The image light guide system of claim 26, further comprising a second optical element operable to redirect the second portion of the image-bearing light beam so that it strikes the second incoupling diffractive optical element at a predetermined angle of incidence.

28. 28. The image light guide system of claim 27, further comprising a third optical element operable to redirect the third portion of the image-bearing light beam so that it strikes the third incoupling diffractive optical element at a predetermined angle of incidence.

29. 1. An image light guide system for conveying a virtual image, comprising: a first waveguide operable to propagate an image-bearing light beam; a first incoupling diffractive optical element formed along the first waveguide, the first incoupling diffractive optical element operable to diffract a first portion of the image-bearing light beam from the image source into the first waveguide in an angularly coded manner; a first outcoupling diffractive optical element formed along the first waveguide, the first outcoupling diffractive optical element operable to bidirectionally replicate the first portion of an image-bearing light beam and direct the replicated first portion of the image-bearing light beam out of the first waveguide in an angularly decoded manner; a second waveguide operable to propagate an image-bearing light beam; a second incoupling diffractive optical element formed along the second waveguide, the second incoupling diffractive optical element operable to diffract a second portion of the image-bearing light beam into the second waveguide in an angularly coded manner; and a second outcoupling diffractive optical element formed along the second waveguide, the second outcoupling diffractive optical element operable to replicate the second portion of the image-bearing light beam in two directions and direct the replicated image-bearing light beam out of the second waveguide in an angularly decoded manner; a third incoupling diffractive optical element formed along the second waveguide, the third incoupling diffractive optical element operable to diffract a third portion of the image-bearing light beam into the second waveguide in an angularly coded manner; and a third outcoupling diffractive optical element formed along the second waveguide, the third outcoupling diffractive optical element operable to replicate a third portion of the image-bearing light beam in two directions and direct the replicated image-bearing light beam out of the second waveguide in an angularly decoded fashion.

30. 30. The image light guide system of claim 29, further comprising a first optical element operable to redirect the first portion of an image-bearing light beam so that it strikes the first incoupling diffractive optical element at a predetermined angle of incidence.

31. 31. The image light guide system of claim 30, further comprising a second optical element operable to redirect the second portion of the image-bearing light beam so that it strikes the second incoupling diffractive optical element at a predetermined angle of incidence.

32. 32. The image light guide system of claim 31, further comprising a third optical element operable to redirect the third portion of the image-bearing light beam so that it strikes the third incoupling diffractive optical element at a predetermined angle of incidence.

33. 1. An image light guide system for conveying a virtual image, comprising: a waveguide operable to propagate an image-bearing light beam; a first incoupling diffractive optical element formed along the waveguide, the first incoupling diffractive optical element operable to diffract a first portion of an image-bearing light beam into the waveguide in an angularly coded manner; a first outcoupling diffractive optical element formed along the waveguide, the first outcoupling diffractive optical element operable to replicate the first portion of the image-bearing light beam in at least one direction and direct the replicated image-bearing light beam out of the waveguide in an angularly decoded manner; a second incoupling diffractive optical element formed along the waveguide, the second incoupling diffractive optical element operable to diffract a second portion of the image-bearing light beam into the waveguide in an angularly coded manner; and a second outcoupling diffractive optical element formed along the waveguide, the second outcoupling diffractive optical element operable to replicate the second portion of the image-bearing light beam in at least one direction and direct the replicated image-bearing light beam out of the waveguide in an angularly decoded manner.

34. a first intermediate diffractive optical element located in an optical path between the first incoupling diffractive optical element and the first outcoupling diffractive optical element; 34. The image light guide system of claim 33, comprising: a second intermediate diffractive optical element located in an optical path between the second incoupling diffractive optical element and the second outcoupling diffractive optical element.

35. 34. The image light guide system of claim 33, wherein the first portion of the image-bearing light beam diffracted by the first incoupling diffractive optical element is approximately a first half of the field of view of the image source, and the second portion of the image-bearing light beam diffracted by the second incoupling diffractive optical element is approximately a second half of the field of view of the image source.

36. 34. The image light guide system of claim 33, further comprising a first optical element interposed between the first incoupling optical element and at least one of the waveguides, the first optical element operable to redirect the first portion of the image-bearing light beam to strike the first incoupling diffractive optical element at a predetermined angle of incidence.

37. 34. The image light guide system of claim 33, wherein the first incoupling diffractive optical element includes a first plurality of periodic diffractive structures and the second incoupling diffractive optical element includes a second plurality of periodic diffractive structures that are orthogonal to the first plurality of periodic diffractive structures of the first incoupling diffractive optical element and have a different pitch.

38. 38. The image light guide system of claim 37, wherein the first outcoupling diffractive optical element includes a third plurality of periodic diffractive structures, the second outcoupling diffractive optical element includes a fourth plurality of periodic diffractive structures, and the third and fourth plurality of periodic diffractive structures are composite diffractive structures.

39. 40. The image light guide system of claim 38, wherein the compound diffractive structures are a plurality of posts having a regular variation in at least one of two or more directions.

40. 40. The image light guide system of claim 39, wherein the compound diffractive structures are a plurality of diamonds.

41. 1. An image light guide system for conveying a virtual image, comprising: a waveguide operable to propagate an image-bearing light beam; a first incoupling diffractive optical element formed along the waveguide, the first incoupling diffractive optical element operable to diffract a first portion of an image-bearing light beam into the waveguide in an angularly coded manner; a second incoupling diffractive optical element formed along the waveguide, the second incoupling diffractive optical element operable to diffract a second portion of the image-bearing light beam into the waveguide in an angularly coded manner; a third incoupling diffractive optical element formed along the waveguide, the third incoupling diffractive optical element operable to diffract a third portion of the image-bearing light beam into the waveguide in an angularly coded manner; a first outcoupling diffractive optical element formed along the waveguide, the first outcoupling diffractive optical element operable to replicate first, second and third portions of the image-bearing light beam in at least one direction and direct the replicated image-bearing light beam from the waveguide in an angularly decoded form.

42. a first intermediate diffractive optical element located in an optical path between the first incoupling diffractive optical element and the first outcoupling diffractive optical element; 42. The image light guide system of claim 41, wherein a second intermediate diffractive optical element is located in the optical path between the second incoupling diffractive optical element and the first outcoupling diffractive optical element.

43. 42. The image light guide system of claim 41, wherein the first outcoupling diffractive optical element comprises a compound diffractive structure having periodicity in two or more directions.

44. 44. The image light guide system of claim 43, wherein the compound diffractive structure is a wavy diffractive feature having a regular variation of the diffractive features in the y-axis direction.

45. 45. The image light guide system of claim 44, wherein the undulating diffractive features define a sawtooth pattern.

46. 45. The image light guide system of claim 44, wherein the wavy diffractive features define a sinusoidal pattern.

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