Image light guide with compact diffractive optical element

Abstract

an image light guide for conveying a virtual image comprising: a first surface and an opposing second surface; an incoupling diffractive optical element disposed on, within, or along one of the first and second surfaces, the incoupling diffractive optical element including a first set of diffractive features having a first grating vector; and an outcoupling diffractive optical element disposed on, within, or along at least one of the first and second surfaces, the outcoupling diffractive optical element comprising a first zone and a second zone, the first zone including one or more diffractive features different from those in the second zone, wherein the first zone of the outcoupling diffractive optical element includes a second set of diffractive features having a second grating vector and a third set of diffractive features having a third grating vector, the second grating vector having a magnitude greater than the third grating vector.

Description

[Technical Field]

[0001] The present disclosure relates generally to electronic display devices, and more particularly to optical image light guide systems having diffractive optical elements operable to transmit image-bearing light to a viewer. [Background technology]

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

[0003] In general, HMD / HUD optics must meet several basic requirements for viewer acceptance, including pupil size and field of view (FOV). Pupil size requirements are based on physiological differences in the viewer's facial structure and gaze direction during viewing. For many tasks and operations, a wide field of view is preferable. Additionally, the virtual image produced should have sufficient brightness for visibility and viewer comfort.

[0004] In addition to optical requirements, HMD / HUD designs must address practical factors such as an acceptable form factor, with expected reductions in size for weight, cost, and ease of use. Summary of the Invention

[0005] It is an object of the present disclosure to advance the technology of virtual image presentation using HMDs and HUDs. These and other aspects, objects, features, and advantages of the present invention will be more clearly understood and appreciated from the following detailed description of embodiments and appended claims, and by reference to the accompanying drawings. In an exemplary embodiment, the present disclosure provides an image light guide for conveying a virtual image, the image light guide including: a first surface and an opposing second surface; an incoupling diffractive optical element disposed on, within, or along one of the first and second surfaces, the incoupling diffractive optical element including a first set of diffractive features having a first grating vector; and an outcoupling diffractive optical element disposed on, within, or along at least one of the first and second surfaces, the outcoupling diffractive optical element comprising a first zone and a second zone, the first zone including one or more diffractive features different from those of the second zone. The first zone of the outcoupling diffractive optical element includes a second set of diffractive features having a second grating vector and a third set of diffractive features having a third grating vector, the second grating vector having a magnitude greater than the third grating vector.

[0006] In another exemplary embodiment, the present disclosure provides an image light guide including a first surface and an opposing second surface, an incoupling diffractive optical element disposed on, in, or along the first surface, an intermediate diffractive optical element disposed on, in, or along the first surface, and an outcoupling diffractive optical element disposed on, in, or along the second surface, the outcoupling diffractive optical element comprising a first zone and a second zone, the first zone including one or more diffractive features different from those of the second zone. In one example, the intermediate diffractive optical element at least partially overlaps with the first zone.

[0007] In another exemplary embodiment, the present disclosure provides an image light guide system including a first image light guide having a first surface and an opposing second surface, a first incoupling diffractive optical element disposed on, within, or along one of the first and second surfaces, and a first outcoupling diffractive optical element disposed on, within, or along at least one of the first and second surfaces, the first outcoupling diffractive optical element comprising a first zone and a second zone, the first zone including one or more diffractive features different from those of the second zone. The image light guide system further includes a second image light guide having a third surface and an opposing fourth surface, a second incoupling diffractive optical element disposed on, within, or along one of the third and fourth surfaces, and a second outcoupling diffractive optical element disposed on, within, or along at least one of the third and fourth surfaces, the second outcoupling diffractive optical element comprising a third zone and a fourth zone, the third zone including one or more diffractive features different from those of the fourth zone.

[0008] In another exemplary embodiment, the present disclosure provides an image light guide including a first surface and an opposing second surface; a first incoupling diffractive optical element disposed on, in, or along one of the first and second surfaces; a second incoupling diffractive optical element disposed on, in, or along one of the first and second surfaces; and an outcoupling diffractive optical element disposed on, in, or along at least one of the first and second surfaces, the outcoupling diffractive optical element comprising a first zone, a second zone, and a third zone, the first zone including one or more diffractive features different from the second zone and the third zone, and the third zone including one or more diffractive features different from the second zone and the first zone.

[0009] The accompanying drawings are incorporated herein as part of this specification. The drawings described herein illustrate embodiments of the disclosed subject matter and illustrate selected principles and teachings of the present disclosure. However, the drawings do not illustrate every possible implementation of the disclosed subject matter and are not intended to limit the scope of the present disclosure in any way. [Brief explanation of the drawings]

[0010] [Figure 1] FIG. 1 is a top view of an image light guide with an exaggerated thickness to illustrate the propagation of light from an image source along the image light guide to an eyebox within which a virtual image can be displayed. [Figure 2] FIG. 2 is a perspective view of an image light guide that includes an incoupling diffractive optical element, which is a rotating diffractive optical element, and an outcoupling diffractive optical element for managing the propagation of an image-bearing light beam. [Figure 3A] FIG. 3A shows a front elevation view of an image light guide according to an exemplary embodiment of the disclosed subject matter. [Figure 3B] FIG. 3B illustrates a front elevation view of an image light guide according to another exemplary embodiment of the disclosed subject matter. [Figure 3C] FIG. 3C is a rear elevational view of an embodiment of an image light guide according to FIG. 3B. [Figure 4A] FIG. 4A is a left side elevational view of an embodiment of an image light guide according to FIG. 3A, with an exaggerated thickness. [Figure 4B] FIG. 4B is a left side elevational view of another embodiment of an image light guide according to FIG. 3A, having an exaggerated thickness. [Figure 4C] FIG. 4C is a left side elevational view of an embodiment of an image light guide according to FIG. 3B with an exaggerated thickness. [Figure 5A] FIG. 5A is a plan view of an embodiment of an image light guide according to FIG. 3A, with an exaggerated thickness. [Figure 5B] FIG. 5B is a top view of an embodiment of an image light guide according to FIG. 3B, with an exaggerated thickness. [Figure 6A]FIG. 6A shows a top view of an embodiment of an image light guide system according to an exemplary embodiment of the presently disclosed subject matter, with an exaggerated thickness. [Figure 6B] FIG. 6B shows a top view of an embodiment of an image light guide system according to another exemplary embodiment of the presently disclosed subject matter, with an exaggerated thickness. [Figure 6C] FIG. 6C illustrates a front elevation view of the image light guide system shown in FIG. 6C, according to another exemplary embodiment of the disclosed subject matter. [Figure 7A] FIG. 7A shows a front elevation view of an image light guide according to another exemplary embodiment of the disclosed subject matter. [Figure 7B] FIG. 7B shows a front elevation view of an image light guide according to another exemplary embodiment of the disclosed subject matter. [Figure 8] FIG. 8 is a plan view of an embodiment of an image light guide according to FIG. 7, with an exaggerated thickness. DETAILED DESCRIPTION OF THE INVENTION

[0011] 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 accompanying drawings and described in the following specification are merely exemplary embodiments of the inventive concepts defined herein. Accordingly, specific dimensions, orientations, or other physical characteristics relating to the disclosed embodiments are not to be considered limiting unless expressly stated otherwise. Also, although not applicable, like elements in the various embodiments described herein may be generally referred to within this section of the specification using like reference numerals.

[0012] Those skilled in the relevant art(s) 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 are not shown or described in detail to avoid obscuring certain aspects of the disclosure. Throughout this specification, references to "one embodiment" or "embodiments" 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 phrases "in one embodiment" or "in an embodiment" throughout this specification do not necessarily refer to the same embodiment. However, particular features, structures, or characteristics described may be combined in any suitable manner in one or more embodiments.

[0013] As used herein, terms such as "first," "second," etc. do not necessarily imply any order, sequence, or priority relationship, but are merely used to more clearly distinguish one element or set of elements from another, unless otherwise specified.

[0014] As used herein, the terms "viewer," "operator," "observer," "wearer," and "user" are considered equivalent and refer to a person or machine wearing a device having an imaging light guide and / or viewing an image using a device having an imaging light guide.

[0015] 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 commonly understood in elementary mathematics. As used herein, the term "subset," unless explicitly stated otherwise, is used to refer to a non-empty proper subset, i.e., a subset of a larger set that has 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.

[0016] As used herein, the terms "coupled," "coupler," or "coupling" in the optical context refer to a connection in which light travels from one optical medium or device to another.

[0017] 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.

[0018] 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 the beam through multiple encounters with optical elements to provide an exit pupil expansion in one or more directions.

[0019] As used herein, the term "about" as applied to a value is intended to mean within the tolerance of the device used to generate the value, or in some examples, ±10%, or ±5%, or ±1%, unless expressly specified otherwise.

[0020] As used herein, the term "substantially" is intended to mean within the tolerances of the device used to generate the value, or in some embodiments, ±10%, or ±5%, or ±1%, unless expressly specified otherwise.

[0021] As used herein, the term "exemplary" is intended to mean "an example of," "serving as an example," or "illustrative," and does not imply any preference or requirement with respect to the disclosed aspects or embodiments.

[0022] Optical systems such as HMDs can generate virtual images. Unlike methods for forming real images, virtual images are not formed on a display surface. That is, when a display surface is positioned at the perceived location of the virtual image, no image is formed on the surface. Virtual images have many advantages unique to augmented reality displays. 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 systems that project real images, a more realistic viewing experience can be provided by forming a virtual image that appears to be at a certain distance. Providing a virtual image also eliminates the need to correct for screen artifacts, which may be required when projecting a real image.

[0023] FIG. 1 is a schematic diagram showing a simplified cross-sectional view of one conventional configuration of an image light guide system 10. The image light guide system 10 includes a planar image light guide 12, an incoupling diffractive optical element IDO, and an outcoupling diffractive optical element ODO. The image light guide 12 includes a transparent substrate S, which may be made of optical glass or plastic, having plane-parallel front and back surfaces 14 and 16. In this example, the incoupling diffractive optical element IDO is shown as a transmission grating disposed on, within, or otherwise engaged with the front surface 14 of the image light guide 12. However, the incoupling diffractive optical element IDO may alternatively be a reflection grating or other type of diffractive optical element (such as a volume hologram or other holographic diffractive element) that diffracts an incident image-bearing light beam WI into the image light guide 12. The incoupling diffractive optical element IDO is located on or within the front surface 14 or back surface 16 of the image light guide 12, or otherwise engages with the front surface 14 or back surface 16, and may be a combination of transmissive or reflective, depending on the direction from which the image-bearing light beam WI approaches the image light guide 12.

[0024] When used as part of a near-eye or head-mounted display system, the incoupling diffractive optical element IDO of conventional image light guide system 10 couples an image-bearing light beam WI from an image source 18 of a real, virtual, or hybrid image into the substrate S of the image light guide 12. Any real image or image dimension formed by the image source 18 is first converted into an array of overlapping, angle-related, collimated beams that encode different locations within the virtual image for presentation to the incoupling diffractive optical element IDO. Typically, the light rays in each bundle forming one of the angle-related beams extend parallel, but the angle-related beams are relatively oblique to one another through an angle that may be defined by two angular dimensions corresponding to the linear dimensions of the image.

[0025] When the angle-related beams engage the incoupling diffractive optical element IDO, at least a portion of the image-bearing light beam WI is diffracted (typically by a first diffraction order) and thereby redirected by the incoupling diffractive optical element IDO into the planar image light guide 12 as an angularly encoded image-bearing light beam WG for further propagation along the length dimension x of the image light guide 12 by total internal reflection (TIR) ​​between the plane-parallel front and back surfaces 14, 16. Although diffracted into different combinations of angle-related beams along the boundaries established by the TIR, the image-bearing light beam WG preserves the image information in an angularly encoded form derivable from the parameters of the incoupling diffractive optical element IDO. The outcoupling diffractive optical element ODO receives the encoded image-bearing light beam WG and diffracts at least a portion of the image-bearing light beam WG from the image light guide 12 as an image-bearing light beam WO (typically also by a first diffraction order) toward a nearby spatial region referred to as the eyebox E, within which a transmitted virtual image can be seen by a viewer's eye or other optical component. The outcoupling diffractive optical element ODO can be designed symmetrically with respect to the incoupling diffractive optical element IDO to restore the original angular relationship of the image-bearing light beam WI from between the output angularly related beams of the image-bearing light beam WO. Furthermore, the outcoupling diffractive optical element ODO can modify the angular relationship of the original field point positions to generate an output virtual image at a finite focusing distance.

[0026] However, to increase one dimension of overlap between the angle-related beams injected into the eyebox E (which defines the size of the area in which the virtual image can be seen), the outcoupling diffractive optical element ODO is positioned with the limited thickness T of the image light guide 12 to encounter the image-bearing light beam WG multiple times, diffracting only a portion of the image-bearing light beam WG at each encounter. The multiple encounters along the length (e.g., in the first direction) of the outcoupling diffractive optical element ODO have the effect of replicating the image-bearing light beam WG and expanding or widening at least one dimension of the eyebox E where the replicated beams overlap. The expanded eyebox E reduces the sensitivity to the position of the viewer's eyes for viewing the virtual image.

[0027] The outcoupling diffractive optical element ODO is shown as a transmissive diffraction grating disposed on or affixed to the front surface 14 of the image light guide 12. However, like the incoupling diffractive optical element IDO, the outcoupling diffractive optical element ODO may be located on, within, or otherwise engaged with the front surface 14 or back surface 16 of the image light guide 12, and may be a combination of transmissive and reflective types, depending on the direction in which the image-bearing light beam WG is intended to exit the image light guide 12. In addition, the outcoupling diffractive optical element ODO may be formed as another type of diffractive optical element, such as a volume hologram or other holographic diffractive element, which diffracts the image-bearing light beam WG propagating from the image light guide 12 as an image-bearing light beam WO propagating toward the eyebox E.

[0028] 2 shows a perspective view of a conventional image light guide system 10 arranged to expand the eyebox E in two dimensions, i.e., along both the x-axis and y-axis of the intended image. To achieve the second dimension of eyebox expansion, the incoupling diffractive optical element IDO is oriented to diffract at least a portion of the image-bearing light beam WG along its grating vector k1, along the image light guide 12, toward the intermediate rotation optical element TO, and its grating vector k2 is oriented to diffract at least a portion of the image-bearing light beam WG in a reflective mode, along the image light guide 12, toward the outcoupling diffractive optical element ODO. It should be appreciated that only a portion of the image-bearing light beam WG is diffracted by each of its multiple encounters with the intermediate rotation optical element TO, thereby laterally replicating each of the angularly related beams of the image-bearing light beam WG as it approaches the outcoupling diffractive optical element ODO. Before exiting the image light guide 12 as the image-bearing light beam WO, the intermediate rotating optical element TO redirects the image-bearing light beam WG towards the outcoupling diffractive optical element ODO (with grating vector k3) to longitudinally replicate an angularly related beam of the image-bearing light beam WG in a second direction. The grating vectors, such as the depicted grating vectors k1, k2, and k3, extend in respective directions perpendicular to the diffractive features (e.g., grooves, lines, or rulers) of the diffractive optical element in the parallel plane of the image light guide 12 and have inverse magnitude to the period or pitch d (i.e., the center-to-center distance between the diffractive features) of the diffractive optical elements IDO, TO, and ODO, respectively.

[0029] As shown in FIG. 2, the incoupling diffractive optical element IDO receives an incident image-bearing light beam WI, which includes a series of angularly related beams corresponding to individual pixels or equivalent locations in an image generated by an image source 18, such as a projector. The full range of angularly coded beams for generating a virtual image can be generated by a physical display device in combination with collimating or other optical components, by a beam scanner to more directly set the beam angle, or by a combination of a one-dimensional physical display device used with a scanner. In this configuration, the image light guide 12 outputs a series of replicated angularly related beams (replicated in two dimensions) by providing multiple encounters of the image-bearing light beam WG with both the intermediate rotation optical element TO and the outcoupling diffractive optical element ODO at different orientations. In the illustrated orientation of the image light guide 12, the intermediate rotation optical element TO provides eyebox expansion in a first direction, e.g., the y-axis direction, and the outcoupling diffractive optical element ODO provides a similar eyebox expansion in a second direction, e.g., the x-axis direction. The relative orientations and respective periods d of the diffractive features of the incoupling optical element IDO, the intermediate rotation optical element TO, and the outcoupling diffractive optical element ODO provide eyebox expansion in two dimensions while maintaining the intended relationship between the angularly related beams of the image-bearing light beam WI that are output from the image light guide system 10 as the image-bearing light beam WO. It will be appreciated that the periods d of the incoupling diffractive optical element IDO, the intermediate rotation optical element TO, and the outcoupling diffractive optical element ODO can each include diffractive features having a common pitch d, and the common pitch d of each optical element can be different.

[0030] In the illustrated configuration, the image-bearing light beam WI input to the image light guide 12 is encoded into a series of different angle-related beams by the incoupling diffractive optical element IDO, but the information necessary to reconstruct the image is preserved by considering the systematic effects of the incoupling diffractive optical element IDO. The intermediate rotation optical element TO, located at an intermediate position between the incoupling diffractive optical element IDO and the outcoupling diffractive optical element ODO, can be positioned so as not to induce any significant changes to the encoding of the image-bearing light beam WG. Therefore, the outcoupling diffractive optical element ODO can be positioned symmetrically with respect to the incoupling diffractive optical element IDO, for example, including diffractive features that share the same period d. Similarly, the period of the intermediate rotation optical element TO can also match the common period of the incoupling diffractive optical element IDO and the outcoupling diffractive optical element ODO. Although the grating vector k2 of the intermediate rotation optical element TO is shown oriented at 45 degrees relative to the other grating vectors, with possible orientations maintained, the grating vector k2 of the intermediate rotation optical element TO can be oriented at 60 degrees relative to the grating vectors k1 and k3 of the incoupling and outcoupling diffractive optical elements IDO and ODO, such that the image-bearing light beam WG is rotated by 120 degrees. By orienting the grating vector k2 of the intermediate rotation optical element TO at 60 degrees relative to the grating vectors k1 and k3 of the incoupling and outcoupling diffractive optical elements IDO and ODO, the grating vectors k1 and k3 of the incoupling and outcoupling diffractive optical elements IDO and ODO are also oriented at 60 degrees relative to each other. Using the common pitch of the incoupling diffractive optical element IDO, the intermediate rotation diffractive optical element TO, and the outcoupling diffractive optical element ODO as the basis for the magnitude of the grating vectors, the three grating vectors k1, k2, and k3 (as directed line segments) form an equilateral triangle and sum to a zero vector magnitude, thereby avoiding asymmetric effects that may result in undesirable aberrations, including chromatic dispersion. Such asymmetric effects can also be avoided by having the grating vectors k1, k2, and k3 have unequal magnitudes in their relative orientations, such that the sum of the three grating vectors k1, k2, and k3 has a zero vector magnitude.

[0031] In a broader sense, the image-bearing light beam WI directed into the image light guide 12 is effectively encoded by the incoupling diffractive optical element IDO, regardless of whether the incoupling optics IDO uses a grating, hologram, prism, mirror, or some other mechanism. Light reflection, refraction, and / or diffraction occurring at the input should be decoded accordingly by the output to recreate the virtual image presented to the viewer. It may be relevant whether any symmetry is maintained between the intermediate rotation optical element TO, the incoupling optics IDO, and the outcoupling diffractive optical element ODO, or whether changes to the angle-related beam encoding of the image-bearing light beam WI occur along the image light guide 12, the intermediate rotation optical element TO, the incoupling diffractive optical element IDO, and the outcoupling diffractive optical element ODO, so that the image-bearing light beam WO output from the image light guide 12 retains or otherwise maintains the original or desired form of the image-bearing light beam WI to generate the intended virtual image.

[0032] As shown in FIG. 2 , the letter “R” represents the orientation of the virtual image as seen by a viewer with their eyes positioned within the eyebox E. 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 beam WI. A change in rotation about the z-axis or angular orientation of the incident image-bearing light beam WI relative 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 image orientation perspective, the intermediate rotation optical element TO simply acts as a type of optical relay, providing one-dimensional eyebox expansion through angle-encoded beam replication of the image-bearing light beam WG along one axis of the image (e.g., along the y-axis). The outcoupling diffractive optical element ODO further provides a second dimension of eyebox expansion through angle-encoded beam replication along another axis (e.g., along the x-axis) while maintaining the original orientation of the virtual image encoded by the image-bearing light beam WI. The intermediate rotating optical element TO is typically a tilted or square grating, or alternatively may be a blazed grating, and is typically disposed on one of the plane-parallel front and back surfaces of the image light guide 12. Of course, the representation of the virtual image "R" created by the image source consists of light focused at infinity, which requires a lens (e.g., the lens of the human eye) to focus the image so that the orientation discussed above can be detected.

[0033] Collectively, the incoupling diffractive optical element IDO, the rotating diffractive optical element TO, and the outcoupling diffractive optical element ODO preferably preserve the angular relationships between the beams of different wavelengths that define the virtual image upon transport from an offset position to a near-eye position of the viewer by the image light guide 12. Meanwhile, the incoupling diffractive optical element IDO, the rotating diffractive optical element TO, and the outcoupling diffractive optical element ODO can be positioned and oriented relative to one another in different ways to control the overall shape of the image light guide 12 and the overall orientation at which angularly related beams can be directed into and out of the image light guide 12.

[0034] FIG. 3A shows an exemplary embodiment of an image light guide 102 according to the present disclosure. In the exemplary embodiment, the image light guide 102 includes an at least partially transparent substrate S (see FIGS. 4A-4C) and has plane-parallel front and back surfaces 104 and 106 (also shown in FIGS. 4A-4C). For example, the image light guide 102 may be made of optical glass, fused silica, or a polymer. The image light guide 102 includes at least one incoupling diffractive optical element IDO and at least one outcoupling diffractive optical element ODO. In one example, as shown in FIGS. 3A, 3B, 4A, and 4C, the incoupling diffractive optical element IDO is disposed on the back surface 106 (shown by the dashed lines in FIGS. 3A and 3B), and the outcoupling diffractive optical element ODO is disposed on the front surface 104. In another example, the incoupling diffractive optical element IDO is disposed on the front surface 104, and the outcoupling diffractive optical element ODO is disposed on the back surface 106. In yet another embodiment, as shown in FIG. 4B , the incoupling diffractive optical element IDO and the outcoupling diffractive optical element ODO are disposed on the front surface 104. As shown in FIGS. 3A-3C, 5A, and 5B , in an exemplary embodiment, the outcoupling diffractive optical element ODO substantially spans the width of the image light guide 102 in the x-direction. For example, the outcoupling diffractive optical element ODO can span at least 90% of the width of the image light guide 102. In another example, the outcoupling diffractive optical element ODO may span at least 95% of the width of the image light guide 102.

[0035] 3A, in one embodiment, the incoupling diffractive optical element IDO is disposed on the back surface 106 (shown in dashed lines) and includes a diffractive pattern 108. The diffractive pattern 108 includes a plurality of diffractive features that are periodic in at least a first direction defined by grating vectors ±k1. For example, the diffractive pattern 108 may include, but is not limited to, linear diffractive features, such as a surface relief grating. Although other shapes are possible, the image light guide 102 is generally shaped as a rectangle having a portion extending in the y-direction (e.g., a dog's leg), with the incoupling diffractive optical element IDO disposed in the portion extending in the y-direction and the outcoupling diffractive optical element ODO disposed in the main body of the rectangular portion.

[0036] 3A , in an exemplary embodiment, the outcoupling diffractive optical element ODO is disposed on the front surface 104 and includes at least two zones of diffractive features, e.g., a first zone 112 and a second zone 114 of diffractive features. The outcoupling diffractive optical element ODO, including the first zone 112 and the second zone 114, includes a generally rectangular geometric shape having a first side 116A, a second side 116B, a third side 116C, and a fourth side 116D. The sides 116A, 116B, 116C, and 116D may also be referred to herein as “edges.” The first side 116A and the third side 116C extend substantially along the y-direction, and the second side 116B and the fourth side 116D extend substantially along the x-direction. In the exemplary embodiment, the first zone 112 defines a generally trimmed triangular shape and is generally disposed within the outcoupling diffractive optical element ODO and below the incoupling diffractive optical element IDO in the -y-direction. For example, the first zone 112 is bounded by: i) a first side 116A extending substantially along the y-direction; ii) a portion of a second side 116B extending substantially along the x-direction beyond the width of the incoupling diffractive optical element IDO; iii) an imaginary line 117 formed as a dividing line between the first zone 112 and the second zone 114 and oriented at an angle θ with respect to the second side 116B of the outcoupling diffractive optical element ODO; and iv) a portion of a fourth side 116D extending substantially along the x-direction between the imaginary line 117 and the first side 116A. It will be appreciated that the imaginary line 117 dividing the first zone 112 and the second zone 114 in the outcoupling diffractive optical element ODO extends from a position along the second side 116B closer to the first side 116A than to the third side 116C, and terminates at a position along the fourth side 116D closer to the third side 116C than to the first side 116A. The angle θ at which the imaginary line 117 defining the boundary / edge of the first zone 112 is oriented may be selected to coincide with the FOV angle of the image-bearing light beam coupled into the image light guide 102 by interaction with the incoupling diffractive optical element IDO.In other words, in the exemplary embodiment, the first zone 112 is configured so that substantially all of the light coupled into the image light guide 102 by interaction with the incoupling diffractive optical element IDO is incident on the first zone 112. In the exemplary embodiment shown in Figures 3B and 3C (described below), the angle θ at which the imaginary line 117 defining the boundary / edge of the first zone 112 is oriented may be selected to match the FOV angle of the light beam coupled into the image light guide 102 by interaction with the incoupling diffractive optical element IDO, although the intermediate diffractive optical element TO may prevent the incidence of a portion of the light coupled into the image light guide 102 on the first zone 112.

[0037] In one example, the second zone 114 of the outcoupling diffractive optical element ODO is positioned adjacent to the first zone 112 in the x-axis direction. In an exemplary embodiment, the first zone 112 includes a first set of diffractive features 118A and a second set of diffractive features 118B (collectively referred to herein as “diffractive features 118”), where the first set of diffractive features 118A at least partially overlap the second set of diffractive features 118B. In some examples, the diffractive features 118 of the first zone 112 approximate linear diffractive features. For example, diffractive feature 118A is oriented parallel to the y-direction and has grating vectors ±k3, and diffractive feature 118B is oriented at an angle α relative to diffractive feature 118A and has grating vectors ±k2. In another example, the diffractive features 118 may include generally diamond-shaped posts with grating vectors ±k2, ±k3. In an exemplary embodiment, the second zone 114 includes a plurality of diffractive features 120, which approximate linear diffractive features oriented parallel to the y-direction and also have grating vectors ±k3. For example, the diffractive features 120 may have substantially the same pitch d and orientation as the diffractive features 118A. In one example, the grating vectors ±k2 of the diffractive features 118B are oriented at an angle less than 60 degrees (e.g., α<60 degrees) relative to the grating vectors ±k1 of the incoupling diffractive optical element IDO. Furthermore, the first zone 112 of the outcoupling diffractive optical element IDO is asymmetrically (i.e., asymmetrically) positioned around the grating vectors ±k1 of the incoupling diffractive optical element IDO. In other words, the grating vectors ±k2 have a larger magnitude than the grating vectors ±k3, creating a grating vector diagram that sums to zero in the shape of a scalene or isosceles triangle (i.e., a non-equilateral triangle).

[0038] When designing an intermediate diffractive optical element, the optical element can be utilized as an “even” or “odd” coupling optical element. Because the diffractive features of an intermediate diffractive optical element are typically parallel to one another, non-zero diffraction orders of incident light have an angular deviation from the original direction of propagation of the incident light ray. However, upon a second interaction with an additional diffractive feature, or any even interaction, the non-zero diffraction orders of that light diffract and become parallel again to the direction of propagation of the incident light. Therefore, any design that optimizes the utilization of a light beam exiting the optical element in the same direction as its original direction of propagation utilizes even interactions, resulting in light exiting the optical element in the same direction as the direction of propagation of the original incident light ray. Conversely, any design that optimizes the utilization of a light beam exiting the optical element in a direction different from the original direction of propagation of the incident light has utilized odd interactions with diffractive features.

[0039] 3A , in an exemplary embodiment, the first zone 112 of the outcoupling diffractive optical element ODO is a compound diffractive optical element having two grating vectors ±k2 and ±k3. The first zone 112 of the outcoupling diffractive optical element ODO is positioned to diffract and replicate (along the −y direction) a set of angularly associated image-bearing light beams coupled into the image light guide 102 by interaction with the incoupling diffractive optical element IDO, and to propagate a set of angularly associated image-bearing light beams in the x-direction toward the second zone 114. For example, as the coupled image-bearing light propagates through the diffractive features 118 of the first zone 112, a portion of the image-bearing light that is incident on and diffracted by diffractive feature 118B is diffracted along the direction of grating vector k3 for every odd-numbered interaction with diffractive feature 118B and along the direction of grating vector k1 for every even-numbered interaction with diffractive feature 118B. Furthermore, during propagation of image-bearing light through first zone 112, a portion of the image-bearing light is outcoupled and propagates toward the eyebox for each even or odd number of interactions with diffractive features 118. Image-bearing light that interacts with diffractive features 118 an odd number of times propagates via TIR toward second zone 114. In an exemplary embodiment, first zone 112 is positioned to diffract and propagate a greater portion of the image-bearing light toward second zone 114 than the portion of the image-bearing light that was outcoupled through first zone 112. In this manner, first zone 112 is configured to perform the functions of an intermediate diffractive optical element as well as an outcoupling diffractive optical element.

[0040] 3B and 3C , in another exemplary embodiment, the image light guide 102 includes a separate or distinct intermediate diffractive optical element TO disposed on the back surface 106 opposite the outcoupling diffractive optical element ODO. For example, the intermediate diffractive optical element TO is similar in shape to the first zone 112 of the outcoupling diffractive optical element ODO, and the intermediate diffractive optical element TO at least partially overlaps with the outcoupling diffractive optical element ODO. In some embodiments, the area of ​​the intermediate diffractive optical element TO is larger than the area of ​​the first zone 112. In one embodiment, the intermediate diffractive optical element TO extends in the x-direction beyond the edge 116A of the first zone 112, and the intermediate diffractive optical element TO extends in the y-direction beyond the area covered by the outcoupling diffractive optical element ODO toward the incoupling diffractive optical element IDO. The intermediate diffractive optical element TO includes a plurality of diffractive features 122 disposed parallel to the diffractive features 118B of the first zone 112, and the diffractive features 122 may also be represented by grating vectors ±k2.

[0041] In the exemplary embodiment, the pitch d1 of diffractive features 118B and the pitch d1 of diffractive features 122 are smaller than the pitch d1 of diffractive features 118A and the pitch d1 of diffractive features 120. For example, the pitch d1 of diffractive features 118B is substantially equal to the pitch d1 of diffractive features 122, and the pitch d of diffractive features 118A is substantially equal to the pitch d1 of diffractive features 120. In the exemplary embodiment, the sum of the grating vectors ±k1, ±k2, and ±k3 is zero, but a decrease in the pitch d1 of diffractive features 118B, 122 (i.e., a larger magnitude of grating vector ±k2) creates an asymmetry about the grating vector ±k1. A decrease in the pitch d1 of diffractive features 118B, 122 (i.e., a larger magnitude of grating vector ±k2) facilitates rotation of image-bearing light through an angle greater than 90 degrees. In exemplary embodiments, the diffractive features 118B, 122 rotate at least a portion of the image-bearing light by an angle greater than 120 degrees. In these examples, the addition of a separate or discrete intermediate diffractive optical element TO disposed on or within the back surface 106 operates to increase the ability to rotate or direct the image-bearing light towards the second zone 114 for outcoupling.

[0042] 5A and 5B, in an exemplary embodiment, image light guide 102 generates an eyebox E large enough to span a user's interpupillary distance. For example, both of a user's eyes may simultaneously receive image-bearing light from eyebox E. However, image light guide 102 may also be sized for use in a monocular or binocular arrangement with one or more image light guides utilized to convey virtual images to the user's eyes. It is an advantage of the presently disclosed subject matter that image light guide 102 provides an outcoupling diffractive optical element (ODO) substantially throughout the entire x-direction of image light guide 102 operable to output image-bearing light substantially uniformly across a large exit pupil E. In the exemplary embodiment shown in FIG. 3A, this uniformity is achieved, at least in part, via a first zone 112 of outcoupling diffractive optical element (ODO), represented by grating vectors ±k2 and ±k3. In the exemplary embodiment shown in FIGS. 3B-3C, this uniformity is further improved, at least in part, via an intermediate diffractive optical element (TO), represented by grating vectors ±k2. Another advantage of the present disclosure is that it provides a large exit pupil E with a compact light path within the image light guide 102.

[0043] In an exemplary embodiment, the image light guide 102 transmits image-bearing light in a first wavelength range (e.g., green light in the range of 520-560 nm) to the eye box E. Referring now to FIG. 6A , in an exemplary embodiment, the second image light guide 102 may transmit polychromatic light to the eye box E, with the first image light guide 102 provided within the waveguide stack of the image light guide system. For example, the first image light guide 102 may be optimized to transmit a second wavelength range (e.g., red light in the range of 630-660 nm) and the second image light guide 102 may be optimized to transmit a third wavelength range (e.g., blue light in the range of 440-470 nm), where image-bearing light in the first wavelength range (e.g., green light in the range of 520-560 nm) is transmitted by both the first image light guide and the second image light guide 102. In an exemplary embodiment, as shown in FIG. 6A, the incoupling diffractive optical element IDO of the first image light guide 102 and the incoupling diffractive optical element IDO of the second image light guide are arranged coaxially around an imaginary axis 132 oriented perpendicular to the first surface 104.

[0044] 6B and 6C, in an exemplary embodiment, the second image light guide 102 may be oriented relative to the first image light guide 102 such that the incoupling diffractive optical element IDO is oriented in the x-direction opposite the imaginary axis 130 (shown in FIG. 6C). For example, the second image light guide 102 includes all of the elements and features of the first image light guide 102, with the features of the second image light guide 102 positioned such that they are mirrored in the x-direction across the imaginary axis 130. In an exemplary embodiment, as shown in FIGS. 6B and 6C, the incoupling diffractive optical element IDO of the first image light guide 102 is positioned about a first imaginary axis 132 oriented perpendicular to the first surface 104, and the incoupling diffractive optical element IDO of the second image light guide 102 is positioned about a second imaginary axis 134 oriented perpendicular to the first surface 104, with the first imaginary axis 132 and the second imaginary axis 134 oriented parallel.

[0045] It should be appreciated that in some exemplary embodiments, the image light guide 102 design described above essentially forms one half of a larger image light guide 202, such that the larger image light guide 202 can receive multiple inputs from one or more projectors or other illumination sources. As shown in FIG. 7A , in exemplary embodiments, the image light guide 202 includes separate or discrete intermediate diffractive optical elements TO1, TO2 disposed on a rear surface 106 (shown in dashed lines) opposite the outcoupling diffractive optical element ODO. As shown in FIG. 7B , in exemplary embodiments, the image light guide 202 does not include separate or discrete intermediate diffractive optical elements TO1, TO2. Referring now to FIGS. 7A-8 , in which like reference characters indicate like elements described above, in exemplary embodiments, the image light guide 202 includes an at least partially transparent substrate having parallel front and rear surfaces 104, 106. For example, the image light guide 202 may be made of optical glass, fused silica, or a polymer. The image light guide 202 includes a first incoupling diffractive optical element IDO1, a second incoupling diffractive optical element IDO2, and at least one outcoupling diffractive optical element ODO. In one embodiment, the incoupling diffractive optical elements IDO1, IDO2 are disposed on the back surface 106, and the outcoupling diffractive optical element ODO is disposed on the front surface 104. In another embodiment, the incoupling diffractive optical elements IDO1, IDO2 are disposed on the front surface 104, and the outcoupling diffractive optical element ODO is disposed on the back surface 106. In yet another embodiment, the incoupling diffractive optical elements IDO1, IDO2 and the outcoupling diffractive optical element ODO are disposed on the front surface 104. In an exemplary embodiment, the outcoupling diffractive optical element ODO substantially spans the width of the image light guide 202 in the x-direction. For example, the outcoupling diffractive optical element ODO can span at least 90% of the width of the image light guide 202. In another embodiment, the outcoupling diffractive optical element ODO may span at least 95% of the width of the image light guide 202.

[0046] The first incoupling diffractive optical element IDO1 includes a plurality of diffractive features 108 that are periodic in at least a first direction defined by grating vectors ±k1. For example, the diffractive features 108 may include linear diffractive features, e.g., surface relief gratings. The second incoupling diffractive optical element IDO2 includes a plurality of diffractive features 208 that are periodic in at least a first direction defined by grating vectors ±k4. For example, the diffractive features 208 may include linear diffractive features, e.g., surface relief gratings. Although other shapes are possible, the image light guide 202 is generally formed as a rectangle having two portions (e.g., doglegs) extending in the y-direction, with the incoupling diffractive optical elements IDO1, IDO2 disposed in each portion extending in the y-direction and the outcoupling diffractive optical element ODO disposed in the main body of the rectangular portion.

[0047] In the exemplary embodiment, the outcoupling diffractive optical element ODO is disposed on the front surface 104 and includes at least three zones of diffractive features, e.g., a first zone 112, a second zone 114, and a third zone 212 of diffractive features. The outcoupling diffractive optical element ODO, including the first zone 112, the second zone 114, and the third zone 212, includes a generally rectangular geometric shape having a first side 116A, a second side 116B, a third side 116C, and a fourth side 116D. The sides 116A, 116B, 116C, and 116D may also be referred to herein as "edges." The first side 116A and the third side 116C extend substantially along the y-direction, and the second side 116B and the fourth side 116D extend substantially along the x-direction.

[0048] In the exemplary embodiment, the first zone 112 generally defines a trimmed triangular shape and is positioned in the -y direction within the outcoupling diffractive optical element ODO and generally below the first incoupling diffractive optical element IDO1, while the third zone 212 generally defines a trimmed triangular shape and is positioned in the -y direction within the outcoupling diffractive optical element ODO and generally below the second incoupling diffractive optical element IDO2. For example, the first zone 112 is bounded by: i) a first side 116A extending substantially along the y-direction; ii) a portion of the second side 116B extending substantially in the x-direction beyond the width of the first incoupling diffractive optical element IDO1 along the x-direction; iii) an imaginary line 117 formed as a dividing line between the first zone 112 and the second zone 114 and oriented at an angle θ relative to the second side 116B of the outcoupling diffractive optical element ODO; and iv) a portion of the fourth side 116D extending substantially along the x-direction between the imaginary line 117 and the first side 116A. It will be appreciated that the imaginary line 117 dividing the first zone 112 and the second zone 114 in the outcoupling diffractive optical element IDO1 extends from a position along the second side 116B closer to the first side 116A than the third side 116C, and terminates at a position along the fourth side 116D closer to the third side 116C than the first side 116A. The angle θ at which the imaginary line 117 defining the boundary / edge of the first zone 112 is oriented may be selected to coincide with the FOV angle of the image-bearing light beam coupled into the image light guide 102 by interaction with the first incoupling diffractive optical element IDO1. In other words, in the exemplary embodiment, the first zone 112 is configured so that substantially all light coupled into the image light guide 102 by interaction with the first incoupling diffractive optical element IDO1 is incident on the first zone 112.In an exemplary embodiment, the angle θ at which the imaginary line 117 defining the boundary / edge of the first zone 112 is oriented may be selected to match the FOV angle of the light beam coupled into the image light guide 102 by interaction with the incoupling diffractive optical element IDO1, although an optional intermediate diffractive optical element TO1 (shown in FIG. 7A) may prevent the incidence of a portion of the light coupled into the image light guide 102 on the first zone 112.

[0049] In one embodiment, the third zone 212 is bounded by: i) a third side 116C extending substantially along the y-direction; ii) a portion of the second side 116B extending substantially in the x-direction beyond the width of the second incoupling diffractive optical element IDO2 along the x-direction; iii) an imaginary line 217 formed as a dividing line between the third zone 212 and the second zone 114 and oriented at an angle θ2 relative to the second side 116B of the outcoupling diffractive optical element ODO; and iv) a portion of the fourth side 116D extending substantially along the x-direction between the imaginary line 217 and the third side 116C. It will be appreciated that the imaginary line 217 dividing the third zone 212 and the second zone 114 within the outcoupling diffractive optical element IDO2 extends from a position along the second side 116B closer to the third side 116C than to the first side 116A, and terminates at a position along the fourth side 116D closer to the first side 116A than to the third side 116C. The angle θ2 at which the imaginary line 217 defining the boundary / edge of the third zone 212 is oriented may be selected to coincide with the FOV angle of the image-bearing light beam coupled into the image light guide 202 by interaction with the second incoupling diffractive optical element IDO2. In other words, in the exemplary embodiment, the third zone 212 is configured so that substantially all light coupled into the image light guide 202 by interaction with the second incoupling diffractive optical element IDO2 is incident on the third zone 212. In an exemplary embodiment, the angle θ2 at which the imaginary line 217 defining the boundary / edge of the third zone 212 is oriented may be selected to match the FOV angle of the light beam coupled into the image light guide 202 by interaction with the second incoupling diffractive optical element IDO2, although an optional intermediate diffractive optical element TO2 may prevent the incidence of a portion of the light coupled into the image light guide 202 on the third zone 212.

[0050] In one example, the second zone 114 of the outcoupling diffractive optical element ODO is disposed between the first zone 112 and the third zone 212 in the x-axis direction. In an exemplary embodiment, the first zone 112 includes a first set of diffractive features 118A and a second set of diffractive features 118B (collectively referred to herein as “diffractive features 118”), as described above. In an exemplary embodiment, the third zone 212 includes a first set of diffractive features 218A and a second set of diffractive features 218B (collectively referred to herein as “diffractive features 218”), where the first set of diffractive features 218A at least partially overlap with the second set of diffractive features 218B. In some examples, the diffractive features 218 of the third zone 212 approximate linear diffractive features. For example, diffractive feature 218A is oriented parallel to the y-direction and has grating vectors ±k3, while diffractive feature 218B is oriented at an angle α relative to diffractive feature 218A and has grating vectors ±k5. In another example, diffractive feature 218 may include generally diamond-shaped posts having grating vectors ±k5 and ±k3. In an exemplary embodiment, second zone 114 includes multiple diffractive features 120 that approximate linear diffractive features oriented parallel to the y-direction and also have grating vectors ±k3. In an exemplary embodiment, the grating vectors ±k5 of diffractive feature 118B are oriented at an angle less than 60 degrees (e.g., α<60 degrees) relative to the grating vectors ±k4 of the second incoupling diffractive optical element IDO2. Furthermore, the third zone 212 of the outcoupling diffractive optical element ODO is asymmetrically (i.e., asymmetrically) positioned around the grating vector ±k4 of the incoupling diffractive optical element IDO2. In other words, the lattice vectors ±k5 have a larger magnitude than the lattice vectors ±k3, creating a lattice vector diagram that sums to zero in the shape of a scalene or isosceles triangle (i.e., a non-equilateral triangle).A person skilled in the relevant art will recognize that the second incoupling diffractive optical element IDO2, the third zone 212, and the optional second intermediate diffractive optical element TO2 may be arranged symmetrically around the imaginary axis 230 with the first incoupling diffractive optical element IDO1, the first zone 112, and the optional first intermediate diffractive optical element TO1, respectively.

[0051] In the exemplary embodiment, the third zone 212 of the outcoupling diffractive optical element ODO is a compound diffractive optical element having two grating vectors ±k5 and ±k3. The third zone 212 of the outcoupling diffractive optical element ODO is positioned to diffract and replicate (along the −y direction) the set of angle-related image-bearing light beams coupled into the image light guide 202 by interaction with the second incoupling diffractive optical element IDO2, and to propagate the set of angle-related image-bearing light beams in the x-direction toward the second zone 114. For example, as the coupled image-bearing light propagates through the diffractive features 218 of the third zone 212, a portion of the image-bearing light that is incident on and diffracted by diffractive feature 218B is diffracted along the direction of grating vector k3 (e.g., in the −x-direction) for every odd-numbered interaction with diffractive feature 218B and along the direction of grating vector k4 for every even-numbered interaction with diffractive feature 218B. Furthermore, during propagation of image-bearing light through third zone 212, a portion of the image-bearing light is outcoupled and propagates toward the eyebox for each even or odd number of interactions with diffractive features 218. Image-bearing light that interacts with diffractive features 218 an odd number of times propagates via TIR toward second zone 114. In an exemplary embodiment, third zone 212 is positioned to diffract and propagate a greater portion of the image-bearing light toward second zone 114 than the portion of the image-bearing light that was outcoupled through third zone 212. In this manner, third zone 212 is configured to perform the functions of an intermediate diffractive optical element as well as an outcoupling diffractive optical element.

[0052] As shown in FIG. 7A , in another exemplary embodiment, the image light guide 202 includes a first separate or discrete intermediate diffractive optical element TO1 disposed on the back surface 106 opposite the outcoupling diffractive optical element ODO. For example, the intermediate diffractive optical element TO1 is similar in shape to the first zone 112 of the outcoupling diffractive optical element ODO, and the intermediate diffractive optical element TO1 at least partially overlaps with the outcoupling diffractive optical element ODO. In some embodiments, the area of ​​the intermediate diffractive optical element TO1 is larger than the area of ​​the first zone 112. In one embodiment, the intermediate diffractive optical element TO1 extends in the x-direction beyond the edge 116A of the first zone 112, and the intermediate diffractive optical element TO1 extends in the y-direction beyond the area covered by the outcoupling diffractive optical element ODO toward the incoupling diffractive optical element IDO1. The intermediate diffractive optical element TO1 includes a plurality of diffractive features 122 disposed parallel to the diffractive features 118B of the first zone 112, and the diffractive features 122 may also be represented by grating vectors ±k2.

[0053] In one embodiment, the image light guide 202 may also include a second separate or distinct intermediate diffractive optical element TO2 disposed on the back surface 106 opposite the outcoupling diffractive optical element ODO. For example, the intermediate diffractive optical element TO2 is similar in shape to the third zone 212 of the outcoupling diffractive optical element ODO, and the intermediate diffractive optical element TO2 at least partially overlaps with the outcoupling diffractive optical element ODO. In some embodiments, the area of ​​the intermediate diffractive optical element TO2 is larger than the area of ​​the third zone 212. In one embodiment, the intermediate diffractive optical element TO2 extends in the x-direction beyond the edge 116C of the third zone 212, and the intermediate diffractive optical element TO2 extends in the y-direction beyond the area covered by the outcoupling diffractive optical element ODO toward the incoupling diffractive optical element IDO2. The intermediate diffractive optical element TO2 includes a plurality of diffractive features 222 disposed parallel to the diffractive features 218B of the third zone 212, and the diffractive features 222 may also be represented by grating vectors ±k5.

[0054] In the exemplary embodiment, the pitch d1 of diffractive features 118B and the pitch d1 of diffractive features 122 are smaller than the pitch d1 of diffractive features 118A and the pitch d1 of diffractive features 120. For example, the pitch d1 of diffractive features 118B is substantially equal to the pitch d1 of diffractive features 122, and the pitch d of diffractive features 118A is substantially equal to the pitch d1 of diffractive features 120. In the exemplary embodiment, the sum of the grating vectors ±k1, ±k2, and ±k3 is zero, but a decrease in the pitch d1 of diffractive features 118B, 122 (i.e., a larger magnitude of grating vector ±k2) creates an asymmetry about the grating vector ±k1. A decrease in the pitch d1 of diffractive features 118B, 122 (i.e., a larger magnitude of grating vector ±k2) facilitates rotation of the image-bearing light through an angle greater than 90°. In exemplary embodiments, diffractive features 118B, 122 rotate at least a portion of the image-bearing light by a greater angle than 120. In these examples, the addition of a separate or discrete intermediate diffractive optical element TO1 disposed on or within back surface 106 operates to increase the ability to rotate or direct the image-bearing light towards second zone 114 for outcoupling.

[0055] In this exemplary embodiment, the pitch d1 of the diffractive features 218B and the pitch d1 of the diffractive features 222 may also be smaller than the pitch d1 of the diffractive features 218A and the pitch d1 of the diffractive features 120. For example, the pitch d1 of the diffractive features 218B is substantially equal to the pitch d1 of the diffractive features 222, and the pitch d1 of the diffractive features 218A is substantially equal to the pitch d1 of the diffractive features 120. In the exemplary embodiment, the sum of the grating vectors ±k4, ±k5, and ±k3 is zero, but a decrease in the pitch d1 of the diffractive features 218B and 222 (i.e., a larger magnitude of the grating vector ±k5) creates an asymmetry about the grating vector ±k4. A decrease in the pitch d1 of the diffractive features 218B and 222 (i.e., a larger magnitude of the grating vector ±k5) facilitates rotation of the image-bearing light through angles greater than −90 degrees (i.e., angles greater than 270 degrees). In exemplary embodiments, the diffractive features 218B, 222 rotate at least a portion of the image-bearing light by an angle greater than −120 degrees (i.e., greater than 240 degrees). In these examples, the addition of a separate or discrete intermediate diffractive optical element TO2 disposed on or within the back surface 106 operates to increase the ability to rotate or direct the image-bearing light toward the second zone 114 for outcoupling.

[0056] In an exemplary embodiment, image light guide 202 generates an eyebox E large enough to span the interpupillary distance of a user. For example, both eyes of a user may simultaneously receive image-bearing light from eyebox E. However, image light guides of the present disclosure may also be sized for use in monocular or binocular arrangements with one or more image light guides utilized to convey virtual images to the user's eyes. It is an advantage of the presently disclosed subject matter that image light guide 202 provides an outcoupling diffractive optical element (ODO) substantially throughout the entire x-direction of image light guide 202 operable to output image-bearing light substantially uniformly across a large exit pupil E. In an exemplary embodiment, this uniformity is achieved, at least in part, via first zone 112 and second zone 212 of outcoupling diffractive optical element (ODO) represented by grating vectors ±k2, ±k3, ±k5. In another exemplary embodiment, this uniformity is further improved, at least in part, via intermediate diffractive optical elements (TO1, TO2) represented by grating vectors ±k2, ±k5. Another advantage of the present disclosure is that it provides a large exit pupil E with a compact light path within the image light guide 202.

[0057] One or more features of the embodiments described herein may be combined to create additional embodiments not shown. While 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 the scope, spirit, or essential characteristics thereof. The above-described embodiments are therefore to be considered in all respects as illustrative and not restrictive. The scope of the 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 for conveying a virtual image, comprising: a first surface and an opposing second surface; a first incoupling diffractive optical element disposed on, within, or along one of the first surface and the second surface, the first incoupling diffractive optical element including a first set of diffractive features having a first grating vector; an outcoupling diffractive optical element disposed on, in, or along at least one of the first surface and the second surface, the outcoupling diffractive optical element comprising a first zone and a second zone, the first zone including one or more diffractive features different from those of the second zone; an image light guide, wherein the first zone of the outcoupling diffractive optical element includes a second set of diffractive features having a second grating vector and a third set of diffractive features having a third grating vector, the second grating vector having a greater magnitude than the third grating vector.

2. 10. The image light guide of claim 1, wherein the second zone includes a fourth set of diffractive features having a fourth grating vector, and the third grating vector and the fourth grating vector are oriented parallel.

3. The image light guide of claim 2 , wherein the second set of diffractive features are positioned to diffract and propagate at least a portion of the image-bearing light toward the second zone.

4. The image light guide of claim 2 , wherein the second set of diffractive features and the third set of diffractive features are asymmetrically arranged about the first grating vector.

5. The image light guide of claim 2 , wherein the third lattice vector and the fourth lattice vector are equal in magnitude.

6. The image light guide of claim 1 , wherein the first zone of the outcoupling diffractive optical element is disposed along the first surface and the incoupling diffractive optical element is disposed along the second surface.

7. 10. The image light guide of claim 1, further comprising an intermediate diffractive optical element disposed along one of the first surface of the outcoupling diffractive optical element and the second surface opposite the first zone.

8. The image light guide of claim 7 , wherein the intermediate diffractive optical element overlaps with at least a portion of the first zone of the outcoupling diffractive optical element.

9. The image light guide of claim 7 , wherein the intermediate diffractive optical element extends further toward the incoupling diffractive optical element than the outcoupling diffractive optical element.

10. 10. The image light guide of claim 1, wherein the outcoupling diffractive optical element is configured to transmit image-bearing light to an eyebox and is operable such that both eyes of a user receive image-bearing light from within the eyebox substantially simultaneously.

11. 1. An image light guide comprising: a first surface and an opposing second surface; an incoupling diffractive optical element disposed on, within, or along the first surface; an intermediate diffractive optical element disposed on, within, or along the first surface; an outcoupling diffractive optical element disposed on, in, or along the second surface, the outcoupling diffractive optical element including a first zone and a second zone, the first zone including one or more diffractive features different from those of the second zone; The image light guide, wherein the intermediate diffractive optical element at least partially overlaps with the first zone.

12. 12. The image light guide of claim 11 , wherein the first zone of the outcoupling diffractive optical element includes a second set of diffractive features having a second grating vector and a third set of diffractive features having a third grating vector, the second grating vector having a greater magnitude than the third grating vector.

13. 13. The image light guide of claim 12, wherein the second zone includes a fourth set of diffractive features having a fourth grating vector, and the third grating vector and the fourth grating vector are oriented parallel.

14. The image light guide of claim 13 , wherein the second set of diffractive features are positioned to diffract and propagate at least a portion of the image-bearing light toward the second zone.

15. The image light guide of claim 13 , wherein the second set of diffractive features and the third set of diffractive features are asymmetrically arranged about the first grating vector.

16. 1. An image light guide system, comprising: a first image light guide, a first surface and an opposing second surface; a first incoupling diffractive optical element disposed on, within, or along one of the first surface and the second surface; a first image light guide including: a first outcoupling diffractive optical element disposed on, in, or along at least one of the first surface and the second surface, the first outcoupling diffractive optical element comprising a first zone and a second zone, the first zone including one or more diffractive features different from those of the second zone; and a second image light guide, a third surface and an opposing fourth surface; a second incoupling diffractive optical element disposed on, within, or along one of the third surface and the fourth surface; and a second image light guide comprising: a second outcoupling diffractive optical element disposed on, in, or along at least one of the third surface and the fourth surface, the second outcoupling diffractive optical element comprising a third zone and a fourth zone, the third zone including one or more diffractive features different from those of the fourth zone.

17. 17. The image light guiding system of claim 16, wherein the first incoupling diffractive optical element and the second incoupling diffractive optical element are coaxially arranged about an imaginary axis oriented perpendicular to the first surface.

18. 17. The image light guiding system of claim 16, wherein the first incoupling diffractive optical element is arranged about a first imaginary axis oriented perpendicular to the first surface, and the second incoupling diffractive optical element is arranged about a second imaginary axis oriented perpendicular to the first surface, and the first imaginary axis and the second imaginary axis are parallel.

19. 1. An image light guide comprising: a first surface and an opposing second surface; a first incoupling diffractive optical element disposed on, within, or along one of the first surface and the second surface; a second incoupling diffractive optical element disposed on, within, or along one of the first surface and the second surface; and an outcoupling diffractive optical element disposed on, in, or along at least one of the first surface and the second surface, the outcoupling diffractive optical element comprising a first zone, a second zone, and a third zone; an image light guide, wherein the first zone includes one or more diffractive features that are different from the second zone and the third zone, and the third zone includes one or more diffractive features that are different from the second zone and the first zone.

20. 20. The image light guide of claim 19, wherein the incoupling diffractive optical element includes a first set of diffractive features having a first grating vector, and the first zone of the outcoupling diffractive optical element includes a second set of diffractive features having a second grating vector and a third set of diffractive features having a third grating vector, the second grating vector having a larger magnitude than the third grating vector.

21. 21. The image light guide of claim 20, wherein the second zone includes a fourth set of diffractive features having a fourth grating vector, and the third grating vector and the fourth grating vector are oriented parallel.

22. 22. The image light guide of claim 21 , wherein the third zone of the outcoupling diffractive optical element includes a fifth set of diffractive features having a fifth grating vector and a sixth set of diffractive features having a sixth grating vector, the fifth grating vector having a greater magnitude than the sixth grating vector.

23. 23. The image light guide of claim 22, wherein the second set of diffractive features and the fifth set of diffractive features are arranged to diffract and propagate at least a portion of image-bearing light toward the second zone of the outcoupling diffractive optical element.

24. 20. The image light guide of claim 19, further comprising a first intermediate diffractive optical element disposed along one of the first surface of the outcoupling diffractive optical element and the second surface opposite the first zone.

25. 25. The image light guide of claim 24, further comprising a second intermediate diffractive optical element disposed along one of the first surface of the outcoupling diffractive optical element and the second surface opposite the third zone.

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