WO2024102409A2

WO2024102409A2 - Image light guide with compact diffractive optics

Info

Publication number: WO2024102409A2
Application number: PCT/US2023/037026
Authority: WO
Inventors: Robert J. Schultz
Original assignee: Vuzix Corporation
Priority date: 2022-11-08
Filing date: 2023-11-08
Publication date: 2024-05-16
Also published as: WO2024102409A3

Abstract

An image light guide for conveying a virtual image including a first surface and an opposing second surface, an in-coupling diffractive optic arranged on, in, or along one of the first surface and the second surface, wherein the in-coupling diffractive optic comprises a first set of diffractive features having a first grating vector, and an out-coupling diffractive optic arranged on, in, or along at least one of the first surface and the second surface, wherein the out-coupling diffractive optic comprises a first zone and a second zone, wherein the first zone includes one or more diffractive features different than the second zone. Wherein the first zone of the out-coupling diffractive optic comprises a second set of diffractive features having a second grating vector and a third set of diffractive features having a third grating vector, and wherein the second grating vector has a greater magnitude than the third grating vector.

Description

IMAGE LIGHT GUIDE WITH COMPACT DIFFRACTIVE OPTICS

TECHNICAL FIELD

[0001] The present disclosure generally relates to electronic displays, and more particularly to optical image light guide systems with diffractive optics operable to convey image-bearing light to a viewer.

BACKGROUND

[0002] Head-Mounted Displays (HMDs) and Heads-Up Displays (HUDs) are being developed for a range of diverse uses, including military, commercial, aviation, industrial, firefighting, and entertainment applications. For many of these applications, there is value in forming a virtual image that can be visually superimposed over the real-world image that lies in the field of view of the HMD/HUD user. An optical image light guide may convey image-bearing light to a viewer for directing the virtual image to the viewer's pupil and enabling this superposition function.

[0003] In general, HMD/HUD optics must meet a number of basic requirements for viewer acceptance, including pupil size and field of view (FOV). Pupil size requirements are based on physiological differences in viewer face structure as well as on gaze direction during viewing. A wide FOV is preferable for many tasks and operations. Further, the virtual image that is generated should have sufficient brightness for visibility and viewer comfort.

[0004] In addition to optical requirements, HMD/HUD designs must also address practical factors such as acceptable form factor with expectations of reduced weight, cost, and ease of use.

SUMMARY

[0005] It is an object of the present disclosure to advance the art 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 the 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 including a first surface and an opposing second surface, an incoupling diffractive optic arranged on, in, or along one of the first surface and the second surface, wherein the in-coupling diffractive optic comprises a first set of diffractive features having a first grating vector, and an out-coupling diffractive optic arranged on, in, or along at least one of the first surface and the second surface, wherein the out-coupling diffractive optic comprises a first zone and a second zone, wherein the first zone includes one or more diffractive features different than the second zone. Wherein the first zone of the out-coupling diffractive optic comprises a second set of diffractive features having a second grating vector and a third set of diffractive features having a third grating vector, and wherein the second grating vector has a greater magnitude 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 in-coupling diffractive optic arranged on, in, or along the first surface, an intermediate diffractive optic arranged on, in, or along the first surface, and an out-coupling diffractive optic arranged on, in, or along the second surface, wherein the out-coupling diffractive optic comprises a first zone and a second zone, and wherein the first zone includes one or more diffractive features different than the second zone. In an example, the intermediate diffractive optic at least partially overlaps with the first zone.

[0007] In another exemplar}- 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 in-coupling diffractive optic arranged on, in, or along one of the first surface and the second surface, and a first out-coupling diffractive optic arranged on, in, or along at least one of the first surface and the second surface, wherein the first out-coupling diffractive optic comprises a first zone and a second zone, wherein the first zone includes one or more diffractive features different than the second zone. The image light guide system further including a second image light guide having a third surface and an opposing fourth surface, a second in-coupling diffractive optic arranged on, in, or along one of the third surface and the fourth surface, and a second out-coupling diffractive optic arranged on, in, or along at least one of the third surface and the fourth surface, wherein the second out-coupling diffractive optic comprises a third zone and a fourth zone, wherein the third zone includes one or more diffractive features different than 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 in-coupling diffractive optic arranged on, in, or along one of the first surface and the second surface, a second in-coupling diffractive optic arranged on, in, or along one of the first surface and the second surface, and an out-coupling diffractive optic arranged on, in, or along at least one of the first surface and the second surface, wherein the out-coupling diffractive optic comprises a first zone, a second zone, and a third zone, wherein the first zone includes one or more diffractive features different than the second zone and the third zone, and the third zone includes one or more diffractive features different than the second zone and the first zone. BRIEF DESCRIPTION OF THE DRAWINGS

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

[0010] FIG. 1 is a top view of an image light guide with an exaggerated thickness for showing the propagation of light from an image source along the image light guide to an eyebox within which the virtual image can be viewed.

[0011] FIG. 2 is a perspective view of an image light guide including an in-coupling diffractive optic, a turning diffractive optic, and out-coupling diffractive optic for managing the propagation of image-bearing light beams.

[0012] FIG. 3A is a front side elevational view of an image light guide according to an exemplary⁷ embodiment of the presently disclosed subject matter.

[0013] FIG. 3B is a front side elevational view' of an image light guide according to another exemplary embodiment of the presently disclosed subject matter.

[0014] FIG. 3C is a back side elevational view of an embodiment of the image light guide according to FIG. 3B.

[0015] FIG. 4A is a left side elevational view' of an embodiment of the image light guide, with an exaggerated thickness, according to FIG. 3A.

[0016] FIG. 4B is a left side elevational view of another embodiment of the image light guide, with an exaggerated thickness, according to FIG. 3A.

[0017] FIG. 4C is a left side elevational view of an embodiment of the image light guide, with an exaggerated thickness, according to FIG. 3B.

[0018] FIG. 5A is a top plan view of an embodiment of the image light guide, with an exaggerated thickness, according to FIG. 3 A.

[0019] FIG. 5B is a top plan view of an embodiment of the image light guide, with an exaggerated thickness, according to FIG. 3B.

[0020] FIG. 6A is a top view of an embodiment of an image light guide system, with an exaggerated thickness, according to an exemplary' embodiment of the presently disclosed subject matter. [0021] FIG. 6B is a top plan view of an embodiment of an image light guide system, with an exaggerated thickness, according to another exemplary embodiment of the presently disclosed subj ect matter.

[0022] FIG. 6C is a front side elevational view of the image light guide system shown in FIG. 6B according to another exemplary' embodiment of the presently disclosed subject matter.

[0023] FIG. 7 A is a front side elevational view of an image light guide according to another exemplary embodiment of the presently disclosed subject matter.

[0024] FIG. 7B is a front side elevational view of an image light guide according to another exemplary embodiment of the presently disclosed subject matter.

[0025] FIG. 8 is a top plan view of an embodiment of the image light guide, with an exaggerated thickness, according to FIG. 7.

DETAILED DESCRIPTION

[0026] It is to be understood that the invention may assume various alternative orientations and step sequences, except where expressly specified to the contrary. It is also to be understood that the specific assemblies and systems illustrated in the attached drawings and described in the following specification are simply exemplary embodiments of the inventive concepts defined herein. Hence, specific dimensions, directions, or other physical characteristics relating to the embodiments disclosed are not to be considered as limiting, unless expressly stated otherwise. Also, although they may not be. like elements in various embodiments described herein may be commonly referred to with like reference numerals within this section of the application.

[0027] One 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 are not shown or described in detail to avoid obscuring certain aspects of the present disclosure. Reference throughout the specification to “one embodiment’⁷ or “an embodiment” means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the present disclosure. Thus, the appearance of the phrase “in one embodiment” or “in an embodiment” throughout the specification is not necessarily referring to the same embodiment. However, the particular features, structures, or characteristics described may be combined in any suitable manner in one or more embodiments. [0028] Where used herein, the terms ‘'first”, “second”, and so on, do not necessarily denote any ordinal, sequential, or priority relation, but are simply used to more clearly distinguish one element or set of elements from another, unless specified otherwise.

[0029] Where used herein, the terms “viewer”, “operator”, “observer”, “wearer”, and “user” are considered equivalents and refer to the person, or machine, that wears and/or views images using a device having an imaging light guide.

[0030] Where 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 widely understood in elementary mathematics. Where used herein, the term “subset”, unless otherwise explicitly stated, refers to a non-empty proper subset, that is, to a subset of the larger set, having one or more members. For a set S, a subset may comprise the complete set S. A “proper subset” of set S, however, is strictly contained in set S and excludes at least one member of set S.

[0031] Where used herein, the terms “coupled,” “coupler.” or “coupling” in the context of optics refer to a connection by which light travels from one optical medium or device to another optical medium or device.

[0032] Where used herein, the terms “wavelength band” and “wavelength range” are equivalent and have their standard connotation as used by those skilled in the art of color imaging and refer to a continuous range of light wavelengths that are used to represent polychromatic images.

[0033] Where used herein, the term “beam expansion” is intended to mean replication of a beam via multiple encounters with an optical element to provide exit pupil expansion in one or more dimensions. Similarly, as used herein, to “expand” a beam, or a portion of a beam, is intended to mean replication of a beam via multiple encounters with an optical element to provide exit pupil expansion in one or more dimensions.

[0034] Where used herein, the term '‘about” when applied to a value is intended to mean within the tolerance range of the equipment used to produce the value, or, in some examples, is intended to mean plus or minus 10%, or plus or minus 5%, or plus or minus 1%, unless otherwise expressly specified.

[0035] Where used herein, the term “substantially” is intended to mean within the tolerance range of the equipment used to produce the value, or. in some examples, is intended to mean plus or minus 10%, or plus or minus 5%, or plus or minus 1%, unless otherwise expressly specified. [0036] Where used herein, the term '‘exemplary” is intended to mean ‘'an example of,” “serving as an example,” or “illustrative,” and does not denote any preference or requirement with respect to a disclosed aspect or embodiment.

[0037] An optical system, such as a HMD, can produce a virtual image. In contrast to methods for forming a real image, a virtual image is not formed on a display surface. That is, if a display surface were positioned at the perceived location of a virtual image, no image would be formed on that surface. Virtual images have a number of inherent advantages for augmented reality presentation. For example, the apparent size of a virtual image is not limited by the size or location of a display surface. Additionally, the source object for a virtual image may be small; for example, a magnifying glass provides a virtual image of an object. In comparison with systems that project a real image, a more realistic viewing experience can be provided by forming a virtual image that appears to be some distance away. Providing a virtual image also obviates the need to compensate for screen artifacts, as may be necessary when projecting a real image.

[0038] FIG. 1 is a schematic diagram showing a simplified cross-sectional view of one conventional configuration of an image light guide system 10. Image light guide system 10 includes a planar image light guide 12, an in-coupling diffractive optic IDO, and an out-coupling diffractive optic ODO. The image light guide 12 includes a transparent substrate S, which can be made of optical glass or plastic, with plane-parallel front and back surfaces 14 and 16. In this example, the in-coupling diffractive optic IDO is shown as a transmissive-type diffraction grating arranged on, in, or otherwise engaged with the front surface 14 of the image light guide 12. However, in-coupling diffractive optic IDO could alternately be a reflective-type diffraction grating or other type of diffractive optic, such as a volume hologram or other holographic diffraction element, that diffracts incoming image-bearing light beams WI into the image light guide 12. The in-coupling diffractive optic IDO can be located on, in, or otherwise engaged with front surface 14 or back surface 16 of the image light guide 12 and can be of a transmissive or reflective-type in a combination that depends upon the direction from which the image-bearing light beams WI approach the image light guide 12.

[0039] When used as a part of a near-eye or head-mounted display system, the in-coupling diffractive optic IDO of the conventional image light guide system 10 couples the image-bearing light beams WI from a real, virtual or hybrid image source 18 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, angularly related, collimated beams encoding the different positions within a virtual image for presentation to the in-coupling diffractive optic IDO. Typically, the rays within each bundle forming one of the angularly related beams extend in parallel, but the angularly related beams are relatively inclined to each other through angles that can be defined in two angular dimensions corresponding to linear dimensions of the image.

[0040] Once the angularly related beams engage with the in-coupling diffractive optic IDO, at least a portion of the image-bearing light beams WI are diffracted (generally through a first diffraction order) and thereby redirected by in-coupling diffractive optic IDO into the planar image light guide 12 as angularly encoded image-bearing light beams WG for further propagation along a length dimension x of the image light guide 12 by total internal reflection (TIR) between the plane-parallel front and back surfaces 14 and 16. Although diffracted into a different combination of angularly related beams in keeping with the boundaries set by TIR, the image-bearing light beams WG preserve the image information in an angularly encoded form that is derivable from the parameters of the in-coupling diffractive optic IDO. The out-coupling diffractive optic ODO receives the encoded image-bearing light beams WG and diffracts (also generally through a first diffraction order) at least a portion of the image-bearing light beams WG out of the image light guide 12, as image-bearing light beams WO, toward a nearby region of space referred to as an eyebox E, within which the transmitted virtual image can be seen by a viewer’s eye or other optical component. The out-coupling diffractive optic ODO can be designed symmetrically with respect to the in-coupling diffractive optic IDO to restore the original angular relationships of the image-bearing light beams WI among outputted angularly related beams of the image-bearing light beams WO. In addition, the out-coupling diffractive optic ODO can modify the original field points’ positional angular relationships producing an output virtual image at a finite focusing distance.

[0041] However, to increase one dimension of overlap among the angularly related beams populating the eyebox E (defining the size of the region within which the virtual image can be seen), the out-coupling diffractive optic ODO is arranged together with a limited thickness T of the image light guide 12 to encounter the image-bearing light beams WG multiple times and to diffract only a portion of the image-bearing light beams WG upon each encounter. The multiple encounters along the length (e.g., a first direction) of the out-coupling diffractive optic ODO have the effect of replicating the image-bearing light beams WG and enlarging or expanding at least one dimension of the eyebox E where the replicated beams overlap. The expanded eyebox E decreases sensitivity to the position of a viewer’s eye for viewing the virtual image.

[0042] The out-coupling diffractive optic ODO is shown as a transmissive-type diffraction grating arranged on or secured to the front surface 14 of the image light guide 12. However, like the in-coupling diffractive optic IDO, the out-coupling diffractive optic ODO can be located on, in, or otherwise engaged with the front or back surface 14 or 16 of the image light guide 12 and can be of a transmissive or reflective-type in a combination that depends upon the direction through which the image-bearing light beams WG is intended to exit the image light guide 12. In addition, the out-coupling diffractive optic ODO could be formed as another type of diffractive optic, such as a volume hologram or other holographic diffraction element, that diffracts propagating image-bearing light beams WG from the image light guide 12 as the image-bearing light beams WO propagating toward the eyebox E.

[0043] FIG. 2 illustrates a perspective view of a conventional image light guide system 10 arranged for expanding the eyebox E in two dimensions, i.e., along both x- and y-axes of the intended image. To achieve a second dimension of eyebox expansion, the in-coupling diffractive optic IDO is oriented to diffract at least a portion of image-bearing light beams WG along a grating vector kl along the image light guide 12 toward an intermediate turning optic TO, whose grating vector k2 is oriented to diffract at least a portion of the image-bearing light beams WG in a reflective mode along the image light guide 12 toward the out-coupling diffractive optic ODO. It should be appreciated that only a portion of the image-bearing light beams WG are diffracted by each of the multiple encounters with intermediate turning optic TO, thereby laterally replicating each of the angularly related beams of the image-bearing light beams WG as they approach the out-coupling diffractive optic ODO. The intermediate turning optic TO redirects the image-bearing light beams WG toward the out-coupling diffractive optic ODO (having a grating vector k3) for longitudinally replicating the angularly related beams of the imagebearing light beams WG in a second direction before exiting the image light guide 12 as the image-bearing light beams WO. Grating vectors, such as the depicted grating vectors kl, k2, and k3, extend within a parallel plane of the image light guide 12 in respective directions that are normal to the diffractive features (e.g., grooves, lines, or rulings) of the diffractive optics and have respective magnitudes inverse to the period or pitch d (i.e., the on-center distance between the diffractive features) of the diffractive optics IDO, TO, and ODO.

[0044] As shown in FIG. 2, in-coupling diffractive optic IDO receives the incoming imagebearing light beams WI containing a set of angularly related beams corresponding to individual pixels or equivalent locations within an image generated by the image source 18, such as a projector. A full range of angularly encoded beams for producing a virtual image can be generated by a real display together with collimating optics or other optical components, by a beam scanner for more directly setting the angles of the beams, or by a combination such as a one-dimensional real display used with a scanner. In this configuration, the image light guide 12 outputs a replicated set of angularly related beams (replicated in two dimensions) by providing multiple encounters of the image-bearing light beams WG with both the intermediate turning optic TO and the out-coupling diffractive optic ODO in different orientations. In the depicted orientation of the image light guide 12, the intermediate turning optic TO provides eyebox expansion in a first dimension, e.g., the y-axis direction, and the out-coupling diffractive optic ODO provides a similar eyebox expansion in a second dimensions, e.g., the x-axis direction. The relative orientations and respective periods d of the diffractive features of the in-coupling optic IDO, intermediate turning optic TO, and out-coupling diffractive optic ODO provide for eyebox expansion in two dimensions while presenting the intended relationships among the angularly related beams of the image-bearing light beams WI that are output from the image light guide system 10 as the image-bearing light beams WO. It should be appreciated that the periods d of the in-coupling diffractive optic IDO, the intermediate turning optic TO, and the out-coupling diffractive optic ODO, can each include diffractive features having a common pitch d, where the common pitch d of each optic can be different.

[0045] In the configuration shown, while the image-bearing light beams WI input into the image light guide 12 are encoded into a different set of angularly related beams by the in-coupling diffractive optic IDO, the information required to reconstruct the image is preserved by accounting for the systematic effects of the in-coupling diffractive optic IDO. The intermediate turning optic TO, located in an intermediate position between the in-coupling and out-coupling diffractive optics IDO and ODO, can be arranged so that it does not induce significant changes to the encoding of the image-bearing light beams WG. As such, the out-coupling diffractive optic ODO can be arranged in a symmetric fashion with respect to the in-coupling diffractive optic IDO, e.g., including diffractive features sharing the same period d. Similarly, the period of the intermediate turning optic TO can also match the common period of the in-coupling and out- coupling diffractive optics IDO and ODO. Although the grating vector k2 of the intermediate turning optic TO is shown oriented at 45 degrees with respect to the other grating vectors, which remains a possible orientation, the grating vector k2 of the intermediate turning optic TO can be oriented at 60 degrees to the grating vectors kl and k3 of the in-coupling and out-coupling diffractive optics IDO and ODO in such a way that the image-bearing light beams WG are turned 120 degrees. By orienting the grating vector k2 of the intermediate turning optic TO at 60 degrees with respect to the grating vectors kl and k3 of the in-coupling and out-coupling diffractive optics IDO and ODO, the grating vectors kl and k3 of the in-coupling and out- coupling diffractive optics IDO and ODO are also oriented at 60 degrees with respect to each other. By basing the grating vector magnitudes on the common pitch shared by the in-coupling, intermediate turning, and out-coupling diffractive optics IDO, TO, and ODO, the three grating vectors kl, k2, and k3 (as directed line segments) form an equilateral triangle and sum to a zero vector magnitude, which avoids asymmetric effects that could introduce unwanted aberrations including chromatic dispersion. Such asymmetric effects can also be avoided by grating vectors kl, k2, and k3 that have unequal magnitudes in relative orientations at which the three grating vectors kl. k2, and k3 sum to a zero vector magnitude.

[0046] In a broader sense, the image-bearing light beams WI that are directed into the image light guide 12 are effectively encoded by the in-coupling diffractive optic IDO, whether the incoupling optic IDO uses gratings, holograms, prisms, mirrors, or some other mechanism. Any reflection, refraction, and/or diffraction of light that takes place at the input should be correspondingly decoded by the output to re-form the virtual image that is presented to the viewer. Whether any symmetries are maintained among the intermediate turning optic TO, the in-coupling optic IDO, and out-coupling diffractive optic ODO, or whether any change to the encoding of the angularly related beams of the image-bearing light beams WI takes place along the image light guide 12, the intermediate turning optic TO and the in-coupling and out-coupling diffractive optics IDO and ODO can be related so that the image-bearing light beams WO that are output from the image light guide 12 preserve or otherwise maintain the original or desired form of the image-bearing light beams WI for producing the intended virtual image.

[0047] As shown in FIG. 2, the letter “R” represents the orientation of the virtual image that is visible to the viewer whose eye is positioned within the eyebox E. As shown, the orientation of the letter “R” in the represented virtual image matches the orientation of the letter "R " as encoded by the image-bearing light beams WI. A change in the rotation about the z axis or angular orientation of incoming image-bearing light beams WI with respect to the x-y plane causes a corresponding symmetric change in rotation or angular orientation of outgoing light from out-coupling diffractive optic (ODO). From the aspect of image orientation, the intermediate turning optic TO simply acts as a type of optical relay, providing one dimension of eyebox expansion through replication of the angularly encoded beams of the image-bearing light beams WG along one axis (e.g., along the y-axis) of the image. Out-coupling diffractive optic ODO further provides a second dimension of eyebox expansion through replication of the angularly encoded beams along another axis (e.g., along the x-axis) while maintaining the original orientation of the virtual image encoded by the image-bearing light beams WI. The intermediate turning optic TO is typically a slanted or square grating or, alternately, can be a blazed grating and is typically arranged on one of the plane-parallel front and back surfaces of the image light guide 12. It should be appreciated that the representation of the virtual image “R” as created by an image source is comprised of infinitely focused light that requires a lens (e.g., the lens in the human eye) to focus the image so that the orientations discussed above can be detected.

[0048] Together, the in-coupling, turning, and out-coupling diffractive optics IDO, TO, and ODO preferably preserve the angular relationships among beams of different wavelengths defining a virtual image upon conveyance by image light guide 12 from an offset position to a near-eye position of the viewer. While doing so. the in-coupling, turning, and out-coupling diffractive optics IDO, TO, and ODO can be relatively positioned and oriented in different ways to control the overall shape of the image light guide 12 as well as the overall orientations at which the angularly related beams can be directed into and out of the image light guide 12.

[0049] FIG. 3 A shows an exemplary embodiment of an image light guide 102 according to the present disclosure. In an example embodiment, the image light guide 102 includes an at least partially transparent substrate S (see FIGS. 4A-4C) with 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 quartz, or polymer. The image light guide 102 includes at least one in-coupling diffractive optic IDO and at least one out-coupling diffractive optic ODO. In one example, as illustrated in FIGS. 3A, 3B. 4A and 4C, an in-coupling diffractive optic IDO is arranged on the back surface 106 (shown by broken lines in FIGS. 3A and 3B) and an out- coupling diffractive optic ODO is arranged on the front surface 104. In another example, an incoupling diffractive optic IDO is arranged on the front surface 104 and an out-coupling diffractive optic ODO is arranged on the back surface 106. In still another embodiment, as illustrated in FIG. 4B, an in-coupling diffractive optic IDO and an out-coupling diffractive optic ODO are arranged on the front surface 104. As illustrated in FIGS. 3A-3C, 5 A, and 5B, in an exemplary embodiment, the out-coupling diffractive optic ODO spans substantially the width of the image light guide 102 in the x-direction. For example, the out-coupling diffractive optic ODO can span at least 90% of the width of the image light guide 102. In another example, the out-coupling diffractive optic ODO can span at least 95% of the width of the image light guide 102.

[0050] As illustrated in FIG. 3A, in an example, the in-coupling diffractive optic IDO is arranged on the back surface 106 (show n by broken lines) and includes a diffractive pattern 108. The diffractive pattern 108 includes a plurality of diffractive features periodic in at least a first direction defining a grating vector ±kl. For example, without limitation, the diffractive pattern 108 may compnse linear diffractive features, e.g., surface relief gratings. Although other shapes are possible, image light guide 102 is formed generally as a rectangle with a portion (e.g., a dogleg) extending in the y-direction, where the in-coupling diffractive optic IDO is arranged in the portion extending in the y-direction and the out-coupling diffractive optic ODO is arranged in the body rectangular portion.

[0051] With continued reference to FIG. 3 A, in an example embodiment, the out-coupling diffractive optic ODO is arranged 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 out- coupling diffractive optic ODO, including the first zone 112 and the second zone 114, comprises a generally rectangular geometry having a first side 116A, second side 116B, third side 116C, and fourth side 116D. The sides 116A, 116B, 116C, 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 an example embodiment, the first zone 112 defines a generally cropped triangular shape and is arranged within the out-coupling diffractive optic ODO and generally beneath the in-coupling diffractive optic IDO in the -y direction. For example, the first zone 112 may be bounded by: i) the first side 116A, extending substantially along in the y-direction; ii) a portion of the second side 116B. extending substantially along the x-direction past the width of the in-coupling diffractive optic IDO in 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 0 with respect to the second side 116B of the out-coupling diffractive optic 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 should be appreciated that the imaginary line 117 dividing the first zone 112 and the second zone 114 within the out-coupling diffractive optic ODO extends from a position along the second side 116B that is closer to first side 116A than third side 116C, and terminates at a position along fourth side 116D that is closer to third side 116C than first side 116A. The angle 0, at which the imaginary line 117 defining a boundary/edge of the first zone 112 is oriented, may be selected to coincide with a FOV angle of the image-bearing light beams coupled into the image light guide 102 by interaction with the in-coupling diffractive optic IDO. In other words, in an example embodiment, the first zone 112 is configured such that substantially all light coupled into the image light guide 102 by interaction with the in-coupling diffractive optic IDO is incident upon the first zone 1 12. In the example embodiments shown in FIGS. 3B and 3C (described below), the angle 0 at which the imaginary line 117 defining a boundary /edge of the first zone 112 is oriented may be selected to coincide with a FOV angle of the light beams coupled into the image light guide 102 by interaction with the in-coupling diffractive optic IDO, but an intermediate diffractive optic TO may prevent the incidence of some portion of light coupled into the image light guide 102 on the first zone 1 12. [0052] In one example, the second zone 114 of the out-coupling diffractive optic ODO is arranged adjacent to the first zone 112 in the x-axis direction. In an example 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 1 18A at least partially overlap the second set of diffractive features 118B. In some examples the diffractive features 118 of the first zone 1 12 approximate straight line diffractive features. For example, diffractive features 118A are oriented parallel to the y- direction and have a grating vector ±k3, and diffractive features 118B are oriented at an angle a relative to the diffractive features 118A and have a grating vector ±k2. In another example, the diffractive features 118 may include generally diamond-shaped posts having grating vectors ±k2, ±k3. In an example embodiment, the second zone 114 includes a plurality of diffractive features 120, where diffractive features 120 approximate straight line diffractive features oriented parallel to the y-direction and also have a grating vector ±k3. For example, the diffractive features 120 may have substantially the same pitch d and orientation as the diffractive features 118A. In an example, the grating vector ±k2 of the diffractive features 118B is oriented at an angle of less than 60° (e.g., a <60°) relative to the grating vector ±kl of the in-coupling diffractive optic IDO. Further, the first zone 112 of the out-coupling diffractive optic ODO is arranged asymmetric (i.e., non-symmetric) about the grating vector ±kl of the in-coupling diffractive optic IDO. In other words, the grating vector ±k2 has a greater magnitude than the grating vector ±k3, creating a grating vector diagram summing to zero in the shape of a scalene or isosceles triangle (i.e., a non-equilateral triangle).

[0053] When designing an intermediate diffractive optic, the optic can be utilized as an “even” coupling optical element or an “odd” coupling optical element. As diffractive features of an intermediate diffractive optic are typically parallel to each other, non-zero order diffraction of incident light will have an angular deviation from the original direction of propagation of the incident light beam(s). However, upon the second or any even number of interactions with additional diffractive features, the non-zero order diffraction of that light will diffract and once again become parallel with the direction of propagation of the incident light. Therefore, any design that optimizes for utilization of the light beams that exit from the optical element in the same direction as the original direction of propagation has utilized an even number of interactions and results in the light exiting the optical element in the same direction as the direction of propagation of the original incident light beams. Conversely, any design that optimizes for utilization of the light beams that exit from the optical element in a different direction than the original direction of propagation of the incident light has utilized an odd number of interactions with the diffractive features.

[0054] Referring now to FIG. 3 A, in an example embodiment, the first zone 112 of the out- coupling diffractive optic ODO is a compound diffractive optic having two grating vectors ±k2, ±k3. The first zone 112 of the out-coupling diffractive optic ODO is arranged to diffract and replicate (along the -y direction) a set of angularly related image-bearing light beams that have been coupled into the image light guide 102 by interaction with the in-coupling diffractive optic IDO as well as to propagate the set of angularly related image-bearing light beams in the x- direction in the direction of the second zone 114. For example, as the coupled image-bearing light propagates through the diffractive features 118 of first zone 112, a portion of the imagebearing light incident upon and diffracted by the diffractive features 118B will be diffracted along the direction of grating vector k3 upon every odd interaction with diffractive features 118B and will be diffracted along the direction of grating vector kl upon every even interaction with diffractive features 118B. Additionally, during propagation of image-bearing light through first zone 112. upon every even or odd interaction with diffractive features 118, a portion of image-bearing light is out-coupled and propagates in the direction of the eyebox. The imagebearing light that interacts with diffractive features 118 an odd number of times will propagate via TIR in the direction of the second zone 114. In an example embodiment, the first zone 112 is arranged to diffract and propagate a greater portion of the image-bearing light towards the second zone 114 than the portion of the image-bearing light that is out-coupled via the first zone 112. In this way, the first zone 112 is configured to perform the function of an intermediate diffractive optic as well as an out-coupling diffractive optic.

[0055] Referring now to FIGS. 3B and 3C, in another example embodiment, the image light guide 102 includes a separate or discrete intermediate diffractive optic TO arranged on the back surface 106 opposite the out-coupling diffractive optic ODO. For example, the intermediate diffractive optic TO is similar in shape to the first zone 112 of the out-couphng diffractive optic ODO, and the intermediate diffractive optic TO at least partially overlaps with the out-coupling diffractive optic ODO. In some examples, the area of the intermediate diffractive optic TO is larger than the area of the first zone 112. In an example, the intermediate diffractive optic TO extends in the x-direction beyond the edge 116A of the first zone 112 and intermediate diffractive optic TO extends in the y-direction towards the in-coupling diffractive optic IDO beyond the area covered by the out-coupling diffractive optic ODO. The intermediate diffractive optic TO includes a plurality of diffractive features 122 arranged parallel with the diffractive features 118B of the first zone 112, wherein the diffractive features 122 may also be expressed by the grating vector ±k2.

[0056] In an example embodiment, the pitch di of the diffractive features 118B and the pitch di of the diffractive features 122 are smaller than the pitch d of the diffractive features 118A and the pitch d of the diffractive features 120. For example, the pitch di of the diffractive features 118B is substantially equal to the pitch di of the diffractive features 122, and the pitch d of the diffractive features 118A is substantially equal to the pitch d of the diffractive features 120. In an example embodiment, the grating vectors ±kl, ±k2, ±k3 sum to zero, but the decreased pitch di (i.e., greater magnitude of the grating vector ±k2) of the diffractive features 118B, 122 creates an asymmetry about the grating vector ±kl. The decreased pitch di (i.e., greater magnitude of the grating vector ±k2) of the diffractive features 118B. 122 facilitates a turn of the image bearing light through an angle greater than 90°. In an example embodiment, the diffractive features 118B, 122 turn at least a portion of the image bearing light through an angle greater than 120°. In these examples, the addition of a separate, discrete, intermediate diffractive optic TO arranged on. or in, the back surface 106 operates to increase the ability to turn, or direct, image-bearing light towards the second zone 114 for out-coupling.

[0057] Referring now to FIGS. 5 A and 5B, in an example embodiment, the image light guide 102 produces an eyebox E large enough to span the interpupillary distance of a user. For example, both eyes of the user may simultaneously receive image-bearing light from the eyebox E. However, the image light guide 102 may also be sized for use in monocular arrangements, or binocular arrangements with one or more image light guides utilized to convey a virtual image to the user’s eyes. It is an advantage of the presently disclosed subject matter, that the image light guide 102 provides an out-coupling diffractive ODO spanning substantially the entire x- direction of the image light guide 102 that is operable to, substantially and uniformly output image-bearing light across the large exit pupil E. In the example embodiment shown in FIG. 3A, this uniformity is achieved, at least in part, via the first zone 112 of the out-coupling diffractive optic ODO expressed by grating vectors ±k2, ±k3. In the example embodiment shown in FIGS. 3B-3C, this uniformity is further improved, at least in part, via the intermediate diffractive optic TO expressed by grating vector ±k2. Another advantage of the present disclosure is the provision of a large exit pupil E with a compact optical path within the image light guide 102.

[0058] In an example embodiment, the image light guide 102 conveys image-bearing light of a first wavelength range (e.g., green light in the 520-560 nm range) to the eyebox E. Referring now to FIG. 6A, in an example embodiment, a second image light guide 102 may be provided with the first image light guide 102 in a waveguide stack of an image light guide system to convey polychromatic light to the eyebox E. For example, the first image light guide 102 may be optimized to convey image-bearing light of a second wavelength range (e.g., red light in the 630-660 nm range) and the second image light guide 102 may be optimized to convey imagebearing light of a third wavelength range (e.g., blue light in the 440-470 nm range), where image-bearing light of the first wavelength range (e.g.. green light in the 520-560 nm range) is conveyed by both the first and second image light guide 102. In an example embodiment, as shown in FIG. 6A, the in-coupling diffractive optic IDO of the first image light guide 102 and the in-coupling diffractive optic IDO of the second image light guide are arranged coaxially about an imaginary axis 132 oriented normal to the first surface 104.

[0059] As illustrated in FIGS. 6B and 6C, in an example embodiment, the second image light guide 102 may be oriented relative with the first image light guide 102 such that the in-coupling diffractive optic IDO is oriented on the opposite side, in the x-direction, of an 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, wherein the features of the second image light guide 102 are arranged such that they are mirrored in the x-direction across the imaginary axis 130. In an example embodiment, as shown in FIGS. 6B and 6C, the in-coupling diffractive optic IDO of the first image light guide 102 is arranged about a first imaginary axis 132 oriented normal to the first surface 104, and the in-coupling diffractive optic IDO of the second image light guide 102 is arranged about a second imaginary axis 134 oriented normal to the first surface 104, wherein the first imaginary axis 132 and the second imaginary axis 134 are oriented in parallel.

[0060] It should be appreciated that, in some example embodiments, the image light guide 102 design described above forms, substantially, one-half of 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 an example embodiment, the image light guide 202 includes separate or discrete intermediate diffractive optics TO1, TO2 arranged on the back surface 106 (shown by broken lines) opposite the out-coupling diffractive optic ODO. As shown in FIG. 7B, in an example embodiment, the image light guide 202 does not include separate or discrete intermediate diffractive optics TO1, TO2. Referring now to FIGS. 7A-8, with like reference characters indicating like elements described above, in an example embodiment, an image light guide 202 includes an at least partially transparent substrate with parallel front and back surfaces 104 and 106. For example, the image light guide 202 may be made of optical glass, fused quartz, or a polymer. The image light guide 202 includes a first in-coupling diffractive optic IDO1, and second in-coupling diffractive optic IDO2, and at least one out- coupling diffractive optic ODO. In one example, the in-coupling diffractive optics IDO1, IDO2 are arranged on the back surface 106 and the out-coupling diffractive optic ODO is arranged on the front surface 104. In another example, the in-coupling diffractive optics IDO1, IDO2 are arranged on the front surface 104 and the out-coupling diffractive optic ODO is arranged on the back surface 106. In still another embodiment, the in-coupling diffractive optics IDOL IDO2 and an out-coupling diffractive optic ODO are arranged on the front surface 104. In an exemplary embodiment, the out-coupling diffractive optic ODO spans substantially the width of the image light guide 202 in the x-direction. For example, the out-coupling diffractive optic ODO can span at least 90% of the width of the image light guide 202. In another example, the out-coupling diffractive optic ODO can span at least 95% of the width of the image light guide 202.

[0061] The first in-coupling diffractive optic IDO1 includes a plurality of diffractive features 108 periodic in at least a first direction defining a grating vector ±kl. For example, the diffractive features 108 may comprise linear diffractive features, e.g., surface relief gratings. The second in-coupling diffractive optic IDO2 includes a plurality of diffractive features 208 periodic in at least a first direction defining a grating vector ±k4. For example, the diffractive features 208 may comprise linear diffractive features, e.g., surface relief gratings. Although other shapes are possible, image light guide 202 is formed generally as a rectangle with two portions (e g., a dog-legs) extending in the y-direction. where the in-coupling diffractive optics IDO1, IDO2 are arranged in the respective portions extending in the y-direction and the out- coupling diffractive optic ODO is arranged in the body of the rectangular portion.

[0062] In an example embodiment, the out-coupling diffractive optic ODO is arranged 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 out-coupling diffractive optic ODO, including the first zone 112, the second zone 114, and the third zone 212 comprises a generally rectangular geometry having a first side 1 16A, second side 116B, third side 116C, and fourth side 116D. The sides 116A, 116B, 116C, 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.

[0063] In an example embodiment, the first zone 112 defines a generally cropped triangular shape and is arranged within the out-coupling diffractive optic ODO and generally beneath the first in-coupling diffractive optic IDO1 in the -y direction, while the third zone 212 defines a generally cropped triangular shape and is arranged within the out-coupling diffractive optic ODO and generally beneath the second in-coupling diffractive optic IDO2 in the -y direction. For example, the first zone 112 may be bounded by: i) the first side 116A, extending substantially along in the y-direction; ii) a portion of the second side 1 16B, extending substantially along the x-direction past the width of the first in-coupling diffractive optic IDO1 in 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 6 with respect to the second side 116B of the out-coupling diffractive optic 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 should be appreciated that the imaginary line 117 dividing the first zone 112 and the second zone 114 within the out-coupling diffractive optic ODO extends from a position along the second side 116B that is closer to the first side 116A than the third side 116C, and terminates at a position along the fourth side 116D that is closer to the third side 116C than the first side 116A. The angle 6 at which the imaginary line 117 defining a boundary /edge of the first zone 112 is oriented may be selected to coincide with a FOV angle of the image-bearing light beams coupled into the image light guide 102 by interaction with the first in-coupling diffractive optic IDO1. In other words, in an example embodiment, the first zone 112 is configured such that substantially all light coupled into the image light guide 102 by interaction with the first incoupling diffractive optic IDO1 is incident upon the first zone 112. In the example embodiments, the angle 0 at which the imaginary line 117 defining a boundary/edge of the first zone 112 is oriented may be selected to coincide with a FOV angle of the light beams coupled into the image light guide 102 by interaction with the in-coupling diffractive optic IDO1, but an optional intermediate diffractive optic TO1 (as shown in FIG. 7A) may prevent the incidence of some portion of light coupled into the image light guide 102 on the first zone 112.

[0064] In an example, the third zone 212 may be bounded by: i) the third side 116C, extending substantially along in the y-direction; ii) a portion of the second side 116B, extending substantially along the x-direction past the width of the second in-coupling diffractive optic IDO2 in 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 02 with respect to the second side 116B of the out-coupling diffractive optic 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 should be appreciated that the imaginary line 217 dividing the third zone 212 and the second zone 114 within the out-coupling diffractive optic ODO extends from a position along the second side 116B that is closer to the third side 116C than the first side 116A, and terminates at a position along the fourth side 116D that is closer to the first side 116A than the third side 116C. The angle 02 at which the imaginary line 217 defining a boundary/edge of the third zone 212 is oriented may be selected to coincide with a FOV angle of the image-bearing light beams coupled into the image light guide 202 by interaction with the second in-coupling diffractive optic IDO2. In other words, in an example embodiment, the third zone 212 is configured such that substantially all light coupled into the image light guide 202 by interaction with the second in-coupling diffractive optic IDO2 is incident upon the third zone 212. In the example embodiments, the angle 92 at which the imaginary line 217 defining a boundary/edge of the third zone 212 is oriented may be selected to coincide with a FOV angle of the light beams coupled into the image light guide 202 by interaction with the second in-coupling diffractive optic IDO2, but an optional intermediate diffractive optic TO2 may prevent the incidence of some portion of light coupled into the image light guide 202 on the third zone 212.

[0065] In one example, the second zone 114 of the out-coupling diffractive optic ODO is arranged between the first zone 112 and the third zone 212 in the x-axis direction. In an example 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 example 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 the second set of diffractive features 218B. In some examples the diffractive features 218 of the third zone 212 approximate straight line diffractive features. For example, diffractive features 218A are oriented parallel to the y-direction and have a grating vector ±k3, and diffractive features 218B are oriented at an angle a relative to the diffractive features 218A and have a grating vector ±k5. In another example, the diffractive features 218 may include generally diamond-shaped posts having grating vectors ±k5, ±k3. In an example embodiment, the second zone 114 includes a plurality of diffractive features 120, where diffractive features 120 approximate straight line diffractive features oriented parallel to the y-direction and also have a grating vector ±k3. In an example embodiment, the grating vector ±k5 of the diffractive features 118B is oriented at an angle of less than 60° (e.g., a <60°) relative to the grating vector ±k4 of the second in-coupling diffractive optic IDO2. Further, the third zone 212 of the out- coupling diffractive optic ODO is arranged asymmetric (i.e., non-symmetric) about the grating vector ±k4 of the in-coupling diffractive optic IDO2. In other words, the grating vector ±k5 has a greater magnitude than the grating vector ±k3, creating a grating vector diagram summing to zero in the shape of a scalene or isosceles triangle (i.e., a non-equilateral triangle). Persons skilled in the relevant art will recognize that the second in-coupling diffractive optic IDO2, third zone 212, and the optional second intermediate diffractive optic TO2 may be arranged symmetric with the first in-coupling diffractive optic IDO1, first zone 112, and the optional first intermediate diffractive optic TO1, respectively, about an imaginary axis 230.

[0066] In an example embodiment, the third zone 212 of the out-coupling diffractive optic ODO is a compound diffractive optic having two grating vectors ±k5, ±k3. The third zone 212 of the out-coupling diffractive optic ODO is arranged to diffract and replicate (along the -y direction) a set of angularly related image-bearing light beams that have been coupled into the image light guide 202 by interaction with the second in-coupling diffractive optic IDO2 as well as to propagate the set of angularly related image-bearing light beams in the x-direction in the direction of the second zone 114. For example, as the coupled image-bearing light propagates through the diffractive features 218 of third zone 212. a portion of the image-bearing light incident upon and diffracted by the diffractive features 218B will be diffracted along the direction of grating vector k3 (e.g., -x-direction) upon every odd interaction with diffractive features 218B and will be diffracted along the direction of grating vector k4 upon every even interaction with diffractive features 218B. Additionally, during propagation of image-bearing light through third zone 212, upon every even or odd interaction with diffractive features 218, a portion of image-bearing light is out-coupled and propagates in the direction of the eyebox. The image-bearing light that interacts with diffractive features 218 an odd number of times will propagate via TIR in the direction of the second zone 114. In an example embodiment, the third zone 212 is arranged to diffract and propagate a greater portion of the image-bearing light towards the second zone 114 than the portion of the image-bearing light that is out-coupled via the third zone 212. In this way, the third zone 212 is configured to perform the function of an intermediate diffractive optic as well as an out-coupling diffractive optic.

[0067] In another example embodiment, as shown in FIG. 7 A, the image light guide 202 includes a first separate or discrete intermediate diffractive optic TO1 arranged on the back surface 106 opposite the out-coupling diffractive optic ODO. For example, the intermediate diffractive optic TO1 is similar in shape to the first zone 112 of the out-coupling diffractive optic ODO and the intermediate diffractive optic TO1 at least partially overlaps with the out- coupling diffractive optic ODO. In some examples, the area of the intermediate diffractive optic TO1 is larger than the area of the first zone 112. In an example, the intermediate diffractive optic TO1 extends in the x-direction beyond the edge 116A of the first zone 112 and intermediate diffractive optic TO1 extends in the y-direction towards the in-coupling diffractive optic IDO1 beyond the area covered by the out-coupling diffractive optic ODO. The intermediate diffractive optic TO1 includes a plurality of diffractive features 122 arranged parallel with the diffractive features 118B of the first zone 112, wherein the diffractive features 122 may also be expressed by the grating vector ±k2.

[0068] In one example, the image light guide 202 may similarly include a second separate or discrete intermediate diffractive optic TO2 arranged on the back surface 106 opposite the out- coupling diffractive optic ODO. For example, the intermediate diffractive optic TO2 is similar in shape to the third zone 212 of the out-coupling diffractive optic ODO and the intermediate diffractive optic TO2 at least partially overlaps with the out-coupling diffractive optic ODO. In some examples, the area of the intermediate diffractive optic TO2 is larger than the area of the third zone 212. In an example, the intermediate diffractive optic TO2 extends in the x-direction beyond the edge 116C of the third zone 212 and intermediate diffractive optic TO2 extends in the y-direction towards the in-coupling diffractive optic IDO2 beyond the area covered by the out-coupling diffractive optic ODO. The intermediate diffractive optic TO2 includes a plurality of diffractive features 222 arranged parallel with the diffractive features 218B of the third zone 212, wherein the diffractive features 222 may also be expressed by the grating vector ±k5.

[0069] In an example embodiment, the pitch di of the diffractive features 118B and the pitch di of the diffractive features 122 are smaller than the pitch d of the diffractive features 118A and the pitch d of the diffractive features 120. For example, the pitch di of the diffractive features 118B is substantially equal to the pitch di of the diffractive features 122, and the pitch d of the diffractive features 118A is substantially equal to the pitch d of the diffractive features 120. In an example embodiment, the grating vectors ±kl, ±k2, ±k3 sum to zero, but the decreased pitch di (i.e., greater magnitude of the grating vector ±k2) of the diffractive features 118B. 122 creates an asymmetry about the grating vector ±kl. The decreased pitch di (i.e., greater magnitude of the grating vector ±k2) of the diffractive features 118B, 122 facilitates a turn of the imagebearing light through an angle greater than 90°. In an example embodiment, the diffractive features 118B, 122 turn at least a portion of the image-bearing light through an angle greater than 120°. In these examples, the addition of a separate, discrete, intermediate diffractive optic TO1 arranged on, or in, the back surface 106 operates to increase the ability to turn, or direct, image-bearing light towards the second zone 114 for out-coupling.

[0070] In this example embodiment, the pitch di of the diffractive features 218B and the pitch di of the diffractive features 222 may also be smaller than the pitch d of the diffractive features 218A and the pitch d of the diffractive features 120. For example, the pitch di of the diffractive features 218B is substantially equal to the pitch di of the diffractive features 222, and the pitch d of the diffractive features 218A is substantially equal to the pitch d of the diffractive features 120. In an example embodiment, the grating vectors ±k4, ±k5, ±k3 sum to zero, but the decreased pitch di (i.e., greater magnitude of the grating vector ±k5) of the diffractive features 218B, 222 creates an asymmetry about the grating vector ±k4. The decreased pitch di (i.e., greater magnitude of the grating vector ±k5) of the diffractive features 218B, 222 facilitates a turn of the image bearing light through an angle greater than -90° (i.e., greater than 270°). In an example embodiment, the diffractive features 218B, 222 turn at least a portion of the image bearing light through an angle greater than -120° (i.e., greater than 240°). In these examples, the addition of a separate, discrete, intermediate diffractive optic TO2 arranged on, or in, the back surface 106 operates to increase the ability to turn, or direct, image-bearing light towards the second zone 114 for out-coupling.

[0071] In an example embodiment, the image light guide 202 produces an eyebox E large enough to span the interpupillary distance of a user. For example, both eyes of the user may simultaneously receive image-bearing light from the eyebox E. However, the presently disclosed image light guide may also be sized for use in monocular arrangements, or binocular arrangements with one or more image light guides utilized to convey a virtual image to the user’s eyes. It is an advantage of the presently disclosed subject matter, that the image light guide 202 provides an out-coupling diffractive ODO spanning substantially the entire x- direction of the image light guide 202 that is operable to, substantially, uniformly output imagebearing light across the large exit pupil E. In an example embodiment, this uniformity is achieved, at least in part, via the first zone 112 and the second zone 212 of the out-coupling diffractive optic ODO expressed by grating vectors ±k2, ±k3, ±k5. In another example embodiment, this uniformity⁷ is further improved, at least in part, via the intermediate diffractive optics TO1, TO2 expressed by grating vectors ±k2, ±k5. Another advantage of the present disclosure is the provision of a large exit pupil E with a compact optical path within the image light guide 202.

[0072] One or more features of the embodiments described herein may be combined to create additional embodiments which are not depicted. While various embodiments have been described in detail above, it should be understood that they have been presented by way of example, and not limitation. It will be apparent to persons skilled in the relevant arts that the disclosed subject matter may be embodied in other specific forms, variations, and modifications without departing from the scope, spirit, or essential characteristics thereof. The embodiments described above 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

CLAIMS What is claimed is:

1. An image light guide for conveying a virtual image, comprising: a first surface and an opposing second surface; an in-coupling diffractive optic arranged on, in, or along one of the first surface and the second surface, wherein the in-coupling diffractive optic comprises a first set of diffractive features having a first grating vector; and an out-coupling diffractive optic arranged on, in, or along at least one of the first surface and the second surface, wherein the out-coupling diffractive optic comprises a first zone and a second zone, wherein the first zone includes one or more diffractive features different than the second zone, wherein the first zone of the out-coupling diffractive optic comprises a second set of diffractive features having a second grating vector and a third set of diffractive features having a third grating vector, and wherein the second grating vector has a greater magnitude than the third grating vector.

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

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

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

5. The image light guide according to claim 2, wherein the third grating vector and the fourth grating vector are equal in magnitude.

6. The image light guide according to claim 1, wherein the first zone of the out-coupling diffractive optic is arranged along the first surface, and the in-coupling diffractive optic is arranged along the second surface.

7. The image light guide according to claim 1, further comprising an intermediate diffractive optic arranged along one of the first surface and the second surface opposite the first zone of the out-coupling diffractive optic.

8. The image light guide according to claim 7, wherein the intermediate diffractive optic overlaps with at least a portion of the first zone of the out-coupling diffractive optic.

9. The image light guide according to claim 7, wherein the intermediate diffractive optic extends further than the out-coupling diffractive optic toward the in-coupling diffractive optic.

10. The image light guide according to claim 1, wherein the out-coupling diffractive optic is configured to convey image-bearing light to an eyebox, wherein both eyes of a user are operable to receive image-bearing light substantially simultaneously from within the eyebox.

11. An image light guide, comprising: a first surface and an opposing second surface; an in-coupling diffractive optic arranged on, in, or along the first surface; an intermediate diffractive optic arranged on, in, or along the first surface; and an out-coupling diffractive optic arranged on, in, or along the second surface, wherein the out-coupling diffractive optic comprises a first zone and a second zone, wherein the first zone includes one or more diffractive features different than the second zone, wherein the intermediate diffractive optic at least partially overlaps with the first zone.

12. The image light guide according to claim 11, wherein the first zone of the out-coupling diffractive optic comprises a second set of diffractive features having a second grating vector and a third set of diffractive features having a third grating vector, and wherein the second grating vector has a greater magnitude than the third grating vector.

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

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

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

16. An image light guide system, comprising: a first image light guide, comprising: a first surface and an opposing second surface; a first in-coupling diffractive optic arranged on, in, or along one of the first surface and the second surface; and a first out-coupling diffractive optic arranged on, in, or along at least one of the first surface and the second surface, wherein the first out-coupling diffractive optic comprises a first zone and a second zone, wherein the first zone includes one or more diffractive features different than the second zone, a second image light guide, comprising: a third surface and an opposing fourth surface; a second in-coupling diffractive optic arranged on, in, or along one of the third surface and the fourth surface; and a second out-coupling diffractive optic arranged on, in, or along at least one of the third surface and the fourth surface, wherein the second out-coupling diffractive optic comprises a third zone and a fourth zone, wherein the third zone includes one or more diffractive features different than the fourth zone.

17. The image light guide system according to claim 16, wherein the first in-coupling diffractive optic and the second in-coupling diffractive optic are arranged coaxially about an imaginary axis oriented normal to the first surface.

18. The image light guide system according to claim 16, wherein the first in-coupling diffractive optic is arranged about a first imaginary axis oriented normal to the first surface and the second in-coupling diffractive optic is arranged about a second imaginary axis oriented normal to the first surface, wherein the first imaginary axis and the second imaginary axis are parallel.

19. An image light guide, comprising: a first surface and an opposing second surface; a first in-coupling diffractive optic arranged on, in, or along one of the first surface and the second surface; a second in-coupling diffractive optic arranged on. in. or along one of the first surface and the second surface; and ant out-coupling diffractive optic arranged on, in, or along at least one of the first surface and the second surface, wherein the out-coupling diffractive optic comprises a first zone, a second zone, and a third zone, wherein the first zone includes one or more diffractive features different than the second zone and the third zone, and the third zone includes one or more diffractive features different than the second zone and the first zone.

20. The image light guide according to claim 19, wherein the in-coupling diffractive optic comprises a first set of diffractive features having a first grating vector, wherein the first zone of the out-coupling diffractive optic comprises a second set of diffractive features having a second grating vector and a third set of diffractive features having a third grating vector, and wherein the second grating vector has a greater magnitude than the third grating vector.

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

22. The image light guide according to claim 21, wherein the third zone of the out-coupling diffractive optic comprises a fifth set of diffractive features having a fifth grating vector and a sixth set of diffractive features having a sixth grating vector, and wherein the fifth grating vector has a greater magnitude than the sixth grating vector.

23. The image light guide according to 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 towards the second zone of the out-coupling diffractive optic.

24. The image light guide according to claim 19, further comprising a first intermediate diffractive optic arranged along one of the first surface and the second surface opposite the first zone of the out-coupling diffractive optic.

25. The image light guide according to claim 24. further comprising a second intermediate diffractive optic arranged along one of the first surface and the second surface opposite the third zone of the out-coupling diffractive optic.