Image light guide with composite incoupling diffractive optical element

Abstract

An image light guide for conveying a virtual image comprising a substrate operable to propagate an image-bearing light beam along its length, an incoupling diffractive optical element formed along the substrate and operable to diffract the image-bearing light beam from an image source into the substrate in an angle-encoded fashion, an outcoupling diffractive optical element formed along the substrate and operable to diffract the image-bearing light beam from the substrate in an angle-decoded fashion, the incoupling diffractive optical element having three plurality of periodic incoupling diffractive structures and the outcoupling diffractive optical element having at least two plurality of periodic outcoupling diffractive structures, the two plurality of periodic outcoupling diffractive structures being parallel to two of the three plurality of periodic incoupling diffractive structures.

Description

[Technical Field]

[0001] FIELD OF THE DISCLOSURE This disclosure relates generally to electronic displays, and more particularly to displays that utilize image light guides having diffractive optical elements to convey image-bearing light to a viewer. [Background technology]

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

[0003] While conventional image light guide configurations have significantly reduced the bulk, weight, and overall cost of near-eye display optics, further improvements are needed. In some cases, eyebox size is limited, forcing HMD designs to limit tolerances for movement and device placement. Furthermore, light is often unevenly distributed across the field of view, which can lead to hot spots, such as higher levels of light in the center of the field of view and lower levels of light in the periphery of the field of view. Another challenge with conventional image light guide configurations relates to beam management features within the waveguide. For example, beam expansion and light distribution features can increase the size of the waveguides, as well as their manufacturing cost and complexity. Summary of the Invention

[0004] In a first exemplary embodiment, an image light guide for conveying a virtual image includes a substrate operable to propagate an image-bearing light beam along its length. An incoupling diffractive optical element is formed along the substrate and operable to diffract the image-bearing light beam into the substrate in an angle-encoded manner. An outcoupling diffractive optical element is formed along the substrate, the outcoupling diffractive optical element operable to diffract the image-bearing light beam from the substrate in an angle-decoded manner. The incoupling diffractive optical element has a plurality of three periodic diffractive structures and the outcoupling diffractive optical element has at least two plurality of periodic diffractive structures. The periodic diffractive structures of the two plurality of the outcoupling diffractive optical element are parallel to two of the periodic diffractive structures of the three plurality of the incoupling diffractive optical element. [Brief explanation of the drawings]

[0005] 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.

[0006] [Figure 1] FIG. 1 shows a schematic side 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 shows a schematic 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 schematic plan view of an image light guide having an incoupling diffractive optical element with three patterns of periodic diffractive structures, according to an exemplary embodiment of the disclosed subject matter. [Figure 3B]FIG. 3B shows a schematic plan view of an image light guide having an incoupling diffractive optical element with a periodic diffractive structure of three patterns and an outcoupling diffractive optical element with a periodic diffractive structure of three patterns, according to an exemplary embodiment of the subject matter of the present disclosure. [Figure 4A] FIG. 4A shows a schematic plan view of an image light guide having an intermediate diffractive optical element positioned at least partially around an incoupling diffractive optical element, according to an exemplary embodiment of the disclosed subject matter. [Figure 4B] FIG. 4B shows a schematic plan view of an image light guide having an intermediate diffractive optical element positioned at least partially around an incoupling diffractive optical element, according to an exemplary embodiment of the disclosed subject matter. [Figure 5] FIG. 5 shows a schematic plan view of an image light guide having incoupling and outcoupling diffractive optical elements arranged as a single continuous diffractive pattern. [Figure 6] FIG. 6 shows a schematic diagram of a portion of a composite diffraction pattern operable to expand and outcouple an image-bearing beam, according to an exemplary embodiment of the disclosed subject matter. [Figure 7] FIG. 7 illustrates an image light guide system having a waveguide stack according to an exemplary embodiment of the disclosed subject matter. [Figure 8] FIG. 8 illustrates a near-eye display system for augmented reality display using an image light guide according to an exemplary embodiment of the disclosed subject matter. DETAILED DESCRIPTION OF THE INVENTION

[0007] It should be understood that the present invention may assume various alternative orientations and step arrangements unless expressly specified to the contrary. It should 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.

[0008] 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.

[0009] As used herein, the term "exemplary" is intended to denote an "example" and is not intended to suggest any preferred or ideal embodiment.

[0010] As used herein, the terms "viewer," "operator," "observer," and "user" are considered equivalent and refer to a person or machine wearing or using a device having an imaging light guide to view an image.

[0011] As used herein, the term "set" refers to a non-empty set, as the concept of a collection of elements, i.e., members of a set, is commonly understood in elementary mathematics. Unless explicitly stated otherwise, the term "subset" herein refers 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.

[0012] As used herein, the terms "coupled" and "coupled" in the optical context refer to a connection in which light travels from one optical medium or device to another optical medium or device.

[0013] As used herein, the term "beam expansion" is intended to mean the duplication of a beam through multiple encounters with optical elements to provide an exit pupil expansion in one or more directions. Similarly, as used herein, "expanding" a beam or a portion of a beam is intended to mean the duplication of a beam through multiple encounters with optical elements to provide an exit pupil expansion in one or more directions.

[0014] Optical systems such as HMDs can generate virtual images. Unlike methods for generating real images, virtual images are not generated on the display surface. That is, when a display surface is positioned at the perceived location of the virtual image, no image is generated on that surface. Virtual images offer numerous 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 an object. Compared to systems that project real images, creating a virtual image that appears to be at a distance can provide a more realistic viewing experience. Providing a virtual image also eliminates the need to correct for screen artifacts, which is required when projecting a real image.

[0015] An image light guide may display a virtual image using image-bearing light from a light source, such as a projector. For example, a parallel, relatively angle-encoded light beam from the projector is coupled into a planar waveguide by an input coupling, such as an incoupling diffractive optical element, which can be attached to or formed on the surface of the planar waveguide or embedded within the waveguide. Such a diffractive optical element can be formed as a diffraction grating, a holographic optical element (HOE), or by other known methods. For example, a diffraction grating can be formed by a surface relief. After propagating along the waveguide, the diffracted light can be redirected from the waveguide by a similar output coupling, such as an outcoupling diffractive optical element, which can be positioned to provide pupil dilation along one dimension of the virtual image. Additionally, a rotation grating can be positioned on or within the waveguide to provide pupil dilation in the orthogonal dimension of the virtual image. The image-bearing light output from the waveguide provides the viewer with an expanded eyebox.

[0016] As shown in FIG. 1 , the image light guide 10 may include a planar waveguide 22 having planar-parallel surfaces 12, 14. The waveguide 22 includes a transparent substrate S, which may be made of optical glass or plastic, for example, having planar-parallel front and back surfaces 12, 14. In this example, an incoupling diffractive optical element IDO and an outcoupling diffractive optical element ODO are disposed on the back surface 14. The incoupling diffractive optical element IDO is a reflective diffraction grating operable to couple image-bearing light WI into the planar waveguide 22. However, the incoupling diffractive optical element IDO may alternatively be a volume hologram, other holographic diffractive element, or other type of optical component that provides diffraction for the incident image-bearing light WI. The incoupling diffractive optical element IDO may be located on the front surface 12 or the back surface 14 of the planar waveguide 22 and may be a transmissive or reflective optical element, depending, at least in part, on the direction from which the image-bearing light WI approaches the planar waveguide 22.

[0017] When used as part of a near-eye display system, the incoupling diffractive optical element IDO couples image-bearing light WI from a real, virtual, or hybrid image source 18 into a substrate S of a planar waveguide 22. Any real image or image dimension is first converted into an array of overlapping angle-related beams that encode different locations within the image for presentation to the incoupling diffractive optical element IDO. Typically, the light rays in each bundle that form 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.

[0018] The image-bearing light WI is diffracted (generally through a first diffraction order) and thereby redirected by the incoupling diffractive optical element IDO into the planar waveguide 22 by total internal reflection (“TIR”) from the plane-parallel front and back surfaces 12, 14 as an angle-encoded, image-bearing light beam WG for further propagation along the length dimension X of the planar waveguide 22. Although diffracted along the boundaries set by the TIR into a generally more condensed range of angle-related beams, the image-bearing light WG preserves the image information in an angle-encoded form derivable from parameters of the incoupling diffractive optical element IDO. The outcoupling diffractive optical element ODO receives the encoded image-bearing light WG and diffracts the image-bearing light WG from the planar waveguide 22 as image-bearing light WO (generally also through a first diffraction order) toward a region of space called the eyebox E, in which a transmitted virtual image can be seen by a viewer's eye. In general, the outcoupling diffractive optical element ODO is designed symmetrically with respect to the incoupling diffractive optical element IDO to restore the original angular relationship of the image-bearing light WI between the output angle-related beams of the image-bearing light WO. However, to increase the one-dimensional overlap between the angle-related beams injected into the eyebox E where the virtual image can be seen, the outcoupling diffractive optical element ODO is arranged with the limited thickness T of the planar waveguide 22 to encounter the image-bearing light WG multiple times and diffract only a portion of the image-bearing light WG at each encounter. The multiple encounters along the length of the outcoupling diffractive optical element ODO have the effect of expanding one dimension of each of the angle-related beams of the image-bearing light WO (i.e., beam expansion), thereby expanding one dimension of the eyebox E where the beams overlap. The expanded eyebox E reduces sensitivity to the viewer's eye position for viewing the virtual image. Embodiments of 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.

[0019] As described above, an outcoupling diffractive optical element having a refractive index variation along a single dimension can expand one dimension of the eyebox by replicating individual angle-related beams in the direction of propagation along the waveguide between encounters with the outcoupling diffractive optical element. Furthermore, an outcoupling diffractive optical element having a refractive index variation along a second dimension can expand the second dimension of the eyebox, providing a two-dimensional expansion of the eyebox. The refractive index variation along the first dimension of the outcoupling diffractive optical element can be arranged to diffract a portion of each beam's energy from the waveguide upon each encounter through a preferred first-order diffraction, while another portion of the beam's energy is preserved for further propagation in the original direction through a zeroth-order diffraction. The refractive index variation along the second dimension of the outcoupling diffractive optical element can be arranged to diffract a portion of each beam's energy upon each encounter through a preferred first-order diffraction into a direction angled relative to the beam's original propagation direction, while another portion of the beam's energy is preserved for further propagation in the original direction through a zeroth-order diffraction.

[0020] The outcoupling diffractive optical element ODO is shown as a transmissive diffraction grating disposed on the back surface 14 of the planar waveguide 22. However, like the incoupling diffractive optical element IDO, the outcoupling diffractive optical element ODO may be located on the front surface 12 or the back surface 14 of the planar waveguide 22 and may be a combination of transmissive or reflective, depending at least in part on the direction in which the image-bearing light WG is intended to exit the planar waveguide 22.

[0021] As shown in FIG. 2, the image light guide 10 may be arranged to expand the eyebox E in two dimensions, i.e., along both the x-axis and the y-axis of the intended image. To achieve the second dimension of beam expansion, the incoupling diffractive optical element IDO with grating vector k0 is oriented to diffract a portion of the image-bearing light WI toward the intermediate optical element TO with grating vector k1, which is oriented to diffract a portion of the image-bearing light WG in a reflective mode toward the outcoupling diffractive optical element ODO. The intermediate optical element TO may also be referred to herein as a rotating grating or a rotating optical element. In one embodiment, the intermediate optical element TO is a surface relief grating. In another embodiment, the intermediate optical element TO is a holographic optical element. Only a portion of the image-bearing light WG is diffracted by each of multiple encounters with the intermediate optical element TO, thereby replicating each of the angle-related beams of the image-bearing light WG in one or more dimensions and providing pupil dilation in one or more dimensions. The intermediate optical element may also, or instead, rotate in the direction of propagation of at least a portion of the image-bearing light beam WG traveling within the waveguide 22. The intermediate optical element TO redirects the image-bearing light WG toward the outcoupling diffractive optical element ODO to longitudinally expand the eyebox E in a second dimension, before exiting the planar waveguide 22 as image-bearing light WO. The grating vectors, such as the depicted grating vectors k0, k1, and k2, extend in a direction perpendicular to the diffractive features (e.g., grooves, lines, or rulers) of the diffractive optical elements IDO, TO, and ODO and have an inverse magnitude to the period or pitch d (i.e., the center-to-center distance between grooves) of the diffractive optical elements IDO, TO, and ODO. The incoupling diffractive optical element IDO, the intermediate optical element TO, and the outcoupling diffractive optical element ODO may each have a different period or pitch d. The intermediate optical element TO may include a reflector array as described in US 2021 / 0215941 A1, the entire contents of which are incorporated herein by reference.

[0022] As shown in FIG. 2, the incoupling diffractive optical element IDO receives incident image-bearing light WI, which includes a series of angle-related beams corresponding to individual pixels or equivalent locations in an image generated by an image source 18, such as a projector. The image source 18, operable to generate a full range of angle-coded beams to generate a virtual image, may be, but is not limited to, a physical display combined with focusing optics, a beam scanner to more directly set the beam angles, or a one-dimensional physical display used in a scanner. The image light guide 10 outputs a series of expanded, angle-related beams in the two dimensions of the image by providing multiple encounters of the image-bearing light WG with both the intermediate optical element TO and the outcoupling diffractive optical element ODO at different orientations. In the original orientation of the planar waveguide 22, the intermediate optical element TO provides beam expansion in the y-axis direction, and the outcoupling diffractive optical element ODO provides a similar beam expansion in the x-axis direction. The reflective properties and respective periods d of the diffractive optical elements IDO, ODO, TO, together with the orientation of their respective grating vectors, provide exit pupil expansion in two dimensions while maintaining the intended relationship between the angularly related beams of image-bearing light WI that are output from the image light guide 10 as image-bearing light WO.

[0023] Although the image-bearing light WI input to the image light guide 10 is encoded into a series of distinct, angle-related beams by the incoupling diffractive optical element IDO, the information necessary to reconstruct the image is preserved by accounting for the systematic effects of the incoupling diffractive optical element IDO. The intermediate optical element TO, located at an intermediate position between the incoupling diffractive optical element IDO and the outcoupling diffractive optical element ODO, is typically positioned so as not to induce any significant changes in the encoding of the image-bearing light WG. The outcoupling diffractive optical element ODO is typically positioned symmetrically with respect to the incoupling diffractive optical element IDO, e.g., including diffractive features that share the same period. Similarly, the period of the intermediate optical element TO typically matches the common period of the incoupling diffractive optical element IDO and the outcoupling diffractive optical element ODO. As shown in Figure 2, the grating vector k1 of the intermediate optical element TO may be oriented at 45 degrees relative to the other grating vectors k0 and k2 (all as undirected line segments). However, in one embodiment, the grating vector k1 of the intermediate optical element TO is oriented at 60 degrees relative to the grating vectors k0, k2 of the incoupling diffractive optical element IDO and the outcoupling diffractive optical element ODO in such a way that the image-bearing light WG is rotated by 120 degrees. By orienting the grating vector k1 of the intermediate optical element TO at 60 degrees relative to the grating vector k0 of the incoupling diffractive optical element IDO and the grating vector k2 of the outcoupling diffractive optical element ODO, the grating vectors k0, k2 are also oriented at 60 degrees relative to each other (again, considered as undirected line segments). Taking the common pitch of the intermediate optical element TO, the incoupling diffractive optical element IDO, and the outcoupling diffractive optical element ODO as the basis for the magnitude of the grating vectors, the three grating vectors k0, k1, k2 (as directed 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.

[0024] The image-bearing light WI diffracted into the planar waveguide 22 is effectively encoded by the incoupling diffractive optical element IDO, regardless of whether the incoupling diffractive optical element IDO uses a grating, hologram, prism, mirror, or some other mechanism. The reflection, refraction, and / or diffraction of light that occurs at the incoupling diffractive optical element IDO must be decoded accordingly by the outcoupling diffractive optical element ODO to recreate the virtual image presented to the viewer. The intermediate optical element TO, located at an intermediate position between the incoupling diffractive optical element IDO and the outcoupling diffractive optical element ODO, is typically designed and oriented so as not to induce any changes to the encoded light. The outcoupling diffractive optical element ODO decodes the image-bearing light WG into its original or desired form of an angle-related beam expanded to fill the eyebox E.

[0025] It is relevant whether any symmetry is maintained between the intermediate optical element TO and the incoupling diffractive optical element IDO and the outcoupling diffractive optical element ODO, or whether changes to the angle-related beam encoding of the image-bearing light WI are made along the planar waveguide 22, the intermediate optical element TO, the incoupling diffractive optical element IDO and the outcoupling diffractive optical element ODO, so that the image-bearing light WO output from the planar waveguide 22 retains or otherwise maintains the original or desired form of the image-bearing light WI for generating the intended virtual image.

[0026] The letter R represents the orientation of the virtual image as seen by a viewer positioned in 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 WI. A change in rotation about the z-axis or angular orientation of the incident image-bearing light 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. Because of the image orientation aspect, the intermediate optical element TO typically acts as a type of optical relay, providing expansion of the angle-encoded beam of the image-bearing light WG along one axis of the image (e.g., along the y-axis). The outcoupling diffractive optical element ODO further expands the angle-encoded beam of the image-bearing light WG along another axis of the image (e.g., along the x-axis) while maintaining the original orientation of the virtual image encoded by the image-bearing light WI. As shown in Figure 2, the intermediate optical element TO may be a tilted or square grating positioned on the front or back surface of the planar waveguide 22. Alternatively, the intermediate optical element TO may be a blazed grating.

[0027] The present disclosure provides an image light guide having improved diffraction efficiency and output intensity of image-bearing light across an output aperture. More specifically, the present disclosure provides a waveguide having, among other things, a compound incoupling diffractive optical element and a compound outcoupling diffractive optical element, operable to expand an image-bearing light beam in two dimensions and output the expanded image-bearing light beam toward the eyebox.

[0028] 3A , in one embodiment, the image light guide 100 may have an incoupling diffractive optical element IDO and an outcoupling diffractive optical element ODO formed on / in a first surface 102 of the image light guide 100. Alternatively, one or both of the incoupling diffractive optical element IDO and the outcoupling diffractive optical element ODO may be formed on / in a second surface of the image light guide 100 opposite the first surface 102. In one embodiment, the incoupling diffractive optical element IDO includes multiple sets of periodic diffractive structures. For example, the incoupling diffractive optical element IDO may include a first set of periodic incoupling linear grating structures 104 parallel to the y-axis, a second set of periodic incoupling linear grating structures 106 rotated / offset by 60 degrees relative to the first set of periodic linear grating structures 104, and a third set of periodic incoupling linear grating structures 108 rotated / offset by −60 degrees relative to the first set of periodic incoupling linear grating structures 104. The first set of periodic incoupling diffraction structures 104 has a grating vector k1 extending perpendicular to the periodic incoupling diffraction structures 104. The second set of periodic incoupling diffraction structures 106 and the third set of periodic incoupling diffraction structures 108 have second grating vectors k2 and third grating vectors k3 extending perpendicular to the periodic incoupling diffraction structures 106, 108, respectively. In one embodiment, the first set of periodic incoupling diffraction structures 104 has a different periodicity than the second set of periodic incoupling diffraction structures 106 and the third set of periodic incoupling diffraction structures 108.

[0029] In one embodiment, the outcoupling diffractive optical element ODO includes a first set of periodic outcoupling diffractive structures 110 and a second set of periodic outcoupling diffractive structures 112. The first set of periodic outcoupling diffractive structures 110 and the second set of periodic outcoupling diffractive structures 112 form a composite diffractive optical element operable to expand and output image-bearing light from the outcoupling diffractive optical element ODO. In one embodiment, the first and second sets of periodic outcoupling diffractive structures 112 include diffraction gratings (e.g., linear rulers), and the diffraction gratings of the first set of periodic outcoupling diffractive structures 110 intersect with the diffraction gratings of the second set of periodic outcoupling diffractive structures 112. As shown in FIG. 3A , in one embodiment, the first set of periodic outcoupling diffractive structures 110 are parallel to the second set of periodic incoupling diffractive structures 106, and the second set of periodic outcoupling diffractive structures 112 are parallel to the third set of periodic incoupling diffractive structures 108. The first set of periodic outcoupling diffractive structures 110 may also have the same periodicity as the second set of periodic incoupling diffractive structures 106, and the second set of periodic outcoupling diffractive structures 112 may have the same periodicity as the third set of periodic incoupling diffractive structures 108. In one embodiment, the outcoupling diffractive optical element ODO has bilateral symmetry across the longitudinal axis 114.

[0030] The first set of periodic outcoupling diffraction structures 110 and the second set of periodic outcoupling diffraction structures 112 have a fourth grating vector k4 and a fifth grating vector k5 that extend perpendicular to the periodic diffraction structures 110, 112, respectively. In one embodiment, the grating vector k4 is offset from the incoupling grating vector k1 and the x-axis by 60 degrees, and the grating vector k5 is offset from the incoupling grating vector k1 and the x-axis by −60 degrees.

[0031] During operation, at least a portion of the image-bearing light beam incident on the first periodic incoupling diffractive structure 104, the second periodic incoupling diffractive structure 106, and the third set of periodic incoupling diffractive structures 108 is diffracted and guided into the image light guide 100 as image-bearing light WG for further propagation within the image light guide 100 by TIR and / or diffractive reflection. To illustrate one or more characteristics of embodiments of the present disclosure, the image light guide 100 is described below particularly with respect to the optical paths of one or more portions of the beam of image-bearing light WI that, upon incidence thereon, are positioned perpendicular to the plane of the incoupling diffractive optical element IDO, unless otherwise noted. However, one skilled in the art will recognize that these descriptions are not limiting and that the image-bearing light WI incident on the incoupling diffractive optical element IDO can be positioned at any angle for which the system is optimized.

[0032] For example, when the center line of a beam of image-bearing light WI is incident on the incoupling diffractive optical element IDO along a direction perpendicular to the incoupling diffractive optical element IDO, a portion of the image-bearing light WI is incident on each of the first set of periodic incoupling diffractive structures 104, the second set of periodic incoupling diffractive structures 106, and the third set of periodic incoupling diffractive structures 108. In this example, the portion of the image-bearing light WI is oriented toward the outcoupling diffractive optical element ODO parallel to the directions of the first grating vector k1, the second grating vector k2, and the third grating vector k3. The second set of periodic incoupling diffractive structures 106 and the third set of periodic incoupling diffractive structures 108 direct the portion of the image-bearing light toward the outer region (y-axis direction) of the outcoupling diffractive optical element ODO. By directing the portion of the image-bearing light incident on the incoupling diffractive optical element IDO toward the outer region (y-axis direction) of the outcoupling diffractive optical element ODO, the intensity of the image-bearing light outcoupled from the center (y-axis direction) of the outcoupling diffractive optical element ODO is reduced. This configuration reduces or eliminates so-called hot spots in the eyebox.

[0033] As shown in the detailed view of FIG. 3B , in one embodiment, the outcoupling diffractive optical element ODO includes a third set of periodic outcoupling diffractive structures 113 having a sixth grating vector k6 extending perpendicular to the periodic diffractive structures 113. The grating vector k6 is parallel to the incoupling grating vector k1 and the x-axis. The first set of periodic outcoupling diffractive structures 110, the second set of periodic outcoupling diffractive structures 112, and the third set of periodic outcoupling diffractive structures 113 are configured to maintain symmetry of at least a portion of the image-bearing light incoupled by the first set of periodic incoupling diffractive structures 104. For example, the pitch of the third set of periodic outcoupling diffractive structures 113 is generally complementary to the pitch of the first set of periodic incoupling diffractive structures 104. In one embodiment, the third set of periodic outcoupling diffractive structures 113 are formed with a shallower depth than the first set of periodic outcoupling diffractive structures 110 and the second set of periodic outcoupling diffractive structures 112 to reduce the diffraction efficiency of the third set of periodic outcoupling diffractive structures 113 compared to the first set of periodic outcoupling diffractive structures 110 and the second set of periodic outcoupling diffractive structures 112. This configuration reduces the protrusion of the third set of periodic outcoupling diffractive structures 113, thereby reducing the outcoupled image-bearing light WG and increasing the light distribution in the y-axis direction towards the outer edge of the outcoupling diffractive optical element ODO.

[0034] 3A , in one embodiment, the sixth grating vector k6 is implicitly defined by the first set of periodic outcoupling diffractive structures 110 and the second set of periodic outcoupling diffractive structures 112. The outcoupling diffractive optical element ODO, having the implicitly described third set of periodic outcoupling diffractive structures, reduces but does not eliminate the outcoupled image-bearing light WG from these implicit diffractive structures to increase the light distribution to the outer edges of the outcoupling diffractive optical element ODO in the y-axis direction. In one embodiment, when the periodic outcoupling diffractive structures 110, 112 are linear grating or holographic diffractive structures, at least a portion of the image-bearing light WG propagating along the direction of the first grating vector k1 is diffracted from the image light guide 100 via incidence on one or more diffractive structures of the first set of periodic outcoupling diffractive structures 110 or the second set of periodic outcoupling diffractive structures 112. For example, at least a portion of the image-bearing light propagating along the direction of the first grating vector k1 is outcoupled upon incidence at a position where the first set of periodic outcoupling diffraction structures 110 and the second set of periodic outcoupling diffraction structures 112 coincide.

[0035] Continuing to refer to FIG. 3A , in one embodiment, portion 116 of the outcoupling diffractive optical element ODO wraps around the incoupling diffractive optical element IDO. In other words, portion 116 of the outcoupling diffractive optical element ODO extends at least partially around the incoupling diffractive optical element IDO such that a beam of image-bearing light incident on the incoupling diffractive optical element IDO perpendicular to its plane is diffracted, and a portion of the image-bearing light WG is directed parallel to the second grating vector k2 and the third grating vector k3 and is incident on portion 116 of the outcoupling diffractive optical element ODO. As shown in FIG. 3A , in one embodiment, the outcoupling diffractive optical element ODO and the incoupling diffractive optical element IDO are laterally separated in the x-axis and y-axis directions by a space 118. The space 118 may be arcuate and does not include any periodic diffractive structure.

[0036] In one embodiment, the depths of the periodic diffractive structures 106, 108, 110, 112 in the incoupling diffractive optical element IDO and the outcoupling diffractive optical element ODO are the same. In another embodiment, the depths of the periodic diffractive structures 104, 106, 108, 110, 112 are varied to increase the efficiency of a selected diffraction order. For example, the second set of periodic incoupling diffractive structures 106 and the third set of periodic incoupling diffractive structures 108 may have a greater depth than the first set of periodic incoupling diffractive structures 104 and the first set of periodic outcoupling diffractive structures 110 and the second set of periodic outcoupling diffractive structures 112.

[0037] As shown in FIG. 4A , in one embodiment, the image light guide 100 may include an intermediate diffractive optical element TDO formed on / in a first surface 102 of the image light guide 100. Alternatively, the intermediate diffractive optical element TDO may be formed on / in a second surface of the image light guide 100 opposite the first surface 102. The intermediate diffractive optical element TDO is located in the path of the image-bearing light WG between the incoupling diffractive optical element IDO and the outcoupling diffractive optical element ODO. The intermediate diffractive optical element TDO and the incoupling diffractive optical element IDO are laterally separated in the x-axis and y-axis directions by a space 118. A portion 116′ of the intermediate diffractive optical element TDO wraps around the incoupling diffractive optical element IDO. In other words, portion 116' of the intermediate diffractive optical element TDO extends at least partially around the incoupling diffractive optical element IDO such that a portion of the image-bearing light WG directed generally parallel to the second grating vector k2 and the third grating vector k3 is incident on portion 116' of the intermediate diffractive optical element TDO.

[0038] Continuing to refer to FIG. 4A , the intermediate diffractive optical element TDO and the outcoupling diffractive optical element ODO are laterally separated in the x-axis direction by a second space 120. The intermediate diffractive optical element TDO includes a first set of periodic intermediate diffractive structures 122 and a second set of periodic intermediate diffractive structures 124. In one embodiment, the first set of periodic intermediate diffractive structures 122 and the second set of periodic intermediate diffractive structures 124 have the same orientation, periodicity, and symmetry as the first set of periodic outcoupling diffractive structures 110 and the second set of periodic outcoupling diffractive structures 112. In one embodiment, the grating vectors k7 and k8 of the first set of periodic intermediate diffractive structures 122 and the second set of periodic intermediate diffractive structures 124 are equal in magnitude and direction to the grating vectors k4 and k5. In another embodiment, the grating vectors k7 and k8 of the first set of periodic intermediate diffractive structures 122 and the second set of periodic intermediate diffractive structures 124 are different in magnitude and direction from the grating vectors k4 and k5. One advantage of the intermediate diffractive optical element TDO is the greater freedom in positioning the outcoupling diffractive optical element ODO.

[0039] A portion of the image-bearing light incident on the first set of periodic intermediate diffractive structures 122 and the second set of periodic intermediate diffractive structures 124 may be outcoupled from the image light guide 100. However, this image-bearing light that is outcoupled at the intermediate diffractive optical element TDO is outside the eyebox and therefore does not affect the formation of the virtual image.

[0040] As shown in FIG. 4B , in one embodiment, the incoupling diffractive optical element IDO includes two plurality of periodic diffractive structures 106, 108. For example, the incoupling diffractive optical element IDO may include a first set of periodic linear grating structures 106 rotated / offset by an angle less than 30 degrees (e.g., 25 degrees) with respect to the x-axis, and a second set of periodic linear grating structures 108 rotated / offset by an angle less than −30 degrees (e.g., −25 degrees) with respect to the x-axis. The first set of periodic incoupling grating structures 106 and the second set of periodic incoupling grating structures 108 intersect. The first set of periodic incoupling grating structures 106 includes a first period, and the second set of periodic incoupling grating structures 108 includes a second period. In one embodiment, the second period is equal to the first period. The first set of periodic incoupling grating structures 106 defines a first grating vector k2, and the second set of periodic incoupling grating structures 108 defines a second grating vector k3.

[0041] The image light guide 100 includes a first intermediate diffractive optical element TDO1 located at least partially in the path of a portion of the incoupled image-bearing light WG. In one embodiment, when the image-bearing light is incident on the incoupling diffractive optical element IDO generally perpendicular to its plane, the first intermediate diffractive optical element TDO1 is located at least partially in the path of the image-bearing light propagating generally parallel to the first grating vector k2. A portion 116A of the first intermediate diffractive optical element TDO1 extends at least partially around the incoupling diffractive optical element IDO such that image-bearing light diffracted generally parallel to the first grating vector k2 is incident on the portion 116A of the first intermediate diffractive optical element TDO1. The image light guide 100 also includes a second intermediate diffractive optical element TDO2 located at least partially in the path of the portion of the incoupled image-bearing light WG. In one embodiment, when image-bearing light is incident on the incoupling diffractive optical element IDO generally perpendicular to its plane, the second intermediate diffractive optical element TDO2 is at least partially located in the path of image-bearing light propagating generally parallel to the second grating vector k3. The portion 116B of the second intermediate diffractive optical element TDO2 extends at least partially around the incoupling diffractive optical element IDO such that image-bearing light diffracted generally parallel to the second grating vector k3 is incident on the portion 116B of the second intermediate diffractive optical element TDO2.

[0042] 5, the image light guide 200 may have an incoupling diffractive optical element IDO and an outcoupling diffractive optical element ODO formed on / in the first surface 202 of the image light guide 200. The incoupling diffractive optical element IDO and the outcoupling diffractive optical element ODO may be configured as a single continuous diffractive pattern having a first set of periodic linear grating structures 206 rotated / offset by 60 degrees relative to the y-axis direction and a second set of periodic linear grating structures 208 rotated / offset by −60 degrees relative to the y-axis direction. In one embodiment, the depths of the first set of periodic linear grating structures 206 and the second set of periodic linear grating structures 208, including the incoupling diffractive optical element IDO, are greater than the depths of the periodic linear grating structures 206, 208, including the outcoupling diffractive optical element ODO. For diffractive optical elements including diffraction gratings, increasing the depth of the grating improves diffraction efficiency.

[0043] In embodiments of the present disclosure, the periodic structures may be, but are not limited to, linear diffractive features, circular posts, or elliptical posts. For example, Figure 6 shows a composite diffractive pattern 300 having diffractive features including circular posts 302. The incoupling diffractive optical element IDO and the outcoupling diffractive optical element ODO of the image light guide 100, 200 may be similarly configured.

[0044] A person skilled in the art will recognize that in one or more embodiments of the diffraction patterns shown in Figures 4A-6, the incoupling diffractive optical element IDO and / or the outcoupling diffractive optical element ODO include a third set of periodic diffractive structures 104, 113, which may be implicit as described above with respect to Figure 3A.

[0045] As shown in FIG. 7 , in one embodiment, stacked image light guide assembly 400 includes a first image light guide 402 coupled with a second image light guide 404. The first image light guide 402 and the second image light guide 404 may each be one of the image light guides 100, 200 described above. The image light guides 402, 404 are formed on separate substrates S1, S2 that are mechanically coupled. For example, the image light guides 402, 404 may be coupled via an adhesive. In one embodiment, stacked image light guide assembly 400 provides two separate color channels. As shown in FIG. 7 , the first image light guide 402 includes a red channel C for red light. R (e.g., in the 630-660 nm range), and the second image light guide 404 has a blue channel C for blue light B. B (eg, in the 440-470 nm range). In one embodiment, first image light guide 402 and second image light guide 404 are generally monochromatic plates that form multicolor image light guide assembly 400.

[0046] Blue light from the projector 18 entering the stacked image light guide assembly 400 is transmitted through the incoupling diffractive optical element IDO1 of the first image light guide 402 and is diffracted by the incoupling diffractive optical element IDO2 of the second image light guide 404. The diffracted blue light is then transmitted through the second image light guide substrate S2 via TIR and directed to the outcoupling diffractive optical element ODO2 of the second image light guide 404. Red light from the projector 18 entering the stacked image light guide assembly 400 is diffracted by the incoupling diffractive optical element IDO1 of the first image light guide 402. The diffracted red light is then transmitted through the first image light guide substrate S1 via TIR and directed to the outcoupling diffractive optical element ODO1 of the first image light guide 402.

[0047] The perspective view of FIG. 8 illustrates a display system 60 for augmented reality display using one or more image light guides of the present disclosure. Display system 60 is shown as an HMD with a right-eye optical system 64R having an image light guide 66R for the right eye. Display system 60 includes an image source 18, such as a picoprojector or similar device, that can be energized to generate an image. In one embodiment, display system 60 includes a left-eye optical system including one or more image light guides and a second image source. The generated image can be a stereoscopic pair of images for a 3D display. The virtual image formed by display system 60 can appear superimposed or overlaid on real-world scene content observed by a viewer through image light guide 66R. Additional components familiar to those skilled in the art of augmented reality visualization, such as mounting one or more cameras on the frame of the HMD for viewing scene content or viewer eye tracking, can also be provided.

[0048] 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 this 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 present invention is indicated by the appended claims, and all changes that come within the meaning and range of equivalents thereof are intended to be embraced therein.

Claims

1. 1. An image light guide for conveying a virtual image, comprising: a substrate operable to propagate an image-bearing light beam along its length; an incoupling diffractive optical element formed along the substrate, the incoupling diffractive optical element operable to diffract the image-bearing light beam into the substrate in an angle-encoded manner; an outcoupling diffractive optical element formed along the substrate, the outcoupling diffractive optical element operable to diffract the image-bearing light beam from the substrate to an eyebox in an angle-decoded manner; the incoupling diffractive optical element includes first, second, and third pluralities of periodic incoupling diffractive structures defining a first grating vector, a second grating vector, and a third grating vector, respectively; the outcoupling diffractive optical element includes first and second pluralities of periodic outcoupling diffractive structures defining a fourth grating vector and a fifth grating vector, respectively, and the first and second pluralities of periodic outcoupling diffractive structures define a sixth grating vector; the first and second plurality of periodic outcoupling diffractive structures are arranged parallel to the second and third plurality of periodic incoupling diffractive structures; the first lattice vector and the sixth lattice vector are parallel to each other; further comprising an intermediate diffractive optical element located in an optical path between the incoupling diffractive optical element and the outcoupling diffractive optical element; a portion of the intermediate diffractive optical element at least partially surrounding the incoupling diffractive optical element; The intermediate diffractive optical element is a first plurality of periodic intermediate diffractive structures oriented parallel to the third plurality of periodic incoupling diffractive structures; a second plurality of periodic intermediate diffractive structures oriented parallel to the second plurality of periodic incoupling diffractive structures; an arcuate space is disposed between the incoupling diffractive optical element and the intermediate diffractive optical element, and the arcuate space does not include any periodic diffractive structure; An image light guide for conveying a virtual image, wherein a space is disposed between the intermediate diffractive optical element and the outcoupling diffractive optical element, and the space does not include any periodic diffractive structure.

2. 2. The image light guide for conveying a virtual image of claim 1, wherein the periodic outcoupling diffractive structure defining the sixth grating vector is configured to outcouple image-bearing light incoupled by the first plurality of periodic incoupling diffractive structures.

3. 2. The image light guide for conveying a virtual image of claim 1, wherein the first and second pluralities of periodic outcoupling diffractive structures have a periodicity equivalent to a periodicity of the second and third pluralities of periodic incoupling diffractive structures.

4. The image light guide for conveying a virtual image of claim 1 , wherein the outcoupling diffractive optical element is located in a path of the first grating vector.

5. 2. An image light guide for conveying a virtual image as described in claim 1, wherein a portion of the outcoupling diffractive optical element is positioned at least partially around the incoupling diffractive optical element, an arcuate space is positioned between the incoupling diffractive optical element and the outcoupling diffractive optical element, and the arcuate space does not include any periodic diffractive structure.

6. 10. An image light guide for conveying a virtual image as described in claim 1, wherein the substrate is a first substrate of a stacked image light guide assembly, a second substrate operable to propagate an image-bearing light beam along its length is coupled to the first substrate, and the first and second substrates include a monochromatic light channel forming a polychromatic image light guide assembly.

7. 2. An image light guide for transmitting a virtual image as described in claim 1, wherein each periodic incoupling diffractive structure of the second plurality of periodic incoupling diffractive structures is positioned at 60 degrees relative to each periodic incoupling diffractive structure of the first plurality of periodic incoupling diffractive structures.

8. 8. An image light guide for conveying a virtual image as described in claim 7, wherein each periodic incoupling diffractive structure of the first and second plurality of periodic incoupling diffractive structures has a greater depth than each periodic outcoupling diffractive structure of the periodic outcoupling diffractive structures.

9. 1. An image light guide for conveying a virtual image, comprising: a substrate operable to propagate an image-bearing light beam along its length; an incoupling diffractive optical element formed along the substrate, the incoupling diffractive optical element operable to diffract the image-bearing light beam into the substrate in an angle-encoded manner, the incoupling diffractive optical element comprising a first plurality of periodic incoupling diffractive structures and a second plurality of periodic incoupling diffractive structures; an outcoupling diffractive optical element formed along the substrate, the outcoupling diffractive optical element operable to diffract the image-bearing light beam from the substrate in an angle-decoded manner, the outcoupling diffractive optical element comprising: a first plurality of periodic outcoupling diffractive structures oriented parallel to the second plurality of periodic incoupling diffractive structures and having a periodicity equivalent to that of the first plurality of periodic incoupling diffractive structures; and a second plurality of periodic outcoupling diffractive structures oriented parallel to the first plurality of periodic incoupling diffractive structures and having a periodicity equivalent to that of the second plurality of periodic incoupling diffractive structures; a first intermediate diffractive optical element located in a first optical path between the incoupling diffractive optical element and the outcoupling diffractive optical element, the first intermediate diffractive optical element comprising a first plurality of periodic intermediate diffractive structures oriented parallel to the second plurality of periodic incoupling diffractive structures and the first plurality of periodic outcoupling diffractive structures; a second intermediate diffractive optical element located in a second optical path between the incoupling diffractive optical element and the outcoupling diffractive optical element, the second intermediate diffractive optical element comprising a second plurality of periodic intermediate diffractive structures oriented parallel to the first plurality of periodic incoupling diffractive structures and the second plurality of periodic outcoupling diffractive structures; and Equipped with a portion of the first intermediate diffractive optical element is positioned at least partially around the incoupling diffractive optical element, and an arcuate space is disposed between the incoupling diffractive optical element and the first intermediate diffractive optical element; a portion of the second intermediate diffractive optical element is positioned at least partially around the incoupling diffractive optical element, and an arcuate space is disposed between the incoupling diffractive optical element and the second intermediate diffractive optical element; the arcuate space does not include any periodic diffractive structure; the first intermediate diffractive optical element and the second intermediate diffractive optical element define a space therebetween that does not include any periodic diffractive structure; an image light guide for conveying a virtual image, wherein a portion of image-bearing light incident on the incoupling diffractive optical element propagates along a third optical path between the first and second intermediate diffractive optical elements toward the outcoupling diffractive optical element.

10. The image light guide for conveying a virtual image of claim 9 , wherein the second plurality of periodic incoupling diffractive structures intersects with the first plurality of periodic incoupling diffractive structures.

11. The image light guide for conveying a virtual image of claim 10 , wherein the first plurality of periodic outcoupling diffractive structures intersect with the second plurality of periodic outcoupling diffractive structures.

12. 10. An image light guide for transmitting a virtual image as described in claim 9, wherein the incoupling diffractive optical element is substantially circular, and a portion of the first intermediate diffractive optical element and a portion of the second intermediate diffractive optical element extend along at least half a perimeter of the incoupling diffractive optical element.

13. An image light guide for transmitting a virtual image as described in claim 9, further comprising a space arranged between the first and second intermediate diffractive optical elements and the outcoupling diffractive optical element, wherein the space does not include any periodic diffractive structure.

Images