Multi-plate split coupler waveguide system

Abstract

An image light guide for conveying a virtual image, including a first waveguide having a first surface and an opposing second surface, a first in-coupling diffractive optic arranged along one of the first surface and the second surface, and a first out-coupling diffractive optic arranged along at least one of the first surface and the second surface; a second waveguide having a first surface and an opposing second surface, a second in-coupling diffractive optic arranged along one of the first surface and the second surface, and a second out-coupling diffractive optic arranged along at least one of the first surface and the second surface; and a third waveguide having a first surface and an opposing second surface, a third in-coupling diffractive optic arranged along one of the first surface and the second surface, and a third out-coupling diffractive optic arranged along at least the first surface or second surface.

Description

MULTI-PLATE SPLIT COUPLER WAVEGUIDE SYSTEMTECHNICAL 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) are being developed for a range of diverse uses, including military, commercial, 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 user. An optical image light guide may convey image-bearing light to a viewer in a narrow space for directing the virtual image to the viewer's pupil and enabling this superposition function.

[0003] In general, HMD optics must meet a number of basic requirements for viewer acceptance, including pupil size, field of view (FOV), and sufficient brightness of the generated virtual image for visibility and viewer comfort. In addition, HMD optics providing polychromatic virtual images to a viewer must also limit ghost images (e.g., unintended secondary images related to the primary image) conveyed to the eyebox to increase clarity of the virtual images and reduce potential eye strain.SUMMARY

[0004] It is an object of the present disclosure to advance the art of virtual image presentation. The aspect, 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 waveguide having a first surface and an opposing second surface, a first in-coupling diffractive optic arranged along one of the first surface and the second surface, and a first out- coupling diffractive optic arranged along at least one of the first surface and the second surface, a second waveguide having a first surface and an opposing second surface, a second in-coupling diffractive optic arranged along one of the first surface and the second surface of the second waveguide, and a second out-coupling diffractive optic arranged along at least one of the first surface and the second surface of the second waveguide, and a third waveguide having a first surface and an opposing second surface, a third in-coupling diffractive optic arranged along one of the first surface and the second surface of the third waveguide, and a third out-couplingdiffractive optic arranged along at least one of the first surface and the second surface of the third waveguide. Wherein one of the first in-coupling diffractive optic, the second in-coupling diffractive optic, and the third in-coupling diffractive optic is arranged laterally offset from the other two in-coupling diffractive optics.

[0005] In an exemplary' embodiment, an image source is utilized in conjunction with the image light guide to provide an image light guide system.

[0006] In an exemplary embodiment, the image light guide system further includes an optical coupler configured to produce two laterally offset light pupils, wherein a first light pupil comprises a first optical path and a second optical path, and a second light pupil comprises a third optical path.

[0007] In an exemplary embodiment, the first in-coupling diffractive optic and the first out- coupling diffractive optic are configured to couple image-bearing light of the first optical path; the second in-coupling diffractive optic and the second out-coupling diffractive optic are configured to couple image-bearing light of the second optical path; and the third in-coupling diffractive optic and the third out-coupling diffractive optic are configured to couple imagebearing light of the third optical path.

[0008] In an exemplary embodiment, the optical coupler includes an input surface configured to receive combined image-bearing light from a light source, a first output surface configured to transmit image-bearing light of at least a first wavelength range, a second output surface laterally offset relative to the first output surface and configured to transmit image-bearing light of a second wavelength range; and a surface configured to reflect the image-bearing light of the second wavelength range toward the second output surface.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. l 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 w ithin 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 schematic a top view of an embodiment of an image light guide, with an exaggerated thickness, according to an exemplary embodiment of the presently disclosed subject matter.

[0013] FIG. 3B is a schematic top view of the image light guide according to FIG. 3A.

[0014] FIG. 3C is a schematic top view of the image light guide according to FIG. 3A.

[0015] FIG. 3D is a schematic top view of the image light guide according to FIG. 3A including one or more optical filters.

[0016] FIG. 4A is schematic a top view of an embodiment of an image light guide sy stem, with an exaggerated thickness, according to an exemplary embodiment of the presently disclosed subject matter.

[0017] FIG. 4B is schematic 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 subj ect matter.

[0018] FIG. 4C is schematic a top view of an embodiment of an image light guide system, with an exaggerated thickness, according to an exemplary7embodiment of the presently disclosed subj ect matter.

[0019] FIG. 4D is schematic 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.

[0020] FIG. 5A is schematic 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 subj ect matter.

[0021] FIG. 5B is schematic 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 subj ect matter.

[0022] FIG. 6A is schematic 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.

[0023] FIG. 6B is schematic 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 subj ect matter.

[0024] FIG. 7 is a schematic illustrating ghost images produced by an image light guide system.DETAILED DESCRIPTION

[0025] 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.

[0026] 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.

[0027] 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.

[0028] 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.

[0029] 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.

[0030] 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.

[0031] 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.

[0032] 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.

[0033] 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.

[0034] 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 differentpositions 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.

[0035] 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 imagebearing 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.

[0036] 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.

[0037] 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-ty pe 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 imagebearing light beams WG from the image light guide 12 as the image-bearing light beams WO propagating toward the eyebox E.

[0038] 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 imagebearing light beams WG toward the out-coupling diffractive optic ODO (having a grating vector k3) for longitudinally replicating the angularly related beams of the image-bearing 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 parallel to the direction of periodicity of the diffractive features (e.g., normal to 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.

[0039] 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 areplicated 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., they-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 preserving 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 imagebearing 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.

[0040] 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-beanng light beams WG are turned 120 degrees. Byorienting 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 diffractiveoptics 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.

[0041] 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 in-coupling 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.

[0042] 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 iscomprised 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.

[0043] 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.

[0044] As described in further detail below, image light guide systems including a stack of three or more waveguides are subject to increased crosstalk (e.g., interference between in-coupled light of different wavelength ranges) between color channels (e.g., wavelength range light paths) as compared to image light guide systems including a stack of two waveguides. The crosstalk often results in ghost images, or unintended secondary images related to the primary image. The presently disclosed subject matter provides an image light guide system including a stack of three or more waveguides configured to reduce crosstalk and the resultant ghost images.

[0045] FIGS. 3A-3C show an image light guide system 10 including a stack of three waveguides 20 A, 20B, 20C. For example, the first waveguide 20A, the second waveguide 20B, and the third waveguide 20C have front and back surfaces 14, 16, with in-coupling diffractive optics IDO1, IDO2, IDO3 and out-coupling diffractive optics ODO1, ODO2, ODO3 arranged along the respective front surfaces 14. In an example arrangement, the in-coupling diffractive optics IDO1, IDO2, IDO3 are aligned along a first imaginary axis normal to the front surface 14 and the out- coupling diffractive optics ODO1, ODO2. ODO3 are aligned along a second imaginary axis normal to the front surface 14.

[0046] The waveguides 20A, 20B, 20C may be made of optical glass or plastic. As illustrated in FIGS. 3A-3C, in an example arrangement, the in-coupling diffractive optics IDO1, IDO2, IDO3 are arranged as transmissive-ty pe diffractive optics such as, without limitation, a surface relief diffraction grating. The out-coupling diffractive optics ODO1, ODO2, ODO3 are arranged as reflective-type diffractive optics such as, without limitation, a surface relief diffraction grating. In exemplary arrangements, one or more of the in-coupling diffractive optics IDO1, IDO2, IDO3 may be arranged as reflective-type diffractive optics, and one or more of the out-coupling diffractive optics ODO1. ODO2, ODO3 may be arranged as transmissive-type diffractive optics. Example embodiments of the waveguides 20A, 20B. 20C may also include an optionalintermediate diffractive optic TO (not shown). For example, one or more of the in-coupling diffractive optics IDO1, IDO2, IDO3 and one or more of the out-coupling diffractive optics ODO1, ODO2, ODO3 may be arranged along the back surface 16 of the respective waveguides 20A, 20B, 20C. In one or more examples, one or more of the out-coupling diffractive optics ODO1. ODO2. ODO3 are arranged to provide eyebox expansion in two dimensions. For example, the diffractive features of one or more of the out-coupling diffractive optics ODO1, ODO2, ODO3 may include posts (e.g., in contrast, without limitation, to linear diffractive features).

[0047] In an exemplary arrangement, the waveguide 20A is optimized to convey image-bearing light in the green wavelength range (e.g., 495 nm - 570 nm), the waveguide 20B is optimized to convey image-bearing light in the red wavelength range (e.g., 620 nm - 750 nm), and the waveguide 20C is optimized to convey image-bearing light in the blue wavelength range (e.g., 450 nm - 495 nm). In an exemplary arrangement, image-bearing light WI is produced by an image source 18 in the form of white light that contains light of three primary' color bands or channels, e.g., WIG for light within the green wavelength, WIR for light within the red wavelength range, and WIB for light within the blue wavelength range. In an exemplary’ arrangement, imagebearing light WIG, WIR, WIB, from the image source 18 is incident upon the first in-coupling diffractive optic IDO1 and a portion of the image-bearing light WIG is diffracted by7the first incoupling diffractive optic IDO1 and generally propagates toward the first out-coupling diffractive optic ODO1 via TIR as WGG. For example, the diffractive features of the first in-coupling diffractive optic IDO1 and the first out-coupling diffractive optic ODO1 are arranged to optimize coupling of a first wavelength range of image-bearing light WIG. A portion of the image-bearing light WIR is diffracted by the second in-coupling diffractive optic IDO2 and generally propagates toward the second out-coupling diffractive optic ODO2 via TIR as WGR. For example, the diffractive features of the second in-coupling diffractive optic IDO2 and the second out-coupling diffractive optic ODO2 are arranged to optimize coupling of a second wavelength range of imagebearing light WIR. A portion of the image-bearing light WIB is diffracted by the third in-coupling diffractive optic IDO3 and generally propagates toward the third out-coupling diffractive optic ODO3 via TIR as WGB. For example, the diffractive features of the third in-coupling diffractive optic IDO3 and the third out-coupling diffractive optic ODO3 are arranged to optimize coupling of a third wavelength range of image-bearing light WIB.

[0048] Referring now to FIG. 3A, the image-bearing light WOG diffracted by the first out- coupling diffractive optic ODO1 toward the eyebox E is incident on the second out-coupling diffractive optic ODO2 and the third out-coupling diffractive optic ODO3. Additionally, the image-bearing light WIR emitted by the image source 18 is incident on the first in-couplingdiffractive optic IDO1 and the image-bearing light WOR diffracted by the second out-coupling diffractive optic ODO2 toward the eyebox E is incident on the third out-coupling diffractive optic ODO3. Also, as shown, the image-bearing light WIB emitted by the image source 18 is incident on the first in-coupling diffractive optic IDO1 and the second in-coupling diffractive optic IDO2. These points of incidence are referred to herein as first-interaction transmission points 30R, 30G, and 30B, respectively. As described above, each wavelength range of image-bearing light experiences two first-interaction transmission points 30R, 30G, 30B, for a total of six first- interaction transmission points 30R, 30G, 30B in the image light guide system 10. As illustrated in FIG. 7, these first-interaction transmission points 30R. 30G, 30B produce what is referred to herein as ghost images. These ghost images are offset from the main image which the system is optimized to convey to the eyebox.

[0049] Referring now to FIG. 3B, a portion of the image-bearing light WIG transmits through the first in-coupling diffractive optic IDO1 (e.g., zero-order diffraction) and is incident upon the second in-coupling diffractive optic IDO2 at interaction point 32G and the third in-coupling diffractive optic IDO3 at interaction point 32G. Additionally, a portion of the image-bearing light WIR transmits through the second in-coupling diffractive optic IDO2 (e.g., zero-order diffraction) and is incident upon the third in-coupling diffractive optic IDO3 at interaction point 32R. The image-bearing light WIG, WIR is diffracted (e.g., in-coupled) inefficiently during these interactions at interaction points 32G, 32R such that any ghost images produced by these interactions have less intensity (e.g., less impact on the resultant image) relative to the ghosting created by the other interference points described herein. In other words, zero-order diffracted light does not refract; so, the zero-order diffracted light is either distributing light where it needs to be, or it is not reacting to diffractive features, and does not contribute to ghost images. Therefore, these interaction points 32G, 32R are not considered first-interaction transmission points.

[0050] Referring now to FIG. 3C, a portion of the image-bearing light WIG transmits through the first in-coupling diffractive optic IDO1 (e.g., zero-order diffraction) and is incident upon the second in-coupling diffractive optic IDO2 and the third in-coupling diffractive optic IDO3 at first- interaction reflection points 40G. Additionally, a portion of the image-bearing light WIR transmits through the second in-coupling diffractive optic IDO2 (e.g., zero-order diffraction) and is incident upon the third in-coupling diffractive optic IDO3 at first-interaction reflection point 40R. Also, a portion of the image-bearing light WIB transmits through the first in-coupling diffractive optic IDO1 (e.g., zero-order diffraction) and is incident upon the second in-coupling diffractive optic IDO2 at first-interaction reflection point 40B. These first-interaction reflection points 40G, 40R, 40B also contribute to ghost images. The image-bearing light WIR incident on the third in-couplingdiffractive optic IDO3 does not reflect with sufficient efficiency to contribute to ghost images because the pitch of the diffractive features in the third in-coupling diffractive optic IDO3 is sufficiently small relative to the wavelength range of the mage-bearing light WIR.

[0051] Referring now to FIG. 3D, in an exemplary embodiment, the image light guide system 10 includes one or more optical filters 50A, 50B configured to selectively transmit image-bearing light of at least one wavelength range, and selectively prevent transmission of image-bearing light of at least one other wavelength range. For example, the one or more optical filters 50A, 50B may be absorptive filters. In another exemplary embodiment, one or more of the optical filters 50A, 50B may be a dichroic filter. As illustrated in FIG. 3D, in an example embodiment, an optical filter 50A may be arranged along the back surface 16 of the first waveguide 20A to substantially prevent transmission of the image-bearing light WIG to the second and third in-coupling diffractive optics IDO2, IDO3, and an optical filter 50B may be arranged along the back surface 16 of the second waveguide 20B to substantially prevent transmission of the image-bearing light WIR to the third in-coupling diffractive optic IDO3.

[0052] However, it should be noted that optical filters present some limitations for preventing crosstalk in the image light guide system 10. For example, optical filters utilized to prevent or limit transmission of out-coupled image-bearing light WOG, WOR from incidence on the out- coupling diffractive optics ODO2, ODO3 would discolor the image transmitted to the eyebox if the optical filter covers the out-coupling diffractive optics ODO2, ODO3. In addition, optical filters 50A, 50B require a high degree of parallelism with the respective back surfaces 16, significantly increasing the cost of the image light guide system 10.

[0053] Referring now to FIGS. 4A-4D, in an exemplary embodiment, the first, second, and third in-coupling diffractive optics IDO1. IDO2, IDO3 include a blazed or slanted diffractive pattern. As shown in FIG. 4 A, the first in-coupling diffractive optic IDO1 may be arranged along the front surface 14 of the first waveguide 20A such that it is not colinear with the second and third incoupling diffractive optics IDO2, IDO3. In other words, the first in-coupling diffractive optic IDO1 is offset from the second and third in-coupling diffractive optics IDO2. IDO3 in the ± x- axis direction. In this arrangement, the number of first-interaction transmission points 30R, 30G, 30B is reduced from six to four, leading to reduced ghost images presented in the out-coupled image. For example, as shown in FIG. 4A, the first-interaction transmission points 30R, 30B at the first in-coupling diffractive optic IDO1 are eliminated. As described above, the image-bearing light WIR incident on the third in-coupling diffractive optic IDO3 at the first-interaction reflection point 40R does not reflect with sufficient efficiency to contribute to ghost images because the pitch of the diffractive features in the third in-coupling diffractive optic IDO3 is sufficiently smallrelative to the wavelength range of the image-bearing light WIR. It should be appreciated that any one of the first, second, and third in-coupling diffractive optics IDO1, IDO2, IDO3 may be offset from the other two of the first, second, and third in-coupling diffractive optics IDO1, IDO2, IDO3 in order to reduce the number of first-interaction transmission points 30R, 30G, 30B. However, offsetting the in-coupling diffractive optic configured for certain wavelength ranges, such as for example the green wavelength range of image-bearing light, has a greater influence on the cpjal ity of the virtual image viewed from within the eyebox E. For example, as described above with reference to FIG. 4 A, offsetting the first in-coupling diffractive optic IDO1, configured to incouple image-bearing light in the green wavelength range, while arranging the second in-coupling diffractive optic IDO2, configured to in-couple image-bearing light in the red wavelength range, before (in order of incidence of the image-bearing light WI) the third in-coupling diffractive optic IDO3, configured to in-couple image-bearing light in the blue wavelength range, eliminates both the first-interaction transmission points 30R, 30B at the first in-coupling diffractive optic IDO1 and the first-interaction reflection point 40R. In general, ghost images in the blue wavelength range are preferable to ghost images in the green wavelength range, because the human eye is more sensitive to the green wavelength range than to the red wavelength range and the blue wavelength range, and the human eye is less sensitive to the blue wavelength range than to the red wavelength range and the green wavelength range. This sensitivity is a result of the combined color perception of the rod and cone photoreceptor cells in the retina. For example, green light strongly stimulates both L cone photoreceptor cells and M cone photoreceptor cells.

[0054] As illustrated in FIG. 4D, in an exemplary embodiment, the image light guide system 10 may be configured to further reduce ghost images resulting from the first-interaction reflection point 40B by arranging the first in-coupling diffractive optic IDO1 offset from the second and third in-coupling diffractive optics IDO2, IDO3 in the (-)x-axis direction. With continued reference to FIG. 4D, in an exemplary embodiment, an anti-reflective coating 80 is arranged along the back surface 16 of at least one of the first, second, or third waveguides 20 A, 20B, 20C to further reduce crosstalk. While illustrated in FIG. 4D, it should be appreciated that the one or more anti-reflective coatings 80 may be utilized in any of the embodiments described herein.

[0055] With continued reference to FIGS. 4A-4D, in an exemplary embodiment, the image light guide system 10 includes a coupler 60 (also referred to herein as an "‘optical coupler’) comprising a color-selective beam splitter 62 and a reflective surface 64. For example, the color-selective beamsplitter 62 may be configured to transmit image-bearing light WIR, WIB in the second and third wavelength ranges, while reflecting image-bearing light WIG in the first wavelength range towards the reflective surface 64. For example, the coupler 60 is configured to produce twolaterally offset light pupils, wherein the first light pupil comprises a first optical path and a second optical path for image-bearing light WIR, WIB, and the second light pupil comprises a third optical path for image-bearing light WIG. The color-selective beamsplitter 62 may include a dichroic mirror 63 or dichroic coating 63 configured to transmit image-bearing light WIR, WIB in the second and third wavelength ranges, while reflecting image-bearing light WIG in the first wavelength range. In turn, the reflective surface 64 may be configured to direct image-bearing light WIG to the offset first in-coupling diffractive optic IDO1. In an example embodiment, the reflective surface 64 may be arranged within a prism optically coupled with the beam splitter 62. In an example, the reflective surface 64 comprises a dichroic mirror or spectrally reflective mirror. In an exemplary embodiment, the coupler 60 includes an input surface 66 configured to receive combined image-bearing light WIR, WIB, WIG from the light source 18. The coupler 60 also includes a first output surface 68 configured to transmit image-bearing light of at least a first wavelength range WIR, WIB, a second output surface 70 laterally offset (e.g., in the ± x-axis direction) relative to the first output surface 68 and configured to transmit image-bearing light of a second wavelength range WIG, and the surface 64 configured to reflect the image-bearing light of the second wavelength range WIG toward the second output surface 70. The first and second output surfaces 68, 70 may be arranged at an oblique angle relative to the input surface 66.

[0056] Referring now to FIG. 4B, in an exemplary embodiment, the first waveguide 20A configured to convex’ image-bearing light WIG to the eyebox E is arranged between the second waveguide 20B configured to convey image-bearing light WIR to the eyebox E and the third waveguide 20C configured to convey image-bearing light WIB to the eyebox E. As described above, the image-bearing light WIR incident on the third in-coupling diffractive optic IDO3 at the first-interaction reflection point 40R (shown in FIG. 4A) does not reflect with sufficient efficiency to contribute to ghost images because the pitch of the diffractive features in the third in-coupling diffractive optic IDO3 is sufficiently small relative to the wavelength range of the image-bearing light WIR. Further, in this arrangement the portion of the image-bearing light WIB incident on the second in-coupling diffractive optic IDO2 at the first-interaction reflection point 40B and reflected is not incident on any other in-coupling diffractive optics, and therefore the reflected portion of the image-bearing light WIB does not contribute to crosstalk or ghost images.

[0057] Referring now to FIG. 4C, in an exemplary embodiment, the image source 18 may be located on the same side of the image light guide system 10 as the eyebox E. As described above, this arrangement results in only four first-interaction transmission points 30R, 30G, 30B. It should be appreciated that the first in-coupling diffractive optic IDO1, or the second in-couplingdiffractive optic IDO2, or the third in-coupling diffractive optic IDO3 may be arranged proximate the optical coupler 60.

[0058] Referring now to FIGS. 5 A and 5B, in an exemplary embodiment, the image source 18 may include a first image source 18 A operable to emit two wavelength ranges of image-bearing light WIR, WIB and a second image source 18B operable to emit at least one wavelength range of image-bearing light WIG. AS shown in FIG. 5A, the image sources 18A, 18B are located on the opposite side of the waveguides 20A, 20B, 20C, as the eyebox E, while FIG. 5B illustrates the image sources 18 A, 18B located on the same side of the waveguides 20 A, 20B, 20C as the eyebox E.

[0059] Referring now to FIGS. 6A and 6B, in an exemplar}7embodiment, the image source 18 may be arranged to emit image-bearing light WIR, WIB, WIG in a direction generally parallel with the front and back surfaces 14, 16 of the waveguides 20 A, 20B, 20C. In other words, the image source 18 may be arranged to emit image-bearing light WIR, WIB, WIG in the x-axis direction. For example, the color-selective beamsplitter 62 may be configured to reflect image-bearing light WIR, WIB in the second and third wavelength ranges toward the second and third in-coupling diffractive optics IDO2, IDO3, while transmitting image-bearing light WIG in the first wavelength range towards the dichroic mirror 64. In turn, the dichroic mirror 64 may be configured to direct image-bearing light WIG to the offset first in-coupling diffractive optic IDO1. As illustrated in FIGS. 6A and 6B, the image source 18 and coupler 60 may be arranged opposite the eyebox E or on the same side of the image light guide system 10 as the eyebox E.

[0060] Referring now7to FIG. 7, a conventional image light guide system 10 (see, for example, FIGS. 3A-3C) having a stack of three waveguides 20A, 20B, 20C produces a number of ghost images caused by the first-interaction transmission points 30R. 30G, 30B and / or the first-interaction reflection points 40G, 40R, 40B as described above. The main image, which the conventional image light guide system 10 is optimized to convey to the eyebox, is illustrated as the English alphabet in upper-case and lower-case, follow ed by the Arabic numerals 1 through 5 and is designated by the reference character WOG. WOR, WOB. Ghost images in the blue wavelength range are designated by reference character WOB, ghost images in the red wavelength range are designated by reference character WOR, and ghost images in the green wavelength range are designated by reference character WOG. These ghost images are offset from the main image which the system is optimized to convey to the eyebox. To increase clarity, the main image and the ghost images are shown in separate and distinct fonts (i.e., typeface). However, it should be appreciated that the main image and the ghost images would appear in the same font to a viewer.

[0061] 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

CLAIMSWhat is claimed is:

1. An image light guide for conveying a virtual image, comprising: a first waveguide, comprising: a first surface and an opposing second surface; a first in-coupling diffractive optic arranged along one of the first surface and the second surface; and a first out-coupling diffractive optic arranged along at least one of the first surface and the second surface; a second waveguide, comprising: a first surface and an opposing second surface; a second in-coupling diffractive optic arranged along one of the first surface and the second surface; and a second out-coupling diffractive optic arranged along at least one of the first surface and the second surface; and a third waveguide, comprising: a first surface and an opposing second surface; a third in-coupling diffractive optic arranged along one of the first surface and the second surface; and a third out-coupling diffractive optic arranged along at least one of the first surface and the second surface; wherein one of the first in-coupling diffractive optic, the second in-coupling diffractive optic, and the third in-coupling diffractive optic is arranged laterally offset from the other two in-coupling diffractive optics.

2. The image light guide according to claim 1, wherein two of the first waveguide, second waveguide, and third waveguide have two or fewer first interaction transmission interference points.

3. The image light guide according to claims 1 or 2, wherein the image light guide system comprises less than or equal to four first interaction transmission interference points of imagebearing light.

4. The image light guide according to claim 1, wherein the second in-coupling diffractive optic comprises one first interaction transmission interference point, the second out-coupling diffractive optic comprises one first interaction transmission interference point, and the third out- coupling diffractive optic comprises two or fewer first interaction transmission interference points.

5. The image light guide according to claim 1, wherein the first in-coupling diffractive optic, the second in-coupling diffractive optic, and the third in-coupling diffractive optic comprise blazed or slanted linear diffractive features.

6. The image light guide according to claim 1, wherein the one of the first in-coupling diffractive optic, second in-coupling diffractive optic, and third in-coupling diffractive optic arranged laterally offset is offset in an original direction of propagation of in-coupled imagebearing light.

7. An image light guide system for conveying a virtual image, comprising: an image source; a first waveguide, comprising: a first surface and an opposing second surface; a first in-coupling diffractive optic arranged along one of the first surface and the second surface; and a first out-coupling diffractive optic arranged along at least one of the first surface and the second surface; a second waveguide, comprising: a first surface and an opposing second surface; a second in-coupling diffractive optic arranged along one of the first surface and the second surface; and a second out-coupling diffractive optic arranged along at least one of the first surface and the second surface; and a third waveguide, comprising: a first surface and an opposing second surface; a third in-coupling diffractive optic arranged along one of the first surface and the second surface; and a third out-coupling diffractive optic arranged along at least one of the first surface and the second surface; wherein one of the first in-coupling diffractive optic, the second in-coupling diffractive optic, and the third in-coupling diffractive optic is arranged laterally offset from the other two.

8. The image light guide system according to claim 7, further comprising an optical coupler configured to produce two laterally offset light pupils, wherein a first light pupil comprises a first optical path and a second optical path, and a second light pupil comprises a third optical path.

9. The image light guide system according to claim 8, wherein the first in-coupling diffractive optic and the first out-coupling diffractive optic are configured to couple image-bearing light of the first optical path; the second in-coupling diffractive optic and the second out-coupling diffractive optic are configured to couple image-bearing light of the second optical path; and the third in-coupling diffractive optic and the third out-coupling diffractive optic are configured to couple image-bearing light of the third optical path.

10. The image light guide system according to claim 9, wherein the third in-coupling diffractive optic is laterally offset from the first in-coupling diffractive optic and the second incoupling diffractive optic.

11. The image light guide system according to claim 10, wherein third in-coupling diffractive optic is proximate the optical coupler.

12. The image light guide system according to claim 10, wherein the first in-coupling diffractive optic, or the second in-coupling diffractive optic, or the third in-coupling diffractive optic is proximate the optical coupler.

13. The image light guide system according to claim 7, further comprising an optical filter arranged between the first in-coupling diffractive optic and the second in-coupling diffractive optic.

14. The image light guide system according to claim 7, further comprising an anti-reflective coating arranged along the first or second surface of at least one of the first, second, and third waveguides, wherein the anti-reflective coating at least partially overlaps the offset in-coupling diffractive optic in the ± x-axis direction.

15. An optical coupler for splitting a combined light path, comprising: an input surface configured to receive combined image-bearing light from a light source; a first output surface configured to transmit image-bearing light of at least a first wavelength range; a second output surface laterally offset relative to the first output surface and configured to transmit image-bearing light of a second wavelength range; a surface configured to reflect the image-bearing light of the second wavelength range toward the second output surface.

16. The optical coupler according to claim 15, wherein the surface configured to reflect the image-bearing light of the second wavelength range is partially reflective or totally reflective.

17. The optical coupler according to claim 15, wherein the first and second output surfaces are parallel.

18. The optical coupler according to claim 15, wherein the first and second output surfaces are arranged at an oblique angle relative to the input surface.

Images