Dual input imaging light guide

Abstract

An image light guide for conveying a virtual image includes a substrate operable to propagate a beam of image-bearing light. A first in-coupling diffractive optic is formed along the substrate and is operable to diffract a first portion of the beam of image-bearing light from an image source into the substrate in an angularly encoded form and to transmit a second portion of the beam of image-bearing light from the image source. An out-coupling diffractive optic is formed along the substrate, wherein the out-coupling diffractive optic is operable to expand the beam of image-bearing light and to direct the expanded beam of image-bearing light from the substrate in an angularly decoded form. A second in-coupling diffractive optic is formed along the substrate and is operable to diffract a portion of the second portion of the beam of image-bearing light into the substrate in an angularly encoded form.

Description

TECHNICAL FIELD

[0001] The present disclosure relates generally to electronic displays and more particularly to displays that utilize an image light guide with diffractive optics to convey image-bearing light to a viewer. BACKGROUND

[0002] Head-mounted displays (HMDs) and virtual image near-eye displays are being developed for a wide variety of uses, including military, commercial, industrial, firefighting, and entertainment applications. For many of these applications, it is of value to form a virtual image that can be visually superimposed on real-world images located in the field of view of the HMD user. An optical image light guide can convey image-bearing light to a viewer in a narrow space in order to direct a virtual image to the viewer's pupil and accomplish this superposition function.

[0003] While conventional image light guide arrangements have provided significant reductions in the bulk, weight, and overall cost of near-eye display optics, further improvements are needed. In some cases, the size of the eyebox is constrained, forcing HMD design limitations on movement and device placement tolerances. Light can often be distributed non-uniformly across the field of view, resulting in hot spots, such as higher levels of light within the center of the field and lower light levels at the periphery of the field. Thus, in some arrangements, the diffraction efficiency of the image light guide is not great enough to produce the desired virtual image brightness. For satisfactory visibility and viewer comfort, the virtual image generated by the image light guide arrangement should have sufficient brightness. SUMMARY

[0004] In a first example embodiment, the present disclosure provides an image light guide for conveying a virtual image, the image light guide comprising a substrate operable to propagate a beam of image-bearing light. A first in-coupling diffractive optic is formed along the substrate, wherein the in-coupling diffractive optic is operable to diffract a first portion of the beam of image-bearing light from an image source into the substrate in an angularly encoded form, and wherein the first in-coupling diffractive optic is operable to transmit a second portion of the beam of image-bearing light from the image source therethrough. An out-coupling diffractive optic is formed along the substrate, wherein the out-coupling diffractive optic is operable to expand the beam of image-bearing light and direct the expanded beam of image-bearing light from the substrate in an angularly decoded form. A second in-coupling diffractive optic is also formed along the substrate, wherein the second in-coupling diffractive optic is operable to diffract a portion of the second portion of the beam of image-bearing light into the substrate in an angularly encoded form. The image light guide further comprises an optical coupler positioned along an axis of the image source, wherein the optical coupler is operable to direct the second portion of the beam of image-bearing light from the image source onto the second in-coupling diffractive optic.

[0005] In a second example embodiment, the present disclosure provides an image light guide system for conveying a virtual image, comprising an image source operable to project a beam of image-bearing light corresponding to the virtual image along a first axis, wherein pixels of the virtual image are focused at infinity. The image light guide system further comprises a first substrate operable to propagate the beam of image-bearing light and a second substrate operable to propagate the beam of image-bearing light, wherein the second substrate is coupled with the first substrate. Each of the first and second substrates comprises a first in-coupling diffractive optic, a second in-coupling diffractive optic, and an out-coupling diffractive optic. The out-coupling diffractive optic is operable to expand the beam of image-bearing light and direct the expanded beam of image-bearing light from the substrate. The image light guide system further comprises an optical coupler positioned along the first axis, wherein the optical coupler is positioned at least partially along a path of the beam of image-bearing light transmitted through the first in-coupling diffractive optic of the first and second substrates. The optical coupler is operable to direct the beam of image-bearing light onto the second in-coupling diffractive optic of the second substrate, wherein the second in-coupling diffractive optic is operable to diffract a portion of the beam of image-bearing light into the second substrate in an angularly encoded form and to transmit a portion of the beam of image-bearing light toward the second in-coupling diffractive optic of the first substrate, wherein the second in-coupling diffractive optic of the first substrate is operable to diffract a portion of the beam of image-bearing light into the first substrate in an angularly encoded form. BRIEF DESCRIPTION OF DRAWINGS

[0006] The accompanying drawings are incorporated in and constitute a part of the specification. The drawings illustrate embodiments of the presently disclosed subject matter and, together with the description, serve to explain the principles and teachings of the present disclosure. However, the drawings are not intended to be an exhaustive illustration of all possible implementations of the presently disclosed subject matter and are not intended to limit the scope of the present disclosure in any way.

[0007] FIG. 1 shows a simplified cross-sectional view of an image light guide showing expansion of image-bearing beams along a propagation direction for expanding one direction of an eyebox.

[0008] FIG. 2 shows a perspective view of an image light guide with a turning grating showing expansion of image-bearing beams perpendicular to a propagation direction for expanding a second direction of an eyebox.

[0009] Figure 3 A schematic plan view of an image light guide with dual in-coupling diffractive optics according to example embodiments of the presently disclosed subject matter is shown.

[0010] Figure 4 A schematic side view of an image light guide according to Figure 3 with an optical coupler according to example embodiments of the presently disclosed subject matter is shown.

[0011] Figure 5A A schematic end view of an image light guide according to Figure 4 with two in-coupling diffractive optics on a first surface is shown.

[0012] Figure 5B A schematic end view of an image light guide according to Figure 4 with a first in-coupling diffractive optic on a first surface and a second in-coupling diffractive optic on a second surface is shown.

[0013] Figure 5C A schematic end view of an image light guide according to Figure 4 with a first in-coupling diffractive optic on a second surface and a second in-coupling diffractive optic on a first surface is shown.

[0014] Figure 5D A schematic end view of an image light guide according to Figure 4 with a first in-coupling diffractive optic on a second surface and a second in-coupling diffractive optic on a second surface is shown.

[0015] Figure 6 A schematic perspective view of an image light guide according to Figure 4 is shown.

[0016] Figure 7A A schematic perspective view of an image light guide according toFigure 4 schematic perspective view of an optical coupler according to

[0017] Figure 7B schematic end view of an optical coupler according to Figure 4

[0018] Figure 8A schematic end view of an image light guide according to Figure 4

[0019] Figure 8B schematic end view of an image light guide according to Figure 8A

[0020] Figure 9 schematic top view of an optical coupler according to Figure 4

[0021] Figure 10A and 10B schematic view of a portion of a periodic diffraction grating according to example embodiments of the subject matter of the present disclosure.

[0022] Figure 11 schematic end view of a stacked imaging light guide system according to example embodiments of the subject matter of the present disclosure.

[0023] Figure 12 schematic side view of a stacked imaging light guide system according to Figure 11

[0024] Figure 13 display system for augmented reality viewing using an imaging light guide according to example embodiments of the subject matter of the present disclosure. DETAILED DESCRIPTION

[0025] It should be understood that the application can take many different instructions and sequences of steps, unless explicitly stated otherwise. It should also be understood that the specific components and systems illustrated in the drawings and described in the following specification are simply exemplary embodiments of the inventive concepts defined herein. Accordingly, unless explicitly stated otherwise, particular dimensions, directions or other physical characteristics related to the disclosed embodiments are not intended to be limiting. Furthermore, although they can not be, in this section of the application, identical elements in the various embodiments described herein can collectively be referred to using the same reference numeral.

[0026] The terms "first", "second", and the like, as used herein do not necessarily connote any ordinal, sequential or priority relationship, but are merely used to more clearly distinguish one element from another, unless otherwise indicated. ​​​​​

[0027] The terms "viewer," "operator," "watcher," and "user" are considered equivalent in their use herein and refer to a person / machine using a device with an imaging light guide to view an image.

[0028] The term "set" as used herein refers to a non-empty set, as the concept of a set or collection of elements or members has been widely understood in elementary mathematics. The term "subset" as used herein refers to a non-empty proper subset, i.e., to a subset of a larger set having one or more members, unless explicitly stated otherwise. A subset can include the complete set S for a set S. However, a "proper subset" of a set S is strictly contained in the set S and excludes at least one member of the set S.

[0029] The terms "coupled," "coupler," or "coupling" as used in the context of optics refer to a connection through which light travels from one optical medium or device to another.

[0030] The terms "beam expansion," "expansion of the image-bearing beam," and "expanded image-bearing light" as used herein are intended to mean replication of the beam via multiple encounters with optical elements to provide exit pupil expansion in one or more directions. Similarly, as used herein, to "expand" a beam or a portion of a beam is intended to mean replication of the beam via multiple encounters with optical elements to provide exit pupil expansion in one or more directions.

[0031] Optical systems such as HMDs can produce virtual images. In contrast to methods for forming real images, virtual images do not form on a display surface. That is, if a display surface were positioned at the perceived location of a virtual image, no image would form on that surface. Virtual images have a number of inherent advantages for augmented reality presentations. For example, the apparent size of a virtual image is not limited by the size or position of a display surface. In addition, the source object for a virtual image can be small; for example, a magnifying glass provides a virtual image of an object. In comparison to systems that project real images, by forming virtual images that appear to be at a distance, a more realistic viewing experience can be provided. Providing virtual images also avoids the need to compensate for screen artifacts, which can be necessary when projecting real images.

[0032] An image light guide can utilize image-bearing light from a light source such as a projector to display a virtual image. For example, a collimated, relatively angularly encoded beam of light from a projector is coupled into a planar waveguide by an input coupling such as an in-coupling diffractive optic that can be mounted or formed on a surface of the planar waveguide or buried within the waveguide. Such a diffractive optic can be formed as a diffraction grating, a holographic optical element (HOE), or in other known ways. For example, a diffraction grating can be formed from a surface relief. After propagating along the waveguide, the diffracted light can be directed back out of the waveguide by a similar output coupling such as an out-coupling diffractive optic that can be arranged to provide pupil expansion in one direction. In addition, a turning grating can be located on / in the waveguide to provide pupil expansion in an orthogonal direction. The image-bearing light output from the waveguide provides an expanded eyebox for a viewer.

[0033] As shown in FIG. 1, an image light guide 10 can include a planar waveguide 22 having planar parallel surfaces. The waveguide 22 includes a transparent substrate S having an outer surface 12 and an inner surface 14 opposite the outer surface 12. In this example, an in-coupling diffractive optic IDO and an out-coupling diffractive optic ODO are arranged on the inner surface 14, and the in-coupling diffractive optic IDO is a reflective diffraction grating through which image-bearing light WI is coupled into the planar waveguide 22. However, the in-coupling diffractive optic IDO can instead be a transmissive diffraction grating, a volume hologram, or other holographic diffractive element, or other type of optical component that provides diffraction for incoming image-bearing light WI. The in-coupling diffractive optic IDO can be located on the outer surface 12 or the inner surface 14 of the planar waveguide 22, and can be a combination transmissive or reflective depending on the direction that the image-bearing light WI approaches the planar waveguide 22.

[0034] When used as part of a virtual display system, the in-coupling diffractive optic IDO couples image-bearing light WI from an image source into the substrate S of the planar waveguide 22. Any real image or dimension is first converted into an array of angularly related beams, encoding different locations within a virtual image to be presented to the in-coupling diffractive optic IDO. The image-bearing light WI is diffracted (typically by a first diffraction order) and thereby redirected by the in-coupling diffractive optic IDO into the planar waveguide 22 as image-bearing light WG for further propagation along the planar waveguide 22 by total internal reflection ("TIR"). Although diffracted into a generally more condensed range of angularly related beams in keeping with the boundaries of the TIR setup, the image-bearing light WG retains the image information in encoded form. The out-coupling diffractive optic ODO receives the encoded image-bearing light WG and diffracts (typically also by a first diffraction order) the image-bearing light WG out of the planar waveguide 22 as image-bearing light WO toward an intended location of a viewer's eye. Typically, the out-coupling diffractive optic ODO is designed symmetrically with respect to the in-coupling diffractive optic IDO to restore the original angular relationships of the image-bearing light WI in the angularly related beams of the output of the image-bearing light WO. However, to increase one dimension of overlap in the angularly related beams in the so-called eyebox E in which the virtual image can be seen, the out-coupling diffractive optic ODO is arranged to multiple encounters of the image-bearing light WG and to diffract only a portion of the image-bearing light WG at each encounter. The multiple encounters along the length of the out-coupling diffractive optic ODO in the direction of propagation have the effect of expanding one direction of the eyebox E in which the beams overlap. The expanded eyebox E reduces the sensitivity to the location of the viewer's eye in order to view the virtual image.

[0035] In this example, the out-coupling diffractive optic ODO is a transmissive diffraction grating arranged on the inner surface 14 of the planar waveguide 22. However, similar to the in-coupling diffractive optic IDO, the out-coupling diffractive optic ODO can be located on the outer surface 12 or the inner surface 14 of the planar waveguide 22 and can be a combined transmissive or reflective type, depending on the direction in which the image-bearing light WG is intended to exit the planar waveguide 22.

[0036] As shown in FIG. 2, the image light guide 20 can be arranged for expanding the eyebox 74 in two directions, i.e., along both the x- and y-axes of the intended image. To achieve the second direction of beam expansion, the in-coupling diffractive optic IDO is oriented to diffract the image-bearing light WG toward an intermediate turning grating TG about a grating vector k0, the grating vector ki of the intermediate turning grating TG being oriented to diffract the image-bearing light WG toward the out-coupling diffractive optic ODO in a reflective mode. Only a portion of the image-bearing light WG is diffracted through each of a plurality of encounters with the intermediate turning grating TG, thereby laterally expanding each of the angle-dependent beams of the image-bearing light WG approaching the out-coupling diffractive optic ODO. The turning grating TG redirects the image-bearing light WG to at least approximately align with a grating vector k2 of the out-coupling diffractive optic ODO in order to longitudinally expand the angle-dependent beams of the image-bearing light WG in the second direction before exiting the planar waveguide 22 as the image-bearing light WO. Grating vectors, such as the depicted grating vectors k0, ki, k2, extend in a direction normal to the diffractive features (e.g., grooves, lines, or rulings) of the diffractive optic and have an amplitude that is inverse to the period or pitch d (i.e., the on-center distance between grooves) of the diffractive optic IDO, TG, ODO.

[0037] As shown in FIG. 2, the in-coupling diffractive optic IDO receives incoming image-bearing light WI comprising a set of angle-dependent beams corresponding to individual pixels or equivalent locations within an image generated by the image source 16. The image source 16, which can be operable to generate a full range of angle-encoded beams in order to produce a virtual image, can be, without limitation, a real display in conjunction with focusing optics, a beam scanner for more directly setting the angles of the beams, or a combination such as a one-dimensional real display used with a scanner. The image light guide 20 outputs an expanded set of angle-dependent beams in two directions by providing multiple encounters of the image-bearing light WG with the intermediate turning grating TG and the out-coupling diffractive optic ODO in different orientations. In the original orientation of the planar waveguide 22, the intermediate grating TG provides beam expansion in the y-axis direction, and the out-coupling diffractive optic ODO provides similar beam expansion in the x-axis direction. The reflectivity characteristics and respective periods d of the diffractive optics IDO, ODO, TG, along with the orientations of their respective grating vectors, provide beam expansion in both directions while preserving the intended relationships among the angle-dependent beams of the image-bearing light WI as the image-bearing light WO is output from the image light guide 20.

[0038] While the image-bearing light WI input into the image light guide 20 is encoded by the in-coupling diffractive optic IDO into different sets of angle-dependent beams, the information required for the reconstruction of the image is preserved by accounting for the system effects of the in-coupling diffractive optic IDO. The turning grating TG, which is located at an intermediate position between the in-coupling and out-coupling diffractive optics IDO, ODO, is generally arranged so that it does not cause any significant changes to the encoding of the image-bearing light WG. The out-coupling diffractive optic ODO is generally arranged in a symmetric fashion with respect to the in-coupling diffractive optic IDO, e.g., including diffractive features that share the same period. Similarly, the period of the turning grating TG is generally also matched to the common period of the in-coupling and out-coupling diffractive optics IDO, ODO. As shown in FIG. 2, the grating vector kl of the turning grating TG can be oriented at 45 degrees with respect to the other grating vectors ko, k2 (all as undirected line segments). However, in embodiments, the grating vector kl of the turning grating TG is oriented at 60 degrees to the grating vectors ko, k2 of the in-coupling and out-coupling diffractive optics IDO, ODO, such as by turning the image-bearing light WG by 120 degrees. By orienting the grating vector kl of the intermediate turning grating TG at 60 degrees with respect to the grating vectors ko, k2 of the in-coupling and out-coupling diffractive optics IDO, ODO, the grating vectors ko, k2 are also oriented at 60 degrees with respect to each other (again, considered as undirected line segments). With the grating vector magnitudes based on the common spacing of the turning grating TG and the in-coupling and out-coupling diffractive optics IDO, ODO, the three grating vectors ko, kl, k2 (as directed line segments) form an equilateral triangle, and sum to a zero vector magnitude, which avoids asymmetric effects that can introduce undesirable aberrations including chromatic dispersion.

[0039] The image-bearing light WI diffracted into the planar waveguide 22 is efficiently encoded by the in-coupling diffractive optic IDO, whether the in-coupling diffractive optic IDO uses gratings, holograms, prisms, mirrors, or some other mechanism. Any reflections, refractions, and / or diffractions of the light that occur at the in-coupling diffractive optic IDO must be correspondingly decoded by the out-coupling diffractive optic ODO to reform the virtual image that is presented to the viewer. The turning grating TG, which is placed at an intermediate position between the in-coupling and out-coupling diffractive optics IDO, ODO, is generally designed and oriented so that it does not cause any changes to the encoded light. The out-coupling diffractive optic ODO decodes the image-bearing light WG into its original or desired form of angle-dependent beams that have been expanded to fill the eyebox 74.

[0040] Regardless of whether any symmetry is maintained in the steering grating TG and the ingress and egress diffractive optics IDO and ODO, or regardless of whether any change in the encoding of the angle-dependent beam of the image-carrying light WI occurs along the planar waveguide 22, the steering grating TG and the ingress and egress diffractive optics IDO and ODO are related such that the image-carrying beam WO output from the planar waveguide 22 retains or otherwise maintains the original or desired form of the image-carrying light WI in order to produce the desired virtual image.

[0041] The letter “R” indicates the orientation of the virtual image visible to the viewer in eyebox 74. As shown, the orientation of the letter “R” in the indicated virtual image matches the orientation of the letter “R” encoded by the image-carrying light WI. A change in the rotation or angular orientation of the incoming image-carrying light WI relative to the xy plane about the z-axis causes a corresponding symmetrical change in the rotation or angular orientation of the outgoing light from the outgoing coupled diffractive optics ODO. From the perspective of image orientation, the steering grating TG simply acts as a type of optical relay, providing an extension of the angle-encoded bundle of the image-carrying light WG along one axis of the image (e.g., along the y-axis). The outgoing coupled diffractive optics ODO also extends the angle-encoded bundle of the image-carrying 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-carrying light WI. As shown in Figure 2, the steering grating TG can be a tilted or square grating arranged on the front or rear surface of the planar waveguide 22. Alternatively, the steering grating TG can be a blazed grating.

[0042] This disclosure provides an image light guide arrangement having improved image-carrying light output intensity across the output aperture. More specifically, this disclosure particularly provides a waveguide having more than one input-coupled diffractive optics and an output-coupled diffractive optics, which are operable to extend the image-carrying beam in two directions and output the extended image-carrying beam toward the eyepiece.

[0043] like Figure 3 , 4 As shown in 5A, the image light guide 100 may have a first input coupling diffraction optics IDO1, a second input coupling diffraction optics IDO2, and an output coupling diffraction optics ODO formed on / in a first surface 102 of the planar waveguide 22. In another embodiment, as shown... Figure 5B As shown, a first input-coupled diffractive optics IDO1 and an output-coupled diffractive optics ODO are formed on / in the first surface 102 of the planar waveguide 22, and a second input-coupled diffractive optics IDO2 is formed on / in the second surface 104 of the planar waveguide 22, which is positioned opposite to the first surface 102. In another embodiment, as... Figure 5CAs shown in FIG. 1, a first in-coupling diffractive optic IDOl is formed on / in the second surface 104 of the planar waveguide 22, and a second in-coupling diffractive optic ID02 and an out-coupling diffractive optic OD0 are located on / in the first surface 102 of the planar waveguide 22. In another embodiment, as shown in FIG. 2, the first and second in-coupling diffractive optics IDOl, ID02 are formed on / in the second surface 104 of the planar waveguide 22, and the out-coupling diffractive optic OD0 is located on / in the first surface 102 of the planar waveguide 22. In yet another embodiment, as shown in FIG. 3, the first and second in-coupling diffractive optics IDOl, ID02 and the out-coupling diffractive optic OD0 are formed on / in the second surface 104 of the planar waveguide 22. Figure 5D As shown in FIG. 1, a first in-coupling diffractive optic IDOl is formed on / in the second surface 104 of the planar waveguide 22, and a second in-coupling diffractive optic ID02 and an out-coupling diffractive optic OD0 are located on / in the first surface 102 of the planar waveguide 22. In another embodiment, as shown in FIG. 2, the first and second in-coupling diffractive optics IDOl, ID02 are formed on / in the second surface 104 of the planar waveguide 22, and the out-coupling diffractive optic OD0 is located on / in the first surface 102 of the planar waveguide 22. In yet another embodiment, as shown in FIG. 3, the first and second in-coupling diffractive optics IDOl, ID02 and the out-coupling diffractive optic OD0 are formed on / in the second surface 104 of the planar waveguide 22.

[0044] Reference is now made to FIG. 4, which illustrates a plan view of a planar waveguide 22 having a first in-coupling diffractive optic IDOl and a second in-coupling diffractive optic ID02, in accordance with an embodiment. Figure 3 In an embodiment, the first and second in-coupling diffractive optics IDOl, ID02 include two pluralities of periodic grating structures 106, 108. For example, the in-coupling diffractive optics ID0 can include a first set of periodic linear grating structures 106 that are rotated / offset by an angle of less than thirty degrees (e.g., 25°) with respect to the x-axis, and a second set of periodic linear grating structures 108 that are rotated / offset by an angle of less than negative thirty degrees (e.g., -25°) with respect to the x-axis. The first and second sets of periodic grating structures 106, 108 are crossed. The first set of periodic grating structures 106 includes a first period, and the second set of periodic grating structures 108 includes a second period. In an embodiment, the second period is equal to the first period.

[0045] In an embodiment, the out-coupling diffractive optic OD0 includes third and fourth sets of periodic grating structures 110, 112. The third and fourth sets of periodic grating structures 110, 112 are parallel to the first and second sets of periodic grating structures 106, 108, respectively. The third and fourth sets of periodic grating structures 110, 112 form a compound diffractive optic that is operable to expand and out-couple image-bearing light from the in-coupling diffractive optics IDOl, ID02. In an embodiment, the third set of periodic grating structures 110 is crossed with the fourth set of periodic grating structures 112. The third and fourth sets of periodic grating structures 110, 112 can also have the same periodicity as the first and second sets of periodic grating structures 106, 108, respectively. In an embodiment, the out-coupling diffractive optic OD0 has bilateral symmetry across the longitudinal axis 115.

[0046] Reference is now made to FIG. 5, which illustrates a plan view of a planar waveguide 22 having a first in-coupling diffractive optic IDOl and a second in-coupling diffractive optic ID02, in accordance with an embodiment. Figures 4-9In an embodiment, the image light guide 100 includes an optical coupler 120. The optical coupler 120 is positioned adjacent to the in-coupling diffractive optics IDOl, ID02 on the side of the planar waveguide 22 opposite the projector 16 (i.e., the image source). In an embodiment, the optical coupler 120 includes a first surface 122 positioned generally proximate to the planar waveguide 22. The optical coupler 120 further includes a second surface 124 disposed at an angle a with respect to the first surface 122, and a third surface 126 disposed at an angle a with respect to the first surface 122, which is bilaterally symmetric. In an embodiment, the optical coupler 120 is assembled from two right angle prisms 120A, 120B. In an embodiment, the second and third surfaces 124, 126 are mirrored surfaces.

[0047] The first surface 122 is an entrance face of the optical coupler 120 and receives image-bearing light from the projector 16 along a first axis Al. The first axis Al is aligned with a central ray of the projector 16. The image-bearing light is reflected from the second surface 124 back to the first surface 122 within a TIR angle range. The first surface 122 is operable to reflect the image-bearing light under TIR, and the image-bearing light reflected from the second surface 124 is reflected by the first surface 122 toward the third surface 126. The third surface 126 also reflects the image-bearing light toward the first surface 122 within an angle range that is operable to be transmitted through the first surface 122. The image-bearing light is output from the optical coupler 120 centered along a second axis A2. The second axis A2 is aligned with a central ray output from the optical coupler 120. The second axis A2 is offset from the first axis Al in the y-axis direction. The optical coupler 120 is designed to have three reflection points within the optical coupler 120 to prevent a virtual image of the image-bearing light incident on the optical coupler 120 from being flipped.

[0048] In operation, image-bearing light WI from the projector 16 is incident on the first in-coupling diffractive optic IDOl, a first portion of the image-bearing light WG1 is diffracted by the first in-coupling diffractive optic IDOl and generally propagates toward the out-coupling diffractive optic ODO via TIR. A second portion of the image-bearing light WI is transmitted through the first in-coupling diffractive optic IDOl and the planar waveguide 22, and is incident on the optical coupler 120. The second portion of the image-bearing light WI is transmitted through the first surface 122 of the optical coupler 120 and is reflected from the second surface 124 of the optical coupler at an angle of incidence operable to be reflected from the first surface 122 via TIR. The second portion of the image-bearing light WI is then reflected from the first surface 122 under TIR and is incident on the third surface 126 of the optical coupler, where the second portion of the image-bearing light WI is reflected back to the first surface 122 and transmitted therethrough along the second axis A2.

[0049] A second portion of the image-bearing light WI centered along the second axis A2 is then incident on the second in-coupling diffractive optic IDO2. A portion of the second portion of the image-bearing light WG2 is diffracted by the second in-coupling diffractive optic IDO2 and propagates generally via TIR toward the out-coupling diffractive optic ODO. In embodiments, the second in-coupling diffractive optic IDO2 is configured to optimize the diffraction efficiency of the image-bearing light output from the optical coupler 120. For example, the first in-coupling diffractive optic IDOl can be configured as a transmissive diffraction grating and the second in-coupling diffractive optic IDO2 can be configured as a reflective diffraction grating. As Figure 10A and 10B As shown in FIGS. 1 6, 108, in the case where the first and second sets of periodic grating structures 106, 108 are surface-relief gratings, the first and second sets of periodic grating structures 106, 108 are tilted by a tilt angle In embodiments, the first set of periodic grating structures 106 of the first in-coupling diffractive optic IDOl can have a tilt angle and the first set of periodic grating structures 106 of the second in-coupling diffractive optic IDO2 can have a tilt angle Similarly, the second set of periodic grating structures 108 of the first in-coupling diffractive optic IDOl can have a tilt angle and the second set of periodic grating structures 108 of the second in-coupling diffractive optic IDO2 can have a tilt angle The periodic grating structures 106, 108 of the first and second in-coupling diffractive optics IDOl, IDO2 can have tilt angles that are rotated one hundred and eighty degrees with respect to each other

[0050] By utilizing the optical coupler 120 and the second in-coupling diffractive optic IDO2, the image guide 100 is operable to in-couple a larger percentage of the image-bearing light from the projector 16. Increasing the percentage of the image-bearing light from the projector 16 that is in-coupled to the planar waveguide 22 increases the brightness of the virtual image viewed within the eyebox.

[0051] In embodiments, as shown in FIG. 1 8, the first and second in-coupling diffractive optics IDOl, IDO2 can be configured to in-couple image-bearing light from the projector 16 having different wavelengths. For example, the first in-coupling diffractive optic IDOl can be configured to in-couple image-bearing light having a first wavelength and the second in-coupling diffractive optic IDO2 can be configured to in-couple image-bearing light having a second wavelength different from the first wavelength. Figure 7BAs shown, the first surface 122 of the optical coupler 120 may include a mirror surface 132. This mirror surface 132 may be formed on the first surface 122 such that a second portion of the image-carrying light reflected from the second surface 124 is incident on the mirror surface 132. The mirror surface 132 may be formed by applying a coating that at least partially reflects light to a portion of the first surface 122 of the optical coupler. Image-carrying light from the image source 16 incident on the first portion 122A of the first surface 122 of the optical coupler is transmitted through it and incident on the second surface 124. Image-carrying light reflected from the second surface 124 is incident on the second portion 122B of the first surface 122 having the mirror surface 132 and is reflected toward the third surface 126. Image-carrying light reflected from the second portion 122B of the first surface 122 is incident on the third surface 126 and is reflected toward the third portion 122C of the first surface 122. Image-carrying light incident on the third portion 122C of the first surface 122 is transmitted therefrom.

[0052] In an embodiment, such as Figure 4 , 5A As shown in -D and 7B, the imaging light guide 100 may include a waveplate 130 located between the optical coupler 120 and the planar waveguide 22. The length of the waveplate 130 is less than the length of the optical coupler 120, such that light transmitted through the planar waveguide 22 and incident on the first surface 122 of the optical coupler 120 does not pass through the waveplate 130, while image-carrying light reflected from the third surface 126 and transmitted through the first surface 122 of the optical coupler 120 passes through the waveplate 130. The waveplate 130 is operable to rotate the polarization direction of the image-carrying light, allowing the imaging light guide 100 to fully utilize the image-carrying light from the projector 16. For example, the waveplate 130 may be a half-wave plate operable to rotate the polarization direction of the image-carrying light orthogonally (90°) or nearly orthogonally. In an embodiment, the waveplate 130 may be a quarter-wave plate operable to rotate the polarization direction of the image-carrying light approximately forty-five degrees (45°). Transmissive diffraction gratings have lower polarization sensitivity than reflective diffraction gratings. When the second ingress-coupled diffraction optics IDO2 is a reflective diffraction grating, the polarization of the image-carrying light via the half-wave plate 130 enables greater diffraction efficiency. In other words, in this embodiment, there is more image-carrying light from the image source 16 that can be coupled into the waveguide 22 via the second ingress-coupled diffraction optics IDO2 with alternating polarization. In this embodiment, the projector 16 includes a digital light processing (“DLP”) projector operable to output unpolarized light.

[0053] In an embodiment, such as Figure 8A As shown, in the event of defects in the manufacture of the optical coupler 120 and / or errors in the alignment of the projector 16 and the optical coupler 120, the image light guide 100 may produce two misaligned virtual images. For example, asFigure 8A As shown, a defect in the optical coupler 120 can cause the image-carrying light WG2 to be incident on the second incident-coupled diffractive optical device IDO2 at an angle relative to the second axis A2; this incident angle is mirrored by the second outgoing beam WO2 at an angle relative to the second axis A2, causing misalignment of the two virtual images. Figure 8B As shown, the planar waveguide 22 can be rotated or rocked about the x-axis and / or y-axis to align the two virtual images generated by the image light guide 100. Rotating the planar waveguide 22 relative to the projector 16 and optical coupler 120 compensates for the effects of misalignment in the center ray alignment of the image beam WG2, which is in-coupled to the planar waveguide 22 via the second in-coupled diffractive optics IDO2 and out-coupled via the out-coupled diffractive optics ODO. Rotating the planar waveguide 22 about the center of the first in-coupled diffractive optics IDO1 allows the second outgoing beam WO2 to be repositioned relative to the second in-coupled diffractive optics IDO2 without changing the centerline ray position of the first outgoing beam WO1 relative to the center of the first diffractive optics IDO1. Figure 8A and 8B As shown, the oscillating planar waveguide 22 aligns the central rays of the image-carrying beams WO1 and WO2 approximately parallel to each other. This feature takes into account larger tolerances in the alignment of the projector 16 and the optical coupler 120. In other words, the projector 16 and the optical coupler 120 do not need to be aligned with extreme precision because the waveguide 22 can be used for the alignment of the virtual image.

[0054] like Figure 11 and 12 As shown, in an embodiment, the stacked image light guide assembly 400 includes a first image light guide 402 coupled to a second image light guide 404. At least one of the first image light guide 402 and the second image light guide 404 is one of the image light guides 100 described above. The image light guides 402, 404 are formed on mechanically coupled separate waveguide substrates 22. In an embodiment, the waveguide substrates 22 of the image light guides 402, 404 are mechanically coupled via an adhesive. In another embodiment, the waveguide substrates 22 are held in place relative to each other by the structural means of the HMD. For example, the HMD that incorporates the image light guides 402, 404 is a smart glasses (see...). Figure 13 In this case, the waveguide substrate 22 can be held in relative position via the eyeglass frame. In an embodiment, the stacked image light guide assembly 400 provides three separate color channels. A first portion of the image-carrying light WI from the projector 16 incident on the first ingress-coupled diffractive optics IDO1 of the first image light guide 402 is diffracted and propagates via TIR toward the egress-coupled diffractive optics ODO of the first image light guide 402.

[0055] A second portion of the image-bearing light WI incident on the first in-coupling diffractive optic of the first image light guide 402 is transmitted therethrough and is incident on the first in-coupling diffractive optic IDOl of the second image light guide 404. A portion of the image-bearing light WG2 incident on the first in-coupling diffractive optic IDOl of the second image light guide 404 is diffracted and propagates via TIR toward the out-coupling diffractive optic ODO of the second image light guide 404. A third portion of the image-bearing light WI is transmitted through the in-coupling diffractive optic IDOl of the second image light guide 404 and is incident on the optical coupler 120, as described above. The third portion of the image-bearing light WI is then output from the optical coupler 120 centered along the second axis A2 and is incident on the second in-coupling diffractive optic ID02 of the second image light guide 404. A portion of the image-bearing light WG3 incident on the second in-coupling diffractive optic ID02 of the second image light guide 404 is diffracted and propagates via TIR toward the out-coupling diffractive optic ODO of the second image light guide 404. A fourth portion of the image-bearing light WI is transmitted through the second in-coupling diffractive optic ID02 of the second image light guide 404 and is incident on the second in-coupling diffractive optic ID02 of the first image light guide 402. A portion of the image-bearing light WG4 incident on the second in-coupling diffractive optic ID02 of the first image light guide 402 is diffracted and propagates via TIR toward the out-coupling diffractive optic ODO of the first image light guide 402. The image-bearing light WG1, WG2, WG3, WG4 incident on the out-coupling diffractive optic ODO of the first and second image light guides 402, 404 is expanded and out-coupled toward an eyebox as image-bearing light WO.

[0056] Figure 13 A perspective view illustrates a display system 60 for augmented reality viewing using one or more image light guides of the present disclosure. The display system 60 is shown as an HMD having a right-eye optical system 64R with an image light guide 66R for the right eye. The display system 60 includes an image source 68, such as a picoprojector or similar device, which can be energized to generate an image. In embodiments, the 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 3D viewing. The virtual image formed by the display system 60 can appear to be superimposed or overlaid onto real-world scene content viewed by the viewer through the image light guide 66R. Additional components familiar to those skilled in the art of augmented reality visualization can also be provided, such as one or more cameras mounted on the frame of the HMD for viewing scene content or viewer gaze tracking.

[0057] One or more features of the embodiments described herein can be combined to create additional embodiments not depicted. While various embodiments have been described in detail, it should be understood that the detailed description is to be considered illustrative of the embodiments rather than limiting. Numerous specific aspects of the disclosed subject matter have been set forth in detail with specific reference to various embodiments. It is clear, however, that these embodiments are illustrative only and that numerous other configurations can be implemented which do not require the use of all the aspects disclosed. Accordingly, it is intended that the scope of the disclosure be defined by the appended claims rather than the description contained herein.

Claims

1. An image optical guide for transmitting virtual images, comprising: Substrate, operable to propagate image-carrying beams; A first ingress-coupled diffraction optics formed along the substrate, wherein the ingress-coupled diffraction optics is operable to diffract a first portion of the image-carrying beam from the image source into the substrate in an angle-coded manner, and wherein the ingress-coupled diffraction optics is operable to transmit a second portion of the image-carrying beam from the image source. An out-coupled diffractive optics formed along the substrate, wherein the out-coupled diffractive optics is operable to extend the eyebox in at least one direction and guide the image-carrying beam from the substrate in an angle-decoding manner; A second in-line coupling diffraction optics is formed offset from the first in-line coupling diffraction optics along the substrate in a direction that laterally bisects the direction in which the image-carrying beam propagates toward the out-coupled diffraction optics, wherein the second in-line coupling diffraction optics is operable to diffract a portion of the second portion of the image-carrying beam into the substrate in an angle-coded manner; and An optical coupler, positioned along the axis of the image source, wherein the optical coupler is operable to guide the second portion of the image-carrying beam to the second ingress coupling diffraction optics.

2. The image optical guide for transmitting virtual images according to claim 1, wherein, The first ingress-coupled diffractive optics is operable to diffract an image beam incident thereon from a first direction parallel to the first portion of the image beam with greater efficiency than the second ingress-coupled diffractive optics, and wherein the second ingress-coupled diffractive optics is operable to diffract an image beam incident thereon from a second direction opposite to the first direction with greater efficiency than the first ingress-coupled diffractive optics.

3. The image optical guide for transmitting virtual images according to claim 1, wherein, The first ingress-coupled diffractive optical device is operable as a transmission diffractive optical device, and the second ingress-coupled diffractive optical device is operable as a reflection diffractive optical device.

4. The image optical guide for transmitting virtual images according to claim 3, wherein, The first and second ingress coupling diffraction optical devices include surface relief gratings.

5. The image optical guide for transmitting virtual images according to claim 3, wherein, The substrate includes first and second opposing surfaces, wherein the first ingress-coupled diffractive optical device and the second ingress-coupled diffractive optical device are located in the first surface, or wherein the first ingress-coupled diffractive optical device is located in the first surface and the second ingress-coupled diffractive optical device is located in the second surface.

6. The image optical guide for transmitting virtual images according to claim 2, wherein, The first and second ingress coupling diffraction optical devices include tilted surface relief grating features, wherein the grating feature of the second ingress coupling diffraction optical device is substantially tilted by 180 degrees relative to the grating feature of the first ingress coupling diffraction optical device.

7. The image optical guide for transmitting virtual images according to claim 2, wherein, The first and second ingress-coupled diffractive optical devices include blazed surface relief grating features, wherein the grating features of the second ingress-coupled diffractive optical device are symmetrical to the grating features of the first ingress-coupled diffractive optical device.

8. The image optical guide for transmitting virtual images according to claim 1, wherein, The optical coupler includes: A first surface operable to transmit the image-carrying beam incident thereon at a first angle relative to the first surface and operable to reflect the image-carrying beam incident thereon at a second angle relative to the first surface. The second surface is operable to reflect the image-carrying beam; and The third surface is operable to reflect the image-carrying beam.

9. The image optical guide for transmitting a virtual image according to claim 8, wherein, The second surface of the optical coupler is symmetrical to the third surface of the optical coupler.

10. The image optical guide for transmitting a virtual image according to claim 8, wherein, The image beam reflected by the second surface and incident on the first surface is reflected from the first surface via total internal reflection.

11. The image optical guide for transmitting a virtual image according to claim 8, wherein, The image-carrying beam reflected by the third surface and incident on the first surface is transmitted through the first surface.

12. The image optical guide for transmitting a virtual image according to claim 8, wherein, The image-carrying beam exits the optical coupler laterally from the position where it enters.

13. The image optical guide for transmitting a virtual image according to claim 8, wherein, The image-carrying beam follows a path in the optical coupler, which includes three reflections, and wherein the image-carrying beam exits the optical coupler at an angle equal in magnitude to the angle of the image-carrying beam incident on the optical coupler.

14. The image optical guide for transmitting a virtual image according to claim 8, wherein, The optical coupler includes two right-angle prisms.

15. The image light guide for transmitting a virtual image according to claim 1, further comprising a waveplate located between the optical coupler and the second incident coupling diffractive optical device, wherein, The waveplate is operable to rotate the polarization of the image-carrying beam, wherein the waveplate includes a half-wave plate or a quarter-wave plate.

16. The image optical guide for transmitting virtual images according to claim 1, wherein: The first portion of the image-carrying beam coupled via the first ingress-coupled diffractive optical device corresponds to the first virtual image. The second portion of the image-carrying beam coupled via the second ingress-coupled diffraction optics corresponds to the second virtual image. The first and second virtual images are essentially the same. The substrate is rotated such that the surface of the substrate is positioned at an angle relative to the first surface of the optical coupler, thereby aligning the first and second virtual images at an infinity focal point.

17. The image optical guide for transmitting virtual images according to claim 1, wherein, The optical coupler includes: A first surface operable to transmit the image-carrying beam incident thereon at a first portion of the first surface and operable to reflect the image-carrying beam incident thereon at a second portion of the first surface, wherein the second portion of the first surface is a mirror surface. The second surface is operable to reflect the image-carrying beam; and A third surface is operable to reflect the image-carrying beam; The image-carrying light beam, reflected from the second surface and incident on the second portion of the first surface, is reflected from the first surface and incident on the third surface. The image-carrying beam reflected and incident on the first surface by the third surface is transmitted through it.

18. An image light guide system for transmitting virtual images, comprising: An image source operable to project an image-carrying beam corresponding to a virtual image along a first axis, wherein the pixels of the virtual image are focused at infinity; A first substrate, operable to propagate the image-carrying beam; A second substrate, operable to propagate the image-carrying beam, wherein the second substrate is coupled to the first substrate; Each of the first and second substrates includes: First-input coupled diffractive optical device Second-input coupled diffractive optical device; and Out-coupled diffractive optics, wherein the out-coupled diffractive optics are operable to extend the eyebox in at least one direction and guide at least a portion of the image-carrying beam from the substrate in an angle-decoding manner; An optical coupler positioned along the first axis, wherein the optical coupler is positioned at least partially along the path of the image-carrying beam transmitted through the first ingress coupling diffraction optics of the first and second substrates, wherein the optical coupler is operable to guide the image-carrying beam to the second ingress coupling diffraction optics of the second substrate, wherein the second ingress coupling diffraction optics is operable to diffract a portion of the image-carrying beam in an angle-coded manner into the second substrate and to transmit a portion of the image-carrying beam toward the second ingress coupling diffraction optics of the first substrate, and wherein the second ingress coupling diffraction optics of the first substrate is operable to diffract a portion of the image-carrying beam in an angle-coded manner into the first substrate. The optical coupler includes: A first surface operable to transmit the image-carrying beam incident thereon at a first angle relative to the first surface and operable to reflect the image-carrying beam incident thereon at a second angle relative to the first surface. The second surface is operable to reflect the image-carrying beam; and The third surface is operable to reflect the image-carrying beam.

19. The image optical guide for transmitting a virtual image according to claim 18, wherein, Each of the first ingress-coupled diffractive optical devices is operable as a transmission diffractive optical device and each of the second ingress-coupled diffractive optical devices is operable as a reflection diffractive optical device.

Images