Method and system for implementing optical imaging in an augmented reality device - Patents.com

Abstract

The image projection system includes an illumination source and an eyepiece waveguide including a plurality of diffractive incoupling optical elements. The eyepiece waveguide includes a region operable to transmit light from the illumination source. The image projection system also includes a first optical element including a reflective polarizer, a second optical element including a partial reflector, a first quarter-wave plate disposed between the first optical element and the second optical element, a reflective spatial light modulator, and a second quarter-wave plate disposed between the second optical element and the reflective spatial light modulator.

Description

[Background technology]

[0001] Modern computing and display technology has facilitated the development of systems for so-called "virtual reality" or "augmented reality" experiences, in which digitally reproduced images or portions thereof are presented to a viewer in a manner that appears, or can be perceived as, real. Virtual reality, or "VR" scenarios typically involve the presentation of digital or virtual image information without transparency to other actual real-world visual inputs, while augmented reality, or "AR" scenarios typically involve the presentation of digital or virtual image information as an augmentation to the visualization of the real world around the viewer.

[0002] With reference to FIG. 1, an augmented reality scene 10 is depicted. A user of the AR technology sees a real-world park-like setting 20 featuring people, trees, buildings in the background, and a concrete platform 30. The user also perceives that they are "seeing" "virtual content," such as a robotic figure 40 standing on the real-world platform 30 and a flying cartoon-like avatar character 50 that appears to be an anthropomorphic bumblebee. These elements 50, 40 are "virtual" in that they do not exist in the real world. The human visual perception system is complex, making it difficult to create AR technology that facilitates a comfortable, natural-feeling, and rich presentation of virtual image elements among other virtual or real-world image elements.

[0003] Despite the advances that have been made in these display technologies, there remains a need in the art for improved methods and systems relating to augmented reality systems, and particularly to display systems. Summary of the Invention [Means for solving the problem]

[0004] The present invention relates generally to methods and systems relating to projection display systems, including wearable displays. More specifically, embodiments of the present invention provide methods and systems for forming optical imagery in augmented reality systems. The present invention is applicable to a variety of applications in computer vision and image display systems.

[0005] According to an embodiment of the present invention, an image projection system is provided. The image projection system includes an illumination source and an eyepiece waveguide including a plurality of diffractive incoupling optical elements. The eyepiece waveguide includes a region operable to transmit light from the illumination source. The image projection system also includes a first optical element including a reflective polarizer, a second optical element including a partial reflector, a first quarter-wave plate disposed between the first optical element and the second optical element, a reflective spatial light modulator, and a second quarter-wave plate disposed between the second optical element and the reflective spatial light modulator.

[0006] The illumination source may include a plurality of light sources arrayed in a sub-pupil configuration. The illumination source may include a plurality of light sources, each of the plurality of light sources aligned along the optical axis. The image projection system may also include a linear polarizer disposed between the illumination source and the eyepiece waveguide. The first optical element may include a refractive lens. The reflective polarizer may be disposed on a surface of the refractive lens facing the eyepiece waveguide. The refractive lens may include an anti-reflective coated surface. The first optical element may include a mirror. The second optical element may include a refractive lens. The partial reflector may be disposed on a surface of the refractive lens facing the reflective spatial light modulator. The illumination light emitted by the illumination source may propagate along a first axial direction, and the encoded light may be incident on the plurality of diffractive internal coupling optical elements along a second axial direction parallel to and laterally offset from the first axial direction.

[0007] According to another embodiment of the invention, a method of operating an optical projection system is provided. The method includes generating illumination light, linearly polarizing the illumination light, and transmitting the illumination light through an eyepiece waveguide. The method also includes reflecting a portion of the illumination light from a partial reflector, reflecting a portion of the illumination light from a reflective polarizer, and encoding the reflected light in a reflective spatial light modulator to provide encoded light. The method further includes reflecting the encoded light from the reflective polarizer, reflecting a portion of the encoded light from the partial reflector, and coupling a portion of the encoded light into the eyepiece waveguide.

[0008] The method may also include transmitting the illumination light through a reflective polarizer and converting the illumination light to circularly polarized light prior to reflecting the portion of the illumination light from the partial reflector. The method may additionally include converting the portion of the illumination light to linearly polarized light prior to reflecting the portion of the illumination light from the reflective polarizer. The method may further include converting the encoded light to circularly polarized light prior to reflecting the encoded light from the reflective polarizer and transmitting the encoded light through a partial reflector. The method may also include converting the encoded light to circularly polarized light prior to reflecting the portion of the encoded light from the partial reflector. The reflective polarizer may be disposed on a surface of the first optical element facing the eyepiece waveguide. The partial reflector may be disposed on a surface of the second optical element facing the reflective spatial light modulator. Producing the illumination light may include generating light from a plurality of light sources arrayed in a sub-pupil configuration. The reflective polarizer can be disposed on a surface of the first optical element facing the eyepiece waveguide, and the partial reflector can be disposed on a surface of the second optical element facing the reflective spatial light modulator. The first optical element can include a first refractive lens, and the second optical element comprises a second refractive lens.

[0009] According to a specific embodiment of the invention, an image projection system is provided. The image projection system includes an illumination source and an eyepiece waveguide including a plurality of diffractive incoupling optical elements. The eyepiece waveguide includes a region operable to transmit light from the illumination source. The image projection system also includes a first optical element including a first quarter-wave plate and a partial reflector disposed between the illumination source and the eyepiece waveguide, a second optical element including a reflective polarizer, a second quarter-wave plate disposed between the first optical element and the second optical element, and a reflective spatial light modulator.

[0010] The illumination source may include a plurality of light sources arrayed in a sub-pupil configuration. The illumination source may include a plurality of light sources, each of the plurality of light sources aligned along the optical axis. The image projection system may also include a linear polarizer disposed between the illumination source and the first quarter wave plate. The first optical element may be a refractive lens. The partial reflector may be disposed on a surface of the refractive lens facing the eyepiece waveguide. The second optical element may be a refractive lens. The reflective polarizer may be disposed on a surface of the refractive lens facing the reflective spatial light modulator. The refractive lens may include an anti-reflective coated surface. The first optical element may be a mirror.

[0011] According to another specific embodiment of the invention, a method of operating an optical projection system is provided. The method includes generating illumination light, circularly polarizing the illumination light, transmitting the illumination light through an eyepiece waveguide, and reflecting the illumination light from a reflective polarizer. The method also includes reflecting a portion of the illumination light from the partial reflector, encoding the reflected light in a reflective spatial light modulator to provide encoded light, reflecting a portion of the encoded light from the partial reflector, reflecting a portion of the encoded light from the reflective polarizer, and coupling a portion of the encoded light into the eyepiece waveguide.

[0012] The method may also include transmitting the illumination light through a partial reflector and converting a portion of the illumination light to linearly polarized light prior to reflecting the illumination light from the reflective polarizer. The method may further include converting the illumination light to circularly polarized light prior to reflecting the portion of the illumination light from the partial reflector. The method may additionally include transmitting the encoded light through a reflective polarizer and converting the encoded light to linearly polarized light prior to reflecting the portion of the encoded light from the partial reflector. In addition, the method may include converting the encoded light to linearly polarized light prior to reflecting the encoded light from the reflective polarizer. The partial reflector may be disposed on a surface of the first optical element facing the eyepiece waveguide. The reflective polarizer may be disposed on a surface of the second optical element facing the reflective spatial light modulator. Producing the illumination light may include generating light from a plurality of light sources arrayed in a sub-pupil configuration. The partial reflector can be disposed on a surface of the first optical element facing the eyepiece waveguide, and the reflective polarizer can be disposed on a surface of the second optical element facing the reflective spatial light modulator. The first optical element can include a first refractive lens, and the second optical element can include a second refractive lens.

[0013] Numerous benefits over conventional techniques are achieved by the methods of the present invention. For example, embodiments of the present invention provide methods and systems that can be used to perform imaging using compact lens structures. In some embodiments, a set of refractive lenses is utilized in a multi-pass configuration to encode illumination light with virtual content. These and other embodiments of the present invention, along with many of its advantages and features, are described in further detail in conjunction with the following text and accompanying figures. [Brief description of the drawings]

[0014] [Figure 1]FIG. 1 illustrates a user's view of an augmented reality (AR) device.

[0015] [Diagram 2] FIG. 2 illustrates a conventional display system for simulating a three-dimensional image for a user.

[0016] [Figure 3A] 3A-3C illustrate the relationship between the radius of curvature and the radius of focus. [Figure 3B] 3A-3C illustrate the relationship between the radius of curvature and the radius of focus. [Figure 3C] 3A-3C illustrate the relationship between the radius of curvature and the radius of focus.

[0017] [Figure 4A] Figure 4A illustrates a representation of the accommodation-vergence-divergence motor response of the human visual system.

[0018] [Figure 4B] FIG. 4B illustrates examples of different accommodation and convergence states of a pair of a user's eyes.

[0019] [Figure 4C] FIG. 4C illustrates an example of a top-down view representation of a user viewing content through a display system.

[0020] [Figure 4D] FIG. 4D illustrates another example of a top-down view representation of a user viewing content through a display system.

[0021] [Diagram 5] FIG. 5 illustrates aspects of an approach for simulating a three-dimensional image by modifying wavefront divergence.

[0022] [Figure 6]FIG. 6 illustrates an embodiment of a waveguide stack for outputting image information to a user.

[0023] [Figure 7] FIG. 7 illustrates an example of an output beam output by a waveguide.

[0024] [Figure 8] FIG. 8 illustrates an example of a stacked waveguide assembly where each depth plane contains an image formed using multiple different primary colors.

[0025] [Figure 9A] FIG. 9A illustrates a cross-sectional side view of an example of a set of stacked waveguides, each of which includes an internal coupling optical element.

[0026] [Figure 9B] FIG. 9B illustrates a perspective view of one or more stacked waveguide embodiments of FIG. 9A.

[0027] [Figure 9C] FIG. 9C illustrates a top-down plan view of one or more stacked waveguide embodiments of FIGS. 9A and 9B.

[0028] [Figure 9D] FIG. 9D illustrates an example of a wearable display system.

[0029] [Figure 10] FIG. 10 is a side view of a projector assembly that includes a polarizing beam splitter with a light source that injects light into one side of the beam splitter, and projection optics that receive light from the other side of the beam splitter.

[0030] [Figure 11A]11A is a side view of an augmented reality display system including a light source, a spatial light modulator, an optical system for illuminating the spatial light modulator and projecting an image of the spatial light modulator (SLM), and a waveguide for outputting image information to a user. The system includes an internal coupling optical element for coupling light from the optical system into the waveguide, and an external coupling optical element for coupling light out of the waveguide to the eye.

[0031] [Figure 11B] 11B is a top view of the augmented reality display system shown in FIG. 11A, showing a waveguide with in-coupling and out-coupling optical elements and a light source disposed thereon. The top view also shows an orthogonal pupil expander.

[0032] [Figure 11C] FIG. 11C is a side view of the augmented reality display system of FIG. 11A with a shared polarizer / analyzer and a polarization-based spatial light modulator (eg, a liquid crystal-on-silicon SLM).

[0033] [Figure 12A] FIG. 12A is a side view of an augmented reality display system including a multi-color light source (e.g., a time-multiplexed RGB LED or laser diode), a spatial light modulator, an optical system for illuminating the spatial light modulator and projecting an image of the spatial light modulator to the eye, and a stack of waveguides, where different waveguides include different color-selective in-coupling optical elements and out-coupling optical elements.

[0034] [Figure 12B] FIG. 12B is a side view of the augmented reality display system of FIG. 12A, further including a MEMS (micro-electro-mechanical) based SLM such as an array of moveable mirrors (eg, digital light processing (DLP™) technology) and a light dump.

[0035] [Figure 12C]FIG. 12C is a top view of a portion of the augmented reality display system of FIG. 12B, illustrating diagrammatically the internal coupling optical elements and the lateral arrangement of one of the light sources as well as the light dump.

[0036] [Figure 13A] 13A is a perspective view of an augmented reality display system including a stack of waveguides, different waveguides including different in-coupling optical elements, the in-coupling optical elements being laterally displaced with respect to one another. One or more light sources, also laterally displaced with respect to one another, are positioned to direct light to individual in-coupling optical elements by passing the light through an optical system, reflecting the light off a spatial light modulator, and passing the reflected light back through the optical system.

[0037] [Figure 13B] FIG. 13B is a side view of the embodiment illustrated in FIG. 13A, showing the incoupling optical element and light source laterally displaced, as well as the optical system and spatial light modulator.

[0038] [Figure 13C] FIG. 13C is a top view of the augmented reality display system shown in FIGS. 13A and 13B, showing one or more laterally displaced internal coupling optical elements and associated one or more laterally displaced light sources.

[0039] [Figure 14A] FIG. 14A is a side view of an augmented reality display system including a waveguide stack, where different waveguides include different internal coupling optical elements that are laterally displaced relative to each other (the lateral displacement occurs in the z-direction in this embodiment).

[0040] [Figure 14B] FIG. 14B is a top view of the display system illustrated in FIG. 14A, showing the incoupling optical elements displaced laterally and the light source.

[0041] [Figure 14C] FIG. 14C is an orthogonal side view of the display system illustrated in FIGS. 14A and 14B.

[0042] [Figure 15] 15 is a top view of an augmented reality display system including a set of stacked waveguides, different waveguides including different incoupling optical elements, the light sources and incoupling optical elements arranged in an alternative configuration to those shown in FIGS.

[0043] [Figure 16A] FIG. 16A is a side view of an augmented reality display system including groups of inter-coupling optical elements that are laterally displaced relative to one another, each group including one or more color-selective inter-coupling optical elements.

[0044] [Figure 16B] FIG. 16B is a top view of the display system in FIG. 16A.

[0045] [Figure 17] 17 is a side view of an augmented reality display system that includes a waveguide that is split with a reflective surface that can couple light guided in a portion of the waveguide proximate the light source out of that portion of the waveguide and into an optics system toward a spatial light modulator. In this example, the optics system and light source are shown disposed on the same side of the waveguide.

[0046] [Figure 18]18 is a side view of an augmented reality display system including a waveguide for receiving light from a light source and directing the light guided in the waveguide into the optical system toward a spatial light modulator. The display system additionally includes a waveguide for receiving light from the spatial light modulator and passing it again through the optical system. The waveguide includes reflective surfaces for out-coupling the light. The waveguide also includes reflective surfaces for in-coupling the light therein. In this example, the optical system and the light source are shown disposed on the same side of the waveguide.

[0047] [Figure 19] 19 is a side view of an augmented reality display system including an adaptive or variable focus optical element. A first variable optical element between the stack of waveguides and the eye can vary the divergence and collimation of light coupled out of the waveguides and directed to the eye, varying the depth at which an object appears to be located. A second variable optical element on the other side of the stack of waveguides can compensate for the effect of the first optical element on light received from the augmented reality display system and the environment in front of the user. The augmented reality display system further includes prescription lenses to provide ophthalmic corrections such as refractive corrections for users with myopia, hyperopia, astigmatism, etc.

[0048] [Figure 20A] 20A is a side view of an augmented reality display system including a color filter array, where one or more laterally displaced in-coupling optical elements are located on different waveguides, and the laterally displaced color filters are aligned with the respective in-coupling optical elements.

[0049] [Figure 20B] FIG. 20B shows the augmented reality display system of FIG. 20A with an analyzer located between the optical system and the spatial light modulator.

[0050] [Figure 20C]FIG. 20C illustrates an augmented reality display system similar to that shown in FIGS. 20A and 20B, however, using a deflection-based spatial light modulator, such as a movable micromirror-based spatial light modulator.

[0051] [Figure 20D] FIG. 20D is a top view of a portion of the augmented reality display system as shown in FIG. 20C, diagrammatically illustrating a laterally displaced light source above a color filter array and a corresponding laterally displaced internal coupling optical element.

[0052] [Figure 20E] FIG. 20E illustrates how a deflection-based spatial light modulator for the augmented reality display system of FIG. 20D directs light away from corresponding internal coupling optical elements and onto a mask that surrounds the filters in the filter array.

[0053] [Figure 20F] FIG. 20F is a side view of an augmented reality display system including a cover glass positioned on the user side of a stack of waveguides and a light source positioned on the world side of the cover glass.

[0054] [Figure 20G] FIG. 20G is a side view of an augmented reality display system including a cover glass disposed on the world side of a stack of waveguides and a light source disposed on the world side of the cover glass.

[0055] [Figure 21] FIG. 21 is a side view of an augmented reality display system that includes a light source equipped with a light recycler configured to reuse light, such as light of a certain polarization.

[0056] [Figure 22]22 is a side view of one or more light sources that propagate light through corresponding light collection optics and one or more apertures. The light may also propagate through a diffuser located proximate to the one or more apertures.

[0057] [Figure 23A] FIG. 23A is a side view of a portion of an augmented reality display system including a light source, an optical system having refractive power, and a waveguide for receiving and outputting image information to a user's eye, the system further including one or more retarders and polarizers configured to reduce reflections from optical surfaces that may be input to the waveguide as a residual image.

[0058] [Figure 23B] FIG. 23B is a side view of a portion of the augmented reality display system as shown in FIG. 23A, with an additional retarder and polarizer configured to reduce reflections that can produce persistent images.

[0059] [Figure 23C] FIG. 23C is a side view of an augmented reality display system as shown in FIGS. 23A and 23B with a reduced retarder and polarizer configured to reduce reflections that can produce persistent images.

[0060] [Figure 24] FIG. 24 is a side view of an augmented reality display system that utilizes a sloped surface, such as a sloped surface on a cover glass, to direct reflections away from the user's eyes, potentially reducing afterimage reflections.

[0061] [Diagram 25] FIG. 25 is an embodiment of the system of FIG. 24 in which an angled surface on the cover glass is configured to direct the reflection toward a light dump, which absorbs the light.

[0062] [Figure 26] FIG. 26 is a simplified schematic diagram illustrating a cross-sectional view of an image projection system, in accordance with an embodiment of the present invention.

[0063] [Figure 27] FIG. 27 is a simplified schematic diagram illustrating a cross-sectional view of a compact image projection system in accordance with an embodiment of the present invention.

[0064] [Figure 28] FIG. 28 is a schematic diagram of an unfolded optical path corresponding to the compact image projection system illustrated in FIG.

[0065] [Figure 29] FIG. 29 is a simplified flowchart illustrating a method of operating a compact image projection system according to an embodiment of the present invention.

[0066] [Diagram 30] FIG. 30 is a simplified schematic diagram illustrating a cross-sectional view of a compact image projection system according to another embodiment of the present invention.

[0067] [Diagram 31] FIG. 31 is a schematic diagram of an unfolded optical path corresponding to the compact image projection system illustrated in FIG.

[0068] [Diagram 32] FIG. 32 is a simplified flowchart illustrating a method of operating a compact image projection system according to another embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0069] DETAILED DESCRIPTION OF SPECIFIC EMBODIMENTS Reference is now made to the drawings, in which like reference numbers refer to like parts throughout, and in which, unless otherwise indicated, the drawings are schematic and are not necessarily drawn to scale.

[0070] FIG. 2 illustrates a conventional display system for simulating a three-dimensional image for a user. It should be understood that when a user's eyes are spaced apart and viewing a real object in space, each eye may have a slightly different view of the object and form an image of the object at a different location on each eye's retina. This may be referred to as binocular disparity and may be exploited by the human visual system to provide a perception of depth. Conventional display systems simulate binocular disparity by presenting two distinctly different images 190, 200 with slightly different views of the same virtual object, one for each eye 210a, 210b, corresponding to a view of the virtual object as it would appear by each eye as if the virtual object were a real object at a desired depth. These images provide binocular cues that the user's visual system may interpret to derive a perception of depth.

[0071] 2, the images 190, 200 are spaced from the eyes 210a, 210b by a distance 230 on the z-axis, which is parallel to the optical axis of the viewer with that eye fixating on an object at optical infinity directly in front of the viewer. The images 190, 200 are flat and at a fixed distance from the eyes 210a, 210b. Based on slightly different views of the virtual object in the images presented to the eyes 210a, 210b, respectively,

[0072] The eyes may necessarily rotate so that the image of the object falls on a corresponding point on each of the eyes' retinas to maintain single binocular vision. This rotation may cause the gaze of each of the eyes 210a, 210b to converge on a point in space where the virtual object is perceived to reside. As a result, providing a three-dimensional image traditionally involves manipulating the convergence and divergence movements of the eyes 210a, 210b to provide binocular cues that the human visual system interprets to provide the perception of depth.

[0073] However, generating a realistic and comfortable perception of depth is difficult. It should be understood that light from an object at different distances from the eye has a wavefront with different amounts of divergence. Figures 3A-3C illustrate the relationship between distance and divergence of light rays. The distance between the object and the eye 210 is represented in the order of decreasing distances R1, R2, and R3. As shown in Figures 3A-3C, the light rays become more divergent as the distance to the object decreases. Conversely, as the distance increases, the light rays become more collimated. In other words, the light field generated by a point (an object or part of an object) can be said to have a spherical wavefront curvature that is a function of the distance the point is away from the user's eye. As the curvature increases, the distance between the object and the eye 210 decreases. Although only a single eye 210 is illustrated in Figures 3A-3C and other figures herein for clarity of illustration, the discussion regarding the eye 210 may apply to both eyes 210a and 210b.

[0074] 3A-3C, light from an object that a viewer's eye is fixating on may have different wavefront divergences. Due to the different wavefront divergences, the light may be focused differently by the eye's lens, which in turn may require the lens to assume a different shape and form a focused image on the eye's retina. If a focused image is not formed on the retina, the resulting retinal blur acts as an accommodative cue, causing the shape of the eye's lens to change until a focused image is formed on the retina. For example, an accommodative cue may induce relaxation or contraction of the ciliary muscle surrounding the eye's lens, thereby modulating the force applied to the suspensory ligament that holds the lens, thus changing the shape of the eye's lens, thereby forming a focused image of the fixated object on the eye's retina (e.g., the fovea) until retinal blur of the fixated object is eliminated or minimized. The process by which the eye lens changes shape may be referred to as accommodation, and the shape of the eye lens required to form a focused image of a fixated object on the eye's retina (e.g., the fovea) may be referred to as the state of accommodation.

[0075] Referring now to FIG. 4A, a representation of the accommodation-vergence response of the human visual system is illustrated. A movement of the eye to fixate an object causes the eye to receive light from the object, which forms an image on each of the eye's retinas. The presence of retinal blur in the image formed on the retina may provide a cue for accommodation, and the relative location of the image on the retina may provide a cue for vergence. A cue for accommodation causes accommodation, resulting in the eye's lens adopting a particular accommodation state in which each of the eye's lenses forms a focused image of the object on the eye's retina (e.g., the fovea). On the other hand, a cue for vergence causes a vergence movement (eye rotation) such that the image formed on each retina of each eye is at a corresponding retinal point that maintains single binocular vision. In these positions, the eye may be said to adopt a particular vergence state. Continuing with reference to FIG. 4A, accommodation can be understood to be the process by which the eye achieves a particular accommodation state, and convergence can be understood to be the process by which the eye achieves a particular convergence state. As shown in FIG. 4A, the accommodation and convergence state of the eye can change when the user fixates a different object. For example, the accommodated state can change when the user fixates a new object at a different depth on the z-axis.

[0076] Without being limited by theory, it is believed that a viewer of an object may perceive the object as being "three-dimensional" due to a combination of vergence-divergence and accommodation. As previously mentioned, vergence-divergence movements of the two eyes relative to one another (e.g., rotation of the eyes such that the pupils move toward or away from one another, converging the gaze of the eyes to fixate on an object) are closely linked to accommodation of the eye's lenses. Under normal conditions, changing the shape of the eye's lenses and shifting focus from one object to another at a different distance will automatically produce a matching change in vergence to the same distance, a relationship known as the "accommodation-vergence-divergence reflex." Similarly, a change in vergence will induce a matching change in lens shape under normal conditions.

[0077] 4B, an example of different accommodation and convergence-divergence states of the eyes is illustrated. Paired eye 222a fixates an object at optical infinity, while paired eye 222b fixates an object 221 at less than optical infinity. Notably, the convergence-divergence states of each pair of eyes are different, paired eye 222a points straight ahead, while paired eye 222 converges on object 221. The accommodation states of the eyes forming each pair of eyes 222a and 222b are also different, as represented by the different shapes of the lenses 220a, 220b.

[0078] Unfortunately, many users of conventional "3-D" display systems may find such conventional systems uncomfortable or may not perceive any depth sensation due to a mismatch between accommodation and vergence states in these displays. As previously mentioned, many stereoscopic or "3-D" display systems display a scene by providing a slightly different image to each eye. Such systems are uncomfortable for many viewers because, among other things, they simply provide a different presentation of the scene, causing changes in the vergence states of the eyes, but without a corresponding change in the accommodation states of those eyes. Rather, images are presented by the display at a fixed distance from the eyes, such that the eyes view all image information in a single accommodation state. Such an arrangement counters the "accommodation-vergence-divergence reflex" by causing changes in vergence states without a matching change in accommodation state. This mismatch is believed to cause viewer discomfort. By providing better matching between accommodation and convergence-divergence movements, display systems may form a more realistic and comfortable simulation of three-dimensional images.

[0079] Without being limited by theory, it is believed that the human eye is typically capable of interpreting a finite number of depth planes to provide depth perception. As a result, a highly realistic simulation of perceived depth may be achieved by providing the eye with different presentations of images corresponding to each of these limited number of depth planes. In some embodiments, the different presentations may provide both vergence cues and matching cues for accommodation, thereby providing physiologically correct accommodation-vergence divergence matching.

[0080] 4B, two depth planes 240 are illustrated, corresponding to different distances in space from the eyes 210a, 210b. For a given depth plane 240, vergence-divergence cues may be provided by displaying different perspective images for each eye 210a, 210b as appropriate. Additionally, for a given depth plane 240, the light forming the image provided to each eye 210a, 210b may have a wavefront divergence corresponding to the light field generated by a point at the distance of that depth plane 240.

[0081] In the illustrated embodiment, the distance along the z-axis of the depth plane 240 containing the point 221 is 1 m. As used herein, the distance or depth along the z-axis may be measured with the zero point located at the exit pupil of the user's eye. Thus, the depth plane 240 located at a depth of 1 m corresponds to a distance of 1 m away from the exit pupil of the user's eye on the optical axis of the eye with the eye pointed towards optical infinity. As an approximation, the depth or distance along the z-axis may be measured from the display (e.g., the surface of the waveguide) in front of the user's eye, and a value for the distance between the device and the exit pupil of the user's eye may be added. That value may be called the pupil distance and may correspond to the distance between the exit pupil of the user's eye and the display worn by the user in front of the eye. In practice, the value for the pupil distance may be a normalized value that is generally used for all viewers. For example, the pupil distance may be assumed to be 20 mm, and the depth plane at a depth of 1 m may be at a distance of 980 mm in front of the display.

[0082] 4C and 4D, examples of matched accommodation-vergence-divergence distances and mismatched accommodation-vergence-divergence distances are illustrated, respectively. As illustrated in FIG. 4C, the display system may provide an image of a virtual object to each eye 210a, 210b. The image may cause the eyes 210a, 210b to assume a convergence-divergence state in which the eyes converge on point 15 on the depth plane 240. In addition, the image may be formed by light having a wavefront curvature corresponding to a real object in that depth plane 240. As a result, the eyes 210a, 210b assume an accommodation state in which the image is focused on the retinas of those eyes. Thus, the user may perceive the virtual object as being at point 15 on the depth plane 240.

[0083] It should be understood that each of the accommodation and convergence states of the eyes 210a, 210b is associated with a particular distance on the z-axis. For example, an object at a particular distance from the eyes 210a, 210b will cause the eyes to assume a particular accommodation state based on the distance of the object. The distance associated with a particular accommodation state is referred to as the accommodation distance A. d Similarly, a particular convergence-divergence distance V associated with the eyes in a particular convergence-divergence state may be referred to as d or positions relative to each other. When the accommodation distance and the vergence distance match, the relationship between accommodation and vergence is said to be physiologically correct. This is considered to be the most comfortable scenario for the viewer.

[0084] However, in a stereoscopic display, the accommodation distance and the vergence distance may not always match. For example, as illustrated in FIG. 4D, the image displayed to the eyes 210a, 210b may be displayed with a wavefront divergence corresponding to the depth plane 240, and the eyes 210a, 210b may be in a particular accommodation state in which the points 15a, 15b on the depth plane are focused. However, the image displayed to the eyes 210a, 210b may provide a cue for vergence that causes the eyes 210a, 210b to converge on a point 15 that is not located on the depth plane 240. As a result, the accommodation distance corresponds in some embodiments to the distance from the exit pupils of the eyes 210a, 210b to the depth plane 240, while the vergence distance corresponds to a larger distance from the exit pupils of the eyes 210a, 210b to the point 15. The accommodation distance is different from the vergence distance. As a result, an accommodation-vergence-divergence mismatch exists. Such a mismatch may be considered undesirable and may cause discomfort to the user. It is understood that the mismatch may correspond to a distance (e.g., VaAd) and be characterized using diopters.

[0085] It should be understood that in some embodiments, reference points other than the exit pupils of the eyes 210a, 210b may be utilized to determine distances for determining accommodation-vergence mismatch, so long as the same reference points are utilized for accommodation distance and vergence distance. For example, distances may be measured from the cornea to the depth plane, from the retina to the depth plane, from the eyepiece (e.g., a waveguide in a display device) to the depth plane, etc.

[0086] Without being limited by theory, it is believed that a user may still perceive an accommodation-vergence-divergence mismatch of up to about 0.25 diopters, up to about 0.33 diopters, and up to about 0.5 diopters as physiologically correct, without the mismatch itself causing significant discomfort. In some embodiments, a display system disclosed herein (e.g., display system 250, FIG. 6) presents an image to a viewer having an accommodation-vergence-divergence mismatch of about 0.5 diopters or less. In some other embodiments, the accommodation-vergence-divergence mismatch of the image provided by the display system is about 0.33 diopters or less. In still other embodiments, the accommodation-vergence-divergence mismatch of the image provided by the display system is about 0.25 diopters or less, including about 0.1 diopters or less.

[0087] FIG. 5 illustrates aspects of an approach for simulating a three-dimensional image by modifying wavefront divergence. The display system includes a waveguide 270 configured to receive light 770 encoded with image information and output the light to a user's eye 210. The waveguide 270 may output light 650 with a defined amount of wavefront divergence that corresponds to the wavefront divergence of a light field generated by a point on a desired depth plane 240. In some embodiments, the same amount of wavefront divergence is provided for all objects presented on that depth plane. In addition, the user's other eye will be illustrated as being provided with image information from a similar waveguide.

[0088] In some embodiments, a single waveguide may be configured to output light with a set wavefront divergence corresponding to a single or limited number of depth planes, and / or the waveguide may be configured to output light of a limited range of wavelengths. As a result, in some embodiments, a stack of waveguides may be utilized to provide different wavefront divergence for different depth planes and / or output light of different ranges of wavelengths. As used herein, it should be understood that a depth plane may follow the contour of a planar or curved surface. In some embodiments, advantageously, for simplicity, a depth plane may follow the contour of a flat surface.

[0089] 6 illustrates an example of a waveguide stack for outputting image information to a user. Display system 250 includes a stack of waveguides or stacked waveguide assembly 260 that may be utilized to provide a three-dimensional perception to the eye / brain using waveguides 270, 280, 290, 300, 310. It should be understood that display system 250 may be considered a light field display in some embodiments. Additionally, waveguide assembly 260 may also be referred to as an eyepiece.

[0090] In some embodiments, the display system 250 may be configured to provide a substantially continuous cue for convergence and multiple discrete cues for accommodation. The cues for convergence may be provided by displaying different images to each of the user's eyes, and the cues for accommodation may be provided by outputting light forming images with selectable discrete amounts of wavefront divergence. In other words, the display system 250 may be configured to output light with variable levels of wavefront divergence. In some embodiments, each discrete level of wavefront divergence corresponds to a particular depth plane and may be provided by a particular one of the waveguides 270, 280, 290, 300, 310.

[0091] Continuing with reference to FIG. 6, the waveguide assembly 260 may also include features 320, 330, 340, 350 between the waveguides. In some embodiments, the features 320, 330, 340, 350 may be one or more lenses. The waveguides 270, 280, 290, 300, 310 and / or features (lenses) 320, 330, 340, 350 may be configured to transmit image information to the eye with various levels of wavefront curvature or light beam divergence. Each waveguide level may be associated with a particular depth plane and may be configured to output image information corresponding to that depth plane. The image input devices 360, 370, 380, 390, 400 may act as light sources for the waveguides and may be utilized to input image information into the waveguides 270, 280, 290, 300, 310, each of which may be configured to disperse incident light across each individual waveguide for output towards the eye 210, as described herein. Light exits output surfaces 410, 420, 430, 440, 450 of the image input devices 360, 370, 380, 390, 400 and is input into corresponding input surfaces 460, 470, 480, 490, 500 of the waveguides 270, 280, 290, 300, 310. In some embodiments, each of the input surfaces 460, 470, 480, 490, 500 may be an edge of the corresponding waveguide or may be a portion of a major surface of the corresponding waveguide (i.e., one of the waveguide surfaces that directly faces the world 510 or the viewer's eye 210). In some embodiments, a single beam of light (e.g., a collimated beam) may be launched into each waveguide, outputting a total field of cloned collimated beams that are directed toward the eye 210 at a particular angle (and divergence) corresponding to the depth plane associated with the particular waveguide. In some embodiments, a single one of the image launch devices 360, 370, 380, 390, 400 may be associated with and launch light into one or more (e.g., three) waveguides 270, 280, 290, 300, 310.

[0092] In some embodiments, each of the image input devices 360, 370, 380, 390, 400 is a discrete display that generates image information for input into the respective waveguides 270, 280, 290, 300, 310. In some other embodiments, the image input devices 360, 370, 380, 390, 400 are the output of a single multiplexed display that may, for example, send image information to each of the image input devices 360, 370, 380, 390, 400 via one or more optical conduits (such as fiber optic cables). It should be understood that the image information provided by the image input devices 360, 370, 380, 390, 400 may include light of different wavelengths or colors (e.g., different primary colors as discussed herein).

[0093] In some embodiments, the light injected into the waveguides 270, 280, 290, 300, 310 is provided by a light projector system 520, which includes a light module 530, which may include a light emitter such as a light emitting diode (LED). The light from the light module 530 may be directed and modified by a light modulator 540, e.g., a spatial light modulator, via a beam splitter 550. The light modulator 540 may be configured to vary the perceived intensity of the light injected into the waveguides 270, 280, 290, 300, 310 and encode the light with image information. Examples of spatial light modulators include liquid crystal displays (LCDs), including liquid crystal on silicon (LCoS) displays. It should be understood that image injection devices 360, 370, 380, 390, 400 are illustrated diagrammatically and in some embodiments these image injection devices may represent different light paths and locations within a common projection system configured to output light into associated ones of waveguides 270, 280, 290, 300, 310. In some embodiments, the waveguides of the waveguide assembly 260 may act as ideal lenses, relaying light injected into the waveguides to the user's eye. In this concept, the object may be a spatial light modulator 540 and the image may be an image on a depth plane.

[0094] In some embodiments, the display system 250 may be a scanning fiber display comprising one or more scanning fibers configured to project light in various patterns (e.g., raster scan, spiral scan, Lissajous patterns, etc.) into one or more waveguides 270, 280, 290, 300, 310 and ultimately to the viewer's eye 210. In some embodiments, the illustrated image injection devices 360, 370, 380, 390, 400 may diagrammatically represent a single scanning fiber or a bundle of scanning fibers configured to inject light into one or more of the waveguides 270, 280, 290, 300, 310. In some other embodiments, the illustrated image injection devices 360, 370, 380, 390, 400 may diagrammatically represent one or more scanning fibers or one or more bundles of scanning fibers, each configured to inject light into an associated one of the waveguides 270, 280, 290, 300, 310. It should be understood that the one or more optical fibers may be configured to transmit light from the optical module 530 to the one or more waveguides 270, 280, 290, 300, 310. It should be understood that one or more intervening optical structures may be provided between the scanning fiber or fibers and the one or more waveguides 270, 280, 290, 300, 310, for example, to redirect light exiting the scanning fiber into the one or more waveguides 270, 280, 290, 300, 310.

[0095] The controller 560 controls the operation of one or more of the stacked waveguide assemblies 260, including the operation of the image input devices 360, 370, 380, 390, 400, the light source 530, and the light modulator 540. In some embodiments, the controller 560 is part of the local data processing module 140. The controller 560 includes programming (e.g., instructions in a non-transient medium) that coordinates the timing and provisioning of image information to the waveguides 270, 280, 290, 300, 310, for example, according to any of the various schemes disclosed herein. In some embodiments, the controller may be a single integrated device or a distributed system connected by wired or wireless communication channels. The controller 560 may be part of the processing module 140 or 150 (FIG. 9D) in some embodiments.

[0096] With continued reference to FIG. 6, the waveguides 270, 280, 290, 300, 310 may be configured to propagate light within each individual waveguide by total internal reflection (TIR). Each of the waveguides 270, 280, 290, 300, 310 may be planar or have another shape (e.g., curved) with major top and bottom surfaces and edges extending between their major top and bottom surfaces. In the illustrated configuration, each of the waveguides 270, 280, 290, 300, 310 may include an outcoupling optical element 570, 580, 590, 600, 610 configured to extract light from the waveguide by redirecting the light and propagating it within each individual waveguide and outputting image information from the waveguide to the eye 210. Although referred to throughout this specification as an "outcoupling optical element," the outcoupling optical element need not be an optical element and may be a non-optical element. The extracted light may also be referred to as out-coupled light, and the out-coupling optical element may also be referred to as a light extraction optical element. The extracted light beam may be output by the waveguide at the location where the light propagating in the waveguide strikes the light extraction optical element. The out-coupling optical element 570, 580, 590, 600, 610 may be a grating, for example, including diffractive optical features as further discussed herein. Although shown disposed on the bottom major surface of the waveguide 270, 280, 290, 300, 310 for ease of explanation and clarity of drawing, in some embodiments, the out-coupling optical element 570, 580, 590, 600, 610 may be disposed on the top and / or bottom major surfaces and / or directly within the volume of the waveguide 270, 280, 290, 300, 310, as further discussed herein. In some embodiments, the outcoupling optical elements 570, 580, 590, 600, 610 may be formed within a layer of material that is attached to a transparent substrate and forms the waveguide 270, 280, 290, 300, 310. In some other embodiments, the waveguide 270, 280, 290, 300, 310 may be a monolithic piece of material and the outcoupling optical elements 570, 580, 590, 600, 610 may be formed on and / or within that piece of material.

[0097] With continued reference to FIG. 6, as discussed herein, each waveguide 270, 280, 290, 300, 310 is configured to output light and form an image corresponding to a particular depth plane. For example, the waveguide 270 closest to the eye may be configured to deliver collimated light (injected into such waveguide 270) to the eye 210. The collimated light may represent an optical infinity focal plane. The next upper waveguide 280 may be configured to send collimated light that passes through a first lens 350 (e.g., a negative lens) before it can reach the eye 210. Such first lens 350 may be configured to generate a slight convex wavefront curvature such that the eye / brain interprets the light originating from the next upper waveguide 280 as originating from a first focal plane closer inward from optical infinity toward the eye 210. Similarly, the third upper waveguide 290 passes its output light through both the first lens 350 and the second lens 340 before reaching the eye 210. The combined refractive powers of the first lens 350 and the second lens 340 may be configured to produce another incremental amount of wavefront curvature such that the eye / brain interprets the light emerging from the third waveguide 290 as emerging from a second focal plane that is closer inward from optical infinity towards the person than was the light from the next upper waveguide 280.

[0098] The other waveguide layers 300, 310 and lenses 330, 320 are similarly configured, with the highest waveguide 310 in the stack sending its output through all of the lenses between it and the eye for an aggregate focal power that represents the focal plane closest to the person. To compensate the stack of lenses 320, 330, 340, 350 when viewing / interpreting light originating from the world 510 on the other side of the stacked waveguide assembly 260, a compensating lens layer 620 may be placed on top of the stack to compensate for the aggregate power of the lens stacks 320, 330, 340, 350 below. Such a configuration provides as many perceived focal planes as there are waveguide / lens pairs available. Both the outcoupling optical elements of the waveguides and the focusing sides of the lenses may be static (i.e., not dynamic or electroactive). In some alternative embodiments, one or both may be dynamic using electroactive features.

[0099] In some embodiments, two or more of the waveguides 270, 280, 290, 300, 310 may have the same associated depth plane. For example, multiple waveguides 270, 280, 290, 300, 310 may be configured to output images set at the same depth plane, or multiple subsets of the waveguides 270, 280, 290, 300, 310 may be configured to output images set at the same one or more depth planes, with one set per depth plane. This may provide the advantage of forming tiled images to provide an extended field of view at those depth planes.

[0100] Continuing with reference to FIG. 6, the outcoupling optical elements 570, 580, 590, 600, 610 may be configured to redirect light from its respective waveguide and output the light with an appropriate amount of divergence or collimation for a particular depth plane associated with the waveguide. As a result, waveguides with different associated depth planes may have different configurations of outcoupling optical elements 570, 580, 590, 600, 610 that output light with different amounts of divergence depending on the associated depth plane. In some embodiments, the light extraction optical elements 570, 580, 590, 600, 610 may be volume or surface features that may be configured to output light at specific angles. For example, the light extraction optical elements 570, 580, 590, 600, 610 may be volume holograms, surface holograms, and / or diffraction gratings. In some embodiments, features 320, 330, 340, 350 may not be lenses. Rather, they may simply be spacers (e.g., cladding layers and / or structures for forming air gaps).

[0101] In some embodiments, the outcoupling optical elements 570, 580, 590, 600, 610 are diffractive features or "diffractive optical elements" (also referred to herein as "DOEs") that form a diffraction pattern. Preferably, the DOEs have a sufficiently low diffraction efficiency such that only a portion of the light in the beam is deflected toward the eye 210 at each intersection of the DOE, while the remainder continues to travel through the waveguide via TIR. The light carrying the image information is thus split into several related exit beams that exit the waveguide at various locations, resulting in a very uniform pattern of exit emission toward the eye 210 for this particular collimated beam bouncing within the waveguide.

[0102] In some embodiments, one or more DOEs may be switchable between an "on" state in which they actively diffract and an "off" state in which they do not significantly diffract. For example, a switchable DOE may comprise a layer of polymer dispersed liquid crystal in which microdroplets comprise a diffractive pattern in a host medium, and the refractive index of the microdroplets may be switched to substantially match the refractive index of the host material (in which case the pattern does not significantly diffract incident light), or the microdroplets may be switched to a refractive index that does not match that of the host medium (in which case the pattern actively diffracts incident light).

[0103] In some embodiments, a camera assembly 630 (e.g., a digital camera, including visible and infrared light cameras) may be provided to capture images of the eye 210 and / or tissue surrounding the eye 210, for example, to detect user input and / or monitor a physiological condition of the user. As used herein, a camera may be any image capture device. In some embodiments, the camera assembly 630 may include an image capture device and a light source that projects light (e.g., infrared light) onto the eye, which may then be reflected by the eye and detected by the image capture device. In some embodiments, the camera assembly 630 may be mounted to the frame 80 (FIG. 9D) and may be in electrical communication with the processing modules 140 and / or 150, which may process image information from the camera assembly 630. In some embodiments, one camera assembly 630 may be utilized per eye, monitoring each eye separately.

[0104] 7, an example of an output beam output by a waveguide is shown. Although one waveguide is shown, it should be understood that other waveguides in the waveguide assembly 260 (FIG. 6) may function similarly and that the waveguide assembly 260 includes multiple waveguides. Light 640 is launched into the waveguide 270 at the input surface 460 of the waveguide 270 and propagates within the waveguide 270 by TIR. At the point where the light 640 impinges on the DOE 570, a portion of the light exits the waveguide as an output beam 650. The output beam 650 is shown as approximately parallel, but may be redirected to propagate to the eye 210 at an angle (e.g., divergent output beam formation) as discussed herein and depending on the depth plane associated with the waveguide 270. It should be understood that a nearly collimated exit beam may refer to a waveguide with outcoupling optics that outcouples light to form an image that appears to be set at a depth plane at a large distance (e.g., optical infinity) from the eye 210. Other waveguides or other sets of outcoupling optics may output an exit beam pattern that is more divergent, which would require the eye 210 to accommodate to a closer distance and focus on the retina, and would be interpreted by the brain as light from a distance closer to the eye 210 than optical infinity.

[0105] In some embodiments, a full color image may be formed at each depth plane by overlaying an image in each of the primary colors, for example, three or more primary colors.

[0106] FIG. 8 illustrates an example of a stacked waveguide assembly, where each depth plane includes an image formed using multiple different primary colors. The illustrated embodiment shows depth planes 240a-240f, but more or less depths are also contemplated. Each depth plane may have three or more primary color images associated with it, including a first image of a first color G, a second image of a second color R, and a third image of a third color B. The different depth planes are indicated in the figure by different numbers for diopters (dpt) following the letters G, R, and B. By way of example only, the numbers following each of these letters indicate the diopters (1 / m), i.e., the inverse distance of the depth plane from the viewer, and each box in the figure represents an individual primary color image. In some embodiments, the exact locations of the depth planes for the different primary colors may be varied to account for differences in the eye's focusing of different wavelengths of light. For example, the different primary color images for a given depth plane may be placed on depth planes that correspond to different distances from the user. Such an arrangement may increase visual acuity and user comfort and / or reduce chromatic aberration.

[0107] In some embodiments, the light of each primary color may be output by a single dedicated waveguide, such that each depth plane may have multiple waveguides associated with it. In such embodiments, each box in the figure containing the letter G, R, or B may be understood to represent an individual waveguide, and three waveguides may be provided per depth plane, with three primary color images provided per depth plane. The waveguides associated with each depth plane are shown adjacent to each other in this drawing for ease of illustration, but it should be understood that in a physical device, the waveguides may all be arranged in a stack with one waveguide per level. In some other embodiments, multiple primary colors may be output by the same waveguide, such that, for example, only a single waveguide may be provided per depth plane.

[0108] 8, in some embodiments, G is green, R is red, and B is blue. In some other embodiments, other colors associated with other wavelengths of light, including magenta and cyan, may be used in addition to or in place of one or more of the red, green, or blue colors.

[0109] It should be understood that references to a given color of light throughout this disclosure will be understood to encompass light of one or more wavelengths within the range of wavelengths of light that are perceived by a viewer to be of that given color. For example, red light may include one or more wavelengths of light within the range of about 620-780 nm, green light may include one or more wavelengths of light within the range of about 492-577 nm, and blue light may include one or more wavelengths of light within the range of about 435-493 nm.

[0110] In some embodiments, the light source 530 (FIG. 6) may be configured to emit light at one or more wavelengths outside the range of visual perception of a viewer, e.g., infrared and / or ultraviolet wavelengths. Additionally, the waveguide in-coupling, out-coupling, and other light redirecting structures of the display 250 may be configured to direct and emit this light from the display toward the eye 210, e.g., for imaging and / or user stimulation applications.

[0111] Referring now to FIG. 9A, in some embodiments, light impinging on a waveguide may need to be redirected to incouple the light into the waveguide. An incoupling optical element may be used to redirect and incoupling the light into its corresponding waveguide. Although "incoupling optical elements" are referenced throughout this specification, the incoupling optical elements need not be optical elements, but may be non-optical elements. FIG. 9A illustrates a cross-sectional side view of an example of a set 660 of stacked waveguides, each including an incoupling optical element. Each of the waveguides may be configured to output light of one or more different wavelengths or one or more different wavelength ranges. Stack 660 may correspond to stack 260 (FIG. 6), and the illustrated waveguides of stack 660 may correspond to portions of waveguides 270, 280, 290, 300, 310, although it should be understood that light from one or more of image injection devices 360, 370, 380, 390, 400 is injected into the waveguides from a location requiring the light to be redirected for internal coupling.

[0112] The illustrated set 660 of stacked waveguides includes waveguides 670, 680, and 690. Each waveguide includes an associated incoupling optical element (which may also be referred to as the light input area on the waveguide), for example, incoupling optical element 700 is disposed on a major surface (e.g., the top major surface) of waveguide 670, incoupling optical element 710 is disposed on a major surface (e.g., the top major surface) of waveguide 680, and incoupling optical element 720 is disposed on a major surface (e.g., the top major surface) of waveguide 690. In some embodiments, one or more of the incoupling optical elements 700, 710, 720 may be disposed on the bottom major surface of the respective waveguides 670, 680, 690 (particularly, one or more of the incoupling optical elements are reflective polarizing optical elements). As shown, the incoupling optical elements 700, 710, 720 may be disposed on the upper major surface of the respective waveguide 670, 680, 690 (or on top of the next lower waveguide), and in particular, the incoupling optical elements are transmissive deflecting optical elements. In some embodiments, the incoupling optical elements 700, 710, 720 may be disposed within the body of the respective waveguide 670, 680, 690. In some embodiments, as discussed herein, the incoupling optical elements 700, 710, 720 are wavelength selective such that they selectively redirect one or more wavelengths of light while transmitting other wavelengths of light. Although illustrated on one side or corner of the respective waveguide 670, 680, 690, it should be understood that the incoupling optical elements 700, 710, 720 may be disposed within other areas of the respective waveguide 670, 680, 690 in some embodiments.

[0113] As shown, the in-coupling optical elements 700, 710, 720 may be laterally offset from one another. In some embodiments, each in-coupling optical element may be offset to receive light without that light passing through another in-coupling optical element. For example, each in-coupling optical element 700, 710, 720 may be configured to receive light from different image input devices 360, 370, 380, 390, and 400 as shown in FIG. 6 and may be separated (e.g., laterally spaced) from the other in-coupling optical elements 700, 710, 720 so as to not substantially receive light from others of the in-coupling optical elements 700, 710, 720.

[0114] Each waveguide also includes an associated optically dispersive element, for example, optically dispersive element 730 is disposed on a major surface (e.g., a top major surface) of waveguide 670, optically dispersive element 740 is disposed on a major surface (e.g., a top major surface) of waveguide 680, and optically dispersive element 750 is disposed on a major surface (e.g., a top major surface) of waveguide 690. In some other embodiments, optically dispersive elements 730, 740, 750 may be disposed on the bottom major surfaces of associated waveguides 670, 680, 690, respectively. In some other embodiments, optically dispersive elements 730, 740, 750 may be disposed on both the top and bottom major surfaces of associated waveguides 670, 680, 690, respectively, or optically dispersive elements 730, 740, 750 may be disposed on different ones of the top and bottom major surfaces in different associated waveguides 670, 680, 690, respectively.

[0115] The waveguides 670, 680, 690 may be spaced apart and separated by, for example, gas, liquid, and / or solid layers of material. For example, as shown, layer 760a may separate the waveguides 670 and 680, and layer 760b may separate the waveguides 680 and 690. In some embodiments, layers 760a and 760b are formed from a low index material (i.e., a material having a lower index of refraction than the material forming the immediate neighbors of the waveguides 670, 680, 690). Preferably, the index of refraction of the material forming layers 760a, 760b is 0.05 or greater, or 0.10 or less, than the index of refraction of the material forming the waveguides 670, 680, 690. Advantageously, the lower refractive index layers 760a, 760b may act as cladding layers to promote total internal reflection (TIR) ​​of light through the waveguides 670, 680, 690 (e.g., TIR between the top and bottom major surfaces of each waveguide). In some embodiments, the layers 760a, 760b are formed from air. Although not shown, it should be understood that the top and bottom of the illustrated set of waveguides 660 may include immediate cladding layers.

[0116] Preferably, for ease of manufacturing and other considerations, the materials forming the waveguides 670, 680, 690 are similar or identical, and the materials forming the layers 760a, 760b are similar or identical. In some embodiments, the materials forming the waveguides 670, 680, 690 may differ between one or more of the waveguides, and / or the materials forming the layers 760a, 760b may differ while still maintaining the various refractive index relationships discussed above.

[0117] 9A, light rays 770, 780, 790 are incident on the set of waveguides 660. It should be understood that light rays 770, 780, 790 may be injected into the waveguides 670, 680, 690 by one or more image injection devices 360, 370, 380, 390, 400 (FIG. 6).

[0118] In some embodiments, the light beams 770, 780, 790 have different properties, e.g., different wavelengths or different wavelength ranges, that may correspond to different colors. Each of the incoupling optical elements 700, 710, 720 deflects the incident light such that the light propagates through a respective one of the waveguides 670, 680, 690 by TIR. In some embodiments, each of the incoupling optical elements 700, 710, 720 selectively deflects one or more particular wavelengths of light while transmitting other wavelengths to the underlying waveguide and associated incoupling optical element.

[0119] For example, incoupling optical element 700 may be configured to deflect light beam 770 having a first wavelength or wavelength range while transmitting light beams 780 and 790 having different second and third wavelengths or wavelength ranges, respectively. The transmitted light beam 780 impinges on and is deflected by incoupling optical element 710, which is configured to deflect light of the second wavelength or wavelength range. Light beam 790 is deflected by incoupling optical element 720, which is configured to selectively deflect light of the third wavelength or wavelength range.

[0120] 9A, the deflected light rays 770, 780, 790 are deflected to propagate through the corresponding waveguides 670, 680, 690. That is, the incoupling optical element 700, 710, 720 of each waveguide deflects the light into its corresponding waveguide 670, 680, 690 and incouplings the light into the corresponding waveguide. The light rays 770, 780, 790 are deflected at an angle that causes the light to propagate through the respective waveguides 670, 680, 690 by TIR. The light rays 770, 780, 790 propagate through the respective waveguides 670, 680, 690 by TIR until they impinge on the corresponding optical dispersive element 730, 740, 750 of the waveguide.

[0121] 9B, a perspective view of the multiple stacked waveguide embodiment of FIG. 9A is illustrated. As previously described, the in-coupled light rays 770, 780, 790 are deflected by the in-coupling optical elements 700, 710, 720, respectively, and then propagate by TIR within the waveguides 670, 680, 690, respectively. The light rays 770, 780, 790 then impinge on the optically dispersive elements 730, 740, 750, respectively. The optically dispersive elements 730, 740, 750 deflect the light rays 770, 780, 790 to propagate towards the out-coupling optical elements 800, 810, 820, respectively.

[0122] In some embodiments, the optically dispersive elements 730, 740, 750 are orthogonal pupil expanders (OPEs). In some embodiments, the OPEs deflect or disperse the light to the out-coupling optical elements 800, 810, 820, and in some embodiments may also increase the beam or spot size of this light as it propagates to the out-coupling optical elements. In some embodiments, the optically dispersive elements 730, 740, 750 may be omitted and the in-coupling optical elements 700, 710, 720 may be configured to deflect the light directly to the out-coupling optical elements 800, 810, 820. For example, referring to FIG. 9A, the optically dispersive elements 730, 740, 750 may be replaced with the out-coupling optical elements 800, 810, 820, respectively. In some embodiments, the external coupling optical element 800, 810, 820 is an exit pupil (EP) or exit pupil expander (EPE) that directs light to the eye 210 (FIG. 7). It should be understood that the OPE may be configured to increase the size of the eyebox in at least one axis, and the EPE may increase the eyebox in an axis that intersects, e.g., perpendicular to, the axis of the OPE. For example, each OPE may be configured to redirect a portion of the light striking the OPE to the EPE of the same waveguide, while allowing the remaining portion of the light to continue propagating down the waveguide. In response to striking the OPE, again, another portion of the remaining light is redirected to the EPE, which continues to propagate further down the waveguide, etc. Similarly, in response to striking the EPE, a portion of the striking light is directed out of the waveguide towards the user, and the remaining portion of the light continues to propagate through the waveguide until it strikes the EP again, at which point another portion of the striking light is directed out of the waveguide, etc. As a result, a single beam of internally coupled light may be "replicated" each time a portion of that light is redirected by an OPE or EPE, thereby forming a cloned beam field of light, as shown in Figure 6. In some embodiments, the OPE and / or EPE may be configured to modify the size of the beam of light.

[0123] Thus, referring to Figures 9A and 9B, in some embodiments, a set of waveguides 660 includes, for each primary color, a waveguide 670, 680, 690, an in-coupling optical element 700, 710, 720, an optical dispersion element (e.g., OPE) 730, 740, 750, and an out-coupling optical element (e.g., EP) 800, 810, 820. The waveguides 670, 680, 690 may be stacked with an air gap / cladding layer between each one. The in-coupling optical element 700, 710, 720 redirects or deflects the incoming light into its waveguide (with different in-coupling optical elements receiving different wavelengths of light). The light then propagates at an angle that will result in TIR within the individual waveguides 670, 680, 690. In the illustrated embodiment, light ray 770 (e.g., blue light) is deflected by the first in-coupling optical element 700 in the manner described above, then continues to bounce back down the waveguide, interacting with the optically dispersive element (e.g., OPE) 730 and then the out-coupling optical element (e.g., EP) 800. Light rays 780 and 790 (e.g., green and red light, respectively) pass through the waveguide 670, where light ray 780 impinges on and is deflected by the in-coupling optical element 710. Light ray 780 will then proceed via TIR back down the waveguide 680, to its optically dispersive element (e.g., OPE) 740 and then the out-coupling optical element (e.g., EP) 810. Finally, light ray 790 (e.g., red light) passes through the waveguide 690 and impinges on the optically in-coupling optical element 720 of the waveguide 690. The light in-coupling optical element 720 deflects the light beam 790 such that it propagates by TIR to a light dispersive element (e.g., OPE) 750 and then by TIR to an out-coupling optical element (e.g., EP) 820. The out-coupling optical element 820 then finally out-couples the light beam 790 to a viewer, who also receives the out-coupled light from the other waveguides 670, 680.

[0124] FIG. 9C illustrates a top-down plan view of the stacked waveguide example of FIGS. 9A and 9B. As shown, the waveguides 670, 680, 690 may be vertically aligned with each waveguide's associated light dispersive element 730, 740, 750 and associated out-coupling optical elements 800, 810, 820. However, as discussed herein, the in-coupling optical elements 700, 710, 720 are not vertically aligned. Rather, the in-coupling optical elements are preferably non-overlapping (e.g., laterally spaced apart, as seen in the top-down view). As discussed further herein, this non-overlapping spatial arrangement facilitates the injection of light from different sources into different waveguides on a one-to-one basis, thereby allowing a specific light source to be uniquely coupled to a specific waveguide. In some embodiments, an arrangement including non-overlapping, spatially separated in-coupling optical elements may be referred to as a shifted pupil system, and the in-coupling optical elements in these arrangements may correspond to sub-pupils.

[0125] 9D illustrates an example of a wearable display system 60 into which the various waveguide and associated systems disclosed herein may be integrated. In some embodiments, the display system 60 is the system 250 of FIG. 6, which diagrammatically illustrates some portions of the system 60 in greater detail. For example, the waveguide assembly 260 of FIG. 6 may be part of the display 70.

[0126] 9D, the display system 60 includes a display 70 and various mechanical and electronic modules and systems to support the functionality of the display 70. The display 70 may be coupled to a frame 80, which is wearable by a display system user or viewer 90 and configured to position the display 70 in front of the eye of the user 90. The display 70 may be considered an eyepiece in some embodiments. In some embodiments, a speaker 100 is coupled to the frame 80 and configured to be positioned adjacent to the ear canal of the user 90 (in some embodiments, another speaker, not shown, may also be optionally positioned adjacent the user's other ear canal to provide stereo / shapeable sound control). The display system 60 may also include one or more microphones 110 or other devices to detect sound. In some embodiments, the microphones may be configured to allow the user to provide input or commands to the system 60 (e.g., voice menu command selection, natural language queries, etc.) and / or enable audio communication with other persons (e.g., other users of a similar display system). The microphone may further be configured as an ambient sensor to collect audio data (e.g., sounds from the user and / or the environment). In some embodiments, the display system 60 may further include one or more outwardly directed environmental sensors 112 configured to detect objects, stimuli, people, animals, places, or other aspects of the world around the user. For example, the environmental sensors 112 may include one or more cameras, which may be positioned, for example, facing outward, to capture images similar to at least a portion of the user 90's normal field of view. In some embodiments, the display system may also include an ambient sensor 120a, which may be separate from the frame 80 and attached to the body of the user 90 (e.g., the head, torso, limbs, etc. of the user 90). The ambient sensor 120a may, in some embodiments, be configured to obtain data characterizing a physiological state of the user 90.For example, the sensor 120a may be an electrode.

[0127] 9D, the display 70 is operably coupled by a communication link 130, such as wired or wireless connectivity, to a local data processing module 140, which may be mounted in a variety of configurations, such as fixedly attached to the frame 80, fixedly attached to a helmet or hat worn by the user, embedded within headphones, or otherwise removably attached to the user 90 (e.g., in a backpack configuration, in a belt-connected configuration). Similarly, the sensor 120a may be operably coupled to the local processor and data module 140 by a communication link 120b, such as wired or wireless connectivity. The local processing and data module 140 may comprise a hardware processor and digital memory, such as non-volatile memory (e.g., flash memory or hard disk drive), both of which may be utilized to aid in processing, caching, and storing data. Optionally, the local processing and data module 140 may include one or more central processing units (CPUs), graphics processing units (GPUs), dedicated processing hardware, and the like. The data may include a) captured from sensors (such as image capture devices (cameras, etc.), microphones, inertial measurement units, accelerometers, compasses, GPS units, wireless devices, gyroscopes, and / or other sensors disclosed herein (e.g., which may be operatively coupled to the frame 80 or otherwise attached to the user 90)) and / or b) data obtained and / or processed using a remote processing module 150 and / or a remote data repository 160 (including data related to the virtual content), possibly for passage to the display 70 after processing or retrieval. The local processing and data module 140 may be operatively coupled to the remote processing module 150 and the remote data repository 160 by communication links 170, 180, such as via wired or wireless communication links, such that these remote modules 150, 160 are operatively coupled to each other and available as resources to the local processing and data module 140.In some embodiments, local processing and data module 140 may include one or more of an image capture device, a microphone, an inertial measurement unit, an accelerometer, a compass, a GPS unit, a wireless device, and / or a gyroscope. In some other embodiments, one or more of these sensors may be mounted on frame 80 or may be a stand-alone structure that communicates with local processing and data module 140 by a wired or wireless communication path.

[0128] 9D , in some embodiments, the remote processing module 150 may comprise one or more processors configured to analyze and process the data and / or image information, and may include, for example, one or more central processing units (CPUs), graphics processing units (GPUs), special purpose processing hardware, etc. In some embodiments, the remote data repository 160 may comprise a digital data storage facility that may be available through the Internet or other networking configurations in a "cloud" resource configuration. In some embodiments, the remote data repository 160 may include one or more remote servers, which provide information, for example, information for generating augmented reality content to the local processing and data module 140 and / or the remote processing module 150. In some embodiments, all data is stored and all calculations are performed within the local processing and data module, allowing for fully autonomous use from the remote modules. Optionally, an external system (e.g., one or more processors, one or more computer systems), including a CPU, GPU, etc., may perform at least a portion of the processing (e.g., generating image information, processing data) and provide information to and receive information from modules 140, 150, 160, e.g., via a wireless or wired connection.

[0129] FIG. 10 is a schematic diagram illustrating a projector assembly 1000 utilizing a polarizing beam splitter (PBS) 1020 to illuminate a spatial light modulator (SLM) 1030 and redirect light from the SLM 1030 through projection optics 1040 to an eyepiece (not shown). The projector assembly 1000 includes an illumination source 1010, which may include, for example, a light emitting diode (LED), a laser (e.g., a laser diode), or other types of light sources. The light may be collimated by a collimating optic. The illumination source 1010 may emit polarized, unpolarized, or partially polarized light. In the illustrated design, the illumination source 1010 may emit light 1012 polarized to have p-polarization. A first optical element 1015 (e.g., a pre-polarizer) is aligned to pass light with a first polarization (e.g., p-polarization).

[0130] This light is directed to a polarizing beam splitter 1020. First, the light passes through an interface 1022 (e.g., a polarizing interface) of the PBS 1020, which is configured to transmit light of a first polarization (e.g., p-polarized). Thus, the light continues and is incident on a spatial light modulator 1030. As shown, the SLM 1030 is a reflective SLM configured to retroreflect the incident light and selectively modulate the light. The SLM 1030 includes one or more pixels, which may have, for example, different states. The light incident on an individual pixel may be modulated based on the state of the pixel. Thus, the SLM 1030 can be driven to modulate the light to provide an image. In this embodiment, the SLM 1030 may be a polarization-based SLM that modulates the polarization of the light incident thereon. For example, in an on state, a pixel of the SLM 1030 changes the input light from a first polarization state (e.g., a p-polarization state) to a second polarization state (e.g., an s-polarization state) such that a bright state (e.g., a white pixel) is indicated. The second polarization state may be the first polarization state that is modulated (e.g., rotated) by 90°. In the on state, light having the second polarization state is reflected by the interface 1022 and propagates downstream of the projector optics 1040. In the off state, the SLM 1030 does not change the polarization state of the light incident thereon, e.g., does not rotate the input light from the first polarization state, and thus a dark state (e.g., a black pixel) is indicated. In the off state, light having the first polarization state is transmitted through the interface 1022 and propagates upstream back to the illumination source 1010, but not to the user's eye.

[0131] After reflecting from the SLM 1030, a portion of the light 1014 (e.g., modulated light) is reflected from interface 1022 and exits the PBS 1020 and is directed to the user's eye. The emitted light passes through projector optics 1040 and is imaged onto an internal coupling grating (ICG) 1050 in the eyepiece (not shown).

[0132] 11A illustrates a system (e.g., an augmented reality display system) 1100A for presenting an image to a user's eye 210 and viewing the world 510, having an alternative configuration to that shown in FIG. 10. The system 1100 includes a light source 1110, a spatial light modulator (SLM) 1140, and a waveguide 1120, also referred to as an eyepiece waveguide, arranged such that light from the light source 1110 illuminates the SLM 1140 and light reflected from the SLM 1140 is coupled into the waveguide 1120 to be directed to the eye 210. The system 1100A includes an optical system 1130 arranged to both illuminate the SLM 1140 and project an image of the SLM 1140. Light from the light source 1110, for example, propagates in a first direction, through the optical system 1130, and onto the SLM 1140, thereby illuminating the SLM 1140. Light reflected from SLM 1140 propagates again through optics 1130 in a second direction opposite the first direction and is directed to and coupled into waveguide 1120.

[0133] The light source 1110 may include a light emitting diode (LED), a laser (e.g., a laser diode), or other types of light sources. The light source 1110 may be a polarized light source, however, the light source 1110 need not be so limited. In some implementations, a polarizer 1115 may be positioned between the light source 1110 and the SLM 1140. As shown, the polarizer 1115 is between the light source 1110 and the waveguide 1120. This polarizer 1115 may also be a light recycler that transmits light of a first polarization and reflects light of a second polarization back to the light source 1110. Such a polarizer 1115 may be, for example, a wire grid polarizer. A coupling optic 1105, such as a non-imaging optical element (e.g., a cone, a compound parabolic concentrator (CPC, lens)), may be positioned relative to the light source 1110 to receive the light output from the light source 1110. The coupling optics 1105 may focus the light from the light source 1110 and, in some cases, reduce the divergence of the light emitted from the light source 1110. The coupling optics 1105 may, for example, collimate the light output from the light source 1110. The coupling optics 1105 may focus light that matches the angular spectrum field of view of the system 1100A. Thus, the coupling optics 1105 may match the angular spectrum of the light output by the light source 1110 with the field of view of the system 1100A. The coupling optics 1105 may have an asymmetric profile and act asymmetrically on the light emitted from the light source 1110. For example, the coupling optics 1105 may reduce the divergence in orthogonal directions (e.g., x and z directions) by different amounts. Such an asymmetry in the coupling optics 1105 may address an asymmetry in the light emitted from the light source 1110, which may include, for example, a laser diode that emits light over a wider range of angles in one direction (e.g., x or z) as opposed to the orthogonal direction (e.g., z or x, respectively).

[0134] As discussed above, the system 1100A includes an optical system 1130 disposed in an optical path between the light source 1110 and the SLM 1140 and configured to illuminate the SLM 1140. The optical system 1130 may include a transmissive optical system that transmits light from the light source 1110 to the SLM 1140. The optical system 1130 may also be configured to project an image of the SLM 1140 or may be formed by the SLM 1140 in the waveguide 1120. The image may be projected into the eye of the eye 210. In some designs, the optical system 1130 may include one or more lenses or optical elements having refractive power. The optical system 1130 may have, for example, a positive refractive power. The optical system 1130 may include one or more refractive optical elements, such as a refractive lens. Other types of optical elements may also potentially be used.

[0135] The SLM 1140 may be reflective and modulate and reflect light therefrom. The SLM 1140 may be a polarization-based SLM configured to modulate polarization. The SLM 1140 may include, for example, a liquid crystal (LC) SLM (e.g., a liquid crystal on silicon (LCOS) SLM). The LC SLM may include, for example, a twisted nematic (TN) liquid crystal. The SLM 1140 may be substantially similar to the SLM 1030 referred to in FIG. 10. The SLM 1140 may include one or more pixels configured to selectively modulate light incident on the pixel, for example, depending on the state of the pixel. For some types of SLM 1140, the pixel may modulate a beam incident thereon by altering the polarization state, for example, by rotating the polarization (e.g., rotating the orientation of linearly polarized light).

[0136] As discussed above, the SLM 1140 may be an LCoS SLM 1140. In a cross-polarizer configuration, the LCoS SLM 1140 may be nominally white. When a pixel is off (e.g., 0 voltage), it has a bright state, and when the pixel is on (e.g., a voltage above a threshold on voltage), it has a dark state. In this cross-polarizer configuration, leakage is minimized when the pixel is on and has a dark state.

[0137] In a parallel polarizer configuration, the LCoS SLM 1140 is nominally black. When the pixel is off (e.g., 0 voltage), it has a dark state, and when the pixel is on (e.g., voltage above the threshold on voltage), it has a light state. In this parallel polarizer configuration, leakage is minimized when the pixel is off and has a dark state. The dark state may be (re)optimized using the rub direction and the compensator angle. The compensator angle may refer to the angle of the compensator, which may be, for example, between the optical system 1130 and the SLM 1140, as illustrated in FIG. 20B.

[0138] The dynamic range and throughput for the parallel polarizer configuration may be different from that of the crossed polarizer configuration. Additionally, the parallel polarizer configuration may be optimized for contrast differently than the crossed polarizer configuration.

[0139] The system 1100A includes a waveguide 1120 for outputting image information to the eye 210. The waveguide 1120 may be substantially similar to the waveguides 270, 280, 290, 300, 310, 670, 680, and 690 discussed above. The waveguide 1120 may include a substantially transparent material having a sufficient index of refraction to guide light therein. As shown, the waveguide 1120 may include a first side 1121, a second side 1123 opposite the first side 1121, corresponding upper and lower major surfaces, and a peripheral edge thereof. The first and second major surfaces 1121, 1123 may be sufficiently flat such that image information may be retained in response to propagating light from the SLM 1140 to the eye 210 such that an image formed by the SLM 1140 may be projected into the eye. The optics 1130 and the SLM 1140 may be positioned on a first side 1121 of the waveguide 1120. The light source 1110 may be disposed on the second side 1123 such that light from the light source 1110 is incident on the second side 1123 prior to passing through the waveguide 1120 and through the optics 1130 to the SLM 1140. Thus, the waveguide 1120 may be disposed between the light source 1110 and the optics 1130. In addition, at least a portion of the waveguide 1120 may extend between the light source 1110 and the optics 1130, thereby passing light through a portion of the waveguide 1120 to the optics 1130. Light emitted from the light source 1110 may thus be directed through the waveguide 1120 into and through the optics 1130 and incident on the SLM 1140. SLM 1140 reflects the light back through optics 1130 into waveguide 1120 .

[0140] The system 1100A also includes an internal coupling optical element 1160 for coupling light from the optical system 1130 into the waveguide 1120. The internal coupling optical element 1160 may be disposed on a major surface (e.g., the upper major surface 1123) of the waveguide 1120. In some designs, the internal coupling optical element 1160 may be disposed on the lower major surface 1121 of the waveguide 1120. In some designs, the internal coupling optical element 1160 may be disposed within the body of the waveguide 1120. Although illustrated on one side or corner of the waveguide 1120, the internal coupling optical element 1160 may be disposed in / on other areas of the waveguide 1120. The internal coupling optical element 1160 may be substantially similar to the internal coupling optical elements 700, 710, 720 described above with reference to FIGS. 9A, 9B, and 9C. The internal coupling optical element 1160 may be a diffractive optical element or a reflector. Other structures may also be used as the in-coupling optical element 1160. The in-coupling optical element 1160 may be configured to direct light incident thereon at a sufficiently large glancing angle (e.g., greater than a critical angle) relative to the upper and lower major surfaces 1123, 1121 of the waveguide 1120 into the waveguide 1120 to be guided therein by total internal reflection. Additionally, the in-coupling optical element 1160 may be configured to operate on a wide range of wavelengths and thus couple multiple colors of light into the waveguide 1120. For example, the in-coupling optical element 1160 may be configured to couple red, green, and blue light into the waveguide 1120. The light source 1110 may emit red, green, and blue light at different times.

[0141] The system 1100A includes an optically dispersive element 1170 disposed on or within the waveguide 1120. The optically dispersive element 1170 may be substantially similar to the optically dispersive elements 730, 740, and 750 described above with respect to FIG. 9B. For example, the optically dispersive element 1170 may be an orthogonal pupil expander (OPE). The optically dispersive element 1170 may be configured to spread light within the waveguide 1120 by redirecting light propagating in the x-direction, e.g., toward the z-direction illustrated in the top view of FIG. 11B. The optically dispersive element 1170 may thus be configured to increase the size of the eyebox along the z-axis (see FIG. 11B). The optically dispersive element 1170 may include one or more diffractive optical elements configured to diffract light propagating within the waveguide 1120 that is incident on the diffractive optical element, e.g., to redirect the light, e.g., in a substantially orthogonal direction. Other configurations are possible.

[0142] As shown in FIG. 11B, the system 1100 may also include an out-coupling optical element 1180 for coupling light out of the waveguide 1120 to the eye 210. The out-coupling optical element 1180 may be configured to redirect light propagating in the waveguide 1120 by total internal reflection (TIR) ​​at an angle more normal to the upper and / or lower major surfaces 1123, 1121 of the waveguide 1120 so that the light is not guided in the waveguide 1120. Instead, the light is directed out of the waveguide 1120, for example, through the lower major surface 1121. The out-coupling optical element 1180 may include one or more diffractive optical elements configured, for example, to diffract light propagating in the waveguide 1120 that is incident on the diffractive optical element so as to redirect the light, for example, out of the waveguide 1120. Other configurations are possible.

[0143] 11B also shows the location of the in-coupling optical element 1160, which is disposed laterally relative to the light dispersing optical element (e.g., orthogonal pupil expander) 1170 and the out-coupling optical element 1180. FIG. 11B also shows the location of the light source 1110, which is disposed laterally relative to the in-coupling optical element 1160, the light dispersing optical element (e.g., orthogonal pupil expander) 1170, and the out-coupling optical element 1180.

[0144] In operation, the light source 1110 of the system 1100A emits light into the coupling optics 1105 and through the polarizer 1115. The light may thus be polarized, e.g., linearly polarized in a first direction. The polarized light may be transmitted through the waveguide 1120, enter the second major surface of the waveguide 1120, and exit the first major surface of the waveguide 1120. The light may propagate through the optics 1130 to the SLM 1140. The optics 1130 quasi-collimates and / or selects the light from the light source 1110 to illuminate the SLM 1140, which may include a polarization-based modulator that modulates the polarization of the light incident thereon, such as by selectively rotating the orientation of the modulator, pixel by pixel, depending on the state of the pixel. For example, a first pixel may be in a first state and rotate the polarization, while a second pixel may be in a second state and not rotate the polarization. The light between the coupling optics 1105 and the optics 1130 may illuminate the SLM 1140 very uniformly. After incident on the SLM 1140, the light is reflected back through the optics 1130. The optics 1130 may be configured to project an image from the SLM 1140 into the waveguide 1120 and ultimately into the eye 210 such that the image is visible to the eye 210. In some designs, the retina of the eye 210 is optically conjugate to the SLM 1140 and / or the image formed by and / or on the SLM 1140. The optical power of the optical system 1130 may facilitate the projection of the image on the SLM 1140 into and onto the retina of the eye 210. In some implementations, optical power, provided by, for example, the external coupling optical element 1180, may assist and / or affect the image ultimately formed within the eye 210. The optics 1130 acts as a projection lens as light reflected from the SLM 1140 travels through the optics and towards the waveguide 1120. The optics may generally function as a Fourier transform of the image on the SLM 1140 to a plane within the waveguide 1120 near the internal coupling optical element 1160. Together, both passes through the optics 1130 (the first pass from the light source 1110 to the SLM 1140, and the second pass from the SLM 1140 to the waveguide 1120) may generally act to image the pupil of the coupling optics 1105.The alignment and orientation of the light source 1110 (and possibly also the coupling optic 1105 and / or polarizer 1115), the optic 1130, and the SLM 1140 are such that light from the light source 1110 reflected from the SLM 1140 is directed onto the incoupling optic 1160. A pupil associated with the coupling optic 1105 may be aligned with the incoupling optic 1160. The light may pass through an analyzer 1150 (e.g., a polarizer) in the optical path between the SLM 1140 and the eye 210. As depicted in FIG. 11A, an analyzer (e.g., a polarizer) 1150 may be disposed in the optical path between the optic 1130 and the incoupling optic 1160. The analyzer 1150 may be, for example, a linear polarizer with an orientation that transmits light of a first polarization (p-polarized) and blocks light of a second polarization (s-polarized), or vice versa. The analyzer 1150 may be a clean-up polarizer that further blocks polarized light that is blocked by another polarizer between the SLM 1140 and the analyzer 1150 or within the SLM 1140. The analyzer 1150 may be, for example, a circular polarizer that acts as an isolator and reduces reflections back toward the SLM 1140 from the waveguide 1120, particularly from the incoupling optical element 1160. The analyzer 1150 may include a wire grid polarizer, such as an absorptive wire grid polarizer, such as any of the polarizers disclosed herein. Such a polarizer may provide substantial absorption of undesired light and therefore increased contrast. Some such polarizers can be fabricated to include one or more dielectric layers on top of the wires and / or multilayer films. In some implementations, the SLM 1140 may be a liquid crystal on silicon (LCOS) SLM and may include an LC cell and a retarder (e.g., a compensator). In some implementations, the analyzer 1150 may be a compensator intended to provide a more consistent polarization rotation (e.g., of 90°) of the SLM 1140 for different angles of incidence and different wavelengths. The compensator may be used to improve the contrast of the display by improving the rotated polarization for light rays incident across a variety of angles and wavelengths.The SLM 1140 may include, for example, a TN LCoS configured to rotate incident light of a first polarization (e.g., s-polarized) to a second polarization (e.g., p-polarized) for a first pixel as the light would pass through the analyzer 1150, producing a bright pixel state. Conversely, the SLM 1140 may be configured not to rotate incident light of a first polarization (e.g., s-polarized) to a second polarization (e.g., p-polarized) for a second pixel such that the reflected light remains at the first polarization, producing a dark pixel state, as the light is attenuated or blocked by the analyzer 1150. In such a configuration, the polarizer 1115 closer to the light source 1110 along the optical path may be oriented differently (e.g., orthogonal) with respect to the analyzer 1150 further from the light source 1110 along the optical path. Other, e.g., opposite, configurations are also possible.

[0145] The light is then deflected, e.g., redirected, by the in-coupling optical element 1160 to be guided within the waveguide 1120, where it propagates by TIR. The light then impinges on the light dispersive element 1170, redirecting the light in another direction (e.g., more towards the z-direction), causing an increase in the size of the eyebox along the direction of the z-axis, as shown in FIG. 11B. The light is thus deflected towards the out-coupling optical element 1180, which directs the light out of the waveguide 1120 towards the eye 210 (e.g., the eye of the user, as shown). The light being out-coupled along the z-direction by different portions of the out-coupling optical element 1180 causes an increase in the size of the eyebox, at least along a direction parallel to the z-axis, as defined in FIG. 11B. It is to be noted that in this configuration, the optical system 1130 is used both to illuminate the SLM 1140 and to project an image onto the in-coupling optical element 1160. Thus, the optical system 1130 may act as projection optics, dispersing (e.g., uniformly) the light from the light source 1110, and imaging optics, providing an image of the SLM 1140 and / or an image formed by the SLM 1140 into the eye. The system 1100A in FIG. 11A / B may be more compact than the system 1000 in FIG. 10 in some instances. In some cases, not employing the PBS 1020 shown in FIG. 10 may potentially reduce the cost and / or size of the system. Additionally, by not using the PBS 1020, the system may be more symmetrical and easier to design by reducing the back focal length of the optical system 1130.

[0146] As referenced above, alternative configurations are also possible. With reference to FIG. 11C, for example, in some designs, the system 1100C may be configured to pass light having a polarization that is not rotated by the SLM 1140. In one implementation, for example, the SLM 1140 may be a liquid crystal (LC)-based SLM, including a vertically aligned (VA) LC-on-silicon (LCoS). The SLM 1140 may have a first pixel in a first state that does not rotate the polarization and a second pixel in a second state that rotates the polarization. In the configuration illustrated in FIG. 11C, a single shared analyzer / polarizer 1155 is utilized. This analyzer 1155 may transmit light of a first polarization (e.g., s-polarized light) and attenuate or reduce the transmission of a second polarization (e.g., p-polarized light). Thus, light incident on a first pixel in a first state that does not rotate the polarization orientation (e.g., s-polarized light) is reflected from the SLM 1140 and passes through the analyzer 1155 to the waveguide 1120. Conversely, light incident on a second pixel in a second state that rotates the polarization orientation (e.g., s-polarized light) is reflected from the SLM 1140 and is attenuated, reduced, or not passed through the analyzer 1155 to the waveguide 1120. This configuration may thereby allow the polarizer 1115 and analyzer 1150 shown in FIG. 11A to be incorporated into a shared optical element, i.e., the analyzer 1155 shown in FIG. 11C, thereby potentially simplifying the system 1100 of FIG. 11A / B by reducing the number of optical components. The analyzer 1155 may be disposed between the waveguide 1120 and the optical system 1130. In other implementations, separate analyzer / polarizer and analyzer / polarizer may be used as shown in system 1100 of Figures 11A / B. Figures 11A and 11B illustrate a polarizer 1115 between the light source 1110 and the waveguide 1120, and an analyzer 1140 between the optical system 1130 and the waveguide 1120.

[0147] Various other configurations may be employed to utilize optical system 1130 for both illumination of SLM 1140 and imaging of images formed by SLM 1140. For example, although FIGS. 11A-11C show a single waveguide 1120, one or more waveguides may be used, such as a stack of waveguides (possibly different waveguides for different colors of light). FIG. 12A illustrates a cross-sectional side view of an example system 1200A including a stack 1205 including waveguides 1120, 1122, 1124, each including an internal coupling optical element 1260, 1262, 1264. Waveguides 1120, 1122, 1124 may each be configured to output light at one or more different wavelengths or ranges of one or more different wavelengths. The stack 1205 may be substantially similar to stacks 260 and 660 (FIGS. 6 and 9A), and the illustrated waveguides 1120, 1122, 1124 of the stack 1205 may correspond to portions of the waveguides 670, 680, 690, however, the stack 1205 and the waveguides 1120, 1122, 1124 need not be so limited. As illustrated in FIG. 12A, the incoupling optical elements 1260, 1262, 1264 may be associated with and included within or on the waveguides 1120, 1122, 1124, respectively, for example. The incoupling optical elements 1260, 1262, 1264 may be color selective and may divert or redirect certain wavelengths into the corresponding waveguides 1120, 1122, 1124 primarily as guided therein. As shown, the incoupling optical elements 1260, 1262, 1264 are color selective, so that the incoupling optical elements 1260, 1262, 1264 do not need to be laterally displaced and may be stacked over one another. Wavelength multiplexing may be employed to couple specific colors into corresponding waveguides. For example, a red incoupling optical element may incoupling red light into a waveguide designated for propagating red light, while not incoupling blue or green light, which is instead coupled into other waveguides by other blue and green selective waveguides, respectively.

[0148] In some implementations, the light source 1110 may be a multi-color light source capable of emitting different colored light at different times. For example, the light source 1110 may emit red, green, and blue (RGB) light and may be configured to emit red and negligible amounts of green and blue during a first period, green and negligible amounts of red and blue during a second period, and blue and negligible amounts of red and green during a third period. These cycles may be repeated and the SLM 1140 may be coordinated to produce a suitable pattern of pixel states for a particular color (red, green, or blue) to provide the appropriate image color components for a given image frame. The different waveguides 1120, 1122, 1124 of the stack 1205 may each be configured to output light with a different individual color. For example, as depicted in FIG. 12A, the waveguides 1120, 1122, 1124 may each be configured to output blue, green, and red light. Of course, other colors are possible, for example, the light source 1110 may emit other colors, and the color-selective incoupling optical elements 1260, 1262, 1264, outcoupling optical elements, etc., may be configured for such other colors. In addition, individual red, green, and blue emitters may be located close enough together to effectively function as a single-pupil light source. The red, green, and blue emitters may be combined with lenses and dichroic splitters to form a single red, green, and blue pupil source. Single-pupil multiplexing may be extended beyond or in addition to color selectivity and may include the use of polarization-dependent gratings and polarization switching. These color or polarization gratings may also be used in combination with multiple display pupils to increase the number of layers that can be addressed.

[0149] Different in-coupling optical elements 1260, 1262, 1264 in different waveguides 1120, 1122, 1124 may be disposed over and / or under one another and laterally aligned (e.g., in the x and z directions shown in FIG. 12A ), as opposed to being laterally displaced and unaligned with respect to one another. Thus, in some implementations, for example, different in-coupling optical elements 1260, 1262, 1264 may be configured such that light of a first color may be coupled into the waveguide 1120 by the in-coupling optical element 1260 to be guided therein, and light of a second color, different from the first color, may pass through the in-coupling optical element 1260 to the next in-coupling optical element 1262 and may be coupled into the waveguide 1122 by the in-coupling optical element 1262 to be guided therein. Light of a third color, different from the first and second colors, may pass through the in-coupling optical elements 1260 and 1262 to the in-coupling optical element 1264 and may be coupled into the waveguide 1124 to be guided therein. In addition, the in-coupling optical elements 1260, 1262, 1264 may be polarization selective. For example, the different in-coupling optical elements 1260, 1262, 1264 may be configured such that light of a certain polarization is either coupled into the waveguide by the corresponding polarization selective in-coupling optical element 1260, 1262, 1264 or passes through the in-coupling optical element 1260, 1262, 1264.

[0150] Depending on the configuration, the SLM 1140 may include a polarization-based SLM that modulates the polarization. The system 1200A may include a polarizer and / or analyzer to modulate the light injected into the stack 1205 on a pixel-by-pixel basis depending on the state of the individual pixel (e.g., whether the pixel rotates the polarization orientation). Various aspects of such systems employing a polarization-based SLM are discussed above, and any one of such features may be employed in combination with any other features described herein. However, other designs are still possible.

[0151] For example, a deflection-based SLM 1140 may be employed. For example, the SLM 1140 may include one or more movable optical elements, such as a movable mirror, that may reflect and / or deflect light along different directions depending on the state of the optical element. The SLM 1140 may include one or more pixels that include such optical elements, such as, for example, micromirrors or reflectors. The SLM 1140 may include, for example, a digital light processing (DLP) TM) technology, which uses a digital micromirror device (DMD). An example of a system 1200B using such a deflection-based SLM 1140 is shown in FIG. 12B. The system 1200B includes a deflection-based SLM 1140 and a light dump 1250. The light dump 1250 may include a light absorbing material or structure configured to absorb light. The deflection-based SLM 1140 may include one or more micro movable mirrors that can be selectively tilted to deflect light in different directions. For example, the deflection-based SLM 1140 may be configured to deflect light from the light source 1110 incident thereon to the incoupling optical elements 1260, 1262, 1264 when a given pixel is in a bright state. As discussed above, this light will thus be coupled into one of the individual waveguides 1120, 1122, 1124 by one of the incoupling optics 1260, 1262, 1264 depending on, for example, the color of the light, and directed to the eye 210. Conversely, when a given pixel is in a dark state, the light from the light source 1110 may be deflected to the light dump 1250, and the light is coupled into one of the individual waveguides 1120, 1122, 1124 by one of the incoupling optics 1260, 1262, 1264 and not directed to the eye 210. The light may instead be absorbed by the light absorbing material that makes up the light dump 1250. In some implementations, the analyzer 1150 may be a polarizer (e.g., a "clean-up" polarizer) used to eliminate undesired reflections from the incoupling optics 1260, 1262, 1264. This polarizer may be useful because the optics 1130 may include plastic optical elements that have birefringence and may modify polarization. A "clean-up" polarizer may attenuate or remove light with undesired polarization (e.g., reflections) from being directed onto the waveguides 1120, 1122, 1124. Other types of light conditioning elements may also be disposed between the SLM 1140 and the waveguides 1120, 1122, 1124, such as between the optics 1130 and the waveguides 1120, 1122, 1124. For example, such light conditioning elements may also include circular polarizers (i.e., linear polarizers and retarders such as quarter-wave plates).The circular polarizer may again reduce the amount of reflection from the waveguides 1120, 1122, 1124 or the internal coupling optical elements 1260, 1262, 1264 that is incident on and coupled into the waveguides 1120, 1122, 1124. The reflected light may be circularly polarized and may possess the opposite circular polarization to that of the incident light (e.g., right-handed circularly polarized light is converted to left-handed circularly polarized light, or vice versa, upon reflection). A retarder in the circular polarizer may convert the circularly polarized light to linearly polarized light, such as the orthogonal polarization of the polarizer, that is attenuated, e.g., absorbed, by the linear polarizer in the circular polarizer. The clean-up polarizer may be used in conjunction with a polarization independent modulator, such as a DMD. As mentioned above, a clean-up polarizer can be useful to suppress reflections and / or improve the coupling of light into the internal coupling optical elements 1260, 1262, 1264 with an optimal polarization state.

[0152] 12B illustrates a side or cross-sectional view of such a system 1200B, while FIG. 12C shows a top view of the lateral arrangement of the incoupling optical element 1264, the light dump 1250, and the light source 1110. The SLM 1140 would be configured to reflect, deflect, and / or direct light from the light source 1110 either to the incoupling optical element 1264 (as well as other incoupling optical elements 1260, 1262) or to a location lateral to the light dump 1250, depending on the state of a particular pixel.

[0153] In one design, the light dump 1250 may include an energy recovery system. The light dump 1250 may include an optical energy conversion element configured to convert, for example, optical energy into electrical energy. The optical energy conversion element may include, for example, a solar cell. The optical energy conversion element may include, for example, a photovoltaic detector that produces an electrical output when light is incident thereon. The optical energy conversion element may be electrically connected to an electrical component, for example, conductive wires for directing the electrical output to provide power to the system 1200B and / or potentially charge one or more batteries.

[0154] Laterally displaced non-color selective or broadband or multi-color in-coupling optical elements may be used in some designs. Figure 13A is a perspective view of a system 1300 including a stack 1305, for example including waveguides. The stack 1305 may be substantially similar to the stack 1205, referenced in Figure 12A. Each waveguide in the stack 1305 may include an in-coupling optical element 1360, 1362, 1364, however, in contrast to the design shown in Figure 12A, the in-coupling optical elements 1360, 1362, 1364 are laterally displaced relative to one another. 13A, 13B, and 13C, the light sources 1110, 1112, 1114 may also be laterally displaced relative to one another and positioned to direct light to respective incoupling optical elements 1360, 1362, 1364 by passing the light through optics 1130, reflecting the light off the SLM 1140, and passing the reflected light back through optics 1130. The system 1300 in FIG. 13B is depicted as though the light source 1114 is located behind the light source 1110 and is therefore not shown in FIG. 13B. The light sources 1110, 1112, 1114 may correspond to the incoupling optical elements 1360, 1362, 1634, respectively. In one design, for example, the light sources 1110, 1112, 1114 and the corresponding in-coupling optical elements 1360, 1362, 1364 are positioned approximately equidistant from (symmetrically about) the center of the optical system 1130 along a common (optical) axis. The common (optical) axis may intersect the center of the optical system 1130. In one design, for example, the light sources 1110, 1112, 1114 and the corresponding in-coupling optical elements 1360, 1362, 1364 are not positioned equidistant from (symmetrically about) the center of the optical system 1130 along the common (optical) axis.

[0155] The incoupling optical elements 1360, 1362, 1364 may be configured to couple multiple colors of light into their respective waveguides. Thus, these incoupling optical elements 1360, 1362, 1364 may be referred to herein as broadband, multicolor, or non-color-selective incoupling optical elements 1360, 1362, 1364. For example, in one case, each one of these incoupling optical elements 1360, 1362, 1364 is configured to incoupling red, green, and blue light into the associated waveguide in which the incoupling optical element 1360, 1362, 1364 is included, and such colored light is guided within the waveguide by TIR. Such broadband incoupling optical elements 1360, 1362, 1364 may operate across, e.g., a wide range of wavelengths, e.g., within the visible range, or may select a wavelength or wavelength range width, e.g., across the visible range. Thus, such broadband or multi-color or non-color selective incoupling optical elements 1360, 1362, 1364 may be configured to redirect light of various different colors (e.g., red, green, and blue) into the waveguide to be guided therein by TIR. Although red, green, blue (RGB) are referred to herein as such in connection with light sources, incoupling optical elements, waveguides, etc., other colors or color systems may be used in addition or as an alternative, such as, but not limited to, magenta, cyan, yellow (CMY), etc.

[0156] As illustrated in FIG. 13A, the light sources 1110, 1112, 1114 are shown above the top waveguide and are displaced relative to each other (e.g., in the x and z directions). Similarly, three internal coupling optical elements 1360, 1362, 1364 are shown on three separate waveguides and are displaced relative to each other (e.g., in the x, y, and z directions). FIG. 13B is a side view of the system 1300 illustrated in FIG. 13A showing the internal coupling optical elements 1360, 1362, 1364 spatially displaced laterally relative to each other (e.g., in the x and z directions) and some of the light sources 1110, 1112, 1114 laterally displaced relative to each other (e.g., in the x and z directions). FIG. 13B also shows the optical system 1130 and the SLM 1140.

[0157] 13C is a top view of the augmented reality display system illustrated in FIGS. 13A and 13B showing the incoupling optical elements 1360, 1362, 1364 and associated light sources 1110, 1112, 1114. In this design, the incoupling optical elements 1360, 1362, 1364 and associated light sources 1110, 1112, 1114 are arranged in a ring-like pattern about a center point of a common (optical) axis. As shown, the light sources 1110, 1112, 1114 and corresponding incoupling optical elements 1360, 1362, 1364 are approximately equidistantly arranged about the center point of the common (optical) axis, however, this need not be the case. In some designs, this center point may correspond to the center of the optical system 1130 along the common (optical) axis and / or a location along the optical axis of the optical system 1130 that intersects with the center of the optical system 1130. Also as a result, the non-color-selective incoupling optical elements 1360, 1362, 1364 and the light sources 1110, 1112, 1114 are laterally displaced relative to one another (eg, in the x and z directions).

[0158] Other arrangements of lateral mounting are also possible. Figures 14A-14C illustrate an alternative configuration of system 1400 including a waveguide-containing stack 1405 in which the in-coupling optical elements 1360, 1362, 1364 and light sources 1110, 1112, 1114 are laterally displaced relative to one another. Figure 14A is a side view, while Figure 14B is a top view, of the system 1400 illustrated in Figure 14A showing the in-coupling optical elements 1360, 1362, 1364 and light sources 1110, 1112, 1114 laterally displaced. Figure 14C is an orthogonal side view of system 1400 illustrated in Figures 14A and 14B.

[0159] The side views of Figures 14A and 14C show how the incoupling optical elements 1360, 1362, 1364 are disposed on separate waveguides in the stack 1405 such that light can be coupled into the corresponding waveguides by the respective laterally displaced incoupling optical elements 1360, 1362, 1364. The incoupling optical elements 1360, 1362, 1364 are shown in Figures 14A and 14C as being disposed within the upper major surfaces of the waveguides. However, the incoupling optical elements 1360, 1362, 1364 could alternatively be disposed on the lower major surfaces of the respective waveguides or within the volume of the waveguides. Various configurations are also possible.

[0160] 14B, the incoupling optical elements 1360, 1362, 1364 are arranged in a row that is laterally displaced with respect to one another along the z-direction, rather than along the x-direction. Similarly, the light sources 1110, 1112, 1114 are also arranged in a row that is laterally displaced with respect to one another along the z-direction, rather than along the x-direction. The incoupling optical elements 1360, 1362, 1364 are laterally displaced in the x-direction with respect to the light sources 1110, 1112, 1114.

[0161] Still other configurations are possible. Figure 15 is a top view of a system 1500 showing an alternative configuration of the light sources 1110, 1112, 1114 and the incoupling optical elements 1360, 1362, 1364. As opposed to having all the light sources 1110, 1112, 1114 generally on one side (e.g., of a ring-like pattern) and all the incoupling optical elements 1360, 1362, 1364 generally on one side (i.e., the opposite side), as in Figure 13C, the light sources 1110, 1112, 1114 and the incoupling optical elements 1360, 1362, 1364 are interspersed or alternating around the circumference of the ring-like pattern.

[0162] However, in some implementations, the incoupling optical elements 1360, 1362, 1364 and associated one or more light sources 1110, 1112, 1114 are also arranged in a ring-like pattern around a central point. As a result, the light sources 1110, 1112, 1114 and corresponding incoupling optical elements 1360, 1362, 1364 may generally be arranged approximately equidistant from the center. In some designs, this center may correspond to the center of the optical system 1130 and / or a location along the optical axis of the optical system along a common central axis that intersects the center of the optical system 1130. Thus, light from the first light source 1110 may be coupled through the optical system 1130 into the incoupling optical element 1360 transverse to the center or central axis or optical axis of the optical system 1130 (as seen from the top view of FIG. 15 ). Similarly, light from the second light source 1112 may be coupled through the optical system 1130 into the incoupling optical element 1362 across the center or central axis or optical axis of the optical system 1130. Similarly, light from the third light source 1114 may be coupled through the optical system 1130 into the incoupling optical element 1364 across the center or central axis or optical axis of the optical system 1130. Also, as a result, the non-color-selective incoupling optical elements 1360, 1362, 1364 and the light sources 1110, 1112, 1114 are laterally displaced relative to one another (e.g., in the x and z directions). The optical system 1130 may be designed such that the focal point is closer into the stack 1405 such that the sub-pupil locations and the incoupling optical elements 1360, 1362, 1364 are closer in the y-direction. In this configuration, the internal coupling optical elements 1360, 1362, 1364 may be smaller because they are closer to the focal point of the optical system 1130. The light source 1110 may be on the user side of the stack 1405 (e.g., similar to FIGS. 17 and 18), thus reducing the distance or optical path between the light source 1110 and the optical system 1130.

[0163] In various implementations such as shown in FIGS. 12A-15 above, stacks (e.g., stacks 1205, 1305, 1405) including multiple waveguides (e.g., stack 1205 including waveguides 1120, 1122, 1124, stack 1305 including waveguides (not labeled), and stack 1405 including waveguides (not labeled)) may be included to handle different colors (e.g., red, green, and blue). Different waveguides may be for different colors. Similarly, multiple stacks can be included to provide different optical properties to light coupled out from individual stacks. For example, waveguides 1120, 1122, 1124 of stack 1205 of FIGS. 12A-12B may be configured to output light having optical properties (e.g., refractive power to provide a particular wavefront shape) possibly associated with the apparent depth from which the light appears to emanate. For example, wavefronts with different amounts of divergence, convergence, or collimation may appear as if projected from different distances from the eye 210. Thus, multiple stacks may be included, with the different stacks configured such that the light outcoupled by the outcoupling optical element has different amounts of convergence, divergence, or collimation, and thus appears to originate from different depths. In some designs, the different stacks may include different lenses, such as diffractive lenses or other diffractive optical elements, to provide different amounts of refractive power to the different stacks. As a result, the different stacks will produce different amounts of convergence, divergence, or collimation, and thus the light from the different stacks will appear as if associated with different depth planes or objects at different distances from the eye 210.

[0164] FIG. 16A is a side view of a system 1600 including stacks 1605, 1610, 1620. As illustrated in FIG. 16A, the system 1600 includes three stacks 1605, 1610, 1620, however, this need not be the case. The system may be conceived with fewer or more stacks. Each of the stacks 1605, 1610, and 1620 includes one or more (e.g., three) waveguides. FIG. 16A also shows groups 1630, 1640, 1650 of internally coupled optical elements. A first group 1630 is associated with the first stack 1605, a second group 1640 is associated with the second stack 1610, and a third group 1650 is associated with the third stack 1620. The groups 1630, 1640, 1650 are laterally displaced with respect to each other. Each of the groups 1630, 1640, 1650 includes color-selective in-coupling optical elements configured to in-couple different individual colors, substantially similar to the in-coupling optical elements 1260, 1262, 1264 of FIG. 12A. As illustrated in FIG. 16A, the in-coupling optical elements within each of the groups 1630, 1640, 1650 are not laterally displaced relative to one another, however, this need not be the case. The system may be devised in which the in-coupling optical elements within a group are laterally displaced relative to one another. The system 1600 may be configured such that the light out-coupled from each of the stacks 1605, 1610, 1620 has a different amount of refractive power. For example, the waveguides within the stacks may have an out-coupling optical element or a diffractive lens with a given refractive power. The refractive powers for the different stacks 1605, 1610, 1615 may be different such that light from one stack may appear to occur at a different depth than light from another stack. The refractive power of one stack, for example, may cause the light from that stack to be collimated, while the refractive power of another stack may cause the light therefrom to be divergent: divergent light appears as it might originate from an object at a close distance from the eye 210, while collimated light appears as it might originate from an object at a far distance.Thus, the light coupled out of the first stack 1605, the second stack 1610, and the third stack 1620 may have different amounts of convergence, divergence, and / or collimation and therefore appear to originate from different depths. In some implementations, the light coupled out of one of the stacks may be collimated, while the light coupled out by a different stack may diverge. The light coupled out of one of the other stacks may also diverge, but by a different amount.

[0165] As illustrated in FIG. 16A , the light source 1110 may be positioned relative to the optical system 1130 and the SLM 1140 to direct light into the group 1630 of incoupling optical elements, the light source 1112 may be positioned relative to the optical system 1130 and the SLM 1140 to direct light into the group 1640 of incoupling optical elements, and the light source 1114 may be positioned relative to the optical system 1130 and the SLM 1140 to direct light into the group 1650 of incoupling optical elements. The light sources 1110, 1112, 1114 may be configured to emit different colors of light at different times. Similarly, light of different individual colors may be coupled into different waveguides in the stack as a result of the color-selective incoupling optical elements in the manner described above. For example, if blue light is emitted from the second light source 1112, the optical system 1130 and the SLM 1140 will direct the blue light into the second group 1640 of incoupling optical elements. The light may pass through a first red in-coupling optical element and a second green in-coupling optical element in the second group 1640 and be redirected by a third blue in-coupling optical element in the second group 1640 into a third waveguide in the second stack 1610. The waveguide in the second stack 1610 may include an out-coupling optical element or other optical element having a refractive power (e.g., a diffractive lens) to provide a beam to the eye 210 associated with a particular depth plane or object distance associated with the second stack 1610.

[0166] Figure 16B is a top view of the system 1600 in Figure 16A. Different groups 1630, 1640, 1650 of incoupling optical elements are shown to be laterally displaced relative to one another (e.g., in the x-direction). Similarly, light sources 1110, 1112, 1114 are shown to be laterally displaced relative to one another (e.g., in the x-direction).

[0167] Various different variations on the above-described system are also possible. For example, the location of the light source 1110 relative to the waveguide and optics 1130 may be different. FIG. 17, for example, is a side view of a system 1700 having the light source 1110 at a different location relative to the waveguide 1720 and optics 1130 than shown in FIGS. 11-16B. In addition, FIG. 17 shows a design with a waveguide 1720 split into a first portion 1720a and a second portion 1720b. The waveguide 1720 may further include a reflector 1730 configured to couple light guided in the first portion 1720a proximal to the light source 1110 out of the first portion 1720a and into the optics 1130 toward the SLM 1140. Additionally or alternatively, the system 1700 may include a diffractive outcoupling optical element for outcoupling light in the first portion 1720a of the waveguide 1720 into the optical system 1130 towards the SLM 1140. The reflector 1730 may be opaque and include an isolator to reduce crosstalk between the first portion 1720a and the second portion 1720b. The waveguide 1720 has a first side 1721 and a second side 1723 opposite the first side 1721, and the optical system 1130 and the SLM 1140 are disposed on the first side 1721 such that light from the SLM 1140 is directed onto the first side 1721. In this embodiment, the light source 1110 is disposed on a first side 1721 of the waveguide 1720 such that light from the light source 1110 is incident on the first side 1721 prior to passing through the optical system 1130 to the SLM 1140. The system 1700 may further include an internal coupling optical element 1710 disposed on or within the first portion 1720a. The internal coupling optical element 1710 may be configured to receive light from the light source 1110 and couple the light into the first portion 1720a. The internal coupling optical element 1710 may include a diffractive optical element or a reflector configured to redirect light incident thereon into the first portion 1720a at an angle such that it is guided therein by TIR.

[0168] The reflector 1730 may be configured to direct light guided within the first portion 1720a out of the first portion 1720a toward the optics 1130 and the SLM 1140. (As discussed above, in some implementations, a diffractive optical element may additionally or alternatively be used to direct light within the first portion 1720a out of the first portion 1720a toward the optics 1130 and the SLM 1140.) Thus, the reflector 1730 may be a mirror, a reflective grating, one or more coatings that reflect the light of the waveguide 1720 toward the SLM 1140. The reflector 1730 causes the light emitted from the first portion 1720a to pass through the optics 1130, impinge on the SLM 1140, and again pass through the optics 1130 and impinge on the second portion 1720b. As described above, light reflected from SLM 1140 that is transmitted through optical system 1130 may be incident on in-coupling optical element 1160 and redirect light guided within second portion 1720b. Light guided within second portion 1720b may be out-coupled therefrom by out-coupling optical element 1180 (not shown) and directed to eye 210.

[0169] As discussed above, the reflector 1730 may be an isolator that reduces crosstalk between the first portion 1720a and the second portion 1720b. The reflector 1730 may include an opaque and / or reflective surface. The reflector 1730 may be disposed within the waveguide 1720 and, in some cases, may define the sides of the first portion 1720a and the second portion 1720b.

[0170] Instead of having first and second portions 1720a, 1720b of the waveguide 1720, separate waveguides may be used. FIG. 18 is a side view of a system 1800 including a first waveguide 1822 that receives light from the light source 1110 and directs the light guided therein to the optical system 1130 and toward the SLM 1140. The system 1800 additionally includes a second waveguide 1820 that receives light from the SLM 1140 after the light has passed again through the optical system 1130. The first waveguide 1822 includes in-coupling and out-coupling optical elements 1730a, 1730b, respectively. These in-coupling and out-coupling optical elements 1730a, 1730b may include reflective surfaces that are oriented to in-coupling and out-coupling light into and out of the waveguide 1822. The in-coupling optical element 1730a may include, for example, a reflective surface positioned to receive light from the light source 1110 and oriented (e.g., tilted) to direct light into the waveguide 1822 at an angle such that it is guided therein by TIR. The out-coupling optical element 1730b may include, for example, a reflective surface oriented (e.g., tilted) to direct light guided in the waveguide 1822 at an angle such that it is exited from the waveguide 1822. The out-coupling optical element 1730b may be positioned such that light redirected out of the waveguide 1822 is directed into the optics 1130, reflected off the SLM 1140, passes again through the optics 1130, and is incident on the in-coupling optical element 1730c of the second waveguide 1820.

[0171] The internal coupling optical element 1730c in the second waveguide 1820 may include a reflective surface that may be positioned and oriented (e.g., tilted) to receive light incident thereon from the SLM 1140 and redirect it to be guided in the second waveguide 1820 by TIR. FIG. 18 illustrates the optical system 1130 and the light source 1110 disposed on the same side of the waveguides 1820, 1822. The system 1800 may further include an isolator that reduces crosstalk between the waveguide 1822 and the waveguide 1820. The isolator may include opaque and / or reflective surfaces. The isolator may be disposed in or on at least one of the waveguides 1820, 1822.

[0172] Various designs, such as those discussed above, can include additional features or components. FIG. 19, for example, shows a side view of a system 1900 including variable focus optical elements (or adaptive optical elements) 1910, 1920. The variable focus optical elements 1910, 1920 may include optical elements configured to be altered to provide variable refractive power. The variable focus optical elements 1910, 1920 may include multiple states, such as a first state and a second state, where in the first state the variable focus optical elements 1910, 1920 have a different refractive power than when in the second state. For example, the variable focus optical elements 1910, 1920 may have a negative refractive power in the first state and zero refractive power in the second state. In some implementations, the variable focus optical elements 1910, 1920 have a positive refractive power in the first state and zero refractive power in the second state. In some implementations, the variable-focus optical element 1910, 1920 has a first negative or positive optical power in a first state and a second different negative or positive optical power in a second state. Some adaptive optical or variable-focus optical elements 1910, 1920 may have more than two states, possibly providing a continuous distribution of optical powers.

[0173] The variable-focus optical elements 1910, 1920 may include lenses (e.g., variable lenses) and may be transmissive. Transmissive or transparent adaptive optical elements or variable-focus optical elements 1910, 1920 are shown in FIG. 7. The variable-focus optical elements 1910, 1920 may include liquid lenses (e.g., movable membranes and / or electrowetting). The variable-focus lenses may also include liquid crystal lenses, such as switchable liquid crystal lenses, such as switchable liquid crystal polarizing lenses, which may comprise, for example, diffractive lenses. Alverez lenses may also be used. Other types of variable-focus optical elements 1910, 1920 may also potentially be employed. Examples of variable-focus optical elements may be found in U.S. Patent Application No. 62 / 518,539, filed June 12, 2017, and entitled "AUGMENTED REALITY DISPLAY HAVING MULTI-ELEMENT ADAPTIVE LENS FOR CHANGING DEPTH PLANES," which is incorporated herein by reference in its entirety. The variable-focus optical elements 1910, 1920 may have an electrical input that receives an electrical signal that controls the amount of refractive power exhibited by the variable-focus optical elements 1910, 1920. The variable-focus optical elements 1910, 1920 may have positive and / or negative refractive power. In addition to variable-focus elements (e.g., polarization switches, geometric phase (GP) lenses, fluid lenses, and the like), the variable-focus elements 1910, 1920 may include fixed lenses (e.g., diffractive lenses, refractive lenses, and the like) to generate desired depth planes within the light field.

[0174] A first variable focus optical element 1910 may be disposed between the stack 1905 and the eye 210. The stack 1905 may include different waveguides for different colors, as discussed above. The first variable optical element 1910 may be configured to introduce different amounts of refractive power, negative and / or positive refractive power. The variable refractive power may be used to vary the divergence and / or collimation of the light coupled out of the stack 1905 and vary the depth at which a virtual object projected by the system 1900 into the eye 210 appears to be located. Thus, a four-dimensional (4D) light field may be created.

[0175] The second variable focus optical element 1920 is on the opposite side of the stack 1905 from the first variable focus optical element 1920. The second variable focus optical element 1920 can thus compensate for the effect of the first optical element 1910 on light received from the world 510 in front of the system 1900 and the eye 210. Thus, the world view may effectively be unaltered or altered, as desired.

[0176] The system 1900 may further include a static or variable prescription or corrective lens 1930. Such a lens 1930 may provide refractive correction for the eye 210. In addition, if the prescription lens 1930 is a variable lens, it may provide different refractive corrections for multiple users. Variable focus lenses are discussed above. The eye 210 may have, for example, myopia, hyperopia, and / or astigmatism. The lens 1930 may have a prescription (e.g., refractive power) to reduce refractive errors of the eye 210. The lens 1930 may be spherical and / or cylindrical, and may be positive or negative. The lens 1930 may be positioned between the stack 1905 and the eye 210 such that light from both the world 510 and the stack 1905 receives the correction provided by the lens 1930. In some implementations, the lens 1930 may be positioned between the eye 210 and the first variable focus optical element 1910. Other locations for the lens 1930 are also possible. In some embodiments, the prescription lenses may be variable, allowing multiple user prescriptions to be implemented.

[0177] In some designs, the system 1900 may include an adjustable dimmer 1940. In some implementations, the adjustable dimmer 1940 may be disposed on the opposite side (e.g., the world side) of the stack of waveguides 1900 from the eye 210. Thus, the adjustable dimmer 1940 may be disposed between the stack of waveguides 1900 and the world 510. The adjustable dimmer 1940 may include an optical element that provides variable attenuation of light transmitted therethrough. The adjustable dimmer 1940 may include an electrical input for controlling the level of attenuation. In some cases, the adjustable dimmer 1940 is configured to increase the attenuation when the eye 210 is exposed to bright light, such as when the user goes outdoors. Thus, the system 1900 may include a light sensor for sensing the brightness of the ambient light and control electronics for driving the adjustable dimmer 1940 and varying the attenuation based on the light level sensed by the light sensor.

[0178] Different types of adjustable dimmers 1940 may be employed. Such adjustable dimmers 1940 may include variable liquid crystal switches with polarizers, electrochromic materials, photochromic materials, and the like. The adjustable dimmers 1940 may be configured to adjust the amount of light incident and / or transmitted from the world 510 through the stack 1905. The adjustable dimmers 1940 may be used in some cases to reduce the amount of light from the surroundings passing through the waveguide stack 1900 to the eye 210, which may otherwise provide glare and reduce the user's ability to perceive virtual objects / images projected from the stack 1905 into the eye 210. Such adjustable dimmers 1940 may reduce incoming bright ambient light so as not to wash out the image projected into the eye 210. The contrast of the virtual objects / images presented to the eye 210 may thus be increased with the adjustable dimmers 1940. In contrast, when the ambient light is low, the adjustable dimmer 1940 may be adjusted to reduce attenuation so that the eye 210 can more easily see objects in the world 510 in front of the user. The darkening or attenuation may be present across the system or may be localized to one or more portions of the system. For example, multiple localized portions may be darkened or set to attenuate light from the world 510 in front of the user 210. These localized portions may be separated from each other by portions without such increased darkening or attenuation. In some cases, only one portion is darkened or caused to provide increased attenuation relative to other portions of the eyepiece. Other components may also be added in different designs. Also, the arrangement of the components may differ. Similarly, one or more components may be omitted from the system.

[0179] An example of another configuration is shown in Figure 20A. Figure 20A shows a side view of a system 2000 including laterally displaced in-coupling optical elements 1360, 1362, 1364 on different waveguides and a color filter array 2030 including laterally displaced color filters 2040, 2042, 2044 aligned with the respective in-coupling optical elements 1360, 1362, 1364. The color filter array 2030 may be located on the side of the stack 2005 proximate to the eye 210 and the optics 1130. The color filter array 2030 may be between the stack 2005 and the optics 1130. The color filter array 2030 may be located in or on a cover glass 2050 located between the stack 2005 and the optics 1130. The color filter array 2030 may include one or more different color filters 2040, 2042, 2044, such as a red color filter, a green color filter, and a blue color filter, disposed laterally relative to one another. The system 2000 includes light sources 1110, 1112, 1114, which are laterally displaced relative to one another. These light sources 1110, 1112, 1114 may include light sources of different colors, such as red, green, and blue light sources. The color filters 2040, 2042, 2044 may be transmissive or transparent filters. In some implementations, the color filters 2040, 2042, 2044 include light absorbing filters, however, the color filters 2040, 2042, 2044 may also include reflective filters. The color filters 2040, 2042, 2044 in the color filter array 2030 may be separated and / or surrounded by masks, such as opaque masks, which would reduce the propagation of stray light. The filters in the color filter array 2030 may be used to reduce or eliminate undesirable reflections in the system, such as from the waveguides and / or the incoupling optical elements 1360, 1362, 1364, so as not to re-enter the waveguides used for the different colors through the incoupling optical elements 1360, 1362, 1364 for the different colors.Examples of color filter arrays can be found in U.S. Patent Application No. 15 / 683,412, filed August 22, 2017, entitled "PROJECTOR ARCHITECTURE INCORPORATING ARTIFACT MITIGATION," which is incorporated herein by reference in its entirety, and U.S. Patent Application No. 62 / 592,607, filed November 30, 2017, entitled "PROJECTOR ARCHITECTURE INCORPORATING ARTIFACT MITIGATION," which is incorporated herein by reference in its entirety. The mask may be a black mask or may include a light absorbing material to reduce stray light propagation and reflection. The light sources 1110, 1112, 1114 may be positioned relative to the optical system 1130 and the SLM 1140 to internally couple light to corresponding color filters 2040, 2042, 2044 in the color filter array 2030. For example, the color filter array 2030 may include first, second, and third (e.g., red, green, and blue) color filters 2040, 2042, 2044 positioned to receive light from the first, second, and third light sources 1110, 1112, 1114, respectively. The first, second, and third (e.g., red, green, and blue) color filters 2040, 2042, 2044 may be aligned (e.g., in the x and z directions) with the respective incoupling optical elements 1360, 1362, 1364. Thus, light from the first light source 1110 will be directed through the first color filter 2040 to the first in-coupling optical element 1360, light from the second light source 1112 will be directed through the second color filter 2042 to the second in-coupling optical element 1362, and light from the third light source 1114 will be directed through the third color filter 2044 to the third in-coupling optical element 1364. In some implementations, the in-coupling optical elements 1360, 1362, 1364 may be color specific. For example, the first and second in-coupling optical elements 1360, 1362 may be configured to couple light of distinct first and second colors into the first and second waveguides, respectively.Similarly, the first, second, and third in-coupling optical elements 1360, 1362, 1364 may be configured to couple light of the individual first, second, and third colors into the first, second, and third waveguides, respectively. The first in-coupling optical element 1360 may be configured to couple light of the first color over the second color (or third color) into the first waveguide. The second in-coupling optical element 1362 may be configured to couple light of the second color over the first color (or third color) into the second waveguide. The third in-coupling optical element 1364 may be configured to couple light of the third color over the first color or the second color into the second waveguide. In other configurations, the in-coupling optical elements 1360, 1362, 1364 may be broadband. For example, the first in-coupling optical element 1360 may be configured to couple light of the first, second, and third colors into the first waveguide. The second in-coupling optical element 1362 may be configured to couple the first, second, and third color light into the second waveguide. The third in-coupling optical element 1364 may be configured to couple the first, second, and third color light into the third waveguide. However, the multiple color filters 2040, 2042, 2044 may be color specific to selectively transmit light of a particular color. For example, the first color filter 2040 may transmit the first color more than the second color (and the third color). The second color filter 2042 may transmit the second color more than the first color (and the third color). The third color filter 2044 may transmit the third color more than the first color and the second color. Similarly, the first, second, and third color filters 2040, 2042, 2044 may be color filters that selectively transmit the first, second, and third colors, respectively. Thus, the first, second, and third color filters 2040, 2042, 2044 may be bandpass filters that selectively pass the first, second, and third colors, respectively. In some implementations, the first, second, and third light sources 1110, 1112, 1114 may selectively emit the first, second, and third colors, respectively. For example, the first light source 1110 may emit the first color over the second color (and the third color).The second light source 2042 may emit a second color rather than the first color (and a third color). The third light source 2044 may transmit a third color rather than the first and second colors. The color filters 2040, 2042, 2044 may reduce the amount of stray light inadvertently directed at a particular internal coupling optical element. In other implementations, one or more of the light sources 1110, 1112, 1114 are broadband light sources. For example, the first light source 1110 may emit a first and second (and possibly a third) color. The second light source 1112 may also emit a first and second (and possibly a third) color. The third light source 1114 may also emit a first and second (and possibly a third) color. Although three filters are shown in FIGS. 20A-20G, more or fewer filters may be included. For example, in some implementations, two filters (rather than three) may be used. Thus, two colors corresponding to the two color filters may be selectively transmitted therein by the filters. In some such implementations, two corresponding in-coupling optical elements may be used and matched with the two filters. In some implementations, the two in-coupling optical elements selectively couple the two colors into two separate waveguides, respectively. In some implementations, two light sources may be used instead of three. Other variations and numbers of components may also be used. Also, the color filters 2040, 2042, 2044 may or may not be integrated together in a single array.

[0180] As discussed above, the components and their locations and arrangements may vary. For example, while FIG. 20A shows the analyzer 1150 disposed between the optical system 1130 and the stack 1905, the analyzer 1150 may be located in a different position. FIG. 20B shows the analyzer 1150 located between the optical system 1130 and the SLM 1140. In some designs, the analyzer (e.g., polarizer) 1150 may be directly attached to the SLM 1140. For example, the analyzer 1150 may be glued or mechanically coupled to the SLM 1140. For example, the analyzer 1150 may be glued or fixed to the SLM 1140 (e.g., an SLM window) using an adhesive. Thus, while FIG. 20B shows a gap between the analyzer 1150 and the SLM 1140, in some designs, there is no gap between the analyzer 1150 and the SLM 1140. The analyzer 1150 may be mechanically affixed to the SLM 1140 (e.g., using a mechanical fastener), which may or may not include a gap between the analyzer 1150 and the SLM 1140. Birefringence from the optical system 1130 may be cleared by positioning a polarizer directly on the SLM 1140, as described above. In some implementations, the analyzer 1150, located between the optical system 1130 and the incoupling optical elements 1360, 1362, 1364, may also be included to clear the polarization of light outward from the optical system 1130 (e.g., as illustrated by the dashed lines in FIG. 20B). In addition, a retarder (not shown), such as a quarter-wave plate, may be included proximate the SLM 1140, e.g., between the optical system 1130 and the SLM 1140. As used herein, a quarter-wave plate may refer to a quarter-wave retarder, regardless of whether the quarter-wave retarder comprises a plate, film, or other structure for providing a quarter-wave phase difference. In FIG. 20B, for example, a retarder (e.g., a quarter-wave plate) may be disposed between the analyzer 1150 and the SLM 1140. The retarder (e.g., a quarter-wave plate) may be used for distorted light management. For example, the retarder (e.g., a quarter-wave plate) may compensate for variations caused by differences in wavelength and angle of incidence on the SLM 1140, for example.As discussed above, a compensator may be included to provide a more consistent polarization rotation (e.g., 90°) of the SLM 1140 for different angles of incidence and different wavelengths. The compensator may be used to increase the contrast of the display by providing a more consistent orthogonal rotation. The compensator may be attached or affixed to the SLM 1140 as described above. For example, glue, cement, or other adhesive may be used. The compensator may also be attached to the SLM 1140 using mechanical fasteners. A gap or no gap may be included between the compensator or the SLM 1140. Other light conditioning optics may also be included, in addition or as an alternative, and may be affixed to the SLM 1140 as described above with respect to the analyzer 1150 and / or the compensator.

[0181] In some embodiments, a large angular width (e.g., about 70 degrees) may be used. The angular width may refer, for example, to the angle of light entering the optical system 1130 from the light sources 1110, 1112, 1114 and / or the angle of light exiting the optical system 1130 into the incoupling optical elements 1360, 1362, 1364. In these embodiments, a thinner SLM 1140 may be used. For example, if the SLM 1140 is a liquid crystal (LC) SLM (e.g., a liquid crystal on silicon (LCoS) SLM), the LC layer may be made thinner to accommodate the large angular width.

[0182] The double pass phase difference through the polarizer and analyzer 1150 may need to be half wave. The polarizer may be between the optical system 1130 and the analyzer 1150. The double pass phase difference may be a function of the ratio of the refractive index of the LCoS SLM 1140 to the thickness of the LCoS SLM 1140. For a given refractive index of the LCoS SLM 1140 and a given thickness of the LCoS SLM 1140, traveling in and out of the LCoS SLM 1140 at large angles creates a longer path length for the light than traveling in and out of the LCoS SLM 1140 at small angles. The path length is proportional to the thickness of the LCoS SLM 1140. In one embodiment, the LCoS SLM may have a first refractive index and a first thickness. For small angles, the double pass phase difference of an LCoS SLM with a first refractive index and a first thickness may be half wave. For large angles, the double-pass phase difference of an LCoS SLM having a first refractive index and a first thickness may not be a half-wave (e.g., may be greater than a half-wave). The thickness of the LCoS SLM may vary from a first thickness to a second thickness, the second thickness being less than the first thickness. For small angles, the double-pass phase difference of an LCoS SLM having a first refractive index and a second thickness may not be a half-wave (e.g., may be less than a half-wave). For large angles, the double-pass phase difference of an LCoS SLM having a first refractive index and a second thickness may be a half-wave.

[0183] Also, although Figures 20A and 20B illustrate the use of a polarization-based SLM 1140, other types of SLMs may also be utilized. Figure 20C illustrates the use of a deflection-based SLM 1140, such as, for example, a moveable micromirror-based SLM. As discussed above, such an SLM 1140 may be used in conjunction with digital light processing (DLP) TM) and digital micromirror device (DMD) technologies. As discussed above, the deflection-based SLM 1140 can couple light from one of the light sources 1110, 1112, 1114 into a respective in-coupling optical element 1360, 1362, 1364 depending on the state of the pixels of the SLM 1140. In one state, the light from the light sources 1110, 1112, 1114 will be directed into the respective in-coupling optical element 1360, 1362, 1364 as illustrated in FIG. 20D. In another state, the light from the light sources 1110, 1112, 1114 will be directed away from the in-coupling optical element 1360, 1362, 1364 as illustrated in FIG. 20E. In some implementations, while in the off state, a black light absorbing mask between the color filters 2040, 2042, 2044 in the color filter array 2030 can act as a light dump. As explained above, the color filters 2040, 2042, 2044 may be surrounded and / or separated by a mask, such as a light absorbing mask (e.g., a black mask). The mask may include a light absorbing material such that incident light is absorbed more than reflected therefrom. The mask may also be opaque.

[0184] Other variations are possible. The light sources are shown as emitters 1110, 1112, 1114 (e.g., LEDs, laser diodes) coupled to a coupling optic 1105, such as a non-imaging optical coupling element (e.g., a compound parabolic concentrator (CPC) or cone), but other configurations are possible. For example, the coupling optic 1105 (e.g., a CPC) may be tilted with respect to the waveguide stack. In some cases, the projector (i.e., the optic 1130 and the SLM 1140) may be tilted with respect to the eyepiece (e.g., the waveguide stack). In some implementations, the lens optic 1130 is tilted with respect to the SLM 1140 to reduce distortions such as key tone distortion. A Scheimplug configuration may be employed to reduce such distortions. Components may be tilted (e.g., the optic 1130 and / or the spatial light modulator 1140) as needed, for example, to fit more conformally around the head and / or face. As described above, the light emitter and / or the coupling optics 1105 may be tilted. In some configurations, the assembly, including the waveguide, may be tilted with the side closer to the eye 210 (e.g., the temple side) closer to the eye 210 to increase the perceived field of view of the binocular system as a whole (at the expense of binocular overlap).

[0185] As discussed above, the components and their locations and arrangements may vary. For example, FIG. 20F is a side view of a system 2000F including a cover glass 2050 disposed between the stack 2005 and the optics 1130. In some designs, the light sources 1110, 1112, 1114 may be disposed on the world side of the cover glass 2050 and configured to propagate light through the cover glass 2050 to the optics 1130 and the SLM 1140. As shown, the cover glass 2050 may extend laterally (e.g., parallel to the x-axis) beyond the stack 2005 such that light emitted by the light sources 1110, 1112, 1114 enters the optics 1130 without passing through a waveguide in the stack 2005. System 2000F depicts a deflection-based SLM 1140, however, a similar configuration of light source may also be used with a non-deflection-based SLM, or with or within any other configuration or feature disclosed herein.

[0186] FIG. 20G is a side view of system 2000G including a cover glass 2060 disposed on the world side of stack 2005 (i.e., opposite the side of stack 2005 proximal to optics 1130). In some designs, light sources 1110, 1112, 1114 may be disposed on the world side of cover glass 2050 and configured to propagate light through cover glass 2050 to optics 1130 and SLM 1140. As shown, cover glass 2060 may extend laterally (e.g., parallel to the x-axis) beyond stack 2005 such that light emitted by light sources 1110, 1112, 1114 enters optics 1130 without passing through a waveguide in stack 2005. Although system 2000G depicts a deflection-based SLM 1140, a similar configuration of light sources may also be used with non-deflection-based SLMs or with or within any other configurations or features disclosed herein.

[0187] In addition, configurations that facilitate light recycling may be employed, as discussed above. FIG. 21 is a partial side view of a system 2100, for example, equipped with a configuration that provides light recycling of light from a light source 1110. The light source 1110 may be positioned relative to a polarizer 1115, configured to recycle light having an undesired polarization. The polarizer 1115 may include, for example, a wire grid polarizer that transmits light of a first polarization and retroreflects light of a second, opposite polarization. Thus, light 2110 may be emitted from the light source 1110 and impinge on the polarizer 1115. The polarizer 1115 may transmit light of a first polarization for which a projector (not shown) is configured to use. For example, an SLM may operate appropriately with light of this first polarization. Light of the second polarization 2120 may be reflected back towards the light source 1110 and recycled. The polarization of the light 2120 may be modified with respect to the rotated polarization after reflection from a portion (e.g., a sidewall) of a coupling optic (not shown), such as a non-imaging optic like a compound parabolic concentrator (CPC) at various angles. A portion of the light may result with a preferred polarization (e.g., polarization orientation) that may be passed by the polarizer 1115. Multiple reflections may change the polarization of the light, causing it to exit with the desired polarization. This recycled light 2130 is then emitted back toward the polarizer 1115. Such a configuration may improve efficiency, e.g., energy efficiency, since a more desired polarization is produced. Additionally or alternatively, a retarder may also be used to change the reflected polarization state and recover the light.

[0188] FIG. 22 shows another configuration including light sources 1110, 1112, 1114 and corresponding light collection optics 2210, 2212, 2214. The light collection optics 2210, 2212, 2214 may include lenses or other optics to collect light from the light sources 1110, 1112, 1114. The light sources 1110, 1112, 1114 may be laser diodes or other emitters that emit light over a wide range of angles. The light collection optics 2210, 2212, 2214 may be used to collect more of that light. The light sources 1110, 1112, 1114 may emit light asymmetrically. For example, light may be emitted over a wider range of angles in one direction (e.g., the x or z direction) rather than in an orthogonal direction (e.g., the z or x direction). Thus, the light collection optics 2210, 2212, 2214 may be asymmetric. For example, the light collection optics 2210, 2212, 2214 may have different refractive powers in different, possibly orthogonal, directions. The light collection optics 2210, 2212, 2214 may include lenses, such as, for example, anamorphic lenses. The light collection optics 2210, 2212, 2214 may also potentially include non-imaging optics. An aperture 2220, 2222, 2224 may also be included. A diffuser 2230 may also be included proximate the aperture 2220, 2222, 2224, for example, when the light source 1110, 1112, 1114 is a laser, such as a laser diode. By using a diffuser proximate the aperture 2220, 2222, 2224, the aperture may appear to be at the location of a laterally displaced light source. The apertures 2220, 2222, 2224 may be matched with incoupling optical elements on the waveguide or with the waveguide via optics and SLM as discussed above. For example, each aperture 2220, 2222, 2224 may be matched with a separate incoupling optical element. Similarly, in one implementation as shown in FIG. 16A, each aperture 2220, 2222, 2224 may be matched with a separate group of (e.g., color-selective) incoupling optical elements.

[0189] A wide range of system variations and configurations are also possible. For example, although linearly polarized light is described as propagating through the optics 1130 to the SLM 1140 and back through the optics to the waveguide stack, in some designs circularly polarized light may be used instead. For example, circularly polarized light may be directed into the optics 1130. A retarder, such as a quarter wave plate, may be positioned such that the light passes through the retarder prior to being incident on the SLM. The retarder (e.g., a quarter wave plate) may be positioned between the optics 1130 and the SLM 1140. In some cases, as described above, the retarder (e.g., a quarter wave plate) may be affixed to the SLM 1140, such as, for example, using an adhesive or mechanical fasteners. The retarder (e.g., a quarter wave plate) may convert the linearly polarized light to circularly polarized light after reflection from the SLM 1140. Thus, in some implementations, the circularly polarized light may again pass through the optical system 1130 towards the stack. For example, another retarder (e.g., a quarter wave plate) proximal to the analyzer 1150 may convert the circularly polarized light to linearly polarized light that may or may not pass through the analyzer depending on the linearly polarized light (e.g., orientation). The pixels of the SLM 1140 may have states that can be varied to rotate or not rotate the polarization. Still other configurations are possible.

[0190] 23A is a side view of an augmented reality display system 2300 including a light source 2305, a polarization rotator 2307, an optic (e.g., a lens) 2320 having refractive power, a polarizer 2312, 2335 such as a linear polarizer (e.g., a horizontal or vertical polarizer), a retarder 2315, 2330, 2340 such as a quarter-wave retarder (e.g., a quarter-wave plate), and at least one waveguide 2348 for outputting image information to a user. Such a configuration can be used to illuminate a reflective spatial light modulator (not shown) such that light emitted from the light source 2305 is coupled into the at least one waveguide 2348 to be reflected from the spatial light modulator and directed to the user's eye. The configuration and placement of these elements, particularly the polarizer and retarder, can reduce or eliminate reflections from optical surfaces in the system, such as surfaces from the optical system 2320, which may otherwise result in a residual image being visible to the user. For example, optical elements that are polarization selective and / or have a phase difference (e.g., polarizers 2312, 2335 and retarders 2315, 2330, 2340) can be arranged and configured to convert linearly polarized light into circularly polarized light that changes from left to right or right to left upon reflection from an optical surface. Similarly, such optical elements that are polarization selective and / or have a phase difference (e.g., polarizers 2312, 2335 and retarders 2315, 2330, 2340) can be arranged and configured to convert circularly polarized light into linearly polarized light that can be attenuated or filtered out by a polarizer (e.g., a linear polarizer). A circular polarizer that converts linearly polarized light to circularly polarized light, or vice versa, may be fabricated with such optical elements (e.g., polarizers 2312, 2335 and retarders 2315, 2330, 2340) that are polarization selective and have a phase difference. For example, a circular polarizer may comprise a linear polarizer and a quarter-wave retarder. A circular polarizer can be used to convert linearly polarized light to circularly polarized light having a first state (e.g., handedness) and filter out circularly polarized light having a second state (e.g., handedness) that is different from the first state.For example, a circular polarizer can be used to convert linearly polarized light with a certain orientation to left-handed circularly polarized light and filter out right-handed circularly polarized circularly polarized light. A circular polarizer can also be used to convert linearly polarized light with a certain orientation to right-handed circularly polarized light and filter out left-handed circularly polarized circularly polarized light. Circular polarizers or other configurations of optical elements, including phase differences, that can be used to convert linearly polarized light to circularly polarized light and back, and selectively filter linearly polarized light, can be used to reduce back reflections from optical surfaces, as discussed below in connection with Figures 23A and 23B.

[0191] Note that left-handed and right-handed circular polarizations are illustrated with clockwise and counterclockwise arrows in Figures 23A and 23B, respectively. Additionally, horizontal and vertical linear polarizations are depicted using horizontal arrows and circular dots, respectively.

[0192] As discussed above, FIG. 23A illustrates a configuration of an augmented reality display system 2300 in which polarizers 2312, 2335, such as linear polarizers (e.g., horizontal polarizers), and retarders 2315, 2330, 2340, such as quarter-wave retarders (e.g., quarter-wave plates), are arranged to reduce back reflections from optical surfaces, such as surfaces of an optical system 2320, in the path of light that illuminates and reflects from a spatial light modulator (not shown). The first polarizer 2312 and the first retarder 2315 are disposed between the light source 2305 and the optical system 2320. The first polarizer 2312 is disposed between the light source 2305 and the first retarder 2315. Similarly, the first retarder 2315 is disposed between the first polarizer 2312 and the optical system 2320.

[0193] As shown, light source 2305 emits light, as represented by light ray 2310. In some implementations, light ray 2310 may pass through polarization rotator 2307. Rotator 2307 is optional and can be used to rotate the polarization of light from light source 2305, e.g., light ray 2310. In various implementations, rotator 2307 can rotate the angle of polarization (e.g., of a linearly polarized light). For example, rotator 2307 can rotate the linear polarization of light ray 2310 to be transmitted therethrough to an orientation that is aligned with first polarizer 2312. In some implementations, polarization rotation 2307 may comprise a retarder, e.g., a half-wave retarder, in some cases. The optical axis of the half-wave retarder may be oriented to rotate the polarization of light from light source 2305 from vertical to horizontal or vice versa. Alternatively, the polarization rotator 2307 may be configured to rotate the angle of polarization of the linearly polarized light emitted from the light source 2305 by a different amount. The polarization rotator 2307 need not be included in the system. For example, in implementations where the light source 2305 emits light having the same polarization as the first polarizer 2312, the polarization rotator 2307 may be omitted. As shown, light, e.g., light ray 2310, passes through the polarizer 2312, shown here as a horizontal polarizer. In instances where the light from the light source 2305 is not polarized, it is transmitted through the horizontal polarizer 2312, and the light shown as light ray 2310 becomes linearly polarized (e.g., horizontally polarized) after passing through the polarizer 2312. Although a horizontal linear polarizer is used in this example, it should be understood that the principles taught can also be applied to the use of a vertical linear polarizer. Alternatively, a linear polarizer having a different orientation other than vertical or linear may also be used.

[0194] Horizontally polarized light beam 2310 travels through retarder 2315, shown here as a quarter-wave retarder. This retarder 2315 may contain sufficient phase difference to convert linearly polarized light to circularly polarized light. For example, horizontally polarized light may be converted to left-handed circularly polarized light, as illustrated by the curved (e.g., clockwise oriented) arrow. In this example, the combination of polarizer 2312 and retarder 2315 (e.g., quarter-wave) forms a circular polarizer, referred to herein as a first circular polarizer, that may convert light of a particular linear polarization (e.g., horizontal or vertical polarization) to a particular circular polarization (e.g., left- or right-handed circular polarization or vice versa). The circular polarizer may also block light of a particular circular polarization (e.g., right- or left-handed circular polarization) depending on the configuration.

[0195] In some implementations, the various optical elements have birefringence. In some such cases, the retarder 2315 may include a sufficient amount of retardation to convert linearly polarized light to circularly polarized light and need not be a quarter wave plate. Retarder 2315 may include more or less than a quarter wave retardation, as retardation may be contributed by other optical elements. Similarly, retardation may be distributed among several optical elements. As another example, multiple retarders may be employed to provide the appropriate amount of retardation.

[0196] The circularly polarized light beam 2310 (here, left-handed circularly polarized) then passes through the optical system 2320. Unwanted reflections may occur at any interface in the system with a medium having a different refractive index, such as, for example, an air / material interface. These reflections may be problematic if the reflected light is allowed to enter the at least one waveguide 2348, as it may be directed into the user's eye and form a visible "afterimage" image in the user's eye. For example, in instances where the display uses the at least one waveguide 2348 to project a first image into the viewer's eye, a second, faint replica image displaced (e.g., displaced laterally) relative to the first image may also be seen by the user. Such "afterimage" images formed by reflections from optical surfaces directed into the user's eye may be distracting or otherwise degrade the viewing experience. For example, as illustrated in FIG. 23A, light such as the reflected light beam 2325 may be reflected off a lens in the optical system 2320. This light may be directed towards at least one waveguide 2348, which is configured to direct the light into the user's eye to present an image thereto. However, in this case, the circularly polarized light reverses handedness. For example, upon reflection from the lens, the direction of the circular polarization is changed (e.g., from left-handed to right-handed). The right-handed reflected light ray 2325 then travels through the retarder 2315 and is converted to linearly polarized light having a different (e.g., orthogonal) linear polarization than that transmitted by the polarizer 2312. In this case, for example, the light reflected from the optical surface of the lens is converted by the retarder 2315 to vertical linear polarization, which is orthogonal to the polarization transmitted by the horizontal linear polarizer 2312. The horizontal linear polarizer 2312 selectively passes horizontally polarized light and filters out vertically polarized light.Thus, the reflected light beam 2325 is attenuated and / or not transmitted by the horizontal linear polarizer 2312 and prevented from reaching the at least one waveguide 2348, or at least a reduced amount of such reflected light reaches or is coupled into the at least one waveguide 2348, for example through an internal coupling optical element (e.g., one or more internal coupling gratings). The result would be similar to a left-handed circularly polarized light beam reflected from a different optical surface of the optical system 2320 or another optical surface on a different optical element.

[0197] As shown, the display system 2300 further includes a second retarder 2330 (e.g., a quarter-wave retarder or a quarter-wave plate) and a second polarizer 2335 (e.g., a linear polarizer) disposed between the optical system 2320 and a spatial light modulator (not shown). The second retarder 2330 and the second linear polarizer 2335 may form a second circular polarizer in some implementations. The second retarder 2330 is disposed between the optical system 2320 and the second polarizer 2335. Similarly, the second polarizer 2335 is disposed between the second retarder 2330 and the spatial light modulator. Thus, after passing through the optical system 2320, the light beam 2310 may pass through the second retarder 2330 (e.g., a quarter-wave retarder). The second retarder 2330 is configured (e.g., with its optical axis appropriately oriented) such that the light beam 2310 is converted from left-handed circular polarization to horizontal linear polarization. Similarly, the second retarder 2330 converts the circularly polarized light back to the original linear polarization state output by the first polarizer 2312. As discussed below, this second retarder 2330 and second polarizer 2312 can be useful in reducing "afterglow" images caused by light reflected from the spatial light modulator passing through an optical surface (e.g., on the refractive optic or lens 2320) as the light travels to the at least one light guide 2348.

[0198] The third retarder 2340 (e.g., a quarter wave retarder or a quarter wave plate) is disposed between the second polarizer 2335 and the spatial light modulator. Thus, the third retarder 2340 is disposed between the second retarder 2330 and the spatial light modulator. Also, in various implementations, as shown, the second polarizer 2335 is between the second and third retarders 2330, 2340. As shown, the light beam 2310 becomes linearly polarized in response to passing through the second polarizer 2335, and in some implementations, the second retarder 2330 / second polarizer 2335 may convert the light to the original linear polarization of the first polarizer 2312 (e.g., horizontally polarized). This linearly polarized light is incident on the third retarder 2340. The third retarder 2340 is configured to convert the light back to circularly polarized light, in some implementations to the same polarization as that output by the first retarder 2315 (e.g., left-handed circularly polarized light in this example). In some implementations, the spatial light modulator is configured to act on circularly polarized light. In some implementations, the spatial light modulator is a reflective spatial light modulator that reflects the incident circularly polarized light back as circularly polarized light. In some embodiments, the circularly polarized light reflected from the spatial light modulator may have the same handedness as that incident on it (e.g., left-handed circularly polarized), possibly depending on whether the spatial light modulator pixel is in an "on" or "off" state. In some embodiments, the spatial light modulator may reflect circularly polarized light of a different handedness than that incident on it (e.g., right-handed circularly polarized), possibly depending on whether the spatial light modulator pixel is in an "on" or "off" state. However, other types of spatial light modulators may also be used.

[0199] FIG. 23A shows light, illustrated as ray 2342, reflected from the spatial light modulator and traveling towards the waveguide 2385. The reflected ray 2342 is depicted as left-handed circularly polarized light. The ray 2342 passes through the third retarder 2340. The third retarder 2340 converts the circularly polarized light to linearly polarized light. In this example, the left-handed circularly polarized light is converted to horizontally polarized light. The linearly polarized light is transmitted through the second polarizer 2335. In this example, the horizontally polarized light passes through the second polarizer 2335. The linearly polarized light is incident on the second retarder 2330 and converted to circularly polarized light. In this example, the horizontally polarized light is converted to left-handed polarization and transmitted to the optical system 2320. Here again, reflections from an optical surface, such as a surface of the optical system 2320 having refractive power, may create a residual image by reflecting light from the spatial light modulator back into at least one waveguide 2348 to the user's eye. As explained above, undesired reflections may occur at any interface involving media with different refractive indices, such as an air / material interface. As referenced above, the inclusion of a second retarder and polarizer 2330, 2335 may attenuate these reflections and reduce the likelihood of residual reflections. FIG. 23A depicts light, for example, illustrated as ray 2346, reflected from an optical surface of the optical system 2320. The act of reflecting from the surface gives rise to a reflected ray 2346, which is circularly polarized to switch handedness, in this example from left-handed circular polarization to right-handed circular polarization. The switched circularly polarized light is attenuated by the second circular polarizer, formed by the second retarder and polarizer 2330, 2335. As shown in FIG. 23A, for example, the reflected circularly polarized light 2346 is incident on the second retarder 2330 and is converted by the second retarder to linearly polarized light having a different, e.g., orthogonal linear polarization, than that selectively transmitted by the second linear polarizer 2335.In this case, for example, right-handed circularly polarized light reflected from an optical surface of optical system 2320 is converted by retarder 2330 to vertical linear polarization, which is orthogonal to the polarization selectively transmitted by polarizer 2335. A second polarizer 2335 attenuates or prevents transmission of this linearly polarized light. In this example, light 2346 is vertically polarized, while second polarizer 2335 is a horizontal polarizer that selectively passes horizontally polarized light and filters out vertically polarized light.

[0200] In contrast, the light 2342 that passes through the optical system 2320 and is incident on the first retarder 2315 is circularly polarized and has a different handedness than the light reflected from the optical surfaces of the optical system 2320. This light 2342 that is directed towards the at least one waveguide 2348 has a polarization (e.g., left-handed polarized) that is converted by the first retarder 2315 to linear polarization (e.g., horizontally linearly polarized light) that is selectively transmitted by the first polarizer 2312. In this way, the light 2342 reaches the at least one waveguide 2348, is coupled into it, and can be directed towards the user's eye.

[0201] In the embodiment shown in FIG. 23A, a first circular polarizer formed by a first polarizer 2312 and a first retarder 2315, and a second circular polarizer formed by a second retarder 2330 and a second polarizer 2335 are on opposite sides of the optical system 2320, one closer to the light source 2305 and one closer to the spatial light modulator, and are used to reduce reflections that may result in "afterimage images." An additional retarder 2340 is included between the second circular polarizer (e.g., the second polarizer 2335) and the spatial light modulator to convert the light to circularly polarized light. However, a wide range of variations are possible. For example, only one circular polarizer may be included. Alternatively, additional circular polarizers or other types of polarizing optics may be included.

[0202] FIG. 23B illustrates a third circular polarizer that may be added to the augmented reality system 2300 as shown in FIG. 23A. In particular, FIG. 23B depicts the second circular polarizer, including the second polarizer 2335 and the second retarder 2330 and the third retarder 2340, as introduced above, and further depicts a spatial light modulator 2375. This spatial light modulator (SLM) 2375 may include a liquid crystal spatial light modulator (e.g., liquid crystal on silicon or LCoS). In some implementations, the SLM 2375 can be covered with a cover glass 2370.

[0203] 23B also shows a third circular polarizer including a fourth retarder 2345, such as a quarter-wave retarder (e.g., a quarter-wave plate), and a third polarizer 2355, such as a linear polarizer, disposed between the second circular polarizer, including the second polarizer 2335 and the second retarder 2330, and the spatial light modulator 2375. The third polarizer 2355 is between the fourth retarder 2345 and the spatial light modulator 2375. An additional fifth retarder 2360, such as a quarter-wave retarder (e.g., a quarter-wave plate), and a compensator 2365 are disposed between the third circular polarizer, including the fourth retarder 2345 and the third polarizer 2355, and the spatial light modulator 2375, or more specifically, the cover glass 2370 shown in FIG. 23B. The fifth retarder 2360 is between the third polarizer 2355 and the compensator 2365. The compensator 2365 is between the fifth retarder 2360 and the spatial light modulator 2375, or more specifically, the cover glass 2370.

[0204] 23B illustrates how light from a light source 2305 (shown in FIG. 23A), for example, light ray 2310, propagates through a second circular polarizer, including retarder 2330 and second polarizer 2335, as well as a third retarder 2340, to a third circular polarizer, including a fourth retarder 2345 and third polarizer 2355. After passing through the second circular polarizer, including second retarder 2330 and second polarizer 2335, light ray 2310 from light source 2305 is incident on the third circular polarizer, specifically, on the fourth retarder 2345. The fourth retarder 2345 may convert the circularly polarized light of light ray 2310 to linearly polarized light. In the embodiment shown in FIG. 23B, the light beam 2310 is circularly polarized (e.g., left-handed circularly polarized) and is converted to linearly polarized light (e.g., horizontally polarized light) by the fourth retarder 2345. This linearly polarized light travels through the third polarizer 2355, which in FIG. 23B includes a horizontal polarizer that selectively transmits horizontally polarized light. This linearly polarized light propagates through the fifth retarder 2360, which may include a quarter-wave retarder that converts the linearly polarized light to circularly polarized light. In the embodiment shown in FIG. 23B, the horizontally linearly polarized light 2310 incident on the fifth retarder 2360 is converted to left-handed circularly polarized light. This circularly polarized light is incident on and passes through the compensator 2365. The compensator 2365 may include a polarizing element that adjusts the polarization to a desired polarization. The compensator 2365 may be used to offset birefringence of various optical elements in the system. For example, the light may be slightly elliptically polarized due to the retardation contribution of one or more optical elements. In various implementations, the light output from the compensator 2365 is circularly polarized light. In the example shown in FIG. 23B, the light output from the compensator 2365 is left-handed circularly polarized light. In various implementations, the compensator 2365 may be used to offset residual retardation in the SLM, which may comprise, for example, a liquid crystal (e.g., LCOS) SLM cell. The compensator may introduce in-plane retardation and / or out-of-plane retardation.In some implementations, the compensator 2365 may include a combination of optical retarders that, when combined, produce a retardation that can potentially cancel out a residual retardation from the SLM (e.g., an LCoS panel).

[0205] In FIG. 23B, the light is incident on the cover glass 2370 and SLM 2375 after passing through the compensator 2365. This light incident on the cover glass 2370 and SLM 2375 is depicted as left-handed circularly polarized light. Depending on the type and state of the spatial modulator, the SLM 2375 may reflect circularly polarized light of the same handedness. For example, when a pixel of the SLM 2375 is in the "on" state (which may be an undriven state in some implementations), the SLM 2375 may introduce a quarter wave phase difference for each pass through the SLM 2375. Thus, upon reflection, the incoming circularly polarized light may remain circularly polarized upon reflection. In various configurations, the handedness may also remain the same. For example, as shown in FIG. 23B, the incoming left-handed circularly polarized light may remain left-handed circularly polarized upon reflection. The circularly polarized light reflected from the SLM 2375, represented by ray 2342, may pass through the cover glass 2370 and the compensator 2365 and impinge on the fifth retarder 2360, which converts the circularly polarized light to linearly polarized light. In the example shown in FIG. 23B, the circularly polarized light incident on the fifth retarder 2360 is rotated left and the fifth retarder 2360 converts the circularly polarized light to horizontally polarized light. The third polarizer 2355 may be configured to selectively transmit the polarization of the light output by the fifth retarder 2360. Thus, in the example shown in FIG. 23B, where the light output from the fifth retarder 2360 is horizontally polarized, the third polarizer 2355 selectively transmits the horizontally polarized light. The linearly polarized light transmitted by polarizer 2355 is incident on the fourth retarder 2345 and converted to circularly polarized light. In the example shown in FIG. 23B, the circularly polarized light is left-handed circularly polarized. The light can travel through a second circular polarizer comprising a second retarder 2330 and a second polarizer 2335, an optical system 2320, a first circular polarizer comprising a first polarizer 2312 and a first retarder 2315, as discussed above in connection with FIG. 23A, onto at least one waveguide 2348 and into the user's eye.

[0206] However, light reflected from the optical surface may be attenuated by the third circular polarizer, thereby reducing the likelihood that such reflections will reach at least one waveguide 2348 and be directed to the user's eye, producing a residual image. To illustrate, FIG. 23B shows an exemplary light ray 2343 reflected from an optical surface of the third retarder 2340, for example, from an interface between air and the third retarder 2340. As discussed above, reflections may occur at any interface between media with different refractive indices, such as an air / material interface, or an interface between different dielectric layers. However, circularly polarized light reverses handedness upon reflection. For example, upon reflection from a surface of the third retarder 2340, the direction of the circular polarization is changed (e.g., from left-handed to right-handed). The right-handed reflected light ray 2343 then travels through the fourth retarder 2345 and is converted to linearly polarized light having a different, e.g., orthogonal, linear polarization than that selectively transmitted by the third polarizer 2355. In this case, for example, the light reflected from the optical surface of the third retarder 2340 is converted by the fourth retarder 2345 to a vertical linear polarization, which is orthogonal to the polarization selectively transmitted by the third polarizer 2355. The third polarizer 2355 selectively passes horizontally polarized light and filters out vertically polarized light. Thus, the reflected light ray 2343 is attenuated and / or not transmitted by the third polarizer 2355 and is prevented from reaching the at least one waveguide 2348 (e.g., by reflecting off another surface), or at least a reduced amount of such reflected light reaches or is coupled into the at least one waveguide 2348.

[0207] The result may be similar to a circularly polarized ray reflected from a different optical surface. FIG. 23B, for example, shows the reflection of an incident ray 2310 from the optical surface of the fourth retarder 2345. The reflection 2350 from the fourth retarder 2345 switches the handedness of the polarization. For example, the incident ray 2310, depicted as being left-handed circularly polarized, is converted to ray 2350, shown to have right-handed circular polarization, upon reflection. The reflected ray 2350 passes through the third retarder 2340 and is converted to vertically polarized light. This vertically polarized light is selectively attenuated or filtered out by the second polarizer 2335.

[0208] As explained above, a pixel of SLM2375 may be, for example, in an "on" state (but in some implementations, an undriven state), in which case light incident on that pixel of SLM2375 is reflected therefrom and coupled into at least one waveguide 2348 and directed to the user's eye. However, a pixel of SLM2375 may be in an "off" state (but in some implementations, may be a driven state), in which case light incident on that pixel of SLM2375 is not coupled into at least one waveguide 2348 and is not coupled into the user's eye. In this "off" state, for example, various implementations of SLM2375 may not introduce a phase difference upon reflection therefrom. Thus, in the embodiment shown in FIG. 23B, circularly polarized light incident on SLM2375 may remain circularly polarized upon reflection from SLM2375. However, the handedness of the circularly polarized light may change upon reflection from SLM2375. For example, the left-handed circularly polarized light beam 2310 shown in FIG. 23B incident on the SLM 2375 may be converted to right-handed circularly polarized light upon reflection from the SLM 2375. However, this reflected light may be selectively attenuated by the third polarizer 2355. For example, the right-handed circularly polarized light reflected from the SLM 2375 may pass through the cover glass 2370, the compensator 2365, and the fifth retarder 2360. The fifth retarder 2360 may convert the right-handed circularly polarized light to vertically polarized light, which is selectively attenuated by the third polarizer 2355, which may include a horizontal polarizer. Thus, in various implementations, the fifth retarder 2360 may convert light reflected from a pixel of the SLM 2375 to a linear polarization that is orthogonal to the linear polarization selectively transmitted by the third polarizer 2355 when the pixel of the SLM is in an “off” state. This third polarizer 2355 may thus selectively attenuate this linearly polarized light, thereby reducing or blocking light from that pixel of the SLM 2375 from reaching the at least one waveguide 2348 and being directed into the eye.

[0209] Variations in configuration are also possible, such as variations in the polarizing optics. For example, more or fewer circular polarizers may be included.

[0210] In various implementations, the third circular polarizer, including, for example, the fourth retarder 2345 and the third polarizer 2355, is omitted as shown in FIG. 23C. In this particular implementation, the fourth retarder 2345, the third polarizer 2355, and the fifth retarder 2360 are not included in the system. FIG. 23C illustrates a design of an augmented reality system 2300 including the components illustrated in FIGS. 23A and 23B, except for the fourth retarder 2345, the third polarizer 2355, and the fifth retarder 2360. It is noted that even with the omission of the third circular polarizer, the augmented reality display system is still configured to reduce the persistence of the image. The second circular polarizer, for example, reduces reflections that would otherwise contribute to the persistence of the image. To illustrate, FIG. 23C depicts light reflected from the third retarder 2340, illustrated as ray 2380. The act of reflecting from the surface of the third retarder 2340 produces a reflected ray 2380, which is circularly polarized to switch handedness. In this example, the polarization is switched from left-handed circular polarization to right-handed circular polarization. The switched circularly polarized light 2380 then passes through the compensator 2365 and is incident on the cover glass 2370 and the SLM 2375. As discussed above, the SLM 2375 can reflect circularly polarized light of the same handedness. Thus, the incoming right-handed circularly polarized light can remain right-handed circularly polarized upon reflection. This circularly polarized light reflected from the SLM 2375 may be represented by light ray 2382, then pass through the cover glass 2370 and the compensator 2365, and be incident on the third retarder 2340. The switched circularly polarized light 2382 is attenuated by the second circular polarizer, and in particular by the third retarder 2340 and the polarizer 2335. As illustrated in FIG. 23C, for example, the circularly polarized light 2382 reflected from the SLM 2375 is incident on the third retarder 2340 and converted by the third retarder 2340 to linearly polarized light having a different, e.g., orthogonal linear polarization, than that selectively transmitted by the second linear polarizer 2335.In this case, for example, right-handed circularly polarized light 2382 is converted by the third retarder 2340 to vertical linearly polarized light, which is orthogonal to the polarization selectively transmitted by the second polarizer 2335. The second polarizer 2335 attenuates or prevents transmission of this linearly polarized light.

[0211] Reflections that may contribute to residual reflections can also potentially be reduced by tilting optical surfaces in the system. FIG. 24 illustrates an example configuration with tilted optical surfaces to reduce reflections that may produce residual reflections. FIG. 24 shows an augmented reality display system 2400 including a light source 2305 that emits light, represented by light rays 2310, that pass through any number of polarizers, retarders, lenses, and / or other optical components as the light travels toward a spatial light modulator (SLM) 2375. Possibly, a first polarizer 2312 and a first retarder 2315 that form a first circular polarizer, as well as a lens 2320, are shown in FIG. 24 for illustrative purposes. However, additional components may be included, or components may be excluded or arranged or configured differently. In the illustrated example, the SLM 2375 includes a cover glass 2370 therewith. The cover glass 2370 may be a contributor to the reflections that produce the residual image. Thus, in some implementations, the cover glass 2370 may be shaped to direct the reflections that may result in residual images away from being directed into the user's eye. As shown, the cover glass 2370 has surfaces that may be tilted such that the surfaces are not parallel to other components or optical surfaces of the system (e.g., the SLM 2375, the first retarder 2315, the first polarizer 2312, the at least one waveguide 2348, etc., or optical surfaces thereof). The major surfaces of the cover glass 2370 may have normals that are not aligned with or tilted such that they are not parallel to the optical axes of optical components therein, such as the augmented reality display system 2400 or the optical system 2320, for example. By being tilted, reflections from the optical surfaces of the cover glass 2370 can be directed away from the at least one waveguide 2348 or an internal coupling optical element (e.g., an internal coupling grating or diffractive optical element) to internally couple light into the at least one waveguide 2348 and reduce the likelihood of reflections from the cover glass 2370 entering the at least one waveguide 2348.As depicted, the reflected light 2405 is directed back towards the light source 2305 and away from at least one waveguide 2348 where such light may ultimately reach the user's eye. In some implementations, the reflected light 2405 is directed back to the light source and at least a portion can be recycled in the light source 2305.

[0212] Although FIG. 24 depicts the cover glass 2370 with a sloped surface, optical surfaces that are sloped to divert reflections away from being coupled into the at least one waveguide 2348 can be included on any component in the system where undesired reflections are possible. Thus, optical surfaces on other components such as polarizers, retarders, etc. may be sloped to reduce reflections that are coupled into the at least one waveguide 2348 and into the user's eye. Variations in the shape and size of the cover glass 2370 or other optical components are also possible. The cover glass 2370 or other optical components may be thinner, for example. Similarly, the cover glass 2370 or other optical components may have a different aspect ratio (length vs. thickness) than that shown in FIG. 24. In some implementations, the cover glass 2370 or other optical components are wedge shaped. However, other shapes are also possible.

[0213] Still other arrangements are possible. Figure 25 illustrates, for example, an implementation of an augmented reality display system 2500 similar to the system 2400 shown in Figure 24, but further including a light dump 2505 to absorb light directed thereto. The system 2500 includes a cover glass 2370 that is tilted to direct a reflection 2510 from the cover glass 2370 to the light dump 2505 instead of being directed back to the light source 2305. The light dump 2505 may include a light absorbing material or structure configured to absorb light. The location of the light dump 2505 can vary depending on the implementation, for example, depending on the angle of the tilted cover glass 2370. As discussed above, this approach can be applied to other optical surfaces in the system. In addition, the shape and size of the optical elements may be different.

[0214] A wide range of variations in the augmented reality display are also possible. Variations in the polarization optical elements are also possible. For example, a horizontal polarizer is used, but in some implementations a vertical polarizer or a combination of horizontal and vertical polarizers are employed. In addition, polarizers characterized by polarization other than vertical or horizontal may be used. Similarly, light shown in the figures need not be horizontally polarized, but may be vertically polarized. Similarly, light shown as vertically polarized may be horizontally polarized in different implementations, or vice versa. Linearly polarized light with polarization other than vertical or horizontal may also be used.

[0215] In addition, the retarders may be configured differently. For example, the polarized light in the figures need not be left-handed circularly polarized, but may be right-handed circularly polarized light, and / or the right-handed polarized light may be left-handed circularly polarized. Still other variations are possible. Different retarder configurations can be employed to produce left-handed and / or right-handed polarization combinations different from those shown. Also, in some implementations, elliptically polarized light may possibly be used instead of circularly polarized light. Retarder may be employed, for example, to convert elliptically polarized light to linearly polarized light and vice versa. Linear polarizers may be used to filter light and may be used to reduce residual reflections as described herein.

[0216] In some implementations, other types of polarizing elements and configurations thereof are employed. For example, the retarders are not limited to quarter-wave retarders or quarter-wave plates. For example, in some implementations, various optical elements have birefringence. In some such cases, any one or more of the retarders 2315, 2330, 2340 may include an amount of retardation sufficient to convert linearly polarized light to circularly polarized light and need not be a quarter-wave retarder. Retardation greater than or less than a quarter wave may be included within any one or more of the retarders 2315, 2330, 2340, as retardation may be contributed by other optical elements. Similarly, retardation may be distributed within several optical elements. As another example, multiple retarders may be employed to provide the appropriate amount of retardation. Also, as explained above, in some implementations, elliptically polarized light may potentially be used instead of circularly polarized light. Retarder may be employed, for example, to convert elliptically polarized light to linearly polarized light and vice versa. Linear polarizers can be used to filter light and may be used to reduce residual reflections as described herein.

[0217] In addition, the optical components may be in the form of optical layers, sheets, and / or films, as well as stacks or one or more layers, sheets, and / or films. Thus, different polarizing elements in different amounts, locations, and arrangements may be used. For example, one or more of the retarders and / or polarizers may comprise a film.

[0218] In some implementations, the spatial light modulator may operate differently, for example, the spatial light modulator may operate on and / or output light other than circularly polarized light.

[0219] FIG. 26 is a simplified schematic diagram illustrating a cross-section of an image projection system according to an embodiment of the present invention. The image projection system 2600 in FIG. 26 includes an illumination source 2610 operable to emit light over a range of wavelengths, e.g., in the visible spectrum. Illumination light, which may be provided in primary colors, e.g., RGB, can enter the image projection system 2600 at different locations (i.e., different x, y locations) relative to the optical axis of the lens. Thus, embodiments include both split-pupil designs in which the illumination light enters at different locations as well as single-pupil designs in which the illumination light enters at the same location. In some implementations, the illumination light enters off-axis and is not aligned with the optical axis of the lens. In some embodiments, a linear polarizer, acting as a linear pre-polarizer, is inserted between the illumination source 2610 and the eyepiece waveguide 2620 to reduce the amount of illumination light in undesired polarizations impinging on the eyepiece waveguide.

[0220] Light emitted by illumination source 2610 propagates through transparent region 2615 of eyepiece waveguide 2620, as discussed above in connection with FIG. 11A. After passing through transparent region 2615 of eyepiece waveguide 2620, the illumination light becomes circularly polarized as the illumination light passes through circular polarizer 2622, which can be implemented by a combination of a linear polarizer and a quarter wave plate. The circular polarization of the illumination light serves to suppress back reflections from refractive lens set 2630.

[0221] In the image projection system 2600, a refractive lens set 2630 is utilized that includes four refractive lenses. Although the refractive lens set 2630 is illustrated as including four refractive lenses, this is not required and other implementations can utilize less than four refractive lenses or more than four refractive lenses. The side of the elements used in the refractive lens set 2630 that faces the illumination source 2610 can be referred to as the object side surface, and the side of the elements used in the refractive lens set 2630 that faces the reflective spatial light modulator 2650 can be referred to as the image side surface since the light emitted by the illumination source 2610 is imaged onto the reflective spatial light modulator 2650. The curvature and refractive index of the lenses in the refractive lens set 2630 are therefore selected to image the light emitted from the illumination source 2610 onto the reflective spatial light modulator 2650, which can be implemented, for example, as a liquid crystal on silicon (LCoS) display. As described more fully herein, the refractive lens set 2630 performs several functions, including: 1) Illuminate the reflective spatial light modulator 2650. 2) Re-images the illumination pupil into the internal coupling element 2624 of the eyepiece waveguide 2620, thereby providing high quality pupil imaging enabling a highly efficient system. 3) Providing a high level of projector MTF performance from the reflective spatial light modulator to the internal coupling element.

[0222] 26, the refractive lens set 2630 includes a first refractive lens 2632, a second refractive lens 2634, a third refractive lens 2636, and a fourth refractive lens 2638. In some embodiments, the first refractive lens 2632 is a positive lens with a convex object-side surface and a convex image-side surface, the second refractive lens 2634 is a negative lens with a concave object-side surface and a convex image-side surface, the third refractive lens 2636 is a positive lens with a concave object-side surface and a convex image-side surface, and the fourth refractive lens 2638 is a positive lens with a convex object-side surface and a concave image-side surface. In other embodiments, other curvatures for the lenses, different thicknesses for the lenses, different spacing between the lenses, fabrication of the lenses from materials with different refractive indices, or the like can be utilized as needed for a particular application.

[0223] Referring again to FIG. 26, a medium stage polarizer (MSP) 2642 is utilized for contrast enhancement. The MSP 2642 can be implemented as a combination of two quarter wave plates with a linear polarizer disposed between the two quarter wave plates. As shown in FIG. 26, the MSP 2642 is tilted with respect to the optical axis 2631 of the refractive lens set 2630 such that the reflection from the MSP 2642 will propagate at an angle to the optical axis 2631, rather than on-axis. As a result, the back reflection from the MSP 2642 will not impinge on the internal coupling element 2624. It should be understood that the tilt of the MSP 2642 can be either a clockwise tilt as illustrated in FIG. 26 or a counterclockwise tilt. A compensator 2644 is provided, for example, on top of the reflective spatial light modulator 2650 to provide additional contrast enhancement in conjunction with the reflective spatial light modulator 2650.

[0224] After the light is reflected from the reflective spatial light modulator 2650, it passes back through the compensator 2644 and the MSP 2642 and is collimated by lenses in the refractive lens set 2630 onto the internal coupling element 2624 of the eyepiece waveguide 2620. The internal coupling element 2624 can be implemented as a diffraction grating. In some embodiments, internal coupling elements 2624 associated with different colors, e.g., red, green, and blue, are located on different layers of the eyepiece waveguide 2620. One skilled in the art would recognize many variations, modifications, and alternatives.

[0225] The refractive lens set 2630 thus enables the image projection system 2600 to operate as a pupil imaging system in which light emitted by the illumination source 2610 is reproduced in the internal coupling element 2624 of the eyepiece waveguide 2620. The sub-pupil arrays of the individual light sources contained within the illumination source 2610 are thus reproduced in the internal coupling element 2624 of the eyepiece waveguide 2620. In some embodiments, to achieve high efficiency, the illumination pupil as well as the projection pupil can be offset axially to separate the illumination and projection paths. Thus, as illustrated in FIG. 26, light is emitted by the illumination source 2610 and is incident on the internal coupling element 2624 at different locations along the x-axis and potentially at different positions along the y-axis, thereby offsetting the propagation axes of the illumination and projection paths in the axial direction, i.e., in a plane that is transverse to the z-direction.

[0226] The embodiments described herein are in contrast to emissive display systems that combine the functionality of the illumination source 2610 and the reflective spatial light modulator 2650 in an emissive display, such as an emissive organic light emitting diode (OLED) display or a micro LED (μLED) display. In systems in which the reflective spatial light modulator 2650 is replaced by an emissive display, the light emitted from the emissive display will make a single pass through the refractive lens set 2630 prior to focusing the light onto the internal coupling element 2624. In contrast, the image projection system 2600 illustrated in FIG. 26 is a pupil imaging system in which the refractive lens set 2630 is designed such that the light emitted by the illumination source 2610 is reproduced in the internal coupling element 2624. As a result, the plane A associated with the illumination source 2610 is reproduced in the plane B associated with the internal coupling element 2624 of the eyepiece waveguide 2620.

[0227] In the embodiment illustrated in FIG. 26 , the first refractive lens 2632, the second refractive lens 2634, the third refractive lens 2636, and the fourth refractive lens 2638 of the refractive lens set 2630 are utilized to refract light, and other than reflections at interfaces which may be reduced using anti-reflective coatings, no substantial reflection or diffraction results from the interaction between the optical elements of the refractive lens set 2630 and light emitted by the illumination source 2610 or reflected from the reflective spatial light modulator 2650.

[0228] FIG. 27 is a simplified schematic diagram illustrating a cross-sectional view of a compact image projection system according to an embodiment of the present invention. The compact image projection system illustrated in FIG. 27 can be utilized in conjunction with the head mounted display system described herein, for example, instead of the optical system 1130 illustrated in FIG. 11A, 11C, 12A, 12B, 13A, 13B, 14A, 14C, 16A, 17-19, 20A-20C, and 20F-20G, and / or the optical system 2320 illustrated in FIG. 23A, 23C, and 24-25. Thus, the compact image projection system described herein can be integrated into any of the head mounted display systems described herein, enabling the head mounted display system to implement a compact design with an improved user experience. The image projection system 2700 in FIG. 27 includes an illumination source 2710 operable to emit light over a range of wavelengths, for example, within the visible spectrum. In some embodiments, a linear polarizer, acting as a linear pre-polarizer, is inserted between the illumination source 2710 and the eyepiece waveguide 2720 to reduce the amount of illumination light in undesired polarizations that impinge on the eyepiece waveguide. Light emitted by the illumination source 2710 propagates through the transparent region 2715 of the eyepiece waveguide 2720, as discussed above in connection with FIG. 26. After passing through the transparent region 2715 of the eyepiece waveguide 2720, the light becomes linearly polarized as the light passes through the linear polarizer 2722.

[0229] In the image projection system 2700, a refractive lens set 2730 is utilized, which includes two refractive lenses. Note that in some embodiments, one or more of the refractive lenses are replaced by reflective optics, e.g., a combination of refractive lenses and reflective optics can be utilized. The side of the elements used in the refractive lens set 2730 that faces the illumination source 2710 can be referred to as the object side surface, and the side of the elements used in the refractive lens set 2730 that faces the reflective spatial light modulator 2750 can be referred to as the image side surface, since the light emitted by the illumination source 2710 is imaged onto the reflective spatial light modulator 2750. The curvature and refractive index of the lenses in the refractive lens set 2730 are therefore selected to image the light emitted from the illumination source 2710 onto the reflective spatial light modulator 2750, which can be implemented, for example, as a liquid crystal on silicon (LCoS) display. As described more fully herein, the refractive lens set 2730 performs several functions, including: 1) Illuminate the reflective spatial light modulator 2750. 2) Re-images the illumination pupil into the internal coupling element 2724 of the eyepiece waveguide 2720, thereby providing high quality pupil imaging enabling a highly efficient system. 3) Providing a high level of projector MTF performance from the reflective spatial light modulator to the internal coupling element.

[0230] As illustrated in FIG. 27, the refractive lens set 2730 includes a first refractive lens 2732 and a second refractive lens 2734. In some embodiments, the first refractive lens 2732 is a positive lens with a convex object-side surface and a convex image-side surface, and the second refractive lens 2734 is a negative lens with a concave object-side surface and a convex image-side surface. In other embodiments, other curvatures for the lenses, including both spherical and aspheric curvatures, freeform surfaces, different thicknesses for the lenses, different spacing between lenses, fabrication of lenses from materials with different refractive indices, holographic elements, diffractive optical elements, or the like, can be utilized as needed for a particular application. While the refractive lens set 2730 utilizes two refractive elements, other embodiments can incorporate additional refractive elements as needed for a particular application.

[0231] 27, the object-side surface 2731 of the first refractive lens 2732 is formed as a reflective polarizer, thereby reflecting a predetermined polarization state in a manner similar to an interface in a polarizing beam splitter. By aligning the transmission axis of the linear polarizer 2722 and the transmission axis of the reflective polarizer present on the object-side surface 2731, the light transmitted through the linear polarizer 2722 passes through the object-side surface 2731 and makes a first pass through the first refractive lens set 2730. The image-side surface 2733 of the first refractive lens 2732 and the object-side surface 2735 of the second refractive lens 2734 are anti-reflective coated in some embodiments to reduce the reflectivity at these interfaces. A quarter-wave plate 2745 is positioned between the first refractive lens 2732 and the second refractive lens 2734. The quarter-wave plate 2745 converts the incident linearly polarized light into circularly polarized light, which thus impinges on the object-side surface 2735, passes through the object-side surface 2735, and impinges on the image-side surface 2737. In the embodiment illustrated in FIG. 27, the image-side surface 2737 is a partial reflector, e.g., a half mirror, that reflects approximately half of the light incident on the image-side surface 2737. A partial reflector, such as a half mirror, can be implemented, for example, by deposition of a thin layer of a reflective material, such as aluminum, on the object-side surface 2735. In other embodiments, a dielectric stack can be utilized to implement a partial reflector on the image-side surface 2737. Because reflectivity will generally be a function of wavelength, it should be understood that the terms "partial reflector" and "half mirror" as used herein include optical structures that reflect substantially half of the incident light over a range of wavelengths, i.e., 50% average transmission over that range of wavelengths, as well as other structures that partially reflect the incident light. Additionally, the terms "partial reflector" and "half mirror" include optical structures that reflect light within a range of about 50% reflectivity, including 40%-60%. Those skilled in the art will recognize many variations, modifications, and alternatives.

[0232] The light reflected from the image-side surface 2737 will be directed towards the illumination source 2710 and will make a second pass through the refractive lens set 2730. Thus, this reflected light propagating through the object-side surface 2735 will be converted from circularly polarized light to linearly polarized light oriented at 90° to the polarization state after passing through the linear polarizer 2722 and will pass through the image-side surface 2733 where it will be reflected from the reflective polarizer onto the object-side surface 2731. After reflection from the object-side surface 2731, the reflected light will propagate towards the reflective spatial light modulator 2750 and will make a third pass through the refractive lens set 2730. In response to this third pass, the light passing through the image-side surface 2733 is converted to circularly polarized light by the quarter-wave plate 2745 and passes through the object-side surface 2735, and half of the incident light passes through the image-side surface 2737 in response to this third pass because the image-side surface 2737 is a partial reflector. A second quarter-wave plate 2747 is positioned between the second refractive lens 2734 and the reflective spatial light modulator 2750, and the light propagating through the second quarter-wave plate 2747 is converted to linearly polarized light having a polarization state that is aligned with the polarization state after passing through the linear polarizer 2722 after transmission through the image-side surface 2737. This linearly polarized light impinges on the reflective spatial light modulator 2750.

[0233] After reflection from the reflective spatial light modulator 2750, encoding the image onto the light provided by the illumination source 2710, the encoded light will make three more passes through the refractive lens set 2730 in a manner similar to the three passes made by the illumination light propagating to the reflective spatial light modulator 2750. Referring again to FIG. 27, the light reflected from the reflective spatial light modulator 2750 is converted to circularly polarized light by the second quarter-wave plate 2747, and half of the circularly polarized light is transmitted through the image-side surface 2737, the object-side surface 2735, and the image-side surface 2733 and converted to linearly polarized light by the quarter-wave plate 2745. The polarization state of this linearly polarized light is oriented 90° with respect to the transmission axis of the reflective polarizer of the object-side surface 2731, resulting in the reflection of this light for a fifth pass through the refractive lens set 2730.

[0234] During the fifth pass, the light passing through the image-side surface 2733 and the object-side surface 2735 is converted to circularly polarized light and partially reflects from the image-side surface 2737. After reflection from the image-side surface 2737, the reflected light makes a sixth pass through the refractive lens set 2730 towards the illumination source 2710. Upon passing through the object-side surface 2735 and the image-side surface 2733, the light is converted to linearly polarized light that is aligned with the transmission axes of the reflective polarizer and the linear polarizer 2722 on the object-side surface 2731, thereby passing through the object-side surface 2731 and the linear polarizer 2722 and impinging on the internal coupling element 2724 of the eyepiece waveguide 2720.

[0235] The internal coupling element 2724 can be implemented as a diffraction grating. In some embodiments, internal coupling elements 2724 associated with different colors, e.g., red, green, and blue, are positioned on different layers of the eyepiece waveguide 2720. One skilled in the art would recognize many variations, modifications, and alternatives.

[0236] The refractive lens set 2730 thus enables the image projection system 2700 to operate as a pupil imaging system in which light emitted by the illumination source 2710 is imaged onto the reflective spatial light modulator 2750 and propagates to the internal coupling element 2724 of the eyepiece waveguide 2720. The sub-pupil arrays of the individual light sources contained within the illumination source 2710 are thus reproduced in the internal coupling element 2724 of the eyepiece waveguide 2720. In some embodiments, to achieve high efficiency, the illumination pupil as well as the projection pupil can be offset axially to separate the illumination and projection paths. Thus, as illustrated in FIG. 27, light is emitted by the illumination source 2710 and is incident on the internal coupling element 2724 at different locations along the x-axis and potentially at different positions along the y-axis, thereby offsetting the propagation axes of the illumination and projection paths in the axial direction, i.e., in a plane that is transverse to the z-direction.

[0237] The embodiments described herein are in contrast to emissive display systems that combine the functionality of the illumination source 2710 and the reflective spatial light modulator 2750 in an emissive display, such as an emissive organic light emitting diode (OLED) display. In systems in which the reflective spatial light modulator 2750 is replaced by an emissive display, light emitted from the emissive display will make a single pass through the refractive lens set 2730 before impinging on the internal coupling element 2724. In contrast, the image projection system 2700 illustrated in FIG. 27 is a pupil imaging system in which the refractive lens set 2730 is designed such that the light emitted by the illumination source 2710 is coupled into the internal coupling element 2724. As a result, the plane A associated with the illumination source 2710 is reproduced in the plane B associated with the internal coupling element 2724 of the eyepiece waveguide 2720.

[0238] FIG. 28 is a non-folded optical path schematic corresponding to the compact image projection system illustrated in FIG. 27. In the non-folded optical path schematic shown in FIG. 28, optical elements and optical interfaces are illustrated. Light from the illumination source 2810 propagates through a transparent region of the eyepiece waveguide (not shown) toward the linear polarizer 2812, which linearly polarizes the illumination light. The polarized light is transmitted through the reflective polarizer because the polarization state of the linearly polarized light and the reflective polarizer are aligned. The polarized light propagates through a quarter-wave plate 2814, which converts the linearly polarized light to circularly polarized light. The light completes a first pass through the refractive lens set by reflecting off a partial reflector 2816.

[0239] The second pass through the refractive lens set includes propagation through a quarter-wave plate 2814, which converts the circularly polarized light to linearly polarized light with a polarization state perpendicular to the polarization state transmitted by the reflective polarizer 2818, which reflects the light after the second pass through the refractive lens set.

[0240] The third pass through the refractive lens set includes propagation through a quarter-wave plate 2814, which converts the linearly polarized light to circularly polarized light, and propagation through a partial reflector and a second quarter-wave plate 2820 before reflection from a spatial light modulator 2822, which encodes the illumination light.

[0241] After reflection from the spatial light modulator 2822, the encoded light propagates through a second quarter wave plate 2820, a partial reflector, and the quarter wave plate 2814 before reflecting from a reflective polarizer 2818 at the end of the fourth pass through the refractive lens set. The fifth pass involves propagation through the quarter wave plate 2814 and reflection from a partial reflector 2816, and the sixth pass involves propagation through the quarter wave plate 2814 and the reflective polarizer before transmission through a linear polarizer and impingement on the internal coupling optical element 2824 of the eyepiece waveguide.

[0242] 29 is a simplified flowchart illustrating a method of operating a compact image projection system according to an embodiment of the present invention. The method 2900 includes generating illumination light (2910) and linearly polarizing the illumination light (2912). The linearly polarized light is transmitted (2914) through an eyepiece waveguide and refracted by a first refractive lens. The front surface, i.e., the surface facing the illumination source and the eyepiece waveguide, is a reflective polarizer, and the input polarization provided by the linear polarizer is aligned with the transmission axis of the reflective polarizer, so that the light is transmitted through the reflective polarizer and onto the front surface of the first refractive lens during this first pass. Continuing on the first pass, the light passes through a quarter wave plate, converting the linearly polarized light to circularly polarized light, and as it passes through the second refractive lens, it is refracted and reflected by the back surface, i.e., the surface of the second refractive lens facing the spatial light modulator, which is a partial reflector (2916).

[0243] During the second pass, the portion of the light reflected by the partial reflector propagates through a quarter-wave plate, converting the circularly polarized light to linearly polarized light, such that the light incident on the reflective polarizer is again linearly polarized, but with a polarization perpendicular to the input polarization. Given this orthogonal linear polarization state, the light is now reflected by the reflective polarizer at the front surface of the first refractive lens towards the spatial light modulator (2918).

[0244] The reflected light makes a third pass through the refractive lens set, including a pass through a first refractive lens, a quarter wave plate, and a second refractive lens, and a portion of the light is transmitted by a partial reflector onto the back surface of the second refractive lens. The combination of refractive lenses focuses the remaining illumination light onto the spatial light modulator, which encodes the illumination light (2920). As will be apparent to one skilled in the art, only a certain percentage of the initial illumination light is present at the spatial light modulator. Thus, discussion of encoding the illumination light is intended to involve encoding the percentage present at the spatial light modulator, rather than all of the illumination light. Similarly, references to light at various optical elements are intended to communicate the percentage of light present at a particular optical element.

[0245] A second quarter wave plate is disposed between the second refractive lens and the spatial light modulator. This second quarter wave plate enables the light reflected from the spatial light modulator to have the same polarization as the input polarization. During the fourth pass through the refractive lens set, the light is transmitted through a partial reflector, propagates through the quarter wave plate, and is reflected from the reflective polarizer (2922). The fifth pass includes propagation through the quarter wave plate and reflection from the partial reflector (2924). After the sixth pass through the refractive lens set, which includes propagation through the quarter wave plate and transmission through the reflective polarizer, the remaining light is coupled into the eyepiece waveguide via an internal coupling optical element (2926).

[0246] It should be understood that the specific steps illustrated in FIG. 29 provide a particular method of operating a compact image projection system according to an embodiment of the present invention. Other sequences of steps may also be performed in accordance with alternative embodiments. For example, alternative embodiments of the present invention may perform the steps outlined above in a different order. Furthermore, individual steps illustrated in FIG. 29 may include multiple sub-steps that may be performed in various sequences, depending on the needs of the individual step. Furthermore, additional steps may be added or removed depending on the particular application. Those skilled in the art will recognize numerous variations, modifications, and alternatives.

[0247] Fig. 30 is a simplified schematic diagram illustrating a cross-sectional view of a compact image projection system according to another embodiment of the present invention. The image projection system 3000 in Fig. 30 includes an illumination source 3010 operable to emit light over a range of wavelengths, e.g., in the visible spectrum. Some of the optical elements illustrated in Fig. 30 share common features with the optical elements illustrated in Fig. 27, and the description provided in relation to Fig. 27 is applicable to Fig. 30, as appropriate.

[0248] Light emitted by the illumination source 3010 propagates through the transparent portion 3015 of the eyepiece waveguide 3020, as discussed above in connection with Figures 26 and 27. In some embodiments, a linear polarizer, acting as a linear pre-polarizer, is inserted between the illumination source 3010 and the eyepiece waveguide 3020 to reduce the amount of illumination light in undesired polarizations impinging on the eyepiece waveguide. After passing through the transparent portion 3015 of the eyepiece waveguide 3020, the light is circularly polarized by the quarter-wave plate 3022. The object-side surface 3031 of the first refractive lens 3032 is formed as a partial reflector. Thus, half of the light incident on the object-side surface 3031 is reflected and half is transmitted to make a first pass through the refractive lens set 3030. The image-side surface 3033 of the first refractive lens 3032 and the object-side surface 3035 of the second refractive lens 3034 are in some embodiments anti-reflection coated to reduce the reflectivity at these interfaces. A quarter-wave plate 3045 is positioned between the first refractive lens 3032 and the second refractive lens 3034. The quarter-wave plate 3045 converts the incident circularly polarized light into linearly polarized light, which thus impinges on, passes through, and impinges on the image-side surface 3037.

[0249] The image-side surface 3037 is formed as a reflective polarizer. The polarization of the light produced by the quarter-wave plate 3045 is oriented at 90° to the transmission axis of the reflective polarizer. Thus, light incident on the image-side surface 3037 is reflected from the image-side surface 3037 for a second passage through the refractive lens set 3030. As the light passes through the object-side surface 3035, the quarter-wave plate 3045, and the image-side surface 3033, the linearly polarized light is converted to circularly polarized light, which is partially reflected from the partial reflector associated with the object-side surface 3031.

[0250] After reflection from the object-side surface 3031, the reflected light makes a third pass through the refractive lens set 3030, passes through the image-side surface 3033, is converted to linearly polarized light that is aligned with the transmission axis of the reflective polarizer on the image-side surface 3037, passes through the object-side surface 3035, and due to the alignment of the polarization states, passes through the image-side surface 3037.

[0251] After reflection from the spatial light modulator 3050, encoding the image onto the light provided by the illumination source 3010, the encoded light will make three more passes through the refractive lens set 3030 in a manner similar to the three passes made by the illumination light propagating to the spatial light modulator 3050. Referring again to FIG. 30, the light reflected from the spatial light modulator 3050 passes through the image-side surface 3037, is converted to circularly polarized light by the quarter-wave plate 3045, and reflects partially from the partial reflector onto the object-side surface 3031. During the fifth pass, the reflected light is converted to circularly polarized light by the quarter-wave plate 3045, transmitted through the object-side surface 3035 and the image-side surface 3033, and converted to linearly polarized light by the quarter-wave plate 3045. This linearly polarized light is oriented at 90° with respect to the transmission axis of the reflective polarizer associated with the image-side surface 3037. Thus, light incident on the image-side surface 3037 is reflected from the image-side surface 3037 for passage to the sixth through the refractive lens set 3030. As the light passes through the object-side surface 3035, the quarter-wave plate 3045, which converts linearly polarized light to circularly polarized light, and the image-side surface 3033, the light is partially transmitted through a partial reflector associated with the object-side surface 3031. The light transmitted through the partial reflector is incident on the internal coupling element 3024 of the eyepiece waveguide 3020.

[0252] FIG. 31 is a non-folded optical path schematic corresponding to the compact image projection system illustrated in FIG. 30. In the non-folded optical path schematic shown in FIG. 31, optical elements and optical interfaces are illustrated. Light from the illumination source 3110 propagates through a transparent region (not shown) of the eyepiece waveguide towards the circular polarizer 3112, which circularly polarizes the illumination light. The circularly polarized light is transmitted through a partial reflector and converted by a quarter wave plate 3114 to linearly polarized light, which is incident on the reflective polarizer 3116. Because the polarization state of the linearly polarized light and the reflective polarizer 3116 are perpendicular, the linearly polarized light is reflected by the reflective polarizer 3116 and begins its second pass through the refractive lens set.

[0253] The second pass through the refractive lens set includes propagation through a quarter-wave plate 3114, which converts the circularly polarized light to linearly polarized light, and reflection from a partial reflector 3118.

[0254] The third pass through the refractive lens set includes propagation through a quarter-wave plate 3114, which converts the circularly polarized light to linearly polarized light, and propagation through a reflective polarizer, as the polarization state of the linearly polarized light and the reflective polarizer are aligned prior to reflection from the spatial light modulator 3120, which encodes the illumination light.

[0255] After reflection from the spatial light modulator 3120, the encoded light propagates through a reflective polarizer and quarter wave plate 3114, which converts the linearly polarized light to circularly polarized light at the end of the fourth pass through the refractive lens set, before reflection from the partial reflector 3118. The fifth pass involves propagation through the quarter wave plate 3114 and reflection from the reflective polarizer 3116, and the sixth pass involves transmission through a circular polarizer and propagation through the quarter wave plate 3114 and partial reflector prior to impingement on the internal coupling optical element 3122 of the eyepiece waveguide.

[0256] Fig. 32 is a simplified flow chart illustrating a method of operating a compact image projection system according to another embodiment of the present invention. The method 3200 illustrated in Fig. 32 shares common elements with the method 2900 illustrated in Fig. 29, and the description provided in relation to Fig. 29 is applicable to Fig. 32, where appropriate.

[0257] The method 3200 includes generating illumination light (3210) and circularly polarizing the illumination light (3212). The illumination light can be provided by a plurality of light sources arrayed in a sub-pupil configuration. A linear polarizer can be used in combination with a second quarter-wave plate to generate the circularly polarized light. The method also includes transmitting the illumination light through a transparent region of the eyepiece waveguide (3214). The circularly polarized light makes a first pass through a refractive lens set, is partially transmitted through a partial reflector, is converted to linear polarization by the quarter-wave plate, and reflects from a reflective polarizer (3216), which can be on a back surface of the second refractive lens facing the spatial light modulator.

[0258] The method further includes converting the illumination light to circularly polarized light and reflecting a portion of the illumination light from a partial reflector, which may be disposed on a surface of the first optical element (e.g., a refractive lens) facing the eyepiece waveguide (3218). After reflection, the reflected light makes a third pass through a refractive lens set and is encoded in a spatial light modulator to provide the encoded light (3220).

[0259] After encoding, the encoded light is transmitted through a reflective polarizer and converted to linearly polarized light using a quarter wave plate. Then, at the end of this fourth pass through the refractive lens set, the method includes reflecting a portion of the encoded light off the partial reflector (3222). The method also includes converting the reflected light to linearly polarized light and reflecting a portion of the encoded light off the reflective polarizer (3224), which enables a sixth pass through the refractive lens set before coupling a portion of the encoded light into the eyepiece waveguide (3226).

[0260] It should be understood that the specific steps illustrated in FIG. 31 provide a particular method of operating a compact image projection system according to an embodiment of the present invention. Other sequences of steps may also be performed in accordance with alternative embodiments. For example, alternative embodiments of the present invention may perform the steps outlined above in a different order. Furthermore, the individual steps illustrated in FIG. 31 may include multiple sub-steps that may be performed in various sequences, depending on the needs of the individual step. Furthermore, additional steps may be added or removed depending on the particular application. Those skilled in the art will recognize numerous variations, modifications, and alternatives.

[0261] 27 and 30 utilize refractive elements, non-refractive, reflective, optical elements may also be utilized in place of the first or second refractive lenses in implementations in which the first or second refractive lenses include partial reflectors. Additionally, the refractive lenses discussed herein may be replaced by diffractive optical elements, volumetric holograms, nanostructured metalenses, or the like. Those skilled in the art will recognize many variations, modifications, and alternatives.

[0262] In the foregoing specification, the disclosure has been described with reference to specific embodiments thereof. It will be apparent, however, that various modifications and changes can be made therein without departing from the broader spirit and scope of the disclosure. The specification and drawings are therefore to be regarded in an illustrative rather than a restrictive sense.

[0263] Indeed, it should be understood that the systems and methods of the present disclosure each have several innovative aspects, none of which is solely responsible for or required for the desirable attributes disclosed herein. The various features and processes described above may be used independently of one another or may be combined in various ways. All possible combinations and subcombinations are intended to fall within the scope of the present disclosure.

[0264] Certain features described herein in the context of separate embodiments may also be implemented in combination in a single embodiment. Conversely, various features described in the context of a single embodiment may also be implemented in multiple embodiments separately or in any suitable subcombination. Furthermore, although features may be described above as acting in a combination and may even be initially claimed as such, one or more features from the claimed combination may in some cases be deleted from the combination, and the claimed combination may be directed to a subcombination or variation of the subcombination. No single feature or group of features is necessary or essential to every embodiment.

[0265] In particular, it should be understood that conditional statements used herein, such as "can," "could," "might," "may," "eg," and the like, are generally intended to convey that certain embodiments include certain features, elements, and / or steps, while other embodiments do not, unless specifically stated otherwise or understood otherwise within the context as used. Thus, such conditional statements are generally not intended to suggest that features, elements, and / or steps are in any way required for one or more embodiments, or that one or more embodiments necessarily include logic for determining whether those features, elements, and / or steps should be included or performed in any particular embodiment, with or without authorial input or prompting. The terms "comprise," "include," "have," and the like, are synonymous and used inclusively in a non-limiting manner and do not exclude additional elements, features, acts, operations, etc. Also, the term "or" is used in its inclusive sense (and not its exclusive sense), thus, for example, when used to connect a list of elements, the term "or" means one, some, or all of the elements in the list. In addition, the articles "a," "an," and "the," as used in this application and the appended claims, should be interpreted to mean "one or more" or "at least one," unless otherwise specified. Similarly, although operations may be depicted in the figures in a particular order, it should be recognized that such operations need not be performed in the particular order depicted, or in sequential order, or that all of the depicted operations need not be performed to achieve desirable results. Additionally, the figures may diagrammatically depict one or more exemplary processes in the form of a flow chart. However, other operations not depicted may also be incorporated within the diagrammatically depicted exemplary methods and processes. For example, one or more additional operations may be performed before, after, simultaneously with, or during any of the depicted operations.In addition, operations may be rearranged or reordered in other embodiments. In some situations, multitasking and parallel processing may be advantageous. Furthermore, the separation of various system components in the embodiments described above should not be understood as requiring such separation in all embodiments, and it should be understood that the program components and systems described may generally be integrated together in a single software product or packaged into multiple software products. Additionally, other implementations are within the scope of the following claims. In some cases, the actions recited in the claims may be performed in a different order and still achieve desirable results.

[0266] Thus, the claims are not intended to be limited to the embodiments shown herein but are to be accorded the widest scope consistent with the present disclosure, the principles and novel features disclosed herein.

Claims

1. 1. An image projection system, comprising: An illumination source; an eyepiece waveguide including a plurality of diffractive incoupling optical elements, the eyepiece waveguide including a region operable to transmit light from the illumination source; a first optical element including a reflective polarizer; a second optical element including a partial reflector; a first quarter-wave plate disposed between the first optical element and the second optical element; A reflective spatial light modulator; a second quarter-wave plate disposed between the second optical element and the reflective spatial light modulator; 1. An image projection system comprising:

2. The image projection system of claim 1 , wherein the illumination source comprises a plurality of light sources arrayed in a sub-pupil configuration.

3. The image projection system of claim 1 , wherein the illumination source comprises a plurality of light sources, each of the plurality of light sources being aligned along an optical axis.

4. The image projection system of claim 1 , further comprising a linear polarizer disposed between the illumination source and the eyepiece waveguide.

5. The image projection system of claim 1 , wherein the first optical element comprises a refractive lens.

6. The image projection system of claim 5 , wherein the reflective polarizer is disposed on a surface of the refractive lens facing the eyepiece waveguide.

7. The image projection system of claim 6 , wherein the refractive lens includes an anti-reflective coated surface.

8. The image projection system of claim 1 , wherein the first optical element comprises a mirror.

9. The image projection system of claim 1 , wherein the second optical element comprises a refractive lens.

10. The image projection system of claim 9 , wherein the partial reflector is disposed on a surface of the refractive lens facing the reflective spatial light modulator.

11. 2. The image projection system of claim 1, wherein the illumination light emitted by the illumination source propagates along a first axial direction and encoded light is incident on the plurality of diffractive internal coupling optical elements along a second axial direction that is parallel to and laterally offset from the first axial direction.

12. 1. A method of operating an optical projection system, the method comprising: Producing illumination light; linearly polarizing the illumination light; transmitting the illumination light through an eyepiece waveguide; reflecting a portion of the illumination light from a partial reflector; reflecting a portion of the illumination light from a reflective polarizer; encoding the reflected light in a reflective spatial light modulator to provide encoded light; reflecting the encoded light from the reflective polarizer; reflecting a portion of the encoded light from the partial reflector; coupling a portion of the encoded light into the eyepiece waveguide; and A method comprising:

13. Prior to reflecting a portion of the illumination light from the partial reflector, transmitting the illumination light through a reflective polarizer; converting the illumination light into circularly polarized light; The method of claim 12 further comprising:

14. 13. The method of claim 12, further comprising converting the portion of the illumination light to linearly polarized light prior to reflecting the portion of the illumination light from the reflective polarizer.

15. prior to reflecting the encoded light from the reflective polarizer; converting the encoded light into circularly polarized light; transmitting the encoded light through the partial reflector; The method of claim 12 further comprising:

16. 13. The method of claim 12, further comprising converting the encoded light to circularly polarized light prior to reflecting a portion of the encoded light from the partial reflector.

17. The method of claim 12 , wherein the reflective polarizer is disposed on a surface of a first optical element facing the eyepiece waveguide.

18. The method of claim 12 , wherein the partial reflector is disposed on a surface of a second optical element facing the reflective spatial light modulator.

19. The method of claim 12 , wherein generating the illumination light comprises generating light from a plurality of light sources arrayed in a sub-pupil configuration.

20. the reflective polarizer is disposed on a surface of the first optical element facing the eyepiece waveguide; the partial reflector is disposed on a surface of a second optical element facing the reflective spatial light modulator. The method of claim 12.

21. 21. The method of claim 20, wherein the first optical element comprises a first refractive lens and the second optical element comprises a second refractive lens.

22. 1. An image projection system, comprising: An illumination source; an eyepiece waveguide including a plurality of diffractive incoupling optical elements, the eyepiece waveguide including a region operable to transmit light from the illumination source; a first quarter wave plate disposed between the illumination source and the eyepiece waveguide; a first optical element including a partial reflector; a second optical element including a reflective polarizer; a second quarter-wave plate disposed between the first optical element and the second optical element; and Reflective spatial light modulator 1. An image projection system comprising:

23. 23. The image projection system of claim 22, wherein the illumination source comprises a plurality of light sources arrayed in a sub-pupil configuration.

24. 23. The image projection system of claim 22, wherein the illumination source comprises a plurality of light sources, each of the plurality of light sources aligned along an optical axis.

25. 23. The image projection system of claim 22, further comprising a linear polarizer disposed between the illumination source and the first quarter wave plate.

26. 23. The image projection system of claim 22, wherein the first optical element comprises a refractive lens.

27. 27. The image projection system of claim 26, wherein the partial reflector is disposed on a surface of the refractive lens facing the eyepiece waveguide.

28. 23. The image projection system of claim 22, wherein the second optical element comprises a refractive lens.

29. 30. The image projection system of claim 28, wherein the reflective polarizer is disposed on a surface of the refractive lens facing the reflective spatial light modulator.

30. 30. The image projection system of claim 29, wherein the refractive lens includes an anti-reflective coated surface.

31. 23. The image projection system of claim 22, wherein the first optical element comprises a mirror.

32. 1. A method of operating an optical projection system, the method comprising: Producing illumination light; circularly polarizing the illumination light; transmitting the illumination light through an eyepiece waveguide; reflecting the illumination light from a reflective polarizer; reflecting a portion of the illumination light from a partial reflector; encoding the reflected light in a reflective spatial light modulator to provide encoded light; reflecting a portion of the encoded light from the partial reflector; reflecting a portion of the encoded light from the reflective polarizer; coupling a portion of the encoded light into the eyepiece waveguide; and A method comprising:

33. Prior to reflecting the illumination light off the reflective polarizer, transmitting the illumination light through the partial reflector; converting a portion of the illumination light into linearly polarized light; 33. The method of claim 32, further comprising:

34. 33. The method of claim 32, further comprising converting the illumination light to circularly polarized light prior to reflecting a portion of the illumination light from the partial reflector.

35. prior to reflecting a portion of the encoded light from the partial reflector; transmitting the encoded light through the reflective polarizer; converting the encoded light into linearly polarized light; 33. The method of claim 32, further comprising:

36. 33. The method of claim 32, further comprising converting the encoded light to linearly polarized light prior to reflecting the encoded light from the reflective polarizer.

37. 33. The method of claim 32, wherein the partial reflector is disposed on a surface of a first optical element facing the eyepiece waveguide.

38. The method of claim 32 , wherein the reflective polarizer is disposed on a surface of a second optical element facing the reflective spatial light modulator.

39. The method of claim 32 , wherein generating the illumination light comprises generating light from a plurality of light sources arrayed in a sub-pupil configuration.

40. the partial reflector is disposed on a surface of the first optical element facing the eyepiece waveguide; the reflective polarizer is disposed on a surface of a second optical element facing the reflective spatial light modulator; 33. The method of claim 32.

41. 41. The method of claim 40, wherein the first optical element comprises a first refractive lens and the second optical element comprises a second refractive lens.

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