Augmented reality display with a waveguide configured to capture images of the eye and / or the environment

Abstract

To provide a suitable augmented reality display with a waveguide configured to capture images of the eye and / or the environment. A head-mounted display system can include a camera, at least one waveguide, at least one coupling optical element configured to couple light into and guide it therein, and at least one out-coupling element. The at least one out-coupling element can be configured to couple light guided in the waveguide out of the waveguide and direct the light to the camera. The camera is positioned in an optical path with respect to the at least one out-coupling optical element so that an image can be captured by the camera, and can receive at least a portion of the light coupled into and guided in the waveguide via the coupling element and coupled out of the waveguide by the out-coupling element.

Description

[Technical Field]

[0001] (CROSS-REFERENCE TO RELATED APPLICATIONS) This application claims the benefit of priority under 35 U.S.C. § 119(e) to U.S. Provisional Application No. 62 / 561,645, filed September 21, 2017, and entitled "AUGUMENTED REALITY DISPLAY WITH EYEPIECE CONFIGURED TO CAPTURE IMAGES OF EYE AND ENVIRONMENT," which is incorporated herein by reference in its entirety.

[0002] The present disclosure relates to optical devices, including augmented reality imaging and visualization systems. [Background technology]

[0003] 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 user 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 input, while augmented reality or "AR" scenarios typically involve the presentation of digital or virtual image information as an augmentation to the user's visualization of the real world around them. Mixed reality or "MR" scenarios are a type of AR scenario that typically involve virtual objects integrated into and responsive to the natural world. For example, MR scenarios may include AR image content that appears blocked by or is perceived to otherwise interact with objects in the real world.

[0004] Referring 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, a building 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 produce AR technology that facilitates a comfortable, natural-feeling, and rich presentation of virtual image elements among other virtual or real-world image elements.

[0005] The systems and methods disclosed herein address various challenges associated with AR or VR technology.

[0006] Polarizing beam splitters may be used in display systems to direct polarized light to a light modulator, which then directs this light to a viewer. Generally, there is a continuing demand to reduce the size of display systems, and consequently, there is also a demand to reduce the size of display system components, including components that utilize polarizing beam splitters. Summary of the Invention [Means for solving the problem]

[0007] Various implementations described herein include a display system configured to provide illumination and / or image projection to the eye. Additionally or alternatively, the display system can image the eye and / or the environment.

[0008] In some embodiments, a head-mounted display system is configured to project light into a user's eye and display augmented reality image content within the user's field of view. The head-mounted display system may include a frame configured to be supported on the user's head. The display system may also include an image projector configured to project an image into the user's eye and display image content within the user's field of view. The display system may include a camera, at least one waveguide, at least one coupling optical element configured to couple light into and guide it therein, and at least one external coupling element. The at least one external coupling element may be configured to couple light guided in the waveguide out of the waveguide and direct the light toward the camera. The camera is disposed in an optical path relative to the at least one external coupling optical element and may receive at least a portion of the light coupled into and guided in the waveguide via the coupling element and coupled out of the waveguide by the external coupling element so that an image may be captured by the camera. The present invention provides, for example, the following. (Item 1) 1. A head mounted display system configured to project light onto a user's eye and display augmented reality image content within the user's field of view, the head mounted display system comprising: a frame configured to be supported on the user's head; and an image projector configured to project an image into the user's eye and display image content within the user's field of view; A camera and at least one waveguide; at least one coupling optical element, the at least one coupling optical element configured to couple light into the waveguide and guide it therein; at least one external coupling element configured to couple light guided within the waveguide out of the waveguide and direct the light to the camera; Equipped with A head-mounted display system, wherein the camera is positioned in an optical path with respect to the at least one external coupling optical element so that an image can be captured by the camera, and receives at least a portion of the light that is coupled into the waveguide via the coupling element, guided therein, and coupled out of the waveguide by the external coupling element. (Item 2) Item 1. The system of item 1, wherein the at least one coupling optical element is configured to couple light from an environment in front of the user wearing the head-mounted display system into and guide it within the at least one waveguide so that an image of the environment can be captured by the camera. (Item 3) Item 10. The system of claim 1, wherein the at least one coupling optical element is configured to couple light reflected from the eye of the user wearing the head-mounted display system into and guide it within the at least one waveguide so that an image of the eye can be captured by the camera. (Item 4) Item 10. The system of claim 1, wherein the at least one coupling optical element is configured to couple and guide light reflected from the eye of the user wearing the head-mounted display system into the waveguide so that an image of the eye can be captured by the camera, and the system is configured to image a front portion of the eye. (Item 5) Item 10. The system of claim 1, wherein the at least one coupling optical element is configured to couple and guide light reflected from the eye of the user wearing the head-mounted display system into the waveguide so that an image of the eye can be captured by the camera, and the system is configured to image the corneal surface of the eye. (Item 6) Item 1, the system of claim 1, wherein the at least one coupling optical element is configured to couple and guide light reflected from the eye of the user wearing the head-mounted display system into the waveguide so that an image of the eye can be captured by the camera, and the system is configured to image the retina of the user's eye. (Item 7) Item 10. The system of item 1, further comprising an eyepiece disposed on the frame, the eyepiece configured to direct light into the user's eye and display augmented reality image content in the user's field of view, at least a portion of the eyepiece being transparent and positioned in a location directly in front of the user's eye when the user wears the head-mounted display, the transparent portion allowing light from an environment in front of the user to pass through to the user's eye and provide a view of the environment in front of the user. (Item 8) Item 8. The system of item 7, wherein the eyepiece is configured to receive light from the image projector, direct the light into the user's eye, and display augmented reality image content in the user's field of view. (Item 9) 8. The system of claim 7, wherein the eyepiece comprises the at least one waveguide. (Item 10) Item 8. The system of item 7, wherein the image projector is configured to direct light into the edge of the eyepiece. (Item 11) Item 10. The system of item 9, wherein the image projector is configured to direct light into an edge of the at least one waveguide. (Item 12) Item 10. The system of item 1, further comprising at least one internal coupling optical element configured to internally couple light from the image projector into the at least one waveguide so as to guide the light from the image projector to provide the image content to the user's eye. (Item 13) Item 10. The system of item 1, wherein the at least one coupling optical element is also configured to couple light from the image projector guided within the waveguide out of the at least one waveguide so that image content can be viewed by a user's eye. (Item 14) 2. The system of claim 1, wherein the same coupling optical element is configured to couple light from the image projector guided within the waveguide out of the waveguide so that image content can be viewed by a user's eye, and to couple light into the at least one waveguide to be guided within the at least one waveguide to the camera. (Item 15) Item 10. The system of item 1, further comprising at least one image content outcoupling optical element configured to couple light from the image projector guided within the waveguide out of the at least one waveguide so that the image content can be viewed by a user's eye. (Item 16) Item 10. The system of item 1, wherein the at least one coupling optical element faces the eye of the user wearing the head-mounted imaging system and receives light from the eye. (Item 17) Item 10. The system of claim 1, wherein the at least one coupling optical element is configured to couple light from an environment in front of the user wearing the head-mounted imaging system into the at least one waveguide and guide it within the at least one waveguide so that an image of the environment can be captured by the camera. (Item 18) Item 1. The system of item 1, wherein the at least one coupling optical element faces the environment in front of the user wearing the head-mounted imaging system and receives light from the environment. (Item 19) Item 16. The system of item 15, wherein the at least one image content outcoupling optical element configured to couple light from the image projector guided within the waveguide out of the at least one waveguide, and at least one coupling optical element configured to couple the light into the waveguide and guide it within the waveguide to the camera, are superimposed on top of each other. (Item 20) Item 16. The system of item 15, wherein the at least one image content outcoupling optical element configured to couple light from the image projector guided within the waveguide out of the at least one waveguide, and at least one coupling optical element configured to couple the light into the waveguide and guide it within the waveguide to the camera, are stacked over one another. [Brief explanation of the drawings]

[0009] [Figure 1] FIG. 1 illustrates a user's view of an augmented reality (AR) device.

[0010] [Figure 2] FIG. 2 illustrates an example of a wearable display system.

[0011] [Figure 3] FIG. 3 illustrates a conventional display system for simulating a three-dimensional image for a user.

[0012] [Figure 4] FIG. 4 illustrates aspects of an approach for simulating a three-dimensional image using multiple depth planes.

[0013] [Figure 5] 5A-5C illustrate the relationship between the radius of curvature and the radius of focus.

[0014] [Figure 6]FIG. 6 illustrates an embodiment of a waveguide stack for outputting image information to a user.

[0015] [Figure 7] FIG. 7 illustrates an example of an output beam output by a waveguide.

[0016] [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.

[0017] [Figure 9A] 9A illustrates a cross-sectional side view of an example of a set of stacked waveguides, each including an internal coupling optical element. As discussed herein, the waveguide stack may comprise an eyepiece.

[0018] [Figure 9B] FIG. 9B illustrates a perspective view of the multiple stacked waveguide embodiment of FIG. 9A.

[0019] [Figure 9C] FIG. 9C illustrates a top-down plan view of the multiple stacked waveguide embodiment of FIGS. 9A and 9B.

[0020] [Figure 10] FIG. 10 diagrammatically illustrates a cross-sectional side view of an exemplary imaging system comprising an eyepiece, an image projector, a light source for illuminating the eye, and a camera for capturing an image of the eye.

[0021] [Figure 11A] FIG. 11A illustrates diagrammatically how both the light source for illuminating the eye and the image projector for projecting an image into the eye emit light toward an internal coupling optical element on the waveguide of the eyepiece.

[0022] [Figure 11B]FIG. 11B illustrates diagrammatically how projected light from a light source and an image projector is coupled into a waveguide.

[0023] [Figure 11C] FIG. 11C illustrates diagrammatically how the internally coupled light can propagate through the waveguide by total internal reflection.

[0024] [Figure 11D] FIG. 11D illustrates diagrammatically how light from the light source and image projector is coupled out through the eyepiece.

[0025] [Figure 11E] 11E schematically illustrates a waveguide and a coupling optical element configured to propagate the intercoupled light at least along all dimensions of the coupling optical element (e.g., along the x-direction). Light entering the eye is shown from an extended source (e.g., imaging light would capture a region of the retina).

[0026] [Figure 12A] FIG. 12A is a cross-sectional view showing a schematic of light reflected from the retina exiting the eye and impinging on the eyepiece.

[0027] [Figure 12B] FIG. 12B diagrammatically illustrates exemplary light being coupled into the waveguide of the eyepiece.

[0028] [Figure 12C] FIG. 12C illustrates diagrammatically how collimated, incoupled light from the eye propagates through a waveguide toward an imaging device.

[0029] [Figure 12D] FIG. 12D shows a schematic of how incoupled light from the eye propagates to one or more outcoupling optical elements.

[0030] [Figure 12E]FIG. 12E diagrammatically illustrates how light from the eye is coupled out of the waveguide by an outcoupling optical element and directed to a camera so that an image of the eye (e.g., the retina) can be captured by the camera.

[0031] [Figure 13A] FIG. 13A diagrammatically illustrates how an imaging system can image various portions of the eye, e.g., the retina, which can allow the orientation of the eye to be determined and the eye position to be tracked.

[0032] [Figure 13B] 13B illustrates a pattern of sequentially displayed fixation targets used to orient the eye in various different directions while the retina is imaged. The resulting images correspond to different portions of the retina. For example, as the eye is oriented in various directions and views differently positioned fixation targets on the display, the images captured by the camera include different portions of the retina. These images can be assembled to form a larger map or composite image of the retina.

[0033] [Figure 14A] 14A schematically illustrates a cross-sectional view of an imaging system comprising an eyepiece and a camera for collecting light from an environment in front of the eyepiece. The light from the environment is shown as reflected or emitted from one or more physical objects in the environment. The collection of light from objects in the environment in front of the eyepiece can allow an image of the environment to be captured.

[0034] [Figure 14B] FIG. 14B illustrates diagrammatically how light from the environment is coupled into the eyepiece waveguide by a coupling optical element.

[0035] [Figure 14C]FIG. 14C illustrates diagrammatically an imaging system for collecting light from the environment using a refractive optical element such as a refractive optical element (e.g., a lens such as a wide field lens) in front of the eyepiece.

[0036] [Figure 15A] 15A schematically illustrates an exemplary imaging system comprising a polarization-selective in-coupling optical element for receiving light from an illumination source and coupling the light into a waveguide within an eyepiece. The eyepiece further includes a polarization-selective light-coupling element for coupling the light out of the waveguide. A polarizer may be used to polarize the light from the illumination source, and a half-wave retarder may be used to rotate the orientation of the linearly polarized light as it is redirected into the waveguide by the polarization-selective in-coupling optical element.

[0037] [Figure 15B] FIG. 15B diagrammatically illustrates how light from the eye (e.g., from the retina illuminated with infrared light from an illumination source) is coupled back into the waveguide and directed to a camera for image capture.

[0038] [Figure 16] 16 schematically illustrates an imaging system configured for imaging the anterior portion of the eye (e.g., the cornea). The imaging system comprises an eyepiece as described above. The imaging system further includes a positive lens for collimating light collected from the anterior portion of the eye for coupling into a waveguide via an optical coupling element and propagation to a camera for image capture. The system further includes a negative lens for offsetting the positive refractive power introduced by the positive lens and preventing inversion of the image of the environment in front of the eyepiece that would otherwise occur with the positive lens.

[0039] [Figure 17]17 schematically illustrates another exemplary imaging system configured for imaging the anterior portion of the eye (e.g., the cornea). The imaging system comprises a curved wavelength-selective reflector that collimates light from the anterior portion of the eye for coupling into a waveguide via an optical coupling element and propagation to a camera for image capture. The wavelength-selective reflector may operate reflectively for infrared light reflected from the eye and transmissively for visible light from the environment in front of the user.

[0040] [Figure 18] 18 also schematically illustrates an exemplary imaging system including a curved wavelength-selective reflector that collimates light from the anterior portion of the eye for coupling into a waveguide via an optical coupling element and propagation to a camera for image capture. Polarization selectivity may be employed to help control the path of light reflected from the eye. Eye illumination is provided via the waveguide instead of multiple light sources between the waveguide and the eye, as shown in FIG. 18.

[0041] [Figure 19] FIG. 19 illustrates diagrammatically an imaging system including a shutter to assist in the noise removal procedure.

[0042] [Figure 20A] 20A-20E diagrammatically illustrate an alternative procedure for removing noise using wavelength modulation in conjunction with a curved wavelength-selective reflector. [Figure 20B] 20A-20E diagrammatically illustrate an alternative procedure for removing noise using wavelength modulation in conjunction with a curved wavelength-selective reflector. [Figure 20C] 20A-20E diagrammatically illustrate an alternative procedure for removing noise using wavelength modulation in conjunction with a curved wavelength-selective reflector. [Figure 20D] 20A-20E diagrammatically illustrate an alternative procedure for removing noise using wavelength modulation in conjunction with a curved wavelength-selective reflector. [Figure 20E]20A-20E diagrammatically illustrate an alternative procedure for removing noise using wavelength modulation in conjunction with a curved wavelength-selective reflector.

[0043] [Figure 21] FIG. 21 shows an exemplary eyepiece that can be used to project light into a user's eye and provide image content thereto while simultaneously receiving image data of the user's eye or the environment in front of the user.

[0044] [Figure 22] FIG. 22 illustrates a cross-sectional side view of an embodiment of a cholesteric liquid crystal grating (CLCG) having a plurality of uniform chiral structures.

[0045] [Figure 23] FIG. 23 illustrates an example imaging system comprising a forward-facing camera configured to image the wearer's eye using a cholesteric liquid crystal (CLC) off-axis mirror.

[0046] The drawings are provided to illustrate example embodiments and are not intended to limit the scope of the present disclosure. Like reference numbers refer to like parts throughout. DETAILED DESCRIPTION OF THE INVENTION

[0047] Reference is now made to the drawings, wherein like reference numerals refer to like parts throughout.

[0048] FIG. 2 illustrates an example of a wearable display system 60. 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 directly in front of the user's 90 eyes. The display 70 may be considered eyewear in some embodiments. In some embodiments, a speaker 100 is coupled to the frame 80 and configured to be positioned adjacent to the user's 90 ear canal (in some embodiments, another speaker, not shown, may optionally be positioned adjacent the user's other ear canal to provide stereo / shapeable sound control). The display system may also include one or more microphones 110 or other devices to detect sound. In some embodiments, the microphones are configured to allow a user to provide input or commands to the system 60 (e.g., voice menu command selections, natural language queries, etc.) and / or enable audio communication with other persons (e.g., other users of similar display systems). 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 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., on the head, torso, limbs, etc. of the user 90). The ambient sensor 120a, in some embodiments, may be configured to obtain data characterizing a physiological state of the user 90. For example, the sensor 120a may be an electrode.

[0049] 2, 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-style configuration, a belt-type configuration). Similarly, the sensor 120a may be operably coupled to the local data processing module 140 by a communication link 120b, e.g., 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 a hard disk drive), both of which may be utilized to aid in processing, caching, and storing data. The data includes a) data 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 (which may be operatively coupled to frame 80 or otherwise attached to user 90, for example) and / or b) data obtained and / or processed using remote processing module 150 and / or remote data repository 160 (including data related to virtual content), possibly for passage to display 70 after processing or retrieval. Local processing and data module 140 may be operatively coupled to remote processing module 150 and 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 local processing and data module 140. In some embodiments, the 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 the frame 80 or may be freestanding structures that communicate with the local processing and data module 140 via wired or wireless communication paths.

[0050] 2 , in some embodiments, remote processing module 150 may comprise one or more processors configured to analyze and process data and / or image information. In some embodiments, remote data repository 160 may comprise a digital data storage facility that may be available through the Internet or other networking configuration in a “cloud” resource configuration. In some embodiments, remote data repository 160 may include one or more remote servers that provide information, for example, information for generating augmented reality content, to local processing and data module 140 and / or remote processing module 150. In some embodiments, all data is stored and all computations are performed within the local processing and data module, allowing for fully autonomous use from the remote module.

[0051] Referring now to FIG. 3, the perception of an image as “three-dimensional” or “3-D” can be achieved by providing a slightly different presentation of the image to each eye of a viewer. FIG. 3 illustrates a conventional display system for simulating a three-dimensional image for a user. Two distinct images 190, 200, one for each eye 210, 220, are output to the user. The images 190, 200 are spaced from the eyes 210, 220 by a distance 230 along an optical axis, or z-axis, parallel to the viewer's line of sight. The images 190, 200 are flat, and the eyes 210, 220 can focus on the images by assuming a single accommodative state. Such a 3-D display system relies on the human visual system to combine the images 190, 200 and provide the perception of depth and / or scale of the combined image.

[0052] However, it should be understood that the human visual system is more complex and providing a realistic perception of depth is more difficult. For example, many viewers of conventional “3-D” display systems find such systems uncomfortable or may not perceive any sense of depth at all. Without being limited by theory, it is believed that a viewer of an object may perceive the object as “three-dimensional” due to a combination of vergence and accommodation. Vergence movement of two eyes relative to each other (e.g., eye rotation, in which the pupils move toward or away from each other to converge the gaze of the eyes and fixate on an object) is closely linked to the focusing (or “accommodation”) of the eye's lens and pupil. Under normal conditions, changing the focus of the eye's lens or accommodating the eye and shifting focus from one object to another at a different distance will automatically produce a matching change in convergence to the same distance, a relationship known as the "accommodation-vergence reflex" and pupil dilation or constriction. Similarly, changes in convergence will, under normal conditions, induce a matching change in accommodation in lens shape and pupil size. As described herein, many stereoscopic or "3-D" display systems display a scene using slightly different presentations (and therefore slightly different images) to each eye so that a three-dimensional perspective is perceived by the human visual system. However, such systems, among other things, simply provide different presentations of a scene, but are uncomfortable for many viewers because the eyes view all image information in a single, accommodated state, working against the "accommodation-vergence reflex." Display systems that offer better matching between accommodation and convergence may produce a more realistic and comfortable simulation of three-dimensional images.

[0053] FIG. 4 illustrates aspects of an approach for simulating a three-dimensional image using multiple depth planes. With reference to FIG. 4 , objects at various distances from the eyes 210, 220 on the z-axis are accommodated by the eyes 210, 220 so that the objects are in focus. The eyes 210, 220 assume a particular accommodated state and focus on objects at different distances along the z-axis. As a result, a particular accommodated state may be said to be associated with a particular one of the depth planes 240 having an associated focal length such that an object or portion of an object at a particular depth plane is in focus when the eye is in the accommodated state for that depth plane. In some embodiments, a three-dimensional image may be simulated by providing a different presentation of an image for each eye 210, 220 and by providing a different presentation of an image corresponding to each of the depth planes. While shown as separate for clarity of illustration, it should be understood that the fields of view of the eyes 210, 220 may overlap, for example, as the distance along the z-axis increases. Additionally, although shown as flat for ease of illustration, it should be understood that the contour of the depth plane may be curved in physical space so that all features within the depth plane are in focus with the eye in a particular accommodative state.

[0054] The distance between an object and the eye 210 or 220 can also change the amount of divergence of light from the object as viewed by that eye. Figures 5A-5C illustrate the relationship between distance and divergence of light rays. The distance between the object and the eye 210 is represented by decreasing distances R1, R2, and R3. As shown in Figures 5A-5C, light rays become more divergent as the distance to the object decreases. 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 from the user's eye. The curvature increases as the distance between the object and the eye 210 decreases. As a result, the divergence of light rays at different depth planes also differs, and the divergence increases as the distance between the depth plane and the viewer's eye 210 decreases. While only a single eye 210 is illustrated in FIGS. 5A-5C and various other figures herein for clarity of illustration, it should be understood that the discussion regarding eye 210 may apply to both eyes 210 and 220 of a viewer.

[0055] 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 can be achieved by providing the eye with different representations of images corresponding to each of these limited number of depth planes. The different representations may be focused separately by the viewer's eyes, thereby serving to provide depth cues to the user based on the ocular accommodation required to focus on different image features for a scene located on the different depth planes and / or based on the observation of different image features on the different depth planes that are out of focus.

[0056] FIG. 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 can be utilized to provide a three-dimensional perception to the eye / brain using multiple waveguides 270, 280, 290, 300, 310. In some embodiments, display system 250 is system 60 of FIG. 2, and FIG. 6 schematically illustrates some portions of system 60 in greater detail. For example, waveguide assembly 260 may be part of display 70 of FIG. 2. 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.

[0057] Continuing with reference to FIG. 6, the waveguide assembly 260 may also include multiple 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 multiple lenses 320, 330, 340, 350 may be configured to transmit image information to the eye using various levels of wavefront curvature or ray divergence. Each waveguide level may be associated with a particular depth plane and configured to output image information corresponding to that depth plane. The image injection devices 360, 370, 380, 390, 400 may act as light sources for the waveguides and may be utilized to inject image information into the waveguides 270, 280, 290, 300, 310, each configured to disperse incident light across each individual waveguide for output toward the eye 210, as described herein. Light exits output surfaces 410, 420, 430, 440, 450 of the image injection devices 360, 370, 380, 390, 400 and is injected into corresponding input surfaces 460, 470, 480, 490, 500 of the waveguides 270, 280, 290, 300, 310. In some embodiments, each input surface 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 multiple (e.g., three) waveguides 270, 280, 290, 300, 310.

[0058] 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 a corresponding waveguide 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 via one or more optical conduits (such as fiber optic cables) to each of the image input devices 360, 370, 380, 390, 400. 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).

[0059] In some embodiments, light injected into the waveguides 270, 280, 290, 300, 310 is provided by a light projector system 520, which includes a light module 540, which may include a light emitter such as a light emitting diode (LED). Light from the light module 540 may be directed and modified by a light modulator 530, e.g., a spatial light modulator, via a beam splitter 550. The light modulator 530 may be configured to vary the perceived intensity of the light injected into the waveguides 270, 280, 290, 300, 310. Examples of spatial light modulators include liquid crystal displays (LCDs), including liquid crystal on silicon (LCOS) displays. It should be understood that image input devices 360, 370, 380, 390, 400 are illustrated diagrammatically and in some embodiments these image input 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.

[0060] 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 pattern, 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 waveguides 270, 280, 290, 300, 310. In some other embodiments, the illustrated image injection devices 360, 370, 380, 390, 400 may diagrammatically represent multiple scanning fibers or multiple 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 one or more optical fibers may be configured to transmit light from the optical module 540 to 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 one or more waveguides 270, 280, 290, 300, 310, for example, to redirect light exiting the scanning fiber into one or more waveguides 270, 280, 290, 300, 310.

[0061] Controller 560 controls the operation of one or more of stacked waveguide assemblies 260, including the operation of image input devices 360, 370, 380, 390, 400, light source 540, and light modulator 530. In some embodiments, controller 560 is part of local data processing module 140. Controller 560 contains programming (e.g., instructions in a non-transitory medium) that coordinates the timing and provisioning of image information to 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 a wired or wireless communication channel. Controller 560 may, in some embodiments, be part of processing module 140 or 150 (FIG. 2).

[0062] Continuing with reference to FIG. 6 , the waveguides 270, 280, 290, 300, and 310 may be configured to propagate light within each individual waveguide by total internal reflection (TIR). Each of the waveguides 270, 280, 290, 300, and 310 may be planar, with major top and bottom surfaces and edges extending between the major top and bottom surfaces, or may have another shape (e.g., curved). In the illustrated configuration, the waveguides 270, 280, 290, 300, and 310 may each include outcoupling optical elements 570, 580, 590, 600, and 610 configured to extract light from the waveguide by redirecting light propagating within each individual waveguide out of the waveguide and outputting image information to the eye 210. The extracted light may also be referred to as outcoupling light, and the outcoupling optical elements may also be referred to as light extraction optical elements. The extracted beam of light may be output by the waveguide at a location where light propagating within the waveguide strikes the light-extraction optical element. The outcoupling optical element 570, 580, 590, 600, 610 may be a grating, for example, including diffractive optical features as discussed further herein. While shown disposed on the bottom major surface of the waveguides 270, 280, 290, 300, 310 for ease of explanation and clarity of the drawings, in some embodiments the outcoupling 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 waveguides 270, 280, 290, 300, 310, as discussed further 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 waveguides 270, 280, 290, 300, 310. In some other embodiments, the waveguides 270, 280, 290, 300, 310 may be monolithic pieces of material, and the outcoupling optical elements 570, 580, 590, 600, 610 may be formed on a surface of and / or within that piece of material.

[0063] Continuing with 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 reaching the eye 210. Such first lens 350 may be configured to generate a slight convex wavefront curvature so that the eye / brain interprets light emerging from the next upper waveguide 280 as emerging 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 power of the first lens 350 and the second lens 340 may be configured to produce another, increasing amount of wavefront curvature such that the eye / brain interprets the light emerging from the third waveguide 290 as originating 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.

[0064] 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 a collective focal power representing the focal plane closest to the person. To compensate for 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 collective power of the lower lens stacks 320, 330, 340, 350. Such a configuration provides as many perceived focal planes as there are available waveguide / lens pairs. Both the waveguide outcoupling optical elements and the focusing sides of the lenses may be static (i.e., not dynamic or electro-active). In some alternative embodiments, one or both may be dynamic using electro-active features.

[0065] 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 waveguides 270, 280, 290, 300, 310 may be configured to output images set at the same 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.

[0066] 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 that waveguide. As a result, waveguides with different associated depth planes may have different configurations of outcoupling optical elements 570, 580, 590, 600, 610, which 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, which 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).

[0067] 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 so 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 traveling through the waveguide via TIR. The light carrying the image information is thus split into several related output beams that exit the waveguide at various locations, resulting in a fairly uniform pattern of output emission toward the eye 210 for this particular collimated beam bouncing within the waveguide.

[0068] 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).

[0069] 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 the physiological state 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 on the frame 80 ( FIG. 2 ) and may be in electrical communication with 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.

[0070] 7, an example of an output beam output by a waveguide is shown. While one waveguide is illustrated, it should be understood that other waveguides in waveguide assembly 260 (FIG. 6) may function similarly, and that waveguide assembly 260 includes multiple waveguides. Light 640 is launched into waveguide 270 at input surface 460 of waveguide 270 and propagates within waveguide 270 by TIR. At the point where light 640 impinges on DOE 570, a portion of the light exits the waveguide as output beam 650. Output beam 650 is illustrated as being approximately parallel, but may be redirected to propagate to eye 210 at an angle (e.g., forming a diverging output beam), as discussed herein and depending on the depth plane associated with 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 a more divergent exit beam pattern, 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.

[0071] In some embodiments, a full-color image may be formed at each depth plane by overlaying images in each of the primary colors, for example, three or more primary colors. FIG. 8 illustrates an example of a stacked waveguide assembly, with each depth plane including an image formed using multiple different primary colors. The illustrated embodiment shows depth planes 240a-240f, but more or fewer depths are also contemplated. Each depth plane may have three or more primary color images associated with it, including a first image in a first color G, a second image in a second color R, and a third image in a third color B. Different depth planes are indicated by different numbers in diopters (dpt) following the letters G, R, and B. By way of example only, the number following each of these letters indicates the diopter (1 / m), i.e., the inverse distance of the depth plane from the viewer, and each box in the diagram represents an individual primary color image. In some embodiments, the exact locations of the depth planes for the different primary colors may vary to account for differences in the eye's focusing of light of different wavelengths. For example, different primary color images for a given depth plane may be placed on depth planes corresponding to different distances from the user. Such an arrangement may increase visual acuity and user comfort and / or reduce chromatic aberration.

[0072] In some embodiments, light for 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 diagram containing the letter G, R, or B may be understood to represent an individual waveguide, and three waveguides may be provided per depth plane, resulting in three primary color images per depth plane. While the waveguides associated with each depth plane are shown adjacent to each other in this drawing for ease of illustration, 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.

[0073] 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 replace one or more of red, green, or blue.

[0074] It should be understood that references throughout this disclosure to a given color of light are understood to encompass light of one or more wavelengths within the range of wavelengths of light that are perceived by a viewer as that given color. For example, red light may include one or more wavelengths of light that are within the range of about 620-780 nm, green light may include one or more wavelengths of light that are within the range of about 492-577 nm, and blue light may include one or more wavelengths of light that are within the range of about 435-493 nm.

[0075] In some embodiments, light source 540 (FIG. 6) may be configured to emit light at one or more wavelengths outside the range of a viewer's visual perception, e.g., infrared and / or ultraviolet wavelengths. Additionally, the waveguide incoupling, outcoupling, and other light redirecting structures of display 250 may be configured to direct and emit this light from the display toward the user's eye 210, e.g., for imaging and / or user stimulation applications.

[0076] Referring now to FIG. 9A , in some embodiments, light impinging on a waveguide may need to be redirected to incoupling the light into the waveguide. An incoupling optical element may be used to redirect and incoupling the light into its corresponding waveguide. FIG. 9A illustrates a cross-sectional side view of an example of a plurality or set 660 of stacked waveguides, each including an incoupling optical element. The waveguides may each be configured to output light of one or more different wavelengths or one or more different wavelength ranges. While stack 660 may correspond to stack 260 ( FIG. 6 ), and the illustrated waveguides of stack 660 may correspond to a portion of multiple waveguides 270, 280, 290, 300, 310, it should be understood that light from one or more of image injection devices 360, 370, 380, 390, 400 is injected into the waveguide from a location requiring the light to be redirected for incoupling.

[0077] The illustrated set 660 of stacked waveguides includes waveguides 670, 680, and 690. Each waveguide includes an associated internal coupling optical element (which may also be referred to as the light input area on the waveguide), for example, internal coupling optical element 700 is disposed on a major surface (e.g., the top major surface) of waveguide 670, internal coupling optical element 710 is disposed on a major surface (e.g., the top major surface) of waveguide 680, and internal coupling 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 internal coupling optical elements 700, 710, 720 may be disposed on the bottom major surface of an individual waveguide 670, 680, 690 (particularly, one or more internal coupling optical elements are reflective polarizing optical elements). As shown, the internal coupling 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 internal coupling optical elements are transmissive turning optical elements. In some embodiments, the internal coupling 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 internal coupling optical elements 700, 710, 720 are wavelength selective so as to selectively redirect one or more wavelengths of light while transmitting other wavelengths of light. While illustrated on one side or corner of the respective waveguide 670, 680, 690, it should be understood that the internal coupling optical elements 700, 710, 720 may be disposed within other areas of the respective waveguide 670, 680, 690 in some embodiments.

[0078] 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 receive substantially no light from others of the in-coupling optical elements 700, 710, 720.

[0079] Each waveguide also includes an associated optically dispersive element, for example, optically dispersive element 730 is disposed on a major surface (e.g., the top major surface) of waveguide 670, optically dispersive element 740 is disposed on a major surface (e.g., the top major surface) of waveguide 680, and optically dispersive element 750 is disposed on a major surface (e.g., the 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.

[0080] Waveguides 670, 680, 690 may be spaced apart and separated, for example, by gas, liquid, and / or solid layers of material. For example, as shown, layer 760a may separate waveguides 670 and 680, and layer 760b may separate waveguides 680 and 690. In some embodiments, layers 760a and 760b are formed from a low refractive index material (i.e., a material having a lower refractive index than the material forming the immediately adjacent ones of waveguides 670, 680, 690). Preferably, the refractive index of the material forming layers 760a, 760b is 0.05 or greater, or 0.10 or less, than the refractive index of the material forming waveguides 670, 680, 690. Advantageously, the lower refractive index layers 760a, 760b may function as cladding layers that 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.

[0081] Preferably, for ease of manufacturing and other considerations, the materials forming waveguides 670, 680, 690 are similar or the same, and the materials forming layers 760a, 760b are similar or the same. In some embodiments, the materials forming waveguides 670, 680, 690 may differ between one or more waveguides, and / or the materials forming layers 760a, 760b may differ while still maintaining the various refractive index relationships discussed above.

[0082] 9A, light rays 770, 780, 790 enter 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).

[0083] In some embodiments, light rays 770, 780, 790 have different properties, e.g., different wavelengths or different wavelength ranges, which may correspond to different colors. Each of the incoupling optical elements 700, 710, 720 deflects 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.

[0084] For example, in-coupling optical element 700 may be configured to deflect light ray 770 having a first wavelength or wavelength range while transmitting light rays 780 and 790 having different second and third wavelengths or wavelength ranges, respectively. Transmitted light ray 780 impinges on and is deflected by in-coupling optical element 710, which is configured to deflect light of the second wavelength or wavelength range. Light ray 790 is deflected by in-coupling optical element 720, which is configured to selectively deflect light of the third wavelength or wavelength range.

[0085] 9A , the deflected light rays 770, 780, 790 are deflected to propagate through the corresponding waveguides 670, 680, 690. That is, the in-coupling optical element 700, 710, 720 of each waveguide deflects the light into its corresponding waveguide 670, 680, 690, in-coupling 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 waveguide's corresponding optical dispersive element 730, 740, 750.

[0086] 9B, a perspective view of the multiple stacked waveguide embodiment of FIG. 9A is illustrated. As previously described, in-coupled light rays 770, 780, 790 are deflected by in-coupling optical elements 700, 710, 720, respectively, and then propagate by TIR within waveguides 670, 680, 690, respectively. Light rays 770, 780, 790 then impinge on optically dispersive elements 730, 740, 750, respectively. Optically dispersive elements 730, 740, 750 deflect light rays 770, 780, 790 to propagate toward out-coupling optical elements 800, 810, 820, respectively.

[0087] In some embodiments, the optically dispersive elements 730, 740, 750 are orthogonal pupil expanders (OPEs). In some embodiments, the OPEs deflect or disperse light into 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 into 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 light directly into the out-coupling optical elements 800, 810, 820. For example, with reference 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 outcoupling optical elements 800, 810, 820 are exit pupils (EPs) or exit pupil expanders (EPEs) that direct light toward the viewer's eye 210 ( FIG. 7 ). It should be understood that an OPE may be configured to increase the size of the eyebox in at least one axis, and that the EPE may increase the eyebox in an axis that intersects the axis of the OPE, e.g., orthogonal to the axis of the OPE. For example, each OPE may be configured to redirect a portion of the light striking the OPE to an EPE of the same waveguide, while allowing the remaining portion of the light to continue propagating down the waveguide. Upon striking the OPE, again, another portion of the remaining light is redirected to the EPE, and the remainder of that portion continues to propagate further down the waveguide, etc. Similarly, upon striking the EPE, a portion of the impinging light is directed out of the waveguide toward the user, and the remaining portion of that light continues to propagate through the waveguide until it again strikes an EP, at which point another portion of the impinging 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.

[0088] 9A and 9B, in some embodiments, a waveguide set 660 includes, for each primary color, waveguides 670, 680, 690, in-coupling optical elements 700, 710, 720, optically dispersive elements (e.g., OPEs) 730, 740, 750, and out-coupling optical elements (e.g., EPs) 800, 810, 820. The waveguides 670, 680, 690 may be stacked with an air gap / cladding layer between each one. The in-coupling optical elements 700, 710, 720 redirect or deflect incident light into that waveguide (with different in-coupling optical elements receiving light of different wavelengths). The light then propagates at an angle that will result in TIR within the individual waveguides 670, 680, 690. In the example shown, light ray 770 (e.g., blue light) is deflected by the first in-coupling optical element 700 in the manner described above, then continues bouncing 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, with light ray 780 impinging on and being deflected by the in-coupling optical element 710. Light ray 780 will then, via TIR, bounce 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 ray 790 so that it propagates by TIR to the light dispersive element (e.g., OPE) 750 and then by TIR to the out-coupling optical element (e.g., EP) 820. The out-coupling optical element 820 then finally out-couples the light ray 790 to a viewer, who also receives the out-coupled light from the other waveguides 670, 680.

[0089] FIG. 9C illustrates a top-down plan view of an example of the multiple stacked waveguides of FIGS. 9A and 9B. As shown, waveguides 670, 680, 690 may be vertically aligned, along with each waveguide's associated optically dispersive elements 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, arrays including non-overlapping, spatially separated in-coupling optical elements may be referred to as shifted-pupil systems, and the in-coupling optical elements in these arrays may correspond to sub-pupils.

[0090] Eye and Environmental Imaging As discussed above, head-mounted displays can be used to provide a user with image content integrated with, combined with, and / or superimposed over a view of the world in front of the wearer. Such head-mounted display systems can be configured to project light into the user's eyes to form augmented reality image content and transmit light from the environment in front of the user to the user. The head-mounted display system may include one or more cameras to image the environment and / or the user's eyes. An outward-facing camera may directly image the environment and be used, for example, to determine where augmented reality image content should be placed relative to objects in the environment. For example, imaging the environment may provide the location of a table so that the head-mounted display may render an image of a person standing next to the table instead of on or in the table. An inward-facing camera may be used to directly image the eyes, such as for eye tracking. Disclosed herein are examples of head-mounted display systems and / or imaging systems that may also be configured to image the eyes and / or the environment. In some designs, the system does not require inward-facing and / or outward-facing cameras to directly image the eye and / or the environment, respectively. Such systems may employ one or more cameras configured to receive light from the eye / environment via an eyepiece, such as one or more waveguides in the eyepiece, in optical communication with the one or more cameras. Once the light is collected by the waveguides, the one or more cameras can generate an image of the eye and / or the environment in front of the user. Using waveguides to collect light for imaging the eye and / or the environment can potentially reduce the form factor of the head-mounted display, making the head-mounted display potentially more compact and / or aesthetically pleasing.

[0091] FIG. 10 illustrates an exemplary imaging system 900 configured to image the eye, integrated with an eyepiece 950, that may be used on a head-mounted display. The eyepiece 950, which may be positioned in front of a user's eye 210, can be used both to inject image content into the eye and to image the eye. FIG. 10 shows one eyepiece 950 in front of one eye 210. Various head-mounted display systems, such as that shown in FIG. 2, may include a pair of eyepieces 950 and associated components positioned in front of the respective left and right eyes 210. While a single waveguide 940 is shown in FIG. 10, the waveguide 940 may include one, two, three, four, six, seven, eight, or more waveguides (e.g., a stack of one or more waveguides).

[0092] Imaging system 900 may include a light source or illumination source 960 to illuminate the eye and facilitate image capture, an eyepiece 950 with a waveguide 940 configured to propagate light therein, and / or an imaging device 920 such as a camera for image capture. Also shown is an image projector 930 for producing an image that may be injected into the eye via the eyepiece 950. Eyepiece 950 may include one or more waveguides 940 configured to carry light from illumination source 960 and / or image projector 930 to the eye and light from the eye to camera 920. Eyepiece 950 may further include one or more coupling optical elements 944 to illuminate the eye and couple light from waveguide 940 out to the eye for image injection and / or from the eye into the waveguide for image capture. The eyepiece 950 may additionally include one or more internal coupling optical elements 942 for coupling light from the illumination source 960 and / or image projector 930 into the waveguide 940, and one or more external coupling optical elements 952 for coupling light from the waveguide to the camera 920.

[0093] The eyepieces 950 may be disposed on a frame that is worn on the head. The eyepieces 950 may be disposed in front of the eyes 210. The eyepieces 950 may have an inner or nasal side that is closer to the wearer's nose and an opposing outer or temporal side that is closer to the wearer's temples and farther from the nose. In FIG. 10 , the coupling optical element 944 is on the inner or nasal side (outer or temporal side) of the inner coupling optical element 942 and the outer coupling optical element 952. The illumination source 960 is also on the inner or nasal side of the image projector 930 (or the image projector is on the outer or temporal side of the illumination source). However, the relative positions may vary. For example, the illumination source 960 may be on the outer or temporal side of the image projector 930 in some designs.

[0094] The waveguide 940 may comprise a sheet or layer having two major surfaces (a front surface and a rear surface) with the largest surface areas arranged opposite each other. The front surface may be farther from the user's eyes 210 when the user wears the head-mounted display (closer to the environment in front of the wearer), and the rear surface is closer to the user's eyes (and farther from the environment in front of the wearer). The waveguide 940 may include a transparent material (e.g., glass, plastic) with a refractive index greater than 1.0 so that light can be guided therein between the major surfaces by total internal reflection. Elements with the same number may have the same functionality for one or more of the embodiments described herein.

[0095] A coupling optical element 944 may be disposed on or within the waveguide 940 for coupling light from the eye 210 to the waveguide 940 and / or from the waveguide to the eye. As shown in FIG. 10 , the coupling optical element 944 may be disposed in an optical path between the user's eye 210 and the waveguide 940 such that light coupled from the waveguide 940 via the coupling optical element 944 may be incident on the user's eye 210 (e.g., to illuminate the eye and / or for imaging). The coupling optical element 944 may comprise a plurality of turning features configured to redirect light guided within the waveguide out of the waveguide or to redirect light incident on the coupling optical element 944 at an angle into the waveguide to be guided therein by total internal reflection. The coupling optical element 944 and the turning features may be physically associated with the waveguide 940. For example, coupling optical element 944 may comprise a holographic or diffractive optical element (e.g., a surface relief grating) patterned (e.g., etched) within or on waveguide 940. Coupling optical element 944 may comprise a layer disposed on waveguide 940, or may be formed within waveguide 940. For example, a volume holographic or other diffractive optical element may be formed by varying the refractive index of the material comprising the waveguide or a layer disposed thereon. Thus, coupling optical element 944 may be disposed within the volume of waveguide 940 or as a layer disposed thereon.

[0096] Depending on the design, the combining optical element 944 may be transmissive or reflective and may operate transmissively or reflectively. For example, the combining optical element 944 may operate transmissively or reflectively, respectively, and may include a transmissive or reflective diffractive optical element (e.g., a grating) or a holographic optical element that, for example, redirects light transmitted through or reflected therefrom. The combining optical element 944 may include a polarization optical element, such as a polarization-selective redirecting element (e.g., a polarizer). The polarization-selective redirecting element may include one or more polarization gratings, diffractive optical elements, and / or holographic optical elements, and may comprise a liquid crystal structure, such as a liquid crystal polarization grating. The combining optical element 944 may be configured to direct light from the image projector 930 and / or the light source 960, which is guided within the waveguide 940 by total internal reflection (TIR), at an angle less than the critical angle (e.g., closer to the normal) to be emitted from the waveguide and toward the eye 210. Additionally or alternatively, the coupling optical element 944 may be configured to couple light from the eye 210 into the waveguide 940 at an angle above the critical angle (e.g., an angle that is not too close to the normal) so that it is guided therein to the camera 920 by total internal reflection.

[0097] As shown in FIG. 10 , an internal coupling optical element 942 for coupling light from an illumination source 960 and / or an image projector 930 into the waveguide 940 may be disposed on or within the waveguide 940. The internal coupling optical element 942 may be disposed in an optical path between the light source 960 and the waveguide 940 such that light coupled from the light source 960 via the internal coupling optical element 942 is guided within the waveguide 940. The internal coupling optical element 942 may comprise a plurality of turning features configured to redirect light incident thereon at an angle into the waveguide, for example, to be guided therein by total internal reflection. The internal coupling optical element 942 may comprise a liquid crystal structure, such as a liquid crystal polarization grating. Additionally or alternatively, the internal coupling optical element 942 may include a blazed grating. The internal coupling optical element 942 may comprise a layer disposed on the waveguide 940, or may be formed (e.g., patterned) on or within the waveguide 940, or otherwise fabricated therein. For example, a surface holographic or diffractive optical element (e.g., a surface relief grating) may be fabricated by patterning (e.g., etching) the surface of the waveguide or a layer thereon. A volume holographic or diffractive optical element may also be formed by changing the refractive index of the material comprising the waveguide or a layer thereon. Thus, the internal coupling optical element 942 may be disposed within the volume of the waveguide 940 or a layer thereon. Depending on the design, the internal coupling optical element 942 may be transmissive or reflective and may operate transmissively or reflectively. For example, the internal coupling optical element 942 may include a transmissive or reflective diffractive optical element (e.g., a grating) or a holographic optical element that operates transmissively or reflectively, e.g., redirecting light transmitted through or reflected therefrom, respectively.

[0098] The internal coupling optical element 942 may comprise a reflective optical element (e.g., a mirror). For example, the internal coupling optical element 942 may comprise an off-axis reflector. Additionally or alternatively, the internal coupling optical element 942 and / or the coupling optical element 944 may include a polarization optical element, such as a polarization-selective redirecting element (e.g., a polarizer). The polarization-selective redirecting element may include one or more polarization gratings, diffractive optical elements, and / or holographic optical elements, and may comprise a liquid crystal structure, such as a liquid crystal polarization grating. For example, one or both of the internal coupling optical element 942 and / or the coupling optical element 944 may include a liquid crystal polarization grating (LCPG). LCPGs can potentially provide high-efficiency diffraction over a wide wavelength range. Thus, LCPGs may be useful for the internal coupling optical element 942 and / or the coupling optical element 944. LCPGs may be polarization-dependent. The LCPG or other type of liquid crystal grating, diffractive optical element, or optical element may include a pattern or arrangement of liquid crystal molecules configured to provide one or more functions, such as redirecting light into or out of a waveguide. Thus, the internal coupling optical element 942 and / or the coupling optical element 944 may comprise a polarization grating. Additionally or alternatively, the internal coupling optical element 942 and / or the coupling optical element 944 can comprise liquid crystals, and thus, in some implementations, one or both may be liquid crystal gratings or liquid crystal diffractive optical elements. Additionally or alternatively, one or both of the internal coupling optical element 942 and / or the coupling optical element 944 can include a blazed grating. In some designs, the internal coupling optical element 942 comprises a liquid crystal reflector, such as a cholesteric liquid crystal reflective lens (e.g., a reflective liquid crystal diffractive lens, a Bragg reflective structure, a reflective liquid crystal diffraction grating, etc.). Some non-limiting examples of liquid crystal gratings, liquid crystal polarization gratings, and other liquid crystal optical elements are discussed in the following published applications (each of which is incorporated herein by reference in its entirety and for all purposes):U.S. Patent Publication No. 2018 / 0143438, entitled "Multilayer Liquid Crystal Diffractive Gratings for Reducing Light of Wide Incident Angle Ranges," filed November 16, 2017; U.S. Patent Publication No. 2018 / 0143485, entitled "Spatially Variable Liquid Crystal Diffraction Gratings," filed November 16, 2017; and U.S. Patent Publication No. 2018 / 0143509, entitled "Waveguide Light Multiplexer Using Crossed Gratings," filed November 16, 2017, and entitled "Display System with Variable Power No. 2018 / 0239147, entitled "VARIABLE-FOCUS VIRTUAL IMAGE DEVICES BASED ON POLARIZATION CONVERSION," filed February 22, 2018; U.S. Patent Publication No. 2018 / 0239177, entitled "VARIABLE-FOCUS VIRTUAL IMAGE DEVICES BASED ON POLARIZATION CONVERSION," filed February 22, 2018; and U.S. Patent Publication No. 2018 / 0164627, entitled "DIFFRACTIVE DEVICES BASED ON CHOLESTERIC LIQUID CRYSTAL," filed December 7, 2017. However, the design of the internal coupling optical element 942 and / or the coupling optical element 944 is not limited thereto and may include other types of optical elements, such as diffractive optical elements, liquid crystal optical elements, liquid crystal gratings, and liquid crystal polarization gratings. Further information regarding examples of cholesteric liquid crystal structures such as reflectors can also be found in the section below entitled "Cholesteric Liquid Crystal Mirrors." As discussed above, other liquid crystal optical elements and other non-liquid crystal optical elements may be used. Thus, many types of coupling optical elements (e.g., internal coupling optical element 942 and / or coupling optical element 944), diffractive optical elements, gratings, polarization gratings, etc., may be used, both those described herein and other types of gratings, diffractive optical elements, liquid crystal elements, and optical elements in general.In various implementations, the internal coupling optical element 942 may be configured to couple light from the image projector 930 and / or the light source 960 into the waveguide at an angle greater than the critical angle so that it is guided within the waveguide 940 to the user's eye 210 by total internal reflection to the eye.

[0099] Waveguide 940 may comprise one or more waveguides. In some implementations, one or more waveguides 940 comprise a stack of waveguides. In some designs, for example, different waveguides of a stack of waveguides are configured to output light with different wavefront divergences, as if projected from different distances from the user's eye. For example, a first waveguide or group of waveguides may be configured to output light that is collimated or has a first divergence, as if projected from a first depth, and a second waveguide or group of waveguides may be configured to output light that is divergent (not collimated) or at a second divergence (greater than the first divergence), as if projected from a second depth closer than the first depth. In some designs, different waveguides may be configured to output light with different associated colors. For example, a first waveguide may be configured to output red light, a second waveguide may be configured to output green light, a third waveguide may be configured to output blue light, and a fourth waveguide may be configured to output and / or input infrared light.

[0100] The outcoupling optical element 952 for coupling light from the waveguide 940 to the camera 920 as shown in FIG. 10 may comprise multiple redirecting features configured to redirect light at an angle, for example, so that light incident thereon is not guided within the waveguide but is redirected out of the waveguide to the camera. The outcoupling optical element 952 may be disposed within the interior of the waveguide 940 or may be patterned (e.g., etched) in or on a surface (e.g., a major surface) of the waveguide 940. For example, a surface holographic or diffractive optical element (e.g., a surface relief grating) may be fabricated by patterning (e.g., etching) the surface of the waveguide or a layer thereon. A volume holographic or diffractive optical element may also be formed by changing the refractive index of the material comprising the waveguide or a layer thereon. Depending on the design, the outcoupling optical element 952 may be transmissive or reflective and may operate transmissively or reflectively. For example, the outcoupling optical element 952 may include a transmissive or reflective diffractive optical element (e.g., a grating) or a holographic optical element that operates transmissively or reflectively, respectively, e.g., redirecting light transmitted through or reflected therefrom.

[0101] The outcoupling optical element 942 may comprise a reflective optical element (e.g., a mirror). For example, the outcoupling optical element 952 may comprise an off-axis reflector. In some designs, the outcoupling optical element 952 may include a polarization optical element, such as a polarization-selective redirecting element (e.g., a polarizer). Thus, the polarization-selective redirecting element may include one or more polarization gratings, diffractive optical elements, and / or holographic optical elements, and may comprise a liquid crystal structure, such as a liquid crystal polarization grating. In some implementations, for example, the outcoupling optical element 952 may include a liquid crystal polarization grating (LCPG). LCPGs can potentially provide high-efficiency diffraction over a wide wavelength range. Similarly, LCPGs may be useful for the outcoupling optical element 952. LCPGs may be polarization-dependent. LCPGs or other types of liquid crystal gratings may include a pattern or arrangement of liquid crystal molecules configured to provide one or more functions, such as redirecting light into or out of a waveguide. Thus, the outcoupling optical element 952 may comprise a polarization grating. Additionally or alternatively, the outcoupling optical element 952 can comprise a liquid crystal and, therefore, in some implementations, may be a liquid crystal grating or other liquid crystal optical element, such as a liquid crystal diffractive optical element. Additionally or alternatively, the outcoupling optical element 952 can include a blazed grating. In some designs, the outcoupling optical element 952 comprises a liquid crystal reflector, such as a cholesteric liquid crystal reflective lens (e.g., a reflective liquid crystal diffractive lens, a Bragg reflective structure, a reflective liquid crystal diffraction grating, etc.). Some non-limiting examples of liquid crystal gratings, liquid crystal polarization gratings, and other liquid crystal optical elements are discussed in the following published applications (each of which is incorporated by reference herein in its entirety and for all purposes):U.S. Patent Publication No. 2018 / 0143438, entitled "Multilayer Liquid Crystal Diffractive Gratings for Reducing Light of Wide Incident Angle Ranges," filed November 16, 2017; U.S. Patent Publication No. 2018 / 0143485, entitled "Spatially Variable Liquid Crystal Diffraction Gratings," filed November 16, 2017; and U.S. Patent Publication No. 2018 / 0143509, entitled "Waveguide Light Multiplexer Using Crossed Gratings," filed November 16, 2017, and entitled "Display System with Variable Power No. 2018 / 0239147, entitled "VARIABLE-FOCUS VIRTUAL IMAGE DEVICES BASED ON POLARIZATION CONVERSION," filed February 22, 2018; U.S. Patent Publication No. 2018 / 0239177, entitled "VARIABLE-FOCUS VIRTUAL IMAGE DEVICES BASED ON POLARIZATION CONVERSION," filed February 22, 2018; and U.S. Patent Publication No. 2018 / 0164627, entitled "DIFFRACTIVE DEVICES BASED ON CHOLESTERIC LIQUID CRYSTAL," filed December 7, 2017. However, the design of the outcoupling optical element 952 is not limited thereto and may include other types of optical elements, such as diffractive optical elements, liquid crystal optical elements, liquid crystal gratings, and liquid crystal polarization gratings. Further information regarding examples of cholesteric liquid crystal structures such as reflectors can also be found in the section below entitled "Cholesteric Liquid Crystal Mirrors." As discussed above, other liquid crystal optical elements and other non-liquid crystal optical elements may be used. Thus, many types of coupling optical elements (e.g., outcoupling optical element 952), diffractive optical elements, gratings, polarization gratings, etc. may be used, both those described herein and other types of gratings, diffractive optical elements, liquid crystal elements, or optical elements in general.As referenced above, the external coupling optical element 952 may be configured to redirect light guided within the waveguide 940 at an angle less than the critical angle so that it is not guided within the waveguide by total internal reflection but is instead emitted to the camera 920.

[0102] In various designs, the coupling optical element 944 may be transparent in the visible spectrum so that the user can see the environment in front of the user through the coupling optical element 944 and the eyepiece 950. The inner coupling optical element 942 may also redirect light in the visible spectrum, for example, when the inner coupling optical element is used to receive light from the image projector 930 and / or when the illumination source 960 is configured to output visible light and illuminate the eye 210 with visible light. In some embodiments, the inner coupling optical element 942 is configured to redirect infrared light, for example, when the illumination source 960 is configured to output infrared light and illuminate the eye 210 with infrared light. In some designs, such as that shown in FIG. 10 , the inner coupling optical element 942 may be more medial or nasal than the outer coupling optical element 952. However, in other designs, the inner coupling optical element 942 may be more lateral or temporal than the outer coupling optical element 952. In one implementation, as shown in FIG. 10, the out-coupling optical element 952 may be adjacent to the in-coupling optical element 942, although non-adjacent positioning is also possible.

[0103] The illumination source 960 may be located on the same side (e.g., posterior or proximal side) of the eyepiece 950 as the eye 210 (proximal may refer to the side closest to the eye 210), as shown in FIG. 10 . Alternatively, the illumination source 960 may be located on the opposite side (e.g., anterior or distal side) from the eye 210. The illumination source 960 may be configured to direct light into at least one of the major surfaces of the waveguide 940 via the internal coupling optical element 942. The light source 960 may be configured to emit invisible light (e.g., infrared light). The light source 960 may include one or more LEDs. The LEDs may comprise infrared LEDs. The light source 960 may be configured to emit coherent light. In some designs, the light source 960 comprises a laser (e.g., an infrared laser). In some designs, the light source 960 emits pulsed light. For example, the camera 920 can be configured to periodically capture images. Thus, the illumination source 960 can be pulsed to coincide with the period during which the camera is acquiring images. The intensity output from the illumination source 960 can be reduced when the camera is not acquiring images. By concentrating the total illumination energy for a short period of time, an increased signal-to-noise ratio can be obtained without exposing the eye 210 to unsafe intensity levels. In some cases, for example, the camera 920 captures one image every 30 milliseconds, and the camera's exposure time is a few milliseconds. The illumination source 960 can be configured to output pulses with a similar period and duration to match that of the camera 920.

[0104] In some implementations, different light sources having different wavelengths are alternatively pulsed to provide different wavelength illumination at different times, as discussed below.

[0105] The in-coupling optical element 942 may be in direct optical communication with the illumination source 960 and / or the image projector 930, for example, to direct light therein from the image projector 930 and / or the light source 960. For example, light emitted by the light source 960 may be incident on the in-coupling optical element 942 before optically interacting with either the coupling optical element 944 and / or the out-coupling optical element 952.

[0106] As shown in FIGS. 11A-11E, light 902 projected from an image projector 930 can form an image on the retina. The image projector 930 may include a light source, a modulator, and / or projection optics. The light source for the image projector 930 may include one or more LEDs, lasers, or other light sources, or may include one or more visible light sources. The modulator may include a spatial light modulator, such as a liquid crystal spatial light modulator. Such a spatial light modulator may be configured, for example, to modulate the intensity of light at different spatial locations. The projection optics may include one or more lenses. Other types of image projectors 930 capable of projecting and / or forming an image may also be employed. For example, the image projector 930 may include a scanning optical fiber.

[0107] Image projector 930 and in-coupling optical element 942 may be in direct optical communication with one another. Image projector 930 may be aligned with in-coupling optical element 942, for example, into which light from image projector 930 is directed. In some cases, image projector 930 is positioned adjacent to corresponding in-coupling optical element 942 and / or waveguide 940. Image projector 930 may also be positioned within an optical path that includes in-coupling optical element 942, coupling optical element 944, and eye 210.

[0108] Image projector 930 may be a separate element from illumination source 960, as shown in Figures 10 and 11A-11E. However, in some cases, image projector 930 may be used as an illumination source. For example, in addition to projecting an image into eye 210, image projector 930 may be used to direct visible and / or infrared light into and illuminate the eye for image capture. However, alternatively, one or more separate light sources 960 may be used to illuminate eye 210 for image capture.

[0109] The light emitted by the illumination source 960 may comprise light in a particular wavelength range, such as, for example, invisible light. The illumination source 960 may be configured to project invisible (e.g., infrared) light onto or into the eye 210 to image one or more portions of the eye 210 (e.g., the cornea, the retina). In one exemplary implementation, the light source 960 may be configured to emit light in a range of approximately 850 nm to 940 nm. The light source 960 may be configured to emit light extending over a wavelength range of at least approximately 20 nm. Other ranges are also possible. The emitted wavelength range may be 5 nm, 10 nm, 15 nm, 50 nm, 75 nm, 100 nm, 150 nm, 200 nm, or any range between any of these values. The light source 960 may be configured to emit light across a broad band of wavelengths, such as any range within the infrared spectrum.

[0110] The imaging device 920, which may comprise a camera, may comprise a detector array and possibly imaging optics. The detector array may comprise, for example, a CCD or CMOS detector array, and the imaging optics may comprise one or more lenses. The one or more lenses may have positive optical power and an associated focal length. In one design, the camera 920 is focused at infinity. For example, the optics may have a focal length f, and the detector array may be positioned at a distance from the optic corresponding to the focal length such that objects at large distances are imaged onto the detector array. Similarly, collimated light from the eye or objects in the environment will also be focused onto the detector array, forming an image of the eye or object thereon.

[0111] The imaging device 920 may be positioned on the opposite side of the waveguide 940 from the illumination source 960 and / or the eye 210. In some designs, the imaging device 920 may be positioned on the same side of the waveguide 940 as the light source 960 and / or the eye 210. As shown in FIG. 10 , the imaging device 920 may be positioned near the outside or temple edge of the eyepiece 950, although other locations are possible.

[0112] 11A-11E illustrate the operation of the example imaging system 900 of FIG. 10. FIG. 11A shows an illumination source 960 emitting light 902 toward an incoupling optical element 942 on a waveguide 940. As shown, the light 902 can be directed to enter the eyepiece 950 at a near-normal angle, although other angles are possible. In some designs, the light source 960 is configured to emit collimated light into the eyepiece 950. As shown in FIG. 11B, the illumination light 902 can be coupled into the waveguide 940 via the incoupling optical element 942. In some designs where the incoupling optical element 942 comprises a diffractive optical element (e.g., a grating, a holographic element), light incident thereon is diffracted at angles above the critical angle of the waveguide, causing the incoupling light 904 to be guided within the eyepiece 950 by total internal reflection (TIR). In some designs, the in-coupling optical element 942 may be configured to direct light toward the coupling optical element 944. The in-coupling optical element 942 may be polarization-selective. For example, the in-coupling optical element 942 may include a polarization-selective redirecting element such as a polarization grating, such as a liquid crystal polarization grating. Figure 11C shows how the in-coupled light 904 propagates through the waveguide 940 by TIR.

[0113] FIG. 11D illustrates an example imaging system 900 that couples light out of an eyepiece 950. As the internally coupled light 904 propagates through the waveguide 940, a portion of the light may be incident on a coupling optical element 944. The coupling optical element 944 can be configured to couple the internally coupled light 904 out of the eyepiece 950 toward the user's eye 210. The coupling optical element 944 may be configured to couple the light as collimated light toward the eye 210. The coupling optical element 944 may be tuned to a specific wavelength range of light. For example, the coupling optical element 944 may be configured to couple infrared light (e.g., approximately 700 nm to 15,000 nm) out of the waveguide 940. In some designs, the coupling optical element 944 can be configured to couple multiple wavelengths of light out of the eyepiece 950. For example, the coupling optical element 944 may be tuned for both infrared and visible light. Coupling optical element 944 can also be configured to couple light into waveguide 940, as described more fully below.

[0114] The coupling optical element 944 can be configured to increase one or more dimensions of the eyebox for the user. For example, the one or more dimensions may be measured along a first axis (e.g., the x-axis). The eyepiece 950 may further include an orthogonal pupil expander (OPE). The OPE may have at least one light redirecting element disposed on or within the waveguide (e.g., on one of the major surfaces), or the OPE may be disposed within the waveguide 940. The OPE may include features similar to or the same as those described above with respect to the light dispersive elements 730, 740, and 750 above. In some implementations, the light redirecting element may comprise a diffractive optical element. The OPE may be configured to increase the dimension of the eyebox along a second axis (e.g., the y-axis) orthogonal to the first axis.

[0115] 11D shows how some of the light exits the eyepiece 950 toward the user's eye 210. In some designs, the combining optical element 944 is configured so that the internally coupled light 904 incident on the combining optical element 944 at various portions of the combining optical element 944 along a first axis (e.g., parallel to the x-axis) exits the eyepiece 950 at each portion of the combining optical element 944 along the first axis. This can provide the user with light to project an image or illuminate the eye for different eye positions or locations.

[0116] As shown in FIGS. 11D-11E, the coupling optical element 944 may be configured to couple the internally coupled light 904 out of the eyepiece 950 as collimated light. This light may also generally be directed approximately normal to the major surfaces of the eyepiece 950 and / or waveguide 940. The collimated light may be directed into the eye and focused onto the retina by the eye (e.g., the cornea and natural lens of the eye). This light 908 incident on the retina may provide illumination to image the retina and / or provide image content to the eye. A portion of this light 908 may, for example, be reflected or scattered from the retina and exit the eye to provide an image of the retina to be captured. The light source 960 may be an extended light source such that the light will illuminate an area of ​​the retina.

[0117] 12A-12E illustrate how the imaging system 900 of FIGS. 11A-11E can additionally or alternatively be used to collect images of the eye 210. FIG. 12A shows how light 910 reflected from the retina exits the eye 210. As shown, light 910 scattered or reflected from the retina, passing through the eye's natural lens, the intraocular pupil, and the cornea, can be collimated. This light can also be incident on the eyepiece 950 at normal incidence (e.g., perpendicular to the major surfaces of the waveguide 940 and / or the coupling optical element 944). The coupling optical element 944 can be configured to couple the light 910 reflected from the retina into the waveguide 940.

[0118] FIG. 12B illustrates exemplary imaging system 900 as it couples light into eyepiece 950. Coupling optical element 944 may include redirecting features, such as a diffractive optical element or other structure, that redirect light at an angle greater than the critical angle to be guided within waveguide 940. Coupling optical element 944 may be configured to direct incoupling light 914 generally toward light source 960 and / or imaging device 920. Coupling optical element 944 can be configured to couple less than a percentage of this light propagating toward camera 920 back out of waveguide 940. For example, a partially reflective element (e.g., a semi-transparent mirror) may be disposed on or within waveguide 940 to reduce leakage of incoupling light 914 out of waveguide 940 along the portion of waveguide 940 where coupling optical element 944 is disposed, while allowing a portion of incoupling light 914 to continue propagating within waveguide 940 by total internal reflection. The fraction of light that does not leak may be any percentage between 0 and 1. For example, the fraction may be 0.90, such that 90% of the light rays propagating through waveguide 940 along coupling optical element 944 are maintained within waveguide 940 at each reflection of the light rays. Other fractions are also possible (e.g., 0.10, 0.20, 0.30, 0.40, 0.50, 0.60, 0.70, 0.80, or any range between any of these values). Such partially reflective elements may also be used in the implementations described below.

[0119] As shown in FIG. 12C , the collimated internally coupled light 914 may continue to propagate through the waveguide 940 toward the imaging device 920. FIG. 12D illustrates that a portion of the internally coupled light 914 may continue to propagate until it is incident on one or more external coupling optical elements 952. To reduce the amount of leakage of the internally coupled light 914 out of the internal coupling optical element 942, the internal coupling optical element 942 can be configured to couple little of this light propagating toward the camera 920 back out of the waveguide. For example, a partially reflective element (e.g., a semi-transparent mirror) may be disposed on or within the waveguide 940 to reduce leakage of the internally coupled light 914 out of the waveguide 940 along the portion of the waveguide 940 where the internal coupling optical element 942 is disposed, while allowing a portion of the internally coupled light 914 to continue propagating within the waveguide 940 by total internal reflection. The portion of light that does not leak out may be any percentage between 0 and 1. For example, the fraction may be 0.90, such that 90% of a light ray propagating through waveguide 940 and along coupling optical element 944 is maintained within waveguide 940 at each reflection of the light ray. Other fractions are also possible (e.g., 0.10, 0.20, 0.30, 0.40, 0.50, 0.60, 0.70, 0.80, or any range between any of these values). Such partially reflective elements can also be used in the implementations described below.

[0120] 12E , the outcoupling optical element 952 can be configured to couple light guided within the waveguide 940 out of the waveguide 940 and onto the imaging device 920. As a result, light propagating within the waveguide 940 that is incident on the outcoupling element 952 can be redirected to exit the waveguide 940, for example, out of a major surface of the waveguide 940 (e.g., at the front or rear side of the waveguide 940), and directed onto the imaging device 920. The outcoupling optical element 952 may be configured to direct the light 926 to exit the waveguide 940 perpendicularly (e.g., normal to) the major surface of the waveguide 940. In some designs, the outcoupling optical element 952 is configured to direct the collimated light 924 onto the imaging device 920 at normal incidence to a light-sensitive portion of the imaging device 920. As discussed above, the camera 920 may be focused at infinity, for example, and the imaging optics may be configured to focus collimated light onto the detector array.

[0121] Thus, waveguide 940 may be configured to guide light coupled from user's eye 210 into waveguide 940 to be received by imaging device 920 (e.g., a camera) to capture an image of at least a portion of user's eye 210. The same waveguide 940 may be configured to guide light coupled from image projector 930 so that light from image projector 930 may be directed to user's eye 210 so that the image from image projector 930 is within the user's field of view. In some implementations, the same waveguide is configured to guide light coupled from illumination source 960 so that light from the illumination source may be directed to user's eye 210 and illuminate the eye so that an image of the eye may be captured by camera 920.

[0122] In some implementations, the same combining optical element 944 can be configured to (i) couple light from the user's eye 210 into the waveguide 940 to be received by the imaging device 920, and (ii) couple light from the image projector 930 out of the waveguide 940 into the user's eye 210 to project image content into the user's field of view. In some implementations, the same combining optical element 944 can be configured to couple light from the illumination source 960 out of the waveguide into the user's eye 210 so that light from the illumination source may illuminate the eye.

[0123] In other designs, different waveguides may be used and / or different coupling optical elements 944 may be used. In some designs, for example, a first waveguide 940 may be configured to guide light coupled from the user's eye 210 to be received by the camera 920 to capture an image of at least a portion of the user's eye 210, and a second waveguide may be configured to guide light coupled from the image projector 930 so that light from the image projector 930 is directed at the user's eye 210. The first and second waveguides may be stacked on top of each other. Another waveguide may additionally or alternatively be configured to guide light coupled from the illumination source 960 so that light from the illumination source may be directed at the user's eye 210 and illuminate the eye.

[0124] Also, in some implementations, the first coupling optical element 944 can be configured to (i) couple light from the user's eye 210 into the waveguide 940 to be received by the imaging device 920, and (ii) couple light from the image projector 930 out of the waveguide 940 into the user's eye 210 to project image content into the user's field of view. Another coupling optical element may additionally or alternatively be configured to couple light from the illumination source 960 out of the waveguide into the user's eye 210 so that light from the illumination source may illuminate the eye.

[0125] In some designs, the coupling optical element 944 can include multiple diffractive optical elements (DOEs). For example, a first DOE can be configured to couple light from the user's eye 210 into the waveguide 940 to be received by the imaging device 920. A second DOE can be configured to couple light from the image projector 930 out of the waveguide 940 to the user's eye 210 and project image content into the user's field of view. Optionally, a third DOE can be configured to couple light from the light source 960 out of the waveguide 940 to the user's eye 210 and illuminate the eye. The first and second (and possibly third) DOEs can be stacked, for example, such that in some implementations, light from an environment in front of the user passes through the first DOE, then impinges on the second DOE, then on the third DOE, and then on the user's eye. However, the order can be different.

[0126] In some designs, the first and second DOEs are integrated within a single element or volume of the waveguide 940. In some implementations, for example, the first and second DOEs are both superimposed on top of each other (e.g., occupy the same or nearly the same volume) within the waveguide 2102. For example, the first and second DOEs may be recorded in the same medium.

[0127] As described above, capturing images of the eye, e.g., the retina, can facilitate eye tracking. Figure 13A illustrates an imaging system 900 configured to image various portions of the eye 210 (e.g., the retina), e.g., at different times when the eye is in different positions. Phases A and B may refer to images of the eye 210 during different eye orientations. Figure 13A shows images of the eye 210 during both Phase A and Phase B imaging and the results.

[0128] In some implementations, light emission 928 (e.g., from illumination source 960 as described above, or from one or more illumination sources configured and / or positioned differently) can be used to acquire one or more images of retina 962, as shown by FIG. 13A. The image of retina 962 may comprise one or more regions 964, 966 imaged during different orientations of eye 210. FIG. 13A shows two regions 964, 966 of an image of retina 962. For example, region 964 of the retina imaged in stage A may be imaged while eye 210 is oriented at a normal angle relative to waveguide 940. Image data for region 966 of the retina imaged in stage B may be acquired while eye 210 is oriented at an acute angle with waveguide 940. A composite image or map of retina 962 may be acquired using one or more orientations of eye 210 during one or more stages of imaging. Processing electronics or a processor, such as data module 140 (see FIG. 2), may be used to find overlapping image data between two nearby regions. Using the image data of the overlapping regions, a composite image of the retina 962 can be determined. A larger-sized (e.g., full-size) composite image or map of the user's retina can be stored.

[0129] As described herein, a head-mounted display can be used to map the retina of a user's eye based on the direction the user's eye is pointed. To use eye gaze to provide realistic and intuitive interaction with objects in the user's environment and / or to identify the wearer of the head-mounted display device, the head-mounted display system can use retinal mapping to incorporate the uniqueness of the user's eye features and other conditions that may have an effect on the eye measurements. For example, an image may be identified based on the location of blood vessels in the corresponding retinal image.

[0130] Retinal mapping may involve a process for enabling a computing device to learn how to associate a user's eye gaze (e.g., as identified in a retinal image) with a gaze point in 2D or 3D space. An eye gaze may be associated with a single point in 2D or 3D space. An eye gaze can also be associated with multiple points in space, which can account for the movement of a virtual object (e.g., a series of points, a moving image location).

[0131] The head-mounted display system can determine the user's eye gaze based on the retinal image. The head-mounted display system can acquire the retinal image using a sensor (e.g., an eye camera, such as imaging device 920). The head-mounted display system can image one or both of the user's eyes while the user changes their eye gaze (e.g., when the user looks around to track a moving or shifting calibration target or a fixation target). To map the user's retina, the head-mounted display system can present a virtual target, e.g., a fixation target, for the user to view. The virtual target may be associated with one or more known points of gaze in 2D or 3D space. While the user views the target, the head-mounted display system can obtain retinal images and associate the images with gaze points. The head-mounted display system can calculate and / or generate a mapping matrix based on the association of the individual retinal images with gaze points associated with the targets.

[0132] The retinal mapping results can reflect the uniqueness within each person's eye. For example, the head-mounted display system can generate a mapping matrix customized to one or both eyes of a specific individual. For example, a user may have a different amount of eye movement or eye line of sight in response to a specific target. Additionally, or alternatively, a user may have different positions, sizes, shapes, and / or orientations of blood vessels within the retina. As a result, by generating calibration results specific to an individual user, the head-mounted display system may enable more accurate user interaction with eye line of sight and / or enable identification of a specific user.

[0133] Thus, when a user puts on a head-mounted display device, the system can detect whether the user is a previous user or a new user. A confusion matrix can be calculated, and scores for particular eye-gaze images stored in system memory are compared with corresponding images of the current user. The confusion matrix can include comparison scores for multiple eye-gazes and associated retinal images. Based on the comparison scores, the system can make a decision regarding the user's identity (e.g., whether the user is the same individual with whom the stored retinal image or composite map is associated) and / or a confidence level for the decision. The confidence level can include, for example, an identification coefficient. The stored image, e.g., the composite image or map, can be compared with a later-acquired image, referred to as an instantaneous or real-time image, acquired for the current user. The system may provide an alert or take other action if it detects that the user is a new user.

[0134] The system may apply filtering, such as digital filtering or image processing, to the retinal images captured by the camera. Such filtering or image processing may enhance features that may be used, for example, for identification, stitching, assembling composite images, eye tracking, etc. Such filtering or image processing may comprise edge enhancement. Such a filter may comprise, for example, a Frangi filter, although other types of filters may also be used. Such a filter or processing (e.g., edge enhancement or Frangi filter) can be used to enhance and / or detect image features such as blood vessels or tubular structures or fibers in the retinal image.

[0135] FIG. 13B illustrates a pattern of sequentially displayed fixation targets that can be used in the retinal mapping process. These virtual targets, onto which a user's eyes would direct their gaze, can redirect the eye's gaze in various different directions while the retina is imaged. The resulting images associated with different gaze directions correspond to different portions of the retina. As discussed above, when the eye gazes in different directions and views differently positioned fixation targets on the display, the images captured by the camera include different portions of the retina. These images can be assembled to form a larger map or composite image of the retina.

[0136] FIG. 13B shows a virtual target at 16 different locations within a user's field of view (FOV) 1200. In various implementations, the virtual target will be presented at a given location at a given time. One or more retinal images will be acquired during the time the virtual target is presented to the user at that particular location. This or these images may be associated with the target location and / or corresponding gaze direction. More or fewer target locations may be used. In the example shown in FIG. 13B, 16 target locations 1202a-1202p are shown. More or fewer target locations may be used. The target locations may also be different. The order in which the targets are presented at different locations may vary. For example, the target may move in a raster pattern from left to right across the user's field of view, then reverse from right to left, and then again from left to right, lowering the target's position within the field of view, with each lateral pass traversing the field of view. However, other patterns and approaches are also possible. Similarly, targets can be rendered at different locations, either similarly or differently. For example, the rendered targets may vary in size, shape, color, etc. Targets can be rendered to the user sequentially during the eye tracking calibration process. For example, as discussed above, the head-mounted display system may render targets in a serpentine pattern. For example, target 1202a may be followed by 1202b, then 1202c, then 1202d, then 1202h, then 1202g, etc. Other patterns are also possible. For example, targets may be displayed in a more random or non-sequential pattern. In some embodiments, a single target is displayed to the user, and the target moves around the user's field of view (e.g., passing through or temporarily stopping at positions 1202a-1202p during the target's movement). The head-mounted display system can obtain images of the user's retina while the user is viewing these targets.For example, the head-mounted display system can acquire a first image when the user is looking at a target at a first location 1202a, acquire a second image when the user is looking at a target at a second location 1202b, acquire a third image when the user is looking at a target at a third location 1202c, and so on. The wearable system can associate the first image with the first location 1202a, the second image with the second location 1202b, the third image with the third location 1202c, and so on. Adjacent images may be stitched together in a database to create a complete or partial retinal map. For example, two images can be stitched together in proper alignment using a feature or portion of a feature (e.g., a blood vessel or portion thereof) common to the images. In various implementations, adjacent target locations will produce overlapping images that can be aligned and stitched together. For example, target locations 1202a and 1202b, and target locations 1202b and 1202c, may produce overlapping and adjacent retinal images that may be stitched together. Thus, several different retinal images may be acquired using different eye lines of sight to assemble a larger image (e.g., a composite image or map) of the retina.

[0137] As discussed above, eye tracking can be performed using the synthetic retinal image or map. For example, after the target is no longer displayed, the user may shift their eye gaze as they view different real objects in front of the user and the head-mounted display or augmented reality (virtual) image content displayed by the head-mounted display. One or more retinal images may be acquired at these times. The terms "instantaneous" or "real-time" images may be used herein to describe images acquired following calibration that may be used for eye tracking (or other purposes, such as acquiring biometric data). These "instantaneous" or "real-time" images likely correspond to portions of the synthetic retinal image or map. The system may be configured to sufficiently match this "instantaneous" or "real-time" retinal image with the portion of the synthetic retinal image or retinal map. Such a match may be based on a feature or portion of a feature (a blood vessel or portion thereof) common to both the "instantaneous" or "real-time" retinal image and the portion of the synthetic retinal image or map. Based on the location of the portion of the synthetic retinal image or map to which this "instantaneous" or "real-time" retinal image matches, gaze direction may be inferred. Different gaze directions will result in retinal images that correspond to different portions of the retinal map. Thus, identifying the location of an "instantaneous" or "real-time" retinal image on a synthetic retinal image or map will provide information about the user's gaze direction. Eye tracking, e.g., tracking eye movement and changes in eye gaze, may be performed using such or similar methods. As discussed above, edge enhancement, edge detection, or other digital filtering and / or processing may be used to enhance and / or correlate different image features with the synthetic retinal image or retinal map.

[0138] In various implementations, after completion of an initial calibration process in which virtual or fixation targets are displayed (e.g., in multiple locations) to assemble a synthetic retinal image or map, the synthetic retinal image or map can still be refined. For example, as additional retinal images are acquired, the synthetic retinal image or map can be further refined or improved using the additional images. Thus, as additional "instantaneous" or "real-time" retinal images are acquired, for example, for purposes of providing eye tracking, the synthetic retinal image or map can be further refined or improved using "instantaneous" or "real-time" images. As the user continues to look at various locations within the display (with or without the aid of a calibration target), the retinal synthetic image or map may be further refined using additional images obtained following the initial calibration in which virtual or fixation targets were displayed. The quality of the synthetic retinal image or map can therefore be increased.

[0139] Additional non-limiting examples of how eye tracking may be performed and / or synthetic retinal images or maps may be produced and how retinal images may be used are described in U.S. Patent Publication No. 2017 / 0205875, entitled "EYE IMAGE COLLECTION," filed January 17, 2017 (the disclosure of which is incorporated herein by reference in its entirety).

[0140] Thus, as discussed above, larger portions of the retina can be recorded and mapped by acquiring retinal images and / or other images of the eye using an imaging system such as those described herein, and such images can facilitate eye tracking. For example, the image of eye 210 shown in FIG. 13A may be captured when the eye is in an arbitrary position. Processing electronics or a processor (such as the same or different from those described above as forming a composite image) can then compare the real-time captured image of the user's retina with a stored composite image or a larger (e.g., full-size) image of the user's retina to track eye movement. A given image of the user's retina captured in real time may show a specific portion of the user's retina. As described above, by comparing such a captured image with a stored image of the user's mapping of larger portions of the user's retina, the system can determine the portion of the user's retina shown in the captured image, and thereby the eye position / orientation that would produce such an image. See, for example, FIG. 13A , which shows two different images of a portion of the retina produced when the eye is in two different positions and / or orientations. Thus, the position and / or orientation of the eye can be determined by capturing different images of the retina and determining the portion of the retina that is visible. Such determination can be performed even if a composite image is not formed; rather, multiple images of the retina for different eye positions / or orientations are recorded and stored in a database. As future images of the retina are acquired, they can be compared to images in the database of stored images to determine an image in the database that is similar to the recently acquired eye image. Matching the recent image to one or more of the images in the database with an associated position and / or orientation can enable the determination of the orientation and / or position of the more recent image. Other approaches to eye tracking can also be used based on images captured using the designs described herein.

[0141] As described herein, retinal images may be employed for other purposes as well. For example, retinal images may be used to verify that a user is the same user for whom a synthetic retinal image or map was acquired. Retinal images acquired while a user is wearing a head-mounted display system (e.g., during a calibration process and / or during subsequent use) may be compared to a stored, previously acquired synthetic retinal image or map (e.g., created the previous day or when the head-mounted display was previously booted up). If a recently acquired retinal image does not sufficiently match a portion of the synthetic retinal image or map, it may be concluded that the current user is different from the previous user (e.g., for whom the synthetic virtual image or map was created). Such methods may be used for security purposes, e.g., to verify that a current user of a head-mounted display device is the device's owner or typical user. Thus, biometric data acquired via retinal imaging may be used for security purposes.

[0142] Retinal imaging may also be used to collect biometric data for monitoring the health of a user. Medically relevant data may be obtained from retinal images. Such medical data may be useful for monitoring the health of a user.

[0143] Various applications of eye imaging, such as eye tracking, health monitoring, and collecting biometric data for security, are discussed herein in the context of retinal imaging, although imaging of other parts of the user, e.g., the user's eyes, may also be employed for these and other purposes.

[0144] While the eyepiece 950 is described above as being utilized to facilitate ocular imaging, the eyepiece can also be used to image the world in front of the user. Figures 14A-14B illustrate an exemplary imaging system 900 that may be used, for example, to image a portion of the environment in front of the user and / or objects within the portion of the environment. The imaging system 900 used may be similar to that described with respect to Figures 11A-11E and / or 12A-12E, except that light is collected by the eyepiece 950 from the environment in front of the eyepiece and the user. Figure 14A illustrates light 970 from the environment, for example, reflected from and / or emitted by one or more physical objects 972 in the environment in front of the user and eyepiece 950. As shown, light 970 from the environment may be nearly collimated because, for example, physical objects 972 in the environment may be located at a sufficiently long distance from imaging system 900 so that light rays reaching imaging system 900 are collimated or nearly collimated (e.g., at infinity). In some implementations, imaging system 900 may be configured to image the environment and / or objects within the environment without the use of any optical elements (e.g., lenses, mirrors) having refractive power within imaging system 900.

[0145] The imaging system 900 shown in Figures 14A and 14B is similar to the imaging systems described above. The imaging system includes an eyepiece 950 with one or more waveguides 940, including a coupling optical element 944, configured to direct light from an image projector 930 (not shown) into the eye 210 and form an image therein. The one or more waveguides may include multiple waveguides (e.g., a stack of waveguides) configured to in-couple / out-couple multiple corresponding colors / wavelengths. Each waveguide in the stack of waveguides may be configured to direct light of a particular color (e.g., red, green, blue). For example, the most distal waveguide (e.g., a stack of waveguides) may be configured for visible light (e.g., red, blue, green) such that the waveguides are configured to in-couple and out-couple the same wavelengths of visible light. Additionally or alternatively, a waveguide configured to in-couple and out-couple invisible (e.g., infrared) light may be positioned proximal to the eye 210. Such multiple waveguides corresponding to waveguide 940 may be used in any other implementations described herein. Imaging system 900 may also include an imaging device (e.g., a camera) 920 and an outcoupling optical element 952 configured to redirect light reflected from eye 210 to be propagated within waveguide 940 to the camera. In Figures 14A and 14B, illumination source 960 is omitted because an illumination source may not be needed to image the environment in front of the user. However, an illumination source (e.g., light source 960 described above) may be used in some designs.

[0146] Eyepiece 950, waveguide 940, coupling optical element 944, out-coupling optical element 952, and camera 920 may be the same as or similar to those described above. For example, coupling optical element 944 may be physically associated with waveguide 940. For example, coupling optical element 944 and / or out-coupling optical element 952 may be positioned in an optical path between the environment in front of eyepiece 950 and camera 920 such that light from the environment is coupled into waveguide 940 via coupling optical element 944 and incident on camera 210 (e.g., to form an image of at least a portion of the environment) and coupled out of the waveguide via the out-coupling optical element. Coupling optical element 944 may comprise a plurality of turning features configured to redirect light guided in the waveguide out of the waveguide or to redirect light incident on coupling optical element 944 at an angle into the waveguide to be guided therein by total internal reflection. The out-coupling optical element 952 may comprise a plurality of turning features configured to redirect light (from the environment) that is guided at an angle within the waveguide so that the light is not guided within the waveguide by total internal reflection, but is directed outward toward the camera. The coupling optical element 944, the out-coupling optical element 952, and the turning features associated with each may be physically associated with the waveguide 940. For example, the coupling optical element 944 and / or the out-coupling optical element 952 may comprise one or more holographic or diffractive optical elements (e.g., surface relief gratings) patterned (e.g., etched) within or on the waveguide 940. The coupling optical element 944 and / or the out-coupling optical element 952 may comprise a layer disposed on the waveguide 940 or may be formed within the waveguide 940. For example, a volume holographic or diffractive optical element may be formed by varying the refractive index of a material comprising the waveguide or a layer disposed thereon. Thus, the coupling optical element 944 and / or the out-coupling optical element 952 may be disposed within the volume of the waveguide 940 or a layer disposed thereon. Depending on the design, the coupling optical element 944 and / or the out-coupling optical element 952 may be transmissive or reflective and may operate transmissively or reflectively.For example, the coupling optical element 944 and / or the out-coupling optical element 952 may each operate transmissively or reflectively, e.g., include a transmissive or reflective diffractive optical element (e.g., a grating) or a holographic optical element that redirects light transmitted therethrough or reflected therefrom. The coupling optical element 944 and / or the out-coupling optical element 952 may include a polarization optical element, such as a polarization-selective redirecting element (e.g., a polarizer). The polarization-selective redirecting element may include one or more polarization gratings, diffractive optical elements, and / or holographic optical elements, and may comprise a liquid crystal structure, such as a liquid crystal polarization grating. In some implementations, the reflective optical element may include a reflector (e.g., a mirror). Other elements, such as the waveguide 940, may similarly be similar to those described above.

[0147] FIG. 14B illustrates the operation of the imaging system 900 shown in FIG. 14A . Light 970 from the environment is coupled into the waveguide 940 by the coupling optical element 944. The coupling optical element 944 may be configured to redirect this collimated light at an angle greater than the critical angle of the waveguide 940, such that at least a portion of the collimated light is guided toward the camera 920 by total internal reflection within the waveguide. The out-coupling optical element 952 can be configured to receive at least a portion of the light from the environment in front of the user that is coupled into and guided within the waveguide 940 via the coupling optical element 944. The out-coupling optical element 952 may be configured to couple the in-coupled light out of the waveguide 940 and toward the camera 920 so that an image of the environment can be captured by the camera 920. The image of the environment may be passed to processing electronics (e.g., one or more processors), such as the data module 140 (see FIG. 2 ). The data module 140 may be configured to recreate a modified image of the environment within an augmented reality context. The processing electronics may communicate with the camera 920 via wired or wireless electronic signals. Additionally or alternatively, the processing electronics may communicate with the camera 920 using one or more remote receivers. The processing electronics may reside remotely (e.g., a cloud computing device, a remote server, etc.).

[0148] The present imaging system 900 can therefore be used to directly image an environment, which can be useful for a variety of reasons. For example, imaging the environment can be used to determine where augmented reality image content should be placed relative to objects in the environment. For example, imaging the environment can provide the location of a table so that a head-mounted display can render an image of a person standing next to the table instead of on or in the table. The imaging system 900 described with respect to imaging an environment may also be used to image the eye 210 as described with respect to FIGS. 10, 11A-11E, and / or 12A-12E.

[0149] It may be desirable to image a wide field of an environment using imaging system 900. FIG. 14C schematically illustrates imaging system 900 for collecting light from an environment using a refractive optical element or lens, such as a refractive optical element 980 (e.g., a wide field lens) in front of the eyepiece. The refractive optical element 980 may have positive refractive power. The refractive optical element 980 (e.g., a positive lens) focuses collimated light 970 from the environment toward waveguide 940. Lens types other than those shown in FIG. 14C may be employed. Transmitted light (not shown) may pass through a refractive optical element or lens, such as a refractive optical element 990 (e.g., a negative lens), configured for an equal but opposite negative refractive power of refractive optical element 980. The negative lens 990 may have a similar or identical refractive power as the positive lens 980 and may offset or cancel the refractive power of the positive lens, or a portion thereof. In this way, light from the environment (e.g., distal to waveguide 940) can pass through negative lens 990, eyepiece 950, and positive lens 980, with substantially no net change in the refractive power introduced to the eye by these two lenses. Negative lens 990 may be configured to offset or counteract the refractive power of positive lens 980, so that a user will not experience the refractive power of the positive lens when viewing the environment in front of eyepiece 950. Negative lens 990 will also counteract the effect of positive lens 980, inverting the image of objects in the environment in front of the wearer. Some light 970 from the environment can be indirectly coupled into waveguide 940 by coupling optical element 944, despite some of the light rays converging. Indirectly coupled light incident on outcoupling optical element 952 can be emitted out of waveguide 940.

[0150] Implementations (e.g., those described by FIGS. 14A-14C ) may be used outside of the augmented reality context. For example, an imaging system 900 configured to image an environment is intended to be implemented in a wearable device, such as, for example, eyeglasses (including non-refractive eyeglasses) or bifocals. Such an imaging system 900 may not require an image projector 930 and / or a light source 960. Additionally or alternatively, such an imaging system 900 may not require internal coupling optical elements configured for a corresponding image projector 930 and / or light source 960.

[0151] It may be advantageous to implement such an imaging system 900 to image an environment onto a viewing screen (e.g., television screen, computer screen) of a handheld device (e.g., cell phone, tablet), etc. The imaging system 900 may improve video chat capabilities. For example, a viewer who sees a chat partner may look at the screen and appear to be looking directly at the viewer. This may be possible because the light rays captured by the imaging system 900 will be captured within the same area the user is looking at (as opposed to viewing a screen, for example, with the light rays captured by a separate outward-facing camera positioned in a different location).

[0152] In implementations in which the imaging system 900 of FIG. 14C is also used to image the eye 210, the light source 960 and / or image projector 930 may be configured to launch light into the waveguide 940. Light reflected from the eye that is incoupled into the waveguide will pass through a refractive optical element 990 (e.g., a negative lens), so a positive power type refractive optical element may be positioned between the light source 960 and / or image projector 930 and the waveguide 940. The positive lens can be configured to offset or cancel any refractive power provided by the refractive optical element 990 before the incoupled light from the light source and / or light projector is incident on the eye 210. Lenses of types other than those shown in FIG. 14C may also be used as the optical element 990. Alternatively, or in addition, processing electronics in communication with the light source and / or image projector can be configured to modify the image sufficiently to present an undistorted image to a user after the light passes through the refractive optical element 990. The corresponding internal coupling optical element, external coupling optical element, and / or coupling optical element may, in some designs, be configured to operate on non-collimated light (e.g., diverging, converging light).

[0153] In various implementations, the same waveguide 940 may be used to (i) transmit light from the eyepiece 950 and the environment in front of the user to the camera 940, and (ii) transmit light from the image projector 930 to the eye 210 and form image content therein. Using the same waveguide 940 may simplify the system and / or eyepiece, making it more compact and potentially providing a reduced form factor. Reducing the thickness of the eyepiece 950 by reducing the number of waveguides 940 may be advantageous for other reasons as well. Lower cost and a simpler manufacturing process may be some such advantages.

[0154] Also, in various designs, the same or different imaging systems may be used within the same head-mounted display to image the eye, for example, by transmitting light from the eye through a waveguide in the eyepiece 950 to the camera 940, as described above. Such systems also use the eyepiece to transfer light from an illumination source to the eye 210 to illuminate the eye. In some designs, the eyepiece may additionally be used to transmit light from the image projector 930 to the eye 210 and form image content therein. Using the eyepiece to image the environment and to assist in imaging the eye (and potentially illuminating the eye) may simplify the system and / or make it more compact, potentially providing a reduced form factor.

[0155] Furthermore, in some implementations, the same waveguide 940 may be used to (i) transmit light from the environment in front of the eyepiece 950 to the camera 940 and (ii) transmit light from the eye 210 to the camera to capture an image of the eye. The same waveguide may be used to transmit light from the image projector 930 to the eye 210 to form image content therein, and / or to transmit light from the illumination source 960 to the eye 210 to illuminate the eye for image capture. Using the same waveguide 940 may simplify the system and / or eyepiece, making them more compact and potentially providing a reduced form factor. Reducing the thickness of the eyepiece 950 by reducing the number of waveguides 940 may be advantageous for other reasons as well. Lower cost and a simpler manufacturing process may be some such advantages.

[0156] Similarly, in addition to coupling light from the environment into waveguide 940, identical coupling optical element 944 may be configured to direct light from image projector 930 to eye 210 to form image content therein and / or to direct light from the eye into waveguide 940 to be directed therein to camera 920. Additionally or alternatively, identical coupling optical element 944 may be configured to couple light from illumination source 960 that is guided within waveguide 940 out of the waveguide and into user's eye 210.

[0157] As discussed above, one or more of coupling optical element 944, internal coupling optical element 942, or external coupling optical element 952 may comprise a polarization-selective coupling element. Thus, in various designs, light input into eyepiece 950 or waveguide 940 is polarized so as to be appropriately acted upon by the polarization-selective redirecting element.

[0158] Thus, in some embodiments, illumination source 960 comprises a polarized source of a suitable polarization to be appropriately acted upon by the polarization selective combining / redirecting element.

[0159] One or more polarization-specific optical filters and polarization-modifying elements may be included in various imaging systems 900, such as those in which the image projector 930 and / or light source 960 are positioned directly opposite each other through the waveguide 940. The polarization-sensitive element may be useful in reducing directional light emission into the imaging device 920 and / or reducing saturation of the imaging device 920, for example, in configurations in which these elements are aligned on opposite sides of the waveguide 940 at the same lateral position. FIGS. 15A-15B illustrate such configurations. The light source 960, as shown in FIG. 15A, can be configured to direct light through a polarization-specific optical filter 982, such as a polarizer (e.g., a linear polarizer), and / or through a polarization-modifying element 986 configured to alter the polarization state of the incident light, such as a polarization rotator. A retarder, such as a half-wave retarder, may, for example, rotate linear polarization. Thus, a properly oriented half-wave retarder or half-wave plate can rotate s-polarized light to p-polarized light or vice versa. Thus, in various implementations, a polarization-specific optical filter 982 and / or polarization-modifying element 986 is positioned in the optical path between light source 960 and internal coupling optical element 942 to provide the internal coupling optical element with properly oriented polarization. In some implementations, imaging system 900 does not include a polarization-modifying element, but does include a properly oriented polarizing optical filter, such as a polarizer.

[0160] Light emitted by light source 960 may pass through an array of optical elements in a particular order. For example, as shown in Figure 15A, light may first pass from light source 960 through a polarization-specific optical filter 982 (e.g., a polarizer) and then through a polarization-modifying element 986 (e.g., a rotator). After the light passes through polarization-modifying element 986, it may be incident on an in-coupling optical element 942, which may direct the light into waveguide 940 to be guided therein.

[0161] For example, the light source 960 may be configured to emit light of mixed polarizations (e.g., s-polarized and p-polarized). The polarization-specific optical filter 982 may be configured to transmit only light of a first polarization state (e.g., p-polarized). As the light continues, the polarization-modifying element 986 may be configured to change the polarization state of the light (e.g., from p-polarized to s-polarized). The internal coupling optical element may be configured to redirect s-polarized light to an angle above the critical angle of the waveguide such that s-polarized light is guided within the waveguide. The internally coupled light 904 may be substantially polarized in a second polarization (s-polarized) as it propagates through the waveguide 940. The coupling optical element 944 may be configured to redirect only light of the second polarization state (s-polarized). The coupling optical element 944 may be configured to couple the internally coupled light 904 out of the waveguide 940 and into the eye 210 to provide illumination for image capture.

[0162] To prevent direct illumination (e.g., saturation) of the imaging device 920, a polarization-modifying element 958 and / or a polarization-specific optical filter 984 may be disposed in or on the waveguide 940 such that only light of a certain polarization state (e.g., p-polarized) may pass through the polarization-specific optical filter 984 to the imaging device 920. The polarization-modifying element 958 (e.g., a half-wave plate) may be configured to change the state of polarization (e.g., from s-polarized to p-polarized). The polarization-specific optical filter 984 may be configured to transmit only light of a certain polarization (e.g., p-polarized) therethrough. In this way, light passing through the polarization-specific optical filter 982 will not be configured to transmit directly through the polarization-specific optical filter 984. In any of the above implementations (e.g., image projector 930 and / or light source 960 are on the same optical axis, as shown in FIG. 15A ), as in FIGS. 10 , 11A-11E, and 12A-12E, the configuration of polarization-specific optical filter 982, polarization-modifying element 986, internal coupling optical element 942, polarization-modifying element 958, and / or polarization-specific optical filter 984 may be implemented according to the design of FIG. 15A . Polarization-specific optical filter 984 may be a transmissive-reflective polarizer (e.g., a polarizer beamsplitter) configured to transmit light of a first polarization and redirect or reflect light of a second polarization different from the first.

[0163] A partially reflective element (e.g., a semi-transparent mirror) may be included to redirect the internally coupled light 904 to the imaging device 920. The partially reflective element may be disposed between the internal coupling optical element 942 and the polarization-modifying element 986 so that a portion of the internally coupled light 914 is reflected toward the imaging device 920 while reducing leakage of the internally coupled light 914 out of the waveguide 940. The fraction of light that does not leak may be any percentage between 0 and 1. For example, the fraction may be 0.90, such that 90% of the light rays propagating through the waveguide 940 along the coupling optical element 944 are maintained within the waveguide 940 at each reflection of the light rays. Other fractions are also possible (e.g., 0.10, 0.20, 0.30, 0.40, 0.50, 0.60, 0.70, 0.80, or any value in a range between these values).

[0164] 15B illustrates the propagation of light reflected or scattered from the retina. A portion of the light 910 reflected from the retina, having a second polarization (s-polarization), incident on the coupling optical element 944, can be redirected by the coupling optical element 944 at an angle above the critical angle of the waveguide 940 and thus guided therein. A portion of the light cannot be coupled into the waveguide 940 and will transmit therethrough as non-incoupled light 912. The incoupled light 904 can propagate through the waveguide 940 toward the camera.

[0165] Other implementations may also benefit from the use of polarization-selective elements proximal to the light source and camera. For example, various systems can be configured to provide illumination with a first polarization and capture images with a camera using light with a different polarization. For example, such a configuration may be used to reduce unwanted reflections from the cornea, etc., when imaging the retina. Reflections from the cornea will be specular. Therefore, when light of a first polarization is incident on the cornea, the light reflected from the cornea will maintain its first polarization. In contrast, the retina is diffuse. When light of a first polarization is incident on the retina, the light reflected from the retina will not maintain only the first polarization. Diffuse reflection is more likely to result in unpolarized light. Therefore, a second polarization different from the first polarization will be present in the reflected light. Similarly, by illuminating with a first polarization and imaging with a second, different polarization, the retina can be imaged with reduced glare from the cornea.

[0166] Thus, in various implementations, polarization-specific optical filters 982, 984 may both be used to reduce unwanted light reflected from eye 210 (e.g., from the cornea). For example, unwanted light, glare, or glint may be reflected from the cornea, which may saturate the image captured by imaging device 920. Light reflected from the cornea may be specular and maintain its polarization. In contrast, light reflected from the retina may be more diffusely reflected and less homogeneously polarized. Similarly, a combination of polarizers may be used to remove some or most of the unwanted reflected light. Initially, polarized light can be used to illuminate eye 210. In some designs, a polarized illumination source (e.g., light source 960) may be used. Additionally or alternatively, a first polarizer (e.g., polarization-specific optical filter 982) may be positioned at the beginning of the optical path of the illumination source to provide an initial polarization of the light. A second polarizer (e.g., polarization-specific optical filter 984) may be positioned in the optical path before the light enters imaging device 920. The second polarizer polarizes the light 90 degrees from the first polarizer. oThe polarizers 982, 984 may be rotated (e.g., the polarizers 982, 984 may be "crossed"). As a result, the eye is illuminated with a first polarization, and some light of the first polarization will be reflected from the cornea. This light will not pass through the polarizer 984 proximal to the camera. However, light reflected from the retina will include light of the second polarization. Similarly, light diffusely reflected from the retina will pass through the polarizer 984 proximal to the camera, allowing an image of the retina to be captured by the camera. Thus, in such a configuration, undesired light received from the eye (e.g., from the cornea) that may enter the imaging device 920 can be reduced or eliminated. Other configurations are also possible. For example, the polarization-selective in-coupling optical element 942 that couples light from the light source 960 into the waveguide 940 and the polarization-selective out-coupling optical element for coupling light out of the waveguide to the camera 920 may be employed to have different polarization selectivity properties. For example, a polarization-selective in-coupling optical element may selectively redirect light from an illumination source having a first polarization into a waveguide, while an out-coupling optical element may selectively redirect light of a second, different polarization out of the waveguide to a camera. The effect may again be to reduce or eliminate undesired light received from the eye (e.g., from the cornea) before entering imaging device 920.

[0167] Various imaging systems 900 capable of collecting light and imaging the retina using an eyepiece 950 are discussed herein. However, the imaging system 900 can also be configured to image other portions of the eye, such as the anterior portion of the eye. FIG. 16 illustrates how the imaging system 900 can be used to image the anterior portion (e.g., the cornea) of the eye 210. The imaging system 900 may include one or more elements of the exemplary imaging system 900 described above. In addition, the exemplary imaging system 900 may include one or more refractive-power optical elements or lenses, such as refractive-power optical elements 980, 990, having refractive power. For example, a positive-power lens or positive lens 980 may be positioned on the proximal side (e.g., closer to the eye 210) of the eyepiece 950 between the eye 210 and the eyepiece. A negative optical power lens or negative lens 990 may be positioned on the distal side of the eyepiece 950 between the eyepiece and the environment in front of the user. One or both of the lenses 980, 990 may be a variable focus element (e.g., a variable focus lens) and / or may include a liquid crystal element. In some designs, one or both of the lenses 980, 990 include a Fresnel lens. The lenses 980, 990 may incorporate liquid crystals to produce Fresnel lens functionality. Such functionality may enable variable focus of one or both of the lenses 980, 990. In some designs, one or more of the lenses 980, 990 may be integrated with and / or manufactured on or within (e.g., formed in) the eyepiece 950.

[0168] In various embodiments, the coupling optical element 944 is configured to redirect collimated light reflected from the eye 210 into the light guide to be guided therein. The positive lens 980 may thus be configured to collimate light reflected from the eye 210, such as from the anterior portion of the eye (e.g., the cornea). The positive lens 980 may therefore have a focal length that is equal to or substantially equal to the distance of the lens to the portion of the eye 210 to be imaged, e.g., the cornea.

[0169] The negative lens 990 may have a similar or identical refractive power as the positive lens 980 and offset or cancel the refractive power of the positive lens. In this way, light from the environment (e.g., distal to the waveguide 940) may pass through the negative lens 990, the eyepiece 950, and the positive lens 980, with substantially no net change in the refractive power introduced by these two lenses. Thus, the negative lens 990 may be configured to offset or cancel the refractive power of the positive lens 980 so that the user will not experience the refractive power of the positive lens when viewing the environment in front of the eyepiece 950. The negative lens 990 will also counteract the effect of the positive lens 980, inverting the image of objects in the environment in front of the wearer.

[0170] FIG. 16 illustrates light 928 incident on and scattered from the cornea. The imaging system 900 may be configured to capture this light 988 reflected from the cornea. For example, a positive lens 980 may collect a portion of the light 988 scattered from the cornea and collimate the light 988. The light 988 collimated by the positive lens 980 is incident on a coupling optical element 944, which is configured to redirect the collimated light into a waveguide 940 at an angle greater than the critical angle of the waveguide so that the light is guided therein by TIR. The coupling optical element 944, the out-coupling optical element 952, and / or the waveguide 940 may be as described above. The resulting out-coupled light 906 may be directed by the out-coupling optical element 952 out of the waveguide 940 to a camera (not shown).

[0171] FIG. 16 shows light 928, such as collimated light, that may result from the eyepiece 950 as described above. An illumination source 960 may couple light into a waveguide 940, and a coupling element 944 may couple this light from the illumination source 960 out of the waveguide. The coupling element 944 may be configured to couple the light out of the waveguide 940 as collimated light. This light illuminates and scatters from the anterior portion of the eye (e.g., the cornea). As discussed above, this scattered light 988 can be collected by a positive lens 980 and imaging system 900 to form an image of the anterior portion of the eye 210. Also, as discussed above, this illumination 928 directed onto the eye 210 may be invisible (e.g., infrared) light.

[0172] FIG. 16 also shows alternative arrangements for illuminating the eye 210. In some designs, one or more light sources 934, such as LEDs or emitters, may be positioned relative to the eye 210 and guided by TIR through a waveguide 940 to direct light thereon, rather than directly onto the eye 210. In some implementations, an eyepiece 950 or waveguide 940 is not in the optical path between the one or more light sources 934 and the eye 210. In some designs, multiple such light sources 934 may be arranged in a pattern (e.g., a circular or ring-like pattern) near and / or around the eye. In some designs, the pattern of light sources 934 may define an illumination axis parallel (e.g., coaxial) with the optical axis of one or more lenses 980, 990. The one or more light sources 934 may be similar to the one or more light sources 960 described above and may be pulsed, for example. Similarly, the one or more light sources 934 may comprise an infrared light source, such as an infrared LED, or another type of invisible light. Alternatively, the one or more light sources may comprise a visible light source that emits visible light, or the one or more light sources may emit both visible and invisible (e.g., infrared) light.

[0173] FIG. 17 illustrates another exemplary imaging system 900 configured to image a portion of the eye 210, such as the anterior portion of the eye (e.g., the cornea). The imaging system 900 shown in FIG. 17 employs a reflective optical element 996 configured to collimate light from the eye, in contrast to the transmissive optical element (lens) 980 shown in FIG. 16. A reflective optical element will have fewer aberrations than a transmissive optical element because chromatic aberrations are generally not applicable to reflective optical elements, such as the reflector 996 shown in FIG. 17. Thus, by using a reflective surface in collecting light from the eye 210, less (e.g., chromatic) aberrations are introduced into the captured image of the eye.

[0174] 17, for example, illustrates an imaging system 900 including a curved transmissive optical element 996 having a wavelength-dependent reflective coating 998. The curved transmissive optical element 996 may be positioned distal to the waveguide 940 (on the environment side of the eyepiece 950). Thus, the curved transmissive optical element 996 may be positioned between the environment in front of the wearer and the waveguide 940 and / or the coupling optical element 944. Similarly, the waveguide 940 and / or the coupling optical element 944 may be positioned between the curved transmissive optical element 996 and the eye 210.

[0175] The wavelength-dependent reflective coating 998 may be configured to reflect light of a certain wavelength or range of wavelengths. In some implementations, for example, the wavelength-dependent reflective coating 998 may be configured to reflect invisible light (e.g., infrared light) within a certain wavelength range, while the wavelength-dependent reflective coating 998 may be configured to transmit visible light. The wavelength-dependent reflective coating 998 may, in some cases, be disposed on a surface of the curved transmissive optical element 996.

[0176] As discussed above, in various designs, the coupling optical element 944 is configured to redirect collimated light reflected from the eye 210 into the waveguide 940 to be guided therein. Thus, the reflective optical element 996 may be configured to collimate light reflected from the eye 210, such as from an anterior portion of the eye (e.g., the cornea). The curved reflective optical element 996 may therefore have positive optical power with respect to light incident on its proximal side that is reflected from the wavelength-dependent reflective coating 998. Notably, in various designs, the reflective optical element 994 may have a focal length that is equal to or substantially equal to the distance from the reflective optical element 996 to the portion of the eye 210 to be imaged, e.g., the cornea, iris, etc. Exemplary values ​​for the focal length may be, for example, 2 cm to 8 cm. In some implementations, the focal length is 4 cm to 6 cm. In some designs, the focal length is approximately 5 cm. The focal length may be within any range formed by any of these values, or may be outside such ranges in different designs.

[0177] In various implementations, the reflective optical element 996 is positioned on the distal side of the eyepiece 950, in front of the eyepiece. Thus, the reflective optical element 996 is positioned between the eyepiece 950 and the environment in front of the user. Similarly, the eyepiece 950 is positioned between the reflective optical element 996 and the eye 210.

[0178] The curved transmissive optical element 996 may have a curved reflective surface with any shape of curvature. In some implementations, the surface is rotationally symmetric. In some implementations, the surface may be spherical or aspherical (e.g., parabolic). Non-rotationally symmetric shapes are also possible. However, in various designs, the reflective surface has positive optical power. The reflective optical element 996 may, for example, comprise a concave mirror, at least for certain wavelengths and / or polarizations.

[0179] The curved transmissive optical element 996 may be configured to have negligible optical power in transmission. Similarly, the curved transmissive optical element 996 may be configured to transmit light without introducing convergence or divergence. In one example, the curved transmissive optical element 996 may have an inner radius curvature that is substantially the same as the outer radius curvature. A thin optical element 996 may, for example, reduce optical aberrations with respect to light transmitted therethrough that is transmitted, may be lighter, and / or may be more compact.

[0180] In various designs, the reflective optical element 996 includes a material that is transmissive to visible light so that the user can see the environment in front of the wearer. In some cases, to improve transmission, the curved transmissive optical element 996 may be coated with an anti-reflective coating on an outer surface (e.g., a distal surface). The anti-reflective coating may be configured to reduce reflection of visible light, such as red, green, and / or blue light. However, the reflective optical element 996 may be configured to reflect a portion of light scattered from the eye 210 to form an image of the eye. Thus, the reflective optical element 996 may act differently on different light. For example, the reflective optical element 996 may act differently on different wavelengths. The reflective optical element 996 may be configured to reflect infrared light and transmit visible light.

[0181] As discussed above, one or more light sources 934 may be configured to illuminate the eye 210 with infrared light. The resulting light 988 reflected from the eye 210 (e.g., the cornea) may diverge, as illustrated diagrammatically in FIG. 17 . A curved transmissive optical element 996 may be positioned to receive this light 988 reflected from the eye (e.g., the cornea, the iris). A wavelength-dependent reflective coating 998 may be configured to reflect the light 988 reflected from the eye because the wavelength illumination used to illuminate the eye is the same wavelength (e.g., 850 nm) reflected by the reflective coating on the curved transmissive optical element 996. For example, the eye may be illuminated with infrared light (e.g., 850 nm), and the curved transmissive optical element 996 may be configured to reflect the infrared light (e.g., 850 nm) and pass visible light. The shape of the curved transmissive optical element 996 may also be configured to collimate the light 988 reflected from the eye and reflect the light to the coupling optical element 944, which redirects the collimated light into the waveguide 940 to be guided therein by TIR.

[0182] In FIG. 17 , one or more light sources 934, such as LEDs or emitters, may be positioned relative to the eye 210 and guided by TIR through a waveguide 940 to direct light thereon, rather than being directed onto the eye 210, as in certain other designs. In some implementations, an eyepiece 950 or a waveguide 940 is not in the optical path between the one or more light sources 934 and the eye 210. In some designs, multiple such light sources 934 may be arranged in a pattern (e.g., a circular or ring-like pattern) near and / or around the eye. In some designs, the pattern of light sources 934 may define an illumination axis parallel (e.g., coaxial) with the optical axis of one or more lenses 980, 990. The one or more light sources 934 may be similar to the one or more light sources 960 described above and may be pulsed, for example. Similarly, the one or more light sources 934 may comprise an infrared light source, such as an infrared LED, or another type of invisible light. However, other types of light sources may also be used.

[0183] FIG. 18 illustrates another exemplary imaging system 900 configured to image a portion of the eye 210, such as the anterior portion of the eye (e.g., the cornea). In the implementation shown in FIG. 18, polarization selectivity is employed to help control the path of light reflected from the eye. In particular, in various designs, the coupling optical element 944 is polarization selective. For example, light having a first polarization is transmitted through the coupling optical element 944, while light of a second, different polarization is redirected by the coupling optical element 944 into the waveguide 940 to be coupled therein by TIR. Thus, in various implementations, the eye 210 is illuminated with polarized light, or a polarizer (not shown) is positioned between the eye and the waveguide 940 so that light from the eye that is incident on the waveguide is polarized. For example, the emitter 934 may emit polarized light, or a polarizer may be positioned in front of the emitter 934 so that the eye 210 is illuminated with polarized light. Thus, in various designs, the polarization of polarized light incident on and / or reflected from the eye 210 that is received by the optical coupling element 944 may initially be polarized so that the light is directed toward the reflector 996.

[0184] Similarly, in various implementations, the coupling optical element 944 (and / or the out-coupling optical element 952) are each configured to transmit light of a first polarization state, such as a first linear, circular, or elliptical polarization state (e.g., p-polarized, left-handed circular, or elliptically polarized, etc.), and redirect light of a second polarization state, such as a second linear, circular, or elliptical polarization state (e.g., s-polarized, right-handed circular, or elliptically polarized, etc.), into and / or out of the waveguide. In some implementations, the eye illuminator 934 may further include a polarization-modifying element (e.g., a polarizer) that may emit only or primarily the first polarization (e.g., p-polarized) or that is configured to transmit only light of the first polarization state (e.g., p-polarized). Additionally, the coupling optical element 944 and / or the out-coupling optical element 952 may each be configured to redirect light of a second polarization (e.g., s-polarized) into and / or out of the waveguide.

[0185] 17, the curved reflector 998 of the imaging system 900 shown in FIG. 17 comprises a curved transmissive optical element 996 having a wavelength-dependent reflective coating 998. The wavelength-dependent reflective coating 998 may be configured to reflect light of a certain wavelength or range of wavelengths. In some implementations, for example, the wavelength-dependent reflective coating 998 may be configured to reflect invisible light (e.g., infrared light) within a certain wavelength range, while the wavelength-dependent reflective coating 998 may be configured to transmit visible light. The wavelength-dependent reflective coating 998 may, in some cases, be disposed on a surface of the curved transmissive optical element 996.

[0186] In various implementations, the curved transmissive optical element 996 is positioned on the distal side of the eyepiece 950, in front of the eyepiece. Thus, the reflective optical element 996 is positioned between the eyepiece 950 and the environment in front of the user. Similarly, the eyepiece 950 is positioned between the reflective optical element 996 and the eye 210.

[0187] Thus, light having a first polarization (e.g., p-polarized light) from the eye 210 is incident on the combining optical element 944 and passes therethrough to the curved transmissive optical element 996. The imaging system 900 further includes a polarization-modifying optical element 978, such as a retarder (e.g., a quarter-wave retarder). The retarder 978 is transmissive and imparts a quarter-wave phase difference to the light transmitted therethrough. The light is incident on and reflected from the curved transmissive optical element 996. The wavelength-dependent reflective coating 998 may be configured to reflect certain wavelengths of light reflected from the eye. As a result, the light is reflected from the curved surface of the curved transmissive optical element 996 and collimated. The collimated light again passes through the retarder 978, thereby imparting another quarter-wave phase difference to the light transmitted therethrough. The phase difference (e.g., full-wave phase difference) introduced in these two passes through the retarder rotates the polarization. Thus, the first polarization (e.g., p-polarized light) transmitted through the polarization-selective coupling optical element 944 on the first pass is converted to the second polarization (s-polarized light) and redirected into the waveguide 940 to be guided by TIR to the camera 920. As discussed above, in various designs, the coupling optical element 944 is configured to redirect collimated light reflected from the eye 210 into the waveguide 940 to be guided therein. Thus, the reflective optical element 996 may be configured to collimate light reflected from the eye 210, such as from the anterior portion of the eye (e.g., the cornea). The curved reflective optical element 996 may therefore have positive optical power. In particular, in various designs, the reflective optical element 994 may have a focal length that is equal to or substantially equal to the distance from the reflective optical element 996 to the portion of the eye 210 to be imaged, such as the cornea, iris, etc. Exemplary values ​​for the focal length may be, for example, 2 cm to 8 cm. In some implementations, the focal length is 4 cm to 6 cm. In some designs, the focal length is approximately 5 cm.

[0188] In various designs, the reflective optical element 996 may comprise a curved surface configured to reflect light. The curved surface may, in some cases, be spherical or rotationally symmetric. The reflective optical element 996 may comprise, for example, a concave mirror, at least for certain wavelengths and / or polarizations.

[0189] In various designs, the reflective optical element 996 includes a material that is transparent to visible light so that the user can see the environment in front of the wearer. A wavelength-dependent reflective coating 998 disposed on the surface of the curved transmissive optical element 996 may therefore be transparent to visible light, or at least some wavelengths of visible light. The curved transmissive optical element 996 may also be coated with an anti-reflective coating on its outer surface (e.g., the distal surface). The anti-reflective coating may be configured to reduce reflection of red, green, and / or blue light. However, the reflective optical element 994 may be configured to reflect a portion of light scattered from the eye 210 to form an image of the eye. Thus, the reflective optical element 996 may act differently on different light. For example, the reflective optical element 996 may act differently on light of different polarization states (and / or wavelengths). The reflective optical element 996 may be configured to transmit visible light and reflect infrared light.

[0190] As shown in FIG. 17 , one or more light sources 934, such as LEDs or emitters in FIG. 18 , may be positioned relative to the eye 210 and guided by TIR through a waveguide 940 to direct light onto, but not onto, the eye 210. Thus, in some implementations, an eyepiece 950 or a waveguide 940 is not in the optical path between the one or more light sources 934 and the eye 210. In some designs, multiple such light sources 934 may be arranged in a pattern (e.g., a circular or ring-like pattern) near and / or around the eye. The one or more light sources 934 may be similar to the one or more light sources 960 described above and may be pulsed, for example. Similarly, the one or more light sources 934 may comprise an infrared light source, such as an infrared LED, or another type of invisible light. Notably, in various implementations, the light source 934 may emit light that is reflected by a wavelength-dependent reflective coating 998 and / or a curved transmissive optical element 996. However, other types of light sources may also be used.

[0191] The polarization-selective coupling optical element 944 is configured to be polarization-selective depending on the type of linearly polarized light incident thereon, although other polarization-selective coupling optical elements may be polarization-selective for other types of polarization states, such as different types of circular or elliptical polarizations. The polarization-selective coupling optical element 944 may be configured, for example, such that a first polarization, such as a first circularly or elliptically polarized light (e.g., left-handed polarized or LHP-polarized light), is transmitted through the polarization-selective coupling optical element 944 and a second polarization, such as a second circularly or elliptically polarized light (e.g., right-handed polarized or RHP), is redirected into the light guide, or vice versa. Such polarization-selective coupling optical elements 944 may comprise liquid crystals, such as cholesteric liquid crystals. Examples of some liquid crystal optical elements are discussed below in the section entitled "Cholesteric Liquid Crystal Mirrors," in U.S. Patent Publication No. 2018 / 0164627, entitled "DIFFRACTIVE DEVICES BASED ON CHOLESTERIC LIQUID CRYSTAL," filed December 7, 2017, and in U.S. Patent Publication No. 2018 / 0239147, entitled "DISPLAY SYSTEM WITH VARIABLE POWER REFLECTOR," filed February 22, 2018, and in U.S. Patent Publication No. 2018 / 0239177, entitled "VARIABLE-FOCUS VIRTUAL IMAGE DEVICES BASED ON POLARIZATION CONVERSION," filed February 22, 2018 (each of which is incorporated by reference herein in its entirety and for all purposes).

[0192] A polarization modifying element or retarder, such as a circular polarizer, may be positioned between the eye and the polarization selective coupling optical element 944 to convert light reflected from the eye to a first polarization (e.g., LHP). The LHP light will pass through the polarization selective coupling optical element 944, reflect off the reflector 998, change polarization to RHP, and be redirected by the polarization selective coupling optical element 944 into the waveguide to the camera.

[0193] In some implementations, the reflector 996 may be polarization-selective in its reflectivity, such that only light of one polarization state is reflected and / or light of a different polarization state is transmitted. Such optical elements may comprise liquid crystals, such as cholesteric liquid crystals. Examples of such optical elements are discussed below in the section entitled "Cholesteric Liquid Crystal Mirror," in U.S. Patent Publication No. 2018 / 0164627, entitled "DIFFRACTIVE DEVICES BASED ON CHOLESTERIC LIQUIDCRYSTAL," filed December 7, 2017, in U.S. Patent Publication No. 2018 / 0239147, entitled "DISPLAY SYSTEM WITH VARIABLE POWER REFLECTOR," filed February 22, 2018, and in U.S. Patent Publication No. 2018 / 0239177, entitled "VARIABLE-FOCUS VIRTUAL IMAGE DEVICES BASED ON POLARIZATION CONVERSION," filed February 22, 2018 (each of which is incorporated by reference herein in its entirety and for all purposes). Such an optical element may reflect light of a first polarization state, such as a first circular or elliptical polarization state (e.g., left-handed circular or elliptically polarized), and transmit light of a second polarization state, such as a second circular or elliptical polarization state (e.g., right-handed circular or elliptically polarized), or vice versa. In some embodiments, liquid crystals are disposed on the curved surface of the reflector 996 such that, in reflection, the reflector has a refractive power, such as a positive refractive power. In various other implementations, the liquid crystal optical element may be flat or planar. For example, the liquid crystals may be disposed on a flat or planar substrate or layer. Despite being flat, refractive power may be included within the liquid crystal optical element. Such an element may be referred to as a cholesteric liquid crystal reflective lens. Thus, light from the eye may be collimated and reflected to the combining optical element 998. The reflector may, for example, reflect light of a first polarization state (e.g., left-handed circular or elliptically polarized) and transmit light of a second polarization (e.g., right-handed circular or elliptically polarized).Thus, the eye 210 is illuminated with left-handed circularly polarized light, or light reflected from the eye is transmitted through a polarizer (e.g., a circular or elliptical polarizer) that transmits light having a first polarization (e.g., left-handed circularly or elliptically polarized light). The coupling optical element 944 may also be polarization-selective, transmitting the LHP light and redirecting the RHP light into the waveguide. The LHP light from the eye passes through the coupling optical element 944. This transmitted LHP light also impinges on and is reflected from a wavelength-selective liquid crystal reflector 996. In one design, the wavelength-selective liquid crystal reflector 996 converts the first polarization state (e.g., LHP) to a second polarization state (e.g., RHP) in response to reflection. This light in the second polarization state (e.g., RHP light) is directed to the coupling optical element 944, which redirects the light in the second polarization state (RHP) into the waveguide 940 to the camera 920.

[0194] In some designs, the combining optical element 944 does not comprise a liquid crystal grating, but instead comprises, for example, a surface relief diffraction grating or a holographic grating. As discussed above, these combining optical elements 944 that do not comprise cholesteric liquid crystals may also comprise volume diffractive or holographic optical elements or gratings.

[0195] Thus, light scattered from the eye is reflected back into the waveguide 940 by the reflective optical element 996 for coupling into the waveguide by the coupling element 944. In contrast, however, a portion of unpolarized light from the environment in front of the wearer, corresponding to a second polarization state (e.g., RHP), will be transmitted through the reflective optical element 996. Thus, the wearer may see objects through the reflective optical element 996.

[0196] However, in various designs, the reflective optical element 996 will have negligible optical power in transmission. For example, the reflective optical element 996 may have curved surfaces with the same curvature on both sides of the optical element, such that the total optical power of the optical element for light transmitted therethrough will be negligible.

[0197] As discussed above, in various implementations, the reflective optical element 996 may be any of the optical elements described below in the section entitled "Cholesteric Liquid Crystal Mirror," U.S. Patent Publication No. 2018 / 0164627, entitled "DIFFRACTIVE DEVICES BASED ON CHOLESTERIC LIQUID CRYSTAL," filed December 7, 2017, and U.S. Patent Publication No. 2018 / 0239147, entitled "DISPLAYSYNTHESIS WITH VARIABLE POWER REFLECTOR," filed February 22, 2018, and entitled "VARIABLE-FOCUS VIRTUAL IMAGE DEVICES BASED ON POLARIZATION," respectively. A cholesteric liquid crystal reflective lens comprising a cholesteric liquid crystal reflective element as discussed in U.S. Patent Publication No. 2018 / 0239177, entitled "IR CONVERSION," filed February 22, 2018 (each of which is incorporated by reference in its entirety and for all purposes). Such optical elements may act on a specific wavelength or range of wavelengths. Thus, light, such as infrared light reflected from the eye, may be acted on by the cholesteric liquid crystal reflective element. However, light not within that wavelength range, such as visible light from the environment, may pass through the cholesteric liquid crystal reflective element without being acted on by the cholesteric liquid crystal reflective element. Thus, the cholesteric liquid crystal reflective element may have negligible refractive power for this visible light from the environment passing therethrough.

[0198] As discussed above, in some implementations, illumination source 960 couples light redirected out of the waveguide into waveguide 940 to illuminate eye 210. In such embodiments, coupling optical element 944 may be polarization selective. For example, coupling optical element 944 may transmit light of a first polarization (p-polarized light) and light of a second polarization (s-polarized light).

[0199] Thus, when light from illumination source 906 propagates through waveguide 940 and is redirected by coupling optical element 944, the illumination will be s-polarized. A polarization-modifying optical element (e.g., a quarter-wave retarder) may be positioned between waveguide 940 and eye 210 to cause a rotation of the polarization of light reflected from the eye. Light from light source 960 that is reflected from eye 210 will pass twice through the quarter-wave retarder, so that the s-polarized light that is emitted from the waveguide by coupling element 944 to illuminate the eye will be converted to p-polarized light.

[0200] This p-polarized light will be transmitted through the coupling optical element 944 and the waveguide and will be incident on the reflective optical element 996 .

[0201] The imaging system 900 may further include a second polarization-modifying element 978, which may comprise, for example, a retarder or a wave plate, as discussed above. The retarder may comprise, for example, a quarter-wave retarder. The second polarization-modifying element 978 may be disposed distal to the waveguide 940, i.e., between the waveguide and the reflector 996. The second polarization-modifying element 978 may also be disposed between the combining element beam 944 and the reflector 996. Light from the eye 210 (p-polarized light) transmitted through the combining element beam 944 passes through the second polarization-modifying element 978 and is converted to circularly polarized light. If the reflector 996 reflects circularly polarized light, the light will again be reflected back to the waveguide 940 after passing through the polarization-modifying element 978. Two passes through this polarization-modifying element (e.g., a quarter-wave retarder) 978 will convert the light to s-polarized light, which will then be redirected into the waveguide by the coupling element 944 to be directed to a camera (not shown).

[0202] 18 , light 988 reflected from eye 210 diverges. The light may be incident on and collimated by a curved or otherwise positively refractive reflector 996. A coupling optical element 944 configured to redirect the collimated light into a waveguide 940 will then direct the collimated light from curved reflective optical element 996 toward imaging device 920 (not shown). Thus, light reflected from eye 210 that is collimated by curved reflective optical element 996 is coupled into waveguide 940 and directed therein toward an outcoupling optical element 952. Outcoupling optical element 952 may be configured to direct the light out of eyepiece 950 toward a camera (not shown).

[0203] Various variations are possible in the configuration of the imaging system. Different types of reflector 996 and combining element 944 may be employed. The reflector 996 and combining element 944 may be configured to affect, for example, linearly polarized light or circularly or elliptically polarized light. As discussed, the reflector 996 has optical power. The reflector 996 and combining element 944 may comprise a cholesteric liquid crystal grating reflector and / or a lens, with or without optical power. A polarization-modifying element 978, such as a retarder, may be included between the combining element 944 and the reflector and / or between the combining element 944 and the eye. In some embodiments, a polarizer, such as a circular or linear polarizer, may be positioned between the eye and the combining element 944. For example, if unpolarized light is reflected from the eye, a polarizer (e.g., a circular or linear polarizer) may be positioned between the eye and the combining element 944. In some such cases, the combining element 944 is polarization-selective.

[0204] In configurations such as those shown in FIGS. 17 and 18 , where light reflected from the eye passes through waveguide 940 to curved reflective optical element 996, is collimated, and is redirected back into the waveguide, background noise is introduced. This background noise arises from light initially passing from the eye through coupling optical element 944. As discussed above, coupling optical element 944 may be configured to redirect collimated light into waveguide 940 to be directed to camera 920 in which an image is formed. However, coupling optical element 944 will redirect some uncollimated light incident thereon. Thus, in its initial pass through coupling optical element 944 and waveguide 940 to curved reflective optical element 996, some of the uncollimated (diverging) light reflected from the eye will be coupled into the waveguide by coupling optical element 944 and will contribute background noise to the image of the eye formed by camera 920. This noise will be superimposed on the image formed by collimated light retro-reflected by curved reflective optical element 996, which is coupled into the waveguide by coupling optical element 944 to be directed to camera 920.

[0205] In one design, this noise can be subtracted from the image. The process for subtracting the noise from the signal may involve (a) measuring the amount of light (referred to as N) coupled by coupling optical element 944 on its initial pass through coupling optical element 944 to curved reflective optical element 996, where it is redirected and reaches camera 920, and (b) measuring the total signal at camera 920 as the light passes through coupling optical element 944 and waveguide 940 to curved reflective optical element 996, is collimated, reflected back to the coupling optical element, and redirected to the camera. This total signal will also include some noise N because uncollimated light reflected from the eye will pass through coupling optical element 944 and reach curved reflective optical element 996, and therefore some of the uncollimated light will be redirected by coupling optical element 944 to camera 920. If the noise N can be measured separately from the total signal T, which includes noise superimposed across the eye image, the noise N can be subtracted from the total signal T as represented by the following equation: I=TN where I represents the image from which the noise component N has been removed.

[0206] The above two measurements (a) and (b) can be obtained in various ways. For example, as shown in Figure 19, a shutter 936 can be positioned between the curved reflective optical element 996 and the waveguide 940 and coupling optical element 944. The shutter 936 can be configured to block light when the shutter is in a first state and to transmit light when the shutter is in a second state. The shutter 936 can comprise, for example, a liquid crystal shutter.

[0207] Thus, noise component N can be measured when shutter 936 is in a first state in which light reflected from eye 210 is incident on coupling optical element 944 and passes through it toward curved reflective optical element 996, but is prevented by the closed shutter from reaching the curved reflective optical element. As discussed above, a portion of the light reflected from eye 210 is not largely collimated, but couples into coupling optical element 944 and is redirected into the waveguide where it is directed to camera 920. As referenced above, this light will not contribute to the formation of an image but will become background noise. Camera 920 may record this noise N when shutter 936 is closed.

[0208] A total signal T, including both noise N and the image, can be measured when the shutter 936 is in a second state in which the shutter is open. The light reflected from the eye 210 again impinges on the coupling optical element 944. A portion of the light reflected from the eye 210, although largely uncollimated, couples into the coupling optical element 944 and is redirected into the waveguide where it is directed to the camera 920. However, most of the light reflected from the eye 210 passes through the coupling optical element 944, through the open shutter 936, and to the curved reflective optical element 996. The curved reflective optical element 996 collimates the light and reflects at least a portion of it back to the coupling optical element 944, which redirects the collimated light into the waveguide 920 to be directed to the camera 920 to form an image of the eye 210. The camera 920 can capture the image of the eye 210.

[0209] Processing electronics (such as processing electronics 140) in communication with camera 920 can receive the noise component N, measured when shutter 936 is in a first, closed state, and the total signal T, measured when the shutter is in a second, open state, and can subtract (TN) the two. In this way, noise N contributed by uncollimated light reflected from eye 210 that is coupled into combining optical element 944 on its initial pass therethrough can be subtracted from the total image signal T. The processing electronics may communicate with camera 920 via wired electronic signals. Additionally or alternatively, the processing electronics may communicate with camera 920 using one or more remote receivers. The processing electronics may reside remotely (e.g., a cloud computing device, a remote server, etc.).

[0210] Other methods may be employed to perform measurements (a) and (b), obtain N and T, and subtract N from T. For example, if the curved reflective optical element 996 is wavelength selective as shown in FIG. 18 , the eye can be illuminated with different wavelengths of light at different times. For example, to perform measurement (a) and quantify the noise N, the eye can be illuminated with a wavelength that is not reflected by the curved reflective optical element 996. However, to perform measurement (b) and quantify the total signal T, the eye can be illuminated with a wavelength that is reflected by the curved reflective optical element 996. The noise N can then be subtracted from the total T (e.g., T N ) as discussed above.

[0211] 20-20E illustrate an example imaging system 900 configured to use wavelength modulation to make measurements and subtract the noise component N as discussed above. The imaging system 900 in FIGS. 20A-20E includes a curved transmissive optical element 996 that is wavelength-selective (such as that described with reference to FIGS. 17 and 18 above). For example, the curved transmissive optical element 996 has a wavelength-dependent reflective coating 998 on its curved surface. The imaging system 900 may also include one or more light sources or illumination sources (not shown) configured to illuminate the eye 210. One or more light sources may be configured to emit infrared light. However, the one or more light sources can be configured to emit different colors or wavelengths of light at different times. Such wavelength modulation can enable separate measurements of N to be subtracted from the total signal T.

[0212] In various implementations, for example, one or more illumination sources 960, 934 may, in a first state, provide one or more wavelengths λ that are reflected by the curved reflective optical element. Reflect In the second state, one or more wavelengths λ are not reflected. Not Reflect In the second state, the curved reflective optical element may be configured to emit a negligible amount or less of wavelength λ Reflect Similarly, in the first state, a negligible amount of wavelength λ is not reflected. Not Reflec t is released.

[0213] In some embodiments, the reflected wavelength λ Reflect The reflected wavelength λ may be approximately 800 nm to 950 nm. Reflect The reflected wavelength λ may be approximately 835 nm to 915 nm. Reflect In some designs, the reflected wavelength λ Reflect is approximately 850 nm. Light emissions 928 from one or more light sources 960 may illuminate the eye.

[0214] As shown in FIG. 20B, the wavelength λ that is not reflected by the curved reflective optical element 944Not Reflect Light 988 having a negligible amount of light λ reflected by the curved reflective optical element 944 (and Reflect ) is reflected from a portion of the eye 210 (e.g., the cornea). This light is reflected from the wavelength λ Not Reflect , light ray 916 is shown propagating through curved reflective optical element 996 into the environment in front of the user.

[0215] Although the light 988 incident on the coupling optical element 944 is not collimated, the coupling optical element nevertheless couples at least some of the light 914 into the waveguide 940 to be directed to the camera 920. Thus, the camera 920 can capture an image (Image #1) corresponding to the noise component N resulting from the uncollimated light redirected by the coupling optical element 944 on its initial pass to the curved reflective optical element 996. This image (Image #1) is background noise and is not a recognizable image of the eye. Processing electronics 140 is shown receiving this first image (Image #1).

[0216] In Figures 20C-20E, an illumination source (not shown) emits light of one or more wavelengths λ that are reflected by a curved reflective optical element. Reflect and a negligible amount of wavelength λ that is not reflected Not Reflect This wavelength λ Reflect can be, for example, 850 nm.

[0217] 20C, on the first pass through the coupling optical element 944, a portion of the light 988 reflected from the eye 210 that is incident on the coupling optical element 944 is coupled by the coupling optical element 944 into the waveguide 940 (as in FIG. 20B) and directed towards the camera 920. In addition, ReflectA curved transmissive optical element 996, which selectively reflects light from the eye 210, reflects and collimates non-intercoupled light 918 reflected from the eye 210 that is incident on the curved transmissive optical element. As shown in FIG. 20E, a coupling optical element 944 redirects this collimated reflected light and couples it into a waveguide 940 toward a camera 920. FIG. 20E shows both components reaching the camera 920: light 988 that is incident on the coupling optical element 944 and reflected from the eye 210 on its first pass through the coupling optical element 944, which is coupled into the waveguide 940 by the coupling optical element, and light that is reflected and collimated by the curved transmissive optical element 996, which is coupled into the waveguide by the coupling optical element. The camera 920 can capture an image (Image #2) corresponding to this total image component T. Processing electronics 140 is shown receiving this second image (Image #2).

[0218] As discussed above, the processing electronics may subtract noise from the image TN. In this example, image #1 may be subtracted from image #2. Thus, the processing electronics 140 may be configured to modify the second image based on the first image. However, other approaches are also possible. For example, the processing electronics 140 may be configured to create a new image representing a version of the second image with reduced optical noise. Implementations for subtracting noise from an image may be used in the implementations described above. For example, the implementations shown in FIGS. 10, 11A-11E, and / or 12A-12E may include a shutter 936 and / or a curved transmissive optical element 996 having a wavelength-dependent reflective coating 998 configured to selectively reflect non-intercoupled light 912 and direct the light toward the imaging device 920.

[0219] As discussed above, Image #1 is a reflection of one or more wavelengths λ where light is not reflected by the curved reflective optical element. Not Reflect and a negligible amount of reflected wavelength λ ReflectImage #2 was acquired for the case where light is illuminated at one or more wavelengths λ , where λ is reflected by the curved reflective optical element. Reflect and a negligible amount of wavelength λ that is not reflected Not Reflect λ = ... Not Reflect and a negligible amount of reflected wavelength λ Reflect The one or more illumination sources may further comprise a first illumination source configured to output one or more wavelengths λ reflected by the curved reflective optical element. Reflect and a negligible amount of wavelength λ that is not reflected Not Reflect The illumination source may include a second illumination source configured to output λ. The intensities of the first and second illumination sources may alternatively be increased and decreased, turned on and off, attenuated and unattenuated, passed and blocked to provide modulation of the wavelength of light to illuminate the eye. For example, during a first time interval, the first illumination source may be blocked while the second illumination source is not blocked. During a subsequent second time interval, the second illumination source may be blocked while the first illumination source is not blocked. This process may be repeated to provide modulation of the wavelength of light to illuminate the eye. In other designs, the wavelength of the light source may be λ. Reflect and λ Not Reflect The wavelength may be tuned and detuned to shift the wavelength back and forth between . Other arrangements are also possible.

[0220] As described above, the imaging system 900 may additionally be included in a head-mounted display, such as an augmented reality display, that provides the ability to image the eye by collecting light with the eyepiece 950. Such an imaging system 900 may be used for eye tracking. Multiple images of the retina or anterior portion of the eye may be acquired. Eye movement and / or repositioning may be ascertained from these images to track eye position and / or orientation. These imaging systems may also be used for biometric imaging and / or to identify a user. For example, an image of a user's eye, such as the retina or iris, may be acquired and recorded. A subsequent image of the wearer's eye (e.g., the retina or iris) may be acquired at a later time. The two images may be compared to determine whether the wearer at the subsequent instance is the wearer at the first instance. However, other uses for the imaging system are also possible.

[0221] Although the illumination system may be described above as being waveguide-based and comprising one or more waveguides, other types of light-redirecting optical elements may be employed in place of waveguides. Such light-redirecting optical elements may include redirecting features to eject light from the light-redirecting optical element onto, for example, a spatial light modulator. Thus, in any of the examples described herein and any of the examples below, any reference to a waveguide may be replaced with a light-redirecting optical element instead of a waveguide. Such light-redirecting optical elements may comprise, for example, a polarizing beam splitter, such as a polarizing beam splitting prism.

[0222] As discussed above, the systems described herein can enable the collection of biometric data and / or biometric identification. For example, an eye or a portion thereof (e.g., a retina) can be imaged to provide such biometric data and / or biometric identification. Images of the eye, such as the retina, may be acquired at various times when the head-mounted display system is worn by a user, perhaps the same user. A collection of such images can be recorded, for example, in a database. These images may be analyzed to collect biometric data. Such biometric data may be useful for monitoring the health or medical status of a user. Different medical parameters can be monitored by imaging a patient, for example, the patient's eye (e.g., a retina). The medical parameters can be recorded and compared with subsequent measurements acquired while the user is wearing the head-mounted display system.

[0223] Additionally, if a person begins wearing a head-mounted display system and an image of the user's eyes is captured that does not match the images stored in the database, a conclusion can be drawn that the person currently wearing the head-mounted display system is different from the previous user. This can be useful in determining whether the headset is being worn by the intended user or by a new user. Such a feature may enable certain medical, security, and / or ease-of-use applications or functionality. For example, the head-mounted display may be configured to identify the wearer based on characteristics of the wearer's eyes. For example, the system can be configured to determine an individual based on the wearer's retinal (e.g., blood vessels), corneal characteristics, or other ocular features. In some implementations, for example, a set of markers may be determined for a particular wearer. Based on the set of markers, the system may be able to determine that the previous user is wearing the headset, or alternatively, that a different user is wearing the headset. The markers may include the shape or center of the user's cornea, the configuration of blood vessels in the user's retina, the intensity and / or location of light reflection from the cornea, the shape of the side of the eye, and / or any other biometric marker. In some implementations, a confusion matrix can be determined. As discussed above, for example, in the discussion of developing a retinal map using virtual / fixation targets at various locations (see, e.g., FIG. 13B), the system may have the user look at a set of predetermined directions or eye poses and develop a matrix of eye or eye portion (e.g., cornea, retina, etc.) characteristics associated with each direction or eye pose. Using such a matrix, the system can determine the identity of the individual. Other methods are also possible.

[0224] Similarly, as discussed above, various configurations of the system are also possible. For example, FIG. 21 shows an exemplary eyepiece 900 that can be used to project light into a user's eye while simultaneously imaging the user's eye. The illustrated eyepiece 900 includes an internal coupling optical element 2104, a light dispersing element 2108, a light focusing element 2116, and an external coupling optical element 2120 on the opposite side of the coupling optical element 2112. Each of these optical elements may be disposed within or on a waveguide 2102. The waveguide 2102 may correspond, for example, to one of the waveguides 670, 680, 690 described herein (see, e.g., FIGS. 9A-9C ). The in-coupling optical element 2104 may correspond to one of the in-coupling optical elements 700, 710, 720 and / or in-coupling optical element 942 described herein (see, e.g., FIG. 10 ) and may be configured to inject image content from a projector into the waveguide and / or inject illumination from light source 960. The light dispersing element 2108 may correspond to one of the light dispersing elements 730, 740, 750 described herein (see, e.g., FIGS. 9A-9C ) and may be used to diffuse light in a given direction and redirect light from the in-coupling optical element 2104 to the coupling optical element 2112. The coupling optical element 2112 may correspond to the coupling optical element 944 described herein (see, e.g., FIG. 10 ). In some designs, the coupling optical element 2112 includes functionality described herein for the out-coupling optical elements 800, 810, 820 (see, e.g., FIGS. 9A-9C ). The focusing element 2116 may be configured to reduce the lateral spatial extent of the light received from the coupling optical element 2112 and redirect the light towards the out-coupling optical element 2120. The out-coupling optical element 2120 may correspond to the out-coupling optical element 952 described herein (see, e.g., FIG. 10 ).

[0225] The internal coupling optical element 2104 may be disposed within or on the waveguide 2102 to receive light, such as from a projector (e.g., image projector 930) and / or an illuminator (e.g., light source 960). The light may be passed through the waveguide 2102 to an associated light-dispersive optical element 2108. Any of the internal coupling optical element 2104, the light-dispersive optical element 2108, or the coupling optical element 2112 may be disposed on a major surface of the waveguide (e.g., on the top or bottom surface) or within the waveguide. Similarly, any one or combination of the light-collecting element 2116 and / or the external coupling optical element 2120 may also be disposed on a major surface of the waveguide 2102 (e.g., on the top or both major surfaces) or within the waveguide.

[0226] The combining optical element 2112 may receive light from the light dispersing element 2108 (e.g., via TIR), expand the light, and direct it toward the user's eye. Thus, the combining optical element 2112 may be positioned in front of the user's eye and project image content therein. Additionally, or alternatively, the combining optical element 2112 may be configured to provide illumination light on and / or into the user's eye.

[0227] Light reflected from the eye (e.g., illumination light from an illumination source) may be reflected and captured by the coupling optical element 2112. Thus, in some embodiments, the coupling optical element 2112 may serve to both outcouple light received from the light dispersive element 2108 and incouple light received from the eye into the waveguide 2102.

[0228] In some embodiments, the coupling optical element 2112 may include one or more diffractive optical elements (DOEs) such that the coupling optical element 2112 has dual functionality. A first DOE (e.g., a grating, a holographic region) may similarly be configured to outcouple light, and a second DOE may be configured to incouple light reflected from the eye into the waveguide 2102. In some embodiments, both the first and second DOEs are superimposed (e.g., occupy the same or nearly the same volume) within the waveguide 2102.

[0229] Alternatively, in some embodiments, the combining optical element 2112 includes at least two DOEs stacked over or in front of one another. For example, referring to Figure 21, the first DOE of the combining optical element 2112 may be positioned over the second diffractive element, while the second diffractive element may be positioned below the first DOE. The order of the DOEs may be reversed in other implementations.

[0230] Cholesteric Liquid Crystal Mirror Some liquid crystals exist in a phase called the chiral or cholesteric phase. In the cholesteric phase, the liquid crystal may exhibit a molecular twist along an axis perpendicular to the director, with the molecular axis parallel to the director. As described herein, a cholesteric liquid crystal (CLC) layer comprises a plurality of liquid crystal molecules in the cholesteric phase that extend in a direction perpendicular to the director, e.g., the layer depth direction, and are continuously rotated or twisted in a rotation direction, e.g., clockwise or counterclockwise. The director of the liquid crystal molecules in the chiral structure may be characterized as a spiral with a helical pitch (p), which corresponds to the length in the layer depth direction that corresponds to the net rotation angle of the liquid crystal molecules in the chiral structure through one rotation in the first rotation direction. In other words, the helical pitch refers to the distance over which the liquid crystal molecules undergo a complete 360° twist. Liquid crystals exhibiting chirality can also be described as having a twist angle or rotation angle (φ), which may refer to, for example, the relative azimuthal rotation between successive liquid crystal molecules in the layer normal direction, and a net twist angle or net rotation angle, which may refer to, for example, the relative azimuthal rotation between the top and bottom liquid crystal molecules across a defined length, for example, the length of the chiral structure or the thickness of the liquid crystal layer. As described herein, a chiral structure refers to multiple liquid crystal molecules in a cholesteric phase that extend in a direction perpendicular to the director, e.g., the layer depth direction, and are continuously rotated or twisted in a rotational direction, e.g., clockwise or counterclockwise. In one aspect, the director of the liquid crystal molecules in the chiral structure can be characterized as a spiral having a helical pitch.

[0231] 22 illustrates a cross-sectional side view of a cholesteric liquid crystal (CLC) layer 1004 comprising multiple uniform chiral structures, according to an embodiment. In the CLC layer 1004, adjacent chiral structures in a lateral direction, e.g., the x-direction, have liquid crystal molecules that are similarly aligned. In the illustrated embodiment, the chiral structures 1012-1, 1012-2, ... 1012-i are similarly configured such that liquid crystal molecules of different chiral structures at approximately the same depth, e.g., the liquid crystal molecules closest to the light-incident surface 1004S, have the same rotation angle, and the sequential rotation angle of consecutive liquid crystal molecules at approximately the same depth, and the net rotation angle of the liquid crystal molecules of each chiral structure.

[0232] The CLC 1004 comprises a CLC layer 1008 comprising liquid crystal molecules arranged in a plurality of chiral structures 1012-1, 1012-2, ... 1012-i, where each chiral structure comprises a plurality of liquid crystal molecules, and i is any suitable integer greater than 2. In operation, when incident light, comprising a combination of a light beam having left-handed circular polarization and a light beam having right-handed circular polarization, is incident on the surface 1004S of the CLC layer 1008 by Bragg reflection, light with one of the circular polarization handednesses is reflected by the CLC layer 1004, while light with the opposite polarization handedness is transmitted through the CLC layer 1008 without substantial interference. As described herein and throughout this disclosure, handedness is defined as viewed in the direction of propagation. According to an embodiment, when the polarization direction or handedness of the light beams 1016-L, 1016-R is aligned so that it has the same rotational direction as the liquid crystal molecules of the chiral structures 1012-1, 1012-2, ..., 1012-i, the incident light is reflected. As shown, incident on the surface 1004S is a light beam 1016-L with left-handed circular polarization and a light beam 1016-R with right-handed circular polarization. In the illustrated embodiment, the liquid crystal molecules of the chiral structures 1012-1, 1012-2, ..., 1012-i are continuously rotated in the clockwise direction, in which the incident light beams 1016-L, 1016-R travel, i.e., in the positive x-direction, which is the same rotational direction as the light beam 1016-R with right-handed circular polarization. As a result, light beam 1016 -R having right-handed circular polarization is substantially reflected, while light beam 1016 -L having left-handed circular polarization is substantially transmitted through CLC layer 1004 .

[0233] As described above, by matching the polarization handedness of incident elliptically or circularly polarized light with the rotation direction of the liquid crystal molecules in the chiral structure of the CLC layer, the CLC layer can be configured as a Bragg reflector. Furthermore, one or more CLC layers with different helical pitches can be configured as wavelength-selective Bragg reflectors with high bandwidth. Based on the concepts described herein with respect to various embodiments, a CLC layer can be configured as an off-axis or on-axis mirror configured to selectively reflect a first wavelength range, e.g., infrared wavelengths (e.g., near-infrared), while transmitting another wavelength range, e.g., visible wavelengths.

[0234] FIG. 23 illustrates an example of an eye tracking system 2300 employing a cholesteric liquid crystal reflector (CLCR), e.g., a wavelength-selective CLCR 1150, configured to image a viewer's eye 302, according to various embodiments. Unlike the CLC layer 1004 described above with respect to FIG. 22, chiral structures within the wavelength-selective CLCR 1150 that are adjacent in a lateral direction, e.g., the x-direction, have liquid crystal molecules that are aligned differently. That is, the chiral structures are configured such that liquid crystal molecules of different chiral structures at approximately the same depth, e.g., the liquid crystal molecules closest to the light-incident surface 1004S, have different rotation angles. As a result, light incident on the CLCR 1150 is rotated at an angle (θ) relative to the layer depth direction, as will be further described below in the context of the eye tracking system 2300. R ) is reflected.

[0235] Eye tracking can be a useful feature in interactive vision or control systems, including the wearable display systems described anywhere herein, for virtual / augmented / mixed reality display applications, among other applications. To achieve effective eye tracking, it may be desirable to capture images of the eye 302 at a low gaze angle, and in this regard, it may be desirable to position the eye tracking camera 702b near the center position of the viewer's eye. However, such a position of the camera 702b may interfere with the user's view. Alternatively, the eye tracking camera 702b may be positioned lower or to the side. However, such a position of the camera may increase the difficulty of obtaining robust and accurate eye tracking because the eye image is captured at a steeper angle. By configuring the CLCR 1150 to selectively reflect infrared (IR) light 2308 (e.g., having a wavelength of 850 nm) away from the eye 302 while transmitting visible light 2304 from the world, the camera 702b can be positioned away from the user's view while capturing eye images at normal or low gaze angles. Such a configuration does not interfere with the user's view because visible light is not reflected. The same CLCR 1150 can also be configured as an IR illumination source 2320 by reflecting IR light from an IR source, e.g., an IR LED, into the eye 302, as shown. The low gaze angle of the IR illuminator can result in less occlusion from eyelashes, for example, which is a configuration that allows for more robust detection of specular reflections and can be a useful feature in modern eye tracking systems.

[0236] 23 , according to various embodiments, the CLCR 1150 comprises one or more cholesteric liquid crystal (CLC) layers each comprising a plurality of chiral structures, each chiral structure comprising a plurality of liquid crystal molecules extending in a layer depth direction (e.g., z-direction) and sequentially rotated in a first rotation direction, as described above. The alignment of the liquid crystal molecules in the chiral structures varies periodically in a lateral direction perpendicular to the layer depth direction such that the one or more CLC layers are configured to substantially Bragg-reflect a first incident light having a first wavelength (λ1) while substantially transmitting a second incident light having a second wavelength (λ2). As described above, each of the one or more CLC layers is configured to substantially Bragg reflect first and second incident light beams of elliptically or circularly polarized light having a polarization handedness that matches a first rotation direction when viewed in the layer depth direction, while substantially transmitting first and second incident light beams of elliptically or circularly polarized light having a polarization handedness opposite to the first rotation direction when viewed in the layer depth direction. According to embodiments, the periodically varying alignment of the liquid crystal molecules in the lateral direction is arranged to have a lateral period such that the ratio between the first wavelength and the period is about 0.5 to about 2.0. According to embodiments, the first wavelength is in the near-infrared range of about 600 nm to about 1.4 μm, e.g., about 850 nm, and the second wavelength is in the visible range, having one or more colors as described elsewhere herein. According to various embodiments, the liquid crystal molecules in the chiral structure are pre-tilted with respect to a direction normal to the layer depth direction. The one or more CLC layers are configured such that the first incident light is incident at a depth of about 50° relative to the layer depth direction. o , about 60 o , about 70 o , or about 80 o The angle (θ R ) is configured to be reflected by

[0237] Thus, the wavelength-selective CLCR 1150 configured comprises one or more cholesteric liquid crystal (CLC) layers each extending in a layer depth direction and comprising a plurality of liquid crystal molecules that are continuously rotated in a first rotation direction, and the arrangement of the chiral liquid crystal molecules varies periodically in a lateral direction perpendicular to the layer depth direction so that the one or more CLC layers are configured to substantially Bragg-reflect first incident light having a first wavelength, e.g., an IR wavelength, while substantially transmitting second incident light having a second wavelength, e.g., a visible wavelength.

[0238] Similar liquid crystal layers and structures may be used for the reflector 996 and coating 998 described above in connection with Figures 17-20E. The coating 998 may comprise, for example, a liquid crystal coating and, in some implementations, may be wavelength and / or polarization selective. However, other types of coatings 998 and reflectors 996 may be employed.

[0239] In the foregoing specification, the invention has been described with reference to specific embodiments thereof. It will, however, be apparent that various modifications and changes can be made therein without departing from the broader spirit and scope of the invention. The specification and drawings are, therefore, to be regarded in an illustrative rather than a restrictive sense.

[0240] Indeed, it should be understood that the systems and methods of the present disclosure each have several innovative aspects, no single one 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.

[0241] 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, while features may be described above as operative in a combination and may even be initially exemplified as such, one or more features from the exemplified combination may, in some cases, be deleted from the combination, and the exemplified combination may be directed to a subcombination or variation of the subcombination. No single feature or group of features is required or essential for every embodiment.

[0242] It should be understood that conditional statements used herein, such as "can," "could," "might," "may," "eg," and the like, in particular, 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 imply 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. Additionally, the articles "a," "an," and "the," as used in this application and the accompanying examples, should be interpreted to mean "one or more" or "at least one," unless otherwise specified. Similarly, while 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 shown, or in sequential order, or that all of the depicted operations need not be performed to achieve desirable results. Furthermore, the figures may diagrammatically depict one or more exemplary processes in the form of a flowchart. 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, concurrently with, or during any of the depicted operations.Additionally, 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 in multiple software products. Additionally, other implementations are within the scope of the following examples. In some cases, the actions recited in the examples can be performed in a different order and still achieve desirable results.

[0243] Thus, the present disclosure is not intended to be limited to the implementations shown herein but is to be accorded the widest scope consistent with the present disclosure, the principles, and novel features disclosed herein. Various exemplary systems and methods are provided below. [Example]

[0244] Working Example Section I Example 1 1. A head-mounted display system configured to project light onto a user's eye and display augmented reality image content within the user's field of view, comprising: a frame configured to be supported on a user's head; and an image projector configured to project an image into the user's eye and display image content within the user's field of view; A camera and at least one waveguide; at least one coupling optical element configured to couple light into and guide it within the waveguide; at least one out-coupling element configured to couple light guided within the waveguide out of the waveguide and direct the light towards the camera; Equipped with A head-mounted display system, wherein a camera is positioned in an optical path relative to the at least one external coupling optical element so that an image can be captured by the camera, and receives at least a portion of the light that is coupled into the waveguide via the coupling element, guided therein, and coupled out of the waveguide by the external coupling element. Example 2 The system described in Example 1, wherein the at least one coupling optical element is configured to couple light from an environment in front of a user wearing the head-mounted display system into and guide it within the at least one waveguide so that an image of the environment can be captured by the camera. Example 3 The system of any of the preceding examples, wherein the at least one coupling optical element is configured to couple light reflected from the eye of a user wearing the head-mounted display system into and guide it within the at least one waveguide so that an image of the eye can be captured by the camera. Example 4 The system of any of the above examples, wherein the at least one coupling optical element is configured to couple light reflected from the eye of a user wearing the head-mounted display system into and guide it within the waveguide so that an image of the eye can be captured by the camera, and the system is configured to image a front portion of the eye. Example 5 The system of any of the above examples, wherein the at least one coupling optical element is configured to couple light reflected from the eye of a user wearing the head-mounted display system into and guide it within the waveguide so that an image of the eye can be captured by the camera, and the system is configured to image the corneal surface of the eye. Example 6 The system of any of the above examples, wherein the at least one coupling optical element is configured to couple and guide light reflected from the eye of a user wearing the head-mounted display system into the waveguide so that an image of the eye can be captured by the camera, and the system is configured to image the retina of the user's eye. Example 7 The system of any of the above examples further comprises an eyepiece disposed on the frame, the eyepiece configured to direct light into the user's eye and display augmented reality image content in the user's field of view, at least a portion of the eyepiece being transparent, the transparent portion being positioned in front of the user's eye when the user wears the head-mounted display so as to transmit light from an environment in front of the user to the user's eye and provide a view of the environment in front of the user. Example 8 The system of Example 7, wherein the eyepiece is configured to receive light from the image projector, direct the light into the user's eye, and display augmented reality image content in the user's field of view. Example 9 A system described in any of Examples 7-8, wherein the eyepiece lens comprises the at least one waveguide. Example 10 A system described in any of Examples 7-9, wherein the image projector is configured to direct light into the edge of the eyepiece. Example 11 11. The system of claim 9 or 10, wherein the image projector is configured to direct light into an edge of the at least one waveguide. Example 12 10. The system of any of the preceding examples, further comprising at least one internal coupling optical element configured to internally couple light from the image projector into the at least one waveguide to guide the light from the image projector to provide the image content to the user's eye. Example 13 The system of any of the above examples, wherein the at least one coupling optical element is also configured to couple light from the image projector guided within the waveguide out of the at least one waveguide so that image content can be viewed by a user's eye. Example 14 The system of any of the above examples, wherein the same coupling optical element is configured to couple light from the image projector guided within the waveguide out of the waveguide so that image content can be viewed by a user's eye, and to couple light into the at least one waveguide to be guided therein to the camera. Example 15 A system described in any of Examples 1-12, further comprising at least one image content external coupling optical element configured to couple light from the image projector guided within the waveguide out of the at least one waveguide so that the image content can be viewed by a user's eye. Example 16 10. The system of any of the preceding embodiments, wherein the at least one coupling optical element faces an eye of a user wearing the head-mounted imaging system and receives light from the eye. Example 17 A system described in any of the above examples, wherein the at least one coupling optical element is configured to couple light from an environment in front of a user wearing the head-mounted imaging system into and guide it within the at least one waveguide so that an image of the environment can be captured by the camera. Example 18 10. The system of any of the preceding embodiments, wherein the at least one coupling optical element faces an environment in front of a user wearing the head-mounted imaging system and receives light from the environment. Example 19 The system of Example 15, wherein the at least one image content external coupling optical element configured to couple light from the image projector guided within the waveguide out of the at least one waveguide, and the at least one coupling optical element configured to couple the light into the waveguide and guide it therein to the camera are superimposed on top of each other. Example 20 The system of Example 15, wherein the at least one image content external coupling optical element configured to couple light from the image projector guided within the waveguide out of the at least one waveguide, and at least one coupling optical element configured to couple the light into the waveguide and guide it therein to the camera, are stacked over one another. Example 21 The system of Example 15, wherein the at least one image content external coupling optical element configured to couple light from the image projector guided within the waveguide out of the at least one waveguide, and at least one coupling optical element configured to couple the light into the waveguide and guide it therein to the camera, are integrated within the same diffractive optical element. Example 22 The system of Example 15, wherein the at least one coupling optical element is configured to couple light into a first waveguide and guide it therein to the camera, and the at least one image content external coupling optical element is configured to couple light from the image projector that is guided within a second waveguide out of the second waveguide. Example 23 10. The system of claim 9, wherein the at least one coupling optical element is configured to couple light into a first waveguide and direct it therein to the camera, and the image projector is configured to couple light into a second waveguide and provide image content to the eye. Example 24 10. The system of any of the preceding embodiments, wherein the image projector comprises a light source, a modulator, and projection optics. Example 25 10. The system of any preceding embodiment, wherein the image projector comprises a scanning optical fiber. Example 26 26. The system of any of Examples 24 or 25, wherein the modulator comprises an optical modulator. Example 27 27. The system of embodiment 26, wherein the light modulator comprises a spatial light modulator. Example 28 10. The system of any preceding embodiment, wherein the camera comprises a detector array and imaging optics. Example 29 29. The system of example 28, wherein the imaging optics is configured to focus collimated light onto the detector array. Example 30 10. The system of any of the preceding examples, wherein the at least one waveguide comprises a material that is transparent to visible light and has a refractive index sufficient to guide light within the waveguide by total internal reflection. Example 31 10. The system of any preceding embodiment, wherein the at least one waveguide comprises a stack of waveguides. Example 32 The system of Example 31, wherein different waveguides of the stack of waveguides are configured to output light with different wavefront divergences, as if projected from different distances from the user's eye. Example 33 33. The system of example 31 or example 32, wherein different waveguides of the stack of waveguides are configured to output light with different colors. Example 34 34. The system of any of Examples 31, 32, or 33, wherein the different waveguides comprise first, second, and third waveguides, the system being configured such that the first is for red light, the second is for green light, and the third is for blue light. Example 35 The system of any of Examples 12-34, wherein the internal coupling optical element comprises a diffractive optical element or a reflector. Example 36 The system of any of Examples 12-34, wherein the internal coupling optical element comprises a diffractive optical element. Example 37 10. The system of any of the preceding embodiments, wherein the coupling optical element comprises a diffractive optical element. Example 38 10. The system of any of the preceding embodiments, wherein the coupling optical element comprises a liquid crystal. Example 39 10. The system of any of the preceding embodiments, wherein the combining optical element comprises a liquid crystal polarization grating. Example 40 10. The system of any of the preceding embodiments, wherein the outcoupling optical element comprises a diffractive optical element. Example 41 10. The system of any of the preceding embodiments, wherein the outcoupling optical element comprises a liquid crystal. Example 42 10. The system of any of the preceding embodiments, wherein the outcoupling optical element comprises a liquid crystal polarization grating. Example 43 10. The system of any of the preceding examples, wherein the coupling element is configured to increase a dimension of the eyebox along at least one axis. Example 44 44. The system of example 43, further comprising an orthogonal pupil expander comprising at least one light redirecting element within or on the at least one waveguide configured to increase a dimension of the eyebox along an axis perpendicular to at least one axis. Example 45 45. The system of embodiment 44, wherein the at least one light redirecting element comprises a diffractive optical element. Example 46 The system of any of the preceding examples, wherein the same coupling element is configured to (a) couple light into the at least one waveguide to be received by the camera, and (b) couple light from the image projector out of the at least one waveguide to the user's eye. Example 47 The system of any of the above examples, wherein the same coupling element is configured to (a) couple light from the environment into the at least one waveguide to be received by the camera, and (b) couple light from the image projector out of the at least one waveguide to the user's eye. Example 48 The system of any of the preceding examples, wherein the same coupling element is configured to (a) couple light from the eye into the at least one waveguide to be received by the camera, and (b) couple light from the image projector out of the at least one waveguide to the user's eye. Example 49 10. The system of any of the preceding examples, further comprising a reflective surface having optical power positioned to receive light reflected from the user's eye that passes through the eyepiece and direct the light back into the eyepiece. Example 50 The system described in Example 49, wherein the at least one coupling element is configured so that light from the user's eye, which passes through at least one waveguide and is reflected from a reflective surface back to the at least one waveguide, is coupled into and guided within the at least one waveguide. Example 51 A system described in any of Examples 49-50, wherein a camera is positioned in an optical path relative to the at least one external coupling optical element and receives at least a portion of light from the user's eye that is reflected from a reflective surface, coupled into the waveguide via the coupling element, guided therein, and coupled out of the waveguide by the external coupling element. Example 52 52. The system of any of Examples 49-51, wherein the reflective surface reflects infrared light but transmits visible light. Example 53 53. The system of any of Examples 49-52, wherein the reflective surface is curved. Example 54 A system described in any of Examples 49-53, wherein the reflective surface is disposed on a curved optical element. Example 55 The system of any of Examples 49-54, wherein the reflective surface is disposed on a concave mirror. Example 56 A system according to any of Examples 49-55, wherein the reflective surface has positive refractive power in reflection and negligible refractive power in transmission. Example 57 A system described in any of Examples 49-56, wherein the reflective surface is configured to collimate light from the user's eye. Example 58 A system described in any of Examples 49-57, wherein the reflective surface is configured to collimate light from the retina of the user's eye. Example 59 A system described in any of Examples 49-58, wherein the reflective surface is configured to collimate light from the front region of the user's eye. Example 60 A system described in any of Examples 49-59, wherein the reflective surface is configured to collimate light from the cornea of ​​the user's eye. Example 61 A system described in any of Examples 49-60, wherein the reflective surface is formed on a curved optical element and comprises an infrared reflective coating. Example 62 62. The system of embodiment 61, wherein the curved optical element has negligible refractive power for light transmitted therethrough. Example 63 63. The system of embodiment 61 or 62, wherein the curved optical element has first and second curved surfaces on opposite sides of the curved optical element, the first and second curved surfaces having the same curvature. Example 64 A system described in any of Examples 49-63, further comprising a retarder positioned relative to the reflective surface and the coupling optical element to rotate the polarization of light passing through at least one waveguide and reflected from the reflective surface back to the at least one waveguide and the coupling optical element. Example 65 10. The system of any of the preceding embodiments, wherein at least one combining element comprises a polarization-selective redirecting element. Example 66 10. The system of any of the preceding embodiments, wherein at least one coupling element comprises a polarization grating. Example 67 10. The system of any of the preceding examples, wherein the at least one coupling element is configured to redirect light guided within the at least one waveguide out of the waveguide and toward the eye as the collimated light is directed toward the user's eye. Example 68 10. The system of any of the preceding embodiments, wherein the at least one coupling element is configured to redirect collimated light from the reflective surface into the at least one waveguide. Example 69 10. The system of any of the preceding embodiments, wherein at least one out-coupling element comprises an off-axis reflector. Example 70 10. The system of any of the preceding embodiments, wherein at least one out-coupling element comprises a polarization-selective redirecting element. Example 71 10. The system of any of the preceding embodiments, wherein at least one out-coupling element comprises a polarization grating. Example 72 10. The system of any of the preceding embodiments, wherein at least one outcoupling element comprises a liquid crystal. Example 73 10. The system of any of the preceding embodiments, wherein at least one outcoupling element comprises a liquid crystal polarization grating. Example 74 10. The system of any of the preceding examples, further comprising a circular polarizer. Example 75 10. The system of any preceding example, wherein the internal coupling element comprises a polarization-selective redirecting element. Example 76 10. The system of any preceding example, wherein the internal coupling element comprises a polarization grating. Example 77 10. The system of any of the preceding embodiments, wherein at least one internal coupling element comprises a diffractive optical element. Example 78 10. The system of any of the preceding embodiments, wherein at least one internal coupling element comprises a diffraction grating. Example 79 10. The system of any preceding example, wherein the internal coupling element comprises an off-axis reflector. Example 80 The system of any of Examples 49-79, wherein the reflective surface comprises a liquid crystal reflector. Example 81 A system described in any of Examples 49-80, wherein the reflective surface comprises a cholesteric liquid crystal reflective lens. Example 82 A system as described in any of the above examples, wherein the same waveguide (a) directs light coupled into the at least one waveguide from the user's eye to be received by the camera so as to capture an image of at least a portion of the user's eye, and (b) directs light coupled from the image projector so that the light from the projector can be directed to the user's eye so that the image from the image projector is within the user's field of view. Example 83 The system of any of the above examples, wherein the same coupling element (a) couples light from the user's eye into the at least one waveguide to be received by the camera, and (b) couples light from the image projector out of the at least one waveguide to the user's eye. Example 84 A system described in any of Examples 49-83, further comprising electronics configured to cause the camera to capture a first image when light reflected from the reflective surface is blocked. Example 85 The system of Example 84, wherein the electronics is configured to cause the camera to capture a second image when the light reflected from the reflective surface is not blocked. Example 86 The system described in Example 85, wherein the electronics is configured to use the first image to modify the second image. Example 87 The system described in Example 85 or 86, wherein the electronics is configured to subtract from the second image based on the first image. Example 88 10. The system of any of the preceding examples, wherein the system is configured to perform eye tracking based on the images of the eye. Example 89 The system of Example 88, wherein the step of performing eye tracking based on the image of the eye includes a step of storing an image of the retina of the eye. Example 90 The system comprises: using the camera to acquire an image of a portion of the retina of the eye; comparing an image of the portion of the retina with one or more stored images of the retina; determining a user's gaze based on a comparison of one or more stored images with an image of a portion of the retina obtained from the camera; 2. The system of claim 1, wherein the system is configured to: Example 91 The system of Example 90, wherein the step of determining the user's line of sight includes a step of determining a portion of the retina corresponding to the image of the portion of the retina. Example 92 A system described in any of Examples 90-91, wherein the step of determining the user's line of sight includes a step of determining eye orientation. Example 93 10. The system of any of the preceding embodiments, wherein the system is configured to acquire biometric data based on one or more images of the user's eyes acquired by the camera. Example 94 10. The system of any of the preceding embodiments, wherein the system is configured to identify a user through biometric sensing based on one or more images of the eye acquired by the camera. Example 95 10. The system of any of the preceding examples, wherein the system is configured to provide illumination of a first polarization and to preferentially capture images with the camera using light of a second polarization different from the first polarization. Example 96 10. The system of any of the preceding examples, wherein the system is configured to illuminate the user's eye with light of a first polarization and preferentially capture images of the user's eye with the camera using light of a second polarization different from the first polarization. Example 97 97. The system of embodiment 95 or 96, wherein the first and second polarizations are orthogonal. Example 98 10. The system of any preceding example, further comprising a light source positioned to provide illumination for capturing images with the camera. Example 99 10. The system of any preceding example embodiment, further comprising a light source positioned to illuminate the user's eye. Example 100 100. The system of embodiment 98 or 99, wherein the light source comprises one or more infrared light sources. Example 101 A system described in any of Examples 98-100, wherein the light source comprises one or more infrared light emitting diodes (LEDs). Example 102 A system described in any of Examples 98-101, wherein the light source is pulsed. (Example 103) A system described in any of Examples 98-102, further comprising an off-axis reflector positioned to receive light from the light source and illuminate the user's eye with the light. Example 104 A system described in any of Examples 98-103, wherein the light source is configured to input light into the waveguide and provide the illumination. Example 105 A system described in any of Examples 98-104, wherein the light source is configured to input light into a waveguide positioned relative to the eye and provide illumination to the eye. Example 106 The system described in Example 104 or 105, further comprising an illumination internal coupling optical element configured to couple light from the light source into the waveguide. (Example 107) A system described in any of Examples 98-103, wherein the light source is configured to input light into the at least one waveguide and provide illumination. Example 108 The system of Example 107 further comprises an illumination internal coupling optical element configured to couple light from the light source into the at least one waveguide and provide illumination. Example 109 A system described in any of Examples 98-103, wherein the light source is configured to input light into the same waveguide as that used to project image content into the user's eye. Example 110 A system described in any of Examples 98-104, wherein the light source is configured to provide illumination to the user's eye and input light into the same waveguide used to direct the light to the camera. Example 111 A system described in any of Examples 98-105, wherein the light source is configured to input light into the same waveguide as that used to guide light from the user's eye to the camera. Example 112 A system described in any of Examples 109-111, further comprising an illumination internal coupling optical element configured to couple light from the light source into the waveguide. Example 113 A system described in any of Examples 106, 108, or 112, wherein the illumination incoupling optical element is a polarization-selective incoupling light of a first polarization. Example 114 The system described in Examples 98-113, wherein the light source is a polarized light source configured to output polarized light having a first polarization. Example 115 A system described in any of Examples 98-114, wherein the light source is configured to direct polarized light having a first polarization onto the eye. Example 116 The system described in Examples 98-115 further comprises an illumination polarizer having a first polarization and positioned in an optical path between the light source and the eye to polarize light directed toward the eye. Example 117 The system of Example 116, wherein an illumination polarizer is positioned in the optical path between the light source and the waveguide and configured to provide illumination. Example 118 A system described in any of Examples 98-117, further comprising an image acquisition polarizer in the optical path between the eye and the camera. Example 119 The system of Example 118, wherein the image acquisition polarizer is proximal to the camera. Example 120 A system as described in Example 118 or 119, wherein the image acquisition polarizer is positioned in an optical path between (a) the at least one waveguide configured to guide light to the camera, and (b) the camera. Example 121 A system described in any of Examples 118-120, wherein the image acquisition polarizer reduces the amount of light of the first polarization that reaches the camera. Example 122 The system described in Examples 118-121, wherein the image acquisition polarizer comprises a polarizer configured to selectively couple light of a second polarization different from the first polarization into the camera. Example 123 10. The system of claim 9, further comprising at least one focusing element disposed in an optical path between the at least one coupling element and the at least one outcoupling optical element, the focusing element reducing a lateral spatial extent of light from the at least one coupling element prior to reaching the at least one outcoupling optical element. Example 124 10. The system of any preceding example embodiment, wherein the at least one light-collecting element comprises a diffractive optical element. Example 125 10. The system of any of the preceding examples, wherein the at least one light-collecting element comprises a hologram or a diffraction grating. Example 126 10. The system of any of the preceding examples, wherein the at least one waveguide comprises a material transparent to infrared light having a refractive index sufficient to guide the infrared light within the waveguide by total internal reflection. Example 127 10. The system of any of the preceding embodiments, wherein the at least one combining optical element comprises an exit pupil expander. Example 128 10. The system of any of the preceding examples, wherein the system includes an optical power for increasing collimation of light reflected from the eye that is coupled into the waveguide to be directed to the camera. Example 129 10. The system of any of the preceding examples, wherein the system includes an optical power for increasing collimation of light reflected from the front portion of the eye that is coupled into the waveguide to be directed to the camera. Example 130 10. The system of any of the preceding examples, wherein the system includes an optical power coupled into the waveguide to increase collimation of light reflected from the cornea of ​​the eye as it is directed to the camera. Example 131 A system described in any of Examples 128-130, wherein the refractive power comprises a positive refractive power. Example 132 The system of any of Examples 128-131, wherein the refractive power is provided by a lens. Example 133 A system described in any of Examples 88-132, wherein one or more stored images of the retina of the eye comprise a composite image of the retina of the eye generated using multiple images of different portions of the retina of the eye. Example 134 A system described in any of Examples 88-133, wherein the composite image of the retina comprises multiple images of the retina stitched together. Example 135 A system described in any of Examples 88-134, wherein the multiple images of the retina stitched together comprise images acquired when a fixation target is displayed within the user's field of view at various locations, respectively. Example 136 A system described in any of Examples 88-135, wherein one or more stored images of the retina comprise images acquired when a fixation target is displayed within the user's field of view at various locations, respectively. Example 137 A system described in any of Examples 88-136, wherein the system is further configured to update the composite image using an acquired image of a portion of the retina of the eye. Example 138 A system described in any of Examples 88-137, wherein the step of updating a composite image of the retina using acquired images of portions of the retina includes the step of stitching the acquired images into sections of the composite image corresponding to portions of the retina shown in the acquired images. Example 139 A system described in any of Examples 88-138, wherein the system is further configured to apply a digital filter to an acquired image of a portion of the retina of the eye and acquire a filtered image of the portion of the retina. Example 140 The system of Example 139, wherein the system is further configured to compare the filtered image of the portion of the retina with one or more stored images of the retina. Example 141 A system described in any of Examples 139-140, wherein the digital filter comprises a Frangi filter. Example 142 A system described in any of Examples 88-139, wherein the system is configured to apply an edge and enhance an acquired image of a portion of the retina. (Example 143) 10. The system of any of the preceding embodiments, wherein the system is configured to perform user identification verification using retinal images. Example 144 The system comprises: using the camera to acquire an image of a portion of the retina of the eye; comparing the image of the portion of the retina with one or more stored images of the retina; 2. The system of claim 1, wherein the system is configured to: Example 145 The system of Example 144, wherein one or more stored images of the retina of the eye comprise a composite image of the retina of the eye generated using multiple images of different portions of the retina of the eye. Example 146 A system described in any of Examples 144-145, wherein the composite image of the retina comprises multiple images of the retina stitched together. Example 147 A system described in any of Examples 144-146, wherein the multiple images of the retina stitched together comprise images acquired when a fixation target is displayed within the user's field of view at various locations, respectively. Example 148 A system described in any of Examples 144-146, wherein one or more stored images of the retina comprise images acquired when a fixation target is displayed within the user's field of view at various locations, respectively. Example 149 A system described in any of Examples 144-148, wherein the system is further configured to update the composite image using an acquired image of a portion of the retina of the eye. Example 150 A system described in any of Examples 144-149, wherein the step of updating the composite image of the retina using acquired images of portions of the retina includes the step of stitching the acquired images into sections of the composite image corresponding to portions of the retina shown in the acquired images. Example 151 A system described in any of Examples 144-150, wherein the system is further configured to apply a digital filter to an acquired image of a portion of the retina of the eye and acquire a filtered image of the portion of the retina. Example 152 The system of Example 151, wherein the system is further configured to compare the filtered image of the portion of the retina with one or more stored images of the retina. Example 153 A system described in any of Examples 144-152, wherein the digital filter comprises a Frangi filter. Example 154 A system described in any of Examples 144-153, wherein the system is configured to apply an edge and enhance an acquired image of a portion of the retina. Example Section II Example 1 1. A head mounted display system configured to project light into a user's eyes and display augmented reality image content within a field of view of the user to image at least a portion of an environment in front of a user wearing the head mounted display system, a frame configured to be supported on a user's head; and an image projector configured to project an image; A camera and an eyepiece disposed on the frame, the eyepiece configured to direct light into the user's eye and display augmented reality image content in the user's field of view, at least a portion of the eyepiece being transparent, the transparent portion being positioned in a location in front of the user's eye when the user wears the head mounted display so as to transmit light from an environment in front of the user to the user's eye and provide a view of the environment in front of the user; the eyepiece (a) at least one waveguide; (b) at least one incoupling optical element configured to incoupling light from the image projector into the at least one waveguide so as to guide the light from the image projector therein; (c) at least one coupling optical element configured to couple light from the image projector guided within the waveguide out of the waveguide and direct the light toward an eye of a user; (d) at least one out-coupling element configured to couple light in the waveguide out of the waveguide and direct the light to the camera; an eyepiece comprising: Equipped with an image projector couples light from the image projector into the waveguide such that the light is positioned in an optical path relative to and guided within the at least one internal coupling optical element such that the light is coupled out of the waveguide by the at least one coupling element to an eye of the user such that the image from the projector is within a field of view of the user; the coupling element is configured to couple light from an environment in front of a user wearing the head mounted display into the waveguide and guide it therein; a camera disposed in an optical path relative to the at least one outcoupling optical element, receiving at least a portion of light from an environment in front of the user that is coupled into and guided within the waveguide via the coupling element and coupled out of the waveguide by the outcoupling element such that an image of the environment can be captured by the camera; The same waveguide (a) directs light coupled from the environment through the waveguide to be received by the camera so as to capture an image of at least a portion of the environment in front of the user, and (b) directs light coupled from the projector so that the light from the projector can be directed to the user's eye so that the image from the projector is within the user's field of view. Head-mounted display system. Example 2 2. The system of example 1, wherein the image projector comprises a light source, a modulator, and projection optics. Example 3 3. The system of any one of claims 1 to 2, wherein the image projector comprises a scanning optical fiber. Example 4 4. The system of any of Examples 2 or 3, wherein the modulator comprises an optical modulator. Example 5 5. The system of example 4, wherein the light modulator comprises a spatial light modulator. Example 6 10. The system of any preceding embodiment, wherein the camera comprises a detector array and imaging optics. Example 7 7. The system of example 6, wherein the imaging optics is configured to focus collimated light onto the detector array. Example 8 10. The system of any of the preceding examples, wherein the at least one waveguide comprises a material that is transparent to visible light and has a refractive index sufficient to guide light within the waveguide by total internal reflection. Example 9 10. The system of any preceding embodiment, wherein the at least one waveguide comprises a stack of waveguides. Example 10 10. The system of example 9, wherein different waveguides of the stack of waveguides are configured to output light with different wavefront divergences, as if projected from different distances from the user's eye. Example 11 11. The system of example 9 or 10, wherein different waveguides of the stack of waveguides are configured to output light with different colors. Example 12 12. The system of any of Examples 9, 10, or 11, wherein the different waveguides comprise first, second, and third waveguides, the system being configured such that the first is for red light, the second is for green light, and the third is for blue light. Example 13 10. The system of any of the previous examples, wherein the incoupling optical element comprises a diffractive optical element or a reflector. Example 14 10. The system of any of the preceding embodiments, wherein the coupling optical element comprises a diffractive optical element. Example 15 10. The system of any of the preceding embodiments, wherein the outcoupling optical element comprises a diffractive optical element. Example 16 10. The system of any of the preceding examples, wherein the coupling element is configured to increase a dimension of the eyebox along at least one axis. Example 17 17. The system of example 16, further comprising an orthogonal pupil expander comprising at least one light redirecting element within or on the at least one waveguide configured to increase a dimension of the eyebox along an axis orthogonal to at least one axis. Example 18 18. The system of example 17, wherein the at least one light redirecting element comprises a diffractive optical element. Example 19 The system of any of the above examples, wherein the same coupling element (a) couples light from the environment into the at least one waveguide to be received by the camera, and (b) couples light from the image projector out of the at least one waveguide to the user's eye. Example 20 10. The system of any of the preceding examples, further comprising a reflective surface having optical power positioned to receive light reflected from the user's eye that passes through the eyepiece and direct the light back into the eyepiece. Example 21 The system of Example 20, wherein the at least one coupling element is configured so that light from the user's eye, which passes through the eyepiece and is reflected back to the eyepiece from a reflective surface, is coupled into and guided within the waveguide. Example 22 A system described in any of Examples 20-21, wherein a camera is positioned in an optical path relative to the at least one external coupling optical element and receives at least a portion of light from the user's eye that is reflected from a reflective surface, coupled into the waveguide via the coupling element, guided therein, and coupled out of the waveguide by the external coupling element. Example 23 23. The system of any of Examples 20-22, wherein the reflective surface reflects infrared light but transmits visible light. Example 24 24. The system of any of Examples 20-23, wherein the reflective surface is curved. Example 25 25. The system of any of Examples 20-24, wherein the reflective surface is disposed on a curved optical element. Example 26 26. The system of any of Examples 20-25, wherein the reflective surface is disposed on a concave mirror. Example 27 27. The system of any of Examples 20-26, wherein the reflective surface has positive refractive power in reflection and negligible refractive power in transmission. Example 28 A system described in any of Examples 20-27, wherein the reflective surface is configured to collimate light from the user's eye. Example 29 A system described in any of Examples 20-28, wherein the reflective surface is configured to collimate light from the retina of the user's eye. Example 30 A system described in any of Examples 20-29, wherein the reflective surface is configured to collimate light from the front region of the user's eye. Example 31 A system described in any of Examples 20-30, wherein the reflective surface is configured to collimate light from the cornea of ​​the user's eye. Example 32 A system described in any of Examples 20-31, wherein the reflective surface is formed on a curved optical element having an infrared reflective coating on the reflective surface. Example 33 34. The system of example 33, wherein the curved optical element has negligible optical power for light transmitted therethrough. Example 34 34. The system of example 32 or example 33, wherein the curved optical element has first and second curved surfaces on opposite sides of the curved optical element, the first and second curved surfaces having the same curvature. Example 35 A system as described in any of the above examples, further comprising a retarder positioned relative to the reflective surface and the combining optical element to rotate the polarization of light passing through the eyepiece and reflected from the reflective surface back to the eyepiece and the combining optical element. Example 36 10. The system of any of the preceding embodiments, wherein at least one combining element comprises a polarization-selective redirecting element. Example 37 10. The system of any of the preceding embodiments, wherein at least one coupling element comprises a polarization grating. Example 38 10. The system of any of the preceding examples, wherein the at least one coupling element is configured to redirect light guided within the at least one waveguide out of the waveguide and toward the eye as the collimated light is directed toward the user's eye. Example 39 10. The system of any of the preceding embodiments, wherein the at least one coupling element is configured to redirect collimated light from the reflective surface into the at least one waveguide. Example 40 10. The system of any of the preceding embodiments, wherein at least one out-coupling element comprises an off-axis reflector. Example 41 10. The system of any of the preceding embodiments, wherein at least one out-coupling element comprises a polarization-selective redirecting element. Example 42 10. The system of any of the preceding embodiments, wherein at least one out-coupling element comprises a polarization grating. Example 43 10. The system of any of the preceding examples, further comprising a circular polarizer. Example 44 10. The system of any preceding example, wherein the internal coupling element comprises a polarization-selective redirecting element. Example 45 10. The system of any preceding example, wherein the internal coupling element comprises a polarization grating. Example 46 10. The system of any preceding example, wherein the internal coupling element comprises an off-axis reflector. Example 47 The system of any of Examples 20-34, wherein the reflective surface comprises a liquid crystal reflector. Example 48 The system of any of Examples 20-34 or 47, wherein the reflective surface comprises a cholesteric liquid crystal reflective lens. Example 49 A system as described in any of the above examples, wherein the same waveguide (a) directs light coupled from the user's eye into the at least one waveguide to be received by the camera so as to capture an image of at least a portion of the user's eye, and (b) directs light coupled from the image projector so that the light from the projector can be directed to the user's eye so that the image from the image projector is within the user's field of view. Example 50 The system of any of the above examples, wherein the same coupling element (a) couples light from the user's eye into the at least one waveguide to be received by the camera, and (b) couples light from the image projector out of the at least one waveguide to the user's eye. Example 51 10. The system of any of the preceding examples, further comprising electronics configured to cause the camera to capture a first image when light reflected from the reflective surface is interrupted. Example 52 The system of Example 51, wherein the electronics is configured to cause the camera to capture a second image when the light reflected from the reflective surface is not blocked. Example 53 53. The system of Example 52, wherein the electronics is configured to use the first image to modify the second image. Example 54 54. The system of Example 53, wherein the electronics is configured to subtract from the second image based on the first image. Example 55 10. The system of any of the preceding examples, wherein the system is configured to perform eye tracking based on the images of the eye. Example 56 The system of Example 55, wherein the step of performing eye tracking based on the image of the eye includes a step of storing an image of the retina of the eye. Example 57 The system comprises: storing an image of the retina of said eye; capturing an image of a portion of the retina of the eye; comparing the stored image of the retina with the image of the portion of the retina; determining the user's gaze based on a comparison of the stored image and the image of the retinal portion; 2. The system of claim 1, wherein the system is configured to: Example 58 The system described in Example 57, wherein the step of determining the user's line of sight includes a step of determining a portion of the retina corresponding to the image of the portion of the retina. Example 59 A system described in any of Examples 57-58, wherein the step of determining the user's line of sight includes a step of determining eye orientation. Example 60 10. The system of any preceding example embodiment, further comprising a light source positioned to illuminate the user's eye. Example 61 The system of Example 60, wherein the light source comprises one or more infrared light sources configured to direct infrared light toward the user's eye. Example 62 62. The system of embodiment 60 or 61, wherein the light source comprises one or more infrared light-emitting diodes (LEDs). Example 63 A system described in any of Examples 60-62, wherein the light source is pulsed. Example 64 10. The system of any preceding example, further comprising an off-axis reflector positioned to receive light from the light source and illuminate the eye with the light. Example 65 1. A head-mounted imaging system configured to image at least a portion of an environment in front of a user wearing the head-mounted imaging system, comprising: a frame configured to be supported on a user's head; and a camera; and an eyepiece disposed on the frame, at least a portion of the eyepiece being transparent, the transparent portion being positioned in front of the user's eye when the user wears the head-mounted imaging system so as to transmit light from an environment in front of the user to the user's eye and provide a view of the environment in front of the user, the eyepiece comprising: (a) at least one waveguide; (b) at least one coupling optical element configured to couple light from an environment in front of a user wearing the head-mounted imaging system into the waveguide and guide it therein; (c) at least one out-coupling element configured to couple light in the waveguide out of the waveguide and direct the light to the camera; an eyepiece comprising: Equipped with A head-mounted imaging system in which a camera is positioned in an optical path relative to the at least one outcoupling optical element and receives at least a portion of light from an environment in front of the user that is coupled into and guided within the waveguide via the coupling element and coupled out of the waveguide by the outcoupling element so that an image of the environment can be captured by the camera. Example 66 66. The system of Example 65, wherein the camera comprises a detector array and imaging optics. Example 67 67. The system of embodiment 66, wherein the imaging optics is configured to focus collimated light onto the detector array. Example 68 A system described in any of Examples 65-67, wherein the at least one waveguide comprises a material that is transparent to visible light and has a refractive index sufficient to guide light within the waveguide by total internal reflection. Example 69 A system described in any of Examples 65-68, wherein the at least one waveguide comprises a stack of waveguides. Example 70 The system of Example 69, wherein different waveguides of the stack of waveguides are configured to output light with different wavefront divergences, as if projected from different distances from the user's eye. Example 71 71. The system of embodiment 69 or 70, wherein different waveguides of the stack of waveguides are configured to output light with different colors. Example 72 A system described in any of Examples 69-71, wherein the different waveguides include a first, a second, and a third waveguide, and the system is configured such that the first is for red light, the second is for green light, and the third is for blue light. Example 73 A system described in any of Examples 65-72, wherein the coupling optical element comprises a diffractive optical element. Example 74 A system described in any of Examples 65-73, wherein the external coupling optical element comprises a diffractive optical element. Example 75 A system described in any of Examples 65-74, wherein the coupling element is configured to increase the dimension of the eyebox along at least one axis. Example 76 The system of Example 75, further comprising an orthogonal pupil expander comprising at least one light redirecting element within or on the at least one waveguide configured to increase the dimension of the eyebox along an axis perpendicular to at least one axis. Example 77 77. The system of embodiment 76, wherein the at least one light redirecting element comprises a diffractive optical element. Example Section III Example 1 1. A head mounted display system configured to project light onto a user's eye, display augmented reality image content within a field of view of the user, and image at least a portion of the eye of a user wearing the head mounted display system, a frame configured to be supported on a user's head; and an image projector configured to project an image; A camera and an eyepiece disposed on the frame, the eyepiece configured to direct light into the user's eye and display augmented reality image content in the user's field of view, at least a portion of the eyepiece being transparent, the transparent portion being positioned in a location in front of the user's eye when the user wears the head mounted display so as to transmit light from an environment in front of the user to the user's eye and provide a view of the environment in front of the user; the eyepiece (a) at least one waveguide; (b) at least one incoupling optical element configured to incoupling light from the image projector into the at least one waveguide so as to guide the light from the image projector therein; (c) at least one coupling optical element configured to couple light from the image projector guided within the waveguide out of the waveguide and direct the light toward an eye of a user; (d) at least one out-coupling element configured to couple the light guided within the waveguide out of the waveguide and direct the light to the camera; an eyepiece comprising: a reflective surface having optical power positioned to receive light reflected from the user's eye passing through the eyepiece and direct the light back to the eyepiece; Equipped with an image projector is disposed in an optical path relative to the at least one incoupling optical element, incoupling light from the image projector into the waveguide such that the light is guided therein by the at least one coupling element to be coupled out of the waveguide to an eye of the user such that the image from the projector is within a field of view of the user; the at least one coupling element is configured such that light from the user's eye, passing through the eyepiece and reflected back to the eyepiece from a reflective surface, is coupled into and guided within the waveguide; a camera disposed in an optical path relative to the at least one outcoupling optical element, receiving at least a portion of light from the user's eye that is reflected from a reflective surface, coupled into and guided within the waveguide via a coupling element, and coupled out of the waveguide by the outcoupling element; Head-mounted display system. Example 2 10. The system of example 1, further comprising a light source positioned to illuminate the user's eye. Example 3 3. The system of example 2, wherein the light source comprises one or more infrared light sources configured to direct infrared light toward the user's eye. Example 4 4. The system of any one of Examples 2 to 3, wherein the light source comprises one or more infrared light emitting diodes (LEDs). Example 5 The system of any of Examples 2-4, wherein the light source is pulsed. Example 6 10. The system of any preceding example, further comprising an off-axis reflector positioned to receive light from the light source and illuminate the eye with the light. Example 7 10. The system of any of the previous examples, wherein the reflective surface reflects infrared light but transmits visible light. Example 8 10. The system of any of the preceding embodiments, wherein the reflective surface is curved. Example 9 10. The system of any of the previous examples, wherein the reflective surface is disposed on a curved optical element. Example 10 10. The system of any of the preceding embodiments, wherein the reflective surface is disposed on a concave mirror. Example 11 10. A system according to any of the previous examples, wherein the reflective surface has positive optical power in reflection and negligible optical power in transmission. Example 12 10. The system of any of the preceding examples, wherein the reflective surface is configured to collimate light from the user's eye. Example 13 10. The system of any of the preceding examples, wherein the reflective surface is configured to collimate light from a retina of the user's eye. Example 14 10. The system of any of the preceding examples, wherein the reflective surface is configured to collimate light from the anterior region of the user's eye. Example 15 10. The system of any of the preceding examples, wherein the reflective surface is configured to collimate light from the cornea of ​​the user's eye. Example 16 10. The system of any of the previous examples, wherein the reflective surface is formed on a curved optical element having an infrared reflective coating thereon. Example 17 17. The system of example 9 or 16, wherein the curved optical element has negligible refractive power for light transmitted therethrough. Example 18 18. A system described in any of Examples 9, 16, or 17, wherein the curved optical element has first and second curved surfaces on opposite sides of the curved optical element, the first and second curved surfaces having the same curvature. Example 19 A system as described in any of the above examples, further comprising a retarder positioned relative to the reflective surface and the combining optical element to rotate the polarization of light passing through the eyepiece and reflected from the reflective surface back to the eyepiece and the combining optical element. Example 20 10. The system of any of the preceding embodiments, wherein at least one combining element comprises a polarization-selective redirecting element. Example 21 10. The system of any of the preceding embodiments, wherein at least one coupling element comprises a polarization grating. Example 22 10. The system of any of the preceding examples, wherein the at least one coupling element is configured to redirect light guided within the at least one waveguide out of the waveguide and toward the eye as the collimated light is directed toward the user's eye. Example 23 10. The system of any of the preceding embodiments, wherein the at least one coupling element is configured to redirect collimated light from the reflective surface into the at least one waveguide. Example 24 10. The system of any of the preceding embodiments, wherein at least one out-coupling element comprises an off-axis reflector. Example 25 10. The system of any of the preceding embodiments, wherein at least one out-coupling element comprises a polarization-selective redirecting element. Example 26 10. The system of any of the preceding embodiments, wherein at least one out-coupling element comprises a polarization grating. Example 27 10. The system of any of the preceding examples, further comprising a circular polarizer. Example 28 10. The system of any preceding example, wherein the internal coupling element comprises a polarization-selective redirecting element. Example 29 10. The system of any preceding example, wherein the internal coupling element comprises a polarization grating. Example 30 10. The system of any preceding example, wherein the internal coupling element comprises an off-axis reflector. Example 31 10. The system of any of the previous examples, wherein the reflective surface comprises a liquid crystal reflector. Example 32 10. The system of any of the previous examples, wherein the reflective surface comprises a cholesteric liquid crystal reflective lens. Example 33 10. The system of any of the preceding embodiments, wherein the image projector comprises a light source, a modulator, and projection optics. Example 34 10. The system of any preceding embodiment, wherein the image projector comprises a scanning optical fiber. Example 35 10. The system of any preceding embodiment, wherein the modulator comprises an optical modulator. Example 36 35. The system of example 34, wherein the light modulator comprises a spatial light modulator. Example 37 10. The system of any preceding embodiment, wherein the camera comprises a detector array and imaging optics. Example 38 37. The system of example 36, wherein the imaging optics is configured to focus collimated light onto a detector array. Example 39 10. The system of any of the preceding examples, wherein the at least one waveguide comprises a material that is transparent to visible light and has a refractive index sufficient to guide light within the waveguide by total internal reflection. Example 40 10. The system of any preceding embodiment, wherein the at least one waveguide comprises a stack of waveguides. Example 41 The system of Example 40, wherein different waveguides of the stack of waveguides are configured to output light with different wavefront divergences, as if projected from different distances from the user's eye. Example 42 42. The system of embodiment 40 or 41, wherein different waveguides of the stack of waveguides are configured to output light with different colors. Example 43 43. The system of any of Examples 40, 41, or 42, wherein the different waveguides comprise first, second, and third waveguides, the system being configured such that the first is for red light, the second is for green light, and the third is for blue light. Example 44 10. The system of any of the previous examples, wherein the incoupling optical element comprises a diffractive optical element or a reflector. Example 45 10. The system of any of the preceding embodiments, wherein the coupling optical element comprises a diffractive optical element. Example 46 10. The system of any of the preceding embodiments, wherein the outcoupling optical element comprises a diffractive optical element. Example 47 10. The system of any of the preceding examples, wherein the coupling element is configured to increase a dimension of the eyebox along at least one axis. Example 48 The system of Example 47, further comprising an orthogonal pupil expander comprising at least one light redirecting element within or on the at least one waveguide configured to increase the dimension of the eyebox along an axis perpendicular to at least one axis. Example 49 49. The system of embodiment 48, wherein the at least one light redirecting element comprises a diffractive optical element. Example 50 A system as described in any of the above examples, wherein the same waveguide (a) directs light coupled from the user's eye into the at least one waveguide to be received by the camera so as to capture an image of at least a portion of the user's eye, and (b) directs light coupled from the image projector so that the light from the projector can be directed to the user's eye so that the image from the image projector is within the user's field of view. Example 51 The system of any of the above examples, wherein the same coupling element (a) couples light from the user's eye into the at least one waveguide to be received by the camera, and (b) couples light from the image projector out of the at least one waveguide to the user's eye. Example 52 10. The system of any of the preceding examples, further comprising electronics configured to cause the camera to capture a first image when light reflected from the reflective surface is interrupted. Example 53 The system of Example 52, wherein the electronics is configured to cause the camera to capture a second image when the light reflected from the reflective surface is not blocked. Example 54 54. The system of embodiment 53, wherein the electronics is configured to use the first image to modify the second image. Example 55 55. The system of Example 54, wherein the electronics is configured to subtract from the second image based on the first image. Example 56 10. The system of any of the preceding examples, wherein the system is configured to perform eye tracking based on the images of the eye. Example 57 The system of Example 56, wherein the step of performing eye tracking based on the image of the eye includes a step of storing an image of the retina of the eye. Example 58 The system comprises: storing an image of the retina of said eye; capturing an image of a portion of the retina of the eye; comparing the stored image of the retina with the image of the portion of the retina; determining the user's gaze based on a comparison of the stored image and the image of the retinal portion; 2. The system of claim 1, wherein the system is configured to: Example 59 The system of Example 58, wherein the step of determining the user's line of sight includes a step of determining a portion of the retina corresponding to the image of the portion of the retina. Example 60 A system described in any of Examples 58-59, wherein the step of determining the user's line of sight includes a step of determining eye orientation. Example 61 A system described in any of the above examples, wherein the coupling element is configured to couple light from an environment in front of a user wearing the head-mounted display into the waveguide and guide it therein. Example 62 A system as described in any of the above examples, wherein a camera is positioned in an optical path with respect to the at least one outcoupling optical element and receives at least a portion of light from an environment in front of the user that is coupled into and guided within the waveguide via the coupling element and coupled out of the waveguide by the outcoupling element so that an image of the environment can be captured by the camera. Example 63 A system as described in any of the above examples, wherein the same waveguide (a) directs light coupled from the environment within the waveguide to be received by the camera so as to capture an image of at least a portion of the environment in front of the user, and (b) directs light coupled from the projector so that the light from the projector can be directed to the user's eyes so that the image from the projector is within the user's field of view. Example 64 The system of any of the above examples, wherein the same coupling element (a) couples light from the environment into the at least one waveguide to be received by the camera, and (b) couples light from the image projector out of the at least one waveguide to the user's eye. Example 65 1. A head mounted display system configured to project light onto a user's eye, display augmented reality image content within a field of view of the user, and image at least a portion of the eye of a user wearing the head mounted display system, a frame configured to be supported on a user's head; and an image projector configured to project an image; A camera and an eyepiece disposed on the frame, the eyepiece configured to direct light into the user's eye and display augmented reality image content in the user's field of view, at least a portion of the eyepiece being transparent, the transparent portion being positioned in a location in front of the user's eye when the user wears the head mounted display so as to transmit light from an environment in front of the user to the user's eye and provide a view of the environment in front of the user; the eyepiece (a) at least one waveguide; (b) at least one incoupling optical element configured to incoupling light from the image projector into the at least one waveguide so as to guide the light from the image projector therein; (c) at least one coupling optical element configured to couple light from the image projector guided within the waveguide out of the waveguide and direct the light toward an eye of a user; (d) at least one out-coupling element configured to couple the light guided within the waveguide out of the waveguide and direct the light to the camera; an eyepiece comprising: a positive lens having positive refractive power, positioned in an optical path between the user's eye and the eyepiece such that light reflected from the user's eye is transmitted through the lens to the eyepiece; a negative lens disposed on the side of the eyepiece opposite the positive lens, the negative lens having a negative refractive power for offsetting the refractive power of the positive lens with respect to light from an environment in front of the user; Equipped with an image projector is disposed in an optical path relative to the at least one internal coupling optical element, and couples light from the image projector into the waveguide such that the light is guided therein by the at least one coupling element to be coupled out of the waveguide to an eye of the user such that the image from the image projector is within a field of view of the user; the at least one coupling element is configured such that light from the user's eye passing through a lens of the eyepiece is coupled into and guided within the waveguide; a camera disposed in an optical path relative to the at least one outcoupling optical element, receiving at least a portion of light from the user's eye that is reflected from a reflective surface, coupled into and guided within the waveguide via a coupling element, and coupled out of the waveguide by the outcoupling element; Head-mounted display system. Example 66 66. The system of example 65, wherein the positive lens comprises a Fresnel lens. Example 67 The system of example 65 or 66, wherein the positive lens is configured to collimate light from the anterior region of the user's eye. Example 68 68. The system of any of Examples 65, 66, or 67, wherein the positive lens is configured to collimate light from the cornea of ​​the user's eye. Example 69 A system described in any of Examples 65-68, wherein the system is configured to perform eye tracking based on the image of the eye. Example 70 A system described in any of Examples 65-69, further comprising a light source positioned to illuminate the user's eye. Example 71 The system of Example 70, wherein the light source comprises one or more infrared light sources configured to direct infrared light toward the user's eye. Example 72 72. The system of embodiment 70 or 71, wherein the light source comprises one or more infrared light-emitting diodes (LEDs). Example 73 10. The system of any of the preceding examples, wherein the system is configured to identify a user via biometric sensing based on the eye image.

Claims

1. A head-mounted display system configured to project light onto a user's eye and display augmented reality image content within the user's field of view, the head-mounted display system comprising: a frame configured to be supported on the user's head; an image projector coupled to the frame, the image projector configured to project an image into the eye of the user and display image content within the field of view of the user; a camera coupled to the frame; a waveguide coupled to the frame, the waveguide optically coupled to the camera; an optical coupling element coupled to the waveguide, the optical coupling element configured to couple light into the waveguide; an external coupling element coupled to the waveguide, the external coupling element configured to direct light emitted from the waveguide to the camera; a first light source coupled to the frame, the first light source configured to direct light toward the eye of the user; electronics coupled to the first light source and the camera, the electronics configured to control the camera to periodically capture images; A head-mounted display system comprising:

2. The waveguide includes first and second major surfaces such that light is guided therein; 2. The head-mounted display system of claim 1, further comprising a reflective optical element configured to collimate light from the eye of the user, the reflective optical element not being arranged within the waveguide between the first and second major surfaces of the waveguide.

3. A head-mounted display system as described in claim 2, wherein the camera is positioned in an optical path relative to the external coupling element so that an image can be captured by the camera, and receives at least a portion of the light that is coupled into the waveguide via the optical coupling element, guided therein, and coupled out of the waveguide by the external coupling element.

4. The first light source is a plurality of infrared light sources positioned between the waveguide and the eye of the user to illuminate the eye of the user, the plurality of infrared light sources being configured to direct light onto the eye of the user without light being coupled into and guided through the waveguide; the optical coupling element, or the outcoupling element, or both, comprise a diffractive optical element; the camera is positioned in an optical path relative to the external coupling element such that an image may be captured by the camera, and receives at least a portion of the light that is coupled into the waveguide via the optical coupling element, guided therein, and coupled out of the waveguide by the external coupling element; The head mounted display system of claim 1 , wherein the plurality of infrared light sources are oriented to face and direct light toward the eyes of the user.

5. A head-mounted display system as described in claim 1, wherein at least the waveguide, the optical coupling element, and the external coupling element form an eyepiece configured to direct the light into the user's eye and display augmented reality image content in the user's field of view, and at least a portion of the eyepiece is transparent and positioned in a location in front of the user's eye when the user wears the head-mounted display system so as to transmit light from an environment in front of the user to the user's eye and provide a view of the environment in front of the user.

6. A head-mounted display system as described in claim 5, further comprising a reflective surface having refractive power arranged to receive light reflected from the user's eye passing through the eyepiece and direct the light back to the eyepiece.

7. A head-mounted display system as described in claim 6, wherein the reflective surface reflects infrared light but transmits visible light.

8. A head-mounted display system as described in claim 6, wherein the reflective surface is curved.

9. A head-mounted display system as described in claim 6, wherein the reflective surface has a positive refractive power in reflection and a negligible refractive power in transmission.

10. A head-mounted display system as described in claim 6, wherein the reflective surface is configured to collimate light from the user's eye.

11. A head-mounted display system as described in claim 6, wherein the reflective surface is configured to collimate light from the retina of the user's eye.

12. A head-mounted display system as described in claim 6, wherein the reflective surface is configured to collimate light from the front region of the user's eye.

13. A head-mounted display system as described in claim 6, wherein the reflective surface is configured to collimate light from the cornea of ​​the user's eye.

14. A head-mounted display system as described in claim 1, wherein the electronics are configured to control the camera to periodically capture images while pulsing the first light source in accordance with the capture of images by the camera so that light emitted by the first light source has a reduced intensity when the camera is not capturing images.

15. A head-mounted display system as described in claim 1, wherein the first light source comprises one or more infrared light sources configured to direct infrared light toward the user's eyes.

16. A head-mounted display system as described in claim 1, wherein the first light source comprises one or more infrared light-emitting diodes (LEDs).

17. A head-mounted display system as described in claim 1, wherein the waveguide includes a stack of waveguides configured to output light with different wavefront divergences as if projected from different distances from the user's eye.

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