Eye imaging using an off-axis imager

Abstract

To provide favorable eye imaging with an off-axis imager.SOLUTION: Examples of an imaging system for use with a head mounted display (HMD) are disclosed. The imaging system can include a forward-facing imaging camera, and a surface of a display of the HMD can include an off-axis diffractive optical element (DOE) or hot mirror configured to reflect light to the imaging camera. The DOE or hot mirror can be segmented. The imaging system can be used for eye tracking, biometric identification, multiscopic reconstruction of the three-dimensional shape of an eye, etc.SELECTED DRAWING: Figure 7A

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 / 222,671, filed September 23, 2015, and entitled “EYE IMAGING WITH AN OFF-AXIS IMAGER,” which is incorporated herein by reference in its entirety.

[0002] (background) The present disclosure relates to virtual reality and augmented reality imaging and visualization systems, and in particular to imaging systems for acquiring images of the eye. [Background technology]

[0003] (Description of related fields) Modern computing and display technologies have facilitated the development of systems for so-called "virtual reality" or "augmented reality" experiences in which digitally reproduced images or parts 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 inputs, augmented reality, or "AR", scenarios typically involve the presentation of digital or virtual image information as an extension of the visualization of the real world around the user, or mixed reality, or "MR", relates to the merging of real and virtual worlds to generate new environments in which physical and virtual objects coexist and interact in real time. In conclusion, the human visual perception system is highly complex, making it difficult to generate VR, AR, or MR technologies that promote a comfortable and natural-feeling rich presentation of virtual image elements among other virtual or real-world image elements. The systems and methods disclosed herein address various challenges associated with VR, AR, and MR technologies. Summary of the Invention [Means for solving the problem]

[0004] An embodiment of a head mounted display (HMD) configured to be worn on a user's head is disclosed. The HMD includes a frame with a pair of ear rests, a pair of optical elements supported by the frame such that each of the pair of optical elements can be positioned in front of the user's eye, a forward-facing imager mounted on one of the pair of ear rests, and a reflective element disposed in or on one of the pair of optical elements, configured to reflect infrared light toward the forward-facing imager configured to receive infrared light reflected by the reflective element. Each of the pair of optical elements can be transparent to visible light. The reflective element can include multiple segments having the same or different optical properties. The imager can be configured to acquire an image of an eye of a wearer of the HMD. The HMD can include a processor that analyzes the image acquired by the imager for eye tracking, biometric identification, multi-view reconstruction of eye shape, estimates the accommodation state of the eye, or images the retina of the eye. The present specification also provides, for example, the following items: (Item 1) 1. A head mounted display (HMD) configured to be worn on a user's head, the HMD comprising: a frame having a pair of ear rests; a pair of optical elements, each of the pair of optical elements supported by the frame such that it can be positioned in front of an eye of the user; a forward-facing imager mounted to one of the pair of ear rests; a reflective element disposed within or on one of the pair of optical elements, the reflective element configured to receive infrared light reflected by the reflective element and to reflect infrared light toward the forward-facing imager; Equipped with an HMD. (Item 2) 2. The HMD of item 1, wherein each of the pair of optical elements is transmissive to visible light. (Item 3) 2. The HMD of item 1, wherein each of the pair of optical elements is configured to display an image to the user. (Item 4) 4. The HMD of item 3, wherein each of the pair of optical elements comprises a light field display. (Item 5) 5. The HMD of claim 4, wherein the light field display comprises a waveguide stack configured to output the image to the user. (Item 6) 6. The HMD of any one of claims 1 to 5, wherein the reflective element comprises a hot mirror, an off-axis diffractive optical element (DOE), an off-axis holographic mirror (OAHM), or an off-axis volumetric diffractive optical element (OAVDOE). (Item 7) 2. The HMD of claim 1, wherein the reflective element is transmissive to visible light. (Item 8) 2. The HMD of claim 1, wherein the reflective element comprises a plurality of segments, each segment within the plurality of segments having optical properties that are different from the optical properties of at least one other segment within the plurality of segments. (Item 9) 9. The HMD of claim 8, wherein the optical properties include a reflection angle or a refractive power. (Item 10) 9. The HMD of claim 8, wherein the plurality of segments comprises 2, 3, 4, 5, 6, 7, 8, or 9 segments. (Item 11) 2. The HMD of claim 1, wherein the forward-facing imager is mounted to a temple portion of one of the pair of ear supports. (Item 12) Item 2. The HMD of item 1, wherein the imager comprises a perspective control lens assembly. (Item 13) Item 13. The HMD of item 12, wherein the perspective control lens assembly comprises a shifting lens, a tilting lens, or a shifting-tilting lens. (Item 14) 1. A display system comprising: an optical element configured to display an image to a user, the optical element configured to be positioned in front of an eye of the user; A forward-facing imager; a reflective element disposed within or on the optical element, the reflective element configured to reflect infrared light received from the user's eye towards the forward-facing imager; A display system comprising: (Item 15) Item 15. The display system of item 14, wherein the optical element comprises a light field display. (Item 16) Item 15. The display system of item 14, wherein the reflective element comprises a hot mirror, an off-axis diffractive optical element (DOE), an off-axis holographic mirror (OAHM), or an off-axis volumetric diffractive optical element (OAVDOE). (Item 17) Item 15. The display system of item 14, wherein the reflective element comprises a plurality of segments having different refractive powers or different reflection angles. (Item 18) a non-transitory memory configured to store an image of the user's eye obtained by the forward-facing imager; and A hardware processor in communication with the non-transitory memory, the hardware processor comprising: accessing an image of the eye; and tracking the eyes of the user; extracting biometric information associated with an eye of the user; reconstructing a shape of a portion of the user's eye; estimating the state of accommodation of the user's eye; or imaging the retina, iris, or other element of the user's eye; and a hardware processor programmed to 18. The display system of any one of items 14 to 17, further comprising: (Item 19) 15. A head-mounted display system comprising a frame configured to support the display system described in item 14 so that the optical element is positioned in front of a first eye of the user. (Item 20) 20. A head-mounted display system as described in item 19, wherein the frame supports a second display system as described in item 14 so that an optical element of the second display system is positioned in front of the second eye of the user.

[0005] Details of one or more implementations of the subject matter described herein are set forth in the accompanying drawings and the following description. Other features, aspects, and advantages will become apparent from the description, drawings, and claims. Neither this Summary nor the following Detailed Description purport to define or limit the scope of the inventive subject matter. [Brief description of the drawings]

[0006] [Figure 1] FIG. 1 depicts an illustration of an augmented reality scenario with a virtual reality object and a real reality object viewed by a person.

[0007] [Diagram 2] FIG. 2 diagrammatically illustrates an embodiment of a wearable display system.

[0008] [Diagram 3] FIG. 3 diagrammatically illustrates aspects of an approach for simulating a three-dimensional image using multiple depth planes.

[0009] [Figure 4]FIG. 4 diagrammatically illustrates an embodiment of a waveguide stack for outputting image information to a user.

[0010] [Diagram 5] FIG. 5 shows an exemplary output beam that may be output by a waveguide.

[0011] [Figure 6] FIG. 6 is a schematic diagram showing a display system including a waveguide device, an optical coupler subsystem for optically coupling light to or from the waveguide device, and a control subsystem for use in generating a multifocal volumetric display, image, or light field.

[0012] [Figure 7A] 7A-7F diagrammatically illustrate an embodiment of an imaging system comprising a forward-facing camera that images the wearer's eye using a reflective off-axis diffractive optical element (DOE). [Figure 7B] 7A-7F diagrammatically illustrate an embodiment of an imaging system comprising a forward-facing camera that images the wearer's eye using a reflective off-axis diffractive optical element (DOE). [Figure 7C] 7A-7F diagrammatically illustrate an embodiment of an imaging system comprising a forward-facing camera that images the wearer's eye using a reflective off-axis diffractive optical element (DOE). [Figure 7D] 7A-7F diagrammatically illustrate an embodiment of an imaging system comprising a forward-facing camera that images the wearer's eye using a reflective off-axis diffractive optical element (DOE). [Figure 7E] 7A-7F diagrammatically illustrate an embodiment of an imaging system comprising a forward-facing camera that images the wearer's eye using a reflective off-axis diffractive optical element (DOE). [Figure 7F] 7A-7F diagrammatically illustrate an embodiment of an imaging system comprising a forward-facing camera that images the wearer's eye using a reflective off-axis diffractive optical element (DOE).

[0013] [Figure 7G] 7G and 7H diagrammatically show examples of DOEs having multiple segments, each of which may have different optical properties (eg, angle of reflection, optical power, etc.). [Figure 7H] 7G and 7H diagrammatically show examples of DOEs having multiple segments, each of which may have different optical properties (eg, angle of reflection, optical power, etc.).

[0014] Throughout the drawings, reference numbers may be reused to indicate correspondence between referenced elements. The drawings are provided to illustrate example embodiments described herein and are not intended to limit the scope of the present disclosure. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0015] overview The eyes of a head mounted display (HMD) wearer can be imaged using a reflective off-axis diffractive optical element (DOE). In some implementations, the DOE may be a holographic optical element (HOE), an off-axis holographic mirror (OAHM), or an off-axis volumetric diffractive optical element (OAVDOE). The resulting images can be used to track one or both eyes, image the retina, reconstruct eye shape in three dimensions, extract biometric information (e.g., iris identification) from the eye, etc.

[0016] Head-mounted displays (HMDs) may use information about the state of the wearer's eyes for various purposes. For example, this information can be used to estimate the wearer's gaze direction or for biometric identification. However, imaging the eyes of a wearer of an HMD can be difficult. The distance between the HMD and the wearer's eyes is short. Furthermore, eye tracking requires a larger field of view, while biometric identification requires a relatively high pixel count target on the iris. For an imaging system that would attempt to accomplish both of these objectives, the requirements of the two tasks are in stark conflict. Moreover, both problems can be further complicated by occlusions by eyelids and eyelashes.

[0017] The embodiments of the imaging system described herein address some or all of these issues. For example, the imaging system can include an imager configured to view the wearer's eye. The imaging system can be mounted (e.g., on a frame of the wearable display system, e.g., an ear rest) proximate to the wearer's temple. In some embodiments, a second imager can be used for the wearer's other eye so that each eye is imaged separately. The imager can include an infrared digital camera that is sensitive to infrared radiation. The imager can be mounted so that it faces forward (in the direction of the wearer's vision) and is directed toward the eye, rather than rearward. By placing the imager closer to the wearer's ear, the weight of the imager can also be closer to the ear, and the HMD can be easier to wear compared to an HMD in which the imager faces rearward and is positioned closer to the front of the HMD. Additionally, by placing a forward-facing imager near the wearer's temple, the distance from the wearer's eye to the imager is approximately doubled compared to a rear-facing imager positioned near the front of the HMD. The depth of field of the image is roughly proportional to this distance, so the depth of field for a front-facing imager is approximately doubled compared to a rear-facing imager. A larger depth of field for the imager can be advantageous for imaging the eye region of wearers with large or prominent noses, brow ridges, etc.

[0018] The imager can be positioned to view an inner surface of the optical element that is otherwise transparent. The optical element can be part of a display of an HMD (or a lens in a pair of glasses). The optical element can comprise a surface that reflects a first range of wavelengths but is substantially transparent to a second range of wavelengths (different from the first range of wavelengths). The first range of wavelengths can be in the infrared and the second range of wavelengths can be in the visible. For example, the optical element can comprise a hot mirror that reflects infrared light but transmits visible light. Visible light from the outside world can be transmitted through the optical element and perceived by the wearer. In effect, the imaging system acts like a virtual imager that is directed back towards the wearer's eye. The virtual imager can image the virtual infrared light that is propagated from the wearer's eye through the optical element. The hot mirror (or other DOEs described herein) can be located on the inner surface of the optical element, on the outer surface of the optical element, or within the optical element (e.g., a solid HOE).

[0019] Infrared radiation can include radiation with wavelengths in the range of 700 nm to 10 μm. Infrared radiation can include near-infrared radiation with wavelengths in the range of 700 nm to 1.5 μm. In many implementations, imaging of the eye is performed in the near-infrared at wavelengths of 700 nm to 900 nm. (3D display)

[0020] Figure 1 depicts an illustration of an augmented reality scenario with certain virtual reality objects and certain actual reality objects viewed by a person. Figure 1 depicts an augmented reality scene 100 in which a user of the AR technology sees a real-world park-like setting 110 featuring people, trees, buildings in the background, and a concrete platform 120. In addition to these items, the user of the AR technology also perceives that they "see" a robotic figure 130 standing on the real-world platform 120 and a flying cartoon-like avatar character 140 that appears to be an anthropomorphic bumblebee, although these elements do not exist in the real world.

[0021] In order for a three-dimensional (3D) display to produce a true depth sensation, and more specifically a simulated sensation of surface depth, it is desirable to generate, for each point in the field of view of the display, an accommodation response that corresponds to its virtual depth. If the accommodation response to a display point does not correspond to the virtual depth of that point as determined by the binocular depth cues of convergence and stereopsis, the human eye may experience accommodation conflicts, resulting in unstable imaging, deleterious eye strain, headaches, and, in the absence of accommodative information, a near-complete lack of surface depth.

[0022] VR, AR, and MR experiences can be provided by a display system having a display in which images corresponding to multiple depth planes are provided to a viewer. The images may be different for each depth plane (e.g., providing slightly different presentations of a scene or object) and 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 of a scene located on different depth planes and / or based on observing different image features on different depth planes that are out of focus. As discussed elsewhere herein, such depth cues provide a believable perception of depth.

[0023] 2 illustrates an example of a wearable display system 200 that may be used to present a VR, AR, or MR experience to a display system wearer or viewer 204. The display system 200 includes a display 208 and various mechanical and electronic modules and systems to support the functionality of the display 208. The display 208 may be coupled to a frame 212 that is wearable by a display system user, wearer, or viewer 204 and configured to position the display 208 in front of the eye of the wearer 204. The display 208 may be a light field display. In some embodiments, a speaker 216 is coupled to the frame 212 and positioned adjacent to the user's ear canal (in some embodiments, another speaker, not shown, is positioned adjacent to the user's other ear canal to provide stereo / shapeable sound control). The display 208 is operably coupled 220 to a local data processing module 224, which may be mounted in a variety of configurations, such as fixedly attached to the frame 212, by wired leads or a wireless connection, fixedly attached to a helmet or hat worn by the user, built into headphones, or otherwise removably attached to the user 204 (e.g., in a backpack configuration, in a belt-connected configuration).

[0024] The local processing and data module 224 may comprise a hardware processor and non-transitory digital memory, such as non-volatile memory (e.g., flash memory), both of which may be utilized to aid in processing, caching, and storing data. The data may include (a) data captured from sensors (e.g., which may be operatively coupled to the frame 212 or otherwise attached to the user 204), such as image capture devices (such as cameras), microphones, inertial measurement units, accelerometers, compasses, GPS units, wireless devices, and / or gyroscopes, and / or (b) data acquired and / or processed using the remote processing module 228 and / or remote data repository 232, possibly for passing through the display 208 after such processing or reading. The local processing and data module 224 may be operatively coupled to the remote processing module 228 and / or remote data repository 232 by communications links 236 and / or 240, such as via wired or wireless communication links, such that these remote modules 228, 232 are available as resources to the local processing and data module 224. In addition, the remote processing module 228 and the remote data repository 232 may be operatively coupled to each other.

[0025] In some embodiments, the remote processing module 228 may comprise one or more processors configured to analyze and process data and / or image information, such as video information captured by an image capture device. The video data may be stored locally within the local processing and data module 224 and / or the remote data repository 232. In some embodiments, the remote data repository 232 may comprise a digital data storage facility, which may be available through the Internet or other networking configurations in a “cloud” resource configuration. In some embodiments, all data is stored and all calculations are performed in the local processing and data module 224, allowing for fully autonomous use from the remote modules.

[0026] The human visual system is complex and difficult to provide a realistic perception of depth. 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 of the two eyes relative to one another (i.e., the rotation of the pupils toward or away from one another to converge the gaze of the eyes and fixate on the object) is closely coupled to the focusing (or "accommodation") of the eye's lenses. Under normal conditions, changing the focus of the eye's lenses, or accommodating the eyes and changing focus from one object to another at a different distance, will automatically produce a matching change in vergence at the same distance, under a relationship known as the "accommodation-vergence reflex." Similarly, a change in vergence will induce a matching change in accommodation under normal conditions. Display systems that provide a better match between accommodation and convergence-divergence may produce a more realistic or comfortable simulation of three-dimensional images.

[0027] FIG. 3 illustrates aspects of an approach for simulating a three-dimensional image using multiple depth planes. With reference to FIG. 3, objects at various distances from the eyes 302 and 304 on the z-axis are accommodated by the eyes 302 and 304 such that the objects are in focus. The eyes 302 and 304 assume particular accommodated states that focus 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 306 with an associated focal length such that an object or part of an object at a particular depth plane is in focus when the eye is in an accommodated state relative to that depth plane. In some embodiments, a three-dimensional image may be simulated by providing different presentations of images for each eye 302 and 304, and by providing different presentations of images corresponding to each of the depth planes. Although shown as separate for clarity of illustration, it should be understood that the fields of view of the eyes 302 and 304 may overlap, for example, as the distance along the z-axis increases. In addition, while shown to be flat for ease of illustration, it should be understood that the contour of the depth plane may be curved in physical space such that all features within the depth plane are in focus with the eye in a particular accommodation state. Without being limited by theory, it is believed that the human eye may typically interpret a finite number of depth planes to provide depth perception. As a result, a highly realistic simulation of perceived depth may be achieved by providing the eye with a different representation of an image corresponding to each of these limited number of depth planes. (Waveguide Stack Assembly)

[0028] 4 illustrates an example of a waveguide stack for outputting image information to a user. The display system 400 includes a stack of waveguides or a stacked waveguide assembly 405 that can be utilized to provide a three-dimensional perception to the eye 410 or the brain using multiple waveguides 420, 422, 424, 426, 428. In some embodiments, the display system 400 may correspond to the system 200 of FIG. 2, of which FIG. 4 diagrammatically illustrates some portions of the system 200 in greater detail. For example, in some embodiments, the waveguide assembly 405 may be integrated into the display 208 of FIG. 2.

[0029] 4, the waveguide assembly 405 may also include a number of features 430, 432, 434, 436 between the waveguides. In some embodiments, the features 430, 432, 434, 436 may be lenses. In some embodiments, the features 430, 432, 434, 436 may not be lenses. Rather, they may be spacers (e.g., cladding layers and / or structures to form air gaps).

[0030] The waveguides 420, 422, 424, 426, 428 and / or the multiple lenses 430, 432, 434, 436 may be configured to transmit image information to the eye with various levels of wavefront curvature or light beam divergence. Each waveguide level may be associated with a particular depth plane and may be configured to output image information corresponding to that depth plane. Image injection devices 440, 442, 444, 446, 448 may be utilized to inject image information into the waveguides 420, 422, 424, 426, 428, which may be configured to disperse incident light across each individual waveguide for output toward the eye 410. Light exits the output surfaces of the image injection devices 440, 442, 444, 446, 448 and is injected into the corresponding input edges of the waveguides 420, 422, 424, 426, 428. In some embodiments, a single beam of light (e.g., a collimated beam) may be launched into each waveguide and output an entire field of cloned collimated beams that are directed towards the eye 410 at a particular angle (and divergence) corresponding to the depth plane associated with the particular waveguide.

[0031] In some embodiments, image input devices 440, 442, 444, 446, 442 are discrete displays that each generate image information for input into a corresponding waveguide 420, 422, 424, 426, 428, respectively. In some other embodiments, image input devices 440, 442, 444, 446, 448 are outputs of a single multiplexed display that may pipe image information to each of image input devices 440, 442, 444, 446, 448, for example, via one or more optical conduits (such as fiber optic cables).

[0032] A controller 450 controls the operation of the stacked waveguide assembly 405 and the image input devices 440, 442, 444, 446, 448. In some embodiments, the controller 450 includes programming (e.g., instructions in a non-transitory computer-readable medium) that coordinates the timing and provision of image information to the waveguides 420, 422, 424, 426, 428. In some embodiments, the controller 450 may be a single integrated device or a distributed system connected by a wired or wireless communication channel. The controller 450 may be part of the processing module 224 or 228 (illustrated in FIG. 2 ) in some embodiments. In some embodiments, the controller may communicate with an inwardly facing imaging system 452 (e.g., a digital camera), an outwardly facing imaging system 454 (e.g., a digital camera), and / or a user input device 466. An inwardly facing imaging system 452 (e.g., a digital camera) can be used to capture images of the eye 410, for example, to determine the size and / or orientation of the pupil of the eye 410. An outwardly facing imaging system 454 can be used to image a portion of the world 456. A user can input commands into the controller 450 and interact with the display system 400 via a user input device 466.

[0033] The waveguides 420, 422, 424, 426, 428 may be configured to propagate light within each individual waveguide by total internal reflection (TIR). The waveguides 420, 422, 424, 426, 428 may each be planar or have another shape (e.g., curved) with major top and bottom surfaces and edges extending between the major top and bottom surfaces. In the illustrated configuration, the waveguides 420, 422, 424, 426, 428 may each include light extraction optical elements 460, 462, 464, 466, 468 configured to extract light from the waveguides by redirecting the light to propagate within each individual waveguide and outputting image information from the waveguides to the eye 410. The extracted light may also be referred to as out-coupled light, and the light extraction optical elements may also be referred to as out-coupling optical elements. The extracted beam of light is output by the waveguide where the light propagating within the waveguide strikes the light redirecting element. The light extraction optical elements (460, 462, 464, 466, 468) may be, for example, reflective and / or diffractive optical features. Although shown disposed on the bottom major surfaces of the waveguides 420, 422, 424, 426, 428 for ease of explanation and clarity of drawing, in some embodiments the light extraction optical elements 460, 462, 464, 466, 468 may be disposed on the top and / or bottom major surfaces and / or directly within the volume of the waveguides 420, 422, 424, 426, 428. In some embodiments the light extraction optical elements 460, 462, 464, 466, 468 may be formed within a layer of material that is attached to a transparent substrate and forms the waveguides 420, 422, 424, 426, 428. In some other embodiments, the waveguides 420, 422, 424, 426, 428 may be a monolithic piece of material and the light extraction optical elements 460, 462, 464, 466, 468 may be formed on and / or within that piece of material.

[0034] Continuing with reference to FIG. 4, as discussed herein, each waveguide 420, 422, 424, 426, 428 is configured to output light and form an image corresponding to a particular depth plane. For example, the waveguide 420 closest to the eye may be configured to deliver collimated light to the eye 410 as it is launched into such waveguide 420. The collimated light may represent an optical infinity focal plane. The next waveguide 422 may be configured to send collimated light that passes through a first lens 430 (e.g., a negative lens) before it can reach the eye 410. The first lens 430 may be configured to generate a slight convex wavefront curvature so that the eye / brain interprets the light emerging from that next waveguide 422 as emerging from a first focal plane closer inward from optical infinity toward the eye 410. Similarly, the third waveguide 424 passes its output light through both a first lens 430 and a second lens 432 before reaching the eye 410. The combined refractive power of the first and second lenses 430 and 432 may be configured to produce another incremental amount of wavefront curvature such that the eye / brain interprets the light originating from the third waveguide 424 as originating from a second focal plane that is even closer inward from optical infinity towards the person than the light from the next waveguide 422.

[0035] Other waveguide layers (e.g., waveguides 426, 428) and lenses (e.g., lenses 434, 436) are similarly configured, with the highest waveguide 428 in the stack sending its output through all of the lenses between it and the eye for an aggregate focal power that represents the focal plane closest to the person. To compensate for the stack of lenses 430, 432, 434, 436 when viewing / interpreting light originating from the world 456 on the other side of the stacked waveguide assembly 405, a compensating lens layer 438 may be placed on top of the stack to compensate for the aggregate power of the lens stacks 430, 432, 434, 436 below. Such a configuration provides as many perceived focal planes as there are waveguide / lens pairs available. The light extraction optical elements 460, 462, 464, 466, 468 of the waveguides 420, 422, 424, 426, 428 and the focusing sides of the lenses 430, 432, 434, 436 may both be static (e.g., not dynamic or electroactive). In some alternative embodiments, either or both may be dynamic using electroactive features.

[0036] Continuing with reference to FIG. 4, the light extraction optical elements 460, 462, 464, 466, 468 may be configured to both redirect light from its respective waveguide and output this light with the appropriate amount of divergence or collimation for the particular depth plane associated with the waveguide. As a result, waveguides with different associated depth planes may have different configurations of light extraction optical elements that output light with different amounts of divergence depending on the associated depth plane. In some embodiments, as discussed herein, the light extraction optical elements 460, 462, 464, 466, 468 may be solid or surface features that may be configured to output light at specific angles. For example, the light extraction optical elements 460, 462, 464, 466, 468 may be solid holograms, surface holograms, and / or diffraction gratings. Light extraction optical elements such as diffraction gratings are described in U.S. Patent Publication No. 2015 / 0178939, published June 25, 2015, which is incorporated by reference in its entirety. In some embodiments, features 430, 432, 434, 436 may not be lenses. Rather, they may simply be spacers (e.g., cladding layers and / or structures to form an air gap).

[0037] In some embodiments, the light extraction optical elements 460, 462, 464, 466, 468 are diffractive features, i.e., "diffractive optical elements" (also referred to herein as "DOEs"), that form a diffraction pattern. Preferably, the DOEs have a relatively low diffraction efficiency, such that only a portion of the light of the beam is deflected toward the eye 410 with each intersection point of the DOE, while the remainder continues traveling through the waveguide via total internal reflection. The light carrying the image information is thus split into several related exit beams that exit the waveguide at multiple locations, resulting in a very uniform exit emission pattern toward the eye 410 for this particular collimated beam bouncing within the waveguide.

[0038] 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 the microdroplets form a diffractive pattern in a host medium, and the refractive index of the microdroplets can be switched to substantially match that of the host material (in which case the pattern does not significantly diffract incident light), or the microdroplets can be switched to a refractive index that does not match that of the host medium (in which case the pattern actively diffracts incident light).

[0039] In some embodiments, the number and distribution of depth planes and / or depths of field may be dynamically varied based on the pupil size and / or orientation of the viewer's eye. In some embodiments, an inwardly facing imaging system 452 (e.g., a digital camera) may be used to capture images of the eye 410 and determine the pupil size and / or orientation of the eye 410. In some embodiments, the inwardly facing imaging system 452 may be mounted to the frame 212 (as illustrated in FIG. 2) and may be in electrical communication with the processing modules 224 and / or 228, which may process image information from the inwardly facing imaging system 452 and, for example, determine the pupil diameter and / or orientation of the eye of the user 204.

[0040] In some embodiments, an inwardly facing imaging system 452 (e.g., a digital camera) can observe user movements, such as eye movement and facial movement. The inwardly facing imaging system 452 may be used to capture images of the eye 410 and determine the size and / or orientation of the pupil of the eye 410. The inwardly facing imaging system 452 can be used to obtain images for use in determining the direction the user is looking (e.g., eye pose) or for biometric identification of the user (e.g., via iris identification). Images obtained by the inwardly facing imaging system 452 may be analyzed to determine the user's eye pose and / or mood, which may be used by the display system 400 to determine audio or visual content to be presented to the user. The display system 400 may also determine head pose (e.g., head position or head orientation) using sensors such as an inertial measurement unit (IMU), accelerometer, gyroscope, etc. Head pose may be used alone or in combination with eye pose to interact with support tracking and / or to present audio content.

[0041] In some embodiments, one camera may be utilized per eye to determine the pupil size and / or orientation of each eye separately, thereby allowing the presentation of image information to each eye to be dynamically adjusted to that eye. In some embodiments, at least one camera may be utilized per eye to independently determine the pupil size and / or eye pose of each eye separately, thereby allowing the presentation of image information to each eye to be dynamically adjusted to that eye. In some other embodiments, the pupil diameter and / or orientation of only one eye 410 (e.g., using only a single camera per pair of eyes) is determined and assumed to be similar for both eyes of the viewer 204.

[0042] For example, the depth of field may vary inversely with the viewer's pupil size. As a result, as the size of the viewer's eye pupil decreases, the depth of field increases so that one plane that is indistinguishable because its location exceeds the eye's focal depth may become distinguishable and appear more focused with a corresponding increase in the depth of field with a reduction in pupil size and a corresponding increase in the depth of field. Similarly, the number of spaced depth planes used to present different images to the viewer may be reduced with a reduced pupil size. For example, the viewer may not be able to clearly perceive details of both the first and second depth planes at one pupil size without adjusting the eye's accommodation from one depth plane to the other. However, these two depth planes may be sufficient to simultaneously focus the user at another pupil size without changing accommodation.

[0043] In some embodiments, the display system may vary the number of waveguides that receive image information based on a determination of pupil size and / or orientation or in response to receiving an electrical signal indicative of a particular pupil size and / or orientation. For example, if the user's eye is unable to distinguish between two depth planes associated with two waveguides, the controller 450 may be configured or programmed to stop providing image information to one of those waveguides. Advantageously, this may reduce the processing burden on the system, thereby increasing the responsiveness of the system. In embodiments in which the DOE for a waveguide is switchable between on and off states, the DOE may be switched to the off state when the waveguide receives image information.

[0044] In some embodiments, it may be desirable to have the exit beam meet a condition that it has a diameter less than the diameter of the viewer's eye. However, meeting this condition may be difficult in light of the variability in the size of the viewer's pupil. In some embodiments, this condition is met over a wide range of pupil sizes by varying the size of the exit beam in response to a determination of the size of the viewer's pupil. For example, as the pupil size decreases, the size of the exit beam may also decrease. In some embodiments, the exit beam size may be varied using a variable aperture.

[0045] The display system 400 may include an outward-facing imaging system 454 (e.g., a digital camera) that images a portion of the world 456. This portion of the world 456 may be referred to as the field of view (FOV), and the imaging system 454 may also be referred to as an FOV camera. The entire area available for viewing or imaging by the viewer 204 may be referred to as the ocular field of view (FOR). The FOR may include a solid angle of 4π steradians surrounding the display system 400. In some implementations of the display system 400, the FOR may include substantially all of the solid angle around the user 204 of the display system 400 (in front, behind, above, below, or to the side of the user) because the user 204 may move his or her head and eyes to view objects surrounding the user. Images obtained from the outward-facing imaging system 454 can be used to track gestures (e.g., hand or finger gestures) performed by the user, detect objects in the world 456 in front of the user, etc.

[0046] The display system 400 may include a user input device 466 through which a user may input commands into the controller 450 and interact with the display system 400. For example, the user input device 466 may include a track pad, a touch screen, a joystick, a multiple degree of freedom (DOF) controller, a capacitive sensing device, a game controller, a keyboard, a mouse, a directional pad (D-pad), a wand, a tactile device, a totem (e.g., functioning as a virtual user input device), and the like. In some cases, a user may use a finger (e.g., a thumb) to press or swipe on a touch-sensitive input device to provide input to the display system 400 (e.g., to provide user input to a user interface provided by the display system 400). The user input device 466 may be held by the user's hand during use of the display system 400. The user input device 466 may communicate with the display system 400 wired or wirelessly.

[0047] 5 shows an example of an exit beam output by a waveguide. Although one waveguide is shown, it should be understood that other waveguides in the waveguide assembly 405 may function similarly and that the waveguide assembly 405 includes multiple waveguides. Light 505 is launched into the waveguide 420 at an input edge 510 of the waveguide 420 and propagates within the waveguide 420 by TIR. At the point where the light 505 impinges on the DOE 460, a portion of the light exits the waveguide as an exit beam 515. Although the exit beams 515 are shown as approximately parallel, they may also be redirected to propagate to the eye 410 at an angle (e.g., forming a diverging exit beam) depending on the depth plane associated with the waveguide 420. It should be understood that a nearly collimated exit beam may refer to a waveguide, with light extraction optics that outcouples light and forms an image that appears to be set on the depth plane at a long distance (e.g., optical infinity) from the eye 410. Other waveguides or other sets of light extraction optics may output a more divergent exit beam pattern that would require the eye 410 to accommodate to closer distances and focus on the retina, and would be interpreted by the brain as light from a distance closer to the eye 410 than optical infinity.

[0048] FIG. 6 illustrates another embodiment of a display system 400 including a waveguide device, an optical coupler subsystem for optically coupling light to or from the waveguide device, and a control subsystem. The display system 400 can be used to generate multifocal stereoscopic images, images, or light fields. The display system 400 can include one or more primary planar waveguides 604 (only one is shown in FIG. 6 ) and one or more DOEs 608 associated with each of at least some of the primary waveguides 604. The planar waveguides 604 can be similar to the waveguides 420, 422, 424, 426, 428 discussed with reference to FIG. 4 . The optical system may employ a dispersive waveguide device to relay light along a first axis (vertical or Y-axis in the view of FIG. 6 ) and expand the effective exit pupil of the light along the first axis (e.g., Y-axis). The distributed waveguide device may include, for example, a dispersive planar waveguide 612 and at least one DOE 616 (illustrated by a double dashed line) associated with the dispersive planar waveguide 612. The dispersive planar waveguide 612 may be similar or the same as the primary planar waveguide 604 with a different orientation therefrom, at least in some respects. Similarly, the at least one DOE 616 may be similar or the same as the DOE 608, at least in some respects. For example, the dispersive planar waveguide 612 and / or the DOE 616 may be made of the same material as the primary planar waveguide 604 and / or the DOE 608, respectively. The optical system shown in FIG. 6 can be integrated into the wearable display system 200 shown in FIG. 2.

[0049] The relayed, exit pupil expanded light is optically coupled from the dispersive waveguide device into one or more primary planar waveguides 604. The primary planar waveguide 662 preferably relays the light along a second axis (e.g., the horizontal or X-axis in the diagram of FIG. 6) that is orthogonal to the first axis. It should be noted that the second axis can be a non-orthogonal axis to the first axis. The primary planar waveguide 604 expands the effective exit path of the light along its second axis (e.g., the X-axis). For example, the dispersive planar waveguide 612 can relay and expand the light along the vertical or Y-axis and pass the light to the primary planar waveguide 604, which relays and expands the light along the horizontal or X-axis.

[0050] The display system 400 may include one or more colored light sources (e.g., red, green, and blue laser light) 620 that may be optically coupled into a proximal end of a single mode optical fiber 624. The distal end of the optical fiber 624 may be threaded or received through a hollow tube 628 of piezoelectric material. The distal end protrudes from the tube 628 as an unfixed flexible cantilever 632. The piezoelectric tube 628 may be associated with four quadrant electrodes (not shown). The electrodes may be, for example, plated on the outside, outer surface or outer periphery, or diameter of the tube 628. A core electrode (not shown) is also located in the core, center, inner periphery, or inner diameter of the tube 628.

[0051] Drive electronics 636, electrically coupled, for example, via wires 640, drive opposing pairs of electrodes to bend the piezoelectric tube 628 independently in two axes. The protruding distal tip of the optical fiber 624 has a mechanical resonant mode. The frequency of the resonance may depend on the diameter, length, and material properties of the optical fiber 624. By oscillating the piezoelectric tube 628 near the first mechanical resonant mode of the fiber cantilever 632, the fiber cantilever 632 may be caused to oscillate and sweep through a large deflection.

[0052] By stimulating resonant vibrations in two axes, the tip of the fiber cantilever 632 is scanned biaxially within an area filling a two-dimensional (2-D) scan. By modulating the intensity of the light source 620 synchronously with the scanning of the fiber cantilever 632, the light emitted from the fiber cantilever 632 forms an image. A description of such a setup is provided in U.S. Patent Publication No. 2014 / 0003762, which is incorporated herein by reference in its entirety.

[0053] An optical coupler subsystem component 644 collimates the light emitted from the scanning fiber cantilever 632. The collimated light is reflected by a mirrored surface 648 into a narrow dispersive planar waveguide 612, which contains at least one diffractive optical element (DOE) 616. The collimated light propagates perpendicularly (with respect to the view of FIG. 6) along the dispersive planar waveguide 612 by total internal reflection, and in so doing repeatedly intersects with the DOE 616. The DOE 616 preferably has a low diffraction efficiency. This causes a portion of the light (e.g., 10%) to diffract toward the edge of the larger primary planar waveguide 604 at each point of intersection with the DOE 616, and a portion of the light to continue on its original trajectory down the length of the dispersive planar waveguide 612 via TIR.

[0054] At each point of intersection with the DOE 616, additional light is diffracted towards the entrance of the primary waveguide 612. By splitting the incoming light into multiple outcoupled sets, the exit pupil of the light is vertically expanded by the DOE 616 within the dispersive planar waveguide 612. This vertically expanded light that is outcoupled from the dispersive planar waveguide 612 enters the edge of the primary planar waveguide 604.

[0055] Light entering the primary waveguide 604 propagates horizontally (with respect to the diagram of FIG. 6) along the primary waveguide 604 via TIR. The light propagates horizontally along at least a portion of the length of the primary waveguide 604 via TIR as it intersects the DOE 608 at multiple points. The DOE 608 may be designed or configured to have a phase profile that is the sum of a linear diffraction pattern and a radially symmetric diffraction pattern to produce both deflection and focusing of the light. The DOE 608 may advantageously have a low diffraction efficiency (e.g., 10%) such that only a portion of the light in the beam is deflected toward the viewer's eye at each intersection of the DOE 608, while the remainder of the light continues to propagate through the primary waveguide 604 via TIR.

[0056] At each point of intersection between the propagating light and the DOE 608, a portion of the light is diffracted towards an adjacent face of the primary waveguide 604, allowing the light to escape the TIR and emerge from the face of the primary waveguide 604. In some embodiments, the radially symmetric diffraction pattern of the DOE 608 additionally imparts a focal level to the diffracted light, both shaping (e.g., imparting curvature) the optical wavefronts of the individual beams and steering the beams to angles that match the designed focal level.

[0057] Thus, these different paths can couple light out of the primary planar waveguide 604 by resulting in different fill patterns at the DOE 608 multiplicity, focus level, and / or exit pupil at different angles. Different fill patterns at the exit pupil can be advantageously used to generate light field displays with multiple depth planes. Each layer or set of layers (e.g., three layers) in the waveguide assembly or stack may be employed to generate individual colors (e.g., red, blue, green). Thus, for example, a first set of three adjacent layers may be employed to generate red, blue, and green light, respectively, at a first focal depth. A second set of three adjacent layers may be employed to generate red, blue, and green light, respectively, at a second focal depth. Multiple sets may be employed to generate full 3D or 4D color image light fields with various focal depths. Exemplary Optical System for Eye Imaging Using an Off-Axis Imager

[0058] The eyes of a wearer of a head mounted display (HMD) (e.g., the wearable display system 200 shown in FIG. 2) can be imaged using a reflective off-axis diffractive optical element (DOE), which in some implementations may be a holographic optical element (HOE). The resulting images can be used to track one or both eyes, image the retina, reconstruct eye shape in three dimensions, extract biometric information from the eye (e.g., iris identification), etc.

[0059] There are various reasons why a head mounted display (HMD) may use information about the state of the wearer's eyes. For example, this information can be used to estimate the wearer's gaze direction or for biometric identification. However, this problem is difficult due to the short distance between the HMD and the wearer's eyes. This is further complicated by the fact that eye tracking requires a larger field of view, while biometric identification requires a relatively high pixel count target on the iris. For an imaging system that would attempt to accomplish both of these objectives, the requirements of the two tasks are significantly in conflict. Finally, both problems are further complicated by occlusion by eyelids and eyelashes. The embodiments of the imaging system described herein address some or all of these problems. Various embodiments of the imaging system 700 described herein with reference to Figures 7A-7H can be used in conjunction with HMDs, including the display devices described herein (e.g., the wearable display system 200 shown in Figure 2, the display system 400 shown in Figures 4 and 6).

[0060] FIG. 7A diagrammatically illustrates an example of an imaging system 700 including an imager 702b used to view the eye 304 and mounted adjacent to the wearer's temple (e.g., on the frame 212 of the wearable display system 200, e.g., an ear rest). In other embodiments, a second imager is used for the wearer's other eye 302 such that each eye is imaged separately. The imager 702b may include an infrared digital camera that is sensitive to infrared radiation. The imager 702b is mounted such that it faces forward (in the direction of the wearer's vision) and is directed toward the eye 304, rather than backward (like the camera 452 shown in FIG. 4). By placing the imager 702b closer to the wearer's ear, the weight of the imager 702b is also closer to the ear, and the HMD may be easier to wear compared to an HMD in which the imager faces backward and is positioned closer to the front of the HMD (e.g., closer to the display 208). Additionally, by placing the front-facing imager 702b near the wearer's temples, the distance from the wearer's eyes 304 to the imager is approximately doubled compared to a rear-facing imager placed near the front of the HMD (e.g., compared to camera 452 shown in FIG. 4). Since the depth of field of the image is approximately proportional to this distance, the depth of field for the front-facing imager 702b is approximately doubled compared to a rear-facing imager. The larger depth of field of imager 702b can be advantageous for imaging the eye region of wearers with large or prominent noses, brow ridges, etc.

[0061] The imager 702b is positioned to view an inner surface 704 of an otherwise transparent optical element 706. The optical element 706 can be part of the display 208 of an HMD (or a lens in a pair of glasses). The optical element can be transparent to at least 10%, 20%, 30%, 40%, 50%, or more of the visible light incident on the optical element. In other embodiments, the optical element 706 need not be transparent (e.g., in a virtual reality display). The optical element 706 can comprise a reflective element 708. The reflective element 708 can be a surface that reflects a first range of wavelengths but is substantially transparent to a second range of wavelengths (different from the first range of wavelengths). The first range of wavelengths can be in the infrared and the second range of wavelengths can be in the visible. For example, the reflective element 708 can comprise a hot mirror that reflects infrared light but transmits visible light. In such an embodiment, infrared light 710a, 712a, 714a from the wearer propagates to and reflects from the optical element 706, resulting in reflected infrared light 710b, 712b, 714b, which can be imaged by the imager 702b. In some embodiments, the imager 702b can be sensitive to or capable of capturing at least a subset (such as a non-empty subset and / or a subset less than all) of the wavelengths in the first range reflected by the reflective element 708. For example, the reflective element 708 may reflect infrared light in the range of 700 nm to 1.5 μm, and the imager 702b may be sensitive to or capable of capturing near-infrared light in wavelengths from 700 nm to 900 nm. As another example, reflective element 708 may reflect infrared light in the range of 700 nm to 1.5 μm, and imager 702b may include a filter that filters out infrared light that is in the range of 900 nm to 1.5 μm such that imager 702b may capture near-infrared light at wavelengths between 700 nm and 900 nm.

[0062] Visible light from the outside world 456 can be transmitted through the optical element 706 and perceived by the wearer. In effect, the imaging system 700 shown in FIG. 7A acts like a virtual imager 702c directed back toward the wearer's eye 304. The virtual imager 702c can image virtual infrared light 710c, 712c, 714c (shown as dotted lines) propagating from the wearer's eye 304 through the optical element 706. The hot mirror (or other DOE described herein) can be disposed on the inner surface 704 of the optical element 706, but this is not a limitation. In other embodiments, the hot mirror or DOE can be disposed on the outer surface of the optical element 706 or within the optical element 706 (e.g., a solid HOE).

[0063] FIG. 7B diagrammatically illustrates another example of an imaging system 700. In this embodiment, perspective distortion can be reduced or eliminated by using a perspective control lens assembly 716b (e.g., a shifting lens assembly, a tilting lens assembly, or a tilt-shifting lens assembly) in conjunction with an imager 702b. In some embodiments, the perspective control lens assembly 716b can be part of the lens of the imager 702b. The perspective control lens 716b can be configured such that the normal to the imager 702b is approximately parallel to the normal to the region of the surface 704 that includes the DOE (or HOE) or hot mirror. In effect, the imaging system 700 shown in FIG. 7B acts like a virtual imager 702c with a virtual perspective control lens assembly 716c pointed back toward the wearer's eye 304.

[0064] Additionally or alternatively, as shown diagrammatically in Fig. 7C, the reflective element 708 of the optical element 706 may have an off-axis holographic mirror (OAHM) on its surface 704 that is used to reflect the light 710a, 712a, 714a and facilitate viewing of the eye 304 by the camera imager 702b, which captures the reflected light 710b, 712b, 714b. The OAHM 708 may have refractive power as well, in which case it may be an off-axis volumetric diffractive optical element (OAVDOE), as shown diagrammatically in Fig. 7D. In the example shown in Fig. 7D, the effective location of the virtual camera 702c is at infinity (not shown in Fig. 7D).

[0065] In some embodiments, the HOE (e.g., OAHM or OAVDOE) can be divided into multiple segments. Each of these segments can have different optical properties or characteristics, including, for example, the reflective angle or refractive power at which the segment reflects incident (infrared) light. The segments can be configured such that light is reflected from each segment toward the imager 702b. As a result, the image acquired by the imager 702b is also divided into a corresponding number of segments, each effectively viewing the eye from a different angle. FIG. 7E diagrammatically illustrates an example of a display system 700 having an OAHM with three segments 718a1, 718a2, 718a3, each acting as a separate virtual camera 702c1, 702c2, 702c3 that images the eye 304 at different angular locations.

[0066] FIG. 7F diagrammatically illustrates another example of a display system 700 having an OAHM with three segments 718a1, 718a2, 718a3, each having a refractive power (e.g., a segmented OAVDOE), with each segment generating a virtual camera at infinity and imaging the eye 304 at a different angular location. Although three segments are diagrammatically illustrated in FIGS. 7E and 7F, this is by way of example and not limitation. In other embodiments, two, four, five, six, seven, eight, nine, or more segments can be utilized. None of these segments of the HOE can have refractive power, or some or all of them can have refractive power.

[0067] The three segments 718a1, 718a2, 718a3 are shown in Figures 7E and 7F spaced horizontally across the optical element 706. In other embodiments, the segments can be spaced vertically on the optical element 706. For example, Figure 7G diagrammatically shows a DOE 718 having two vertically spaced segments 718a1 and 718a2, where segment 718a1 is configured to reflect light back toward imager 702b (which may be in the same approximate horizontal plane as segment 718a1) and segment 718a2 is configured to reflect light upward toward imager 702b. Similar to a bifocal lens, the arrangement shown in FIG. 7G can be advantageous in enabling the imaging system 700 to use a reflected image captured by imager 702b from upper segment 718a1 (shown diagrammatically via solid arrow lines) when the wearer is looking straight ahead through the upper portion of the HMD, and a reflected image from lower segment 718a2 (shown diagrammatically via dashed arrow lines) when the wearer is looking downward through the lower portion of the HMD.

[0068] A mix of horizontally and vertically spaced segments can also be used in other embodiments. For example, FIG. 7H shows another example of an HOE 718 with a 3×3 array of segments. The imager 702b can acquire reflection data from each of these nine segments representing rays originating from different areas and angular orientations of the eye region. Two example rays propagating from the eye region of the HOE 718 and reflecting back to the imager 702b are shown as solid and dashed lines. The imaging system 700 (or processing module 224 or 228) can analyze the reflection data from the multiple segments and multifocally calculate the three-dimensional shape of the eye or the gaze direction of the eye (e.g., eye posture).

[0069] An embodiment of the optical system 700 utilizing segments may have several advantages. For example, the segments can be used individually by selecting the particular segment best suited for a particular task, or they can be used collectively to estimate the three-dimensional shape or pose of the eye multifocally. In the former case, this selectivity can be used, for example, to select the image of the wearer's iris that has the least obstruction by eyelids or eyelashes. In the latter case, the three-dimensional reconstruction of the eye can be used to estimate the orientation (e.g., by estimating the location of the corneal bulge) or the accommodation state (e.g., by estimating the lens-induced distortion on the apparent location of the pupil). (Additional Aspects)

[0070] In a first aspect, a head mounted display (HMD) configured to be worn on a user's head is disclosed. The HMD includes a frame with a pair of ear rests, a pair of optical elements supported by the frame such that each of the pair of optical elements can be positioned in front of a user's eye, a forward-facing imager mounted on one of the pair of ear rests, and a reflective element disposed within or on one of the pair of optical elements, the reflective element configured to reflect infrared light toward the forward-facing imager configured to receive infrared light reflected by the reflective element.

[0071] In a second aspect, the HMD of aspect 1, wherein each of the pair of optical elements is transmissive to visible light.

[0072] In a third aspect, the HMD of aspect 1 or aspect 2, wherein each of the pair of optical elements is configured to display an image to a user.

[0073] In a fourth aspect, the HMD of aspect 3, wherein each of the pair of optical elements comprises a light field display.

[0074] In a fifth aspect, the HMD of aspect 4, wherein the light field display comprises a waveguide stack configured to output an image to a user.

[0075] In a sixth aspect, the HMD of any one of aspects 1 to 5, wherein the reflective element comprises a hot mirror, an off-axis diffractive optical element (DOE), an off-axis holographic mirror (OAHM), or an off-axis volumetric diffractive optical element (OAVDOE).

[0076] In a seventh aspect, the HMD of any one of aspects 1 to 6, wherein the reflective element is transparent to visible light.

[0077] In an eighth aspect, an HMD described in any one of aspects 1 to 7, wherein the reflective element comprises a plurality of segments, each segment within the plurality of segments having optical properties that are different from the optical properties of at least one other segment within the plurality of segments.

[0078] In a ninth aspect, the HMD of aspect 8, wherein the optical properties include a reflection angle or a refractive power.

[0079] In a tenth aspect, the HMD of aspect 8 or aspect 9, wherein the plurality of segments comprises 2, 3, 4, 5, 6, 7, 8, or 9 segments.

[0080] In an eleventh aspect, the HMD of any one of aspects 1 to 10, wherein the forward-facing imager is mounted in the temple portion of one of the pair of ear supports.

[0081] In a twelfth aspect, the HMD of any one of aspects 1 to 11, wherein the imager comprises a perspective control lens assembly.

[0082] In a thirteenth aspect, the HMD of aspect 12, wherein the perspective control lens assembly comprises a shifting lens, a tilting lens, or a shifting-tilting lens.

[0083] In a fourteenth aspect, a display system is disclosed comprising an optical element configured to display an image to a user, the optical element configured to be positioned in front of an eye of the user, a forward-facing imager, and a reflective element disposed within or on the optical element, the reflective element configured to reflect infrared light received from the eye of the user towards the forward-facing imager.

[0084] In a fifteenth aspect, the display system of aspect 14, wherein the optical element comprises a light field display.

[0085] In a sixteenth aspect, the display system of aspect 14 or 15, wherein the reflective element comprises a hot mirror, an off-axis diffractive optical element (DOE), an off-axis holographic mirror (OAHM), or an off-axis volumetric diffractive optical element (OAVDOE).

[0086] In a seventeenth aspect, the display system of any one of aspects 14 to 16, wherein the reflective element comprises a plurality of segments having different refractive powers or different reflection angles.

[0087] In an eighteenth aspect, the display system of any one of aspects 14 to 17 further comprises a non-transitory memory configured to store an image of the user's eye obtained by the forward-facing imager, and a hardware processor in communication with the non-transitory memory, the hardware processor being programmed to access the image of the eye and perform one or more of: tracking the user's eye, extracting biometric information associated with the user's eye, reconstructing the shape of a portion of the user's eye, estimating the accommodation state of the user's eye, or imaging the retina, iris, or other elements of the user's eye.

[0088] In a nineteenth aspect, a head mounted display system is disclosed, the HDM comprising a frame configured to support the display system of any one of aspects 14 to 18 such that the optical element is positioned in front of a first eye of a user.

[0089] In a twentieth aspect, a head-mounted display system as described in aspect 19, wherein the frame supports a second display system as described in any one of aspects 14 to 18 so that an optical element of the second display system is positioned in front of the user's second eye.

[0090] In a twenty-first aspect, an imaging system is disclosed that includes a reflective element that reflects light within a first wavelength range and an imager that is sensitive to light in a non-empty subset of less than all of the first wavelength range, the imager being configured to be oriented to capture light reflected by the reflective element.

[0091] In a twenty-second aspect, the imaging system of aspect 21, wherein the reflective element comprises a hot mirror, a holographic optical element (HOE), an off-axis holographic mirror (OAHM), or an off-axis volumetric diffractive optical element (OAVDOE).

[0092] In a 23rd aspect, the imaging system of any one of aspects 21-22, wherein the first wavelength range comprises an infrared wavelength range.

[0093] In a 24th aspect, the imaging system of any one of aspects 21-23 comprises an optical element, the optical element comprising a reflective element, the optical element being transmissive to at least 50% of visible light incident on the optical element.

[0094] In a 25th aspect, the imaging system of any one of aspects 21-24, wherein the reflective element comprises a plurality of segments.

[0095] In a twenty-sixth aspect, an imaging system as described in aspect 25, wherein a first segment in the plurality of segments has optical properties that are different from optical properties of a second segment in the plurality of segments.

[0096] In a twenty-seventh aspect, the imaging system of aspect 26, wherein the optical properties of a first segment in the plurality of segments or the optical properties of a second segment in the plurality of segments comprise a reflection angle or a refractive power.

[0097] In a 28th aspect, the imaging system of any one of aspects 25-27, wherein the plurality of segments comprises at least two segments.

[0098] In a 29th aspect, an imaging system described in any one of aspects 25-28, wherein two of the multiple segments are arranged horizontally.

[0099] In a 30th aspect, the imaging system of any one of aspects 25-29, wherein two of the multiple segments are arranged vertically.

[0100] In a thirty-first aspect, an imaging system described in any one of aspects 25-30, wherein some of the multiple segments are arranged in a grid.

[0101] In a thirty-second aspect, the imaging system of any one of aspects 21-31, wherein the imager further comprises a perspective control lens assembly.

[0102] In a thirty-third aspect, the imaging system of aspect 32, wherein the perspective control lens assembly comprises a shifting lens, a tilting lens, or a shifting-tilting lens.

[0103] In a thirty-fourth aspect, an imaging system for indirectly capturing an image of a user's eye is disclosed, the imaging system comprising: a reflective element that reflects light within a first wavelength range, the reflective element comprising an off-axis holographic mirror (OAHM) or an off-axis volumetric diffractive optical element (OAVDOE), oriented to reflect light propagating from the user's eye when the imaging system is placed in front of the user's eye, and an imager sensitive to light in a non-empty subset of the first wavelength range less than all of the first wavelength range, the imager oriented to capture an image of the user's eye by capturing light propagating from the user's eye that is reflected by the reflective element.

[0104] In a thirty-fifth aspect, the imaging system of aspect 34, wherein an image of the user's eye captured by the imager and an image of the user's eye captured by a camera positioned in front of the user's eye are indistinguishable.

[0105] In a thirty-sixth aspect, the imaging system of aspect 35, wherein the image of the user's eye captured by the imager is captured by a camera positioned substantially in front of the user's eye.

[0106] In a thirty-seventh aspect, the imaging system of any one of aspects 35-36, wherein the effective location of the camera placed in front of the user's eye is at infinity.

[0107] In a thirty-eighth aspect, the imaging system of any one of aspects 35-37, wherein the first wavelength range comprises an infrared wavelength range.

[0108] In a thirty-ninth aspect, the imaging system is an imaging system described in any one of aspects 35-38, wherein the imaging system comprises an optical element, the optical element comprising a reflective element, and the optical element is transmissive to at least 50% of visible light incident on the optical element.

[0109] In a 40th aspect, the imaging system of any one of aspects 35-39, wherein the reflective element comprises a plurality of segments.

[0110] In a forty-first aspect, an imaging system as described in aspect 40, wherein a first segment in the plurality of segments has optical properties that are different from optical properties of a second segment in the plurality of segments.

[0111] In a forty-second aspect, the imaging system of aspect 41, wherein the optical properties of a first segment in the plurality of segments or the optical properties of a second segment in the plurality of segments comprise a reflection angle or a refractive power.

[0112] In a 43rd aspect, the imaging system of any one of aspects 40-42, wherein the plurality of segments comprises at least two segments.

[0113] In a forty-fourth aspect, an imaging system as described in any one of aspects 40-43, wherein two of the plurality of segments are arranged horizontally.

[0114] In a forty-fifth aspect, the imaging system of any one of aspects 40-44, wherein two of the plurality of segments are arranged vertically.

[0115] In a forty-sixth aspect, an imaging system according to any one of aspects 40-45, wherein some of the plurality of segments are arranged in a grid.

[0116] In a forty-seventh aspect, the imaging system of any one of aspects 34-46, wherein the imager further comprises a perspective control lens assembly.

[0117] In a forty-eighth aspect, the imaging system of aspect 47, wherein the perspective control lens assembly comprises a shifting lens, a tilting lens, or a shifting-tilting lens.

[0118] In a forty-ninth aspect, an imaging system is disclosed that includes a display including a reflective element that reflects light within a first wavelength range, the reflective element including a hot mirror, an off-axis holographic mirror (OAHM), or an off-axis volumetric diffractive optical element (OAVDOE), and an imager sensitive to light within the first wavelength range, the imager configured to be oriented to capture at least the light reflected by the reflective element.

[0119] In a 50th aspect, the imaging system of aspect 49, wherein the first wavelength range comprises an infrared wavelength range.

[0120] In a fifty-first aspect, the imaging system of aspect 49 or aspect 50, wherein the display is substantially transparent to visible light.

[0121] In a 52nd aspect, an imaging system described in any one of aspects 49-51, wherein the reflective element comprises a plurality of segments, each segment within the plurality of segments having optical properties that are different from the optical properties of at least one other segment within the plurality of segments.

[0122] In a 53rd aspect, the imaging system of aspect 52, wherein the optical property includes a reflection angle or a refractive power.

[0123] In a 54th aspect, the imaging system of aspect 52 or aspect 53, wherein the plurality of segments comprises 2, 3, 4, 5, 6, 7, 8, or 9 segments.

[0124] In aspect 55, the imaging system of any one of aspects 49 to 54, wherein the imager further comprises a perspective control lens assembly.

[0125] In a fifty-sixth aspect, the imaging system of aspect 55, wherein the perspective control lens assembly comprises a shifting lens, a tilting lens, or a shifting-tilting lens.

[0126] In a 57th aspect, the imaging system of any one of aspects 21 to 56 further comprises a non-transitory data storage device configured to store images acquired by the imager, and a hardware processor in communication with the non-transitory data storage device, the hardware processor being programmed with executable instructions to analyze the images and perform one or more of eye tracking, biometric identification, multi-view reconstruction of eye shape, estimation of eye accommodation state, or retinal, iris, or other imaging to distinguish eye patterns.

[0127] In a fifty-eighth aspect, a head mounted display (HMD) is disclosed. The HMD includes the imaging system of any one of aspects 21 to 57.

[0128] In a fifty-ninth aspect, the HMD is an HMD as described in aspect 58, wherein the HMD comprises a frame having a portion configured to be worn near an ear, and the imager is positioned near the portion.

[0129] In a 60th aspect, the imaging system is configured to image a first eye of a wearer, and the HMD includes a second imaging system described in any one of aspects 21 to 57, and the second imaging system is configured to image a second eye of the wearer, an HMD described in aspect 58 or aspect 59.

[0130] In a 61st aspect, the HMD of any one of aspects 58-60 is an augmented reality device (ARD).

[0131] In a sixty-second aspect, a method of creating a virtual camera is disclosed. The method includes the steps of providing an imaging system in front of an object to be imaged, creating a virtual camera in front of the object, the imaging system comprising a reflective element that reflects light within a first wavelength range, the reflective element comprising an off-axis holographic mirror (OAHM) or an off-axis volumetric diffractive optical element (OAVDOE), the reflective element being oriented to reflect light propagating from the object when the imaging system is placed in front of the object, and an imager sensitive to light in a non-sky subset of less than all of the first wavelength range, the imager being oriented to capture an image of the object by capturing light propagating from the object reflected by the reflective element, the image of the object captured by the imager and the image of the object captured by a camera in front of the object being indistinguishable.

[0132] In a 63rd aspect, the method of aspect 62, wherein the first wavelength range comprises an infrared wavelength range.

[0133] In a 64th aspect, the imaging system comprises an optical element, the optical element comprising a reflective element, and the optical element is transmissive to at least 50% of visible light incident on the optical element, a method according to any one of aspects 62-63.

[0134] In a 65th aspect, the method of any one of aspects 62-64, wherein the reflective element comprises a plurality of segments.

[0135] In a 66th aspect, the method of aspect 65, wherein a first segment in the plurality of segments has optical properties that are different from optical properties of a second segment in the plurality of segments.

[0136] In a 67th aspect, the method of aspect 66, wherein the optical property of a first segment in the plurality of segments or the optical property of a second segment in the plurality of segments comprises a reflection angle or a refractive power.

[0137] In a 68th aspect, the method of any one of aspects 65-67, wherein the plurality of segments comprises at least two segments.

[0138] In a sixty-ninth aspect, the method of any one of aspects 65-68, wherein two of the plurality of segments are arranged horizontally.

[0139] In a 70th aspect, the method of any one of aspects 65-69, wherein two of the plurality of segments are arranged vertically.

[0140] In a 71st aspect, the method of any one of aspects 65-70, wherein some of the plurality of segments are arranged in a grid.

[0141] In aspect 72, the method of any one of aspects 62-71, wherein the imager further comprises a perspective control lens assembly.

[0142] In a seventy-third aspect, the method of aspect 72, wherein the perspective control lens assembly comprises a shifting lens, a tilting lens, or a shifting-tilting lens.

[0143] In a seventy-fourth aspect, a method of imaging an object using a virtual camera is disclosed, the method includes providing an imaging system in front of an object to be imaged, creating a virtual camera in front of the object, the imaging system including a reflective element that reflects light in a first wavelength range, the reflective element comprising an off-axis holographic mirror (OAHM) or an off-axis volumetric diffractive optical element (OAVDOE), the reflective element being oriented to reflect light propagating from the object when the imaging system is placed in front of the object, and an imager that is sensitive to light in a non-empty subset of less than all of the first wavelength range, the imager being oriented to capture an image of the object by capturing light propagating from the object reflected by the reflective element, and imaging the object using the virtual camera, the image of the object being captured by capturing light propagating from the object reflected by the reflective element, the image of the object being indistinguishable from the image of the object captured by the imager and the image of the object being captured by a camera in front of the object.

[0144] In a 75th aspect, the method of aspect 74, wherein the first wavelength range comprises an infrared wavelength range.

[0145] In aspect 76, the imaging system comprises an optical element, the optical element comprising a reflective element, and the optical element is transmissive to at least 50% of visible light incident on the optical element, a method according to any one of aspects 74-75.

[0146] In a 77th aspect, the method of any one of aspects 74-76, wherein the reflective element comprises a plurality of segments.

[0147] In a 78th aspect, the method of aspect 77, wherein a first segment in the plurality of segments has optical properties that are different from optical properties of a second segment in the plurality of segments.

[0148] In a seventy-ninth aspect, the method of aspect 78, wherein the optical property of a first segment in the plurality of segments or the optical property of a second segment in the plurality of segments comprises a reflection angle or a refractive power.

[0149] In an 80th aspect, the method of any one of aspects 77-79, wherein the plurality of segments comprises at least two segments.

[0150] In an 81st aspect, the method of any one of aspects 77-80, wherein two of the plurality of segments are arranged horizontally.

[0151] In an 82nd aspect, the method of any one of aspects 77-81, wherein two of the plurality of segments are arranged vertically.

[0152] In an 83rd aspect, the method of any one of aspects 77-82, wherein some of the plurality of segments are arranged in a grid.

[0153] In an 84th aspect, the method of any one of aspects 74-83, wherein the imager further comprises a perspective control lens assembly.

[0154] In an 85th aspect, the method of aspect 84, wherein the perspective control lens assembly comprises a shifting lens, a tilting lens, or a shifting-tilting lens.

[0155] In an aspect of the eighty-sixth aspect, an imaging assembly is disclosed that includes a see-through element (e.g., a display), a viewing camera positioned to view the display, a lens associated with the camera, and a reflective element on the display that renders the display reflective to all or a portion of the wavelengths to which the display is sensitive.

[0156] In an 87th aspect, the assembly of aspect 86, wherein the reflective element comprises a hot mirror, an off-axis holographic mirror (OAHM) or an off-axis volumetric diffractive optical element (OAVDOE).

[0157] In an 88th aspect, the assembly of any one of aspects 86-87 is integrated into a wearable structure such as a pair of glasses or a helmet.

[0158] In an 89th aspect, the assembly of any one of aspects 86-88, wherein the reflective element is segmented.

[0159] In a 90th aspect, the assembly is configured for use of the segmented OAHM to select the best possible viewing angle for a particular task (e.g., eye tracking or biometric identification), the assembly being described in aspect 89.

[0160] In a 91st aspect, the assembly is an assembly described in any one of aspects 89-90, wherein the assembly is configured for use of multiple segment sub-images for stereoscopic vision or multi-view 3D reconstruction of the shape of the eye.

[0161] In aspect 92, the assembly of aspect 91, wherein the three-dimensional reconstruction of the shape of the eye is used to estimate the accommodation state of the eye.

[0162] In a 93rd aspect, the assembly of aspect 92, wherein estimating the state of accommodation of the eye includes comparing the apparent location and shape of the pupil and iris of the eye across multiple images of the same wearer of the assembly.

[0163] In aspect 94, the assembly of any one of aspects 92-93, wherein the estimation of the accommodation state of the eye is used to determine the expansion state of the crystalline lens.

[0164] In a 95th aspect, the assembly of any one of aspects 86-94, wherein the assembly is configured for use of the image segments as input to an information fusion algorithm.

[0165] In a 96th aspect, the assembly described in aspect 95, wherein the information fusion algorithm is used to improve the apparent resolution of the eye or the quality of information extraction therefrom.

[0166] In an aspect of the 97th aspect, the assembly of any one of aspects 95-96, wherein the information fusion algorithm comprises an image super-resolution technique.

[0167] In a 98th aspect, the assembly of any one of aspects 95-97, wherein the information fusion algorithm is used to improve an image of the iris of the eye.

[0168] In a 99th aspect, the assembly of any one of aspects 95-98, wherein the information fusion algorithm comprises iris code extraction (e.g., John Daugman, et al. 2006) and subsequent fusion of the resulting iris codes to form a single estimate of the wearer's iris code.

[0169] In a 100th aspect, the assembly of any one of aspects 86-99, wherein the assembly is configured for use of image segments to improve eye pose estimation or tracking.

[0170] In aspect 101, the assembly described in aspect 100, wherein a 3D reconstruction of the eye, iris, pupil, and cornea (or any subset thereof) is used directly in conjunction with image segments to improve eye coverage in pose estimation.

[0171] In aspect 102, the assembly of any one of aspects 86-101 comprises an OAVDOE, the reflective element including an optical power for adding or reducing beam divergence.

[0172] In the 103rd aspect, the assembly of any one of aspects 86-102, wherein the reflective element includes any number of segments (e.g., 2, 3, 6, or 9 segments).

[0173] In aspect 104, the assembly of any one of aspects 86-103, wherein the reflective element is configured to reflect infrared light and the visual camera is sensitive to infrared light.

[0174] In aspect 105, the assembly of aspect 104, wherein the reflective element comprises a hot mirror configured to reflect infrared light but otherwise be transmissive to visible light.

[0175] In aspect 106, the assembly of any one of aspects 86-105 further comprises an offset lens (e.g., as in tilt-shift photography) with a normal to the viewing camera parallel to the normal of the surface comprising the reflective element.

[0176] In a 107th aspect, a head mounted display (HMD) is disclosed. The HMD includes a pair of displays, each display including an imaging assembly as described in any one of aspects 86-106, one assembly of the pair configured for each eye of a wearer. (Conclusion)

[0177] Each of the processes, methods, and algorithms described herein and / or depicted in the accompanying figures may be embodied in code modules executed by one or more physical computing systems, hardware computer processors, application-specific circuits, and / or electronic hardware configured to execute specific and particular computer instructions, and may be fully or partially automated thereby. For example, the computing system may include a general-purpose computer (e.g., a server) or a special-purpose computer programmed with specific computer instructions, special-purpose circuits, etc. The code modules may be written in a programming language that may be compiled and linked into an executable program, installed in a dynamic link library, or interpreted. In some implementations, certain operations and methods may be performed by circuitry specific to a given function.

[0178] Furthermore, certain implementations of the functionality of the present disclosure may be sufficiently mathematically, computationally, or technically complex that special purpose hardware (utilizing appropriate specialized executable instructions) or one or more physical computing devices may be required to implement the functionality, e.g., due to the amount or complexity of the calculations involved, or to provide results in substantially real-time. For example, a video may contain many frames, each frame may have millions of pixels, and specifically programmed computer hardware is required to process the video data to provide the desired image processing task or application in a commercially reasonable amount of time.

[0179] The code modules or any type of data may be stored on any type of non-transitory computer readable medium, such as physical computer storage devices, including hard drives, solid state memory, random access memory (RAM), read only memory (ROM), optical disks, volatile or non-volatile storage devices, combinations of the same, and / or the like. The methods and modules (or data) may also be transmitted as data signals (e.g., as part of a carrier wave or other analog or digital propagating signal) generated over a variety of computer readable transmission media, including wireless-based and wired / cable-based media, and may take a variety of forms (e.g., as part of a single or multiplexed analog signal, or as multiple discrete digital packets or frames). The results of the disclosed processes or process steps may be stored persistently or otherwise in any type of non-transitory tangible computer storage device or communicated via a computer readable transmission medium.

[0180] Any process, block, state, step, or functionality in the flow diagrams described herein and / or depicted in the accompanying figures should be understood as potentially representing a code module, segment, or portion of code that includes one or more executable instructions for implementing a specific function (e.g., logical or arithmetic) or step in the process. The various processes, blocks, states, steps, or functionality can be combined, rearranged, added, deleted, modified, or otherwise altered from the illustrative examples provided herein. In some embodiments, additional or different computing systems or code modules may perform some or all of the functionality described herein. The methods and processes described herein are also not limited to any particular sequence, and the blocks, steps, or states associated therewith can be performed in other sequences as appropriate, e.g., serially, in parallel, or in some other manner. Tasks or events may be added to or removed from the disclosed exemplary embodiments. Furthermore, the separation of various system components in the implementations described herein is for illustrative purposes and should not be understood as requiring such separation in all implementations. It should be understood that the described program components, methods, and systems may generally be integrated together in a single computer product or packaged into multiple computer products. Many implementation variations are possible.

[0181] The process, method, and system may be implemented in a network (or distributed) computing environment. Network environments include enterprise-wide computer networks, intranets, local area networks (LANs), wide area networks (WANs), personal area networks (PANs), cloud computing networks, crowdsourced computing networks, the Internet, and the World Wide Web. The network may be a wired or wireless network or any other type of communication network.

[0182] The systems and methods of the present disclosure each have several innovative aspects, none of which is solely responsible for or required for the desirable attributes disclosed herein. The various features and processes described above may be used independently of one another or may be combined in various ways. All possible combinations and subcombinations are intended to fall within the scope of the present disclosure. Various modifications of the implementations described in the present disclosure may be readily apparent to those skilled in the art, and the general principles defined herein may be applied to other implementations without departing from the spirit or scope of the present disclosure. Thus, the claims are not intended to be limited to the implementations shown herein, but should be accorded the widest scope consistent with the present disclosure, the principles, and novel features disclosed herein.

[0183] Certain features described herein in the context of separate implementations can also be implemented in combination in a single implementation. Conversely, various features described in the context of a single implementation can also be implemented separately in multiple implementations or in any suitable subcombination. Furthermore, although features may be described above as acting in a combination and may even be initially claimed as such, one or more features from the claimed combination may in some cases be deleted from the combination, and the claimed combination may be directed to a subcombination or variation of the subcombination. No single feature or group of features is necessary or essential to every embodiment.

[0184] In particular, conditional statements used herein, such as "can," "could," "might," "may," "eg," and the like, are generally intended to convey that certain embodiments include certain features, elements, and / or steps, while other embodiments do not, unless specifically stated otherwise or understood otherwise within the context as used. Thus, such conditional statements are generally not intended to suggest that features, elements, and / or steps are in any way required for one or more embodiments, or that one or more embodiments necessarily include logic for determining whether those features, elements, and / or steps should be included or performed in any particular embodiment, with or without authorial input or prompting. The terms "comprise," "include," "have," and the like, are synonymous and used inclusively in a non-limiting manner and do not exclude additional elements, features, acts, operations, etc. Also, the term "or" is used in its inclusive sense (and not its exclusive sense), thus, for example, when used to connect a list of elements, the term "or" means one, some, or all of the elements in the list. In addition, the articles "a," "an," and "the," as used in this application and the appended claims, unless otherwise specified, should be interpreted to mean "one or more" or "at least one."

[0185] As used herein, a phrase referring to a list of items "at least one of" refers to any combination of those items, including single elements. As an example, "at least one of A, B, or C" is intended to cover A, B, C, A and B, A and C, B and C, and A, B, and C. Transitive phrases such as "at least one of X, Y, and Z" are generally understood differently in the context in which they are used to convey that an item, term, etc. may be at least one of X, Y, or Z, unless specifically stated otherwise. Thus, such transitive phrases are generally not intended to suggest that an embodiment requires that at least one of X, at least one of Y, and at least one of Z, respectively, be present.

[0186] Similarly, although operations may be depicted in the figures in a particular order, it should be appreciated that such operations need not be performed in the particular order depicted, or in sequential order, or that all of the depicted operations need not be performed to achieve desirable results. Additionally, the figures may diagrammatically depict one or more exemplary processes in the form of a flow chart. However, other operations not depicted may also be incorporated within the diagrammatically depicted exemplary methods and processes. For example, one or more additional operations may be performed before, after, simultaneously with, or during any of the depicted operations. Additionally, operations may be rearranged or reordered in other implementations. In some circumstances, multitasking and parallel processing may be advantageous. Additionally, the separation of various system components in the implementations described above should not be understood as requiring such separation in all implementations, and it should be understood that the described program components and systems 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 claims. In some cases, the actions recited in the claims can be performed in a different order and still achieve desirable results.

Claims

1. 1. A display system comprising: an optical element configured to display an image to a user, the optical element configured to be positioned in front of an eye of the user; a reflective element disposed within or on the surface of the optical element; a forward-looking imager sensitive to a first infrared light, the forward-looking imager oriented to capture the first infrared light reflected by the reflective element, the forward-looking imager configured to be mounted on the same side of the optical element as an eye of a user, the forward-looking imager comprising a perspective-control lens assembly, the perspective-control lens assembly comprising a shifting lens, a tilting lens, or a shifting-tilting lens; a virtual rear-facing imager formed by a second infrared light propagating from the user's eye through the optical element that corresponds to the first infrared light reflected by the reflective element and captured by the front-facing imager; Equipped with A display system, wherein the virtual rear-facing imager and the front-facing imager are positioned on opposite sides of the optical element, and the virtual rear-facing imager and the front-facing imager are equidistant from the optical element.

2. The display system of claim 1 , wherein the optical element comprises a light field display.

3. 10. The display system of claim 1, wherein the reflective element comprises a hot mirror, an off-axis diffractive optical element (DOE), an off-axis holographic mirror (OAHM), or an off-axis volumetric diffractive optical element (OAV-DOE).

4. 10. The display system of claim 1, wherein the reflective element comprises a plurality of segments having different refractive powers or different angles of reflection.

5. The display system of claim 4 , wherein each of the plurality of segments is configured as a virtual camera imaging the eye at a correspondingly different angular location.

6. 5. The display system of claim 4, wherein the forward-facing imager uses an upper segment when the user is looking upwards and a lower segment when the user is looking downwards to image the eye.

7. The display system of claim 4 , wherein for imaging the eye, the display system selects the segment of the plurality of segments that has the least occlusion by the user's eyelashes or eyelids.

8. a non-transitory memory configured to store an image of the user's eye obtained by the forward-facing imager; and a hardware processor in communication with the non-transitory memory; Further equipped with The hardware processor includes: accessing an image of the user's eye; tracking the eyes of the user; extracting biometric information associated with an eye of the user; reconstructing a shape of a portion of the user's eye; estimating the state of accommodation of the user's eye; or Imaging the retina, iris, or other element of the user's eye; and 10. The display system of claim 1, programmed to:

9. The display system of claim 8 , wherein the hardware processor is programmed to estimate an accommodation state of the user's eye.

10. 10. The display system of claim 9, wherein to estimate the state of accommodation of the user's eye, the hardware processor is programmed to estimate a distortion of the apparent location of the pupil of the user's eye.

11. The display system of claim 8 , wherein the hardware processor is programmed to reconstruct a shape of a portion of the user's eye.

12. The display system of claim 11 , wherein the hardware processor is programmed to estimate an orientation of the user's eye by utilizing the shape of the portion of the user's eye.

13. The display system of claim 12 , wherein to estimate the orientation of the user's eye, the hardware processor is programmed to estimate a location of a corneal bulge of the user's eye.

14. A head mounted display system comprising a frame configured to support the display system of claim 1 such that the optical element is positioned in front of a first eye of the user.

15. A head-mounted display comprising a frame configured to support two display systems according to claim 1, wherein an optical element of a first of the two display systems is positioned in front of a first eye of the user and an optical element of a second of the two display systems is positioned in front of a second eye of the user.

Images