System for collecting light

Abstract

To provide a system for collecting light.SOLUTION: A display system is configured to provide illumination and / or image projection to the eye. Additionally, or alternatively, the display system can image the eye and / or the environment. A thin transparent layer can be integrated into a head-mounted display device and disposed in front of a wearer's eyes. The thin transparent layer may be configured to output light such that the light is directed onto the eye to create reflections from there that can be used, for example, for glint-based tracking. The thin transparent layer can be configured to reduce obstructions in the user's field of view.SELECTED DRAWING: Figure 41B

Description

[Technical Field]

[0001] (CROSS-REFERENCE TO RELATED APPLICATIONS) This application claims the benefit of priority to U.S. Provisional Application No. 62 / 821,406 (Attorney Docket No. MLEAP.239PR), entitled "SYSTEM FOR COLLECTING LIGHT," filed March 20, 2019, and U.S. Provisional Application No. 62 / 821,977 (Attorney Docket No. MLEAP.239PR3), entitled "SYSTEM FOR COLLECTING LIGHT," filed March 21, 2019. The entirety of each application referenced in this paragraph is incorporated herein by reference.

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

[0003] 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 portions thereof are presented to a user in a manner that appears or can be perceived as real. Virtual reality, or "VR," scenarios typically involve the presentation of digital or virtual image information without transparency to other actual real-world visual input, while augmented reality, or "AR," scenarios typically involve the presentation of digital or virtual image information as an augmentation to the user's visualization of the real world around them. Mixed reality, or "MR," scenarios are a type of AR scenario that typically involve virtual objects integrated into and responsive to the natural world. For example, MR scenarios may include AR image content that appears blocked by or is perceived to otherwise interact with objects in the real world.

[0004] Referring to FIG. 1 , an augmented reality scene 10 is depicted. A user of the AR technology sees a real-world park-like setting 20 featuring people, trees, a building in the background, and a concrete platform 30. The user also perceives that they "see" "virtual content," such as a robotic figure 40 standing on the real-world platform 30 and a flying, cartoon-like avatar character 50 that appears to be an anthropomorphic bumblebee. These elements 50, 40 are "virtual" in that they do not exist in the real world. The human visual perception system is complex, making it difficult to produce AR technology that facilitates a comfortable, natural-feeling, and rich presentation of virtual image elements among other virtual or real-world image elements.

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

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

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

[0008] In some embodiments, a head-mounted display system is configured to project light into a user's eye and display augmented reality image content within the user's field of view. The head-mounted display system may include a frame configured to be supported on the user's head. The display system may also include an image projector configured to project an image into the user's eye and display image content within the user's field of view. The display system may include a camera, at least one waveguide, at least one coupling optical element configured to couple light into and guide it therein, and at least one out-coupling element. The at least one out-coupling element may be configured to couple light guided in the waveguide out of the waveguide and direct the light toward the camera. The camera may be positioned in an optical path with respect to the at least one out-coupling optical element to receive at least a portion of the light coupled into and guided in the waveguide via the coupling element and coupled out of the waveguide by the out-coupling element so that an image may be captured by the camera. The present invention provides, for example, the following. (Item 1) 1. A head-mounted display system configured to project light onto a user's eye and display augmented reality image content within the user's field of view, the head-mounted display system comprising: a frame configured to be supported on the user's head; an image projector configured to project an image into the user's eye and display image content within the user's field of view; A camera and at least one waveguide; at least one coupling optical element, the at least one coupling optical element configured to couple light into the waveguide and guide it therein; first and second light redirecting elements, the first and second light redirecting elements positioned to receive light from the at least one coupling optical element guided within the waveguide; and Equipped with the first light redirecting element is configured to direct at least a portion of the light received from the at least one coupling optical element to the second light redirecting element for outcoupling into the camera; the second light redirecting element is configured to direct at least a portion of the light received from the at least one coupling element to the first light redirecting element for outcoupling to the camera. Head-mounted display system. (Item 2) 10. The system of claim 1, wherein the first and second light redirecting elements form an angle with respect to each other. (Item 3) 10. The system of claim 9, wherein the first and second light redirecting elements form an angle with each other that is greater than 0° and less than 180°. (Item 4) 10. The system of claim 1, wherein the first and second light redirecting elements form an angle with each other that is greater than 75° and less than 160°. (Item 5) 10. The system of claim 1, wherein the first and second light redirecting elements are angled relative to each other to form a chevron shape. (Item 6) 10. The system of claim 1, wherein the first and second light redirecting elements comprise diffractive optical elements. (Item 7) 10. The system of claim 9, wherein the first and second light redirecting elements each comprise a diffractive feature, and the diffractive feature of the first redirecting element and the diffractive feature of the second redirecting element are oriented at an angle relative to each other. (Item 8) 10. The system of claim 9, wherein the diffractive features of the first redirecting element and the diffractive features of the second redirecting element are oriented at an angle greater than 90° and less than 170° relative to each other. (Item 9) 10. The system of claim 1, wherein the diffractive features of the first redirecting element and the diffractive features of the second redirecting element are oriented at an angle greater than 100° and less than 140° relative to each other. (Item 10) 10. The system of claim 9, wherein the first and second redirecting elements have a straight boundary line therebetween, and the first and second redirecting elements are configured to direct light toward the boundary line. (Item 11) 10. The system of claim 1, wherein the first and second redirecting elements have a non-linear boundary therebetween. (Item 12) 10. The system of claim 1, wherein the first and second redirecting elements have a wavy boundary therebetween. (Item 13) 10. The system of claim 1, wherein the first and second redirecting elements have a sawtooth-shaped boundary therebetween. (Item 14) Item 10. The system of any preceding item, wherein the first and second redirecting elements are interlocked. (Item 15) 10. The system of claim 9, wherein a region of the first light redirecting element extends farther from the center of the second light redirecting element than a portion of the first light redirecting element and closer to the center of the first light redirecting element. (Item 16) 10. The system of claim 9, wherein a region of the second light redirecting element extends farther from the center of the second light redirecting element than a portion of the first light redirecting element and closer to the center of the first light redirecting element. (Item 17) 10. The system of claim 1, wherein the first and second redirecting elements each have a grating vector, the grating vectors being angled relative to one another. (Item 18) 10. The system of claim 1, wherein the first and second redirecting elements each have a grating vector, the grating vectors being angled at approximately 120° relative to one another. (Item 19) 2. The system of claim 1, wherein the first and second redirecting elements each have a grating vector, and the grating vectors are angled at 130° to 150° relative to each other. (Item 20) 2. The system of claim 1, wherein the first and second redirecting elements each have a grating vector, and the grating vectors are angled at 140° to 160° relative to each other. (Item 21) 10. The system of claim 9, wherein the first and second redirecting elements each have a grating vector, the grating vector being angled at approximately 60 degrees relative to a centerline between the first and second redirecting elements. (Item 22) 10. The system of claim 9, wherein the first and second redirecting elements each have a grating vector, the grating vector being angled between 50° and 70° with respect to a centerline between the first and second redirecting elements. (Item 23) 10. The system of claim 9, wherein the first and second redirecting elements each have a grating vector, the grating vector being angled at an angle between 40° and 80° relative to a centerline between the first and second redirecting elements. (Item 24) 10. The system of claim 9, wherein the first and second redirecting elements each have a grating vector, and the at least one combining optical element has a grating vector, the sum of the grating vectors being less than ½ degree. (Item 25) 10. The system of claim 9, wherein the first and second redirecting elements each have a grating vector, and the at least one combining optical element has a grating vector, the sum of which is zero. (Item 26) 10. The system of claim 9, further comprising at least one external coupling element configured to couple light from the at least one coupling element guided within the light guide out of the light guide. (Item 27) 10. The system of claim 1, wherein the at least one external coupling element is between the at least one coupling optical element and the first and second light redirecting elements. (Item 28) 10. The system of claim 1, wherein at least one out-coupling element is aligned along a centerline between the first light redirecting element and the second light redirecting element. (Item 29) 10. The system of claim 1, wherein at least one out-coupling element is aligned along a gap between the first light redirecting element and the second light redirecting element. (Item 30) 10. The system of claim 9, further comprising at least one external coupling element configured to couple light from the at least one coupling optical element guided within the light guide out of the light guide that would otherwise pass through a gap between the first light redirecting element and the second light redirecting element. (Item 31) 10. The system of claim 1, wherein one or more of the first and second light redirecting optical elements and the at least one combining optical element comprise a liquid crystal grating. (Item 32) 10. The system of claim 1, wherein the first and second light redirecting optical elements and the at least one combining optical element comprise liquid crystal gratings. (Item 33) 10. The system of claim 1, wherein the second light redirecting element is configured to couple at least a portion of the light from the first redirecting element out of the waveguide to the camera. (Item 34) 10. The system of claim 1, wherein the first light redirecting element is configured to couple at least a portion of the light from the second light redirecting element out of the waveguide to the camera. (Item 35) The system of any preceding item, wherein the field of view produced by light collected by the at least one combining optical element that reaches the camera and contributes to the image produced by the camera after being directed by the first and second light redirecting elements to the combining area is larger than the field of view produced by light collected by the at least one combining optical element that reaches the camera and contributes to the image produced by the camera after being directed by only one of the first or second light redirecting elements to the combining area. (Item 36) The system described in any of the preceding items, wherein the at least one coupling optical element is configured so that light reflected from the eye of the user wearing the head-mounted display system is coupled into and guided within the at least one waveguide so that an image of the eye can be captured by the camera. (Item 37) The system of any of the preceding items further comprises an eyepiece disposed on the frame, the eyepiece configured to direct light into the user's eye and display augmented reality image content in the user's field of view, at least a portion of the eyepiece being transparent, and positioned in a location directly in front of the user's eye so that when the user wears the head-mounted display, the transparent portion allows light from an environment in front of the user to pass through to the user's eye and provide a view of the environment in front of the user. (Item 38) Item 38. The system of item 37, wherein the eyepiece is configured to receive light from the image projector, direct the light into the user's eye, and display augmented reality image content in the user's field of view. (Item 39) A system described in any of items 37-38, wherein the eyepiece lens comprises the at least one waveguide. (Item 40) The system of any of the preceding items, further comprising at least one internal coupling optical element configured to internally couple light from the image projector into the at least one waveguide so as to guide the light from the image projector to provide the image content to the user's eye. (Item 41) The system of any of the preceding items, wherein the at least one coupling optical element is also configured to couple light from the image projector guided within the waveguide out of the at least one waveguide so that image content is visible to the user's eye. (Item 42) A system described in any of the above items, wherein the same coupling optical element is configured to couple light from the image projector that is guided within the waveguide out of the waveguide so that image content can be viewed by the user's eye, and to couple light into the at least one waveguide to be guided therein to the camera. (Item 43) A system described in any of items 1-40, further comprising at least one image content external coupling optical element, wherein the at least one image content external coupling optical element is configured to couple light from the image projector guided within the waveguide out of the at least one waveguide so that image content is visible by the user's eye. (Item 44) 10. The system of claim 1, wherein the at least one coupling optical element is directed toward the eye of the user wearing the head-mounted imaging system and receives light from the eye. (Item 45) 1. A head-mounted display system configured to project light onto a user's eye and display augmented reality image content within the user's field of view, the head-mounted display system comprising: a frame configured to be supported on the user's head; an image projector configured to project an image into the user's eye and display image content within the user's field of view; A camera and at least one waveguide; a coupling optical element configured to couple light into the waveguide and guide it therein; an outcoupling optical element, the outcoupling optical element being positioned to receive light from the coupling element that is guided within the waveguide; and Equipped with The head-mounted display system, wherein the outcoupling optical element is configured to outcoupling light from the coupling optical element that is guided within the waveguide out of the waveguide to the camera. (Item 46) 10. The system of claim 9, wherein the out-coupling optical element is positioned to receive light from the coupling optical element guided within the waveguide via an optical path extending from the coupling optical element to the out-coupling optical element without any intervening light redirecting optical elements or gratings. (Item 47) 2. The system of claim 1, wherein the coupling optical element and the outcoupling optical element each have a grating vector, the sum of which is less than ½ degree. (Item 48) 10. The system of claim 1, wherein the coupling optical element and the outcoupling optical element each have a grating vector, the sum of which is zero. (Item 49) 10. The system of claim 1, wherein one or more of the coupling element and the outcoupling optical element comprises a liquid crystal grating. (Item 50) 10. The system of claim 1, wherein the coupling element and the outcoupling optical element comprise a liquid crystal grating. (Item 51) The system of any of the preceding items, wherein the coupling optical element is configured such that light reflected from the eye of the user wearing the head-mounted display system is coupled into and guided within the at least one waveguide so that an image of the eye can be captured by the camera. (Item 52) The system of any of the preceding items further comprises an eyepiece disposed on the frame, the eyepiece configured to direct light into the user's eye and display augmented reality image content in the user's field of view, at least a portion of the eyepiece being transparent, and positioned in a location directly in front of the user's eye so that when the user wears the head-mounted display, the transparent portion allows light from an environment in front of the user to pass through to the user's eye and provide a view of the environment in front of the user. (Item 53) Item 53. The system of item 52, wherein the eyepiece is configured to receive light from the image projector, direct the light into the user's eye, and display augmented reality image content in the user's field of view. (Item 54) A system described in any of items 52-53, wherein the eyepiece lens comprises the at least one waveguide. (Item 55) The system of any of the preceding items, further comprising at least one internal coupling optical element configured to internally couple light from the image projector into the at least one waveguide so as to guide the light from the image projector to provide the image content to the user's eye. (Item 56) The system of any of the preceding items, wherein the coupling optical element is also configured to couple light from the image projector guided within the waveguide out of the at least one waveguide so that the image content is visible to the user's eye. (Item 57) A system described in any of the above items, wherein the same coupling optical element is configured to couple light from the image projector that is guided within the waveguide out of the waveguide so that image content can be viewed by the user's eye, and to couple light into the at least one waveguide to be guided therein to the camera. (Item 58) 56. The system of any of items 1-55, further comprising at least one image content outcoupling optical element, the at least one image content outcoupling optical element configured to couple light from the image projector guided within the waveguide out of the at least one waveguide so that image content is visible by the user's eye. (Item 59) 10. The system of claim 1, wherein the coupling optical element is directed toward the eye of the user wearing the head-mounted imaging system and receives light from the eye. (Item 60) 45. The system of any of items 1-44, wherein the first and second light redirecting elements are disposed on opposite sides of the waveguide. (Item 61) 45. The system of any of items 1-44, wherein the first light redirecting element is disposed on a front side of the waveguide and the second light redirecting element is disposed on a back side of the waveguide, or the second light redirecting element is disposed on a front side of the waveguide and the first light redirecting element is disposed on a back side of the waveguide. (Item 62) Item 62. The system of any of items 60 or 61, wherein the first and second light redirecting elements have an overlapping area. (Item 63) 10. The system of claim 1, wherein the combining optical element, the first light redirecting element, the second light redirecting element, or any combination thereof comprises a graded diffractive optical element. (Item 64) 10. The system of claim 1, wherein the combining optical element, the first light redirecting element, the second light redirecting element, or any combination thereof comprises a graded diffractive optical element having a graded diffraction efficiency. (Item 65) 10. The system of claim 9, wherein the combining optical element, the first light redirecting element, the second light redirecting element, or any combination thereof comprises a graded diffractive optical element having a graded diffraction efficiency to increase image uniformity. (Item 66) 10. The system of claim 1, wherein the combining optical element, the first light redirecting element, the second light redirecting element, or any combination thereof comprises a graded diffractive optical element having a graded grating thickness or duty cycle. (Item 67) 10. The system of claim 1, wherein the combining optical element, the first light redirecting element, the second light redirecting element, or any combination thereof comprises a graded liquid crystal diffractive optical element having a graded grating thickness or helical pitch. [Brief explanation of the drawings]

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

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

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

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

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

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

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

[0016] [Figure 8] FIG. 8 illustrates an example of a stacked waveguide assembly where each depth plane contains an image formed using multiple different primary colors.

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

[0046] [Figure 24]24 shows another exemplary eyepiece that can be used to receive image data of a user's eye or the environment in front of the user while simultaneously projecting light into the user's eye and providing image content thereto. In this example, the coupling optical element configured to receive light from the user or the environment in front of the user is laterally displaced from the image content out-coupling optical element (e.g., an exit pupil expander).

[0047] [Figure 25] Figure 25 shows another exemplary eyepiece similar to that shown in Figure 24, in which a coupling optical element configured to receive light from a user or an environment in front of the user is spaced laterally from an image content out-coupling optical element (e.g., an exit pupil expander). However, in the implementation shown in Figure 25, no space laterally separates the coupling optical element 2111 from the out-coupling optical element 2110.

[0048] [Figure 26] FIG. 26 shows an exemplary eyepiece including first and second coupling optical elements configured to couple light received from a user's eye or the environment into a waveguide to be guided therein, and first and second out-coupling optical elements configured to couple light guided within the waveguide out of the waveguide to one or more cameras.

[0049] [Figure 27] Figure 27 is a cross section through the waveguide, collection optics, and outcoupling optics shown in Figure 26, showing a polarizer in the optical path between one of the outcoupling optics and the camera. The polarizer may be used to remove unwanted glint reflections from the cornea when acquiring images of the retina.

[0050] [Figure 28]28A and 28B are front and perspective views of a coupling optical element for coupling light into a waveguide and an out-coupling optical element for coupling light out of the waveguide to a camera, the coupling optical element having a pinhole coupling area. The out-coupling optical element is similarly sized and shaped in this implementation.

[0051] [Figure 29] 29A and 29B are front and perspective views of a coupling optical element for coupling light into a waveguide and an out-coupling optical element for coupling light out of the waveguide to a camera, the coupling optical element having an arc-slit shaped coupling area, and the out-coupling optical element having a pinhole-sized coupling area.

[0052] [Figure 30] 30A and 30B are front and perspective views of a coupling optical element for coupling light into a waveguide and an out-coupling optical element for coupling light out of the waveguide to a camera, the coupling optical element having a non-arcuate (e.g., rectilinear rectangular) slit-shaped coupling area, and the out-coupling optical element having a pinhole-sized coupling area.

[0053] [Figure 31] 31 is a front view of an eyepiece including a coupling optical element for coupling light into a waveguide and an out-coupling optical element for coupling light out of the waveguide to a camera, the coupling optical element having a non-arcuate (e.g., rectilinear) slit-shaped coupling area. The eyepiece further includes an image content in-coupling optical element for receiving light from an image projector and a light distribution element for directing light from the in-coupling optical element to an out-coupling optical element for coupling light guided in the waveguide to a user for viewing the image content.

[0054] [Figure 32]32A and 32B are front and perspective views of a pair of coupling optical elements for coupling light into a waveguide and a pair of out-coupling optical elements for coupling light out of the waveguide to a camera, where the coupling optical elements have a non-arcuate (e.g., rectilinear rectangular) slit-shaped coupling area. Such a configuration can be useful for imaging different parts of the eye, such as the retina and cornea (or phosphenes thereon).

[0055] [Figure 33] 33 is a front view of an eyepiece including a pair of coupling optical elements for coupling light into a waveguide and a pair of out-coupling optical elements for coupling light out of the waveguide to a camera, the coupling optical elements having a non-arcuate (e.g., rectilinear) slit-shaped coupling area. The eyepiece further includes an image content in-coupling optical element for receiving light from an image projector and a light distribution element for directing light from the in-coupling optical element to the out-coupling optical element for coupling light guided in the waveguide to a user for viewing the image content.

[0056] [Figure 34] 34A and 34B are front and perspective views of a pair of coupling optical elements for coupling light into a waveguide and a pair of out-coupling optical elements for coupling light out of the waveguide to a camera, where the coupling optical elements have a non-arcuate (e.g., rectilinear rectangular) slit-shaped coupling area. The arrangement is different from that shown in FIGS. 32A and 32B.

[0057] [Figure 35] Figure 35 is a front view of an eyepiece similar to that shown in Figures 30A and 30B, including a pair of coupling optical elements for coupling light into a waveguide and a pair of out-coupling optical elements for coupling light out of the waveguide to a camera. The eyepiece further includes an image content in-coupling optical element for receiving light from an image projector, and a light distribution element for directing light from the in-coupling optical element to the out-coupling optical element for coupling light guided in the waveguide to a user for viewing the image content.

[0058] [Figure 36A] 36A and 36B are side views of a transparent layer that can be integrated into an eyepiece to direct light to the eye and used, for example, for phosphene-based eye tracking. [Figure 36B] 36A and 36B are side views of a transparent layer that can be integrated into an eyepiece to direct light to the eye and used, for example, for phosphene-based eye tracking.

[0059] [Figure 37A] 37A and 37B are side views showing transparent layers positioned in different locations within the eyepiece for directing light to the user's eye. [Figure 37B] 37A and 37B are side views showing transparent layers positioned in different locations within the eyepiece for directing light to the user's eye.

[0060] [Figure 38A] 38A and 38B are front and side views of a transparent layer including multiple optical fibers therein that can be configured to direct light toward the eye. [Figure 38B] 38A and 38B are front and side views of a transparent layer including multiple optical fibers therein that can be configured to direct light toward the eye.

[0061] [Figure 39] FIG. 39 is a perspective view of a transparent layer including a plurality of optical rods therein that can be configured to direct light toward the eye.

[0062] [Figure 40A] 40A-40C are side, perspective, and top views of a transparent layer that includes a pair of angled surfaces that reflect light guided through the transparent layer toward the eye. [Figure 40B]40A-40C are side, perspective, and top views of a transparent layer that includes a pair of angled surfaces that reflect light guided through the transparent layer toward the eye. [Figure 40C] 40A-40C are side, perspective, and top views of a transparent layer that includes a pair of angled surfaces that reflect light guided through the transparent layer toward the eye.

[0063] [Figure 40D] 40D-40F are top views of additional designs of the transparent layer that include a plurality of angled surfaces configured to reflect light guided through the transparent layer toward the eye. [Figure 40E] 40D-40F are top views of additional designs of the transparent layer that include a plurality of angled surfaces configured to reflect light guided through the transparent layer toward the eye. [Figure 40F] 40D-40F are top views of additional designs of the transparent layer that include a plurality of angled surfaces configured to reflect light guided through the transparent layer toward the eye.

[0064] [Figure 41A] 41A, 41B, 42, 43A, 43B, and 44 diagrammatically illustrate exemplary eyepieces. [Figure 41B] 41A, 41B, 42, 43A, 43B, and 44 diagrammatically illustrate exemplary eyepieces. [Figure 42] 41A, 41B, 42, 43A, 43B, and 44 diagrammatically illustrate exemplary eyepieces. [Figure 43A] 41A, 41B, 42, 43A, 43B, and 44 diagrammatically illustrate exemplary eyepieces. [Figure 43B] 41A, 41B, 42, 43A, 43B, and 44 diagrammatically illustrate exemplary eyepieces. [Figure 44] 41A, 41B, 42, 43A, 43B, and 44 diagrammatically illustrate exemplary eyepieces.

[0065] The drawings are provided to illustrate example embodiments and are not intended to limit the scope of the present disclosure. Like reference numbers refer to like parts throughout. DETAILED DESCRIPTION OF THE INVENTION

[0066] Reference is now made to the drawings, wherein like reference numbers refer to like parts throughout.

[0067] FIG. 2 illustrates an example of a wearable display system 60. The display system 60 includes a display 70 and various mechanical and electronic modules and systems to support the functionality of the display 70. The display 70 may be coupled to a frame 80 that is wearable by a display system user or viewer 90 and configured to position the display 70 directly in front of the user's 90's eyes. The display 70 may, in some embodiments, be considered eyewear. In some embodiments, a speaker 100 is coupled to the frame 80 and configured to be positioned adjacent to the user's 90's ear canal (in some embodiments, another speaker, not shown, may optionally be positioned adjacent the user's other ear canal to provide stereo / shapeable sound control). The display system may also include one or more microphones 110 or other devices to detect sound. In some embodiments, the microphones may be configured to allow a user to provide input or commands (e.g., voice menu command selections, natural language queries, etc.) to the system 60 and / or enable audio communication with other persons (e.g., other users of similar display systems). The microphone may further be configured as an ambient sensor to collect audio data (e.g., sounds from the user and / or the environment). In some embodiments, the display system may also include ambient sensor 120a, which may be separate from frame 80 and mounted on the body of user 90 (e.g., on the head, torso, limbs, etc. of user 90). Ambient sensor 120a, in some embodiments, may be configured to obtain data characterizing a physiological state of user 90. For example, sensor 120a may be an electrode.

[0068] 2 , display 70 is operably coupled by a communications link 130, such as by wired or wireless connectivity, to a local data processing module 140, which may be mounted in a variety of configurations, such as fixedly attached to frame 80, fixedly attached to a helmet or hat worn by the user, built into headphones, or otherwise removably attached to user 90 (e.g., in a backpack-style configuration, in a belt-coupled configuration). Similarly, sensor 120 a may be operably coupled to local data processing module 140 by a communications link 120 b, e.g., by wired or wireless connectivity. Local processing and data module 140 may comprise a hardware processor and digital memory, such as non-volatile memory (e.g., flash memory or a hard disk drive), both of which may be utilized to aid in processing, caching, and storing data. The data includes a) data captured from sensors (e.g., which may be operatively coupled to frame 80 or otherwise attached to user 90), such as image capture devices (such as cameras), microphones, inertial measurement units, accelerometers, compasses, GPS units, wireless devices, gyroscopes, and / or other sensors disclosed herein, and / or b) data obtained and / or processed using remote processing module 150 and / or remote data repository 160 (including data related to virtual content), possibly for processing or retrieval and then passing to display 70. Local processing and data module 140 may be operatively coupled to remote processing module 150 and remote data repository 160 by communication links 170, 180, such as via wired or wireless communication links, such that these remote modules 150, 160 are operatively coupled to each other and available as resources to local processing and data module 140.In some embodiments, local processing and data module 140 may include one or more of an image capture device, a microphone, an inertial measurement unit, an accelerometer, a compass, a GPS unit, a wireless device, and / or a gyroscope. In some other embodiments, one or more of these sensors may be mounted to frame 80 or may be a freestanding structure that communicates with local processing and data module 140 by a wired or wireless communication path.

[0069] 2 , in some embodiments, remote processing module 150 may comprise one or more processors configured to analyze and process data and / or image information. In some embodiments, remote data repository 160 may comprise a digital data storage facility, which may be available through the Internet or other networking configuration in a “cloud” resource configuration. In some embodiments, remote data repository 160 may include one or more remote servers that provide information, e.g., information for generating augmented reality content, to local processing and data module 140 and / or remote processing module 150. In some embodiments, all data is stored and all calculations are performed in the local processing and data module, allowing for fully autonomous use from the remote module.

[0070] Referring now to FIG. 3, the perception of an image as “three-dimensional” or “3-D” can be achieved by providing a slightly different presentation of the image to each eye of a viewer. FIG. 3 illustrates a conventional display system for simulating a three-dimensional image for a user. Two distinct images 190, 200 are output to the user, one for each eye 210, 220. The images 190, 200 are spaced from the eyes 210, 220 by a distance 230 along the optical or z-axis parallel to the viewer's line of sight. The images 190, 200 are flat, and the eyes 210, 220 can focus on the images by assuming a single accommodative state. Such a 3-D display system relies on the human visual system to combine the images 190, 200 and provide the perception of depth and / or scale of the combined image.

[0071] However, it should be understood that the human visual system is more complex and providing a realistic perception of depth is more difficult. For example, many viewers of conventional “3-D” display systems find such systems uncomfortable or may not perceive any sense of depth at all. Without being limited by theory, it is believed that viewers of an object may perceive the object as “three-dimensional” due to a combination of vergence-divergence and accommodation. The vergence-divergence of the two eyes relative to one another (i.e., the rotational movement of the pupils toward or away from one another to converge the gaze of the eyes and fixate on an object) is closely linked to the focusing (or “accommodation”) of the eye lens and pupil. Under normal conditions, changing the focus of the eye lens or accommodating the eye to change focus from one object to another at a different distance will automatically produce a corresponding change in vergence-divergence to the same distance, a relationship known as the “accommodation-vergence-divergence reflex” and pupil dilation or constriction. Similarly, changes in convergence-divergence will induce corresponding changes in accommodation in lens shape and pupil size under normal conditions. As described herein, many stereoscopic or "3-D" display systems display a scene using slightly different presentations (and therefore slightly different images) to each eye so that a three-dimensional perspective is perceived by the human visual system. However, such systems are uncomfortable for many viewers, particularly because they simply provide different presentations of the scene but work against the "accommodation-vergence-divergence reflex" when the eyes view all image information in a single, accommodated state. Display systems that provide a better match between accommodation and convergence-divergence may produce more realistic and comfortable simulations of three-dimensional images.

[0072] FIG. 4 illustrates aspects of an approach for simulating a three-dimensional image using multiple depth planes. With reference to FIG. 4 , objects at various distances from the eyes 210, 220 on the z-axis are accommodated by the eyes 210, 220 so that the objects are in focus. The eyes 210, 220 assume particular accommodated states and focus on objects at different distances along the z-axis. As a result, a particular accommodated state may be said to be associated with a particular one of the depth planes 240 having an associated focal length such that an object or portion of an object at a particular depth plane is in focus when the eye is in an accommodated state relative to that depth plane. In some embodiments, a three-dimensional image may be simulated by providing a different presentation of an image for each eye 210, 220 and by providing a different presentation of an image corresponding to each of the depth planes. While shown as separate for clarity of illustration, it should be understood that the fields of view of the eyes 210, 220 may overlap, for example, as the distance along the z-axis increases. Additionally, although shown as flat for ease of illustration, it should be understood that the contour of the depth plane may be curved in physical space so that all features within the depth plane are in focus with the eye in a particular accommodative state.

[0073] The distance between an object and the eye 210 or 220 can also change the amount of divergence of light from the object as viewed by that eye. Figures 5A-5C illustrate the relationship between distance and divergence of light rays. The distance between the object and the eye 210 is represented by decreasing distances R1, R2, and R3. As shown in Figures 5A-5C, light rays become more divergent as the distance to the object decreases. As the distance increases, the light rays become more collimated. In other words, the light field generated by a point (an object or part of an object) can be said to have a spherical wavefront curvature that is a function of the distance the point is from the user's eye. The curvature increases as the distance between the object and the eye 210 decreases. As a result, the divergence of light rays at different depth planes also differs, and the divergence increases as the distance between the depth plane and the viewer's eye 210 decreases. While only a single eye 210 is illustrated in Figures 5A-5C and other figures herein for clarity of illustration, it should be understood that the discussion regarding eye 210 may apply to both eyes 210 and 220 of a viewer.

[0074] Without being limited by theory, it is believed that the human eye can typically interpret a finite number of depth planes to provide depth perception. As a result, a highly realistic simulation of perceived depth can be achieved by providing the eye with different representations of images corresponding to each of these limited number of depth planes. The different representations can be focused separately by the viewer's eyes, thereby serving to provide depth cues to the user based on the ocular accommodation required to focus on different image features for a scene located on different depth planes and / or based on observing different image features on different depth planes that are out of focus.

[0075] FIG. 6 illustrates an example of a waveguide stack for outputting image information to a user. Display system 250 includes a stack of waveguides or stacked waveguide assembly 260 that can be utilized to provide a three-dimensional perception to the eye / brain using multiple waveguides 270, 280, 290, 300, 310. In some embodiments, display system 250 is system 60 of FIG. 2 , and FIG. 6 diagrammatically illustrates some portions of system 60 in greater detail. For example, waveguide assembly 260 may be part of display 70 of FIG. 2 . It should be understood that display system 250 may be considered a light field display in some embodiments. Additionally, waveguide assembly 260 may also be referred to as an eyepiece.

[0076] Continuing with reference to FIG. 6 , the waveguide assembly 260 may also include multiple features 320, 330, 340, 350 between the waveguides. In some embodiments, the features 320, 330, 340, 350 may be one or more lenses. The waveguides 270, 280, 290, 300, 310 and / or multiple lenses 320, 330, 340, 350 may be configured to transmit image information to the eye using various levels of wavefront curvature or ray divergence. Each waveguide level may be associated with a particular depth plane and configured to output image information corresponding to that depth plane. The image injection devices 360, 370, 380, 390, 400 may act as light sources for the waveguides and may be utilized to inject image information into the waveguides 270, 280, 290, 300, 310, each configured to distribute incident light across each individual waveguide for output toward the eye 210, as described herein. Light exits output surfaces 410, 420, 430, 440, 450 of the image injection devices 360, 370, 380, 390, 400 and is injected into corresponding input surfaces 460, 470, 480, 490, 500 of the waveguides 270, 280, 290, 300, 310. In some embodiments, each input surface 460, 470, 480, 490, 500 may be an edge of the corresponding waveguide or a portion of a major surface of the corresponding waveguide (i.e., one of the waveguide surfaces that directly faces the world 510 or the viewer's eye 210). In some embodiments, a single beam of light (e.g., a collimated beam) may be launched into each waveguide, outputting a total field of cloned collimated beams directed toward the eye 210 at a particular angle (and divergence) corresponding to the depth plane associated with the particular waveguide. In some embodiments, a single one of the image launch devices 360, 370, 380, 390, 400 may be associated with and launch light into multiple (e.g., three) waveguides 270, 280, 290, 300, 310.

[0077] In some embodiments, each of the image input devices 360, 370, 380, 390, 400 is a discrete display that generates image information for input into a corresponding waveguide 270, 280, 290, 300, 310. In some other embodiments, the image input devices 360, 370, 380, 390, 400 are the output of a single multiplexed display that may, for example, send image information to each of the image input devices 360, 370, 380, 390, 400 via one or more optical conduits (such as fiber optic cables). It should be understood that the image information provided by the image input devices 360, 370, 380, 390, 400 may include light of different wavelengths or colors (e.g., different primary colors, as discussed herein).

[0078] In some embodiments, the light injected into the waveguides 270, 280, 290, 300, 310 is provided by a light projector system 520 comprising a light module 540, which may include a light emitter such as a light emitting diode (LED). Light from the light module 540 may be directed via a beam splitter 550 to and modified by a light modulator 530, e.g., a spatial light modulator. The light modulator 530 may be configured to change the perceived intensity of the light injected into the waveguides 270, 280, 290, 300, 310. Examples of spatial light modulators include liquid crystal displays (LCDs), including liquid crystal on silicon (LCOS) displays. It should be understood that image input devices 360, 370, 380, 390, 400 are illustrated diagrammatically and in some embodiments these image input devices may represent different light paths and locations within a common projection system that are configured to output light into associated ones of waveguides 270, 280, 290, 300, 310.

[0079] In some embodiments, the display system 250 may be a scanning fiber display comprising one or more scanning fibers configured to project light in various patterns (e.g., raster scan, spiral scan, Lissajous pattern, etc.) into one or more waveguides 270, 280, 290, 300, 310 and ultimately to the viewer's eye 210. In some embodiments, the illustrated image injection devices 360, 370, 380, 390, 400 may diagrammatically represent a single scanning fiber or a bundle of scanning fibers configured to inject light into one or more waveguides 270, 280, 290, 300, 310. In some other embodiments, the illustrated image injection devices 360, 370, 380, 390, 400 may diagrammatically represent multiple scanning fibers or multiple bundles of scanning fibers, each configured to inject light into an associated one of the waveguides 270, 280, 290, 300, 310. It should be understood that one or more optical fibers may be configured to transmit light from the optical module 540 to one or more waveguides 270, 280, 290, 300, 310. It should be understood that one or more intervening optical structures may be provided between the scanning fiber or fibers and one or more waveguides 270, 280, 290, 300, 310, for example, to redirect light exiting the scanning fiber into one or more waveguides 270, 280, 290, 300, 310.

[0080] Controller 560 controls the operation of one or more of stacked waveguide assemblies 260, including the operation of image input devices 360, 370, 380, 390, 400, light source 540, and light modulator 530. In some embodiments, controller 560 is part of local data processing module 140. Controller 560 contains programming (e.g., instructions in a non-transitory medium) that coordinates the timing and provision of image information to waveguides 270, 280, 290, 300, 310, for example, according to any of the various schemes disclosed herein. In some embodiments, the controller may be a single integrated device or a distributed system connected by a wired or wireless communication channel. Controller 560 may, in some embodiments, be part of processing module 140 or 150 (FIG. 2).

[0081] Continuing with reference to FIG. 6 , the waveguides 270, 280, 290, 300, and 310 may be configured to propagate light within each individual waveguide by total internal reflection (TIR). Each of the waveguides 270, 280, 290, 300, and 310 may be planar 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 270, 280, 290, 300, and 310 may each include outcoupling optical elements 570, 580, 590, 600, and 610 configured to extract light from the waveguide by redirecting light propagating within each individual waveguide out of the waveguide and outputting image information to the eye 210. The extracted light may also be referred to as outcoupling light, and the outcoupling optical elements may also be referred to as light extraction optical elements. The extracted beam of light may be output by the waveguide at a location where light propagating within the waveguide strikes the light extraction optical element. The outcoupling optical element 570, 580, 590, 600, 610 may be, for example, a grating including diffractive optical features as discussed further herein. While shown disposed on the bottom major surface of the waveguides 270, 280, 290, 300, 310 for ease of explanation and clarity of drawing, in some embodiments, the outcoupling optical element 570, 580, 590, 600, 610 may be disposed on the top and / or bottom major surfaces and / or directly within the volume of the waveguides 270, 280, 290, 300, 310, as discussed further herein. In some embodiments, the outcoupling optical elements 570, 580, 590, 600, 610 may be formed within a layer of material that is attached to a transparent substrate and forms the waveguides 270, 280, 290, 300, 310. In some other embodiments, the waveguides 270, 280, 290, 300, 310 may be a monolithic piece of material, and the outcoupling optical elements 570, 580, 590, 600, 610 may be formed on and / or within that piece of material.

[0082] Continuing with reference to FIG. 6 , as discussed herein, each waveguide 270, 280, 290, 300, 310 is configured to output light and form an image corresponding to a particular depth plane. For example, the waveguide 270 closest to the eye may be configured to deliver collimated light (injected into such waveguide 270) to the eye 210. The collimated light may represent an optical infinity focal plane. The next upper waveguide 280 may be configured to send collimated light that passes through a first lens 350 (e.g., a negative lens) before reaching the eye 210. Such first lens 350 may be configured to generate a slight convex wavefront curvature so that the eye / brain interprets light emerging from the next upper waveguide 280 as emerging from a first focal plane closer inward from optical infinity toward the eye 210. Similarly, the third upper waveguide 290 passes its output light through both the first 350 and second lenses 340 before reaching the eye 210. The combined refractive power of the first 350 and second lenses 340 may be configured to produce another, increasing amount of wavefront curvature such that the eye / brain interprets the light emerging from the third waveguide 290 as originating from a second focal plane that is closer inward from optical infinity towards the person than was the light from the next upper waveguide 280.

[0083] The other waveguide layers 300, 310 and lenses 330, 320 are similarly configured, with the highest waveguide 310 in the stack sending its output through all of the lenses between it and the eye for a collective focal power representing the focal plane closest to the person. To compensate for the stack of lenses 320, 330, 340, 350 when viewing / interpreting light originating from the world 510 on the other side of the stacked waveguide assembly 260, a compensating lens layer 620 may be placed on top of the stack to compensate for the collective power of the lower lens stacks 320, 330, 340, 350. Such a configuration provides as many perceived focal planes as there are available waveguide / lens pairs. Both the waveguide outcoupling optical elements and the focusing sides of the lenses may be static (i.e., not dynamic or electro-active). In some alternative embodiments, one or both may be dynamic using electro-active features.

[0084] In some embodiments, two or more of the waveguides 270, 280, 290, 300, 310 may have the same associated depth plane. For example, multiple waveguides 270, 280, 290, 300, 310 may be configured to output images set at the same depth plane, or multiple subsets of the waveguides 270, 280, 290, 300, 310 may be configured to output images set at the same depth planes, with one set per depth plane. This may provide advantages for forming tiled images to provide an extended field of view at those depth planes.

[0085] Continuing with reference to FIG. 6 , the outcoupling optical elements 570, 580, 590, 600, 610 may be configured to redirect light out of their respective waveguides and output the light with an 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 differently configured outcoupling optical elements 570, 580, 590, 600, 610 that output light with different amounts of divergence depending on the associated depth plane. In some embodiments, the light-extracting optical elements 570, 580, 590, 600, 610 may be volume or surface features that may be configured to output light at specific angles. For example, the light-extracting optical elements 570, 580, 590, 600, 610 may be volume holograms, surface holograms, and / or diffraction gratings. In some embodiments, the features 320, 330, 340, 350 may not be lenses. Rather, they may simply be spacers (eg, cladding layers and / or structures to form an air gap).

[0086] In some embodiments, the outcoupling optical elements 570, 580, 590, 600, 610 are diffractive features or "diffractive optical elements" (also referred to herein as "DOEs") that form a diffraction pattern. Preferably, the DOEs have a sufficiently low diffraction efficiency so that only a portion of the light in the beam is deflected toward the eye 210 at each intersection of the DOE, while the remainder continues traveling through the waveguide via TIR. The light carrying the image information is thus split into several related output beams that exit the waveguide at multiple locations, resulting in a very uniform pattern of output emission toward the eye 210 for this particular collimated beam bouncing within the waveguide.

[0087] In some embodiments, one or more DOEs may be switchable between an "on" state in which they actively diffract and an "off" state in which they do not significantly diffract. For example, a switchable DOE may comprise a layer of polymer-dispersed liquid crystal in which microdroplets comprise a diffractive pattern within a host medium, and the refractive index of the microdroplets may be switched to substantially match the refractive index of the host material (in which case the pattern does not significantly diffract incident light), or the microdroplets may be switched to a refractive index that does not match that of the host medium (in which case the pattern actively diffracts incident light).

[0088] In some embodiments, a camera assembly 630 (e.g., a digital camera, including a visible light and infrared light camera) may be provided to capture images of the eye 210 and / or tissue surrounding the eye 210, for example, to detect user input and / or monitor the physiological state of the user. As used herein, a camera may be any image capture device. In some embodiments, the camera assembly 630 may include an image capture device and a light source that projects light (e.g., infrared light) onto the eye, which may then be reflected by the eye and detected by the image capture device. In some embodiments, the camera assembly 630 may be mounted on the frame 80 ( FIG. 2 ) and may be in electrical communication with processing modules 140 and / or 150, which may process image information from the camera assembly 630. In some embodiments, one camera assembly 630 may be utilized per eye, monitoring each eye separately.

[0089] 7, an example of an output beam output by a waveguide is shown. While one waveguide is illustrated, it should be understood that other waveguides in waveguide assembly 260 (FIG. 6) may function similarly, and that waveguide assembly 260 includes multiple waveguides. Light 640 is launched into waveguide 270 at input surface 460 of waveguide 270 and propagates within waveguide 270 by TIR. At the point where light 640 impinges on DOE 570, a portion of the light exits the waveguide as output beam 650. Output beam 650 is illustrated as being approximately parallel, but may be redirected to propagate to eye 210 at an angle (e.g., forming a diverging output beam), as discussed herein and depending on the depth plane associated with waveguide 270. It should be understood that a nearly collimated exit beam may refer to a waveguide with outcoupling optics that outcouples light to form an image that appears to be set at a depth plane at a long distance (e.g., optical infinity) from the eye 210. Other waveguides or other sets of outcoupling optics may output a more divergent exit beam pattern, which would require the eye 210 to accommodate to a closer distance to focus on the retina and would be interpreted by the brain as light from a distance closer to the eye 210 than optical infinity.

[0090] In some embodiments, a full-color image may be formed at each depth plane by overlaying an image in each of the primary colors, for example, three or more primary colors. FIG. 8 illustrates an example of a stacked waveguide assembly in which each depth plane includes an image formed using multiple different primary colors. The illustrated embodiment shows depth planes 240a-240f, but more or fewer depths are also contemplated. Each depth plane may have three or more primary color images associated with it, including a first image in a first color G, a second image in a second color R, and a third image in a third color B. Different depth planes are indicated in the diagram by different numbers for diopters (dpt) following the letters G, R, and B. By way of example only, the number following each of these letters indicates the diopter (1 / m), i.e., the inverse distance of the depth plane from the viewer, and each box in the diagram represents an individual primary color image. In some embodiments, the exact locations of the depth planes for different primary colors may be varied to account for differences in the eye's focusing of light of different wavelengths. For example, different primary color images for a given depth plane may be placed on depth planes corresponding to different distances from the user. Such an arrangement may increase visual acuity and user comfort and / or reduce chromatic aberrations.

[0091] In some embodiments, light for each primary color may be output by a single dedicated waveguide, such that each depth plane may have multiple waveguides associated with it. In such embodiments, each box in the diagram containing the letter G, R, or B may be understood to represent an individual waveguide, and three waveguides may be provided per depth plane, with three primary color images provided per depth plane. While the waveguides associated with each depth plane are shown adjacent to each other in this drawing for ease of illustration, it should be understood that in a physical device, the waveguides may all be arranged in a stack with one waveguide per level. In some other embodiments, multiple primary colors may be output by the same waveguide, such that, for example, only a single waveguide may be provided per depth plane.

[0092] 8, in some embodiments, G is green, R is red, and B is blue. In some other embodiments, other colors associated with other wavelengths of light, including magenta and cyan, may be used in addition to or replace one or more of red, green, or blue.

[0093] It should be appreciated that references to a given color of light throughout this disclosure will be understood to encompass light of one or more wavelengths within the range of wavelengths of light that are perceived by a viewer as being of that given color. For example, red light may include one or more wavelengths of light within a range of about 620-780 nm, green light may include one or more wavelengths of light within a range of about 492-577 nm, and blue light may include one or more wavelengths of light within a range of about 435-493 nm.

[0094] In some embodiments, light source 540 (FIG. 6) may be configured to emit light at one or more wavelengths outside the range of a viewer's visual perception, e.g., infrared and / or ultraviolet wavelengths. Additionally, the waveguide incoupling, outcoupling, and other light redirecting structures of display 250 may be configured to direct and emit this light from the display toward the user's eye 210, e.g., for imaging and / or user stimulation applications.

[0095] Referring now to FIG. 9A , in some embodiments, light impinging on a waveguide may need to be redirected to incoupling the light into the waveguide. An incoupling optical element may be used to redirect and incoupling the light into its corresponding waveguide. FIG. 9A illustrates a cross-sectional side view of an example of a plurality or set 660 of stacked waveguides, each including an incoupling optical element. The waveguides may each be configured to output light of one or more different wavelengths or one or more different wavelength ranges. Stack 660 may correspond to stack 260 ( FIG. 6 ), and the illustrated waveguides of stack 660 may correspond to a portion of the plurality of waveguides 270, 280, 290, 300, 310, although it should be understood that light from one or more of image injection devices 360, 370, 380, 390, 400 is injected into the waveguide from a location requiring the light to be redirected for incoupling.

[0096] The illustrated set 660 of stacked waveguides includes waveguides 670, 680, and 690. Each waveguide includes an associated internal coupling optical element (which may also be referred to as the light input area on the waveguide), for example, internal coupling optical element 700 is disposed on a major surface (e.g., the top major surface) of waveguide 670, internal coupling optical element 710 is disposed on a major surface (e.g., the top major surface) of waveguide 680, and internal coupling optical element 720 is disposed on a major surface (e.g., the top major surface) of waveguide 690. In some embodiments, one or more of internal coupling optical elements 700, 710, 720 may be disposed on the bottom major surface of an individual waveguide 670, 680, 690 (particularly, one or more internal coupling optical elements are reflective polarizing optical elements). As shown, the internal coupling optical elements 700, 710, 720 may be disposed on the upper major surface of the respective waveguides 670, 680, 690 (or on top of the next lower waveguide), and in particular, the internal coupling optical elements are transmissive turning optical elements. In some embodiments, the internal coupling optical elements 700, 710, 720 may be disposed within the body of the respective waveguides 670, 680, 690. In some embodiments, as discussed herein, the internal coupling optical elements 700, 710, 720 are wavelength selective, such that they selectively redirect one or more wavelengths of light while transmitting other wavelengths of light. While illustrated on one side or corner of the respective waveguides 670, 680, 690, it should be understood that the internal coupling optical elements 700, 710, 720 may be disposed within other areas of the respective waveguides 670, 680, 690 in some embodiments.

[0097] As shown, the in-coupling optical elements 700, 710, 720 may be laterally offset from one another. In some embodiments, each in-coupling optical element may be offset to receive light without that light passing through another in-coupling optical element. For example, each in-coupling optical element 700, 710, 720 may be configured to receive light from a different image input device 360, 370, 380, 390, and 400, as shown in FIG. 6 , and may be separated (e.g., laterally spaced) from the other in-coupling optical elements 700, 710, 720 so as to receive substantially no light from others of the in-coupling optical elements 700, 710, 720.

[0098] Each waveguide also includes an associated optically dispersive element, for example, optically dispersive element 730 is disposed on a major surface (e.g., the top major surface) of waveguide 670, optically dispersive element 740 is disposed on a major surface (e.g., the top major surface) of waveguide 680, and optically dispersive element 750 is disposed on a major surface (e.g., the top major surface) of waveguide 690. In some other embodiments, optically dispersive elements 730, 740, 750 may be disposed on the bottom major surfaces of associated waveguides 670, 680, 690, respectively. In some other embodiments, optically dispersive elements 730, 740, 750 may be disposed on both the top and bottom major surfaces of associated waveguides 670, 680, 690, respectively, or optically dispersive elements 730, 740, 750 may be disposed on different ones of the top and bottom major surfaces in different associated waveguides 670, 680, 690, respectively.

[0099] Waveguides 670, 680, 690 may be spaced apart and separated, for example, by gas, liquid, and / or solid layers of material. For example, as shown, layer 760a may separate waveguides 670 and 680, and layer 760b may separate waveguides 680 and 690. In some embodiments, layers 760a and 760b are formed from a low refractive index material (i.e., a material having a lower refractive index than the material forming the immediately adjacent ones of waveguides 670, 680, 690). Preferably, the refractive index of the material forming layers 760a, 760b is 0.05 or more, or 0.10 or less, relative to the refractive index of the material forming waveguides 670, 680, 690. Advantageously, the lower refractive index layers 760a, 760b may function as cladding layers that promote total internal reflection (TIR) ​​of light through the waveguides 670, 680, 690 (e.g., TIR between the top and bottom major surfaces of each waveguide). In some embodiments, the layers 760a, 760b are formed from air. Although not shown, it should be understood that the top and bottom of the illustrated set of waveguides 660 may include immediate cladding layers.

[0100] Preferably, for ease of manufacturing and other considerations, the materials forming waveguides 670, 680, 690 are similar or the same, and the materials forming layers 760a, 760b are similar or the same. In some embodiments, the materials forming waveguides 670, 680, 690 may vary between one or more waveguides, and / or the materials forming layers 760a, 760b may vary while still maintaining the various refractive index relationships described above.

[0101] 9A, light rays 770, 780, 790 enter the set of waveguides 660. It should be understood that light rays 770, 780, 790 may be injected into the waveguides 670, 680, 690 by one or more image injection devices 360, 370, 380, 390, 400 (FIG. 6).

[0102] In some embodiments, light rays 770, 780, 790 have different properties, e.g., different wavelengths or different wavelength ranges, which may correspond to different colors. Each of the incoupling optical elements 700, 710, 720 deflects incident light such that the light propagates through a respective one of the waveguides 670, 680, 690 by TIR. In some embodiments, each of the incoupling optical elements 700, 710, 720 selectively deflects one or more particular wavelengths of light while transmitting other wavelengths to the underlying waveguide and associated incoupling optical element.

[0103] For example, in-coupling optical element 700 may be configured to deflect light ray 770 having a first wavelength or wavelength range while transmitting light rays 780 and 790 having different second and third wavelengths or wavelength ranges, respectively. Transmitted light ray 780 impinges on and is deflected by in-coupling optical element 710, which is configured to deflect light of the second wavelength or wavelength range. Light ray 790 is deflected by in-coupling optical element 720, which is configured to selectively deflect light of the third wavelength or wavelength range.

[0104] 9A , the deflected light rays 770, 780, 790 are deflected to propagate through the corresponding waveguides 670, 680, 690. That is, the in-coupling optical element 700, 710, 720 of each waveguide deflects the light into its corresponding waveguide 670, 680, 690 and in-couples the light into its corresponding waveguide. The light rays 770, 780, 790 are deflected at an angle that causes the light to propagate through the respective waveguides 670, 680, 690 by TIR. The light rays 770, 780, 790 propagate through the respective waveguides 670, 680, 690 by TIR until they impinge on the waveguide's corresponding optical dispersive element 730, 740, 750.

[0105] 9B, a perspective view of the multiple stacked waveguide embodiment of FIG. 9A is illustrated. As described above, in-coupled light rays 770, 780, 790 are deflected by in-coupling optical elements 700, 710, 720, respectively, and then propagate by TIR within waveguides 670, 680, 690, respectively. Light rays 770, 780, 790 then impinge on optically dispersive elements 730, 740, 750, respectively. Optically dispersive elements 730, 740, 750 deflect light rays 770, 780, 790 to propagate toward out-coupling optical elements 800, 810, 820, respectively.

[0106] In some embodiments, the optically dispersive elements 730, 740, 750 are orthogonal pupil expanders (OPEs). In some embodiments, the OPEs deflect or disperse light into the out-coupling optical elements 800, 810, 820, and in some embodiments may also increase the beam or spot size of this light as it propagates into the out-coupling optical elements. In some embodiments, the optically dispersive elements 730, 740, 750 may be omitted, and the in-coupling optical elements 700, 710, 720 may be configured to deflect light directly into the out-coupling optical elements 800, 810, 820. For example, with reference to FIG. 9A , the optically dispersive elements 730, 740, 750 may be replaced with the out-coupling optical elements 800, 810, 820, respectively. In some embodiments, the outcoupling optical elements 800, 810, 820 are exit pupils (EPs) or exit pupil expanders (EPEs) that direct light toward the viewer's eye 210 ( FIG. 7 ). It should be understood that an OPE can be configured to increase the size of the eyebox in at least one axis, and that the EPE can increase the eyebox in an axis that intersects the axis of the OPE, e.g., orthogonal to the axis of the OPE. For example, each OPE may be configured to redirect a portion of the light striking the OPE to an EPE in the same waveguide, while allowing the remaining portion of the light to continue propagating down the waveguide. In response to striking the OPE again, another portion of the remaining light is redirected to the EPE, which continues to propagate further down the waveguide, etc. Similarly, in response to striking the EPE, a portion of the impinging light is directed out of the waveguide toward the user, and the remaining portion of that light continues to propagate through the waveguide until it again strikes the EP, at which point another portion of the impinging light is directed out of the waveguide, etc. As a result, a single beam of internally coupled light may be "replicated" each time a portion of that light is redirected by an OPE or EPE, thereby forming a cloned beam field of light, as shown in Figure 6. In some embodiments, the OPE and / or EPE may be configured to modify the size of the beam of light.

[0107] 9A and 9B, in some embodiments, a waveguide set 660 includes, for each primary color, waveguides 670, 680, 690, in-coupling optical elements 700, 710, 720, optically dispersive elements (e.g., OPEs) 730, 740, 750, and out-coupling optical elements (e.g., EPs) 800, 810, 820. The waveguides 670, 680, 690 may be stacked with an air gap / cladding layer between each one. The in-coupling optical elements 700, 710, 720 redirect or deflect incident light into that waveguide (with different in-coupling optical elements receiving light of different wavelengths). The light then propagates at an angle that will result in TIR within the individual waveguides 670, 680, 690. In the example shown, light ray 770 (e.g., blue light) is deflected by the first in-coupling optical element 700 in the manner described above, then continues bouncing down the waveguide, interacting with the optically dispersive element (e.g., OPE) 730 and then the out-coupling optical element (e.g., EP) 800. Light rays 780 and 790 (e.g., green and red light, respectively) pass through the waveguide 670, with light ray 780 impinging on and being deflected by the in-coupling optical element 710. Light ray 780 will then, via TIR, bounce down the waveguide 680, to its optically dispersive element (e.g., OPE) 740 and then the out-coupling optical element (e.g., EP) 810. Finally, light ray 790 (e.g., red light) passes through the waveguide 690 and impinges on the optically in-coupling optical element 720 of the waveguide 690. The light in-coupling optical element 720 deflects the light ray 790 so that it propagates by TIR to the light dispersive element (e.g., OPE) 750 and then by TIR to the out-coupling optical element (e.g., EP) 820. The out-coupling optical element 820 then finally out-couples the light ray 790 to a viewer, who also receives light out-coupled from the other waveguides 670, 680.

[0108] FIG. 9C illustrates a top-down plan view of an example of the multiple stacked waveguides of FIGS. 9A and 9B. As shown, waveguides 670, 680, 690 may be vertically aligned, along with each waveguide's associated optically dispersive element 730, 740, 750 and associated out-coupling optical elements 800, 810, 820. However, as discussed herein, the in-coupling optical elements 700, 710, 720 are not vertically aligned. Rather, the in-coupling optical elements are preferably non-overlapping (e.g., laterally spaced apart, as seen in the top-down view). As discussed further herein, this non-overlapping spatial arrangement facilitates the injection of light from different sources into different waveguides on a one-to-one basis, thereby allowing a specific light source to be uniquely coupled to a specific waveguide. In some embodiments, arrays including non-overlapping, spatially separated in-coupling optical elements may be referred to as shifted-pupil systems, and the in-coupling optical elements in these arrays may correspond to sub-pupils.

[0109] Eye and Environmental Imaging As discussed above, head-mounted displays can be used to provide a user with image content integrated with, combined with, and / or superimposed over a view of the world in front of the wearer. Such head-mounted display systems can be configured to project light into the user's eyes to form augmented reality image content and transmit light from the environment in front of the user to the user. The head-mounted display system may include one or more cameras to image the environment and / or the user's eyes. An outward-facing camera may directly image the environment and be used, for example, to determine where augmented reality image content should be placed relative to objects in the environment. For example, imaging the environment may provide the location of a table so that the head-mounted display may render an image of a person standing next to the table instead of on or in the table. An inward-facing camera may be used to directly image the eyes, such as for eye tracking. Disclosed herein are examples of head-mounted display systems and / or imaging systems that may be configured to image the eyes and / or the environment as well. In some designs, the system does not require inward-facing and / or outward-facing cameras to directly image the eye and / or the environment, respectively. Such systems may employ one or more cameras configured to receive light from the eye / environment via an eyepiece, such as one or more waveguides in the eyepiece, in optical communication with the one or more cameras. Once the light is collected by the waveguides, the one or more cameras can generate an image of the eye and / or the environment in front of the user. Using waveguides to collect light for imaging the eye and / or the environment can potentially reduce the form factor of the head-mounted display, making the head-mounted display potentially more compact and / or aesthetically pleasing.

[0110] FIG. 10 illustrates an exemplary imaging system 900 configured to image the eye, integrated with an eyepiece 950, that may be used on a head-mounted display. The eyepiece 950, which may be positioned in front of a user's eye 210, can be used both to inject image content into the eye and to image the eye. FIG. 10 shows one eyepiece 950 in front of one eye 210. Various head-mounted display systems, such as that shown in FIG. 2, may include a pair of eyepieces 950 and associated components positioned in front of the respective left and right eyes 210. While a single waveguide 940 is shown in FIG. 10, the waveguide 940 may include one, two, three, four, six, seven, eight, or more waveguides (e.g., a stack of one or more waveguides).

[0111] Imaging system 900 may include a light source or illumination source 960 to illuminate the eye and facilitate image capture, an eyepiece 950 with a waveguide 940 configured to propagate light therein, and / or an imaging device 920 such as a camera for image capture. Also shown is an image projector 930 for producing an image that may be injected into the eye via the eyepiece 950. Eyepiece 950 may include one or more waveguides 940 configured to carry light from illumination source 960 and / or image projector 930 to the eye and light from the eye to camera 920. Eyepiece 950 may further include one or more coupling optical elements 944 to illuminate the eye and couple light from waveguide 940 out to the eye for image injection and / or from the eye into the waveguide for image capture. The eyepiece 950 may additionally include one or more internal coupling optical elements 942 for coupling light from the illumination source 960 and / or image projector 930 into the waveguide 940, and one or more external coupling optical elements 952 for coupling light from the waveguide to the camera 920.

[0112] The eyepieces 950 may be disposed on a frame that is worn on the head. The eyepieces 950 may be disposed in front of the eyes 210. The eyepieces 950 may have an inner or nasal side that is closer to the wearer's nose and an opposing outer or temporal side that is closer to the wearer's temples and farther from the nose. In FIG. 10 , the coupling optical element 944 is on the inner or nasal side (outer or temporal side relative to the coupling optical element 944) relative to the inner coupling 942 and outer coupling 952 optical elements. The illumination source 960 is also on the inner or nasal side relative to the image projector 930 (or the image projector is on the outer or temporal side relative to the illumination source). However, the relative positions may vary. For example, the illumination source 960 may be on the outer or temporal side relative to the image projector 930 in some designs.

[0113] The waveguide 940 may comprise a sheet or layer having two major surfaces (front and rear surfaces) with the largest surface areas arranged opposite each other. The front surface may be farther from the user's eyes 210 when the user wears the head-mounted display (closer to the environment in front of the wearer), and the rear surface is closer to the user's eyes (and farther from the environment in front of the wearer). The waveguide 940 may include a transparent material (e.g., glass, plastic) with a refractive index greater than 1.0 so that light can be guided therein between the major surfaces by total internal reflection. Elements with the same number may have the same functionality for one or more of the embodiments described herein.

[0114] A coupling optical element 944 may be disposed on or within the waveguide 940 for coupling light from the eye 210 to the waveguide 940 and / or from the waveguide to the eye. As shown in FIG. 10 , the coupling optical element 944 may be disposed in an optical path between the user's eye 210 and the waveguide 940 such that light coupled from the waveguide 940 via the coupling optical element 944 may be incident on the user's eye 210 (e.g., to illuminate the eye and / or for imaging). The coupling optical element 944 may comprise a plurality of turning features configured to redirect light guided within the waveguide out of the waveguide or to redirect light incident on the coupling optical element 944 at an angle into the waveguide to be guided therein by total internal reflection. The coupling optical element 944 and the turning features may be physically engaged with the waveguide 940. For example, coupling optical element 944 may comprise a holographic or diffractive optical element (e.g., a surface relief grating) patterned (e.g., etched) within or on waveguide 940. Coupling optical element 944 may comprise a layer disposed on waveguide 940, or may be formed within waveguide 940. For example, a volume holographic or other diffractive optical element may be formed by varying the refractive index of the material comprising the waveguide or a layer disposed thereon. Thus, coupling optical element 944 may be disposed within the volume of waveguide 940 or as a layer disposed thereon.

[0115] Depending on the design, the combining optical element 944 may be transmissive or reflective and may operate transmissively or reflectively. For example, the combining optical element 944 may operate transmissively or reflectively, respectively, and may include a transmissive or reflective diffractive optical element (e.g., a grating) or a holographic optical element that, for example, redirects light transmitted through or reflected therefrom. The combining optical element 944 may include a polarization optical element, such as a polarization-selective redirecting element (e.g., a polarizer). The polarization-selective redirecting element may include one or more polarization gratings, diffractive optical elements, and / or holographic optical elements, and may comprise a liquid crystal structure, such as a liquid crystal polarization grating. The combining optical element 944 may be configured to direct light from the image projector 930 and / or the light source 960, which is guided within the waveguide 940 by total internal reflection (TIR), at an angle less than the critical angle (e.g., more normal) to be emitted from the waveguide out toward the eye 210. Additionally or alternatively, the coupling optical element 944 may be configured to couple light from the eye 210 into the waveguide 940 at an angle greater than the critical angle (e.g., an angle that is less than normal) so that it is guided therein to the camera 920 by total internal reflection.

[0116] As shown in FIG. 10 , an internal coupling optical element 942 for coupling light from an illumination source 960 and / or an image projector 930 into the waveguide 940 may be disposed on or within the waveguide 940. The internal coupling optical element 942 may be disposed in an optical path between the light source 960 and the waveguide 940 such that light coupled from the light source 960 via the internal coupling optical element 942 is guided within the waveguide 940. The internal coupling optical element 942 may comprise a plurality of turning features configured to redirect light incident thereon at an angle into the waveguide, for example, to be guided therein by total internal reflection. The internal coupling optical element 942 may comprise a liquid crystal structure, such as a liquid crystal polarization grating. Additionally or alternatively, the internal coupling optical element 942 may include a blazed grating. The internal coupling optical element 942 may comprise a layer disposed on the waveguide 940, or may be formed (e.g., patterned) on or within the waveguide 940, or otherwise fabricated therein. For example, a surface holographic or diffractive optical element (e.g., a surface relief grating) may be fabricated by patterning (e.g., etching) the surface of the waveguide or a layer thereon. A volume holographic or diffractive optical element may also be formed by changing the refractive index of the material comprising the waveguide or a layer thereon. Thus, the internal coupling optical element 942 may be disposed within the volume of the waveguide 940 or a layer thereon. Depending on the design, the internal coupling optical element 942 may be transmissive or reflective and may operate transmissively or reflectively. For example, the internal coupling optical element 942 may include a transmissive or reflective diffractive optical element (e.g., a grating) or a holographic optical element that operates transmissively or reflectively, e.g., redirecting light transmitted through or reflected therefrom, respectively.

[0117] The internal coupling optical element 942 may comprise a reflective optical element (e.g., a mirror). For example, the internal coupling optical element 942 may comprise an off-axis reflector. Additionally or alternatively, the internal coupling optical element 942 and / or the coupling optical element 944 may include a polarization optical element, such as a polarization-selective redirecting element (e.g., a polarizer). The polarization-selective redirecting element may include one or more polarization gratings, diffractive optical elements, and / or holographic optical elements, and may comprise a liquid crystal structure, such as a liquid crystal polarization grating. For example, one or both of the internal coupling optical element 942 and / or the coupling optical element 944 may include a liquid crystal polarization grating (LCPG). LCPGs can potentially provide high-efficiency diffraction over a wide wavelength range. Thus, LCPGs may be useful for the internal coupling optical element 942 and / or the coupling optical element 944. LCPGs may be polarization-dependent. The LCPG or other type of liquid crystal grating, diffractive optical element, or optical element may include a pattern or arrangement of liquid crystal molecules configured to provide one or more functions, such as redirecting light into or out of a waveguide. Thus, the internal coupling optical element 942 and / or the coupling optical element 944 may comprise a polarization grating. Additionally or alternatively, the internal coupling optical element 942 and / or the coupling optical element 944 can comprise liquid crystals, and thus, in some implementations, one or both may be liquid crystal gratings or liquid crystal diffractive optical elements. Additionally or alternatively, one or both of the internal coupling optical element 942 and / or the coupling optical element 944 can include a blazed grating. In some designs, the internal coupling optical element 942 comprises a liquid crystal reflector, such as a cholesteric liquid crystal reflective lens (e.g., a reflective liquid crystal diffractive lens, a Bragg reflective structure, a reflective liquid crystal diffraction grating, etc.).Some non-limiting examples of liquid crystal gratings, liquid crystal polarization gratings, and other liquid crystal optical elements are described in the following published applications, each of which is incorporated herein by reference in its entirety and for all purposes: U.S. Patent Publication No. 2018 / 0143438, entitled "MULTILAYER LIQUID CRYSTAL DIFFRACTIVE GRATINGS FOR REDIRECTING LIGHT OF WIDE INCIDENT ANGLE RANGES," filed November 16, 2017; U.S. Patent Publication No. 2018 / 0143485, entitled "SPATIALLY VARIABLE LIQUID CRYSTAL DIFFRACTION GRATINGS," filed November 16, 2017; and U.S. Patent Publication No. 2018 / 0143485, entitled "WAVEGUIDE LIGHT MULTIPLEXER USING CROSSED ANGLE RANGES," filed November 16, 2017. These and other related applications are discussed in U.S. Patent Publication No. 2018 / 0143509, entitled "DISPLAY SYSTEM WITH VARIABLE POWER REFLECTOR," filed November 16, 2017; U.S. Patent Publication No. 2018 / 0239147, entitled "DISPLAY SYSTEM WITH VARIABLE POWER REFLECTOR," filed February 22, 2018; U.S. Patent Publication No. 2018 / 0239177, entitled "VARIABLE-FOCUS VIRTUAL IMAGE DEVICES BASED ON POLARIZATION CONVERSION," filed February 22, 2018; and U.S. Patent Publication No. 2018 / 0164627, entitled "DIFFRACTIVE DEVICES BASED ON CHOLESTERIC LIQUID CRYSTAL," filed December 7, 2017. However, the design of the internal coupling optical element 942 and / or the coupling optical element 944 is not limited thereto and may include other types of optical elements, diffractive optical elements, liquid crystal optical elements, liquid crystal gratings, and liquid crystal polarization gratings. Further information regarding examples of cholesteric liquid crystal structures such as reflectors may also be found in the section below entitled "Cholesteric Liquid Crystal Mirrors." As discussed above, other liquid crystal optical elements and other non-liquid crystal optical elements may also be used.Thus, many types of coupling optical elements (e.g., internal coupling optical element 942 and / or coupling optical element 944), diffractive optical elements, gratings, polarization gratings, etc. may be used, both those described herein and other types of gratings, diffractive optical elements, liquid crystal elements, and optical elements in general. In various implementations, internal coupling optical element 942 may be configured to couple light from image projector 930 and / or light source 960 into the waveguide at an angle above the critical angle so that the light is guided within waveguide 940 to user's eye 210 by total internal reflection to the eye.

[0118] Waveguide 940 may comprise one or more waveguides. In some implementations, one or more waveguides 940 comprise a stack of waveguides. In some designs, for example, different waveguides of a stack of waveguides are configured to output light with different wavefront divergences, as if projected from different distances from the user's eye. For example, a first waveguide or group of waveguides may be configured to output light that is collimated or has a first divergence, as if projected from a first depth, and a second waveguide or group of waveguides may be configured to output light that is divergent (not collimated) or at a second divergence (greater than the first divergence), as if projected from a second depth closer than the first depth. In some designs, different waveguides may be configured to output light with different associated colors. For example, a first waveguide may be configured to output red light, a second waveguide may be configured to output green light, a third waveguide may be configured to output blue light, and a fourth waveguide may be configured to output and / or input infrared light.

[0119] The outcoupling optical element 952 for coupling light from the waveguide 940 to the camera 920 as shown in FIG. 10 may comprise multiple redirecting features configured to redirect light at an angle, for example, so that light incident thereon is not guided within the waveguide but is redirected out of the waveguide to the camera. The outcoupling optical element 952 may be disposed within the interior of the waveguide 940 or may be patterned (e.g., etched) in or on a surface (e.g., a major surface) of the waveguide 940. For example, a surface holographic or diffractive optical element (e.g., a surface relief grating) may be fabricated by patterning (e.g., etching) the surface of the waveguide or a layer thereon. A volume holographic or diffractive optical element may also be formed by changing the refractive index of the material comprising the waveguide or a layer thereon. Depending on the design, the outcoupling optical element 952 may be transmissive or reflective and may operate transmissively or reflectively. For example, the outcoupling optical element 952 may include a transmissive or reflective diffractive optical element (e.g., a grating) or a holographic optical element that operates transmissively or reflectively, respectively, e.g., redirecting light transmitted through or reflected therefrom.

[0120] The outcoupling optical element 942 may comprise a reflective optical element (e.g., a mirror). For example, the outcoupling optical element 952 may comprise an off-axis reflector. In some designs, the outcoupling optical element 952 may include a polarization optical element, such as a polarization-selective redirecting element (e.g., a polarizer). Thus, the polarization-selective redirecting element may include one or more polarization gratings, diffractive optical elements, and / or holographic optical elements, and may comprise a liquid crystal structure, such as a liquid crystal polarization grating. In some implementations, for example, the outcoupling optical element 952 may include a liquid crystal polarization grating (LCPG). LCPGs can potentially provide high-efficiency diffraction over a wide wavelength range. Similarly, LCPGs may be useful for the outcoupling optical element 952. LCPGs may be polarization-dependent. LCPGs or other types of liquid crystal gratings may include a pattern or arrangement of liquid crystal molecules configured to provide one or more functions, such as redirecting light into or out of a waveguide. Thus, the outcoupling optical element 952 may comprise a polarization grating. Additionally or alternatively, the outcoupling optical element 952 can comprise a liquid crystal and, therefore, in some implementations, may be a liquid crystal grating or other liquid crystal optical element, such as a liquid crystal diffractive optical element. Additionally or alternatively, the outcoupling optical element 952 can include a blazed grating. In some designs, the outcoupling optical element 952 comprises a liquid crystal reflector, such as a cholesteric liquid crystal reflective lens (e.g., a reflective liquid crystal diffractive lens, a Bragg reflective structure, a reflective liquid crystal diffraction grating, etc.).Some non-limiting examples of liquid crystal gratings, liquid crystal polarization gratings, and other liquid crystal optical elements are described in the following published applications, each of which is incorporated herein by reference in its entirety and for all purposes: U.S. Patent Publication No. 2018 / 0143438, entitled "MULTILAYER LIQUID CRYSTAL DIFFRACTIVE GRATINGS FOR REDIRECTING LIGHT OF WIDE INCIDENT ANGLE RANGES," filed November 16, 2017; U.S. Patent Publication No. 2018 / 0143485, entitled "SPATIALLY VARIABLE LIQUID CRYSTAL DIFFRACTION GRATINGS," filed November 16, 2017; and U.S. Patent Publication No. 2018 / 0143485, entitled "WAVEGUIDE LIGHT MULTIPLEXER USING CROSSED ANGLE RANGES," filed November 16, 2017. These and other related applications are discussed in U.S. Patent Publication No. 2018 / 0143509, entitled "DISPLAY SYSTEM WITH VARIABLE POWER REFLECTOR," filed November 16, 2017; U.S. Patent Publication No. 2018 / 0239147, entitled "DISPLAY SYSTEM WITH VARIABLE POWER REFLECTOR," filed February 22, 2018; U.S. Patent Publication No. 2018 / 0239177, entitled "VARIABLE-FOCUS VIRTUAL IMAGE DEVICES BASED ON POLARIZATION CONVERSION," filed February 22, 2018; and U.S. Patent Publication No. 2018 / 0164627, entitled "DIFFRACTIVE DEVICES BASED ON CHOLESTERIC LIQUID CRYSTAL," filed December 7, 2017. However, the design of the outcoupling optical element 952 is not limited to these and may include other types of optical elements, diffractive optical elements, liquid crystal optical elements, liquid crystal gratings, and liquid crystal polarization gratings. Further information regarding examples of cholesteric liquid crystal structures such as reflectors may also be found in the section below entitled "Cholesteric Liquid Crystal Mirrors." As discussed above, other liquid crystal optical elements and other non-liquid crystal optical elements may also be used.Thus, many types of coupling optical elements (e.g., outcoupling optical element 952), both those described herein and other types of gratings, diffractive optical elements, liquid crystal elements, or optical elements in general, may be used, such as diffractive optical elements, gratings, polarization gratings, etc. As referenced above, outcoupling optical element 952 may be configured to redirect light guided in waveguide 940 at an angle less than the critical angle so that it is not guided in the waveguide by total internal reflection, but is instead injected into camera 920.

[0121] In various designs, the coupling optical element 944 may be transparent in the visible spectrum so that the user can see the environment in front of the user through the coupling optical element 944 and the eyepiece 950. The inner coupling optical element 942 may also redirect light in the visible spectrum, for example, when the inner coupling optical element is used to receive light from the image projector 930 and / or when the illumination source 960 is configured to output visible light and illuminate the eye 210 with visible light. In some embodiments, the inner coupling optical element 942 is configured to redirect infrared light, for example, when the illumination source 960 is configured to output infrared light and illuminate the eye 210 with infrared light. In some designs, such as that shown in FIG. 10 , the inner coupling optical element 942 may be more medial or nasal than the outer coupling optical element 952. However, in other designs, the inner coupling optical element 942 may be more lateral or temporal than the outer coupling optical element 952. In one implementation, as shown in FIG. 10, the out-coupling optical element 952 may be adjacent to the in-coupling optical element 942, although non-adjacent positioning is also possible.

[0122] The illumination source 960 may be located on the same side (e.g., posterior or proximal side) of the eyepiece 950 as the eye 210 (proximal may refer to the side closest to the eye 210), as shown in FIG. 10 . Alternatively, the illumination source 960 may be located on the opposite side (e.g., anterior or distal side) from the eye 210. The illumination source 960 may be configured to direct light into at least one of the major surfaces of the waveguide 940 via the internal coupling optical element 942. The light source 960 may be configured to emit invisible light (e.g., infrared light). The light source 960 may include one or more LEDs. The LEDs may comprise infrared LEDs. The light source 960 may be configured to emit coherent light. In some designs, the light source 960 comprises a laser (e.g., an infrared laser). In some designs, the light source 960 emits pulsed light. For example, the camera 920 can be configured to periodically capture images. Thus, the illumination source 960 can be pulsed to coincide with the period during which the camera is acquiring images. The intensity output from the illumination source 960 can be reduced when the camera is not acquiring images. By concentrating the total illumination energy for a short period of time, an increased signal-to-noise ratio can be obtained without exposing the eye 210 to unsafe intensity levels. In some cases, for example, the camera 920 captures one image every 30 milliseconds, and the camera's exposure time is a few milliseconds. The illumination source 960 can be configured to output pulses with a similar period and duration to match that of the camera 920.

[0123] In some implementations, different light sources having different wavelengths are alternatively pulsed to provide different wavelength illumination at different times, as discussed below.

[0124] The in-coupling optical element 942 may be in direct optical communication with the illumination source 960 and / or the image projector 930, for example, to direct light therein from the image projector 930 and / or the light source 960. For example, light emitted by the light source 960 may be incident on the in-coupling optical element 942 before optically interacting with either the coupling optical element 944 and / or the out-coupling optical element 952.

[0125] As shown in FIGS. 11A-11E, light 902 projected from an image projector 930 can form an image on the retina. The image projector 930 may include a light source, a modulator, and / or projection optics. The light source for the image projector 930 may include one or more LEDs, lasers, or other light sources, or may include one or more visible light sources. The modulator may include a spatial light modulator, such as a liquid crystal spatial light modulator. Such a spatial light modulator may be configured, for example, to modulate the intensity of light at different spatial locations. The projection optics may include one or more lenses. Other types of image projectors 930 capable of projecting and / or forming an image may also be employed. For example, the image projector 930 may include a scanning optical fiber.

[0126] Image projector 930 and in-coupling optical element 942 may be in direct optical communication with one another. Image projector 930 may be aligned with in-coupling optical element 942, for example, into which light from image projector 930 is directed. In some cases, image projector 930 is positioned adjacent to corresponding in-coupling optical element 942 and / or waveguide 940. Image projector 930 may also be positioned within an optical path that includes in-coupling optical element 942, coupling optical element 944, and eye 210.

[0127] Image projector 930 may be a separate element from illumination source 960, as shown in Figures 10 and 11A-11E. However, in some cases, image projector 930 may be used as an illumination source. For example, in addition to projecting an image into eye 210, image projector 930 may be used to direct visible and / or infrared light into and illuminate the eye for image capture. However, alternatively, one or more separate light sources 960 may be used to illuminate eye 210 for image capture.

[0128] The light emitted by the illumination source 960 may comprise light in a particular wavelength range, such as, for example, invisible light. The illumination source 960 may be configured to project invisible (e.g., infrared) light onto or into the eye 210 to image one or more portions of the eye 210 (e.g., the cornea, the retina). In one exemplary implementation, the light source 960 may be configured to emit light in a range of approximately 850 nm to 940 nm. The light source 960 may be configured to emit light extending over a wavelength range of at least approximately 20 nm. Other ranges are also possible. The emitted wavelength range may be 5 nm, 10 nm, 15 nm, 50 nm, 75 nm, 100 nm, 150 nm, 200 nm, or any range between any of these values. The light source 960 may be configured to emit light across a broad band of wavelengths, such as any range within the infrared spectrum.

[0129] The imaging device 920, which may comprise a camera, may comprise a detector array and possibly imaging optics. The detector array may comprise, for example, a CCD or CMOS detector array, and the imaging optics may comprise one or more lenses. The one or more lenses may have positive optical power and an associated focal length. In one design, the camera 920 is focused at infinity. For example, the optics may have a focal length f, and the detector array may be positioned at a distance from the optics corresponding to the focal length such that objects at large distances are imaged onto the detector array. Similarly, collimated light from the eye or objects in the environment will also be focused onto the detector array, forming an image of the eye or object thereon.

[0130] The imaging device 920 may be positioned on the opposite side of the waveguide 940 from the illumination source 960 and / or the eye 210. In some designs, the imaging device 920 may be positioned on the same side of the waveguide 940 as the light source 960 and / or the eye 210. As shown in FIG. 10 , the imaging device 920 may be positioned near the outside or temple edge of the eyepiece 950, although other locations are possible.

[0131] 11A-11E illustrate the operation of the example imaging system 900 of FIG. 10. FIG. 11A shows an illumination source 960 emitting light 902 toward an incoupling optical element 942 on a waveguide 940. As shown, the light 902 can be directed to enter the eyepiece 950 near normal, although other angles are possible. In some designs, the light source 960 is configured to emit collimated light into the eyepiece 950. As shown in FIG. 11B, the illumination light 902 can be coupled into the waveguide 940 via the incoupling optical element 942. In some designs where the incoupling optical element 942 comprises a diffractive optical element (e.g., a grating, a holographic element), light incident thereon is diffracted at angles above the critical angle of the waveguide, causing the incoupling light 904 to be guided within the eyepiece 950 by total internal reflection (TIR). In some designs, the in-coupling optical element 942 may be configured to direct light toward the coupling optical element 944. The in-coupling optical element 942 may be polarization-selective. For example, the in-coupling optical element 942 may include a polarization-selective redirecting element such as a polarization grating, such as a liquid crystal polarization grating. Figure 11C shows how the in-coupled light 904 propagates through the waveguide 940 by TIR.

[0132] FIG. 11D illustrates an example imaging system 900 that couples light out of an eyepiece 950. As the internally coupled light 904 propagates through the waveguide 940, a portion of the light may be incident on a coupling optical element 944. The coupling optical element 944 can be configured to couple the internally coupled light 904 out of the eyepiece 950 toward the user's eye 210. The coupling optical element 944 may be configured to couple the light as collimated light toward the eye 210. The coupling optical element 944 may be tuned to a specific wavelength range of light. For example, the coupling optical element 944 may be configured to couple infrared light (e.g., approximately 700 nm to 15,000 nm) out of the waveguide 940. In some designs, the coupling optical element 944 can be configured to couple multiple wavelengths of light out of the eyepiece 950. For example, the coupling optical element 944 may be tuned for both infrared and visible light. Coupling optical element 944 can also be configured to couple light into waveguide 940, as described more fully below.

[0133] The coupling optical element 944 can be configured to increase one or more dimensions of the eyebox for the user. For example, the one or more dimensions may be measured along a first axis (e.g., the x-axis). The eyepiece 950 may further include an orthogonal pupil expander (OPE). The OPE may have at least one light redirecting element disposed on or within the waveguide (e.g., on one of the major surfaces), or the OPE may be disposed within the waveguide 940. The OPE may include features similar to or the same as those described above with respect to the light dispersive elements 730, 740, and 750 above. In some implementations, the light redirecting element may comprise a diffractive optical element. The OPE may be configured to increase the dimension of the eyebox along a second axis (e.g., the y-axis) orthogonal to the first axis.

[0134] 11D shows how some of the light exits the eyepiece 950 toward the user's eye 210. In some designs, the combining optical element 944 is configured so that the internally coupled light 904 incident on the combining optical element 944 at various portions of the combining optical element 944 along a first axis (e.g., parallel to the x-axis) exits the eyepiece 950 at each portion of the combining optical element 944 along the first axis. This can provide the user with light to project an image or illuminate the eye for different eye positions or locations.

[0135] As shown in FIGS. 11D-11E, the coupling optical element 944 may be configured to couple the internally coupled light 904 out of the eyepiece 950 as collimated light. This light may also generally be directed approximately normal to the major surfaces of the eyepiece 950 and / or the waveguide 940. The collimated light may be directed into the eye and focused onto the retina by the eye (e.g., the cornea and natural lens of the eye). This light 908 incident on the retina may provide illumination to image the retina and / or provide image content to the eye. A portion of this light 908 may, for example, be reflected or scattered from the retina and exit the eye to provide an image of the retina to be captured. The light source 960 may be an extended light source such that the light will illuminate an area of ​​the retina.

[0136] 12A-12E illustrate how the imaging system 900 of FIGS. 11A-11E can additionally or alternatively be used to collect images of the eye 210. FIG. 12A shows how light 910 reflected from the retina exits the eye 210. As shown, light 910 scattered or reflected from the retina, passing through the eye's natural lens, the intraocular pupil, and the cornea, can be collimated. This light can also be incident on the eyepiece 950 at normal incidence (e.g., perpendicular to the major surfaces of the waveguide 940 and / or the coupling optical element 944). The coupling optical element 944 can be configured to couple the light 910 reflected from the retina into the waveguide 940.

[0137] FIG. 12B illustrates exemplary imaging system 900 as it couples light into eyepiece 950. Coupling optical element 944 may include redirecting features, such as a diffractive optical element or other structure, that redirect light at an angle greater than the critical angle to be guided within waveguide 940. Coupling optical element 944 may be configured to direct incoupling light 914 generally toward light source 960 and / or imaging device 920. Coupling optical element 944 can be configured to couple less than a percentage of this light propagating toward camera 920 back out of waveguide 940. For example, a partially reflective element (e.g., a semi-transparent mirror) may be disposed on or within waveguide 940 to reduce leakage of incoupling light 914 out of waveguide 940 along the portion of waveguide 940 where coupling optical element 944 is disposed, while allowing a portion of incoupling light 914 to continue propagating within waveguide 940 by total internal reflection. The fraction of light that does not leak may be any percentage between 0 and 1. For example, the fraction may be 0.90, such that 90% of the light rays propagating through waveguide 940 along coupling optical element 944 are maintained within waveguide 940 at each reflection of the light rays. Other fractions are also possible (e.g., 0.10, 0.20, 0.30, 0.40, 0.50, 0.60, 0.70, 0.80, or any range between any of these values). Such partially reflective elements may also be used in the implementations described below.

[0138] As shown in FIG. 12C , the collimated internally coupled light 914 may continue to propagate through the waveguide 940 toward the imaging device 920. FIG. 12D illustrates that a portion of the internally coupled light 914 may continue to propagate until it is incident on one or more external coupling optical elements 952. To reduce the amount of leakage of the internally coupled light 914 out of the internal coupling optical element 942, the internal coupling optical element 942 can be configured to couple little of this light propagating toward the camera 920 back out of the waveguide. For example, a partially reflective element (e.g., a semi-transparent mirror) may be disposed on or within the waveguide 940 to reduce leakage of the internally coupled light 914 out of the waveguide 940 along the portion of the waveguide 940 where the internal coupling optical element 942 is disposed, while allowing a portion of the internally coupled light 914 to continue propagating within the waveguide 940 by total internal reflection. The portion of light that does not leak out may be any percentage between 0 and 1. For example, the fraction may be 0.90, such that 90% of a light ray propagating through waveguide 940 and along coupling optical element 944 is maintained within waveguide 940 at each reflection of the light ray. Other fractions are also possible (e.g., 0.10, 0.20, 0.30, 0.40, 0.50, 0.60, 0.70, 0.80, or any range between any of these values). Such partially reflective elements can also be used in the implementations described below.

[0139] 12E , the outcoupling optical element 952 can be configured to couple light guided within the waveguide 940 out of the waveguide 940 and onto the imaging device 920. As a result, light propagating within the waveguide 940 that is incident on the outcoupling element 952 can be redirected to exit the waveguide 940, for example, out of a major surface of the waveguide 940 (e.g., at the front or rear side of the waveguide 940), and be directed onto the imaging device 920. The outcoupling optical element 952 may be configured to direct the light 926 to exit the waveguide 940 perpendicularly (e.g., normal to) the major surface of the waveguide 940. In some designs, the outcoupling optical element 952 is configured to direct the collimated light 924 onto the imaging device 920 at normal incidence to a light-sensitive portion of the imaging device 920. As discussed above, the camera 920 may be focused at infinity, for example, and the imaging optics may be configured to focus collimated light onto the detector array.

[0140] Thus, waveguide 940 may be configured to guide light coupled from user's eye 210 into waveguide 940 to be received by imaging device 920 (e.g., a camera) to capture an image of at least a portion of user's eye 210. The same waveguide 940 may be configured to guide light coupled from image projector 930 so that light from image projector 930 may be directed to user's eye 210 so that the image from image projector 930 is within the user's field of view. In some implementations, the same waveguide is configured to guide light coupled from illumination source 960 so that light from the illumination source may be directed to user's eye 210 and illuminate the eye so that an image of the eye may be captured by camera 920.

[0141] In some implementations, the same combining optical element 944 can be configured to (i) couple light from the user's eye 210 into the waveguide 940 to be received by the imaging device 920, and (ii) couple light from the image projector 930 out of the waveguide 940 into the user's eye 210 to project image content into the user's field of view. In some implementations, the same combining optical element 944 can be configured to couple light from the illumination source 960 out of the waveguide into the user's eye 210 so that light from the illumination source may illuminate the eye.

[0142] In other designs, different waveguides may be used and / or different coupling optical elements 944 may be used. In some designs, for example, a first waveguide 940 may be configured to guide light coupled from the user's eye 210 to be received by the camera 920 to capture an image of at least a portion of the user's eye 210, and a second waveguide may be configured to guide light coupled from the image projector 930 so that light from the image projector 930 is directed at the user's eye 210. The first and second waveguides may be stacked on top of each other. Another waveguide may additionally or alternatively be configured to guide light coupled from the illumination source 960 so that light from the illumination source may be directed at the user's eye 210 and illuminate the eye.

[0143] Also, in some implementations, the first coupling optical element 944 can be configured to (i) couple light from the user's eye 210 into the waveguide 940 to be received by the imaging device 920, and (ii) couple light from the image projector 930 out of the waveguide 940 into the user's eye 210 to project image content into the user's field of view. Another coupling optical element may additionally or alternatively be configured to couple light from the illumination source 960 out of the waveguide into the user's eye 210 so that light from the illumination source may illuminate the eye.

[0144] In some designs, the coupling optical element 944 can include multiple diffractive optical elements (DOEs). For example, a first DOE can be configured to couple light from the user's eye 210 into the waveguide 940 to be received by the imaging device 920. A second DOE can be configured to couple light from the image projector 930 out of the waveguide 940 to the user's eye 210 and project image content into the user's field of view. Optionally, a third DOE can be configured to couple light from the light source 960 out of the waveguide 940 to the user's eye 210 and illuminate the eye. The first and second (and possibly third) DOEs can be stacked, for example, such that in some implementations, light from an environment in front of the user passes through the first DOE, then impinges on the second DOE, then on the third DOE, and then on the user's eye. However, the order can be different.

[0145] In some designs, the first and second DOEs are integrated within a single element or volume of the waveguide 940. In some implementations, for example, the first and second DOEs are both superimposed on top of each other (e.g., occupy the same or nearly the same volume) within the waveguide 2102. For example, the first and second DOEs may be recorded in the same medium.

[0146] As described above, image capture of the eye, e.g., the retina, can facilitate eye tracking. Figure 13A illustrates an imaging system 900 configured to image various portions of the eye 210 (e.g., the retina), e.g., at different times when the eye is in different positions. Phases A and B may refer to images of the eye 210 during different eye orientations. Figure 13A shows images of the eye 210 during both Phase A and Phase B imaging and the results.

[0147] In some implementations, light emission 928 (e.g., from illumination source 960 as described above, or from one or more illumination sources configured and / or positioned differently) can be used to acquire one or more images of retina 962, as shown by FIG. 13A. The image of retina 962 may comprise one or more regions 964, 966 imaged during different orientations of eye 210. FIG. 13A shows two regions 964, 966 of the image of retina 962. For example, region 964 of the retina imaged in stage A may be imaged while eye 210 is oriented at a normal angle relative to waveguide 940. Image data for region 966 imaged in stage B may be acquired while eye 210 is oriented at an acute angle with waveguide 940. A composite image or map of retina 962 may be acquired using one or more orientations of eye 210 during one or more stages of imaging. Processing electronics or a processor, such as data module 140 (see FIG. 2), may be used to find overlapping image data between two nearby regions. Using the image data of the overlapping regions, a composite image of the retina 962 can be determined. A larger-sized (e.g., full-size) composite image or map of the user's retina can be stored.

[0148] As described herein, a head-mounted display can be used to map the retina of a user's eye based on the direction the user's eye is pointed. To use eye gaze to provide realistic and intuitive interaction with objects in the user's environment and / or to identify the wearer of the head-mounted display device, the head-mounted display system can use retinal mapping to incorporate the uniqueness of the user's eye features and other conditions that may have an effect on the eye measurements. For example, an image may be identified based on the location of blood vessels in the corresponding retinal image.

[0149] Retinal mapping may involve a process for enabling a computing device to learn how to associate a user's eye gaze (e.g., as identified in a retinal image) with a gaze point in 2D or 3D space. An eye gaze may be associated with a single point in 2D or 3D space. An eye gaze can also be associated with multiple points in space, which can account for the movement of a virtual object (e.g., a series of points, a moving image location).

[0150] The head-mounted display system can determine the user's eye gaze based on the retinal image. The head-mounted display system can acquire the retinal image using a sensor (e.g., an eye camera, such as imaging device 920). The head-mounted display system can image one or both of the user's eyes while the user changes their eye gaze (e.g., when the user looks around to track a moving or shifting calibration target or a fixation target). To map the user's retina, the head-mounted display system can present a virtual target, e.g., a fixation target, for the user to view. The virtual target may be associated with one or more known points of gaze in 2D or 3D space. While the user views the target, the head-mounted display system can obtain retinal images and associate the images with gaze points. The head-mounted display system can calculate and / or generate a mapping matrix based on the association of the individual retinal images with gaze points associated with the targets.

[0151] The retinal mapping results can reflect the uniqueness within each person's eye. For example, the head-mounted display system can generate a mapping matrix customized to one or both eyes of a specific individual. For example, a user may have a different amount of eye movement or eye line of sight in response to a specific target. Additionally, or alternatively, a user may have different positions, sizes, shapes, and / or orientations of blood vessels within the retina. As a result, by generating calibration results specific to an individual user, the head-mounted display system may enable more accurate user interaction with eye line of sight and / or enable identification of a specific user.

[0152] Thus, when a user puts on a head-mounted display device, the system can detect whether the user is a previous user or a new user. A confusion matrix can be calculated, and scores for particular eye-gaze images stored in system memory are compared with corresponding images of the current user. The confusion matrix can include comparison scores for multiple eye-gazes and associated retinal images. Based on the comparison scores, the system can make a decision regarding the user's identity (e.g., whether the user is the same individual with whom the stored retinal image or composite map is associated) and / or a confidence level for the decision. The confidence level can include, for example, an identification coefficient. The stored image, e.g., the composite image or map, can be compared with a later-acquired image, referred to as an instantaneous or real-time image, acquired for the current user. The system may provide an alert or take other action if it detects that the user is a new user.

[0153] The system may apply filtering, such as digital filtering or image processing, to the retinal images captured by the camera. Such filtering or image processing may enhance features that may be used, for example, for identification, stitching, assembling composite images, eye tracking, etc. Such filtering or image processing may include edge enhancement. Such a filter may comprise, for example, a Frangi filter, although other types of filters may also be used. Such a filter or processing (e.g., edge enhancement or Frangi filter) can be used to enhance and / or detect image features such as blood vessels or tubular structures or fibers in the retinal image.

[0154] FIG. 13B illustrates a pattern of sequentially displayed fixation targets that can be used in the retinal mapping process. These virtual targets, onto which a user's eyes would direct their gaze, can redirect the eye's gaze in various different directions while the retina is imaged. The resulting images associated with different gaze directions correspond to different portions of the retina. As discussed above, when the eye gazes in different directions and views differently positioned fixation targets on the display, the images captured by the camera include different portions of the retina. These images can be assembled to form a larger map or composite image of the retina.

[0155] FIG. 13B shows a virtual target at 16 different locations within a user's field of view (FOV) 1200. In various implementations, the virtual target will be presented at a given location at a given time. One or more retinal images will be acquired during the time the virtual target is presented to the user at that particular location. This or these images may be associated with the target location and / or corresponding gaze direction. More or fewer target locations may be used. In the example shown in FIG. 13B, 16 target locations 1202a-1202p are shown. More or fewer target locations may be used. The target locations may also be different. The order in which the targets are presented at different locations may vary. For example, the target may move in a raster pattern from left to right across the user's field of view, then reverse from right to left, and then again from left to right, lowering the target's position within the field of view, with each lateral pass traversing the field of view. However, other patterns and approaches are also possible. Similarly, targets can be rendered at different locations, either similarly or differently. For example, the rendered targets may vary in size, shape, color, etc. Targets can be rendered to the user sequentially during the eye tracking calibration process. For example, as discussed above, the head-mounted display system may render targets in a serpentine pattern. For example, target 1202a may be followed by 1202b, then 1202c, then 1202d, then 1202h, then 1202g, etc. Other patterns are also possible. For example, targets may be displayed in a more random or non-sequential pattern. In some embodiments, a single target is displayed to the user, and the target moves around the user's field of view (e.g., passing through or temporarily stopping at positions 1202a-1202p during the target's movement). The head-mounted display system can obtain images of the user's retina while the user is viewing these targets.For example, the head-mounted display system can acquire a first image when the user is looking at a target at a first location 1202a, acquire a second image when the user is looking at a target at a second location 1202b, acquire a third image when the user is looking at a target at a third location 1202c, and so on. The wearable system can associate the first image with the first location 1202a, the second image with the second location 1202b, the third image with the third location 1202c, and so on. Adjacent images may be stitched together in a database to create a complete or partial retinal map. For example, two images can be stitched together in proper alignment using a feature or portion of a feature (e.g., a blood vessel or portion thereof) common to the images. In various implementations, adjacent target locations will produce overlapping images that can be aligned and stitched together. For example, target locations 1202a and 1202b and target locations 1202b and 1202c may produce overlapping and adjacent retinal images that may be stitched together. Thus, several different retinal images may be acquired using different eye lines of sight to assemble a larger image (e.g., a composite image or map) of the retina.

[0156] As discussed above, eye tracking can be performed using the synthetic retinal image or map. For example, after the target is no longer displayed, the user may shift their eye gaze as they view different real objects in front of the user and the head-mounted display or augmented reality (virtual) image content displayed by the head-mounted display. One or more retinal images may be acquired at these times. The terms "instantaneous" or "real-time" images may be used herein to describe images acquired following calibration that may be used for eye tracking (or other purposes, such as acquiring biometric data). These "instantaneous" or "real-time" images likely correspond to portions of the synthetic retinal image or map. The system may be configured to sufficiently match this "instantaneous" or "real-time" retinal image with the portion of the synthetic retinal image or retinal map. Such a match may be based on a feature or portion of a feature (a blood vessel or portion thereof) common to both the "instantaneous" or "real-time" retinal image and the portion of the synthetic retinal image or map. Based on the location of the portion of the synthetic retinal image or map to which this "instantaneous" or "real-time" retinal image matches, gaze direction may be inferred. Different gaze directions will result in retinal images corresponding to different portions of the retinal map. Thus, identifying the location of an "instantaneous" or "real-time" retinal image on a synthetic retinal image or map will provide information about the user's gaze direction. Eye tracking, e.g., tracking eye movement and changes in eye gaze, may be performed using such or similar methods. As discussed above, edge enhancement, edge detection, or other digital filtering and / or processing may be used to highlight different image features and / or correlate them with the synthetic retinal image or retinal map.

[0157] In various implementations, after completion of an initial calibration process in which virtual or fixation targets are displayed (e.g., in multiple locations) to assemble a synthetic retinal image or map, the synthetic retinal image or map can still be refined. For example, as additional retinal images are acquired, the synthetic retinal image or map can be further refined or improved using the additional images. Thus, as additional "instantaneous" or "real-time" retinal images are acquired, for example, for purposes of providing eye tracking, the synthetic retinal image or map can be further refined or improved using "instantaneous" or "real-time" images. As the user continues to look at various locations within the display (with or without the aid of a calibration target), the retinal synthetic image or map may be further refined using additional images obtained following the initial calibration in which virtual or fixation targets were displayed. The quality of the synthetic retinal image or map can therefore be increased.

[0158] Additional non-limiting examples of how eye tracking may be performed and / or synthetic retinal images or maps may be produced and how retinal images may be used are described in U.S. Patent Publication No. 2017 / 0205875, entitled "EYE IMAGE COLLECTION," filed January 17, 2017 (the disclosure of which is incorporated herein by reference in its entirety).

[0159] Thus, as discussed above, larger portions of the retina may be recorded and mapped by acquiring retinal images and / or other images of the eye using an imaging system such as those described herein, and such images may facilitate eye tracking. For example, the image of eye 210 shown in FIG. 13A may be captured when the eye is in an arbitrary position. Processing electronics or a processor (such as the same or different from those described above as forming a composite image) may then compare the real-time captured image of the user's retina with a stored composite or larger-size (e.g., full-size) image of the user's retina to track eye movement. A given image of the user's retina captured in real time may show a specific portion of the user's retina. As described above, by comparing such a captured image with a stored image of the user's mapping of larger portions of the user's retina, the system can determine the portion of the user's retina shown in the captured image, and thereby the eye position / orientation that would produce such an image. See, for example, FIG. 13A, which shows two different images of a portion of the retina produced when the eye is in two different positions and / or orientations. Thus, the position and / or orientation of the eye can be determined by capturing different images of the retina and determining the portions of the retina that are visible. Such determination can be performed even if a composite image is not formed; rather, multiple images of the retina for different eye positions / or orientations are recorded and stored in a database. As future images of the retina are acquired, they can be compared to images in the database of stored images to determine images in the database that are similar to recently acquired eye images. Matching a recent image to one or more of the images in the database with associated positions and / or orientations can enable the determination of the orientation and / or position of the more recent image. Other approaches to eye tracking can also be used based on images captured using the designs described herein.

[0160] As described herein, retinal images may be employed for other purposes as well. For example, retinal images may be used to verify that a user is the same user for whom a synthetic retinal image or map was acquired. Retinal images acquired while a user is wearing a head-mounted display system (e.g., during a calibration process and / or during subsequent use) may be compared to a stored, previously acquired synthetic retinal image or map (e.g., created the previous day or when the head-mounted display was previously booted up). If a recently acquired retinal image does not sufficiently match a portion of the synthetic retinal image or map, it may be concluded that the current user is different from the previous user (e.g., for whom the synthetic virtual image or map was created). Such methods may be used for security purposes, e.g., to verify that a current user of a head-mounted display device is the device's owner or typical user. Thus, biometric data acquired via retinal imaging may be used for security purposes.

[0161] Retinal imaging may also be used to collect biometric data for monitoring the health of a user. Medically relevant data may be obtained from retinal images. Such medical data may be useful for monitoring the health of a user.

[0162] Various applications of eye imaging, such as eye tracking, health monitoring, and collecting biometric data for security, are discussed herein in the context of retinal imaging, although imaging of other parts of the user, e.g., the user's eyes, may also be employed for these and other purposes.

[0163] While the eyepiece 950 is described above as being utilized to facilitate ocular imaging, the eyepiece can also be used to image the world in front of the user. Figures 14A-14B illustrate an exemplary imaging system 900 that may be used, for example, to image a portion of the environment in front of the user and / or objects within the portion of the environment. The imaging system 900 used may be similar to that described with respect to Figures 11A-11E and / or 12A-12E, except that light is collected by the eyepiece 950 from the environment in front of the eyepiece and the user. Figure 14A illustrates light 970 from the environment, for example, reflected from and / or emitted by one or more physical objects 972 in the environment in front of the user and eyepiece 950. As shown, light 970 from the environment may be nearly collimated because, for example, physical objects 972 in the environment may be located at a sufficiently long distance from imaging system 900 so that light rays reaching imaging system 900 are collimated or nearly collimated (e.g., at infinity). In some implementations, imaging system 900 may be configured to image the environment and / or objects within the environment without the use of any optical elements (e.g., lenses, mirrors) having refractive power within imaging system 900.

[0164] The imaging system 900 shown in Figures 14A and 14B is similar to the imaging systems described above. The imaging system includes an eyepiece 950 with one or more waveguides 940, including a coupling optical element 944, configured to direct light from an image projector 930 (not shown) into the eye 210 and form an image therein. The one or more waveguides may include multiple waveguides (e.g., a stack of waveguides) configured to in-couple / out-couple multiple corresponding colors / wavelengths. Each waveguide in the stack of waveguides may be configured to direct light of a particular color (e.g., red, green, blue). For example, the most distal waveguide (e.g., a stack of waveguides) may be configured for visible light (e.g., red, blue, green) such that the waveguides are configured to in-couple and out-couple the same wavelengths of visible light. Additionally or alternatively, a waveguide configured to in-couple and out-couple invisible (e.g., infrared) light may be positioned proximal to the eye 210. Such multiple waveguides corresponding to waveguide 940 may be used in any other implementations described herein. Imaging system 900 may also include an imaging device (e.g., a camera) 920 and an outcoupling optical element 952 configured to redirect light reflected from eye 210 to be propagated within waveguide 940 to the camera. In Figures 14A and 14B, illumination source 960 is omitted because an illumination source may not be needed to image the environment in front of the user. However, an illumination source (e.g., light source 960 described above) may be used in some designs.

[0165] Eyepiece 950, waveguide 940, coupling optical element 944, out-coupling optical element 952, and camera 920 may be the same as or similar to those described above. For example, coupling optical element 944 may be physically engaged with waveguide 940. For example, coupling optical element 944 and / or out-coupling optical element 952 may be positioned in an optical path between the environment in front of eyepiece 950 and camera 920 such that light from the environment is coupled into waveguide 940 via coupling optical element 944 and incident on camera 210 (e.g., to form an image of at least a portion of the environment) and coupled out of the waveguide via the out-coupling optical element. Coupling optical element 944 may comprise multiple turning features configured to redirect light guided in the waveguide out of the waveguide or to redirect light incident on coupling optical element 944 at an angle into the waveguide to be guided therein by total internal reflection. The out-coupling optical element 952 may comprise a plurality of turning features configured to redirect light (from the environment) that is guided at an angle within the waveguide so that the light is not guided within the waveguide by total internal reflection but is directed outward toward the camera. The coupling optical element 944, the out-coupling optical element 952, and each associated turning feature may physically engage with the waveguide 940. For example, the coupling optical element 944 and / or the out-coupling optical element 952 may comprise one or more holographic or diffractive optical elements (e.g., surface relief gratings) patterned (e.g., etched) within or on the waveguide 940. The coupling optical element 944 and / or the out-coupling optical element 952 may comprise a layer disposed on the waveguide 940 or may be formed within the waveguide 940. For example, a volume holographic or diffractive optical element may be formed by varying the refractive index of a material comprising the waveguide or a layer disposed thereon. Thus, the coupling optical element 944 and / or the out-coupling optical element 952 may be disposed within the volume of the waveguide 940 or a layer disposed thereon. Depending on the design, the coupling optical element 944 and / or the out-coupling optical element 952 may be transmissive or reflective and may operate transmissively or reflectively.For example, the coupling optical element 944 and / or the out-coupling optical element 952 may each operate transmissively or reflectively, e.g., include a transmissive or reflective diffractive optical element (e.g., a grating) or a holographic optical element that redirects light transmitted therethrough or reflected therefrom. The coupling optical element 944 and / or the out-coupling optical element 952 may include a polarization optical element, such as a polarization-selective redirecting element (e.g., a polarizer). The polarization-selective redirecting element may include one or more polarization gratings, diffractive optical elements, and / or holographic optical elements, and may comprise a liquid crystal structure, such as a liquid crystal polarization grating. In some implementations, the reflective optical element may include a reflector (e.g., a mirror). Other elements, such as the waveguide 940, may similarly be similar to those described above.

[0166] FIG. 14B illustrates the operation of the imaging system 900 shown in FIG. 14A . Light 970 from the environment is coupled into the waveguide 940 by the coupling optical element 944. The coupling optical element 944 may be configured to redirect this collimated light at an angle greater than the critical angle of the waveguide 940, such that at least a portion of the collimated light is guided toward the camera 920 by total internal reflection within the waveguide. The out-coupling optical element 952 can be configured to receive at least a portion of the light from the environment in front of the user that is coupled into and guided within the waveguide 940 via the coupling optical element 944. The out-coupling optical element 952 may be configured to couple the in-coupled light out of the waveguide 940 and toward the camera 920 so that an image of the environment can be captured by the camera 920. The image of the environment may be passed to processing electronics (e.g., one or more processors), such as the data module 140 (see FIG. 2 ). The data module 140 may be configured to recreate a modified image of the environment within an augmented reality context. The processing electronics may communicate with the camera 920 via wired or wireless electronic signals. Additionally or alternatively, the processing electronics may communicate with the camera 920 using one or more remote receivers. The processing electronics may reside remotely (e.g., a cloud computing device, a remote server, etc.).

[0167] The present imaging system 900 may therefore be used to image an environment directly, which may be useful for a variety of reasons. For example, imaging the environment can be used to determine where augmented reality image content should be placed relative to objects in the environment. For example, imaging the environment may provide the location of a table so that a head-mounted display may render an image of a person standing next to the table instead of on or in the table. The imaging system 900 described with respect to imaging an environment may also be used to image the eye 210 as described with respect to FIGS. 10, 11A-11E, and / or 12A-12E.

[0168] It may be desirable to image a wide field of view of an environment using imaging system 900. FIG. 14C schematically illustrates imaging system 900 for collecting light from an environment using a refractive optical element or lens, such as a refractive optical element 980 (e.g., a wide-angle lens) in front of the eyepiece. The refractive optical element 980 may have positive refractive power. The refractive optical element 980 (e.g., a positive lens) focuses collimated light 970 from the environment toward waveguide 940. Lens types other than those shown in FIG. 14C may be employed. Transmitted light (not shown) may pass through a refractive optical element or lens, such as a refractive optical element 990 (e.g., a negative lens), configured for an equal but opposite negative refractive power of refractive optical element 980. The negative lens 990 may have a similar or identical refractive power as the positive lens 980 and may offset or cancel the refractive power of the positive lens, or a portion thereof. In this way, light from the environment (e.g., distal to waveguide 940) can pass through negative lens 990, eyepiece 950, and positive lens 980, with substantially no net change in the refractive power introduced to the eye by these two lenses. Negative lens 990 may be configured to offset or counteract the refractive power of positive lens 980, so that a user will not experience the refractive power of the positive lens when viewing the environment in front of eyepiece 950. Negative lens 990 will also counteract the effect of positive lens 980, inverting the image of objects in the environment in front of the wearer. Some light 970 from the environment can be indirectly coupled into waveguide 940 by coupling optical element 944, despite some of the light rays converging. Indirectly coupled light incident on outcoupling optical element 952 can be emitted out of waveguide 940.

[0169] Implementations (e.g., those described by FIGS. 14A-14C ) may be used outside of the augmented reality context. For example, an imaging system 900 configured to image an environment is intended to be implemented in a wearable device, such as, for example, eyeglasses (including non-refractive eyeglasses) or bifocals. Such an imaging system 900 may not require an image projector 930 and / or a light source 960. Additionally or alternatively, such an imaging system 900 may not require internal coupling optical elements configured for a corresponding image projector 930 and / or light source 960.

[0170] It may be advantageous to implement such an imaging system 900 to image an environment onto a viewing screen (e.g., television screen, computer screen) of a handheld device (e.g., cell phone, tablet), etc. The imaging system 900 may improve video chat capabilities. For example, a viewer who sees a chat partner may look at the screen and appear to be looking directly at the viewer. This may be possible because the light rays captured by the imaging system 900 will be captured within the same area the user is looking at (as opposed to viewing a screen, for example, with the light rays captured by a separate outward-facing camera positioned in a different location).

[0171] In implementations in which the imaging system 900 of FIG. 14C is also used to image the eye 210, the light source 960 and / or image projector 930 may be configured to launch light into the waveguide 940. Light reflected from the eye that is incoupled into the waveguide will pass through a refractive optical element 990 (e.g., a negative lens), so a positive power type refractive optical element may be positioned between the light source 960 and / or image projector 930 and the waveguide 940. The positive lens can be configured to offset or cancel any refractive power provided by the refractive optical element 990 before the incoupled light from the light source and / or light projector is incident on the eye 210. Lenses of types other than those shown in FIG. 14C may also be used as the optical element 990. Alternatively, or in addition, processing electronics in communication with the light source and / or image projector can be configured to modify the image sufficiently to present an undistorted image to a user after the light passes through the refractive optical element 990. The corresponding internal coupling optical element, external coupling optical element, and / or coupling optical element may, in some designs, be configured to operate on non-collimated light (e.g., diverging, converging light).

[0172] In various implementations, the same waveguide 940 may be used to (i) transmit light from the eyepiece 950 and the environment in front of the user to the camera 940, and (ii) transmit light from the image projector 930 to the eye 210 and form image content therein. Using the same waveguide 940 may simplify the system and / or eyepiece, making it more compact and potentially providing a reduced form factor. Reducing the thickness of the eyepiece 950 by reducing the number of waveguides 940 may be advantageous for other reasons as well. Lower cost and a simpler manufacturing process may be some such advantages.

[0173] Also, in various designs, the same or different imaging systems may be used within the same head-mounted display to image the eye, for example, by transmitting light from the eye through a waveguide in the eyepiece 950 to the camera 940, as described above. Such systems may also use the eyepiece to transfer light from an illumination source to the eye 210 to illuminate the eye. In some designs, the eyepiece may additionally be used to transmit light from the image projector 930 to the eye 210 and form image content therein. Using the eyepiece to image the environment and to assist in imaging the eye (and potentially illuminating the eye) may simplify the system and / or make it more compact, potentially providing a reduced form factor.

[0174] Furthermore, in some implementations, the same waveguide 940 may be used to (i) transmit light from the environment in front of the eyepiece 950 to the camera 940 and (ii) transmit light from the eye 210 to the camera to capture an image of the eye. The same waveguide may be used to transmit light from the image projector 930 to the eye 210 to form image content therein, and / or to transmit light from the illumination source 960 to the eye 210 to illuminate the eye for image capture. Using the same waveguide 940 may simplify the system and / or eyepiece, making them more compact and potentially providing a reduced form factor. Reducing the thickness of the eyepiece 950 by reducing the number of waveguides 940 may be advantageous for other reasons as well. Lower cost and a simpler manufacturing process may be some such advantages.

[0175] Similarly, in addition to coupling light from the environment into waveguide 940, identical coupling optical element 944 may be configured to direct light from image projector 930 to eye 210 to form image content therein and / or to direct light from the eye into waveguide 940 to be directed therein to camera 920. Additionally or alternatively, identical coupling optical element 944 may be configured to couple light from illumination source 960 that is guided within waveguide 940 out of the waveguide and into user's eye 210.

[0176] As discussed above, one or more of coupling optical element 944, internal coupling optical element 942, or external coupling optical element 952 may comprise a polarization-selective coupling element. Thus, in various designs, light input into eyepiece 950 or waveguide 940 is polarized so as to be appropriately acted upon by the polarization-selective redirecting element.

[0177] Thus, in some embodiments, illumination source 960 comprises a polarized source of a suitable polarization to be appropriately acted upon by the polarization selective combining / redirecting element.

[0178] One or more polarization-specific optical filters and polarization-modifying elements may be included in various imaging systems 900, such as those in which the image projector 930 and / or light source 960 are positioned directly opposite each other through the waveguide 940. The polarization-sensitive element may be useful in reducing directional light emission into the imaging device 920 and / or reducing saturation of the imaging device 920, for example, in configurations in which these elements are aligned on opposite sides of the waveguide 940 at the same lateral position. FIGS. 15A-15B illustrate such configurations. The light source 960, as shown in FIG. 15A, can be configured to direct light through a polarization-specific optical filter 982, such as a polarizer (e.g., a linear polarizer), and / or through a polarization-modifying element 986 configured to alter the polarization state of the incident light, such as a polarization rotator. A retarder, such as a half-wave retarder, may, for example, rotate linear polarization. Thus, a properly oriented half-wave retarder or half-wave plate can rotate s-polarized light to p-polarized light or vice versa. Thus, in various implementations, a polarization-specific optical filter 982 and / or polarization-modifying element 986 is positioned in the optical path between light source 960 and internal coupling optical element 942 to provide properly oriented polarized light to the internal coupling optical element. In some implementations, imaging system 900 does not include a polarization-modifying element, but does include a properly oriented polarizing optical filter, such as a polarizer.

[0179] Light emitted by light source 960 may pass through an array of optical elements in a particular order. For example, as shown in Figure 15A, light may first pass from light source 960 through a polarization-specific optical filter 982 (e.g., a polarizer) and then through a polarization-modifying element 986 (e.g., a rotator). After the light passes through polarization-modifying element 986, it may be incident on an in-coupling optical element 942, which may direct the light into waveguide 940 to be guided therein.

[0180] For example, the light source 960 may be configured to emit light of mixed polarizations (e.g., s-polarized and p-polarized). The polarization-specific optical filter 982 may be configured to transmit only light of a first polarization state (e.g., p-polarized). As the light continues, the polarization-modifying element 986 may be configured to change the polarization state of the light (e.g., from p-polarized to s-polarized). The internal coupling optical element may be configured to redirect s-polarized light to an angle above the critical angle of the waveguide such that s-polarized light is guided within the waveguide. The internally coupled light 904 may be substantially polarized in a second polarization (s-polarized) as it propagates through the waveguide 940. The coupling optical element 944 may be configured to redirect only light of the second polarization state (s-polarized). The coupling optical element 944 may be configured to couple the internally coupled light 904 out of the waveguide 940 and into the eye 210 to provide illumination for image capture.

[0181] To prevent direct illumination (e.g., saturation) of the imaging device 920, a polarization-modifying element 958 and / or a polarization-specific optical filter 984 may be disposed in or on the waveguide 940 such that only light of a certain polarization state (e.g., p-polarized light) may pass through the polarization-specific optical filter 984 to the imaging device 920. The polarization-modifying element 958 (e.g., a half-wave plate) may be configured to change the state of polarization (e.g., from s-polarized light to p-polarized light). The polarization-specific optical filter 984 may be configured to transmit only light of a certain polarization (e.g., p-polarized light) therethrough. In this way, light passing through the polarization-specific optical filter 982 will not be configured to transmit directly through the polarization-specific optical filter 984. In any of the above implementations (e.g., image projector 930 and / or light source 960 are on the same optical axis, as shown in FIG. 15A ), as in FIGS. 10 , 11A-11E, and 12A-12E, the configuration of polarization-specific optical filter 982, polarization-modifying element 986, internal coupling optical element 942, polarization-modifying element 958, and / or polarization-specific optical filter 984 may be implemented according to the design of FIG. 15A . Polarization-specific optical filter 984 may be a transmissive-reflective polarizer (e.g., a polarizer beamsplitter) configured to transmit light of a first polarization and redirect or reflect light of a second polarization different from the first.

[0182] A partially reflective element (e.g., a semi-transparent mirror) may be included to redirect the internally coupled light 904 to the imaging device 920. The partially reflective element may be disposed between the internal coupling optical element 942 and the polarization-modifying element 986 so that a portion of the internally coupled light 914 is reflected toward the imaging device 920 while reducing leakage of the internally coupled light 914 out of the waveguide 940. The fraction of light that does not leak may be any percentage between 0 and 1. For example, the fraction may be 0.90, such that 90% of the light rays propagating through the waveguide 940 along the coupling optical element 944 are maintained within the waveguide 940 at each reflection of the light rays. Other fractions are also possible (e.g., 0.10, 0.20, 0.30, 0.40, 0.50, 0.60, 0.70, 0.80, or any value in a range between these values).

[0183] 15B illustrates the propagation of light reflected or scattered from the retina. A portion of the light 910 reflected from the retina, having a second polarization (s-polarization), incident on the coupling optical element 944, can be redirected by the coupling optical element 944 at an angle above the critical angle of the waveguide 940 and thus guided therein. A portion of the light cannot be coupled into the waveguide 940 and will transmit therethrough as non-incoupled light 912. The incoupled light 904 can propagate through the waveguide 940 toward the camera.

[0184] Other implementations may also benefit from the use of polarization-selective elements proximal to the light source and camera. For example, various systems can be configured to provide illumination with a first polarization and capture images with a camera using light with a different polarization. For example, such a configuration may be used to reduce unwanted reflections from the cornea, etc., when imaging the retina. Reflections from the cornea will be specular. Thus, if light of a first polarization is incident on the cornea, the light reflected from the cornea will retain its first polarization. In contrast, the retina is diffuse. If light of a first polarization is incident on the retina, the light reflected from the retina will not retain only the first polarization. Diffuse reflection is more likely to result in unpolarized light. Thus, a second polarization different from the first polarization will be present in the reflected light. Similarly, by illuminating with a first polarization and imaging with a second, different polarization, the retina can be imaged with reduced glare from the cornea.

[0185] Thus, in various implementations, polarization-specific optical filters 982, 984 may both be used to reduce unwanted light reflected from eye 210 (e.g., from the cornea). For example, unwanted light, glare, or glint may be reflected from the cornea, which may saturate the image captured by imaging device 920. Light reflected from the cornea may be specular and maintain its polarization. In contrast, light reflected from the retina may be more diffusely reflected and less homogeneously polarized. Similarly, a combination of polarizers may be used to remove some or most of the unwanted reflected light. Initially, polarized light can be used to illuminate eye 210. In some designs, a polarized illumination source (e.g., light source 960) may be used. Additionally or alternatively, a first polarizer (e.g., polarization-specific optical filter 982) may be positioned at the beginning of the optical path of the illumination source to provide an initial polarization of the light. A second polarizer (e.g., polarization-specific optical filter 984) may be positioned in the optical path before the light enters imaging device 920. The second polarizer polarizes the light 90 degrees from the first polarizer. oThe polarizers 982, 984 may be rotated (e.g., the polarizers 982, 984 may be "crossed"). As a result, the eye is illuminated with a first polarization, and some light of the first polarization will be reflected from the cornea. This light will not pass through the polarizer 984 proximal to the camera. However, light reflected from the retina will include the second polarization. Similarly, light diffusely reflected from the retina will pass through the polarizer 984 proximal to the camera, allowing an image of the retina to be captured by the camera. Thus, in such a configuration, undesired light received from the eye (e.g., from the cornea) that may enter the imaging device 920 can be reduced or eliminated. Other configurations are also possible. For example, the polarization-selective in-coupling optical element 942 for coupling light from the light source 960 into the waveguide 940 and the polarization-selective out-coupling optical element for coupling light out of the waveguide to the camera 920 may be employed to have different polarization selectivity properties. For example, a polarization-selective in-coupling optical element may selectively redirect light from an illumination source having a first polarization into a waveguide, while an out-coupling optical element may selectively redirect light of a second, different polarization out of the waveguide to a camera. The effect may again be to reduce or eliminate undesired light received from the eye (e.g., from the cornea) before entering imaging device 920.

[0186] Various imaging systems 900 capable of collecting light and imaging the retina using an eyepiece 950 are discussed herein. However, the imaging system 900 can also be configured to image other portions of the eye, such as the anterior portion of the eye. FIG. 16 illustrates how the imaging system 900 can be used to image the anterior portion (e.g., the cornea) of the eye 210. The imaging system 900 may include one or more elements of the exemplary imaging system 900 described above. In addition, the exemplary imaging system 900 may include one or more refractive power optical elements or lenses, such as refractive power optical elements 980, 990, having refractive power. For example, a positive power lens or positive lens 980 may be positioned on the proximal side (e.g., closer to the eye 210) of the eyepiece 950 between the eye 210 and the eyepiece. A negative refractive power lens or negative lens 990 may be positioned on the distal side of the eyepiece 950 between the eyepiece and the environment in front of the user. One or both of the lenses 980, 990 may be a variable focus element (e.g., a variable focus lens) and / or may include a liquid crystal element. In some designs, one or both of the lenses 980, 990 include a Fresnel lens. The lenses 980, 990 may incorporate liquid crystals to produce Fresnel lens functionality. Such functionality may enable variable focus of one or both of the lenses 980, 990. In some designs, one or more of the lenses 980, 990 may be integrated with and / or manufactured on or within (e.g., formed in) the eyepiece 950.

[0187] In various embodiments, the coupling optical element 944 is configured to redirect collimated light reflected from the eye 210 into the light guide to be guided therein. The positive lens 980 may thus be configured to collimate light reflected from the eye 210, such as from the anterior portion of the eye (e.g., the cornea). The positive lens 980 may therefore have a focal length that is equal to or substantially equal to the distance of the lens to the portion of the eye 210 to be imaged, e.g., the cornea.

[0188] The negative lens 990 may have a similar or identical refractive power as the positive lens 980 and offset or cancel the refractive power of the positive lens. In this way, light from the environment (e.g., distal to the waveguide 940) may pass through the negative lens 990, the eyepiece 950, and the positive lens 980, with substantially no net change in the refractive power introduced by these two lenses. Thus, the negative lens 990 may be configured to offset or cancel the refractive power of the positive lens 980 so that the user will not experience the refractive power of the positive lens when viewing the environment in front of the eyepiece 950. The negative lens 990 will also counteract the effect of the positive lens 980, inverting the image of objects in the environment in front of the wearer.

[0189] FIG. 16 illustrates light 928 incident on and scattered from the cornea. The imaging system 900 may be configured to capture this light 988 reflected from the cornea. For example, a positive lens 980 may collect a portion of the light 988 scattered from the cornea and collimate the light 988. The light 988 collimated by the positive lens 980 is incident on a coupling optical element 944, which is configured to redirect the collimated light into a waveguide 940 at an angle greater than the critical angle of the waveguide so that the light is guided therein by TIR. The coupling optical element 944, the out-coupling optical element 952, and / or the waveguide 940 may be as described above. The resulting out-coupled light 906 may be directed by the out-coupling optical element 952 out of the waveguide 940 to a camera (not shown).

[0190] FIG. 16 shows light 928, such as collimated light, that may result from the eyepiece 950 as described above. An illumination source 960 may couple light into a waveguide 940, and a coupling element 944 may couple this light from the illumination source 960 out of the waveguide. The coupling element 944 may be configured to couple the light out of the waveguide 940 as collimated light. This light illuminates and scatters from the anterior portion of the eye (e.g., the cornea). As discussed above, this scattered light 988 can be collected by a positive lens 980 and imaging system 900 to form an image of the anterior portion of the eye 210. Also, as discussed above, this illumination 928 directed onto the eye 210 may be invisible (e.g., infrared) light.

[0191] FIG. 16 also shows alternative arrangements for illuminating the eye 210. In some designs, one or more light sources 934, such as LEDs or emitters, may be positioned relative to the eye 210 and guided by TIR through a waveguide 940 to direct light thereon, rather than directly onto the eye 210. In some implementations, an eyepiece 950 or waveguide 940 is not in the optical path between the one or more light sources 934 and the eye 210. In some designs, multiple such light sources 934 may be arranged in a pattern (e.g., a circular or ring-like pattern) near and / or around the eye. In some designs, the pattern of light sources 934 may define an illumination axis parallel (e.g., coaxial) with the optical axis of one or more lenses 980, 990. The one or more light sources 934 may be similar to the one or more light sources 960 described above and may be pulsed, for example. Similarly, the one or more light sources 934 may comprise an infrared light source, such as an infrared LED, or another type of invisible light. Alternatively, the one or more light sources may comprise a visible light source that emits visible light, or the one or more light sources may emit both visible and invisible (e.g., infrared) light.

[0192] FIG. 17 illustrates another exemplary imaging system 900 configured to image a portion of the eye 210, such as the anterior portion of the eye (e.g., the cornea). The imaging system 900 shown in FIG. 17 employs a reflective optical element 996 configured to collimate light from the eye, in contrast to the transmissive optical element (lens) 980 shown in FIG. 16. A reflective optical element will have fewer aberrations than a transmissive optical element because chromatic aberrations are generally not applicable to reflective optical elements, such as the reflector 996 shown in FIG. 17. Thus, by using a reflective surface in collecting light from the eye 210, less (e.g., chromatic) aberrations are introduced into the captured image of the eye.

[0193] 17, for example, illustrates an imaging system 900 including a curved transmissive optical element 996 having a wavelength-dependent reflective coating 998. The curved transmissive optical element 996 may be positioned distal to the waveguide 940 (on the environment side of the eyepiece 950). Thus, the curved transmissive optical element 996 may be positioned between the environment in front of the wearer and the waveguide 940 and / or the coupling optical element 944. Similarly, the waveguide 940 and / or the coupling optical element 944 may be positioned between the curved transmissive optical element 996 and the eye 210.

[0194] The wavelength-dependent reflective coating 998 may be configured to reflect light of a certain wavelength or range of wavelengths. In some implementations, for example, the wavelength-dependent reflective coating 998 may be configured to reflect invisible light (e.g., infrared light) within a certain wavelength range, while the wavelength-dependent reflective coating 998 may be configured to transmit visible light. The wavelength-dependent reflective coating 998 may, in some cases, be disposed on a surface of the curved transmissive optical element 996.

[0195] As discussed above, in various designs, the coupling optical element 944 is configured to redirect collimated light reflected from the eye 210 into the waveguide 940 to be guided therein. Thus, the reflective optical element 996 may be configured to collimate light reflected from the eye 210, such as from an anterior portion of the eye (e.g., the cornea). The curved reflective optical element 996 may therefore have positive optical power with respect to light incident on its proximal side that is reflected from the wavelength-dependent reflective coating 998. Notably, in various designs, the reflective optical element 994 may have a focal length that is equal to or substantially equal to the distance from the reflective optical element 996 to the portion of the eye 210 to be imaged, e.g., the cornea, iris, etc. Exemplary values ​​for the focal length may be, for example, 2 cm to 8 cm. In some implementations, the focal length is 4 cm to 6 cm. In some designs, the focal length is approximately 5 cm. The focal length may be within any range formed by any of these values, or may be outside such ranges in different designs.

[0196] In various implementations, the reflective optical element 996 is positioned on the distal side of the eyepiece 950, in front of the eyepiece. Thus, the reflective optical element 996 is positioned between the eyepiece 950 and the environment in front of the user. Similarly, the eyepiece 950 is positioned between the reflective optical element 996 and the eye 210.

[0197] The curved transmissive optical element 996 may have a curved reflective surface with any shape of curvature. In some implementations, the surface is rotationally symmetric. In some implementations, the surface may be spherical or aspherical (e.g., parabolic). Non-rotationally symmetric shapes are also possible. However, in various designs, the reflective surface has positive optical power. The reflective optical element 996 may, for example, comprise a concave mirror, at least for certain wavelengths and / or polarizations.

[0198] The curved transmissive optical element 996 may be configured to have negligible optical power in transmission. Similarly, the curved transmissive optical element 996 may be configured to transmit light without introducing convergence or divergence. In one example, the curved transmissive optical element 996 may have an inner radius curvature that is substantially the same as the outer radius curvature. A thin optical element 996 may, for example, reduce optical aberrations with respect to light transmitted therethrough, may be lighter in weight, and / or may be more compact.

[0199] In various designs, the reflective optical element 996 includes a material that is transmissive to visible light so that the user can see the environment in front of the wearer. In some cases, to improve transmission, the curved transmissive optical element 996 may be coated with an anti-reflective coating on an outer surface (e.g., a distal surface). The anti-reflective coating may be configured to reduce reflection of visible light, such as red, green, and / or blue light. However, the reflective optical element 996 may be configured to reflect a portion of light scattered from the eye 210 to form an image of the eye. Thus, the reflective optical element 996 may act differently on different light. For example, the reflective optical element 996 may act differently on different wavelengths. The reflective optical element 996 may be configured to reflect infrared light and transmit visible light.

[0200] As discussed above, one or more light sources 934 may be configured to illuminate the eye 210 with infrared light. The resulting light 988 reflected from the eye 210 (e.g., the cornea) may diverge, as illustrated diagrammatically in FIG. 17 . A curved transmissive optical element 996 may be positioned to receive this light 988 reflected from the eye (e.g., the cornea, the iris). A wavelength-dependent reflective coating 998 may be configured to reflect the light 988 reflected from the eye because the wavelength illumination used to illuminate the eye is the same wavelength (e.g., 850 nm) reflected by the reflective coating on the curved transmissive optical element 996. For example, the eye may be illuminated with infrared light (e.g., 850 nm), and the curved transmissive optical element 996 may be configured to reflect the infrared light (e.g., 850 nm) and pass visible light. The shape of the curved transmissive optical element 996 may also be configured to collimate the light 988 reflected from the eye and reflect the light to the coupling optical element 944, which redirects the collimated light into the waveguide 940 to be guided therein by TIR.

[0201] In FIG. 17 , one or more light sources 934, such as LEDs or emitters, may be positioned relative to the eye 210 and guided by TIR through a waveguide 940 to direct light thereon, rather than being directed onto the eye 210, as in certain other designs. In some implementations, an eyepiece 950 or a waveguide 940 is not in the optical path between the one or more light sources 934 and the eye 210. In some designs, multiple such light sources 934 may be arranged in a pattern (e.g., a circular or ring-like pattern) near and / or around the eye. In some designs, the pattern of light sources 934 may define an illumination axis that is parallel (e.g., coaxial) with the optical axis of one or more lenses 980, 990. The one or more light sources 934 may be similar to the one or more light sources 960 described above and may be pulsed, for example. Similarly, the one or more light sources 934 may comprise an infrared light source, such as an infrared LED, or another type of invisible light. However, other types of light sources may also be used.

[0202] FIG. 18 illustrates another exemplary imaging system 900 configured to image a portion of the eye 210, such as the anterior portion of the eye (e.g., the cornea). In the implementation shown in FIG. 18, polarization selectivity is employed to help control the path of light reflected from the eye. In particular, in various designs, the coupling optical element 944 is polarization selective. For example, light having a first polarization is transmitted through the coupling optical element 944, while light of a second, different polarization is redirected by the coupling optical element 944 into the waveguide 940 to be coupled therein by TIR. Thus, in various implementations, the eye 210 is illuminated with polarized light, or a polarizer (not shown) is positioned between the eye and the waveguide 940 so that light from the eye that is incident on the waveguide is polarized. For example, the emitter 934 may emit polarized light, or a polarizer may be positioned in front of the emitter 934 so that the eye 210 is illuminated with polarized light. Thus, in various designs, the polarization of the polarized light received by the optical coupling element 944, incident on and / or reflected from the eye 210 may be a first polarization such that the light is directed to the reflector 996.

[0203] Similarly, in various implementations, the coupling optical element 944 (and / or the out-coupling optical element 952) are each configured to transmit light of a first polarization state, such as a first linear, circular, or elliptical polarization state (e.g., p-polarized, left-handed, or elliptically polarized, etc.), and redirect light of a second polarization state, such as a second linear, circular, or elliptical polarization state (e.g., s-polarized, right-handed, or elliptically polarized, etc.), into and / or out of the waveguide. In some implementations, the eye illuminator 934 may further include a polarization-modifying element (e.g., a polarizer) that may emit only or primarily the first polarization (e.g., p-polarized) or that is configured to transmit only light of the first polarization state (e.g., p-polarized). Additionally, the coupling optical element 944 and / or the out-coupling optical element 952 may each be configured to redirect light of a second polarization (e.g., s-polarized) into and / or out of the waveguide.

[0204] Similar to the imaging system 900 shown in FIG. 17, the curved reflector 998 shown in FIG. 17 comprises a curved transmissive optical element 996 having a wavelength-dependent reflective coating 998. The wavelength-dependent reflective coating 998 may be configured to reflect light of a certain wavelength or range of wavelengths. In some implementations, for example, the wavelength-dependent reflective coating 998 may be configured to reflect invisible light (e.g., infrared light) within a certain wavelength range, while the wavelength-dependent reflective coating 998 may be configured to transmit visible light. The wavelength-dependent reflective coating 998 may, in some cases, be disposed on a surface of the curved transmissive optical element 996.

[0205] In various implementations, the curved transmissive optical element 996 is positioned on the distal side of the eyepiece 950, in front of the eyepiece. Thus, the reflective optical element 996 is positioned between the eyepiece 950 and the environment in front of the user. Similarly, the eyepiece 950 is positioned between the reflective optical element 996 and the eye 210.

[0206] Thus, light having a first polarization (e.g., p-polarized light) from the eye 210 is incident on the combining optical element 944 and passes therethrough to the curved transmissive optical element 996. The imaging system 900 further includes a polarization-modifying optical element 978, such as a retarder (e.g., a quarter-wave retarder). The retarder 978 is transmissive and imparts a quarter-wave phase difference to the light transmitted therethrough. The light is incident on and reflected from the curved transmissive optical element 996. The wavelength-dependent reflective coating 998 may be configured to reflect certain wavelengths of light reflected from the eye. As a result, the light is reflected from the curved surface of the curved transmissive optical element 996 and collimated. The collimated light again passes through the retarder 978, thereby imparting another quarter-wave phase difference to the light transmitted therethrough. The phase difference (e.g., full-wave phase difference) introduced in these two passes through the retarder rotates the polarization. Thus, the first polarization (e.g., p-polarized light) transmitted through the polarization-selective coupling optical element 944 on the first pass is converted to the second polarization (s-polarized light) and redirected into the waveguide 940 to be guided by TIR to the camera 920. As discussed above, in various designs, the coupling optical element 944 is configured to redirect collimated light reflected from the eye 210 into the waveguide 940 to be guided therein. Thus, the reflective optical element 996 may be configured to collimate light reflected from the eye 210, such as from the anterior portion of the eye (e.g., the cornea). The curved reflective optical element 996 may therefore have positive optical power. In particular, in various designs, the reflective optical element 994 may have a focal length that is equal to or substantially equal to the distance from the reflective optical element 996 to the portion of the eye 210 to be imaged, such as the cornea, iris, etc. Exemplary values ​​for the focal length may be, for example, 2 cm to 8 cm. In some implementations, the focal length is 4 cm to 6 cm. In some designs, the focal length is approximately 5 cm.

[0207] In various designs, the reflective optical element 996 may comprise a curved surface configured to reflect light. The curved surface may, in some cases, be spherical or rotationally symmetric. The reflective optical element 996 may comprise, for example, a concave mirror, at least for certain wavelengths and / or polarizations.

[0208] In various designs, the reflective optical element 996 includes a material that is transparent to visible light so that the user can see the environment in front of the wearer. A wavelength-dependent reflective coating 998 disposed on the surface of the curved transmissive optical element 996 may therefore be transparent to visible light, or at least some wavelengths of visible light. The curved transmissive optical element 996 may also be coated with an anti-reflective coating on an outer surface (e.g., a distal surface). The anti-reflective coating may be configured to reduce reflection of red, green, and / or blue light. However, the reflective optical element 994 may be configured to reflect a portion of light scattered from the eye 210 to form an image of the eye. Thus, the reflective optical element 996 may act differently on different light. For example, the reflective optical element 996 may act differently on light of different polarization states (and / or wavelengths). The reflective optical element 996 may be configured to transmit visible light and reflect infrared light.

[0209] As shown in FIG. 17 , one or more light sources 934, such as LEDs or emitters in FIG. 18 , may be positioned relative to the eye 210 and guided by TIR through a waveguide 940 to direct light onto, but not onto, the eye 210. Thus, in some implementations, an eyepiece 950 or a waveguide 940 is not in the optical path between the one or more light sources 934 and the eye 210. In some designs, multiple such light sources 934 may be arranged in a pattern (e.g., a circular or ring-like pattern) near and / or around the eye. The one or more light sources 934 may be similar to the one or more light sources 960 described above and may be pulsed, for example. Similarly, the one or more light sources 934 may comprise an infrared light source, such as an infrared LED, or another type of invisible light. Notably, in various implementations, the light source 934 may emit light that is reflected by a wavelength-dependent reflective coating 998 and / or a curved transmissive optical element 996. However, other types of light sources may also be used.

[0210] The polarization-selective coupling optical element 944 is configured to be polarization-selective depending on the type of linearly polarized light incident thereon, although other polarization-selective coupling optical elements may be polarization-selective for other types of polarization states, such as different types of circular or elliptical polarizations. The polarization-selective coupling optical element 944 may be configured, for example, such that a first polarization, such as a first circularly or elliptically polarized light (e.g., left-handed or LHP-polarized light), is transmitted through the polarization-selective coupling optical element 944 and a second polarization, such as a second circularly or elliptically polarized light (e.g., right-handed or RHP-polarized light), is redirected into the light guide, or vice versa. Such polarization-selective coupling optical elements 944 may comprise liquid crystals, such as cholesteric liquid crystals. Examples of some liquid crystal optical elements are discussed below in the section entitled "Cholesteric Liquid Crystal Mirrors," in U.S. Patent Publication No. 2018 / 0164627, entitled "DIFFRACTIVE DEVICES BASED ON CHOLESTERIC LIQUID CRYSTAL," filed December 7, 2017, and in U.S. Patent Publication No. 2018 / 0239147, entitled "DISPLAY SYSTEM WITH VARIABLE POWER REFLECTOR," filed February 22, 2018, and in U.S. Patent Publication No. 2018 / 0239177, entitled "VARIABLE-FOCUS VIRTUAL IMAGE DEVICES BASED ON POLARIZATION CONVERSION," filed February 22, 2018 (each of which is incorporated by reference herein in its entirety and for all purposes).

[0211] A polarization modifying element or retarder, such as a circular polarizer, may be positioned between the eye and the polarization selective coupling optical element 944 to convert light reflected from the eye to a first polarization (e.g., LHP). The LHP light will pass through the polarization selective coupling optical element 944, reflect off the reflector 998, change polarization to RHP, and be redirected by the polarization selective coupling optical element 944 into the waveguide to the camera.

[0212] In some implementations, the reflector 996 may be polarization-selective in its reflectivity, such that only light of one polarization state is reflected and / or light of a different polarization state is transmitted. Such optical elements may comprise liquid crystals, such as cholesteric liquid crystals. Examples of such optical elements are discussed below in the section entitled "Cholesteric Liquid Crystal Mirror," in U.S. Patent Publication No. 2018 / 0164627, entitled "DIFFRACTIVE DEVICES BASED ON CHOLESTERIC LIQUID CRYSTAL," filed December 7, 2017, and in U.S. Patent Publication No. 2018 / 0239147, entitled "DISPLAY SYSTEM WITH VARIABLE POWER REFLECTOR," filed February 22, 2018, and in U.S. Patent Publication No. 2018 / 0239177, entitled "VARIABLE-FOCUS VIRTUAL IMAGE DEVICES BASED ON POLARIZATION CONVERSION," filed February 22, 2018 (each of which is incorporated by reference herein in its entirety and for all purposes). Such an optical element may reflect light of a first polarization state, such as a first circular or elliptical polarization state (e.g., left-handed or elliptically polarized), and transmit light of a second polarization state, such as a second circular or elliptical polarization state (e.g., right-handed or elliptically polarized), or vice versa. In some embodiments, liquid crystals are disposed on the curved surface of the reflector 996 such that, in reflection, the reflector has a refractive power, such as a positive refractive power. In various other implementations, the liquid crystal optical element may be flat or planar. For example, the liquid crystals may be disposed on a flat or planar substrate or layer. Despite being flat, refractive power may be included within the liquid crystal optical element. Such an element may be referred to as a cholesteric liquid crystal reflective lens. Thus, light from the eye may be collimated and reflected to the combining optical element 998. The reflector may, for example, reflect light of a first polarization state (e.g., left-handed or elliptically polarized) and transmit light of a second polarization (e.g., right-handed or elliptically polarized).Thus, the eye 210 is illuminated with left-handed circularly polarized light, or light reflected from the eye is transmitted through a polarizer (e.g., a circular or elliptical polarizer) that transmits light having a first polarization (e.g., left-handed circularly or elliptically polarized light). The coupling optical element 944 may also be polarization-selective, transmitting the LHP light and redirecting the RHP light into the waveguide. The LHP light from the eye passes through the coupling optical element 944. This transmitted LHP light also impinges on and is reflected from a wavelength-selective liquid crystal reflector 996. In one design, the wavelength-selective liquid crystal reflector 996 converts the first polarization state (e.g., LHP) to a second polarization state (e.g., RHP) in response to reflection. This light in the second polarization state (e.g., RHP light) is directed to the coupling optical element 944, which redirects the light in the second polarization state (RHP) into the waveguide 940 to the camera 920.

[0213] In some designs, the combining optical element 944 does not comprise a liquid crystal grating, but instead comprises, for example, a surface relief diffraction grating or a holographic grating. As discussed above, these combining optical elements 944 that do not comprise cholesteric liquid crystals may also comprise volume diffractive or holographic optical elements or gratings.

[0214] Thus, light scattered from the eye is reflected back to the waveguide 940 by the reflective optical element 996 for coupling into the waveguide by the coupling element 944. In contrast, however, a portion of unpolarized light from the environment in front of the wearer, corresponding to a second polarization state (e.g., RHP), will be transmitted through the reflective optical element 996. Thus, the wearer may see objects through the reflective optical element 996.

[0215] However, in various designs, the reflective optical element 996 will have negligible optical power in transmission. For example, the reflective optical element 996 may have curved surfaces with the same curvature on both sides of the optical element, such that the total optical power of the optical element for light transmitted therethrough will be negligible.

[0216] As discussed above, in various implementations, the reflective optical element 996 may be any of the optical elements described below in the section entitled "Cholesteric Liquid Crystal Mirror," U.S. Patent Publication No. 2018 / 0164627, entitled "DIFFRACTIVE DEVICES BASED ON CHOLESTERIC LIQUID CRYSTAL," filed December 7, 2017, and U.S. Patent Publication No. 2018 / 0239147, entitled "DISPLAY SYSTEM WITH VARIABLE POWER REFLECTOR," filed February 22, 2018, and entitled "VARIABLE-FOCUS VIRTUAL IMAGE DEVICES BASED ON POLARIZATION," all of which are incorporated herein by reference. The present invention includes a cholesteric liquid crystal reflective lens, which is a cholesteric liquid crystal reflective element as discussed in U.S. Patent Publication No. 2018 / 0239177, entitled "IR CONVERSION," filed February 22, 2018 (each of which is incorporated by reference in its entirety and for all purposes). Such optical elements may act on a specific wavelength or range of wavelengths. Thus, light, such as infrared light reflected from the eye, may be acted on by the cholesteric liquid crystal reflective element. However, light not within that wavelength range, such as visible light from the environment, may pass through the cholesteric liquid crystal reflective element without being acted on by the cholesteric liquid crystal reflective element. Thus, the cholesteric liquid crystal reflective element may have negligible refractive power for this visible light from the environment passing therethrough.

[0217] As discussed above, in some implementations, illumination source 960 couples light redirected out of the waveguide into waveguide 940 to illuminate eye 210. In such embodiments, coupling optical element 944 may be polarization selective. For example, coupling optical element 944 may transmit light of a first polarization (p-polarized light) and light of a second polarization (s-polarized light).

[0218] Thus, when light from illumination source 906 propagates through waveguide 940 and is redirected by coupling optical element 944, the illumination will be s-polarized. A polarization-modifying optical element (e.g., a quarter-wave retarder) may be positioned between waveguide 940 and eye 210 to cause a rotation of the polarization of light reflected from the eye. Light from light source 960 that is reflected from eye 210 will pass twice through the quarter-wave retarder, so that the s-polarized light that is emitted from the waveguide by coupling element 944 to illuminate the eye will be converted to p-polarized light.

[0219] This p-polarized light will be transmitted through the coupling optical element 944 and the waveguide and will be incident on the reflective optical element 996 .

[0220] The imaging system 900 may further include a second polarization-modifying element 978, which may comprise, for example, a retarder or a wave plate, as discussed above. The retarder may comprise, for example, a quarter-wave retarder. The second polarization-modifying element 978 may be disposed distal to the waveguide 940, i.e., between the waveguide and the reflector 996. The second polarization-modifying element 978 may also be disposed between the combining element beam 944 and the reflector 996. Light from the eye 210 (p-polarized light) transmitted through the combining element beam 944 passes through the second polarization-modifying element 978 and is converted to circularly polarized light. If the reflector 996 reflects circularly polarized light, the light will again be reflected back to the waveguide 940 after passing through the polarization-modifying element 978. Two passes through this polarization-modifying element (e.g., a quarter-wave retarder) 978 will convert the light to s-polarized light, which will then be redirected into the waveguide by the coupling element 944 to be directed to a camera (not shown).

[0221] 18 , light 988 reflected from eye 210 diverges. The light may be incident on and collimated by a curved or otherwise positively refractive reflector 996. A coupling optical element 944 configured to redirect the collimated light into a waveguide 940 will then direct the collimated light from curved reflective optical element 996 toward imaging device 920 (not shown). Thus, light reflected from eye 210 that is collimated by curved reflective optical element 996 is coupled into waveguide 940 and directed therein toward an outcoupling optical element 952. Outcoupling optical element 952 may be configured to direct the light out of eyepiece 950 toward a camera (not shown).

[0222] Various variations are possible in the configuration of the imaging system. Different types of reflector 996 and combining element 944 may be employed. The reflector 996 and combining element 944 may be configured to affect, for example, linearly polarized light or circularly or elliptically polarized light. As discussed, the reflector 996 has optical power. The reflector 996 and combining element 944 may comprise a cholesteric liquid crystal grating reflector and / or a lens, with or without optical power. A polarization-modifying element 978, such as a retarder, may be included between the combining element 944 and the reflector and / or between the combining element 944 and the eye. In some embodiments, a polarizer, such as a circular or linear polarizer, may be positioned between the eye and the combining element 944. For example, if unpolarized light is reflected from the eye, a polarizer (e.g., a circular or linear polarizer) may be positioned between the eye and the combining element 944. In some such cases, the combining element 944 is polarization-selective.

[0223] In configurations such as those shown in FIGS. 17 and 18 , where light reflected from the eye passes through waveguide 940 to curved reflective optical element 996, is collimated, and is redirected back into the waveguide, background noise is introduced. This background noise arises from light initially passing from the eye through coupling optical element 944. As discussed above, coupling optical element 944 may be configured to redirect collimated light into waveguide 940 to be directed to camera 920 in which an image is formed. However, coupling optical element 944 will redirect some uncollimated light incident thereon. Thus, in its initial pass through coupling optical element 944 and waveguide 940 to curved reflective optical element 996, some of the uncollimated (diverging) light reflected from the eye will be coupled into the waveguide by coupling optical element 944 and will contribute background noise to the image of the eye formed by camera 920. This noise will be superimposed on the image formed by collimated light retro-reflected by curved reflective optical element 996, which is coupled into the waveguide by coupling optical element 944 to be directed to camera 920.

[0224] In one design, this noise can be subtracted from the image. The process for subtracting the noise from the signal may involve (a) measuring the amount of light (referred to as N) coupled by coupling optical element 944 on its initial pass through coupling optical element 944 to curved reflective optical element 996, where it is redirected and reaches camera 920, and (b) measuring the total signal at camera 920 as the light passes through coupling optical element 944 and waveguide 940 to curved reflective optical element 996, is collimated, reflected back to the coupling optical element, and redirected to the camera. This total signal will also include some noise N because uncollimated light reflected from the eye will pass through coupling optical element 944 and reach curved reflective optical element 996, and therefore some of the uncollimated light will be redirected by coupling optical element 944 to camera 920. If the noise N can be measured separately from the total signal T, which includes noise superimposed across the eye image, the noise N can be subtracted from the total signal T as represented by the following equation: I=TN where I represents the image from which the noise component N has been removed.

[0225] The above two measurements (a) and (b) can be obtained in various ways. For example, as shown in Figure 19, a shutter 936 can be positioned between the curved reflective optical element 996 and the waveguide 940 and coupling optical element 944. The shutter 936 can be configured to block light when the shutter is in a first state and to transmit light when the shutter is in a second state. The shutter 936 can comprise, for example, a liquid crystal shutter.

[0226] Thus, noise component N can be measured when shutter 936 is in a first state in which light reflected from eye 210 is incident on coupling optical element 944 and passes through it towards curved reflective optical element 996, but is prevented by the closed shutter from reaching the curved reflective optical element. As discussed above, a portion of the light reflected from eye 210 is not largely collimated, but couples into coupling optical element 944 and is redirected into the waveguide where it is directed to camera 920. As referenced above, this light will not contribute to the formation of an image but will become background noise. Camera 920 may record this noise N when shutter 936 is closed.

[0227] A total signal T, including both noise N and the image, can be measured when the shutter 936 is in a second state in which the shutter is open. The light reflected from the eye 210 again impinges on the coupling optical element 944. A portion of the light reflected from the eye 210, although largely uncollimated, couples into the coupling optical element 944 and is redirected into the waveguide where it is directed to the camera 920. However, most of the light reflected from the eye 210 passes through the coupling optical element 944, through the open shutter 936, and to the curved reflective optical element 996. The curved reflective optical element 996 collimates the light and reflects at least a portion of it back to the coupling optical element 944, which redirects the collimated light into the waveguide 920 to be directed to the camera 920 to form an image of the eye 210. The camera 920 can capture the image of the eye 210.

[0228] Processing electronics (such as processing electronics 140) in communication with camera 920 can receive the noise component N, measured when shutter 936 is in a first, closed state, and the total signal T, measured when the shutter is in a second, open state, and can subtract (T) the two. In this way, noise N contributed by uncollimated light reflected from eye 210 that is coupled into combining optical element 944 on its initial pass therethrough can be subtracted from the total image signal T. The processing electronics may communicate with camera 920 via wired electronic signals. Additionally or alternatively, the processing electronics may communicate with camera 920 using one or more remote receivers. The processing electronics may reside remotely (e.g., a cloud computing device, a remote server, etc.).

[0229] Other methods may be employed to perform measurements (a) and (b), obtain N and T, and subtract N from T. For example, if the curved reflective optical element 996 is wavelength selective as shown in FIG. 18 , the eye can be illuminated with different wavelengths of light at different times. For example, to perform measurement (a) and quantify the noise N, the eye can be illuminated with a wavelength that is not reflected by the curved reflective optical element 996. However, to perform measurement (b) and quantify the total signal T, the eye can be illuminated with a wavelength that is reflected by the curved reflective optical element 996. The noise N can then be subtracted from the total T (e.g., T N ) as discussed above.

[0230] 20-20E illustrate an example imaging system 900 configured to use wavelength modulation to make measurements and subtract the noise component N as discussed above. The imaging system 900 in FIGS. 20A-20E includes a curved transmissive optical element 996 that is wavelength-selective (such as that described with reference to FIGS. 17 and 18 above). For example, the curved transmissive optical element 996 has a wavelength-dependent reflective coating 998 on its curved surface. The imaging system 900 may also include one or more light sources or illumination sources (not shown) configured to illuminate the eye 210. One or more light sources may be configured to emit infrared light. However, the one or more light sources can be configured to emit different colors or wavelengths of light at different times. Such wavelength modulation can enable separate measurements of N to be subtracted from the total signal T.

[0231] In various implementations, for example, one or more illumination sources 960, 934 may, in a first state, provide one or more wavelengths λ that are reflected by the curved reflective optical element. Reflect In the second state, one or more wavelengths λ are not reflected. Not Reflect In the second state, the curved reflective optical element may be configured to emit a negligible amount or less of wavelength λ Reflect Similarly, in the first state, a negligible amount of wavelength λ is not reflected. Not Reflect is released.

[0232] In some embodiments, the reflected wavelength λ Reflect The reflected wavelength λ may be approximately 800 nm to 950 nm. Reflect The reflected wavelength λ may be approximately 835 nm to 915 nm. Reflect In some designs, the reflected wavelength λ Reflect is approximately 850 nm. Light emissions 928 from one or more light sources 960 may illuminate the eye.

[0233] As shown in FIG. 20B, the wavelength λ that is not reflected by the curved reflective optical element 944Not Reflect Light 988 having a negligible amount of light λ reflected by the curved reflective optical element 944 (and Reflect ) is reflected from a portion of the eye 210 (e.g., the cornea). This light is reflected from the wavelength λ Not Reflect , light ray 916 is shown propagating through curved reflective optical element 996 into the environment in front of the user.

[0234] Although the light 988 incident on the coupling optical element 944 is not collimated, the coupling optical element nevertheless couples at least some of the light 914 into the waveguide 940 to be directed to the camera 920. Thus, the camera 920 can capture an image (Image #1) corresponding to the noise component N resulting from the uncollimated light redirected by the coupling optical element 944 on its initial pass to the curved reflective optical element 996. This image (Image #1) is background noise and is not a recognizable image of the eye. Processing electronics 140 is shown receiving this first image (Image #1).

[0235] In Figures 20C-20E, an illumination source (not shown) emits light of one or more wavelengths λ that are reflected by a curved reflective optical element. Reflect and a negligible amount of wavelength λ that is not reflected Not Reflect This wavelength λ Reflect can be, for example, 850 nm.

[0236] 20C, on the first pass through the coupling optical element 944, a portion of the light 988 reflected from the eye 210 that is incident on the coupling optical element 944 is coupled by the coupling optical element 944 into the waveguide 940 (as in FIG. 20B) and directed towards the camera 920. In addition, ReflectA curved transmissive optical element 996, which selectively reflects light from the eye 210, reflects and collimates non-intercoupled light 918 reflected from the eye 210 that is incident on the curved transmissive optical element. As shown in FIG. 20E, a coupling optical element 944 redirects this collimated reflected light and couples it into a waveguide 940 toward a camera 920. FIG. 20E shows both components reaching the camera 920: light 988 that is incident on the coupling optical element 944 and reflected from the eye 210 on its first pass through the coupling optical element 944, which is coupled into the waveguide 940 by the coupling optical element, and light that is reflected and collimated by the curved transmissive optical element 996, which is coupled into the waveguide by the coupling optical element. The camera 920 can capture an image (Image #2) corresponding to this total image component T. Processing electronics 140 is shown receiving this second image (Image #2).

[0237] As discussed above, the processing electronics may subtract noise from the image TN. In this example, image #1 may be subtracted from image #2. Thus, the processing electronics 140 may be configured to modify the second image based on the first image. However, other approaches are also possible. For example, the processing electronics 140 may be configured to create a new image representing a version of the second image with reduced optical noise. Implementations for subtracting noise from an image may be used in the implementations described above. For example, the implementations shown in FIGS. 10, 11A-11E, and / or 12A-12E may include a shutter 936 and / or a curved transmissive optical element 996 having a wavelength-dependent reflective coating 998 configured to selectively reflect non-intercoupled light 912 and direct the light toward the imaging device 920.

[0238] As discussed above, Image #1 is a reflection of one or more wavelengths λ where light is not reflected by the curved reflective optical element. Not Reflect and a negligible amount of reflected wavelength λ ReflectImage #2 was acquired for the case where light is illuminated at one or more wavelengths λ , where λ is reflected by the curved reflective optical element. Reflect and a negligible amount of wavelength λ that is not reflected Not Reflect λ = ... Not Reflect and a negligible amount of reflected wavelength λ Reflect The one or more illumination sources may further comprise a first illumination source configured to output one or more wavelengths λ reflected by the curved reflective optical element. Reflect and a negligible amount of wavelength λ that is not reflected Not Reflect The illumination source may include a second illumination source configured to output λ. The intensities of the first and second illumination sources may alternatively be increased and decreased, turned on and off, attenuated and unattenuated, passed and blocked to provide modulation of the wavelength of light to illuminate the eye. For example, during a first time interval, the first illumination source may be blocked while the second illumination source is not blocked. During a subsequent second time interval, the second illumination source may be blocked while the first illumination source is not blocked. This process may be repeated to provide modulation of the wavelength of light to illuminate the eye. In other designs, the wavelength of the light source may be λ. Reflect and λ Not Reflect The wavelength may be tuned and detuned to shift the wavelength back and forth between . Other arrangements are also possible.

[0239] As described above, the imaging system 900 may additionally be included in a head-mounted display, such as an augmented reality display, that provides the ability to image the eye by collecting light with the eyepiece 950. Such an imaging system 900 may be used for eye tracking. Multiple images of the retina or anterior portion of the eye may be acquired. Eye movement and / or repositioning may be ascertained from these images to track eye position and / or orientation. These imaging systems may also be used for biometric imaging and / or to identify a user. For example, an image of a user's eye, such as the retina or iris, may be acquired and recorded. A subsequent image of the wearer's eye (e.g., the retina or iris) may be acquired at a later time. The two images may be compared to determine whether the wearer at the subsequent instance is the wearer at the first instance. However, other uses for the imaging system are also possible.

[0240] Although the illumination system may be described above as being waveguide-based and comprising one or more waveguides, other types of light-redirecting optical elements may be employed in place of waveguides. Such light-redirecting optical elements may include redirecting features to eject light from the light-redirecting optical element onto, for example, a spatial light modulator. Thus, in any of the examples described herein and any of the examples below, any reference to a waveguide may be replaced with a light-redirecting optical element instead of a waveguide. Such light-redirecting optical elements may comprise, for example, a polarizing beam splitter, such as a polarizing beam splitting prism.

[0241] As discussed above, the systems described herein can enable the collection of biometric data and / or biometric identification. For example, an eye or a portion thereof (e.g., a retina) can be imaged to provide such biometric data and / or biometric identification. Images of the eye, such as the retina, may be acquired at various times when the head-mounted display system is worn by a user, perhaps the same user. A collection of such images can be recorded, for example, in a database. These images may be analyzed to collect biometric data. Such biometric data may be useful for monitoring the health or medical status of a user. Different medical parameters can be monitored by imaging a patient, for example, the patient's eye (e.g., a retina). The medical parameters can be recorded and compared with subsequent measurements acquired while the user is wearing the head-mounted display system.

[0242] Additionally, if a person begins wearing a head-mounted display system and an image of the user's eyes is captured that does not match the images stored in the database, a conclusion can be drawn that the person currently wearing the head-mounted display system is different from the previous user. This can be useful in determining whether the headset is being worn by the intended user or by a new user. Such a feature may enable certain medical, security, and / or ease-of-use applications or functionality. For example, the head-mounted display may be configured to identify the wearer based on characteristics of the wearer's eyes. For example, the system can be configured to determine an individual based on the wearer's retinal (e.g., blood vessels), corneal features, or other ocular features. In some implementations, for example, a set of markers may be determined for a particular wearer. Based on the set of markers, the system may be able to determine that the previous user is wearing the headset, or alternatively, that another user is wearing the headset. The markers may include the shape or center of the user's cornea, the configuration of blood vessels in the user's retina, the intensity and / or location of light reflection from the cornea, the shape of the side of the eye, and / or any other biometric marker. In some implementations, a confusion matrix can be determined. As discussed above, for example, in the discussion of developing a retinal map using virtual / fixation targets at various locations (see, e.g., FIG. 13B), the system may have the user look at a set of predetermined directions or eye poses and develop a matrix of eye or eye portion (e.g., cornea, retina, etc.) characteristics associated with each direction or eye pose. Using such a matrix, the system can determine the identity of the individual. Other methods are also possible.

[0243] Similarly, as discussed above, various configurations of the system are also possible. For example, FIG. 21 shows an exemplary eyepiece 900 that can be used to project light into a user's eye while simultaneously imaging the user's eye. The illustrated eyepiece 900 includes an internal coupling optical element 2104, a light dispersing element 2108, a light focusing element 2116, and an external coupling optical element 2120 on the opposite side of the coupling optical element 2112. Each of these optical elements may be disposed within or on a waveguide 2102. The waveguide 2102 may correspond, for example, to one of the waveguides 670, 680, 690 described herein (see, e.g., FIGS. 9A-9C ). The in-coupling optical element 2104 may correspond to one of the in-coupling optical elements 700, 710, 720 and / or in-coupling optical element 942 described herein (see, e.g., FIG. 10 ) and may be configured to inject image content from a projector into the waveguide and / or inject illumination from light source 960. The light dispersing element 2108 may correspond to one of the light dispersing elements 730, 740, 750 described herein (see, e.g., FIGS. 9A-9C ) and may be used to diffuse light in a given direction and redirect light from the in-coupling optical element 2104 to the coupling optical element 2112. The coupling optical element 2112 may correspond to the coupling optical element 944 described herein (see, e.g., FIG. 10 ). In some designs, the coupling optical element 2112 includes functionality described herein for the out-coupling optical elements 800, 810, 820 (see, e.g., FIGS. 9A-9C ). The focusing element 2116 may be configured to reduce the lateral spatial extent of the light received from the coupling optical element 2112 and redirect the light towards the out-coupling optical element 2120. The out-coupling optical element 2120 may correspond to the out-coupling optical element 952 described herein (see, e.g., FIG. 10 ).

[0244] The in-coupling optical element 2104 may be disposed within or on the waveguide 2102 to receive light, such as from a projector (e.g., image projector 930) and / or an illuminator (e.g., light source 960). The light may be passed through the waveguide 2102 to an associated light-dispersive optical element 2108. Any of the in-coupling optical element 2104, the light-dispersive optical element 2108, or the coupling optical element 2112 may be disposed on a major surface of the waveguide (e.g., on the top or bottom surface) or within the waveguide. Similarly, any one or combination of the light-collecting element 2116 and / or the out-coupling optical element 2120 may also be disposed on a major surface of the waveguide 2102 (e.g., on the top or both major surfaces) or within the waveguide.

[0245] The combining optical element 2112 may receive light from the light dispersing element 2108 (e.g., via TIR), expand the light, and direct it toward the user's eye. Thus, the combining optical element 2112 may be positioned in front of the user's eye and project image content therein. Additionally, or alternatively, the combining optical element 2112 may be configured to provide illumination light on and / or into the user's eye.

[0246] Light reflected from the eye (e.g., illumination light from an illumination source) may be reflected and captured by the coupling optical element 2112. Thus, in some embodiments, the coupling optical element 2112 may serve to both outcouple light received from the light dispersive element 2108 and incouple light received from the eye into the waveguide 2102.

[0247] In some embodiments, the coupling optical element 2112 may include one or more diffractive optical elements (DOEs) such that the coupling optical element 2112 has dual functionality. A first DOE (e.g., a grating, a holographic region) may similarly be configured to outcouple light, and a second DOE may be configured to incouple light reflected from the eye into the waveguide 2102. In some embodiments, both the first and second DOEs are superimposed (e.g., occupy the same or nearly the same volume) within the waveguide 2102.

[0248] Alternatively, in some embodiments, the combining optical element 2112 includes at least two DOEs stacked over or in front of one another. For example, referring to Figure 21, the first DOE of the combining optical element 2112 may be positioned over the second diffractive element, while the second diffractive element may be positioned below the first DOE. The order of the DOEs may be reversed in other implementations.

[0249] Cholesteric Liquid Crystal Mirror Some liquid crystals exist in a phase called the chiral or cholesteric phase. In the cholesteric phase, the liquid crystal may exhibit molecular twisting along an axis perpendicular to the director, with the molecular axis parallel to the director. As described herein, a cholesteric liquid crystal (CLC) layer comprises a plurality of liquid crystal molecules in the cholesteric phase that extend in a direction perpendicular to the director, e.g., the layer depth direction, and are continuously rotated or twisted in a rotation direction, e.g., clockwise or counterclockwise. The director of the liquid crystal molecules in the chiral structure may be characterized as a spiral with a helical pitch (p), which corresponds to the length in the layer depth direction that corresponds to the net rotation angle of the liquid crystal molecules in the chiral structure through one rotation in the first rotation direction. In other words, the helical pitch refers to the distance over which the liquid crystal molecules undergo a complete 360° twist. Liquid crystals exhibiting chirality can also be described as having a twist angle or rotation angle (φ), which may refer to, for example, the relative azimuthal rotation between successive liquid crystal molecules in the layer normal direction, and a net twist angle or net rotation angle, which may refer to, for example, the relative azimuthal rotation between the top and bottom liquid crystal molecules across a defined length, for example, the length of the chiral structure or the thickness of the liquid crystal layer. As described herein, a chiral structure refers to multiple liquid crystal molecules in a cholesteric phase that extend in a direction perpendicular to the director, e.g., the layer depth direction, and are continuously rotated or twisted in a rotational direction, e.g., clockwise or counterclockwise. In one aspect, the director of the liquid crystal molecules in the chiral structure can be characterized as a spiral having a helical pitch.

[0250] 22 illustrates a cross-sectional side view of a cholesteric liquid crystal (CLC) layer 1004 comprising multiple uniform chiral structures, according to an embodiment. In the CLC layer 1004, adjacent chiral structures in a lateral direction, e.g., the x-direction, have liquid crystal molecules that are similarly aligned. In the illustrated embodiment, the chiral structures 1012-1, 1012-2, ... 1012-i are similarly configured such that liquid crystal molecules of different chiral structures at approximately the same depth, e.g., the liquid crystal molecules closest to the light-incident surface 1004S, have the same rotation angle, and the sequential rotation angle of consecutive liquid crystal molecules at approximately the same depth, and the net rotation angle of the liquid crystal molecules of each chiral structure.

[0251] The CLC 1004 comprises a CLC layer 1008 comprising liquid crystal molecules arranged in a plurality of chiral structures 1012-1, 1012-2, ... 1012-i, where each chiral structure comprises a plurality of liquid crystal molecules, and i is any suitable integer greater than 2. In operation, when incident light, comprising a combination of a light beam having left-handed circular polarization and a light beam having right-handed circular polarization, is incident on the surface 1004S of the CLC layer 1008 by Bragg reflection, light with one of the circular polarization handednesses is reflected by the CLC layer 1004, while light with the opposite polarization handedness is transmitted through the CLC layer 1008 without substantial interference. As described herein and throughout this disclosure, handedness is defined as viewed in the direction of propagation. According to an embodiment, when the polarization direction or handedness of the light beams 1016-L, 1016-R is aligned so that it has the same rotational direction as the liquid crystal molecules of the chiral structures 1012-1, 1012-2, ..., 1012-i, the incident light is reflected. As shown, incident on the surface 1004S is a light beam 1016-L with left-handed circular polarization and a light beam 1016-R with right-handed circular polarization. In the illustrated embodiment, the liquid crystal molecules of the chiral structures 1012-1, 1012-2, ..., 1012-i are continuously rotated in the clockwise direction, in which the incident light beams 1016-L, 1016-R travel, i.e., in the positive x-direction, which is the same rotational direction as the light beam 1016-R with right-handed circular polarization. As a result, the light beam 1016 -R having right-handed circular polarization is substantially reflected, while the light beam 1016 -L having left-handed circular polarization is substantially transmitted through the CLC layer 1004 .

[0252] As described above, by matching the polarization handedness of incident elliptically or circularly polarized light with the rotation direction of the liquid crystal molecules in the chiral structure of the CLC layer, the CLC layer can be configured as a Bragg reflector. Furthermore, one or more CLC layers with different helical pitches can be configured as wavelength-selective Bragg reflectors with high bandwidth. Based on the concepts described herein with respect to various embodiments, a CLC layer can be configured as an off-axis or on-axis mirror configured to selectively reflect a first wavelength range, e.g., infrared wavelengths (e.g., near-infrared), while transmitting another wavelength range, e.g., visible wavelengths.

[0253] FIG. 23 illustrates an example of an eye tracking system 2300 employing a cholesteric liquid crystal reflector (CLCR), e.g., a wavelength-selective CLCR 1150, configured to image a viewer's eye 302, according to various embodiments. Unlike the CLC layer 1004 described above with respect to FIG. 22, chiral structures within the wavelength-selective CLCR 1150 that are adjacent in a lateral direction, e.g., the x-direction, have liquid crystal molecules that are aligned differently. That is, the chiral structures are configured such that liquid crystal molecules of different chiral structures at approximately the same depth, e.g., the liquid crystal molecules closest to the light-incident surface 1004S, have different rotation angles. As a result, light incident on the CLCR 1150 is rotated at an angle (θ) relative to the layer depth direction, as will be further described below in the context of the eye tracking system 2300. R ) is reflected.

[0254] Eye tracking can be a useful feature in interactive vision or control systems, including the wearable display systems described anywhere herein, for virtual / augmented / mixed reality display applications, among other applications. To achieve effective eye tracking, it may be desirable to capture images of the eye 302 at a low gaze angle, and in this regard, it may be desirable to position the eye tracking camera 702b near the center position of the viewer's eye. However, such a position of the camera 702b may interfere with the user's view. Alternatively, the eye tracking camera 702b may be positioned lower or to the side. However, such a position of the camera may increase the difficulty of obtaining robust and accurate eye tracking because the eye image is captured at a steeper angle. By configuring the CLCR 1150 to selectively reflect infrared (IR) light 2308 (e.g., having a wavelength of 850 nm) away from the eye 302 while transmitting visible light 2304 from the world, the camera 702b can be positioned away from the user's view while capturing eye images at a normal or low gaze angle. Such a configuration does not interfere with the user's view because visible light is not reflected. The same CLCR 1150 can also be configured as an IR illumination source 2320 by reflecting IR light from an IR source, e.g., an IR LED, into the eye 302, as shown. The low gaze angle of the IR illuminator can result in less occlusion from eyelashes, for example, which is a configuration that allows for more robust detection of specular reflections and can be a useful feature in modern eye tracking systems.

[0255] 23 , according to various embodiments, the CLCR 1150 comprises one or more cholesteric liquid crystal (CLC) layers each comprising a plurality of chiral structures, each chiral structure comprising a plurality of liquid crystal molecules extending in a layer depth direction (e.g., z-direction) and sequentially rotated in a first rotation direction, as described above. The alignment of the liquid crystal molecules in the chiral structures varies periodically in a lateral direction perpendicular to the layer depth direction such that the one or more CLC layers are configured to substantially Bragg-reflect a first incident light having a first wavelength (λ1) while substantially transmitting a second incident light having a second wavelength (λ2). As described above, each of the one or more CLC layers is configured to substantially Bragg reflect first and second incident light beams of elliptically or circularly polarized light having a polarization handedness that matches a first rotation direction when viewed in the layer depth direction, while substantially transmitting first and second incident light beams of elliptically or circularly polarized light having a polarization handedness opposite to the first rotation direction when viewed in the layer depth direction. According to embodiments, the periodically varying alignment of the liquid crystal molecules in the lateral direction is arranged to have a lateral period such that the ratio between the first wavelength and the period is about 0.5 to about 2.0. According to embodiments, the first wavelength is in the near-infrared range of about 600 nm to about 1.4 μm, e.g., about 850 nm, and the second wavelength is in the visible range, having one or more colors as described elsewhere herein. According to various embodiments, the liquid crystal molecules in the chiral structure are pre-tilted with respect to a direction normal to the layer depth direction. The one or more CLC layers are configured such that the first incident light is incident at a depth of about 50° relative to the layer depth direction. o , about 60 o , about 70 o , or about 80 o The angle (θ R ) is configured to be reflected by

[0256] Thus, the wavelength-selective CLCR 1150 configured comprises one or more cholesteric liquid crystal (CLC) layers each extending in a layer depth direction and comprising a plurality of liquid crystal molecules that are continuously rotated in a first rotation direction, and the arrangement of the chiral liquid crystal molecules varies periodically in a lateral direction perpendicular to the layer depth direction so that the one or more CLC layers are configured to substantially Bragg-reflect first incident light having a first wavelength, e.g., an IR wavelength, while substantially transmitting second incident light having a second wavelength, e.g., a visible wavelength.

[0257] Similar liquid crystal layers and structures may be used for the reflector 996 and coating 998 described above in connection with Figures 17-20E. The coating 998 may comprise, for example, a liquid crystal coating and, in some implementations, may be wavelength and / or polarization selective. However, other types of coatings 998 and reflectors 996 may be employed.

[0258] For example, as discussed above in connection with FIG. 16 , a lens 980 may be used to modify (e.g., collimate) the propagation of light directed to the coupling optical element 944. This light may be light reflected from the user's eye, such as the anterior surface (e.g., the corneal surface) of the user's eye. The distance from the eye, e.g., the anterior surface (e.g., the corneal surface), to the coupling optical element 944 may be, for example, about 20 mm. A positive lens 980, such as a lens having a focal length of about 20 mm, may be configured to collimate light reflected from the eye 210, such as the anterior portion of the eye (e.g., the cornea). Light reflected from the anterior surface of the eye may be coupled into the waveguide 940 and directed therein to the camera. With the focal length set to the distance to the anterior surface of the eye, the camera can image such surface. Thus, in various implementations, the positive lens 980 may have a focal length that is therefore equal to or substantially equal to the distance from the lens to the portion of the eye 210 to be imaged, for example, the cornea.

[0259] Although a refractive optical element is shown, other types of lenses or optical elements with refractive power, such as positive refractive power, may be used. For example, the lens may comprise a diffractive optical element, such as a diffractive lens or a hologram. Such a lens may, in some implementations, be positioned between the eye and the coupling optical element 944.

[0260] In various implementations, the combining optical element 944 may include refractive power. The combining optical element 944 may comprise, for example, a diffractive optical element having refractive power. The diffractive optical element may comprise, for example, a diffraction grating. The diffractive optical element may comprise a holographic optical element or a hologram. The diffractive optical element may have diffractive features, such as surface features, configured to both redirect light into the waveguide and provide refractive power. Other types of diffractive optical elements are also possible. In various implementations, the diffractive optical element may comprise a liquid crystal or may comprise a liquid crystal grating. The diffractive optical element may also comprise a polarization grating. In addition, the diffractive optical element may comprise a liquid crystal polarization grating. Some non-limiting examples of liquid crystal gratings, liquid crystal polarization gratings, and other liquid crystal optical elements are described in the following published applications, each of which is incorporated herein by reference in its entirety and for all purposes: U.S. Patent Publication No. 2018 / 0143438, entitled "MULTILAYER LIQUID CRYSTAL DIFFRACTIVE GRATINGS FOR REDIRECTING LIGHT OF WIDE INCIDENT ANGLE RANGES," filed November 16, 2017; U.S. Patent Publication No. 2018 / 0143485, entitled "SPATIALLY VARIABLE LIQUID CRYSTAL DIFFRACTION GRATINGS," filed November 16, 2017; and U.S. Patent Publication No. 2018 / 0143485, entitled "WAVEGUIDE LIGHT MULTIPLEXER USING CROSSED ANGLE RANGES." These and other related art applications are discussed in U.S. Patent Publication No. 2018 / 0143509, filed November 16, 2017, entitled "VARIABLE-FOCUS VIRTUAL IMAGE DEVICES BASED ON POLARIZATION CONVERSION," U.S. Patent Publication No. 2018 / 0239177, filed February 22, 2018, and U.S. Patent Publication No. 2018 / 0164627, filed December 7, 2017, entitled "DIFFRACTIVE DEVICES BASED ON CHOLESTERIC LIQUID CRYSTAL," and U.S. Patent Publication No. 2018 / 0164627, filed December 7, 2017.

[0261] The diffractive optical element may have optical power that alters the propagation of light incident thereon. The diffractive optical element may collimate reflected light, for example, as a surface having a distance from the diffractive optical element corresponding to the focal length of the diffractive optical element. Such a distance may be, for example, about 15-20 mm (e.g., 20 mm or an approximation thereof). Such a focal length may provide collimation of light reflected from the anterior surface of the eye, such as the corneal surface (e.g., the cornea). Other distances are also possible. For example, the distance may be in the range of about 10-40 mm, 10-50 mm, 5-40 mm, or 5-50 mm, or any range between any of the distance values ​​herein. Values ​​outside these ranges are also possible.

[0262] FIG. 24 shows an example of a coupling optical element (e.g., a coupling grating) 2111 disposed on the waveguide 2102 of the eyepiece 950. The coupling optical element 2111 comprises a diffractive optical element configured to couple light incident thereon into the waveguide 2102. The diffractive optical element also includes refractive power. For example, the diffractive optical element includes diffractive features, such as surface diffractive features, that provide refractive power, e.g., configured to collimate light incident thereon from the anterior surface of the eye (e.g., the corneal surface). A focusing element 2116 and an out-coupling optical element 2120 are also shown disposed on the waveguide 2102. The focusing element 2116 is positioned to receive light coupled into the waveguide 2102 by the coupling element 2111. The focusing element 2116 is configured to redirect light incident thereon from the coupling optical element 2111 to the out-coupling optical element 2120. The light collecting element 2116 is configured to reduce the lateral spatial extent of light (e.g., a light beam) from the at least one coupling element prior to reaching the at least one out-coupling optical element, the out-coupling optical element 2120. In some configurations, fewer optical elements may be used, possibly to reduce cost and / or optical losses, or for other reasons. For example, the light collecting element 2116 may be omitted in some embodiments. In such embodiments, light may be in-coupled from the input coupling element 2111 (e.g., after being reflected from the eye 210) and directly coupled to the out-coupling optical element 2120. The light may propagate through the eyepiece 950 between the input coupling element 2111 and the out-coupling optical element 2120. Other configurations are also possible. A camera is positioned relative to the out-coupling optical element 2120 and receives light therefrom. The out-coupling optical element 2120 is configured to direct the light received from the light collecting element 2116 to the camera to capture an image.

[0263] 24 also shows an in-coupling optical element 2104, a light dispersing element 2108, and an image content out-coupling optical element 2110 disposed on the waveguide 2102. The in-coupling optical element 2104 may be configured to couple light received from an image projector into the waveguide 2102. The light distributing element 2108 may be configured to redirect light received from the in-coupling optical element 2104 to the out-coupling optical element 2110 and additionally increase the spatial extent of the light, as discussed above. The out-coupling optical element 2110 may be configured to couple light guided within the waveguide 2102 out of the waveguide and direct such light to the eye for viewing image content from the projector.

[0264] In various implementations, one or more of these optical elements 2111, 2116, 2120, 2110, 2108, 2104 may be disposed within or on the waveguide 2102. Similarly, as discussed above, one or more of these optical elements 2111, 2116, 2120, 2110, 2108, 2104 may comprise a diffractive optical element.

[0265] 24, a coupling optical element (e.g., a coupling grating) 2111 may be laterally displaced from the out-coupling optical element 2110 on the waveguide 2102. In the implementation shown, a space separates the coupling optical element 2111 laterally from the out-coupling optical element 2110.

[0266] 25 shows another similar implementation in which a coupling optical element (e.g., a coupling grating) 2111 is laterally displaced from the external coupling optical element 2110 on the waveguide 2102. However, in the implementation shown in FIG. 25, no space separates the coupling optical element 2111 laterally from the external coupling optical element 2110.

[0267] Displacing the coupling optical element (e.g., coupling grating) 2111 laterally from the out-coupling optical element 2110 on the waveguide 2102 can enable the coupling optical element to include a refractive power that, for example, collimates light received from the anterior surface of the eye (e.g., the corneal surface) such that the refractive power does not affect the propagation of light from and / or through the out-coupling optical element 2110 to the eye. The image presented to the eye from the image projector and the view of the environment in front of the user and head-mounted display therefore need not be affected (e.g., distorted or defocused, etc.) by the refractive power of the coupling optical element 2111.

[0268] FIG. 26 illustrates an implementation of an imaging system 900 configured to image multiple portions of the eye. For example, the imaging system 900 shown in FIG. 26 may be configured to image both the anterior surface of the eye (e.g., the corneal surface) and the retina. The imaging system 900 includes a pair of internal coupling optical elements, a first internal coupling optical element 2111a and a second internal coupling optical element, disposed on the waveguide 2102 of the eyepiece. The imaging system 900 additionally includes a pair of focusing elements, a first focusing optical element 2116a and a second focusing optical element 2116b, disposed on the waveguide 2102. In some configurations, fewer optical elements may be used, possibly to reduce cost and / or optical losses, or for other reasons. For example, the focusing elements 2116a and 2116b may be omitted in some embodiments. In such an embodiment, light may be in-coupled from the first and second input coupling elements 2111 a, 2111 b (e.g., after being reflected from a portion of the eye 210, such as the retina and / or cornea) and directly coupled to the corresponding first and second out-coupling optical elements 2120 a, 2120 b. The light may propagate through the eyepiece 950 (e.g., via a waveguide, such as waveguide 2102) between the first and second input coupling elements 2111 a, 2111 b and the corresponding out-coupling optical elements 2120 a, 2120 b. Other configurations are also possible. In addition, the imaging system 900 additionally includes a pair of light out-coupling optical elements, i.e., a first out-coupling optical element 2120 a and a second out-coupling optical element 2120 b, disposed on the waveguide 2102.

[0269] The first coupling optical element 2111a is configured to couple light incident thereon into the waveguide 2102. The first focusing element 2116a is positioned to receive light coupled into the waveguide 2102 by the first coupling element 2111a. The first focusing element 2116a is configured to redirect light incident thereon from the first coupling optical element 2111a to the first out-coupling optical element 2120a. The first focusing element 2116a is also configured to reduce the lateral spatial extent of light (e.g., a light beam) from the first coupling element 2111a prior to reaching the first out-coupling optical element 2120a. A camera is positioned relative to the first out-coupling optical element 2120a to receive light therefrom. The camera is not shown in FIG. 26 , but an area corresponding to the detection area 2130 of the camera is shown. The first outcoupling optical element 2120a is configured to direct the light received from the first light collection element 2116a to a camera, and in particular to a detection area 2130 shown in FIG. 26, to capture an image.

[0270] Similarly, the second coupling optical element 2111b is configured to couple light incident thereon into the waveguide 2102. The second light collecting element 2116b is positioned to receive light coupled into the waveguide 2102 by the second coupling element 2111b. The second light collecting element 2116b is configured to redirect light incident thereon from the second coupling optical element 2111b to the second out-coupling optical element 2120b. The second light collecting element 2116b is also configured to reduce the lateral spatial extent of light (e.g., a light beam) from the second coupling element 2111a prior to reaching the second out-coupling optical element 2120a. A camera is positioned relative to the second out-coupling optical element 2120b to receive light therefrom. The camera is not shown in FIG. 26 , but an area corresponding to the detection area 2130 of the camera is shown. The second outcoupling optical element 2120b is configured to direct the light received from the second light collection element 2116b to a camera, and in particular to a detection area 2130 shown in FIG. 26, to capture an image.

[0271] 26 also shows an in-coupling optical element 2104, a light dispersing element 2108, and an image content out-coupling optical element 2110 disposed on the waveguide 2102. The in-coupling optical element 2104 may be configured to couple light received from an image projector into the waveguide 2102. The light distributing element 2108 may be configured to redirect light received from the in-coupling optical element 2104 to the out-coupling optical element 2110 and additionally increase the spatial extent of the light, as discussed above. The out-coupling optical element 2110 may be configured to couple light guided within the waveguide 2102 out of the waveguide and direct such light to the eye for viewing image content from the projector.

[0272] 26 , the first and second coupling optical elements (e.g., coupling gratings) 2111 a, 2111 b are laterally displaced from the external coupling optical element 2110 on the waveguide 2102. In the implementation shown, a space laterally separates the first and second coupling optical elements 2111 a, 2111 b from the external coupling optical element 2110. Further, in the example of FIG. 26 , the first and second coupling optical elements 2111 a, 2111 b are laterally displaced from each other on the waveguide 2102. In other implementations, two or more of the first coupling optical element (e.g., coupling grating) 2111 a, the second coupling optical element 2111 b, and the external coupling optical element 2110 need not be laterally displaced from each other on the waveguide 2102.

[0273] In various implementations, one or more of these optical elements 2111a, 2111b, 2116a, 2116b, 2120a, 2120b, 2110, 2108, 2104 may be disposed within or on the waveguide 2102. Similarly, as discussed above, one or more of these optical elements 2111a, 2111b, 2116a, 2116b, 2120a, 2120b, 2110, 2108, 2104 may comprise diffractive optical elements.

[0274] The imaging system 900 of FIG. 26 can be configured to image multiple portions of the eye. For example, the imaging system 900 may be configured to image both the anterior surface of the eye (e.g., the corneal surface) and the retina. The first internal coupling optical element 2111a may have, for example, a lens disposed on its front surface having or with refractive power. The first coupling optical element 2111a may comprise, for example, a diffractive optical element configured to couple light into the waveguide 2102 but also configured to impart refractive power thereto. Additionally or alternatively, a lens having refractive power may be disposed on the front surface of the first coupling optical element 2111a. The refractive power may be configured to modify the propagation of light received by the first internal coupling optical element 2111a so that a particular portion of the eye can be imaged. In some embodiments, the refractive power may be positive. Furthermore, the refractive power may be such that the anterior surface of the eye can be imaged. The optical power may correspond to a focal length of, for example, approximately 15-25 mm (e.g., approximately 20 mm). As a result, light reflected from the anterior surface of the eye, which may be approximately 15-25 mm (e.g., approximately 20 mm) from the first coupling optical element 2111a, may be collimated and coupled into the waveguide. Other focal lengths are also possible. For example, the focal length may be in the range of approximately 10-40 mm, or 10-50 mm, 5-40 mm, or 5-50 mm, or any range between any of the distance values ​​herein. Values ​​outside these ranges are also possible.

[0275] In contrast, in various implementations, the second coupling optical element 2111b may have no refractive power and may not include a lens disposed in front of it. The lack of refractive power associated with the second coupling optical element 2111b would result in light from the anterior portion of the eye (e.g., the corneal surface) not being collimated and not being imaged by the camera. However, light reflected from the retina may be collimated in response to passing through the natural lens of the user's eye. This light collimated by the natural lens of the eye may be coupled into the waveguide 2102 by the second coupling optical element 2111b and imaged by the camera. In this manner, the light collected by the first coupling optical element 2111a may image the anterior surface of the eye (e.g., the corneal surface of the eye), and the second coupling optical element 2111b may image the retina of the user's eye. In some implementations, such a configuration allows light collected by the first combining optical element 2111a to form an image of the phosphene on the eye, for example, on the anterior surface of the eye (e.g., the corneal surface of the eye). The second combining optical element 2111b may image the retina of the user's eye, as discussed above. In some examples, the second combining optical element 2111b and / or a lens disposed in front of it may have a net refractive power (e.g., a non-zero amount of net refractive power) that is weaker than that of the first combining optical element 2111a and / or a lens disposed in front of the first combining optical element 2111a. In particular, the second combining optical element 2112b may have a refractive power and / or a lens associated therewith, however, the total refractive power of the second combining optical element 2112b and / or any lens associated with the second combining optical element is less than the refractive power of the first combining optical element and / or any lens associated with the first combining optical element.

[0276] In some implementations, the image formed by the light collected by the first combining optical element 2111 a is adjacent to (e.g., not superimposed over) the image formed by the light collected by the second combining optical element 2111 b. For example, an image of the anterior surface of the user's eye (e.g., cornea) may be formed adjacent to (e.g., not superimposed over) an image of the retina.

[0277] Polarization techniques can be used to attenuate or remove light from the anterior surface (e.g., the corneal surface) so that it does not affect the image formed by the light collected by the second coupling optical element 2111b. For example, the eye can be illuminated with polarized light having a first polarization, and the camera can form an image using light from the second out-coupling optical element 2120b, which uses light of a second, different polarization. For example, the second out-coupling optical element 2111b can be a polarization-selective coupling element that selectively out-couples light of a second polarization different from the first polarization. Additionally or alternatively, a polarizer 2140 that filters out the first polarization (e.g., selectively transmits the second polarization) may be included between the second outcoupling optical element 2120b and the camera 920, as illustrated in FIG. 27, which is a cross section through the waveguides 950, 2102, the focusing optical elements 2116a, 2116b, and the outcoupling optical elements 2120a, 2120b shown in FIG. 26.

[0278] Such a configuration may be used to reduce undesired reflections (e.g., glints) from the cornea when imaging the retina. Reflections from the cornea will be specular. Therefore, when light of a first polarization is incident on the cornea, the light reflected from the cornea will retain the first polarization. In contrast, the retina is diffuse. When light of a first polarization is incident on the retina, the light reflected from the retina will not simply retain the first polarization. Diffuse reflection is more likely to result in unpolarized light. Therefore, a second polarization, different from the first polarization, will be present in the light reflected from the retina. As a result, by forming an image using light outcoupled from the second outcoupling optical element 2120b using light of the second polarization, an image of the retina will be obtained, while images of the cornea or glints will be suppressed. Similarly, by illuminating with a first polarization and imaging with a second, different polarization, the retina can be imaged with reduced glare from the cornea.

[0279] Thus, in various implementations, polarization-specific optical filters or polarization-selective optical elements (e.g., coupling gratings) may be used to reduce unwanted light reflected from the eye 210 (e.g., the cornea). For example, unwanted light, glare, or flashes may be reflected from the cornea in a way that may saturate the image captured by the camera. As discussed above, light reflected from the cornea may be specular and maintain its polarization. In contrast, light reflected from the retina may be more diffusely reflected and less homogeneously polarized. Similarly, a combination of polarizers may be used to remove some or most of the unwanted light reflected from the cornea. Initially, polarized light can be used to illuminate the user's eye. In some designs, a polarized illumination source (e.g., a light source) may be used. Additionally or alternatively, a first polarizer (e.g., a polarization-specific optical filter or polarization-selective optical coupling element that couples illumination light into the illumination waveguide) may be positioned at the beginning of the illumination source's optical path to provide an initial polarization of light to the eye. A second polarizer (e.g., a polarization-specific optical filter or a polarization-selective combining element) may be positioned in the optical path before the light enters the camera. The second polarizer may be positioned 90° from the first polarizer. oThe polarizer 2111b may be rotated (e.g., the polarizer may be "crossed"). As a result, the eye will be illuminated with a first polarization, with light of the first polarization reflected from the cornea. This light will not pass through a crossed polarizer (which preferentially passes light of the second polarization) located proximal to the camera. However, light reflected from the retina will contain the second polarization. Similarly, light diffusely reflected from the retina will pass through the polarizer 2140 proximal to the camera, allowing an image of the retina to be captured by the camera. Thus, in such a configuration, undesired light received from the eye (e.g., the cornea) and entering the camera can be reduced or eliminated from the image captured using light from the second coupling optical element 2111b. Other configurations are also possible. For example, the polarization-selective coupling element 2111b and / or the polarization-selective out-coupling optical element 2120b may be used in addition to or as an alternative to a polarizer such as the polarizer 2140 proximal to the camera. Additionally or alternatively, a polarized light source may be used for illumination (e.g., illuminating the eye), the effect of which may again be to reduce or eliminate unwanted light received from the eye (e.g., the cornea) before entering imaging device 920.

[0280] As illustrated in FIG. 27 , in various implementations, such a polarizer is not used in the optical path from the first coupling optical element 2111a and the camera or between the first out-coupling optical element 2120a and the camera. As a result, images of the cornea and phosphene may be obtained from light coupled into the waveguide by the first coupling optical element 2111a and / or light coupled out of the waveguide from the first out-coupling optical element 2120a. As discussed above, this first coupling optical element 2111a may have optical power or a lens associated therewith that is specifically used to image the cornea and / or phosphene. Similarly, a polarization-selective coupling optical element 2111a or a polarization-selective out-coupling optical element 2120a that filters out light of the first polarization would not be used as the first coupling optical element 2111a and out-coupling optical element 2120a, respectively. Additionally, a polarizer 2140 between the coupling optical element 2111a and the camera 920 or between the out-coupling optical element 2111a and the camera 920 that filters out light of the first polarization would also not be used.

[0281] Various variations are possible. For example, while the first and second outcoupling optical elements 2120a, 2120b are described above as combining light and forming an image on a single camera (e.g., a single detection area 2130), in other implementations the first and second outcoupling optical elements 2120a, 2120b can combine light and form an image on separate first and second cameras. Other variations are also possible.

[0282] Additionally, in some implementations, one or more of the eyepieces described above with reference to Figures 24-27 (e.g., eyepiece 950) may be a dedicated imaging eyepiece layer (e.g., omitting in-coupling optical element 2104, light dispersive element 2108, and / or out-coupling element 2110). In such implementations, the imaging eyepiece layer may be included as a layer within the waveguide stack. One or more other layers within the waveguide stack may include in-coupling optical element 2104, light dispersive element 2108, and / or out-coupling element 2110.

[0283] In some embodiments, the dedicated imaging eyepiece layer can be configured to capture images of the environment. In some such embodiments, the imaging eyepiece layer may be positioned proximate to the environment when disposed in a head-mounted display. In some such configurations, the dedicated imaging eyepiece layer may be the outermost layer in a waveguide stack, positioned between other layers (e.g., waveguides) and the environment. In some embodiments, the dedicated imaging eyepiece layer can be configured to capture images of the user's eye 210. In some such embodiments, the imaging eyepiece layer may be positioned proximate to the user when disposed in a head-mounted display. In some implementations, the dedicated imaging eyepiece layer may be the innermost layer in a waveguide stack, positioned between other layers (e.g., waveguides) and the user. Other configurations are also possible.

[0284] In some embodiments, the first and second coupling elements 2111 a, 2111 b may be laterally aligned but displaced in depth (e.g., along the z-axis, i.e., towards the other side of the page in FIG. 26 ). For example, in such an embodiment, the first and second coupling elements 2111 a, 2111 b may be positioned on opposite sides of the same waveguide. In some embodiments, the first input coupling element 2111 a may be disposed on or within a first waveguide, and the second input coupling element 2111 b may be disposed on or within a second waveguide. Additionally or alternatively, the first and second light-collecting elements 2116 a, 2116 b and / or the first and second external coupling optical elements 2120 a, 2120 b may be disposed on opposite sides of the same waveguide and / or may be disposed on or within corresponding separate waveguides.

[0285] One or more of the coupling optical elements 2111, 2111a, 2111b described above with reference to Figures 24-27 may be wavelength-selective, such that the optical element is configured to interact only with a certain wavelength or band of wavelengths. The wavelength or band of wavelengths may include invisible light (e.g., infrared light or a specific band thereof). In some implementations, the first input coupling element 2111a may be configured to operate on lower wavelengths than those for the second input coupling element 2111b (or vice versa). For example, the first coupling optical element 2111a may be configured to interact with approximately 800 nm light, and / or the second coupling optical element 2111b may be configured to interact with approximately 950 nm light (or vice versa). Optical filters may also be used to provide similar wavelength selectivity. In various implementations, therefore, the light coupled into the waveguide by the first coupling optical element that reaches the at least one camera can be of a different wavelength than the light coupled into the waveguide by the second optical element that reaches the at least one camera. Other configurations are also possible.

[0286] Various variations are possible in the structure and design of the coupling optical element 2120 and the out-coupling optical element 2112. For example, the size and shape of the coupling optical element 2120 for coupling light into the waveguide 2102 and the out-coupling optical element 2112 for coupling light out of the waveguide 2102 to the camera, and in particular the coupling area of ​​the coupling optical element 2120 and the size and shape of the out-coupling optical element 2112, can be varied. Coupling area as used herein refers to the area of ​​an optical element configured to receive light and couple the light into or out of a waveguide for use by the system, for example, to image (e.g., the eye or the environment in front of the user). In some implementations, the coupling area may correspond to the area of ​​the entire optical element or a portion of the area of ​​the optical element configured to be used in the system to couple light into or out of a waveguide for use by the system. For example, in some implementations, including a diffractive optical element used to couple light (from the eye or the environment in front of the user) into a waveguide, the coupling area of ​​the coupling element is the area of ​​the diffractive optical element used by the system to couple the light into the waveguide. The coupling optical element, e.g., a diffraction grating or diffractive optical element, may have a larger coupling area in some cases. For example, an opaque object, such as an opaque element or layer having a small aperture therein, may obstruct the propagation of light to a portion of the diffraction grating or diffractive optical element, thereby reducing the coupling area. Thus, the size and shape of the coupling area may be controlled by the size and perimeter of the optical element and other optical elements or other components or features (e.g., the spatial extent of the diffractive optical element or grating) that may block light from reaching a portion of the optical element. Other factors may also potentially reduce, alter, or otherwise affect the size and shape of the coupling area.

[0287] 28A and 28B show a coupling optical element 2120 for coupling light into the waveguide 2102, where the coupling optical element has a reduced size. In particular, the coupling optical element 2120 has a pinhole-sized coupling area. The size of the coupling area may be, for example, approximately 1.5 mm by 1.5 mm. As shown in FIG. 28A , for example, the coupling area of ​​the coupling optical element 2120 may have a length L and a thickness T. Both the length and thickness may be approximately 1.5 mm in some implementations. The reduced size of the coupling area eliminates multiple (e.g., residual) images from being collected by the coupling optical element 2120. The pinhole-sized coupling area of ​​the coupling optical element 2120 for coupling light from an object, such as a user's eye, or an object in the environment in front of the user and eyewear has an effect similar to that of a pinhole camera with respect to light collection and resulting imaging. The reduced coupling area size of the coupling optical element 2120 is similar to the reduced size of a pinhole camera coupling area. As a result, a large depth of focus or depth of field is provided without the need for lenses. The combining optical element 2120 also need not have optical power, and no lenses need be provided in the combining optical element 2120. Nevertheless, a large range of object distances are in focus with such a design.

[0288] The out-coupling optical element 2112 shown in Figures 28A and 28B for coupling light out of the waveguide 2102 to the camera is also reduced in size. In this particular implementation, the size and shape of the coupling optical element 2120 and the out-coupling optical element 2112 are similar or identical. The out-coupling optical element 2112 may also be 1.5 x 1.5 mm.

[0289] As discussed above, the coupling optical element 2120 and the out-coupling optical element 2112 may comprise diffractive optical elements such as diffraction gratings. The coupling optical element 2120 and the out-coupling optical element 2112 may comprise holograms or holographic optical elements. As discussed herein, the coupling optical element 2120 and the out-coupling optical element 2112 may comprise liquid crystals, liquid crystal gratings, polarization gratings, and / or liquid crystal polarization gratings. The coupling optical element 2120 may be configured to receive light (e.g., from a user's eye or an environment in front of the user) and couple at least a portion of the light into the waveguide 2102. The coupling optical element 2120 may also be configured to redirect and direct a portion of the light to the out-coupling optical element 2112. The out-coupling optical element 2112 may be configured to couple light received from the coupling optical element 2120 and guided within the waveguide 2102 out of the waveguide, for example, to a camera. In the configuration shown, a collection optical element as described above is not included.

[0290] The size and shape of the coupling areas of the coupling optical element 2120 and the external coupling optical element 2112 may vary. For example, while the coupling optical element 2120 and the external coupling optical element 2112 are shown as square, the shape of one or both may be different. In some implementations, the respective sizes and relative placement of the optical elements 2120, 2112 may be selected based, at least in part, on the desired distance from the user's eye (i.e., focal length), the wavelength of light to be captured, or both. The desired distance between the waveguide and the user's eye may be, for example, approximately 15 mm to 25 mm. Other configurations are also possible. In some embodiments, the optical elements 2120, 2112 may be positioned, for example, 15 mm to 25 mm apart from each other on or within the waveguide. The shape of the coupling areas may be, for example, circular or otherwise rounded. The size of the coupling areas may also vary. For example, the dimension (e.g., length L or thickness T) (e.g., average or maximum value) of the bond area along one direction may be 0.1 to 3 mm, 0.1 to 0.3 mm, 0.1 to 0.5 mm, 0.5 to 3 mm, 0.5 to 2 mm, 1 to 3 mm, 1 to 2 mm, 0.5 to 2.5 mm, 1.0 to 2.5 mm, 1.0 mm to 1.5 mm, or 1.5 mm to 2 mm, or any range formed by any of these values. Values ​​outside these ranges are also possible. Similarly, the dimension (e.g., length L or thickness T) (e.g., maximum or average value) along another direction of the bond area may be 0.1 to 3 mm, 0.1 to 0.3 mm, 0.1 to 0.5 mm, 0.5 to 3 mm, 0.5 to 2 mm, 1 to 3 mm, 1 to 2 mm, 0.5 to 2.5 mm, 1.0 to 2.5 mm, 1.0 mm to 1.5 mm, or 1.5 mm to 2 mm, or any range formed by any of these values. Values ​​outside these ranges are also possible. These two directions may be orthogonal in some implementations. The dimensions along the two directions need not be identical. Thus, the bond area may be symmetrical or asymmetrical.For example, the aspect ratio of the bond area (e.g., as measured by the ratio of length to thickness, such as maximum length to maximum thickness or average length to average thickness) may be 1 to 2, 1 to 1.75, 1 to 1.5, 1 to 1.3, 1 to 1.2, or 1 to 1.1, or any range formed by any of these values. Values ​​outside these ranges are also possible.

[0291] As discussed above, other shapes are also possible. For example, Figures 29A and 29B show a coupling optical element 2120 for coupling light into waveguide 2102 and an out-coupling optical element 2112 for coupling light out of the waveguide to a camera, where coupling optical element 2120 has an arc-slit shaped coupling area. (Out-coupling optical element 2112 has a pinhole coupling area similar to that shown in Figures 28A and 28B.)

[0292] A slit may be advantageous in that it is larger than a pinhole and may therefore collect more light. However, the narrowness of the slit provides an effect similar to that of a pinhole. For example, a reduced thickness T of the coupling area may eliminate multiple images from being collected by the coupling optical element 2120. Image persistence and / or blurring may thereby be reduced. As illustrated in FIG. 25A , the coupling area of ​​the coupling optical element 2120 may have a length L and a thickness T. In some implementations, the thickness T may be approximately 1.0 mm or 1.5 mm. The pinhole-sized thickness T of the coupling optical element 2120 for coupling light from an object, such as an eye, or from an object in the environment in front of the user and eyewear has an effect similar to that of a pinhole camera in terms of light collection and resulting imaging. The reduced size of the coupling area of ​​the coupling optical element 2120 is similar to the reduced size of the coupling area of ​​a pinhole camera. As a result, a large depth of focus or depth of field is provided without the need for a lens. The combining optical element 2120 also need not have any optical power, nor need a lens be provided in the combining optical element 2120. Nevertheless, a large range of object distances are in focus with such a design.

[0293] The outcoupling optical element 2112 shown in Figures 29A and 29B for coupling light out of the waveguide to the camera is also reduced in size. In this particular implementation, the size and shape of the outcoupling optical element 2112 is similar to or the same as that described above in connection with Figures 28A and 28B. The outcoupling optical element 2112 may also be, for example, 1.5 x 1.5 mm.

[0294] As discussed above, the coupling optical element 2120 and the out-coupling optical element 2112 may comprise diffractive optical elements such as diffraction gratings. The coupling optical element 2120 and the out-coupling optical element 2112 may comprise holograms or holographic optical elements. As discussed herein, the coupling optical element 2120 and the out-coupling optical element 2112 may comprise liquid crystals, liquid crystal gratings, polarization gratings, liquid crystal polarization gratings, or any combination thereof. The coupling optical element 2120 may be configured to receive light (e.g., from a user's eye or an environment in front of the user) and couple at least a portion of the light into the waveguide 2102. The coupling optical element 2120 may also be configured to redirect and direct a portion of the light to the out-coupling optical element 2112. The out-coupling optical element 2112 may be configured to couple light received from the coupling optical element 2120 and guided within the waveguide 2102 to the out-coupling optical element 2112 out of the waveguide, for example, to a camera. In the configuration shown, no collection optics as described above are included.

[0295] The shapes of the coupling areas of the coupling optical element 2120 and the out-coupling optical element 2112 may vary. In theory, a curved slit could potentially facilitate directing light from the coupling optical element 2120 to the out-coupling optical element. Furthermore, in some implementations, the arc-shaped slit may have a curvature described by a radius of curvature and a center of curvature. The curvature of the slit may be such that the out-coupling optical element 2112 is at the center of curvature of the arc-shaped slit. However, the curvature may be different, e.g., greater or less. Furthermore, other variations in shape are also possible. For example, the edges of the arc-shaped slit may be rounded.

[0296] The size of the bond area may also vary. For example, the smaller dimension along one direction of the bond area, i.e., thickness T, may be 0.1-0.3 mm, 0.1-0.5 mm, 0.3-0.5 mm, 0.2-0.5 mm, 0.1-1.0 mm, 0.3-1.0 mm, 0.5-3 mm, 0.5-2 mm, 1-3 mm, 1-2 mm, 0.5-2.5 mm, 1.0-2.5 mm, 1.0 mm-1.5 mm, or 1.5 mm-2 mm, or any range formed by any of these values. Values ​​outside these ranges are also possible. This dimension, i.e., thickness T, may be smaller than the other dimension, i.e., length L, which may correspond to the length from one end to the other or the resulting displacement. Alternatively, the path length P, in this case, arc length, may be used to provide a measure of the larger dimension of the bond area. In some implementations, the length L or path length or arc length P may be 5 mm to 40 mm, 10 to 40 mm, 10 to 30 mm, 15 to 30 mm, 15 to 25 mm, 1 to 5 mm, or 3 to 5 mm, or any range formed by any of these values. Values ​​outside these ranges are also possible. These two directions may be orthogonal in some implementations; however, the directions need not be orthogonal. The slit is asymmetric. For example, the aspect ratio of the bonded area (e.g., measured by the ratio of length L to thickness, where length can be either the resulting displacement from one end to the other or the path length, such as arc length P) may be 5 to 100, 10 to 100, 15 to 100, 20 to 100, 10 to 40, or 10 to 50, or any range formed by any of these values. Values ​​outside these ranges are also possible. In some embodiments, a dimension along one direction of the coupling area of ​​the coupling optical element 2120 may be less than or equal to 2.5% of the distance between the center of the coupling optical element 2120 and the center of the external coupling optical element 2112. As an example, the center-to-center distance between the optical elements 2120, 2112 may be about 20 mm, and the dimension (e.g., thickness T) may be less than or equal to about 0.5 mm (e.g., 2.5% of 20 mm). Other configurations or values ​​are also possible.For example, the dimension (e.g., thickness T) may be less than or equal to 2%, 1.5%, and / or 1% of the distance between the center of the coupling optical element 2120 and the center of the external coupling optical element 2112. Dimensions, referred to herein as thickness T, length L, path length P, etc., may be single measurements, average values, maximum values, or minimum values.

[0297] The shape and size of the external coupling optical element 2112 may also vary. For example, while the external coupling optical element 2112 is shown as a square, the shape may be different. The shape of the bonding area may be, for example, circular or otherwise rounded. The size of the bonding area may also vary. For example, the dimension along one direction of the bonding area, e.g., the thickness T, may be 0.1-0.3 mm, 0.1-0.5 mm, 0.3-0.5 mm, 0.5-3 mm, 0.5-2 mm, 1-3 mm, 1-2 mm, 0.5-2.5 mm, 1.0-2.5 mm, 1.0 mm-1.5 mm, or 1.5 mm-2 mm, or any range formed by any of these values. Values ​​outside these ranges are also possible. Similarly, the dimension of the bonding area along another direction, e.g., the length L, may be 0.1 to 0.3 mm, 0.1 to 0.5 mm, 0.3 to 0.5 mm, 0.5 to 3 mm, 0.5 to 2 mm, 1 to 3 mm, 1 to 2 mm, 0.5 to 2.5 mm, 1.0 to 2.5 mm, 1.0 mm to 1.5 mm, or 1.5 mm to 2 mm, or any range formed by any of these values. Values ​​outside these ranges are also possible. These two directions may be orthogonal in some implementations. The dimensions along the two directions need not be identical. Thus, the bonding area may be symmetrical or asymmetrical. For example, the aspect ratio of the bond area (e.g., measured by the ratio of length L to thickness T, where length can be either the resulting displacement from one end to the other or the path length, such as the arc length P) may be 1 to 2, 1 to 1.75, 1 to 1.5, 1 to 1.3, 1 to 1.2, or 1 to 1.1, or any range formed by any of these values. Values ​​outside these ranges are also possible. As noted above, dimensions referred to herein as thickness T, length L, path length P, etc., may be single measurements, averages, maximum values, or minimum values.

[0298] As discussed above, different shapes and sizes of coupling area are also possible. Figures 30A and 30B show a coupling optical element 2120 for coupling light into waveguide 2102 having a non-arcuate slit-shaped coupling area. In particular, coupling optical element 2120 has a linear slit coupling area. The slit is rectangular in shape. In contrast, out-coupling optical element 2112 has a pinhole-sized coupling area similar to those shown in Figures 28A and 28B and 29A and 29B.

[0299] As discussed above, a slit has the advantage of being larger than a pinhole and therefore may collect more light. However, the narrowness of the slit provides an effect similar to that of a pinhole. For example, a reduced thickness T of the coupling area may eliminate multiple images from being collected by the combining optical element 2120. Image persistence and / or blurring may thereby be reduced. As illustrated in FIG. 30A , the coupling area of ​​the combining optical element 2120 may have a length L and a thickness T. In some implementations, the thickness T may be approximately 1.0 mm or 1.5 mm. The pinhole-sized thickness T of the combining optical element 2120 for coupling light from an object, such as an eye, or from an object in the environment in front of the user and eyewear has an effect similar to that of a pinhole camera with respect to light collection and resulting imaging. The reduced size of the coupling area of ​​the combining optical element 2120 is similar to the reduced size of a pinhole camera aperture. As a result, a large depth of focus or depth of field is provided without the need for a lens. The combining optical element 2120 also need not have any optical power, nor need a lens be provided in the combining optical element 2120. Nevertheless, a large range of object distances are in focus with such a design.

[0300] The outcoupling optical element 2112 shown in Figures 30A and 30B for coupling light out of the waveguide to the camera is also reduced in size. In this particular implementation, the size and shape of the outcoupling optical element 2112 is similar to or the same as that described above in connection with Figures 28A and 28B and 29A and 29B. The outcoupling optical element 2112 may also be, for example, 1.5 x 1.5 mm.

[0301] As discussed above, the coupling optical element 2120 and the out-coupling optical element 2112 may comprise diffractive optical elements such as diffraction gratings. The coupling optical element 2120 and the out-coupling optical element 2112 may comprise holograms or holographic optical elements. As discussed herein, the coupling optical element 2120 and the out-coupling optical element 2112 may comprise liquid crystals, liquid crystal gratings, polarization gratings, liquid crystal polarization gratings, or any combination thereof. The coupling optical element 2120 may be configured to receive light (e.g., from a user's eye or an environment in front of the user) and couple at least a portion of the light into the waveguide 2102. The coupling optical element 2120 may also be configured to redirect and direct a portion of the light to the out-coupling optical element 2112. The out-coupling optical element 2112 may be configured to couple light received from the coupling optical element 2120 and guided within the waveguide 2102 to the out-coupling optical element 2112 out of the waveguide, for example, to a camera. In the configuration shown, no collection optics as described above are included.

[0302] As shown, the shapes of the coupling areas of the coupling optical element 2120 and the out-coupling optical element 2112 may vary. As discussed above, in theory, a curved slit could potentially facilitate directing light from the coupling optical element 2120 to the out-coupling optical element. However, a non-arcuate slit can also be used. A straight slit or a rectangular slit, as shown in FIGS. 30A and 30B, can direct enough light to the out-coupling optical element 2112 to capture an image using a camera. However, other variations in shape are also possible. For example, the edges of the slit may be rounded.

[0303] The size of the bond area may also vary. For example, the smaller dimension along one direction of the bond area, i.e., thickness T, may be 0.1-0.3 mm, 0.1-0.5 mm, 0.3-0.5 mm, 0.5-3 mm, 0.5-2 mm, 1-3 mm, 1-2 mm, 0.5-2.5 mm, 1.0-2.5 mm, 1.0-1.5 mm, or 1.5-2 mm, or any range formed by any of these values. Values ​​outside these ranges are also possible. This dimension, i.e., thickness T, may be smaller than the other dimension, i.e., length L. The other dimension, i.e., length L, may correspond to the length from one end to the other or the resulting displacement. As discussed above, the path length P may alternatively be used to provide a measure of the larger dimension of the bond area. In this example, if the slit is straight, the length L as measured by the displacement from one end to the other is identical to the path length P. In some implementations, the length L or path length or arc length P may be 1 to 5 mm, 1 to 3 mm, 5 to 40 mm, 10 to 40 mm, 10 to 30 mm, 15 to 30 mm, or 15 to 25 mm, or any range formed by any of these values. Values ​​outside these ranges are also possible. As discussed, these two directions may be orthogonal in some implementations, such as with a straight or rectangular slit; however, the directions need not be orthogonal. The slit may be asymmetric. For example, the aspect ratio of the bonded area (e.g., measured by the ratio of length L to thickness T, where length can be either the resulting displacement from one end to the other or the path length, such as arc length P) may be 5 to 100, 10 to 100, 15 to 100, 20 to 100, 10 to 40, or 10 to 50, or any range formed by any of these values. Values ​​outside these ranges are also possible. As noted above, dimensions, referred to herein as thickness T, length L, path length P, etc., may be single measurements, average values, maximum values, or minimum values.

[0304] The shape and size of the external coupling optical element 2112 may also vary. For example, while the external coupling optical element 2112 is shown as a square, one or both shapes may be different. The shape of the bonding area may be, for example, circular or otherwise rounded. The size of the bonding area may also vary. For example, the dimension along one direction of the bonding area, e.g., thickness T, may be 0.1-0.3 mm, 0.1-0.5 mm, 0.3-0.5 mm, 0.5-3 mm, 0.5-2 mm, 1-3 mm, 1-2 mm, 0.5-2.5 mm, 1.0-2.5 mm, 1.0 mm-1.5 mm, or 1.5 mm-2 mm, or any range formed by any of these values. Values ​​outside these ranges are also possible. Similarly, the dimension of the bonding area along another direction, e.g., the length L, may be 0.1 to 0.3 mm, 0.1 to 0.5 mm, 0.3 to 0.5 mm, 0.5 to 3 mm, 0.5 to 2 mm, 1 to 3 mm, 1 to 2 mm, 0.5 to 2.5 mm, 1.0 to 2.5 mm, 1.0 mm to 1.5 mm, or 1.5 mm to 2 mm, or any range formed by any of these values. Values ​​outside these ranges are also possible. These two directions may be orthogonal in some implementations. The dimensions along the two directions need not be identical. Thus, the bonding area may be symmetrical or asymmetrical. For example, the aspect ratio of the bond area (e.g., measured by the ratio of length L to thickness T, where length can be either the resulting displacement from one end to the other or the path length, such as the arc length P) can be 1 to 2, 1 to 1.75, 1 to 1.5, 1 to 1.3, 1 to 1.2, 1 to 1.1, or any range formed by any of these values. Values ​​outside these ranges are also possible. Dimensions, referred to herein as thickness T, length L, path length P, etc., can be single measurements, average values, maximum values, or minimum values ​​(e.g., average thickness, maximum thickness, average length, maximum length).

[0305] 31 shows an eyepiece including a coupling optical element 2112 for coupling light into a waveguide 2102 and an out-coupling optical element 2120 for coupling light out of the waveguide 2102 to a camera, the coupling optical element 2112 having a non-arcuate (e.g., rectilinear rectangular) slit-shaped coupling area included with an image content in-coupling optical element 2104 for receiving light from an image projector, a light distribution element 2108 for directing light from the image content in-coupling optical element 2104 to the out-coupling optical element 2110, and the out-coupling optical element 2110 for coupling light guided in the waveguide to a user for viewing the image content. In some implementations, the coupling optical element 2112 has a lens associated therewith that includes or provides refractive power. This refractive power may collimate light from an object at a specific distance, such as from the anterior surface of the eye (e.g., the cornea), to facilitate image capture of the object (e.g., a phosphene on the cornea). The optical power of the first coupling optical element 2112a and / or its associated lens may correspond to a focal length in the range of approximately 15-25 mm, 10-40 mm, 10-50 mm, 5-40 mm, or 5-50 mm, or any range between any of the distance values ​​herein. Values ​​outside these ranges are also possible.

[0306] The slit coupling optical element 2112 is laterally displaced from the outcoupling optical element 2110. In other embodiments, such as those shown in Figures 30A and 30B, the system 900 need not be included on the eyepiece with such components for presenting an image to the user.

[0307] 32A and 32B show first and second coupling optical elements 2112a, 2112b for coupling light into the waveguide 2102 and first and second out-coupling optical elements 2120a, 2120b for coupling light out of the waveguide to a camera, where the coupling optical elements 2112a and 2112b have non-arcuate (e.g., rectilinear rectangular) slit-shaped coupling areas. Such a configuration can be useful for simultaneously imaging different objects. In some implementations, different parts of the eye, such as the retina and cornea (or phosphenes thereon), can be imaged using a pair of coupling optical elements 2112a, 2112b, a pair of out-coupling optical elements 2120a, 2120b, and one or more cameras. In some implementations, the first combining optical element 2112a has a refractive power or is associated with a lens, while the second combining optical element 2112b does not have a similar refractive power or a similar lens (e.g., has neither a refractive power nor a lens associated therewith). In some implementations, the second combining optical element 2112b may have a refractive power and / or a lens associated therewith, however, the total refractive power of the second combining optical element 2112b and / or any lens associated therewith is less than the refractive power of the first combining optical element and / or any lens associated therewith. As discussed above, such a system 900 may be configured, for example, to image the anterior portion of the eye using the first combining optical element 2112a and the retina using the second combining optical element 2112b. As discussed above, in some implementations, the eye is illuminated with light having a first polarization, and the second outcoupling optical element 2120b has a polarizer associated therewith that is polarization selective or configured to filter out light of the first polarization so as to remove reflections from the cornea, such as glints, so as not to degrade the image at the retina.

[0308] 33 shows first and second coupling optical elements 2112a, 2112b for coupling light into the waveguide 2102 and first and second out-coupling optical elements 2120a, 2120b for coupling light out of the waveguide 2102 to a camera, where the coupling optical elements 2112a and 2112b have non-arc (e.g., rectilinear) slit-shaped coupling areas integrated onto the eyepiece. The eyepiece further includes an image content in-coupling optical element 2104 for receiving light from an image projector and a light distribution element 2108 for directing light from the in-coupling optical element 2104 to an out-coupling optical element 2110 for coupling light guided in the waveguide 2102 to a user for viewing the image content. In other embodiments, such as those shown in Figures 32A and 32B, the system 900 need not be included on a waveguide with such components 2104, 2108, 2110 to present an image to a user.

[0309] 34A and 34B show first and second coupling optical elements 2112a, 2112b for coupling light into the waveguide 2102 and first and second out-coupling optical elements 2120a, 2120b for coupling light out of the waveguide to a camera, where the coupling optical elements 2112a, 2112b have non-arcuate (e.g., rectilinear) slit-shaped coupling areas. Such a configuration may be useful for simultaneously imaging different objects. In some implementations, different portions of the eye, such as the retina and cornea (or phosphenes thereon), can be imaged using a pair of coupling optical elements 2112a, 2112b, a pair of out-coupling optical elements 2120a, 2120b, and one or more cameras. In some implementations, the first combining optical element 2112a has a refractive power or is associated with a le...

Claims

1. 1. A head mounted display system configured to display augmented reality image content within a user's field of view by projecting light onto the user's eyes, the head mounted display system comprising: a frame configured to be supported on the user's head; an image projector configured to display image content within the user's field of view by projecting an image into the user's eye; A camera and A waveguide; an internal coupling optical element coupled to the waveguide, the internal coupling optical element arranged to couple the light into the waveguide such that the light propagates within the waveguide; an outcoupling optical element coupled to the waveguide, the outcoupling optical element arranged to receive the light propagating in the waveguide from the incoupling optical element and to outcoupling the light from the waveguide to the camera; Equipped with one of the internal coupling optical element and the external coupling optical element has a pinhole-sized coupling area; A head-mounted display system, wherein a first dimension of the pinhole-sized coupling area is 2.5% or less of the distance between the center of the internal coupling optical element and the center of the external coupling optical element, and the first dimension corresponds to a length or width of the pinhole-sized coupling area.

2. The head mounted display system of claim 1 , wherein each of the length and width of the pinhole-sized bonding area is less than 1.5 mm.

3. The head mounted display system of claim 1 , wherein each of the in-coupling optical element and the out-coupling optical element comprises a diffraction grating.

4. Each of the internal coupling optical element and the external coupling optical element is a hologram. The head mounted display system of claim 1 comprising a Fick optical element.

5. The head mounted display system of claim 1 , wherein each of the in-coupling optical element and the out-coupling optical element comprises a liquid crystal.

6. The head mounted display system of claim 1 , wherein the other of the internal coupling optical element and the external coupling optical element comprises a slit-shaped coupling area.

7. The head mounted display system of claim 6 , wherein the slit-shaped coupling area is arc-shaped.

8. 8. The head mounted display system of claim 7, wherein an aspect ratio of an arc length of the slit-shaped coupling area to a width of the slit-shaped coupling area is 5-100.

9. The head mounted display system of claim 6 , wherein the slit-shaped coupling area is rectangular.

10. 10. The head mounted display system of claim 9, wherein an aspect ratio of the length of the slit-shaped coupling area to the width of the slit-shaped coupling area is 5-100.

11. the internal coupling optical element is a first internal coupling optical element, and the external coupling optical element is a first external coupling optical element; The head mounted display system comprises: a second internal coupling optical element coupled to the waveguide; a second outcoupling optical element coupled to the waveguide; and 2. The head mounted display system of claim 1, further comprising: one of the second inward coupling optical element and the second outward coupling optical element having a second pinhole-sized coupling area, the length and width of the second pinhole-sized coupling area being less than 1.5 mm.

12. the other of the first inward coupling optical element and the first outward coupling optical element includes a rectangular slit coupling area; The head mounted display system of claim 11 , wherein the other of the second in-coupling optical element and the second out-coupling optical element comprises a rectangular shaped slit coupling area.

13. 12. The head-mounted display system of claim 11, wherein the first outcoupling optical element has refractive power or is associated with a lens, and the second outcoupling optical element does not have refractive power or is associated with a lens.

14. An eyepiece, the eyepiece comprising: A waveguide; an internal coupling optical element coupled to the waveguide, the internal coupling optical element arranged to couple the light into the waveguide such that the light propagates within the waveguide; an outcoupling optical element coupled to the waveguide, the outcoupling optical element arranged to receive the light propagating in the waveguide from the incoupling optical element and to outcoupling the light from the waveguide; Equipped with One of the internal coupling optical element and the external coupling optical element is a pinhole-sized and having a bond area of An eyepiece lens wherein a first dimension of the pinhole-sized coupling area is 2.5% or less of the distance between the center of the internal coupling optical element and the center of the external coupling optical element, and the first dimension corresponds to the length or width of the pinhole-sized coupling area.

15. 15. The eyepiece of claim 14, wherein the length and width of the pinhole-sized coupling area are each less than 1.5 mm.

16. The eyepiece of claim 14 , wherein each of the internal coupling optical element and the external coupling optical element comprises a diffraction grating.

17. The eyepiece of claim 14 , wherein each of the internal coupling optical element and the external coupling optical element comprises a holographic optical element.

18. The eyepiece of claim 14 , wherein each of the internal coupling optical element and the external coupling optical element comprises a liquid crystal.

19. The eyepiece of claim 14 , wherein the other of the internal coupling optical element and the external coupling optical element comprises a slit-shaped coupling area.