PATENT DOCUMENT

Publication Number: US-11874530-B2
Application Number: US-201816612336-A
Country: US
Kind Code: B2

Title: Head-mounted display device with vision correction

Abstract:
A head-mounted display may include a display system and an optical system in a housing. The display system may have displays that produce images. Positioners may be used to move the displays relative to the eye positions of a user&#39;s eyes. An adjustable optical system may include tunable lenses such as tunable cylindrical liquid crystal lenses. The displays may be viewed through the lenses when the user&#39;s eyes are at the eye positions. A sensor may be incorporated into the head-mounted display to measure refractive errors in the user&#39;s eyes. The sensor may include waveguides and volume holograms, and a camera for gathering light that has reflected from the retinas of the user&#39;s eyes. Viewing comfort may be enhanced by adjusting display positions relative to the eye positions and/or by adjusting lens settings based on the content being presented on the display and/or measured refractive errors.

Claims:
What is claimed is: 
     
       1. A head-mounted device configured to generate images viewable by a user having an eye with refractive errors that is located at an eye position, comprising:
 a display configured to display the images; 
 a lens through which the images are viewable; 
 a sensor having a waveguide configured to receive light from a light source and to provide the received light towards the eye position and having a camera configured to receive a reflected version of the light from the eye position, wherein the waveguide, the lens, and the display overlap the eye position along a same direction in front of the eye position; 
 a positioner coupled to the display; and 
 control circuitry configured to measure the refractive errors with the sensor and configured to adjust the positioner based on the measured refractive errors. 
 
     
     
       2. The head-mounted device defined in  claim 1 , wherein the sensor includes an additional waveguide that overlaps the eye position. 
     
     
       3. The head-mounted device defined in  claim 2 , wherein the sensor includes an input coupler that couples the reflected version of the light into the additional waveguide and includes an output coupler that couples the reflected version of the light out of the additional waveguide. 
     
     
       4. The head-mounted device defined in  claim 3 , wherein the input coupler is configured to allow the images to pass from the display to the eye position. 
     
     
       5. The head-mounted device defined in  claim 4 , wherein the input coupler and the output coupler are volume holograms. 
     
     
       6. The head-mounted device defined in  claim 5 , wherein the camera measures the reflected version of the light from the output coupler. 
     
     
       7. The head-mounted device defined in  claim 6 , wherein the waveguide has an additional input coupler that couples the light into the waveguide and that has an additional output coupler that directs the light out of the waveguide towards the eye position, wherein the light source is selected from the group consisting of: a laser and a light emitting diode. 
     
     
       8. The head-mounted device defined in  claim 7 , further comprising a lens array interposed between the output coupler and the camera, wherein the control circuitry is configured to measure the refractive errors by analyzing light spots produced by the lens array at the camera. 
     
     
       9. The head-mounted device defined in  claim 8 , wherein the sensor is configured to form a Shack-Hartmann aberrometer. 
     
     
       10. The head-mounted device defined in  claim 6 , wherein the sensor is configured to form a Tscherning aberrometer and wherein the control circuitry is configured to measure the refractive errors by analyzing light spots at the camera that are produced while an array of dots are provided to the eye position. 
     
     
       11. The head-mounted device defined in  claim 6 , wherein the sensor is configured to form a ray tracing aberrometer and wherein the control circuitry is configured to measure the refractive errors by analyzing a light pattern at the camera that is produced while a shape is provided to the eye position. 
     
     
       12. The head-mounted device defined in  claim 1 , wherein the control circuitry is configured to allow the eye to relax by periodically presenting content on the display while adjusting at least a selected one of: the display and the lens to an infinity focus setting. 
     
     
       13. The head-mounted device defined in  claim 1 , further comprising an input-output device, wherein the control circuitry is configured to receive user input on the refractive errors with the input-output device. 
     
     
       14. The head-mounted device defined in  claim 13 , wherein the user input comprises an eyeglasses prescription and wherein the control circuitry is configured to adjust a position of the display with the positioner based on the eyeglasses prescription. 
     
     
       15. The head-mounted device defined in  claim 1 , wherein the lens comprises a tunable lens and wherein the control circuitry is configured to adjust the tunable lens based at least partly on the measured refractive errors. 
     
     
       16. The head-mounted device defined in  claim 15 , wherein the tunable lens comprises at least one tunable liquid crystal cylindrical lens, wherein the measured refractive errors are associated with astigmatism in the eye, and wherein the control circuitry is configured to adjust the tunable liquid crystal cylindrical lens based on the measured refractive errors to correct the astigmatism. 
     
     
       17. The head-mounted device defined in  claim 1 , wherein the lens includes a vision correction lens. 
     
     
       18. The head-mounted device defined in  claim 17 , wherein the vision correction lens is rotationally asymmetric and is configured to compensate for astigmatism. 
     
     
       19. The head-mounted device defined in  claim 17 , wherein the vision correction lens is a Fresnel lens. 
     
     
       20. The head-mounted device defined in  claim 1 , wherein the lens includes a fixed lens and a removable vision correction lens that is configured to overlap the fixed lens. 
     
     
       21. The head-mounted device defined in  claim 20 , wherein the removable vision correction lens comprises rotational alignment structures configured to rotationally align the removable vision correction lens relative to the fixed lens. 
     
     
       22. A head-mounted device, comprising:
 a display configured to display images; 
 a lens; 
 a sensor that includes a light source configured to produce light, a waveguide configured to receive the light produced by the light source via an input coupler, and an output coupler configured to couple the received light out of the waveguide towards an eye position, wherein the display and the output coupler overlap the eye position in a same direction in front of the eye position; and 
 control circuitry configured to measure refractive errors in eyes with the sensor based on the light coupled out of the waveguide and configured to adjust at least one of: the lens and a position of the display based on the measured refractive errors. 
 
     
     
       23. The head-mounted device defined in  claim 22 , wherein the sensor includes a camera, wherein the refractive errors include astigmatism, wherein the lens comprises an adjustable liquid crystal cylindrical lens, and wherein the control circuitry is configured to adjust the adjustable liquid crystal cylindrical lens to correct the astigmatism as the display is viewed. 
     
     
       24. The head-mounted device defined in  claim 22  wherein the lens overlaps the eye position along the same direction in front of the eye position. 
     
     
       25. A head-mounted device, comprising:
 a display; 
 a lens through which the display is viewable from an eye position; 
 a waveguide; 
 an input coupler on the waveguide through which the display is viewable from the eye position, wherein the input coupler, the lens, and the display overlap the eye position along a same direction in front of the eye position; 
 a camera; and 
 control circuitry configured to measure eye refractive errors based on measurements with the camera on light exiting the waveguide. 
 
     
     
       26. The head-mounted device defined in  claim 25 , further comprising:
 an output coupler on the waveguide configured to couple the light out of the waveguide towards the camera.

Description:
This application claims priority to provisional patent application No. 62/507,671, filed May 17, 2017, which is hereby incorporated by reference herein in its entirety. 
    
    
     BACKGROUND 
     This relates generally to optical systems and, more particularly, to optical systems for head-mounted devices. 
     Head-mounted devices such as virtual reality glasses and augmented reality glasses use displays to generate images and use lenses to present the images to the eyes of a user. 
     If care is not taken, a head-mounted device may be cumbersome and tiring to wear. Optical systems for head-mounted devices may be bulky and heavy and may not be sufficiently adjustable. Extended use of a head-mounted device with this type of optical system may be uncomfortable. 
     SUMMARY 
     A head-mounted display device may include a display system and an optical system in a housing. The display system may have displays that produce images. Positioners may be used to move the displays relative to a user&#39;s eyes. The positioners may be used to adjust the horizontal separation of the displays from each other to accommodate differences in interpupillary distance between users, may be used to make vertical display location adjustments to accommodate differences in facial anatomy between users, and may be used in adjusting eye-to-display spacing to alter focus. 
     The optical system may include tunable lenses such as tunable cylindrical liquid crystal lenses. The displays may be viewed through the lenses. The optical system may include fixed spherical lenses that are used in conjunction with the tunable cylindrical lenses. 
     A sensor may be incorporated into the head-mounted device to measure refractive errors in the user&#39;s eyes. Viewing comfort may be enhanced by adjusting display position relative to the eye positions of the user&#39;s eyes and/or by adjusting lens settings based on the content being presented on the display and/or based on measured eye refractive errors. The sensor may include waveguides and volume holograms and a camera for gathering light that has reflected from the retinas of the user&#39;s eyes. Refractive errors such as farsightedness, nearsightedness, and astigmatism may be corrected by tuning the lenses and/or adjusting display positions. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    is a diagram of an illustrative head-mounted device in accordance with an embodiment. 
         FIG.  2    is a diagram of an illustrative head mounted device with adjustable displays and lenses in accordance with an embodiment. 
         FIG.  3    is a cross-sectional side view of an illustrative adjustable lens in accordance with an embodiment. 
         FIG.  4    is a graph showing how the index of refraction of the lens of  FIG.  3    may be adjusted in accordance with an embodiment. 
         FIG.  5    is a diagram showing how the index of refraction of the lens of  FIG.  3    may be adjusted when forming a Fresnel lens in accordance with an embodiment. 
         FIG.  6 A  is a diagram of an illustrative Shack-Hartmann sensor for a head-mounted device in accordance with an embodiment. 
         FIGS.  6 B,  6 C, and  6 D  are diagrams of alternative light sources for the Shack-Hartmann sensor in accordance with embodiments. 
         FIGS.  7 A and  7 B  are diagrams of source and detector portions of a Tscherning sensor in accordance with an embodiment. 
         FIGS.  8 A and  8 B  are diagrams of source and detector portions of a ray tracing sensor in accordance with an embodiment. 
         FIG.  9    is a flow chart of illustrative operations involved in operating a head-mounted device in accordance with an embodiment. 
         FIG.  10    is a side view of illustrative lens and an associated vision correction lens in accordance with an embodiment. 
         FIG.  11    is a front view of an illustrative vision correction lens coupled to a lens mount in accordance with an embodiment. 
         FIG.  12    is a side view of an illustrative lens and associated Fresnel vision correction lens in accordance with an embodiment. 
         FIG.  13    is a front view of an illustrative spherical Fresnel lens in accordance with an embodiment. 
         FIG.  14    is a front view of an illustrative cylindrical Fresnel lens in accordance with an embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     Head-mounted devices such as head-mounted displays may be used for virtual reality and augmented reality systems. For example, a pair of virtual reality glasses that is worn on the head of a user may be used to provide a user with virtual reality content. 
     An illustrative system in which a head-mounted device such as a pair of virtual reality glasses is used in providing a user with virtual reality content is shown in  FIG.  1   . As shown in  FIG.  1   , head-mounted display  10  may include a display system such as display system  40  that creates images and may have an optical system such as optical system  20  through which a user (see, e.g., user&#39;s eyes  46 ) may view the images produced by display system  40  in direction  48 . 
     Display system  40  may be based on a liquid crystal display, an organic light-emitting diode display, a display having an array of crystalline semiconductor light-emitting diode dies, a liquid-crystal-on-silicon display, a microelectromechanical systems (MEMs) display, and/or displays based on other display technologies. Separate left and right displays may be included in system  40  for the user&#39;s left and right eyes or a single display may span both eyes. 
     Visual content (e.g., image data for still and/or moving images) may be provided to display system  40  using control circuitry  42  that is mounted in head-mounted device  10  and/or control circuitry that is mounted outside of head-mounted device  10  (e.g., in an associated portable electronic device, laptop computer, or other computing equipment). Control circuitry  42  may include storage such as hard-disk storage, volatile and non-volatile memory, electrically programmable storage for forming a solid-state drive, and other memory. Control circuitry  42  may also include one or more microprocessors, microcontrollers, digital signal processors, graphics processors, baseband processors, application-specific integrated circuits, and other processing circuitry. Communications circuits in circuitry  42  may be used to transmit and receive data (e.g., wirelessly and/or over wired paths). Control circuitry  42  may use display system  40  to display visual content such as virtual reality content (e.g., computer-generated content associated with a virtual world), pre-recorded video for a movie or other media, or other images. 
     System  40  may include electrically controlled positioners that can be used to adjust the positions of the displays in system  40 . Lens system  20  may include tunable lenses. During operation, control circuitry  42  may make position adjustments to the displays in system  40 , may adjust the tunable lenses in lens system  20 , and/or may make other adjustments to the components of device  10  while using system  40  to present the user with image content. 
     Input-output devices  44  may be coupled to control circuitry  42 . Input-output devices  44  may be used to gather user input from a user, may be used to make measurements on the environment surrounding device  10 , may be used to provide output to a user, and/or may be used to supply output to external electronic equipment. Input-output devices  44  may include buttons, joysticks, keypads, keyboard keys, touch sensors, track pads, displays, touch screen displays, microphones, speakers, light-emitting diodes for providing a user with visual output, and sensors (e.g., force sensors, temperature sensors, magnetic sensor, accelerometers, gyroscopes, and/or other sensors for measuring orientation, position, and/or movement of glasses  10 , proximity sensors, capacitive touch sensors, strain gauges, gas sensors, pressure sensors, ambient light sensors, and/or other sensors). If desired, input-output devices  44  may include a sensing system that measures the eye characteristics of the user&#39;s eyes  46 . For example, a wavefront sensor such as a Shack-Hartmann wavefront sensor, Tscherning sensor, or a ray tracing sensor may be used to measure refractive errors in a user&#39;s eyes such as astigmatism, farsightedness, and nearsightedness. Devices  44  can also include cameras (digital image sensors) for capturing images of the user&#39;s surroundings, cameras for performing gaze detection operations by viewing eyes  46 , and/or other cameras. 
       FIG.  2    is a diagram of portions of head-mounted device  10  viewed in direction  48  of  FIG.  1    (along the Z axis in  FIG.  2   ). As shown in  FIG.  2   , optical system components such as left lens  20 L and right lens  20 R and display system components such as left display  40 L and right display  40 R for device  10  may be mounted in a housing such as housing  12 . Housing  12  may have the shape of a frame for a pair of glasses (e.g., head-mounted device  10  may resemble eyeglasses), may have the shape of a helmet (e.g., head-mounted device  10  may form a helmet-mounted display), may have the shape of a pair of goggles, or may have any other suitable housing shape that allows housing  12  to be worn on the head of a user. Configurations in which housing  12  supports optical system  20  and display system  40  in front of a user&#39;s eyes (e.g., eyes  46 ) as the user is viewing optical system  20  and display system  40  in direction  48  may sometimes be described herein as an example. If desired, housing  12  may have other suitable configuration. 
     Housing  12  may be formed from plastic, metal, fiber-composite materials such as carbon-fiber materials, wood and other natural materials, glass, other materials, and/or combinations of two or more of these materials. Electrically controlled positioners (e.g., computer-controlled stepper motors, piezoelectric actuators, or other computer-controlled positioning devices that are controlled by control signals from control circuitry  42 ) can be coupled to components of device  10  and used in positioning these components in desired positions relative to housing  12  and relative to the user wearing device  10 . For example, positioners  50 X may be used to adjust the respective X-axis positions of displays  40 L and  40 R. Positioners  50 Y may be used to adjust the respective positions of displays  40 L and  40 R along the Y-axis of  FIG.  2   . The Z-axis positions of displays  40 L and  40 R (respectively, the distances of displays  40 L and  40 R to the user&#39;s left and right eyes  46 ) may be adjusted using positioners  50 Z. Positioners  50 L (e.g., X-axis, Y-axis, Z-axis, and/or rotational positioners) may be used in adjusting the positions of lenses  20 L and  20 R. Lens properties can also be electrically tuned in response to control signals from control circuitry  42 . The positioners in device  10  may be coupled to housing  12  (e.g., to move the position of a component relative to housing  12 ) and/or may be coupled to movable structures in device  10  (e.g., to adjust the position of one component relative to another component or relative to a movable support structure). If desired, lens  20 L may be coupled to display  40 L using fixed support structures and lens  20 R may be coupled to display  40 R using fixed support structures so that the displays and corresponding lenses move together. In other configurations, the positions of lenses  20 L and  20 R can be fixed (or adjustable) with respect to the user&#39;s eyes while the positions of displays  40 L and  40 R relative to the user&#39;s eyes can be independently adjusted using the positioners for displays  40 L and  40 R. In some arrangements, lens positioners  50 L may be omitted. Arrangements in which lens positioners only provide rotational positioning for lenses  20 L and  20 R may also be used. 
     The adjustability of the positions of displays  40 L and  40 R and/or of lenses  20 L and  20 R along the Z-axis allows images on displays  40 L and  40 R to be brought into focus for the user. Inward and outward position adjustments parallel to the X-axis allow device  10  to accommodate users with different interpupillary distances; each lens and panel pair (corresponding to one eye) must be adjusted together. Adjustments along the Y dimension may allow device  10  to accommodate differences in user head and face anatomy (e.g., to place the displays and lenses at different heights along axis Y relative to the user&#39;s eyes). Positioner operations may be controlled in response to user input. For example, control circuitry  42  can use the positioners of  FIG.  2    to make position adjustments based on button press input, touch sensor input, voice input, on-screen menu selections, and/or other user input to devices  44  of  FIG.  1   . Position adjustments (e.g., for focus tuning) can also be made by control circuitry  42  automatically based on measured refractive characteristics of the eyes of a user. 
     In addition to using lens movement and/or display movement to perform focusing operations, lenses  20 L and  20 R may be electrically tuned based on control signals from control circuitry  42 . Lenses  20 L and  20 R may be, for example, tunable lenses such as tunable liquid crystal lenses or other lenses that can be dynamically tuned to exhibit different focal lengths. In the example of  FIG.  3   , tunable lens  20 T (e.g., lens  20 L and/or lens  20 R) has been formed from a pair of orthogonally oriented stacked tunable cylindrical lenses. In particular, tunable lens  20 T has a first tunable cylindrical lens CL 1  and a second tunable lens CL 2  formed from liquid crystal lens structures. Polarizers (e.g., linear polarizers with aligned pass axes) may be placed above CL 2  and below CL 1 . 
     Lens  20 T may include substrates such as substrates  52 . Substrates  52  may be formed from clear plastic, transparent glass, or other suitable transparent material. Transparent conductive electrodes such as electrodes  54 ,  56 ,  58 , and  60  may be formed on substrates  52 . The transparent conductive electrodes may be formed from indium tin oxide or other transparent conductive material. Photolithography and etching, shadow mask patterning, or other patterning techniques may be used in patterning the electrodes into desired shapes (e.g., rings, strips, pads in an array, etc.). 
     With one illustrative configuration, which is shown in  FIG.  3   , lower electrode  54  of tunable cylindrical lens CL 1  is formed from a blanket layer of transparent conductive material and upper electrode  56  of tunable cylindrical lens CL 1  is formed from patterned strips of transparent conductive material running parallel to the Y axis. Liquid crystal material  62  is interposed between electrode  54  and electrode  56 . The index of refraction of liquid crystal material varies as a function of applied voltage (electric field through the liquid crystal). By independently adjusting the voltages on each of electrodes  56  across dimension X, the index of refraction of liquid crystal material  62  can be adjusted under each electrode  56  and the focal length of cylindrical lens CL 1  can therefore be adjusted. 
     Because electrodes  56  run along the Y axis of  FIG.  3   , the elongated axis of cylindrical lens CL 1  also runs parallel to the Y axis. In upper tunable cylindrical lens CL 2 , liquid crystal material  64  is interposed between electrode  60  and electrode  58 . Electrode  58  may be a uniform layer of transparent conductive material and upper electrode  60  may be formed from patterned strips of transparent conductive material running parallel to the X-axis. By adjusting the voltages applied to the electrode strips of electrode  60 , the focal length of tunable cylindrical lens CL 2  may be adjusted. The electrode strips of electrode  60  extend along the X-axis, so the longitudinal axis of lens CL 2  also extends along the X axis. Because lenses CL 1  and CL 2  are perpendicular to each other, selected cylindrical lens powers in orthogonal directions may be produced through tuning of lenses CL 1  and CL 2 . Spherical lens powers may be produced by driving both CL 1  and CL 2  (electrodes in X and Y) parametrically. 
       FIG.  4    is a graph showing how the focal length of a tunable cylindrical lens (e.g., the focal length of CL 1 ) can be adjusted. In a first configuration, a smoothly varying profile of voltages is applied to across the electrode strips of the tunable cylindrical lens, causing the index-of-refraction n for the lens to be characterized by refractive index profile  66  of  FIG.  4   . The value of refractive index n varies in a curved shape across dimension X, thereby creating a cylindrical lens from the liquid crystal material. 
     To tune the lens, another smoothly varying voltage profile (e.g., with a larger magnitude) may be applied to the liquid crystal material, thereby creating refractive index profile  68 . As these examples demonstrate, the refractive index profile of a tunable cylindrical lens can be adjusted dynamically to adjust the focal length of the lens (e.g., to have a longer focal length and weaker lens power as illustrated by profile  66  or to have a shorter focal length and stronger lens power as illustrated by profile  68 ). If desired, index-of-refraction profiles of the type shown by tunable cylindrical lens index profile  70  of  FIG.  5    may be dynamically produced to implement a cylindrical lens of a desired power using a Fresnel lens configuration. 
     In a tunable lens configuration of the type shown by lens  20 T, the longitudinal axes of lenses CL 1  and CL 2  are orthogonal, allowing a cylindrical lens to be dynamically produced along either the X or Y axis. To help correct the vision of a user with astigmatism, cylindrical lens power along the X and/or Y dimensions can be controlled using lenses CL 1  and CL 2  of tunable lens  20 T. If desired, a tunable cylindrical lens may be rotated using a positioner. For example, lens system  20  may include a mechanically or electrically rotatable cylindrical tunable lens of varying power (e.g., to compensate for eye astigmatism that is not symmetrical about the X or Y axis). Configurations in which the angular orientation of lens  20 T is fixed and electrical tuning is used to tune lens CL 1  and/or lens CL 2  are described herein as an example. 
     Lens system  20  may include a fixed (or tunable) spherical lens in alignment with lens  20 L and a fixed (or tunable) spherical lens in alignment with lens  20 R. When a spherical lens is combined with a tunable cylindrical lens, device  10  may adjust tunable lenses in system  20  to correct the vision of a user&#39;s eye using a spherical equivalent (e.g., a combination of a spherical lens and a cylindrical lens of appropriate powers to approximate a desired aspherical lens for correcting a user&#39;s astigmatism). 
     If desired, a sensor that is configured to operate as an aberrometer (e.g., a Shack-Hartmann, Tscherning, or ray tracing sensor or other suitable refractive error measurement equipment) may be used by control circuitry  42  to automatically measure refractive errors in the user&#39;s eyes. Holographic couplers, waveguides, and other structures of the type shown in  FIG.  6 A  may be used in forming the wavefront sensor so that the wavefront sensor can be reduced in size sufficiently to be carried in head mounted device  10 . 
     Device  10  may include displays such as illustrative display  40  of  FIG.  6 A . Each display  40  may have an array of pixels P for generating images. As described in connection with  FIG.  2   , device  10  may have two displays (e.g., displays  40 L and  40 R) for providing images for the user&#39;s left and right eyes  46 , respectively. Only one eye  46  and one corresponding display  40  are shown in the example of  FIG.  6 A . 
     Position sensors of the type shown in  FIG.  2    may be used in adjusting the position of display  40  relative to eye  46  so that the images are in focus and can be comfortably viewed by the user. For example, the separation between display  40  and eye  46  can be adjusted using a Z-axis positioner (as an example). Lens system  20  may include fixed and/or tunable lenses (e.g., a fixed and/or tunable spherical lens, tunable cylindrical lenses, etc.). 
     In a Shack-Hartmann sensor configuration of the type shown in  FIG.  6 A , light source  72  and camera  106  may be used in supplying light to eye  46  and measuring reflected light to measure the optical properties of eye  46 . Light source  72  may produce light  74  at any suitable wavelength. For example, light source  72  may be an infrared light source such as a laser or light-emitting diode that produces near infrared light (e.g., light at 750-1400 nm, light with a wavelength of at least 700 nm, light with a wavelength of at least 750 nm, light with a wavelength of at least 800 nm, light with a wavelength of less than 1500 nm, light with a wavelength of less than 1000 nm, light with a wavelength of less than 900 nm, or light with a wavelength of less than 850 nm, etc.). Other wavelengths of light (longer infrared wavelengths, visible wavelengths, etc.) can also be used if desired. 
     For a light source such as a laser, objective lens  75 , pinhole aperture  76 , collimating lens  80 , and iris  81  may be used to collimate and control the beam size of light  74 . These optical elements make up collimation optics assembly  71 . Objective lens  75  focuses light  74  onto pinhole aperture  76 , which acts as a spatial filter that removes uneven intensity distributions in the beam. A beam with a smooth Gaussian profile emerges from pinhole aperture  76 . Lens  80  may be used to collect and collimate the spatially filtered light. Iris  81  may be used to control the collimated beam size. The lenses and apertures in assembly  71  may be fixed components, or may be be adjusted either manually or electronically in response to control signals from control circuitry  42 . 
     Light source  72  may be a light-emitting diode (LED)  73  that emits at any suitable wavelength. Because of the finite size of the LED, the beam will diverge slightly after collimation. For an LED source, collimation optics assembly  71  may contain different components to mitigate beam divergence after collimation.  FIG.  6 B  shows a configuration an aspheric lens pair  77 A collimates the light  74  from LED source  73 . If desired, a single aspheric lens can be used for collimation instead. In  FIG.  6 C , collimation optics assembly  71  may contain just an LED  73  and compound parabolic concentrator  77 B. By sitting at the focus of the hollow parabolic mirror  77 B, light  74  can be collected and collimated. Parabolic concentrator  77 B is advantageous in cases where the LED source  73  carries a large emission profile that cannot fully be captured by a simple lens. In  FIG.  6 D , assembly  71  may contain a lens array pair  77 C and condenser lens  79 . The combination of two lens arrays produces uniform illumination whose beam size can be controlled by condenser lens  79 . If desired, a single lens array may be used instead. 
     Input and output couplers such as volume holograms or other holographic couplers may be used in coupling light into and out of the ends of waveguides  84  and  94 . The couplers are directional, meaning that light can enter the volume hologram in one direction. For example, input coupler  82  may be used to couple light  74  into waveguide  84 . Once coupled into waveguide  84 , this light may travel to output coupler  86  in direction  93  within waveguide  84 . Output coupler  86  may be aligned with user&#39;s eye  46  (e.g., output coupler  86  may be interposed between display  40  (and lens  20 ) and the user&#39;s eye  46 ). With this configuration, output coupler  86  couples light that is traveling in direction  93  in waveguide  84  out of waveguide  84  and towards eye  46  as indicated by output light  88 . This illuminates the user&#39;s eye with light  74 . After passing through the lens of eye  46 , light  88  is reflected in direction  48 , as indicated by reflected light  90 . Input coupler  92  couples light  90  into waveguide  94 . Couplers  86  and  92  may be tuned to the wavelength of light  74  and may therefore be transparent to the user as the user is viewing images on display  40  in direction  48 . 
     In waveguide  94 , light collected from input coupler  92  travels to output coupler  83  in direction  96 . Output coupler  83  couples the light exiting waveguide  94  that is traveling in direction  96  towards camera  106  as output light  91 . Output light  91  passes through lens  98 , low pass filter  100  (which is located at the focus of lens  98  and is used to filter out noise from the light), and lenslet array  102 . Lenslet array  102  may include a two-dimensional array of lenses. These lenses focus light  91  onto camera  106  (e.g., a digital image sensor) in a two-dimensional array of spots  104 . 
     The individual intensities of the spots in the two-dimensional pattern of spots  104  at camera  106  can be analyzed by control circuitry  42  to characterize any refractive errors present in user&#39;s eye  46  (e.g., astigmatism, nearsightedness, or farsightedness). With one illustrative arrangement, control circuitry  42  fits Zernike polynomials to the measured intensities of spots  104  and processes the Zernike polynomials to determine the user&#39;s eye refractive errors (e.g., a diopter value or other eyeglasses prescription information specifying optical system settings to correct the user&#39;s vision by correcting refractive errors associated with eye  46 ). The information on the measured refractive errors can then be used by control circuitry  42  to adjust the position of display  40  relative to eye  46  and/or to adjust one or more tunable lenses in optical system  20 . 
     Consider, as an example, a nearsighted user with astigmatism having a right eye (OD) prescription of sphere: −3.00 diopters, cylinder: −1.50 diopters, axis: 180°. This prescription indicates that the user needs spherical and cylindrical corrections of −3.00 and −1.5 diopters, respectively. The axis value of 180° indicates the user&#39;s astigmatism correction is horizontal. In this scenario, the spherical correction can be obtained by adjusting the separation between display  40  and eye  46  with the Z-axis positioner and the cylindrical correction can be obtained by tuning the horizontally oriented tunable cylindrical lens to produce −1.5 diopters of cylindrical lens power. The user&#39;s right eye refractive errors can be independently corrected by control circuitry  42  based on the measured characteristics of the user&#39;s right eye. 
     The content that is provided to the user may contain distant images (e.g., images of mountains) and may contain foreground content (e.g., an image of a person standing 50 cm from the user). Three-dimensional content can be provided by presenting slightly different images to the user&#39;s left and right eyes with respective displays  40 L and  40 R. 
     Accommodation-vergence mismatch has the potential to lead to eyestrain. To minimize eyestrain, device  10  may perform operations that help allow the use&#39;s ciliary muscles to relax. For example, control circuitry  42  may periodically (e.g., every 20 minutes) present distant content (e.g., content at an apparent distance of at least 20 feet away) to the user and may direct the user to look at this distant content for a predetermined amount of time (e.g., 20 seconds). Adjustments can also be made to the diopter correction or other optical system settings associated with device  10  to help enhance user eye comfort. For example, device  10  can be calibrated during manufacturing so that control circuitry  42  is able to place display  14  and optical system  20  in a low-eye-strain configuration during normal operation. When calibrating device  10 , device  10  can be tested to determine the position of display  40  that corresponds to a virtual image at infinity focus. This calibration information may then be stored in control circuitry  42 . 
     If a user has perfect vision (no eye correction needed) and if device  10  is displaying distant content (e.g., content for which the user&#39;s vergence is associated with an object located at an infinite distance from the user), device  10  can adjust optical system  20  so that the extra diopter power of device  10  is zero. In this arrangement, the user will be able to comfortably view the distant content without eyestrain. 
     If, as another example, the user is nearsighted and typically needs a −1.00 diopter lens for comfortable viewing of distant images, control circuitry  42  can make a −1.00 diopter adjustment when distant images are presented and corresponding increased diopter changes as closer content is being presented. 
     If desired, eye characteristics can be sensed using a Tscherning sensor system or a ray tracing sensor system in addition to or instead of using a Shack-Hartmann sensor to measure refractive errors. 
     Portions of an illustrative Tscherning sensor system (Tscherning aberrometer) are shown in  FIGS.  7 A and  7 B . In a Tscherning sensor system, collimated light  74  from a light source such as laser  72  or LED  73  is passed through a mask such as mask  120 . Mask  120  has an array of openings such as an array of circular openings in a grid pattern having rows and columns. The presence of mask  120  converts light  74  into a series of parallel beams aligned with the array of openings in mask  120 . These parallel beams are coupled into waveguide  84  and directed to eye  46  as light  88  as described in connection with  FIG.  6 A . After passing through eye  46  and forming images on the user&#39;s retina, these light beams return to waveguide  94  as light  90  ( FIG.  6 A ). Waveguide  94  supplies light  90  to lens  122  as light  91 , as shown in  FIG.  7 B . Camera  106  can measure the resulting array of spots of light associated with the reflected beams of light after light  91  passes through lens  122 . Control circuitry  42  can analyze the measurements made by camera  106  to characterize refractive errors for the user&#39;s eye (e.g., using Zernike polynomials). 
     If desired, light source  72 , mask  120 , and waveguide  84  may be omitted and the array of light beams that would otherwise be passing through mask  120  may be generated instead by presenting an array of spots on display  40 . Just prior to sensing the user&#39;s eyes, the user&#39;s eyes may be placed in a relaxed condition by forming an image on display  40  and moving this virtual target to infinity (e.g., by slowly increasing the separation between display  40  and eyes  46  until the infinity focus position has been reached and/or by tuning lenses in system  20 ). In this type of scenario, the light spots in the array may pass from display  40  to eye  46  without being routed to eye  46  using waveguide  84 . Reflected light  90  may be supplied (as light  91 ) to camera  106  for analysis by control circuitry  42  (e.g., Zernike polynomial fitting, etc.). 
     Portions of a ray tracing aberrometer are shown in  FIGS.  8 A and  8 B . In a ray tracing system, a beam of light  74  from a light source such as laser  72  or LED  73  is scanned by an electrically controlled beam scanning device such as scanning mirror  124  (e.g., a mirror or other device controlled by control circuitry  42 ). The scanned beam is projected on the retina of eye  46  by waveguide  84  while the intensity of light  74  is pulsed by laser  72  or LED  73 . This assembly forms an array of spots on the retina of eye  46 . As each spot is projected onto eye  46  in sequence, reflected light for that spot (see, e.g., light  90  of  FIG.  6 A ) is directed through waveguide  94  to lens  122  as light  91  of  FIG.  8 B . After passing through lens  122 , camera  106  can capture an image of each of the spots and control circuitry  42  can analyze the captured image data (e.g., using Zernike polynomial fitting). 
     If desired, light for a ray-tracing sensing system (ray-tracing aberrometer) may be produced by forming patterns on display  40  after relaxing the user&#39;s eye  46 . For example, a circle (ring of light) or other pattern may be formed on display  40 . The user&#39;s eye  46  may be relaxed by moving the virtual target formed by the circle or other pattern to an infinity focus position before eye measurements are made. In this type of configuration, light source  72 , mask  120 , and waveguide  84  may be omitted. During measurements, the circular pattern of light on display  40  is directed onto the user&#39;s retina and reflected as reflected light  90 . After passing through waveguide  94  in direction  96  and exiting as light  91 , camera  106  can capture images of the circle (which may have the shape of an ellipse) for analysis by control circuitry  42 . The magnification of the ellipse can be used in determining the spherical portion of the user&#39;s prescription, the major and minor axis of the ellipse can be used in determining the cylindrical portion of the user&#39;s prescription, and the axis of the user&#39;s prescription can be determined from the angle of the major axis of the ellipse measured with camera  106 . 
     Illustrative operations involved in using device  10  are shown in  FIG.  9   . 
     During the operations of block  108 , device  10  may be calibrated. For example, device  10  (or a representative device in a batch of devices being calibrated) can be characterized using test equipment. During testing, display  40  may create a test image while control circuitry  42  directs positioners in device  10  to position display  40  at its infinity focus location and directs lenses in lens system  20  to tune to their infinity focus location. An image sensor (e.g., a dummy eye) or other test sensor may be placed in the position of the user&#39;s eye while the image is displayed. Display position offsets and/or lens tuning offsets that might be needed to bring the virtual image at infinity into focus on the test sensor may then be determined and stored in device  10  to calibrated device  10  for future use by a user. 
     During user operations at block  110 , device  10  may be adjusted (automatically and/or manually) so that lenses  20  and displays  40  are at appropriate locations relative to the user&#39;s eyes and face (e.g., so that lenses  20  and displays  40  are separated by an appropriate distance that matches the user&#39;s interpupillary distance, so that lenses  20  and displays  40  have appropriate Y locations, etc.). After these initial adjustments have been performed, device  10  may use an eye sensing system (e.g., an aberrometer such as a Hartmann-Shack, Tscherning, or ray tracing sensor or other suitable refractive error measurement equipment) to measure the characteristics of a user&#39;s eye (e.g., to automatically measure refractive errors for the user&#39;s eyes and therefore determine a user&#39;s eye prescription for both the user&#39;s left and right eyes). If desired, a user may manually supply information on the user&#39;s prescription to control circuitry  42  using input-output devices. A user may, for example, be prompted to supply prescription values (sphere, cylinder, axis) using a touch screen, keys, voice input, etc. 
     During the operations of block  112 , control circuitry may adjust the position of display  40  (e.g., the separation in dimension Z of the left display from the user&#39;s left eye and the separation in dimension Z of the right display from the user&#39;s right eye) and/or may adjust tunable lenses in optical system  10  to bring content on display  40  into focus for the user while correcting for astigmatism, farsightedness, nearsightedness, and other refractive errors in the user&#39;s vision. The focus may be adjusted based on the nature of the content being displayed (e.g., based on the whether the content is distant content such as mountains in a landscape or is close-up content such as a nearby person) to minimize accommodation-vergence mismatch while taking into account user preferences and user refractive errors. 
     After the focus is adjusted at block  112 , control circuitry  42  may use display system  40  to display images for the user. While displaying the images, control circuitry  42  can determine whether any of the content is associated with distant objects (distant virtual objects such as computer-generated distant mountains in a landscape) or is otherwise associated with the user&#39;s relaxed eye focus state (eyes focusing at infinity). A timer may be maintained to track the amount of time elapsed between periods in which long-distance (e.g., infinity focus) content is being displayed for more than a predetermined amount of time (e.g., at least 20 seconds, at least 10 seconds, a threshold amount of time less than 2 minutes, etc.). 
     When the timer expires (e.g., after at least 15 minutes, at least 20 minutes, 10-30 minutes, a time period of less than 40 minutes, or other suitable time limit beyond which the user is not allowed to continue without eye relaxation), control circuitry  42  can conclude that it is time for the user to relax their eyes. Accordingly, content at a large distance (e.g., at infinity or greater than 20 feet away) can be presented to the user (block  116 ). As the user views this distant content (and as control circuitry  42  adjust the position of display  40  and optical system  20  to their corresponding infinity focus states), the user&#39;s ciliary muscles in eyes  46  relax. After a suitable eye relaxation period has passed (e.g., after at least 10 s, at least 20 s, at least 30 s, at least 15-30 s, a time period less than 3 min, or other suitable relaxation time period), processing may return to block  112 , as indicated by line  118 . The eye relaxation content (long distance) content that is displayed during the operations of block  116  may include a message such as “relax eyes” that is presented at an infinity focus point or other suitably large distance or may include embedded content (e.g., mountains at an infinity focus or other suitable large distance) that is forced into the content that is otherwise being presented to the user. For example, a user playing a video game may be in a confined space and close to surrounding objects. To allow the user&#39;s eyes to relax during the operations of block  116 , a distant mountain scene may be inserted into the video game, thereby avoiding the need to interrupt the user with a text message (“relax eyes”) or other content that might disrupt the user&#39;s enjoyment of the video game. 
     A user of device  10  may not have perfect vision. For example, a user may be nearsighted, may be farsighted, and/or may have astigmatism. To correct for imperfect vision, vision correction lenses may be coupled to device  10 . Lenses  20  may, for example, have a fixed portion and a removable vision correction portion. 
     Vision correction lenses may, for example, have a positive diopter (to correct for farsightedness or a negative diopter (to correct for nearsightedness). Astigmatism may also be corrected. Corrective lenses that correct for astigmatism are not be rotationally symmetric. To ensure that vision correction lenses that are not rotationally symmetric are oriented properly, device  10  may be provided with vision correction lens orientation features (e.g., a magnetic coupling structure or mechanical coupling structure that accurately aligns the corrective lens while coupling the corrective lens to lens  20 L or  20 R in device  10  so that the corrective lens has a desired angular orientation with respect to device  10  and display  40  and therefore to the user&#39;s eyes when device  10  is being worn by the user). 
     An illustrative vision correction lens arrangement is shown in  FIG.  10   . In the example of  FIG.  10   , vision correction lens  130  has been mounted within device  10  overlapping lens  20 . Lens  20  may be a catadioptric lens or other suitable lens. Lens  20  may be tunable or may be fixed. Lens  130  may be rotationally symmetric or may be rotationally asymmetric. As shown in  FIG.  10   , lens  130  may have a convex outer surface SF 3  that faces lens  20  and may have a concave inner surface. In configurations in which lens  130  is rotationally asymmetric to compensate for astigmatism, the concave inner surface of lens  130  may be characterized by a first curvature (shown by cross-sectional profile SF 1 ) along a first dimension (e.g., along the X axis) and may be characterized by a different second curvature (shown by cross-sectional profile SF 2 ) along a second dimension (e.g., along the Y axis). When lens  130  overlaps lens  20 , a two-part lens is formed that is corrected to compensate for the user&#39;s vision problems. 
     Vision correction lens  130  may have a support structure such as vision correction lens mounting ring  132 . Lens  20  may be mounted in a support structure such as lens mounting structure  134  (e.g., a portion of a housing or other structural support in device  10 ). Structure  134  may have an opening (e.g., a circular opening or an opening of other suitable shape) that receives mounting ring  132 . When ring  132  is received within structure  134 , alignment features associated with ring  132  and structure  134  accurately align vision correction ring  132  with respect to structure  134  (e.g., the angular orientation of ring  132  and therefore vision correction lens  130  with respect to lens  20 , display  40 , and other portions of device  10  is established within less than 2o, within less than 4o, or other suitable amount). 
     With one illustrative configuration, magnetic alignment structures may be used on ring  132  and structure  134 . As shown in  FIG.  11   , for example, lens  130  may be mounted within ring  132  and may potentially rotate with respect to center point CP as ring  132  rotates within a circular opening in support structure  134 . To place vision correction lens  130  into a desired rotational alignment with respect to structure  134  and the rest of device  10 , ring  132  may be provided with one or more magnets such as magnets  138  and  140  and structure  134  may be provided with one or more corresponding magnets  136  and  142 . When vision correction lens  130  is mounted to device  10 , magnetic attraction between magnet  138  and magnet  136  and magnetic attraction between magnet  140  and  142  will help align and hold lens  130  in a desired angular orientation within device  10 , thereby ensuring that lens  130  satisfactorily corrects a user&#39;s astigmatism. 
     If desired, vision correction lens  130  may be a Fresnel lens, as shown in  FIG.  12   . Fresnel vision correction lens  130  (e.g., lens  130  of  FIG.  12   ) may be a spherical lens (e.g., a rotationally symmetric lens) as shown in the front view of lens  130  of  FIG.  13    or may be a cylindrical lens (e.g., a cylindrical lens with no spherical power or a hybrid cylindrical-spherical lens) as shown in the front view of illustrative rotationally asymmetric lens  130  of  FIG.  14   . 
     To ensure that a user&#39;s vision is corrected satisfactorily when using device  10 , vision correction lenses  130  may be coupled to device  10  in alignment with lenses  20  before use of device  10 . For example, a left vision correction lens may be coupled to device  10  in alignment with (overlapping) left lens  20 L and a right vision correction lens may be coupled to device  10  in alignment with right lens  20 R. Vision correction lenses  130  may be coupled to device  10  magnetically (e.g., using magnets and/or magnetic material), using threaded retention rings, using clips, using adhesive, and/or using other suitable mounting structures. In some configurations, vision correction lenses  130  are removably coupled to device  10  (e.g., so that a different user may replace the vision correction lenses  130  with a different set of vision correction lenses if desired). 
     When vision correction lenses  130  are incorporated into device  10 , lenses  130  and  20  operate together. For example, lenses  20  may serve to provide most of the optical power used in bringing display  40  into focus, while lenses  130  may correct for user-specific vision problems such as astigmatism, etc. If desired, tunable lens structures may be used in combination with vision correction lenses  130  and/or other fixed lenses (e.g., catadioptric lenses, Fresnel lenses, etc.). 
     In accordance with an embodiment, a head-mounted device configured to generate images viewable by a user having an eye with refractive errors that is located at an eye position is provided that includes a display configured to display the images, a lens through which the images are viewable, a sensor, a positioner coupled to the display, and control circuitry configured to measure the refractive errors with the sensor and configured to adjust the positioner based on the measured refractive errors. 
     In accordance with another embodiment, the sensor includes at least one waveguide. 
     In accordance with another embodiment, the sensor includes an input coupler that couples light into the waveguide and includes an output coupler that couples light out of the waveguide. 
     In accordance with another embodiment, the output coupler is configured to allow images to pass from the display to the eye position. 
     In accordance with another embodiment, the input coupler and output coupler are volume holograms. 
     In accordance with another embodiment, the sensor further includes a camera that measures light from the output coupler. 
     In accordance with another embodiment, the head-mounted device includes a light source selected from the group consisting of a laser and a light emitting diode that supplies light, an additional waveguide having an additional input coupler that couples the light into the additional waveguide and that has an additional output coupler that directs the light out of the additional waveguide towards the eye position. 
     In accordance with another embodiment, the head-mounted device includes a lens array interposed between the output coupler and the camera, the control circuitry is configured to measure the refractive errors by analyzing light spots produced by the lens array at the camera. 
     In accordance with another embodiment, the sensor is configured to form a Shack-Hartmann aberrometer. 
     In accordance with another embodiment, the sensor is configured to form a Tscherning aberrometer and the control circuitry is configured to measure the refractive errors by analyzing light spots at the camera that are produced while an array of dots are displayed on the display. 
     In accordance with another embodiment, the sensor is configured to form a ray tracing aberrometer and the control circuitry is configured to measure the refractive errors by analyzing a light pattern at the camera that is produced while a shape is displayed on the display. 
     In accordance with another embodiment, the shape includes a circle. 
     In accordance with another embodiment, the control circuitry is configured to allow the eye to relax by periodically presenting content on the display while adjusting at least a selected one of: the display and the lens to an infinity focus setting. 
     In accordance with another embodiment, the head-mounted device includes an input-output device, the control circuitry is configured to receive user input on the refractive errors with the input-output device. 
     In accordance with another embodiment, the user input includes an eyeglasses prescription and the control circuitry is configured to adjust a position of the display with the positioner based on the eyeglasses prescription. 
     In accordance with another embodiment, the lens includes a tunable lens and the control circuitry is configured to adjust the tunable lens based at least partly on the measured refractive errors. 
     In accordance with another embodiment, the tunable lens includes at least one tunable liquid crystal cylindrical lens, the measured refractive errors are associated with astigmatism in the eye, and the control circuitry is configured to adjust the tunable liquid crystal cylindrical lens based on the measured refractive errors to correct the astigmatism. 
     In accordance with another embodiment, the lens includes a vision correction lens. 
     In accordance with another embodiment, the vision correction lens is rotationally asymmetric and is configured to compensate for astigmatism. 
     In accordance with another embodiment, the vision correction lens is a Fresnel lens. 
     In accordance with another embodiment, the lens includes a fixed lens and a removable vision correction lens that is configured to overlap the fixed lens. 
     In accordance with another embodiment, the removable vision correction lens includes rotational alignment structures configured to rotationally align the removable vision correction lens relative to the fixed lens. 
     In accordance with another embodiment, the rotational alignment structures include a magnet. 
     In accordance with an embodiment, a head-mounted device is provided that includes a display configured to display images, a lens, a sensor that includes at least one hologram, and control circuitry configured to measure refractive errors in eyes with the sensor and configured to adjust at least one of: the lens and a position of the display based on the measured refractive errors. 
     In accordance with another embodiment, the sensor includes a camera, the refractive errors includes astigmatism, the lens includes an adjustable liquid crystal cylindrical lens, and the control circuitry is configured to adjust the adjustable liquid crystal cylindrical lens to correct the astigmatism as the display is viewed. 
     In accordance with an embodiment, a head-mounted device is provided that includes a display, a lens through which the display is viewable from an eye position, a waveguide, a hologram on the waveguide through which the display is viewable from the eye position, a camera, and control circuitry configured to measure eye refractive errors based on measurements with the camera on light exiting the waveguide. 
     The foregoing is merely illustrative and various modifications can be made to the described embodiments. The foregoing embodiments may be implemented individually or in any combination.

Metadata:
Filing Date: 20180503
Publication Date: 20240116
Grant Date: 20240116
Priority Date: 20170517
Inventors: CHAN, VICTORIA C.
GAMBACORTA, CHRISTINA G.
MYHRE, GRAHAM B.
CHOI, Hyungryul
ZHU, Nan
HOBSON, Phil M.
SPRAGUE, WILLIAM W.
Valko, Edward A.
HUANG, Qiong
PETLJANSKI, BRANKO
JOHNSON, PAUL V.
CLARKE, Brandon E.
KLEEMAN, Elijah H.
Assignee: APPLE INC
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Family ID: 62555141