PATENT DOCUMENT

Publication Number: US-10520734-B1
Application Number: US-201815866195-A
Country: US
Kind Code: B1

Title: Optical system

Abstract:
An electronic device may include a display with a concave surface. A linear polarizer may be formed on the concave surface. A quarter wave plate may receive light from the linear polarizer. A catadioptric lens may have first and second lens elements. The first lens element may have first and second opposing surfaces. The second lens element may have opposing third and fourth surfaces. The first surface may be convex and may face the display. The fourth surface may be concave. The second surface may be concave. The third surface may be convex and may match the second surface. An additional quarter wave plate may be formed as a coating on the third surface. A partially reflective coating may be formed on the first surface. A reflective polarizer may be formed as a coating on the fourth surface. An additional polarizer may be formed on the reflective polarizer.

Claims:
What is claimed is: 
     
       1. An electronic device configured to display images, comprising:
 an array of pixels configured to produce the images, wherein the array of pixels has a concave surface; 
 a linear polarizer through which light associated with the images passes; 
 a first quarter wave plate that receives the light from the linear polarizer; 
 a first lens element having a convex surface and an opposing concave surface; 
 a second lens element having a concave surface and an opposing convex surface that matches the concave surface of the first lens element; 
 a partially reflective mirror on the convex surface of the first lens element; 
 a second quarter wave plate between the first and second lens elements; and 
 a reflective polarizer on the concave surface of the second lens element. 
 
     
     
       2. The electronic device defined in  claim 1  further comprising an additional linear polarizer through which the light passes after passing through the reflective polarizer. 
     
     
       3. The electronic device defined in  claim 1  wherein the second quarter wave plate is formed as a coating on the convex surface of the second lens element. 
     
     
       4. The electronic device defined in  claim 1  wherein the linear polarizer is attached with adhesive to the concave surface of the array of pixels. 
     
     
       5. The electronic device defined in  claim 1  wherein the first quarter wave plate is a coating. 
     
     
       6. The electronic device defined in  claim 1  wherein the linear polarizer is between the convex surface of the first lens element and the array of pixels. 
     
     
       7. The electronic device defined in  claim 1  wherein the first quarter wave plate is formed as a coating on the partially reflective mirror on the convex surface of the first lens element. 
     
     
       8. The electronic device defined in  claim 1  wherein the array of pixels has a curvature, the electronic device further comprising:
 a display curvature adjusting device; and 
 control circuitry configured to control the display curvature adjusting device to adjust the curvature of the array of pixels. 
 
     
     
       9. The electronic device defined in  claim 8  wherein the display curvature adjusting device comprises a pump. 
     
     
       10. The electronic device defined in  claim 1  further comprising an additional linear polarizer that is formed on the reflective polarizer. 
     
     
       11. The electronic device defined in  claim 1  wherein the reflective polarizer is formed as a coating on the concave surface of the second lens element. 
     
     
       12. Apparatus, comprising:
 an array of pixels with a concave surface configured to produce images; 
 a linear polarizer through which light associated with the images passes; 
 a first quarter wave plate that receives the light from the linear polarizer; 
 a first lens element having first and second opposing surfaces; 
 a second lens element having third and fourth opposing surfaces, wherein the second surface is a concave surface, wherein the third surface is a convex surface faces the second surface, wherein the first surface is a convex surface facing the array of pixels, and wherein the fourth surface is a concave surface; 
 a partially reflective mirror on the first surface; 
 a second quarter wave plate that is between the second and third surfaces; and 
 a reflective polarizer on the fourth surface. 
 
     
     
       13. The apparatus defined in  claim 12  further comprising an additional linear polarizer that receives light that has passed through the reflective polarizer. 
     
     
       14. The apparatus defined in  claim 13  wherein the reflective polarizer is a coating on the concave fourth surface. 
     
     
       15. The apparatus defined in  claim 14  wherein the additional linear polarizer is formed on the reflective polarizer. 
     
     
       16. The apparatus defined in  claim 12  wherein the second quarter wave plate is a coating on the convex third surface. 
     
     
       17. The apparatus defined in  claim 16  wherein the linear polarizer is attached to the concave surface of the pixel array. 
     
     
       18. The apparatus defined in  claim 17  wherein the first quarter wave plate is a coating on the reflective polarizer on the first surface. 
     
     
       19. An electronic device, comprising:
 a support structure; 
 a display with a concave surface, wherein the display is supported by the support structure and produces light for images; and 
 a catadioptric lens supported by the support structure that focuses the light, wherein the catadioptric lens includes a first lens element having a first surface that is convex and having an opposing second surface, a partially reflecting mirror on the first surface, a quarter wave plate at the second surface, a second lens element having a third surface at the quarter wave plate that matches the second surface of the first lens element and having an opposing fourth surface that is concave, and a reflective polarizer that is formed from a coating layer at the fourth surface. 
 
     
     
       20. The electronic device defined in  claim 19  wherein the quarter wave plate is a coating on the third surface. 
     
     
       21. The electronic device defined in  claim 19  wherein the field of view of the catadioptric lens is at least 120°. 
     
     
       22. The electronic device defined in claim  19  wherein the first and second lens elements each have a radius of curvature of 20-40 mm. 
     
     
       23. The electronic device defined in  claim 19  wherein the catadioptric lens has a lens power with a refractive contribution and a reflective contribution and wherein the reflective contribution is at least five times more than the refractive contribution. 
     
     
       24. The electronic device defined in  claim 19  wherein the first lens element has a first thickness that varies by less than 5% throughout the first lens element and wherein the second lens element has a second thickness that varies by less than 5% throughout the second lens element. 
     
     
       25. The electronic device defined in  claim 19  wherein the display is a self emitting display.

Description:
This patent application claims the benefit of provisional patent application No. 62/523,647 filed on Jun. 22, 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 devices with displays. 
     Lenses may sometimes be used to allow a viewer to view a nearby display. For example, electronic devices such as virtual reality glasses use lenses to display images for a user. 
     If care is not taken, lenses and other optical components in these electronic devices may be bulky and heavy and may not exhibit satisfactory optical performance. 
     SUMMARY 
     An electronic device such as a head-mounted device or other electronic device may include a display system and an optical system. The display system and optical system may be supported by support structures that are configured to be worn on the head of a user. The electronic device may use the display system and optical system to present images to the user while the device is being worn by the user. 
     The display system may have a pixel array that produces image light associated with the images. The pixel array may have a concave surface. The display system may also have a linear polarizer through which image light from the pixel array passes and a quarter wave plate through which the light passes after passing through the linear polarizer. The linear polarizer and quarter wave plate may be located between the pixel array and the optical system to produce circularly polarized light. For example, the linear polarizer may be formed on the concave surface of the pixel array and the quarter wave plate may be formed on a convex surface of the optical system facing the pixel array. 
     The optical system may be a catadioptric optical system having lens elements formed from clear materials such as glass or plastic and having reflective structures. The surfaces of the lens elements and the surface of the pixel array may include convex surfaces and concave surfaces. 
    
    
     
       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 graph in which modeled field curvature values have been plotted versus viewing angle for a lens in accordance with an embodiment. 
         FIG. 3  is a graph in which the modulus of the optical transfer function for a lens has been plotted as a function of spatial frequency in accordance with an embodiment. 
         FIG. 4  is a front view of a portion of an illustrative device in accordance with an embodiment. 
         FIG. 5  is a cross-sectional side view of a portion of an illustrative display in a device with a variable pressure chamber to adjust display curvature in accordance with an embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     Electronic devices such as head-mounted display devices may be used for virtual reality and augmented reality systems (sometimes referred to as mixed 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 that includes an electronic device such as a head-mounted device is shown in  FIG. 1 . As shown in  FIG. 1 , electronic device  10  (e.g., a head-mounted device with support structures configured to be worn on the head of a user such as glasses, goggles, a helmet, hat, etc.) may include a display system with one or more displays  40  (e.g., a display for each of a user&#39;s eyes such as eye  46 ). A single display  40  is shown in  FIG. 1 . Systems with a pair of displays  40  may present images to a user&#39;s left and right eyes simultaneously. 
     Display  40  has an array of pixels P (pixel array  14 ) that present images to a user (see, e.g., user eye  46 , which is viewing display  40  in direction  48  through an optical system based on catadioptric lens  20 ). Pixel array  14  of display  40  may be based on a liquid crystal display, an organic light-emitting diode display, an emissive display having an array of crystalline semiconductor light-emitting diode dies, and/or displays based on other display technologies. In a preferred embodiment, the display is a self emitting display, which can be more compact since illumination optics are not required. Separate left and right displays may be included in device  10  for the user&#39;s left and right eyes. Each display such as display  40  of  FIG. 1  may be spherically (or aspherically) curved, e.g., surface S 4  of display  40 , which faces eye  46 , may be concave. 
     Visual content (e.g., image data for still and/or moving images) may be provided to display  40  using control circuitry  42  that is mounted in device  10  and/or control circuitry that is mounted outside of 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  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. Illustrative configurations in which control circuitry  42  provides a user with virtual reality content using displays such as display  40  may sometimes be described herein as an example. In general, however, any suitable content may be presented to a user by control circuitry  42  using display  40 . 
     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, sensors (e.g., a force sensors, temperature sensors, magnetic sensors, accelerometers, gyroscopes, and/or other sensors for measuring orientation, position, and/or movement of device  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 one or more cameras (e.g., cameras for capturing images of the user&#39;s surroundings, cameras for performing gaze detection operations by viewing eyes  46 , and/or other cameras). 
     As shown in  FIG. 1 , display  40  may have a concave surface S 4 . With one illustrative configuration, concave surface S 4  of pixel array  14  and display  40  may be a spherical surface and may be radially symmetric about axis  41 . Aspherical surface shapes may also be used for surface S 4 . Catadioptric lens  20  may be configured to focus image light from pixel array  14  into eye box  43  (e.g., a circle of about 10-20 mm in diameter). Eye  46  may be located about 10-30 mm from the innermost surface of lens  20 . The field of view of lens  20  may be characterized by angles A 1  and A 2  with respect to axis  41 . Angle A 1  may be at least 70° or at least 80° and angle A 2  may be at least 30° or at least 40° (e.g., when eye  46  is a right eye and when lens  20  is being viewed from above). Nasal (nose-facing) angle A 2  is preferably less than about 50°, because the user&#39;s nose prevents a wider nasal field of view. The temporal (temple-facing) angle of view A 1  may be larger (e.g., at least 80°) to expand a user&#39;s peripheral vision. Overall, the field of view of each lens  20  (e.g., the field of view per eye) may be at least 120°, at least 125°, less than 160°, or other suitable value and the resulting binocular field of view (the field of view for both of a user&#39;s eyes taken together) may be at least 150°, at least 160° or other suitable value. 
     Catadioptric lens  20  may include lens elements such as lens elements  26  and  32 . Lens elements  26  and  32  may be formed from glass, polymer, or other materials. Lens elements  26  and  32  may be characterized by curved surfaces S 1 , S 2 , and S 3 . Curved surfaces S 1 , S 2 , and S 3  of lens element  26  and  32  may be spherical and curved surface S 4  of display  40  may be spherical. If desired, one or more of these surfaces may be aspherical. Surface S 3  may be a convex surface and may face concave surface S 4  of pixel array  14 . Lens element  36  may have opposing convex and concave surfaces. Surface S 3  may form the convex surface of lens element  26  and surface S 2 ′ may form the opposing concave surface of lens element  26 . Lens element  32  may also have opposing convex and concave surfaces. Surface S 1  may form the concave surface of lens element  32  and surface S 2  may form the convex surface of lens element  32 . Concave surface S 2 ′ has a curvature that matches that of convex surface S 2 , so concave surface S 2 ′ may sometimes be referred to as surface S 2  or surfaces S 2  and S 2 ′ may collectively be referred to as the curved surface between elements  26  and  32 . 
     Optical structures such as partially reflective coatings, wave plates, reflective polarizers, linear polarizers, antireflection coatings, and/or other optical components may be incorporated into device  10 . These optical structures may allow light rays from display  40  to be emitted from surface S 4  of display  40  and to pass through and/or reflect from surfaces in lens  20  such as surfaces S 1 , S 2 , and S 3 . The radius of curvature of surfaces S 1 , S 2 , S 3 , and S 4  may be about 10-70 mm, at least 20 mm, less than 60 mm, 15-35 mm, 20-30 mm, 20-40 mm, or other suitable size. As shown in  FIG. 1 , lens elements  26  and  32  may be concentric dome lenses that together form a cemented doublet with films and coatings on the various surfaces to control the path of the image light as it passes through the catadioptric lens  20  and may have respective thicknesses TH 1  and TH 2 . Thickness TH 1  may be uniform throughout element  26  (e.g., TH 1  may vary by less than 5%, less than 10%, or less than another suitable amount throughout element  26 ). Thickness TH 2  may be uniform throughout element  32  (e.g., TH 2  may vary by less than 5%, less than 10%, or less than another suitable amount throughout element  26 ). 
     Chromatic aberrations may be minimized by forming most of the lens power of lens  20  from the reflective structures of lens  20  and by forming only a small amount (e.g., negligible amount) of the lens power of lens  20  through refraction by lens elements  32  and  26 . As an example, lens  20  may be characterized by a refractive effective focal length of −170 mm and a total effective focal length of +35 mm. With this type of configuration the overall focal length of lens  20  has a positive sign rather than a negative sign when the reflective contribution and the refractive contribution are combined because the reflective structures of lens  20  dominate the overall performance of the lens. This helps reduce chromatic aberrations which are associated with refractive lens power. In general, lens  20  may have any suitable focal length (e.g., 30-40 mm, at least 15 mm, at least 25 mm, less than 45 mm, less than 55 mm, etc.). The reflective contribution to the lens power of lens  20  may be greater than the refractive contribution to the lens power (e.g., the reflective contribution may be at least three times, at least five times, at least ten times, or more than the refractive contribution). 
     Linear polarizer  16  and a retarder such as a quarter wave plate  15  may be located between pixel array  14  and lens element  26 . Linear polarizer  16  and quarter wave plate  15  may be used to circularly polarize light emitted by display  40 . Linear polarizer  16  may have a pass axis aligned with the X-axis of  FIG. 1  (as an example) and the fast axis of the quarter wave plate  14  is aligned at 45 degrees to the pass axis of the linear polarizer. 
     With the illustrative arrangement of  FIG. 1 , linear polarizer  16  is formed on surface S 4  of pixel array  14 . Linear polarizer  16  may be formed from a polarizer film that is thermoformed into a shape to match concave surface S 4  and attached to surface S 4  with a layer of adhesive such as optically clear adhesive  11 . If desired, linear polarizer  16  may be formed on convex surface S 3  of lens element  26  or may be located at other suitable locations between surfaces S 4  and S 3 . The quarter wave plate  14  can be a film or coating that is attached to the linear polarizer  16  and surface S 3 . Optional antireflection coating may be formed on any surfaces that are exposed to air (e.g., the polarizer surface or the quarter wave surface) to enhance light transmission. 
     Alternatively, quarter wave plate  15  may be located on surface S 3 , shown as quarter wave plate  18  in  FIG. 1 , where quarter wave plate  18  may be a formed film or a coating that is applied to partially reflective mirror coating  22 . Optional antireflection coating  19  may be formed on quarter wave plate  18  to enhance light transmission. 
     Surface S 3  may have significant curvature, so the use of a coating process may help ensure satisfactory formation of quarter wave plate  18 . With one illustrative configuration, quarter wave plate  18  may be a liquid-crystal-based retarder layer (e.g., a birefringent coating formed from liquid crystals in a liquid polymer binder that is applied to surface S 3  on top of layer  22  by spin coating or other suitable deposition techniques followed by ultraviolet light curing and/or thermal curing). In either embodiment, associating a quarter wave plate ( 15  or  18 ) with a linear polarizer  16  will cause the image light entering the lens  20  to be circularly polarized provided that the fast axis of the quarter wave plate is oriented at 45 degrees to the pass axis of the linear polarizer  16 . 
     A partially reflective mirror coating forms partially reflective mirror  22 . The coating for mirror  22  is a metal mirror coating or other mirror coating layer such as a dielectric multilayer coating with a 50% transmission and a 50% reflection or other suitable light transmission and reflection values. Partially reflective mirror  22  may be formed on convex surface S 3  of lens element  26 . When circularly polarized image light (e.g., ray R 1 ) strikes partially reflective mirror  22 , a portion of ray R 1  will pass through partially reflective mirror  22  to become reduced-intensity ray R 2 . Simultaneously, a portion of ray R 1  will be reflected by the partially reflective mirror  22 . This reflected portion of ray R 1  will pass back through the quarter wave plate  18  or  15  such that the circularly polarized light is converted to linearly polarized light with the opposite polarization state so that it will be absorbed by the linear polarizer  16 , thereby trapping the reflected light and reducing stray light in the optics of the electronic device  10 . 
     Ray R 2  is circularly polarized. A second quarter wave plate such as quarter wave plate  28  may be included in optical system  20  between the partially reflective mirror  22  and a reflective polarizer  30 , to convert the circular polarization state of ray R 2  into a linear polarization state. The second quarter wave plate may be formed under the partially reflective mirror  22  on surface S 3  (not shown), on convex surface S 2  of lens element  32  (shown as quarter wave plate  28 ), on associated concave surface S 2 ′ of lens element  26 , and/or may be formed on the concave surface S 1  of lens element  32  (not shown) with reflective polarizer  30  on top of the quarter wave plate. Alternatively, a thin (about 1 mm) curved spherical dome lens  34  may be provided with an optically clear adhesive  35  that adhesively bonds the reflective polarizer to it. The dome lens  34  with the reflective polarizer  30  can then be adhesively bonded to surface S 1 . In the illustrative configuration of  FIG. 1 , quarter wave plate  28  has been formed from a coating layer (e.g., a birefringent liquid-crystal-based polymer layer) on surface S 2 . Optically clear adhesive layer  29  may be used to attach lens elements  26  and  32  together. 
     Quarter wave plate  28  may convert circularly polarized ray R 2  into a linearly polarized ray R 3  aligned with the Y-axis of  FIG. 1 . Reflective polarizer  30  may be a polymer film (e.g., a multilayer reflective polarizer film or a wire-grid polarizer film) that is thermoformed onto concave surface S 1  of lens element  32 . However, surface S 1  may have significant curvature making thermoforming undesirable due to the large distortion imparted to the reflective polarizer film, as a result, it may be desirable to form reflective polarizer  30  from a coating layer. With one illustrative configuration, reflective polarizer  30  may be a wire-grid polarizer formed using a sol-gel process. During formation of reflective polarizer  30 , a glass-based sol-gel liquid is applied to surface S 1  and is patterned using a stamper with a nanoscale polarizer pattern, where the solgel can included electrically conductive components or electrically conductive materials can be preferentially applied to the solgel pattern to form an array of nanoscale wire conductors that together form the wire-grid polarizer. Other reflective polarizer coating techniques may be used, if desired. 
     Reflective polarizer  30  may have orthogonal reflection and pass axes. Light that is polarized parallel to the reflection axis of reflective polarizer  30  will be reflected by reflective polarizer  30 . Light that is polarized perpendicular to the reflection axis and therefore parallel to the pass axis of reflective polarizer  30  will pass through reflective polarizer  30 . In the illustrative arrangement of  FIG. 1 , reflective polarizer  30  has a reflection axis that is aligned with the Y-axis, so ray R 3  will reflect from reflective polarizer  30  at surface S 1  as reflected ray R 4 . 
     Reflected ray R 4  has a linear polarization aligned with the Y-axis. After passing through quarter wave plate  28 , the linear polarization of ray R 4  will be converted into circular polarization (i.e., ray R 4  will become circularly polarized ray R 5 ). 
     Circularly polarized ray R 5  will travel through lens element  26  and a portion of ray R 5  will be reflected in the Z direction by the partially reflective mirror  22  on the convex surface S 3  of lens element  26  as reflected ray R 6 . The reflection from the curved shape of surface S 3  provides optical system  20  with additional optical power. The portion of ray R 5  that is transmitted by partially reflective mirror  22  is converted from circularly polarized light to linearly polarized light by quarter wave plate  18 . This linearly polarized light has a polarization aligned with the Y axis so that it is absorbed by linear polarizer  16 . As a result, contrast degradation and stray light artifacts from the transmitted portion of ray R 5  are prevented in the image viewed by the user. 
     Ray R 6  is circularly polarized. After passing back through lens element  26  and quarter wave plate  28 , ray R 6  will become linearly polarized (ray R 7 ). The linear polarization of ray R 7  is aligned with the X-axis of  FIG. 1 , which is parallel to the pass axis of reflective polarizer  30 . Accordingly, ray R 7  will pass through reflective polarizer  30  to provide a viewable image to the user. If desired, device  10  may include an additional linear polarizer such as a clean-up linear polarizer (not shown) positioned between the reflective polarizer  30  and the user&#39;s eye  46 , where the clean-up linear polarizer  34  has a pass axis aligned with the pass axis of reflective polarizer  30  (i.e., parallel to the X-axis in this example) and will therefore remove any residual non-X-axis polarization from ray R 7  before ray R 7  reaches viewers eye  46 . The clean-up polarizer will also absorb any light from the environment that would otherwise be reflected by the reflective polarizer  30 . The clean-up linear polarizer may be a polarizer film that is thermoformed onto reflective polarizer  30  and attached using adhesive  35  or may be located elsewhere between the reflective polarizer  30  and eye  46 . 
     Deposition techniques that may be used in forming coatings in lens  20  and on display  40  include liquid coating techniques (ink-jet printing, screen printing, pad printing, spinning, dipping, dripping, painting, and spraying), atomic layer deposition, physical vapor deposition techniques such as sputtering and evaporation, chemical vapor deposition, plasma-enhanced chemical vapor deposition, and/or other thin-film deposition techniques. 
     The configuration of  FIG. 1  (e.g., the curved concave emitting surface S 4  of display  40 ) may help improve optical performance for device  10 . As an example, curved surface S 4  may help reduce field curvature across the displayed field of view so that the user is presented an image with more uniform sharpness. Field curvature (in diopters D or m −1 ) for the arrangement of  FIG. 1  has been modeled and plotted as a function of light ray angle A (e.g., angle A 1  and A 2 ) relative to axis  48  in the graph of  FIG. 2 . As shown by curves  50  (tangential) and  52  (sagittal), field curvature may be less than 0.15 diopters across all expected angles of view (e.g., 0-80° in the example of  FIG. 2 ). In  FIG. 3 , the modulus of the optical transfer function for lens  20  has been plotted as a function of spatial frequency. Curve  58  represents the diffraction limit. Curves  54  and  56 , which correspond to light rays oriented at an angle A of 80° with respect to axis  41  of  FIG. 1 , respectively show how tangential light and sagittal light may exhibit satisfactory transfer function values and therefore shows how lens  20  exhibits satisfactory optical performance at large field angles. The curved concave emitting surface S 4  of the display  40  also reduces the cone angle of image light at each surface.  FIG. 1  shows that the image light (R 1  to R 7 ) is provided such that the chief ray angle at surfaces S 4 , S 3 , S 2  and S 1  is less than 10 degrees from normal. By reducing the angular range that the linear polarizer, quarter wave plate, partially reflective mirror coating and reflective polarizer need to operate with, the performance of the films and coatings can be greatly improved so that image contrast is increased and ghosting is reduced. 
       FIG. 4  is a front view of a portion of device  10  showing an illustrative outline (e.g., an illustrative shape when viewed along axis Z) of lens  20  relative to display  40  and support structures  60 , where the lens  20  or the display  40  may be ovoid shaped or polyhedral shaped to better fit the contours of the user&#39;s face or eye socket. System components such as display  40  and lens  20  may be supported by support structures  60  that are configured to be worn on the head of a user. Support structures  60 , which may sometimes be referred to as a device housing or body, may support a pair of lenses (e.g., left and right lenses respectively for a user&#39;s left and right eyes and associated left and right displays  40 ) such as catadioptric lens  20  of  FIG. 1 . Support structures (housing structures)  60  may have the shape of a frame for a pair of glasses (e.g., device  10  may resemble eyeglasses), may have the shape of a helmet (e.g., device  10  may form a helmet-mounted display), may have the shape of a pair of goggles, or may have any other suitable head-mounted shape that allows support structures  60  to be worn on the head of a user. As shown in  FIG. 1 , support structures  60  of  FIG. 4  may support lens  20  and display(s)  40  in front of a user&#39;s eyes (see, e.g., eye  46  of  FIG. 1 ) so that the user may view display  40  through lens  20  in direction  48 . If desired, support structures  60  may have other suitable configurations. 
     Support structures  60  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. 
     Input-output devices  44  and control circuitry  42  of  FIG. 1  may be mounted in support structures  60  and/or portions of input-output devices  44  and control circuitry  42  may be coupled to device  10  using a cable, wireless connection, or other signal paths. 
     If desired, the curvature of display  40  or position of the display  40  relative to the lens  20  may be adjusted dynamically. For example, control circuitry  42  may adjust the curvature of display  40  to adjust the focus of device  10 . The position of the display  40  relative to the lens  20  may be made with actuators and guidance mechanisms to move the components relative to one another in a controlled fashion. Focus adjustments may be made, for example, to correct user vision defects such as myopia and farsightedness or may be made dynamically based on the type of content being displayed on display  40  (distant content such as mountains or close-up content such as the faces of nearby people in a scene) to reduce vergence-accommodation mismatch effects. 
     An illustrative configuration that may be used in device  10  to adjust the curvature of display  40  is shown in  FIG. 5 . As shown in  FIG. 5 , display  40  may be mounted in a support structure such as frame  62 . Frame  62  may have an opening that receives display  40  so that an air-tight cavity such as cavity  64  is formed behind display  40 . A pump (or diaphragm actuator) such as pump  66  may receive control signals from control circuitry  42  via control input  68 . In response to control signals from control circuitry  42 , pump  66  may increase or decrease the pressure of air or other gas or fluid in cavity  64 . Increases in pressure will tend to flatten display  40  so that display  40  is more planar. Decreases in pressure will tend to bow display  40  in the −Z direction so that display  40  is more curved and less planar. Adjustments to the curvature of display  40  and/or the spacing between display  40  and lens  20  may also be made using piezoelectric actuators or other actuators having structures that expand and contract in response to changes in applied voltage, using shape memory alloys, using electromagnetic actuators, using servomotors, other actuators, and/or other display curvature adjusting device. The use of a display curvature adjusting device such as a pressure-based actuator is illustrative. 
     In embodiments, the lens is comprised of two or more dome lenses with films or coatings on each surface. 
     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: 20180109
Publication Date: 20191231
Grant Date: 20191231
Priority Date: 20170622
Inventors: CHAN, VICTORIA C.
BORDER, JOHN N.
PETROV, YURY A.
YOKOYAMA, YOSHIHIKO
Assignee: APPLE INC
CPC Classifications: [{"code": "G06F3/033", "inventive": false, "first": false, "tree": "[]"}, {"code": "G02B2027/0185", "inventive": false, "first": false, "tree": "[]"}, {"code": "G02B27/28", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02B27/0176", "inventive": false, "first": false, "tree": "[]"}, {"code": "G02B17/0856", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02B27/0172", "inventive": true, "first": true, "tree": "[]"}, {"code": "G02B27/0172", "inventive": true, "first": true, "tree": "[]"}, {"code": "G02B27/0955", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02B27/0176", "inventive": false, "first": false, "tree": "[]"}, {"code": "G02B27/0176", "inventive": false, "first": false, "tree": "[]"}, {"code": "G02B27/0955", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02B27/0172", "inventive": true, "first": true, "tree": "[]"}, {"code": "G06F3/01", "inventive": true, "first": false, "tree": "[]"}]
Family ID: 69057588