PATENT DOCUMENT

Publication Number: US-11099386-B1
Application Number: US-201916283550-A
Country: US
Kind Code: B1

Title: Display device with optical combiner

Abstract:
An optical system may include equipment with a housing that is configured to receive external equipment such as a cellular telephone. The external equipment may have a display mounted on a front face of the external equipment and may have additional components such as a front-facing camera. Communications circuitry in the equipment may support wired and wireless communications with the external equipment. An optical combiner in the equipment may be used to combine display image light emitted from pixels in the display with real-world image light received from external objects. The optical combiner may have a reflector with a concave lens shape that focuses light from the display towards eye boxes in which a viewer&#39;s eyes are located. The reflector may be a partial mirror or a reflective polarizer. The reflective polarizer and additional components may be used in implementing a tunable tint layer.

Claims:
What is claimed is: 
     
       1. Equipment operable to receive real-world image light from external real-world objects, comprising:
 a housing configured to receive a removable electronic device with a display that has pixels configured to emit display image light, wherein the removable electronic device comprises wireless communications circuitry; and 
 an optical combiner configured to combine the display image light with the real-world image light, wherein the optical combiner comprises:
 a reflective polarizer with a concave lens shape configured to reflect the display image light; 
 a liquid crystal layer configured to receive the real-world image light; and 
 electrodes configured to apply electric fields to the liquid crystal layer. 
 
 
     
     
       2. The equipment defined in  claim 1  wherein the display image light emitted by the pixels comprises circularly polarized light and wherein the equipment further comprises a quarter wave plate configured to convert the circularly polarized light into linearly polarized light that reflects from the reflective polarizer. 
     
     
       3. The equipment defined in  claim 2  wherein the removable electronic device comprises a cellular telephone, wherein the pixels are configured to form the display in the cellular telephone, and wherein the quarter wave plate is configured to overlap the display. 
     
     
       4. The equipment defined in  claim 2  wherein the reflective polarizer comprises a stack of dielectric layers. 
     
     
       5. The equipment defined in  claim 2  wherein the reflective polarizer comprises a wire grid polarizer. 
     
     
       6. The equipment defined in  claim 5  wherein the wire grid polarizer comprises wires shorted together to form at least some of the electrodes. 
     
     
       7. The equipment defined in  claim 2  further comprising a linear polarizer, wherein the liquid crystal layer is interposed between the reflective polarizer and the linear polarizer. 
     
     
       8. The equipment defined in  claim 2  wherein the electrodes include first electrodes of transparent conductive material and second electrodes of transparent conductive material and wherein the liquid crystal layer is interposed between the first and second electrodes. 
     
     
       9. The equipment defined in  claim 1  further comprising a first linear polarizer and a second linear polarizer, wherein the first linear polarizer is interposed between the liquid crystal layer and the reflective polarizer and wherein the liquid crystal layer is interposed between the first linear polarizer and the second linear polarizer. 
     
     
       10. The equipment defined in  claim 1  wherein the reflective polarizer comprises a wire grid polarizer and wherein there are no polyimide liquid crystal alignment layers between the wire grid polarizer and the liquid crystal layer. 
     
     
       11. The equipment defined in  claim 1  wherein the electrodes include strips of transparent conductive material and a polyimide alignment layer that covers the strips of transparent conductive material. 
     
     
       12. The equipment defined in  claim 1  further comprising first and second transparent substrates, wherein the liquid crystal layer is interposed between the first and second transparent substrates, wherein the reflective polarizer is formed on a first side of the substrate and wherein the liquid crystal layer is on an opposing second side of the first substrate. 
     
     
       13. The equipment defined in  claim 12  further comprising a linear polarizer, wherein the second substrate is interposed between the linear polarizer and the liquid crystal layer. 
     
     
       14. The equipment defined in  claim 1  wherein the housing comprises a head-mountable housing. 
     
     
       15. The equipment defined in  claim 14  further comprising:
 communications circuitry configured to communicate with the removable electronic device; 
 a gaze tracking sensor; and 
 visual inertial odometry circuitry. 
 
     
     
       16. Equipment operable to receive real-world image light from external real-world objects, comprising:
 a housing configured to receive a removable electronic device with a camera and a battery, wherein the removable electronic device has pixels configured to emit display image light; and 
 an optical combiner configured to combine the display image light with the real-world image light, wherein the optical combiner comprises a reflective polarizer with a concave lens shape configured to reflect the display image light. 
 
     
     
       17. The equipment defined in  claim 16  wherein the housing comprises a head-mountable housing, the equipment further comprising:
 a liquid crystal layer; 
 first and second electrodes, wherein the liquid crystal layer is interposed between the first and second electrodes; and 
 a linear polarizer, wherein the liquid crystal layer and the first and second electrodes are interposed between the linear polarizer and the reflective polarizer. 
 
     
     
       18. The equipment defined in  claim 16 , further comprising:
 a circular polarizer coupled to the housing that is configured to overlap the camera in the removable electronic device wherein the circular polarizer does not overlap the pixels when the removable electronic device is received within the housing. 
 
     
     
       19. The equipment defined in  claim 18  wherein the removable electronic device comprises a cellular telephone, wherein the pixels form a display on a front face of the cellular telephone, wherein the camera comprises a front-facing camera on the cellular telephone, and wherein the circular polarizer includes a quarter wave plate and a linear polarizer. 
     
     
       20. The equipment defined in  claim 19  wherein the linear polarizer is interposed between the quarter wave plate and the front-facing camera. 
     
     
       21. Equipment operable to receive real-world image light from external real-world objects, comprising:
 a housing configured to receive external equipment with a display that has pixels configured to emit display image light; and 
 an optical combiner configured to combine the display image light with the real-world image light, wherein the optical combiner comprises:
 a reflective polarizer with a concave lens shape configured to reflect the display image light; 
 a liquid crystal layer configured to receive the real-world image light; 
 electrodes configured to apply electric fields to the liquid crystal layer; and 
 a first linear polarizer and a second linear polarizer, wherein the first linear polarizer is interposed between the liquid crystal layer and the reflective polarizer and wherein the liquid crystal layer is interposed between the first linear polarizer and the second linear polarizer.

Description:
This application claims priority to U.S. provisional patent application No. 62/637,260 filed Mar. 1, 2018, which is hereby incorporated by reference herein in its entirety. 
    
    
     FIELD 
     This relates generally to optical systems, and, more particularly, to optical systems with optical combiners. 
     BACKGROUND 
     Optical systems may be used to provide images to a viewer. In some optical systems, it is desirable for both computer-generated and real-world images to be viewed simultaneously. In this type of system, an optical combiner can be used to merge image light from a display with real-world image light. If care is not taken, however, stray light reflections in an optical combiner or excessive light from an external object can adversely affect system performance. 
     SUMMARY 
     An optical system may include equipment with a housing that is configured to receive external equipment such as a cellular telephone. The housing may be a head-mountable housing. 
     The external equipment may have a display mounted on a front face of the external equipment and may have additional components such as a front-facing camera. Communications circuitry in the equipment may support wired and wireless communications with the external equipment. 
     An optical combiner in the equipment may be used to combine display image light emitted from pixels in the display with real-world image light received from external objects. The optical combiner may have a reflector with a concave lens shape that redirects and focuses light from the display towards eye boxes in which a viewer&#39;s eyes are located. 
     With one arrangement, the reflector may be a partial mirror. An optical component such as a circular polarizer may overlap the front-facing camera without overlapping the display on the front face of the cellular telephone to suppress stray light reflections from the display into the front-facing camera. 
     With another arrangement, the reflector may be a reflective polarizer. The reflective polarizer and additional components such as layers of electrodes, additional polarizer layers, and a liquid crystal layer may be used in implementing a tunable tint layer. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a diagram of an illustrative optical system in accordance with an embodiment. 
         FIG. 2  is a cross-sectional side view of an illustrative optical system in accordance with an embodiment. 
         FIG. 3  is a cross-sectional side view of an illustrative display in accordance with an embodiment. 
         FIG. 4  is a cross-sectional side view of an illustrative stack of dielectric layers in accordance with an embodiment. 
         FIG. 5  is a cross-sectional side view of an illustrative optical system in accordance with an embodiment. 
         FIG. 6  is a cross-sectional side view of an illustrative tunable tint layer in accordance with an embodiment. 
         FIG. 7  is a front view of illustrative electrodes that may be used in a two-dimensional tunable tint layer in an optical system in accordance with an embodiment. 
         FIG. 8  is a cross-sectional side view of a substrate having electrodes and antireflection layers in accordance with an embodiment. 
         FIG. 9  is a graph showing illustrative arrangements for controlling liquid crystals in a tunable tint layer in accordance with embodiments. 
         FIGS. 10 and 11  are cross-sectional side views of illustrative optical combiners with tunable tint layers in accordance with embodiments. 
     
    
    
     DETAILED DESCRIPTION 
     Optical systems may be used to present images to a user. In some mixed reality systems, displays present computer-generated content that is overlaid on top of real-world images. An optical system may use an optical combiner to combine light from real-world images with image light from a display. The optical combiner may include a tunable tint layer. The tunable tint layer may be used to selectively adjust the amount of real-world image light that is passing to a viewer relative to the computer-generated (virtual reality) content from the display. 
     An illustrative optical system is shown in  FIG. 1 . As shown in  FIG. 1 , optical system  8  may include equipment  10 A and  10 B. Equipment  10 A may be, for example, a portable electronic device such as a cellular telephone. Equipment  10 B may be a head-mounted device with an optical combiner. In some configurations, the components of equipment  10 A and  10 B may be formed as an integral unit. In other configurations, equipment  10 B may serve as a support structure for equipment  10 A. With this type of arrangement, equipment  10 A may be used in conjunction with equipment  10 B or may be used separately. Configurations for system  8  in which system  8  includes removable equipment  10 A may sometimes be described herein as an example. 
     In the illustrative arrangement of  FIG. 1 , system  8  includes a support structure such as housing  12 . Housing  12  may be formed from glass, polymer, metal, fabric, natural materials, ceramic, and/or other materials. Housing  12  may be configured to be worn on the head of a user. For example, housing  12  may have head-mounted portions  12 ′ that are configured to form head-mountable support structures such as straps, helmet support structures, portions of a hat, goggles, or glasses, etc. Housing  12  may be formed as part of equipment  10 B and may be configured to receive equipment  10 A when it is desired to support equipment  10 A during use of system  8 . Housing  12  may, as an example, have portions forming a recess that receives equipment  10 A and holds equipment  10 A in place while equipment  10 A is presenting computer-generated images on a display in equipment  10 A. 
     Equipment  10 A and/or  10 B may include components such as control circuitry  14 , input-output devices  16 , and other components  18 . Control circuitry  14  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  14  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  14  may be used to transmit and receive data (e.g., wirelessly and/or over wired paths). This allows equipment  10 A and  10 B to communicate wirelessly and/or over a wired connection between equipment  10 A and  10 B. The communications circuits of circuitry  14  may also be used to support wired and/or wireless circuitry with external equipment (e.g., remote controls, host computers, on-line content servers, etc.). 
     In some arrangements, control circuitry  14  in equipment  10 A and/or  10 B may use a display in equipment  10 A to display images. These images, which may sometimes be referred to as computer-generated content or computer-generated images, may be associated with a virtual world, may include pre-recorded video for a movie or other media, or may include other images. Image light  24  (display image light) from computer-generated images in equipment  10 A may be provided to equipment  10 B (e.g., through free space). Equipment  10 B may include an optical combiner. The optical combiner may combine real-world image light  22  associated with real-world images of real-world objects  20  with display image light  24  associated with computer-generated (non-real-world) images, thereby producing merged image light  26  for viewing by viewer (viewer eye)  30  in eye box  28 . System  8  may have two associated eye boxes  28  for providing images to a user&#39;s left and right eyes. 
     Input-output devices  16  in equipment  10 A and/or  10 B may be coupled to control circuitry  14  in equipment  10 A and/or  10 B. Input-output devices  16  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  16  may include buttons, joysticks, keypads, keyboard keys, touch sensors, track pads, displays, touch screen displays, microphones, speakers, light-emitting diodes and/or lasers 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 system  8 , proximity sensors, capacitive touch sensors, strain gauges, gas sensors, pressure sensors, ambient light sensors, and/or other sensors). Devices  16  can include cameras (digital image sensors) for capturing images of the user&#39;s surroundings, cameras for performing gaze detection operations by viewing eyes  30 , and/or other cameras. For example, input-output devices  16  may include one or more cameras for producing data that is fused with data from an inertial measurement unit having an accelerometer, compass, and/or gyroscope for implementing a visual inertial odometry system). Devices  16  may also include depth sensors (e.g., sensors using structured light and/or using binocular cameras). In some configurations, light-based and/or radio-frequency-based sensors may be used for external object tracking (e.g., lidar, radar, and/or other detection and ranging applications). 
     Equipment  10 A and/or  10 B may also include other components  18 . Components  18  may include batteries for powering the electrical components of equipment  10 A and/or  10 B, optical components, and/or other devices. To combine display image light  24  from a display in equipment  10 A with real-world image light  22  to produce merged light  26 , components  18  in equipment  10 B may include an optical combiner. The optical combiner may be passive (e.g., a partially reflective mirror combiner) and/or may include one or more adjustable components (e.g., a tunable tint layer, sometimes referred to as an adjustable light modulator or adjustable light absorbing layer). Adjustable optical components in the optical combiner may impart global changes to light  22  (e.g., a global change in light intensity) and/or may be two-dimensional components (e.g., pixelated components) that can impart changes in particular regions of the optical combiner (e.g., localized increases in light absorption). This allows real-world image light  22  to be locally dimmed (as an example) to help reduce external light intensity when virtual objects in image light  24  are being overlaid on portions of a real-world scene. 
     A cross-sectional side view of system  8  in an illustrative configuration in which housing  12  of equipment  10 B serves as head-mounted support structures for receiving a removable device (equipment  10 A) is shown in  FIG. 2 . Equipment  10 B includes optical combiner  34 . Combiner  34  has a curved shape (see, e.g., curved inner surface such as concave lens shaped surface  36 ) and includes a reflective layer that has a corresponding concave lens shape. The reflective layer may be a partially reflective mirror, a reflective polarizer, or other reflective structures for reflecting light  24  towards eye box  28  and eye  30 . The reflective layer may be formed in a curved shape (e.g., on curved inner surface  26 ) to form a concave lens shape that allows the reflective layer to form a reflective lens that focuses images displayed on the display of equipment  10 A for viewing by user&#39;s eye(s)  30 . At the same time, combiner  34  passes real-world image light  22  to eye  30  without significant distortion so that the user may view real-world objects such as external object  20 . 
     Input-output components  16  (e.g., a gaze tracking system, a front-facing or side-facing camera, a camera in visual odometry circuitry, depth sensors and other sensors, etc.) can be mounted in one or more locations on housing  12  such as locations  32  and may point towards eye  30 , external object  20  and/or other external and/or internal directions. Housing  12  may, if desired, have a transparent portion such as portion  12 G (e.g., a planar layer of glass, transparent polymer, etc.) that receives the front face (and display) of equipment  10 A when equipment  10 A is received within equipment  10 B. One or more coatings or other optical layers may be formed on all or part of a transparent substrate in portion  12 G. 
       FIG. 3  is a cross-sectional side view of an illustrative display for system  8 . Display  38  may be a liquid crystal display, an organic light-emitting diode display or other light-emitting diode display, a liquid crystal-on-silicon display, a microelectromechanical systems (MEMS) display, and electrophoretic display, and/or other suitable display. Display  38  may include one or more support structures such as substrate  40 . An array of pixels  42  may be formed on substrate  40  to form a display. The display may emit display images (e.g., computer-generated content) based on information from control circuitry  14 . 
     Optical layers such as layers  44 ,  46 ,  48 , and/or additional layers may be formed on pixels  42  (e.g., as coating layers that overlap pixels  42 ). With one illustrative configuration, layer  44  is a wave plate such as a quarter wave plate and layer  46  is a linear polarizer. Together, layer  44  and layer  46  form a circular polarizer that helps suppress ambient light reflections from reflective structures in pixels  42 . Layer  48  may be a wave plate such as a quarter wave plate. Emitted display image light from pixels  42  is linearly polarized upon passing through linear polarizer layer  46 . After passing through quarter wave plate layer  48 , this linearly polarized image light  24  may become circularly polarized (e.g., to enhance compatibility with users wearing polarized sunglasses). 
     Some configurations for system  8  include antireflection coatings and other layers formed from a stack of dielectric films (sometimes referred to as thin-film interference filters). An illustrative dielectric stack is shown in  FIG. 4 . As shown in  FIG. 4 , dielectric stack  50  includes a stack of dielectric layers  52 . Layers  52  may be organic layers (e.g., polymer layers) and/or inorganic dielectric layers (e.g., metal oxides such as titanium oxide, niobium oxide, tantalum oxide, aluminum oxide, zinc oxide, other inorganic layers such as a silicon oxide layer, a silicon oxynitride layer, a nitride layer such as a silicon nitride layer, etc.). Layers  52  may have alternating refractive index values (e.g., to form a thin-film filter that serves as a partial mirror or an antireflection coating). In some optical components (e.g., a reflective polarizer film used as a reflective layer in optical combiner  34 ), layers  52  may include birefringent films (e.g., stretched polymer films) that alternate with non-birefringent dielectric layers  52 . 
       FIG. 5  is a cross-sectional side view of system  8  in an illustrative configuration in which optical combiner  34  includes a substrate such as substrate  70  having a concave-lens-shaped inner surface that supports a reflective layer such as partially reflective mirror layer  72 . The reflectively of mirror layer  72  may be, for example, about 10%-90%, 30-70%, 40-60%, or other suitable non-negligible reflectivity value that helps reflect light from display  38  towards the eye of a user while exhibiting non-negligible transmission (e.g., 10-90%, 30-70%, 40-60%, or other suitable non-negligible light transmission value) that helps transmit light from real-world objects towards the eye of a user. Mirror layer  72  may be formed from a thin metal layer, a dielectric stack such as stack  50  (e.g., a thin-film interference filter configured to form a partial mirror), or other reflective layer that is relatively polarization insensitive (as an example). 
     Transparent portion  12 G of housing  12  may have a transparent substrate such as substrate  58  that partially or fully overlaps display  38  on the front face of equipment  10 A (e.g., the front face of a cellular telephone or other portable electronic device). Substrate  58 , which may be formed from transparent glass, transparent polymer, or other transparent material, may help support equipment  10 A when equipment  10 A is coupled to equipment  10 B. A front-facing camera such as camera  54  in equipment  10 A may capture images of external objects through combiner  34 . To suppress reflections of stray light  24  emitted by display  38 , a circular polarizer such as circular polarizer  62  may be provided on portion  12 G of housing  12  (e.g., on substrate  58 ) in a location that overlaps front-facing camera  54  without overlapping display  38 . Antireflection coating layers  60  formed from dielectric stacks (e.g., thin-film interference filters including stacks  50  of layers  52  of  FIG. 4 ) may be formed on one or both sides of substrate  58 . As shown by optional coating layer  60 ′, an antireflection coating layer may be formed over circular polarizer  62 . 
     During operation, display  38  emits image light  24  that is reflected from a reflective layer on concave lens surface  36  of combiner  34  such as mirror layer  72  towards the user&#39;s eyes. Display  38  may also emit stray light  24  (e.g., light emitted at oblique angles that is not reflected towards the user&#39;s eyes by mirror layer  72 ). This stray light  24 , which may be circularly polarized as described in connection with emitted light  24  of  FIG. 3 , may be reflected towards front-facing camera  54  from mirror  72  as circularly polarized stray light  56 . Unless suppressed, these stray light reflections will tend to interfere with the operation of camera  54 . 
     Circular polarizer  62  may include layers such as wave plate  64  (e.g., a birefringent layer of dielectric) and linear polarizer  66 . Wave plate  64  is configured to convert circularly polarized stray light  56  to linearly polarized light. Linear polarizer  66  is configured with a pass axis that is orthogonal to the polarization axis of this linearly polarized light. As a result, polarizer  66  will absorb the reflected stray light  56  after the reflected stray light has been converted to a linearly polarized state by quarter wave plate  64 . Unpolarized light (e.g., light  22  from external objects  20 ) passes through combiner  34  and wave plate  64  without becoming linearly polarized. As a result, a portion (e.g., half) of this unpolarized real-world image light passes through linear polarizer  66  and is received and imaged by camera (image sensor)  54 . 
     If desired, optical combiner  34  may include a tunable tint layer. The tunable tint layer may impart global changes in light intensity to light passing through optical combiner  34  and/or may have pixelated regions that allow light intensity to be adjusted more granularly. Illustrative configurations of such as two-dimensional pixelated tunable tint layer may sometimes be described herein as an example. 
     Tunable tint layers may be based on guest-host liquid crystal devices and other liquid crystal components or other suitable light modulator devices. A cross-sectional side view of an illustrative tunable tint layer based on a non-guest-host liquid crystal device is shown in  FIG. 6 . 
     As shown in  FIG. 6 , tunable tint layer  74  may include transparent inner substrate  88  and transparent outer substrate  80 . Substrates  80  and  88  may be formed from transparent materials such as glass, polymer, etc. Liquid crystal layer  84  may be interposed between substrate  80  and  88 . Patterned transparent conductive electrodes  86  may be formed on the surfaces of substrates  80  and  88  that face liquid crystal layer  84 . During operation, signals (voltages) may be applied to electrodes  86  and  82  to impart a desired pattern of electric fields across layer  84 , thereby adjusting the optical properties of liquid crystal layer  84  (e.g., to locally rotate liquid crystals and thereby selectively adjust the polarization of light passing through layer  84 ). Liquid crystal layer  84  is interposed between front polarizer  100  and rear polarizer  102 , so changes in the polarization state of light passing through layer  84  can be used to adjust the light transmission of that light and thereby selectively adjust the tint (light transmission level) of tunable tint layer  74 . Polarizer layers  100  and  102  may be formed from layers that are on the inner and/or outer surfaces of substrates  88  and  80  and/or on other layers in combiner  34 . In one illustrative configuration polarizer layer  102  includes a reflective polarizer and an optional clean-up linear polarizer. 
     Electrodes  82  and  86  may have any suitable patterns and may be formed from any suitable transparent conductive materials. For example, electrodes  82  and/or  86  may be formed from patches, strips, or blanket films of a transparent conductive material such as indium tin oxide. With another illustrative arrangement, wire grid polarizer structures (e.g., narrow wires of about 100 nm in width and about 100 nm in period) may be patterned to form electrodes. In this type of arrangement, the wire grid polarizer structures may serve both to form a polarizer layer such as polarizer layer  102  and to form a set of electrodes for tunable (adjustable) tint layer  74 . Wire grid wires may also serve as a liquid crystal alignment layer. 
     With one illustrative configuration, which is illustrated in  FIG. 7 , electrodes  86  are strip-shaped electrodes (columns) each of which includes multiple wires from a wire grid polarizer layer. Each wire may be formed from a narrow strip of metal or other conductor (e.g., a wire with a width of 10-200 nm, 50 nm, at least 20 nm, less than 100 nm, or other suitable width) and each wire may be spaced from the next with a period of 100 nm, at least 30 nm, at least 70 nm, less than 150 nm, less than 250 nm, or other suitable period. Sets of adjacent wires in the wire grid polarizer may be shorted together by horizontal metal paths to form respective vertical electrode strips. Horizontal strip-shaped electrodes (rows) may be formed from respective strips of indium tin oxide or other conductive material (electrodes  82 ). If desired, both row electrodes (electrodes  82 ) and column electrodes (electrodes  86 ) may be formed from elongated rectangular strips of indium tin oxide or other conductive material. Electrodes with other patterns may also be used. The configuration of  FIG. 7  is illustrative. 
       FIG. 8  is a cross-sectional side view of a portion of a tunable tint layer with indium tin oxide electrodes  82 . As shown in  FIG. 8 , antireflection coating layers  90  (e.g., dielectric stacks forming thin-film interference filters such as stack  50  of  FIG. 4 ) may be formed above and/or below each indium tin oxide electrode to reduce reflections from the electrode (e.g., reflections that might otherwise exist because of the relatively large index of refraction of the indium tin oxide material and the resulting large index mismatch between the indium tin oxide material and the glass or polymer of substrate  80 ). This approach may be used for electrodes  86  in configurations in which electrodes  86  are formed from indium tin oxide. 
       FIG. 9  is a graph of illustrative control signals that may be applied the electrodes of tunable tint layer  74  by control circuitry  14  in equipment  10 A and/or equipment  10 B to adjust light transmission through optical coupler  34  in desired areas of coupler  34 . 
     With one illustrative configuration, which is illustrated in connection with traces  92 , liquid crystal layer  84  is a twisted nematic layer. The response (liquid crystal rotation) of the liquid crystals in layer  84  is time averaged. By varying the length of the control pulses applied in each frame and by selecting the location (e.g., the lateral position) of these control pulses (e.g., by adjusting the voltages across different portions of layer  84  by applying corresponding control signals appropriately to electrodes  82  and  86 ), the amount of liquid crystal rotation and therefore the amount of light polarization rotation that is achieved by layer  84  can be dynamically adjusted across the two-dimensional surface of tunable tint layer  74  and therefore optical combiner  34 . 
     With another illustrative configuration, which is illustrated in connection with traces  94 , liquid crystal layer  84  is formed from a bistable ferroelectric liquid crystal material. In this type of arrangement, the polarity of the control signals can be adjusted by control circuitry  14  when it is desired to change the state of liquid crystal layer  84  and thereby adjust the light polarization rotation properties of layer  84  (e.g., when it is desired to change the light transmission state of layer  74  in one or more locations across the surface of layer  74 ). 
     Cross-sectional side views of optical combiner  34  are shown in  FIGS. 10 and 11 . 
     In the illustrative configuration of  FIG. 10 , a tunable tint layer with a non-wire-grid reflective polarizer has been used in forming optical combiner  34 . Combiner  34  may have linear polarizer  100  on the outer surface of substrate  80 . As unpolarized real-world image light  22  passes through polarizer  100  it becomes linearly polarized (e.g., parallel to vertical direction  130 ). Electrodes  82  may be formed on the inner surface of substrate  80  and may be coated with a liquid crystal alignment layer such as polyimide layer  110 . The outwardly facing surface of substrate  88  may be provided with corresponding electrodes  86  covered with a liquid crystal alignment layer such as polyimide layer  112 . The orientations of layers  110  and  112  are configured to twist the liquid crystals in layer  84  so that in the absence of applied electric field across layer  84 , linearly polarized real-world image light (e.g., light  22  that has passed through linear polarizer  100 ) will be rotated 90° in polarization so that this light is polarized along direction  132  (e.g., into the page of  FIG. 10 ) as this light exits layer  84  towards the user. 
     Reflective polarizer  116  is oriented with its reflection axis along direction  130  and its transmission axis along direction  132 . As a result, light  22  that has passed through portions of layer  84  with no applied electric field and that is therefore polarized along direction  132  will be transmitted to the user as part of light  26  (e.g., light transmission will be maximized in areas of combiner  34  with no applied electric field across liquid crystal layer  84 ). In areas of optical combiner  34  for which lower light transmission values are desired, control circuitry  14  may apply an electric field across layer  84  with electrodes  86  and  82 . This changes the orientation of the liquid crystals in layer  84 , changes the associated polarization of light  22  that has passed through layer  84  (e.g., so that this light is partially or fully polarized parallel to direction  130 ), and thereby causes some or all of this light to be absorbed in reflective polarizer  116  (e.g., light transmission for areas of combiner  34  with an electric field applied across layer  84  will be low). 
     Light  24  from display  28  is initially circularly polarized, as described in connection with  FIG. 3 . An optical layer (e.g., a linear polarizer or a quarter wave plate such as quarter wave plate  150  of  FIG. 2 ) may be included on a substrate in portion  12 G of housing  12  to convert the circularly polarized light  24  that is emitted from display  38  to linearly polarized light (e.g., light polarized along direction  130 . This causes light  24  to reflect from reflective polarizer  116 , which has its reflection axis parallel to direction  130 . As a result, the reflected light  24  forms part of light  26  and is viewed by the user in eye boxes  30 . 
     In a configuration of the type shown in  FIG. 10 , reflective polarizer  116  may be formed from a dielectric stack having odd layers of a first index of refraction interleaved with even birefringent dielectric layers. The birefringent dielectric layers may exhibit the first index of refraction in a first polarization direction and may exhibit a second index of refraction in a second polarization direction that is orthogonal to the first polarization direction. When light is oriented along the first polarization direction, the stack will not reflect the light. When light is oriented along the second polarization direction, the stack will form a thin-film interference filter mirror that reflects the light. 
     If desired, an optional clean-up polarizer layer such as linear polarizer  114  may be interposed between reflective polarizer layer  116  and substrate  88 . Polarizer  114  may have a pass axis aligned with the pass axis of reflective polarizer  116  (e.g., along direction  132 ) and may help ensure that light polarized orthogonal to this pass axis is absorbed. 
     In the illustrative configuration of  FIG. 11 , the reflective polarizer (reflective polarizer  120 ) is formed using a wire grid polarizer. The wires of the wire grid polarizer may serve as a liquid crystal alignment layer, so polyimide layer  112  of  FIG. 10  may, if desired, be omitted. The wires of the wire grid structure forming reflective polarizer  20  may also be patterned to form electrodes, as described in connection with electrodes  86  of  FIG. 7 , so electrode layer  86  of  FIG. 10  can be omitted. If desired, separate electrodes  86  (e.g., indium tin oxide strips) may be added to combiner  34  of  FIG. 11 . In some arrangements, optional linear polarizer  114  (e.g., a clean-up polarizer) may be included (e.g., as layer  122 ) and/or a polyimide alignment layer may be included. The wire grid reflective polarizer arrangement of  FIG. 11  is illustrative. 
     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: 20190222
Publication Date: 20210824
Grant Date: 20210824
Priority Date: 20180301
Inventors: CHOI, Hyungryul
ZHAO, LEI
WANG, CHAOHAO
DORJGOTOV, ENKHAMGALAN
FAN JIANG, SHIH-CHYUAN
GE, ZHIBING
MYHRE, GRAHAM B.
Assignee: APPLE INC
CPC Classifications: [{"code": "G02B2027/0118", "inventive": false, "first": false, "tree": "[]"}, {"code": "G02B27/0172", "inventive": true, "first": true, "tree": "[]"}, {"code": "G02F1/133536", "inventive": false, "first": false, "tree": "[]"}, {"code": "G02F1/1313", "inventive": false, "first": false, "tree": "[]"}, {"code": "G02F1/13439", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02F1/133536", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02B2027/0118", "inventive": false, "first": false, "tree": "[]"}, {"code": "G02F1/133723", "inventive": false, "first": false, "tree": "[]"}, {"code": "G02B27/0172", "inventive": true, "first": true, "tree": "[]"}, {"code": "G02F1/133548", "inventive": false, "first": false, "tree": "[]"}, {"code": "G02F1/133536", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02F1/133723", "inventive": false, "first": false, "tree": "[]"}, {"code": "G02B2027/0118", "inventive": false, "first": false, "tree": "[]"}, {"code": "G02B27/0172", "inventive": true, "first": true, "tree": "[]"}, {"code": "G02F1/133548", "inventive": false, "first": false, "tree": "[]"}, {"code": "G02F1/13439", "inventive": true, "first": false, "tree": "[]"}]
Family ID: 77389909