PATENT DOCUMENT

Publication Number: US-10943959-B1
Application Number: US-201916270142-A
Country: US
Kind Code: B1

Title: Display device with a light modulating layer

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 include a display. To control the persistence of the display, the optical system may include a light modulating layer. The light modulating layer may switch between a transparent state in which display image light is passed through the light modulating layer to reach the viewer and an opaque state in which display image light is blocked by the light modulating layer from reaching the viewer. The light modulating layer may be placed in the transparent state for a portion of each display frame and the opaque state for the remaining portion of each display frame. The light modulating layer may be formed in the housing of the equipment that receives the external equipment or may be formed with the external equipment directly.

Claims:
What is claimed is: 
     
       1. Equipment configured to operate in combination with a removable electronic device that has a display with pixels, the equipment comprising:
 a housing configured to receive the removable electronic device; and 
 a light modulating layer in the housing that receives display image light from the pixels in the display of the removable electronic device, wherein the light modulating layer is configured to switch between a transparent state in which the display image light passes through the light modulating layer and an opaque state in which the display image light is blocked by the light modulating layer and wherein the light modulating layer is configured to be placed in the transparent state for a first length of time during each display frame of the pixels and the opaque state for a second, remaining, length of time during each display frame. 
 
     
     
       2. The equipment defined in  claim 1 , wherein the light modulating layer comprises a layer of liquid crystal material. 
     
     
       3. The equipment defined in  claim 2 , wherein the light modulating layer comprises an upper electrode layer and a lower electrode layer and the layer of liquid crystal material is interposed between the upper electrode layer and the lower electrode layer. 
     
     
       4. The equipment defined in  claim 3 , wherein the light modulating layer comprises first and second linear polarizers, wherein the lower electrode layer is interposed between the first linear polarizer and the layer of liquid crystal material, and wherein the upper electrode layer is interposed between the second linear polarizer and the layer of liquid crystal material. 
     
     
       5. The equipment defined in  claim 4 , wherein the light modulating layer comprises a quarter wave plate and wherein the first linear polarizer is interposed between the quarter wave plate and the lower electrode layer. 
     
     
       6. The equipment defined in  claim 5 , wherein the quarter wave plate receives circularly polarized display image light from the pixels. 
     
     
       7. The equipment defined in  claim 1 , wherein the light modulating layer comprises a twisted nematic cell. 
     
     
       8. The equipment defined in  claim 1 , wherein the light modulating layer comprises switchable glass. 
     
     
       9. The equipment defined in  claim 1 , wherein the first length of time is less than six milliseconds. 
     
     
       10. The equipment defined in  claim 1 , wherein the light modulating layer has two or more zones that are each independently controllable between the transparent state and the opaque state. 
     
     
       11. Equipment configured to operate in combination with external equipment that has pixels configured to emit light in a plurality of display frames, the equipment comprising:
 a housing configured to receive the external equipment; and 
 a light modulating layer in the housing that receives the light from the pixels in the external equipment, wherein the light modulating layer is configured to switch between a transparent state and an opaque state in each display frame of the plurality of display frames. 
 
     
     
       12. The equipment defined in  claim 11 , wherein the light modulating layer is configured to be placed in the transparent state for a first length of time during each display frame of the plurality of display frames and the opaque state for a second, remaining, length of time during each display frame of the plurality of display frames. 
     
     
       13. The equipment defined in  claim 12 , wherein the second length of time is longer than the first length of time. 
     
     
       14. The equipment defined in  claim 12 , wherein the first length of time is less than six milliseconds. 
     
     
       15. Equipment operable to receive real-world image light from external real-world objects, comprising:
 a housing configured to receive external equipment that has pixels configured to emit display image light; 
 an optical combiner configured to combine the display image light with the real-world image light; and 
 a light modulating layer interposed between the external equipment and the optical combiner when the external equipment is received by the housing, wherein the light modulating layer is configured to switch between a first state with a first transmittance and a second state with a second transmittance that is higher than the first transmittance and wherein the light modulating layer is configured to be placed in the second state for a subset of each display frame of the pixels. 
 
     
     
       16. The equipment defined in  claim 15 , wherein the light modulating layer comprises a twisted nematic cell that has a liquid crystal layer interposed between first and second electrode layers. 
     
     
       17. The equipment defined in  claim 15 , wherein the first transmittance is less than twenty percent and the second transmittance is greater than eighty percent. 
     
     
       18. The equipment defined in  claim 15 , wherein the first transmittance is less than ten percent and the second transmittance is greater than ninety percent.

Description:
This application claims priority to U.S. provisional patent application No. 62/630,684 filed on Feb. 14, 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 a light modulating layer. 
     BACKGROUND 
     Optical systems may include a display that is used to provide images to a viewer. If care is not taken, the user may detect motion blur when viewing images from the display. One cause of motion blur is high persistence. Frames may have a typical frame duration, and light may only be emitted for a fraction of the frame duration. Persistence may refer to the length of time light is emitted during each frame. The longer the persistence, the more motion blur a user may detect. It would therefore be desirable to be able to provide improved displays with low persistence. 
     SUMMARY 
     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 include a display with pixels that emit display image light. To control the persistence of the display, the optical system may include a light modulating layer. The light modulating layer may switch between a transparent state in which display image light is passed through the light modulating layer to reach the viewer and an opaque state in which display image light is blocked by the light modulating layer from reaching the viewer. The light modulating layer may be placed in the transparent state for a portion of each display frame and the opaque state for the remaining portion of each display frame. 
     The light modulating layer may include a liquid crystal layer that is interposed between two electrode layers. The light modulating layer may also include first and second linear polarizers. The electrode layers may be controlled to either allow or block passage of incoming light. The light modulating layer may include a twisted nematic cell. In another arrangement, the light modulating layer may be formed from switchable glass. 
     The light modulating layer may be divided into multiple, independently controllable zones. Each zone may be switched between the transparent state and the opaque state as desired. The light modulating layer may be formed in the housing of the equipment that receives the external equipment or may be formed with the external equipment directly. 
    
    
     
       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 display in accordance with an embodiment. 
         FIG. 3  is a cross-sectional side view of an illustrative light modulating layer that modulates light from a display in accordance with an embodiment. 
         FIG. 4  is a cross-sectional side view of an illustrative light modulating layer with a twisted nematic cell that modulates light from a display in accordance with an embodiment. 
         FIG. 5  is atop view of an illustrative light modulating layer with independently controllable zones in accordance with an embodiment. 
         FIG. 6A  is a cross-sectional side view of an illustrative light modulating layer that has been incorporated with a display in electronic equipment in accordance with an embodiment. 
         FIG. 6B  is a cross-sectional side view of an illustrative light modulating layer that has been incorporated with an accessory that is configured to receive electronic equipment with a display in accordance with an embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     Optical systems may be used to present images to a user. An optical system may use a light modulating layer to control the persistence of each frame. The light modulating layer may be selectively made transparent or opaque. Light from the display may only be received by the viewer when the light modulating layer is transparent, allowing the light modulating layer to control the persistence of 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 an accessory configured to operate in combination with equipment  10 A. In one illustrative example, 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. 
       FIG. 2  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). 
     Display  38  may also include a display cover layer  50 . Display cover layer  50  may be a layer of clear glass, plastic, or other dielectric that covers the light-emitting surface of the underlying display pixels. In another suitable arrangement, display cover layer  50  may be a color filter layer, thin-film transistor layer, or other display layer). 
     Light may be emitted from display  38  in a series of display frames. Frames may have a typical frame duration, and light may only be emitted for a fraction of the frame duration. Persistence may refer to the length of time light is emitted during each frame. Persistence is proportional to motion blur perceived by the viewer. Therefore, to reduce motion blur it is desirable for display  38  to have low persistence. A light modulating layer may be incorporated to overlap display  38  to reduce persistence in the display. 
       FIG. 3  is a cross-sectional side view of an illustrative optical system with a light modulating layer that overlaps the display. Light modulating layer  52  may receive light from display  38 . Light modulating layer  52  may be placed in either a transparent state or an opaque state. In the opaque state, light from display  38  is blocked from reaching the viewer of the display. In the transparent state, light from display  38  passes through light modulating layer  52  and reaches the viewer. In this way, light modulating layer  52  may be used to implement a low persistence display. For each frame, light modulating layer  52  may be made selectively transparent for only a fraction of the frame. The period of time in each frame for which light modulating layer  52  is transparent defines the persistence of that frame. The period of time in each frame for which light modulating layer  52  is transparent may take place in any desired portion(s) of the frame. For example, the light modulating layer may be in the transparent state then the opaque state in each frame, the light modulating layer may be in the opaque state then the transparent state in each frame, the light modulating layer may be in the opaque state, then the transparent state, then the opaque state in each frame, etc. In general, the period of time in each frame for which the light modulating layer is transparent may take place in any desired portion of the frame and may be split between multiple periods. 
     The light modulating layer may transmit any desired amount of light in the opaque state and the transparent state. The light modulating layer may have a transmittance of greater than 99%, greater than 95%, greater than 90%, greater than 80%, greater than 70%, greater than 60%, less than 99%, less than 95%, or another desired transmittance while in the transparent state. The light modulating layer may have a transmittance of less than 1%, less than 5%, less than 10%, less than 20%, less than 30%, less than 40%, greater than 1%, greater than 5%, or another desired transmittance while in the opaque state. The transmittance of the light modulating layer may be higher in the transparent state than in the opaque state. 
     In one embodiment, the light modulating layer may be operable in only the transparent state or the opaque state (e.g., the light modulating layer is always in either the transparent state or the opaque state). The transmittance may be the same any time the light modulating layer is in the transparent state. Alternatively, the transmittance may vary in the transparent state (e.g., in a first frame the light modulating layer may be controlled to have a transparent state with 95% transmittance and in a second frame the light modulating layer may be controlled to have a transparent state with 90% transmittance). The transmittance may be the same any time the light modulating layer is in the opaque state. Alternatively, the transmittance may vary in the opaque state (e.g., in a first frame the light modulating layer may be controlled to have a transparent state with 5% transmittance and in a second frame the light modulating layer may be controlled to have a transparent state with 10% transmittance). 
     Light modulating layer  52  may be formed from any desired materials capable of switching between a transparent state and an opaque state. In one illustrative embodiment, light modulating layer  52  may be formed from a layer of liquid crystal material. The layer of liquid crystal may have electrodes on either side. When a first voltage (or no voltage) is applied to the electrodes, the layer of liquid crystal material may be opaque. When a second voltage (or no voltage) is applied to the electrodes, the layer of liquid crystal material may be transparent. In one embodiment, the light modulating layer may be a twisted nematic (TN) liquid crystal cell. The light modulating layer may be a super-twisted nematic (STN) liquid crystal cell. In yet another embodiment, the light modulating layer may be a ferroelectric liquid crystal display layer. These examples are merely illustrative and other types of light modulating layers with liquid crystal material may be used if desired. 
     In another embodiment, light modulating layer  52  may be formed from switchable glass. Switchable glass is glass that can change from a transparent state to an opaque state. Any desired type of switchable glass may be used as light modulating layer  52 . For example, light modulating layer  52  may be a suspended particle layer (in which nano-scale particles are suspended in liquid), an electrochromic layer, or any other desired type of switchable glass. 
     In yet another embodiment, light modulating layer  52  may be a mechanical shutter. The mechanical shutter may be formed from an opaque material that either closes in the opaque state to block light from display  38  from reaching the viewer or opens in the transparent state to allow light from display  38  to reach the viewer. 
     Light modulating layer  52  may be used to provide display  38  with any desired persistence. For example, the persistence may be less than 1 millisecond, less than 2 milliseconds, less than 4 milliseconds, less than 6 milliseconds, less than 10 milliseconds, less than 15 milliseconds, greater than 1 millisecond, greater than 2 milliseconds, greater than 4 milliseconds, greater than 6 milliseconds, greater than 10 milliseconds, greater than 15 milliseconds, between 1 millisecond and 6 milliseconds, between 1 millisecond and 3 milliseconds, etc. 
     To provide display  38  with the desired persistence, light modulating layer  52  may be synchronized with display  38 . For example, light modulating layer  52  may receive a timing (control) signal from equipment  10 A (e.g., from display  38  in equipment  10 A) that controls the timing of the light modulating layer. The light modulating layer may then switch between the transparent and opaque states based on the received control signal from equipment  10 A (even if light modulating layer is located in equipment  10 B). The control signal may be a vertical synchronization (V-sync) signal, a horizontal synchronization (H-sync) signal, or a block synchronization (B-sync) signal. 
     An example in which light modulating layer  52  is formed using a twisted nematic (TN) cell is shown in  FIG. 4 . As shown in  FIG. 4 , light modulating layer  52  may receive light  24  from display  38 . Light modulating layer  52  includes a quarter wave plate (QWP)  62 , a lower linear polarizer  64  (POL), a lower electrode layer  66 , a layer of liquid crystal material  68 , an upper electrode layer  70 , an upper linear polarizer  72  (POL), and optical layer(s)  74  and  76 . 
     Light modulating layer  52  may receive circularly polarized light from display  38  (e.g., the display depicted in  FIG. 2 ). Quarter wave plate  62  may convert the incoming circularly polarized light from display  38  into linearly polarized light. Linear polarizer  64  may then transmit only light of a first polarization state (whereas light of the second polarization state is not transmitted). The linearly polarized light may then pass through the twisted nematic (TN) cell formed by liquid crystal material  68 , lower electrode layer  66 , and upper electrode layer  70 . After passing through the TN-cell, the light may pass through linear polarizer  72 . Linear polarizer  72  may only transmit light of the second polarization state (whereas light of the first polarization state is not transmitted). When the light modulator layer is in an opaque state, a voltage (or no voltage) may be applied to electrodes  66  and  70  such that the light that is received (of the first polarization state) exits with the same polarization state. Therefore, the light will exit the TN-cell with the first polarization state and not be able to pass through linear polarizer  72 . In contrast, when the TN-cell is in a transparent state, a voltage (or no voltage) may be applied to electrodes  66  and  70  such that the light that is received (of the first polarization state) exits with a different polarization state (e.g., the second polarization state). Therefore, the light will exit the TN-cell with the second polarization state and will pass through linear polarizer  72 . 
     Light modulating layer  52  may optionally include one or more additional optical layers such as optical layer(s)  74  and optical layer(s)  76 . Optical layers  74  may include one or more optical layers. For example, optical layers  74  may include an anti-reflection coating (ARC) to suppress reflections or a hard-coating to increase durability of the light modulating layer. In the embodiment shown in  FIG. 4 , light will pass through upper linear polarizer  72  of light modulating layer  52  before exiting the light modulating layer. The light emitted from light modulating layer  52  in  FIG. 4  is therefore linear polarized. This example is merely illustrative. If desired, optical layers  74  may include a quarter wave plate so that circularly polarized light is emitted from the light modulating layer. Alternatively, optical layers  74  may include a half wave plate to change the polarization of the emitted linearly polarized light. Optical layers  76  may also include one or more optical layers. For example, optical layers  76  may include an anti-reflection coating (ARC) to suppress reflections or a hard-coating to increase durability of the light modulating layer. 
     Additional modifications may be made to the light modulating layer shown in  FIG. 4 . For example, additional layers may be incorporated into the light modulating layer. Each electrode may be coated with a respective polyimide layer (sometimes referred to as a liquid crystal alignment layer). For example, a liquid crystal alignment layer may be interposed between electrode  70  and liquid crystal layer  68  and a liquid crystal alignment layer maybe interposed between electrode  66  and liquid crystal layer  68 . The orientations of the liquid crystal alignment layers may be configured to twist the liquid crystals in layer  68  so that in the absence of applied electric field across layer  68 , linearly polarized light (e.g., light  24  that has passed through linear polarizer  64 ) will be rotated 90° in polarization (e.g., from the first polarization to the second polarization) as this light exits layer  68  towards the viewer. 
     The light modulating layer may also include an additional optical layer between lower linear polarizer  64  and lower electrode  66  and an additional optical layer between upper linear polarizer  70  and upper electrode  68 . These optical layers may help ensure uniform color and luminance output, for example. 
     The presence of quarter wave plate  62  in light modulating layer  52  is also optional. For example, if display  38  were to emit linearly polarized light, quarter wave plate  62  may be omitted from the light modulating layer. In general, light modulating layer  52  may include any desired number and type of wave plates, polarizers, liquid crystal layers, electrodes, anti-reflective coatings, hard-coatings, and/or other type of optical layers. 
     In one possible embodiment, the light modulating layer may be controlled globally (meaning that either the entire light modulating layer is in the transparent state or the entire light modulating layer is in the opaque state). However, this example is merely illustrative. If desired, the light modulating layer may be split into two or more zones that are each controlled independently. Each zone may be switched between the transparent state and the opaque state as described above. However, different zones may be in different states at the same time if desired (e.g., a first zone may be transparent while a second zone is opaque). 
     A top view of a light modulating layer with separately controllable zones is shown in  FIG. 5 . As shown, upper electrode  70  may be patterned to have a first electrode portion  70 - 1 , a second electrode portion  70 - 2 , a third electrode portion  70 - 3 , and a fourth electrode portion  70 - 4 . Each electrode portion may be configured to receive an applied voltage to control a respective portion of the light modulating layer. For example, electrode  70 - 1  overlaps a first portion of the display and may be switched between a transparent state and an opaque state to control whether light from the first portion of the display reaches the viewer. Electrode  70 - 2  overlaps a second portion of the display and may be switched between a transparent state and an opaque state to control whether light from the second portion of the display reaches the viewer. Electrode  70 - 3  overlaps a third portion of the display and may be switched between a transparent state and an opaque state to control whether light from the third portion of the display reaches the viewer. Electrode  70 - 4  overlaps a fourth portion of the display and may be switched between a transparent state and an opaque state to control whether light from the fourth portion of the display reaches the viewer. 
     The example in  FIG. 5  in which light modulating layer  52  has four independently controllable zones is merely illustrative. In general, light modulating layer  52  may have any desired number of independently controllable zones (e.g., two zones, three zones, four zones, more than four zones, more than six zones, more than ten zones, more than twenty zones, more than fifty zones, more than one hundred zones, more than one thousand zones, more than ten thousand zones, less than six zones, less than ten zones, less than twenty zones, less than fifty zones, less than one hundred zones, less than one thousand zones, less than ten thousand zones, etc.). Additionally, as previously discussed the light modulating layer  52  may have only one zone (e.g., controlled globally). Each zone may have any desired size (e.g., the zones may be the same size or have different sizes). Each zone may cover (e.g., receive light from) any desired number of pixel rows/columns in display  38 . For example, the zones may be aligned with rows of pixels such that each zone covers a portion of a row, a single row, two or more rows, ten or more rows, a hundred or more rows, etc. Alternatively, the zones may be aligned with columns of pixels such that each zone covers a portion of a column, a single column, two or more columns, ten or more columns, a hundred or more columns, etc. The zones may have irregular shapes if desired. 
     The zones of light modulating layer  52  may be arranged in the same direction as the display line update direction of display  38  in equipment  10 A. In the example of  FIG. 5 , the display line update direction may be from the top of the display to the bottom of the display (e.g., all of the pixels in the first row of the display are updated simultaneously, then all of the pixels in the second row of the display are updated simultaneously, etc.). Therefore, the zones of light modulating layer  52  are arranged to cover complete rows (and only partial columns) of the display. 
     In one illustrative embodiment, the zones of the light modulating layer may be controlled by a propagating control signal (sometimes referred to as dependent control). In this type of arrangement, the control of one zone will trigger the control of another zone. For example, the zones may be selectively made transparent with a control signal that propagates vertically (e.g., in the same direction as the display line update direction). 
     Light modulating layer  52  may be arranged in any desired manner that allows light emitted from display  38  to pass through the light modulating layer. For example, in one illustrative arrangement, the components of light modulating layer  52  may be incorporated into electronic equipment  10 A (e.g., along with display  38 ). Electronic equipment  10 A may be, for example, a cellular telephone. In this type of arrangement, the light modulating layer  52  may be considered a portion of display  38 . Light emitted from display pixels in display  38  may pass through light modulating layer  52  before exiting electronic equipment  10 A. For example, in the display pictured in  FIG. 2 , the components of light modulating layer  52  (e.g., from  FIG. 4 ) may be interposed between display cover layer  50  and pixels  42 . Alternatively, the components of light modulating layer  52  may be incorporated into equipment  10 B (an accessory such as a head-mounted device configured to operate in combination with equipment  10 A). The light modulating layer  52  may be incorporated into equipment  10 B such that the light modulating layer overlaps and/or receives light from display  38  of equipment  10 A when equipment  10 A is supported by equipment  10 B (e.g., housing  12  in  FIG. 1  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 display  38  that are received by a light modulating layer in equipment  10 B). In yet another embodiment, some of the components of light modulating layer  52  may be formed in equipment  10 A and some of the components of light modulating layer  52  may be formed in equipment  10 B. 
       FIGS. 6A and 6B  are cross-sectional side views of illustrative arrangements for light modulating layer  52 .  FIG. 6A  shows an embodiment where light modulating layer  52  is incorporated into electronic equipment  10 A (e.g., a cellular telephone).  FIG. 6B  shows an alternate embodiment where light modulating layer  52  is in housing  12  of equipment  10 B. As shown in  FIG. 6B , housing  12  may support light modulating layer  52  in a position where light modulating layer  52  receives light from display  38  of equipment  10 A when equipment  10 A is operated in combination with equipment  10 B. In embodiments where equipment  10 B includes an optical combiner (e.g., to combine display image light  24  from a display in equipment  10 A with real-world image light  22  to produce merged light  26  as shown in  FIG. 1 ), the light modulating layer may be interposed between display  38  and the optical combiner such that display image light  24  from display  38  passes through light modulating layer  52  before reaching the optical combiner. 
     Regardless of whether light modulating layer  52  is positioned in equipment  10 A or equipment  10 B, light modulating layer  52  may be controlled by control circuitry  14  in equipment  10 A and/or  10 B. For example, if light modulating layer  52  is positioned in equipment  10 A, the light modulating layer may be controlled by control circuitry  14  in equipment  10 A, control circuitry  14  in equipment  10 B, or both. Similarly, if light modulating layer  52  is positioned in equipment  10 B, the light modulating layer may be controlled by control circuitry  14  in equipment  10 A, control circuitry  14  in equipment  10 B, or both. 
     In another possible embodiment, backlight strobing may be used to implement a low persistence display. For example, display  38  of equipment  10 A may have a backlight that emits light that passes through pixels  42 . When the backlight is on, the pixels may be illuminated and the display may emit a visible image. When the backlight is off, the pixels may not be illuminated and the display may not emit a visible image. Therefore, backlight strobing may also be used to control persistence in the display. 
     To control persistence, the length of time light is emitted during each display frame must be controlled. The backlight may be turned on and off to control when light is emitted during each display frame and therefore control the persistence. The backlight may be controlled globally or have independently controllable zones (similar to as discussed above in connection with  FIG. 5 ). In general, any light source (e.g., a light source in equipment  10 A, a light source in  10 B, etc.) that may be turned on and off to allow pixels of display  38  to be alternately visible and not visible may be used to control the persistence in the display. 
     In various embodiments, equipment configured to operate in combination with external equipment that has pixels may include a housing configured to receive the external equipment and a light modulating layer in the housing that receives display image light from the pixels in the external equipment. The light modulating layer may be configured to switch between a transparent state in which the display image light passes through the light modulating layer and an opaque state in which the display image light is blocked by the light modulating layer. 
     The light modulating layer may include a layer of liquid crystal material. The light modulating layer may include an upper electrode layer and a lower electrode layer and the layer of liquid crystal material may be interposed between the upper electrode layer and the lower electrode layer. The light modulating layer may include first and second linear polarizers, the lower electrode layer may be interposed between the first linear polarizer and the layer of liquid crystal material, and the upper electrode layer may be interposed between the second linear polarizer and the layer of liquid crystal material. The light modulating layer may include a quarter wave plate and the first linear polarizer may be interposed between the quarter wave plate and the lower electrode layer. The quarter wave plate may receive circularly polarized display image light from the pixels in the external equipment. 
     The light modulating layer may include a twisted nematic cell. The light modulating layer may include switchable glass. The light modulating layer may be configured to be placed in the transparent state for a first length of time during each display frame of the pixels in the external equipment and the opaque state for a second, remaining, length of time during each display frame. The first length of time may be less than six milliseconds. The light modulating layer may have two or more zones that are each independently controllable between the transparent state and the opaque state. 
     To clarify, the first length of time (in the transparent state) and the second length of time (in the opaque state) in each display frame may occur in any desired order and may be split into multiple separate time periods. For example, the light modulating layer may be in the opaque state before being in the transparent state or may be in the opaque state, then the transparent state, then the opaque state in each display frame. 
     In various embodiments, equipment may be configured to operate in combination with external equipment that has pixels configured to emit light in a plurality of display frames and the equipment may include a housing configured to receive the external equipment and a light modulating layer in the housing that receives the light from the pixels in the external equipment. The light modulating layer may be configured to switch between a transparent state and an opaque state in each display frame of the plurality of display frames. 
     The light modulating layer may be configured to be placed in the transparent state for a first length of time during each display frame of the plurality of display frames and the opaque state for a second, remaining, length of time during each display frame of the plurality of display frames. The second length of time may be longer than the first length of time. The first length of time may be less than six milliseconds. 
     In various embodiments, equipment operable to receive real-world image light from external real-world objects may include a housing configured to receive external equipment that has pixels configured to emit display image light, an optical combiner configured to combine the display image light with the real-world image light, and a light modulating layer interposed between the external equipment and the optical combiner when the external equipment is received by the housing. The light modulating layer may be configured to switch between a first state with a first transmittance and a second state with a second transmittance that is higher than the first transmittance. 
     The light modulating layer may include a twisted nematic cell that has a liquid crystal layer interposed between first and second electrode layers. The light modulating layer may be configured to be placed in the second state for a subset of each display frame of the pixels. The first transmittance may be less than twenty percent and the second transmittance may be greater than eighty percent. The first transmittance may be less than ten percent and the second transmittance may be greater than ninety percent. 
     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: 20190207
Publication Date: 20210309
Grant Date: 20210309
Priority Date: 20180214
Inventors: HOLSTEEN, AARON L.
WANG, CHAOHAO
CHEN, CHENG
LI, JUN
FAN JIANG, SHIH-CHYUAN
LI, XIAOKAI
YANG, YOUNG CHEOL
GE, ZHIBING
Assignee: APPLE INC
CPC Classifications: [{"code": "G02F1/13471", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02F1/1347", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02F1/13476", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02F1/133541", "inventive": false, "first": false, "tree": "[]"}, {"code": "G02F1/13363", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02F1/133528", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02F1/133308", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02F1/133308", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01L27/3232", "inventive": true, "first": true, "tree": "[]"}, {"code": "G02F1/133528", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02F1/1347", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02F1/13363", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02F1/13476", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02F1/133541", "inventive": false, "first": false, "tree": "[]"}, {"code": "G02F1/13476", "inventive": true, "first": true, "tree": "[]"}, {"code": "H10K59/50", "inventive": true, "first": true, "tree": "[]"}, {"code": "H10K59/50", "inventive": true, "first": false, "tree": "[]"}]
Family ID: 74851829