PATENT DOCUMENT

Publication Number: US-11435583-B1
Application Number: US-201816221330-A
Country: US
Kind Code: B1

Title: Electronic device with back-to-back displays

Abstract:
An electronic device may have back-to-back displays. A user-facing display may have microlenses, tunable lens structures, holograms, lasers, and other structures for displaying images in multiple eye boxes while the electronic device is being worn on the head of a user. In some configurations, a switchable diffuser may be incorporated into the user-facing display. In one mode, the switchable diffuser allows microlenses of the pixels of the user-facing display to provide images to eye boxes in which images from the display are viewable. In another mode, the switchable diffuser diffuses light from the pixels so that the user-facing display may be used while the device is being held in the hand of the user.

Claims:
What is claimed is: 
     
       1. An electronic device, comprising:
 first and second displays mounted back to back, wherein the first display has a higher resolution than the second display and has pixels with light directing elements; 
 head-mounted support structures configured to support the first and second displays; 
 an opaque support structure interposed between the first and second displays; and 
 control circuitry configured to adjust the pixels of the first display to shift a location of images between multiple selectable eye boxes within the head-mounted support structures, wherein the images are displayed at only one of the multiple selectable eye boxes at a time. 
 
     
     
       2. The electronic device defined in claim  1  wherein the light directing elements comprise light directing elements selected from the group consisting of: microlenses and holographic light conditioning and directing devices. 
     
     
       3. The electronic device defined in  claim 2  wherein the pixels include at least first and second subsets of pixels and wherein the control circuitry is configured to display the images in a first of the multiple selectable eye boxes by using the first subset of pixels and is configured to display the images in a second of the multiple selectable eye boxes by using the second subset of pixels. 
     
     
       4. The electronic device defined in  claim 2  wherein the light directing elements comprise adjustable microlenses and wherein the control circuitry is configured to adjust the adjustable microlenses to accommodate user vision defects. 
     
     
       5. The electronic device defined in  claim 2  wherein the control circuitry is configured to adjust the light directing elements to direct the images into a selected one of the multiple selectable eye boxes or to correct for myopia or hyperopia. 
     
     
       6. The electronic device defined in  claim 1  wherein each of the pixels includes a light source that emits light that passes through a respective one of the light directing elements. 
     
     
       7. The electronic device defined in  claim 6  wherein each of the light sources comprises a laser diode. 
     
     
       8. The electronic device defined in  claim 7  wherein each of the laser diodes is a laser selected from the group consisting of: a vertical cavity surface emitting laser and a crystalline semiconductor die laser. 
     
     
       9. The electronic device defined in  claim 1  wherein the first display includes a switchable diffuser that overlaps the pixels. 
     
     
       10. The electronic device defined in  claim 1  wherein each pixel has a light directing element formed from multiple holographic recordings each of which directs light to a different respective eye box. 
     
     
       11. The electronic device defined in  claim 1  further comprising:
 a switchable diffuser that overlaps the pixels of the first display, wherein the control circuitry is configured to adjust the switchable diffuser of the first display between a non-light-diffusing mode in which the pixels of the first display present images to a given one of the multiple selectable eye boxes and a light-diffusing mode in which light from the pixels is diffused and images are viewable on the first display. 
 
     
     
       12. The electronic device defined in  claim 11  wherein each pixel includes a laser. 
     
     
       13. The electronic device defined in  claim 12  wherein the laser of each pixel is a vertical cavity surface emitting laser. 
     
     
       14. The electronic device defined in  claim 12  wherein the laser of each pixel is a micro-light-emitting diode mounted to a substrate with a pick-and-place tool. 
     
     
       15. The electronic device defined in  claim 11  wherein the second display is configured to display publicly viewable images while the control circuitry is presenting virtual reality images to a user in the given one of the multiple selectable eye boxes. 
     
     
       16. The electronic device defined in  claim 11  wherein each of the pixels includes a respective light steering structure. 
     
     
       17. The electronic device defined in  claim 11  wherein the first display faces the multiple selectable eye boxes and the second display faces away from the multiple selectable eye boxes. 
     
     
       18. An electronic device, comprising:
 first and second displays mounted back to back and separated by an opaque member, wherein the first and second displays have pixels configured to display images and wherein the pixels of the first display include first and second sets of pixels; 
 head-mounted support structures configured to support the first and second displays; 
 an optical system that overlaps the first display, wherein the optical system includes a lens that directs light into an eye box in which the images from the pixels of the first display are viewable, wherein the first set of pixels are used without the second set of pixels to display the images at a first eye box location without displaying the images at a second eye box location, wherein the second set of pixels are used without the first set of pixels to display the images at the second eye box location without displaying the images at the first eye box location, wherein the second eye box location is different from the first eye box location, and wherein the first and second eye box locations are within the head-mounted support structures; and 
 control circuitry that selects whether to use the first set of pixels or the second set of pixels based on gaze tracking information. 
 
     
     
       19. The electronic device defined in  claim 18  wherein the lens includes a lens selected from the group consisting of: a Fresnel lens, a holographic lens, and lens in a holographic output coupler in a waveguide. 
     
     
       20. The electronic device defined in  claim 18  wherein the pixels of the first display include lasers. 
     
     
       21. An electronic device, comprising:
 a display that has pixels configured to display an image, wherein each pixel has a light source; 
 head-mounted support structures configured to support the display; 
 an optical system that overlaps the display, wherein the optical system includes microlenses overlapping the pixels to direct light from the pixels into an eye box in which the image from the pixels is viewable and wherein the microlenses include a first set of microlenses having a first fixed lens power interleaved with a second set of microlenses having a second fixed lens power different from the first fixed lens power; and 
 control circuitry configured to adjust the pixels to shift the image from a first eye box location to a second eye box location within the head-mounted support structures, wherein at least some of the pixels and microlenses are not in use when the image is displayed at the first eye box location. 
 
     
     
       22. The electronic device defined in  claim 21  further comprising an additional display supported by the head-mounted support structures that faces away from the eye box.

Description:
This application claims the benefit of provisional patent application No. 62/618,502, filed Jan. 17, 2018, which is hereby incorporated by reference herein in its entirety. 
    
    
     FIELD 
     This relates generally to electronic devices and, more particularly, to electronic devices with displays. 
     BACKGROUND 
     Electronic devices such as head-mounted devices have displays. Head-mounted devices such may be used to provide a user with virtual content. In some arrangements, computer-generated content may be overlaid on top of real-world content. Cellular telephones and other portable devices have displays for presenting a user with text message content, web pages, and other images when the device is held in the user&#39;s hand. 
     These types of devices may be relatively inflexible and may not be able to provide a user with desired content in a variety of situations. 
     SUMMARY 
     An electronic device may have back-to-back displays. A first of the displays may be used to display content for a user. A second of the displays may display publically viewable images while the electronic device is being worn on the head of the user. 
     The first display may be operated in one or more modes. For example, the first display may be operated in a first mode in which a user may view images directly on the display while the device is being held in the hand of the user. In a second mode, the user may be presented with images such as virtual reality images while the electronic device is being worn on the head of the user and while lenses in the display are used to direct the images into an eye box. The second display may be used to display images for the user (e.g., when the user is holding the device in the first mode) or publicly viewable images (e.g., when the device is being worn on the user&#39;s head in the second mode). 
     The first display may have microlenses, tunable lens structures, holograms, lasers, and other structures for displaying images in multiple selectable eye boxes while the electronic device is being worn on the head of a user. These structures may include tunable lenses or other optical components that allow control circuitry in the device to adjust the first display to accommodate vision defects of the user such as nearsightedness. 
     In some configurations, a switchable diffuser may be incorporated into the second display. In the second mode of operation, the switchable diffuser may allow microlenses of the pixels of the second display to produce collimated light that is focused by a user&#39;s eyes to form virtual images. The virtual images may be overlaid on images of the real world that are captured by a front-facing camera on the electronic device while the electronic device is being worn by the user. In the first mode of operation, the switchable diffuser may diffuse light from the pixels so that the second display may be used while the device is being held in the hand of the user. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic diagram of an illustrative electronic device in accordance with an embodiment. 
         FIGS. 2, 3, and 4  are side views of illustrative displays mounted in a back-to-back configuration in accordance with an embodiment. 
         FIGS. 5 and 6  are side views of illustrative pixels in accordance with embodiments. 
         FIGS. 7 and 8  are side views of illustrative back to-back displays including a display that may be used to display virtual reality images in multiple selectable eye boxes in accordance with an embodiment. 
         FIG. 9  is a side view of an illustrative pixel with an optical wedge interposed between a light source and a light redirecting structure such as a hologram (hologram lens) in accordance with an embodiment. 
         FIG. 10  is a side view of an illustrative display in which a holographic layer has been configured to form holographic light conditioning and directing devices that serve as beam steering elements for pixels in accordance with an embodiment. 
         FIG. 11  is a cross-sectional side view of illustrative tunable lens structures in accordance with an embodiment. 
         FIG. 12  is side view of an illustrative display with a switchable diffuser layer in accordance with an embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     A schematic diagram of an illustrative electronic device such as a head-mounted device is shown in  FIG. 1 . As shown in  FIG. 1 , electronic device  10  may have control circuitry  12 . Control circuitry  12  may include storage and processing circuitry for controlling the operation of electronic device  10 . Circuitry  12  may include storage such as nonvolatile memory (e.g., electrically-programmable-read-only memory configured to form a solid state drive), volatile memory (e.g., static or dynamic random-access-memory), etc. Processing circuitry in control circuitry  12  may be based on one or more microprocessors, microcontrollers, digital signal processors, baseband processors, power management units, audio chips, graphics processing units, application specific integrated circuits, and other integrated circuits. Software code may be stored on storage in circuitry  12  and run on processing circuitry in circuitry  12  to implement control operations for device  10  (e.g., data gathering operations such as operations involved in gathering information with sensors, operations involving the adjustment of components using control signals, operations involving the presentation of images on displays in device  10 , etc.). 
     Electronic device  10  may include communications circuitry for operating with external devices such as eternal equipment  30  over wired and/or wireless communications links such as communications link  32 . Electronic device  10  may, for example, include wireless circuitry  14 . Wireless circuitry  14  may include wireless communications circuitry. The wireless communications circuitry may include one or more antennas and radio-frequency transceiver circuitry for transmitting and receiving wireless signals over wireless links such as illustrative wireless link  32  with external equipment  30 . If desired, external equipment  30  may be coupled to device  10  using wired connections in addition to or instead of using wireless communications. External equipment  30  may be a peer device (e.g., another device having the components of device  10  of  FIG. 1 ), may be accessories, may be host computers or other host equipment, may include online data sources (e.g., servers for supplying weather information and/or other information), and/or may be other circuitry external to device  10 . 
     Wireless communications circuitry in device  10  (e.g., circuitry in wireless circuitry  14 ) may be used in communicating with wireless local area network equipment (e.g., WiFi® equipment in equipment  30 ). Wireless communications circuitry in device  10  may also communicate using cellular telephone frequencies, using near-field communications, and/or using other wireless communications bands and protocols. If desired, wireless communications circuitry or other wireless circuitry  14  in device  10  may be used to detect and/or identify electronic devices (e.g., equipment  30 ) associated with people in the vicinity of device  10 . For example, equipment  30  may be a portable electronic device associated with an acquaintance of the user of device  10 . Equipment  30  may broadcast local wireless signals that identify equipment  30  as belonging to the acquaintance of the user (e.g., short-range signals having a range of 0-10 m, at least 1 m, at least 2 m, less than 20 m, etc.). In this type of arrangement, device  10  can use wireless circuitry  14  to detect the broadcast wireless signals and thereby detect when the acquaintance of the user is in the vicinity of device  10  and the user. Other techniques for identifying nearby individuals may also be used by device  10 , if desired. 
     Device  10  may also include input-output circuitry  16 . Input-output circuitry  16  includes user input devices  18 . User input devices  18  may include electrical components that allow a user of device  10  to supply control circuitry  12  with user input. For example, user input devices  18  may include buttons, joysticks, track pads, force-sensitive buttons, keyboards, gesture recognition sensors (e.g., sensors based on image sensors and/or other sensors that detect user gestures such as hand wave gestures, etc.), microphones for gathering voice commands, and/or other circuitry for gathering commands and other input from a user. If desired, devices  18  may include virtual reality gloves that track a user&#39;s hand motions and finger motions and that use these motions in controlling device  10 . 
     Device  10  may also include environmental sensors  20 . Environmental sensors  20  may include devices such as ambient light sensors, temperature sensors, humidity sensors, moisture sensors, air particulate sensors, carbon dioxide sensors and other gas concentration sensors, barometric pressure sensors and other air pressure sensors, magnetic sensors, cameras (e.g., one or more cameras that capture real-time images of the real-world environment currently surrounding device  10  so that these images may be presented in real time on a user viewable display and/or for recording images), gaze detection components (e.g., to detect a gaze of an external person in the vicinity of device  10 ), and/or other sensors that can gather readings on the environment surrounding the user of device  10 . 
     User monitoring sensors  22  may be used to monitor the user of device  10 . For example, sensors  22  may include image sensors (cameras) for gathering images of a user&#39;s face and other portions of a user. In some configurations, user monitoring sensors  22  may include cameras (digital image sensors) and other components that form part of a gaze tracking system. The camera(s) or other components of the gaze tracking system may face a user&#39;s eyes and may track the user&#39;s gaze (e.g., images and other information captured by the gaze tracking system may be analyzed by the circuitry of device  10  such as control circuitry  12  to determine the direction in which the user&#39;s eyes are oriented). This gaze information may be used to determine the location on a user-facing display in device  10  where the user&#39;s eyes are directed (sometimes referred to as the point of gaze of the user). If desired, the gaze tracking system may also gather information on the focus of the user&#39;s eyes and other information such as eye movement information. The gaze tracking system of user monitoring sensors  22  may sometimes be referred to as a gaze detection system, eye tracking system, gaze tracking system, or eye monitoring system. If desired, image sensors other than cameras (e.g., infrared and/or visible light-emitting diodes and light detectors, etc.) may be used in monitoring a user&#39;s gaze in system  62 . 
     User monitoring sensors  22  may also include heart rate sensors (e.g., optical heart rate sensors that emit light and process detected reflected light signals, pressure-based heart rate sensors, etc.), blood oxygen level sensors, perspiration sensors (e.g., sensors based on image sensors and/or moisture sensors that detect user skin moisture levels), blood pressure sensors, electrocardiogram sensors, accelerometers to measure body movements, other physiological sensors, and/or other sensors that can measure attributes associated with a user. If desired, user monitoring sensors  22  may include motion sensors that measure the motion of device  10  and user  34 . The motion sensors may be inertial measurement units based on components such as accelerometers, gyroscopes, and/or compasses, and/or may include other circuitry that measures motion. A motion sensor in sensors  22  may, for example, determine whether a user is sitting or is otherwise at rest or is walking, running, riding a bicycle, or is otherwise in motion and/or engaged in a physical activity. 
     Output devices  24  may include devices such as displays  26  and other visual output devices. In some configurations, status indicators may be used to present visual information. A status indicator or other non-display visual output device may include a light-emitting diode or other light-emitting component to convey information (e.g., a component that produces illumination using a fixed color, using multiple colors, using a time-varying light pattern, etc.). For example, a status indicator formed from a pair of light-emitting diodes of different colors may emit light of a first color when the user is busy and viewing content and may emit light of a second color when the user is not busy and is available for social interactions. In other configurations, non-status-indicator visual output devices may be used in presenting visual information such as images. Non-status-indicator visual output devices may include devices for presenting adjustable text, devices for presenting still and/or moving graphics, and displays (e.g., displays with pixel arrays having at least 1000 pixels, at least 10,000 pixels, fewer than million pixels, or other suitable number of pixels for presenting images). 
     In general, displays and other light-emitting components that emit light (e.g., light-emitting diodes, lasers such as vertical cavity surface emitting laser diodes, lamps, status indicator lights formed from multiple light sources such as these, backlit low-resolution output components such as backlight electrophoretic components, backlit patterned ink symbols, etc.) may be used to present any suitable visual information (e.g., icons, icons that flash with predetermined patterns or that have predetermined colors to convey information about the state of the user, whether content is being presented to the user, and/or other status information). Non-display components may have relatively few adjustable light-emitting components (e.g., 2-10 light-emitting diodes, fewer than 15 light-emitting diodes, at least one light-emitting diode, etc.). Displays  26 , which generally include thousands of pixels or more, may be liquid crystal displays, liquid crystal-on-silicon displays, microelectromechanical systems displays, electrophoretic displays, light-emitting diode displays (e.g., organic light-emitting diode displays, displays based on pixels formed from crystalline semiconductor dies, sometimes referred to as micro-light-emitting diodes or microLEDs, etc.), or displays based on other display technologies. Displays  26  may include touch sensitive displays (e.g., displays with two-dimensional touch sensors formed from two-dimensional capacitive touch sensor electrode arrays) or may be insensitive to touch. 
     As shown in  FIG. 2 , displays  26  of device  10  may be supported by support structures  34 . Support structures  34  may be head-mountable support structures (e.g., portions of glasses, a helmet, a hat, goggles, or other head-mounted device). Support structures  34  may have a substrate portion such as portion  34 P that helps support displays  26 . The circuitry of device  10  (see, e.g., the components of  FIG. 1 ) may be mounted in positions such as positions  36  within a head-mounted support structure such as structures  34 . This allows these components to input and/or output information in directions such as directions  38 . 
     Displays  26  may include one or more inwardly facing displays such as display  46  that are visible to a user of head-mounted device  10  such as user  50 , who is viewing display  46  in direction  52 , and may include one or more outwardly facing displays such as display  44  that are visible to people in the vicinity of user  50  such as person  54 , who is viewing display  44  in direction  56 . Display  46  and display  44  may include pixels P that are configured to display images. In some configurations, device  10  may be operated while being held in the hand of the user. In this operating scenario, display  46  can be adjusted to display images directly on the face of display  46  for viewing by the user. 
     Inwardly facing displays such as display  46 , which may sometimes be referred to as user viewable displays or internal display assemblies, may have display surfaces (pixel arrays) that are oriented towards a user&#39;s eyes when device  10  is worn on a user&#39;s head. In this scenario, display  46  may be hidden from view by individuals other than the user. Outwardly facing displays, which may sometimes be referred to as publicly viewable displays or external display assemblies may have display surfaces that are oriented away from the user. Outwardly facing displays will be visible to people in the vicinity of a user of device  10  such as person  54  but will not generally be visible to the user of device  10  such as user  50 . An inwardly facing display may have the same resolution as an outwardly facing display or, if desired, the inwardly facing display may have a higher resolution than the outwardly facing display to enhance display quality for the user. 
     Outwardly facing displays can provide information that enables outward interactions of the user with the real world (e.g., people in the vicinity of the user). Outwardly facing displays may, for example, display information about the content that a user is viewing, information on the identity of the user, information on whether a user is occupied or is available for social interactions, and other information on the state of the user. If desired, an eye tracking system may be used to track a user&#39;s eyes and an outwardly facing display may be used to display virtual eyes that change appearance based on information on the state of the user&#39;s eyes gathered using the eye tracking system or other components. Facial features such as virtual eyebrows, emojis, and/or other content representative of the user&#39;s current emotional state may also be displayed on the outwardly facing display. An outwardly facing display may be used in forming a graphical user interface for people in the vicinity of the user (e.g., selectable on-screen items when the outwardly facing display is a touch screen or displays information responsive to voice commands from people in the vicinity of the user, etc.). When device  10  is not being worn by user  50 , support structures  34  (e.g., hinged members, detachable members, etc.) may be stowed, allowing device  10  to be used as a cellular telephone, other portable electronic device, or other equipment that is not mounted on a user&#39;s head. In some configurations, portions of support structures  34  may be decoupled from displays  46  (e.g., to help make device  10  more compact and pocketable). 
     Displays  26 , which may sometimes be referred to as back-to-back displays or oppositely oriented displays, may be attached back-to-back on opposing sides of an opaque support structure such as support structure substrate  34 P of  FIG. 3 . Substrate  34 P may be an opaque member formed from polymer, metal, and/or other materials. 
     Optical system  60  may be used to help a nearby user focus on images produced by display  46  (e.g., when the user&#39;s eyes are within 10 cm or so of display  26  while device  10  is on the user&#39;s head). With one illustrative arrangement, optical system  60  includes lenses  64  on transparent spacer  62 . There may be left and right lenses  64  in lenses  64  corresponding to the left and right eyes of user  50 . Lenses  64  may be Fresnel lenses, holographic lenses, or other lenses. Spacer  62  may be formed from transparent polymer, clear glass, or other transparent material. 
     In the illustrative configuration of  FIG. 4 , light engine  66  (e.g., a microelectromechanical systems display) produces images that are guided by total internal reflection in waveguide  68 . In region  70 , a holographic output coupler with a built-in lens may be used to couple images out of waveguide  68  towards a user in direction  71 . The holographic output coupler may be configured to have a lens power that allows the user to view the images at a close distance (e.g., when displays  26  are mounted directly in front of the user&#39;s eyes at a distance of 1-10 cm, at least 0.5 cm, less than 8 cm, etc.). 
     If desired, display  46  may have light directing structures associated with pixels P. The light directing structures, which may sometimes be referred to as light steering structures, beam steering structures, or light redirecting structures, may collimate and steer the light emitted from pixels P. Each pixel may, for example, have a prism, a microlens, a holographic microlens (sometimes referred to as a holographic light conditioning and directing device) or other structure that directs light in a desired direction. Configurations in which display  46  has pixels with microlenses may sometimes be described herein as an example. Prisms or other light direction structures may also be used. 
     As shown in  FIG. 5 , display  46  may have pixels P that each include a light source such as light source  72 . Light source  72  may be a vertical cavity surface emitting laser (VCSEL), a non-VCSEL laser diode (e.g., a crystalline semiconductor diode die such as a micro-light-emitting diode without a vertical cavity structure), or other light source. In some configurations, multiple vertical cavity surface emitting lasers may be formed on a common substrate that serves as the substrate for display  46 . In other configurations, pick and place operations may be used to place vertical cavity surface emitting diodes or other laser diodes in desired locations on a substrate. For example, a pick-and-place tool may be used to mount an array of micro-light-emitting diodes onto a substrate such as a printed circuit or a semiconductor die to form an array of pixels P for display  46 . 
     In each pixel P of  FIG. 5 , light source  72  emits light (e.g., red light for red pixels R, green light for green pixels G, and blue light for blue pixels B). The emitted light  74  is directed in a beam in a desired direction by a light redirecting structure such as a prism, holographic structure, or microlens  70  (e.g., a polymer lens or a lens formed from other transparent material). When the microlens  70  of a given pixel P is centered over the light source  72  of that pixel, light  74  is directed perpendicular to display  46  (e.g., parallel to surface normal n of display  46 ), as shown in  FIG. 5 . When the microlens  70  of a given pixel P is laterally offset (in the plane of display  46 ) from the center of its associated light source  72 , emitted light  74  is directed at a non-zero angle A with respect to surface normal n, as shown in  FIG. 6 . If desired, each pixel P may emit a light beam of a desired angle by tilting the laser or other light source  72  that emits the light beam. The strengths and lateral offsets of microlenses  70  (or the characteristics of other light directing elements) may be configured so that images from display  46  are projected towards eye boxes for a user&#39;s left and right eyes. 
     As device  10  shifts relative to the eyes of the user, a user&#39;s eyes may potentially move out of a fixed eye box. Accordingly, display  46  may be configured to display images in multiple selectable eye boxes. During operation, gaze tracking sensor circuitry in device  10  can be used by control circuitry  12  to determine the current location of the user&#39;s eyes and an appropriate matching eye box into which images are directed can be selected dynamically. 
     An illustrative configuration that allows display  46  to project images into multiple selectable eye boxes is shown in  FIG. 7 . As shown in  FIG. 7 , microlenses  70  may have different powers and lateral offsets, so that a first subset of pixels P direct light  74  to form images in a first corresponding eye box  80  (e.g., an eye box located 0.5-10 cm from display  46 ), as shown in  FIG. 8 . As shown in  FIG. 8 , an interleaved second subset of pixels P (different from the first subset) may direct light  74  to form images in a different second corresponding eye box  82  that is laterally offset from eye box  80 . 
     Additional subsets of pixels P may be used to produce images in one or more additional laterally offset eye boxes, if desired. The positions of the eye boxes may be arranged to overlap slightly at the eye box edges, to provide complete coverage without gaps in the event that a user&#39;s eyes move to a different eye box position during use of device  10 . The pixels P that produce images in each of the laterally offset eye boxes may use any suitable light redirecting structures for oriented emitted light in desired directions (e.g., a prism, a hologram, a microlens, etc.). If desired, the hologram overlapping each light source  72  may be a transmission hologram. Transmission holograms may not be 100% efficient, so some light that is emitted perpendicular to the surface of the display by light source  72  may like through the transmission hologram rather than being redirected at a desired angle towards a desired eye box location. There is a risk that this leaked light, which may sometimes be referred to as zero order light, might result in undesirable image ghosts and contrast reduction. To reduce undesired effects such as these, an optical wedge may be interposed between light source  72  and the overlapping hologram. Consider, as an example, the arrangement of  FIG. 9 . As shown in  FIG. 9 , optical wedge  73  may be interposed between light source  72  and hologram  75 . Wedge  73  may direct vertical emitted light  74  from light source  74  at a non-zero angle from surface normal n. As a result, the zeroth order light will be directed away from the user&#39;s eyes and will not appear as an undesirable ghost image. Hologram  75  may be configured to direct the off-axis zeroth order light towards a desired direction (e.g., towards an appropriate eye box). With this arrangement, even if hologram  75  is not 100% efficient, leaked light will not be received at the eye box and will therefore not be visible to the user. 
     Control circuitry  12  can dynamically select the set of pixels P to use in presenting images to the user (e.g., control circuitry  12  can dynamically select which eye box to use in presenting images to the user) based on gaze tracking sensor output or other information on the current position of the user&#39;s eyes relative to support structures  34  and other portions of device  10 . In addition to accommodating shifting movement of device  10  relative to the head of a user, dynamic eye box control operations can be used to accommodate different user interpupillary distances. 
     If desired, display  46  may have holographic structures that help expend and collimate beams of light  74  from light sources  72  (e.g., to help increase pixels per inch and image resolution). This type of arrangement is shown in  FIG. 10 . As shown in  FIG. 10 , holographic layer  86  may overlap pixels P. Holographic layer  86  may be formed from a photosensitive polymer layer that changes index of refraction in response to light exposure during a hologram writing operation. Lasers may be used to record holographic structures  88  (e.g., gratings) into layer  86 . The holographic structures form lenses (light directing structures) that help expand and collimate light from light sources  72 . Separate holographic structures for red, green, and blue light can be recorded into the same holographic layer  86 , or multiple holographic layers that are each configured to expand and collimate light  74  of a different respective wavelength can be laminated together to form layer  86 . If desired multiple holographic structures may be formed on each pixel (e.g., different hologram recordings may be formed on each pixel). In this type of arrangement, each recording may serve as a separate holographic microlens that is used in directing light to a different eye box. 
     If desired, display  46  may have an array of lenses such as microlenses  70  that are formed from adjustable lens structures. These lenses exhibit variable lens power and may be tuned dynamically by control circuitry  12  to correct for a user&#39;s vision defects (nearsightedness, etc.) and/or to dynamically move an eye box (e.g., by dynamically shifting the center of the lens laterally). Variable lenses may be formed using mechanical deformation (e.g., using piezoelectric actuators, electrostatic actuators, etc.), using electro-optical refractive index adjustment structures, using tunable liquid crystal lens structures, using adjustable and/or fixed holograms, etc. 
     An illustrative tunable liquid crystal lens  90  is shown in  FIG. 11 . Liquid crystal material  92  is placed between upper and lower transparent layers  94  (e.g., layers of polyimide or other clear polymer, etc.). Transparent material  98  (e.g., transparent polymer) may overlap lenses  90  to hold the lenses in a desired shape. Electrodes  96  may be formed above and below liquid crystal material  92 . During operation, a voltage may be applied across terminals  100  by control circuitry  12 . The signals on terminals  100  are applied to electrodes  96  and form an adjustable electric field through liquid crystal material  92 . The refractive index of material  92  may be adjusted by adjusting the voltage applied to terminals  100  and the associated electric field through liquid crystal material  92 . Passive matrix addressing or other control schemes may be used in tuning multiple lenses to form a desired pattern of lenses for vision correction, eye box position shifting, etc. 
     As shown in  FIG. 12 , display  46  may be provided with a switchable diffuser layer such as switchable diffuser layer  108 . Layer  108  may include liquid crystal layer  112  and embedded particles  110 . Electrodes  104  may be used by control circuitry  12  to apply an adjustable electric field to liquid crystal layer  112 . When the electric field has a first value, the refractive index of layer  112  matches that of particles  110 , so that the light from light sources  72  is not significantly scattered (see, e.g., collimated light  74 C). When the electric field has a different second value, the refractive index of layer  112  differs from that of particles  110 . This refractive index discontinuity causes light emitted from light sources  72  in pixels P to be scattered (diffused) as indicated by scattered light  74 D. When it is desired to use display  46  to display virtual reality images for user  50  while device  10  is mounted on the user&#39;s head, control circuitry  12  can place switchable diffuser layer  108  in its non-light-diffusing state. This allows microlenses  70  to collimate light and allows the light to be focused by the user&#39;s eye (e.g., the computer-generated virtual images may be viewed by the user and may, if desired, be overlaid on real-world images captured using a front-facing camera on support structures  34 ). When it is desired to use display  46  in an off-the-head configuration (e.g., when device  10  is being used as a handheld cellular telephone or other non-head-mounted electronic device), control circuitry  12  can place switchable diffuser layer  108  in a light-diffusing state. The light from pixels P will then be scattered (diffused) so that images may be viewed directly on the surface of display  46  (e.g., display  46  will operate as a cellular telephone display and will not project images toward a distant eye box). 
     The foregoing is merely illustrative and various modifications can be to the described embodiments. The foregoing embodiments may be implemented individually or in any combination.

Metadata:
Filing Date: 20181214
Publication Date: 20220906
Grant Date: 20220906
Priority Date: 20180117
Inventors: PEDDER, JAMES E.
FOSTER, JAMES H.
PUSKARICH, PAUL G.
GREGORY, THOMAS M.
TOPLISS, Richard J.
GILL, Patrick R.
Assignee: APPLE INC
CPC Classifications: [{"code": "G02B2027/0174", "inventive": false, "first": false, "tree": "[]"}, {"code": "G02B2027/0123", "inventive": false, "first": false, "tree": "[]"}, {"code": "G02B27/0172", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02B3/0043", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02B5/0242", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02B3/0056", "inventive": true, "first": false, "tree": "[]"}, {"code": "G06F1/163", "inventive": true, "first": false, "tree": "[]"}, {"code": "G06F1/1637", "inventive": true, "first": false, "tree": "[]"}, {"code": "G06F3/011", "inventive": true, "first": false, "tree": "[]"}, {"code": "G09G2300/023", "inventive": false, "first": false, "tree": "[]"}, {"code": "G09G3/20", "inventive": true, "first": false, "tree": "[]"}, {"code": "G06F1/1647", "inventive": true, "first": false, "tree": "[]"}, {"code": "G06F3/1423", "inventive": true, "first": true, "tree": "[]"}, {"code": "G06F3/013", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02B2027/0174", "inventive": false, "first": false, "tree": "[]"}, {"code": "G06F3/1423", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02B2027/014", "inventive": false, "first": false, "tree": "[]"}, {"code": "G02B2027/0123", "inventive": false, "first": false, "tree": "[]"}, {"code": "G02B27/0172", "inventive": true, "first": true, "tree": "[]"}, {"code": "G02B27/0176", "inventive": false, "first": false, "tree": "[]"}, {"code": "G02B27/0176", "inventive": false, "first": false, "tree": "[]"}, {"code": "G02B2027/014", "inventive": false, "first": false, "tree": "[]"}, {"code": "G02B27/0172", "inventive": true, "first": true, "tree": "[]"}, {"code": "G02B2027/0123", "inventive": false, "first": false, "tree": "[]"}, {"code": "G02B2027/0174", "inventive": false, "first": false, "tree": "[]"}, {"code": "G06F3/1423", "inventive": true, "first": false, "tree": "[]"}, {"code": "G06F3/013", "inventive": true, "first": false, "tree": "[]"}]
Family ID: 83149967