PATENT DOCUMENT

Publication Number: US-10054734-B2
Application Number: US-201514881062-A
Country: US
Kind Code: B2

Title: Liquid crystal display with backlight

Abstract:
A display may have an array of pixels that display images for a user. The backlight unit may have a light-guide layer. An array of light-emitting diodes may emit light into an edge of the light-guide layer. The light guide layer may overlap a backlight reflector. A quarter wave plate may be interposed between the light guide layer and the backlight reflector. A turning film may be interposed between a lower polarizer in the array of pixels and the light guide layer. The lower polarizer may be a reflective polarizer. Light exiting the upper surface of the turning film may have a dominant polarization. A half wave plate may be used to rotate the dominant polarization into alignment with a pass axis of the reflective polarizer.

Claims:
What is claimed is: 
     
       1. A display, comprising:
 display layers forming an array of pixels, wherein the display layers include a reflective polarizer; and 
 backlight structures that provide backlight illumination for the pixels, wherein the backlight structures include:
 a light guide layer; 
 a light collimating film interposed between the light guide layer and the reflective polarizer; 
 a half wave plate interposed between the light collimating film and the reflective polarizer; 
 a backlight reflector; and 
 a quarter wave plate interposed between the backlight reflector and the light guide layer. 
 
 
     
     
       2. The display defined in  claim 1  wherein the light collimating film comprises a turning film. 
     
     
       3. The display defined in  claim 2  wherein the reflective polarizer has a pass axis and wherein the turning film has a prism axis that is perpendicular to the pass axis. 
     
     
       4. The display defined in  claim 3  wherein light exiting the turning film towards the half wave plate is characterized by a dominant polarization that is oriented at an angle with respect to the pass axis and wherein the half wave plate has an optical axis that bisects the angle so that the dominant polarization is rotated into alignment with the pass axis as the light that is exiting the turning film passes through the half wave plate. 
     
     
       5. The display defined in  claim 1  wherein the reflective polarizer has a pass axis, wherein light exiting the light collimating film towards the half wave plate is characterized by a dominant polarization, and wherein the half wave plate is oriented so that the dominant polarization is rotated into alignment with the pass axis. 
     
     
       6. The display defined in  claim 5  wherein the display layers include a liquid crystal layer. 
     
     
       7. The display defined in  claim 6  wherein the display layers include an upper polarizer and wherein the liquid crystal layer is interposed between the upper polarizer and the reflective polarizer. 
     
     
       8. The display defined in  claim 7  wherein the light collimating film comprises a turning film with elongated prisms that run along a prism axis and that face the light guide layer. 
     
     
       9. The display defined in  claim 8  wherein the light guide layer comprises a polycarbonate layer. 
     
     
       10. The display defined in  claim 8  wherein the reflective polarizer has a non-reflective polarizer film and a reflective polarizer film. 
     
     
       11. The display defined in  claim 8  wherein the backlight structures include an array of light emitting diodes that emit light into an edge of the light guide layer along a direction that is perpendicular to the prism axis. 
     
     
       12. A display, comprising:
 display layers forming an array of pixels, wherein the display layers include a polarizer; and 
 backlight structures that provide backlight illumination for the pixels, wherein the backlight structures include:
 a light guide layer into which light is provided by light-emitting diodes; 
 a light collimating film interposed between the light guide layer and the polarizer; 
 a half wave plate interposed between the light collimating film and the polarizer; 
 a backlight reflector; and 
 a quarter wave plate interposed between the backlight reflector and the light guide layer. 
 
 
     
     
       13. The display defined in  claim 12  wherein the display layers include a layer of liquid crystal material. 
     
     
       14. The display defined in  claim 13  further comprising an additional polarizer, wherein the liquid crystal material is interposed between the polarizer and the additional polarizer and wherein the polarizer comprises a reflective polarizer. 
     
     
       15. The display defined in  claim 14  wherein the reflective polarizer is interposed between the liquid crystal layer and the half wave plate. 
     
     
       16. The display defined in  claim 15  wherein the light-emitting diodes run along an edge of the light guide layer and wherein the light collimating film has grooves that run parallel to the edge. 
     
     
       17. The display defined in  claim 12  wherein the reflective polarizer has a pass axis, wherein the light exiting the light guide layer towards the half wave plate has a dominant polarization that is oriented at an angle with respect to the pass axis, and wherein the half wave plate has an optical axis that bisects the angle. 
     
     
       18. A backlight for a liquid crystal display having a layer of liquid crystal material sandwiched between an upper polarizer and a lower polarizer, wherein the lower polarizer is a reflective polarizer having a pass axis, the backlight comprising:
 a light guide layer into which light is emitted by light-emitting diodes; 
 a light collimating film interposed between the light guide layer and the reflective polarizer; 
 a half wave plate interposed between the light collimating film and the polarizer; 
 a backlight reflector; and 
 a quarter wave plate interposed between the backlight reflector and the light guide layer. 
 
     
     
       19. The backlight defined in  claim 18  wherein the light collimating film comprises a prism film having prisms that face the light guide layer.

Description:
This application claims the benefit of provisional patent application No. 62/159,146 filed on May 8, 2015, which is hereby incorporated by reference herein in its entirety. 
    
    
     BACKGROUND 
     This relates generally to electronic devices, and more particularly, to electronic devices with displays. 
     Electronic devices often include displays. For example, cellular telephones, tablet computers, and laptop computers often include displays for presenting information to a user. 
     Liquid crystal displays contain a layer of liquid crystal material sandwiched between upper and lower polarizers. Pixels in a liquid crystal display contain thin-film transistors and electrodes for applying electric fields to the liquid crystal material. The strength of the electric field in a pixel controls the polarization state of the liquid crystal material and thereby adjusts the brightness of the pixel. A liquid crystal display may have an array of color filter elements to provide the display with the ability to display color images. 
     The pixels in the liquid crystal display can be illuminated using a backlight unit. The backlight unit may include a light guide layer. The light guide layer may be formed from a transparent material such as a transparent polymer. An array of light-emitting diodes may emit light into the edge of the light guide layer. The light that is emitted into the edge of the light guide layer may be distributed throughout the light guide layer in accordance with the principle of total internal reflection. 
     The light guide layer may be provided with light scattering features that scatter the light that is traveling within the interior of the light guide layer. Light that is scattered outwards from the light guide layer through the pixels of the liquid crystal display can serve as backlight for the display. 
     Display brightness can be adversely affected by the optical characteristics of the display. As an example, the lower polarizer in a display may transmit only a fraction of the light that scattered outwards from the light guide layer, decreasing backlight efficiency and the brightness level of the display. 
     It would therefore be desirable to be able to provide improved displays such as improved backlit liquid crystal displays. 
     SUMMARY 
     A display may have an array of pixels that display images for a user. The array of pixels may be formed from liquid crystal display layers. The array of pixels may be provided with backlight illumination by a backlight unit. 
     The backlight unit may have a light-guide layer. An array of light-emitting diodes may emit light into an edge of the light-guide layer. The light guide layer may overlap a backlight reflector. A quarter wave plate may be interposed between the light guide layer and the backlight reflector. 
     The array of pixels may include upper and lower polarizers. A liquid crystal layer may be interposed between the upper and lower polarizers. The lower polarizer may be a reflecting polarizer. A turning film may be interposed between the reflecting polarizer and the light guide layer. The turning film may have prisms with a prism axis that is perpendicular to the direction in which the light is emitted from the light-emitting diodes. The prisms of the turning film may face the light guide layer. 
     Light exiting the upper surface of the turning film may have a dominant polarization. A half wave plate may be interposed between the turning film and the reflective polarizer. The half wave plate may be used to rotate the dominant polarization into alignment with a pass axis of the reflective polarizer. The quarter wave plate below the light guide layer may be used to rotate the polarization of light emitted from the bottom of the light guide layer into alignment with the dominant polarization. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of an illustrative electronic device such as a laptop computer with a display in accordance with an embodiment. 
         FIG. 2  is a perspective view of an illustrative electronic device such as a handheld electronic device with a display in accordance with an embodiment. 
         FIG. 3  is a perspective view of an illustrative electronic device such as a tablet computer with a display in accordance with an embodiment. 
         FIG. 4  is a perspective view of an illustrative electronic device such as a computer display with display structures in accordance with an embodiment. 
         FIG. 5  is a cross-sectional side view of an illustrative display in accordance with an embodiment. 
         FIG. 6  is a cross-sectional side view of a portion of an illustrative backlight unit in accordance with an embodiment. 
         FIG. 7  is a diagram showing how light that is emitted from the light guide layer in a display backlight unit of the type shown in  FIG. 6  may be polarized in accordance with an embodiment. 
         FIG. 8  is a diagram showing how light may be polarized upon exiting from a turning film in a display backlight unit in accordance with an embodiment. 
         FIG. 9  is a diagram showing how light may be polarized upon exiting from a half wave plate in a display backlight unit in accordance with an embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     Electronic devices may include displays. The displays may be used to display images for a user. Illustrative electronic devices that may be provided with displays are shown in  FIGS. 1, 2, 3, and 4 . 
       FIG. 1  shows how electronic device  10  may have the shape of a laptop computer having upper housing  12 A and lower housing  12 B with components such as keyboard  16  and touchpad  18 . Device  10  may have hinge structures  20  that allow upper housing  12 A to rotate in directions  22  about rotational axis  24  relative to lower housing  12 B. Display  14  may be mounted in upper housing  12 A. Upper housing  12 A, which may sometimes referred to as a display housing or lid, may be placed in a closed position by rotating upper housing  12 A towards lower housing  12 B about rotational axis  24 . 
       FIG. 2  shows how electronic device  10  may be a handheld device such as a cellular telephone, music player, gaming device, navigation unit, or other compact device. In this type of configuration for device  10 , housing  12  may have opposing front and rear surfaces. Display  14  may be mounted on a front face of housing  12 . Display  14  may, if desired, have openings for components such as button  26 . Openings may also be formed in display  14  to accommodate a speaker port (see, e.g., speaker port  28  of  FIG. 2 ). 
       FIG. 3  shows how electronic device  10  may be a tablet computer. In electronic device  10  of  FIG. 3 , housing  12  may have opposing planar front and rear surfaces. Display  14  may be mounted on the front surface of housing  12 . As shown in  FIG. 3 , display  14  may have an opening to accommodate button  26  (as an example). 
       FIG. 4  shows how electronic device  10  may be a display such as a display with an embedded computer, a display without an embedded computer, or other suitable equipment for displaying images. With this type of arrangement, housing  12  for device  10  may be mounted on a support structure such as stand  30  or stand  30  may be omitted (e.g., to mount device  10  on a wall). Display  14  may be mounted on a front face of housing  12 . 
     The illustrative configurations for device  10  that are shown in  FIGS. 1, 2, 3, and 4  are merely illustrative. In general, electronic device  10  may be a laptop computer, a computer monitor or other display containing an embedded computer, a tablet computer, a cellular telephone, a media player, or other handheld or portable electronic device, a smaller device such as a wrist-watch device, a pendant device, a headphone or earpiece device, or other wearable or miniature device, a computer display or other monitor that does not contain an embedded computer, a gaming device, a navigation device, an embedded system such as a system in which electronic equipment with a display is mounted in a kiosk or automobile, equipment that implements the functionality of two or more of these devices, or other electronic equipment. 
     Housing  12  of device  10 , which is sometimes referred to as a case, may be formed of materials such as plastic, glass, ceramics, carbon-fiber composites and other fiber-based composites, metal (e.g., machined aluminum, stainless steel, or other metals), other materials, or a combination of these materials. Device  10  may be formed using a unibody construction in which most or all of housing  12  is formed from a single structural element (e.g., a piece of machined metal or a piece of molded plastic) or may be formed from multiple housing structures (e.g., outer housing structures that have been mounted to internal frame elements or other internal housing structures). 
     Display  14  may be a touch sensitive display that includes a touch sensor or may be insensitive to touch. Touch sensors for display  14  may be formed from an array of capacitive touch sensor electrodes, a resistive touch array, touch sensor structures based on acoustic touch, optical touch, or force-based touch technologies, or other suitable touch sensor components. 
     Display  14  for device  10  may include pixels formed from liquid crystal display (LCD) components. A display cover layer may cover the surface of display  14  or a display layer such as a color filter layer or other portion of a display may be used as the outermost (or nearly outermost) layer in display  14 . The outermost display layer may be formed from a transparent glass sheet, a clear plastic layer, or other transparent member. 
     A cross-sectional side view of an illustrative configuration for display  14  of device  10  (e.g., for display  14  of the devices of  FIG. 1 ,  FIG. 2 ,  FIG. 3 ,  FIG. 4  or other suitable electronic devices) is shown in  FIG. 5 . As shown in  FIG. 5 , display  14  may include backlight structures such as backlight unit  42  for producing backlight  44 . During operation, backlight illumination  44  travels outwards (vertically upwards in dimension Z in the orientation of  FIG. 5 ) and passes through display pixel structures in display layers  46 . This illuminates any images that are being produced by the display pixels for viewing by a user. For example, backlight  44  may illuminate images on display layers  46  that are being viewed by viewer  48  in direction  50 . 
     Display layers  46  may be mounted in chassis structures such as a plastic chassis structure and/or a metal chassis structure to form a display module for mounting in housing  12  or display layers  46  may be mounted directly in housing  12  (e.g., by stacking display layers  46  into a recessed portion in housing  12 ). Display layers  46  may form a liquid crystal display or may be used in forming displays of other types. 
     Display layers  46  may include a liquid crystal layer such a liquid crystal layer  52 . Liquid crystal layer  52  may be sandwiched between display layers such as display layers  58  and  56 . Layers  56  and  58  may be interposed between lower polarizer layer  60  and upper polarizer layer  54 . 
     Layers  58  and  56  may be formed from transparent substrate layers such as clear layers of glass or plastic. Layers  58  and  56  may be layers such as a thin-film transistor layer and/or a color filter layer. Conductive traces, color filter elements, transistors, and other circuits and structures may be formed on the substrates of layers  58  and  56  (e.g., to form a thin-film transistor layer and/or a color filter layer). Touch sensor electrodes may also be incorporated into layers such as layers  58  and  56  and/or touch sensor electrodes may be formed on other substrates. 
     With one illustrative configuration, layer  58  may be a thin-film transistor layer that includes an array of pixel circuits based on thin-film transistors and associated electrodes (pixel electrodes) for applying electric fields to liquid crystal layer  52  and thereby displaying images on display  14 . Layer  56  may be a color filter layer that includes an array of color filter elements for providing display  14  with the ability to display color images. If desired, layer  58  may be a color filter layer and layer  56  may be a thin-film transistor layer. Configurations in which color filter elements are combined with thin-film transistor structures on a common substrate layer in the upper or lower portion of display  14  may also be used. 
     During operation of display  14  in device  10 , control circuitry (e.g., one or more integrated circuits on a printed circuit) may be used to generate information to be displayed on display  14  (e.g., display data). The information to be displayed may be conveyed to a display driver integrated circuit such as circuit  62 A or  62 B using a signal path such as a signal path formed from conductive metal traces in a rigid or flexible printed circuit such as printed circuit  64  (as an example). 
     Backlight structures  42  may include a light guide layer such as light guide layer  78 . Light guide layer  78  may be formed from a transparent material such as clear glass or plastic (e.g., molded plastic such as polymethyl methacrylate or other clear thermoplastic that forms a light guide plate, a thin flexible plastic film such as a sheet of polycarbonate or other thin polymer film, etc.). During operation of backlight structures  42 , a light source such as light source  72  may generate light  74 . Light source  72  may be, for example, an array of light-emitting diodes. 
     Light  74  from light source  72  may be coupled into edge surface  76  of light guide plate  78  and may be distributed in dimensions X and Y throughout light guide layer  78  due to the principal of total internal reflection. Light guide layer  78  may include light-scattering features such as pits or bumps or other light-scattering structures. The light-scattering features may be located on an upper surface and/or on an opposing lower surface of light guide layer  78 . Light source  72  may be located at the left of light guide layer  78  as shown in  FIG. 5  or may be located along the right edge of layer  78  and/or other edges of layer  78 . 
     Light  74  that scatters upwards in direction Z from light guide layer  78  may serve as backlight  44  for display  14 . Light  74  that scatters downwards may be reflected back in the upwards direction by reflector  80 . Reflector  80  may be formed from a reflective material such as a layer of plastic covered with a dielectric mirror thin-film coating. Reflective tape (e.g., white plastic tape or tape formed from other reflective materials) may be incorporated into the backlight reflector for display  14 . For example, backlight structures  42  may include a strip of tape that runs along the edge of reflector  80  that is adjacent to light-emitting diodes  72 . 
     Backlight structures  42  may include optical films  70 . Optical films  70  may include diffuser layers for helping to homogenize backlight  44  and thereby reduce hotspots, compensation films for enhancing off-axis viewing, and light collimating films such as turning films (prism films, brightness enhancement films, etc.) for collimating backlight  44 . Optical films  70  may overlap the other structures in backlight unit  42  such as light guide layer  78  and reflector  80 . For example, if light guide layer  78  has a rectangular footprint in the X-Y plane of  FIG. 5 , optical films  70  and reflector  80  may have a matching rectangular footprint. If desired, films such as compensation films may be incorporated into other layers of display  14  (e.g., polarizer layers). 
     To enhance backlight efficiency, backlight unit  42  may be provided with structures of the type shown in  FIG. 6 . As shown in  FIG. 6 , backlight unit  42  may include light guide layer  78 . Light  74  may be distributed throughout layer  78  in accordance with the principle of total internal reflection. Light scattering features in layer  78  may cause some of light  74  to escape upwards as light  44 - 1  and may cause some of light  74  to escape downwards as light  44 - 2 . Light  44 - 1  and light  44 - 2  may have different polarizations (e.g., light  44 - 1  may be predominantly p-polarized and light  44 - 2  may be predominantly s-polarized). The diagram of  FIG. 7  shows an illustrative ray of light  44 - 1  exiting the upper surface of light guide layer  78 . Different rays of light  44 - 1  have different angular directions and different polarizations. Ray of light  44 - 1  of  FIG. 7  is shown as an example. 
     Backlight unit  42  may have a light collimating film such as turning film  100 . Turning film  100  may be formed from elongated ridge-shaped prisms  104  formed on substrate  102  and may sometimes be referred to as a prism film. The prisms may have triangular cross-sectional shapes that point upward towards lower polarizer  60  or that point downward towards light guide film  78 , as shown in  FIG. 6 . An optional diffuser layer may, if desired, be interposed between film  100  and polarizer  60 . 
     Substrate  102  of turning film  100  may be formed from a layer of clear polymer such as a polyethylene terephthalate (PET) layer. Prisms  104  may be formed from a clear polymer that is deposited and embossed or otherwise patterned onto the surface of substrate  102 . Other techniques for forming turning film  100  may be used if desired. Moreover, the shapes of the optical features on the light collimating film of backlight unit  42  may be different (e.g., the periodicity of the prisms or other features may vary as a function of position on the surface of the film to reduce Moire effects that might arise due to interference between these features and the rows and columns of pixels in display  14 , the shapes of the downward protruding features may have rounded cross-sectional shapes or other shapes with non-triangular profiles, shapes other than elongated ridges etc.). 
     In the example of  FIG. 6 , the ridge shaped protruding features of film  100  (i.e., elongated prisms  104 ) extend in parallel ridges into the page in the orientation of  FIG. 6  and are form a series of parallel grooves. The groove axis (sometimes referred to as the prism axis) of turning film  100  is parallel to the X axis and is perpendicular to the Y axis. Light rays  74  from light-emitting diodes  72  are emitted in the Y direction into edge  76  of light guide layer  78  (i.e., light rays  74  may propagate in a direction that is perpendicular to the prism axis of turning film  100 ). Other orientations for the prism axis (groove axis) of turning film  100  may be used, if desired. 
     After passing through turning film  100 , light  44 - 1  becomes collimated and is more aligned with vertical axis Z (see, e.g., collimated light  44 - 3  of  FIG. 6 ). The polarization of light  44 - 3  is changed from that of light  44 - 1  due to optical interactions between light  44 - 1  and turning film  100 .  FIG. 8  is a diagram in which the polarization of light  44 - 3  has been projected onto the X-Y plane. As shown in  FIG. 8 , light  44 - 3  may be characterized by a dominant polarization DP that is oriented at an angle AG with respect to the Y-axis (in the X-Y plane). 
     In the illustrative arrangement of  FIG. 6 , lower polarizer  60  has a pass axis that is aligned with the Y-axis (perpendicular to the prism axis of turning film  100 ). Half-wave plate  106  is interposed between polarizer  60  and turning film  100 . Half-wave plate  106  may, for example, be attached to the lower surface of lower polarizer  60  with adhesive. The optical axis of half-wave plate  106  may be oriented along vector HWP of  FIG. 8 . 
     The optical axis of the half-wave plate is preferably oriented at an angle AG/ 2  with respect to polarizer pass axis Y (i.e., the optical axis of half-wave plate  106  bisects the angle AG that characterizes the orientation of dominant light polarization DP with respect to pass axis Y). As a result, the light of dominant polarization DP (light  44 - 3 ) is rotated by an angle AG into alignment with pass axis Y as this light passes through half-wave plate  106 , as illustrated in  FIG. 9 . As shown in  FIG. 9 , the orientation of dominant polarization DP for light  44 - 4  that is exiting the upper surface of half-wave plate  106  is aligned with pass axis Y. Because the dominant polarization of light  44 - 4  is aligned with the pass axis of polarizer  60 , light  44 - 4  can be transmitted through polarizer  60  with minimized loss to serve as backlight illumination  44  for display  14 . The use of half-wave plate  106  therefore helps to rotate the dominant polarization of the backlight that is exiting turning film  100  into alignment with the pass axis of polarizer  60  to minimize losses. 
     Polarizer  60  may be a reflective polarizer formed from polarizer layers  60 - 1  and  60 - 2 . Layer  60 - 2  may be attached to the lower surface of layer  60 - 1  with a layer of adhesive or other suitable attachment mechanism. Polarizer layer  60 - 1  may be a non-reflective polarizer layer that has a pass axis aligned with axis Y. Polarizer layer  60 - 2  may have a pass axis aligned with axis Y and may be a reflective polarizer layer (i.e., a polarizer that reflects light with off-axis polarizations to produce reflected light  44 - 5 ). Other types of reflective polarizer structures may be used for forming polarizer  60 , if desired. The illustrative configuration of  FIG. 6  in which reflective polarizer  60  includes a pair of polarizer films is merely an example. 
     Reflected light  44 - 5  that is directed downwards from reflective polarizer  60  to backlight reflector  80  may be reflected off of reflector  80  back in upwards direction Z through polarizer  60 . When traversing the layers of backlight unit  42 , the polarization of reflected light  44 - 5  may become scrambled, so at least some of the recycled light  44 - 5  that is being reflected off of reflector  80  and that is traveling in upwards direction Z will be polarized along pass axis Y when reaching polarizer  60  and will pass through polarizer  60  to contribute to backlight  44 . The presence of reflective polarizer portion  60 - 2  of bottom polarizer  60  (e.g., the use of a reflective polarizer to implement polarizer  60 ) therefore helps to avoid light loss due to mismatches between the polarization of light  44 - 4  and the pass axis of polarizer  60 . 
     Light  44 - 1  that is scattered out of the top surface of light guide layer  78  has predominantly p polarization, whereas light  44 - 2  has predominantly s polarization. A quarter wave plate such as quarter wave plate  110  may be attached to the upper surface of reflector  80  (e.g., using a layer of adhesive) or may otherwise be interposed between light guide layer  78  and reflector  80 . Light  44 - 2  passes through quarter wave plate  110  twice. On a first pass, light  44 - 2  passes downwards through quarter wave plate  110  to reflector  80 . Upon reaching reflector  80 , this light is reflected back in upwards direction Z and makes a second pass through quarter wave plate  110  before passing upwards through light guide layer  78  to turning film  100 . Together, the first and second passes of light  44 - 2  rotate the dominant polarization of light  44 - 2  by 90° into alignment with the dominant polarization of light  44 - 1 . 
     Due to the operation of turning film  100  and half wave plate  106 , light with the polarization of light  44 - 1  (i.e., light  74  that scatters upwards from the upper surface of light guide layer  78  and light  44 - 2  that has passed twice through quarter wave plate  110 ) may be rotated into alignment with the pass axis of polarizer  60  and transmitted through display layers  46  to serve as backlight  44 . The presence of quarter wave plate  110  may therefore help to improve the efficiency with which downwards scattered light  44 - 2  can contribute to the backlight illumination produced by backlight unit  42 . 
     If desired, wave plates such as layers  106  and  110  may be formed using structures that enhance viewing angle and reduce dispersion (e.g., Pancharatnam achromatic wave plate designs and/or Lyot wide-field-of-view wave plate designs). 
     The foregoing is merely illustrative and various modifications can be made by those skilled in the art without departing from the scope and spirit of the described embodiments. The foregoing embodiments may be implemented individually or in any combination.

Metadata:
Filing Date: 20151012
Publication Date: 20180821
Grant Date: 20180821
Priority Date: 20150508
Inventors: HUANG, YI
ZHU, XINYU
QI, JUN
Assignee: APPLE INC
CPC Classifications: [{"code": "G02B6/0073", "inventive": true, "first": true, "tree": "[]"}, {"code": "G02F1/13362", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02F1/13362", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02B6/0041", "inventive": false, "first": false, "tree": "[]"}, {"code": "G02F1/133615", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02B6/0073", "inventive": true, "first": true, "tree": "[]"}, {"code": "G02F1/133615", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02F1/13362", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02F1/133615", "inventive": true, "first": true, "tree": "[]"}, {"code": "G02B6/0041", "inventive": false, "first": false, "tree": "[]"}, {"code": "G02B1/045", "inventive": false, "first": false, "tree": "[]"}]
Family ID: 57223354