PATENT DOCUMENT

Publication Number: US-9921356-B2
Application Number: US-201615091444-A
Country: US
Kind Code: B2

Title: Display Backlight with Light Mixing Structures

Abstract:
A display may have a backlight unit with a row of light-emitting diodes that emit light into the edge of a light guide layer. The light guide layer may have opposing upper and lower surfaces. The upper surface of the light guide layer may have ridges and the lower surface of the light guide layer may have bumps. The edge of the light guide layer may have light mixing structures. The light mixing structures may include an alternating pattern of protrusions with different shapes. For example, triangular protrusions of a first size may be patterned with triangular protrusions of a second size. The light mixing structures may reduce the mixing distance of the backlight unit.

Claims:
What is claimed is: 
     
       1. A display backlight comprising:
 a row of light-emitting diodes; and 
 a light guide layer having first and second opposing surfaces connected by an edge, wherein the edge receives light from the row of light-emitting diodes, wherein the edge has a first plurality of protrusions that each have a first shape and a second plurality of protrusions that each have a second shape that is different than the first shape, wherein each of the first plurality of protrusions is interposed directly between respective first and second protrusions of the second plurality of protrusions, and wherein each of the second plurality of protrusions is interposed directly between respective first and second protrusions of the first plurality of protrusions. 
 
     
     
       2. The display backlight defined in  claim 1 , wherein the first shape comprises a first triangular shape, and wherein the second shape comprises a second triangular shape. 
     
     
       3. The display backlight defined in  claim 2 , wherein the edge has a planar portion, wherein the first triangular shape comprises first and second surfaces that are at a first angle relative to the planar portion of the edge, and wherein the second triangular shape comprises third and fourth surfaces that are at a second angle relative to the planar portion of the edge. 
     
     
       4. The display backlight defined in  claim 3 , wherein the first angle is between 17.5° and 22.5°, and wherein the second angle is between 25° and 40°. 
     
     
       5. The display backlight defined in  claim 4 , wherein the first angle is 20°. 
     
     
       6. The display backlight defined in  claim 5 , wherein the second angle is 30°. 
     
     
       7. The display backlight defined in  claim 5 , wherein the second angle is 35°. 
     
     
       8. The display backlight defined in  claim 3 , wherein the first angle is between 10° and 15°, and wherein the second angle is between 20° and 30°. 
     
     
       9. The display backlight defined in  claim 8 , wherein the first angle is 12.5°. 
     
     
       10. The display backlight defined in  claim 9 , wherein the second angle is 25°. 
     
     
       11. The display backlight defined in  claim 1 , further comprising:
 a reflector that is parallel to the first and second opposing surfaces of the light guide layer. 
 
     
     
       12. A light guide layer comprising:
 a top surface; 
 a bottom surface; and 
 first and second opposing surfaces that connect the top and bottom surfaces, wherein the first surface has a pattern of light mixing structures configured to distribute light, wherein the pattern comprises a first plurality of light mixing structures with a first shape that alternates with a second plurality of light mixing structures with a second shape that is different than the first shape, wherein each light mixing structure of the first plurality of light mixing structures is interposed between respective first and second light mixing structures of the second plurality of light mixing structures without any intervening light mixing structures, wherein each light mixing structure of the second plurality of light mixing structures is interposed between respective first and second light mixing structures of the first plurality of light mixing structures without any intervening light mixing structures, wherein each light mixing structure of the first plurality of light mixing structures is a protrusion, and wherein each light mixing structure of the second plurality of light mixing structures is a protrusion. 
 
     
     
       13. The light guide layer defined in  claim 12 , wherein each light mixing structure of the first plurality of light mixing structures comprises a triangular protrusion with first and second surfaces of a first length. 
     
     
       14. The light guide layer defined in  claim 13 , wherein each light mixing structure of the second plurality of light mixing structures comprises a triangular protrusion with third and fourth surfaces of a second length that is different than the first length. 
     
     
       15. The light guide layer defined in  claim 12 , wherein the top surface of the light guide layer has ridges, and wherein the bottom surface of the light guide layer has bumps. 
     
     
       16. A liquid crystal display comprising:
 first and second transparent substrates; 
 a liquid crystal layer between the first and second substrates; 
 a light guide layer configured to pass backlight through the first and second substrates and the liquid crystal layer, wherein the light guide layer has first and second opposing edges; and 
 at least first and second light-emitting diodes that each emit light into the first edge of the light guide layer, wherein the first edge of the light guide layer comprises a pattern of protrusions configured to distribute light, wherein the pattern comprises a first plurality of protrusions with a first shape that alternates with a second plurality of protrusions with a second shape that is different than the first shape, wherein the first and second pluralities of protrusions are the only protrusions on the first edge of the light guide layer, wherein each of the first plurality of protrusions is interposed directly between respective first and second protrusions of the second plurality of protrusions, and wherein each of the second plurality of protrusions is interposed directly between respective first and second protrusions of the first plurality of protrusions.

Description:
This application claims the benefit of provisional patent application No. 62/222,603 filed on Sep. 23, 2015, which is hereby incorporated by reference herein in its entirety. 
    
    
     BACKGROUND 
     This relates generally to electronic devices with displays, and, more particularly, to displays with backlights. 
     Electronic devices such as computers and cellular telephones have displays. Some displays such as plasma displays and organic light-emitting diode displays have arrays of pixels that generate light. In displays of this type, backlighting is not necessary because the pixels themselves produce light. Other displays contain passive pixels that can alter the amount of light that is transmitted through the display to display information for a user. Passive pixels do not produce light themselves, so it is often desirable to provide backlight for a display with passive pixels. 
     In a typical backlight assembly for a display, a light guide layer is used to distribute backlight generated by a light source such as a light-emitting diode light source. Optical films such as a diffuser layer and prism films may be placed on top of the light guide layer. A reflector may be formed under the light guide layer to improve backlight efficiency. 
     A strip of light-emitting diodes may provide light to an edge of a light guide layer. Light from the strip of light-emitting diodes is initially concentrated in the vicinity of the outputs of the light-emitting diodes. The light must travel a sufficient distance into the light guide layer to mix enough to be used as backlight illumination. Backlight units that require large mixing distances may consume more volume within a display than desired. 
     It would therefore be desirable to be able to provide displays with improved backlights. 
     SUMMARY 
     A display may have an array of pixels for displaying images for a viewer. The array of pixels may be formed from display layers such as a color filter layer, a liquid crystal layer, a thin-film transistor layer, and polarizer layers. 
     A backlight unit may be used to produce backlight illumination for the display. The backlight illumination may pass through the polarizers, the thin-film transistor layer, the liquid crystal layer, and the color filter layer. The backlight unit may have a row of light-emitting diodes that emit light into a light guide layer. 
     The light guide layer may have first and second opposing surfaces connected by an edge that receives light from the row of light-emitting diodes. The edge of the light guide layer may have a pattern of light mixing structures configured to distribute light. The pattern may include a first plurality of light mixing structures with a first shape that alternates with a second plurality of light mixing structures with a second shape that is different than the first shape. Each light mixing structure of the first plurality of light mixing structures may be interposed between respective first and second light mixing structures of the second plurality of light mixing structures. 
     The light mixing structures may include triangular protrusions with varying sizes. The different shaped protrusions may mix the backlight quickly without producing a cross-hatched pattern of light. 
     Further features will be more apparent from the accompanying drawings and the following detailed description. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic diagram of an illustrative electronic device having a display in accordance with an embodiment. 
         FIG. 2  is a cross-sectional side view of an illustrative display in an electronic device in accordance with an embodiment. 
         FIG. 3  is a top view of an illustrative display in accordance with an embodiment. 
         FIG. 4  is cross-sectional side view of an illustrative symmetrically tapered portion of a light guide layer for a display backlight in accordance with an embodiment. 
         FIG. 5  is a cross-sectional side view of an illustrative light guide layer with light-scattering features such as bumps on its lower surface in accordance with an embodiment. 
         FIG. 6  is graph in which bump density has been plotted as a function of position along the length of a light guide layer in accordance with an embodiment. 
         FIG. 7  is a cross-sectional side view of a light guide layer showing how different light rays interact with the surfaces of the light guide layer by different amounts in accordance with an embodiment. 
         FIG. 8  is a cross-sectional perspective view of a light guide layer showing how rounded ridges may extend along the upper surface of the light guide layer in accordance with an embodiment. 
         FIG. 9  is a perspective view of an illustrative light guide layer with light mixing structures along an edge in accordance with an embodiment. 
         FIG. 10  is a top view of an illustrative light guide layer showing protrusions for mixing light in accordance with an embodiment. 
         FIG. 11  is a top view of an illustrative light guide layer showing a cross-hatched pattern of light that results from protrusions of the type shown in  FIG. 10  in accordance with an embodiment. 
         FIG. 12  is a top view of an illustrative light guide layer with an alternating pattern of protrusions in accordance with an embodiment. 
         FIG. 13  is a top view of illustrative protrusions with non-uniform shape in accordance with an embodiment. 
         FIG. 14  is a perspective view of a light guide layer processing tool in accordance with an embodiment. 
         FIG. 15  is a flowchart showing illustrative steps involved with processing a light guide layer to include light mixing structures in accordance with an embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     An illustrative electronic device of the type that may be provided with a display is shown in  FIG. 1 . As shown in  FIG. 1 , electronic device  10  may have control circuitry  16 . Control circuitry  16  may include storage and processing circuitry for supporting the operation of device  10 . The storage and processing circuitry may include storage such as hard disk drive storage, nonvolatile memory (e.g., flash memory or other 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  16  may be used to control the operation of device  10 . The processing circuitry may be based on one or more microprocessors, microcontrollers, digital signal processors, baseband processors, power management units, audio chips, application specific integrated circuits, etc. 
     Input-output circuitry in device  10  such as input-output devices  12  may be used to allow data to be supplied to device  10  and to allow data to be provided from device  10  to external devices. Input-output devices  12  may include buttons, joysticks, scrolling wheels, touch pads, key pads, keyboards, microphones, speakers, tone generators, vibrators, cameras, sensors, light-emitting diodes and other status indicators, data ports, etc. A user can control the operation of device  10  by supplying commands through input-output devices  12  and may receive status information and other output from device  10  using the output resources of input-output devices  12 . 
     Input-output devices  12  may include one or more displays such as display  14 . Display  14  may be a touch screen display that includes a touch sensor for gathering touch input from a user or display  14  may be insensitive to touch. A touch sensor for display  14  may be based on an array of capacitive touch sensor electrodes, acoustic touch sensor structures, resistive touch components, force-based touch sensor structures, a light-based touch sensor, or other suitable touch sensor arrangements. 
     Control circuitry  16  may be used to run software on device  10  such as operating system code and applications. During operation of device  10 , the software running on control circuitry  16  may display images on display  14 . 
     Device  10  may be a tablet computer, laptop computer, a desktop computer, a television, a cellular telephone, a media player, a wristwatch device or other wearable electronic equipment, or other suitable electronic device. 
     Display  14  for device  10  includes an array of pixels. The array of pixels may be formed from liquid crystal display (LCD) components or other suitable display structures. Configurations based on liquid crystal display structures are sometimes described herein as an example. 
     A display cover layer may cover the surface of display  14  or a display layer such as a color filter layer, thin-film transistor 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  is shown in  FIG. 2 . As shown in  FIG. 2 , display  14  may include a backlight unit such as backlight unit  42  (sometimes referred to as a backlight or backlight structures) for producing backlight  44 . During operation, backlight  44  travels outwards (vertically upwards in dimension Z in the orientation of  FIG. 2 ) and passes through pixel structures in display layers  46 . This illuminates any images that are being produced by the 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 a housing in device  10  or display layers  46  may be mounted directly in an electronic device housing for device  10  (e.g., by stacking display layers  46  into a recessed portion in a metal or plastic housing). Display layers  46  may form a liquid crystal display or may be used in forming displays of other types. 
     In a configuration in which display layers  46  are used in forming a liquid crystal display, 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  56  and  58  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 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). Integrated circuits such as integrated circuit  62 A and/or flexible printed circuits such as flexible printed circuit  64  may be attached to substrate  58  in ledge region  66  (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. Light guide layer  78  may sometimes be referred to as a light guide plate or a light guide film. 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 (e.g., a series of light-emitting diodes that are arranged in a row that extends into the page in the orientation of  FIG. 2 ). The array of light-emitting diodes may be mounted to a rigid or flexible printed circuit. The printed circuit may be adhered to adjacent layers in the electronic device. In certain embodiments, the printed circuit may be adhered to portions of light guide layer  78 . 
     Light  74  from light source  72  may be coupled into edge surface  76  of light guide layer  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, bumps, grooves, or ridges that help light exit light guide layer  78  for use as backlight  44 . These features may be located on an upper surface and/or on an opposing lower surface of light guide layer  78 . With one illustrative configuration, which is described herein as an example, a first surface such as the lower surface of light guide layer  78  has a pattern of bumps and an opposing second surface such as the upper surface of light guide layer  78  has a pattern of ridges (sometimes referred to as lenticules, lenticular structures, or lenticular ridges). Light source  72  may be located at the left of light guide layer  78  as shown in  FIG. 2  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 upward direction by reflector  80 . Reflector  80  may be formed from a reflective structure such as a substrate layer of plastic coated with a dielectric mirror formed from alternating high-index-of-refraction and low-index-of-refraction inorganic or organic layers. Reflector  80  may be formed from a reflective material such as a layer of white plastic or other shiny materials. 
     To enhance backlight performance for backlight structures  42 , 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. Optical films  70  may also include prism films (sometimes referred to as turning films) 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. 2 , optical films  70  and reflector  80  may each have a matching rectangular footprint. Optical films  70  may include compensation films for enhancing off-axis viewing or compensation films may be formed within the polarizer layers of display  14  or elsewhere in display  14 . 
       FIG. 3  is a top view of a portion of display  14  showing how display  14  may have an array of pixels  90  formed within display layers  46 . Pixels  90  may have color filter elements of different colors such as red color filter elements R, green color filter elements G, and blue color filter elements B. Pixels  90  may be arranged in rows and columns and may form active area AA of display  14 . The borders of active area AA may be slightly inboard of the borders of light-guide layer  78  to ensure that there are no visible hotspots in display  14  (i.e., no areas in which the backlight illumination for display  14  is noticeably brighter than surrounding areas). For example, border  92  of active area AA may be offset by a distance  82  from lower edge  76  of light guide layer. It is generally desirable to minimize the size of distance  82  so that display  14  is as compact as possible for a given active area size. Nevertheless, distance  82  should not be too small to ensure that there is adequate light mixing. In particular, distance  82  should be sufficiently large to allow light  74  that is emitted from light-emitting diodes  72  to homogenize enough to serve as backlight illumination. Distance  82  is often as long as necessary to ensure light from light-emitting diodes  72  is sufficiently mixed. Accordingly, distance  82  may sometimes be referred to as mixing distance  82 . When light  74  is initially emitted from individual light-emitting diodes  72 , light  74  is concentrated at the exits of light-emitting diodes  72  and is absent in the spaces between light-emitting diodes  72 . After light  74  has propagated sufficiently far within light-guide layer  78  (i.e., after light  74  has traversed a sufficiently large mixing distance  82 ), light  74  will be smoothly distributed along dimension X and will no longer be concentrated near the exits of respective individual light-emitting diodes  72 . 
     To enhance the efficiency with which light  74  is coupled into edge  76  of light guide layer from light-emitting diodes  72  without overly thickening light-guide layer  78 , it may be desirable to provide light-guide layer  78  with an outwardly tapered (flared) edge. Conventional edge tapers are formed by creating a taper in the upper surface of a light guide layer adjacent to the light-emitting diodes and leaving the opposing planar lower surface of the light guide layer untouched. If care is not taken, however, this type of taper may have an angle that is too steep, raising the potential for excessive light leakage due to the loss of total internal reflection conditions in the taper region. With the illustrative taper configuration shown in the cross-sectional side view of illustrative light guide layer  78  of  FIG. 4 , excessive light losses are avoided by providing light guide layer  78  with both upper and lower taper structures  100  and  102 , respectively. Tapers  102  and  100  may be symmetrical or tapers  102  and  100  may have different shapes. In region  96 , light-guide layer  78  is planar and has planar parallel opposing upper and lower surfaces  106  and  108 , respectively. In taper region  98 , light guide layer  78  has a thickness that varies from the thickness of region  96  (T 2 ) to enlarged thickness T 1  at edge  76 , so taper structure surfaces  112  and  104  are angled at non-zero angles with respect to planar upper and lower light guide layer surfaces  106  and  108 . Thickness T 2  may be about 400 microns 300-500 microns, less than 600 microns, more than 200 microns, or other suitable thickness. The enlarged size of dimension T 1  helps light guide layer  78  receive light  74  from light-emitting diodes  72 . The taper in light guide layer  78  formed by taper structures  100  and  102  helps concentrate light  74  into region  96  of light guide layer for use in forming backlight  44 . 
     As shown in  FIG. 5 , lower surface  96  of light guide layer  78  may be provided with light scattering features such as bumps (protrusions)  114 . Bumps  114  may help redirect light  74  that is traveling within the interior of light guide layer  78  upwards in direction Z to serve as backlight  44  for display  14 . 
     As light  74  that is traveling within light guide layer  78  is directed upwards in direction Z to serve as backlight  44 , the intensity of the light  74  that remains in light guide layer  78  decreases. As a result, the intensity of light  74  is greatest at edge  76  of light guide layer  78  adjacent to light-emitting diodes  72  and decreases with increasing distance along axis Y away from edge  76 . It is generally desirable for the intensity of backlight  44  to be evenly distributed across the surface of light guide layer  78  in dimensions X and Y. To ensure that backlight  44  is not too dim at large values of Y, the density of bumps  114  can be increased as a function of increasing value of Y, as shown in  FIG. 6 . The increase in the density of bumps  114  at larger Y values offsets the decrease in the intensity of light  74  within light guide layer at larger Y values and thereby ensures that backlight  44  has a uniform intensity as a function of dimension Y. 
     Light-emitting diodes  72  emit light  74  in a cone. This cone of light includes highly angled off-axis light rays. As shown in the cross-sectional side view of light guide layer  78  of  FIG. 7 , some of the highly angled light rays such as light ray  74 - 1  lie primarily in the YZ plane. These light rays interact strongly with upper surface  106  and lower surface  108  of light guide layer and therefore tend to be heavily extracted by bumps  114  on lower surface  108 . Other highly angled light rays in the cone of emitted light  74  such as illustrative light ray  74 - 2  in  FIG. 7  lie primarily in the XY plane. These rays are angled more along dimension X than dimension Z and therefore interact with surfaces  106  and  108  less frequently than ray  74 - 1 . To ensure that light rays such as light ray  74 - 2  are adequately extracted and can serve as backlight  44 , light guide layer  78  may be provided with lenticular ridges such as ridges  130  of  FIG. 8 . Ridges  130  may be formed on upper surface  106  of light guide layer  78  (as an example). As shown in  FIG. 8 , ridges  130  may run parallel to dimension Y (i.e., the direction in which the exit faces of light-emitting diodes  72  are oriented and the direction in which light  74  is emitted into edge  76  of light guide layer  78 ). Ridges  130  may have semicircular cross-sectional shapes or may have other suitable shapes (triangular, etc.). As shown in  FIG. 8 , the presence of ridges  130  may help extract highly angled light rays such as light ray  74 - 2  that are propagating close to the XY plane to produce corresponding backlight  44 . 
       FIG. 9  is a perspective view of an illustrative light guide layer. As shown, the light guide layer may have protruding portions  94  that extend between light-emitting diodes  72 . The light-emitting diodes  72  may be positioned on a rigid or flexible printed circuit (not shown in  FIG. 9 ). Protruding portions  94  may act as a substrate for securing the printed circuit. For example, adhesive may attach the bottom surface of protruding portions  94  to a rigid or flexible printed circuit. Light-emitting diodes may be positioned on the printed circuit such that each light-emitting diode is interposed between two protruding portions  94  when the printed circuit is adhered to protruding portions  94 . Any type of adhesive may be used to attach protruding portions  94  to a rigid or flexible printed circuit (e.g., pressure sensitive adhesive, liquid cured adhesive, light cured adhesive, etc.). 
     As discussed in connection with  FIG. 3 , a given mixing distance may be necessary to ensure that light from light-emitting diodes is homogenous before entering the active area of the display. In order to reduce the size of display  14  and, accordingly, electronic device  10 , it may be desirable to reduce the length of mixing distance  82 . To reduce mixing distance  82 , edge  76  of light guide layer  78  may include light mixing structures. Edge  76  may be defined as the surface that connects the top surface of light guide layer  78  to the bottom surface of light guide layer  78 . Edge surface  76  may be substantially perpendicular to the top and bottom surfaces of light guide layer  78 . Edge surface  76  may be substantially perpendicular to optical films  70  and reflector  80 . Regions  75  of edge surface  76  (e.g., the regions in front of the light-emitting diodes) may include light mixing structures. Light mixing structures may be included on the edge of light guide layer  78  for the portions of edge  76  that are directly in front of light-emitting diodes  72 . This will ensure that light exiting light-emitting diodes  72  travels through the light mixing structures while entering light guide layer  78 . 
       FIG. 10  is a top view of an illustrative light guide layer with light mixing structures. As shown in  FIG. 10 , edge  76  of light guide layer  78  may be provided with locally raised features such as protrusions  122 . Protrusions  122  may have semicircular profiles, or may have other shapes. For example, each protrusion  122  may have a triangular shape. Angle  124  may be about 5-45° or another suitable value to help refract light  74  at angles in layer  78 , thereby enhancing light mixing and helping to reduce mixing distance  82  ( FIG. 3 ). Protrusions  122  may have widths (in dimension X) of about 25-75 microns or other suitable widths. Protrusions  122  may be spaced apart by about 200 microns (i.e., 200 microns may separate the tip of one protrusion from the tip of an adjacent protrusion), 150-250 microns, less than 320 microns, or more than 150 microns (as examples). Protrusions  122  may be spread evenly along edge  76  or may be clustered adjacent to respective light-emitting diodes  72 . 
     Protrusions  122  may all be a uniform size and shape. For example, each protrusion  122  may have a triangular shape with identical dimensions (as shown in  FIG. 10 ). In these embodiments, light that travels through protrusions may travel in the pattern shown in  FIG. 11 . As shown, light may be emitted from a light emitting diode such as light emitting diode  72 A. The light that passes through protrusions  122  may be split into two cones of light. A first cone  74 A may be diverted in the negative X-direction while a second cone  74 B may be diverted in the positive X-direction. Both cones  74 A and  74 B may also travel in the positive Y-direction. 
     Because the light mixing structures on edge  76  of light guide layer  78  are all identical (as shown in  FIG. 10 ), the light from each light emitting diode  72  may be split into similar cones of light. The result is a cross-hatched pattern of light as shown in  FIG. 11 . There may be a pattern of regions such as region  126  where light from the cones of light overlap, producing a brighter area of light. Other regions such as region  128  may not be overlapped by any of the cones and therefore be a dimmer area of light. This regular pattern of bright regions in the backlight may be visible to the user of the electronic device. 
     In  FIG. 11 , the cones of light are illustrated as evenly spaced columns of light. This is merely illustrative and it should be understood that the actual cones of light would have much more spreading and exhibit a much less regular pattern. However, a simplified version of the light pattern is shown so as to not obfuscate the cross-hatched pattern formed from uniform light mixing structures such as those shown in  FIG. 10 . 
     To avoid the cross-hatched pattern of light shown in  FIG. 11 , edge  76  of light guide layer  78  may include light mixing structures with different shapes, as shown in  FIG. 12 . As shown, light guide layer  78  may include a first set of protrusions  122 A and a second set of protrusions  122 B. Each set of protrusions may have a different shape. The protrusions may be arranged in an alternating pattern such that each protrusion  122 A is only adjacent to protrusions  122 B and protrusions  122 B are only adjacent to protrusions  122 A. Including light mixing structures such as protrusions  122 A and  122 B may reduce mixing distance  82  without resulting in the cross-hatched pattern shown in  FIG. 11 . 
     The example of two sets of protrusions with different shapes is merely illustrative. If desired, there may be three sets of protrusions with different shapes, four sets of protrusions with different shapes, or more than four sets of protrusions with different shapes. The sets of protrusions may be arranged in any desired pattern. A pattern may be used where a single protrusion from each set is arranged sequentially and then this unit is repeated in an alternating pattern. However, more than one protrusion from each set may be arranged sequentially (e.g., two protrusions from the first set, two protrusions from the second set, two protrusions from the third set) and the pattern repeated. In general, any pattern of protrusions that uses protrusions with at least two different shapes may be used. 
     It should also be understood that the light mixing structures are not limited exclusively to protrusions. For example, recesses may be used that provide the same spreading characteristics as protrusions. In certain embodiments, prisms that spread light may be included to spread the light. Additionally, the shape of the light mixing features is not limited to triangles. Protrusions  122  may have a triangular shape, a semicircular shape, a semi-oval shape, or any other desired shape. 
       FIG. 13  is a close-up view of light mixing structures with different shapes on edge  76  of light guide layer  78 . As shown, protrusion  122 A may be a triangle with a first shape, while protrusion  122 B may be a triangle with a second shape that is different than the first shape. Protrusions  122 A and  122 B may both be symmetrical triangles (e.g., isosceles triangles), or other types of triangles. The edge of light guide layer  78  may have a planar portion from which protrusions  122 A and  122 B extend. Protrusion  122 A may have a first surface  132  that is at an angle  136  with respect to the planar portion of the edge. Protrusion  122 A may have a second surface  134  that is at an angle  138  with respect to the planar portion of the edge. Angles  136  and  138  may be the same or may be different. Similarly, surface  132  and surface  134  may have the same lengths or different lengths. In one illustrative embodiment, angles  136  and  138  are the same and both between 25° and 40° or both between 20° and 30°. Angles  136  and  138  may both be 25°, may both be 30°, or may both be 35°. Angles  136  and  138  may be less than 30° or less than 60°. The base of protrusion  122 A may have a length  140  of between 25 microns and 75 microns, about 50 microns, less than 25 microns, more than 25 microns, or any other desired length. 
     Protrusion  122 B may have a first surface  142  that is at an angle  146  with respect to the planar portion of the edge. Protrusion  122 B may have a second surface  144  that is at an angle  148  with respect to the planar portion of the edge. Angles  146  and  148  may be the same or may be different. Similarly, surface  142  and surface  144  may have the same lengths or different lengths. In one illustrative embodiment, angles  146  and  148  are the same and both between 17.5° and 22.5°, both between 10° and 22.5°, both between 5° and 25°, or both between 10° and 15°. Angles  146  and  148  may both be 20° or may both be 12.5°. Angles  146  and  148  may be less than 30° or less than 60°. The base of protrusion  122 B may have a length  150  of between 25 microns and 75 microns, about 50 microns, less than 25 microns, more than 25 microns, or any other desired length. 
     Length  150  of each protrusion  122 B may be the same as the length  140  of each protrusion  122 A. Alternatively, length  150  of each protrusion  122 B may be different than the length  140  of each protrusion  122 A. The distance between the tips of each protrusion (distance  154 ) may be any desired distance (e.g., between 100 and 300 microns, less than 100 microns, more than 100 microns, about 200 microns, etc.). Distance  154  may be the same throughout the pattern of protrusions (i.e., the distance between each protrusion is the same). Alternatively, some protrusions may be spaced closer together and some protrusions may be spaced further apart. 
       FIG. 14  shows light guide layer processing tool  160  for forming protrusions such as protrusions  122 A and  122 B in  FIGS. 12 and 13 . Light guide layer processing tool  160  may include a robotically or manually controlled positioner  162  that is attached to bit  164 . Light guide layer processing tool  160  may use bit  164  to cut light guide layer  78  and form protrusions. Bit  164  may be, for example, a diamond bit. 
       FIG. 15  shows an illustrative method for forming light mixing structures on a light guide layer. The method of  FIG. 15  may be used to form light mixing structures such as the protrusions shown in  FIGS. 12 and 13 . At step  172 , a first light guide layer processing tool may be used to form a first plurality of light mixing structures with a first shape. The light guide layer processing tool may be, for example, light guide layer processing tool  160  in  FIG. 14 . At step  174 , a second light guide layer processing tool may be used to form a second plurality of light mixing structures with a second shape that is different than the first shape. The second light guide processing tool may be, for example, light guide layer processing tool  160  in  FIG. 14 . 
     In certain embodiments, the same light guide layer processing tool may be used in both steps  172  and  174 . In other embodiments, different light guide layer processing tools may be used for each step. In one embodiment, a light guide layer processing tool with a first bit  164  may be used in step  172 . After completing step  172 , a different bit  164  may be attached to positioner  162 . The tool may then be used in step  174  with the new bit. The bit for step  172  may be a certain size that is configured to cut light mixing structures with the first shape, while the bit for step  174  may be a different size that is configured to cut light mixing structures with the second shape. 
     In various embodiments of the invention, a display backlight may include a row of light-emitting diodes and a light guide layer. The light guide layer may have first and second opposing surfaces connected by an edge that may receive light from the row of light-emitting diodes. The edge may have a first plurality of protrusions that each have a first shape and a second plurality of protrusions that each have a second shape that is different than the first shape. The first plurality of protrusions and second plurality of protrusions may be arranged in a pattern. The first plurality of protrusions and the second plurality of protrusions may be arranged in an alternating pattern. In the alternating pattern, each protrusion of the first plurality of protrusions may be positioned adjacent to a respective protrusion of the second plurality of protrusions. The first shape may be a first triangular shape, and the second shape may be a second triangular shape. 
     The edge may have a planar portion. The first triangular shape may include first and second surfaces that are at a first angle relative to the planar portion of the edge, and the second triangular shape may include third and fourth surfaces that are at a second angle relative to the planar portion of the edge. The first angle may be between 17.5° and 22.5°, and the second angle may be between 25° and 40°. The first angle may be 20°. The second angle may be 30° or 35°. The first angle may be between 10° and 15°, and the second angle may be between 20° and 30°. The first angle may be 12.5°, and the second angle may be 25°. The display backlight may also include a reflector that is parallel to the first and second opposing surfaces of the light guide layer. 
     In various embodiments of the invention, a light guide layer may include a top surface, a bottom surface, and first and second opposing surfaces that connect the top and bottom surfaces. The first surface may have a pattern of light mixing structures configured to distribute light, and the pattern may include a first plurality of light mixing structures with a first shape that alternates with a second plurality of light mixing structures with a second shape that is different than the first shape. Each light mixing structure of the first plurality of light mixing structures may be interposed between respective first and second light mixing structures of the second plurality of light mixing structures. Each light mixing structure of the first plurality of light mixing structures may include a triangular protrusion with first and second surfaces of a first length. Each light mixing structure of the second plurality of light mixing structures may include a triangular protrusion with third and fourth surfaces of a second length that is different than the first length. The top surface of the light guide layer may have ridges, and the bottom surface of the light guide layer may have bumps. 
     In various embodiments of the invention, a liquid crystal display may include first and second transparent substrates, a liquid crystal layer between the first and second substrates, a light guide layer configured to pass backlight through the first and second substrates and the liquid crystal layer, and at least first and second light-emitting diodes that each emit light into the first edge of the light guide layer. The light guide layer may have first and second opposing edges. The first edge of the light guide layer may include a pattern of protrusions configured to distribute light, and the pattern may include a first plurality of protrusions with a first shape that alternates with a second plurality of protrusions with a second shape that is different than the first shape. 
     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: 20160405
Publication Date: 20180320
Grant Date: 20180320
Priority Date: 20150923
Inventors: BROWN MICHAEL J.
Assignee: APPLE INC
CPC Classifications: [{"code": "G02B6/005", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02B6/0028", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02B6/002", "inventive": true, "first": true, "tree": "[]"}, {"code": "G02B6/0038", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02B6/0068", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02B6/0018", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02B6/0055", "inventive": false, "first": false, "tree": "[]"}, {"code": "G02B6/0036", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02B6/0043", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02F1/133615", "inventive": false, "first": false, "tree": "[]"}, {"code": "G02B6/0021", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02F1/133615", "inventive": false, "first": false, "tree": "[]"}, {"code": "G02B6/0055", "inventive": false, "first": false, "tree": "[]"}, {"code": "G02B6/005", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02B6/0043", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02B6/0021", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02B6/0018", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02B6/0068", "inventive": true, "first": true, "tree": "[]"}, {"code": "G02B6/0028", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02B6/0055", "inventive": false, "first": false, "tree": "[]"}, {"code": "G02B6/0028", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02B6/0018", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02B6/0043", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02B6/005", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02B6/0021", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02B6/0068", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02B6/0036", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02B6/0038", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02B6/002", "inventive": true, "first": true, "tree": "[]"}]
Family ID: 58282307