PATENT DOCUMENT

Publication Number: US-10571618-B2
Application Number: US-201514943202-A
Country: US
Kind Code: B2

Title: Display backlight with an optical film

Abstract:
A backlight unit may include a turning film that receives light from a light guide layer. The turning film may have a plurality of elongated protrusions that extend across the turning film. Each protrusion may have a concave surface. The concave surface may be a curved surface that curves inward towards the interior of the turning film. Light from the light guide layer may pass through the turning film and be reflected towards a viewer by the concave surfaces of the protrusions. In a liquid crystal display, the turning film may be interposed between the light guide layer and a lower polarizer. In certain embodiments, the turning film may be the only optical layer interposed between the light guide layer and the lower polarizer. In other embodiments, the turning layer and a diffuser layer may be the only optical layers interposed between the light guide layer and the lower polarizer.

Claims:
What is claimed is: 
     
       1. A display comprising:
 a plurality of light-emitting diodes; 
 an upper polarizer; 
 a lower polarizer; 
 first and second transparent substrates interposed between the upper and lower polarizers; 
 a liquid crystal layer between the first and second transparent substrates; 
 a turning film that comprises a plurality of protrusions, wherein each protrusion of the plurality of protrusions comprises a concave surface and a surface that is positioned at an angle with respect to the concave surface; and 
 a light guide layer configured to pass backlight from the plurality of light-emitting diodes through the turning film, the lower and upper polarizers, the first and second substrates, and the liquid crystal layer, wherein the turning film has a top surface, wherein the turning film is interposed between the liquid crystal layer and the light guide layer, wherein each protrusion of the plurality of the protrusions extends away from the top surface of the turning film towards the light guide layer, wherein the turning film further comprises a plurality of recesses, wherein a recess of the plurality of recesses is interposed between each adjacent pair of protrusions in the plurality of protrusions, wherein each recess defines a respective second surface that meets the concave surface of a respective protrusion, wherein the second surface is planar, and wherein the second surface of each protrusion is interposed between the concave surface of that protrusion and the surface of a respective adjacent protrusion. 
 
     
     
       2. The display defined in  claim 1 , wherein the turning film is the only optical layer interposed between the light guide layer and the lower polarizer. 
     
     
       3. The display defined in  claim 1 , further comprising a diffuser layer interposed between the turning film and the lower polarizer, wherein the turning film and the diffuser layer are the only optical layers interposed between the light guide layer and the lower polarizer. 
     
     
       4. The display defined in  claim 1 , wherein the turning film is configured to reflect ambient light through the lower and upper polarizers, the first and second substrates, and the liquid crystal layer. 
     
     
       5. The display defined in  claim 4 , wherein the turning film is formed from a material that is not birefringent. 
     
     
       6. The display defined in  claim 1 , further comprising a diffuser layer embedded in the turning film. 
     
     
       7. A turning film for a display backlight, the turning film comprising:
 a top surface; 
 first and second opposing edges connected by the top surface; and 
 a plurality of elongated protrusions that extend along the turning film from the first edge to the second edge, wherein each elongated protrusion comprises a first planar surface and a curved surface separated by an angle, and wherein the curved surface of each elongated protrusion curves inward towards an interior of the turning film; and 
 a plurality of recesses, wherein a recess of the plurality of recesses is interposed between each adjacent pair of elongated protrusions in the plurality of elongated protrusions, wherein each recess defines a respective second planar surface that meets the curved surface of a respective elongated protrusion, and wherein the second planar surface of each elongated protrusion is interposed between the curved surface of that elongated protrusion and the first planar surface of a respective adjacent elongated protrusion. 
 
     
     
       8. The turning film defined in  claim 7 , wherein the angle is between 30° and 60°.

Description:
This application claims the benefit of provisional patent application No. 62/206,605 filed on Aug. 18, 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 plate is used to distribute backlight generated by a light source such as a light-emitting diode light source. Optical films may be placed on top of the light guide plate. A reflector may be formed under the light guide plate to improve backlight efficiency. 
     In conventional backlight assemblies, a large number of optical films are used to collimate and diffuse the light that is emitted from the light guide plate. For example, four or more films may be required to manipulate the backlight. This may result in the backlight assembly having a larger than desirable thickness. 
     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, an upper polarizer layer, and a lower polarizer layer. 
     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 backlight unit may include a turning film that receives light from the light guide layer. The turning film may have a plurality of protrusions. Each protrusion may be an elongated protrusion that extends across the entire turning film. Each protrusion may have a concave surface. The concave surface may be a curved surface that curves inward towards the interior of the turning film. Light from the light guide layer may pass through the turning film and be reflected towards the viewer of the display by the concave surfaces of the protrusions. 
     In a liquid crystal display, the turning film may be interposed between the light guide layer and the lower polarizer. In certain embodiments, the turning film may be the only optical layer interposed between the light guide layer and the lower polarizer. In other embodiments, a diffuser layer may be included. The turning layer and diffuser layer may be the only optical layers interposed between the light guide layer and the lower polarizer. In yet another embodiment, a brightness enhancement film may be interposed between the lower polarizer and the diffuser layer. 
     Further features of the invention, its nature and various advantages will be more apparent from the accompanying drawings and the following detailed description of the preferred embodiments. 
    
    
     
       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 a cross-sectional side view of an illustrative display backlight unit with a turning film in accordance with an embodiment. 
         FIG. 5  is a cross-sectional side view of an illustrative diffuser layer for a display backlight unit in accordance with an embodiment. 
         FIG. 6  is a cross-sectional side view of an illustrative backlight unit with a turning film that has protrusions with concave surfaces and a diffuser layer in accordance with an embodiment. 
         FIG. 7  is a cross-sectional side view of an illustrative turning film that has protrusions with concave surfaces in accordance with an embodiment. 
         FIG. 8  is a cross-sectional side view of an illustrative display backlight with a turning film that reflects ambient light in accordance with an embodiment. 
         FIG. 9  is a cross-sectional side view of an illustrative turning film with a protrusion having a concave surface and a convex surface in accordance with an embodiment. 
         FIG. 10A  is a cross-sectional side view of an illustrative turning film with no surface features for spreading light along the X-axis in accordance with an embodiment. 
         FIG. 10B  is a cross-sectional side view of an illustrative turning film with spreading features on the top surface of the turning film in accordance with an embodiment. 
         FIG. 10C  is a cross-sectional side view of an illustrative turning film with spreading features on surfaces of protrusions in accordance with an embodiment. 
         FIG. 11  is a cross-sectional side view of an illustrative turning film for a display backlight unit in accordance with an embodiment. 
         FIG. 12  is a cross-sectional side view of an illustrative turning film for a display backlight unit that has protrusions without sharply formed vertices in accordance with an embodiment. 
         FIG. 13  is a cross-sectional side view of an illustrative turning film with recesses in between protrusions in accordance with an embodiment. 
         FIG. 14  is a cross-sectional side view of an illustrative turning film with recesses in between protrusions 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. 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 didoes 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, 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  78 . 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 plate  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 . 
       FIG. 4  is a cross-sectional side view of an illustrative display backlight unit with a turning film. As shown in  FIG. 4 , light emitting diodes  72  may emit light  74  that travels in the Y-direction along the length of light guide layer  78 . The light guide layer and reflector  80  may combine to emit light  86 A out of the light guide layer. Light  86 A may exit light guide layer  78  at a “shallow” angle. This means that light  86 A is travelling primarily in the Y-direction as opposed to the Z-direction. Turning film  84 , which may sometimes be referred to as a prism film or an optical layer, may collimate light  86 A. Shallow light  86 A may enter turning film  84  and exit turning film  84  as steeply angled light  86 B. Light  86 B may have a “steep” angle, meaning that light  86 B travels primarily in the Z-direction as opposed to the Y-direction. Turning film  84  may use reflection and/or refraction to direct light in the Z-direction towards the viewer of the display. In certain embodiments, turning film  84  may be the only optical film  70  included in the display backlight. In other embodiments, turning film  84  may be used in combination with one, two, three, four, or more than four additional optical films  70 . 
     Optical layers  70  in display  14  may include a diffuser layer such as diffuser layer  88 . Diffuser layer  88  may help homogenize light  74  and thereby reduce hotspots.  FIG. 5  shows a cross-sectional side view of an illustrative diffuser layer for a display backlight unit. As shown, light  74  may approach diffuser layer  88  in a cone. The cone of light  74  may enter diffuser layer having an angle  102 . The initial angle may be less than 10°, less than 20°, less than 30°, more than 30°, etc. The diffuser layer  88  may homogenize the incoming light and widen the angle of the cone of light. As shown in  FIG. 5 , light  74  may exit the diffuser layer in a cone with an angle  104 . Angle  104  may be greater than angle  102 . In one illustrative example, light  74  may approach diffuser layer  88  with an angle  102  of 15°. The light may exit with an angle  104  of 30° after being homogenized by diffuser layer  88 . The wider angle of the cone of light may improve the performance of display  14 . 
       FIG. 6  shows a cross-sectional side view of an illustrative backlight unit with a turning film and a diffuser layer. As shown in  FIG. 6 , turning film  84  may be positioned above light guide layer  78 . Diffuser layer  88  may be positioned above turning film  84 . Turning film  84  may have a number of protrusions  106 . The protrusions may be elongated protrusions that extend along the entire width of turning film  84  in the X-direction. The protrusions may be configured to collimate and spread light that is received from light guide layer  78 . Each protrusion  106  may include a concave surface  108 . 
     In certain embodiments, turning film  84  and diffuser  88  may be the only optical films  70  in backlight unit  42 . In other embodiments, additional optical films such as a brightness enhancement film may be provided. There may be no additional optical layers interposed between the turning film and the light guide layer. There may be no additional optical layers interposed between the diffuser layer and the lower polarizer. Turning film  84  and diffuser layer  88  may be the only optical layers interposed between the light guide layer and the lower polarizer of display  14 . In other embodiments, diffuser layer  88  may be formed as an integral portion of turning film  84 . Diffuser layer  88  may be embedded in turning film  84 . In these embodiments, a single optical layer  84  may both turn and diffuse light from light guide layer  78 . In embodiments where only turning film  84  is included in display backlight  42 , no additional optical layers may be included in the backlight. There may be no additional optical layers interposed between the turning film and the lower polarizer. There may be no additional optical layers interposed between the turning film and the light guide layer. 
       FIG. 7  is a cross-sectional side view of an illustrative turning film with protrusions having concave surfaces. As shown in  FIG. 7 , protrusions  106  may include a concave surface  108  that is positioned at an angle with respect to surface  110 . Concave surface  108  and surface  110  may be separated by an angle  112  (between 40° and 50°, between 30° and 60°, between 20° and 70°, less than 70°, more than 20°, etc.). Angle  112  may be selected based on the specific design needs for the particular display. As shown, light may enter the turning film through surface  110 . Light rays  74 A,  74 B, and  74 C may enter turning film  84  from a variety of angles. In general, light may enter turning film  84  primarily through surface  110  (as opposed to concave surface  108 ). Surface  110  may face light-emitting diodes  72 , which means that most light will exit light guide layer  78  and strike surface  110  of the protrusions of the turning film. 
     Protrusions  106  of turning film  84  may be configured to spread light along the Y-direction. Light rays  74 A,  74 B, and  74 C may enter turning film  84  in a cone with an angle  114 . The light rays may be refracted when passing through surface  110  and entering turning film  84 . After passing through surface  110 , the light rays may be reflected off of concave surface  108 . The shape of concave surface  108  enables the light rays to be reflected in the Z-direction. This way, the incoming light (which travels primarily in the Y-direction) can be turned to travel in the Z-direction towards the viewer of the display. Additional refraction may occur when the light passes through diffuser layer  88 . The light may exit the optical films  70  in a cone with an angle  116 . Angle  116  may be greater than angle  114 . The shape of protrusions  106  may be designed to control the paths of light  74  as light passes through the turning film. For example, if desired the concave surface may be altered to produce light with a narrower or larger angle  116 . Concave surface  108  may be a curved surface that curves inward towards the interior of the turning film. Concave surface  108  may asymptotically approach a plane that is parallel to the top surface of turning film  84 . 
     Light rays such as light rays  74 A,  74 B, and  74 C may be reflected off of concave surface  108  due to total internal reflection. Additionally, concave surface  108  may be provided with a reflective material if desired. White plastic or other shiny materials may be used to ensure concave surface  108  is a reflective surface. 
       FIG. 7  depicts diffuser layer  88  as being positioned above turning film  84 . As discussed previously, diffuser layer  88  may be a layer formed separately from the turning film. In these embodiments, diffuser layer  88  may be formed directly on top of and in direct contact with turning film  84  or diffuser layer  88  may be separated from the top surface of turning film  84  by a gap. Alternatively, diffuser layer  88  may be a portion of turning film  84  that is formed integrally with turning film  84 . 
     In  FIGS. 6 and 7 , protrusions  106  of turning film  84  are depicted as uniform shape and separation across the turning film. However, this example is merely illustrated. If desired, the shape of each protrusion may be uniform (e.g.,  FIG. 6 ). Alternatively, at least some of the protrusions may have a varying shape. For example, the shape of each protrusion may vary along the Y-axis. The cross-section of each protrusion may also vary. For example, a first portion of a protrusion may have a first cross-section and a second portion of a protrusion may have a second cross-section that is different than the first cross-section. In  FIG. 6 , protrusions  106  are depicted as being spaced uniformly (e.g., the distance between each protrusion is the same across the entire turning film). This example is purely illustrative. If desired, the distance between each protrusion may vary in a regular or irregular pattern. 
       FIG. 8  is a cross-sectional side view of an illustrative display backlight with a turning film that reflects ambient light. The protrusions of turning film  84  may enable ambient light to be recycled and emitted from the display as backlight. This enhances the efficiency of the display, particularly in situations with high ambient light levels (e.g., high sunlight exposure). Ambient light that reaches turning film  84  may first pass through display layers  46  including upper polarizer  54  and lower polarizer  60 . Therefore, ambient light that reaches turning film  84  may be linearly polarized. Turning film  84  may be formed from a material that is not birefringent to ensure the polarization of light is not changed as light passes through the turning film. Turning film  84  may have low or zero birefringence, which may increase the efficiency of the display. 
     As shown, both shallow and steep ambient light rays such as  74 D and  74 E may be reflected and emitted as backlight by turning film  84 . Light ray  74 D may approach turning film  84  at an angle. The light ray may be reflected off of surface  110  of protrusion and approach concave surface  108  of protrusion  106 . Because light ray  74 D approaches concave surface  108  from a substantially perpendicular angle, light ray  74 D may pass through concave surface  108 . Light ray  74 D may then pass through light guide layer  78  and be reflected by reflector  80 . Light ray  74 D may exit light guide layer  78  and act with the same characteristics as light emitted from the light-emitting diodes that exits the light guide layer (e.g., light rays  74 A,  74 B, and  74 C in  FIG. 7 ). 
     Light ray  74 E may approach turning film  84  at a relatively steep angle. Light ray  74 E may be reflected off of both surface  110  and concave surface  108 . The light ray  74 E may then exit the turning film and act as backlight for the display. 
     The depicted paths of light rays  74 D and  74 E are merely illustrative, and ambient light may follow any number of paths when passing through turning film  84 . In general, the structure of turning film  84  results in ambient light being recycled and used as backlight for the display. The ambient light may be reflected by the turning film and immediately be recycled as backlight or pass through the turning film and be introduced to the light guide layer where the light will then act as backlight. In either scenario, the ambient light is being used to light the display and the efficiency of the display is increased. 
     In  FIGS. 6-8 , surface  110  of each protrusion  106  is depicted as being a planar surface. However, surface  110  may have any desired shape. In particular, surface  110  may be a convex surface.  FIG. 9  is a cross-sectional side view of an illustrative turning film with a protrusion having a concave surface and a convex surface. Convex surface  110  may be a curved surface that curves outward towards the exterior of the turning film. When surface  110  has a convex shape, incident light from the light guide layer may be more narrowly focused after being refracted by convex surface  110 . This may result in increased control of how the light travels through turning film  84 . 
     Surface  110  and concave surface  108  of protrusions  106  primarily spread light in the Y-direction. However, it may be desirable to spread light in the X-direction as well.  FIG. 10A  is a cross-sectional side view of an illustrative turning film with no surface features for spreading light along the X-axis. Surface  110  may merely be a planar or convex surface with no additional microlenses, prisms, or other spreading features. 
       FIG. 10B  is a cross-sectional side view of an illustrative turning film with spreading features on the top surface of the turning film. As shown, spreading features  118  may be positioned on the top surface of the turning film. The spreading features may be prisms or microlenses that spread light in the X-direction. The spreading features may be elongated ridges (sometimes referred to as lenticular features) that extend along the length of the turning film in the Y-direction. The ridges may have a curved surface or may be triangular. The ridges may run parallel to the 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 ). Spreading features  118  may all be symmetrical with respect to the Z-axis. In other embodiments, some or all of spreading features  118  may not be symmetrical with respect to the Z-axis. In  FIG. 10B , spreading features  118  are shown as spaced evenly across the top surface of turning film  84 . This example is merely illustrative. If desired, spreading features  118  may be unevenly spaced, or there may be no gaps between each spreading feature. 
       FIG. 10C  is a cross-sectional side view of an illustrative turning film with spreading features on surface  110  of protrusions  106 . As shown, each protrusion  106  may be provided with spreading features  118  on surface  110 . The spreading features may be prisms, microlenses, or elongated ridges. The spreading features may be positioned on surface  110  of each protrusion  106 . In one illustrative embodiment, the spreading features may be elongated ridges that run parallel to the respective surface  110  of each protrusion. As incident light passes through surface  110  of the protrusions, spreading features  118  may spread the light along the X-axis. Similar to the spreading features discussed in connection with  FIG. 10B , spreading features  118  in  FIG. 10C  may be evenly spaced or may be unevenly spaced. In certain embodiments, there may be no gaps between each spreading feature. Spreading features  118  may be positioned at any desired angle with respect to the Z-axis. In  FIG. 10C , spreading features  118  are shown as being positioned in the YZ plane. However, this example is merely illustrative and spreading features  118  may be positioned at an angle with respect to the YZ plane. 
     The spreading features of  FIGS. 10B and 10C  may be formed integrally with turning film  84 . For example, the turning film may be shaped to have an integral surface that will spread light in the X-direction. Alternatively or in combination, spreading features  118  may be formed separately from turning film  84  and positioned adjacent to turning film  84 . 
       FIG. 11  is a cross-sectional side view of an illustrative turning film for a display backlight unit. As shown, the concave surface  108  of each protrusion  106  in turning film  84  may include structures  120  on the surface. Structures  120  may help reduce artifacts from being displayed by display  14 . Structures  120  may be any combination of protrusions, recesses, planar portions, etc. 
       FIG. 12  is a cross-sectional side view of an illustrative turning film for a display backlight unit. In some embodiments, protrusions  106  may have a vertex where surface  110  meets concave surface  108 . This vertex may be a sharply formed vertex (e.g.,  FIGS. 6-9 and 11 ). However, this example is merely illustrative. If desired, protrusions  106  may instead have an additional surface  122  that connects surface  110  to concave surface  108 . Surface  122  may be planar. Surface  122  may be parallel to the top surface of turning film  84 . Surface  122  may also be curved. For example, surface  122  may be a concave surface or a convex surface. 
     Turning film  84  may be formed by cutting a roll of film with a diamond tool. For example, a diamond bit may be used to cut a roll of stock film to form turning film  84 . Portions of turning film  84  may also be formed with a secondary manufacturing process. However, these examples are merely illustrative and turning film  84  may be formed with any desired method. Forming protrusions  106  with a sharp vertex (e.g.,  FIGS. 6-9 and 11 ) may be more difficult than forming protrusions  106  with a surface  122  in between surfaces  108  and  110  (e.g.,  FIG. 12 ). Therefore, the protrusions  106  may be formed with surface  122  for ease of manufacturing. 
       FIGS. 13 and 14  are cross-sectional side views of an illustrative turning film with recesses  124  in between protrusions  106 . As shown in previous embodiments, concave surface  108  may be separated from the top surface of turning film  84  by distance  126 . In certain embodiments, surface  110  may meet concave surface  108  directly such that distance  126  is the minimum thickness of turning film  84 . In other embodiments (e.g.,  FIG. 13 ), turning film  84  may be provided with recessed portions  124 . The recessed portions  124  may result in an additional surface  130  that meets concave surface  108 . Additionally, the recessed portions ensure that the minimum thickness of turning film  84  is distance  128 . Distance  128  may be smaller than distance  126 . Providing turning film  84  with recessed portions  124  and surface  130  may ensure that light reflects off of surface  108  or  130  after passing through surface  110 . In previous embodiments, some light may pass through surface  110  and travel above concave surface  108  through the gap between concave surface  108  and the top surface of the turning film. Recessed portions  124  in  FIG. 13  minimize the size of that gap and ensure that as much light as possible is reflected off of concave surface  108  or surface  130  towards the viewer of the display. 
     In  FIG. 13 , surface  110  is shown as meeting surface  130 . A continuous surface connects surface  130  to concave surface  108 . This example is purely illustrative. If desired, an additional surface  132  may be used to connect surface  130  to surface  110 , as shown in  FIG. 14 . This may enable protrusions  106  to be spaced closer together than in the embodiment of  FIG. 13 . In general, recessed portions  124  may have any desired shape and may be defined by any number of surfaces. 
     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: 20151117
Publication Date: 20200225
Grant Date: 20200225
Priority Date: 20150818
Inventors: LIU, RONG
SUN, YU P.
QI, JUN
YIN, VICTOR H.
Assignee: APPLE INC
CPC Classifications: [{"code": "G02B6/0051", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02F1/133615", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02B6/005", "inventive": true, "first": true, "tree": "[]"}, {"code": "G02B6/0051", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02B6/005", "inventive": true, "first": true, "tree": "[]"}, {"code": "G02F1/133615", "inventive": true, "first": false, "tree": "[]"}, {"code": "G09G3/3406", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02B6/005", "inventive": true, "first": true, "tree": "[]"}, {"code": "G02B6/0051", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02F1/133615", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02F2001/133607", "inventive": false, "first": false, "tree": "[]"}, {"code": "G02F1/133607", "inventive": false, "first": false, "tree": "[]"}, {"code": "G02F1/133607", "inventive": false, "first": false, "tree": "[]"}]
Family ID: 58158029