PATENT DOCUMENT

Publication Number: US-10249262-B2
Application Number: US-201213693989-A
Country: US
Kind Code: B2

Title: Displays with adjustable circular polarizers

Abstract:
An electronic device display may have an organic light-emitting diode layer that emits light to form images for a user. Reflective structures such as metal signal lines may be present in the organic light-emitting diode layer. Ambient light reflections from the metal signal lines may be suppressed using a circular polarizer on the organic light-emitting diode layer. To increase light emission efficiency from the organic light-emitting diode display layer under low ambient light conditions in which ambient light reflections are not significant, the polarization efficiency of the circular polarizer may be reduced. Control circuitry may make measurements of ambient light intensity using an ambient light sensor and can control the polarization efficiency of the circular polarizer accordingly by applying adjustable amounts of light or electric field. Polarization efficiency may also be adjusted using a photosensitive polarizer material that responds directly to changes in ambient light level.

Claims:
What is claimed is: 
     
       1. A display, comprising:
 a display layer that emits light that forms images; and 
 a circular polarizer on the display layer that suppresses reflections from structures in the display layer, wherein the circular polarizer comprises a polarizer layer with an adjustable polarization efficiency, wherein the polarizer layer comprises a layer of photosensitive material, and wherein the polarization efficiency is adjusted in response to light applied to the photosensitive material. 
 
     
     
       2. The display defined in  claim 1  wherein the display layer comprises an organic light-emitting diode layer. 
     
     
       3. The display defined in  claim 1  further comprising a light source that is configured to apply the light to the layer of photosensitive material. 
     
     
       4. The display defined in  claim 3  wherein the light source is configured to produce ultraviolet light. 
     
     
       5. The display defined in  claim 1  wherein first and second amounts of light are applied to the photosensitive material, wherein the first amount of light is greater than the second amount of light, wherein the photosensitive material increases polarization efficiency in response to the first amount of light, and wherein the photosensitive material decreases polarization efficiency in response to the second amount of light. 
     
     
       6. An electronic device, comprising:
 an ambient light sensor that is configured to measure ambient light levels; 
 control circuitry coupled to the ambient light sensor; 
 a display having an adjustable polarizer that receives light emitted from the display in a first direction, wherein the control circuitry is configured to adjust the adjustable polarizer based on measured ambient light levels from the ambient light sensor; and 
 a light source that applies additional light to the adjustable polarizer from a second direction that is different than the first direction, wherein the control circuitry is configured to direct the light source to apply the additional light to the adjustable polarizer based on the ambient light levels. 
 
     
     
       7. The electronic device defined in  claim 6  wherein the control circuitry is configured to direct the light source to apply a first amount of the additional light to the adjustable polarizer in response to measuring a first amount of ambient light with the ambient light sensor, wherein the control circuitry is configured to direct the light source to apply a second amount of the additional light to the adjustable polarizer in response to measuring a second amount of ambient light with the ambient light sensor, and wherein the first amount of ambient light is different than the second amount of ambient light. 
     
     
       8. The electronic device defined in  claim 7  wherein the display comprises an organic light-emitting diode display. 
     
     
       9. The electronic device defined in  claim 7  wherein the adjustable polarizer comprises a circular polarizer. 
     
     
       10. The electronic device defined in  claim 6  wherein the adjustable polarizer comprises a circular polarizer. 
     
     
       11. The electronic device defined in  claim 6 , further comprising:
 an electronic device housing in which the ambient light sensor, the control circuitry, the display, and the light source are mounted. 
 
     
     
       12. The electronic device defined in  claim 6  wherein the adjustable polarizer has an adjustable polarization efficiency, wherein the adjustable polarizer has a layer of photosensitive material, and wherein the control circuitry is configured to direct the light source to apply the additional light to the adjustable polarizer to change the polarization efficiency. 
     
     
       13. A method of operating an organic light-emitting diode display that has an adjustable circular polarizer in an electronic device that has an ambient light sensor and control circuitry, wherein the adjustable circular polarizer comprises electrodes for applying an electric field to a layer of material that exhibits changes in polarization efficiency based on applied electric field levels, the method comprising:
 with the control circuitry, gathering ambient light readings from the ambient light sensor; and 
 with the control circuitry, adjusting a transmittance of the adjustable circular polarizer from a first non-zero transmittance value to a second non-zero transmittance value and from the second non-zero transmittance value to a third non-zero transmittance value based on the ambient light readings, wherein the first, second, and third non-zero transmittance values are different, wherein adjusting the adjustable circular polarizer comprises controlling how much electric field is applied to the layer of material with the electrodes. 
 
     
     
       14. The method defined in  claim 13  wherein the layer of material comprises a guest-host dye liquid crystal material and wherein adjusting the circular polarizer comprises adjusting electric fields applied to the guest-host dye liquid crystal material based on the ambient light readings to increase polarization efficiency at higher ambient light levels to suppress reflections from metal lines in the organic light-emitting diode display and to decrease polarization efficiency at lower ambient light levels to increase light emission efficiency from the organic light-emitting diode display.

Description:
BACKGROUND 
     This relates generally to electronic devices, and more particularly, to electronic devices with displays. 
     Electronic devices often include displays. For example, cellular telephones and portable computers often include displays for presenting information to a user. 
     Some devices incorporate organic light-emitting diode displays. Organic light-emitting diode displays use thin-film circuitry to produce images. In bright ambient lighting conditions, organic light-emitting diodes can be prone to glare as ambient light is reflected from metal lines in the thin-film circuitry. Ambient light reflections can be suppressed by covering an organic light-emitting diode display with a circular polarizer. The presence of the circular polarizer helps minimized unwanted ambient light reflections, but reduces display brightness. The output level of a display with a circular polarizer can be maintained at desired levels by increasing drive currents in the thin-film circuitry, but this increases power consumption and reduces battery life. 
     It would therefore be desirable to provide improved displays such as organic light-emitting diode displays. 
     SUMMARY 
     An electronic device may be provided with a display mounted in a housing. The display may have an organic light-emitting diode layer that emits light to form images for a user. Structures such as metal signal lines may be present in the organic light-emitting diode layer. 
     Ambient light reflections from the metal signal lines may be suppressed by forming a circular polarizer on the organic light-emitting diode layer. The polarization efficiency of the circular polarizer may be varied as a function of ambient light level. 
     To increase light emission efficiency from the organic light-emitting diode display layer under low ambient light conditions in which ambient light reflections do not significantly impair use of the display, the polarization efficiency of the circular polarizer may be reduced. By reducing polarization efficiency in response to low ambient light levels, undesired reductions in display output efficiency due to the polarization properties of the circular polarizer can be avoided whenever the ambient light levels in the vicinity of the display are low. 
     At higher ambient light levels, the polarization efficiency of the circular polarizer can be restored to ensure that the circular polarizer can adequately suppress reflections from the reflective structures in the organic light-emitting display layer. 
     Control circuitry may make measurements of ambient light intensity using an ambient light sensor and can control the polarization efficiency of the circular polarizer accordingly by applying adjustable amounts of light or electric field to the circular polarizer. Polarization efficiency may also be adjusted using a photosensitive polarizer material in the circular polarizer that responds directly to changes in ambient light level. 
     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 perspective view of an illustrative electronic device such as a laptop computer with a display in accordance with an embodiment of the present invention. 
         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 of the present invention. 
         FIG. 3  is a perspective view of an illustrative electronic device such as a tablet computer with a display in accordance with an embodiment of the present invention. 
         FIG. 4  is a perspective view of an illustrative electronic device such as a computer display with display structures in accordance with an embodiment of the present invention. 
         FIG. 5  is a schematic diagram of an illustrative electronic device of the type that may be provided with a display in accordance with an embodiment of the present invention. 
         FIG. 6  is a cross-sectional side view of an electronic device with a display in accordance with an embodiment of the present invention. 
         FIG. 7  is a cross-sectional side view of a portion of an illustrative organic light-emitting diode display in accordance with an embodiment of the present invention. 
         FIG. 8  is a cross-sectional side view of an organic light-emitting diode display that has been provided with an ambient light sensitive circular polarizer in accordance with an embodiment of the present invention. 
         FIG. 9  is a graph showing how polarization efficiency may vary as a function of ambient light levels in an adjustable circular polarizer for a display accordance with an embodiment of the present invention. 
         FIG. 10  is a graph showing how the amount of light that is emitted from an organic light-emitting diode display having an ambient light level sensitive circular polarizer may vary as a function of polarization efficiency in accordance with an embodiment of the present invention. 
         FIG. 11  is a graph showing how the amount of light that is reflected from an organic light-emitting diode display having an ambient light level sensitive circular polarizer may vary as a function of polarization efficiency in accordance with an embodiment of the present invention. 
         FIG. 12  is a schematic diagram of electronic device structures in a configuration in which an internal light source is used to adjust circular polarizer efficiency for an organic light-emitting diode display in accordance with an embodiment of the present invention. 
         FIG. 13  is a schematic diagram of electronic device structures in a configuration in which control circuitry that applies an adjustable electric field to a guest-host dye liquid crystal system layer is used to adjust circular polarizer efficiency for an organic light-emitting diode display in accordance with an embodiment of the present invention. 
     
    
    
     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 computer display or a computer that has been integrated into a computer display. With this type of arrangement, housing  12  for device  10  may be mounted on a support structure such as stand  27 . 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 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 television, a computer display 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  includes display pixels formed from organic light-emitting diode display components or other suitable image pixel structures. Display  14  may, for example, be an organic light-emitting diode display formed from a rectangular array of organic light-emitting diodes on a rigid substrate or a flexible substrate. Top emission or bottom emission organic light-emitting diode display structures may be used in forming display  14 . 
     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 schematic diagram of device  10  is shown in FIG.  5 . As shown in  FIG. 5 , electronic device  10  may include control circuitry such as storage and processing circuitry  40 . Storage and processing circuitry  40  may include one or more different types of storage such as hard disk drive storage, nonvolatile memory (e.g., flash memory or other electrically-programmable-read-only memory), volatile memory (e.g., static or dynamic random-access-memory), etc. Processing circuitry in storage and processing circuitry  40  may be used in controlling the operation of device  10 . The processing circuitry may be based on a processor such as a microprocessor and other integrated circuits. 
     With one suitable arrangement, storage and processing circuitry  40  may run software on device  10  such as internet browsing applications, email applications, media playback applications, operating system functions, software for capturing and processing images, software for implementing functions associated with gathering and processing sensor data, etc. 
     Input-output circuitry  32  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 circuitry  32  may include wired and wireless communications circuitry  34 . Communications circuitry  34  may include radio-frequency (RF) transceiver circuitry formed from one or more integrated circuits, power amplifier circuitry, low-noise input amplifiers, passive RF components, one or more antennas, and other circuitry for handling RF wireless signals. Wireless signals can also be sent using light (e.g., using infrared communications). 
     Input-output circuitry  32  may include input-output devices  36  such as buttons, joysticks, click wheels, scrolling wheels, a touch screen such as display  14 , other touch sensors such as track pads or touch-sensor-based buttons, vibrators, audio components such as microphones and speakers, image capture devices such as a camera module having an image sensor and a corresponding lens system, keyboards, status-indicator lights, tone generators, key pads, and other equipment for gathering input from a user or other external source and/or generating output for a user. 
     Sensors  38  may include an ambient light sensor for gathering information on ambient light levels. The ambient light sensor may include one or more semiconductor detectors (e.g., silicon-based detectors) or other light detection circuitry. Sensors  38  may also include proximity sensor components. The proximity sensor components may include a dedicated proximity sensor and/or a proximity sensor formed from touch sensors (e.g., a portion of the capacitive touch sensor electrodes in a touch sensor array for display  14  that are otherwise used in gathering touch input for device  10 ). Proximity sensor components in device  10  can include capacitive proximity sensor components, infrared-light-based proximity sensor components, proximity sensor components based on acoustic signaling schemes, or other proximity sensor equipment. Sensors  38  may also include a pressure sensor, a temperature sensor, an accelerometer, a gyroscope, and other circuitry for making measurements of the environment surrounding device  10 . 
     As shown in the cross-sectional side view of electronic device  10  of  FIG. 6 , electronic device  10  may include internal device components such as components  48 . Components  48  may include sensors, integrated circuits, buttons, connectors, and other circuitry of the type shown in  FIG. 5 . Components  48  may be mounted on one or more substrates such as substrate  46 . Substrate  46  may be a dielectric carrier such as a molded plastic carrier or a printed circuit. For example, substrate  46  may be a printed circuit such as a rigid printed circuit formed from a material such as fiberglass-filled epoxy or may be a flexible printed circuit formed from a sheet of polyimide or other flexible polymer layer. 
     Display  14  may include a display cover layer such as display cover layer  42  and a display module such as display module  44 . Display cover layer  42  may be formed from a transparent layer of material such as a clear glass layer or a transparent planar member. Display module  44  may be formed from an organic light-emitting diode layer (sometimes referred to as an organic light-emitting diode display or organic light-emitting diode array). 
     During operation of device  10 , viewer  54  may view display  14  in direction  56 . Organic light-emitting diode display layer  44  may emit light  50  that forms images for viewer  54  on display  14 . Ambient light  52  may also reflect off of structures within display layer  44 . In particular, reflective structures such as metal lines in organic light-emitting diode display  44  may have a tendency to reflect ambient light  52 . To avoid image degradation from ambient light that is reflected from structures such as metal lines, a circular polarizer may be formed on the surface of organic light-emitting diode display  44 . The polarizer may reduce ambient light reflections. 
       FIG. 7  is a cross-sectional side view of an illustrative organic light-emitting diode display structure of the type that may be used in forming organic light-emitting diode display layer  44  of  FIG. 6 . In the example of  FIG. 7 , organic light-emitting diode display layer  44  is a top emission display. If desired, display  44  may be implemented using bottom emission display technology. 
     As shown in  FIG. 7 , organic light-emitting diode display  44  may have a substrate such as substrate  60 . Substrate  60  may be, for example, a layer of glass. Signal lines such as metal signal lines  62  may be formed on glass layer  60 . Planarization layer  64  may be formed on top of signal lines  62  and substrate  60 . Light  50  may be produced by driving current through organic emissive material  66  using lower electrode  72  and upper electrode  70  (e.g., a layer of indium tin oxide). Spacer structures such as dielectric spacers  68  may help separate adjacent display pixels in the array of display pixels that forms display layer  44 . 
     Ambient light reflections from metal lines such as lines  62  of  FIG. 7  may be suppressed by forming a circular polarizer such as circular polarizer  74  of  FIG. 8  on top of organic light-emitting diode array layer  44 . Adhesive  76  may be used to attach circular polarizer  74  to layer  44 . Polarizer  74  may include supporting layers of material such one or more layers of tri-acetyl cellulose (TAC), a linear polarizer layer such as linear polarizer layer  82 , a quarter wave plate such as layer  80  (to convert linearly polarized light into circularly polarized light), and an additional layer  84 . 
     A circular polarizer layer can suppress ambient light reflections from reflective structures in layer  44  such as metal lines  62  of  FIG. 7 , but has the potential to reduce the amount of emitted light  50  from layer  44  that reaches viewer  54 . In particular, the amount of light  50  that passes through a polarizer layer will depend on the polarization state of that light (e.g., parallel to the linear polarizer as illustrated by electric field orientation Eparallel of  FIG. 8  or perpendicular to the linear polarizer as illustrated by electric field orientation E perpendicular of  FIG. 8 ). 
     Particularly in dim lighting conditions in which ambient light reflections are low, the potential reduction in emitted light efficiency due to the presence of a circular polarizer on top of layer  44  is a concern. In this type of situation, the polarizer is not needed to suppress ambient light reflections, but has the potential to reduce the amount of light that is transmitted out of the display. 
     Display  14  preferably incorporates an adjustable polarizer to address this challenge. The adjustable polarizer, which may sometimes be referred to as an ambient light sensitive polarizer or controllable polarizer, may exhibit polarization characteristics that vary as a function of ambient light level. At relatively large ambient light levels, when the full reflection-suppressing capabilities of the circular polarizer layer are needed, the polarizer is configured to operate with its maximum efficiency. At relatively low ambient light levels, however, when high polarization efficiencies merely serve to cut down on transmitted light intensities and thereby dim the display, the polarizer is configured to operate with a reduced amount of polarization efficiency. Polarization efficiency may be controlled based on ambient light level by using a polarizer material that is directly sensitive to light exposure and/or by using ambient light sensor structures to monitor ambient light conditions and using control circuitry to adjust the properties of the polarizer accordingly. 
       FIG. 9  is a graph showing how transmitted light intensity from display layer  44  may vary as a function of ambient light intensity for both the parallel and perpendicular electric field orientations of  FIG. 8 . In this example, linear polarizer layer  82  has a polarization efficiency that varies as a function of ambient light intensity. 
     Transmittance Tparallel of  FIG. 9  represents that amount of light that is transmitted through circular polarizer layer  74  as a function of ambient light intensity when the light has an electric field (Eparallel) that is aligned with linear polarizer  82 . Because Eparallel is aligned with polarizer  82 , light with polarization Eparallel is transmitted through polarizer  82  regardless of the efficiency of polarizer  82  (and therefore regardless of ambient light intensity), as indicated by the flat shape of curve  86 . 
     Transmittance Tperpendicular of  FIG. 9  represents the amount of light that is transmitted through circular polarizer layer  74  as a function of ambient light intensity when the light has an electric field (Eperpendicular) that is perpendicular to the polarization direction of linear polarizer  82 . Because Eperpendicular is perpendicular to the orientation of linear polarizer  82 , light with polarization Eperpendicular is blocked (i.e., transmittance Tperpendicular is small) when the polarizer is operating efficiently at high ambient light intensities. At low ambient light intensities, the efficiency of polarizer  82  is low, so even though Eperpendicular is perpendicular to polarizer  82 , polarizer  82  becomes ineffective at blocking light with polarization Eperpendicular (i.e., transmittance Tperpendicular is high). 
     The impact of changes in polarization efficiency on reflected ambient light and transmitted light  50  from organic light-emitting diode layer  44  is shown in the graphs of  FIGS. 10 and 11 . The graph of  FIG. 10  is a normalized plot of the amount of light  50  that has been emitted from organic light-emitting diode layer  44  and that has been successfully transmitted through polarizer  74  as a function of polarization efficiency. 
     As shown in  FIG. 10 , at relatively high polarization efficiencies (i.e., at relatively high ambient light levels where the efficiency of polarizer  82  and therefore polarizer  74  is high), half of light  50  is blocked (i.e., the half of light  50  that is polarized perpendicular to polarizer  82 ) and half of light  50  is transmitted (i.e., the half of light  50  that is polarized parallel to polarizer  82 ). The normalized amount of light emitted by display  14  when ambient light levels are high and polarizer efficiency is at 100% is therefore 0.5. 
     At relatively low polarization efficiencies (i.e., at relatively low ambient light levels where the efficiency of polarizer  82  and therefore polarizer  74  is low), the half of light  50  that would be blocked at high polarization efficiencies is transmitted through polarizer  82 , even though its polarization is perpendicular to polarizer  82 . The normalized amount of light emitted when ambient light levels are low and polarizer efficiency is at 0% is therefore high (i.e., 1.0). 
     The impact of changes in polarization efficiency on reflected ambient light is shown in the graph of  FIG. 11 . The graph of  FIG. 11  is a normalized plot of the amount of ambient light  52  that is reflected from organic light-emitting diode layer  44  (display  14 ) as a function of polarization efficiency. 
     As shown in  FIG. 11 , at relatively high polarization efficiencies (i.e., at relatively high ambient light levels), the efficiency of circular polarizer  74  is high. As a result, the ability of circular polarizer  74  to suppress light reflections from metal structures in display module  44  such as lines  62  is maximized and the normalized amount of reflected ambient light is 0. 
     At relatively low polarization efficiencies (i.e., at relatively low ambient light levels), the efficiency of circular polarizer  74  is low. As a result, the ability of circular polarizer  74  to suppress light reflections from metal structures in display module  44  such as lines  62  is reduced. The normalized amount of reflected ambient light is 1. Even though ambient light reflections are not well suppressed in this situation, the absolute (not normalized) amount of ambient light that is reflected from display  14  is not too high, because the total amount of ambient light that is present in this situation is low. 
     As the curves of  FIGS. 10 and 11  demonstrate, the variable polarization efficiency of polarizer  74  allows undesired ambient light reflections at high ambient light levels to be satisfactorily suppressed, because polarizer  74  has high efficiency at high ambient light levels (see, e.g., the right-hand side of  FIG. 11 ). The variable polarization efficiency of polarizer  74  also allows power to be conserved in situations in which ambient light levels are low. This is because polarization efficiency is low at low ambient light levels, which effectively turns off the undesired emitted light blocking characteristic of polarizer  74  (see, e.g., the left-hand side of  FIG. 10 ). 
     Polarizer efficiency can be varied as a function of ambient light intensity by using a photosensitive material for forming polarizer layer  82  (e.g., a material that exhibits polarization efficiency changes based on exposure to ultraviolet light or other light in the ambient light). Polarization efficiency for polarizer  74  can also be adjusted by dynamically measuring ambient light levels using an ambient light sensor (e.g., one of sensors  38  of  FIG. 5 ) and applying light or electrical signals to polarizer layer  82  that change the polarization efficiency of polarizer layer  82 . 
       FIG. 12  is a system diagram of an illustrative portion of device  10  in which the polarization of circular polarizer  74  is adjusted by applying light  92  to polarizer  82  as a function of measured ambient light level. Readings from ambient light sensor  38  are processed by control circuitry  40 . Control circuitry  40  can use ambient light sensor  38  to measure how much ambient light is striking device  10  and display  14  during operation of device  10  by a user. 
     The amount of ambient light that is measured by control circuitry  40  may be used by control circuitry  40  in adjusting light output from light source  90 . Light source  90  may be a laser, a light-emitting diode, a lamp, part of layer  44 , or other light source that produces light  92 . Light  92  may include infrared light, visible light, and/or ultraviolet light. Light  92  may be applied to linear polarizer  82 . For example, light  92  may be launched into one of the edges of linear polarizer  82 , so that light  92  travels through the interior of polarizer  82  due to total internal reflection. Alternatively, light  92  may be applied to linear polarizer  82  through other layers in display  14 . 
     Polarizer layer  82  may be formed from a photosensitive film that is responsive to light  92 . When a first amount of light  92  is applied to layer  82 , polarizer  82  may be characterized by a first polarization efficiency. When a second amount of light  92  is applied to layer  82  that is different than the first amount of light, polarizer  82  may be characterized by a second polarization efficiency that is different than the first polarization efficiency. The amount of polarization efficiency change that is exhibited by polarizer  82  as a function of a given amount of change in the magnitude of applied light  92  may be linear or nonlinear. 
     During operation, control circuitry  40  can determine ambient light levels using ambient light data from ambient light sensor  38 . When measured ambient light levels are relatively high, control circuitry  40  can use light source  92  to generate an amount of light  92  that makes polarization layer  82  exhibit a relatively high polarization efficiency. In this situation, ambient light reflections will be well suppressed by the operation of circular polarizer  74 . In response to measuring ambient light levels that are relatively low, control circuitry  40  can use light source  92  to generate an amount of light  92  that makes polarization layer  82  exhibit a relatively low polarization efficiency. In this situation, polarizer  74  will block a reduced amount of light from layer  44  and light emission efficiency for display  14  will be high, allowing power to be conserved. 
       FIG. 13  is a system diagram of an illustrative portion of device  10  in which the polarization of circular polarizer  74  is adjusted by applying an electric field to polarizer  82 . Circular polarizer  74  may be attached to the surface of organic light-emitting diode display layer  44  using a layer of adhesive such as adhesive  76 . Quarter wave plate  80  may be formed between linear polarizer  82  and a structural layer of polymer such as polymer layer  78  (e.g., a layer of tri-acetyl cellulose). 
     Polarizer  82  may be formed from a material such as guest-host liquid crystal system layer  100 , which changes its polarization efficiency as a function of applied electric field. Layer  100  may be sandwiched between upper transparent electrode  98  and lower transparent electrode  102 . Electrodes  98  and  102  may be formed from sheets of transparent conductive material such as indium tin oxide. 
     An electric field may be applied across layer  100  by applying a voltage across electrodes  98  and  102  with control circuitry  40 . During operation, readings from ambient light sensor  38  are processed by control circuitry  40 . The magnitude of ambient light that is measured using ambient light sensor  38  may be used by control circuitry  40  in adjusting the magnitude of the voltage applied across electrodes  98  and  102 . This allows control circuitry  40  to adjust the polarization layer  74  as a function of measured ambient light level. 
     When measured ambient light levels are relatively high, control circuitry  40  can apply an electric field to layer  100  that causes polarizer  74  to exhibit a relatively high polarization efficiency. In this situation, ambient light reflections will be well suppressed by the operation of polarizer  74 . In response to measuring ambient light levels that are relatively low, control circuitry  40  can apply an electric field to layer  100  that causes polarizer  74  to exhibit a relatively low polarization efficiency. In this situation, polarizer  74  will block a reduced amount of light from layer  44  and light emission efficiency for display  14  will be high, allowing power to be conserved. 
     The foregoing is merely illustrative of the principles of this invention and various modifications can be made by those skilled in the art without departing from the scope and spirit of the invention.

Metadata:
Filing Date: 20121204
Publication Date: 20190402
Grant Date: 20190402
Priority Date: 20121204
Inventors: YANG, YOUNG CHEOL
CHEN, CHENG
Assignee: APPLE INC
CPC Classifications: [{"code": "G09G2320/0238", "inventive": false, "first": false, "tree": "[]"}, {"code": "G09G2360/144", "inventive": false, "first": false, "tree": "[]"}, {"code": "G09G5/10", "inventive": true, "first": true, "tree": "[]"}, {"code": "G09G2300/023", "inventive": false, "first": false, "tree": "[]"}, {"code": "F21V9/14", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01L51/5281", "inventive": true, "first": false, "tree": "[]"}, {"code": "G09G3/001", "inventive": false, "first": false, "tree": "[]"}, {"code": "G09G3/3208", "inventive": false, "first": false, "tree": "[]"}, {"code": "G09G2300/023", "inventive": false, "first": false, "tree": "[]"}, {"code": "G09G2300/023", "inventive": false, "first": false, "tree": "[]"}, {"code": "G09G2320/0238", "inventive": false, "first": false, "tree": "[]"}, {"code": "F21V9/14", "inventive": true, "first": false, "tree": "[]"}, {"code": "G09G5/10", "inventive": true, "first": true, "tree": "[]"}, {"code": "G09G3/3208", "inventive": false, "first": false, "tree": "[]"}, {"code": "G09G2320/0238", "inventive": false, "first": false, "tree": "[]"}, {"code": "G09G3/3208", "inventive": false, "first": false, "tree": "[]"}, {"code": "G09G3/001", "inventive": false, "first": false, "tree": "[]"}, {"code": "G09G2360/144", "inventive": false, "first": false, "tree": "[]"}, {"code": "G09G2360/144", "inventive": false, "first": false, "tree": "[]"}, {"code": "G09G3/001", "inventive": false, "first": false, "tree": "[]"}, {"code": "H10K50/86", "inventive": true, "first": false, "tree": "[]"}, {"code": "H10K59/60", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02F1/133541", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02F1/13725", "inventive": true, "first": false, "tree": "[]"}, {"code": "H10K59/8791", "inventive": true, "first": true, "tree": "[]"}, {"code": "H10K59/8791", "inventive": true, "first": true, "tree": "[]"}]
Family ID: 50825019