PATENT DOCUMENT

Publication Number: US-10288935-B2
Application Number: US-201615064097-A
Country: US
Kind Code: B2

Title: Electronic device display with switchable film structures

Abstract:
An electronic device may generate content that is to be displayed on a display. The display may have an array of liquid crystal display pixels for displaying image frames of the content. The display may be operated in at least a normal viewing mode, a privacy mode, an outdoor viewing mode, and a power saving mode. The different view modes may exhibit different viewing angles. In one configuration, the display may include a switchable phase retarder that can be selectively activated to help reduce contrast ratios at higher viewing angles. A rotated pixel design that includes one or more groups of parallel fingers can be used to help properly align the low contrast regions. In another configuration, the display may include multiple electrically controlled birefringence (ECB) layers that can be selectively activated to provide a desired cone of vision, a region outside of which exhibits substantially reduced contrast ratios.

Claims:
What is claimed is: 
     
       1. An electronic device display, comprising:
 a switchable phase retarder that is configured in an isotropic state when the electronic device display is operated in a normal viewing mode and that is configured in an anisotropic state when the electronic device display is operated in a privacy mode to provide a contrast profile having low contrast regions and high contrast regions, wherein the display is coplanar with an X-Y plane; and 
 display layers having thin-film transistor structures, wherein the display layers comprise parallel pixel finger electrodes shorted by a conductive sidebar, wherein the parallel pixel finger electrodes are tilted at an angle with respect to the conductive sidebar so that the low contrast regions are positioned at viewing angles of 0° and 180° in the X-Y plane during the privacy mode, and wherein the angle is within a range of 10° to 55°. 
 
     
     
       2. The electronic device display of  claim 1 , further comprising:
 an upper polarizer; and 
 a lower polarizer, wherein the switchable phase retarder is interposed between the upper polarizer and the display layers. 
 
     
     
       3. The electronic device display of  claim 1 , further comprising:
 an upper polarizer; and 
 a lower polarizer, wherein the switchable phase retarder is interposed between the lower polarizer and the display layers. 
 
     
     
       4. The electronic device display of  claim 1 , wherein the switchable phase retarder comprises blue phase liquid crystal material. 
     
     
       5. The electronic device display of  claim 1 , wherein the switchable phase retarder provides reduced contrast ratios at viewing angles greater than 30° during the privacy mode. 
     
     
       6. The electronic device display of  claim 1 , wherein the switchable phase retarder receives a bias voltage during the privacy mode such that the switchable phase retarder is configured to provide a predetermined amount of phase retardation. 
     
     
       7. The electronic device display of  claim 1 , wherein the angle is 35°. 
     
     
       8. An electronic device display, comprising:
 display layers having thin-film transistor structures, wherein the display layers comprise parallel pixel finger electrodes, wherein the parallel pixel finger electrodes are shorted by a conductive crossbar that is perpendicular to the parallel pixel finger electrodes, and wherein the conductive crossbar bisects only one of the parallel pixel finger electrodes into two equal and colinear segments; and 
 a switchable phase retarder that is configured in an isotropic state when the electronic device display is operated in a normal viewing mode and that is configured in an anisotropic state when the electronic device display is operated in a privacy mode. 
 
     
     
       9. The electronic device display of  claim 8 , wherein the conductive crossbar and the parallel pixel finger electrodes have different widths. 
     
     
       10. An electronic device display, comprising:
 display layers having thin-film transistor structures, wherein the display layers comprise:
 a switchable phase retarder that is configured in an isotropic state when the electronic device display is operated in a normal viewing mode and that is configured in an anisotropic state when the electronic device display is operated in a privacy mode to provide a contrast profile; 
 a conductive crossbar; 
 a first set of parallel pixel electrode fingers formed at a first non-obtuse angle with respect to the conductive crossbar; and 
 a second set of parallel pixel electrode fingers formed at a second non-obtuse angle with respect to the conductive crossbar, wherein the second non-obtuse angle is different than the first non-obtuse angle, and wherein the first and second sets of parallel pixel electrode fingers are shorted to the conductive crossbar. 
 
 
     
     
       11. The electronic device display of  claim 10 , wherein the first non-obtuse angle is equal to 90 degrees. 
     
     
       12. The electronic device display of  claim 11 , wherein the second non-obtuse angle is less than 90 degrees. 
     
     
       13. The electronic device display of  claim 1 , wherein the low contrast regions are further positioned at viewing angles of 90° and 270° in the X-Y plane during the privacy mode. 
     
     
       14. The electronic device display of  claim 1 , wherein the high contrast regions are positioned at viewing angles of 45° and 135° in the X-Y plane during the privacy mode.

Description:
This application claims the benefit of provisional patent application No. 62/170,603 filed on Jun. 3, 2015, which is hereby incorporated by reference herein in its entirety. 
    
    
     BACKGROUND 
     This relates generally to electronic devices, and more particularly, to electronic devices with displays. 
     Electronic devices often include displays. For example, cellular telephones and portable computers often include displays for presenting information to a user. 
     Liquid crystal displays contain a layer of liquid crystal material. Pixels in a liquid crystal display contain thin-film transistors and pixel electrodes for applying electric fields to the liquid crystal material. The strength of the electric field in a pixel controls the polarization state of the liquid crystal material and thereby adjusts the brightness of the pixel. 
     Conventional liquid crystal displays typically exhibit a fixed viewing angle. For example, a user of the liquid crystal display may be able to view images on the display up to 45 degrees deviation from the normal viewing axis. In certain scenarios, however, it may be desirable to adjust and/or to reduce the viewing angle of the display. Existing solutions for reducing the viewing angle of liquid crystal displays involve use of an external privacy filter that needs to be mounted over the display. The use of external privacy filters or other types of external brightness adjustment films may, however, introduce unwanted reflections and glare and are often costly and unwieldy for the user to purchase and maintain. 
     It would therefore be desirable to be able to provide displays with built-in adjustable light output profiles. 
     SUMMARY 
     An electronic device may generate content that is to be displayed on a display. The display may be a liquid crystal display have an array of liquid crystal display pixels. Display driver circuitry in the display may display image frames on the array of pixels. 
     For example, the display may be operable in a normal viewing mode, a privacy mode, an outdoor viewing mode, and a power saving mode. When operated in the privacy mode, the display may be limited to at most a 30° viewing angle. The normal viewing mode may provide a nominal on-axis luminance level, whereas the outdoor viewing mode may provide an elevated on-axis luminance level that is greater than the nominal on-axis luminance level without actually consuming more power than in the normal viewing mode. In the power saving mode, the display may also provide the nominal on-axis luminance while actually consuming less power than the normal viewing mode. 
     In accordance with an embodiment, the display may include display layers having thin-film transistor structures and a switchable phase retarder that is configured in an isotropic state when the electronic device display is operated in the normal viewing mode and that is configured in an anisotropic state when the electronic device display is operated in the privacy mode (which may also include the outdoor viewing mode and the power saving mode). 
     The switchable phase retarder may include blue phase liquid crystal material. The switchable phase retarder may be used to provide reduced contrast ratios at viewing angles greater than 30° during the privacy mode. The switchable phase retarder may receive a bias voltage during the privacy mode such that the switchable phase retarder is configured to provide a predetermined amount of phase retardation. 
     The display may be implemented using a pixel design having parallel pixel finger electrodes angled at less than 80° (e.g., less than 75°, less than 60°, equal to or less than 55°, equal to or less than 35°, etc.). The parallel pixel finger electrodes may be shorted using a conductive vertical sidebar. The parallel pixel finger electrodes may also be shorted using a conductive crossbar, which may have a different width then each of the finger electrodes. 
     In accordance with another suitable embodiment, display circuitry is provided that includes a front polarizer, a back polarizer, a liquid crystal display (LCD) layer, first and second electrically controlled birefringence (ECB) layers that are selectively activated to place the display circuitry in the privacy mode and deactivated to place the display circuitry in the normal viewing mode. The front polarizer may exhibit a first absorption (transmittance) axis while the back polarizer may exhibit a second absorption axis that is perpendicular to the first absorption axis. 
     During the normal viewing mode, the first ECB layer may exhibit an optical axis that is parallel to the first absorption axis, whereas the second ECB layer may exhibit an optical axis that is parallel to the second absorption axis. During the privacy mode, the optical axis of the first ECB layer is adjusted to be out of alignment from the first absorption axis while the optical axis of the second ECB layer is adjusted to be out of alignment from the second absorption axis. The first and second ECB layers help provide a uniform cone of vision during the privacy mode, where the contrast ratio is substantially reduced outside the cone of vision. In yet other suitable embodiments, the display may include only one ECB layer. 
     Further features of the invention, its nature and various advantages will be more apparent from the accompanying drawings and following detailed description. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of an illustrative electronic device such as a laptop computer with a display in accordance with an embodiment. 
         FIG. 2  is a perspective view of an illustrative electronic device such as a handheld electronic device with a display in accordance with an embodiment. 
         FIG. 3  is a perspective view of an illustrative electronic device such as a tablet computer with a display in accordance with an embodiment. 
         FIG. 4  is a perspective view of an illustrative electronic device such as a computer or other device with display structures in accordance with an embodiment. 
         FIG. 5  is a cross-sectional side view of an illustrative display in accordance with an embodiment. 
         FIG. 6  is a diagram showing how an illustrative display can be configured to operate in different viewing modes in accordance with an embodiment. 
         FIG. 7  is a diagram showing different light output profiles associated with the different view modes of  FIG. 6  in accordance with an embodiment. 
         FIG. 8  is a cross-sectional side view of an illustrative backlight unit with a switchable diffuser in accordance with an embodiment. 
         FIG. 9  is a cross-sectional side view of an illustrative switchable diffuser having a single layer of polymer dispersed liquid crystal (PDLC) in accordance with an embodiment. 
         FIG. 10  is a cross-sectional side view of an illustrative switchable diffuser having two layers of PDLC with different droplet sizes in accordance with an embodiment. 
         FIG. 11  is a cross-sectional side view of an illustrative switchable diffuser formed using PDLC with asymmetric droplets in accordance with an embodiment. 
         FIG. 12  is a cross-sectional side view of an illustrative switchable diffuser formed using PDLC with embedded microlens structures in accordance with an embodiment. 
         FIG. 13  is a perspective view of an illustrative switchable diffuser formed using switching liquid crystal (LC) lens array structures in accordance with an embodiment. 
         FIG. 14  is a cross-sectional side view of an illustrative switchable microarray structure for selectively collimating backlight in accordance with an embodiment. 
         FIG. 15  is a cross-sectional side view of an illustrative pyramid microarray with switchable mirror structures for selectively collimating backlight in accordance with an embodiment. 
         FIG. 16  is a cross-sectional side view of an illustrative microlens array with switchable mirror structures for selectively collimating backlight in accordance with an embodiment. 
         FIG. 17  is a perspective view of illustrative tunable microlens array structures for selectively collimating backlight in accordance with an embodiment. 
         FIG. 18  is a perspective view of illustrative switchable optical fiber bundle structures for selectively collimating backlight in accordance with an embodiment. 
         FIG. 19  is a cross-sectional side view of a display with a switchable phase retarder in accordance with an embodiment. 
         FIG. 20A  is a diagram illustrating a switchable phase retarder in normal viewing mode in accordance with an embodiment. 
         FIG. 20B  is a diagram illustrating a switchable phase retarder in privacy mode in accordance with an embodiment. 
         FIG. 21  is a plot of contrast ratio versus phase retardation that is provided by a switchable phase retarder at a particular viewing angle in accordance with an embodiment. 
         FIG. 22  is a plot of phase retardation versus bias voltage for a switchable phase retarder in accordance with an embodiment. 
         FIG. 23  is diagram illustrating different viewing angles of a display panel in accordance with an embodiment. 
         FIG. 24A  is a diagram of an exemplary display pixel design in accordance with an embodiment. 
         FIG. 24B  is a cross-sectional side view showing the conductive pixel fingers in accordance with an embodiment. 
         FIG. 25  is a plot showing regions of low contrast ratio for a display implemented using the display pixel design of  FIG. 24A  in accordance with an embodiment. 
         FIG. 26  is a diagram of an improved display pixel design having a rotated pixel alignment orientation in accordance with an embodiment. 
         FIG. 27  is a plot showing regions of low contrast ratio for a display implemented using the display pixel design of  FIG. 26  in accordance with an embodiment. 
         FIG. 28  is a diagram of an illustrative single-domain display pixel design having a crossbar in accordance with an embodiment. 
         FIG. 29  is a diagram of an illustrative dual-domain display pixel design with a crossbar in accordance with an embodiment. 
         FIG. 30  is a plot of contrast ratio versus viewing angle for a display implemented using a display pixel design of the type shown in the embodiments of  FIGS. 26, 28, and 29  in accordance with an embodiment. 
         FIG. 31  is a diagram of a display with multiple electrically controlled birefringence (ECB) layers in a normal viewing mode in accordance with an embodiment. 
         FIG. 32  is a diagram of the display of  FIG. 31  configured in privacy mode in accordance with an embodiment. 
         FIG. 33  is a plot showing the contrast ratio for the display in  FIG. 31  in accordance with an embodiment. 
         FIG. 34  is a plot showing regions of low contrast ratio for the display in  FIG. 32  in accordance with an embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     Electronic devices may include displays. The displays may be used to display images to 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, watch, 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 ). In compact devices such as wrist-watch devices, port  28  and/or button  26  may be omitted and device  10  may be provided with a strap or lanyard. 
       FIG. 3  shows how electronic device  10  may be a tablet computer. In electronic device  10  of  FIG. 3 , housing  12  may have opposing planar front and rear surfaces. Display  14  may be mounted on the front surface of housing  12 . As shown in  FIG. 3 , display  14  may have an opening to accommodate button  26  (as an example). 
       FIG. 4  shows how electronic device  10  may be a display such as a computer monitor, a computer that has been integrated into a computer display, or other device with a built-in display. With this type of arrangement, housing  12  for device  10  may be mounted on a support structure such as stand  30  or stand  30  may be omitted (e.g., to mount device  10  on a wall). Display  14  may be mounted on a front face of housing  12 . 
     The illustrative configurations for device  10  that are shown in  FIGS. 1, 2, 3, and 4  are merely illustrative. In general, electronic device  10  may be a laptop computer, a computer monitor containing an embedded computer, a tablet computer, a cellular telephone, a media player, or other handheld or portable electronic device, a smaller device such as a wrist-watch device, a pendant device, a headphone or earpiece device, or other wearable or miniature device, a computer display that does not contain an embedded computer, a gaming device, a navigation device, an embedded system such as a system in which electronic equipment with a display is mounted in a kiosk or automobile, equipment that implements the functionality of two or more of these devices, or other electronic equipment. 
     Housing  12  of device  10 , which is sometimes referred to as a case, may be formed of materials such as plastic, glass, ceramics, carbon-fiber composites and other fiber-based composites, metal (e.g., machined aluminum, stainless steel, or other metals), other materials, or a combination of these materials. Device  10  may be formed using a unibody construction in which most or all of housing  12  is formed from a single structural element (e.g., a piece of machined metal or a piece of molded plastic) or may be formed from multiple housing structures (e.g., outer housing structures that have been mounted to internal frame elements or other internal housing structures). 
     Display  14  may be a touch sensitive display that includes a touch sensor or may be insensitive to touch. Touch sensors for display  14  may be formed from an array of capacitive touch sensor electrodes, a resistive touch array, touch sensor structures based on acoustic touch, optical touch, or force-based touch technologies, or other suitable touch sensor components. 
     Display  14  for device  10  may include pixels formed from liquid crystal display (LCD) components. A display cover layer may cover the surface of display  14  or a display layer such as a color filter layer or other portion of a display may be used as the outermost (or nearly outermost) layer in display  14 . The outermost display layer may be formed from a transparent glass sheet, a clear plastic layer, or other transparent member. 
     A cross-sectional side view of an illustrative configuration for display  14  of device  10  (e.g., for display  14  of the devices of  FIG. 1 ,  FIG. 2 ,  FIG. 3 ,  FIG. 4  or other suitable electronic devices) is shown in  FIG. 5 . As shown in  FIG. 5 , display  14  may include backlight structures such as backlight unit  42  for producing backlight  44 . During operation, backlight  44  travels outwards (vertically upwards in dimension Z in the orientation of  FIG. 5 ) and passes through display pixel structures in display layers  46 . This illuminates any images that are being produced by the display pixels for viewing by a user. For example, backlight  44  may illuminate images on display layers  46  that are being viewed by viewer  48  in direction  50 . 
     Display layers  46  may be mounted in chassis structures such as a plastic chassis structure and/or a metal chassis structure to form a display module for mounting in housing  12  or display layers  46  may be mounted directly in housing  12  (e.g., by stacking display layers  46  into a recessed portion in housing  12 ). Display layers  46  may form a liquid crystal display or may be used in forming displays of other types. 
     Display layers  46  may include a liquid crystal layer such a liquid crystal layer  52 . Liquid crystal layer  52  may be sandwiched between display layers such as display layers  58  and  56 . Layers  56  and  58  may be interposed between lower polarizer layer  60  and upper polarizer layer  54 . 
     Layers  58  and  56  may be formed from transparent substrate layers such as clear layers of glass or plastic. Layers  58  and  56  may be layers such as a thin-film transistor layer and/or a color filter layer. Conductive traces, color filter elements, transistors, and other circuits and structures may be formed on the substrates of layers  58  and  56  (e.g., to form a thin-film transistor layer and/or a color filter layer). Touch sensor electrodes may also be incorporated into layers such as layers  58  and  56  and/or touch sensor electrodes may be formed on other substrates. 
     With one illustrative configuration, layer  58  may be a thin-film transistor layer that includes an array of pixel circuits based on thin-film transistors and associated electrodes (pixel electrodes) for applying electric fields to liquid crystal layer  52  and thereby displaying images on display  14 . Layer  56  may be a color filter layer that includes an array of color filter elements for providing display  14  with the ability to display color images. If desired, layer  58  may be a color filter layer and layer  56  may be a thin-film transistor layer. Configurations in which color filter elements are combined with thin-film transistor structures on a common substrate layer in the upper or lower portion of display  14  may also be used. 
     During operation of display  14  in device  10 , control circuitry (e.g., one or more integrated circuits on a printed circuit) may be used to generate information to be displayed on display  14  (e.g., display data). The information to be displayed may be conveyed to a display driver integrated circuit such as circuit  62 A or  62 B using a signal path such as a signal path formed from conductive metal traces in a rigid or flexible printed circuit such as printed circuit  64  (as an example). 
     Backlight structures  42  may include a light guide plate such as light guide plate  78 . Light guide plate  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. 
     Light  74  from light source  72  may be coupled into edge surface  76  of light guide plate  78  and may be distributed in dimensions X and Y throughout light guide plate  78  due to the principal of total internal reflection. Light guide plate  78  may include light-scattering features such as pits or bumps. The light-scattering features may be located on an upper surface and/or on an opposing lower surface of light guide plate  78 . Light source  72  may be located at the left of light guide plate  78  as shown in  FIG. 5  or may be located along the right edge of plate  78  and/or other edges of plate  78 . 
     Light  74  that scatters upwards in direction Z from light guide plate  78  may serve as backlight  44  for display  14 . Light  74  that scatters downwards may be reflected back in the upwards direction by reflector  80 . Reflector  80  may be formed from a reflective material such as a layer of plastic covered with a dielectric mirror thin-film coating. 
     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, compensation films for enhancing off-axis viewing, and brightness enhancement films (also 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 plate  78  and reflector  80 . For example, if light guide plate  78  has a rectangular footprint in the X-Y plane of  FIG. 5 , optical films  70  and reflector  80  may have a matching rectangular footprint. If desired, films such as compensation films may be incorporated into other layers of display  14  (e.g., polarizer layers). 
     In accordance with an embodiment of the present invention, display  14  may be configured to operate in various user viewing modes.  FIG. 6  is a diagram showing different viewing modes in which display  14  can be configured to operate. As shown in  FIG. 6 , display  14  may be configured to operate in at least a normal viewing mode  100 , a privacy viewing mode  102 , an outdoor viewing mode  104 , and a power saving mode  106 . Under normal lighting conditions (e.g., when display  14  is used indoors), display  14  may be placed in normal viewing mode  100  that exhibits a nominal viewing angle and a nominal display brightness level. When it is desired to reduce the viewing angle of display  14  below the nominal view angle, display  14  may be placed in privacy mode  102 . Under bright ambient lighting conditions (e.g., when display  14  is used outdoors in bright sunny conditions), display  14  may be placed in outdoor viewing mode  104  that boosts the display brightness beyond the nominal level so that the content on display  14  is more visible to the user. When it is desired to minimize power consumption of the electronic device, display  14  may be placed in power saving mode  106  that exhibits a reduced display brightness level and optionally reduced viewing angle. 
       FIG. 7  is a diagram plotting average picture luminance versus viewing angle illustrating different light output profiles associated with the different view modes of  FIG. 6 . As shown in  FIG. 7 , curve  110  represents the light output profile for normal view mode  100 ; curve  112  represents the light output profile for privacy mode  102 ; curve  114  represents the light output profile for outdoor viewing mode  104 ; and curve  116  represents the light output profile for power saving mode  106 . Curve  110  shows how the normal viewing mode exhibits a relatively wide viewing angle with a cone of vision of greater than 30° (e.g., with a viewing angle of more than 45° or more than 60°). While this may be convenient for collaborative purposes when display  14  is used to display content to a group of users positioned at varying angles relative to the normal viewing axis, the user may sometimes wish for the display to have a more limited cone of vision for privacy purposes. Curve  112  shows how the privacy mode exhibits a substantially reduced viewing angle with a viewing angle of less than 45° or less than 30° (see, curve  112  is substantially “narrower” than curve  110 ). 
     Curve  114  shows how display  14  may be configured to focus its light output to provide a boosted on-axis luminance intensity during bright ambient lighting conditions. If desired, curve  114  may exhibit an even narrower cone of vision than curve  112 . By focusing the light towards the user without wasting energy emitting light at larger viewing angles, the outdoor viewing mode is able to provide a boosted brightness level (e.g., with up to two times or more of the on-axis luminance intensity of the normal viewing mode) without increasing a net neutral display power consumption relative to the normal viewing mode. Curve  116  shows how display  14  may be configured to save power by also reducing the viewing angle without compromising on the brightness level along the normal viewing axis. In certain embodiments, power saving mode  106  may be similar or identical to privacy mode  102  and/or outdoor mode  104 , except the on-axis luminance level for the outdoor mode may be higher to facilitate the display of content in sunny conditions. 
     In accordance with an embodiment, the different display modes described above may be implemented using a switchable diffuser film in the backlight unit.  FIG. 8  is a cross-sectional side view showing how backlight unit  42  may be provided with a switchable diffuser. As shown in  FIG. 8 , backlight unit  42  may include a light source  72  (e.g., an LED light source) for emitting light  74  into light guide plate  78 , a brightness enhancement film such as a turning film  202 , and a switchable diffuser film  200 . Switchable diffuser  200  may be configured in an on state, an off state, or optionally one or more intermediate states for enhanced tunability. 
     In the embodiment of  FIG. 8 , light guide plate  78  may include light scattering features for emitting a generally scattered light source  210  upwards in direction Z. Turning film  202  may serve to convert scattered light  210  into a collimated light source  212 . The use of turning films as part of the backlight unit is generally relatively rare in the art since turning films output a light source with a fairly limited cone of vision, which is oftentimes unsuitable for use in normal electronic device displays. Turning film  202  can, however, be paired with switchable diffuser  200  to either generate scattered light  220  when switchable diffuser  200  is the off state or to pass through the focused light  222  when switchable diffuser  200  is in the on state. The configuration of the different display modes in  FIG. 6  can therefore be controlled by adjusting the state of switchable diffuser  200  (e.g., diffuser  200  can be turned off to place the display in normal viewing mode or can be turned on to place the display in one of modes  102 ,  104 , or  106 ). 
       FIG. 9  is a cross-sectional side view of an illustrative switchable diffuser film  200  having a single layer of polymer dispersed liquid crystal (PDLC) in accordance with an embodiment. As shown in  FIG. 9 , liquid crystal droplets  254  may be dispersed in a layer of polymer  256  between transparent substrates  250 - 1  and  250 - 2 . Substrates  250 - 1  and  250 - 2  may be formed from glass, plastic, or other transparent substrate material. Transparent conductive materials such as a layer of indium tin oxide (ITO)  252  may be formed on each of substrates  250 - 1  and  250 - 2  to control the behavior of the PDLC. In the example of  FIG. 9 , a voltage source  258  may be used to apply some amount of voltage onto layers  252  to control the orientation of the liquid crystal material in droplets  254 . For example, switchable diffuser  200  may be placed in the off state when no voltage is applied or may be placed in the on state when a nominal voltage level is applied. If desired, an intermediate voltage level that is between zero volts and the nominal high voltage level may be applied to fine tune the optical behavior of diffuser film  200  to place display  14  in a selected one of the user viewing modes (e.g., the different viewing modes as described in connection with  FIG. 6 ). 
       FIG. 10  shows another suitable arrangement in which switchable diffuser  200  is provided with two layers of PDLC. As shown in  FIG. 10 , liquid crystal droplets  254 - 1  formed between transparent substrates  250 - 1  and  250 - 2  may have a first size, whereas liquid crystal droplets  254 - 2  formed between transparent substrates  250 - 2  and  250 - 3  may have a second size that is different than the first size. A first voltage source  258 - 1  may be used to control the behavior of droplets  254 - 1 , whereas a second voltage source  258 - 2  may be used to control the behavior of droplets  254 - 2 . For example, display  14  may be placed in the normal viewing mode by turning off both voltage sources  258 - 1  and  258 - 2 . Display  14  may be placed in the privacy mode by turning on only voltage source  258 - 1 , in the outdoor mode by turning on only voltage source  258 - 2 , or in the power saving mode by turning on both voltage sources  258 - 1  and  258 - 2 . This example is merely illustrative. If desired, voltage sources  258 - 1  and  258 - 2  can be tuned individually to provide the desired light output profile for each of the various user viewing modes. 
       FIGS. 11 and 12  show other suitable arrangements of the switchable diffuser film  200 . As shown in  FIG. 11 , the switchable diffuser film may be provided with asymmetric droplets  255 . As shown in  FIG. 12 , the switchable diffuser may be provided with embedded microlens structures  260  for further control of the transmitted light. The microlens structures  260  of  FIG. 12  may not be switchable. 
     The different embodiments of  FIGS. 9-12  for implementing a switchable diffuser film using PDLC is merely illustrative and do not serve to limit the scope of the present invention. If desired, switchable diffuser film  200  may be implemented using polymer network liquid crystal (PNLC) material, polymer stabilized cholesteric texture (PSCT) material, a combination of these materials, and/or other suitable adjustable light diffusing materials. 
     In another suitable arrangement, the switchable diffuser film may also be implemented using a switchable liquid crystal (LC) lens array structure (see, e.g., switchable diffuser  200 ′ in  FIG. 13 ). As shown in  FIG. 13 , switchable diffuser  200 ′ may include a first adjustable LC lens array  290 - 1  stacked with a second adjustable LC lens array  290 - 2 . Each layer of adjustable LC lens array may include rows of cylindrical lenses  292  covered with liquid crystal material  294 . The cylindrical microlenses in layer  290 - 1  may be formed perpendicular to the cylindrical microlenses in layer  290 - 2  to help focus light from two orthogonal directions. In particular, lenses  292  may be polymer microlenses and may exhibit a “concave-up” orientation for selectively scattering light. Layers  290 - 1  and  290 - 2  may be provided with patterned electrodes (e.g., conductive ITO structures) that may be selectively biases using voltage sources (not shown) to modulate the optical properties of the LC material  294 . 
     For example, a high voltage may be applied across the liquid crystal material  294  so that the liquid crystal material  294  exhibits the same index of refraction as the polymer microlenses  292 . When microlenses  292  and the liquid crystal material  294  are index-matched, no lensing effect is provided and the collimated light  212  from the backlight unit is allowed to pass through substantially unscattered. When a low voltage is applied across the liquid crystal material  294 , the liquid crystal material  294  may exhibit a different refractive index as the polymer microlenses  292 . When the index of refraction of the microlenses  292  and the liquid crystal material  294  are mismatched, microlenses  292  are effectively switched into use to scatter the incoming collimated backlight  212  to generate a scattered outgoing light  220 . This example is merely illustrative. In general, any desired amount of voltage can be applied to the LC material so that switchable diffuser  200 ′ exhibits the desired optical transmission/scattering property for each of the different view modes described in connection with  FIG. 6 . The example of  FIG. 13  in which the microlenses are formed in a regular periodic configuration is merely illustrative. If desired, the microlens structures may be formed with random varying pitches and widths and may exhibit non-cylindrical shapes. 
     In certain embodiments, the switchable diffuser may also be implemented using a switchable optical fiber bundle. As shown in  FIG. 18 , switchable optical fiber bundle  400  may include optical fibers  402  made of glass, plastic, or other suitable fiber material bundled together and bonded using polymer adhesive  404 . In one configuration, switchable material such as PDLC or PNLC may be used as the binding material. In another configuration, the switchable material may be filled within the core of each optical fiber. When the switchable material is placed in a first state, the incoming collimated light  410  may be allowed to pass through substantially unaltered. When the switchable material is placed in a second state that is different than the first state, the incoming collimated light  410  may be altered and output as scattered light  412 . If desired, the switchable optical fiber bundle  400  may also receive scattered backlight and can be used to selectively output collimated light. 
     In accordance with another embodiment, the different display modes described above may be implemented using a switchable microarray structure in the backlight unit.  FIG. 14  is a cross-sectional side view showing how backlight unit  42  may be provided with a switchable microarray structure  300  that may be configured in an on state, an off state, or optionally one or more intermediate states for enhanced tunability. 
     In the embodiment of  FIG. 14 , light guide plate  78  may include light scattering features for emitting a generally scattered light source  210  upwards in direction Z. Switchable microarray structure  300  may directly receive the scattered light source  210  (without an intervening turning film) and may serve to convert the scattered light  210  into a collimated light source  304  or may otherwise pass through or further scatter the incoming light  210  to output scattered light  302 . The configuration of the different display modes in  FIG. 6  can therefore be controlled by adjusting the state of switchable microarray structure  300  (e.g., diffuser  300  can be turned off to place the display in normal viewing mode or can be turned on to place the display in one of modes  102 ,  104 , or  106 ). 
       FIG. 15  is a cross-sectional side view of an illustrative pyramid microarray with switchable mirror structures for selectively collimating backlight in accordance with an embodiment. As shown in  FIG. 15 , microarray structure  300  may include switchable mirror layer  310  having openings  314  and polymer material  316  that is formed over switchable mirror layer  310  and that may be patterned to form pyramid-shaped cavities  312 . The cavities  312  may be filled with air or other material having a refractive index that is different than polymer  316 . 
     Switchable mirror layer  310  may be implemented using cholesteric liquid crystal material, electrochromic material, or other types of materials with adjustable reflectivity. Similar to the PDLC material, mirror layer  310  may be selectively activated using a voltage source (not shown). When mirror  310  is configured in the on state, any backlight striking mirror  310  will be reflected back down towards reflector  80  (as indicated by path  321 ) whereas light may only be allowed to travel through layer  310  via the gaps  314 . Any light that propagates through these gaps  314  will be guided by the pyramid-shaped cavities  312  to generate a collimated light source  320 . The switchable mirror  310  operated in this way helps to convert the light emit directly from the light guide plate  78  into an array of point light sources. Light reflected from the mirror will therefore be recycled through the light guide and reflector  80 , which helps to improve output efficiency. When mirror  310  is configured in the off state, mirror  310  will be effectively switched out of use (e.g., mirror  310  will no longer exhibit reflective capabilities) and light exiting structures  300  will remain uncollimated in the scattered state. 
     The pyramidal shape of cavities  312  in structure  300  is merely illustrative. If desired, cavities  312  may be formed with a conical shape, a trapezoidal shape, or other suitable shapes for guiding and focusing the light in a way to produce the desired viewing angle when mirror  310  is switched into use. 
       FIG. 16  shows yet another suitable arrangement in which structure  300  includes a microlens array  330  that is formed over switchable mirror structures  310 . As shown in  FIG. 16 , the center of each microlens in array  330  may be aligned to corresponding gaps  314  in mirror layer  310 . When mirror  310  is activated, any backlight striking mirror  310  will be reflected back down towards reflector  80  (as indicated by path  321 ) while some of the light may travel through layer  310  via openings  314 . Any light that propagates through these openings will be focused using the microlens structures  330  to generate a collimated light source  321 . The switchable mirror  310  operated in this way serves to convert the light emit from the light guide plate  78  into an array of point light sources at the gap locations. When switchable mirror  310  is deactivated, mirror  310  will be effectively switched out of use (e.g., mirror  310  will no longer exhibit reflective capabilities) and light exiting structure  300  will remain uncollimated in the scattered state. 
     In another suitable embodiment, the adjustable microarray structure may be implemented using a switchable liquid crystal (LC) lens array structure (see, e.g., switchable microlens array structure  300 ′ in  FIG. 17 ). As shown in  FIG. 17 , structure  300 ′ may include a first adjustable LC lens array  350 - 1  stacked with a second adjustable LC lens array  350 - 2 . Each layer of adjustable LC lens array may include rows of cylindrical lenses  352  covered with liquid crystal material  354 . The cylindrical microlenses in layer  350 - 1  may be formed perpendicular to the cylindrical microlenses in layer  350 - 2  to help focus light from two orthogonal directions. In particular, lenses  352  may be polymer microlenses and may exhibit a “concave-down” orientation for selectively focusing light when the microlenses are switched into use. Layers  350 - 1  and  350 - 2  may be provided with patterned electrodes (e.g., conductive ITO structures) that can be selectively biases using voltage sources (not shown) to modulate the optical properties of the LC material  354 . 
     For example, a high voltage may be applied across the liquid crystal material  354  so that the liquid crystal material  354  exhibits the same index of refraction as the polymer microlenses  352 . When the polymer microlenses  352  and the liquid crystal material  354  are index-matched, no lensing effect is provided and the incoming scattered light  210  from the backlight unit is allowed to pass through without being collimated. When a low voltage is applied across the liquid crystal material  354 , the liquid crystal material  354  may exhibit a different refractive index as the polymer microlenses  352 . When the index of refraction of the microlenses  352  and the liquid crystal material  354  are mismatched, microlenses  352  are effectively switched into use to collimate the incoming scattered backlight  210  to generate a collimated outgoing light  304 . This example is merely illustrative. In general, any desired amount of voltage can be applied to the LC material so that switchable microarray structure  300 ′ exhibits the desired optical transmission/scattering property for each of the different view modes described in connection with  FIG. 6 . The example of  FIG. 17  in which the microlenses are formed in a regular periodic configuration is merely illustrative. If desired, the microlens structures may be formed with random varying pitches and widths and may exhibit non-cylindrical shapes. 
     The tunable lens structures described in connection with  FIGS. 13 and 17  are merely illustrative and do not serve to limit the scope of the present invention. In yet other suitable embodiments, the tunable microlens array structures may be implemented using mechanically driven microlens structures, microfluidic devices, polymer network liquid crystal (PNLC) based microlens structures, piezoelectrically driven liquid lens structures (e.g., dynamorph microlenses), ultrasonic transparent gel based lens structures, just to name a few. If desired, these tunable lens structures may be used in conjunction with switchable mirror structures (e.g., mirror  310  of  FIGS. 15 and 16 ) and switchable diffuser film structures (e.g., as part of the embedded microlens array  260  of  FIG. 12 ) to provide further tunability in the output light profile. 
     The embodiments described above in which the light output from the backlight unit is selectively collimated depending on the current viewing mode effectively reduces the luminance at higher viewing angles (e.g., the display appears darker as the user moves away from the normal axis of the display panel) and are therefore sometimes referred to as implementing a “black” mode. 
     In accordance with another suitable arrangement of the present invention, a switchable structure may be placed above the liquid crystal display layer to dynamically adjust the contrast ratio as a function of the viewing angle. For example, the switchable structure may be configured to reduce the contrast ratio as the user moves away from the normal axis of the display panel, thereby making the display appear lighter or more faded. Privacy mode implemented by reducing the contrast ratio is therefore sometimes referred to as “white” mode. 
     In accordance with an embodiment, the white privacy mode can be implemented using a switchable phase retarder that is stacked with the liquid crystal display (LCD) layer. As shown in  FIG. 19 , display layers  46  may include an LCD layer  500  formed between upper polarizer  54  and lower polarizer  60  and a dynamically tunable structure such as switchable phase retarder layer  502  interposed between upper polarizer  54  and LCD layer  500 . Layer  500  may, for example, include layers  56 ,  52 , and  50  of  FIG. 5 . 
     The exemplary configuration of  FIG. 19  in which switchable phase retarder  502  is formed between upper polarizer  54  and LCD layer  500  is merely illustrative and does not serve to limit the scope of the present invention. If desired, switchable phase retarder  502  may be alternatively formed between lower polarizer  60  and LCD layer  500 . In yet other suitable arrangements, a first switchable phase retarder may be sandwiched between upper polarizer  54  and LCD layer  500  while a second switchable phase retarder is sandwiched between bottom polarizer  54  and LCD layer  500 . 
     Switchable phase retarder layer  502  may be configured to control the contrast of the display image at higher, oblique viewing angles (e.g., from 30° to 90°). Typically, display  14  may include phase compensation films such as optical films  70  described in connection with  FIG. 5  to suppress light leakage at large viewing angles (i.e., to help enhance off-axis viewing by providing high contrast at wide viewing angles). By adding an additional switchable phase retarder film such as switchable phase retarder  502  into the display stack, the phase compensation function for oblique viewing angles can be adjusted. 
     Switchable phase retarder  502  may be operable in at least two modes.  FIG. 20A  shows switchable phase retarder  502  configured in normal viewing mode, whereas  FIG. 20B  shows switchable phase retarder  502  configured in privacy mode (which may also include the outdoor viewing mode and the power saving mode). As shown in  FIG. 20 , liquid crystal molecules  514  may be dispersed between transparent substrates  510  and  512 . Substrates  510  and  512  may be formed from glass, plastic, or other transparent substrate material. Transparent conductive materials such as a layer of indium tin oxide (ITO) may be formed on each of substrates  510  and  512  to control the behavior of molecules  514 . 
     In the example of  FIG. 20A , retarder layer  502  may be placed in an off state when no voltage is applied so that molecules  514  are in an isotropic state. When operated in the isotropic mode, the phase retarder does not affect any phase or polarization of the propagating light because the retarder is optically isotropic with visible light; the retarder is therefore effectively switched out of use. 
     In the example of  FIG. 20B , a voltage source may apply some amount of voltage across substrates  510  and  512  to create an electric field  516  so that the molecules are placed in an anisotropic state  514 ′ (sometimes referred to as a chiral nematic phase). In the anisotropic mode, light coming from on-axis will not experience any phase retardation, and the polarization of the on-axis light is maintained. However, light passing through retarder  502  at oblique angles will experience phase retardation. As a result, images view on-axis will exhibit high contrast while images view from oblique angles will exhibit low contrast. By controlling the voltage applied, the resulting electric field may induce a birefringence in any suitable liquid crystal material via the Kerr effect to switch layer  502  between the two modes. As examples, switchable phase retarder  502  may be implemented using blue phase LC material, discotic phase LC material, bowlic phase LC material, lyotropic LC materials, micellar cubic phase LC materials, hexagonal phase LC material, metallotropic LC material, a combination of these materials, and/or other suitable types of switchable material. 
       FIG. 21  is a plot of contrast ratio versus phase retardation that can be provided by switchable phase retarder  502  at an exemplary viewing angle of 30° in accordance with an embodiment. As shown by curve  600  in  FIG. 21 , contrast ratio may generally decrease as the amount of phase retardation is increased. In particular, line  602  may represent a threshold level below which the contrast ratio should be maintained in privacy mode. For example, a maximum contrast ratio of 1.2 may be deemed a sufficiently low contrast ratio to prevent users from reading the display at viewing angles greater than 30°. In the example of  FIG. 21 , a minimum phase retardation of 900 nanometers (nm) may be necessary to maintain the contrast ratio below predetermined threshold  602 . 
     The amount of phase retardation may be controlled by the voltage applied across the switchable phase retarder.  FIG. 22  is a plot of phase retardation versus bias voltage for switchable phase retarder  502  in accordance with an embodiment. As shown by curve  610  in  FIG. 22 , the amount of phase retardation generally increases as a function of applied voltage. To meet the 900 nm phase retardation requirement discussed in connection with  FIG. 21  (as indicated by dotted threshold line  612  in  FIG. 22 ), a minimum bias voltage of 50 V may have to be applied across the switchable phase retarder. Voltages of greater than 50 V may also be applied to provide extra margin at the expense of power consumption. The amount of phase retardation and the amount of bias voltage that are required to provide the desired contrast ratio shown in  FIGS. 21 and 22  are merely illustrative and are not intended to limit the scope of the present invention. Other threshold contrast levels corresponding to other phase retardation and bias voltage levels may be used to provide the desired amount of privacy. 
       FIG. 23  is diagram illustrating different viewing angles of a display panel. The X-Y axes form a plane that is coplanar with the display panel, whereas the Z axis represents a normal axis that is orthogonal to the plane of the display panel. Angle θ represents a viewing angle from the Z axis. If angle ϕ is fixed at zero degrees, then angle θ will correspond to the viewing angles illustrated and described in connection with  FIG. 7 . On the other hand, angle ϕ represents a viewing angle in the X-Y plane. Assuming the display panel is in the upright position on the tabletop, a viewer&#39;s elevation will change as angle ϕ is varied. In general, it is desirable for a display to exhibit reduced contrast ratios for angles θ greater than 30° at an angle ϕ of zero or 180 degrees during privacy viewing modes. 
       FIG. 24A  is a diagram of an exemplary display pixel design in accordance with an embodiment. As shown in  FIG. 24A , the display may include pixel electrodes  700  patterned in a conventional chevron formation, where each separate electrode is angled at approximately 80°. 
       FIG. 24B  is a cross-sectional side view of the display pixel circuitry shown in  FIG. 24A  cut along line AA′. As shown in  FIG. 24B , pixel electrodes  700  (e.g., indium tin oxide electrodes or “fingers”) may be formed on TFT layer  58  (see, e.g.,  FIG. 5 ). TFT layer  58  may include TFT circuitry  722  such as thin-film transistor structures formed over TFT substrate  720 . Liquid crystal material  52  may formed over pixel fingers  700  between TFT layer  58  and color filter layer  56 . If desired, the order of TFT layer  58  and color filter layer  56  can be flipped such that light exits the display by passing through color filter layer  56  before passing through TFT layer  58 . 
       FIG. 25  is a plot showing regions of low contrast ratio in the X-Y plane for a display implemented using the chevron pixel electrode arrangement of  FIG. 24A . As shown in  FIG. 25 , the lighter regions corresponding to dotted axes  702  where angle ϕ is approximately zero or 90 degrees represent areas of high contrast, whereas the darker regions  704  centered at angles ϕ of approximately 45, 135, 215, and 315 degrees represent areas of low contrast. Note that the contrast ratio generally decreases as one moves away from the center of the plot (i.e., as viewing angle θ increases). 
     In the example of  FIG. 25 , the low contrast regions  704  are undesirably offset by 45°. As described above, it is generally desirable to align the low contrast regions to angles ϕ of zero or 180 degrees since that would reduce view-ability from undesired, nearby or adjacent onlookers. In an effort to effectively rotate the contrast profile provided by the switchable phase retarder, an improved display pixel design is provided (see, e.g.,  FIG. 26 ). As shown in  FIG. 26 , the pixel electrodes  750  (sometimes referred to here as conductive “fingers”) are angled at 55°. This difference in finger angle relative to the chevron design of  FIG. 25  provides the desired rotation. The pixel fingers  750  may be formed from indium tin oxide (ITO) or other suitable transparent conductive material and may be interconnected using a vertical shorting sidebar member  752 . 
       FIG. 27  is a plot showing regions of low contrast ratio in the X-Y plane for a display implemented using the rotated pixel finger arrangement of  FIG. 26 . As shown in  FIG. 26 , the low contrast regions  712  have been aligned to angles ϕ of zero and 180 degrees. Additionally, users viewing from directly above and below (i.e., at ϕ of 90 and 270 degrees) will also perceive the reduced contrast ratio. Configured in this way, the display will be able to provide the desired privacy protection from viewers sitting laterally with respect to the intended user. 
     In accordance with another suitable arrangement,  FIG. 28  shows a rotated pixel design having fingers  760  interconnected by a conductive crossbar such as ITO crossbar  762 . In the example of  FIG. 28 , crossbar  762  may be relatively thinner than fingers  760  to help improve transmittance. As an example, the fingers  760  may be 3 microns wide while crossbar  762  may be only 2 microns wide. The configuration of  FIG. 28  may also provide a contrast profile similar to that shown in  FIG. 27 . The embodiments of  FIGS. 26 and 28  in which all of the conductive fingers are formed parallel to one another are sometimes referred to as a single-domain pixel electrode implementation. 
     In accordance with yet another suitable arrangement,  FIG. 29  shows a rotated pixel design having fingers formed at multiple different angles. As shown in  FIG. 29 , a first group of parallel fingers  770 - 1  may be formed at an angle of 55°, whereas a second group of parallel fingers  770 - 2  may be formed at angle of 35°. The two groups of fingers  770 - 1  and  770 - 2  may be shorted using a conductive crossbar such as ITO crossbar  772 . This configuration in which there are two sets of conductive fingers formed at slightly different angles is sometimes referred to as a dual-domain pixel electrode implementation. 
     The pixel designs of  FIGS. 26, 28, and 29  are merely illustrative and are not intended to limit the scope of the present invention. The pixel electrodes in  FIGS. 26, 28, and 29  can also be formed as part of TFT layer  58  as shown in  FIG. 24B . In general, the display may include pixel electrode fingers patterned at any suitable angle that yields the contrast plot of  FIG. 27  and may include any number of domains of parallel fingers. 
       FIG. 30  is a plot of contrast ratio versus viewing angle for a display implemented using a display pixel finger design of the type shown in the embodiments of  FIGS. 26, 28, and 29  in accordance with an embodiment. As shown by curve  790  in  FIG. 30 , the contrast ratio falls below the threshold level CR Th  for viewing angle θ of greater than 30°. Curve  790  in  FIG. 30  corresponds to the contrast profile at ϕ of zero degrees. If desired, the crossover point where curve  790  intersects with the desired privacy threshold level CR Th  may be adjusted (e.g., to 45°, 60°, etc.) by changing the amount of phase retardation, the amount of bias voltage, the pixel electrode finger design, the type of switchable phase retarder material, etc. 
     In accordance with another suitable embodiment, display layers  46  may also be provided with electrically controlled birefringence (ECB) layers that can help provide reduced visibility during privacy mode (which may also include the outdoor viewing mode and the power saving mode).  FIG. 31  is a diagram of a display with multiple electrically controlled birefringence (ECB) layers in a normal viewing mode in accordance with an embodiment. As shown in  FIG. 31 , a first ECB cell  802  and a second ECB cell  804  may be interposed between LCD layer  800  and lower polarizer  60 . Layer  800  may, for example, include layers  56 ,  52 , and  58  of  FIG. 5 . This is merely illustrative. In another suitable arrangement, first and second ECB cells  802  and  804  may be interposed between upper polarizer  54  and LCD layer  800 . In yet another suitable arrangement, first ECB cell  802  may be interposed between upper polarizer  54  and LCD layer  800  while second ECB cell  804  may be interposed between lower polarizer  60  and LCD layer  800 . 
     Front polarizer  54  may have an absorption axis (sometimes also referred to as transmittance axis) oriented towards the right of the page, whereas back polarizer  60  may have an absorption axis oriented straight out of the page. During normal viewing mode, the ECB cells may be switched out of use such that ECB cell  802  exhibits an optical axis  814  that is parallel to the absorption axis of upper polarizer  54  while ECB cell  804  exhibits an optical axis  816  that is parallel to the absorption axis of lower polarizer  60 . 
       FIG. 32  shows the display layers  46  when privacy mode is engaged. Voltage may be applied to rotate the optical axes of the ECB cells. As shown in  FIG. 32 , the optical axis of ECB cell  802  may be rotated to a new orientation  815  (e.g., towards the right of the page but slightly up towards the front polarizer) that is out of alignment with the absorption axis of front polarizer  54 . Similarly, the optical axis of ECB cell  804  may also be rotated to a new orientation  817  (e.g., out of the page but slightly up towards the front polarizer) that is out of alignment with the absorption axis of back polarizer  60 . 
       FIG. 33  is a plot showing the contrast ratio for the display in  FIG. 31  during normal user mode. As shown in  FIG. 33 , the display does not exhibit any reduction in contrast ratio in any direction when the ECB cells are switched out of use.  FIG. 34  is a plot showing the contrast ratio for the display in  FIG. 32  during privacy mode (or outdoor viewing mode or power saving mode). As shown in  FIG. 34 , the display may exhibit high contrast for the intended cone of vision  900  while providing substantially reduced contrast levels outside region  900 . Comparing the profiles of  FIG. 34  with that of  FIG. 27 , the dual ECB cell implementation may provide additional privacy since it offers reduced visibility from all directions. 
     The dual ECB layer implementation described in connection with  FIGS. 31 and 32  is merely illustrative and is not intended to limit the scope of the present embodiments. If desired, only one ECB layer or more than two ECB layers may be provided in the display. If desired, other types of nematic display layers may be engaged to help limit the viewability of the display to the desired cone of vision. For example, one or more dual-domain ECB cells (e.g., an ECB cell in which the optical axis in different regions of the ECB cell tilt in opposite directions but in the same plane) may also be used within the display. 
     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: 20160308
Publication Date: 20190514
Grant Date: 20190514
Priority Date: 20150603
Inventors: CHOI, HYUNGRYUL J.
JIANG, SHIH-CHYUAN FAN
CARBONE, GIOVANNI
Assignee: APPLE INC
CPC Classifications: [{"code": "G02F1/133526", "inventive": false, "first": false, "tree": "[]"}, {"code": "G02F1/1334", "inventive": false, "first": false, "tree": "[]"}, {"code": "G02F1/13439", "inventive": false, "first": false, "tree": "[]"}, {"code": "G02F1/1393", "inventive": false, "first": false, "tree": "[]"}, {"code": "G02F2203/50", "inventive": false, "first": false, "tree": "[]"}, {"code": "G02F1/1323", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02B6/005", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02F1/133526", "inventive": false, "first": false, "tree": "[]"}, {"code": "G02F1/1336", "inventive": true, "first": false, "tree": "[]"}, {"code": "G09G2320/068", "inventive": false, "first": false, "tree": "[]"}, {"code": "G02B6/0051", "inventive": true, "first": true, "tree": "[]"}, {"code": "G02F1/1334", "inventive": false, "first": false, "tree": "[]"}, {"code": "G02F1/1336", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02F1/13338", "inventive": false, "first": false, "tree": "[]"}, {"code": "G02F1/133528", "inventive": false, "first": false, "tree": "[]"}, {"code": "G02F1/134309", "inventive": false, "first": false, "tree": "[]"}, {"code": "G02F2203/50", "inventive": false, "first": false, "tree": "[]"}, {"code": "G02F1/1323", "inventive": true, "first": false, "tree": "[]"}, {"code": "G09G2320/068", "inventive": false, "first": false, "tree": "[]"}, {"code": "G02F1/13439", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02B6/0051", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02F1/1336", "inventive": true, "first": true, "tree": "[]"}, {"code": "G02F1/133528", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02F2001/133626", "inventive": false, "first": false, "tree": "[]"}, {"code": "G02F1/1334", "inventive": false, "first": false, "tree": "[]"}, {"code": "G02F2001/13793", "inventive": false, "first": false, "tree": "[]"}, {"code": "G02F1/134309", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02F1/133526", "inventive": false, "first": false, "tree": "[]"}, {"code": "G02B6/005", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02F1/1393", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02F2001/294", "inventive": false, "first": false, "tree": "[]"}, {"code": "G02F2203/50", "inventive": false, "first": false, "tree": "[]"}, {"code": "G02F1/13338", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02B6/005", "inventive": true, "first": true, "tree": "[]"}, {"code": "G02F1/133626", "inventive": false, "first": false, "tree": "[]"}, {"code": "G02F1/133626", "inventive": false, "first": false, "tree": "[]"}, {"code": "G02F1/13793", "inventive": false, "first": false, "tree": "[]"}, {"code": "G02F1/294", "inventive": false, "first": false, "tree": "[]"}, {"code": "G02F1/294", "inventive": false, "first": false, "tree": "[]"}]
Family ID: 57450951