Optical stack for imaging directional backlights

Abstract

The present invention provides an imaging directional backlight source device, which includes a waveguide, a visual source array, and is used to provide large-area guided illumination from a local light source. The waveguide can include a stepped structure, wherein the step can also include an extraction feature structure, which is optically hidden to the guided light propagating in a first forward direction. The return light propagating in a second backward direction can be refracted, diffracted or reflected by the feature structure to provide a discrete illumination beam leaving the top surface of the waveguide. A delay plate stacking arrangement is provided to reduce the display visibility of a peeper located in the extreme viewing area of ​​the display when achieving a minimum reduction in oncoming brightness. Further visibility of light reflections from a car windshield may be reduced.

Description

Technical Field

[0001] The present disclosure relates generally to illumination of light modulating devices, and more particularly to light guides for providing large area illumination from localized light sources for use in 2D, 3D and / or autostereoscopic display devices. Background Art

[0002] Spatially multiplexed autostereoscopic displays typically align a parallax component (such as a lenticular screen or parallax barrier) with an image array that is arranged as at least a first set of pixels and at least a second set of pixels on a spatial light modulator (e.g., an LCD). The parallax component directs light from each of the sets of pixels to different respective directions to provide a first viewing window and a second viewing window in front of the display. An observer places his eye in the first viewing window to see the first image with light from the first set of pixels; and places his eye in the second viewing window to see the second image with light from the second set of pixels.

[0003] Such displays have reduced spatial resolution compared to the native resolution of the spatial light modulator, and in addition, the structure of the viewing window is determined by the pixel hole shape and the parallax component imaging function. The gaps between pixels (e.g., for electrodes) generally produce a non-uniform viewing window. Undesirably, such displays exhibit image flicker when the observer moves laterally relative to the display, thereby limiting the viewing freedom of the display. Such flicker can be reduced by defocusing the optical elements; however, such defocusing leads to increased image crosstalk and increased visual fatigue for the observer. Such flicker can be reduced by adjusting the shape of the pixel hole, however, such changes can reduce display brightness and can cause the addressing of the electronics in the spatial light modulator to be impaired. Summary of the invention

[0004] According to the present disclosure, a directional lighting device may include an imaging directional backlight source for guiding light, an illuminator array for providing light to the imaging directional backlight source. The imaging directional backlight source may include a waveguide for guiding light. The waveguide may include a first light guiding surface and a second light guiding surface opposite to the first light guiding surface.

[0005] Display backlights typically employ waveguides and edge-lit sources. Certain imaging directional backlights have the additional ability to direct illumination through the display panel into a viewing window. An imaging system may be formed between multiple sources and corresponding window images. An example of an imaging directional backlight is an optical valve that may employ a folded optical system and therefore may also be an example of a folded imaging directional backlight. Light may propagate through the optical valve in one direction with substantially no loss, while reverse propagating light may be extracted by reflection off the tilted facets, as described in U.S. Pat. No. 9,519,153, which is incorporated herein by reference in its entirety.

[0006] Gass et al., “Privacy LCD Technology for Cellular Phones” (Sharp Technical Journal, No. 27, 2007), describes a display that uses a switchable ECB liquid crystal cell to provide a weak privacy protection effect.

[0007] According to a first aspect of the present disclosure, a display device is provided, which includes: a backlight source arranged to output light including a plurality of light sources; and a directional waveguide, the directional waveguide including: an input end extending in a lateral direction along a side of the waveguide, the light source being disposed along the input end and arranged to input the input light into the waveguide; and first and second relative guide surfaces extending from the input end across the waveguide for guiding the light input at the input end along the waveguide, the waveguide being arranged to deflect the input light guided through the waveguide to leave through the first guide surface; a transmissive spatial light modulator arranged to receive the output light from the backlight source; an output An input polarizer, which is arranged on the input side of the spatial light modulator between the backlight source and the spatial light modulator; an output polarizer, which is arranged on the output side of the spatial light modulator; at least one additional polarizer, which is arranged on the input side of the input polarizer between the input polarizer and the backlight source, or is arranged on the output side of the output polarizer; and at least one delay plate, which is arranged between the at least one additional polarizer and the input polarizer when the additional polarizer is arranged on the input side of the input polarizer, or between the at least one additional polarizer and the output polarizer when the additional polarizer is arranged on the output side of the input polarizer.

[0008] Advantageously, a privacy display is achieved with reduced visibility of the image to a peeping person than would be provided by a directional backlight alone.

[0009] The at least one retarder may include at least one corrected passive retarder and at least one switchable liquid crystal retarder. Advantageously, the viewing angle at which a snooper may perceive the displayed image is reduced. Furthermore, the brightness for the primary user is substantially maintained between the wide angle and anti-peep modes.

[0010] The waveguide may be arranged to image the light source in a lateral direction such that output light from the light source is directed into the corresponding optical window in output directions distributed according to the input position of the light source.

[0011] Advantageously, in this embodiment, in cooperation with the anti-peep backlight device, the off-axis brightness is desirably reduced to achieve improved anti-peep characteristics in certain viewing directions. In addition, the image displayed on the spatial light modulator may be less visible to a peeper at a position off-axis at a lateral angle and an elevation angle than a display without at least one retarder. In addition, the brightness to the user at a position of zero lateral angle or zero elevation angle may be substantially unchanged, thereby achieving high efficiency. Additional low-thickness components may be provided to achieve a thin stack.

[0012] The additional polarizer may be arranged on the input side of the input polarizer, and the at least one retarder may be arranged between the additional polarizer and the input polarizer.The additional polarizer may be a reflective polarizer.

[0013] Advantageously, the device thickness and device efficiency may not be altered in the head-on direction compared to a display in which the at least one retarder is not present and a reflective polarizer is present.

[0014] In the case where the additional polarizer is arranged on the input side of the input polarizer, the additional polarizer has an electric vector transmission direction that is parallel to the electric vector transmission of the input polarizer, or in the case where the additional polarizer is arranged on the output side of the input polarizer, the additional polarizer has an electric vector transmission direction that is parallel to the electric vector transmission of the output polarizer.

[0015] Advantageously, the efficiency of the device in the head-on direction may be substantially the same compared to a display in which the at least one retarder is not present.

[0016] The additional polarizer may be arranged on the input side of the input polarizer, and the at least one retarder may be arranged between the additional polarizer and the input polarizer. The additional polarizer may be arranged on the output side of the output polarizer, and the at least one retarder may be arranged between the additional polarizer and the output polarizer. Advantageously, an existing display polarizer may provide one of a pair of parallel polarizers, reducing device cost and thickness while achieving improved efficiency compared to two additional polarizers.

[0017] The at least one retarder may be at least one of a pair of crossed A-plates, or the C-plate may be a pair of crossed A-plates. In this embodiment, the crossed A-plates may have substantially orthogonal slow axes.

[0018] Advantageously, the crossed A plates may each comprise a single stretched material which is less expensive than the C plates. Additional achromatic compensation may be more easily provided.

[0019] At least one retarder may comprise a pair of retarder plates having a slow axis in the plane of the intersecting retarder plates. The pair of retarder plates have a slow axis that can each extend at 45° relative to the electric vector transmission direction parallel to the electric vector transmission of the input polarizer in the case where the additional polarizer is arranged on the input side of the input polarizer, or the pair of retarder plates have a slow axis that can each extend at 45° relative to the electric vector transmission direction parallel to the electric vector transmission of the output polarizer in the case where the additional polarizer is arranged on the output side of the input polarizer. The pair of retarder plates can each comprise a single A-plate. Advantageously, cost and complexity can be reduced.

[0020] The pair of retarders may each include a plurality of A plates having respective slow axes aligned at different angles to each other. At least one retarder may include a retarder having a slow axis perpendicular to the plane of the retarder. The retarder having a slow axis perpendicular to the plane of the retarder includes a C plate. Advantageously, thickness and complexity may be reduced.

[0021] At least one retarder may further include a C-plate and a pair of retarder plates having slow axes in the planes of the intersecting retarder plates. The pair of retarder plates have slow axes that extend at 0° and 90°, respectively, relative to the electric vector transmission direction parallel to the electric vector transmission of the input polarizer, when the additional polarizer is arranged on the input side of the input polarizer, or the pair of retarder plates have slow axes that extend at 0° and 90°, respectively, relative to the electric vector transmission direction parallel to the electric vector transmission of the output polarizer, when the additional polarizer is arranged on the output side of the input polarizer.

[0022] Advantageously, the variation of chromaticity with viewing angle can be reduced.

[0023] The at least one retarder may include a retarder having a slow axis orientation having a component perpendicular to a plane of the retarder and at least one component in the plane of the retarder. The retarder may include an O-plate.

[0024] Advantageously, brightness field control may be provided over areas of increased or decreased brightness field distribution, enabling increased control over the location to reduce privacy brightness compared to C-plates or crossed A-plates.

[0025] At least one retarder may include a retarder having a slow axis orientation having a component perpendicular to the plane of the retarder, a component orthogonal to the electric vector transmission direction of the input polarizer in the plane of the retarder, and substantially no component parallel to the electric vector transmission direction of the input polarizer in the plane of the retarder. Advantageously, the privacy brightness can be reduced for lower elevation angles compared to a C-plate or crossed A-plates. The privacy brightness can be reduced in both quadrants, thereby improving performance in wide angle mode for viewing angles where the likelihood of a snooper position is low.

[0026] At least one retarder may include a retarder having a slow axis orientation having a component perpendicular to the plane of the retarder, a component parallel to the electric vector transmission direction of the input polarizer in the plane of the retarder, and substantially no component orthogonal to the electric vector transmission direction of the input polarizer in the plane of the retarder. Advantageously, the privacy brightness at vertical viewing angles can be reduced.

[0027] The retarder may include a switchable liquid crystal retarder that can be switched between an O-plate retarder and an A-plate retarder by a voltage applied across the switchable liquid crystal retarder. Reduced privacy mode brightness may be provided in privacy mode, and the off-axis brightness provided by the retarder is not reduced in wide-angle mode. Advantageously, the privacy appearance may be improved, and wide-angle mode performance may be substantially unaffected by the retarder.

[0028] The switchable liquid crystal retarder may comprise at least one vertical alignment layer and may further comprise at least one corrective passive retarder, the at least one corrective passive retarder being arranged between the at least one additional polarizer and the input polarizer in the case where the additional polarizer is arranged on the input side of the input polarizer, or between the additional polarizer and the output polarizer in the case where the additional polarizer is arranged on the output side of the input polarizer. The corrective passive retarder may comprise a negative C-plate or a crossed positive A-plate.

[0029] The liquid crystal retarder may have an optical thickness between 500nm and 1000nm, preferably between 700nm and 900nm, and most preferably between 775nm and 825nm. The at least one corrected passive retarder has an optical thickness between 400nm and 800nm, preferably between 550nm and 750nm, and more preferably between 625nm and 675nm.

[0030] Advantageously, the polar region from which reduced brightness is provided to a snooper can be increased in size and privacy protection can be improved. Further color changes can be minimized.

[0031] The switchable liquid crystal retarder may include at least a first region and a second region that are independently addressed using a first applied voltage and a second applied voltage. Advantageously, different privacy levels may be provided to different regions of the display. When the privacy brightness of critical data is reduced, increased viewing freedom comfort may be provided for non-critical data provided in the image.

[0032] At least one retarder may include a switchable first O-plate retarder and a second O-plate retarder. Advantageously, a first reduced privacy brightness region and a second reduced privacy brightness region may be provided that cooperate to (i) reduce the overall privacy brightness for a given lateral angle and elevation angle and / or (ii) increase the polar distribution for which a low privacy level is achieved. Further power consumption in privacy mode may be reduced.

[0033] A surface relief structure may be provided at the interface of the first O-plate retarder and the second O-plate retarder. Advantageously, an increased wide angle distribution width may be provided in a wide angle operation mode, and a reduced distribution width may be provided in a privacy mode operation mode.

[0034] According to a second aspect of the present disclosure, a display device according to the first aspect can be provided, wherein a backlight source comprises: a light source array; a waveguide, the waveguide being arranged to receive input light from the light source at different input positions, and comprising: a first guide surface and a second guide surface opposite to each other, the first guide surface and the second guide surface opposite to each other being used to guide the input light along the waveguide; a side surface, the side surface extending between the first guide surface and the second guide surface; and a reflective end, the reflective end being used to reflect the input light back along the waveguide; wherein the second guide surface is arranged to deflect the reflected input light through the first guide surface as output light, and the waveguide is arranged to image the light source in a lateral direction between the side surfaces of the waveguide, so that the output light from the light source is guided into a corresponding optical window in an output direction distributed according to the input position of the light source. The first guide surface may be arranged to guide light by total internal reflection, and the second guide surface may include light extraction features and an intermediate region between the light extraction features, the light extraction features being oriented to deflect reflected input light through the first guide surface as output light, and the intermediate region being arranged to guide light through the waveguide without extracting the light. The light extraction features may be curved and have positive optical power in a lateral direction between the sides of the waveguide extending between the first guide surface and the second guide surface. The reflective end may have a lateral positive optical power extending between the sides of the waveguide extending between the first guide surface and the second guide surface. The waveguide may include an input end opposite the reflective end, and the light source may be arranged to input light into the waveguide through the input end. The light source may be arranged to input light into the waveguide through the sides of the waveguide.

[0035] The additional polarizer may be a reflective polarizer arranged on the input side of the input polarizer, and may be arranged to transmit a first polarization component of the output light, and reflect a second polarization component of the output light having a polarization state orthogonal to the polarization state of the first polarization component as blocked light; and a back reflector may be disposed behind the second guide surface, the back reflector being arranged to reflect the blocked light to be supplied back to the spatial light modulator, the back reflector comprising a linear array of paired reflective angle facets extending in a predetermined direction perpendicular to the normal of the spatial light modulator, such that the back reflector converts the polarization of the blocked light having two reflections from a pair of the angle facets into the polarization of the first polarization component. The paired reflective angle facets may be curved and have optical power in a lateral direction.

[0036] According to a third aspect of the present disclosure, a display device according to the first aspect or the second aspect may be provided. A control system is also included, which is arranged to control the light source. The backlight source can switch between modes in which the output light is output to observation windows of different widths. Advantageously, the switchable anti-peeping display can be provided with reduced visibility of the anti-peeping image to a peeper.

[0037] The control system may also be arranged to control the applied voltage across the switchable liquid crystal retarder. Advantageously, the privacy reduction of the switchable liquid crystal O-plate may be controlled or removed. The extreme position of the reduced privacy area may be controlled.

[0038] The control system is arranged to provide switching between: in a first operating mode, controlling the light source to provide an illumination distribution from the waveguide having a first angular width; and a first applied voltage across the switchable liquid crystal retarder; in a second operating mode, controlling the light source to provide an illumination distribution from the waveguide having a second angular width greater than the first angular width; and a second applied voltage across the switchable liquid crystal retarder different from the first applied voltage. The second applied voltage may be less than the first applied voltage.

[0039] Advantageously, in the wide angle mode of operation, the angular distribution can be the same as for the directional backlight. Furthermore, for a given privacy level, the width of the angular distribution can be increased compared to the width of a display without a switchable liquid crystal O-panel. Furthermore, for a given angular distribution of the backlight, the privacy level can be tuned.

[0040] In case the additional polarizer is arranged at the input side of the input polarizer, the switchable liquid crystal retarder between the additional polarizer and the input polarizer, or in case the additional polarizer is arranged at the output side of the input polarizer, the switchable liquid crystal retarder between the additional polarizer and the output polarizer may have a maximum attenuation polar coordinate with an elevation angle greater than zero relative to the direction of the normal to the spatial light modulator. The maximum attenuation polar coordinate may have an elevation angle between 10 and 50 degrees, preferably between 15 and 35 degrees, most preferably between 20 and 30 degrees. The maximum attenuation polar coordinate may have a lateral angle of 30 to 60 degrees, preferably 40 to 50 degrees and most preferably 45 degrees.

[0041] Advantageously, the visibility of the image to typical snooper positions may be increased and the cost of the voltage control system may be reduced.

[0042] The control system may be capable of controlling the spatial light modulator and of selectively operating the light sources to direct light into corresponding optical windows, wherein stray light in the directional backlight source is directed in an output direction outside of the optical window corresponding to the selectively operated light source, the control system being arranged to control the spatial light modulator and the array of light sources synchronously with each other so that: (a) the spatial light modulator displays a primary image when at least one primary light source is selectively operated to direct light into at least one primary optical window for viewing by a primary viewer, and (b) in the case of displaying the primary image in a time multiplexed manner, the spatial light modulator displays a secondary image when at least one light source different from the at least one primary light source is selectively operated to direct light into a secondary optical window outside of the at least one primary optical window, the secondary image perceived by the secondary viewer outside of the primary optical window obscures the primary image modulating the stray light directed outside of the primary optical window. The control system may be arranged to control the applied voltage across the switchable liquid crystal retarder in a time multiplexed manner.

[0043] Advantageously, the contrast and brightness can be reduced for the position of the snooper. The privacy protection may be further enhanced.

[0044] The display device may further comprise means for determining a position of a snooper relative to the display, wherein the control system is arranged to adjust the first applied voltage in response to the position of the snooper. Advantageously, for a given snooper position, the brightness of the image of the snooper may be reduced.

[0045] The display device may be arranged in a vehicle. The display device may be arranged below a transparent window in a vehicle. The display device is arranged in front of a seat of a vehicle. Advantageously, reduced visibility of reflections from a windshield and other transparent surfaces of the vehicle may be provided for an automotive display. Furthermore, the transmission of light seen head-on may be substantially the same as an unmodified display increasing display efficiency.

[0046] In the case where the additional polarizer is arranged on the input side of the input polarizer, at least one of the at least one delay plate between the at least one additional polarizer and the input polarizer, or in the case where the additional polarizer is arranged on the output side of the input polarizer, at least one of the at least one delay plate between the additional polarizer and the output polarizer is controlled by the addressing electrode. The addressing electrode can be patterned to provide at least two pattern areas. The pattern area can be a camouflage pattern. At least one of the pattern areas can be individually addressable and can be arranged to operate in an anti-peeping mode of operation. Advantageously, the image viewed by a snooper in the anti-peeping mode of operation can have camouflage, the level of which can be controlled.

[0047] The display device may also include at least one additional additional polarizer and at least one additional corrective passive delay plate and at least one additional switchable liquid crystal delay layer, in the case where the additional additional polarizer is arranged on the input side of the input polarizer, the at least one additional corrective passive delay plate and the at least one additional switchable liquid crystal delay layer are arranged between the at least one additional additional polarizer and the input polarizer, or in the case where the additional additional polarizer is arranged on the output side of the input polarizer, the at least one additional corrective passive delay plate and the at least one additional switchable liquid crystal delay layer are arranged between the additional additional polarizer and the output polarizer. The alignment direction of the upper alignment layer of the first switchable liquid crystal layer may be parallel or anti-parallel to the alignment direction of the upper alignment layer of the additional switchable liquid crystal layer, and the alignment direction of the lower alignment layer of the first switchable liquid crystal layer may be parallel or anti-parallel to the alignment direction of the lower alignment layer of the additional switchable liquid crystal layer. The alignment direction of at least the first corrective passive delay plate may be parallel or anti-parallel to the alignment direction of at least one additional corrective passive delay plate. Advantageously, a reduced brightness is provided to the peeper, thereby improving the anti-peeping performance over an increased polar viewing area.

[0048] The alignment direction of the upper alignment layer of the first switchable liquid crystal layer may be orthogonal to the alignment direction of the upper alignment layer of the further switchable liquid crystal layer, and the alignment direction of the lower alignment layer of the first switchable liquid crystal layer may be parallel or anti-parallel to the alignment direction of the lower alignment layer of the further switchable liquid crystal layer. The alignment direction of at least the first corrective passive retarder may be orthogonal to the alignment direction of at least one further corrective passive retarder. Advantageously, the privacy-protected user may have reduced visibility of images viewed from above the head of the primary viewer.

[0049] According to a fourth aspect of the present disclosure, a display device is provided, which includes: a backlight source, which is arranged to output light; a transmissive spatial light modulator, which is arranged to receive the output light from the backlight source; an input polarizer, which is arranged on the input side of the spatial light modulator between the backlight source and the spatial light modulator; an output polarizer, which is arranged on the output side of the spatial light modulator; an additional polarizer, which is arranged on the input side of the input polarizer between the input polarizer and the backlight source, or is arranged on the output side of the output polarizer. on the output side; and at least one corrective passive delay plate and a switchable liquid crystal delay plate, in the case where the additional polarizer is arranged on the input side of the input polarizer, the at least one corrective passive delay plate and the switchable liquid crystal delay plate are arranged between the at least one additional polarizer and the input polarizer, or in the case where the additional polarizer is arranged on the output side of the input polarizer, the at least one corrective passive delay plate and the switchable liquid crystal delay plate are arranged between the additional polarizer and the output polarizer, wherein at least one switchable liquid crystal delay plate includes electrodes and can be switched by applying a voltage to the electrodes of the switchable liquid crystal delay plate.

[0050] Compared to the first aspect, a non-directional backlight may be provided which enables an increase in the width of the viewing cone in the wide angle operation mode.

[0051] The display device may include at least one additional polarizer and at least one additional corrective passive delay plate and at least one additional switchable liquid crystal delay plate, in which case the additional additional polarizer is arranged on the input side of the input polarizer, the at least one additional corrective passive delay plate and the at least one additional switchable liquid crystal delay layer are arranged between the at least one additional polarizer and the input polarizer, or in which the additional additional polarizer is arranged on the output side of the input polarizer, the at least one additional corrective passive delay plate and the at least one additional switchable liquid crystal delay plate are arranged between the additional additional polarizer and the output polarizer, wherein at least one additional switchable liquid crystal delay plate includes electrodes and can be switched by applying a voltage to the electrodes of the switchable liquid crystal delay plate.

[0052] The alignment of the upper alignment layer of the first switchable liquid crystal layer may be parallel or anti-parallel to the alignment of the upper alignment layer of the further switchable liquid crystal layer, and the alignment of the lower alignment layer of the first switchable liquid crystal layer may be parallel or anti-parallel to the alignment of the lower alignment layer of the further switchable liquid crystal layer. The alignment of at least the first corrective passive retarder may be parallel or anti-parallel to the alignment of at least one further corrective passive retarder.

[0053] The alignment of the upper alignment layer of the first switchable liquid crystal layer may be orthogonal to the alignment of the upper alignment layer of the additional switchable liquid crystal layer, and the alignment of the lower alignment layer of the first switchable liquid crystal layer may be parallel or antiparallel to the alignment of the lower alignment layer of the additional switchable liquid crystal layer. The alignment of at least the first corrective passive delay plate may be orthogonal to the alignment of at least one additional corrective passive delay plate. The corrective passive delay plate may include a negative C plate or a crossed positive A plate. The switchable liquid crystal delay plate may include at least one surface alignment layer disposed adjacent to the liquid crystal to provide vertical alignment in the adjacent liquid crystal. The liquid crystal delay plate has an optical thickness between 500nm and 1000nm, preferably between 700nm and 900nm, and most preferably between 775nm and 825nm. At least one corrective passive delay plate may have an optical thickness between 400nm and 800nm, preferably between 550nm and 750nm, and more preferably between 625nm and 675nm.

[0054] Any aspect of the present disclosure may be applied in any combination.

[0055] Embodiments herein can provide an autostereoscopic display that provides wide-angle observation that can allow directional observation and conventional 2D compatibility. Wide-angle observation mode can be used for observer tracking autostereoscopic 3D display, observer tracking 2D display (for example, for anti-peep or energy-saving applications), for wide-viewing angle 2D display or for wide-viewing angle stereoscopic 3D display. In addition, embodiments can provide controlled illuminators to obtain efficient autostereoscopic display. Such components can be used in directional backlight sources to provide directional displays including autostereoscopic displays. In addition, embodiments can relate to directional backlight source devices and directional displays that can be combined with the directional backlight source devices. Such equipment can be used for autostereoscopic display, anti-peep display, multi-user display and can realize other directional display applications such as energy-saving operation and / or high-brightness operation.

[0056] Embodiments herein can provide autostereoscopic displays with large areas and thin structures. In addition, as will be described, the optical valves of the present disclosure can achieve thin optical components with large back working distances. Such components can be used in directional backlights to provide directional displays including autostereoscopic displays. In addition, embodiments can provide controlled illuminators to obtain efficient autostereoscopic displays.

[0057] Embodiments of the present disclosure may be used in a variety of optical systems. Embodiments may include or utilize various projectors, projection systems, optical components, displays, microdisplays, computer systems, processors, self-contained projector systems, visual and / or audio-visual systems, and electrical and / or optical devices. In fact, aspects of the present disclosure may be used with almost any device related to optical and electrical devices, optical systems, demonstration systems, or any device that may include any type of optical system. Therefore, embodiments of the present disclosure may be used in optical systems, devices used in visual and / or optical demonstrations, visual peripherals, etc., and may be used in a variety of computing environments.

[0058] Before discussing the disclosed embodiments in detail, it should be understood that the present invention is not limited in application or formation to the details of the specific arrangements shown, as the present invention is capable of other embodiments. In addition, various aspects of the present disclosure may be described in different combinations and arrangements to define the uniqueness of the embodiments in their own right. In addition, the terminology used herein is for illustrative purposes only and not limiting.

[0059] Directional backlights typically provide control of illumination emitted from substantially the entire output surface by modulating individual LED light sources arranged on the input aperture side of an optical waveguide. Controlling the directional distribution of emitted light can enable single-person viewing for safety functions, where the display can only be viewed by a single observer from a limited range of angles; high electrical efficiency, where illumination is provided primarily within a small angular directional distribution; left-right eye alternating viewing for sequential stereoscopic and autostereoscopic displays; and low cost.

[0060] These and other advantages and features of the present disclosure will become apparent to those of ordinary skill in the art after reading the entire disclosure. BRIEF DESCRIPTION OF THE DRAWINGS

[0061] Embodiments are illustrated by way of example in the accompanying drawings, in which like reference numerals refer to like parts, and in which:

[0062] Figure 1A is a schematic diagram showing a front view of light propagation in one embodiment of a directional display device;

[0063] Figure 1B is a schematic diagram showing Figure 1A A side view of light propagation in one embodiment of a directional display device;

[0064] Figure 2A is a schematic diagram illustrating light propagation in another embodiment of a directional display device in top view;

[0065] Figure 2B is a schematic diagram, which shows a front view of Figure 2ADirectional light propagation of display devices;

[0066] Figure 2C is a schematic diagram showing in side view Figure 2A Directional light propagation of display devices;

[0067] Figure 3 is a schematic diagram showing a directional display device in side view;

[0068] Figure 4A is a schematic diagram showing, from a front view, the creation of a viewing window in a directional display device including curved light extraction features;

[0069] Figure 4B is a schematic diagram showing, from a front view, the generation of a first viewing window and a second viewing window in a directional display device including a curved light extraction feature;

[0070] Figure 5 is a schematic diagram illustrating the generation of a first viewing window in a directional display device including a linear light extraction feature structure;

[0071] Fig. 6A is a schematic diagram illustrating one embodiment of the generation of a first observation window in a time multiplexed directional display device in a first time slot;

[0072] Figure 6B is a schematic diagram showing another embodiment of the generation of a second observation window in a time multiplexed directional display device in a second time slot;

[0073] Figure 6C is a schematic diagram showing another embodiment of the generation of the first observation window and the second observation window in a time-multiplexed directional display device;

[0074] Figure 7 is a schematic diagram showing a viewer tracking automatic stereoscopic directional display device;

[0075] Figure 8 is a schematic diagram showing a multi-viewer directional display device;

[0076] Fig. 9 is a schematic diagram showing an anti-peeping directional display device;

[0077] Fig.10 is a schematic diagram showing the structure of a time multiplexed directional display device in side view;

[0078] Fig.11 is a schematic diagram showing a directional display device including a directional display device and a control system;

[0079] Fig. 12Ais a schematic diagram showing a perspective view of a directional display device optical stack including a directional waveguide having a light input on a side opposite to a reflective side;

[0080] Fig. 12B is a schematic diagram showing a perspective view of an optical window formed by a directional display device including a directional waveguide having a light input on a side opposite to a reflective side;

[0081] Fig. 12C is a schematic diagram showing a perspective view of a directional display device optical stack including a directional waveguide having a light input on a side adjacent to a reflective side;

[0082] Fig.12D is a schematic diagram showing a perspective view of an optical window formed by a directional display device including a directional waveguide having a light input on a side adjacent to a reflective side;

[0083] Fig.13 is a diagram illustrating the orientation of the polarizer electric vector, the retarder slow axis, and the polarization state of other figures in the present disclosure;

[0084] Fig.14A is a schematic brightness field diagram showing brightness variation in a wide-angle operation mode of a directional display;

[0085] Fig. 14B is a schematic diagram showing the variation of brightness with viewing angle in a wide-angle operation mode of a directional display;

[0086] Fig. 14C is a schematic diagram showing the variation of display brightness with viewing angle for a wide-angle operating mode of a directional display;

[0087] Fig.15A is a schematic brightness field diagram, which shows the brightness change of the anti-peeping operation mode of the directional display;

[0088] Fig. 15B is a schematic diagram showing the variation of brightness of the anti-peeping operation mode of the directional display with the viewing angle;

[0089] Fig. 15C is a schematic diagram showing the change in display brightness with viewing angle in an anti-peeping operation mode of a directional display;

[0090] Fig.16A is a schematic diagram showing in side view a directional display including a directional waveguide and a crossed A-plate disposed between a spatial light modulator and a directional backlight;

[0091] Fig. 16Bis a schematic diagram showing, in perspective front view, the orientation of the retarder and polarizer axes of an optical stack for a directional display including directional waveguides and crossed A-plates;

[0092] Fig.17A is a schematic brightness field diagram showing the brightness of the display in the anti-peeping mode of operation. Fig. 16B Variations in brightness of the optical stack;

[0093] Fig. 17B is a schematic diagram showing the variation of brightness of the anti-peeping operation mode of the directional display with the viewing angle;

[0094] Fig. 17C is a schematic diagram showing the Fig. 16B Variation of display brightness with viewing angle in an anti-peeping operation mode of a directional display of an optical stack;

[0095] Fig.18A is a schematic brightness field diagram showing the wide-angle operating mode. Fig. 16B Variations in brightness of the optical stack;

[0096] Fig.18B is a schematic diagram showing the variation of brightness with viewing angle in a wide-angle operation mode of a directional display;

[0097] Fig.18C is a schematic diagram showing the Fig. 16B Variation of display brightness with viewing angle in a wide-angle operating mode of a directional display of an optical stack;

[0098] Fig.19A is a schematic diagram showing in perspective the illumination of a retardation layer by off-axis light;

[0099] Fig.19B is a schematic diagram showing in perspective the illumination of a retardation layer by off-axis light of a first linear polarization state at 0 degrees;

[0100] Fig.19C is a schematic diagram showing in perspective the illumination of a retardation layer by off-axis light of a first linear polarization state at 90 degrees;

[0101] Fig.19D is a schematic diagram showing in perspective view illumination of a retardation layer by off-axis light of a first linear polarization state at 45 degrees;

[0102] Fig.19E is a schematic diagram showing a Poincare sphere representation of coaxial polarization control across an A-plate retarder in a perspective front view;

[0103] Fig.19F is a schematic diagram showing in perspective front view a Fig. 16Bthe orientation of the retarder axis of the achromatic A-plate retarder of the optical stack including the composite retarder;

[0104] Figure 19G is a schematic diagram showing in perspective front view Fig.19E Poincare sphere representation of the coaxial polarization control of the first composite A-plate retarder pair;

[0105] Fig.19H is a schematic diagram showing in perspective front view Fig.19E Poincare sphere representation of the coaxial polarization control of the second composite A-plate retarder pair;

[0106] Fig. 20A is a schematic diagram showing in perspective the illumination of crossed A-plate retardation layers by off-axis polarized light having a positive elevation angle;

[0107] Fig. 20B is a schematic diagram showing in perspective the illumination of crossed A-plate retardation layers by off-axis polarized light having a negative transverse angle;

[0108] Fig. 20C is a schematic diagram showing in perspective the illumination of crossed A-plate retardation layers by off-axis polarized light having a positive elevation angle and a negative transverse angle;

[0109] Fig.20D is a schematic diagram showing in perspective view the illumination of crossed A-plate retardation layers by off-axis polarized light having a positive elevation angle and a positive transverse angle;

[0110] Fig.21A is a schematic brightness field diagram, which shows Fig. 16B A change in the transmitted brightness of an optical stack wherein the retardation layer is a quarter wave plate;

[0111] Fig. 21B is a schematic brightness field diagram, which shows Fig. 16B A change in the transmitted brightness of an optical stack wherein the retardation layer is a half-wave plate;

[0112] Fig. 21C is a schematic diagram showing, in perspective front view, the orientation of the retarder and polarizer axes of an optical stack for a directional display including additional polarizers and input polarizers arranged at + / - 45 degrees and crossed A-plates;

[0113] Fig.21D is a schematic brightness field diagram, which shows Fig. 21C A change in the transmitted brightness of an optical stack wherein the retardation layer is a quarter wave plate;

[0114] Fig.22A , Fig. 22B , Fig. 22C and Fig.22D is a schematic diagram showing an optical stack including crossed A-plates in side view;

[0115] Fig.23A is a schematic diagram showing in side view a directional display comprising a directional waveguide and crossed A-plates arranged in front of a spatial light modulator;

[0116] Fig. 23B is a schematic diagram showing in perspective front view a Fig.23A The orientation of the retarder and polarizer axes of the optical stack;

[0117] Fig.24A is a schematic diagram showing in side view a directional display including a directional waveguide and a C-plate arranged between a spatial light modulator and a directional backlight;

[0118] Fig. 24B is a schematic diagram showing in perspective front view a Fig.24A The orientation of the retarder and polarizer axes of the optical stack;

[0119] Fig.25A is a schematic diagram showing in side view a directional display including a directional waveguide and a C-plate arranged in front of a spatial light modulator;

[0120] Fig.25B is a schematic diagram showing in perspective front view a Fig.25A The orientation of the retarder and polarizer axes of the optical stack;

[0121] Fig.26A is a schematic diagram showing in perspective the illumination of a C-plate layer by off-axis polarized light having a positive elevation angle;

[0122] Fig.26B is a schematic diagram showing in perspective the illumination of a C-sheet layer by off-axis polarized light having a negative transverse angle;

[0123] Fig.26C is a schematic diagram showing in perspective view the illumination of a C-sheet layer by off-axis polarized light having a positive elevation angle and a negative transverse angle;

[0124] Fig.26D is a schematic diagram showing in perspective view the illumination of a C-plate layer by off-axis polarized light having a positive elevation angle and a positive transverse angle;

[0125] Fig.27A is a schematic brightness field diagram, which shows Fig. 24B A change in the transmitted brightness of an optical stack wherein the retardation layer is a half-wave plate;

[0126] Fig.27B is a schematic brightness field diagram, which shows Fig. 24B A change in the transmitted brightness of an optical stack wherein the retardation layer is a full wave plate;

[0127] Fig.28A is a schematic brightness field diagram, which shows Fig. 24B a change in the transmitted brightness of an optical stack including a high retardation layer;

[0128] Fig.28B and Fig.28C is a schematic brightness field diagram, which shows Fig. 24B changes in chromatic aberration coordinates of an optical stack including a high retardation layer;

[0129] Fig.29A is a schematic diagram showing in perspective the illumination of a C-plate layer and crossed A-plate layers by off-axis polarized light having a positive elevation angle;

[0130] Fig.29B is a schematic diagram showing in perspective front view a Fig.29A The orientation of the retarder and polarizer axes of the optical stack;

[0131] Fig. 30A is a schematic brightness field diagram, which shows Fig.29B a change in the transmitted brightness of an optical stack including a high retardation layer;

[0132] Fig. 30B and Fig. 30C is a schematic brightness field diagram, which shows Fig.29B changes in chromatic aberration coordinates of an optical stack including a high retardation layer;

[0133] Fig.31 is a schematic diagram showing in side view a directional display including a first directional waveguide, a second wide-angle waveguide and a C-plate arranged behind a spatial light modulator;

[0134] Fig.32A is a schematic diagram showing in top view the illumination of a car cabin and the driver from a centrally mounted display;

[0135] Fig.32B is a schematic diagram showing in side view the illumination of a car cabin and the driver from a centrally mounted display;

[0136] Fig.32C is a schematic brightness field diagram showing the brightness of a display and windshield reflection in a car;

[0137] Fig.33A is a schematic diagram showing in perspective the illumination of an O-sheet layer by off-axis polarized light having a positive elevation angle;

[0138] Fig.33Bis a schematic brightness field diagram, which shows the arrangement of Fig.33A Changes in the transmitted brightness of the O-plate between the parallel polarizers;

[0139] Fig.33C is a schematic brightness field diagram, which shows that the Fig.33A Variation of the transmission brightness of the wide-angle display of the O-plate between the parallel polarizers;

[0140] Fig.33D is a schematic diagram showing the change in brightness of a wide-angle display with a viewing angle, the wide-angle display further comprising a Fig.33A O-plates between parallel polarizers;

[0141] Fig.34 is a schematic diagram showing in side view a directional display including a directional waveguide and an O-plate arranged between a spatial light modulator and a directional backlight;

[0142] Fig.35 is a schematic diagram showing in perspective front view a Fig.34 orientation of some of the retarders and polarizer axes of an optical stack;

[0143] Fig.36A is a schematic diagram showing in perspective side view a Fig.34 orientation of some of the retarders and polarizer axes of an optical stack;

[0144] Fig.36B is a schematic diagram showing in perspective front view Fig.36A The orientation of the birefringent molecules in the arrangement of

[0145] Fig.36C is a schematic brightness field diagram, which shows Fig.34 A change in the transmitted brightness of an optical stack;

[0146] Fig.36D is a schematic diagram showing the change in brightness of an anti-peeping operation mode of a directional display including an O-plate with respect to a viewing angle;

[0147] Fig.36E is a schematic brightness field diagram, which shows the change of the transmission brightness of the O plate;

[0148] Fig.36F is a schematic brightness field diagram showing the variation of the transmitted brightness of a directional backlight source;

[0149] Figure 36G is a schematic brightness field diagram, which shows Fig.34 The variation of the transmitted brightness of the directional backlight source in the anti-peeping observation angle area;

[0150] Fig.36H is a schematic brightness field diagram, which shows Fig.34 The variation of the transmitted brightness of the optical stack in the angular region of anti-peeping observation;

[0151] Fig.37A is a schematic diagram showing in perspective side view a Fig.34 orientation of some of the retarder and polarizer axes of an optical stack wherein the birefringent molecules are arranged to provide control of brightness in a single viewing quadrant;

[0152] Fig.37B is a schematic diagram showing in perspective front view Fig.37A The orientation of the birefringent molecules in the arrangement of

[0153] Fig.37C is a schematic brightness field diagram, which shows Fig.37A A change in the transmitted brightness of an optical stack;

[0154] Fig.37D is a schematic brightness field diagram, which shows Fig.37A A change in the transmitted brightness of an optical stack;

[0155] Fig.38A is a schematic diagram showing, in perspective side view, the orientation of some of the retarders and polarizer axes for an optical stack, wherein the O-plate orientation is aligned parallel to the transverse direction;

[0156] Fig.38B is a schematic diagram showing in perspective front view Fig.38A The orientation of the birefringent molecules in the arrangement of

[0157] Fig.38C is a schematic brightness field diagram, which shows the arrangement of Fig.38A Changes in the transmitted brightness of the O-plate between the parallel polarizers;

[0158] Fig.38D is a schematic brightness field diagram, which shows Fig.38A A change in the transmitted brightness of an optical stack;

[0159] Fig.39A is a schematic diagram showing in side view a directional display comprising a directional waveguide and a uniformly aligned switchable liquid crystal O-plate disposed between a spatial light modulator and a directional backlight;

[0160] Fig.39B is a schematic diagram showing in side view Fig.39A Switching of uniformly aligned switchable liquid crystal O-plates in a directional display;

[0161] Fig.39Cis a schematic diagram showing a graphical representation of the liquid crystal director tilt of a cell with applied voltage versus the thickness of the liquid crystal cell;

[0162] Fig.39D is a schematic diagram showing in perspective front view a Fig.39A orientation of some of the retarders, alignment layers, and polarizer axes of an optical stack;

[0163] Fig.39E is a schematic diagram showing a flow chart for controlling a directional display device including a switchable directional backlight source, a switchable delay sheet, and an anti-peeping display control system;

[0164] Fig.39F is a schematic diagram showing changes in illumination of a directional display device including a switchable directional backlight, a switchable retarder, and an anti-peeping display control system;

[0165] Figure 39G is a schematic diagram showing in side view a directional display comprising a directional waveguide and a uniformly aligned switchable liquid crystal O-plate disposed between a spatial light modulator and an output polarizer;

[0166] Fig.40A is a schematic diagram showing in perspective side view a first applied voltage for Fig.39A orientation of some of the retarders, alignment layers, and polarizer axes of an optical stack;

[0167] Fig.40B is a schematic brightness field diagram, which shows the arrangement of Fig.40A Changes in the transmitted brightness of the O-plate between the parallel polarizers;

[0168] Fig.40C is a schematic brightness field diagram showing the brightness of the display in the anti-peeping mode of operation. Fig.40A Changes in the transmitted brightness of the optical stack;

[0169] Fig.41A is a schematic diagram showing in perspective side view the operation of the wide angle mode without applying voltage. Fig.39A orientation of some of the retarders, alignment layers, and polarizer axes of an optical stack;

[0170] Fig.41B is a schematic brightness field diagram showing the arrangement of the Fig.41A The change of the transmitted brightness of the A plate between the parallel polarizers;

[0171] Fig.41C is a schematic brightness field diagram showing the wide-angle operating mode. Fig.41A Changes in the transmitted brightness of the optical stack;

[0172] Fig.42A is a flow chart describing adjustment of the uniformly aligned switchable liquid crystal O-plate voltage corresponding to display viewing conditions;

[0173] Fig.42B is a schematic brightness field diagram, which shows the Fig.41A Changes in the transmitted brightness of the O-plate between the parallel polarizers;

[0174] Fig.43 is a schematic diagram showing, in perspective side view, the orientation of a plurality of parallel uniformly aligned switchable liquid crystal O-plates arranged between a directional backlight and a spatial light modulator;

[0175] Fig.44A is a schematic diagram showing, in perspective side view, the orientation of a plurality of orthogonally oriented uniformly aligned switchable liquid crystal O-plates disposed between a directional backlight and a spatial light modulator;

[0176] Fig.44B is a schematic brightness field diagram showing the Fig.44A Variation of the transmission brightness of a plurality of uniformly aligned switchable liquid crystal O-plates;

[0177] Fig.44C is a schematic brightness field diagram showing the wide-angle operating mode. Fig.44A Changes in the transmitted brightness of the optical stack;

[0178] Fig.45 is a schematic diagram showing, in perspective side view, the orientation of a uniformly aligned switchable liquid crystal O-plate and a plurality of parallel C-plates arranged between a directional backlight and a spatial light modulator;

[0179] Fig.46A is a schematic diagram showing, in perspective side view, the orientation of a uniformly aligned switchable liquid crystal O-plate disposed between a directional backlight and a spatial light modulator, and a C-plate disposed between the spatial light modulator and an additional polarizer;

[0180] Fig.46B is a schematic diagram showing in side view a directional display comprising a directional waveguide and a uniformly aligned switchable liquid crystal O-plate disposed between a spatial light modulator and an output polarizer, and a C-plate disposed between the spatial light modulator and an additional polarizer;

[0181] Fig.47A is a schematic brightness field diagram showing the Fig.45 Variation of the transmission brightness of multiple uniformly aligned switchable liquid crystal O-plates of AB;

[0182] Fig.47B is a schematic brightness field diagram showing the brightness of the display in the anti-peeping mode of operation. Fig.45 Changes in the transmitted brightness of the optical stack of AB;

[0183] Fig.47C is a schematic brightness field diagram showing the wide-angle operating mode. Fig.45 Changes in the transmitted brightness of the optical stack of AB;

[0184] Fig.48A is a schematic diagram showing, in perspective side view, the orientation of a vertically aligned switchable liquid crystal O-plate disposed between a directional backlight and a spatial light modulator and a negative C-plate disposed between the spatial light modulator and an additional polarizer in a wide angle operating mode;

[0185] Fig.48B is a schematic brightness field diagram showing the wide-angle operating mode. Fig.48A Changes in the transmitted brightness of the optical stack;

[0186] Fig.48C is a schematic diagram showing, in perspective side view, the orientation of a vertically aligned switchable liquid crystal O-plate disposed between a directional backlight and a spatial light modulator and a negative C-plate disposed between the spatial light modulator and an additional polarizer in an anti-peeping mode of operation;

[0187] Fig.48D is a schematic brightness field diagram showing the brightness of the display in the anti-peeping mode of operation. Fig.48C Changes in the transmitted brightness of the optical stack;

[0188] Fig.48E is a schematic brightness field diagram, which shows the change of the transmission brightness of the directional backlight source in the extreme area;

[0189] Fig.48F is a schematic diagram showing the Fig.40A The optical stack further modulates Fig.48F The variation of the transmitted brightness of the directional backlight source in the polar region;

[0190] Figure 48G is a schematic diagram showing the Fig.48C The optical stack further modulates Fig.48F The variation of the transmitted brightness of the directional backlight source in the polar region;

[0191] Figure 48H is a schematic diagram showing, in perspective side view, the orientation of a plurality of parallel homeotropically aligned switchable liquid crystal O-plates and a corrective passive retarder disposed between a backlight source and a spatial light modulator;

[0192] Figure 48Iis a schematic diagram showing, in perspective side view, the orientation of a plurality of orthogonal vertically aligned switchable liquid crystal O-plates and a corrective passive retarder disposed between a backlight source and a spatial light modulator;

[0193] Fig.48J is a schematic brightness field diagram showing the brightness of the display in the anti-peeping mode of operation. Figure 48I Changes in the transmitted brightness of the optical stack;

[0194] Fig.49A is a schematic diagram illustrating, in perspective side view, the orientation of a patterned switchable liquid crystal O-plate in vertical alignment alignment disposed between a directional backlight source and a spatial light modulator arranged to include a switchable camouflage region in an anti-peeping mode of operation;

[0195] Fig.49B is a schematic diagram showing, in a perspective front view, the illumination of a privacy display to a primary observer and a snooper controlled by the brightness of the camouflage;

[0196] Fig.49C is a schematic diagram showing, in a perspective side view, the illumination of a privacy display to a peeper controlled by the brightness of the camouflage;

[0197] Fig.50A is a schematic diagram showing, in perspective side view, the orientation of a vertically aligned switchable liquid crystal O-plate disposed between a directional backlight and a spatial light modulator and a crossed A-plate disposed between the spatial light modulator and an additional polarizer in a wide angle mode of operation;

[0198] Fig.50B is a schematic brightness field diagram showing the wide-angle operating mode. Fig.50A Changes in the transmitted brightness of the optical stack;

[0199] Fig.50C is a schematic diagram showing, in perspective side view, the orientation of a vertically aligned switchable liquid crystal O-plate disposed between a directional backlight and a spatial light modulator and a crossed A-plate disposed between the spatial light modulator and an additional polarizer in an anti-peeping mode of operation;

[0200] Fig.50D is a schematic brightness field diagram showing the brightness of the display in the anti-peeping mode of operation. Fig.50C Changes in the transmitted brightness of the optical stack;

[0201] Fig.51A is a schematic diagram showing, in perspective side view, the orientation of a hybrid-aligned switchable liquid crystal O-plate disposed between a directional backlight and a spatial light modulator and a negative C-plate disposed between the spatial light modulator and an additional polarizer in a wide-angle operating mode;

[0202] Fig.51Bis a schematic brightness field diagram showing the wide-angle operating mode. Fig.51A Changes in the transmitted brightness of the optical stack;

[0203] Fig.51C is a schematic diagram showing, in perspective side view, the orientation of a hybrid-aligned switchable liquid crystal O-plate disposed between a directional backlight and a spatial light modulator and a negative C-plate disposed between the spatial light modulator and an additional polarizer in an anti-peeping mode of operation;

[0204] Fig.51D is a schematic brightness field diagram showing the brightness of the display in the anti-peeping mode of operation. Fig.51C Changes in the transmitted brightness of the optical stack;

[0205] Fig.52A is a schematic diagram showing, in perspective side view, the orientation of a vertically aligned switchable liquid crystal O-plate disposed between a directional backlight and a spatial light modulator and a negative C-plate disposed between the spatial light modulator and an additional polarizer in a wide angle operating mode;

[0206] Fig.52B is a schematic brightness field diagram showing the wide-angle operating mode. Fig.52A Changes in the transmitted brightness of the optical stack;

[0207] Fig.52C is a schematic diagram showing, in perspective side view, the orientation of a vertically aligned switchable liquid crystal O-plate disposed between a directional backlight and a spatial light modulator and a negative C-plate disposed between the spatial light modulator and an additional polarizer in an anti-peeping mode of operation;

[0208] Fig.52D is a schematic brightness field diagram showing the brightness of the display in the anti-peeping mode of operation. Fig.52C Changes in the transmitted brightness of the optical stack;

[0209] Fig.53A is a schematic diagram showing, in perspective side view, the orientation of uniformly aligned switchable liquid crystal O-plates disposed between a directional backlight and a spatial light modulator and crossed A-plates disposed between the spatial light modulator and an additional polarizer in a wide angle mode of operation;

[0210] Fig.53B is a schematic brightness field diagram showing the wide-angle operating mode. Fig.51A Changes in the transmitted brightness of the optical stack;

[0211] Fig.53C is a schematic diagram showing, in perspective side view, the orientation of a vertically aligned switchable liquid crystal O-plate disposed between a directional backlight and a spatial light modulator and a negative C-plate disposed between the spatial light modulator and an additional polarizer in an anti-peeping mode of operation;

[0212] Fig.53D is a schematic brightness field diagram showing the brightness of the display in the anti-peeping mode of operation. Fig.51C Changes in the transmitted brightness of the optical stack;

[0213] Fig.54 is a schematic diagram showing, in side view, the orientation of a switchable liquid crystal O-plate and a fixed O-plate that may be arranged with a directional backlight and a spatial light modulator, wherein the interface between the O-plates is substantially planar;

[0214] Fig.55 is a schematic diagram showing, in side view, the orientation of a switchable liquid crystal O-plate and a fixed O-plate that may be arranged with a directional backlight and a spatial light modulator, wherein the interface between the O-plates is rough;

[0215] Fig.56 is a schematic diagram showing a side view of a directional display device optical stack including a directional waveguide, wherein a switchable retarder is arranged between the waveguide and a spatial light modulator, and a surface is arranged to provide reduced damage by an external compressive force;

[0216] Fig.57 is a schematic diagram showing a side view of a directional display control system including control of a spatial light modulator, a delay layer, and a light source array;

[0217] Fig.58A , Fig.58B , Fig.58C , Fig.58D and Fig.58E is a schematic diagram illustrating operation of a directional display in a privacy mode, wherein a primary image is provided on a spatial light modulator in at least one phase of operation;

[0218] Fig.59A , Fig.59B , Fig.59C , Fig.59D and Fig.59E is a schematic diagram illustrating operation of a directional display in a second phase in a privacy mode, wherein a primary image is provided on a spatial light modulator in a first phase and a secondary image is provided on a spatial light modulator in a second phase;

[0219] Fig.60 is a schematic diagram showing a side view of a directional display device optical stack including a collimating waveguide, a wide angle waveguide, a switchable liquid crystal O-plate, and a corrective passive retarder; and

[0220] Fig.61 is a schematic diagram showing a side view of a directional display device optical stack including a collimating waveguide and a switchable diffuser, a switchable liquid crystal O-plate and a corrective passive retarder. DETAILED DESCRIPTION

[0221] A time-multiplexed autostereoscopic display can advantageously improve the spatial resolution of the autostereoscopic display by directing light from all pixels of a spatial light modulator to a first viewing window in a first time slot and directing light from all pixels to a second viewing window in a second time slot. Thus, an observer whose eyes are arranged to receive light in the first viewing window and the second viewing window will see a full resolution image throughout the display through multiple time slots. A time-multiplexed display can advantageously achieve directional illumination by directing an array of illuminators through a substantially transparent time-multiplexed spatial light modulator using directional optical elements, wherein the directional optical elements substantially form an image of the array of illuminators in the window plane.

[0222] The uniformity of the viewing window may advantageously be independent of the arrangement of the pixels in the spatial light modulator. Advantageously, such a display may provide an observer tracking display with low flicker and low levels of crosstalk to a moving observer.

[0223] In order to achieve high uniformity in the window plane, it is desirable to provide an array of lighting elements with high spatial uniformity. The illuminator elements of a sequential lighting system may be provided, for example, by a combination of a pixel of a spatial light modulator of approximately 100 micrometers in size and a lens array. However, such pixels may suffer from similar challenges to spatially multiplexed displays. In addition, such devices may have lower efficiency and higher cost, requiring additional display components.

[0224] High window plane uniformity can be conveniently achieved with a combination of macroscopic illuminators (e.g., LED arrays) and uniformizing and diffusing optical elements, which are typically 1 mm or larger in size. However, the increased size of the illuminator elements means a proportional increase in the size of the directional optical elements. For example, a 16 mm wide illuminator imaged to a 65 mm wide viewing window may require a back working distance of 200 mm. Thus, the increased thickness of the optical elements may hinder effective application, for example, in mobile displays or large area displays.

[0225] To address the above shortcomings, optical valves as described in commonly owned U.S. Patent No. 9,519,153 may advantageously be arranged in combination with a fast switching transmissive spatial light modulator to achieve time multiplexed autostereoscopic illumination in a thin package while providing high resolution images with flicker-free observer tracking and low crosstalk levels. A one-dimensional array of viewing positions or windows is described that can display different images in a first (usually horizontal) direction, but include the same image when moved in a second (usually vertical) direction.

[0226] Conventional non-imaging display backlights typically employ optical waveguides and have edge lighting from a light source such as an LED. However, it should be understood that there are many fundamental differences in function, design, structure, and operation between such conventional non-imaging display backlights and the imaging directional backlights discussed in this disclosure.

[0227] In general, for example, according to the present disclosure, an imaging directional backlight is arranged to direct illumination from a plurality of light sources in at least one axis through a display panel to a corresponding plurality of viewing windows. Each viewing window is substantially formed as an image in at least one axis of the light source by an imaging system of the imaging directional backlight. The imaging system may be formed between the plurality of light sources and the corresponding window images. In this manner, light from each of the plurality of light sources is substantially invisible to an observer's eye outside the corresponding viewing window.

[0228] In contrast, conventional non-imaging backlights or light guide plates (LGPs) are used for illumination of 2D displays. See, e.g., et al.,Backlight Unit With Double Surface Light Emission,J.Soc.Inf.Display,Vol.12,Issue 4,pp.379-387(Dec.2004)( et al., Double-sided luminous backlight unit, Journal of the International Society for Information Display, Vol. 12, No. 4, pp. 379-387, December 2004). Non-imaging backlights are typically arranged to direct illumination from multiple light sources through the display panel into a viewing area that is substantially common to each of the multiple light sources to achieve a wide viewing angle and high display uniformity. Thus, the non-imaging backlight does not form an observation window. In this way, light from each of the multiple light sources can be visible to the observer's eyes at substantially all positions across the viewing area. Such conventional non-imaging backlights may have some directionality, for example, to increase screen gain compared to Lambertian illumination, which can be achieved by a brightness enhancement film such as BEF from 3M. TM provided. However, such directionality may be substantially the same for each of the corresponding light sources. Thus, for these reasons, and others that should be apparent to one of ordinary skill, conventional non-imaging backlights differ from imaging directional backlights. Edge-lit non-imaging backlight illumination structures may be used in liquid crystal display systems, such as those seen in 2D laptop computers, monitors, and televisions. Light propagates from the edge of a lossy waveguide, which may include sparse features; typically localized indentations in the surface of the guide that cause light loss regardless of the direction of propagation of the light.

[0229] As used herein, an optical valve is an optical structure that may be a type of light directing structure or device referred to, for example, as a light valve, an optical valve directional backlight, and a valve directional backlight ("v-DBL"). In the present disclosure, an optical valve is distinguished from a spatial light modulator (even though a spatial light modulator may sometimes be generally referred to as a "light valve" in the art). An example of an imaging directional backlight is an optical valve that may employ a folded optical system. Light may propagate through the optical valve in one direction with substantially no loss, may impinge on an imaging reflector, and may propagate in the reverse direction so that the light may be extracted by reflection off an angled light extraction feature and directed to a viewing window, as described in U.S. Patent No. 9,519,153, which is incorporated herein by reference in its entirety.

[0230] Additionally, as used herein, a stepped waveguide imaging directional backlight source may be at least one of the optical valves. A stepped waveguide is a waveguide for an imaging directional backlight source, comprising a waveguide for guiding light, and further comprising: a first light guiding surface; and a second light guiding surface opposite the first light guiding surface, and further comprising a plurality of light guiding features interspersed with a plurality of extraction feature structures arranged in steps.

[0231] In operation, light may propagate from the input surface to the reflective side in a first direction within the exemplary optical valve and may be transmitted substantially without loss. The light may be reflected at the reflective side and propagate in a second direction substantially opposite to the first direction. When the light propagates in the second direction, the light may be incident on a light extraction feature structure that is operable to redirect the light out of the optical valve. In other words, the optical valve generally allows light to propagate in a first direction and may allow light to be extracted when propagating in a second direction.

[0232] Optical valves can achieve time-sequential directional illumination of large display areas. In addition, optical elements thinner than the working distance behind the optical element can be used to direct light from a macroscopic illuminator to the window plane. Such displays can use arrays of light extraction features arranged to extract light propagating in opposite directions in substantially parallel waveguides.

[0233] Implementations of thin imaging directional backlight sources for use with LCDs have been proposed and described by 3M, for example, U.S. Patent 7,528,893; Microsoft, for example, U.S. Patent 7,970,246, which may be referred to herein as a "wedge type directional backlight"; RealD, for example, U.S. Patent No. 9,519,153, which may be referred to herein as an "optical valve" or "optical valve directional backlight", all of the above patents are incorporated herein by reference in their entirety.

[0234] The present disclosure provides a stepped waveguide imaging directional backlight source, wherein light may be reflected back and forth between, for example, the inner surfaces of a stepped waveguide, which may include a first side and a first set of features. As the light travels along the length of the stepped waveguide, the light may not substantially change the angle of incidence relative to the first side and the first set of surfaces, and therefore the critical angle of the medium cannot be reached at these inner surfaces. Light extraction may be advantageously achieved by a second set of surfaces (the step "risers"), which are oblique to the first set of surfaces (the step "pedals"). It should be noted that the second set of surfaces may not be part of the light guiding operation of the stepped waveguide, but may be arranged to provide light extraction from the structure. In contrast, a wedge-shaped imaging directional backlight source may allow light to be guided within a wedge-shaped profile waveguide having a continuous inner surface. Therefore, an optical valve is not a wedge-shaped imaging directional backlight source.

[0235] Figure 1A is a schematic diagram showing a front view of light propagation in one embodiment of a directional display device, and Figure 1B It is shown Figure 1A Schematic diagram of a side view of light propagation in a directional display device.

[0236] Figure 1A A front view in the xy plane of a directional backlight of a directional display device is shown, and includes an illuminator array 15 that can be used to illuminate the stepped waveguide 1. The illuminator array 15 includes illuminator elements 15a to 15n (where n is an integer greater than 1). In one example, Figure 1A The stepped waveguide 1 may be a stepped, display-sized waveguide 1. The lighting elements 15a to 15n are light sources that may be light emitting diodes (LEDs). Although LEDs are discussed herein as the illuminator elements 15a-15n, other light sources may be used, such as but not limited to diode sources, semiconductor sources, laser sources, localized field emission sources, organic emitter arrays, etc. In addition, Figure 1BA side view in the xz plane is shown, and includes the illuminator array 15, SLM 48, extraction features 12, guiding features 10, and stepped waveguide 1 arranged as shown. Figure 1B The side view provided in Figure 1A An alternative view of the front view shown in . Therefore, Figure 1A and Figure 1B The illuminator arrays 15 correspond to each other, and Figure 1A and Figure 1B The stepped waveguides 1 may correspond to each other.

[0237] In addition, Figure 1B In the embodiment of the present invention, the stepped waveguide 1 may have a thinner input end 2 and a thicker reflection end 4. Thus, the waveguide 1 extends between the input end 2, which receives input light, and the reflection end 4, which reflects the input light back through the waveguide 1. The length of the input end 2 in the lateral direction across the waveguide is greater than the height of the input end 2. The illuminator elements 15a-15n are arranged at different input positions in the lateral direction across the input end 2.

[0238] The waveguide 1 has opposing first and second guide surfaces extending between the input end 2 and the reflective end 4 for guiding light back and forth along the waveguide 1. The second guide surface has a plurality of light extraction features 12 facing the reflective end 4 and is arranged to reflect at least some of the light guided through the waveguide 1 back from the reflective end through the first guide surface from different input positions across the input end in different directions, the different directions depending on the input position.

[0239] In this example, the light extraction features 12 are reflective facets, but other reflective features may be used. The light extraction feature structures 12 do not guide light through the waveguide, while the intermediate areas of the second guide surface between the light extraction feature structures 12 guide light without extracting it. Those areas of the second guide surface are flat and may extend parallel to the first guide surface or at a relatively low inclination angle. The light extraction feature structures 12 extend laterally to those areas so that the second guide surface has a stepped shape, which may include the light extraction feature structures 12 and the intermediate areas. The light extraction feature structures 12 are oriented so that light from the light source is reflected through the first guide surface after being reflected from the reflective end 4.

[0240] The light extraction feature 12 is arranged to guide input light from different input positions in the lateral direction across the input end in different directions relative to the first guide surface, the different directions depending on the input position. Since the lighting elements 15a-15n are arranged at different input positions, the light from the corresponding lighting elements 15a-15n is reflected in those different directions. In this way, each lighting element in the lighting elements 15a-15n guides light to a respective optical window in an output direction distributed in a lateral direction, the output direction depending on the input position. For the output light, the lateral direction of the input end 2 in which the input positions are distributed corresponds to the lateral direction of the normal of the first guide surface. The lateral directions as defined at the input end 2 and for the output light remain parallel in this embodiment, wherein the deflection at the reflective end 4 and the first guide surface is generally orthogonal to the lateral direction. Under the control of the control system, the illuminator elements 15a-15n can be selectively operated to guide light to a selectable optical window. The optical window can be used as an observation window individually or in groups.

[0241] The SLM 48 extends across the waveguide and modulates the light output therefrom. While the SLM 48 may be a liquid crystal display (LCD), this is by way of example only, and other spatial light modulators or displays may be used, including LCOS, DLP devices, etc., since the illuminator may operate in a reflective manner. In this example, the SLM 48 is disposed across the first guide surface of the waveguide and modulates the light output that passes through the first guide surface after reflection from the light extraction feature 12.

[0242] The operation of the directional display device that can provide a one-dimensional observation window array is Figure 1A It is shown in front view, and its side profile is shown in Figure 1B In operation, Figure 1A and Figure 1B , light may be emitted from an array of illuminators 15, such as an array of illuminator elements 15a to 15n, which are located at different positions y along the surface x=0 of the thin end side 2 of the stepped waveguide 1. The light may propagate in the first direction along +x within the stepped waveguide 1, while at the same time, the light may be emitted in a fan shape in the xy plane and may substantially or completely fill the curved end side 4 after reaching the distant curved end side 4. While propagating, the light may spread out into a set of angles in the xz plane that are up to but not exceeding the critical angle of the guiding material. The extraction feature 12 of the guiding feature 10 linked to the bottom side of the stepped waveguide 1 may have a tilt angle greater than the critical angle, and thus substantially all light propagating along +x in the first direction may miss the extraction feature 12, thereby ensuring substantially lossless forward propagation.

[0243] Continue the discussion Figure 1A and Figure 1B, the curved end side 4 of the stepped waveguide 1 can be made reflective, typically by coating it with a reflective material (such as silver), but other reflection techniques can also be used. The light can thus be redirected in a second direction, back along the guide in the -x direction and can be substantially collimated in the xy or display plane. The angular spread can be substantially maintained in the xz plane about the primary propagation direction, which can allow light to strike the edge of the riser and reflect off the guide. In an embodiment having an extraction feature structure 12 tilted at approximately 45 degrees, the light can be effectively guided approximately perpendicular to the xy display plane, wherein the xz angular spread is substantially maintained relative to the propagation direction. This angular spread can increase when the light leaves the stepped waveguide 1 by refraction, but can be slightly reduced depending on the reflective characteristics of the extraction feature structure 12.

[0244] In some embodiments having uncoated extraction features 12, reflections may be reduced when total internal reflection (TIR) ​​is not possible, thereby squeezing the xz angular profile and deviating from normal. However, in other embodiments having extraction features coated with silver or metallized, the increased angular spread and center normal direction may be retained. Continuing with the description of the embodiments having silver coated extraction features, in the xz plane, light may exit the stepped waveguide 1 approximately collimated and may be directed away from normal in proportion to the y position of the corresponding illuminator elements 15a-15n in the illuminator array 15 from the center of the input edge. Having independent illuminator elements 15a-15n along the input edge 2 thus enables light to exit from the entire first light guiding side 6 and propagate at different exterior angles, such as Figure 1A as shown in .

[0245] Using such a device to illuminate a spatial light modulator (SLM) 48 (such as a fast liquid crystal display (LCD) panel) can achieve autostereoscopic 3D, such as Figure 2A The top view in the yz-plane or viewed from the end of the illuminator array 15, Figure 2B The front view and Figure 2C As shown in the side view. Figure 2A is a schematic diagram showing the propagation of light in a directional display device in a top view, Figure 2B is a schematic diagram showing the propagation of light in a directional display device in a front view, and Figure 2C Schematic diagram showing the propagation of light in a directional display device in a side view. Figure 2A , Figure 2B and Figure 2CAs shown, the stepped waveguide 1 can be located behind a fast (e.g., greater than 100 Hz) LCD panel SLM 48 that displays sequential right-eye and left-eye images. In synchronization, specific illuminator elements 15a to 15n (where n is an integer greater than one) of the illuminator array 15 can be selectively turned on and off to provide illumination light that enters the right eye and the left eye substantially independently by virtue of the directionality of the system. In the simplest case, multiple groups of illuminator elements of the illuminator array 15 are turned on together to provide a one-dimensional observation window 26 or pupil having a limited width in the horizontal direction but extending in the vertical direction, in which both eyes separated horizontally can observe the left eye image; and provide another observation window 44, in which both eyes can observe mainly the right eye image; and provide a center position, in which both eyes can observe different images. In this way, 3D can be observed when the observer's head is approximately centered. Movement to the side away from the center position can cause the scene to collapse on the 2D image.

[0246] The reflective end 4 may have positive optical power in a lateral direction across the waveguide 1. In other words, the reflective end may have positive optical power in a direction extending between the sides of the waveguide, which extend between the first and second guide surfaces and between the input end and the reflective end. The light extraction feature 12 may have positive optical power in a direction between the sides of the waveguide, which extend between the first and second guide surfaces 6, 8 and between the input end 2 and the reflective end.

[0247] The waveguide 1 may also include a reflective end 4 for reflecting input light from the light source back along the waveguide 1, the second guide surface 8 is arranged to deflect the reflected input light through the first guide surface 6 as output light, and the waveguide 1 is arranged to image the light sources 15a-n so that the output light from these light sources is directed into the corresponding optical windows 26a-n in output directions, and these output directions are laterally distributed depending on the input position of the light source.

[0248] In embodiments where the reflective end 4 has generally positive optical power, the optical axis may be defined with reference to the shape of the reflective end 4, such as a line passing through the center of curvature of the reflective end 4 and coinciding with the axis of reflection symmetry of the end 4 about the x-axis. In the case where the reflective surface 4 is flat, the optical axis may be similarly defined with respect to other components having optical power (such as the light extraction features 12 if they are curved) or the Fresnel lens 62 described below. The optical axis 238 is generally coincident with the mechanical axis of the waveguide 1. In embodiments of the present invention that generally include a substantially cylindrical reflective surface at the end 4, the optical axis 238 is a line passing through the center of curvature of the surface at the end 4 and coinciding with the axis of reflection symmetry of the side 4 about the x-axis. The optical axis 238 is generally coincident with the mechanical axis of the waveguide 1. The cylindrical reflective surface at the end 4 may generally include a spherical profile to optimize performance for on-axis and off-axis viewing positions. Other profiles may be used.

[0249] Figure 3 is a schematic diagram showing a directional display device in a side view. In addition, Figure 3 1 shows further details of the operation of a side view of a stepped waveguide 1, which may be a transparent material. The stepped waveguide 1 may include an illuminator input side 2, a reflective side 4, a first light guiding side 6, which may be substantially flat, and a second light guiding side 8 including guiding features 10 and light extraction features 12. In operation, light from an illuminator array 15 (which may be, for example, an addressable LED array) is directed to the light source. Figure 3 Light 16 of illuminator element 15c (not shown) can be guided in stepped waveguide 1 to reflective side 4, which can be a mirror surface, by total internal reflection of first light guiding side 6 and total internal reflection of guiding feature 10. Although reflective side 4 can be a mirror surface and can reflect light, in some embodiments, light may also pass through reflective side 4.

[0250] Continue the discussion Figure 3 , light 18 reflected by the reflective side 4 may be further guided in the stepped waveguide 1 by total internal reflection at the reflective side 4 and may be reflected by the extraction feature 12. Light 18 incident on the extraction feature 12 may be substantially deflected away from the guided mode of the stepped waveguide 1 and may be directed as shown by light 20 through the side 6 to the pupil of an observation window 26 that may form an autostereoscopic display. The width of the observation window 26 may be determined by at least the size of the illuminator, the side 4 and the output design distance and the optical power in the extraction feature 12. The height of the observation window may be primarily determined by the reflection cone angle of the extraction feature 12 and the illumination cone angle input at the input side 2. Therefore, each observation window 26 represents a series of separate output directions relative to the surface normal direction of the spatial light modulator 48 that intersects the plane at the nominal viewing distance.

[0251] Figure 4A is a schematic diagram showing a directional display device that can be illuminated by a first illuminator element and includes a curved light extraction feature structure from a front view. In addition, Figure 4A Light rays from illuminator elements 15c of illuminator array 15 are further directed in stepped waveguide 1 in a front view. Each of the output light rays is directed from a corresponding illuminator 14 toward the same viewing window 26. Thus, light ray 30 may intersect light ray 20 in window 26, or may have a different height in the window, as shown by light ray 32. Additionally, in various embodiments, side 22 and side 24 of waveguide 1 may be transparent surfaces, mirrored surfaces, or blackened surfaces. Continued Discussion Figure 4A , the light extraction feature 12 may be elongated, and the light extraction feature 12 is on the light guiding side 8 (the light guiding side 8 is on Figure 3 shown in Figure 4AThe orientation of light extraction features 12 in first region 34 (not shown) may be different from the orientation of light extraction features 12 in second region 36 of light directing side 8.

[0252] Figure 4B is a schematic diagram showing an optical valve that can be illuminated by a second illuminator element from a front view. In addition, Figure 4B Light rays 40, 42 are shown from a second illuminator element 15h of the illuminator array 15. The curvature of the side 4 and the reflective end on the light extraction feature 12 cooperate with the light rays from the illuminator element 15h to create a second viewing window 44 that is laterally separated from the viewing window 26.

[0253] The advantage is that Figure 4B The arrangement shown in FIG. 1 can provide a real image of the illuminator element 15 c at the viewing window 26, where the optical power in the reflective side 4 cooperates with the optical power that may be caused by the different orientations of the elongated light extraction features 12 between regions 34 and 36 to form the real image, as shown in FIG. Figure 4A as shown in . Figure 4B The arrangement may enable improved aberration of the imaging of the illuminator element 15c to a lateral position in the viewing window 26. The improved aberration may enable an extended viewing freedom of the autostereoscopic display while achieving a low crosstalk level.

[0254] Figure 5 is a schematic diagram showing an embodiment of a directional display device having substantially linear light extraction features from a front view. In addition, Figure 5 1 (where corresponding elements are similar), with one difference being that the light extraction features 12 are substantially linear and parallel to each other. Advantageously, such an arrangement can provide substantially uniform illumination across the display surface and is consistent with Figure 4A and Figure 4B It is easier to manufacture than the bending extraction feature structure.

[0255] Fig. 6A is a schematic diagram showing an embodiment of generating a first observation window in a time multiplexed imaging directional display device in a first time slot, Figure 6B is a schematic diagram showing another embodiment of the generation of a second observation window in a time multiplexed imaging directional backlight device in a second time slot, and Figure 6C is a schematic diagram showing another embodiment of the generation of the first observation window and the second observation window in the time multiplexing imaging directional display device. In addition, Fig. 6A The generation of an illumination window 26 by a stepped waveguide 1 is schematically shown. A group 31 of illuminator elements in the illuminator array 15 may provide a cone of light 17 directed towards the observation window 26. Figure 6BThe generation of an illumination window 44 is schematically shown. The group 33 of illuminator elements in the illuminator array 15 may provide a light cone 19 directed towards the observation window 44. In cooperation with a time multiplexed display, the windows 26 and 44 may be provided in sequence, e.g. Figure 6C If the spatial light modulator 48 ( Fig. 6A , Figure 6B , Figure 6C If an image on a directional backlight (not shown) is provided, an autostereoscopic image can be achieved for an observer in a suitable position. Similar operation can be achieved with all directional backlights described herein. It should be noted that illuminator element groups 31 and 33 each include one or more illuminator elements from illuminator elements 15a to 15n, where n is an integer greater than one.

[0256] Figure 7 FIG. 1 is a schematic diagram showing an embodiment of an observer tracking automatic stereoscopic directional display device. Figure 7 As shown, selectively turning on and off the illuminator elements 15a to 15n along the axis 29 provides directional control of the viewing window. The position of the head 45 may be monitored using a camera, motion sensor, motion detector, or any other suitable optical, mechanical, or electrical device, and the appropriate illuminator elements of the illuminator array 15 may be turned on and off to provide substantially independent images to each eye regardless of the position of the head 45. The head tracking system (or a second head tracking system) may provide for more than one head 45, 47 (where the head 47 is in the Figure 7 The directional backlight source described herein can be used to monitor the directional backlight source, and the same left-eye image and right-eye image can be provided to the left eye and right eye of each observer, thereby providing 3D to all observers. Similarly, similar operations can be achieved with all directional backlight sources described herein.

[0257] Figure 8 is a schematic diagram showing an embodiment of a multi-viewer directional display device as an example including an imaging directional backlight source. Figure 8 As shown in , at least two 2D images may be directed toward a pair of observers 45 , 47 such that each observer may view a different image on a spatial light modulator 48 . Figure 8 The two 2D images can be compared with Figure 7 The similar manner is generated because the two images will be displayed sequentially and synchronously with the source whose light is directed toward the two observers. One image is presented on the spatial light modulator 48 in a first stage, and the second image is presented on the spatial light modulator 48 in a second stage different from the first stage. Corresponding to the first stage and the second stage, the output illumination is adjusted to provide a first observation window and a second observation window 26, 44, respectively. An observer with two eyes in the window 26 will perceive the first image, while an observer with two eyes in the window 44 will perceive the second image.

[0258] Fig. 9 2D display systems may also utilize directional backlight sources for security and efficiency purposes, where the light may be directed primarily toward the eyes of a first observer 45, such as Fig. 9 In addition, Fig. 9 , although the first observer 45 may be able to observe the image on the device 50, the light is not directed toward the second observer 47. Therefore, the second observer 47 is prevented from observing the image on the device 50. Each of the embodiments of the present disclosure can advantageously provide autostereoscopic, dual image or anti-peeping display functions.

[0259] Fig.10 is a schematic diagram showing the structure of a time-multiplexed directional display device as an example of an imaging directional backlight source in a side view. In addition, Fig.10 An autostereoscopic display device is shown in side view, which may include a stepped waveguide 1 and a Fresnel lens 62, which is arranged to provide a viewing window 26 in a window plane 106 at a nominal viewing distance from the spatial light modulator for a substantially collimated output across the output surface of the stepped waveguide 1. A vertical diffuser 68 may be arranged to further extend the height of the window 26. The light may then be imaged by the spatial light modulator 48. The illuminator array 15 may include light emitting diodes (LEDs), which may be, for example, phosphor-converted blue LEDs, or may be separate RGB LEDs. Alternatively, the illuminator elements in the illuminator array 15 may include a uniform light source and a spatial light modulator arranged to provide separate illumination areas. Alternatively, the illuminator elements may include one or more laser sources. The laser output may be directed onto the diffuser by scanning, for example using a galvanometer scanner or a MEMS scanner. In one example, the laser may therefore be used to provide the appropriate illuminator elements in the illuminator array 15 to provide a substantially uniform light source with an appropriate output angle, and further provide a reduction in speckle. Alternatively, the illuminator array 15 may be an array of laser emitting elements. Additionally, in one example, the diffuser may be a wavelength converting phosphor so that the illumination may be at a different wavelength than the visible output light.

[0260] Another wedge-type directional backlight is generally discussed by U.S. Pat. No. 7,660,047, which is incorporated herein by reference in its entirety. Wedge-type directional backlights and optical valves further process light beams differently. In a wedge-type waveguide, light input at an appropriate angle will be output at a defined location on the major surface, but the light rays will exit at substantially the same angle and substantially parallel to the major surface. In contrast, light input at an angle to a stepped waveguide of an optical valve may be output from a point across the first side, where the output angle is determined by the input angle. Advantageously, the stepped waveguide of an optical valve may not require an additional light redirecting film to extract light toward the viewer, and angular non-uniformity of the input may not provide non-uniformity across the display surface.

[0261] The following description will now be based on and includes FIGS. 1 to 3. Fig.10 Some waveguides, directional backlight sources and directional display devices of the structure are described below. Except for the modified forms and / or additional characteristic structures that will now be described, the above description is also applicable to the following waveguides, directional backlight sources and display devices, but will not be repeated for the sake of brevity. The waveguides described below can be incorporated into the directional backlight sources or directional display devices described above. Similarly, the directional backlight sources described below can be incorporated into the directional display devices described above.

[0262] Fig.11 is a schematic diagram showing a directional display device including a directional display device and a control system. The arrangement and operation of the control system will now be described and can be applied to each of the display devices disclosed herein with modifications as necessary. The directional backlight source includes a waveguide 1 and an array 15 of lighting elements 15a-15n arranged as described above. The control system is arranged to selectively operate the lighting elements 15a-15n to direct light into a selectable viewing window.

[0263] The reflective end 4 focuses the reflected light. The Fresnel lens 62 may be arranged to cooperate with the reflective end 4 to realize an observation window at the observation plane. The transmissive spatial light modulator 48 may be arranged to receive light from a directional backlight source. The image displayed on the SLM 48 may be presented synchronously with the illumination of the light source of the array 15.

[0264] The control system may include a sensor system arranged to detect the position of the observer 99 relative to the display device 100. The sensor system includes a position sensor 406, such as a camera arranged to determine the position of the observer 408; and a head position measurement system 404, which may, for example, include a computer vision image processing system. The position sensor 406 may include known sensors, including sensors having a camera and an image processing unit arranged to detect the position of the observer's face. The position sensor 406 may also include a stereo sensor, which is arranged to improve the measurement of the longitudinal position compared to a monoscopic camera. Alternatively, the position sensor 406 may include a measurement of the interocular distance to give a measurement of the required position of the corresponding array of viewing windows from the directional display tile.

[0265] The control system may also include an illumination controller and an image controller 403 , both of which are provided with the detected position of the observer provided by the head position measurement system 404 .

[0266] The illumination controller comprises an LED controller 402 arranged to cooperate with the waveguide 1 to determine which light sources of the array 15 should be switched to direct light to the respective eyes of the observer 408, and an LED driver 400 arranged to control the operation of the light sources of the light source array 15 via drive lines 407. The illumination controller 74 selects the illuminator elements 15 to be operated in dependence on the position of the observer detected by the head position measurement system 72, so that the observation windows 26 into which the light is directed are located at positions corresponding to the left and right eyes of the observer 99. In this way, the lateral output directivity of the waveguide 1 corresponds to the observer position.

[0267] The image controller 403 is arranged to control the SLM 48 to display images. To provide an autostereoscopic display, the image controller 403 and the illumination controller can operate as follows. The image controller 403 controls the SLM 48 to display the left eye image and the right eye image multiplexed in time and the LED controller 402 operates the light source 15 to direct the light into the position corresponding to the left eye and the right eye of the observer in the observation window, and synchronously displays the left eye and the right eye images. In this way, the autostereoscopic effect is achieved using time division multiplexing technology. In one example, a single observation window can be illuminated by operating the light source 409 (which may include one or more LEDs) with a drive line 410, wherein the other drive lines are not driven as described elsewhere.

[0268] The head position measurement system 404 detects the position of the observer relative to the display device 100. The LED controller 402 selects the light source 15 to be operated according to the position of the observer detected by the head position measurement system 404, so that the observation window into which the light is directed is at a position corresponding to the left eye and the right eye of the observer. In this way, the output directivity of the waveguide 1 corresponding to the position of the observer can be achieved, so that the first image can be directed to the right eye of the observer in the first stage, and to the left eye of the observer in the second stage.

[0269] Thus, the directional display device may include a directional display apparatus and a control system arranged to control the light sources 15a to 15n.

[0270] Fig. 12A is a schematic diagram showing a perspective view of an optical stack of a directional display device including a directional waveguide with light input on the side opposite to the reflective side.

[0271] The reflective end 4 may be provided by a Fresnel mirror. In addition, a tapered region 204 may be arranged at the input of the waveguide 1 to increase the input coupling efficiency of the light sources 15a-15n in the array of illuminator elements 15 and to increase the uniformity of the illumination. A shielding layer 206 having holes 203 may be arranged to hide the light scattering region at the edge of the waveguide 1. The back reflector 300 may include facets 302 that may be curved and arranged to provide an observation window to the window plane from an optical window group provided by the imaging light source of the array 15. The optical stack 208 may include a reflective polarizer, a delay sheet layer, and a diffuser. The back reflector 300 and the optical stack 208 are further described in U.S. Patent Publication 2014-0240828, which is incorporated herein by reference in its entirety.

[0272] The spatial light modulator 48 may include a liquid crystal display, which may include an input polarizer 210, a TFT glass substrate 212, a liquid crystal layer 214, a color filter glass substrate 216, and an output polarizer 218. Red pixels 220, green pixels 222, and blue pixels 224 may be arranged in an array at the liquid crystal layer 214. White pixels, yellow pixels, additional green pixels, or other color pixels (not shown) may also be arranged in the liquid crystal layer to increase transmission efficiency, color gamut, or perceived image resolution.

[0273] Fig. 12B is a schematic diagram showing a perspective view of an optical window formed by a directional display device comprising a directional waveguide with a light input on the side opposite to the reflective side. Thus, the input surface 2 may be the end of the waveguide 1 opposite to the reflective end.

[0274] Fig. 12C2 is a schematic diagram showing a perspective view of an optical stack of a directional display device including a directional waveguide having an optical input on a side adjacent to a reflective side, as described elsewhere in U.S. Patent Publication No. 2016-0349444, which is incorporated herein by reference in its entirety. Waveguide 301 includes input sides 322, 324 with aligned light sources 317a-n and 319a-n on the respective sides. End 302 opposite to reflective end 304 can be arranged as an absorbing end or a reflecting end to provide low levels of crosstalk or improved efficiency, respectively.

[0275] Fig.12D 1 is a schematic diagram showing a perspective view of an optical window formed by a directional display device including a directional waveguide having a light input on a side adjacent to the reflective side. Light sources 317a-n and 319a-n at input facet 321 are arranged to provide optical windows 27a-n and 29a-n respectively about axis 197. Fresnel mirror 304 is arranged with first and second optical axes 287, 289. Thus, the input surface may be a side surface 322 of waveguide 301 extending away from reflective end 304 toward thinner end 3020.

[0276] Therefore, the directional backlight source includes a first guiding surface 6 and a second guiding surface 8, the first guiding surface being arranged to guide light by total internal reflection, and the second guiding surface comprising a plurality of light extraction feature structures 12 and an intermediate region 10 between the light extraction feature structures 12, the plurality of light extraction feature structures being oriented to guide light guided along waveguide 1, waveguide 301 in a direction allowing light to leave through the first guiding surface 6 as output light, and the light extraction feature structures being arranged to guide light along waveguides 1, 301.

[0277] Considering FIG. 12A to FIG. 12D The second guide surface 6 may have a stepped shape, wherein the light extraction feature 12 is a small facet between the intermediate regions 10. The light extraction feature 12 may have a positive optical power in a direction between the side surfaces 22, 24 or 322, 324 of the waveguide 1, 301, which extend between the first guide surface 6 and the second guide surface 8. The reflective end 4, 304 may have a positive optical power in a direction extending between the side surfaces 22, 24 or 322, 324 of the reflective end 4, 304, which extend between the first guide surface and the second guide surface 6, 8.

[0278] Thus, all sides 2, 4, 6, 8, 22, 24 provide reflections to achieve uniform illumination and low crosstalk in the privacy mode of operation. If features are applied to many areas of the surface, non-uniformities may be provided due to the spatial location of waveguide extraction losses at the features.

[0279] Therefore, the directional display device may include a waveguide, wherein the input surface 322 is a surface of a side of the waveguide 1 extending away from the reflective end 304 .

[0280] It is desirable to optimize the efficiency of polarization recycling in directional display devices.The present disclosure relates to the propagation of polarized light in directional backlights.

[0281] Fig.13 is a legend showing symbols for polarization electric vector orientation, retarder slow axis and polarization state and direction of light propagation used in other figures in this disclosure, unless otherwise indicated. The symbols are located on or near the corresponding light rays in the figures herein.

[0282] Fig.14A is a schematic luminance field diagram illustrating luminance variation for a wide angle mode of operation of a directional display. The isoluminance contours 518, 544 may be substantially rotationally symmetric in polar coordinates.

[0283] Angular viewing position 520 represents a desired on-axis viewing direction having a zero degree elevation angle and a zero degree lateral angle.

[0284] Angular viewing position 522 represents a desired off-axis viewing direction having an elevation angle of 20 degrees and a lateral angle of zero degrees. Such a viewing position may be provided for a user in a central position such that the display is rotated about a horizontal axis.

[0285] Angular viewing positions 524, 525 represent occasionally desired off-axis viewing directions having zero degree elevation angles and + / - 45 degree lateral angles. In wide angle mode, such viewing positions are likely to be occupied by intended users, so relatively high brightness is desired.

[0286] Angular viewing positions 526, 527 represent occasionally desirable off-axis viewing directions having 45 degree off-axis positions along respective axes 590, 592 that are 45 degrees from the lateral and elevation directions.

[0287] Fig. 14B is a schematic diagram showing the lateral variation of brightness of the wide-angle operating mode of the directional display with the viewing angle. Thus, as shown by line 542, the brightness distribution 540 at the lateral angle position 544 can have half of the peak brightness. Thus, in this illustrative example, the half-maximum full width of the lateral angle brightness distribution 540 can be 50 degrees. In addition, as shown by line 519, the brightness distribution can have greater than 10% of the peak brightness at the lateral angle position 518 of 45 degrees.

[0288] Fig. 14C1 is a schematic diagram showing the variation of display brightness with viewing angle for a wide angle mode of operation of a directional display. Thus, when a uniform white image is provided on the spatial light modulator in a wide angle mode at viewing angle positions 520, 522, the appearance of the display 100 is provided such that from each respective viewing angle position, the display brightness is greater than 50% of the peak brightness. When viewed from position 520, the peak brightness may be provided at the center of the display.

[0289] Advantageously, the display can be conveniently rotated about a horizontal axis while maintaining comfortable brightness for an on-axis observer in the lateral direction (0 degree lateral angle).

[0290] In addition, if Fig.14A The angular viewing positions 524, 526, 525, 527 shown in FIG. 5 may have a brightness between 2% and 50%.

[0291] A luminance field distribution can therefore be provided for the display so that the display can be conveniently viewed from a wide range of viewing angles.

[0292] The angular brightness distribution of a display operating in the privacy mode of operation will now be described.

[0293] Fig.15A is a schematic brightness field diagram, which shows the brightness change of the anti-peeping operation mode of the directional display; Fig. 15B is a schematic diagram showing the variation of brightness of the anti-peeping operation mode of the directional display with the viewing angle; and Fig. 15C is a schematic diagram showing the variation of display brightness with viewing angle in the anti-peeping operation mode of a directional display.

[0294] Desired and undesired viewing positions in the privacy mode of operation will now be described with reference to snoopers - that is, those observers who undesirably attempt to view images on the display when the display is operating in the privacy mode.

[0295] Angular viewing positions 520, 522 represent viewing directions typically desired by a primary display user operating the display in privacy mode.

[0296] Angular viewing positions 524, 525 represent undesirable off-axis viewing directions for a snooper positioned laterally relative to the display. It is desirable to reduce display brightness in the privacy protection mode of operation for such a snooper.

[0297] Angular viewing positions 526, 527 represent other undesirable and common off-axis viewing directions for a snooper.

[0298] In the anti-peeping operation mode, the lateral brightness distribution can be adjusted by controlling the directional backlight source 101 so as to provide a rotationally asymmetric trajectory 551 with a brightness of 50% and a rotationally asymmetric trajectory 553 with a brightness of 2%.

[0299] At an angular viewing position 524 of 45 degrees lateral angle and 0 degrees elevation, the brightness may be less than 2%, preferably less than 1.5%, and more preferably less than 1%, of the peak brightness of, for example, distribution 546. In this illustrative example, the relative brightness 555 at a lateral angle of 40 degrees and an elevation angle of 0 degrees may be 2%. Thus, the display may be provided with an angular brightness distribution to achieve low brightness for a lateral off-axis observer, thereby achieving anti-peeping operation.

[0300] Thus, the angular viewing positions 520, 522 may see a brightness greater than 50%. Advantageously, a comfortable display appearance may be provided in the privacy mode of operation such that the display is rotated about a horizontal axis.

[0301] At angular viewing positions 524, 525 having an elevation angle of zero and at angular viewing positions 526, 527 having an off-axis position of 45 degrees from the lateral and elevation directions along respective axes 590, 592, a brightness of less than 2% may be provided. Advantageously, the display may have limited visibility for such viewing positions.

[0302] A brightness level of 2% may adversely provide visibility of information on the display content. It is desirable to further reduce image visibility at the peeper locations at the upper quadrant locations 526, 527, such as to desirably reduce the privacy rating to less than 1%.

[0303] Fig.16A is a schematic diagram showing in side view a directional display including a directional waveguide and crossed A-plates 502, 504 arranged between a spatial light modulator 48 and a directional backlight source 101; and Fig. 16B is a schematic diagram showing, in a perspective front view, the orientation of the retarder and polarizer axes of an optical stack for a directional display comprising directional waveguides and crossed A-plates 502, 504.

[0304] Thus, the directional display includes a directional backlight 101 and a transmissive spatial light modulator 48 arranged to receive output light from the backlight 101. The directional backlight 101 may include a rear reflector 300 including reflective facets 303, 305 as described in U.S. Patent Publication 2014-0240828 and U.S. Patent Publication 2017-0339398, which are incorporated herein by reference in their entirety. The interlayer 510 may include a delay plate as described in U.S. Patent Application 15 / 860,853 (Agent Reference No. 400001) entitled "Optical stack for imaging directional backlights" filed on January 3, 2018, which is incorporated herein by reference in its entirety.

[0305] Further considerations Fig. 12A , Fig. 12B and Fig.16A The backlight source may also include: a light source array 15; a waveguide 1, which is arranged to receive input light from the light source 15 at different input positions, and includes: opposite first and second guide surfaces 6, 8, the opposite first and second guide surfaces 6, 8 are used to guide the input light along the waveguide 1; side surfaces 22, 24, which extend between the first and second guide surfaces 6, 8; and a reflective end 4, which is used to reflect the input light back along the waveguide 1; wherein the second guide surface 8 is arranged to deflect the reflected input light through the first guide surface 6 as output light, and the waveguide 1 is arranged to image the light source 15 in a lateral direction between the sides of the waveguide 1, so that the output light from the light source is guided to the corresponding optical window 26 in an output direction distributed according to the input position of the light source 15.

[0306] The first guiding surface 6 may be arranged to guide light by total internal reflection, and the second guiding surface 8 may include light extraction feature structures 12 and an intermediate region 10 between the light extraction feature structures 12, wherein the light extraction feature structures 12 are oriented to deflect reflected input light through the first guiding surface 6 as output light, and the intermediate region 10 is arranged to guide light through the waveguide 1 without extracting the light.

[0307] The light extraction feature may be curved and have positive optical power in a lateral direction between the sides 22, 24 of the waveguide 1 extending between the first and second guide surfaces 6, 8. The reflective end 4 may have a lateral positive optical power extending between the sides 22, 24 of the waveguide 1 extending between the first and second guide surfaces 6, 8. The waveguide 1 may include an input end 2 opposite the reflective end 4, and the light source 15 may be arranged to input light into the waveguide 1 through the input end 2. Fig. 12CAs shown, the light source 15 may be arranged to input light into the waveguide through the sides 22 , 24 of the waveguide 1 .

[0308] The input polarizer 210 is arranged on the input side of the spatial light modulator 48 between the backlight 101 and the spatial light modulator 48 , and the output polarizer 218 is arranged on the output side of the spatial light modulator 48 .

[0309] The additional polarizer 500 is arranged on the input side of the input polarizer 210 between the input polarizer 210 and the backlight 101. The additional polarizer may be a reflective polarizer, such as a DBEF TM .

[0310] Therefore, the display device may include an additional polarizer 500, which is a reflective polarizer arranged on the input side of the input polarizer 210, and is arranged to transmit the first polarization component 704 of the output light 700 from the waveguide 1, and reflect the second polarization component 706 of the output light having a polarization state orthogonal to the polarization state of the first polarization component 704 as the light 702 as the blocking light; and a rear reflector 300 is arranged behind the second guide surface 8 of the waveguide 1, and the rear reflector is arranged to reflect the blocking light to supply it back to the spatial light modulator 48, and the rear reflector 300 includes a linear array of paired reflective angle facets 303, 305 extending in a predetermined direction perpendicular to the normal of the spatial light modulator 48, so that the rear reflector 300 converts the blocking light with two reflections from a pair of diagonal facets as the polarization of the light 702 into the polarization of the first polarization component 704. As shown in FIG. Fig. 16B As further shown, the pair of reflective angle facets 303, 305 may be curved and have optical power in a lateral direction.

[0311] The additional corrective retarder 506 is arranged to rotate the polarization component 706 reflected by the reflective polarizer 500. In the illustrative example, the slow optical axis of the retarder 506 can be at an angle of 22.5 degrees to the electric vector transmission direction of the reflective additional polarizer 500, which can be 0 degrees relative to the transverse direction. Such an arrangement can, for example, include an in-plane switching LCD (IPS-LCD), in which the output polarizer 218 is set to 90 degrees to the transverse direction. In an embodiment including a twisted nematic LCD (TN-LCD), the corrective retarder 506 can be omitted. Advantageously, the polarization component 706 reflected by the reflective polarizer is incident on the elongated facets 303, 305 of the rear reflector at 45 degrees relative to the transverse direction and is rotated to a polarization component 704 transmitted through the reflective additional polarizer 500 and the input polarizer 210.

[0312] Thus, the additional polarizer 500 may be arranged to provide increased display brightness by recycling light from the directional backlight 101 and the back reflector 300. Advantageously, display brightness may be increased compared to embodiments in which the additional polarizer 500 is an absorbing polarizer.

[0313] like Fig.11 As further shown, the display device may also include a display apparatus according to any of the preceding claims; and a control system 400 arranged to control the light source 15. Advantageously, a display may be provided that may be arranged to switch between a wide-angle mode and a privacy mode.

[0314] Modification of the angular privacy performance of the display will now be further described.

[0315] At least one retarder, which may be a pair of crossed A-plates 502, 504, is arranged between the additional polarizer 500 and the input polarizer 210. Fig.16A In an embodiment of the present invention, the additional polarizer 500 is arranged on the input side of the input polarizer 210, and the pair of crossed A-plates 502, 504 are arranged between the additional polarizer 500 and the input polarizer 210. In this embodiment, the at least one retarder can be one of the pair of crossed A-plates 502, 504 or C-plate 560, as will be described elsewhere herein.

[0316] The angular brightness viewing characteristics of the display will now be described. Fig.16A -B displays the operation.

[0317] Fig.17A is a schematic brightness field diagram showing the brightness of the display in the anti-peeping mode of operation. Fig. 16B Variations in brightness of the optical stack; Fig. 17B is a schematic diagram showing the variation of brightness of the anti-peeping operation mode of the directional display with the viewing angle; and Fig. 17C is a schematic diagram showing the Fig. 16B Variation of display brightness with viewing angle in an anti-peeping operating mode of a directional display of an optical stack.

[0318] In this disclosure, the coordinates of a position in polar space are described as polar coordinates, where the transverse angle refers to the angle in the transverse direction (y-axis) and the elevation angle refers to the angle in the vertical direction (x-axis). These terms provide coordinates in the brightness field diagram, such as Fig.17A As shown. Positive lateral angles and negative lateral angles correspond to viewing the display from the right and left, respectively; and positive elevation angles and negative elevation angles correspond to viewing the display from above or below, respectively. Here, the description of polar coordinates is not based on polar angles (tilted from the normal direction) or azimuth angles (rotated coordinates).

[0319] The crossed A-plates 502, 504 and the additional polarizer 500 can be arranged to provide a reduced brightness region 557 in the quadrant where the display is viewed. The brightness region 557 is a region of reduced brightness in an angular region having non-zero lateral and elevation angles. The brightness quadrants can be arranged symmetrically about the 45 degree axes 590, 592 of the brightness field distribution, for example to advantageously reduce brightness to the viewer angular positions 526, 527.

[0320] like Fig. 17B As shown, along the 45 degree axis of the brightness field diagram, a distribution 547 can be provided, which is similar to the distribution 547 having a brightness of 521. Fig. 15B Compared to distribution 546, the brightness at trajectory 559 can be reduced.

[0321] Advantageously, the brightness of undesirable output light is reduced for the peepers 526, 527 in the upper viewing quadrant. In addition, as will be described herein, the brightness of the head-on angle viewing position 520 and the off-axis viewing positions 522, 524, 525 can be minimally reduced. Fig. 17C As shown, the privacy protection of the display can be improved for a peeper at angled viewing positions 526, 527 without reducing the display efficiency for the desired viewing position.

[0322] In the illustrative example, the brightness of the display at viewing positions 526, 527 can be reduced by 50%, thereby reducing the privacy protection level from 2% to 1%. In operation, the inventors have experienced that such a difference in perceived brightness can provide an effective improvement in the privacy protection performance of the display.

[0323] We will now describe Fig.16A The performance of the display in wide-angle mode.

[0324] Fig.18A is a schematic brightness field diagram showing the wide-angle operating mode. Fig. 16B Variations in brightness of the optical stack; Fig.18B is a schematic diagram showing the variation of brightness with viewing angle in a wide-angle operating mode of a directional display; and Fig.18C is a schematic diagram showing the Fig. 16B Variation of display brightness with viewing angle in a wide-angle operating mode of a directional display of an optical stack.

[0325] Thus, for a given polar angular position, the brightness in the quadrant defined by position 557 may be reduced in proportion to Fig.17A590, 592 can advantageously achieve a small reduction in the maximum width of the half-height full width. Because the brightness in the upper quadrant can be significantly higher than the anti-peep mode of operation, the user can still clearly see the display in the angled viewing positions 526, 527. In addition, as will be described, the brightness can be substantially unchanged in the lateral (zero elevation angle) and vertical (zero lateral angle) directions, which are more common viewing positions for users of the display in the wide-angle mode.

[0326] Advantageously, wide angle mode performance may have a low impact on conventional display usage.

[0327] Fig.19A 630. A corrective retarder 630 may include a birefringent material represented by an index ellipsoid 632 having a slow axis orientation 634 at 0 degrees from the x-axis and having a thickness 631. Normal ray 636 propagates such that the path length in the material is the same as thickness 631. Ray 637 in the yz plane has an increased path length; however, the birefringence of the material is substantially the same as ray 636. By comparison, ray 638 in the xz plane has an increased path length in the birefringent material and additionally has a birefringence different from that of normal 636.

[0328] Therefore, the retardation of the retarder 630 depends on the angle of incidence of the corresponding light ray and also on the plane of incidence, ie, the light ray 638 in the xz plane will have a different retardation than the normal 636 and the light ray 637 in the yz plane.

[0329] The interaction of polarized light with retarder 630 will now be described. To distinguish from the first and second polarization components during operation of directional backlight 101, the following explanation will refer to third and fourth polarization components.

[0330] Fig.19B is a schematic diagram showing in perspective the illumination of the retardation layer by off-axis light of a third linear polarization state at 90 degrees to the x-axis, and Fig.19C 63 is a schematic diagram showing in perspective the illumination of the retardation layer by off-axis light of a fourth linear polarization state at 0 degrees to the x-axis. In such an arrangement, the incident linear polarization state is aligned with the optical axis of the birefringent material represented by the ellipse 632. Therefore, no phase difference between the third orthogonal polarization component and the fourth orthogonal polarization component is provided, and no change in the polarization state of the linear polarization input is produced for each light ray 636, 637, 638.

[0331] Fig.19D630 is a schematic diagram showing in perspective the illumination of the retarder layer 630 by off-axis light of a linear polarization state at 45 degrees. The linear polarization state can be decomposed into a third polarization component and a fourth polarization component orthogonal to and parallel to the direction of the slow axis 634, respectively. The retarder thickness 631 and the material delay represented by the refractive index ellipsoid 632 can provide a net effect of relatively shifting the phase of the third polarization component and the fourth polarization component incident thereon by half a wavelength in the normal direction represented by the light ray 636 for the design wavelength. The design wavelength can be, for example, in the range of 500nm to 550nm.

[0332] At the design wavelength and for light propagating normally along ray 636, then at -45 degrees the output polarization may be rotated 90 degrees to a linear polarization state 640. Light propagating along ray 637 may see a phase difference that is similar to, but different from, the phase difference along ray 637 due to the thickness variation, and may therefore output an elliptical polarization state 639 that may have a major axis similar to the linear polarization axis of the output light of ray 636.

[0333] In contrast, the phase difference of the incident linear polarization state along the ray 638 can be significantly different, and in particular can provide a lower phase difference. Such a phase difference can provide an output polarization state 644 that is substantially circular at a given tilt angle 642.

[0334] In embodiments of the present invention, the slow axis generally refers to the orientation orthogonal to the normal direction, where linearly polarized light having an electric vector direction parallel to the slow axis travels at the slowest speed. The slow axis direction is the direction in which the light has the highest refractive index at the design wavelength.

[0335] For positive dielectric anisotropic uniaxial birefringent materials, the slow axis direction is the extraordinary axis of the birefringent material. The ordinary axis in such materials is usually parallel to the normal direction and orthogonal to both the normal direction and the slow axis.

[0336] The terms half-wavelength and quarter-wavelength refer to the operation of the retarder for a design wavelength λ0 which can typically be between 500nm and 570nm. A retarder provides a phase shift between two perpendicular polarization components of a light wave incident thereon and is characterized by the amount of relative phase it imparts to the two polarization components; which is related to the birefringence Δn and thickness d of the retarder by the following formula

[0337] Γ=2.π.Δn.d / λ0 Equation 1

[0338] where Δn is defined as the difference between the extraordinary refractive index and the ordinary refractive index, i.e.

[0339] Δn=n e -n o Equation 2

[0340] For a half-wave retarder, the relationship between d, Δn and λ0 is chosen so that the phase shift between the polarization components is Γ = π. For a quarter-wave retarder, the relationship between d, Δn and λ0 is chosen so that the phase shift between the polarization components is Γ = π / 2.

[0341] The term half-wave retarder herein generally refers to light propagating perpendicular to the retarder and perpendicular to the spatial light modulator.

[0342] In this disclosure, "A-plate" refers to an optical retarder utilizing a birefringent material layer whose optical axis is parallel to the plane of the layer. The plane of the retarder means that the slow axis of the retarder extends in one plane, ie, the xy plane.

[0343] The “positive A-plate” refers to a positive birefringent A-plate, that is, an A-plate having a positive Δn.

[0344] In the present disclosure, "C-plate" refers to an optical retardation plate using a birefringent material layer whose optical axis is perpendicular to the plane of the layer. "Positive C-plate" refers to a positive birefringent C-plate, ie, a C-plate with positive Δn.

[0345] In the present disclosure, "O-plate" refers to an optical retardation plate using a birefringent material layer whose optical axis has a component parallel to the plane of the layer and a component perpendicular to the plane of the layer. "Positive O-plate" refers to a positive birefringent O-plate, i.e., an O-plate with positive Δn.

[0346] Achromatic retarders may be provided, wherein the material of the retarders has an optical thickness Δn.d that varies with wavelength λ, such as

[0347] Δn.d / λ=κ Equation 3

[0348] Where κ is substantially a constant. Examples of suitable materials include modified polycarbonates from Teijin Films. An achromatic retarder may be provided in this embodiment to advantageously minimize color variations between polar viewing directions with low brightness reduction and polar viewing directions with increased brightness reduction, as described below.

[0349] Various other terms used in this disclosure related to retarders and liquid crystals will now be described.

[0350] Uniform alignment refers to the alignment of the liquid crystal in a switchable liquid crystal display, where the molecules are aligned substantially parallel to the substrate. Uniform alignment is sometimes referred to as planar alignment. Uniform alignment can typically be provided with a small pre-tilt, such as 2 degrees, so that the molecules on the surface of the alignment layer of the liquid crystal cell are slightly tilted, as described below. The pre-tilt is arranged to minimize degeneracy in cell switching.

[0351] In the present disclosure, the vertical alignment is a state in which rod-like liquid crystal molecules are aligned substantially perpendicular to the substrate. In discotic liquid crystals, the vertical alignment is defined as a state in which the axis of the columnar structure formed by the discotic liquid crystal molecules therein is aligned perpendicular to the surface. In the vertical alignment, the pretilt is a tilt angle of the molecules close to the alignment layer and is generally close to 90 degrees and may be, for example, 88 degrees.

[0352] Liquid crystal molecules with positive dielectric anisotropy are switched from a homeotropic alignment (such as an A-plate retarder alignment) to a homeotropic alignment (such as a C-plate or O-plate retarder alignment) by an applied electric field.

[0353] Liquid crystal molecules with negative dielectric anisotropy are switched from a homeotropic alignment (such as a C-plate or O-plate retarder alignment) to a uniform alignment (such as an A-plate retarder alignment) by an applied electric field.

[0354] Rod-shaped molecules have positive birefringence, so that n e >n o , as described in Equation 2. The discotic molecule has negative birefringence, so that n e <n o .

[0355] Positive retardation plates such as A plates, positive O plates and positive C plates can generally be provided by stretched films or rod-like liquid crystal molecules. Negative retardation plates such as negative C plates can be provided by stretched films or discotic liquid crystal molecules.

[0356] Parallel cell alignment refers to alignment directions of the homogeneous alignment layers being parallel or more typically antiparallel. For pre-tilted homeotropic alignment, the alignment layers may have substantially parallel or antiparallel components. Hybrid aligned cells may have one homogeneous alignment layer and one homeotropic alignment layer. Twisted cells may be provided by alignment layers that do not have parallel alignment, for example oriented at 90 degrees to each other.

[0357] Crossed A-plates, C-plates and O-plates are known retarder elements for use in LCDs to compensate for contrast degradation at off-axis viewing positions, for example in European Patent Publication EP1726987, which is incorporated herein by reference in its entirety.

[0358] Thus, in prior art arrangements, crossed A-plates, C-plates and O-plates may be provided between the input polarizer and the output polarizer to operate in conjunction with a liquid crystal layer also disposed between the input polarizer and the output polarizer. In such prior art arrangements, the retarders are arranged to compensate for the variation in birefringence of the liquid crystal molecules with viewing angle. Such compensation is arranged to provide increased display contrast for off-axis viewing positions. The contrast viewing angle properties of the display may therefore be improved.

[0359] In this embodiment, a crossed A-plate, C-plate or O-plate is provided between the additional polarizer 500 and the input polarizer 210. Such a polarizer and retarder arrangement does not change the contrast of the off-axis viewing position of the display device, and does not further reduce the off-axis brightness as the arrangement in the prior art. In addition, such a retarder layer does not cooperate with the liquid crystal material in the transmissive spatial light modulator 48.

[0360] We will now describe this diagram relative to the Poincare sphere. Fig. 16B The operation is for coaxial light.

[0361] Fig.19E is a schematic diagram showing a Poincare sphere 600 representation of coaxial polarization control across an A-plate retarder in a perspective front view, for example, as Fig. 16B As shown, in the example of a half-wave plate for an A-plate. The Poincare sphere can represent a general elliptical polarization state, with a horizontal polarization state position 602, a +45 degree linear polarization state position 604, a vertical polarization state position 606, and circular polarization state positions 601, 603. In operation, the input horizontal polarization state 602 is rotated 90 degrees by the first A-plate 502 in the direction of arrow 614 about the axis 610 in the Poincare sphere, which represents a 45 degree orientation of the polarization state 606 for the first wavelength in real space. If the retarder is dispersive, a polarization state 616 is provided for the second wavelength. Such polarization states are elliptical and therefore provide reduced brightness if analyzed, thereby producing a chromatic aberration output for the light from the first A-plate 502. A second A-plate having axis 609 rotates polarization states 606, 616 in relative directions indicated by arrows 618 so that the chromaticity of A-plate 504 compensates for the chromaticity of A-plate 502 and provides an achromatic polarization state 602 at input polarizer 210. Advantageously, the chromaticity of light at viewing location 520 is substantially the same as the chromaticity of the input light.

[0362] Fig. 16B A pair of retarders 502, 504 each comprises a single A-plate. It may be desirable to provide further control over chromaticity in reduced brightness angular viewing positions. Composite retarders will now be described.

[0363] Fig.19F is a schematic diagram showing in perspective front view a Fig. 16BThe orientation of the retarder axis of the A-plate retarder of the optical stack including the composite retarder. The functions of A-plates 502, 504 can be provided by two A-plates, respectively, which are arranged in respective orientations, as will be described. In the illustrative example, A-plate 502 can alternatively be provided by A-plates 580, 582 having retarder orientations 581, 583 of -22.5 degrees and +22.5 degrees. In addition, A-plate 504 can alternatively be provided by A-plates 584, 586 having retarder orientations 585, 587 of 67.5 degrees and +112.5 degrees. Therefore, A-plate 580 crosses A-plate 584, and A-plate 582 crosses A-plate 586.

[0364] Thus, a pair of retarders 502, 504 each includes a plurality of A-plates 580, 582 and 584, 586 having respective slow axes 581, 583 and 585, 587 aligned at different angles to one another.

[0365] In this embodiment, "crossed" means that the slow axis is at an angle of 90°, or close enough to 90° to function as a crossed A-plate. Fig.19F The slow axes of the pair of A-plates in the 2000 MHz and 2000 MHz do cross each other at an angle less than 90°, but in this sense they do not "cross" when used together as a single A-plate.

[0366] We will now describe this diagram relative to the Poincare sphere. Fig.19F The operation is for coaxial light.

[0367] Figure 19G is a schematic diagram showing in perspective front view Fig.19F A Poincare sphere 600 is shown for coaxial polarization control of a first composite A-plate retarder pair 580, 582. In operation, first retarder 580 provides polarization state rotation to polarization states 604, 622 at angle 610 in direction 620 about axis 611 for respective first and second wavelengths.

[0368] Since the retardation is compensated for by the two respective wavelengths corresponding to states 604, 622, the second retarder 582 provides an additional polarization state rotation about axis 613 at angle 612 to state 606 that is substantially achromatic in directions 624, 626. Thus, the composite retarder 580, 582 achieves a substantially achromatic linear polarization state 606 for incident on the second composite retarder 584, 586.

[0369] Fig.19H is a schematic diagram showing in perspective front view Fig.19FThe Poincare sphere 600 of the coaxial polarization control of the second composite A-plate retarder pair 584, 586 is shown. Therefore, the linear polarization state 606 from the first pair 580, 582 is rotated about axis 615 in directions 628, 630 at an angle 614, and further rotated about axis 617 in direction 632 at an angle 616 to the horizontal linear polarization state 602. Therefore, the composite retarder 580, 582, 584, 586 is rotated with the horizontal linear polarization state 602. Fig.19E The single A-plate operates in a similar manner.

[0370] Advantageously, therefore, a composite retarder may be provided to replace Fig. 16B Advantageously, further degrees of freedom in the design of the retarder stack may be provided to achieve improved off-axis chromaticity compensation.

[0371] In this embodiment, in cooperation with the privacy directional backlight 101 device, the off-axis brightness is desirably reduced to achieve improved privacy characteristics in certain viewing directions.

[0372] Angular brightness control of the crossed A-plates 502, 504 between the additional polarizer 500 and the input polarizer 210 will now be described for various off-axis illumination arrangements.

[0373] Fig. 20A is a schematic diagram showing in perspective the illumination of crossed A-plate retardation layers by off-axis polarized light having a positive elevation angle. A linear polarizer 500 having an electric vector transmission direction 501 is used to provide a linear polarization state 704 parallel to the transverse direction on a first A-plate 502 of the crossed A-plates 502, 504. The slow axis direction 503 is tilted +45 degrees with respect to the transverse direction. The retardation of the retardation plate 502 in the positive elevation direction for the off-axis angle θ1 provides a synthetic polarization component 650, which is generally elliptical at output. The polarization component 650 is incident on a second A-plate 504 of the crossed A-plates 502, 504, the second A-plate having a slow axis direction 505 orthogonal to the slow axis direction 503 of the first A-plate 502. In Fig. 20A In the incident plane of , the retardation of the off-axis angle θ1 of the second A-plate 504 is equal and opposite to the retardation of the first A-plate 502. Therefore, a net zero retardation is provided for the incident polarization component 704, and the output polarization component is the same as the input polarization component 704.

[0374] The output polarization component is aligned with the electric vector transmission direction of the LCD input polarizer 210 and is therefore efficiently transmitted. Advantageously, there is substantially no loss for light rays having a lateral angle component of zero, so that full transmission efficiency is achieved.

[0375] Fig. 20Bis a schematic diagram showing in perspective the illumination of the crossed A-plate retardation layers by off-axis polarized light having a negative transverse angle. Thus, the input polarization component is converted by the first A-plate 502 into an intermediate polarization component 652, which is generally an elliptical polarization state. The second A-plate 504 again provides the same and opposite retardation as the first A-plate, so that the output polarization component is the same as the input polarization component 704, and the light is effectively transmitted through the input polarizer 210.

[0376] Thus, at least one retarder comprises a pair of retarder plates 502, 504 having intersecting slow axes in the plane of the retarder plates 502, 504, in the present embodiment the xy plane. The pair of retarder plates 502, 504 have slow axes 503, 505 that can each extend at 45° relative to the electric vector transmission direction parallel to the electric vector transmission of the input polarizer 210 in the case where the additional polarizer 500 is arranged on the input side of the input polarizer 210, or the pair of retarder plates have slow axes that can each extend at 45° relative to the electric vector transmission direction parallel to the electric vector transmission of the output polarizer 218 in the case where the additional polarizer 500 is arranged on the output side of the input polarizer 210.

[0377] Advantageously, there are substantially no losses for light rays having an elevation angle component of zero, so that full transmission efficiency is achieved.

[0378] Fig. 20C is a schematic diagram showing in perspective the illumination of the crossed A-plate retardation layers by off-axis polarized light having a positive elevation angle and a negative transverse angle. The polarization component 704 is converted into an elliptically polarized component 654 by the first A-plate 502. Fig. 20A -B arrangement, the birefringent material of the second A-plate 504 is not aligned with the compensation angle of the birefringent material of the first A-plate 502, and thus the resulting elliptical component 656 is output from the second A-plate 504. The elliptical component 656 is analyzed by the input polarizer 210 at a reduced brightness compared to the input brightness of the first polarization component 704.

[0379] Fig.20D is a schematic diagram showing in perspective the illumination of the crossed A-plate retardation layers by off-axis polarized light having a positive elevation angle and a positive transverse angle. Fig. 20C Illustrating in a similar manner, the first and second A-plates 502, 504 provide polarization components 658 and 660 since the net retardation of the first and second retarders provides no compensation.

[0380] Thus, for light having a non-zero lateral angle and a non-zero elevation angle component, the brightness is reduced. Advantageously, the privacy of the display may be improved for a peeper disposed in the viewing quadrant without substantially reducing the light efficiency for the primary display user.

[0381] Now it will be relative to Fig.21A To describe the simulated change of the transmitted brightness field, the figure shows Fig. 16B Schematic brightness field diagram of the change of the transmission brightness of the optical stack, where the A plates 502 and 504 are coaxial light at the design wavelength λ o a quarter wave plate at Fig. 21B is a schematic brightness field diagram, which shows Fig. 16B The variation of the transmitted brightness of an optical stack, where the retardation layer is coaxial with the light at the design wavelength λ o The half-wave plate at .

[0382] Fig.21A The isoluminance contours are shown in 10% steps, so that the brightness at the angular viewing position 526 is 80% of the peak brightness. By comparison, for Fig. 21B For the arrangement of 520, the brightness at the angle viewing position 526 is about 65% of the peak brightness. In both arrangements, the head-on brightness for the angle viewing position 520 is unchanged.

[0383] Advantageously, the selection of the retardation of the A-plate can be used to provide a desired brightness reduction in the viewing quadrant. Additionally, achromatic retarders can be used to minimize color changes with viewing angle.

[0384] For off-axis angles that are oriented vertically and horizontally relative to the display orientation, it may be desirable to further reduce the brightness of the privacy display.

[0385] Fig. 21C is a schematic diagram showing, in a perspective front view, the orientation of the retarder and polarizer axes of an optical stack for a directional display including an additional polarizer and an input polarizer arranged at + / - 45 degrees and crossed A-plates. Such an arrangement can be provided for a twisted nematic (TN) LCD. Optionally, an in-plane switching (IPS) LCD may also include retarders (not shown) arranged to rotate the polarization state relative to the additional polarizer 500 and the input polarizer 210. Thus, the additional polarizer 500 and the input polarizer 210 may have polarizer transmission directions 501, 211 oriented at +45 degrees, and the retarders 502, 504 may have retarder orientations 503, 505 at 90 degrees and 0 degrees, respectively.

[0386] Fig.21D is a schematic brightness field diagram, which shows Fig. 21C The change in transmission brightness of the optical stack of FIG. 5, wherein the retardation layer is a quarter wave plate. Thus, reduced brightness transmission can be provided for observation positions 525, 529, while substantially no reduced brightness can be provided for positions 520, 526.

[0387] Advantageously, the vertical and lateral viewing positions may have reduced brightness, thereby improving the privacy level in both vertical and horizontal viewing directions.

[0388] The construction of an optical stack including crossed A-plates will now be described.

[0389] Fig.22A -D is a schematic diagram showing an optical stack including crossed A-plates in side view. Fig.22A The input polarizer 210 and the additional polarizer 500 are shown to include a protective layer 550, which may be TAC (triacetate cellulose), for example, surrounding an absorbing polarizer layer 552, such as an iodine-doped PVA layer. An adhesive layer 556, which may be an optically clear adhesive layer and / or a pressure sensitive adhesive layer, may be arranged to attach the crossed A-plates 502, 504.

[0390] Fig. 22B It is shown that the absorbing polarizer 500 can be provided by a reflective polarizer and can be as Fig.16A -An additional delay layer 506 is provided as shown in FIG.

[0391] It is desirable to reduce the thickness of the input polarizer stack.

[0392] Fig. 22C It is shown that one of the protective layers for the input polarizer may be provided by a second A-plate 504. For example, a birefringent TAC substrate may be provided with combined protective and A-plate properties. Advantageously, thickness and cost may be reduced.

[0393] Fig.22D An arrangement is shown in which the additional polarizer 500 is provided by (i) an absorbing polarizer 552, 550 and a protective layer comprising an A-plate 502 and (ii) a reflective polarizer 549. Advantageously, leakage from the reflective polarizer 549 may be reduced.

[0394] An arrangement in which crossed A-plates are arranged at the output of the spatial light modulator 48 will now be described.

[0395] Fig.23A is a schematic diagram showing in side view a directional display comprising a directional waveguide 1 and crossed A-plates 502, 504 arranged in front of a spatial light modulator 48; and Fig. 23B is a schematic diagram showing in perspective front view a Fig.23A Orientation of the retarder and polarizer axes of the optical stack.

[0396] The additional polarizer 500 is arranged on the output side of the output polarizer 218; and a pair of crossed A-plates are arranged between the additional polarizer 500 and the output polarizer 218. The additional polarizer 500 is arranged on the output side of the output polarizer, and the pair of crossed A-plates 502, 504 are arranged between the additional polarizer and the input polarizer.

[0397] The operation and advantages of the display are similar to those of the reference FIG. 17A to FIG. 18C Such an arrangement may be provided in a display without a reflective polarizer.

[0398] It is desirable to reduce the number of separate optical layers in a switchable directional display that includes mitigation for snoopers in the viewing quadrant.

[0399] Fig.24A is a schematic diagram showing in side view a directional display including a directional waveguide and a C-plate 560 disposed between a spatial light modulator 48 and a directional backlight source 101; and Fig. 24B is a schematic diagram showing in perspective front view a Fig.24A Orientation of the retarder and polarizer axes of the optical stack.

[0400] A C-plate 560 having an optical axis direction 561 is arranged between the additional polarizer 500 and the input polarizer 210, and its polarization transmission direction 211 is parallel to the polarization transmission direction 501 of the additional polarizer 500. Therefore, the additional polarizer 500 is arranged on the input side of the input polarizer 210, and the C-plate is arranged between the additional polarizer 500 and the input polarizer 210.

[0401] Fig.25A is a schematic diagram showing a directional display including a directional waveguide 1 and a C-plate 560 arranged in front of a spatial light modulator 48 in a side view; and Fig.25B is a schematic diagram showing in perspective front view a Fig.25A The orientation of the retarder and polarizer axes of the optical stack. The additional polarizer 500 is arranged on the output side of the output polarizer 218; and the C-plate 560 is arranged between the additional polarizer 500 and the output polarizer 218.

[0402] A C-plate 560 having an optical axis direction 561 is arranged between the additional polarizer 500 and the output polarizer 218, and its polarization transmission direction 219 is parallel to the polarization transmission direction 501 of the additional polarizer 500. Therefore, the additional polarizer 500 is arranged on the output side of the output polarizer 218, and the C-plate is arranged between the additional polarizer 500 and the output polarizer 218.

[0403] The operation of the C-plate between the parallel polarizers 500, 210 will now be described.

[0404] Fig.26A is a schematic diagram showing in perspective the illumination of the C-plate layer by off-axis polarized light having a positive elevation angle. An incident linear polarization component 704 is incident on the birefringent material 632 of the C-plate 560 in an optical axis direction 507 perpendicular to the plane of the retarder 560. Polarization component 704 sees no net phase difference when transmitted through the liquid crystal molecules, and thus the output polarization component is the same as component 704. Therefore, maximum transmission can be seen through the polarizer 210. Therefore, at least one retarder includes a retarder 560 having a slow axis 561 perpendicular to the plane of the retarder 560, i.e., the xy plane. The retarder 560 having a slow axis perpendicular to the plane of the retarder includes a C-plate.

[0405] The C-plate may comprise a transparent birefringent material such as polycarbonate or a reactive mesogen cast onto a substrate that provides homeotropic alignment, for example; Zeonex TM Cyclic olefin polymer (COP); discotic polymer; and NittoDenko TM Bi-stretch polycarbonate.

[0406] Fig.26B is a schematic diagram showing in perspective the illumination of a C-sheet layer by off-axis polarized light having a negative transverse angle. Fig.26A As with the arrangement of FIG. 1 , polarization state 704 sees no net phase difference and is transmitted with maximum brightness.

[0407] Fig.26C is a schematic diagram showing in perspective the illumination of a C-sheet layer by off-axis polarized light having a positive elevation angle and a negative transverse angle. Fig.26A Compared to the arrangement of -B, polarization state 704 is resolved into eigenstates 703, 705 with respect to birefringent material 632, thereby providing a net phase difference when transmitted through retarder 560. Fig.26A The resulting elliptically polarized component 656 is transmitted through polarizer 210 with reduced brightness compared to the light shown in -B.

[0408] Fig.26D is a schematic diagram showing in perspective the illumination of a C-plate layer by off-axis polarized light having a positive elevation angle and a positive transverse angle. Fig.26C In a similar manner, the polarization component 704 is decomposed into eigenstates 703, 705 that experience a net phase difference and provide an elliptically polarized component 660 that reduces the brightness of the corresponding off-axis rays after transmission through the polarizer.

[0409] Advantageously, compared to a single plate, the crossed A plates may each comprise a single stretched material which is less expensive than the C plates. Additional achromatic compensation may be more easily provided.

[0410] Fig.27A is a schematic brightness field diagram, which shows Fig. 24B The variation of the transmitted brightness of an optical stack in which the retardation layer is a half-wave plate. Therefore, the brightness field distribution is similar to that of the A-plate including the cross Fig. 21B Similar.

[0411] In this disclosure, the brightness field diagram represents the polar variation of transmitted brightness with viewing angle.

[0412] Fig.27B is a schematic brightness field diagram, which shows Fig. 24B The variation of the transmitted brightness of an optical stack of , where the retardation layer is a full-wave plate. For example, Fig.17A An increased brightness reduction is provided in the viewing quadrant for viewer angular positions 226, 227.

[0413] Advantageously, enhanced image privacy from snoopers can be provided in the viewing quadrant without reducing oncoming brightness compared to arrangements without a C-plate between the parallel input or output polarizers and the additional polarizer. In addition, the thickness and complexity of the optical stack can be reduced, thereby reducing cost.

[0414] It would be desirable to provide a further reduction in chromaticity variation with respect to viewing angle.An illustrative example simulation of a high retardation C-plate comprising a 650 nm retardation for a 500 nm nominal wavelength will now be described.

[0415] Fig.28A is a schematic brightness field diagram, which shows Fig. 24B The change in transmitted brightness of an optical stack including a high retardation layer.

[0416] Fig.28B -C is a schematic brightness field diagram, which shows the high delay layer Fig. 24B 1 and 1 . Undesirably, for a luminance drop of 70% from peak luminance, a color shift of approximately 0.07 on the x-coordinate and approximately 0.06 on the y-coordinate between viewing positions 520 and 526 may be provided. Such color shifts in the viewing quadrant may be clearly visible and are undesirable.

[0417] Fig.29A is a schematic diagram showing in perspective the illumination of a C-sheet layer and crossed A-sheet layers by off-axis polarized light having a positive elevation angle; and Fig.29B is a schematic diagram showing in perspective front view a Fig.29A The orientation of the retarder and polarizer axes of the optical stack. Fig. 16BCompared to the embodiment of the present invention, the A plate 502 can be aligned orthogonal to the polarizer 500, and the A plate 504 can be aligned parallel to the polarizer 504. Therefore, the at least one delay plate also includes a pair of delay plates 502, 504, which have a slow axis in the plane (xy plane) of the intersecting delay plates 502, 504. In the case where the additional polarizer 500 is arranged on the input side of the input polarizer, the pair of delay plates 502, 504 have slow axes 503, 505 that can extend at 0° and 90° respectively relative to the electric vector transmission direction 211 parallel to the electric vector transmission of the input polarizer 210, or in the case where the additional polarizer 500 is arranged on the output side of the input polarizer 210, the pair of delay plates have slow axes that can extend at 0° and 90° respectively relative to the electric vector transmission direction 211 parallel to the electric vector transmission direction 219 of the output polarizer 218.

[0418] Fig. 30A is a schematic brightness field diagram, which shows Fig.29B The change in the transmitted brightness of an optical stack including a high retardation layer, and Fig. 30B -C is a schematic brightness field diagram showing a high-retardation layer Fig.29B Changes in the 1931 CIE x- and y-color difference coordinates of an optical stack.

[0419] For a 70% drop in brightness from peak brightness, a color shift of about 0.01 on the x-coordinate and about 0.02 on the y-coordinate between viewing positions 520 and 526 can be provided. Fig.28B -C, the color shift for observation position 526 can be significantly reduced.

[0420] In addition to those displays comprising an imaging waveguide 1 with a reflective end 4, this embodiment may also be arranged with a switchable directional display.

[0421] Fig.31 is a schematic diagram showing in side view a directional display including a first directional waveguide 801a, a second wide angle waveguide 1b, and a C-plate 560 arranged between an additional polarizer 500 and an input polarizer 210 arranged behind a spatial light modulator 48. Alternatively, the additional polarizer and retardation layer may be arranged in front of the spatial light modulator, as described elsewhere herein.

[0422] The light source 815a may be arranged along at least one edge of the waveguide 801a, and the light source 815b may be arranged along at least one edge of the waveguide 801b.

[0423] The switchable directional display may further include a backscattering reflector 812 , an intermediate diffusion layer 810 , and a prismatic input layer 804 including first and second input facets 803 , 805 .

[0424] When operating in narrow angle mode, light source 815a may be arranged to provide light 820 into first waveguide 801a. Upper surface 806a and lower surface 808a of waveguide 801a may be provided with scattering microstructures arranged to extract light from waveguide 801a in a substantially grazing direction (close to parallel to surface 806a). Light 820 is incident on surface 803 of prism input layer 804 and is guided by total internal reflection from surface 805 to be incident on spatial light modulator in a narrow cone angle direction to provide a first narrow width observation window 821.

[0425] When operating in wide angle mode, light source 815b may be arranged to provide light 822 into second waveguide 801b. Upper surface 806b and lower surface 808b of waveguide 801b may be provided with scattering microstructures arranged to extract light from waveguide 801b with a cone angle having a nominal angle close to parallel to surface 806b. Light 822 is incident on surface 805 of prism input layer 804 and is guided by total internal reflection from surface 803 to be incident on spatial light modulator in the direction of a wide cone angle. Further diffusion of the scattered light at scattering reflector 812 and diffuser 810 may be arranged to increase the output cone angle to provide a second observation window 823 having a width greater than the first observation window 821.

[0426] Additionally, both light sources 815a, 815b may illuminate in a wide angle pattern to provide some control over the output directionality.

[0427] In this way, for example, it is possible to provide Fig. 12A Comparison of different types of directional displays. More generally, a directional backlight 101 is provided which can be switched between modes in which the output light is output into viewing windows 821, 823 of different widths.

[0428] Such an arrangement uses scattering to provide narrow and wide directional cones of light, respectively, for rays 820, 822. Such scattering may provide some high-angle light in the narrow-angle operating mode and reduce privacy protection performance.

[0429] This embodiment provides an additional reduction in brightness of the viewing cone angle that a snooper can see. Advantageously, as described elsewhere herein, privacy protection may be enhanced.

[0430] Fig.32A is a schematic diagram showing in top view an automobile cabin 700 and the lighting of a driver 706 from a centrally mounted display device 704; and Fig.32Bis a schematic diagram showing in side view a vehicle cabin 700 and lighting of a driver 706 from a centrally mounted display 704, wherein the display device is arranged in the vehicle and is arranged below a window 702 in the vehicle and is arranged in front of a seat 701 in the vehicle.

[0431] In the present disclosure, a viewing window is different from a transparent window. A viewing window refers to the angular illumination light cone of a display device at a desired viewing distance. A transparent window refers to a physically transparent surface, such as a windshield, windshield, side window, or other transparent surface, and is typically made of glass, glass composites, or other transparent materials.

[0432] In either embodiment, the display device 704 may alternatively be arranged at a non-central area relative to the driver to provide off-axis illumination of light 705 from the center of the display 704 in a negative lateral angular direction at a lateral angle 708 toward the driver 706. In operation, the light 705 is directed toward the driver 706 by reflection at the windshield 702, and additional light 707 is directed toward the driver 706, thereby forming a virtual image 714. The image 714 may be distracting to the driver, so it is desirable to reduce its brightness.

[0433] The lateral angular direction 708 of light output from the display 704 may be the same for light rays 705, 707, whereas the corresponding elevation angular directions 710, 712 are different.

[0434] Fig.32C is a schematic brightness field diagram showing the brightness of the display and windshield reflection in the automobile cabin 700.

[0435] In the illustrative example, the lateral angle 708 of the two light rays 705, 707 may be -30 degrees, while the corresponding elevation angles may be 10 degrees and 45 degrees. Thus, the polar coordinates 720, 722 of the directly observed display 704 and the virtual image 714 of the display 704 are at different polar coordinates. The brightness attenuation provided by the trajectory 557 of the polarization control arrangement of the present embodiment achieves a significant reduction in the brightness of the virtual image 714 reflected from the windshield compared to the directly observed light. In addition, the Fresnel reflectivity of the light ray 707 from the windshield 702 provides a significantly lower brightness of the virtual image 714 of the display 704.

[0436] Advantageously, with the polarizer arrangement of this embodiment, reflections from the windshield can be greatly reduced for the driver's viewing direction.

[0437] It is desirable to provide reduced off-axis brightness and reduced visibility of off-axis non-uniformity in the lateral direction to achieve reduced visibility of the user's image content to a snooper.

[0438] Fig.33A is a schematic diagram showing in perspective the illumination of the O-sheet layer 800 by an off-axis polarized light 638 having a positive elevation angle. Fig.26A By comparison, the O-plate retarder 800 comprises birefringent molecules 802 having a slow axis 804 tilted 808 about the y-axis. The molecules 802 may have an angle 806 of substantially 90 degrees relative to the xz plane. Thus, the O-plate may be considered a tilted C-plate. The optical properties of the O-plate retarder 800 between the parallel polarizers 500, 210 will be described in more detail below.

[0439] Fig.33B 8 is a schematic brightness field diagram showing an example of a change in the transmission brightness of an O-plate arranged between parallel polarizers. Thus, a brightness field profile 811 representing 10% increments of equal brightness is provided so that the brightness can be varied in the lateral direction and a high transmittance can be provided in the zero lateral angle direction.

[0440] Fig.33C is a schematic brightness field diagram, which shows that the Fig.33A The transmission brightness of the wide-angle display of the O-plate between the parallel polarizers changes, and the device brightness is the product of the brightness field distribution of the directional backlight source 101 and the brightness field distribution of the delay plate.

[0441] Therefore, the contour 811 covers Fig.14A Therefore, by Fig.33B The brightness distribution and Fig.14A The brightness distribution of the display is multiplied by the brightness distribution of the display. The resulting brightness is not Fig.33C Shown in.

[0442] Fig.33D is a schematic diagram showing the change in brightness of a wide-angle display with a viewing angle, the wide-angle display further comprising a Fig.33A The typical wide-angle display brightness distribution is 540. Fig.33A The lateral angular distribution 841 of the O-plate retarder 800 and polarizer 210, 500 arrangement is modified.

[0443] The viewing properties of displays including typical wide-angle displays, such as LCDs and conventional diffuse wide-angle non-directional backlights, and Fig.33A O-plate arrangement.

[0444] At a typical peeper viewing angle, such as 45 degrees off-axis in the lateral direction, the brightness of the wide-angle backlight source can be, for example, 20% of the peak head-on illumination. The brightness of the O-plate can be 10% or less, achieving a combined brightness of less than 2%. However, at a wider viewing angle (such as 60 degrees), the backlight source may have a brightness of 10%, but the transmittance of the O-plate may be 50%, providing 5% brightness to the peeper. Such values ​​can provide high visibility of the anti-peeping image to the peeper.

[0445] It is desirable to provide a privacy-protected image having less than 2%, and more preferably less than 1%, over a wide range of lateral peeper viewing directions.

[0446] Fig.34 is a schematic diagram showing a directional display including a directional waveguide and an O-plate arranged between a spatial light modulator and a directional backlight source 101 in a side view; and Fig.35 is a schematic diagram showing in perspective front view a Fig.34 Orientation of some of the retarders and polarizer axes of an optical stack.

[0447] Relative to Fig.36A Further describing the arrangement of the O-plate and display components, the figure is a schematic diagram showing in perspective side view the Fig.34 the orientation of some of the retarders and polarizer axes of the optical stack; and Fig.36B is a schematic diagram showing in perspective front view Fig.36A The orientation of the birefringent molecules in the arrangement of , and the tilted molecules 800 of the O-plate arranged in the retardation layer 802 are also shown.

[0448] The delay plate 800 includes an O-plate. Therefore, at least one delay plate of the present embodiment includes a delay plate 800 having a slow axis 804 orientation, the delay plate having the slow axis 804 orientation having a component 831 perpendicular to the plane of the delay plate 800 and at least one component in the plane of the delay plate 800. In addition, in the present embodiment, at least one delay plate may include a delay plate 800 having a slow axis 804 orientation, the delay plate having the slow axis 804 orientation having a component 531 perpendicular to the plane of the delay plate 800, a component 833 orthogonal to the electric vector transmission direction 211 of the input polarizer 210 in the plane of the delay plate 800, and substantially no component parallel to the electric vector transmission direction of the input polarizer 210 in the plane of the delay plate 800.

[0449] The O-plate retardation layer 800 may be formed, for example, of a cured reactive mesogen material that has been aligned on an aligned substrate prior to crosslinking, for example by exposure to UV light. An example of a reactive mesogen material is Licriview® from Merck. TMMaterials. As shown in the C-plate and A-plate retarder embodiments of this article, the retarder 800 can be arranged between the reflective polarizer 500 aligned with the absorbing polarizer 210. Advantageously, the thickness can be reduced and the transmission can be increased. The O-plate can also be arranged on a transparent support substrate 801 to achieve convenient alignment of the substrate and processing. Alternatively, the O-plate can be formed directly on the polarizer 210 or the reflective polarizer 500, thereby advantageously achieving a reduced thickness.

[0450] Fig.36C is a schematic brightness field diagram, which shows Fig.34 The change in the transmitted brightness of the optical stack of the device brightness is the product of the brightness field distribution of the underlying directional backlight 101 and the brightness field distribution of the retarder; and Fig.36D is a schematic diagram showing the variation of brightness of the anti-peeping operation mode of a directional display including an O-plate with respect to viewing angle. Fig.33D Compared to the non-directional display arrangement, the angular distribution 546 of the directional backlight source 101 has significantly reduced brightness at high viewing angles (e.g., less than 2%). It is further provided that the O-plate retarder of this embodiment can provide a privacy level that is substantially maintained at less than 2% for a wide range of off-axis viewing positions.

[0451] Another exemplary embodiment will now be described.

[0452] Fig.36E is a schematic brightness field diagram, which shows the change of the transmission brightness of the O-plate 800; Fig.36F is a schematic brightness field diagram, which shows the change of the transmitted brightness of the directional backlight 101.

[0453] In operation, the area of ​​interest for off-axis privacy viewing is Figure 36G , which is a schematic brightness field diagram, which shows the angle area 569 of the anti-peeping observation. Fig.36F The change in the transmitted brightness of the directional backlight source 101.

[0454] Fig.36H is a schematic brightness field diagram, which shows the angle area 569 for anti-peeping observation. Fig.34 The change in the transmitted brightness of the optical stack 101, 800. Therefore, Fig.36C As shown, the brightness in the anti-spying viewing area can be reduced. Advantageously, the above-mentioned axis brightness for anti-spying viewing, which is a possible direction for a snooper, can be significantly reduced.

[0455] Advantageously, the privacy level is reduced. Furthermore, the brightness of the non-uniformities in the off-axis privacy image is reduced, thereby achieving a reduction in the visibility of the non-uniformities.

[0456] It may be desirable to reduce off-axis brightness in a single quadrant of a display, such as to provide reduced light to a passenger or driver in an automotive application.

[0457] Fig.37A is a schematic diagram showing in perspective side view a Fig.34 Orientation of some of the retarder 800 and polarizer axes of an optical stack in which the birefringent molecules 802 are arranged to provide control of brightness in a single upper viewing quadrant.

[0458] Fig.37B is a schematic diagram showing in perspective front view Fig.37A The at least one retarder may include a retarder 800 having a slow axis 804 orientation, the retarder having a slow axis 804 orientation having a component 531 perpendicular to the plane of the retarder 800, a component 833 orthogonal to the electric vector transmission direction 211 of the input polarizer 210 in the plane of the retarder 800, and a component 835 parallel to the electric vector transmission direction 211 of the input polarizer 210 in the plane of the retarder 800.

[0459] Fig.37C is a schematic brightness field diagram, which shows Fig.37A a change in the transmitted brightness of the optical stack; and Fig.37D is a schematic brightness field diagram, which shows Fig.37A The change in the transmitted brightness of the optical stack, the device brightness is the product of the brightness field distribution of the directional backlight source 101 and the brightness field distribution of the delay plate.

[0460] The brightness of the upper quadrant may be reduced compared to the brightness field distribution of the directional backlight 101. Advantageously, the privacy or stray level of the display may be reduced in the upper quadrant, thereby providing improved performance for users looking down at the display.

[0461] It may be desirable to provide a privacy display having narrow viewing angles in the vertical direction as well as in the lateral direction, for example to increase the level of privacy protection for a wider range of viewing positions.

[0462] Fig.38A is a schematic diagram showing, in perspective side view, the orientation of some of the retarder and polarizer axes for an optical stack, wherein the O-plate retarder 800 slow axis 804 is oriented aligned parallel to the transverse direction; and Fig.38B is a schematic diagram showing in perspective front view Fig.38AThe at least one retarder may include a retarder 800 having a slow axis 804 orientation, the retarder having a slow axis 804 orientation having a component 831 perpendicular to the plane of the retarder, a component 835 parallel to the electric vector transmission direction 211 of the input polarizer 210 in the plane of the retarder, and substantially no component orthogonal to the electric vector transmission direction 211 of the input polarizer 210 in the plane of the retarder 800.

[0463] Fig.38C is a schematic luminance field diagram showing an arrangement for an exemplary embodiment. Fig.38A The variation in the transmitted brightness of the O-plate retarder 800 between the parallel polarizers 500, 210, where the O-plate may include a birefringence of 0.12, a layer thickness of 10 microns, and a tilt angle 808 of 70 degrees.

[0464] Fig.38D is a schematic brightness field diagram, which shows Fig.38A The change in the transmitted brightness of the optical stack, the device brightness is the product of the brightness field distribution of the directional backlight source 101 and the brightness field distribution of the delay plate.

[0465] Therefore, the brightness can be controlled in the vertical direction as well as the lateral direction, thereby advantageously improving the all-round anti-peeping performance of the display.

[0466] It may be desirable to provide reduced brightness to off-axis snoopers in the privacy mode of operation of the directional backlight 101, while providing a wide field of view in the wide mode of operation of the directional backlight 101. In addition, it may be desirable to provide reduced stray light for nighttime operation of the display; such operation may be achieved by using a privacy mode display even though there may be no snoopers. The switchable privacy display operation will now be described.

[0467] Fig.39A is a schematic diagram showing in side view a directional display including a directional waveguide and a uniformly aligned switchable liquid crystal O-plate retarder 800 arranged between the spatial light modulator 48 and the directional backlight source 101. The uniformly aligned switchable liquid crystal O-plate retarder 800 may be provided by a switchable liquid crystal layer between transparent substrates 812, 816, such as Fig.39B As shown, this figure is a schematic diagram, which shows a side view Fig.39A Switching of uniformly aligned switchable liquid crystal O-plates 800 in a directional display.

[0468] The switchable retarder may be provided, for example, by a parallel uniformly aligned liquid crystal cell. As shown in region 853, when operating in the undriven state, the molecules 802 are tilted by alignment layers 852, 854 together with a pre-tilt 809, which may be, for example, a rubbed polyimide or a photo-alignment layer. The pre-tilt may be, for example, 2 degrees and may be arranged to minimize degeneracy in the switching of the liquid crystal retarder 800 layer. Thus, such a retarder is essentially an in-plane A-plate retarder.

[0469] As shown in region 851, when driver 884 provides a voltage across the liquid crystal cell through electrodes 850, 856, molecules not adjacent to alignment layer 852 reorient to provide a tilt 808 in the liquid crystal retarder 800 layer. Thus, such a retarder is essentially an out-of-plane O-plate retarder.

[0470] Fig.39C is a schematic diagram showing a plot of the liquid crystal director tilt of a cell with applied voltage versus the thickness of the liquid crystal cell. Fig.39C In an exemplary embodiment of the invention, the slow axis of the retarder can be provided by a liquid crystal director and can have a tilt that varies across the thickness of the cell, as shown by the tilt profile 813. At the alignment surface, the tilt 809 can be, for example, 2 degrees, while at the center of the cell, a tilt 808 can be provided that can be, for example, 68 degrees.

[0471] Thus, a uniformly aligned tilt profile 8113 of the switchable liquid crystal O-plate retarder 800 may be provided by controlling the applied voltage from the driver 884. Advantageously, control over the angular viewing properties of a directional display may be provided as described elsewhere herein.

[0472] Fig.39D is a schematic diagram showing in perspective front view a Fig.39A Orientation of some of the retarder 800, alignment layers 812, 816 and polarizers 500, 210, 218 of the optical stack. The rubbing directions of the alignment layers 812, 816 may be provided antiparallel and arranged to orient the direction of the slow axis components 833, 835 in the plane of the retarder 800.

[0473] The electrodes 850, 856 may be patterned to provide regions with different levels of control of privacy brightness for off-axis viewing positions.The switchable liquid crystal retarder 800 comprises at least first and second regions 851, 853 which are independently addressable using first and second applied voltages.

[0474] Advantageously, different levels of privacy protection may be provided across display areas.

[0475] Fig.39E8 is a schematic diagram showing a flow chart of controlling a directional display device including a switchable directional backlight source 101, a switchable delay plate 800 and an anti-peeping display control system 880. Fig.11 As shown, the anti-peeping display controller can control the backlight source 101 and the spatial light modulator 48. In addition, the controller 882 can be arranged to provide a voltage output from the switchable retarder driver 884. Therefore, the control system 880, 882, 884 is arranged to control the applied voltage across the switchable liquid crystal retarder 800.

[0476] Fig.39F is a schematic diagram showing the Fig.39E The switchable directional backlight, the switchable retarder and the anti-peeping display control system can be arranged to change the illumination of the directional display device. Therefore, the control system can be arranged to provide switching between the first operating mode and the second operating mode.

[0477] In a first mode of operation, the light source is controlled to provide an illumination distribution 842 having a first angular width 862 (which may be full width at half maximum for a desired elevation angle) from waveguide 1. A first applied voltage is provided across the switchable liquid crystal retarder to achieve a reduction in off-axis brightness at a desired elevation angle.

[0478] In a second mode of operation, the light source is controlled to provide an illumination distribution 540 from the waveguide 1 having a second angular width 860 greater than the first angular width 862; and a second applied voltage different from the first applied voltage is provided across the switchable liquid crystal retarder 800. The second applied voltage is less than the first applied voltage and may be zero, so that an A-plate is provided by the switchable retarder 800.

[0479] Advantageously, the privacy mode of operation may be arranged to provide cooperation of a directional backlight source with a switchable retarder to reduce brightness to a peeping eye and to reduce stray light.

[0480] Figure 39G is a schematic diagram showing in side view a directional display comprising a directional waveguide and a uniformly aligned switchable liquid crystal O-plate retarder 800 arranged between the spatial light modulator 48 and the output polarizer 218. Such an arrangement may have Fig.39A In addition, the uniformly aligned switchable liquid crystal O-panels can be provided with touch screen functionality.

[0481] We will now further describe Fig.39A and Fig.39E The optical properties of the arrangement.

[0482] Fig.40A is a schematic diagram showing in perspective side view a first applied voltage for Fig.39AThe orientation of some of the retarder, alignment layer and polarizer axes of the optical stack. Thus, the birefringent molecules 802 can be oriented in a manner similar to Fig.36B The slow axis is aligned on the x-axis in a similar manner as shown. Fig.36A Compared to the embodiment of FIG. 8 , the molecules 802 are aligned by the electric field provided by the electrodes 850 , 856 of the liquid crystal cell, rather than being arranged as a fixed matrix like a cured reactive mesogen film.

[0483] Fig.40B is a schematic brightness field diagram, which shows Fig.40A The change in the transmission brightness of the O-plate arranged between the parallel polarizers, and Fig.40C is a schematic brightness field diagram showing the brightness of the display in the anti-peeping mode of operation. Fig.40A The change in the transmitted brightness of the optical stack, the device brightness is the product of the brightness field distribution of the directional backlight source 101 and the brightness field distribution of the delay plate.

[0484] exist Fig.40B In an exemplary embodiment of , a liquid crystal with a birefringence of 0.09 can be provided in a 10 micron thick cell with a 2° pretilt and an applied voltage of 3.1 V. Such a cell provides the greatest brightness reduction at an elevation angle of 20 degrees and a lateral angle of + / - 45°.

[0485] Therefore, it can be Fig.33C A similar approach as shown is used to achieve enhanced anti-peeping performance.

[0486] This embodiment provides minimum brightness at a viewing angle of 45 degrees in the lateral direction and 22.5 degrees in the elevation direction.

[0487] The operation of the display in wide angle mode will now be described.

[0488] Fig.41A is a schematic diagram showing in perspective side view the voltage for no voltage applied Fig.39A The orientation of some of the retarders, alignment layers and polarizer axes of the optical stack. Fig.39E As shown, when operating in wide angle mode, the applied voltage can be controlled to control the switchable retarder 800. Typically, the voltage can be removed so that the molecule 802 is aligned with the pre-tilt of the alignment layer 852, 854. Since the pre-tilt is typically small, such as 2 degrees, the molecules are essentially arranged as an A plate for the purposes of this disclosure. Therefore, the retarder includes a switchable liquid crystal retarder 800, which can be switched between an O-plate retarder and an A-plate retarder having a slow axis orientation parallel to the x-axis by controlling the applied voltage across the switchable liquid crystal retarder 800. Additional additional light sources of the array 15 can be illuminated to provide a wide angle brightness distribution from the backlight source.

[0489] Table 1 shows Fig.41A and Fig.40A An exemplary embodiment of an arrangement of .

[0490]

[0491] Table 1

[0492] Fig.41B is a schematic brightness field diagram showing the arrangement of the Fig.41A A change in the transmitted brightness of the A plate 800 between the parallel polarizers; and Fig.41C is a schematic brightness field diagram showing the wide-angle operating mode. Fig.41A The change in the transmitted brightness of the optical stack of , the device brightness is the product of the brightness field distribution of the directional backlight source 101 and the brightness field distribution of the delay plate. Therefore, Fig.41A The arrangement results in essentially no loss of light for off-axis viewing positions.

[0493] Advantageously, wide mode viewing achieves high efficiency over a wide viewing angle range compared to the privacy mode of operation.

[0494] During assembly of the switchable directional backlight source 101, a light control structure such as a light absorption region at the input side 2 of the waveguide can be provided to reduce reflection of light reflected from the reflective end 4. The present embodiment achieves a reduced off-axis privacy level, so that, for example, the amount of light absorbed at the input end 2 can be reduced while maintaining the desired privacy level. The efficiency of the light input from the input end can therefore be increased while achieving the desired privacy level. Advantageously, the display brightness at the off-axis viewing position can be increased compared to an arrangement of switchable liquid crystal O-plates that are not uniformly aligned. In addition, in the wide-angle operating mode, the half-height full width maximum value of the brightness distribution can be increased, thereby achieving improved display visibility in the wide operating mode.

[0495] It may be desirable to provide control over the extreme position of the reduced privacy level area provided by the uniformly aligned switchable liquid crystal O-plate 800.

[0496] Fig.42A is a flow chart describing adjustment of a uniformly aligned switchable liquid crystal O-plate voltage corresponding to display viewing conditions; and Fig.42B is a schematic brightness field diagram showing the arrangement of the Fig.41A The change in the transmitted brightness of the O-plate between the parallel polarizers. Therefore, the applied voltage can provide control of the position of the brightness field minimum in the anti-peeping operation mode. In addition, the brightness minimum can be controlled between the elevation angle below zero and the elevation angle in the upper quadrant of the polar coordinate distribution.

[0497] In a first step 870, the user can enable a privacy mode of operation. Such privacy mode settings can be provided by manual settings (e.g., keyboard operations) or by automatic sensing using sensors to locate the presence of snoopers, such as in U.S. Patent Publication 2017-0236494, which is incorporated herein by reference in its entirety.

[0498] In a second step 872, the snooper position may be detected, for example, by a camera or by a keyboard setting or other method. In an illustrative example, an "OFFICE" setting may be provided, where it may be desirable to optimize the snooping performance for a snooper moving around a shared office environment, and thus optimize the performance for the downward looking viewing quadrant. By comparing in a FLIGHT setting, it may be desirable to provide a snooping level optimization for a seated snooper, where the snooping level is improved compared to an elevation angle less than that desired for the OFFICE setting.

[0499] In a third step 876, the O-plate box voltage may be adjusted, and in a fourth step 878, the O-plate box voltage may be adjusted using Fig.39E The control system shown is used to adjust the LED distribution.

[0500] Thus, the control system may further comprise means for determining a position of a snooper relative to the display, wherein the control system is arranged to adjust the first applied voltage in response to the position of the snooper.

[0501] Advantageously, the privacy protection operation of the display may be controlled to optimize the snooper viewing geometry.

[0502] It may also be desirable to optimize the privacy-resistant appearance of a display having a single control line to the voltage driver 844 where no voltage tuning for snooper position is provided.

[0503] A typical primary viewer position has a lateral angle close to zero, e.g., + / - 10 degrees in the anti-peep mode of operation. A typical snooper viewer position has a lateral angle at a larger angle, e.g., greater than + / - 30 degrees. A typical primary viewer position has an elevation angle of, e.g., + / - 25 degrees in the anti-peep mode of operation, which is based on seating position, desired display tilt, and minimizing reflections from the surrounding environment. By comparison to an anti-peep display that has been tuned for a zero elevation snooper position, it has been recognized in the present embodiment that a typical snooper viewer position for devices such as laptops, cellular phones, and tablets in public places has an elevation angle greater than zero, and is typically between 20 and 60 degrees, and more typically between 20 and 45 degrees.

[0504] In the case where the additional polarizer 500 is arranged on the input side of the input polarizer 210, the maximum attenuation brightness field of the switchable liquid crystal retarder 800 between the additional polarizer 500 and the input polarizer 210, or in the case where the additional polarizer 512 is arranged on the output side of the input polarizer 210, the switchable liquid crystal retarder 800 between the additional polarizer 512 and the output polarizer 218 has an elevation angle greater than zero relative to the normal direction of the spatial light modulator 48. In embodiments where the brightness distribution is symmetrical, the maximum attenuation polar coordinates 875a, 875b can be provided, for example, by equal and opposite lateral angles.

[0505] Thus, the maximum attenuation polar coordinate has an elevation angle between 10 and 50 degrees, preferably between 15 and 35 degrees, most preferably between 20 and 30 degrees. The maximum attenuation polar coordinate has a lateral angle of 30 to 60 degrees, preferably 40 to 50 degrees, and most preferably 45 degrees.

[0506] Advantageously, the control system for the voltage driver 844 can have reduced complexity and reduced cost. In addition, the lowest brightness can be provided for the most likely location of a snooper, thereby reducing visibility and improving privacy protection.

[0507] It may be desirable to provide more reduced privacy image visibility to a snooper.In addition, it may be desirable to improve the width 860 of the wide angle mode distribution 540.

[0508] Fig.43 4 is a schematic diagram showing, in perspective side view, the orientation of some of a plurality of parallel uniformly aligned switchable liquid crystal O-plates arranged between a directional backlight and a spatial light modulator 48.

[0509] A first uniformly aligned switchable liquid crystal O-plate retarder and a second uniformly aligned switchable liquid crystal O-plate retarder and a first and a second additional polarizer 500a, 500b are provided. Alternatively, one or two uniformly aligned switchable liquid crystal O-plate retarder may be provided on the output side of the output polarizer 218 of the spatial light modulator 48. The combined output in the anti-peeping mode of operation will be provided by the multiplied brightness of the two switchable retarders 800. With e.g. Fig.42B The display brightness field output distribution in anti-peep mode can therefore provide an increased brightness reduction for a given lateral angle, or can provide an extended range of elevation angles with reduced brightness, compared to the arrangement of FIG.

[0510] An additional corrective passive retarder 890a is disposed between the additional polarizer 500a and the input polarizer 210, and a corrective passive retarder 890b is disposed between the additional polarizer 500b and the additional polarizer 890a. The operation of the corrective retarder 890a, 890b increases the polar region over which the brightness is reduced, as will be further described below.

[0511] Advantageously, for a given privacy level, the brightness or increased polar distribution of the privacy performance can be improved.Except for the loss due to the additional polarizer 500b, the additional oncoming brightness is substantially maintained.

[0512] Light control methods in the backlight may be reduced, thereby providing higher efficiency and a wider width 860 of the distribution 540 and having higher efficiency.

[0513] It may be desirable to provide enhanced privacy protection for high altitudes of zero elevation operation.

[0514] Fig.44A is a schematic diagram showing, in perspective side view, the orientation of a plurality of orthogonal uniformly aligned switchable liquid crystal O-panels arranged between a directional backlight source and a spatial light modulator 48; Fig.44B is a schematic brightness field diagram showing the Fig.44A A change in the transmissive brightness of a plurality of uniformly aligned switchable liquid crystal O-panels; and Fig.44C is a schematic brightness field diagram showing the wide-angle operating mode. Fig.44A The change in the transmitted brightness of the optical stack, the device brightness is the product of the brightness field distribution of the directional backlight source 101 and the brightness field distribution of the delay plate.

[0515] For illustrative purposes, for an arrangement in which the effects of the corrective passive retarders 890a, 890b, which will be described below, are not included, the operation of the display is similar to Fig.43 The operation is shown in . The alignment direction of one of the layers is orthogonal to provide rotational privacy reduction via the switchable retarder 800b.

[0516] Advantageously, a privacy protection operation may be provided to allow a snooper to fully view the display.

[0517] It may be desirable to enhance the privacy level for zero altitude viewing and also for viewing from the viewing quadrant.

[0518] Fig.45 is a schematic diagram showing, in a perspective side view, the orientation of a uniformly aligned switchable liquid crystal O-plate 800 and a plurality of parallel C-plates 560 arranged between a directional backlight 101 and a spatial light modulator 48.

[0519] Fig.46Ais a schematic diagram showing in a perspective side view the orientation of a uniformly aligned switchable liquid crystal O-plate 800 arranged between the directional backlight 101 and the spatial light modulator 48 and a C-plate 560 arranged between the spatial light modulator and the further additional polarizer 512. An additional compensating passive retarder 890, which will be described below, may be provided between the additional polarizer 500 and the input polarizer 210.

[0520] Fig.46B is a schematic diagram showing in side view a directional display comprising a directional waveguide 1 and a uniformly aligned switchable liquid crystal O-plate arranged between the spatial light modulator output polarizer 218 and the further output polarizer 512, and a C-plate 560 arranged between the spatial light modulator and the additional polarizer.

[0521] The operation of the C-plate 560 and the operation of the switchable liquid crystal O-plate 800 provide multiplied functions as described elsewhere, however these functions are separated into the front and rear portions of the display. The C-plate 560 and polarizer 512 can be arranged as layers of a front touch screen device 777 for interaction with the finger 775, thereby advantageously reducing cost and complexity.

[0522] Fig.47A is a schematic brightness field diagram showing the Figures 45 to 46B Variation of the transmission brightness of the uniformly aligned switchable liquid crystal O-plate and C-plate; Fig.47B is a schematic brightness field diagram showing the brightness of the display in the anti-peeping mode of operation. Fig.45 and Fig.46B The device brightness is the product of the brightness field distribution of the directional backlight source 101 and the brightness field distribution of the retarder; and Fig.47C is a schematic brightness field diagram showing the wide-angle operating mode. Fig.45 and Fig.46B The change in the transmitted brightness of the optical stack, the device brightness is the product of the brightness field distribution of the directional backlight source 101 and the brightness field distribution of the delay plate.

[0523] Thus, the display device may include a backlight source 101 arranged to output light, a transmissive spatial light modulator 48 arranged to receive the output light from the backlight source 101, an input polarizer 210 arranged on the input side of the spatial light modulator 48 between the backlight source 101 and the spatial light modulator 48, and an output polarizer 218 arranged on the output side of the spatial light modulator 48. Additional polarizers 500, 512 are arranged on the input side of the input polarizer 210 and the output side of the output polarizer 218, respectively, between the input polarizer 210 and the backlight source 101. In the case where the additional polarizer 500 is arranged on the input side of the input polarizer 210, at least one retarder 800 is arranged between the additional polarizer 500 and the input polarizer 210. In case the additional polarizer 512 is arranged on the output side of the input polarizer 210 , at least one retarder 560 is arranged between the additional polarizer 512 and the output polarizer 218 .

[0524] In addition to Fig.42B In addition to the switchable control of brightness at lower elevation angles shown, it is also possible to provide brightness reduction in the quadrants as shown elsewhere herein, the polar distribution being multiplicative. Fig.43 and Fig.44A The passive C-plate 560 may advantageously have reduced thickness, complexity, and cost compared to arrangements of FIG.

[0525] For example, Fig.42B The brightness field distribution provides a maximum attenuation polar region around coordinate 875, which is a relatively small polar region. When the switchable liquid crystal retarder is activated, it is expected that the area of ​​the polar region is increased and the off-axis brightness of the polar region is reduced. In addition, it is expected that the brightness distribution is not substantially reduced or the power consumption is increased in the wide-angle operation mode.

[0526] Embodiments will now be described in which the switchable liquid crystal retarder comprises at least one vertical alignment layer. In the case where the additional polarizer 500 is arranged on the input side of the input polarizer 210, at least one corrective passive retarder is arranged between the at least one additional polarizer 500 and the input polarizer 210, or in the case where the additional polarizer is arranged on the output side of the input polarizer 210, at least one corrective passive retarder is arranged between the additional polarizer 512 and the output polarizer 218. The corrective passive retarder comprises a negative C-plate or a crossed A-plate.

[0527] Fig.48Ais a schematic diagram showing in perspective side view the orientation of a switchable liquid crystal O-plate 892 aligned in a homeotropic orientation in a wide-angle mode of operation (thus essentially providing a positive C-plate); and a negative C-plate corrective passive retarder 890 arranged between the input polarizer 210 of the spatial light modulator and the additional polarizer 500. Thus, the display may be provided with at least one retarder comprising at least one corrective passive retarder 890 and at least one switchable liquid crystal retarder 892.

[0528] Fig.48B is a schematic brightness field diagram showing the wide-angle operating mode. Fig.48A The negative C-plate material 893 is shown as discotic liquid crystal molecules (which may be in a cured film); as described elsewhere, the negative C-plate may alternatively include, for example, a stretched film.

[0529] In operation with off-axis incident light, the increase in birefringence of rays passing through the switchable positive O-plate is compensated by the decrease in birefringence of rays passing through the negative C-plate. Thus, for all viewing angles, there is essentially no net birefringence, and the combination achieves a wide viewing angle.

[0530] Advantageously, zero voltage drive and therefore zero power is achieved for the wide angle mode, and substantially no change to the wide angle brightness distribution is achieved.

[0531] Fig.48C is a schematic diagram showing the voltage applied by the driver to the switchable liquid crystal O-plate 892 by applying a voltage across the liquid crystal material 891 when the driver 884 is in the anti-peeping mode of operation. Fig.48A implementation plan, and Fig.48D is a schematic brightness field diagram showing the brightness of the display in the anti-peeping mode of operation. Fig.48C Variation of the transmitted brightness of an optical stack.

[0532] By comparing with e.g. Fig.42B Compared with the arrangement of , for example, the area of ​​the polar region with less than 20% attenuation is greatly increased. Advantageously, the polar coordinates from which a snooper can perceive the data on the display can be greatly reduced.

[0533] Fig.48E 5 is a schematic brightness field diagram, which shows the change of the transmission brightness of the directional backlight source in the polar region 569, as shown in FIG. Fig.48D This image has a privacy threshold setting of 3%, so some areas may be significantly above that level.

[0534] Fig.48F is a schematic diagram showing the Fig.40A The optical stack further modulates Fig.48FTherefore, although there is a significant reduction in the anti-peeping level around the illustrated peeper viewing angle of 45 degrees lateral angle and 20 degrees elevation angle, the basic image brightness is not reduced in other areas, so the peeper can perceive the image more easily.

[0535] Figure 48G is a schematic diagram showing the Fig.48C The optical stack further modulates Fig.48F The variation of the transmitted brightness of the directional backlight source in the extreme area.

[0536] In the present disclosure, the liquid crystal retarder may have an optical thickness between 500nm and 1000nm, preferably between 700nm and 900nm, and most preferably between 775nm and 825nm. In addition, at least one corrected passive retarder may have an optical thickness between 400nm and 800nm, preferably between 550nm and 750nm, and more preferably between 625nm and 675nm.

[0537] Table 2 describes Fig.48A and Fig.48C An exemplary embodiment of an arrangement of .

[0538]

[0539] Table 2

[0540] In another illustrative example, active LC retarder 892 may have an optical thickness of 800 nm, and corrective passive retarder 890 may be a C-plate having an optical thickness of -650 nm.

[0541] exist Fig.48D The low brightness vertical band 567 seen in the exemplary field of view of FIG. 5 translates to higher lateral angles (i.e., is pushed away) with reduced active LC retarder box optical thickness and reduced corrective passive retarder optical thickness. Maximum attenuation is achieved at larger horizontal viewing angles compared to the arrangement of Table 2. Such an arrangement will achieve a wider horizontal viewing angle, advantageously reducing brightness variations with viewing angle and angular color variations.

[0542] In addition, optimization of the best privacy protection performance can be provided at, for example, a 45 degree lateral angle and a 22.5 degree elevation angle. Such a display provides increased privacy protection for typical snooper angle positions.

[0543] and Fig.48F and Fig.40A Compared with the exemplary embodiment of the present invention, the area where a snooper can perceive the image is advantageously greatly reduced. The voltage is further reduced and the power consumption is reduced.

[0544] It is desirable to provide a high level of privacy protection in displays having conventional wide-angle backlights.

[0545] Figure 48H is a schematic diagram showing in perspective side view the orientation of a plurality of parallel vertically aligned switchable liquid crystal O-plates 892A, 892B and corrective passive retarders 890A, 890B arranged between the backlight source 101 and the spatial light modulator 48. The backlight source 101 may be, for example, a conventional (non-directional) backlight source, or may be a directional backlight source that is not switchable between at least two different lateral brightness distributions. The pairs of stacks 890A, 892A and stacks 890B, 892B are Fig.48D The multiplicative effect of the brightness of the distribution shown advantageously achieves a significant reduction in the privacy rating of 892A, 892B over a larger field of view. Further cost and complexity of the backlight source can be reduced, and extended wide angle performance is achieved.

[0546] Therefore, the display device may also include at least one additional polarizer 500B and at least one additional corrective passive delay plate 890B and at least one additional switchable liquid crystal delay layer 892B, and in the case where the additional additional polarizer 500B is arranged on the input side of the input polarizer, the at least one additional corrective passive delay plate and the at least one additional switchable liquid crystal delay layer are arranged between the at least one additional additional polarizer 500B and the input polarizer 210, or in the case where the additional additional polarizer 500B is arranged on the output side of the input polarizer 210, the at least one additional corrective passive delay plate and the at least one additional switchable liquid crystal delay layer are arranged between the additional additional polarizer 500B and the output polarizer 218.

[0547] The electrodes 850A and 856A of the first switchable liquid crystal delay layer 892A may also have a corresponding alignment layer (not shown) arranged between the corresponding electrodes and the liquid crystal delay layer 892A; and the electrodes 850B and 856B of the first switchable liquid crystal delay layer 892B may also have a corresponding alignment layer (not shown) arranged between the corresponding electrodes and the liquid crystal delay layer 892B.

[0548] The alignment direction 822A of the upper alignment layer of the first switchable liquid crystal layer 892A may be parallel or anti-parallel to the alignment direction 822B of the upper alignment layer of the further switchable liquid crystal layer 892B, and the alignment direction 820A of the lower alignment layer of the first switchable liquid crystal layer 892A may be parallel or anti-parallel to the alignment direction 820B of the lower alignment layer of the further switchable liquid crystal layer 892B.

[0549] Furthermore, the alignment direction of at least the first corrective passive retarder 890A may be parallel or antiparallel to the alignment direction of at least one additional corrective passive retarder 890B. The alignment direction may be determined by rubbing an alignment layer, photo-alignment, or other known alignment methods. In a film, the alignment direction may be determined by a stretching direction or a molecular pre-tilt.

[0550] It may be desirable to provide privacy protection in a display in both the horizontal and vertical directions.

[0551] Figure 48I is a schematic diagram showing in a perspective side view the orientation of a plurality of orthogonal vertically aligned switchable liquid crystal O-plates 892A, 892B and corrective passive retarders 890A, 890B arranged between the directional backlight source 101 and the spatial light modulator 48. The alignment directions of the corresponding layers on each stack can be orthogonal to provide a rotated brightness distribution.

[0552] The alignment direction 822A of the upper alignment layer of the first switchable liquid crystal layer 892A may be orthogonal to the alignment direction 822B of the upper alignment layer of the further switchable liquid crystal layer 892B, and the alignment direction 820A of the lower alignment layer of the first switchable liquid crystal layer 892A may be orthogonal to the alignment direction 820B of the lower alignment layer of the further switchable liquid crystal layer 892B.

[0553] Furthermore, the alignment direction of at least a first corrective passive retarder 890A may be orthogonal to the alignment direction of at least one additional corrective passive retarder 890B.

[0554] Fig.48J is a schematic brightness field diagram showing the brightness of the display in the anti-peeping mode of operation. Figure 48I The distribution profiles 577a, 577b are provided orthogonally and multiplied together to provide high on-axis brightness, and have reduced brightness for the peep at both elevation and lateral off-axis viewing positions. Advantageously, the image visibility of the peep observing from above the head of the primary observer can be reduced.

[0555] It may be desirable to further reduce the visibility of the privacy image to a snooper 47 .

[0556] Fig.49Ais a schematic diagram showing, in a perspective side view, the orientation of a vertically aligned patterned switchable liquid crystal O-plate 892 arranged between a directional backlight source 101 (not shown) and a spatial light modulator 48 (not shown) arranged to include a switchable camouflage region in an anti-peeping mode of operation. At least one of the electrodes 850, 856 may be patterned, in which example, the electrode 856 is patterned to have regions 856a, 856b, 856c, and is driven by a corresponding voltage driver 884a, 884b, 884c with voltages Va, Vb, Vc. A gap 885 may be provided between the electrode regions 856a, 856b, 856c. The tilt of the molecules 891a, 891b, 891c may therefore be independently adjusted to reveal a camouflage pattern with different brightness levels for off-axis viewing.

[0557] Thus, in the case where the additional polarizer 500 is arranged on the input side of the input polarizer, at least one of the at least one retarder between the at least one additional polarizer 500 and the input polarizer 210, or in the case where the additional polarizer 500 is arranged on the output side of the input polarizer 210, at least one of the at least one retarder between the additional polarizer 500 and the output polarizer 218 is controlled by the addressing electrodes 856a, 856b, 856c and the uniform electrode 850. The addressing electrodes may be patterned to provide at least two pattern regions including the electrode 856a and the gap 885.

[0558] Fig.49B 1 is a schematic diagram showing the illumination of the primary observer and the snooper by the privacy display controlled by the brightness of the camouflage in a perspective front view. The display 100 may have dark image data 1601 and white background data 1603 visible to the primary observer 45 in the viewing window 26p. By comparison, the snooper 47 in the viewing position 1600 may be as shown in FIG. Fig.49C The camouflage image shown is a schematic diagram showing the illumination of the anti-peeping display to a snooper controlled by the brightness of the camouflage in a perspective side view. Thus, in the white background area 1603, a camouflage structure with a mixed brightness of the white area 1603 can be provided. Thus, the pattern area of ​​electrodes 856a, 856b, 856c is a camouflage pattern. At least one of the pattern areas is individually addressable and is arranged to operate in an anti-peeping mode of operation.

[0559] The pattern areas can be arranged to provide camouflage for multiple spatial frequencies by controlling which patterns are provided during the anti-peeping mode of operation. In an illustrative example, 20 mm high text can be provided to the presentation system. A camouflage pattern with a similar pattern size can be provided with a first control of the electrode pattern. In a second example, a photo of a large area of ​​content that is most visible to the snooper 47 can be provided. By combining the first electrode area and the second electrode area to provide a voltage and achieve a resulting lower spatial frequency pattern, the spatial frequency of the camouflage pattern can be reduced to hide a larger area structure.

[0560] Advantageously, a controllable camouflage structure can be provided by adjusting the voltages Va, Vb, Vc on layer 892. For head-on operation, the visibility of the camouflage structure is almost invisible. In addition, the camouflage image can be removed by providing the same Va, Vb and Vc.

[0561] Lowered expectations Fig.48A and Fig.48C The cost of the negative C-plate corrected passive delay plate 890.

[0562] Fig.50A is a schematic diagram showing in perspective side view the orientation of a vertically aligned switchable liquid crystal O-plate disposed between a directional backlight and a spatial light modulator and crossed A-plates 502, 504 disposed between the spatial light modulator input polarizer 210 and an additional polarizer 500 in a wide angle mode of operation; and Fig.50B is a schematic brightness field diagram showing the wide-angle operating mode. Fig.50A Variation of the transmitted brightness of an optical stack. Fig.50C is a schematic diagram showing in perspective side view the orientation of a vertically aligned switchable liquid crystal O-plate corrected passive retarder 890 disposed between a directional backlight source and a spatial light modulator and a crossed A-plate disposed between the spatial light modulator and an additional polarizer in an anti-peeping mode of operation; and Fig.50D is a schematic brightness field diagram showing the brightness of the display in the anti-peeping mode of operation. Fig.50C Table 3 describes an exemplary embodiment.

[0563]

[0564] Table 3

[0565] and Fig.49A and Fig.49C Compared to the arrangement of , the crossed A-plates can have improved anti-peeping performance for look-down operation, while maintaining low drive voltage for low drive system cost and reduced power consumption in anti-peeping mode. Fig.48A and Fig.48CCompared with the negative C plate, the cost of the A plate can be reduced.

[0566] It may be desirable to further increase the low light area for snoopers in the privacy mode of operation.

[0567] Fig.51A is a schematic diagram showing in perspective side view the orientation of a hybrid aligned switchable liquid crystal O-plate 897 arranged between a directional backlight and a spatial light modulator and a negative C-plate arranged between the spatial light modulator input polarizer 210 and an additional polarizer 500 in a wide angle operating mode. H To drive the liquid crystal layer 897 to the O-plate retardation film. Fig.51B is a schematic brightness field diagram showing the wide-angle operating mode. Fig.51A Variation of the transmitted brightness of an optical stack.

[0568] Fig.51C is a schematic diagram showing in perspective side view the orientation of a hybrid aligned switchable liquid crystal O-plate 897 disposed between a directional backlight and a spatial light modulator and a negative C-plate disposed between the spatial light modulator and an additional polarizer in an anti-peeping mode of operation. Low voltage state V L The delay of the liquid crystal layer 897 cooperates with the delay of the fixed negative C-plate corrected passive delay plate 890 to achieve Fig.51D Table 4 describes an exemplary embodiment. Fig.50A and Fig.50C A negative C-plate corrected passive retarder 890 is provided by crossed A-plates in a similar manner.

[0569]

[0570] Table 4

[0571] Advantageously, an increased viewing area with reduced privacy is achieved.

[0572] By comparison, now FIG. 52A to FIG. 53D The exemplary embodiments of Table 5 and Table 5 describe arrangements that do not include at least one vertically aligned alignment layer.

[0573] Fig.52A is a schematic diagram showing in a perspective side view the orientation of a vertically aligned switchable liquid crystal O-plate 800 arranged between the additional polarizer 500 and the spatial light modulator input polarizer and a negative C-plate corrected passive retarder 890 arranged between the spatial light modulator and the additional polarizer in a wide angle operating mode. Fig.52B is a schematic brightness field diagram, which shows the high voltage V input from the driver 884 H In wide-angle operating mode Fig.52AVariation of the transmitted brightness of an optical stack. Fig.52C is a schematic diagram showing in perspective side view the low voltage supply V in the anti-peeping mode of operation. L Orientation of the vertically aligned switchable liquid crystal O-plate 800 arranged between the directional backlight source 101 and the spatial light modulator input polarizer and the negative C-plate arranged between the spatial light modulator and the additional polarizer 500. Fig.52D is a schematic brightness field diagram showing the brightness of the display in the anti-peeping mode of operation. Fig.52C Variation of the transmitted brightness of an optical stack.

[0574] Fig.53A is a schematic diagram showing in perspective side view the high voltage V input from the driver 884 H , the orientation of the uniformly aligned switchable liquid crystal O-plate and crossed A-plates 502, 504 arranged between the additional polarizer 500 and the spatial light modulator input polarizer 210 in the wide angle mode of operation; and Fig.53B is a schematic brightness field diagram showing the wide-angle operating mode. Fig.53A Variation of the transmitted brightness of an optical stack. Fig.53C is a schematic diagram showing in perspective side view the low voltage supply V in the anti-peeping mode of operation. L an orientation of a vertically aligned switchable liquid crystal O-plate disposed between the directional backlight source and the spatial light modulator and a negative C-plate disposed between the spatial light modulator and the additional polarizer; and Fig.53D is a schematic brightness field diagram showing the brightness of the display in the anti-peeping mode of operation. Fig.53C Variation of the transmitted brightness of an optical stack.

[0575]

[0576] Table 5

[0577] It may be desirable to provide voltage in the wide operating mode but not in the privacy operating mode, for example, for a display that is used primarily in the privacy mode where the user values ​​the power savings of privacy mode operation.

[0578] Fig.54800 and a fixed O-plate 807 that may be arranged with a directional backlight source 101 and a spatial light modulator 48, wherein the interface between the O-plates is substantially planar. Compared to the above-described embodiments, the retarder material of the fixed O-plate 807 may have a negative dielectric anisotropy, i.e., the refractive index of the fast axis is arranged to be tilted. In contrast to rod-shaped materials such as the positive dielectric anisotropy material shown in material 802, such materials may be referred to as disc-shaped materials. The molecules of one of the O-plates 807, 800 may be arranged as a fixed retarder, such as a cured reactive liquid crystal element layer. In this embodiment, the retarder 807 has a fixed retardation, while the retarder 800 is switchable.

[0579] In operation in the driven state for region 855, the tilted molecules of O-plate 807 are arranged to provide equal and relative delays to the tilted molecules of O-plate 800. Therefore, in the driven state, the net delay is zero. By comparison in the undriven state of region 857, the molecules 802 in the delay plate 800 relax and no longer compensate for the O-plate of the delay plate 807, so that an angular distribution suitable for anti-peep mode operation described elsewhere herein is provided.

[0580] Advantageously, the undriven state has lower power consumption and is therefore more convenient than, for example, Fig.39B Compared with the arrangement of , the overall power consumption of the anti-peep mode can be further reduced.

[0581] It may be desirable to provide increased diffusion in the wide angle mode of operation as compared to the privacy mode of operation.

[0582] Fig.55 is a schematic diagram showing in a perspective side view the orientation of a uniformly aligned switchable liquid crystal O-plate 800 and a fixed O-plate 807 which may be arranged with a directional backlight and a spatial light modulator with no applied voltage, wherein the interface 845 between the O-plates is rough.

[0583] In operation in the driven state, the liquid crystal molecules of the retarders 800, 807 are matched so that for a given polarization state, the interface has substantially the same refractive index on each side and no refractive index is step-wise. Such an arrangement produces no optical deflection at the rough surface 845, and therefore the input light 861 is substantially undeflected.

[0584] By comparison in the undriven state, a reflectivity step is provided on the rough surface 845 so that the light 863 is provided with a diffuse angular distribution.

[0585] Advantageously, narrow-angle diffusion is provided in anti-peep mode, while wide-angle diffusion is provided in wide-angle mode. Fig.54Angular brightness control is provided, thereby achieving reduced image visibility at off-axis viewing positions as described elsewhere herein.

[0586] It is desirable to minimize damage to the display device during assembly and handling.

[0587] Fig.56 is a schematic diagram showing a side view of an optical stack 1760 of a directional display device including a directional waveguide 1, wherein switchable liquid crystal retarders 892, 816, 812 are arranged between the waveguide 1 and the spatial light modulator 48, and the surfaces of interfaces 1776, 1770, 1772 and 1774 are arranged to reduce damage by external compressive force 718, as described in U.S. Provisional Patent Application 62 / 565,973, entitled “Optical stack for imaging directional backlights” (Agent Reference Number 407000), filed on September 29, 2017, the entirety of which is incorporated herein by reference.

[0588] Thus, the optical component 1726 includes interfaces 1776, 1770, 1772, 1774 whose surface properties are arranged to provide: (i) a high coefficient of friction under an applied compressive load 1718, which may be through wetting or optical contact to the surface 6, 1753; (ii) release from the surface 6 of the waveguide 1 when the compressive load is removed; (iii) hardness and brittleness characteristics similar to the material of the waveguide 1 to minimize damage to any friction that does occur. Layer 1724 may also include a diffusion function, which may be an asymmetric diffuser that diffuses less in the lateral direction (y-axis) than in the direction orthogonal to the lateral direction (x-axis).

[0589] Advantageously, a privacy display can be provided that can be viewed from a wide range of viewing angles with low image visibility, has low sensitivity to damage caused by externally applied compressive forces 1718, and has an extended lifespan and improved uniformity.

[0590] As described elsewhere herein, it may be desirable to further reduce image visibility to off-axis snoopers by reducing image contrast as well as image brightness. Reduced off-axis contrast in directional displays incorporating directional backlights is described in U.S. Patent Publication 2015-0378085, which is incorporated herein by reference in its entirety.

[0591] Fig.57is a schematic diagram showing a side view of a directional display control system including control of a spatial light modulator, a delay layer, and a light source array. The control system may include a directional display controller 401, which is arranged to provide control signals to an image controller 403 and a light source array controller 402. In addition, a delay plate controller 405 may be arranged to provide control signals to a speed reducer driver 884. The spatial light modulator 48 may be arranged to have a high frame rate, for example, compared to 60 Hz, which may be typically used in other embodiments described elsewhere herein, with 120 Hz or higher. The display controller 410 may be arranged to provide at least a first stage and a second stage of signals to the image controller 403, the light source array controller 402, and optionally to the delay plate controller 405. The operation of the display to provide a reduced contrast to an off-axis snooper will now be described.

[0592] FIG. 58A to FIG. 58E is a schematic diagram illustrating the operation of a directional display in a privacy mode, wherein a primary image is provided on a spatial light modulator in at least a first stage of operation.

[0593] Fig.58A The relative luminous flux 2262 of the light sources 15a-n in the light source array 15 relative to the position 2260 is shown. Such an illumination structure will provide a primary illumination structure 2272 in the window plane of the display. The window plane is the plane of the image of the light sources of the array 15, for example in Fig. 12B At the position of window 26n and optical axis 197.

[0594] Thus, this is an example where there are multiple primary light sources. Therefore, the individual light source flux 2264 may be uniform in a region near the center of the array and zero in other regions. Alternatively, the light source flux 2264 may vary across the illuminated elements, providing graded brightness with varying viewing angles within the primary viewing cone.

[0595] Fig.58B An exemplary primary image 2261 displayed on the spatial light modulator 48 is shown, which includes low transmittance regions 2268 (eg, 0% transmittance) and high transmittance regions 2266 (eg, 100% transmittance).

[0596] Fig.58C 22 shows a graph of relative brightness and contrast in the window plane as a function of viewing angle 2270 of display 100. Distribution 2272 may be provided by a directional display including, for example, an active retarder layer 892 and an additional polarizer, such as Fig.48D shown.

[0597] Thus, brightness profile 2272 includes a central viewing window 2247 and a stray light region 2241 where the brightness is non-zero, such as, in the illustrative example below, 1% at angular position 2251. In operation, the amount of stray light may vary within region 2241, as shown.

[0598] Fig.58C Also shown is a distribution 2274 of the contrast of the perceived image as seen on the spatial light modulator 48 having a viewing angle, which can be substantially uniform except for high viewing angles. The extreme viewing angle properties of the distribution 2274 are determined by the optical properties of the liquid crystal layer 214 and the polarizers 210, 218 and the retarder between the polarizers 210, 218, and are therefore substantially independent of the optical properties of the backlight device.

[0599] Fig.58D A primary image 2280 as perceived by a primary viewer in primary viewing window 2247 is shown, wherein the relative brightness of regions 2267, 2269 are 100% and 0%, substantially equivalent to the relative transmittance of regions 2266, 2268, respectively.

[0600] Fig.58E Using perspective representation, secondary image 2282 including regions 2271, 2273 as perceived at angular position 2251 is shown. Region 2273 may have substantially 0% brightness, while region 2271 may have 1% brightness, which is the transmittance of region 2266 modulated by the brightness of stray light at angular position 2251, in this illustrative example.

[0601] therefore, FIG. 58A to FIG. 58E The arrangement can provide anti-peep mode operation, where the brightness seen by the secondary viewer is 1% of the brightness seen by the primary viewer. Such image brightness can provide blurring of the primary image to the secondary viewer by brightness as described elsewhere herein.

[0602] The contrast of the primary image to the secondary observer may be substantially the same, so image features may still be visible.

[0603] It may be desirable to further reduce the visibility of the image, for example in a dark environment where a small amount of light may still provide image readability to a snooper. In this embodiment, a first operating stage of the time multiplexed display may be provided. FIG. 58A to FIG. 58E A second stage of operation is provided to achieve further image blurring, for example using a frame update rate greater than 60 Hz (eg 120 Hz).

[0604] Figures 59A to 59Eis a schematic diagram illustrating the operation of a directional display in a second phase in a privacy mode, wherein a primary image is provided on a spatial light modulator in a first phase and a secondary image is provided on a spatial light modulator in a second phase.

[0605] This is an example where there are multiple secondary light sources. Fig.59A The light sources of array 15 are shown operated so that the secondary light sources output light having a different light flux distribution 2265. Thus, a secondary lighting structure is achieved so that the light source flux 2265 is arranged to provide substantially the same brightness as stray light from the primary lighting in stray light region 2241.

[0606] Fig.59B The secondary image 2263 is shown having 0% transmittance in region 2290 and 100% transmittance in region 2292. Thus, the displayed secondary image 2263 may be inverted, for example, compared to the displayed primary image 2261.

[0607] like Fig.59C As shown, brightness structure 2294 can substantially match structure 2272 in stray light region 2241, so in this exemplary embodiment, 1% brightness can be achieved at angular position 2251. Angular contrast distribution 2274 in the secondary stage is the same as that in the primary stage.

[0608] Fig.59D A secondary image 2281 including an area 2284 having 0% brightness and an area 2286 having 1% brightness as perceived by the primary viewer 300 is shown, the secondary image including stray light 2295 from the secondary light source. Fig.59E A perspective representation of a perceived secondary image 2283 is shown including an area 2288 having 0% brightness and an area 2290 having 1% brightness, the brightness of these areas being determined by the SLM 48 transmittance of area 2292 and the brightness at location 2251 .

[0609] It will be observed that for off-axis viewing positions, the perceived image 2283 in the second stage is essentially the inverse of the perceived image 2282 in the first stage. The images are combined to obtain a perceived secondary image with very low contrast. Advantageously, the primary image seen by the secondary viewer in the secondary viewing window 2241 can be blurred at an elevation angle due to the reduced contrast.

[0610] In operation, a match of the perceived primary and secondary images 2282, 2283 may be achieved at a small range of viewing positions, such as position 2251. At other viewing areas, the brightness match in the two stages in the off-axis viewing area 2241 may not match as well, and residual image contrast may be perceived. In the present disclosure, the brightness is reduced for off-axis viewing.

[0611] Compared to a directional display without the switchable liquid crystal retarder of the present disclosure, the brightness difference at these mismatched angles in the first and second stages is smaller. The residual image brightness difference in the first and second stages is reduced, and advantageously, the image contrast is further reduced, thereby advantageously reducing the image visibility to a snooper.

[0612] In other words, the control systems 401, 403, 402 are capable of controlling the spatial light modulator 48 and are capable of selectively operating the light sources 15a-n to direct light into corresponding optical windows 26a-n, wherein stray light in the directional backlight source is directed in the output direction 2251 outside the optical window 26 corresponding to the selectively operated light source 2264.

[0613] The control system is also arranged to control the spatial light modulator 48 and the light source 15a-n array to be synchronized with each other so that: (a) when at least one primary light source is selectively operated to direct light into at least one primary optical window for observation by a primary viewer (not a peeper), the spatial light modulator 48 displays a primary image 2261, and (b) when the primary image 2261 is displayed in a time-multiplexed manner, when at least one light source different from the at least one primary light source is selectively operated to direct light into at least one secondary optical window outside the primary optical window, the spatial light modulator 48 displays a secondary image 2263, and the secondary image 2282 perceived by the secondary viewer (not a peeper) outside the primary optical window blurs the primary image 2282 modulated by the stray light directed outside the primary optical window 2247.

[0614] It may be desirable to further reduce the power consumption of a display.

[0615] The control system may be arranged to control the applied voltage across the switchable liquid crystal retarder in a time multiplexed manner. Thus, the retarder controller 405 is further arranged to control the voltage across the switchable retarder in synchronism with the switching of the spatial light modulator and the light source. The stray light distribution may be adjusted together with the light flux on the array of light sources 15. Fig.58A In the described first operating phase, the switchable retarder may be provided with a narrow output brightness distribution in the lateral direction, whereas in the second operating phase a wider output brightness distribution may be provided.

[0616] In operation, if the switchable retarder has a higher off-axis output in the second operating stage, a reduced light flux can be provided in the second operating mode. Advantageously, power consumption can be reduced in the second stage of operation and the light source can be driven more effortlessly, thereby extending life and improving efficiency.

[0617] Directional backlights including other types of waveguides will now be described.

[0618] Fig.60 is a schematic diagram showing a side view of the optical stack of a directional display device including a collimating waveguide 1901, a wide angle waveguide 1920, a switchable liquid crystal O-plate 892 and a corrective passive delay plate 890 arranged between the additional polarizer 500 and the input polarizer 210.

[0619] In operation, a light source 1915 illuminates the fixed collimating waveguide 1901 on the side 1902. The fixed collimating waveguide is provided with a taper having a cross-sectional shape with an increasing width to cause light to propagate in the waveguide in a direction away from the light source at the input end. The tapered waveguide may alternatively or additionally be provided by a tapered light redirecting microstructure, as will be described in FIG. 33 . Light rays 1910 leak from the upper surface 1906 and are incident on the prism array 1926. The prism array 1927 deflects the grazing incident light 1910 towards the normal direction, thereby providing a narrow cone angle in the lateral direction (yz plane), which may be partially diffused by the diffuser 1929. The direction of the ray 1910 is substantially independent of the position of the light source 1915 on the input side 1902, and in contrast to the imaging waveguide 1 providing an optical window, the fixed collimating waveguide 1901 does not image the light source 1915.

[0620] Thus, the directional backlight may include a waveguide 1920 further including a taper, the waveguide being arranged to deflect input light rays 1910 directed from the light source 1915 through the waveguide 1920 to exit through the first guide surface 1906. Thus, one of the optical components 726 includes a prism array 1927 arranged to deflect light rays 1910 exiting through the first guide surface 1906 of the waveguide 1901.

[0621] In order to provide a wide angle operation mode, a second wide angle waveguide 1920 may be provided. The wide angle waveguide 1920 has microstructures (not shown) on surfaces 1921, 1919 to provide scattered light for light 1930 from light source 1925.

[0622] The switchable liquid crystal retarder 892 and the corrected passive retarder 890 may advantageously achieve a significant reduction in the visibility of off-axis images to a peeper in an anti-peeping mode of operation.

[0623] Fig.61is a schematic diagram showing a side view of a directional display device optical stack including a collimating waveguide and a switchable diffuser, a switchable liquid crystal O-plate and a corrective passive retarder.

[0624] Fixed collimating waveguide 1951 may be provided with a microstructure 1953 that couples some light 1970 from light source 1955 into a vertical direction by reflection from prism array 726. Fig.60 A single tapered waveguide operates in a similar manner, whereby at least one tapered waveguide comprises an array of tapered microstructures 1953.

[0625] The backlight may also incorporate a switchable diffuser layer 1960 comprising polymer dispersed liquid crystal (PDLC) 1955. In a narrow angle mode of operation, the liquid crystal is arranged to transmit light 1972 that passes through the microstructures 1953. The light 1972 is absorbed by the absorber layer 1962 and is therefore not output through the spatial light modulator 48.

[0626] In a wide angle mode of operation, the liquid crystal molecules in the PDLC 1955 are switched to provide a scattering function to the surrounding medium so that light 1974 is scattered to a wide range of viewing positions.

[0627] The switchable liquid crystal retarder 892 and the corrected passive retarder 890 may advantageously achieve a significant reduction in the visibility of off-axis images to a peeper in an anti-peeping mode of operation.

[0628] As may be used herein, the terms "substantially" and "approximately" provide industry-accepted tolerances for their corresponding terms and / or relativity between terms. Such industry-accepted tolerances are in the range of 0% to 10% and correspond to, but are not limited to, component values, angles, etc. This relativity between items is in the range of approximately 0% to 10%.

[0629] Although various embodiments according to the principles disclosed herein are described above, it should be understood that these embodiments are shown by way of example only and are not intended to be limiting. Therefore, the breadth and scope of the present disclosure should not be limited by any of the above-described exemplary embodiments, but should only be limited by any claims issued from the present disclosure and their equivalents. In addition, the above-described advantages and characteristic structures are provided in the described embodiments, but the application of these issued claims should not be limited to methods and structures for achieving any or all of the above-described advantages.

[0630] In addition, the section titles of this article are provided to comply with the recommendations of 37CFR 1.77, or to provide organizational clues. These titles should not limit or characterize the one or more embodiments listed in any claims that may arise from this disclosure. Specifically and by way of example, although the title refers to the "technical field", the claims should not be limited by the language selected under this title to describe the so-called field. In addition, the description of the technology in the "background technology" should not be understood as an admission that certain technologies are prior art for any one or more embodiments in this disclosure. "Invention content" is also not to be regarded as a characterization of one or more embodiments described in the claims issued. In addition, any reference to the singular form of "invention" in this disclosure should not be used to argue that there is only a single novel point in this disclosure. Multiple embodiments can be elaborated according to the limitations of multiple claims arising from this disclosure, and such claims therefore limit one or more embodiments and their equivalents protected by them. In all cases, the scope should be considered based on the characteristics of the claims themselves according to this disclosure, and should not be constrained by the titles given herein.

Claims

1. A display device, comprising: Transmissive spatial light modulator; A backlight source arranged to output light, the backlight source comprising: two sets of multiple light sources; and two waveguides arranged behind the transmissive spatial light modulator, Each waveguide comprises an input end extending in a lateral direction along a side of the waveguide, wherein the input ends of the two waveguides are on opposite sides of the display device, one of the two plurality of light sources is disposed along the input end of a first waveguide of the two waveguides and arranged to input input light into the first waveguide, and the other of the two plurality of light sources is disposed along the input end of a second waveguide of the two waveguides and arranged to input input light into the second waveguide; and Each waveguide further comprises opposing first and second guide surfaces extending across the waveguide from the input end for guiding light input at the input end along the waveguide, each waveguide being arranged to extract input light guided through the waveguide in a glancing direction relative to the first guide surface to exit through the first guide surface; and a prism input layer between the transmissive spatial light modulator and the two waveguides, the prism input layer being arranged to receive light extracted from the two waveguides in the glancing direction relative to the first guide surface and to direct the received light to be incident on the transmissive spatial light modulator, wherein the backlight sources are arranged so that light from respective waveguides is directed to provide viewing windows having different widths; an input polarizer disposed on an input side of the transmissive spatial light modulator between the backlight source and the transmissive spatial light modulator; an output polarizer disposed on an output side of the transmissive spatial light modulator; an additional polarizer disposed on an input side of the input polarizer between the input polarizer and the backlight; and At least one retarder is arranged between the additional polarizer and the input polarizer.

2. A display device according to claim 1, wherein the at least one retarder comprises at least one switchable liquid crystal retarder and at least one corrective passive retarder.

3. The display device according to claim 1, wherein the waveguide is arranged to image the light source in the lateral direction so that the output light from the light source is guided into the corresponding optical window in an output direction distributed according to an input position of the light source. 4 . The display device according to claim 1 , wherein the additional polarizer is arranged on the input side of the input polarizer, and the at least one delay plate is arranged between the additional polarizer and the input polarizer. The display device of claim 1 , wherein the additional polarizer is a reflective polarizer. 6 . The display device of claim 1 , wherein the additional polarizer has an electric vector transmission direction that is parallel to an electric vector transmission direction of the input polarizer.

7. The display device according to claim 1, wherein the additional polarizer is arranged on the output side of the output polarizer, and the at least one delay plate is arranged between the additional polarizer and the output polarizer.

8. The display device of claim 2, wherein the at least one corrective passive retarder comprises a pair of retarders having slow axes in planes where the retarders intersect.

9. A display device according to claim 8, wherein the pair of retarders have slow axes each extending at 45° relative to an electric vector transmission direction parallel to an electric vector transmission direction of the input polarizer.

10. The display device of claim 8, wherein the pair of retarders each comprises a single A-plate. 11 . The display device according to claim 8 , wherein the pair of retardation plates each comprises a plurality of A plates having respective slow axes aligned at different angles from each other.

12. The display device of claim 2, wherein the at least one corrective passive retarder comprises a retarder having a slow axis perpendicular to a plane of the retarder.

13. The display device of claim 12, wherein the retarder having a slow axis perpendicular to the plane of the corrected passive retarder comprises a C-plate.

14. The display device according to claim 1, wherein the at least one retarder further comprises a pair of retarder plates having slow axes in planes of the retarder plates intersecting.

15. The display device of claim 14, wherein the pair of retarders have slow axes extending at 0° and 90°, respectively, relative to an electric vector transmission direction parallel to an electric vector transmission direction of the input polarizer.

16. A display device according to claim 2, wherein the at least one corrective passive delay plate includes a delay plate with a slow axis orientation, and the delay plate with a slow axis orientation has a component perpendicular to the plane of the delay plate and at least one component in the plane of the delay plate.

17. A display device according to claim 1, wherein the at least one delay plate includes a delay plate with a slow axis orientation, wherein the delay plate with a slow axis orientation has a component perpendicular to the plane of the delay plate, a component orthogonal to the electric vector transmission direction of the input polarizer in the plane of the delay plate, and substantially no component parallel to the electric vector transmission direction of the input polarizer in the plane of the delay plate.

18. A display device according to claim 1, wherein the at least one delay plate includes a delay plate with a slow axis orientation, wherein the delay plate with a slow axis orientation has a component perpendicular to the plane of the delay plate, a component parallel to the electric vector transmission direction of the input polarizer in the plane of the delay plate, and substantially no component orthogonal to the electric vector transmission direction of the input polarizer in the plane of the delay plate. The display device according to claim 18 , wherein the retardation plate comprises an O-plate.

20. A display device according to claim 18, wherein the delay plate comprises a switchable liquid crystal delay plate, and the switchable liquid crystal delay plate can be switched between an O-plate delay plate and an A-plate delay plate by applying a voltage across the switchable liquid crystal delay plate.

21. The display device of claim 20, wherein the switchable liquid crystal retarder comprises at least one vertical alignment layer.

22. The display device of claim 21, further comprising at least one corrective passive retarder arranged between the additional polarizer and the input polarizer.

23. The display device of claim 22, wherein the corrective passive retarder comprises a negative C-plate or a crossed positive A-plate.

24. The display device of claim 2, wherein the liquid crystal retarder has an optical thickness between 500 nm and 1000 nm.

25. The display device of claim 24, wherein the at least one corrective passive retarder has an optical thickness between 400 nm and 800 nm.

26. A display device according to claim 2, wherein the switchable liquid crystal retarder includes at least a first region and a second region, the first region and the second region being independently addressable using a first applied voltage and a second applied voltage. 27 . The display device of claim 1 , wherein the at least one retarder comprises a first O-plate retarder and a second O-plate retarder that are switchable. 28 . The display device according to claim 27 , wherein a surface relief structure is provided at an interface between the first O-plate retarder and the second O-plate retarder.

29. The display device according to claim 1, wherein the backlight source comprises: Light source array; A waveguide, which is arranged to receive input light from the light source at different input positions, and includes: a first guide surface and a second guide surface relative to each other, the first guide surface and the second guide surface relative to each other, for guiding the input light along the waveguide; a side surface, the side surface extending between the first guide surface and the second guide surface; and a reflective end, the reflective end for reflecting the input light back along the waveguide; wherein the second guide surface is arranged to deflect the reflected input light through the first guide surface as output light, and the waveguide is arranged to image the light source in a lateral direction between the side surfaces of the waveguide, so that the output light from the light source is guided into a corresponding optical window in an output direction distributed according to the input position of the light source.

30. A display device according to claim 29, wherein the first guiding surface is arranged to guide light by total internal reflection, and the second guiding surface includes light extraction feature structures and an intermediate region between the light extraction feature structures, the light extraction feature structures are oriented to deflect the reflected input light through the first guiding surface as output light, and the intermediate region is arranged to guide light through the waveguide without extracting the light.

31. The display device of claim 30, wherein the light extraction features are curved and have positive optical power in the lateral direction between sides of the waveguide extending between the first and second guide surfaces.

32. The display device of claim 29, wherein the reflective end has positive optical power in the lateral direction extending between sides of the waveguide extending between the first guide surface and the second guide surface.

33. The display device of claim 29, wherein the waveguide comprises an input end opposite to the reflective end, and the light source is arranged to input light into the waveguide through the input end.

34. The display device of claim 29, wherein the light source is arranged to input light into the waveguide through the side surface of the waveguide.

35. The display device according to claim 29, wherein The additional polarizer is a reflective polarizer arranged on the input side of the input polarizer and is arranged to transmit a first polarization component of the output light and reflect a second polarization component of the output light having a polarization state orthogonal to that of the first polarization component as blocked light; and A rear reflector is disposed behind the second guiding surface, the rear reflector being arranged to reflect the blocked light to supply back to the transmissive spatial light modulator, the rear reflector comprising a linear array of paired reflective angular facets extending in a predetermined direction perpendicular to a normal line of the transmissive spatial light modulator, so that the rear reflector converts the polarization of the blocked light with two reflections from a pair of angular facets into the polarization of the first polarization component.

36. The display device of claim 35, wherein the pairs of reflective angle facets are curved and have optical power in the lateral direction.

37. The display device of claim 2, further comprising a control system arranged to control the light source.

38. A display device according to claim 37, wherein the control system is further arranged to control an applied voltage across the switchable liquid crystal retarder.

39. A display device according to claim 37, wherein the control system is arranged to provide switching between in a first operating mode, controlling the light source to provide an illumination distribution from the waveguide having a first angular width; and a first applied voltage across the switchable liquid crystal retarder; in a second operating mode, controlling the light source to provide an illumination distribution from the waveguide having a second angular width greater than the first angular width; and a second applied voltage across the switchable liquid crystal retarder that is different from the first applied voltage.

40. The display device according to claim 39, wherein the second applied voltage is smaller than the first applied voltage.

41. A display device according to claim 2, wherein the switchable liquid crystal retarder between the additional polarizer and the input polarizer The transmissive spatial light modulator has a maximum attenuation polar coordinate having an elevation angle greater than zero relative to a normal direction of the transmissive spatial light modulator.

42. The display device of claim 41, wherein the maximum attenuation polar coordinate has an elevation angle between 10 degrees and 50 degrees.

43. The display device of claim 41, wherein the maximum attenuation polar coordinate has a lateral angle of 30 degrees to 60 degrees.

44. The display device of claim 39, wherein the control system is capable of controlling the transmissive spatial light modulator and is capable of selectively operating the light source to direct light into a corresponding optical window, wherein stray light in the backlight source is directed in an output direction out of the optical window corresponding to the selectively operated light source, The control system is arranged to control the transmissive spatial light modulator and the light source array in synchronism with each other such that: (a) the transmissive spatial light modulator displays a primary image when at least one primary light source is selectively operated to direct light into at least one primary optical window for viewing by a primary observer, and (b) in the case of displaying the primary image in a time multiplexed manner, when at least one light source different from the at least one primary light source is selectively operated to direct light into a secondary optical window outside the at least one primary optical window, the transmissive spatial light modulator displays a secondary image, and the secondary image perceived by a secondary observer outside the primary optical window blurs the primary image that modulates the stray light directed outside the primary optical window.

45. A display device according to claim 44, wherein the control system is arranged to control the applied voltage across the switchable liquid crystal retarder in a time multiplexed manner.

46. ​​The display device according to claim 44, further comprising: Means for determining a position of a snooper relative to the display device, wherein the control system is arranged to adjust the first applied voltage in response to the position of the snooper.

47. The display device of claim 1, wherein the backlight source is switchable between modes for outputting the output light into viewing windows of different widths.

48. The display device of claim 1, wherein the display device is disposed in a vehicle.

49. The display device of claim 48, wherein the display device is arranged below a transparent window in the vehicle.

50. The display device of claim 48, wherein the display device is arranged in front of a seat in the vehicle.

51. A display device according to claim 1, wherein at least one of the at least one delay plate arranged between the additional polarizer and the input polarizer is controlled by an addressing electrode.

52. The display device of claim 51, wherein the address electrodes are patterned to provide at least two pattern areas.

53. The display device of claim 52, wherein the pattern area is a camouflage pattern.

54. A display device according to claim 52, wherein at least one of the pattern areas is individually addressable and is arranged to operate in a privacy mode of operation.

55. The display device according to claim 2 further includes at least one additional polarizer and at least one additional corrective passive delay plate and at least one additional switchable liquid crystal delay layer, and the at least one additional corrective passive delay plate and the at least one additional switchable liquid crystal delay layer are arranged between the at least one additional additional polarizer and the input polarizer.

56. A display device according to claim 55, wherein the alignment direction of the upper alignment layer of the first switchable liquid crystal layer is parallel or anti-parallel to the alignment direction of the upper alignment layer of the at least one additional switchable liquid crystal delay layer, and the alignment direction of the lower alignment layer of the first switchable liquid crystal layer is parallel or anti-parallel to the alignment direction of the lower alignment layer of the at least one additional switchable liquid crystal delay layer.

57. A display device according to claim 55, wherein the alignment direction of the at least one corrective passive retarder is parallel or anti-parallel to the alignment direction of the at least one additional corrective passive retarder.

58. A display device according to claim 55, wherein the alignment direction of the upper alignment layer of the first switchable liquid crystal layer is orthogonal to the alignment direction of the upper alignment layer of the at least one additional switchable liquid crystal delay layer, and the alignment direction of the lower alignment layer of the first switchable liquid crystal layer is parallel or anti-parallel to the alignment direction of the lower alignment layer of the at least one additional switchable liquid crystal delay layer.

59. A display device according to claim 55, wherein the alignment direction of the at least one corrective passive retarder is orthogonal to the alignment direction of the at least one additional corrective passive retarder.

60. The display device of claim 1, wherein the backlight further comprises a backscattering reflector disposed behind the two waveguides.

61. The display device of claim 1, wherein the backlight source further comprises an intermediate diffusion layer disposed between the two waveguides.

62. A display device according to claim 1, wherein the first guiding surface and the second guiding surface of the two waveguides include scattering microstructures, and the scattering microstructures are arranged to extract input light guided through the waveguide in the glancing direction relative to the first guiding surface to exit through the first guiding surface.

63. A display device according to claim 1, wherein the prism input layer includes a first input facet and a second input facet, wherein light extracted from the first waveguide is received by the first input facet and light extracted from the second waveguide is received by the second input facet.

64. A display device, comprising: Transmissive spatial light modulator; A backlight source arranged to output light, the backlight source comprising: two sets of multiple light sources; and two waveguides arranged behind the transmissive spatial light modulator, Each waveguide comprises an input end extending in a lateral direction along a side of the waveguide, wherein the input ends of the two waveguides are on opposite sides of the display device, one of the two plurality of light sources is disposed along the input end of a first waveguide of the two waveguides and arranged to input input light into the first waveguide, and the other of the two plurality of light sources is disposed along the input end of a second waveguide of the two waveguides and arranged to input input light into the second waveguide; and Each waveguide further comprises opposing first and second guide surfaces extending across the waveguide from the input end for guiding light input at the input end along the waveguide, each waveguide being arranged to extract input light guided through the waveguide in a glancing direction relative to the first guide surface to exit through the first guide surface; and a prism input layer between the transmissive spatial light modulator and the two waveguides, the prism input layer being arranged to receive light extracted from the two waveguides in the glancing direction relative to the first guide surface and to direct the received light to be incident on the transmissive spatial light modulator, wherein the backlight sources are arranged so that light from respective waveguides is directed to provide viewing windows having different widths; an input polarizer disposed on an input side of the transmissive spatial light modulator between the backlight source and the transmissive spatial light modulator; an output polarizer disposed on an output side of the transmissive spatial light modulator; an additional polarizer disposed on an input side of the input polarizer between the input polarizer and the backlight; and at least one corrective passive retarder and at least one switchable liquid crystal retarder, the at least one corrective passive retarder and the at least one switchable liquid crystal retarder being arranged between the additional polarizer and the input polarizer, Wherein the at least one switchable liquid crystal retarder comprises electrodes and is switchable by applying a voltage to the electrodes of the at least one switchable liquid crystal retarder.

65. The display device of claim 64, further comprising at least one further additional polarizer and at least one further corrective passive retarder and at least one further switchable liquid crystal retarder, the at least one further corrective passive retarder and the at least one further switchable liquid crystal retarder being arranged between the at least one further additional polarizer and the input polarizer, Wherein the at least one further switchable liquid crystal retarder comprises electrodes and is switchable by applying a voltage to the electrodes of the at least one switchable liquid crystal retarder.

66. A display device according to claim 65, wherein the alignment of the upper alignment layer of the first switchable liquid crystal layer is parallel or anti-parallel to the alignment of the upper alignment layer of at least one other switchable liquid crystal layer, and the alignment of the lower alignment layer of the first switchable liquid crystal layer is parallel or anti-parallel to the alignment of the lower alignment layer of the at least one other switchable liquid crystal layer.

67. A display device according to claim 65, wherein the alignment of the at least one corrective passive retarder is parallel or anti-parallel to the alignment of the at least one additional corrective passive retarder.

68. A display device according to claim 65, wherein the alignment of the upper alignment layer of the first switchable liquid crystal layer is orthogonal to the alignment of the upper alignment layer of at least one additional switchable liquid crystal layer, and the alignment of the lower alignment layer of the first switchable liquid crystal layer is parallel or anti-parallel to the alignment of the lower alignment layer of the at least one additional switchable liquid crystal layer.

69. A display device according to claim 65 or claim 68, wherein the alignment of the at least one corrective passive retarder is orthogonal to the alignment of the at least one further corrective passive retarder.

70. The display device of claim 64, wherein the corrective passive retarder comprises a negative C-plate or a crossed positive A-plate.

71. A display device according to claim 64, wherein the at least one switchable liquid crystal retarder includes at least one surface alignment layer arranged adjacent to the liquid crystal to provide vertical alignment in the adjacent liquid crystal material.

72. A display device according to claim 64, wherein the liquid crystal retarder has an optical thickness between 500nm and 1000nm.

73. A display device according to claim 72, wherein the at least one corrective passive retarder has an optical thickness between 400nm and 800nm.

74. A display device, comprising: Transmissive spatial light modulator; A backlight source arranged to output light, the backlight source comprising: two sets of multiple light sources; and two waveguides arranged behind the transmissive spatial light modulator, Each waveguide comprises an input end extending in a lateral direction along a side of the waveguide, wherein the input ends of the two waveguides are on opposite sides of the display device, one of the two plurality of light sources is disposed along the input end of a first waveguide of the two waveguides and arranged to input input light into the first waveguide, and the other of the two plurality of light sources is disposed along the input end of a second waveguide of the two waveguides and arranged to input input light into the second waveguide; and Each waveguide further comprises opposing first and second guide surfaces extending across the waveguide from the input end for guiding light input at the input end along the waveguide, each waveguide being arranged to extract input light guided through the waveguide in a glancing direction relative to the first guide surface to exit through the first guide surface; and a prism input layer between the transmissive spatial light modulator and the two waveguides, the prism input layer being arranged to receive light extracted from the two waveguides in the glancing direction relative to the first guide surface and to direct the received light to be incident on the transmissive spatial light modulator, wherein the backlight sources are arranged so that light from respective waveguides is directed to provide viewing windows having different widths; an input polarizer disposed on an input side of the transmissive spatial light modulator between the backlight source and the transmissive spatial light modulator; an output polarizer disposed on an output side of the transmissive spatial light modulator; an additional polarizer disposed on an output side of the output polarizer; and At least one retarder is arranged between the additional polarizer and the output polarizer.

75. A display device, comprising: Transmissive spatial light modulator; A backlight source arranged to output light, the backlight source comprising: two sets of multiple light sources; and two waveguides arranged behind the transmissive spatial light modulator, Each waveguide comprises an input end extending in a lateral direction along a side of the waveguide, wherein the input ends of the two waveguides are on opposite sides of the display device, one of the two plurality of light sources is disposed along the input end of a first waveguide of the two waveguides and arranged to input input light into the first waveguide, and the other of the two plurality of light sources is disposed along the input end of a second waveguide of the two waveguides and arranged to input input light into the second waveguide; and Each waveguide further comprises opposing first and second guide surfaces extending across the waveguide from the input end for guiding light input at the input end along the waveguide, each waveguide being arranged to extract input light guided through the waveguide in a glancing direction relative to the first guide surface to exit through the first guide surface; and a prism input layer between the transmissive spatial light modulator and the two waveguides, the prism input layer being arranged to receive light extracted from the two waveguides in the glancing direction relative to the first guide surface and to direct the received light to be incident on the transmissive spatial light modulator, wherein the backlight sources are arranged so that light from respective waveguides is directed to provide viewing windows having different widths; an input polarizer disposed on an input side of the transmissive spatial light modulator between the backlight source and the transmissive spatial light modulator; an output polarizer disposed on an output side of the transmissive spatial light modulator; an additional polarizer disposed on an output side of the output polarizer; and at least one corrective passive retarder and at least one switchable liquid crystal retarder, the at least one corrective passive retarder and the at least one switchable liquid crystal retarder being arranged between the additional polarizer and the output polarizer, Wherein the at least one switchable liquid crystal retarder comprises electrodes and is switchable by applying a voltage to the electrodes of the at least one switchable liquid crystal retarder.

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