Optical stacks for switchable directional displays

Abstract

SOLUTION: To provide a privacy display comprising a spatial light modulator and a compensated switchable liquid crystal retarder arranged between first and second polarizers arranged in series with the spatial light modulator.EFFECT: In a privacy mode of operation, on-axis light from the spatial light modulator is directed without loss, whereas off-axis light has reduced luminance. Visibility of the display to off-axis snoopers is reduced by means of luminance reduction over a wide polar field. In a wide angle mode of operation, a switchable liquid crystal retarder is adjusted so that off-axis luminance is substantially unmodified.SELECTED DRAWING: Figure 1A

Description

[Technical field]

[0001] FIELD OF THE DISCLOSURE This disclosure relates generally to illumination from light modulating elements, and more particularly to switchable optical stacks for controlling illumination for use in displays, such as privacy displays. [Background technology]

[0002] Privacy displays provide image visibility to primary users, typically in on-axis locations, and reduce visibility of image content to snoopers, typically in off-axis locations. Privacy functionality can be provided by microlouver optical films that transmit some light from the display in the on-axis direction and have low brightness in off-axis locations. However, such films are lossy for frontal illumination, and the microlouvers can introduce moiré due to pixel beating of the spatial light modulator. The pitch of the microlouvers must be selected according to the panel resolution choice, which can increase inventory and costs.

[0003] A switchable privacy display can be provided by control of the off-axis light output.

[0004] The control can be provided by, for example, brightness reduction by a switchable backlight of a liquid crystal display (LCD) spatial light modulator. Display backlights generally use a waveguide and an edge-emitting light source. Certain imaging directional backlights have the additional function of directing illumination through a display panel to a viewing window. An imaging system can be formed between multiple light sources and the respective window images. An example of an imaging directional backlight is a light valve that can use a folded optical system, which can therefore also be an example of a folded imaging directional backlight. Light can propagate substantially losslessly in one direction through the light valve, while counter-propagating light can be extracted by reflective inclined facets, as described in U.S. Pat. No. 9,519,153, which is incorporated herein by reference in its entirety.

[0005] Off-axis privacy control can further be provided by contrast reduction, for example, by adjusting the liquid crystal bias tilt in an in-plane switching LCD. Summary of the Invention

[0006] According to a first aspect of the present disclosure, there is provided a display device comprising a spatial light modulator, a display polarizer arranged on a side of the spatial light modulator, an additional polarizer arranged on the same side of the spatial light modulator as the display polarizer, and a number of retarders arranged between the additional polarizer and the display polarizer, the number of retarders comprising a switchable liquid crystal retarder comprising a layer of liquid crystal material arranged between the display polarizer and the additional polarizer, and at least one passive compensation retarder.

[0007] The multiple retarders may be configured to have no effect on the brightness of light passing through the display polarizer, the additional polarizer, and the multiple retarders along an axis normal to the plane of the retarder, and / or to reduce the brightness of light passing through the display polarizer, the additional polarizer, and the multiple retarders along an axis tilted relative to the normal to the plane of the retarder.

[0008] At least one passive compensation retarder may be configured to introduce no phase shift into the polarization components of light passing through one of the display polarizers and the additional polarizer on the input side of the multiple retarders along an axis normal to the plane of the at least one passive compensation retarder, and / or to introduce a phase shift into the polarization components of light passing through one of the display polarizers and the additional polarizer on the input side of the multiple retarders along an axis tilted relative to the normal to the plane of the at least one passive compensation retarder.

[0009] The switchable liquid crystal retarder may be configured to introduce no phase shift into the polarization components of light passing through one of the display polarizers and the additional polarizer on the input side of the plurality of retarders along an axis normal to the plane of the switchable liquid crystal retarder, and / or to introduce a phase shift into the polarization components of light passing through one of the display polarizers and the additional polarizer on the input side of the plurality of retarders in the switchable state of the switchable liquid crystal retarder along an axis tilted relative to the normal to the plane of the switchable liquid crystal retarder.

[0010] Advantageously, a switchable privacy display may be provided that may be switched between wide-angle and privacy operating states. The field of view of the privacy operation may be expanded and lower off-axis brightness levels may be achieved compared to known devices, improving the degree of privacy observed by off-axis snoopers. Furthermore, on-axis brightness relative to the primary on-axis user may be maintained in both the wide-angle and privacy operating states.

[0011] The display polarizer and the additional polarizer may have parallel electric vector transmission directions.

[0012] In one alternative, the switchable liquid crystal retarder may comprise two surface alignment layers disposed adjacent to and on either side of the layer of liquid crystal material, each configured to provide homeotropic alignment in the adjacent liquid crystal material. The layer of liquid crystal material of the switchable liquid crystal retarder may comprise a liquid crystal material having a negative dielectric anisotropy. The layer of liquid crystal material may have a retardance in the range of 500 nm to 1000 nm, preferably in the range of 600 nm to 900 nm, most preferably in the range of 700 nm to 850 nm for light of a wavelength of 550 nm.

[0013] When two surface alignment layers providing homeotropic alignment are provided, the at least one passive compensation retarder may comprise a retarder having an optic axis perpendicular to the plane of the retarder, the at least one passive retarder having a retardance in the range of -300nm to -900nm, preferably in the range of -450nm to -800nm, most preferably in the range of -500nm to -725nm for light of wavelength 550nm.

[0014] Alternatively, when two surface alignment layers providing homeotropic alignment are provided, the at least one passive compensation retarder may comprise a pair of retarders with optic axes in the plane of the crossed retarders, each retarder of the pair having a retardance in the range of 300 nm to 800 nm, preferably in the range of 500 nm to 700 nm, most preferably in the range of 550 nm to 675 nm for light of wavelength 550 nm. Advantageously, in this case, the field of view in the wide-angle operation mode may be expanded. Furthermore, zero voltage operation in the wide-angle operation mode may be provided to reduce power consumption.

[0015] In another alternative, the switchable liquid crystal retarder may comprise two surface alignment layers disposed adjacent to and on either side of the layer of liquid crystal material, each configured to provide homogeneous alignment within the adjacent liquid crystal material, which may advantageously provide improved resilience to the visibility of flow of the liquid crystal material during application of pressure, compared to homeotropic alignment on either side of the liquid crystal.

[0016] The layer of liquid crystal material of the switchable liquid crystal retarder may comprise a liquid crystal material with positive dielectric anisotropy and may have a retardance in the range of 500nm to 900nm, preferably in the range of 600nm to 850nm, most preferably in the range of 700nm to 800nm ​​for light of wavelength 550nm.

[0017] When two surface alignment layers providing homogeneous alignment are provided, the at least one passive compensation retarder may comprise a retarder having an optic axis perpendicular to the plane of the retarder, the at least one passive retarder having a retardance in the range of -300nm to -700nm, preferably in the range of -350nm to -600nm, most preferably in the range of -400nm to -500nm for light of a wavelength of 550nm.

[0018] Alternatively, when two surface alignment layers providing homogeneous alignment are provided, the at least one passive compensation retarder may comprise a pair of retarders with optic axes in the plane of the crossed retarders, each retarder of the pair having a retardance in the range 300nm to 800nm, preferably 350nm to 650nm, most preferably 450nm to 550nm for light of wavelength 550nm. Advantageously, in this case, resilience to visibility of flow of liquid crystal material during application of pressure may be improved.

[0019] In another alternative, the switchable liquid crystal retarder may comprise two surface alignment layers disposed adjacent to and on either side of the layer of liquid crystal material, one of the surface alignment layers configured to provide homeotropic alignment in the adjacent liquid crystal material and the other of the surface alignment layers configured to provide homogeneous alignment in the adjacent liquid crystal material.

[0020] When a surface alignment layer configured to provide homogeneous alignment is between the layer of liquid crystal material and the compensating retarder, the layer of liquid crystal material may have a retardance in the range of 700nm to 2000nm, preferably in the range of 1000nm to 1500nm, most preferably in the range of 1200nm to 1500nm for light of a wavelength of 550nm.

[0021] When a surface alignment layer configured to provide homogeneous alignment is between the layer of liquid crystal material and the compensating retarder, the at least one passive compensating retarder may comprise a retarder having an optic axis that is perpendicular to the plane of the retarder, the at least one passive retarder having a retardance in the range of -400nm to -1800nm, preferably in the range of -700nm to -1500nm, most preferably in the range of -900nm to -1300nm for light of a wavelength of 550nm.

[0022] Where a surface alignment layer configured to provide homogeneous alignment is between the layer of liquid crystal material and the compensating retarder, the at least one passive compensating retarder may comprise a pair of retarders having optic axes in the plane of the crossed retarders, each of the pair having a retardance in the range of 400 nm to 1800 nm, preferably in the range of 700 nm to 1500 nm, most preferably in the range of 900 nm to 1300 nm for light of a wavelength of 550 nm.

[0023] When a surface alignment layer configured to provide homeotropic alignment is between the layer of liquid crystal material and the compensating retarder, the layer of liquid crystal material may have a retardance in the range of 500nm to 1800nm, preferably in the range of 700nm to 1500nm, most preferably in the range of 900nm to 1350nm for light of a wavelength of 550nm.

[0024] If a surface alignment layer configured to provide homeotropic alignment is between the layer of liquid crystal material and the compensation retarder, the at least one passive compensation retarder may comprise a retarder having an optic axis that is perpendicular to the plane of the retarder, and the at least one passive retarder has a retardance in the range of -300nm to -1600nm, preferably in the range of -500nm to -1300nm, most preferably in the range of -700nm to -1150nm for light of a wavelength of 550nm.

[0025] In the case where a surface alignment layer configured to provide homeotropic alignment is between the layer of liquid crystal material and the compensating retarder, the at least one passive compensating retarder may comprise a pair of retarders having optic axes in the plane of the crossed retarders, each retarder of the pair having a retardance in the range of 400nm to 1600nm, preferably in the range of 600nm to 1400nm, most preferably in the range of 800nm ​​to 1300nm for light of wavelength 550nm. Advantageously, in this case, resilience to visibility of flow of the liquid crystal material during application of pressure may be improved.

[0026] Each alignment layer may have a pretilt with the pretilt direction being parallel or antiparallel to the electric vector transport direction of the display polarizer, or orthogonal to the in-plane component of the liquid crystal layer. Advantageously, the display may be provided with a narrow lateral viewing angle and high viewing freedom for rotation of the display about a horizontal axis. Such a display may be easy to view for a frontal display user and difficult to view for an off-axis display user.

[0027] The at least one passive retarder may comprise at least two passive retarders having optical axes in at least two different directions, which may have optical axes in the planes of the intersecting retarders. The field of view of the homogeneously aligned liquid crystal retarder is increased while restoring visibility of the flow of liquid crystal material under pressure.

[0028] A pair of passive retarders may have optic axes extending at 45° and 135°, respectively, with respect to an electric vector propagation direction that is parallel to the electric vector propagation direction of the display polarizer. The passive retarders may be provided using stretched films, advantageously providing low cost and high uniformity.

[0029] The switchable liquid crystal retarder may be disposed between a pair of passive retarders. Advantageously, the thickness and complexity of multiple retarders may be reduced.

[0030] The transparent electrodes and liquid crystal alignment layers may be formed on either side of a pair of passive retarders adjacent to the switchable liquid crystal retarder, and may further comprise a first substrate and a second substrate with the switchable liquid crystal retarder disposed therebetween, each of the first substrate and the second substrate comprising one of the pair of passive retarders, each of the pair of passive retarders having a retardance in the range of 150nm to 800nm ​​for light of a wavelength of 550nm, preferably in the range of 200nm to 700nm, most preferably in the range of 250nm to 600nm.

[0031] In one alternative, the at least one passive compensation retarder may comprise a retarder having an optical axis perpendicular to the plane of the retarder. Advantageously, the thickness and complexity of the passive retarder stack may be reduced.

[0032] The at least one passive compensation retarder may comprise two passive retarders with an optical axis perpendicular to the plane of the passive retarders, and the switchable liquid crystal retarder is provided between the two passive retarders. Advantageously, the thickness and complexity of the multiple retarders may be reduced. High frontal efficiency may be achieved in both wide-angle and privacy modes, with a wide field of view in the wide-angle mode and snoopers may not be able to perceive image data from a wide range of off-axis viewing positions.

[0033] A transparent electrode and a liquid crystal alignment layer may be formed on each side of the two passive retarders adjacent to the switchable liquid crystal retarder. The first and second substrates may be provided with the switchable liquid crystal retarder therebetween, each of the first and second substrates comprising one of the two passive retarders. The two passive retarders may have a total retardance in the range of -300nm to -700nm, preferably in the range of -350nm to -600nm, most preferably in the range of -400nm to -500nm, for light of wavelength 550nm.

[0034] In another alternative, the at least one passive compensation retarder may comprise a retarder having an optical axis with a component perpendicular to the plane of the retarder and a component in the plane of the retarder. Advantageously, the field of view of the wide angle mode may be increased, and a snooper may not be able to perceive image data from a wide range of off-axis viewing positions.

[0035] The in-plane component of the passive retarder may extend at 0° with respect to an electric vector transfer direction that is parallel or perpendicular to the electric vector transfer of the display polarizer. The at least one passive retarder may further comprise a passive retarder having an optic axis that is perpendicular to the plane of the passive retarder, or a pair of passive retarders having optic axes in the planes of the crossed passive retarders.

[0036] The retardance of the at least one passive compensation retarder may be equal and opposite to the retardance of the switchable liquid crystal retarder.

[0037] The switchable liquid crystal retarder may have a first pretilt and a second pretilt, and the at least one passive compensation retarder may comprise a compensation retarder having a first pretilt and a second pretilt, the first pretilt of the compensation retarder being identical to the first pretilt of the liquid crystal retarder, and the second pretilt of the compensation retarder being identical to the second pretilt of the liquid crystal retarder.

[0038] The switchable liquid crystal retarder may further comprise electrodes configured to apply a voltage to control the layer of liquid crystal material. The electrodes may be on either side of the layer of liquid crystal material. The display may be switched by control of the liquid crystal layer and may advantageously provide a switchable privacy display or other display with reduced off-axis stray light. The display may further comprise a control system configured to control a voltage applied across the electrodes of the at least one switchable liquid crystal retarder.

[0039] The electrodes may be patterned to provide at least two patterned regions. Advantageously, privacy performance may be improved by obscuring the image data. The display may be switched between a wide-angle mode with no visibility of the camouflage structure and a privacy mode with additional camouflage to reduce visibility to off-axis snoopers without the camouflage pattern being substantially visible to a frontal user.

[0040] The control system may further comprise means for determining a position of a snooper relative to the display, the control system being configured to adjust the voltage applied across the electrodes of the at least one switchable liquid crystal retarder in response to the position of the snooper. Advantageously, visibility of the image to a detected snooper may be minimized for a range of snooper positions.

[0041] The display device may further comprise at least one further retarder and a further additional polarizer, the at least one further retarder being arranged between said further additional polarizer and the further additional polarizer. Advantageously, the off-axis brightness may be further reduced, reducing the visibility of the image to an off-axis snooper.

[0042] In one alternative display device, the spatial light modulator is a transmissive spatial light modulator configured to receive output light from a backlight, which can advantageously reduce off-axis brightness compared to emissive displays.

[0043] The backlight may provide a luminance at polar angles greater than 45 degrees relative to the spatial light modulator normal that is up to 33% of the luminance along the normal to the spatial light modulator, preferably up to 20% of the luminance along the normal to the spatial light modulator, and most preferably up to 10% of the luminance along the normal to the spatial light modulator. Advantageously, the luminance may be reduced for off-axis snoopers.

[0044] The backlight may comprise an array of light sources, a directional waveguide comprising an input end extending laterally along a side of the directional waveguide, the light sources being disposed along the input end and configured to input input light into the waveguide, and opposing first and second guide surfaces extending across the directional waveguide from the input end to guide the light input at the input end along the waveguide, the waveguide being configured to deflect input light guided through the directional waveguide to exit through the first guide surface. Advantageously, uniform wide area illumination may be provided with high efficiency.

[0045] The backlight may further comprise a light turning film, and the directional waveguide is a collimating waveguide. The collimating waveguide may comprise (i) a plurality of elongated lenticular elements and (ii) a plurality of angled light extraction features, the plurality of elongated lenticular elements and the plurality of angled light extraction features oriented to deflect input light guided through the directional waveguide to exit through the first guide surface. Advantageously, a narrow angle output may be provided by the backlight.

[0046] The directional waveguide may be an imaging waveguide configured to image the light source laterally such that output light from the light source is directed into the respective optical window with output directions that are distributed depending on the input position of the light source. The imaging waveguide may include a reflective end for reflecting input light back along the imaging waveguide, the second guide surface configured to deflect the reflected input light through the first guide surface as output light, the second guide surface including light extraction features and intermediate regions between the light extraction features, the light extraction features oriented to deflect the reflected input light through the first guide surface as output light, the intermediate regions configured to direct the light through the waveguide without extracting light, and the reflective end may have positive optical power in a lateral direction extending between the sides of the waveguide extending between the first and second guide surfaces. Advantageously, switchable directional illumination may be provided that may be switched between narrow-angle illumination and wide-angle illumination.

[0047] In one alternative where the spatial light modulator is a transmissive spatial light modulator, the display polarizer may be an input display polarizer located at the input side of the spatial light modulator between the backlight and the spatial light modulator, and an additional polarizer is located between the input display polarizer and the backlight. Advantageously, the efficiency of the display is improved. The additional polarizer may be a reflective polarizer.

[0048] In this case, the display device may further comprise an output polariser arranged at the output side of the spatial light modulator.

[0049] In one alternative where the spatial light modulator is a transmissive spatial light modulator, the display polarizer may be an output polarizer disposed at the output side of the spatial light modulator, advantageously improving the efficiency of the display.

[0050] The display device may further comprise an input polariser disposed at the input side of the spatial light modulator.

[0051] The display device may further comprise a further polarizer arranged at the input side of the spatial light modulator and at least one further retarder arranged between the at least one further polarizer and the input polarizer. Advantageously, the brightness may be reduced for off-axis snoopers.

[0052] In one alternative of the display device, the spatial light modulator may comprise an emissive spatial light modulator configured to output light. In this case, the display polarizer may be an output display polarizer arranged at the output side of the emissive spatial light modulator. Advantageously, the thickness of the display may be reduced compared to a display having a backlight, and conveniently, a flexible and bendable display may be provided.

[0053] The display device may comprise at least one further retarder and a further additional polarizer, the at least one further retarder being arranged between said further additional polarizer and the further additional polarizer. Advantageously, the brightness may be reduced for off-axis snoopers.

[0054] The various optional features and alternatives discussed above in relation to the first aspect of the present invention may be applied together in any combination.

[0055] According to a second aspect of the present disclosure, there is provided a viewing angle control optical element for application to a display device comprising a spatial light modulator and a display polarizer arranged to a side of the spatial light modulator, the viewing angle control optical element comprising a control polarizer and a plurality of retarders for disposing between the additional polarizer and the display polarizer when applying the viewing angle control optical element to the display device, the plurality of retarders comprising a switchable liquid crystal retarder comprising a layer of liquid crystal material and at least one passive compensation retarder.

[0056] Advantageously, the viewing angle control optical element may be distributed as an aftermarket element and may be installed in a display device by a display user. The element does not require complicated adjustment. There is no moiré beat between the element and the pixels of the display, and no component selection is required for pixel pitch. Inventory costs are reduced.

[0057] Alternatively, the viewing angle control optics may be conveniently installed in the display device at the factory.

[0058] The various features and alternatives discussed above in relation to the first aspect of the invention may be equally applied to the second aspect of the present disclosure.

[0059] The embodiments of the present disclosure may be used in a wide variety of optical systems. Some embodiments may include or work with various projectors, projection systems, optical components, displays, microdisplays, computer systems, processors, self-contained projector systems, visual and / or audiovisual systems, and electrical and / or optical devices. Aspects of the present disclosure may be used in virtually any device related to optical and electrical devices, optical systems, presentation systems, or any device that may include any type of optical system. Thus, embodiments of the present disclosure may be used in optical systems, optical devices used in visual and / or optical presentations, visual peripherals, and the like, as well as in many computer environments.

[0060] Before proceeding to the disclosed embodiments in detail, it should be understood that the disclosure is not limited to the details of the particular arrangements shown in the application or construction, as other example embodiments are possible. Moreover, aspects of the disclosure may be described in various combinations and arrangements to define unique embodiments. Additionally, the terminology used herein is for purposes of description and not of limitation.

[0061] These and other advantages and features of the present disclosure will become apparent to those of ordinary skill in the art from reading this disclosure in its entirety. [Brief description of the drawings]

[0062] By way of example, embodiments are illustrated in the accompanying drawings in which like reference symbols refer to similar parts and in which:

[0063] [Figure 1A] FIG. 1 is a schematic diagram showing a side perspective view of the optical stack of a directional display device with a switchable front retarder.

[0064] [Figure 1B]FIG. 1B is a schematic diagram illustrating the orientation of optical layers within the optical stack of FIG. 1A in a front view.

[0065] [Figure 1C] FIG. 2 is a schematic diagram showing a side perspective view of the optical stack of a directional display device comprising an emissive spatial light modulator and a switchable compensation retarder disposed at the output of the emissive spatial light modulator.

[0066] [Figure 1D] FIG. 2 is a schematic diagram showing a side perspective view of a viewing angle control optical element comprising a passive compensation retarder, a switchable liquid crystal retarder and a control polarizer.

[0067] [Figure 2A] FIG. 1 is a schematic diagram showing a side perspective view of the optical stack of a directional display device comprising a backlight, a switchable rear compensation retarder, and a transmissive spatial light modulator, where the additional polarizer comprises a reflective polarizer.

[0068] [Figure 2B] FIG. 2B is a schematic diagram illustrating the orientation of optical layers in the optical stack of FIG. 2A in a front view.

[0069] [Figure 2C] FIG. 1 is a schematic diagram showing a side perspective view of the optical stack of a directional display device comprising a backlight, a switchable rear compensating retarder, and a transmissive spatial light modulator, where the additional polarizer comprises a dichroic polarizer.

[0070] [Diagram 3] FIG. 1 is a schematic diagram showing a switchable compensation liquid crystal retarder configuration in a side view.

[0071] [Figure 4A] FIG. 1 is a schematic diagram illustrating a switchable compensation retarder configuration with a negative C-plate in a perspective side view in a wide-angle operation mode.

[0072] [Figure 4B]FIG. 1 is a schematic diagram showing a graph of liquid crystal director angle versus fractional position through a switchable liquid crystal retarder cell.

[0073] [Figure 4C] 4B is a schematic diagram illustrating, in a side view, the propagation of output light from the spatial light modulator through the optical stack of FIG. 4A in a wide angle mode of operation.

[0074] [Figure 4D] 4D is a schematic graph showing the variation of output transmission with polarity direction of the transmitted light beam of FIG. 4C;

[0075] [Figure 5A] FIG. 1 is a schematic diagram illustrating a switchable compensation retarder configuration with a negative C-plate in a privacy mode of operation in a perspective side view.

[0076] [Figure 5B] 5B is a schematic diagram illustrating, in a side view, the propagation of output light from the spatial light modulator through the optical stack of FIG. 5A in a privacy mode of operation.

[0077] [Figure 5C] 5C is a schematic graph showing the change in output transmission with the polarity direction of the transmitted light beam of FIG. 5B;

[0078] [Figure 6A] FIG. 1 is a schematic diagram illustrating in perspective view the observation of transmitted output light for a display operating in privacy mode.

[0079] [Figure 6B] FIG. 2 is a schematic diagram showing, in a front perspective view, how the display of FIGS. 1A to 1C appears when operating in a privacy mode.

[0080] [Figure 6C] FIG. 1 is a schematic diagram showing a side view of an automotive vehicle having a switchable directional display positioned within the passenger compartment for both entertainment and shared modes of operation.

[0081] [Figure 6D] FIG. 1 is a schematic diagram showing a front view of an automotive vehicle having a switchable directional display disposed within the passenger compartment in an entertainment mode of operation.

[0082] [Figure 6E] FIG. 1 is a schematic diagram showing a top view of an automotive vehicle having a switchable directional display positioned within the passenger compartment in a shared mode of operation.

[0083] [Figure 6F] FIG. 1 is a schematic diagram illustrating a top view of an automotive vehicle having a switchable directional display positioned within the passenger compartment for both nighttime and daytime operating modes.

[0084] [Figure 6G] FIG. 1 is a schematic diagram showing a side view of an automotive vehicle having a switchable directional display disposed within the passenger compartment in a nighttime mode of operation.

[0085] [Figure 6H] FIG. 1 is a schematic diagram showing a side view of an automotive vehicle having a switchable directional display disposed within the passenger compartment in a daytime operating mode.

[0086] [Figure 7A] FIG. 13 is a schematic diagram showing the change in output transmission with polarity direction for different driving voltages. [Figure 7B] FIG. 13 is a schematic diagram showing the change in output transmission with polarity direction for different driving voltages. [Figure 7C] FIG. 13 is a schematic diagram showing the change in output transmission with polarity direction for different driving voltages. [Figure 7D] FIG. 13 is a schematic diagram showing the change in output transmission with polarity direction for different driving voltages.

[0087] [Figure 8] 13 is a flowchart showing control of a privacy display.

[0088] [Figure 9A] FIG. 2 is a schematic diagram illustrating in a perspective side view a switchable compensation retarder configuration in a wide-angle operation mode, comprising a crossed A-plate passive compensation retarder and a homeotropically aligned switchable liquid crystal retarder.

[0089] [Figure 9B] FIG. 1 is a schematic diagram showing in a perspective side view a switchable compensation retarder configuration for a privacy mode of operation comprising a crossed A-plate passive compensation retarder and a homeotropically aligned switchable liquid crystal retarder.

[0090] [Figure 9C] 9B is a schematic graph showing the variation of output transmission with polarity direction of the transmitted light beam of FIG. 9A in a wide angle mode of operation.

[0091] [Figure 9D] 9C is a schematic graph showing the variation of output transmission with polarity direction of the transmitted light beam of FIG. 9B in a privacy mode of operation.

[0092] [Figure 10A] 1A-1C are schematic diagrams illustrating in perspective side views switchable compensation retarder configurations for wide-angle and privacy operation modes, respectively, comprising a homogeneously aligned switchable liquid crystal retarder and a negative passive C-plate retarder. [Figure 10B] 1A-1C are schematic diagrams illustrating in perspective side views switchable compensation retarder configurations for wide-angle and privacy operation modes, respectively, comprising a homogeneously aligned switchable liquid crystal retarder and a negative passive C-plate retarder.

[0093] [Figure 10C] FIG. 10B is a schematic diagram showing a graph of liquid crystal director angle versus fractional position through the switchable liquid crystal retarder cell of FIG. 10A for different applied voltages.

[0094] [Figure 11A]1 is a schematic graph showing the change in output transmission with the polarity direction of the transmitted light beam of a switchable compensation retarder comprising a homogeneously aligned liquid crystal cell and a negative C plate in a privacy mode and two different wide-angle modes corresponding to respective driving voltages. [Figure 11B] 1 is a schematic graph showing the change in output transmission with the polarity direction of the transmitted light beam of a switchable compensation retarder comprising a homogeneously aligned liquid crystal cell and a negative C plate in a privacy mode and two different wide-angle modes corresponding to respective driving voltages. [Figure 11C] 1 is a schematic graph showing the change in output transmission with the polarity direction of the transmitted light beam of a switchable compensation retarder comprising a homogeneously aligned liquid crystal cell and a negative C plate in a privacy mode and two different wide-angle modes corresponding to respective driving voltages.

[0095] [Figure 12A] FIG. 1 is a schematic diagram showing in a perspective side view a switchable compensation retarder configuration for a privacy mode of operation comprising a crossed A-plate passive compensation retarder and a homogeneously aligned switchable liquid crystal retarder.

[0096] [Figure 12B] 13 is a schematic graph showing the variation of output transmission with transmitted light polarity direction of a switchable compensation retarder comprising a homogeneously aligned liquid crystal cell and crossed A-plates in privacy mode and wide angle mode for different driving voltages. [Figure 12C] 13 is a schematic graph showing the variation of output transmission with transmitted light polarity direction of a switchable compensation retarder comprising a homogeneously aligned liquid crystal cell and crossed A-plates in privacy mode and wide angle mode for different driving voltages. [Figure 12D] 13 is a schematic graph showing the variation of output transmission with transmitted light polarity direction of a switchable compensation retarder comprising a homogeneously aligned liquid crystal cell and crossed A-plates in privacy mode and wide angle mode for different driving voltages.

[0097] [Figure 13A] FIG. 2 is a schematic diagram showing in side view a portion of a display comprising a switchable compensation retarder and an optical coupling layer. [Figure 13B] FIG. 2 is a schematic diagram showing in side view a portion of a display comprising a switchable compensation retarder and an optical coupling layer.

[0098] [Figure 14] FIG. 1 is a schematic diagram showing a perspective side view of a switchable compensation retarder configuration in a privacy mode of operation, comprising a crossed A-plate passive compensation retarder and a homogeneously aligned switchable liquid crystal retarder, and further comprising a passive rotation retarder.

[0099] [Figure 15A] FIG. 1 is a schematic diagram illustrating a switchable compensation retarder configuration in a privacy mode of operation in a perspective side view, comprising a homeotropically aligned switchable liquid crystal retarder disposed between a first C-plate passive compensation retarder and a second C-plate passive compensation retarder.

[0100] [Figure 15B] 15B is a schematic graph showing the variation of output transmission with polarity direction of transmitted light in the optical stack of FIG. 15A in wide angle and privacy modes of operation, respectively. [Figure 15C] 15B is a schematic graph showing the variation of output transmission with polarity direction of transmitted light in the optical stack of FIG. 15A in wide angle and privacy modes of operation, respectively.

[0101] [Figure 16A] FIG. 1 is a schematic diagram showing in a perspective side view a display comprising a switchable liquid crystal retarder disposed between first and second substrates each comprising a C-plate passive compensation retarder.

[0102] [Figure 16B]FIG. 2 is a schematic diagram showing in side view a portion of a display comprising a switchable liquid crystal retarder disposed between first and second substrates each comprising a C-plate passive compensation retarder;

[0103] [Figure 17A] FIG. 1 is a schematic diagram showing a perspective side view of a switchable compensation retarder configuration in a wide-angle operating mode, comprising a homogeneously oriented switchable liquid crystal retarder arranged between a first crossed A-plate passive compensation retarder and a second crossed A-plate passive compensation retarder.

[0104] [Figure 17B] 17B is a schematic graph showing the variation of output transmission with polarity direction of the transmitted light beam for the configuration of FIG. 17A in wide angle mode and privacy mode, respectively; [Figure 17C] 17B is a schematic graph showing the variation of output transmission with polarity direction of the transmitted light beam for the configuration of FIG. 17A in wide angle mode and privacy mode, respectively;

[0105] [Figure 18A] FIG. 1 is a schematic diagram showing in a perspective side view a switchable compensation retarder configuration in a privacy mode of operation, comprising a switchable liquid crystal retarder with homogeneous and homeotropic alignment and a negative passive C-plate retarder.

[0106] [Figure 18B] 18B is a schematic graph showing the variation of output transmission with polarity direction of the transmitted light beam of FIG. 18A in a privacy mode of operation.

[0107] [Figure 18C] 18B is a schematic graph showing the variation of output transmission with polarity direction of the transmitted light beam of FIG. 18A in a wide angle mode of operation.

[0108] [Figure 19A] FIG. 1 is a schematic diagram illustrating the configuration of a homogeneously aligned switchable liquid crystal retarder in a perspective side view.

[0109] [Figure 19B] 19B is a schematic graph showing the change in output transmission in the polarity direction of the transmitted light beam of FIG. 19A for a first applied voltage;

[0110] [Figure 19C] 19B is a schematic graph showing the change in output transmission in the polarity direction of the transmitted light beam of FIG. 19A for a second applied voltage that is greater than the first applied voltage;

[0111] [Figure 19D] FIG. 2 is a schematic diagram illustrating a perspective side view of a C-plate placed between parallel polarizers.

[0112] [Figure 19E] 19E is a schematic graph showing the change in output transmission with the polarity direction of the transmitted light beam of FIG. 19D.

[0113] [Figure 20A] FIG. 1 is a schematic diagram illustrating in a perspective side view a configuration of a homogeneously aligned switchable liquid crystal retarder placed between parallel polarizers in series with a C-plate placed between the parallel polarizers.

[0114] [Figure 20B] 20B is a schematic graph showing the change in output transmission with polarity direction of the transmitted light beam of FIG. 20A for a first applied voltage;

[0115] [Figure 20C] 20B is a schematic graph showing the change in output transmission in the polarity direction of the transmitted light beam of FIG. 20A for a second applied voltage that is greater than the first applied voltage;

[0116] [Figure 21A] FIG. 1 is a schematic diagram showing, in a perspective side view, a configuration of a homogeneously aligned switchable liquid crystal retarder in series with a C-plate compensation retarder, where the homogeneously aligned switchable liquid crystal retarder and the C-plate compensation retarder are disposed between a pair of parallel polarizers.

[0117] [Figure 21B] 21B is a schematic graph showing the change in output transmission in the polarity direction of the transmitted light beam of FIG. 21A for a first applied voltage;

[0118] [Figure 21C] 21B is a schematic graph showing the change in output transmission in the polarity direction of the transmitted light beam of FIG. 21A for a second applied voltage that is greater than the first applied voltage;

[0119] [Figure 22A] FIG. 1 shows a perspective side view of a switchable compensation retarder configuration in a privacy operation mode, comprising a negative C-plate passive compensation retarder and a homeotropically aligned switchable liquid crystal retarder arranged between an output polarizer and an additional polarizer, and a negative C-plate passive compensation retarder and a homeotropically aligned switchable liquid crystal retarder arranged between the additional polarizer and a further additional polarizer.

[0120] [Figure 22B] FIG. 2 is a schematic diagram showing in a perspective side view an arrangement of a first switchable compensation retarder arranged on the input side of a liquid crystal display and a second switchable compensation retarder arranged on the output side of the liquid crystal display.

[0121] [Figure 22C] FIG. 1 is a schematic diagram showing a side perspective view of a viewing angle control optical element comprising a first passive compensation retarder, a first switchable liquid crystal retarder, a first control polarizer, a second passive compensation retarder, a second switchable liquid crystal retarder, and a second control polarizer.

[0122] [Figure 22D] FIG. 1 is a schematic diagram showing a top view of an automotive vehicle having a switchable directional display positioned within the passenger compartment for a daytime and / or shared operating mode.

[0123] [Figure 22E]FIG. 1 is a schematic diagram showing a side view of an automotive vehicle having a switchable directional display positioned within the passenger compartment for a daytime and / or shared operating mode.

[0124] [Figure 22F] FIG. 1 is a schematic diagram illustrating a top view of an automotive vehicle having a switchable directional display positioned within the passenger compartment for a nighttime and / or entertainment mode of operation.

[0125] [Figure 22G] FIG. 1 is a schematic diagram illustrating a side view of an automotive vehicle having a switchable directional display disposed within the passenger compartment for a nighttime and / or entertainment mode of operation.

[0126] [Figure 23A] A schematic diagram showing in perspective side view an arrangement of a reflective additional polarizer and a passive retarder positioned on the input side of a liquid crystal display, and a switchable compensating retarder and additional polarizer positioned on the output side of the liquid crystal display.

[0127] [Figure 23B] FIG. 2 is a schematic diagram showing a side perspective view of a viewing angle control optical element comprising a passive retarder, a first control polarizer, a passive compensation retarder, a switchable liquid crystal retarder, and a second control polarizer.

[0128] [Figure 24A] FIG. 1 is a schematic diagram showing a side perspective view of an optical stack of a passive retarder comprising a negative O-plate tilted in a plane perpendicular to the electric vector transmission direction of the display polarizer and the negative C-plate, and a negative C-plate, configured to change the field of view of a display device.

[0129] [Figure 24B] 24B is a schematic graph showing the variation of output transmission with polarity direction of the transmitted light beam for the passive retarder of FIG. 24A.

[0130] [Figure 24C] FIG. 2 is a schematic diagram showing a side perspective view of a passive retarder optical stack comprising a crossed A-plate and a positive O-plate.

[0131] [Figure 24D] 24D is a schematic graph showing the change in output transmission with polarization direction of the transmitted light beam for the passive retarder of FIG. 24C.

[0132] [Figure 24E] FIG. 1 is a schematic diagram showing a side perspective view of an optical stack of a passive retarder comprising two pairs of crossed A-plates.

[0133] [Figure 24F] 24F is a schematic graph showing the change in output transmission with polarization direction of the transmitted light beam for the passive retarder of FIG. 24E.

[0134] [Figure 25A] FIG. 1 is a schematic diagram showing a perspective side view of a switchable compensation retarder configuration in a privacy mode of operation, comprising a negative C-plate passive compensation retarder and a homeotropically aligned switchable liquid crystal retarder, further comprising a patterned electrode layer.

[0135] [Figure 25B] FIG. 1 is a schematic diagram showing illumination of the primary viewer and snoopers by a camouflaged brightness-controlled privacy display from a front perspective view.

[0136] [Figure 25C] FIG. 1 is a schematic diagram showing illumination of a snooper by a camouflaged brightness-controlled privacy display in a side perspective view.

[0137] [Figure 26A] FIG. 1 is a schematic diagram illustrating a directional backlight from a front perspective view.

[0138] [Figure 26B] FIG. 2 is a schematic diagram illustrating a non-directional backlight from a front perspective view.

[0139] [Figure 26C] 1 is a schematic graph showing the variation of luminance with lateral viewing angle for a display having different viewing angles;

[0140] [Figure 27A] FIG. 1 is a schematic diagram showing in side view a switchable directional display device comprising an imaging waveguide and a switchable liquid crystal retarder;

[0141] [Figure 27B] FIG. 13 is a schematic diagram illustrating the operation of an imaging waveguide in a narrow angle mode of operation in a rear perspective view.

[0142] [Figure 27C] FIG. 27C is a schematic graph showing the viewing luminance plot of the output of FIG. 27B when used in a display device that does not have a switchable liquid crystal retarder.

[0143] [Figure 28A] FIG. 2 is a schematic diagram showing in side view a switchable directional display device comprising a switchable collimating waveguide and a switchable liquid crystal retarder operated in a privacy mode of operation.

[0144] [Figure 28B] FIG. 2 is a schematic diagram showing the output of a collimating waveguide in a top view.

[0145] [Figure 28C] 28B is a schematic graph showing an isoluminant viewing polar plot of the display device of FIG. 28A;

[0146] [Figure 29A] FIG. 1 is a schematic diagram illustrating illumination of a retarder layer with off-axis light in a perspective view.

[0147] [Figure 29B] FIG. 2 is a schematic diagram illustrating, in a perspective view, illumination of a retarder layer with off-axis light of a first linear polarization state at 0 degrees.

[0148] [Figure 29C] FIG. 1 is a schematic diagram illustrating, in a perspective view, illumination of a retarder layer with off-axis light of a first linear polarization state at 90 degrees.

[0149] [Figure 29D] FIG. 1 is a schematic diagram illustrating, in a perspective view, illumination of a retarder layer with off-axis light of a first linear polarization state at 45 degrees.

[0150] [Figure 30A] FIG. 1 is a schematic diagram illustrating illumination of a C-plate retarder with off-axis polarized light with a positive elevation angle in a perspective view.

[0151] [Figure 30B] FIG. 1 is a schematic diagram illustrating, in a perspective view, illumination of a C-plate retarder with off-axis polarized light having a negative transverse angle.

[0152] [Figure 30C] FIG. 1 is a schematic diagram illustrating, in a perspective view, illumination of a C-plate retarder with off-axis polarized light with positive elevation angle and negative lateral angle.

[0153] [Figure 30D] FIG. 1 is a schematic diagram showing a perspective view of illumination of a C-plate retarder with off-axis polarized light having positive elevation and positive lateral angles.

[0154] [Figure 30E] 30A-30D are schematic graphs showing the change in output transmission with the polarity direction of the transmitted light beam.

[0155] [Figure 31A] FIG. 1 is a schematic diagram illustrating, in a perspective view, illumination of a crossed A-plate retarder layer with off-axis polarized light having a positive elevation angle.

[0156] [Figure 31B] FIG. 1 is a schematic diagram illustrating, in a perspective view, illumination of a crossed A-plate retarder layer with off-axis polarized light having a negative transverse angle.

[0157] [Figure 31C] FIG. 1 is a schematic diagram illustrating, in a perspective view, illumination of a crossed A-plate retarder layer with off-axis polarized light having a positive elevation angle and a negative transverse angle.

[0158] [Figure 31D] FIG. 1 is a schematic diagram illustrating, in a perspective view, illumination of a crossed A-plate retarder layer with off-axis polarized light having positive elevation and positive lateral angles.

[0159] [Figure 31E] 31A-31D are schematic graphs showing the change in output transmission with the polarity direction of the transmitted light beam. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0160] For purposes of this disclosure, a terminology relating to optical retarders will now be explained.

[0161] In a layer containing uniaxially birefringent material, there is a direction that dominates the optical anisotropy, while all directions perpendicular to that direction (or at a given angle to that direction) have equivalent birefringence.

[0162] The optic axis refers to the direction of propagation of a ray of light in a uniaxially birefringent material where no birefringence occurs. For light propagating perpendicular to the optic axis, the optic axis is the slow axis if linearly polarized light with an electric vector direction parallel to the slow axis travels slowest. The slow axis direction is the direction with the highest refractive index at the design wavelength. Similarly, the fast axis direction is the direction with the lowest refractive index at the design wavelength.

[0163] In a positive dielectric anisotropy uniaxial birefringent material, the slow axis direction is the extraordinary axis of the birefringent material. In a negative dielectric anisotropy uniaxial birefringent material, the fast axis direction is the extraordinary axis of the birefringent material.

[0164] The terms "half wavelength" and "quarter wavelength" refer to the operation of the retarder at a design wavelength λ, which may typically be between 500 nm and 570 nm. In this exemplary embodiment, exemplary retardance values ​​are provided for a wavelength of 550 nm unless otherwise specified.

[0165] A retarder introduces a phase shift between the two perpendicularly polarized components of a light wave incident on it and is characterized by the amount of relative phase Γ (related to the birefringence Δn and the retarder thickness d as follows):

number

[0166] In Equation 1, Δn is defined as the difference between the extraordinary and ordinary refractive indices, that is,

number

[0167] For a half-wave retarder, the relationship between d, Δn, and λ0 is chosen such 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 such that the phase shift between the polarization components is Γ=π / 2.

[0168] The term "half-wave retarder" herein typically refers to light propagating perpendicular to the retarder and perpendicular to the spatial light modulator.

[0169] In this disclosure, "A-plate" refers to an optical retarder that uses a layer of birefringent material with its optic axis parallel to the (xy) plane of the layer.

[0170] "Positive A-plate" refers to a positively birefringent A-plate, i.e., an A-plate that has a positive Δn.

[0171] In this disclosure, "C-plate" refers to an optical retarder that uses a layer of birefringent material with its optic axis perpendicular to the plane of the layer. "Positive C-plate" refers to a positive birefringent C-plate, i.e., a C-plate with positive Δn. "Negative C-plate" refers to a negative birefringent C-plate, i.e., a C-plate with negative Δn.

[0172] "O-plate" refers to an optical retarder that uses a layer of birefringent material whose optic 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 positively birefringent O-plate, i.e., an O-plate with positive Δn.

[0173] An achromatic retarder may be provided, in which the retardance Δn.d of the retarder material varies with wavelength λ as follows:

number

[0174] where κ is substantially constant.

[0175] An example of a suitable material is modified polycarbonate from Teijin Films. In this embodiment, an achromatic retarder may be provided to advantageously minimize color change between polar angle viewing directions with low and increased luminance falloff, as described below.

[0176] Various other terms used in this disclosure with respect to retarders and liquid crystals are now explained.

[0177] A liquid crystal cell has a retardance given by Δn.d, where Δn is the birefringence of the liquid crystal material in the liquid crystal cell and d is the thickness of the liquid crystal cell which is independent of the orientation of the liquid crystal material within the liquid crystal cell.

[0178] Homogeneous alignment refers to the alignment of liquid crystals in a switchable liquid crystal display where the molecules are aligned substantially parallel to the substrate. Homogeneous alignment is sometimes also called planar alignment. Homogeneous alignment may typically comprise a small pretilt, such as 2 degrees, such that the molecules at the surface of the alignment layer of the liquid crystal cell are slightly tilted, as described below. The pretilt is configured to minimize degeneracy in switching the cell.

[0179] In this disclosure, homeotropic alignment is the state in which rod-like liquid crystal molecules are aligned substantially perpendicular to the substrate. Discotic liquid crystal homeotropic alignment is defined as the state in which the axis of the column structure formed by the disk-like liquid crystal molecules is aligned perpendicular to the surface. In homeotropic alignment, the pretilt is the tilt angle of the molecules close to the alignment layer, which is typically close to 90 degrees, for example 88 degrees.

[0180] Liquid crystal molecules with positive dielectric anisotropy can be switched from a homogeneous 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.

[0181] Liquid crystal molecules with negative dielectric anisotropy can be switched from a homeotropic alignment (such as a C-plate or O-plate retarder alignment) to a homogeneous alignment (such as an A-plate retarder alignment) by an applied electric field.

[0182] Rod-like molecules have positive birefringence. Therefore, as described in Equation 2, n e >n0. Discotic molecules have negative birefringence. Therefore, n e <n0である。

[0183] Positive retarders, such as A-plates, positive O-plates, and positive C-plates, can typically be provided by stretched films or rod-like liquid crystal molecules. Negative retarders, such as negative C-plates, can typically be provided by stretched films or discotic liquid crystal molecules.

[0184] Parallel liquid crystal cell alignment refers to the alignment direction of the homogeneous alignment layer being parallel or, more typically, antiparallel. In the case of pretilted homeotropic alignment, the alignment layer may have components that are substantially parallel or antiparallel. A hybrid alignment liquid crystal cell may have one homogeneous alignment layer and one homeotropic alignment layer. A twisted liquid crystal cell may be provided by alignment layers that do not have parallel alignment, for example, oriented at 90 degrees to each other.

[0185] The transmissive spatial light modulator may further comprise a retarder between the input display polarizer and the output display polarizer, for example as disclosed in U.S. Pat. No. 8,237,876, the entirety of which is incorporated herein by reference. Such a retarder (not shown) is in a different location than the passive retarder of this embodiment. Such a retarder compensates for the degradation of contrast at off-axis viewing positions, which has a different effect on the brightness reduction at off-axis viewing positions of this embodiment.

[0186] The optically isolated retarder between the display polarizer and the OLED display emissive layer is further described in U.S. Patent No. 7,067,985. The optically isolated retarder is in a different location than the passive retarder in this embodiment. The isolated retarder reduces frontal reflections from the OLED display emissive layer. This has a different effect on the brightness falloff at off-axis viewing positions in this embodiment.

[0187] The structure and operation of various switchable display devices will now be described. In this description, common elements will have common reference numerals. It should be noted that the disclosure relating to any element applies to each device in which the same or corresponding element is provided. Therefore, for the sake of brevity, such disclosure will not be repeated.

[0188] FIG. 1A is a schematic diagram showing a side perspective view of an optical stack for a display device.

[0189] The display device 100 comprises a spatial light modulator 48 that comprises at least one display polarizer, which is an output polarizer 218. The backlight 20 is configured to output light, and the spatial light modulator 48 comprises a transmissive spatial light modulator 48 that is configured to receive output light from the backlight 20. The display device 100 is configured to output light 400 having an angular luminance characteristic as described herein.

[0190] In this disclosure, the spatial light modulator 48 may comprise a liquid crystal display comprising substrates 212, 216 and a liquid crystal layer 214 having red, green, and blue pixels 220, 222, 224. The spatial light modulator 48 has an input display polarizer 210 and an output display polarizer 218 on either side of it. The output display polarizer 218 is configured to provide high extinction for light from the pixels 220, 222, 224 of the spatial light modulator 48. Exemplary polarizers 210, 218 may be absorptive polarizers, such as dichroic polarizers.

[0191] Optionally, a reflective polarizer 208 may be provided between the dichroic input display polarizer 210 and the backlight 210 to provide recycled light and improve display efficiency, which may be advantageous.

[0192] The backlight 20 may include an input light source 15, a waveguide 1, a back reflector 3, and an optical stack 5 that may include diffusers, turning films, and other known optical backlight structures. An asymmetric diffuser, which may include, for example, asymmetric surface relief features, may be provided in the optical stack 5 to increase diffusion in the elevation direction compared to the lateral direction. Advantageously, image uniformity may be improved.

[0193] In this embodiment, the backlight 20 may be configured to provide an angular light distribution having reduced brightness for off-axis viewing positions compared to the front brightness, as described below in Figures 26A-28C. The backlight 20 may further comprise a switchable backlight configured to switch the output angular brightness profile to provide reduced off-axis brightness in a privacy mode of operation and increased off-axis brightness in a wide angle mode of operation. Such a switching backlight 20 may cooperate with the switchable compensation retarder 300 of this embodiment.

[0194] An additional polarizer 318 is positioned at the output side of the spatial light modulator 48 as the display output polarizer 218, which may be an absorptive dichroic polarizer.

[0195] The display polarizer 218 and the additional polarizer 318 have parallel electric vector propagation directions 219, 319. As described below, such a parallel orientation provides high transmission at the central viewing position.

[0196] The multiple retarders, together referred to in this specification as switchable compensation retarder 300, are positioned between the additional polarizer 318 and the display polarizer 218 and comprise: (i) a switchable liquid crystal retarder 301 comprising a layer 314 of liquid crystal material positioned between the display polarizer 218 and the additional polarizer 318; and (ii) a passive compensation retarder 330.

[0197] Figure 1B is a schematic diagram showing the orientation of the optical layers in the optical stack of Figure 1A in a front view. An input electric vector transmission direction 211 at an input display polarizer 210 of a spatial light modulator 48 provides an input polarization component that can be transformed by a liquid crystal layer 214 to provide an output polarization component determined by an electric vector transmission direction 219 of an output display polarizer 218. The passive compensation retarder 330 may comprise a retardation layer including a discotic birefringent material 430, and the switchable liquid crystal retarder 301 may include a liquid crystal material.

[0198] The switchable compensation retarder 300 therefore comprises a switchable liquid crystal retarder 301 comprising a switchable liquid crystal retarder 301 and substrates 312, 316, and a passive compensation retarder 330 disposed between the additional polarizer 318 and the display polarizer 218.

[0199] The substrates 312, 316 may be glass substrates or polymer substrates such as polyimide substrates. Flexible substrates may be provided on which transparent electrodes may be conveniently provided. Advantageously, curved, bent and foldable displays may be provided.

[0200] The display device 100 further comprises a control system 352 configured to control the voltage applied by the voltage driver 350 across the electrodes of the switchable liquid crystal retarder 301 .

[0201] It may be desirable to reduce stray light or provide privacy control in a light-emitting display.

[0202] FIG. 1C is a schematic diagram illustrating a side perspective view of the optical stack of a directional display device comprising an emissive spatial light modulator 48 and a switchable compensation retarder 300 disposed at the output of the emissive spatial light modulator 48.

[0203] Alternatively, the spatial light modulator 48 may be provided by other display types that provide the output light 400 by emitting light, such as an organic LED display (OLED), and includes an output display polarizer 218, substrates 512, 516, and an emissive layer 514. The output polarizer 218 may reduce the brightness of light reflected from the OLED pixel plane by one or more retarders 518 inserted between the output display polarizer 218 and the OLED pixel plane. The one or more retarders 518 may be quarter wave plates and are different from the compensation retarder 330 of the present disclosure.

[0204] In the embodiment of FIG. 1C, spatial light modulator 48 comprises an emissive spatial light modulator and the display polarizer is output display polarizer 218 .

[0205] Otherwise, the directional display device of FIG. 1C is the same as that of FIG. 1A, as described above.

[0206] We now describe a viewing angle control optical element 260 for application in a display device. The viewing angle control optical element 260 may be added to a spatial light modulator with display polarizers 210, 218 to achieve switchable viewing characteristics.

[0207] FIG. 1D is a schematic diagram illustrating in a side perspective view a viewing angle control optical element 260 for application in a display device comprising a passive compensation retarder 330, a switchable liquid crystal retarder 301, and a control polarizer 250.

[0208] In use, the viewing angle control optics 260 may be user or factory attached to the polarizing output spatial light modulator 48. The viewing angle control optics 260 may be provided as a flexible film for curved and bent displays. Alternatively, the viewing angle control optics 260 may be provided on a rigid substrate, such as a glass substrate.

[0209] Advantageously, aftermarket privacy and / or stray light control elements can be provided that do not need to match the pixel resolution of the panel to avoid moiré artifacts. Viewing angle control optics 260 can further be provided for factory installation on the spatial light modulator 48.

[0210] By attaching the viewing angle control optical element 260 of FIG. 1D to an existing display device, a display device such as that shown in any one of FIGS. 1A to 1C can be formed.

[0211] 1A-1D control the polarity brightness of light 400 output from spatial light modulator 48. That is, switchable compensation retarder 300 (comprising switchable liquid crystal retarder 301 and passive compensation retarder 330) does not affect the brightness of light passing through input display polarizer 210, switchable compensation retarder 300, and additional polarizer 318 along an axis normal to the plane of switchable compensation retarder 300, but switchable compensation retarder 300 reduces the brightness of light passing along an axis tilted with respect to the normal to the plane of switchable compensation retarder 300 in at least one of its switchable states. The principle behind this effect is explained in more detail below with reference to Figures 29A-31E and results from the presence or absence of phase shifts introduced by the switchable liquid crystal retarder 301 and the passive compensation retarder 330 for light along axes that make different angles with respect to the liquid crystal material of the switchable liquid crystal retarder 301 and the passive compensation retarder 330. A similar effect is achieved in all the devices described below.

[0212] Furthermore, the provision of a passive compensation retarder 330 in addition to the switchable liquid crystal retarder 301 improves performance, as will be explained in more detail with reference to some specific display devices and by comparison with some comparative examples described with reference to Figures 19A to 19E.

[0213] It may be desirable to reduce the number of optical layers between the spatial light modulator 48 and the observer. A configuration will now be described in which multiple retarders 300 are positioned at the input side of the spatial light modulator 48.

[0214] Figure 2A is a schematic diagram showing in a side perspective view the optical stack of a directional display device comprising a backlight 20, a switchable rear compensating retarder 300, and a transmissive spatial light modulator 48, where the additional polarizer 318 comprises a reflective polarizer. Figure 2B is a schematic diagram showing in a front view the orientation of the optical layers in the optical stack of Figure 2A.

[0215] The display device 100 includes a spatial light modulator 48 and a display polarizer 210 disposed on the input side of the spatial light modulator 48. An additional polarizer 318 is disposed on the same side of the spatial light modulator 48 as the display polarizer 210. The additional polarizer 318 is a reflective polarizer that works in conjunction with the backlight 20 to improve efficiency.

[0216] The multiple retarders 300 are disposed between the reflective additional polarizer 318 and the display polarizer 210. As in Fig. 1A, the multiple retarders 300 comprise a switchable liquid crystal retarder 301 comprising a layer of liquid crystal material 314 disposed between the display polarizer 210 and the reflective additional polarizer 318, and a passive compensation retarder 330. Thus, the reflective additional polarizer 318 is disposed on the input side of the input display polarizer 210 between the input display polarizer 210 and the backlight 20, and the multiple retarders 300 are disposed between the reflective additional polarizer 318 and the input display polarizer 210.

[0217] The electric vector transmission direction 319 of the reflective additional polarizer 318 is parallel to the electric vector transmission direction 211 of the input polarizer 210 to achieve a switchable directional characteristic, as described below.

[0218] In alternative embodiments, the additional polarizer 318 may comprise both a reflective polarizer and an absorptive dichroic polarizer, or may comprise only a dichroic polarizer.

[0219] The reflective additional polarizer 318 may be, for example, a multilayer film such as DBEF™ from 3M Corporation, or may be a wire grid polarizer. Advantageously, by recycling light from the polarized reflection from the polarizer 372, display efficiency may be improved. Compared to using both an absorbing dichroic polarizer and a reflective polarizer as the additional polarizer 318, cost and thickness may be further reduced.

[0220] Compared to the configuration of FIG. 1A, FIG. 2A reduces the number of layers between the pixels 220, 222, 224 and the viewer, which may improve front to front screen image contrast.

[0221] 2C is a schematic diagram showing a side perspective view of the optical stack of a directional display device comprising a backlight 20, a switchable rear compensation retarder 300, and a transmissive spatial light modulator 48, in which the additional polarizer 318 comprises a dichroic polarizer. Compared to the reflective additional polarizer 318 of FIG. 2A, the dichroic additional polarizer 318 does not recycle high angle light to the backlight, which may reduce off-axis brightness compared to the configuration of FIG. 2A. Advantageously, privacy performance is improved.

[0222] The construction and operation of the switchable compensation retarder 300 and additional polarizer 318 of FIGS. 1A-1C and 2A-2B will now be described.

[0223] 3 is a schematic diagram illustrating in side view an exemplary configuration of a switchable liquid crystal retarder 301 comprising a layer 314 of liquid crystal material 414 having negative dielectric anisotropy. Substrates 312, 316 may have transparent electrodes 413, 415 disposed thereon and homeotropic surface alignment layers 409, 411 disposed on either side of the switchable liquid crystal retarder 301. The homeotropic alignment layers 409, 411 may provide a homeotropic alignment with a pretilt angle 407 in the adjacent liquid crystal material 414.

[0224] The orientation of the liquid crystal material 414 in the xy-plane is determined by the pretilt direction of the alignment layers such that each alignment layer has a pretilt having a component 417a, 417b in the plane of the switchable liquid crystal retarder 301 that is parallel or anti-parallel or orthogonal to the electric vector transport direction 303 of the output display polarizer 218.

[0225] The pretilt 407a, 407b may be, for example, 88 degrees, so that the component 417 is small, reducing disclination in the relaxed (zero voltage) state of the orientation of the layer 314 of liquid crystal material 414. Thus, the layer 314 is provided with a substantially positive C-plate in the zero voltage configuration. In effect, the liquid crystal layer still has a slight O-plate characteristic provided by the pretilt of the homeotropic alignment layer at angle 407a and the residual component 417.

[0226] The switchable liquid crystal retarder 301 comprises electrodes 413, 415 disposed adjacent to and on either side of the switchable liquid crystal retarder 301. A layer 314 of liquid crystal material 414 is switchable by a voltage applied across the electrodes 413, 415.

[0227] In the undriven state, the liquid crystal material 414 is aligned with a component 418 perpendicular to the plane of the retarder 301 and a component 417 in the plane of the retarder.

[0228] The retarder 330 is illustrated as comprising a negative passive O-plate comprising a discotic birefringent material 430. The retardance of the passive compensation retarder 330 may be equal and opposite to the retardance of the switchable liquid crystal retarder 301. The switchable liquid crystal retarder 301 may comprise a first pretilt 407a and a second pretilt 407b, and the passive compensation retarder 330 may comprise a compensation retarder having a first pretilt 405a and a second pretilt 405b, where the first pretilt 405a of the compensation retarder 330 is the same as the first pretilt 407a of the liquid crystal retarder 301, and the second pretilt 405b of the compensation retarder 330 is the same as the second pretilt 307b of the liquid crystal retarder 301.

[0229] The passive O-plate may comprise a cured reactive mesogen layer, which may be, for example, a discotic reactive mesogen. The pretilt of the compensation retarder may be achieved by curing the reactive mesogen material after alignment with a suitable alignment layer. The O-plate may also comprise a double-stretched polymer film, such as polycarbonate.

[0230] In operation, the switchable liquid crystal retarder 301 is switchable between two orientation states. The first state may provide for multiple viewer viewing of the display. The second state may provide a narrow angle mode for privacy operation or reduced stray light, for example in nighttime operation. As will be further described below, such an element can provide high transmission for a wide range of polar angles in a wide angle operation mode, and limited luminance polar viewing in a privacy operation mode.

[0231] The operation of the display of FIG. 1A in the wide angle mode, representing a first state, will now be described.

[0232] Figure 4A is a schematic diagram showing a perspective side view of the configuration of the switchable compensation retarder 300 in a wide angle mode of operation. Zero voltage is provided across the switchable liquid crystal retarder 301. In Figure 4A and other schematic diagrams below, some layers of the optical stack are omitted for clarity. For example, the switchable liquid crystal retarder 301 is shown without the substrates 312, 316.

[0233] The switchable liquid crystal retarder 301 comprises two surface alignment layers adjacent to either side of the liquid crystal material 414 and configured to provide homeotropic alignment in the adjacent liquid crystal material 414. As described above, the liquid crystal material 414 may be provided with a pre-tilt, for example 88 degrees from horizontal, to remove degeneracy in the alignment of the liquid crystal material 414.

[0234] The passive compensation retarder 330 comprises a negative C-plate retarder with the optic axis being the fast axis perpendicular to the plane of the retarder. The material 430 of the C-plate retarder may therefore have a negative dielectric anisotropy. The C-plate may comprise, for example, transparent birefringent materials such as polycarbonate or reactive mesogens, Zeonex™ cycloolefin polymers (COP), discotic polymers, and Nitto Denko™ double-stretched polycarbonate cast onto a substrate to provide homeotropic alignment.

[0235] FIG. 4B is a schematic diagram showing a graph of liquid crystal director angle 407 versus fractional position 440 through a switchable liquid crystal retarder cell, where the fractional position 440 varies between position 0 at the surface alignment layer 409 and position 1 at the surface alignment layer 411.

[0236] In the homeotropic mode with no voltage applied as shown in Figure 4A, the liquid crystal director is tilted 407 at 88 degrees through the thickness of the cell as shown by tilt profile 442. The tilt profile of layer 314 may be identical to profile 442. The compensation retarder 330 may compensate for the pretilt direction of the switchable liquid crystal retarder 301. Alternatively, the compensation retarder 330 may have a uniform tilt angle of 90 degrees, and such difference in the pretilt of the liquid crystal layer will result in negligible difference in the off-axis viewing characteristics.

[0237] Thus, the off-axis retardance of the compensation retarder 330 is substantially equal and opposite to the off-axis retardance of the switchable liquid crystal retarder 301 when no voltage is applied.

[0238] FIG. 4C is a schematic diagram showing a side view of the propagation of output light from spatial light modulator 48 through the optical stack of FIG. 1A in a wide-angle operating mode, and FIG. 4D is a schematic graph showing the change in output transmission with the polarity direction of the transmitted light beam of FIG. 4C in a wide-angle operating mode.

[0239] An ideal switchable compensation retarder 300 comprises a compensation retarder 330 in combination with a switchable variable liquid crystal retarder 301, the compensation retarder 330 having a dielectric constant, anisotropy, and anisotropic dispersion that are equal and opposite to those of the layer 314. The retardance of the passive compensation retarder 330 is equal and opposite to that of the switchable liquid crystal retarder 301.

[0240] Such an ideal compensation switchable retarder would achieve compensation of transmitted light for all polar angles in the first wide angle state of the layer 314 of liquid crystal material 414 and achieve a narrow lateral field of view in the second privacy state of the switchable liquid crystal retarder 301.

[0241] Moreover, the optic axis of the compensation retarder 330 has the same direction as the optic axis of the liquid crystal retarder 301 in the wide-angle state. Such compensation retarder 330 cancels the retardation of the liquid crystal retarder for all viewing angles, resulting in an ideal wide-angle viewing state with no brightness loss for all viewing directions.

[0242] We now describe the wide angle transmission polar profile of non-ideal material choices.

[0243] Exemplary embodiments of the present disclosure show a compensation retarder 330 that cannot exactly compensate for the retardation of the switchable liquid crystal retarder 301 due to small differences in material properties that are typical of the retarders 330, 301. Advantageously, however, such deviations are small and high performance wide and narrow angle states can be achieved if such deviations are close to ideal performance.

[0244] Thus, when the switchable liquid crystal retarder 301 is in the first of the two aforementioned states, the switchable compensation retarder 300 does not fully convert the polarization components 360, 361 for light ray 402 etc., and outputs light ray 400 passing perpendicular to the plane of the switchable retarder or at an acute angle to the perpendicular to the plane of the switchable retarder.

[0245] Polarization component 362 is substantially identical to polarization component 360, and polarization component 364 is substantially identical to polarization component 361. Thus, the angular transmission profile of Figure 4D has substantially uniform transmission over a wide polarity range.

[0246] In other words, when the layer of liquid crystal material 414 is in a first of the two orientation states, the multiple retarders 330, 301 provide no overall retardance to light passing perpendicular to the plane of the retarders or at an acute angle to the perpendicular to the plane of the retarders 330, 301.

[0247] Advantageously, the change in display luminance with the viewing angle of the first state is substantially unchanged. Multiple users can advantageously view the display from a wide range of viewing angles.

[0248] We now describe the operation of the compensation retarder 300 and the additional polarizer 318 in the narrow angle mode, for example, for use in a privacy mode of operation.

[0249] FIG. 5A is a schematic diagram illustrating in a perspective side view the configuration of a switchable compensation retarder 300 in a privacy mode of operation, comprising a negative C-plate passive compensation retarder 330 and a homeotropically aligned switchable liquid crystal retarder 301 in the privacy mode of operation.

[0250] The liquid crystal retarder 301 further comprises transparent electrodes 413, 415, such as ITO electrodes, disposed across the switchable liquid crystal retarder 301. The electrodes 413, 415 control the switchable liquid crystal retarder 301 by adjusting the voltage applied to the electrodes 413, 415.

[0251] The control system 352 is configured to control the voltage applied across the electrodes 413 , 415 of the switchable liquid crystal retarder 301 by the voltage driver 350 .

[0252] Returning to FIG. 4B, application of a voltage results in an outwardly diverging tilt profile 444 of the switchable liquid crystal retarder 301, which in turn changes the retardance of the layer 314 of liquid crystal material 414.

[0253] The direction of optimal privacy performance may be adjusted depending on the observer's position by controlling the drive voltage. In other uses, or to provide controlled brightness to off-axis observers, for example in an automotive environment, a passenger or driver may wish to use intermediate voltage levels to provide some visibility rather than completely obscuring the displayed image.

[0254] FIG. 5B is a schematic diagram showing in side view the propagation of output light from the spatial light modulator 48 through the optical stack of FIG. 1A in a privacy mode of operation, in which the switchable liquid crystal retarder 301 is oriented by an applied voltage.

[0255] In this embodiment, the switchable compensation liquid crystal retarder 330 may be configured in combination with the display polarizers 210, 218, 316 and the additional polarizer 318 to have the effect of reducing the brightness of the light output from the display device at acute angles to the optical axis (off-axis) (i.e., compared to when the retarder is not present). The switchable compensation liquid crystal retarder 330 may also be configured in combination with the display polarizers 210, 218, 316 and the additional polarizer 318 to have the effect of not reducing the brightness of the light output from the display device along the optical axis (on-axis) (i.e., compared to when the retarder is not present).

[0256] Polarization component 360 from the output display polarizer 218 is transmitted by the output display polarizer 218 and enters the switchable compensation retarder 300. On-axis light has an unaltered polarization component 362 from component 360, and off-axis light has a polarization component 364 that is transformed by the retarder of the switchable compensation retarder 300. At a minimum, polarization component 361 is transformed to a linear polarization component 364 and absorbed by the additional polarizer 318. More generally, polarization component 361 is transformed to an elliptically polarized component and partially absorbed by the additional polarizer 318.

[0257] Thus, when the switchable liquid crystal retarder 301 is in a second of its two orientation states, the multiple retarders 301, 330 provide no overall retardance to light passing along an axis that is perpendicular to the plane of the retarder, but provide a non-zero overall retardance to light passing therethrough at some polar angles 363 that are acute angles with the perpendicular to the plane of the retarders 301, 330.

[0258] In other words, when the switchable liquid crystal retarder 301 is in the second of its two states, the switchable compensation retarder 330 does not fully convert the polarization component 360 for the output ray 400 passing along an axis that is perpendicular to the plane of the switchable retarder 301, but does fully convert the polarization component 361 for the passing ray 402 for some polar angles that are acute with respect to the perpendicular to the plane of the retarders 301, 330.

[0259] An exemplary material system describes narrow angle operation.

[0260] FIG. 5C is a schematic graph showing the change in output transmission with polarity direction of the transmitted light beam of FIG. 5B, having parameters listed in Table 1. [Table 1]

[0261] In this embodiment, the desired ranges of retardation and voltage are established by simulation of the retarder stack and experimentation with display optics stacks.

[0262] The switchable liquid crystal retarder 300 comprises a first surface alignment layer 409 disposed on a first side of a layer of liquid crystal material 414 and a second surface alignment layer 411 disposed on a second side of the layer of liquid crystal material 414 opposite the first side, where the first surface alignment layer 409 is a homeotropic alignment layer and the second surface alignment layer 411 is a homeotropic alignment layer, and where the layer of liquid crystal material has a retardance of 500nm to 1000nm, preferably 600nm to 900nm, most preferably 700nm to 850nm for light of a wavelength of 550nm.

[0263] When the passive compensation retarder 330 comprises a retarder with its optic axis perpendicular to the plane of the retarder, the passive retarder has a retardance for light of 550 nm wavelength between -300 nm and -900 nm, preferably between -450 nm and -800 nm, and most preferably between -500 nm and -725 nm.

[0264] The polarity distribution of the light transmission shown in FIG. 5C changes the polarity distribution of the luminance output from the underlying spatial light modulator 48 and, if applicable, the backlight 20 as well.

[0265] Advantageously, a privacy display is provided that has low brightness for off-axis snoopers while maintaining high brightness for on-axis observers. A broad polar region is provided over which the brightness of the display is reduced for off-axis snoopers. Furthermore, the primary display user in the privacy mode of operation is substantially unaffected by the on-axis brightness.

[0266] The voltage applied across the electrodes is zero in the first orientation state and non-zero in the second orientation state. Advantageously, no additional power consumption is incurred in the wide angle mode of operation and the failure mode of the drive of the switchable liquid crystal retarder 301 is for the wide angle mode.

[0267] The operation of the privacy mode of the display of FIG. 1A will now be further described.

[0268] FIG. 6A is a schematic diagram showing the observation of transmitted output light for a display operating in privacy mode in a front perspective view. The display device 100 may comprise a white region 603 and a black region 601. A snooper can observe an image on the display if a luminance difference between the observation regions 601, 603 can be perceived. In operation, a primary user 45 observes a full luminance image with light rays 400 to a viewing position 26, which may be an optical window of a directional display. A snooper 47 observes a reduced luminance light ray 402 at a viewing position 27, which may be an optical window of a directional display. Regions 26, 27 further represent the on-axis and off-axis regions of FIG. 5C.

[0269] Figure 6B is a schematic diagram showing the appearance of the display of Figure 1A operating in Privacy Mode 1 from a front perspective, with the luminance varying as shown in Figure 5C. Thus, the top viewing quadrants 530, 532, the bottom viewing quadrants 534, 536 and the side viewing positions 526, 528 provide reduced luminance, while the top / bottom central viewing regions 522, 520 and frontal viewing provide higher luminance.

[0270] It may be desirable to provide controllable display lighting in automotive vehicles.

[0271] 6C is a schematic diagram illustrating an automotive vehicle in side view with a switchable directional display 100 disposed within a cabin 602 of a vehicle 600 for both entertainment and shared modes of operation. A light cone 610 (e.g., representing a cone of light whose luminance is greater than 50% of its peak luminance) may be provided by the elevational luminance distribution of the display 100 and is non-switchable.

[0272] 6D is a schematic diagram showing a front view of an automotive vehicle having a switchable directional display 100 disposed within a passenger compartment 602 in an entertainment mode of operation and operating similarly to a privacy display. A light cone 612 is provided at a narrow angle such that a passenger 606 can see the display 100, but the driver 604 cannot see the image on the display 100. Advantageously, entertainment images can be displayed to the passenger 606 without distracting the driver 604.

[0273] 6E is a schematic diagram showing a top view of an automotive vehicle with a switchable directional display 100 disposed within a passenger compartment 602 in a shared mode of operation. A light cone 614 is provided with a wide angular range so that all occupants can perceive the image on the display 100, for example, when the display is not moving or an undistracting image is provided.

[0274] Figure 6F is a schematic diagram showing a top view of an automotive vehicle with a switchable directional display 100 positioned within a passenger compartment 602 for both night and day operating modes. Compared to the configurations of Figures 6C-6E, the optical output is rotated such that the elevation direction of the display is along an axis between the positions of the driver 604 and passenger 606. A light cone 620 illuminates both the driver 604 and passenger 606.

[0275] 6G is a schematic diagram showing a side view of an automotive vehicle having a switchable directional display 100 disposed within a passenger compartment 602 in a nighttime mode of operation. The display may thus provide a narrow angle output light cone 622. Stray light illuminating the interior surfaces and passengers of the passenger compartment 602 and advantageously distracting the driver 604 may be substantially reduced. Both the driver 604 and passengers 606 may advantageously observe the displayed image.

[0276] 6H is a schematic diagram illustrating an automotive vehicle in side view having a switchable directional display 100 disposed within a passenger compartment 602 in a daytime operating mode. The display may thus provide a narrow angle output light cone 624. Advantageously, the display may be conveniently viewed by all occupants of the passenger compartment 602.

[0277] The displays 100 of Figures 6C-6H may be placed in other vehicle cabin locations, such as driver instrument displays, center console displays, and seat back displays.

[0278] 7A-7D are schematic diagrams showing the change in output transmission with polarity direction for four different driving voltages from 2.05V to 2.35V in 0.1V increments. Thus, the applied voltage can control the luminance viewing minimum position in the privacy mode of operation. Furthermore, the luminance minimum can be controlled between elevation angles below zero for elevation angles in the upper quadrant of the polarity profile.

[0279] 8 is a flow chart illustrating the control of a privacy display performed by a control system, which may be applied to each of the devices described herein.

[0280] In a first step 870, a user may enable a privacy mode of operation.

[0281] When a first and a further compensation switchable liquid crystal retarder 300B are provided (for example in the device of Figure 22A described below), the control system is arranged in a second orientation state to control the voltage applied across the electrodes 413, 415 of said switchable liquid crystal retarder 314A and also to control the voltage applied across the electrodes of the further switchable liquid crystal retarder 314B, such that the overall retardance for light passing through said first switchable liquid crystal retarder 314A and said passive compensation retarder 330A at some polar angles acutely perpendicular to the plane of the retarders 31A, 330A is different from the overall retardance for light passing through the further switchable liquid crystal retarder 314B and the further passive compensation retarder 330B at some polar angles.

[0282] Such privacy mode settings may be provided by manual setting (e.g., keyboard operation) or by automatic detection using a sensor to identify the presence of a snooper, for example, as described in U.S. Patent Application Publication No. 2017-0236494, which is incorporated by reference herein in its entirety. Optionally, the orientation of the display with respect to the snooper may be further detected by detector 873.

[0283] In a second step 872, the location of the snooper may be detected, for example, by a camera or keyboard setup or other methods. In an exemplary embodiment, an office setup may be provided, which may be desirable to optimize privacy performance for a snooper moving around a shared office environment, thus optimizing performance for the lower viewing quadrant. Compared to the flight setup, this may provide an optimized privacy level for a seated snooper, and may improve privacy levels for elevation angles smaller than those desired for the office setup.

[0284] In a third step 876, the voltage applied to the switchable liquid crystal retarder 301 may be adjusted, and in a fourth step 878, the control system can adjust the LED profile.

[0285] The control system may therefore further comprise means 872 for determining the position of the snooper 47 with respect to the display device 100, the control system being configured to adjust the voltage applied across the electrodes 413, 415 of the switchable liquid crystal retarder 314 by the drive 350 in response to the measured position of the snooper 47.

[0286] Advantageously, the privacy behavior of the display can be controlled to optimize the viewing geometry of the snooper.

[0287] Returning to the discussion of this embodiment, further configurations of the switchable compensation retarder 300 will now be described.

[0288] Figure 9A is a schematic diagram showing a perspective side view of a switchable compensation retarder configuration in a privacy operation mode comprising crossed A-plate passive compensation retarders 308A, 308B and a homeotropically aligned switchable liquid crystal retarder 301, and Figure 9B is a schematic diagram showing a perspective side view of a switchable compensation retarder configuration in a privacy operation mode comprising a crossed A-plate passive compensation retarder and a homeotropically aligned switchable liquid crystal retarder.

[0289] 4A and 5A, the compensation retarder 330 may alternatively comprise a pair of retarders 308A, 308B with their optic axes in the planes of the intersecting retarders. The compensation retarder 330 therefore comprises a pair of retarders 308A, 308B each comprising a single A-plate.

[0290] The pair of retarders 308A, 308B each comprises a number of A-plates with respective optic axes 309A, 309B oriented at different angles with respect to each other. The pair of retarders have optic axes 309A, 309B each extending at 45° with respect to the electric vector transfer direction that is parallel to the electric vector transfer direction 211 of the input display polarizer 210 when the additional polarizer 318 is disposed on the input side of the input display polarizer, and parallel to the electric vector transfer direction 219 of the output display polarizer 218 when the additional polarizer 318 is disposed on the output side of the input display polarizer 218.

[0291] FIG. 9C is a schematic graph showing the change in output transmission with the polarity direction of the transmitted light beam of FIG. 9A in a wide angle operating mode, and FIG. 9D is a schematic graph showing the change in output transmission with the polarity direction of the transmitted light beam of FIG. 9B in a privacy operating mode, as provided by the exemplary embodiment of Table 2. [Table 2]

[0292] When the passive compensation retarder 330 comprises a pair of retarders having their optical axes in the plane of the intersecting retarders, each retarder of the pair has a retardance in the range of 300 nm to 800 nm, preferably in the range of 500 nm to 700 nm, and most preferably in the range of 550 nm to 675 nm for light of a wavelength of 550 nm.

[0293] Advantageously, the A-plate can be conveniently manufactured at a lower cost than the C-plate retarders of Figures 4A and 5A. For wide angle operation modes, a zero voltage state can also be provided to minimize power consumption during wide angle operation.

[0294] In this embodiment, "crossed" refers to an angle of substantially 90° between the optical axes of the two retarders in the plane of the retarders. To reduce the cost of the retarder material, it is desirable to provide a material with some variation in retarder orientation, for example due to stretching errors during film manufacturing. Variations in retarder orientation away from the preferred direction can reduce the front brightness and increase the minimum transmittance. Preferably, angle 310A is at least 35° and at most 55°, more preferably at least 40° and at most 50°, and most preferably at least 42.5° and at most 47.5°. Preferably, angle 310B is at least 125° and at most 145°, more preferably at least 130° and at most 135°, and most preferably at least 132.5° and at most 137.5°.

[0295] When mechanically distorted, such as when the display is touched, the homeotropically aligned liquid crystal retarder 301 of Figures 9A-9B may have an unnecessarily long recovery time resulting in visible misalignment artifacts. Fast recovery after mechanical distortion is desirable.

[0296] 10A-10B are schematic diagrams illustrating in perspective side views, respectively, of a switchable compensation retarder configuration in a wide-angle and privacy mode of operation, in which the C-plate retarder 330 comprises a liquid crystal material 414 with positive dielectric anisotropy and a passive negative C-plate for a first and second drive voltage, respectively, and comprises a homogeneously aligned switchable liquid crystal retarder.

[0297] The switchable liquid crystal retarder further comprises surface alignment layers 431, 433 adjacent to the layer of liquid crystal material 414 and each configured to provide a homogeneous alignment in the adjacent liquid crystal material. In other words, the switchable liquid crystal retarder comprises two surface alignment layers 431, 433 adjacent to and disposed on either side of the layer of liquid crystal material 414 and each configured to provide a homogeneous alignment in the adjacent liquid crystal material 414.

[0298] FIG. 10C is a schematic diagram showing a graph of the liquid crystal director angle 407 versus fractional position 440 through the switchable liquid crystal retarder 301 of FIG. 10A for a variety of different applied voltages. FIG. 10C differs from FIG. 4B in that the pretilt angle is small and increases with applied voltage. Profile 441 shows the tilt angle of the liquid crystal material 414 for an applied voltage of 0V, tilt profile 443 shows the director orientation for 2.5V, and tilt profile 445 shows the director orientation for 5V. Thus, the liquid crystal layer is typically tilted in the desired switching state and is compensated by the compensation retarder 330. Increasing the voltage from above 2.5V to 10V progressively reduces the thickness of the retarder 301 where the tilt exists, advantageously increasing the polar field where the transmission is maximized.

[0299] The resolved components 419a, 419b of the liquid crystal tilt relative to the direction perpendicular to the plane of the retarder are substantially higher than the components 417a, 417b in FIG. 5A.

[0300] The increased size of the resolved components 419a, 419b may result in increased restoring force after mechanical distortion, for example, compared to the configuration of Figure 9A. Sensitivity to mechanical distortion, such as when touching the display, may be advantageously reduced.

[0301] The voltage of operation can be reduced to less than 10V for an acceptable wide angle field of view, reducing power consumption and reducing the cost and complexity of electric drives.

[0302] 11A-11C are schematic graphs showing the variation of output transmission with the polarity direction of the transmitted light of a switchable compensation retarder comprising a homogeneously aligned liquid crystal retarder 301 and a negative passive C-plate compensation retarder 330 similar to the display device of FIGS. 10A and 10B in a privacy mode and two different wide angle modes for different driving voltages, including the embodiments shown in Table 3. [Table 3]

[0303] The desired ranges of optical retardance of the active LC retarder 301 with homogeneous alignment layers 431, 433 on both substrates, and the negative passive C-plate compensation retarder 330 are further described in Table 4. [Table 4]

[0304] Thus, the switchable liquid crystal retarder 300 comprises a first surface alignment layer 431 arranged on a first side of the layer of liquid crystal material 414 and a second surface alignment layer 433 arranged on a second side of the layer of liquid crystal material 414 opposite the first side, wherein the first surface alignment layer 409 is a homogeneous alignment layer and the second surface alignment layer is a homogeneous alignment layer, and the layer of liquid crystal material has a retardance in the range of 500nm to 1000nm for light of a wavelength of 550nm, preferably in the range of 600nm to 850nm and most preferably in the range of 700nm to 800nm. Thus, when the first alignment layer and the second alignment layer are each homogeneous alignment layers and the passive compensation retarder 330 comprises a retarder having an optical axis perpendicular to the plane of the retarder, the passive retarder has a retardance in the range of -300 nm to -700 nm, preferably in the range of -350 nm to -600 nm, and most preferably in the range of -400 nm to -500 nm, for light of a wavelength of 550 nm.

[0305] Advantageously, off-axis privacy may be provided by increasing the level of privacy and reducing the luminance over a wide polar region. Further resistance to visual artifacts resulting from flow of the liquid crystal material within layer 314 may be improved compared to homeotropic alignment.

[0306] Various alternative configurations and operations of the optical structure of FIG. 10A will now be described.

[0307] Operation at 5V results in lower power consumption and lower cost electronics while achieving acceptable brightness roll-off in the wide-angle mode. The field of view in the wide-angle mode can be further expanded by operation at 10V.

[0308] FIG. 12A is a schematic diagram showing a perspective side view of a switchable compensation retarder configuration in a privacy operation mode, comprising a crossed A-plate passive compensation retarder 308A, 308B and a homogeneously aligned switchable liquid crystal retarder 301; and FIGS. 12B-12D are schematic graphs showing the variation of output transmission with transmitted light polarity direction of the switchable compensation retarder 301 comprising a homogeneously aligned liquid crystal material 414 and a negative passive crossed A-plate retarder 308A, 308B in privacy mode and wide angle mode for different driving voltages, including the respective embodiments shown in Table 5. [Table 5]

[0309] The desired ranges of optical retardance for the active LC retarder 301 with homogeneous alignment layers 409, 411 on both substrates and the positive active crossed A-plate compensation retarders 308A, 308B are further described in Table 6. [Table 6]

[0310] Thus, the first and second alignment layers are each homogeneous alignment layers, the layer of liquid crystal material has a retardance in the range of 500nm to 1000nm, preferably in the range of 600nm to 850nm, and most preferably in the range of 700nm to 800nm ​​for light of a wavelength of 550nm, and the passive compensation retarder 330 comprises a pair of retarders having an optic axis in the plane of the crossed retarders, each retarder of the pair having a retardance of 300nm to 800nm, preferably 350nm to 650nm, and most preferably 450nm to 550nm for light of a wavelength of 550nm.

[0311] The further crossed A-plates may conveniently be provided from low cost materials.

[0312] Various other exemplary embodiments of the optical structure and drive of Fig. 12A will now be described, by way of illustration. Fig. 12C and Fig. 12D further illustrate that by adjusting the address voltage and retardance, different wide angle viewing angles can be advantageously achieved.

[0313] Here, the configuration of the optical laminated structure will be further described.

[0314] 13A and 13B are schematic diagrams showing a side view of a portion of a display comprising a switchable compensation retarder and an optical coupling layer 380. The optical coupling layer 380 may be provided on the laminate film and substrate to improve efficiency and reduce brightness at high viewing angles in privacy mode. Furthermore, an air gap 384 may be provided between the spatial light modulator 48 and the switchable compensation retarder 300. At least one of the switchable compensation retarder 300 or the spatial light modulator 48 may be provided with a wetting prevention surface 382 to reduce wetting of the two surfaces in the air gap 384.

[0315] A passive compensation retarder 330 may be provided between the switchable liquid crystal layer 301 and the spatial light modulator 48 as shown in Figure 13A, or between the additional polarizer 318 and the switchable liquid crystal retarder 301 as shown in Figure 13B. Both systems provide substantially identical optical performance.

[0316] 13A shows that the optical layers are bonded to the outside of the substrates 312, 316. Advantageously, stresses built up during lamination can reduce bending of the substrates 312, 316 from the attached layers, maintaining the flatness of the display.

[0317] Similarly, the switchable compensation retarder 300 may be positioned such that the output polarizer 218 is the display polarizer. Scattering that may be introduced by the spatial light modulator 48, such as from phase structures in the pixels 220, 222, 224, does not degrade the output brightness profile compared to a configuration in which the switchable compensation retarder 301 is positioned behind the spatial light modulator 48.

[0318] It may be desirable to provide an additional polarizer with an electric vector transmission direction different from that of the display polarizer.

[0319] FIG. 14 is a schematic diagram showing in a perspective side view a switchable compensation retarder configuration in a privacy mode of operation comprising a crossed A-plate passive compensation retarder 308A, 308B and a homogeneously aligned switchable liquid crystal retarder 301 as described above, but further comprising a passive rotation retarder 460.

[0320] The display polarizer 218 may have an electric vector transmission direction 219, which in the case of a twisted nematic LCD display may be at an angle 317 of, for example, 45 degrees. An additional polarizer 318 may be positioned to provide vertically polarized light to a user who may wear polarized sunglasses that typically transmit vertically polarized light.

[0321] The passive rotating retarder 460 differs from the compensation retarder 330 in this embodiment, and its operation is described here.

[0322] The passive rotating retarder 460 may include a birefringent material 462 and may be a half wave plate, for example having a retardance of 275 nm at a wavelength of 550 nm.

[0323] The passive rotating retarder 460 has a fast axis orientation 464 that is tilted at an angle 466, which may be 22.5 degrees, with respect to the electric vector transmission direction 319 of the additional polarizer 318. The passive rotating retarder 460 thus rotates the polarization from the output polarizer 218 such that the polarization direction of the light entering the compensation retarder 308B is parallel to direction 319.

[0324] The passive rotating retarder 460 changes the on-axis polarization state by rotating the angles of the polarization components from the display polarizer 218. In comparison, both compensation retarders 308A, 308B do not change the on-axis polarization state.

[0325] Furthermore, the passive rotating retarder 460 rotates the polarization, which may be substantially independent of viewing angle. In comparison, the compensation retarders 308A, 308B produce a substantial change in output brightness with viewing angle.

[0326] Advantageously, the display may have an output polarization direction 319 that differs from the polarization direction 219 of the display polarizer, for example to allow viewing when wearing polarized sunglasses.

[0327] In an alternative embodiment, the separate retarder 460 may be omitted and the retardance of retarder 308B in FIG. 11A may be increased to provide an additional half-wave rotation compared to the retardance of retarder 308A. To continue with the exemplary embodiment, the retardance of retarder 308B at a wavelength of 550 nm may be 275 nm greater than the retardance of retarder 308A. Advantageously, the number of layers, complexity, and cost may be reduced.

[0328] It is desirable to reduce the thickness and total number of optical components.

[0329] FIG. 15A is a schematic diagram illustrating a configuration of a switchable compensation retarder in a privacy mode of operation in a perspective side view, comprising a homogeneously aligned switchable liquid crystal retarder 301 disposed between a first C-plate passive compensation retarder 330A and a second C-plate passive compensation retarder 330B, and is further shown in Table 7. [Table 7]

[0330] 15B and 15C are schematic graphs illustrating the variation of output transmission with polarity direction of transmitted light in the optical stack of FIG. 15A in wide angle and privacy modes of operation, respectively.

[0331] The passive compensation retarder 330 comprises a first C-plate 330A and a second C-plate 330B, and the switchable liquid crystal layer 301 is provided between the first C-plate 330A and the second C-plate 330B.

[0332] The passive compensation retarder 330A, 330B comprises two passive retarders with their optical axes perpendicular to the plane of the passive retarders, and the switchable liquid crystal retarder 301 is provided between the two passive retarders. Thus, the first substrate 312 and the second substrate 316 of FIG. 1A each include one of the two passive retarders 330A, 330B.

[0333] In combination, the two passive retarders 330A, 330B have a total retardance in the range of -300nm to -800nm, preferably in the range of -350nm to -700nm, and most preferably in the range of -400nm to -600nm for light of a wavelength of 550nm.

[0334] FIG. 16A is a schematic diagram showing a perspective side view of a display comprising a switchable liquid crystal retarder 301 disposed between a first substrate and a second substrate comprising a C-plate passive compensation retarder 330A, 330B, respectively, and FIG. 16B is a schematic diagram showing a side view of a portion of a display comprising a switchable liquid crystal retarder 301 disposed between a first substrate and a second substrate comprising a C-plate passive compensation retarder 330A, 330B, respectively.

[0335] The first C plate 330A has a transparent electrode layer 415 and a liquid crystal alignment layer 411 formed on one side, and the second C plate 330B has a transparent electrode layer 413 and a liquid crystal alignment layer 409 formed on one side.

[0336] A layer of liquid crystal material 314 is provided between a first substrate 312 and a second substrate 316, each of which comprises one of a first C-plate 330A and a second C-plate 330B. The C-plates may be provided in a double stretched COP film that is ITO coated to provide electrodes 413, 415 and has liquid crystal alignment layers 409, 411 formed thereon.

[0337] Advantageously, the number of layers may be reduced compared to the configurations of Figures 1A, 1B, 1C and 1D, reducing thickness, cost and complexity. Additionally, the C-plates 330A, 330B may be flexible substrates, providing a flexible privacy display.

[0338] It is desirable to provide a layer 314 of liquid crystal material between the first and second A-plate substrates.

[0339] FIG. 17A is a schematic diagram showing a perspective side view of a switchable compensation retarder 300 configuration in a wide-angle operation mode, comprising a homogeneously aligned switchable liquid crystal retarder 301 disposed between a first crossed A-plate passive compensation retarder 330A and a second crossed A-plate passive compensation retarder 330B, as described above, and FIG. 17B and FIG. 17C are schematic graphs showing the change in output transmission with the polarity direction of the transmitted light beam of the structure of FIG. 17A when driven in the wide-angle operation mode and the privacy operation mode, respectively, each including further exemplary embodiments shown in Table 7.

[0340] Compared to the configuration of FIG. 15A, advantageously, the A-plate may be manufactured at reduced cost compared to the C-plate.

[0341] Here, a hybrid alignment structure comprising both homogeneous and homeotropic alignment layers is described.

[0342] FIG. 18A is a schematic diagram showing in a perspective side view a switchable compensation retarder configuration in a privacy mode of operation comprising a homogeneously and homeotropically aligned switchable liquid crystal retarder 301 containing a liquid crystal material 423 and a negative passive C-plate retarder 330.

[0343] 18B-18C are schematic graphs illustrating the variation of output transmission with polarity direction of the transmitted light beam of FIG. 18A in wide angle and privacy modes of operation, respectively, and are provided by the construction of Table 8. [Table 8]

[0344] The hybrid alignment switchable liquid crystal retarder 301 has a variable tilt such that the effective birefringence is reduced for a given material and cell thickness selection. Therefore, the retarder design needs to be adjusted to compensate compared to a configuration in which the alignment layers are identical. The switchable liquid crystal retarder 330 comprises a first surface alignment layer 441 disposed on a first side of the layer of liquid crystal material 423 and a second surface alignment layer 443 disposed on a second side of the layer of liquid crystal material 423 opposite the first side. The first surface alignment layer 441 is a homeotropic alignment layer configured to provide homeotropic alignment in the adjacent liquid crystal material 423 and the second surface alignment layer 443 is a homogeneous alignment layer configured to provide homogeneous alignment in the adjacent liquid crystal material 423.

[0345] Furthermore, the optimum design of the retarder is related to the relative position of the passive compensation retarder 330 with respect to the homeotropic and homogeneous alignment layers.

[0346] When the surface alignment layer 443 is configured to provide homogeneous alignment between the layer of liquid crystal material 423 and the compensation retarder 330, the layer of liquid crystal material 423 has a retardance in the range of 500 nm to 1800 nm for light of a wavelength of 550 nm, preferably in the range of 700 nm to 1500 nm, and most preferably in the range of 900 nm to 1350 nm. Where the surface alignment layer 443 is configured to provide homogeneous alignment between the layer of liquid crystal material 423 and the compensation retarder 330, the passive compensation retarder may comprise a retarder 330 having an optic axis perpendicular to the plane of the retarder as shown in FIG. 18A, the passive retarder 330 having a retardance in the range of -300 nm to -1600 nm, preferably in the range of -500 nm to -1300 nm, and most preferably in the range of -700 nm to -1150 nm for light of a wavelength of 550 nm; alternatively, the passive compensation retarder may comprise a pair of retarders (not shown) having optic axes in the intersecting retarder planes, each retarder of the pair having a retardance in the range of 400 nm to 1600 nm, preferably in the range of 600 nm to 1400 nm, and most preferably in the range of 800 nm to 1300 nm for light of a wavelength of 550 nm.

[0347] When the surface alignment layer 441 is configured to provide homeotropic alignment between the layer of liquid crystal material 423 and the compensation retarder 330, the layer of liquid crystal material 423 has a retardance in the range of 700 nm to 2000 nm for light of a wavelength of 550 nm, preferably in the range of 1000 nm to 1700 nm, and most preferably in the range of 1200 nm to 1500 nm. Where the surface alignment layer 441 is configured to provide homeotropic alignment between the layer of liquid crystal material 423 and the compensation retarder 330, the passive compensation retarder may comprise a retarder 330 having an optic axis perpendicular to the plane of the retarder as shown in FIG. 18A, the passive retarder having a retardance in the range of -400nm to -1800nm, preferably in the range of -700nm to -1500nm, most preferably in the range of -900nm to -1300nm for light of a wavelength of 550nm; alternatively, the passive compensation retarder may comprise a pair of retarders (not shown) having optic axes in the plane of the intersecting retarders, each retarder of the pair having a retardance in the range of 400nm to 1800nm, preferably in the range of 700nm to 1500nm, most preferably in the range of 900nm to 1300nm for light of a wavelength of 550nm.

[0348] Compared to the configuration of FIG. 5A, the privacy mode of operation may advantageously increase the resilience of the liquid crystal retarder to the appearance of material flow upon compression.

[0349] Here, the performance of a retarder between parallel polarizers in series arrangement will be described for comparison with this embodiment. First, the field of view of the liquid crystal retarder 301 in homogeneous alignment for two different driving voltages will be described.

[0350] Fig. 19A is a schematic diagram in perspective side view showing the configuration of a homogeneously aligned switchable liquid crystal retarder 390. Fig. 19B is a schematic graph showing the change in output transmission in the polar direction of the transmitted light beam of Fig. 19A for a first applied voltage, and Fig. 19C is a schematic graph showing the change in output transmission in the polar direction of the transmitted light beam of Fig. 19A for a second applied voltage that is greater than the first applied voltage, with the structure shown in Table 9. The homogeneously aligned switchable liquid crystal retarder 390 corresponds to the switchable liquid crystal retarder 330 described above, and may be applied as the switchable liquid crystal retarder in any of the devices disclosed herein.

[0351] Figure 19D is a schematic diagram showing a perspective side view of a passive C-plate retarder 392 disposed between parallel polarizers, and Figure 19E is a schematic graph showing the output transmission variation with polarity direction of the transmitted light beam of Figure 19D, with the structure shown in Table 9. The passive C-plate retarder 392 corresponds to the passive compensation retarder 330 and may be applied as at least one passive compensation retarder in any of the devices disclosed herein. [Table 9]

[0352] FIG. 20A is a schematic diagram showing in a perspective side view a configuration of a homogeneously aligned switchable liquid crystal retarder 390 arranged between parallel polarizers 394, 396 in series with a field-control passive retarder comprising a C-plate retarder 392 arranged between parallel polarizers 396, 398; FIG. 20B is a schematic graph showing the change in output transmission in the polarity direction of the transmitted light beam of FIG. 20A for a first applied voltage; and FIG. 20C is a schematic graph showing the change in output transmission in the polarity direction of the transmitted light beam of FIG. 20A for a second applied voltage that is greater than the first applied voltage, with the structure shown in Table 9.

[0353] FIG. 21A is a schematic diagram showing in a perspective side view a configuration of a homogeneously aligned switchable liquid crystal retarder 301 in series with a C-plate compensation retarder 330, where the homogeneously aligned switchable liquid crystal material 712 and the C-plate compensation retarder 330 are disposed between a pair of parallel polarizers; FIG. 21B is a schematic graph showing the variation of output transmission in the polarity direction of the transmitted light beam of FIG. 21A for a first applied voltage; and FIG. 21C is a schematic graph showing the variation of output transmission in the polarity direction of the transmitted light beam of FIG. 21A for a second applied voltage, which is greater than the first applied voltage, with a structure as shown in Table 9.

[0354] Unexpectedly, the optimum condition for maximum viewing operation is provided by an equal and opposite net retardation of the compensation retarder 330 compared to the switchable liquid crystal retarder 301 in its undriven state. When configured to provide a narrow angle state, an ideal compensation retarder 330 and switchable liquid crystal retarder 301 (i) do not alter the wide angle mode performance from the input light, and (ii) can optimally reduce the lateral viewing angle for all elevation angle off-axis positions. This teaching may be applied to all display devices disclosed herein.

[0355] It may be desirable to increase the luminance falloff for off-axis viewing positions, in particular it would be desirable to increase privacy reduction in liquid crystal displays with wide angle backlights.

[0356] FIG. 22A is a schematic diagram showing a perspective side view (showing reverse viewing with the z-axis along which the output light is directed downwards) of a switchable compensation retarder configuration in a privacy mode of operation, comprising a first switchable compensation retarder 300A (in this case a negative C-plate passive compensation retarder 330A and a homeotropically aligned switchable liquid crystal retarder 301A, but this is only an example and may be substituted with any of the other configurations of retarders disclosed herein) arranged between the output display polarizer 218 and an additional polarizer 318A, and a further switchable compensation retarder 300B (in this case a negative C-plate passive compensation retarder 330B and a homeotropically aligned switchable liquid crystal retarder 301B, but this is only an example and may be substituted with any of the other configurations of retarders disclosed herein) arranged between the aforementioned additional polarizer 318A and a further additional polarizer 318B, and having an electric vector transfer direction 319B.

[0357] As an alternative, the aforementioned additional polarizer 318A may be positioned on the input side of the input display polarizer 210 (in which case the further additional polarizer 318B may be positioned on the input side of the input display polarizer 210 between the aforementioned additional polarizer 318A and the backlight 20), and the further switchable compensation retarder 300B may be positioned between the further additional polarizer 318B and the aforementioned additional polarizer 318A.

[0358] In both of these alternatives, each of the first plurality of retarders 300A and the further plurality of retarders 300B is disposed between a respective pair of polarizers, thereby having a similar effect as the corresponding structure in the device described above.

[0359] The pretilt direction 307A, 309AA of the alignment layer of the further switchable liquid crystal retarder 301A may have a component in the plane of the liquid crystal layer that is aligned parallel or anti-parallel or orthogonal to the pretilt direction of the alignment layer 307B, 309AB of the first switchable liquid crystal retarder 301B. In a wide angle mode of operation, both switchable liquid crystal retarders 301A, 301B are driven to provide a wide viewing angle. In a privacy mode of operation, the switchable liquid crystal retarders 301B, 301A can cooperate to advantageously increase the luminance falloff and thus improve privacy in one axis.

[0360] The retardation provided by the first switchable liquid crystal retarder 301B and the further switchable liquid crystal retarder 301A may be different. The switchable liquid crystal retarder 301B and the further switchable liquid crystal retarder 301A may be driven by a common voltage, and the liquid crystal material 408B in the first switchable liquid crystal retarder 301B may be different to the liquid crystal material 408A in the further switchable liquid crystal retarder 301A. The chromaticity shift of the polar luminance profile shown elsewhere herein may be reduced, resulting in advantageously improved off-axis color appearance.

[0361] Alternatively, the switchable liquid crystal retarders 301B, 301A may have orthogonal orientations such that luminance is reduced in both the horizontal and vertical directions, advantageously providing privacy operation in both the horizontal and vertical directions.

[0362] Alternatively, layers 301A, 301B may be driven with different drive voltages. Control of the roll-off of the luminance profile can be advantageously increased, or one can switch between lateral and privacy operation.

[0363] The retardance control layer 330B may comprise a passive compensation retarder 330A disposed between the first additional polarizer 318A and the further additional polarizer 318B. More generally, the switchable liquid crystal retarder 301A may be omitted and a fixed brightness reduction may be provided by the passive compensation retarder 330A. For example, the brightness reduction in the viewing quadrant may be provided by the layer 330A alone. Advantageously, the polar region area may be increased to reduce the brightness. Furthermore, a backlight with a wider angle of illumination output than a collimated backlight may be provided to enhance the visibility of the display in a wide angle operating mode.

[0364] FIG. 22B is a schematic diagram illustrating in perspective side view an arrangement of a first switchable compensation retarder located at the input side of a liquid crystal display and a second switchable compensation retarder located at the output side of the liquid crystal display.

[0365] The aforementioned additional polariser 318A is arranged at the input side of the input display polariser 210 between the input display polariser 210 and the backlight 20, and the display device further comprises a further additional polariser 318B arranged at the output side of the output display polariser 218, and a further retarder 301B, 330B arranged between the further additional polariser 318B and the output display polariser 218. The further retarder comprises a further switchable liquid crystal retarder 301B comprising a layer of liquid crystal material 414B and electrodes 413B, 415B on either side of the layer of liquid crystal material 414B, which is switchable between two alignment states by a voltage applied across the electrodes 413B, 415B.

[0366] Figure 22C is a schematic diagram illustrating in a side perspective view a viewing angle control optical element comprising a first passive compensation retarder, a first switchable liquid crystal retarder, a first control polarizer 250, a second passive compensation retarder, a second switchable liquid crystal retarder, and a second control polarizer 250. When provided in a display device 100 comprising a spatial light modulator 48, such an element can achieve similar performance to the arrangement of Figure 22B.

[0367] In an automotive vehicle, it may be desirable to provide both an entertainment mode and a nighttime mode of operation.

[0368] Figure 22D is a schematic diagram showing a top view and Figure 22E is a schematic diagram showing a side view of an automotive vehicle having a switchable directional display as shown in Figure 22B disposed within the passenger compartment 602 for daytime and / or shared modes of operation. The light cones 630, 632 have a wide angle field of view so that the display can be advantageously viewed by multiple occupants.

[0369] FIG. 22F is a schematic diagram showing a top view of an automobile vehicle having a switchable directional display as shown in FIG. 22B arranged in the passenger compartment 602 for nighttime and / or entertainment operation modes. FIG. 22G is a schematic diagram showing a side view of an automobile vehicle having a switchable directional display arranged in the passenger compartment 602 for nighttime and / or entertainment operation modes. The light cones 634, 636 have a narrow angle of field of view, so that advantageously only a single occupant can see the display. Advantageously, stray light for nighttime operation is reduced, improving driver safety. Additionally, reflection of the display from the windshield 601 is reduced, minimizing distraction for the driver 604.

[0370] It would be desirable to reduce the field of view of the light cone at low cost with a wide-angle illumination backlight and an emissive spatial light modulator.

[0371] Fig. 23A is a schematic diagram showing in perspective side view an arrangement of a reflective additional polarizer 318A and a passive retarder 270 arranged at the input side of a spatial light modulator 48. At the output of the spatial light modulator 48, there are multiple retarders 300 similar to those in the device of Fig. 22B. Compared to the arrangement of Fig. 22B, the passive retarder 270 is provided instead of the switchable rear compensation liquid crystal retarder 300A. Advantageously, the cost and thickness are reduced while achieving low off-axis illumination in privacy operation mode and acceptable viewing angle in wide angle operation mode.

[0372] 23B is a schematic diagram showing in a side perspective view a viewing angle control optical element comprising a passive retarder 270, a first control polarizer 250A, a passive compensation retarder 330, a switchable liquid crystal retarder 301 and a second control polarizer 250B, which is placed in front of a spatial light modulator 48 to provide a display device.

[0373] We now describe various passive retarders 270 that may be applied in any of the above devices.

[0374] FIG. 24A is a schematic diagram showing a side perspective view of an optical stack of a passive retarder 270 comprising a negative O-plate retarder 272A and a negative C-plate retarder 272B tilted in a plane perpendicular to the electric vector transfer direction of the display polarizer, configured to provide a viewing field change in a display device; and FIG. 24B is a schematic graph showing the change in output transmission with the polarity direction of the transmitted light beam of the passive retarder of FIG. 24A, having a structure shown in Table 10. [Table 10]

[0375] Thus, the passive retarder 270 comprises a passive retarder 272A that is a negative O-plate having an optic axis with a component in the plane of the passive retarder 272A and a component perpendicular to the plane of the passive retarder 272A. Furthermore, the component in the plane of the passive retarder extends at 90° with respect to an electric vector transfer direction that is parallel to the electric vector transfer 219 of the display polarizer 218. The passive retarder 272B comprises a passive retarder with an optic axis perpendicular to the plane of the passive retarder.

[0376] Advantageously, brightness can be reduced for lateral viewing directions, and the mobile display can be comfortably rotated about the horizontal axis to provide privacy for lateral off-axis snoopers.

[0377] FIG. 24C is a schematic diagram showing a side perspective view of an optical stack of a passive retarder 270 comprising a crossed A plate and a positive O plate, and FIG. 24D is a schematic graph showing the variation of output transmission with polarity direction of transmitted light in the passive retarder of FIG. 24C, with the structure shown in Table 11. [Table 11]

[0378] Thus, the passive retarder 270 comprises passive retarders 272A, 272B that are crossed A-plates, and a retarder 272C having an optic axis with a component in the plane of the passive retarder 272C and a component perpendicular to the plane of the passive retarder 272C. The in-plane component of the passive retarder extends at 90° with respect to an electric vector transfer direction that is parallel to the electric vector transfer 219 of the display polarizer 218. Advantageously, brightness can be reduced for lateral viewing directions. Mobile displays can be comfortably rotated about a horizontal axis and privacy can be achieved for lateral off-axis snoopers.

[0379] It may be desirable to reduce the brightness in both the lateral and elevation directions.

[0380] FIG. 24E is a schematic diagram showing an optical stack of passive retarders 272A-D in a side perspective view, comprising two pairs of crossed A plates, and FIG. 24F is a schematic graph showing the variation of output transmission with polarity direction of transmitted light for the passive retarder of FIG. 24E, comprising the structure shown in Table 12. [Table 12]

[0381] Thus, the retarder 270 comprises a pair of passive retarders 272A, 272D with optic axes in the plane of the crossed retarders. The pair of retarders each comprise a number of A-plates with their respective optic axes oriented at different angles to each other. The pair of passive retarders 272B, 272C have optic axes extending at 90° and 0°, respectively, with respect to an electric vector transfer direction that is parallel to the electric vector transfer 211 of the display polarizer 210.

[0382] A pair of passive retarders 272 A, 272 D have optic axes extending at 45° and 135°, respectively, with respect to an electric vector propagation direction 211 that is parallel to the electric vector propagation of the display polarizer 218 .

[0383] The display further comprises an additional pair of passive retarders 272B, 272C disposed between the aforementioned pair of passive retarders 272A, 272D and having their optic axes in the plane of the crossed retarders. The additional pair of passive retarders 272B, 272C have their optic axes extending at 0° and 90° respectively with respect to the electric vector propagation directions 211, 317 which are parallel to the electric vector propagation of the display polarizers 210, 316.

[0384] The retardance of each A-plate for light of wavelength 550 nm may be in the range of 600 nm to 850 nm, preferably in the range of 650 nm to 730 nm, and most preferably in the range of 670 nm to 710 nm. Discoloration of absorbed light from the central to off-axis viewing positions may be advantageously reduced.

[0385] In further exemplary embodiments, preferably angle 273A is at least 40° and at most 50°, more preferably at least 42.5° and at most 47.5°, and most preferably at least 44° and at most 46°. Preferably angle 273D is at least 130° and at most 140°, more preferably at least 132.5° and at most 137.5°, and most preferably at least 134° and at most 136°.

[0386] In further exemplary embodiments, the inner retarder pair 272B, 272C may have looser tolerances than the outer retarder pair 272A, 272D. Preferably, the angle 273B is at least -10° and at most 10°, more preferably at least -5° and at most 5°, and most preferably at least -2° and at most 2°. Preferably, the angle 273C is at least 80° and at most 100°, more preferably at least 85° and at most 95°, and most preferably at least 88° and at most 92°.

[0387] This embodiment provides a transmission profile with some degree of rotational symmetry. Advantageously, the privacy display can reduce the visibility of the image from a wide field of view for snooper lateral or elevation viewing positions. Furthermore, such a configuration can be used to improve privacy operation for mobile display lateral and vertical operation. Such a configuration can be provided in a vehicle to reduce stray light for off-axis occupants and also to reduce light incident on the windshield and other glass surfaces in the vehicle.

[0388] It would be desirable to improve the appearance of the private images viewed by snooper 47 in the privacy mode of operation by adding camouflage to the images.

[0389] 25A is a schematic diagram illustrating in a perspective side view a switchable retarder configuration in a privacy mode of operation comprising a negative C-plate passive compensation retarder and a homeotropically aligned switchable liquid crystal retarder, further comprising a layer of patterned electrodes 415. Accordingly, the electrodes 415a, 415b, 415c are patterned to provide at least two patterned regions.

[0390] At least one of the electrodes 413, 415 may be patterned, in this example the electrode 415 is patterned with regions 415a, 415b, 415c and driven with voltages Va, Vb, Vc by respective voltage drivers 350a, 350b, 350c. Gaps 417 may be provided between the electrode regions 415a, 415b, 415c. Thus, the slopes of the materials 414a, 414b, 414c can be independently adjusted to reveal camouflage patterns with different brightness levels for off-axis viewing.

[0391] Thus, the switchable liquid crystal retarder disposed between the output display polarizer 218 and the additional absorbing polarizer 318 is controlled by address electrodes 415a, 415b, 415c and uniform electrode 413. The address electrodes may be patterned to provide at least two patterned regions comprising electrodes 415a and gaps 417.

[0392] FIG. 25B is a schematic diagram showing the illumination of the primary viewer and the snooper by a camouflaged brightness-controlled privacy display in a front perspective view. The display device 100 may have dark image data 601 and white background data 603 visible to the primary viewer 45 in the viewing window 26p. In comparison, the snooper 47 may see a camouflaged image as shown in FIG. 25C, which is a schematic diagram showing the illumination of the snooper by a camouflaged brightness-controlled privacy display in a side perspective view. Thus, in the white background region 603, a camouflage structure with a mixed brightness of the white region 603 may be provided. Thus, the pattern regions of the electrodes 415a, 415b, 415c are camouflage patterns. At least one of the pattern regions is individually addressable and configured to operate in a privacy mode of operation.

[0393] The pattern areas may be configured to camouflage for multiple spatial frequencies by controlling the pattern provided during the privacy mode of operation. In an exemplary embodiment, 20 mm high text may be presented. A camouflage pattern with a similar pattern size may comprise a first control of the electrode pattern. In a second example, a photo may be provided for wide area content that is best visible to the snooper 47. The spatial frequency of the camouflage pattern may be reduced by providing voltages to a combination of first and second electrode areas to achieve a resulting lower spatial frequency pattern to conceal structures in a larger area.

[0394] Advantageously, a controllable camouflage structure can be produced by adjusting the voltages Va, Vb, Vc across layer 892. A substantially invisible camouflage structure may be visible in frontal operation. Furthermore, the camouflage image can be removed by applying Va, Vb, and Vc to the image.

[0395] For example, it may be desirable to provide less than 1% off-axis brightness to a snooper. It will now be described that a directional backlight providing low off-axis brightness may be used with the switchable compensation liquid crystal retarder of the present embodiment. Directional backlights will now be further described.

[0396] Similar patterning may be applied in any of the devices described herein.

[0397] It may be desirable to further reduce off-axis brightness by directional illumination from the spatial light modulator 48. Directional illumination of the spatial light modulator 48 by the directional backlight 20 will now be described.

[0398] Figure 26A is a schematic diagram showing a directional backlight 20 in a front perspective view, and Figure 26B is a schematic diagram showing a non-directional backlight 20 in a front perspective view, either of which may be applied in any of the devices described herein. Thus, the directional backlight 20 shown in Figure 26A provides a narrow cone 450, whereas the non-directional backlight 20 as shown in Figure 26B provides a wide angular distribution cone 452 of output light rays.

[0399] 26C is a schematic graph showing the change in luminance with lateral viewing angle for a variety of different backlight arrangements. The graph in FIG. 26C may be a cross-section of a polar viewing profile as described herein.

[0400] A Lambertian backlight has a luminance profile 846 that is independent of viewing angle.

[0401] A typical wide angle backlight has a roll-off at higher angles such that the full width at half maximum of the relative luminance 866 may be greater than 40°, preferably greater than 60°, and most preferably greater than 80°. Additionally, the relative luminance 864 at ±45° is preferably greater than 7.5%, more preferably greater than 10%, and most preferably greater than 20%.

[0402] In comparison, directional backlight 20 has a roll-off at higher angles such that the full width at half maximum 862 of the relative luminance may be less than 60°, preferably less than 40°, and most preferably less than 20°. Furthermore, backlight 20 may provide a luminance at polar angles greater than 45 degrees relative to the normal to spatial light modulator 48 that is up to 33% of the luminance along the normal to spatial light modulator 48, preferably up to 20% of the luminance along the normal to spatial light modulator 48, and most preferably up to 10% of the luminance along the normal to spatial light modulator 48.

[0403] When the switchable retarder 300 is located between the input display polarizer 210 and the additional polarizer 318, scattering and diffraction within the spatial light modulator 48 may degrade operation in the privacy mode. The brightness at polar angles greater than 45 degrees relative to the spatial light modulator normal may be increased in a configuration in which the switchable retarder 300 is located between the output display polarizer 218 and the additional polarizer 318 compared to a configuration in which the switchable retarder 300 is located between the input display polarizer 210 and the additional polarizer 318.

[0404] Advantageously, lower off-axis brightness may be achieved with the configuration of FIG. 1A compared to the same backlight 20 of FIG. 2A.

[0405] In the exemplary embodiment of Figure 1A, the brightness at polar angles greater than 45 degrees relative to the normal of spatial light modulator 48 may be up to 18%, while in the exemplary embodiment of Figure 2A, the brightness at polar angles greater than 45 degrees relative to the normal of spatial light modulator 48 may be up to 10%. Advantageously, the embodiment of Figure 1A may provide greater viewing freedom in a wide angle mode of operation while achieving similar viewing freedom in a privacy mode of operation as the embodiment of Figure 2A.

[0406] Such a brightness profile may be provided by a directional backlight 20 described below, or may be provided by a wide-angle backlight in combination with an additional polarizer 318B and a passive retarder 270, or an additional switching compensation liquid crystal retarder 300B.

[0407] Figure 27A is a schematic diagram illustrating in a side view a switchable directional display device 100 comprising a switchable liquid crystal retarder 300 and a backlight 20. The backlight 20 of Figure 27A may be applied in any of the devices described herein and comprises an imaging waveguide 1 illuminated by a light source array 15 through an input end 2. Figure 27B is a schematic diagram illustrating the operation of the imaging waveguide 1 of Figure 27A in a narrow angle mode of operation in a rear perspective view.

[0408] The imaging waveguide 1 is a waveguide of the type described in U.S. Patent No. 9,519,153, which is incorporated herein by reference in its entirety. The waveguide 1 has an input end 2 that extends laterally along the waveguide 1. An array of light sources 15 are disposed along the input end 2 and input light into the waveguide 1.

[0409] The waveguide 1 also has opposing first and second guide surfaces 6 and 8 that extend across the waveguide 1 from the input end 2 to the reflecting end 4 and guide the light input at the input end 2 forward and backward along the waveguide 1. The second guide surface 8 faces the reflecting end 4 and has a number of light extraction features 12 that are configured to deflect at least a portion of the light guided back through the waveguide 1 from the reflecting end 4 from different input locations across the input end 2 in different directions through the first guide surface 6 depending on the input location.

[0410] In operation, light rays are directed from the light source array 15 through the input end and guided between the first guide surface 6 and the second guide surface 8 without loss to the reflecting end 4. The reflected light rays are incident on the facet 12 and are either output by reflection as light ray 230 or transmitted as light ray 232. The transmitted light ray 232 is directed back through the waveguide 1 by the facets 803, 805 of the back reflector 800. The operation of the back reflector is further described in U.S. Pat. No. 10,054,732, which is incorporated herein by reference in its entirety.

[0411] 27B, the optical power of the curved reflective end 4 and facet 12 is transmitted through the spatial light modulator 48, resulting in an optical window 26 having an axis 197 that is typically aligned with the optical axis 199 of the waveguide 1. A similar optical window 26 is provided by the transmitted light ray 232 that is reflected by the back reflector 800.

[0412] FIG. 27C is a schematic graph showing the viewing luminance plot of the output of FIG. 27B when used in a display device that does not have a switchable liquid crystal retarder.

[0413] Thus, for off-axis viewing positions as observed by snooper 47, the brightness may be reduced by, for example, 1% to 3% of the central peak brightness at 0 degree elevation and ±45 degree lateral angles. Further reduction in off-axis brightness is achieved by the multiple retarders 301, 330 of this embodiment.

[0414] Now, another type of directional backlight with low off-axis brightness is described.

[0415] Figure 28A is a schematic diagram showing in side view a switchable directional display device comprising a backlight 20 including a switchable collimating waveguide 901, a switchable liquid crystal retarder 300 and an additional polarizer 318. The backlight 20 of Figure 28A may be applied in any of the devices described herein and is configured as follows.

[0416] The waveguide 901 has an input end 902 that extends laterally along the waveguide 901. An array of light sources 915 are disposed along the input end 902 and input light into the waveguide 1. The waveguide 901 also has opposing first and second guide surfaces 906, 908 that extend across the waveguide 1 from the input end 2 to the reflecting end 4, directing light input at the input end 2 forwards and backwards along the waveguide 1. In operation, light is guided between the first and second guide surfaces 906, 908.

[0417] The first guide surface 906 may comprise a lenticular structure 904 comprising a plurality of elongated lenticular elements 905, and the second guide surface 908 may comprise prism structures 912 that are tilted and act as light extraction features. The plurality of elongated lenticular elements 905 of the lenticular structure 904 and the plurality of tilted light extraction features deflect input light guided through the waveguide 901 to exit through the first guide surface 906.

[0418] A back reflector 903 , which may be a planar reflector, is provided to direct the light back through the waveguide 901 through a surface 908 .

[0419] Output rays incident on both the prism structure 912 and the lenticular elements 905 of the lenticular structure 904 are output at angles close to grazing incidence on the surface 906. A prismatic turning film 926 with facets 927 is configured to redirect the output rays 234 by total internal reflection through the spatial light modulator 48 and the switchable compensation liquid crystal retarder 300.

[0420] 28B is a schematic diagram showing the output of the collimating waveguide 901 in a top view. The prism structures 912 are configured to provide light at an angle of incidence to the lenticular structure 904 that is less than the critical angle and therefore may escape. Upon incidence at the edge of the lenticular surface, the slope of the surface deflects the light to allow it to escape, resulting in a collimating effect. Light ray 234 may be provided by rays 188a-c and rays 189a-c, and is incident on the lenticular structure 904 of the collimated waveguide 901 at location 185.

[0421] Figure 28C is a schematic graph showing an isoluminance viewing polar plot for the display device of Figure 28 A. Thus, a narrow output light cone may be provided, with the size determined by the structures 904, 912 and turning film 926.

[0422] Advantageously, in areas where a snooper may be located at a lateral angle of, for example, 45 degrees or more, the output brightness from the display is small, typically less than 2%. It would be desirable to further reduce the output brightness. Such further reduction is provided by a switchable compensation liquid crystal retarder 300 and an additional polarizer 318, as shown in Figure 28A. Advantageously, a high performance privacy display with low off-axis brightness can be provided over a wide viewing area.

[0423] A directional backlight such as the type described in Figures 27A and 28A, when used in conjunction with the multiple retarders 301, 330 of this embodiment, can achieve off-axis brightness of less than 1.5%, preferably less than 0.75%, and most preferably less than 0.5% for a typical snooper 47 position. Furthermore, it can provide high on-axis brightness and uniformity to the primary user 45. Advantageously, a high performance privacy display with low off-axis brightness can be provided over a wide field of view, which can be switched to a wide angle mode by control of the switchable retarder 301 using the control system 352 shown in Figure 1A.

[0424] We now further describe the operation of the retarder layer between parallel polarizers for off-axis illumination. In the various devices mentioned above, the retarder is arranged between a pair of polarizers (typically the additional polarizer 318 and one of the input polarizer 210 and the output polarizer 218) in various different configurations. In any case, the retarder is configured in at least one of the switchable states of the switchable compensation retarder 300 to not affect the brightness of the light passing through the pair of polarizers and the retarders along an axis normal to the plane of the retarder, but to reduce the brightness of the light passing through the pair of polarizers and the retarders along an axis tilted relative to the normal to the plane of the retarder. We now describe this effect in more detail. This principle can be generally applied to all the devices mentioned above.

[0425] 29A is a schematic diagram illustrating illumination of a retarder layer by off-axis light in a perspective view. The compensation retarder 630 may include a birefringent material represented by an index ellipsoid 632 with an optical axis direction 634 of 0 degrees relative to the x-axis and having a thickness 631. Ordinary ray 636 propagates such that its path length in the material is the same as the thickness 631. Ray 637 has an increased path length in the yz-plane, but the birefringence of the material is substantially the same as ray 636. In comparison, ray 638, which is in the xz-plane, has an increased path length in the birefringent material and also has a different birefringence than ordinary ray 636.

[0426] The retardance of retarder 630 thus depends on the angle of incidence of each ray, and the plane of incidence for ray 638 in xz has a different retardance than normal 636 and ray 637 in the yz plane.

[0427] We now describe the interaction of polarized light with retarder 630. To distinguish between the first and second polarization components during operation in a directional backlight 101, the following description refers to the third and fourth polarization components.

[0428] FIG. 29B is a schematic diagram showing, in a perspective view, illumination of the retarder layer by off-axis light in a third linear polarization state at 90 degrees relative to the x-axis, and FIG. 29C is a schematic diagram showing, in a perspective view, illumination of the retarder layer by off-axis light in a fourth linear polarization state at 0 degrees relative to the x-axis. In such a configuration, the input linear polarization state is aligned with the optical axis of the birefringent material represented by the ellipse 632. Thus, no phase difference is provided between the third and fourth orthogonal polarization components, resulting in no change in the polarization state of the linearly polarized input for each of the light rays 636, 637, 638. Thus, the retarder 630 does not introduce a phase shift in the polarization components of the light that passes through the polarizer on the input side of the retarder 630 along an axis normal to the plane of the retarder 630. Thus, the retarder 630 does not affect the brightness of the light passing through the retarder 630, and the polarizers (not shown) on either side of the retarder 630. Although Figures 29A-C are specifically directed to a passive retarder 630, a similar effect can be achieved with a switchable liquid crystal retarder, and with multiple retarders in the devices described above.

[0429] FIG. 29D is a schematic diagram illustrating, in a perspective view, illumination of a layer of retarder 630 with off-axis light of a 45 degree linear polarization state. The linear polarization state can be decomposed into third and fourth polarization components that are orthogonal and parallel, respectively, to the direction of the optical axis 634. The retarder thickness 631 and material retardance, as indicated by the index ellipsoid 632, can have the net effect of relatively shifting the phase of the normally incident third and fourth polarization components, as indicated by light ray 636, by half a wavelength for the design wavelength. The design wavelength can be, for example, in the range of 500-550 nm.

[0430] For the design wavelength and light propagating vertically along ray 636, the output polarization may be rotated 90 degrees at -45 degrees to a linear polarization state 640. Light propagating along ray 637 may experience a phase difference similar to, but not identical to, the phase difference along ray 637 due to thickness changes, and thus an elliptical polarization state 639 may be output that may have a principal axis similar to the linear polarization axis of the output light in ray 636.

[0431] In contrast, the phase difference of the incident linear polarization state along the light ray 638 may be significantly different, and in particular, a lower phase difference may be provided. Such a phase difference may result in an output polarization state 644 that is substantially circular at a given tilt angle 642. Thus, the retarder 630 introduces a phase shift to the polarization components of the light passing through the polarizer on the input side of the retarder 630 along an axis corresponding to the light ray 638 that is tilted with respect to the normal to the plane of the retarder 630. Although FIG. 29D relates to a passive retarder 630, a similar effect is achieved with a switchable liquid crystal retarder, and in the multiple retarders described above, in which the switchable states of the switchable liquid crystal retarder correspond to the privacy modes.

[0432] To illustrate the off-axis behavior of the retarder stack, we now discuss the angular brightness control of the C-plates 308A, 308B between the additional polarizer 318 and the output display polarizer 218 for various off-axis illumination configurations with reference to the operation of the C-plate 560 between parallel polarizers 500, 210.

[0433] FIG. 30A is a schematic diagram showing, in a perspective view, the illumination of a C-plate layer with off-axis polarized light with a positive elevation angle. An incident linearly polarized component 704 is incident on the birefringent material 632 of the retarder 560, which is a C-plate with an optic axis direction 507 perpendicular to the plane of the retarder 560. The output polarization component is the same as component 704, since the polarization component 704 experiences no net phase difference in transmission of the liquid crystal molecules. Thus, maximum transmission occurs at the polarizer 210. Thus, the retarder comprises a retarder 560 with an optic axis 561 perpendicular to the plane of the retarder 560, which is the xy plane. A retarder with an optic axis perpendicular to the plane of the retarder 560 comprises a C-plate.

[0434] FIG. 30B is a schematic diagram showing, in a perspective view, illumination of a C-plate layer with off-axis polarized light having a negative transverse angle. As with the configuration of FIG. 30A, polarization state 704 results in no net phase difference and is transmitted with maximum brightness. Thus, retarder 560 introduces no phase shift to the polarization components of light passing through the polarizer on the input side of retarder 560 along an axis normal to the plane of retarder 560. Thus, retarder 560 has no effect on the brightness of light passing through retarder 560, and on the polarizers (not shown) on either side of retarder 560. Although FIGS. 29A-C are specifically directed to a passive retarder 560, similar effects are achieved with switchable liquid crystal retarders, and with multiple retarders in the devices described above.

[0435] Figure 30C is a schematic diagram showing illumination of a C-plate layer with off-axis polarized light with positive elevation and negative transverse angles in a perspective view. Compared to the configuration in Figures 30A-B, the polarization state 704 decomposes into eigenstates 703, 705 with respect to the birefringent material 632, resulting in a net phase difference in transmission of the retarder 560. The resulting elliptically polarized component 656 is transmitted through the polarizer 210 and has reduced brightness compared to the light beam shown in Figures 30A-B.

[0436] FIG. 30D is a schematic diagram showing in a perspective view the illumination of a C-plate layer with off-axis polarized light having a positive elevation angle and a positive transverse angle. Similar to FIG. 30C, the polarized light components 704 are decomposed into eigenstates 703, 705 that experience a net phase difference, resulting in an elliptically polarized light component 660 that reduces the brightness of each off-axis ray after transmission through the polarizer. Thus, the retarder 560 introduces a phase shift to the polarized components of light that pass through the polarizer on the input side of the retarder 560 along an axis that is tilted with respect to the normal to the plane of the retarder 560. Although FIG. 29D concerns a passive retarder 560, a similar effect is achieved with a switchable liquid crystal retarder and in the multiple retarders described above, with the switchable states of the switchable liquid crystal retarder corresponding to the privacy modes.

[0437] Figure 30E is a schematic graph showing the change in output transmission with polarity direction of the transmitted light beam of Figures 30A-30D. Thus, the C-plate can provide brightness reduction in the polar quadrants. In combination with a switchable liquid crystal retarder 301 described elsewhere herein, (i) the C-plate brightness reduction can be eliminated in a first, wide-angle operating state, and (ii) an extended polar region for brightness reduction can be achieved in a second, privacy operating state.

[0438] To illustrate the off-axis behavior of the retarder stack, we now describe the angular brightness control of crossed A-plates 308A, 308B between the additional polarizer 318 and the output display polarizer 218 for various off-axis illumination configurations.

[0439] FIG. 31A is a schematic diagram showing the illumination of a crossed A-plate retarder layer with off-axis polarized light having a positive elevation angle in a perspective view. A linear polarizer 218 with an electric vector transfer direction 219 is used to produce a linear polarization state 704 on the first A-plate 308A of the crossed A-plates 308A, 308B that is parallel to the horizontal direction. The optical axis direction 309A is tilted +45 degrees to the horizontal direction. The retardance of the retarder 308A for the off-axis angle θ1 in the positive elevation direction provides a resultant polarization component 650 at the output side that is approximately elliptical. The polarization component 650 is incident on the second A-plate 308B of the crossed A-plates 308A, 308B with an optical axis direction 309B perpendicular to the optical axis direction 309A of the first A-plate 308A. 31A, the retardance of the second A-plate 308B for off-axis angle θ1 is equal and opposite to the retardance of the first A-plate 308A. Thus, the input polarization component 704 has a net zero retardation and the output polarization component is identical to the input polarization component 704.

[0440] The output polarization components match the electric vector transmission direction of the additional polarizer 318 and are therefore efficiently transmitted. Advantageously, light rays with zero transverse angular components experience substantially zero loss, resulting in perfect transmission efficiency.

[0441] 31B is a schematic diagram showing, in a perspective view, illumination of a crossed A-plate retarder layer with off-axis polarized light having a negative transverse angle. Thus, the input polarization component is converted by the first A-plate 308A into an intermediate polarization component 652, which is an approximately elliptical polarization state. The second A-plate 308B again introduces an equal and opposite retardation to the first A-plate, so that the output polarization component is identical to the input polarization component 704, and the light is efficiently transmitted through the polarizer 318.

[0442] The retarder thus comprises a pair of retarders 308A, 308B which are crossed and have their optic axes in the plane of the retarders 308A, 308B, i.e. in the xy plane in this embodiment. The pair of retarders 308A, 308B have their optic axes 309A, 309B which extend at 45° respectively with respect to the electric vector propagation direction which is parallel to the electric vector propagation of the polarizer 318.

[0443] Advantageously, light rays having a zero elevation angular component experience substantially zero loss, resulting in perfect transmission efficiency.

[0444] 31C is a schematic diagram illustrating illumination of a crossed A-plate retarder layer with off-axis polarized light having a positive elevation angle and a negative transverse angle in a perspective view. Polarized light component 704 is converted to an elliptically polarized light component 654 by the first A-plate 308A. The resulting elliptically polarized light component 656 is output from the second A-plate 308B. The elliptically polarized light component 656 is analyzed by the input polarizer 318 and has a reduced intensity compared to the input intensity of the first polarized light component 704.

[0445] 31D is a schematic diagram illustrating illumination of a crossed A-plate retarder layer with off-axis polarized light having positive elevation and positive transverse angles in a perspective view. Polarization components 658 and 660 are introduced by the first A-plate 308A and the second A-plate 308B because the net retardance of the first and second retarders does not compensate.

[0446] Thus, brightness is reduced for rays with non-zero lateral and non-zero elevation components. Advantageously, visibility for the primary display user is not substantially reduced, but the privacy of the display can be improved for snoopers located in the viewing quadrant.

[0447] Figure 31E is a schematic graph showing the change in output transmission with polarity direction of the transmitted light beam of Figures 31A-31D. Compared to the configuration of Figure 30E, the area of ​​brightness drop increases for off-axis viewing. However, the switchable liquid crystal retarder 301 may have reduced uniformity compared to the C-plate configuration for off-axis viewing in the first wide angle operating mode state.

[0448] As may be used herein, the terms "substantially" and "approximately" provide an industry-accepted tolerance for corresponding terms and / or relative items. Such industry-accepted tolerances may range from 0 percent to 10 percent, including, but not limited to, component values, angles, and the like. Such relative items may range from about 0 percent to 10 percent.

[0449] Although various embodiments according to the principles disclosed herein have been described above, it should be understood that they are presented by way of example only and not by way of limitation. Thus, the breadth and scope of this disclosure should not be limited by any of the exemplary embodiments described above, but should be defined only in accordance with any of the claims and their equivalents derived from this disclosure. Furthermore, while the above-mentioned advantages and features are provided in the described embodiments, it is not intended to limit the application of such published claims to methods and structures that achieve any or all of the above-mentioned advantages.

[0450] In addition, the section headings herein are provided as organizational markers, as required by 37 CFR 1.77, and are not intended to limit or characterize the embodiment(s) set forth in the claims that may arise from this disclosure. In particular, by way of example, there is a heading entitled "Technical Field," but the language selected under this heading to describe the so-called field is not intended to limit the scope of the claims. Furthermore, any description of technology in the "Background" section should not be construed as an admission that a particular technology is prior art to any embodiment(s) in this disclosure. Nor should the "Summary" section be considered as characterizing the embodiment(s) set forth in the published claims. Furthermore, any reference to "invention" in the singular form in this disclosure should not be used to assert that there is only one novel feature in this disclosure. Multiple embodiments may be set forth by this disclosure, subject to the limitations of the published claims. Accordingly, these claims are intended to define and protect this embodiment(s) and their equivalents. In all instances, the scope of such claims shall be considered on their own merits in light of this disclosure, and should not be constrained by the headings set forth herein.

[0451] [Item 1] 1. A display device, comprising: A spatial light modulator; a display polarizer disposed on a side of the spatial light modulator; an additional polarizer disposed on the same side of the spatial light modulator as the display polarizer; a plurality of retarders disposed between the additional polarizer and the display polarizer; A plurality of retarders a switchable liquid crystal retarder comprising a layer of liquid crystal material; and at least one passive compensation retarder; A display device comprising: [Item 2] 2. The display device according to item 1, wherein the display polarizer and the additional polarizer have electric vector transmission directions that are parallel. [Item 3] 3. A display device according to item 1 or 2, wherein the switchable liquid crystal retarder comprises two surface alignment layers disposed adjacent to and on either side of the layer of liquid crystal material, each configured to induce homeotropic alignment in the adjacent liquid crystal material. [Item 4] 4. The display device of item 3, wherein the layer of liquid crystal material of the switchable liquid crystal retarder comprises a liquid crystal material having negative dielectric anisotropy. [Item 5] 5. A display device according to item 3 or 4, wherein the layer of liquid crystal material has a retardance for light of wavelength 550 nm in the range of 500 nm to 1000 nm, preferably in the range of 600 nm to 900 nm, most preferably in the range of 700 nm to 850 nm. [Item 6] the at least one passive compensation retarder comprises a retarder having an optic axis perpendicular to the plane of the retarder, the at least one passive retarder having a retardance in the range of -300 nm to -900 nm, preferably in the range of -450 nm to -800 nm, most preferably in the range of -500 nm to -725 nm for light of wavelength 550 nm; or 6. The display device according to any one of items 3 to 5, wherein the at least one passive compensation retarder comprises a pair of retarders having an optical axis in a plane of the crossed retarders, each retarder of the pair having a retardance in the range of 300 nm to 800 nm, preferably in the range of 500 nm to 700 nm, and most preferably in the range of 550 nm to 675 nm for light of a wavelength of 550 nm. [Item 7] 3. A display device according to item 1 or 2, wherein the switchable liquid crystal retarder comprises two surface alignment layers disposed adjacent to and on either side of the layer of liquid crystal material, each configured to provide a homogeneous alignment within the adjacent liquid crystal material. [Item 8] 8. The display device of item 7, wherein the layer of liquid crystal material of the switchable liquid crystal retarder comprises a liquid crystal material having positive dielectric anisotropy. [Item 9] 9. A display device according to item 7 or 8, wherein the layer of liquid crystal material has a retardance for light of wavelength 550 nm in the range of 500 nm to 1000 nm, preferably in the range of 600 nm to 850 nm, most preferably in the range of 700 nm to 800 nm. [Item 10] the at least one passive compensation retarder comprises a retarder having an optic axis perpendicular to the plane of the retarder, the at least one passive retarder having a retardance in the range of -300 nm to -700 nm, preferably in the range of -350 nm to -600 nm, most preferably in the range of -400 nm to -500 nm for light of wavelength 550 nm; or 10. The display device according to any one of items 7 to 9, wherein the at least one passive compensation retarder comprises a pair of retarders having an optical axis in a plane of the crossed retarders, each retarder of the pair having a retardance in the range of 300 nm to 800 nm, preferably in the range of 350 nm to 650 nm, most preferably in the range of 450 nm to 550 nm for light of wavelength 550 nm. [Item 11] 3. A display device as described in item 1 or 2, wherein the switchable liquid crystal retarder comprises two surface alignment layers disposed adjacent to and on either side of the layer of liquid crystal material, one of the surface alignment layers being configured to provide a homeotropic alignment in the adjacent liquid crystal material and the other of the surface alignment layers being configured to provide a homogeneous alignment in the adjacent liquid crystal material. [Item 12] a surface alignment layer configured to provide homogeneous alignment between the layer of liquid crystal material and the passive compensation retarder; the layer of liquid crystal material has a retardance in the range of 700 nm to 2000 nm, preferably in the range of 1000 nm to 1500 nm, and most preferably in the range of 1200 nm to 1500 nm, for light of a wavelength of 550 nm; the at least one passive compensation retarder comprises a retarder having an optic axis perpendicular to the plane of the retarder, the at least one passive retarder having a retardance in the range of -400 nm to -1800 nm, preferably in the range of -700 nm to -1500 nm, most preferably in the range of -900 nm to -1300 nm for light of wavelength 550 nm; or 12. The display device according to item 11, wherein the at least one passive compensation retarder comprises a pair of retarders having an optical axis in the plane of the crossed retarders, each retarder of the pair having a retardance in the range of 400nm to 1800nm, preferably in the range of 700nm to 1500nm, most preferably in the range of 900nm to 1300nm for light of wavelength 550nm. [Item 13] a surface alignment layer configured to provide homeotropic alignment is between the layer of liquid crystal material and the passive compensation retarder; the layer of liquid crystal material has a retardance in the range of 500 nm to 1800 nm, preferably in the range of 700 nm to 1500 nm, and most preferably in the range of 900 nm to 1350 nm for light of a wavelength of 550 nm; the at least one passive compensation retarder comprises a retarder having an optic axis perpendicular to the plane of the retarder, the at least one passive retarder having a retardance in the range of -300 nm to -1600 nm, preferably in the range of -500 nm to -1300 nm, most preferably in the range of -700 nm to -1150 nm for light of wavelength 550 nm; or 12. The display device according to item 11, wherein the at least one passive compensation retarder comprises a pair of retarders having an optical axis in the plane of the crossed retarders, each retarder of the pair having a retardance in the range of 400nm to 1600nm, preferably in the range of 600nm to 1400nm, most preferably in the range of 800nm ​​to 1300nm for light of wavelength 550nm. [Item 14] 14. A display device according to any one of items 3 to 13, wherein each alignment layer has a pretilt with the pretilt direction with the component in the plane of the liquid crystal layer being parallel or antiparallel or orthogonal to the electric vector transport direction of the display polariser. [Item 15] Item 15. The display device of any one of items 1 to 14, wherein the at least one passive retarder comprises at least two passive retarders having at least two different optical axis orientations. [Item 16] Item 16. The display device of any one of items 1 to 15, wherein the at least one passive compensation retarder comprises a pair of passive retarders having optical axes in the planes of the intersecting retarders. [Item 17] Item 17. The display device of item 16, wherein the pair of passive retarders have optic axes extending at 45° and 135°, respectively, with respect to an electric vector propagation direction that is parallel to the electric vector propagation of the display polarizer. [Item 18] 18. A display device according to item 16 or 17, wherein the switchable liquid crystal retarder is disposed between a pair of passive retarders. [Item 19] 20. The display device of item 18, further comprising transparent electrodes and liquid crystal alignment layers formed on each side of the pair of passive retarders adjacent the switchable liquid crystal retarder. [Item 20] 20. The display device of item 19, further comprising a first substrate and a second substrate having a switchable liquid crystal retarder therebetween, the first substrate and the second substrate each comprising one of a pair of passive retarders. [Item 21] 21. The display device according to item 20, wherein each of the pair of passive retarders has a retardance in the range of 150nm to 800nm ​​for light of wavelength 550nm, preferably in the range of 200nm to 700nm, most preferably in the range of 250nm to 600nm. [Item 22] Item 22. The display device of any one of items 1 to 21, wherein the at least one passive compensation retarder comprises a retarder having an optical axis that is perpendicular to a plane of the retarder. [Item 23] 23. A display device as described in item 22, wherein the at least one passive compensation retarder comprises two passive retarders having an optical axis perpendicular to the plane of the passive retarders, and the switchable liquid crystal retarder is provided between the two passive retarders. [Item 24] 24. The display device of item 23, further comprising transparent electrodes and liquid crystal alignment layers formed on each side of the two passive retarders adjacent to the switchable liquid crystal retarder. [Item 25] 25. The display device of claim 23 or 24, further comprising a first substrate and a second substrate between which a switchable liquid crystal retarder is provided, the first substrate and the second substrate each comprising one of two passive retarders. [Item 26] 26. The display device according to any one of items 23 to 25, wherein the two passive retarders have a total retardance in the range of -300nm to -700nm, preferably in the range of -350nm to -600nm, most preferably in the range of -400nm to -500nm for light of wavelength 550nm. [Item 27] 27. A display device according to any one of claims 1 to 26, wherein at least one passive compensation retarder comprises a retarder having an optical axis including a component perpendicular to the plane of the retarder and a component in the plane of the retarder. [Item 28] 28. The display device of item 27, wherein the in-plane component of the retarder extends at 0° with respect to an electric vector propagation direction that is parallel or perpendicular to the electric vector propagation of the display polarizer. [Item 29] 29. The display device of item 27 or 28, wherein the at least one passive retarder further comprises a passive retarder having an optical axis perpendicular to the plane of the passive retarder, or a pair of passive retarders having optical axes in the planes of the intersecting passive retarders. [Item 30] 30. A display device according to any one of items 1 to 29, wherein the retardance of the at least one passive compensation retarder is equal and opposite to the retardance of the switchable liquid crystal retarder. [Item 31] the switchable liquid crystal retarder has a first pretilt and a second pretilt; the at least one passive compensation retarder comprises a compensation retarder having a first pretilt and a second pretilt; Item 31. The display device of any one of items 1 to 30, wherein a first pretilt of the compensation retarder is identical to a first pretilt of the liquid crystal retarder, and a second pretilt of the compensation retarder is identical to a second pretilt of the liquid crystal retarder. [Item 32] A display device described in any one of items 1 to 31, wherein at least one passive compensation retarder is configured to introduce no phase shift into the polarization components of light passing through one of the display polarizers and the additional polarizer on the input side of the multiple retarders along an axis normal to the plane of the at least one passive compensation retarder. [Item 33] 33. A display device according to any one of items 1 to 32, wherein at least one passive compensation retarder is configured to introduce a phase shift into the polarization components of light passing through one of the display polarizers and the additional polarizer on the input side of the plurality of retarders along an axis tilted relative to the normal to the plane of the at least one passive compensation retarder. [Item 34] Item 34. A display device according to any one of items 1 to 33, wherein the switchable liquid crystal retarder is configured such that, along an axis normal to the plane of the switchable liquid crystal retarder, one of the display polarizers and the additional polarizer on the input side of the plurality of retarders does not introduce a phase shift into the polarized components of light passing therethrough. [Item 35] Item 35. A display device according to any one of items 1 to 34, wherein the switchable liquid crystal retarder is configured to introduce a phase shift in the polarised components of light passing through one of the display polarisers and the additional polariser on the input side of the plurality of retarders along an axis tilted relative to the normal to the plane of the switchable liquid crystal retarder, in the switchable state of the switchable liquid crystal retarder. [Item 36] Item 36. A display device according to any one of items 1 to 35, wherein the multiple retarders are configured so as not to affect the brightness of light passing through the display polarizer, the additional polarizer, and the multiple retarders along an axis normal to the plane of the retarders. [Item 37] Item 37. The display device of any one of items 1 to 36, wherein the multiple retarders are configured to reduce the brightness of light passing through the display polarizer, the additional polarizer, and the multiple retarders along an axis tilted relative to the normal to the plane of the retarders. [Item 38] Item 38. A display device according to any one of items 1 to 37, wherein the switchable liquid crystal retarder further comprises electrodes configured to apply a voltage to control the layer of liquid crystal material. [Item 39] Item 39. The display device of item 38, wherein the electrodes are on either side of the layer of liquid crystal material. [Item 40] 40. The display device of item 38 or 39, wherein the electrode is patterned to provide at least two patterned regions. [Item 41] 41. A display device according to any one of items 38 to 40, further comprising a control system configured to control the voltage applied across the electrodes of the at least one switchable liquid crystal retarder. [Item 42] Item 42. A display device as described in Item 41, wherein the control system further comprises means for determining a position of the snooper with respect to the display device, the control system being configured to adjust the voltage applied across the electrodes of at least one switchable liquid crystal retarder in response to the position of the snooper. [Item 43] Item 43. The display device of any one of items 1 to 42, further comprising at least one further retarder and a further additional polarizer, the at least one further retarder being arranged between the further additional polarizer and the further additional polarizer. [Item 44] Item 44. The display device according to any one of items 1 to 43, further comprising a backlight configured to output light, and the spatial light modulator is a transmissive spatial light modulator configured to receive output light from the backlight. [Item 45] 45. The display device of claim 44, wherein the backlight provides a luminance at a polar angle greater than 45 degrees relative to the normal to the spatial light modulator that is up to 33% of the luminance along the normal to the spatial light modulator, preferably up to 20% of the luminance along the normal to the spatial light modulator, and most preferably up to 10% of the luminance along the normal to the spatial light modulator. [Item 46] The backlight is an array of light sources; A directional waveguide, comprising: an input end extending laterally along a side of the directional waveguide, the light source being disposed along the input end and configured to input input light into the waveguide; a directional waveguide comprising first and second opposing guide surfaces extending from an input end across the directional waveguide for guiding an optical input along the waveguide at the input end, the waveguide being configured to deflect input light guided through the directional waveguide to exit through the first guide surface; Item 46. A display device according to item 44 or 45, comprising: [Item 47] Item 47. The display device of item 46, wherein the backlight further comprises a light turning film and the directional waveguide is a collimating waveguide. [Item 48] The collimating waveguide is (i) a plurality of elongated lenticular elements; (ii) a plurality of tilted light extraction features; Item 48. A display device as described in Item 47, wherein the plurality of elongated lenticular elements and the plurality of inclined light extraction features are oriented to deflect input light guided through the directional waveguide to exit through the first guide surface. [Item 49] Item 47. The display device of item 46, wherein the directional waveguide is an imaging waveguide configured to image the light source laterally such that output light from the light source is directed into each optical window in output directions that diverge depending on the input position of the light source. [Item 50] the imaging waveguide comprises a reflective end for reflecting the input light back along the imaging waveguide, the second guide surface is configured to deflect the input light reflected through the first guide surface as output light, the second guide surface comprises light extraction features and intermediate regions between the light extraction features, the light extraction features oriented to deflect the input light reflected through the first guide surface as output light, the intermediate regions configured to direct the light through the waveguide without extracting light; 50. The display device of claim 49, wherein the reflective end has positive optical power in a lateral direction extending between sides of the waveguide that extend between the first guide surface and the second guide surface. [Item 51] 51. The display device of any one of items 44 to 50, wherein the display polarizer is an input display polarizer positioned on the input side of the spatial light modulator between the backlight and the spatial light modulator, and the additional polarizer is positioned between the input display polarizer and the backlight. [Item 52] Item 52. The display device of item 51, wherein the additional polarizer is a reflective polarizer. [Item 53] 53. The display device according to item 51 or 52, further comprising an output polarizer arranged on the output side of the spatial light modulator. [Item 54] 51. The display device according to any one of items 1 to 50, wherein the display polarizer is an output polarizer disposed at the output side of the spatial light modulator. [Item 55] Item 55. The display device of item 54, further comprising an input polarizer disposed on the input side of the spatial light modulator. [Item 56] 56. The display device of item 55, further comprising an additional polarizer disposed on the input side of the spatial light modulator, and at least one additional retarder disposed between the at least one additional polarizer and the input polarizer. [Item 57] Item 44. The display device of any one of items 1 to 43, wherein the spatial light modulator comprises an emissive spatial light modulator configured to output light, and the display polarizer is an output display polarizer disposed on the output side of the emissive spatial light modulator. [Item 58] 58. The display device of item 57, further comprising at least one further retarder and a further additional polarizer, the at least one further retarder being disposed between the further additional polarizer and the further additional polarizer. [Item 59] A viewing angle control optical element for application to a display device comprising a spatial light modulator and a display polarizer disposed to a side of the spatial light modulator, the viewing angle control optical element comprising a control polarizer and a plurality of retarders for placement between the additional polarizer and the display polarizer when applying the viewing angle control optical element to the display device, the plurality of retarders comprising: a switchable liquid crystal retarder comprising a layer of liquid crystal material; At least one passive compensation retarder; A viewing angle control optical element comprising:

Claims

1. 1. A switchable privacy display device, comprising: A spatial light modulator; a display polarizer disposed on a side of the spatial light modulator; an additional polarizer disposed on the same side of the spatial light modulator as the display polarizer, the display polarizer and the additional polarizer having electric vector transmission directions that are parallel; a plurality of retarders disposed between the additional polarizer and the display polarizer; The plurality of retarders are a switchable liquid crystal retarder having a layer of liquid crystal material and two surface alignment layers disposed adjacent and on either side of the layer of liquid crystal material, the surface alignment layers being respectively configured to induce homeotropic alignment in the adjacent liquid crystal material; at least one passive compensation retarder, the at least one passive compensation retarder comprising a passive retarder having an optic axis perpendicular to a plane of the passive retarder, the at least one passive retarder having a retardance in the range of -300 nm to -900 nm for light of a wavelength of 550 nm; or the at least one passive compensation retarder comprises a pair of passive retarders having optical axes in intersecting passive retarder planes, each retarder of the pair of passive retarders having a retardance in the range of 300 nm to 800 nm for light having a wavelength of 550 nm; 1. A switchable privacy display device comprising:

2. 10. The switchable privacy display device of claim 1, wherein the layer of liquid crystal material of the switchable liquid crystal retarder comprises a liquid crystal material having negative dielectric anisotropy.

3. 10. The switchable privacy display device of claim 1, wherein the layer of liquid crystal material has a retardance in the range of 500nm to 1000nm for light of a wavelength of 550nm.

4. 2. The switchable privacy display device of claim 1, wherein each alignment layer has a pretilt with the pretilt direction being parallel or antiparallel or orthogonal to the electric vector transport direction of the display polarizer with the component in the plane of the liquid crystal layer.

5. The switchable privacy display device of claim 1 , wherein the at least one passive compensation retarder comprises at least two passive retarders having at least two different optic axis orientations.

6. The switchable privacy display device of claim 1 , wherein the at least one passive compensation retarder comprises a pair of passive retarders having optic axes in the planes of the intersecting retarders.

7. 7. The switchable privacy display device of claim 6, wherein the pair of passive retarders have optic axes extending at 45° and 135°, respectively, with respect to an electric vector propagation direction that is parallel to an electric vector propagation direction of the display polarizer.

8. The switchable privacy display device of claim 6 , wherein the switchable liquid crystal retarder is disposed between the pair of passive retarders.

9. 9. The switchable privacy display device of claim 8, further comprising a transparent electrode and a liquid crystal alignment layer formed on each side of the pair of passive retarders adjacent to the switchable liquid crystal retarder.

10. 10. The switchable privacy display device of claim 9, further comprising a first substrate and a second substrate between which the switchable liquid crystal retarder is disposed, the first substrate and the second substrate each comprising one of the pair of passive retarders.

11. The switchable privacy display device of claim 1 , wherein the at least one passive compensation retarder comprises a retarder having an optic axis that is perpendicular to a plane of the retarder.

12. 12. The switchable privacy display device of claim 11, wherein the at least one passive compensation retarder comprises two passive retarders having an optical axis perpendicular to the plane of the passive retarders, and the switchable liquid crystal retarder is disposed between the two passive retarders.

13. 13. The switchable privacy display device of claim 12, further comprising a transparent electrode and a liquid crystal alignment layer formed on each side of the two passive retarders adjacent to the switchable liquid crystal retarder.

14. 13. The switchable privacy display device of claim 12, further comprising a first substrate and a second substrate between which the switchable liquid crystal retarder is provided, the first substrate and the second substrate each comprising one of the two passive retarders.

15. The switchable privacy display device of claim 12, wherein the two passive retarders have a total retardance in the range of -300nm to -700nm for light with a wavelength of 550nm.

16. 10. The switchable privacy display device of claim 1, wherein the at least one passive compensation retarder comprises a retarder having an optic axis that includes a component that is perpendicular to a plane of the retarder and a component in the plane of the retarder.

17. 17. The switchable privacy display device of claim 16, wherein the in-plane component of the retarder extends at 0[deg.] with respect to an electric vector propagation direction that is parallel or perpendicular to the electric vector propagation of the display polarizer.

18. 17. The switchable privacy display device of claim 16, wherein the at least one passive compensation retarder further comprises a passive retarder having an optical axis perpendicular to a plane of the passive retarder, or a pair of passive retarders having optical axes in intersecting passive retarder planes.

19. The switchable privacy display device of claim 1 , wherein the retardance of the at least one passive compensation retarder is equal and opposite to the retardance of the switchable liquid crystal retarder.

20. the switchable liquid crystal retarder has a first pretilt and a second pretilt; the at least one passive compensation retarder comprises a compensation retarder having a first pretilt and a second pretilt; 2. The switchable privacy display device of claim 1, wherein the first pretilt of the compensation retarder is the same as the first pretilt of the liquid crystal retarder, and the second pretilt of the compensation retarder is the same as the second pretilt of the liquid crystal retarder.

21. 2. The switchable privacy display device of claim 1, wherein the at least one passive compensation retarder is configured to introduce no phase shift into the polarization components of light passing through one of the display polarizer and the additional polarizer on the input side of the plurality of retarders along an axis normal to the plane of the at least one passive compensation retarder.

22. 2. The switchable privacy display device of claim 1, wherein the at least one passive compensation retarder is configured to introduce a phase shift to the polarization components of light passing through one of the display polarizer and the additional polarizer on the input side of the plurality of retarders along an axis tilted relative to a normal to the plane of the at least one passive compensation retarder.

23. 2. The switchable privacy display device of claim 1, wherein the switchable liquid crystal retarder is configured such that, along an axis normal to the plane of the switchable liquid crystal retarder, one of the display polarizer and the additional polarizer on the input side of the plurality of retarders does not introduce a phase shift into the polarization components of light passing therethrough.

24. 2. The switchable privacy display device of claim 1, wherein the switchable liquid crystal retarder is configured to introduce a phase shift in the polarization components of light passing through one of the display polarizer and the additional polarizer on the input side of the plurality of retarders along an axis tilted relative to a normal to the plane of the switchable liquid crystal retarder in the switchable state of the switchable liquid crystal retarder.

25. 2. The switchable privacy display device of claim 1, wherein the multiple retarders are configured to have no effect on the brightness of light passing through the display polarizer, the additional polarizer, and the multiple retarders along an axis normal to the plane of the retarders.

26. 2. The switchable privacy display device of claim 1, wherein the multiple retarders are configured to reduce the brightness of light passing through the display polarizer, the additional polarizer, and the multiple retarders along an axis tilted relative to a normal to the plane of the retarders.

27. 10. The switchable privacy display device of claim 1, wherein the switchable liquid crystal retarder further comprises electrodes configured to apply a voltage to control the layer of liquid crystal material.

28. 28. The switchable privacy display device of claim 27, wherein the electrodes are on either side of the layer of liquid crystal material.

29. 30. The switchable privacy display device of claim 27, wherein the electrode is patterned to provide at least two patterned regions.

30. 30. The switchable privacy display device of claim 27, further comprising a control system configured to control a voltage applied across the electrodes of the at least one switchable liquid crystal retarder.

31. 31. The switchable privacy display device of claim 30, wherein the control system further comprises means for determining a position of a snooper with respect to the switchable privacy display device, the control system being configured to adjust a voltage applied across the electrodes of the at least one switchable liquid crystal retarder in response to the position of the snooper.

32. 2. The switchable privacy display device of claim 1, further comprising at least one further retarder and a further additional polarizer, the at least one further retarder being disposed between the further polarizer and the further additional polarizer.

33. 10. The switchable privacy display device of claim 1, further comprising a backlight configured to output light, the spatial light modulator being a transmissive spatial light modulator configured to receive output light from the backlight.

34. 34. The switchable privacy display device of claim 33, wherein the backlight provides a luminance at polar angles greater than 45 degrees relative to a normal to the spatial light modulator that is up to 33% of the luminance along the normal to the spatial light modulator.

35. The backlight is an array of light sources; A directional waveguide, comprising: an input end extending laterally along a side of the directional waveguide, the light source being disposed along the input end and configured to input input light into the waveguide; a directional waveguide comprising: first and second opposing guide surfaces extending from the input end across the directional waveguide for guiding an optical input at the input end along the waveguide, the waveguide being configured to deflect input light guided through the directional waveguide to exit through the first guide surface; 34. The switchable privacy display device of claim 33, comprising:

36. 36. The switchable privacy display device of claim 35, wherein the backlight further comprises a light turning film and the directional waveguide is a collimating waveguide.

37. The collimating waveguide is (i) a plurality of elongated lenticular elements; (ii) a plurality of angled light extraction features; 37. The switchable privacy display device of claim 36, wherein the plurality of elongated lenticular elements and the plurality of angled light extraction features are oriented to deflect input light guided through the directional waveguide to exit through the first guide surface.

38. 36. The switchable privacy display device of claim 35, wherein the directional waveguide is an imaging waveguide configured to laterally image the light source such that output light from the light source is directed into respective optical windows with output directions that diverge depending on the input position of the light source.

39. the imaging waveguide comprises a reflective end for reflecting the input light back along the imaging waveguide, the second guide surface is configured to deflect input light reflected through the first guide surface as output light, the second guide surface comprises light extraction features and intermediate regions between the light extraction features, the light extraction features oriented to deflect input light reflected through the first guide surface as output light, the intermediate regions configured to direct light through the imaging waveguide without extracting light; 40. The switchable privacy display device of claim 38, wherein the reflective end has positive optical power in a lateral direction extending between sides of the imaging waveguide that extend between the first guide surface and the second guide surface.

40. 34. The switchable privacy display device of claim 33, wherein the display polarizer is an input display polarizer positioned at the input side of the spatial light modulator between the backlight and the spatial light modulator, and the additional polarizer is positioned between the input display polarizer and the backlight.

41. 41. The switchable privacy display device of claim 40, wherein the additional polarizer is a reflective polarizer.

42. 41. The switchable privacy display device of claim 40, further comprising an output polarizer disposed at an output side of the spatial light modulator.

43. The switchable privacy display device of claim 1 , wherein the display polarizer is an output polarizer disposed at the output side of the spatial light modulator.

44. 44. The switchable privacy display device of claim 43, further comprising an input polarizer disposed on an input side of the spatial light modulator.

45. 45. The switchable privacy display device of claim 44, further comprising: a further polarizer disposed on the input side of the spatial light modulator; and at least one further retarder disposed between the at least one further polarizer and the input polarizer.

46. 10. The switchable privacy display device of claim 1 , wherein the spatial light modulator comprises an emissive spatial light modulator configured to output light, and the display polarizer is an output display polarizer disposed on an output side of the emissive spatial light modulator.

47. 47. The switchable privacy display device of claim 46, further comprising at least one further retarder and a further additional polarizer, said at least one further retarder being disposed between said further polarizer and said further additional polarizer.

48. 1. A switchable privacy display device, comprising: A spatial light modulator; a display polarizer disposed on a side of the spatial light modulator; an additional polarizer disposed on the same side of the spatial light modulator as the display polarizer, the display polarizer and the additional polarizer having electric vector transmission directions that are parallel; a plurality of retarders disposed between the additional polarizer and the display polarizer; The plurality of retarders are 1. A switchable liquid crystal retarder having a layer of liquid crystal material and two surface alignment layers adjacent to and disposed on either side of the layer of liquid crystal material, a switchable liquid crystal retarder, one of the surface alignment layers disposed between the layer of liquid crystal material and at least one passive compensation retarder, and arranged to provide a homeotropic alignment to the adjacent liquid crystal material, and the other of the surface alignment layers arranged to provide a homogeneous alignment to the adjacent liquid crystal material; at least one passive compensation retarder, the at least one passive compensation retarder comprising a passive retarder having an optic axis perpendicular to a plane of the passive retarder, the at least one passive retarder having a retardance in the range of -300 nm to -1600 nm for light of a wavelength of 550 nm; or the at least one passive compensation retarder comprises a pair of passive retarders having optical axes in intersecting passive retarder planes, each retarder of the pair of passive retarders having a retardance in the range of 400 nm to 1600 nm for light having a wavelength of 550 nm; Equipped with A switchable privacy display device, wherein the at least one passive compensation retarder is configured to introduce a phase shift into the polarization components of light passing through one of the display polarizer and the additional polarizer on the input side of the multiple retarders along an axis tilted relative to the normal to the plane of the at least one passive compensation retarder.

49. 49. The switchable privacy display device of claim 48, wherein the layer of liquid crystal material has a retardance in the range of 500nm to 1800nm ​​for light of a wavelength of 550nm.

50. 49. The switchable privacy display device of claim 48, wherein each alignment layer has a pretilt with a pretilt direction with the component in the plane of the liquid crystal layer being parallel or antiparallel or orthogonal to the electric vector transport direction of the display polarizer.

51. 49. The switchable privacy display device of claim 48, wherein the at least one passive compensation retarder comprises at least two passive retarders having at least two different optic axis orientations.

52. 49. The switchable privacy display device of claim 48, wherein the at least one passive compensation retarder comprises a pair of passive retarders having optic axes in the planes of the intersecting retarders.

53. 53. The switchable privacy display device of claim 52, wherein the pair of passive retarders have optic axes extending at 45° and 135°, respectively, with respect to an electric vector propagation direction that is parallel to an electric vector propagation direction of the display polarizer.

54. 53. The switchable privacy display device of claim 52, wherein the switchable liquid crystal retarder is disposed between the pair of passive retarders.

55. 55. The switchable privacy display device of claim 54, further comprising a transparent electrode and a liquid crystal alignment layer formed on each side of the pair of passive retarders adjacent to the switchable liquid crystal retarder.

56. 56. The switchable privacy display device of claim 55, further comprising a first substrate and a second substrate between which the switchable liquid crystal retarder is disposed, the first substrate and the second substrate each comprising one of the pair of passive retarders.

57. 49. The switchable privacy display device of claim 48, wherein the at least one passive compensation retarder comprises a retarder having an optic axis that is perpendicular to a plane of the retarder.

58. 58. The switchable privacy display device of claim 57, wherein the at least one passive compensation retarder comprises two passive retarders having an optical axis perpendicular to the plane of the passive retarders, and the switchable liquid crystal retarder is disposed between the two passive retarders.

59. 60. The switchable privacy display device of claim 58, further comprising a transparent electrode and a liquid crystal alignment layer formed on each side of the two passive retarders adjacent to the switchable liquid crystal retarder.

60. 60. The switchable privacy display device of claim 58, further comprising a first substrate and a second substrate between which the switchable liquid crystal retarder is provided, the first substrate and the second substrate each comprising one of the two passive retarders.

61. 60. The switchable privacy display device of claim 58, wherein the two passive retarders have a total retardance in the range of -300nm to -700nm for light with a wavelength of 550nm.

62. 49. The switchable privacy display device of claim 48, wherein the at least one passive compensation retarder comprises a retarder having an optic axis that includes a component that is perpendicular to a plane of the retarder and a component in the plane of the retarder.

63. 63. The switchable privacy display device of claim 62, wherein the in-plane component of the retarder extends at 0[deg.] with respect to an electric vector propagation direction that is parallel or perpendicular to the electric vector propagation of the display polarizer.

64. 63. The switchable privacy display device of claim 62, wherein the at least one passive retarder further comprises a passive retarder having an optical axis perpendicular to a plane of the passive retarder, or a pair of passive retarders having optical axes in intersecting passive retarder planes.

65. 49. The switchable privacy display device of claim 48, wherein the retardance of said at least one passive compensation retarder is equal and opposite to the retardance of said switchable liquid crystal retarder.

66. 49. The switchable privacy display device of claim 48, wherein the at least one passive compensation retarder is configured to introduce no phase shift into the polarization components of light passing through one of the display polarizer and the additional polarizer on the input side of the plurality of retarders along an axis normal to the plane of the at least one passive compensation retarder.

67. 49. The switchable privacy display device of claim 48, wherein the switchable liquid crystal retarder is configured such that one of the display polarizer and the additional polarizer on the input side of the plurality of retarders does not introduce a phase shift into the polarization components of light passing therethrough along an axis normal to the plane of the switchable liquid crystal retarder.

68. 49. The switchable privacy display device of claim 48, wherein the switchable liquid crystal retarder is configured to introduce a phase shift in the polarization components of light passing through one of the display polarizer and the additional polarizer on the input side of the plurality of retarders along an axis tilted relative to a normal to the plane of the switchable liquid crystal retarder in the switchable state of the switchable liquid crystal retarder.

69. 49. The switchable privacy display device of claim 48, wherein the multiple retarders are configured so as not to affect the brightness of light passing through the display polarizer, the additional polarizer, and the multiple retarders along an axis normal to the plane of the retarder.

70. 49. The switchable privacy display device of claim 48, wherein the multiple retarders are configured to reduce the brightness of light passing through the display polarizer, the additional polarizer, and the multiple retarders along an axis tilted relative to a normal to the plane of the retarders.

71. 49. The switchable privacy display device of claim 48, wherein the switchable liquid crystal retarder further comprises electrodes configured to apply a voltage to control the layer of liquid crystal material.

72. 72. The switchable privacy display device of claim 71, wherein the electrodes are on either side of the layer of liquid crystal material.

73. 72. The switchable privacy display device of claim 71, wherein the electrode is patterned to provide at least two patterned regions.

74. 72. The switchable privacy display device of claim 71, further comprising a control system configured to control a voltage applied across the electrodes of the at least one switchable liquid crystal retarder.

75. 75. The switchable privacy display device of claim 74, wherein the control system further comprises means for determining a position of a snooper with respect to the switchable privacy display device, the control system being configured to adjust the voltage applied across the electrodes of the at least one switchable liquid crystal retarder in response to the position of the snooper.

76. 49. The switchable privacy display device of claim 48, further comprising at least one further retarder and a further additional polarizer, the at least one further retarder being disposed between the further polarizer and the further additional polarizer.

77. 49. The switchable privacy display device of claim 48, further comprising a backlight configured to output light, the spatial light modulator being a transmissive spatial light modulator configured to receive output light from the backlight.

78. 78. The switchable privacy display device of claim 77, wherein the backlight provides a luminance at polar angles greater than 45 degrees relative to the normal to the spatial light modulator that is up to 33% of the luminance along the normal to the spatial light modulator, preferably up to 20% of the luminance along the normal to the spatial light modulator, and most preferably up to 10% of the luminance along the normal to the spatial light modulator.

79. The backlight is an array of light sources; A directional waveguide, comprising: an input end extending laterally along a side of the directional waveguide, the light source being disposed along the input end and configured to input input light into the waveguide; a directional waveguide comprising: first and second opposing guide surfaces extending from the input end across the directional waveguide for guiding an optical input at the input end along the waveguide, the waveguide being configured to deflect input light guided through the directional waveguide to exit through the first guide surface; 78. The switchable privacy display device of claim 77, comprising:

80. 80. The switchable privacy display device of claim 79, wherein the backlight further comprises a light turning film and the directional waveguide is a collimating waveguide.

81. The collimating waveguide is (i) a plurality of elongated lenticular elements; (ii) a plurality of angled light extraction features; 81. The switchable privacy display device of claim 80, wherein the plurality of elongated lenticular elements and the plurality of angled light extraction features are oriented to deflect input light guided through the directional waveguide to exit through the first guide surface.

82. 80. The switchable privacy display device of claim 79, wherein the directional waveguide is an imaging waveguide configured to laterally image the light source such that output light from the light source is directed into respective optical windows with output directions that diverge depending on the input position of the light source.

83. the imaging waveguide comprises a reflective end for reflecting the input light back along the imaging waveguide, the second guide surface is configured to deflect input light reflected through the first guide surface as output light, the second guide surface comprises light extraction features and intermediate regions between the light extraction features, the light extraction features oriented to deflect input light reflected through the first guide surface as output light, the intermediate regions configured to direct light through the imaging waveguide without extracting light; 83. The switchable privacy display device of claim 82, wherein the reflective end has positive optical power in a lateral direction extending between sides of the imaging waveguide that extend between the first guide surface and the second guide surface.

84. 78. The switchable privacy display device of claim 77, wherein the display polarizer is an input display polarizer positioned on the input side of the spatial light modulator between the backlight and the spatial light modulator, and the additional polarizer is positioned between the input display polarizer and the backlight.

85. 85. The switchable privacy display device of claim 84, wherein the additional polarizer is a reflective polarizer.

86. 85. The switchable privacy display device of claim 84, further comprising an output polarizer disposed at an output side of the spatial light modulator.

87. 49. The switchable privacy display device of claim 48, wherein the display polarizer is an output polarizer disposed at the output side of the spatial light modulator.

88. 88. The switchable privacy display device of claim 87, further comprising an input polarizer disposed on an input side of the spatial light modulator.

89. 90. The switchable privacy display device of claim 88, further comprising: a further polarizer disposed on the input side of the spatial light modulator; and at least one further retarder disposed between the at least one further polarizer and the input polarizer.

90. 49. The switchable privacy display device of claim 48, wherein the spatial light modulator comprises an emissive spatial light modulator configured to output light, and the display polarizer is an output display polarizer disposed on the output side of the emissive spatial light modulator.

91. 91. The switchable privacy display device of claim 90, further comprising at least one further retarder and a further additional polarizer, said at least one further retarder being disposed between said further polarizer and said further additional polarizer.

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