Off-Axis Display Devices

Abstract

A switchable backlight for a switchable privacy display device includes a collimated backlight arranged to provide two off-axis beams and at least one polarized liquid crystal retarder positioned between parallel polarizers. The orientation layer of the liquid crystal retarder rotates relative to the polarizer's electric vector propagation direction. When used in a vehicle center stack, one operating mode provides high image brightness and high image visibility to passengers while hiding the image from the driver. Another operating mode provides the driver with an image that reduces stray light relative to passengers for nighttime operation. A third operating mode allows both the passengers and the driver to view an image with high brightness and image visibility.

Description

[Technical field]

[0001] The present disclosure relates generally to illumination from light modulating devices, and more particularly to control of privacy displays. [Background technology]

[0002] Privacy displays provide image visibility to a primary user, typically at an on-axis location, and reduce the visibility of image content to voyeurs, typically at off-axis locations. Privacy functionality can be provided by microlouver optical films that conduct light from the display in an on-axis direction while providing low brightness to off-axis locations. However, such films are lossy for front illumination, and the microlouvers can cause moiré artifacts due to collisions with the spatial light modulator pixels. The pitch of the microlouvers necessitates a choice of panel resolution, which can increase inventory and costs.

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

[0004] Control may be provided by brightness reduction, for example, by switchable backlights for liquid crystal display (LCD) spatial light modulators. Display backlights generally use waveguides and edge-emitting sources. Certain imaging directional backlights have the additional function of directing illumination through the display panel to a viewing window. An imaging system may be formed between multiple sources and the respective window images. An example of an imaging directional backlight is an optical valve that may use a folded optical system and thus may also be an example of a folded imaging directional backlight. Light may propagate substantially without loss in one direction through the optical valve, and the counter-propagating light may be extracted by reflection off an angled facet, as described in U.S. Pat. No. 9,519,153, which is incorporated herein by reference in its entirety.

[0005] In a known privacy display, the privacy mode is provided by adding a removable louver film, such as that sold by 3M, which may not be reliably installed or removed by the user, and thus in practice is not diligently installed by the user every time the user is outside the office. In another known privacy display, control of the privacy mode is activated electronically, but control is given to the user, who must execute a keystroke to enter the privacy mode. Summary of the Invention

[0006] According to a first aspect of the disclosure, there is provided a display device comprising: a spatial light modulator arranged to output spatially modulated light; a display polarizer arranged on one side of the spatial light modulator, the display polarizer being a linear polarizer; an additional polarizer arranged on the same side of the spatial light modulator as the display polarizer, the additional polarizer being a linear polarizer; and at least one pole-controlled retarder arranged between the display polarizer and the additional polarizer, the at least one pole-controlled retarder comprising a switchable liquid crystal retarder comprising a layer of liquid crystal material and two surface alignment layers disposed adjacent to and on either side of the layer of liquid crystal material, at least one of the surface alignment layers having a pretilt with a pretilt direction with a component in the plane of the layer of liquid crystal material that makes a non-zero acute angle with an electric vector propagation direction of at least one of the display polarizer and the additional polarizer, in at least a portion of the display device.

[0007] Advantageously, the polar direction for maximum transmission may be inclined at an acute angle to the normal to the surface of the display device, and the polar direction for minimum transmission may be inclined in another direction.

[0008] The display polarizer and the additional polarizer may have electric vector transmission directions which may be parallel. Advantageously, the transmission in the maximum transmission direction is maximized.

[0009] One of the surface alignment layers is arranged to provide a horizontal alignment in the adjacent liquid crystal material, the one of the surface alignment layers having a pretilt direction with a component in the plane of the layer of liquid crystal material that may form a non-zero acute angle with respect to an electric vector propagation direction of at least one of the display polarizer and the additional polarizer in at least a portion of the display device. Advantageously enhanced resiliency to applied mechanical forces may be realized.

[0010] The other of the surface alignment layers may be arranged to provide homeotropic alignment in the adjacent liquid crystal material. Advantageously, the size of the polar regions over which low light transmission is provided may be increased.

[0011] The other of the surface alignment layers may be arranged to provide horizontal alignment in the adjacent liquid crystal material, advantageously reducing the thickness of the layer or liquid crystal material.

[0012] In this case, when the display polarizer and the additional polarizer have parallel electric vector transport directions, the other of the surface alignment layers may have a pretilt having a pretilt direction with a component in the plane of the layer of liquid crystal material that is parallel or perpendicular to the electric vector transport directions of the display polarizer and the additional polarizer.

[0013] The other of the surface alignment layers may have a pretilt with a pretilt direction with a component in the plane of the layer of liquid crystal material that may make a non-zero acute angle with respect to the electric vector transport direction of at least one of the display polarizer and the additional polarizer in at least a portion of the display device. Advantageously, the size of the polar regions over which low light transmission is provided may be increased.

[0014] Each of the surface alignment layers may be arranged to provide a vertical alignment in the adjacent liquid crystal material, and the surface alignment layers may have a pretilt with a component in the plane of the layer of liquid crystal material that may form a non-zero acute angle with respect to an electric vector transmission direction of at least one of the display polarizer and the additional polarizer in at least a portion of the display device. Advantageously, a wide angle mode of operation may be achieved without an applied voltage to achieve reduced power consumption.

[0015] Each of the surface alignment layers may have a pretilt with a pretilt direction with a component in the plane of the layer of liquid crystal material that may make a non-zero acute angle with respect to the electric vector transport direction of at least one of the display polarizer and the additional polarizer in at least a portion of the display device. Advantageously, the size of the polar regions over which low light transmission is provided may be increased.

[0016] The at least one pole controlled retarder may further include at least one passive compensation retarder. Advantageously, the size of the pole region over which low light transmission is provided may be increased.

[0017] At least one passive compensation retarder may include a passive compensation retarder having an optical axis perpendicular to the plane of the retarder. Advantageously, the thickness of the pole controlled retarder may be reduced.

[0018] The at least one passive compensation retarder may comprise a pair of passive compensation retarders that may have optical axes in the plane of the retarders that may intersect. Advantageously, increased delay may be achieved and costs may be reduced.

[0019] The angle between the optical axes may be bisected by the electric vector transfer direction of at least one of the display polarizer and the additional polarizer. Advantageously, the size of the polar regions where low light transmission is provided may be increased.

[0020] At least one of the surface alignment layers may have a pretilt that makes the same non-zero acute angle with respect to the electric vector transport direction of the display polarizer and the additional polarizer at all positions across the surface alignment layer and has a pretilt direction with a component in the plane of the layer of liquid crystal material. Advantageously, the cost and complexity of manufacturing the surface alignment layer may be reduced.

[0021] At least one of the surface alignment layers may have a pretilt with a pretilt direction with a component in the plane of the layer of liquid crystal material that may make a non-zero acute angle with respect to the electric vector transport direction of the display polarizer and the additional polarizer that varies monotonically along a predetermined axis transverse to the surface alignment layer in at least a portion of the display device. Advantageously, the uniformity of the luminance reduction may be increased for off-axis voyeurs.

[0022] If the non-zero angles vary monotonically, the non-zero acute angles may have a non-zero acute angle average value. Advantageously, the polar direction for maximum transmission may be tilted at an acute angle relative to the normal to the surface of the display device.

[0023] The display polarizer may be an output display polarizer located at the output side of the spatial light modulator. Advantageously, the pole controlled retarder may be attached after fabrication of the spatial light modulator, reducing complexity. The emissive display may include off-axis brightness control.

[0024] In some embodiments, no reflective polarizer may be disposed between the output display polarizer and the at least one pole-controlled retarder. Advantageously, thickness and cost can be reduced. Reflectivity of the front surface of the display to ambient light is reduced.

[0025] In other embodiments, a reflective polarizer can be positioned between the output polarizer and the at least one pole-controlled retarder, where the reflective polarizer is a linear polarizer positioned to pass the same linearly polarized polarization component as the output polarizer.

[0026] The spatial light modulator may include an emissive spatial light modulator arranged to emit spatially modulated light. Advantageously, the thickness of the display may be reduced.

[0027] The display device may further comprise a backlight arranged to output light, the backlight may comprise a transmissive spatial light modulator arranged to receive and spatially modulate output light from the backlight, which may advantageously increase the reduction of light in undesirable polar directions.

[0028] The display device may further comprise a backlight arranged to output light, the spatial light modulator may comprise a transmissive spatial light modulator arranged to receive and spatially modulate the output light from the backlight, the display polarizer may be an input display polarizer arranged on the input side of the spatial light modulator. Advantageously, the thickness of the front surface of the screen is reduced. Front surface reflections may be reduced.

[0029] The display device may further comprise an output display polarizer disposed at the output side of the spatial light modulator, a further additional polarizer disposed at the output side of the spatial light modulator, the further additional polarizer being a linear polarizer having an electric vector transmission direction parallel to the electric vector transmission direction of the display polarizer and the further additional polarizer, and at least one further pole-controlled retarder disposed between the further additional polarizer and the output display polarizer. Advantageously, an increased reduction in off-axis brightness may be achieved. An enhanced security factor may be provided.

[0030] The display device may further comprise a further polarizer disposed on the same side of the spatial light modulator as the further polarizer outside the further polarizer, the further polarizer being a linear polarizer having an electric vector transmission direction parallel to the electric vector transmission directions of the display polarizer and the further polarizer, and at least one further pole-controlled retarder disposed between the further polarizer and the further polarizer. Advantageously, the size of the pole region in which low light transmission is provided may be increased.

[0031] The backlight may comprise at least one first light source arranged to provide input light, at least one second light source arranged to provide input light in an opposite direction to the at least one first light source, a waveguide arrangement comprising at least one waveguide arranged to receive input light from the at least one first light source and the at least one second light source and cause light from the at least one first light source and the at least one second light source to exit the waveguide arrangement by breaking total internal reflection, and a light redirecting film component comprising an input surface arranged to receive light exiting the waveguide through a light guide surface of the waveguide by breaking total internal reflection, the input surface extending across a plane, and an output surface facing the input surface, the input surface may comprise an array of elongated prismatic elements. Advantageously, at least two different illumination characteristics may be provided that achieve improved efficiency in desired polar angle regions.

[0032] The waveguide arrangement may comprise a waveguide extending across a plane and comprising opposing first and second light guide surfaces arranged to guide light along the light guide, the second light guide surface arranged to guide light by total internal reflection, and first and second input ends arranged between the first and second light guide surfaces, the first and second input ends extending laterally between the first and second light guide surfaces, at least one first light source may be arranged to input light into the waveguide via the first input end and at least one second light source may be arranged to input light into the waveguide via the second input end, and the waveguide may be arranged to cause light from the at least one first light source and the at least one second light source to exit the waveguide via one of the first and second light guide surfaces by breaking total internal reflection. Advantageously, the thickness may be reduced.

[0033] The waveguide arrangement includes a first waveguide extending across a plane and opposing first and second light guide surfaces arranged to guide light along the light guide, the second light guide surface arranged to guide light by total internal reflection, a first input end disposed between the first and second light guide surfaces, the first input end extending laterally between the first and second light guide surfaces. and a first waveguide having a first input end, at least one first light source may be arranged to input light into the first waveguide through the first input end, the first waveguide may be arranged to cause light from the at least one first light source to exit the first waveguide through one of the first light guide surface and the second light guide surface by breaking total internal reflection, and a second waveguide extending across the plane arranged in series with the first waveguide and guiding the light along the light guide. and a second input end disposed between the first and second light guide surfaces, the second input end extending laterally between the first and second light guide surfaces, wherein at least one second light source may be disposed to input light into the second waveguide via the second input end, the second waveguide may be disposed to cause light from the at least one second light source to exit the second waveguide via one of the first and second light guide surfaces by breaking total internal reflection, and the first and second waveguides may be oriented such that the at least one first light source and the at least one second light source input light into the first and second waveguides in opposing directions. Advantageously, greater uniformity of brightness may be achieved across the area of ​​the display.

[0034] Each prismatic element may comprise a pair of elongated facets defining a ridge therebetween. Advantageously, light from the waveguide may be directed towards a desired viewer position.

[0035] The ridge may extend laterally across the plane at a non-zero angle, which may advantageously provide off-axis illumination.

[0036] The ridges may extend laterally parallel across the plane. The light sources may be located at the top and bottom of the display, advantageously reducing the width of the left and right side bezels.

[0037] The embodiments of the present disclosure can be used in a variety of optical systems. The embodiments can include or operate with a variety of projectors, projection systems, optical components, displays, microdisplays, computer systems, processors, self-contained projection systems, visual and / or audiovisual systems, and electrical and / or optical devices. Aspects of the present disclosure can be used with virtually any apparatus related to optical and electrical devices, optical systems, presentation systems, or any apparatus that can include any type of optical system. Thus, the embodiments of the present disclosure can be used in optical systems, devices used in visual and / or optical presentations, visual peripherals, and the like, as well as in numerous computing environments.

[0038] Before proceeding to details of the disclosed embodiments, it should be understood that the disclosure is not limited in its application or construction to the details of the particular arrangements shown, since other embodiments are possible. Moreover, aspects of the disclosure can be described in different combinations and arrangements to define unique embodiments in themselves. Also, the terminology used herein is for purposes of description and not of limitation.

[0039] These and other advantages and features of the present disclosure will become apparent to those of ordinary skill in the art upon reading the present disclosure in its entirety. [Brief description of the drawings]

[0040] Embodiments are illustrated by way of example in the accompanying figures, in which like reference numbers indicate similar parts, and in which:

[0041] [Figure 1A] FIG. 1 is a schematic diagram illustrating a front perspective overview of a switchable privacy display with a transmissive spatial light modulator. [Figure 1B] 1B is a schematic graph illustrating a front perspective overview of the stack of optical components in the apparatus of FIG. 1A. [Figure 2A] FIG. 1 is a schematic diagram illustrating a front perspective overview of an alternative optical stack for a switchable privacy display. [Figure 2B] 2B is a schematic graph illustrating a front perspective overview of the stack of optical components in the apparatus of FIG. 2A. [Figure 2C] FIG. 1 is a schematic diagram illustrating a front perspective overview of an alternative stack of optical components for a switchable privacy display. [Diagram 3] FIG. 1 is a schematic diagram illustrating a front perspective overview of a switchable privacy display with an emissive spatial light modulator. [Figure 4A] FIG. 2 is a schematic diagram illustrating a top view of a privacy display for an automobile; [Figure 4B] FIG. 2 is a schematic diagram illustrating a side view of a switchable lighting device having different solid angles in the first and second lobe directions; [Figure 5A] A schematic diagram illustrating a front perspective overview of a polar-controlled retarder comprising a liquid crystal retarder with an alignment layer having a pretilt direction with a component in the plane of the layer of liquid crystal material that forms a non-zero acute angle with respect to the electric vector transmission direction of the display polarizer and the additional polarizer. [Figure 5B] FIG. 1 is a schematic diagram illustrating a front view of an alignment layer having a pretilt direction with a component in the plane of the layer of liquid crystal material that makes a non-zero acute angle with respect to the electric vector transport direction of the display polarizer and the additional polarizer. [Figure 5C]A schematic diagram illustrating a front perspective overview of a polar-controlled retarder comprising a liquid crystal retarder with a horizontal alignment layer having a pretilt direction with a component in the plane of the layer of liquid crystal material that forms a non-zero acute angle with respect to the electric vector transmission direction of the display polarizer and the additional polarizer, and a vertical alignment layer having a pretilt direction with a component in the plane of the layer of liquid crystal material that forms a zero angle with respect to the electric vector transmission direction of the display polarizer and the additional polarizer. [Figure 5D] A schematic diagram illustrating a front perspective overview of a horizontal alignment layer having a pretilt direction with a component in the plane of the layer of liquid crystal material that forms a non-zero acute angle with the electric vector transmission direction of the display polarizer and the additional polarizer, and a vertical alignment layer having a pretilt direction with a component in the plane of the layer of liquid crystal material that forms a zero acute angle with the electric vector transmission direction of the display polarizer and the additional polarizer. [Figure 6A] 5C is a schematic graph illustrating the polar variation of the transmission of the pole-controlled retarder of FIG. 5B with a first pretilt direction of 30°; [Figure 6B] 5C is a schematic graph illustrating the polar variation of the transmission of the pole-controlled retarder of FIG. 5B with a second pretilt direction of 20°; [Figure 6C] 5C is a schematic graph illustrating the polar variation of the transmission of the pole-controlled retarder of FIG. 5B with a second pretilt direction of 0°; [Figure 7A] 1 is a schematic diagram illustrating a side view of a switchable backlight including a waveguide arrangement, a back reflector and a light redirecting film, outputting a light beam having the same solid angle in the first and second lobe directions. [Figure 7B] FIG. 2 is a schematic diagram illustrating a front view of a waveguide arrangement. [Figure 8A] FIG. 7B is a schematic diagram illustrating a front perspective overview of a light guide for the waveguide arrangement of FIG. 7A with microstructures on a first side and a second side of the light guide. [Figure 8B] FIG. 7B is a schematic diagram illustrating a front perspective view of an alternative light guide for the waveguide arrangement of FIG. 7A with microstructures on the same side of the light guide. [Figure 9A]FIG. 7B is a schematic diagram illustrating a front perspective overview of a light redirecting film component for the backlight of FIG. 7A. [Figure 9B] FIG. 2 is a schematic diagram illustrating a side view of a light redirecting film component. [Figure 9C] 7B is a schematic diagram illustrating a front perspective overview of an alternative light redirecting film component surface for the backlight of FIG. 7A. FIG. [Figure 10] 7B is a schematic graph illustrating polar variations in luminance output of the backlight of FIG. 7A operative to direct light to a first user and provide a private image to a second user; [Figure 11] 1B is a schematic graph illustrating the polar variation of front surface reflectance of the display device of FIG. 1A. [Figure 12] 11 is a schematic graph illustrating the backlight luminance characteristics of FIG. 10 with the display front luminance of polar variations of the visual security level S in the privacy operation mode for the display device of FIG. 1A and the value Ymax measured in nits, which is half the illuminance of the value I measured in lux. [Figure 13A] 7B is a schematic graph illustrating polar variations in luminance output of the backlight of FIG. 7A operative to direct light to first and second users; [Figure 13B] 7B is a schematic graph illustrating polar variations in luminance output of the backlight of FIG. 7A operative to direct light to first and second users; [Figure 14] 13B is a schematic graph illustrating the backlight luminance characteristics of FIG. 13B with the display front luminance of polar variations of the visual security level S in a dual user operating mode for the display device of FIG. 1A and a value Ymax measured in nits, which is half the illuminance of the value I measured in lux. [Figure 15] A schematic diagram illustrating a side view of an alternative switchable backlight including a waveguide arrangement including two waveguides arranged in series, a rear reflector and a light redirecting film, outputting a light beam in a first and second lobe direction. [Figure 16A]16 is a schematic graph illustrating polar variations in luminance output of the backlight of FIG. 15 operating to direct light to a first user and provide a private image to a second user. [Figure 16B] 11 is a schematic graph illustrating the pole variation of the transmission of a first pole-controlled delay; [Figure 16C] 16B is a schematic graph illustrating the characteristics of FIG. 16B with the display front luminance of polar variations of the visual security level S in the privacy operation mode for the display device of FIG. 1A and the value Ymax measured in nits, which is half the illuminance of the value I measured in lux. [Figure 16D] 16 is a schematic graph illustrating polar variations in luminance output of the backlight of FIG. 15 operative to direct light to first and second users. [Figure 16E] 16D with display front luminance, a value Ymax measured in nits being half the illuminance of value I measured in lux, and a schematic graph illustrating the backlight luminance characteristics of FIG. 16D with extreme variations in visual security level S in a dual user operating mode for the display device of FIG. 1A. [Figure 17A] FIG. 1 is a schematic diagram illustrating a top view of a privacy display for use by automobile passengers. [Figure 17B] 16 is a schematic graph illustrating polar variations in luminance output of the alternative backlight of FIG. 15 operative to direct light primarily towards passengers; [Figure 17C] FIG. 1 is a schematic diagram showing a front perspective overview of a switchable privacy display with a transmissive spatial light modulator. [Figure 17D] 11 is a schematic graph illustrating the polar variation of the transmission of a first pole-controlled retarder with a non-rotating alignment layer. [Figure 17E] 11 is a schematic graph illustrating the polar variation of the transmission of a second pole-controlled retarder with a non-rotating alignment layer. [Figure 17F]17D-E are schematic graphs illustrating the characteristics of FIG. 17D-E with the display front luminance of polar variations of the visual security level S in the privacy operating mode for the display device of FIG. 1A and the value Ymax measured in nits, which is half the illuminance of the value I measured in lux. [Figure 17G] 11 is a schematic graph illustrating the polar variation of the transmission of a first pole-controlled retarder with a rotating alignment layer. [Figure 17H] 11 is a schematic graph illustrating the polar variation of the transmission of a second pole-controlled retarder with a rotating alignment layer. [Figure 17I] 17A-17H are schematic graphs illustrating the characteristics of Figs. 17G-H with the display front luminance of polar variations of the visual security level S in the privacy operating mode for the display device of Fig. 1A and the value Ymax measured in nits, which is half the illuminance of the value I measured in lux. [Figure 18A] FIG. 13 is a schematic diagram illustrating a front view of an alternative waveguide arrangement. [Figure 18B] FIG. 18B is a schematic diagram illustrating a rear perspective view of a light redirecting film component for use in a backlight comprising the waveguide arrangement of FIG. 18A. [Figure 19A] 18B is a schematic graph illustrating polar variations in luminance output of the backlight of FIG. 18A operative to direct light to a first user and provide a private image to a second user; [Figure 19B] 11 is a schematic graph illustrating the pole variation of the transmission of a first pole-controlled delay; [Figure 19C] 18B is a schematic graph illustrating polar variation of front surface reflectance for a display device including the backlight of FIG. 18A. [Figure 19D] 11 is a schematic graph illustrating the pole variation of the transmission of a second pole-controlled delay; [Figure 19E] 11 is a schematic graph illustrating the pole variation of the transmission of a third pole-controlled delay; [Figure 19F]19A-E are schematic graphs illustrating the characteristics of Figures 19A-E with the display front luminance of polar variations of the visual security level S in the privacy operating mode for the display device of Figure 1A, and the value Ymax measured in nits, which is half the illuminance of the value I measured in lux. [Figure 20A] 16 is a schematic graph illustrating polar variations in luminance output of the backlight of FIG. 15 operative to direct light towards a second user. [Figure 20B] 20A is a schematic graph illustrating the backlight luminance characteristics of FIG. 20A with the display front luminance of polar variations of the visual security level S in a low stray light operating mode for the display device of FIG. 1A and a value Ymax measured in nits, which is half the illuminance of the value I measured in lux. [Figure 21A] 16 is a schematic graph illustrating polar variations in luminance output of the backlight of FIG. 15 operative to direct light to first and second users. [Figure 21B] 21A is a schematic graph illustrating the backlight luminance characteristics of FIG. 21A with display front luminance for polar variations in visual security level S in a dual user operating mode for the display device of FIG. 1A and a value Ymax measured in nits, which is half the illuminance of value I measured in lux. [Figure 22] FIG. 1 is a schematic diagram illustrating a side view of an alternative switchable backlight comprising a waveguide arrangement with asymmetric light extraction facets, a rear reflector, and a light redirecting film, outputting light beams in first and second lobe directions with different angular distributions. [Diagram 23] FIG. 23 is a schematic diagram illustrating a front perspective overview of a light guide for the waveguide arrangement of FIG. 22 with microstructures on first and second sides of the light guide. [Figure 24A] 23 is a schematic graph illustrating polar variations in luminance output of the backlight of FIG. 22 operating to direct light to a first user and provide a private image to a second user. [Figure 24B] 4 is a schematic graph showing the pole variation of the transmission of the first pole-controlled delay; [Figure 24C]23 is a schematic graph illustrating the polar variation of front surface reflectance of a display device including the backlight of FIG. 22. [Figure 24D] 11 is a schematic graph illustrating the pole variation of the transmission of a second pole-controlled delay; [Figure 24E] 24A-D with the display front luminance, and the polar variation of the visual security level S in the privacy operating mode for the display device of FIG. 1A, and the value Ymax measured in nits, which is half the illuminance of the value I measured in lux; [Figure 25A] 23 is a schematic graph illustrating polar variations in luminance output of the backlight of FIG. 22 operative to direct light towards a second user. [Figure 25B] 23 is a schematic graph illustrating polar variations in luminance output of the backlight of FIG. 22 operative to direct light to first and second users. [Figure 26] 25B is a schematic graph illustrating the characteristics of FIG. 25B with the display front luminance of polar variations of the visual security level S in the public operating mode for the display device of FIG. 1A and the value Ymax measured in nits, which is half the illuminance of the value I measured in lux. [Figure 27A] FIG. 23 is a schematic diagram illustrating a front perspective view of an alternative light guide for the waveguide arrangement of FIG. 22 with microstructures on the same side of the light guide. [Figure 27B] FIG. 23 is a schematic diagram illustrating a front perspective view of an alternative light guide for the waveguide arrangement of FIG. 22 with microstructures on the same side of the light guide. [Figure 28] FIG. 2 is a schematic diagram illustrating a top view of a segmented backlight. [Figure 29A] A schematic diagram illustrating a front perspective view of an alignment layer having a pretilt direction with a component in the plane of the layer of liquid crystal material that forms a non-zero angle with respect to the electric vector transport direction of the display polarizer and additional polarizer that varies across the plane of the alignment layer. [Figure 29B] FIG. 2 is a schematic diagram illustrating pupil shaping of a pole-controlled retarder; and FIG. 3 is a graph showing the polar variation of transmission with position across the plane of the alignment layer. [Figure 30A] FIG. 13 is a schematic diagram illustrating a side view of an alternative switchable backlight with a light redirecting film in which the facet tilt varies in a direction orthogonal to the lateral direction across the plane of the light redirecting film. [Figure 30B] FIG. 13 is a schematic diagram illustrating a side view of an alternative switchable backlight with a light redirecting film in which the facet tilt varies in a direction orthogonal to the lateral direction across the plane of the light redirecting film. [Figure 30C] FIG. 13 is a schematic diagram illustrating a rear perspective view of light output from a pupil-shaped linear light redirecting film component with variable tilt facets. [Figure 31A] FIG. 13 is a schematic diagram illustrating a front perspective view of the operation of facets of a curved light redirecting film component of a pupil-shaped backlight for light from a first light source. [Figure 31B] FIG. 1 is a schematic diagram illustrating a rear perspective view of light output from a curved light redirecting film component with uniform tilt facets. [Figure 31C] FIG. 13 is a schematic diagram illustrating a rear perspective view of light output from a curved light redirecting film component with variable tilt facets with a common optical window distance. [Figure 31D] FIG. 1 is a schematic diagram illustrating a rear perspective view of light output from a curved light redirecting film component with variable tilt facets with first and second different optical window distances. [Figure 32A] 1 is a schematic diagram illustrating a side view of the operation of a turning film including variable tilt facets in a pupil-like backlight. [Figure 32B] 1 is a schematic diagram illustrating a top view of the operation of a curved light redirecting film component in a pupil-like backlight. [Diagram 33] 4 is a schematic diagram illustrating a side view of the operation of the emissive spatial light modulator of FIG. 3. [Diagram 34] FIG. 2 is a schematic diagram illustrating a side view of light propagation through the pole-controlled retarder of FIGS. 1A-B in a privacy mode of operation (narrow angle). [Diagram 35]FIG. 2 is a schematic diagram illustrating a side view of the propagation of light through the pole-controlled retarder of FIGS. 1A-B in a wide-angle mode of operation. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0042] We now explain the terminology associated with optical retarders for the purposes of this disclosure.

[0043] In a layer comprising a uniaxially birefringent material, there is a direction that dominates the optical anisotropy, but all directions perpendicular to it (or at a given angle relative to it) have equivalent birefringence.

[0044] The optical axis of the optical retarder refers to the direction of propagation of light rays in a uniaxially birefringent material where no birefringence occurs, which is different from the optical axis of the optical system, which may be, for example, parallel to a line of symmetry or perpendicular to the display surface through which the principal ray propagates.

[0045] For light propagating perpendicular to the optic axis, the optic axis is the slow axis when linearly polarized light with the electric vector parallel to the slow axis travels slowest. The slow axis direction is the direction in which the refractive index is highest at the design wavelength. Similarly, the fast axis direction is the direction in which the refractive index is lowest at the design wavelength.

[0046] For uniaxial birefringent materials with positive dielectric anisotropy, the slow axis direction is the extraordinary axis of the birefringent material. For uniaxial birefringent materials with negative dielectric anisotropy, the fast axis direction is the extraordinary axis of the birefringent material.

[0047] The terms half-wave and quarter-wave refer to the operation of the retarder relative to a design wavelength λ0, which may typically be between 500 nm and 570 nm. In this embodiment, exemplary retardation values ​​are provided for a wavelength of 550 nm, unless otherwise specified.

[0048] A retarder provides 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 it imparts to the two polarization components, Γ, which is related to the birefringence Δn and the retarder thickness d as follows: Γ=2.π.Δn.d / λ0 Equation 1

[0049] In Equation 1, Δn is defined as the difference between the extraordinary and ordinary refractive indices. Δn=n e -n o formula 2

[0050] 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.

[0051] The term half-wave retarder herein typically refers to light propagating perpendicular to the retarder and perpendicular to the spatial light modulator.

[0052] We now describe some aspects of the propagation of light rays through a transparent retarder between a pair of polarizers.

[0053] The state of polarization (SOP) of a beam of light is represented by the relative amplitude and phase shift between any two orthogonally polarized components. A transparent retarder does not change the relative amplitude of these orthogonally polarized components, but only affects their relative phase. Providing a net phase shift between the orthogonally polarized components changes the SOP, while maintaining the net relative phase preserves the SOP. In this description, the SOP may be referred to as the state of polarization.

[0054] A linear SOP has a non-zero amplitude polarization component and an orthogonal polarization component with zero amplitude.

[0055] A linear polarizer transmits a unique linear SOP that has a linear polarization component parallel to the electric vector transmission direction of the linear polarizer and attenuates light with a different SOP.

[0056] An absorbing polarizer is one that absorbs one polarization component of incident light and transmits a second, orthogonal polarization component. An example of an absorbing linear polarizer is a dichroic polarizer.

[0057] A reflective polarizer is a polarizer that reflects one polarization component of incident light and transmits a second orthogonal polarization component. Examples of reflective polarizers that are linear polarizers include multilayer polymer film stacks such as DBEF™ or APF™ manufactured by 3M, or wire grid polarizers such as ProFlux™ manufactured by Moxtek. A reflective linear polarizer may further comprise a cholesteric reflective material and a quarter-wave plate arranged in series.

[0058] A retarder placed between a linear polarizer and a parallel linear analyzing polarizer, which introduces no relative net phase shift, provides perfect transmission of light except for residual absorption in the linear polarizer.

[0059] A retarder, which provides a relative net phase shift between the orthogonal polarization components, changes the SOP and provides attenuation at the analyzing polarizer.

[0060] In this disclosure, "A-plate" refers to an optical retarder that utilizes a layer of birefringent material whose optic axis is parallel to the plane of the layer.

[0061] A "positive A-plate" refers to a positively birefringent A-plate, i.e., an A-plate with a positive Δn.

[0062] In this disclosure, "C-plate" refers to an optical retarder utilizing a layer of birefringent material whose optical axis is perpendicular to the plane of the layer. "Positive C-plate" refers to a positively birefringent C-plate, i.e., a C-plate with positive Δn. "Negative C-plate" refers to a negatively birefringent C-plate, i.e., a C-plate with negative Δn.

[0063] "O-plate" refers to an optical retarder utilizing 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 a positive Δn.

[0064] An achromatic retarder can be provided, the retarder material being provided with a retardation Δn.d that varies with wavelength λ. Δn.d / λ=κ Equation 3

[0065] where κ is essentially a constant.

[0066] Examples of suitable materials include modified polycarbonates manufactured by Teijin Films, Inc. In this embodiment, an achromatic retarder may be provided to advantageously minimize color shifts between polar angle viewing directions with less luminance reduction and those with increased luminance reduction, as described below.

[0067] Various other terms used in this disclosure in connection with retarders and liquid crystals will now be explained.

[0068] The liquid crystal cell has a retardation given by Δn.d, where Δn is the birefringence of the liquid crystal material 414 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 414 in the liquid crystal cell.

[0069] Horizontal alignment refers to the alignment of liquid crystals in a switchable liquid crystal display where the molecules are aligned substantially parallel to the substrates. Horizontal alignment is sometimes called planar alignment. Horizontal alignment can typically be provided with a small pretilt, such as 2 degrees, so that the molecules at the surface of the alignment layer of the liquid crystal cell are slightly tilted, as explained below. The pretilt is arranged to minimize degeneracy in switching the cell.

[0070] In this disclosure, vertical alignment is the state in which rod-shaped liquid crystal molecules are aligned substantially perpendicular to the substrate. For discotic liquid crystals, vertical alignment is defined as the state in which the axis of the column structure formed by the disc-shaped liquid crystal molecules is aligned perpendicular to the surface. In vertical alignment, the pretilt is the tilt angle of the molecules close to the alignment layer, which is usually close to 90 degrees, and can be, for example, 88 degrees.

[0071] In a twisted liquid crystal layer, a twisted configuration (also known as a helical structure or helix) of nematic liquid crystal molecules is provided. The twist can be achieved by non-parallel alignment of the alignment layers. Additionally, cholesteric dopants can be added to the liquid crystal material 414 to eliminate the degeneracy of the twist direction (clockwise or counterclockwise) and further control the pitch of the twist in the relaxed (usually undriven) state. A supertwisted liquid crystal layer has a twist greater than 180 degrees. Twisted nematic layers used in spatial light modulators typically have a twist of 90 degrees.

[0072] Liquid crystal molecules with positive dielectric anisotropy can be switched from a horizontal alignment (eg, A-plate retarder alignment) to a vertical alignment (eg, C-plate or O-plate retarder alignment) by an applied electric field.

[0073] Liquid crystal molecules with negative dielectric anisotropy can be switched from a vertical alignment (such as a C-plate or O-plate retarder alignment) to a horizontal alignment (such as an A-plate retarder alignment) by an applied electric field.

[0074] Rod-like molecules have positive birefringence, so n e >n o Since discotic molecules have negative birefringence, n e <n o It is.

[0075] Positive retarders such as A-plates, positive O-plates, and positive C-plates can usually be provided by stretched films or rod-like liquid crystal molecules. Negative retarders such as negative C-plates can be provided by stretched films or discotic-like liquid crystal molecules.

[0076] Parallel liquid crystal cell alignment refers to the alignment direction of the horizontal alignment layer being parallel or more commonly anti-parallel. In the case of pre-tilted vertical alignment, the alignment layer may have components that are substantially parallel or anti-parallel. A hybrid alignment liquid crystal cell may have one horizontal alignment layer and one vertical 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.

[0077] The transmissive spatial light modulator may further include a retarder between the input display polarizer and the output display polarizer, for example as disclosed in U.S. Patent No. 8,237,876, which is incorporated by reference in its entirety. Such a retarder (not shown) is in a different location than the passive compensation retarder of the present embodiment. Such a retarder compensates for contrast reduction for off-axis viewing positions, which is a different effect than the brightness reduction for off-axis viewing positions of the present embodiment.

[0078] Here, terms relating to the appearance of the privacy display will be explained.

[0079] The private operating mode of a display is one in which the observer sees a low contrast sensitivity so that the image is not clearly visible. Contrast sensitivity is a measure of the ability to distinguish different levels of luminance in a still image. Inverse contrast sensitivity can be used as a measure of visual security, in that a high visual security level (VSL) corresponds to low image visibility.

[0080] For a privacy display that presents an image to a viewer, visual security is obtained as follows. VSL=(Y+R) / (YK) Equation 4

[0081] where VSL is the visual security level, Y is the luminance of the white state of the display at the voyeur's viewing angle, K is the luminance of the black state of the display at the voyeur's viewing angle, and R is the luminance of the reflected light from the display.

[0082] The contrast ratio of the panel is given by: C=Y / K formula 5

[0083] For a high contrast optical LCD mode, the white state transmittance remains substantially constant with viewing angle. In the reduced contrast LCD mode of the present embodiment, the white state transmittance typically decreases as the black state transmittance increases, such that: Y+K~PL Equation 6

[0084] The visual security level can then be further obtained as follows:

number

[0085] where the off-axis relative luminance P is usually defined as a percentage of the frontal luminance, L at the voyeur angle, and the display may have an image contrast ratio C and a surface reflectance ρ.

[0086] The off-axis relative luminance P is sometimes referred to as the privacy level, however such privacy level P describes the relative luminance of a display at a given polar angle compared to the luminance at the front, and is not a measure of the appearance of privacy.

[0087] The display may be illuminated with a Lambertian ambient illuminance, I. Thus, in a completely dark environment, a high contrast display will have a VSL of approximately 1.0. As the ambient illuminance increases, the perceived image contrast degrades, the VSL increases, and a private image is perceived.

[0088] For a typical LCD display, the panel contrast C exceeds 100:1 at almost all viewing angles, so the visual security level can be roughly calculated as follows: VSL=1+I.ρ / (π.PL) Equation 8

[0089] The security of the perceived image can be determined from the logarithmic response of the eye, which is: S=log 10 (V) Equation 9

[0090] The desired limits of S were determined as follows: In a first step, a privacy display device was provided. Measurements of the change in privacy level, P(θ) of the display device with polar viewing angles, and the change in reflectance ρ(θ) of the display device with polar viewing angles were made using a photopic measurement instrument. A light source, such as a light box of substantially uniform luminance, was positioned to provide illumination to an observer position at a polar angle greater than 0° relative to the normal to the display device from an illumination area positioned to illuminate the privacy display device along a direction of incidence for reflection. The change in illuminance I(θ) of the substantially Lambertian luminance light box with polar viewing angles was determined by measuring the change in the recorded reflected luminance with polar viewing angles, taking into account the change in reflectance ρ(θ). The measurements of P(θ), r(θ), and I(θ) were used to determine the change in security factor S(θ) with polar viewing angles along the zero elevation axis.

[0091] In a second step, a series of high-contrast images were presented to the privacy display, including (i) small text images with a maximum font height of 3 mm, (ii) large text images with a maximum font height of 30 mm, and (iii) a moving image.

[0092] In the third step, each observer (using vision correction for viewing at 1000 mm if necessary) viewed each of the images from a distance of 1000 m and adjusted the polar coordinate angle at zero altitude until the image was no longer visible with one eye from a location on the display at or near the centerline of the display. The polar positions of the observer's eyes were recorded. From the relationship S(θ), the security factor at that polar position was determined. Measurements were made for various images, various display luminances Y max , was repeated for different light box illuminances I(q=0), different background lighting conditions, and different observers.

[0093] From the above measurements, S<1.0 provides low or no visual security, 1.0≦S<1.5 provides visual security that depends on the contrast, spatial frequency, and temporal frequency of the image content, 1.5≦S<1.8 provides acceptable image invisibility (i.e., image contrast is not observable) for most images and most observers, and S≧1.8 provides complete image invisibility for all observers, regardless of image content.

[0094] Compared to privacy displays, the desirable wide-angle displays are easily observed in standard ambient lighting conditions. One measure of image visibility is given by contrast sensitivity, such as the Michelson contrast, given by the following formula: M=(I max -I min ) / (I max +I min ) Equation 10

[0095] So, M=((Y+R)-(K+R)) / ((Y+R)+(K+R))=(YK) / (Y+K+2.R) Equation 11

[0096] Therefore, the visual security level (VSL) is comparable (but not identical) to 1 / M. In this study, for a given off-axis relative luminance P, the wide-angle image visibility W is approximated as follows: W=1 / VSL=1 / (1+I.ρ / (π.PL)) Equation 12

[0097] In this study, we consider the desired white point (u w ',v w Output color from (u w '+Δu', v w The color change Δε of λ(λ+Δv) can be determined by the CIELUV color difference metric assuming a typical display spectral illuminant, given by: Δε = (Δu' 2 +Δv'2 ) 1 / 2 formula 13

[0098] Catadioptric elements use both refraction and reflection, which can be total internal reflection or reflection from a metallized surface.

[0099] The structure and operation of various directional display devices will now be described. In this description, common elements will have common reference numbers. It should be noted that the disclosure regarding any element applies to each device in which the same or corresponding element is provided. Thus, for the sake of brevity, such disclosure will not be repeated.

[0100] Next, a switchable privacy display device is described.

[0101] FIG. 1A is a schematic diagram illustrating a front perspective view of a switchable privacy display device 100 comprising a transmissive spatial light modulator 48, and FIG. 1B is a schematic graph showing a front perspective view of a stack of optical components in the device of FIG. 1A.

[0102] The display device 100 comprises a backlight device 20 and a spatial light modulator 48 arranged to receive light from the backlight device 20. The spatial light modulator 48 includes a transmissive spatial light modulator 48 arranged to receive and spatially modulate the output light from the backlight device 20.

[0103] The spatial light modulator 48 comprises a display output polarizer 218, a display input polarizer 210 disposed at the input side of the spatial light modulator 48, the display polarizers 210, 218 being linear polarizers. 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 output display polarizer 218 is crossed with the display input polarizer 210 and positioned to provide a high extinction ratio for light from the pixels 220, 222, 224 of the spatial light modulator 48. Exemplary polarizers 210, 218 may be absorbing polarizers, such as dichroic polarizers.

[0104] The additional polarizer 318A is located on the same side of the spatial light modulator 48 as the input display polarizer 210, and the additional polarizer 318A is a linear polarizer. The pole-controlled retarder 300 is located between the display input polarizer 210 and the additional polarizer 318.

[0105] The display input polarizer 210, the additional polarizer 318A, and the further additional polarizer 318B have electric vector propagation directions 211, 319A, 319B parallel to the x-axis and to each other. The electric vector propagation direction 219 is set to be parallel to the y-axis to provide high image contrast at the spatial light modulator 48.

[0106] The at least one pole-controlled delay 300A further includes at least one passive compensation delay 330A. The at least one passive compensation delay 330 includes a passive compensation delay 330A whose optical axis 331A is perpendicular to the plane of the delay 330A, i.e., the delay 330A is a negative C-plate.

[0107] The display device 100 further comprises a backlight 20 arranged to output light 445, 447, and the spatial light modulator 48 comprises a transmissive spatial light modulator 48 arranged to receive and spatially modulate the output light from the backlight 20.

[0108] The display device 100 further comprises a further additional polarizer 318B arranged outside and on the same side of the further additional polarizer 318A of the spatial light modulator 48, the further additional polarizer 318B being a linear polarizer having an electric vector transmission direction parallel to the electric vector transmission directions 211, 319 of the display polarizer 210 and the further additional polarizer 318A, and at least one further pole-controlled retarder 300B arranged between the further additional polarizer 318A and the further additional polarizer 318B.

[0109] The pole controlled retarders 300A, 300B each include a switchable liquid crystal retarder 301A, 301B comprising a layer 314A, 314B of liquid crystal material 414A, 414B. The materials 414A, 414B may be the same or different, as described further below. The liquid crystal retarder 301 further comprises transparent substrates 312, 316, electrodes, and alignment layers, as described further with respect to FIG. 5B.

[0110] The backlight 20 comprises at least one first light source 15 (a plurality of first light sources 15 are shown as a non-limiting example) arranged to provide input light 445, and at least one second light source 17 (a plurality of second light sources 17 are shown as a non-limiting example) arranged to provide input light 447 in an opposite direction to the at least one first light source 15.

[0111] The waveguide arrangement 11 is arranged to receive input light 445, 447 from the first light source 15 and the second light source 17 and to output light from the first light source 15 and the second light source 17 from the waveguide arrangement 11 by breaking total internal reflection. The light sources 15, 17 each comprise an array of light sources, such as an array of LEDs. The backlight device 20 further comprises a light source control system 354 arranged to independently control the at least one first light source 15 and the at least one second light source 17.

[0112] The backlight apparatus 20 further comprises a back reflector 3 arranged to receive light exiting from surfaces 6, 8 of the waveguide 1 and return the received light back through the waveguide 1 as will be further described below.

[0113] The backlight apparatus 20 further comprises a light redirecting film component 50 arranged to receive light extracted from the waveguide 1, the operation of which is described further below.

[0114] The optical stack 5 may include diffusers, reflective polarizers, and other known optical backlight structures. For example, an asymmetric diffuser, which may include asymmetric surface relief features, may be provided in the optical stack 5 with increased diffusion in the elevation direction compared to the lateral direction. Advantageously, image uniformity may be increased.

[0115] 1B, various optical axis orientations and electric vector propagation directions are disclosed. The liquid crystal retarders 301A, 301B have pretilt directions with components 417AAp, 417BAp in the planes of the layers 314A, 314B of liquid crystal material 414A, 414B that make non-zero acute angles 617A, 617B with respect to the electric vector propagation directions 211, 319A, 319B of the display device polarizer 210 and additional polarizers 318A, 318B. More generally, at least one of the alignment layers 419A, 419B may have a pretilt direction with a component 417AAp, 417BAp in the plane of the layer 314 of liquid crystal material 414 that forms a non-zero acute angle 617AA, 617BA with at least one of the electric vector propagation directions 211, 319A, 319B of the display device polarizer 218 and the additional polarizers 318A, 318B.

[0116] In this specification, references to a component of the pretilt direction that is at a "non-zero acute angle" with respect to the electric vector transport direction of the polarizer are references to the angle seen perpendicular to the plane in which the component is defined, which may be equated to the angle between the component of the pretilt direction and the projection of the electric vector transport direction onto the plane in which the component is defined, as shown, for example, in Figure 1B and corresponding drawings.

[0117] The structure of the liquid crystal retarders 301A, 301B may be further discussed with respect to FIGS. 5A-B below.

[0118] The structure of the alternative pole-controlled delay and the control of the pole-controlled delay are further described below.

[0119] Figure 2A is a schematic diagram illustrating a front perspective overview of an alternative optical stack of a switchable privacy display device 100, and Figure 2B is a schematic graph illustrating a front perspective overview of a stack of optical components in the apparatus of Figure 2A. Features of the embodiments of Figures 2A-B that are not discussed in further detail can be assumed to correspond to features with like reference numbers discussed above, including potential variations of features.

[0120] 2A illustrates an output polarizer 218 of a spatial light modulator 48. The backlight 20 and the transmissive spatial light modulator 48 may be disposed on the input side of the polarizer 218.

[0121] 1A-B in the alternative embodiment of Figures 2A-B, the pole-controlled retarders 300A, 300B are arranged at the output side of the spatial light modulator 48. Thus, the display device 100 further comprises an output display polarizer 218 arranged at the output side of the spatial light modulator 48, a further additional polarizer 318B arranged at the output side of the spatial light modulator 48, the further additional polarizer 318B being a linear polarizer with an electric vector transmission direction parallel to the electric vector transmission directions 219, 319 of the display polarizer 218 and the further polarizer 318A, and at least one further pole-controlled retarder 300 arranged between the further additional polarizer 318B and the output display polarizer 218.

[0122] Advantageously, the arrangement of Figure 2A may be retrofitted to the output side of spatial light modulator 48 by a display user or during manufacture. Moreover, such an arrangement may be provided for use with an emissive spatial light modulator in a manner similar to that illustrated in Figure 3 below.

[0123] 2A-B further illustrate an alternative embodiment of the negative C-plate passively controlled retarders 330A, 330B of FIGS. 1A-B, where at least one passive compensation retarder 330 comprises a pair of passive compensation retarders 330A, 330B having optical axes 331A, 331B in the plane of the intersecting retarders 330A, 330B. The angle between the optical axes 331A, 331B is bisected by the electric vector transmission directions 211, 219, 319 of the display polarizers 210, 218 and the additional polarizer 318, which are parallel in this example. More generally, the angle between the optical axes 331A, 331B is bisected by the electric vector transmission directions 211, 219, 319 of at least one of the display polarizers 210, 218 and the additional polarizer 318, respectively. The passive A-plate retarders 330AA, 330AB, 330BA, 330BB of FIG. 2C may advantageously be easier to manufacture in large areas at lower cost than the C-plate retarders of FIGS. 1A-B.

[0124] Figures 2A-B further illustrate that the electric vector transmission directions 219, 319A, 319B of the polarizers 219, 318A, 318B are rotated 90 degrees relative to that illustrated in Figures 1A-B. The liquid crystal retarders 301A, 301B have pretilt directions with components 417AAp, 417BAp in the planes of the layers 314A, 314B of liquid crystal material 414A, 414B in the same orientation as illustrated in Figures 1A-B, and therefore make non-zero acute angles 617AA, 617BA with the electric vector transmission directions 219, 319A, 319B of the display device polarizer 218 and additional polarizers 318A, 318B that are complementary to the corresponding angles in Figures 1A-B. The operation of the display 100 is substantially unaffected by such a 90 degree rotation of the electric vector propagation directions 219, 319A, 319B of the polarizers 219, 318A, 318B.

[0125] 2A-B further illustrate that a display 100 including the display of FIG 1A may further comprise a control system arranged to control the pole-controlled delays 300A, 300B by the drivers 350A, 350B to vary the operating voltages of the liquid crystal layers 314A, 314B, respectively. A controller 352 is provided to control the drivers 350A, 350B and further to control the light source controller 354 of FIG 1A.

[0126] As described further below, the display device 100 is arranged to display an image and can operate in at least a public mode (for two or more users), a privacy single-user mode, and a low stray light single-user mode. In the privacy mode, privacy functionality is provided, where image visibility to off-axis viewers is reduced compared to the public mode, and image visibility to a primary user in an off-axis position remains visible in both the privacy and public modes. The control systems 350, 352, 354 each selectively operate the display device 100 in the public mode, the privacy mode, or the low stray light mode for at least one region of the displayed image, typically the entire displayed image. Such a display device can be used in applications such as switchable privacy displays for laptops, monitors, TVs, mobile phones, tablets, wearable displays, ATM displays, automotive displays, and the like, but are not limited to such applications.

[0127] 2C is a schematic diagram illustrating a front perspective overview of an alternative stack of optical components for a switchable privacy display device 100. Features of the embodiment of FIG. 2C that are not discussed in further detail can be assumed to correspond to features with like reference numbers discussed above, including potential variations of features.

[0128] The alternative arrangement of FIG. 2C differs from that of FIGS. 1A-B and 2A in a first respect. The first pole-controlled retarder 300A comprises a liquid crystal pole-controlled retarder 301A and a C-plate 330A, and the second pole-controlled retarder 300B comprises a liquid crystal pole-controlled retarder 301B and crossed A-plates 330BA, 330BB. By selecting different pole-controlled retarders 300A, 300B, advantageously increased off-axis control of the display output can be achieved. The structure allows for an additional air gap behind the spatial light modulator 48 while maintaining image contrast, improving assembly yield, and reducing costs.

[0129] In another respect, the first pole-controlled retarder 300A is disposed on the output side of the output polarizer 218, and the second pole-controlled retarder 300B is disposed on the input side of the input polarizer 210. Advantageously, the efficiency of light extraction from the backlight 20 can be increased.

[0130] Next, the emissive display structure will be described.

[0131] 3 is a schematic diagram illustrating a front perspective overview of a switchable privacy display device 100 including an emissive spatial light modulator 48. Features of the embodiment of FIG. 3 that are not discussed in further detail can be assumed to correspond to features with like reference numbers discussed above, including potential variations of features.

[0132] The spatial light modulator 48 includes an emissive spatial light modulator 48 arranged to emit spatially modulated light. The emissive display 100 may further include a quarter wave plate 228 and a display output polarizer 218 arranged to reduce front surface reflections from the pixel plane 214 of the emissive display 100. The display polarizer is an output display polarizer 2218 arranged at the output side of the spatial light modulator 48.

[0133] The embodiment of Figure 3 illustrates a single pole-controlled delay 300. Alternatively, two pole-controlled delays 300A, 300B and an additional polarizer 318B as illustrated in Figure 2A may be provided.

[0134] The emissive display 100 further comprises a parallax barrier 700 which includes light absorbing regions 704 and light transmissive aperture regions 702. The operation of the parallax barrier 700 in this embodiment is further described with reference to Figure 33 below.

[0135] Next, the operation of the display 100 in an automobile will be described.

[0136] 4A is a schematic diagram showing a top view of the privacy display device 100 in an automobile 650, and FIG. 4B is a schematic diagram showing a side view of the privacy display device 100 in an automobile 650. As shown in FIG.

[0137] The display 100 is positioned in a center stack display (CSD) position, i.e., between two occupant users 45, 47, who may be the front passenger and the driver, respectively. Light 445, 447 may be output to user 45 and user 47, respectively. The display 100 illustrates an alternative embodiment that includes a first portion 101L that may provide an image to both the passenger 45 and the driver 47, and a second portion 101R that includes a switchable off-axis privacy display as described elsewhere herein.

[0138] In public mode it may be desirable to make the image available to both users 45, 47.

[0139] In privacy mode, it may be desirable to provide images to passengers 45 that are not visible to the driver 47. Advantageously, the passengers can view entertainment information without distracting the driver.

[0140] In a low stray light mode, it may be desirable to provide an image to the driver at a desired brightness while reducing the brightness for passengers. Advantageously, the brightness of the interior surfaces of the vehicle may be reduced during night driving, reducing driver distraction. Additionally, a larger area display may desirably have lower interior cabin lighting.

[0141] Additionally, it may be desirable to provide a low level of stray light 442 directed towards the vehicle windows 654 to reduce the visibility of the reflected image data.

[0142] Next, the structure of the pole controlled delay 300 for off-axis illumination control will be described.

[0143] 5A is a schematic diagram showing a front perspective overview of a pole-controlled retarder 300 including a liquid crystal retarder 301 with alignment layers 419A, 419B having a pretilt direction 417 with components 417Ap, 417Bp in the plane of the layer 314 of liquid crystal material 414 that make a non-zero acute angle 617A, 617B with the electric vector transmission directions 219, 319 of the display device polarizer 218 and the additional polarizer 318, which are parallel in this example. More generally, at least one of the alignment layers 419A, 419B may have a pretilt direction 417 with components 417Ap, 417Bp in the plane of the layer 314 of liquid crystal material 414 that make a non-zero acute angle 617A, 617B with at least one of the electric vector transmission directions 219, 319 of the display device polarizer 218 and the additional polarizer 318. In this example, non-zero acute angles 617A, 617B are present throughout the entire display device 100. This is true for all embodiments unless otherwise noted. More generally, however, non-zero acute angles 617A, 617B may be present throughout any portion of the display device 100 for which the technical effects described below are realized.

[0144] Figure 5B is a schematic diagram showing a front view of one alignment layer 419B having a pretilt direction 417B with a component 417Bp in the plane of the layer 314 of liquid crystal material 414 that makes a non-zero acute angle 617B with respect to the electric vector transmission direction 219 of the display device polarizer 218 and the additional polarizer 318.

[0145] Features of the embodiment of FIGS. 5A-B that are not discussed in further detail can be assumed to correspond to features bearing like reference numbers discussed above, including potential variations of features.

[0146] At least one pole-controlled retarder 300 comprises a switchable liquid crystal retarder 301 comprising a layer 314 of liquid crystal material 414. Electrodes 413, 415 are disposed on substrates 312, 316 (as illustrated in FIG. 1A ), and a driver 350 is arranged to provide a voltage across the layer 314 in at least one mode of operation.

[0147] Two surface alignment layers 419A, 419B are disposed adjacent to and on either side of the layer 314 of liquid crystal material 414, and each of the surface alignment layers 419A, 419B has a pretilt having a pretilt direction 417 with components 417Ap, 417Bp in the plane of the layer 314 of liquid crystal material 414 that make non-zero acute angles 617A, 617B with respect to the electric vector propagation directions 211, 219, 319 of the display polarizers 210, 218 and the additional polarizer 318.

[0148] The switchable liquid crystal retarder 301 further comprises two surface alignment layers 419A, 419B disposed adjacent to and on either side of the layer 314 of liquid crystal material 414, the surface alignment layers 419A, 419B each having a pretilt with a pretilt direction 417 with components 417Ap, 417Bp in the plane of the layer 314 of liquid crystal material 414 that form a non-zero angle 617 with respect to the electric vector propagation directions 211, 219, 319 of the display polarizers 210, 218 and the additional polarizer 318.

[0149] 5A illustrates a surface alignment layer 419B arranged to provide horizontal alignment in the adjacent liquid crystal material 414, the surface alignment layer 419B having a pretilt direction 417 with a component 417Bp in the plane of the layer 314 of liquid crystal material 414 that makes a non-zero acute angle 617B with the electric vector transport directions 219, 319 of the display polarizer 218 and the additional polarizer 318. In other embodiments, such as FIG. 1A, the component 417Bp makes a non-zero acute angle 617B with the electric vector transport directions 211, 319 of the display polarizer 210 and the additional polarizer 318.

[0150] The other surface alignment layer 419A is arranged to provide a vertical alignment in the adjacent liquid crystal material 414. The other surface alignment layer 419A has a pretilt with a pretilt direction 417A with a component 417Ap in the plane of the layer 314 of liquid crystal material 414 that makes a non-zero angle 617A with the electric vector transport directions 211, 319 of the display polarizer 218 and the additional polarizer 318. Thus, each of the surface alignment layers 419A, 419B has a pretilt with a pretilt direction 417A, 417B with a component 417Ap, 417Bp in the plane of the layer 314 of liquid crystal material 414 that makes a non-zero acute angle 617A, 617B with the electric vector transport directions 211, 219, 319 of the display polarizer 210, 218 and the additional polarizer 318.

[0151] Figure 5B illustrates that the pretilt direction can be the same at all positions across the surface alignment layer 419B, such that the surface alignment layers 419A, 419B each have a pretilt with a pretilt direction 417 in the plane of the layer 314 of liquid crystal material 414 that is at the same non-zero acute angles 617A, 617B relative to the electric vector propagation directions 211, 219, 319 of the display polarizers 210, 218 and the additional polarizer 318.

[0152] It may be desirable to reduce the cost and complexity of the liquid crystal retarder 301.

[0153] Figure 5C is a schematic diagram illustrating a front view of a pole-controlled retarder 300 comprising a liquid crystal retarder 301 with a horizontal alignment layer 419B having a pretilt direction 417B with a component 417Bp in the plane of the layer of liquid crystal material 414 that makes a non-zero acute angle 617B with respect to the electric vector transmission directions 219, 319 of the display polarizer 218 and the additional polarizer 318, and a vertical alignment layer 419A having a pretilt direction 417A with a component 417Ap in the plane of the layer of liquid crystal material 414 that is parallel (at zero angle) to the electric vector transmission directions 219, 319 of the display polarizer 218 and the additional polarizer 219. Alternatively, the vertical alignment layer 419A may have a pretilt direction 417A with a component 417Ap in the plane of the layer of liquid crystal material 414 perpendicular to the electric vector transport directions 219, 319 of the display polarizer 218 and the additional polarizer 219, in which alternative the operation is substantially unaffected.

[0154] Figure 5D is a schematic diagram illustrating a front view of a pole-controlled retarder 300 comprising a horizontal alignment layer 419B having a pretilt direction 417B with a component 417Bp in the plane of the layer of liquid crystal material 414 that makes a non-zero acute angle 617B with respect to the electric vector transmission directions 219, 319 of the display polarizer 218 and the additional polarizer 318, and a vertical alignment layer 419A having a pretilt direction 417A with a component 417Ap in the plane of the layer of liquid crystal material 414 oriented (at zero angle) in the electric vector transmission directions 219, 319 of the display polarizer 218 and the additional polarizer 318.

[0155] Compared to the arrangement of Fig. 5A, the alternative arrangement of Fig. 5C includes a constant alignment direction aligned with the edge of the display. Such an arrangement is more convenient and less costly to manufacture. The arrangement in which the alignment direction changes as shown in Fig. 29A advantageously reduces the complexity and cost of manufacturing the vertical alignment layer 419A.

[0156] We now describe the transmission of light propagating through the structure of FIG. 5A.

[0157] 6A is a schematic graph illustrating the polar variation of the transmission of the pole-controlled retarder 300 of FIG. 5B with the first pretilt direction 417 of Table 1 when the angle 617 is 30° for both alignment layers 419A, 419B; FIG. 6B is a schematic graph illustrating the polar variation of the transmission of the pole-controlled retarder 300 of FIG. 5B with the second pretilt direction 417 of Table 1 when the angle 617 is 20° for both alignment layers 419A, 419B; and FIG. 6C is a schematic graph illustrating the polar variation of the transmission of the pole-controlled retarder 300 of FIG. 5B with the second pretilt direction 417 of Table 1 when the angle 617 is 0° for both alignment layers 419A, 419B. [Table 1]

[0158] The polar profile also illustrates the fields of view 65, 67 of users 45, 47, respectively, of a 14 inch landscape 16:9 aspect ratio display, offset laterally by 400 mm, viewed from a distance of 700 mm in the z-axis. In a private mode of operation, it is desirable to provide high image visibility to off-axis user 45 and a high level of image security to off-axis user 47. The non-zero acute angle 617 advantageously provides high transmission for user 45 with field of view 65 and low transmission for user 47 with field of view 67.

[0159] In comparison to the present embodiment, Figure 6C shows that the transmittance at angle 617 of 0 degrees is symmetrical about the on-axis direction, achieving equal reduction in luminance for both users 45, 47, i.e., no off-axis asymmetry. Undesirably, such an arrangement would not achieve different privacy properties for the two off-axis users 45, 47.

[0160] In this embodiment, no reflective polarizer is placed between the output display polarizer 210, 218 and the at least one pole-controlled retarder 300. If such a reflective polarizer 302 were placed between the output polarizer 218 and the polarizer-controlled retarder 300B of Figure 2A, light could be selectively reflected from the display at off-axis angles depending on the driving conditions of the liquid crystal retarder 301. However, the reflection characteristics would be symmetric and therefore would not achieve the desired off-axis reflection characteristics of this embodiment.

[0161] The elevation position 69 of the transmission minimum may be adjusted by a control voltage for operation of the liquid crystal retarder 301. Such position 69 may thus be arranged to provide an optimum user position 47 at a non-zero elevation position, and may be adjusted corresponding to the position of the user 47, for example, by sensing the position of the user 47 and setting the drive voltages by the drivers 350A, 350B accordingly. Advantageously, the freedom of positioning of the user 47 for optimum privacy performance may be increased.

[0162] Next, the desired illumination for the off-axis display 100 of FIG. 4A will be described.

[0163] Figure 7A is a schematic diagram illustrating a side view of a switchable backlight 20 comprising a waveguide arrangement 11, a back reflector 3 and a light redirecting film component 50, outputting light beams 445, 447 with the same angular distributions 455, 457 in first and second lobe directions, and Figure 7B is a schematic diagram illustrating a front view of the waveguide arrangement 11. Features of the embodiments of Figures 7A-B that are not discussed in further detail may be assumed to correspond to features with like reference numbers discussed above, including potential variations of features.

[0164] The waveguide arrangement 11 comprises a waveguide 1 extending across a plane and having first and second opposing light guiding surfaces 6, 8 arranged to guide light along the light guide 1, the second light guiding surface 8 being arranged to guide light by total internal reflection.

[0165] The first and second input ends 2,4 are disposed between the first and second light guide surfaces 6,8 and extend laterally between the first and second light guide surfaces 6,8.

[0166] At least one first light source 15 is arranged to input light 445 into the waveguide 1 via the first input end 2, and at least one second light source 17 is arranged to input light 447 into the waveguide 1 via the second input end 4.

[0167] The waveguide 1 is arranged to cause light 445, 447 from at least one first light source 15 and at least one second light source 17 to exit the waveguide 1 through one of the first and second light guide surfaces 6, 8 by breaking total internal reflection.

[0168] The light redirecting film component 50 comprises an input surface 56 extending across a plane and positioned to receive light exiting the waveguide 1 through the light guide surfaces 6, 8 of the waveguide 1 by blocking total internal reflection, and an output surface 58 facing the input surface 56, the input surface including an array of elongated prismatic elements 52 with ridges 54.

[0169] The waveguide 1 is arranged such that light 445 , 447 from at least one first light source 15 and at least one second light source 17 exits the waveguide 1 with a common angular distribution 455 , 457 .

[0170] Exemplary waveguide structures for use in the embodiment of Figures 7A-B will now be described.

[0171] Figure 8A is a schematic diagram illustrating a front perspective view of the light guide 1 of the waveguide arrangement 11 of Figure 7A including microstructures on a first side and a second side of the light guide 1, and Figure 8B is a schematic diagram showing a front perspective view of an alternative light guide 1 of the waveguide arrangement 11 of Figure 7A including microstructures on the same side of the light guide 1. Features of the embodiments of Figures 8A-B that are not discussed in further detail may be assumed to correspond to features with like reference numbers discussed above, including potential variations of features.

[0172] The waveguide 1 comprises an array of tilted facets 32A, 32B extending along the lateral (x-axis) direction. The waveguide 1 in Fig. 8A includes lenticular microstructures 30, while the waveguide 1 in Fig. 8B includes prismatic elements 29 extending orthogonally to the lateral direction. The facets 32 and elements 29, 30 of the waveguide 1 are arranged to tailor the propagation of the guided light 445, 447 within the waveguide 1 such that some light escapes the waveguide 1 by blocking internal reflections.

[0173] FIG. 9A is a schematic diagram illustrating a front perspective overview of a light redirecting film component 50 for the backlight 20 of FIG. 7A.

[0174] Each of the prismatic elements 52 includes a pair of elongated facets 53 defining therebetween a ridge 54. The ridges 54 extend laterally parallel across the plane, and the ridges 54 are straight. The output surface 58 is planar.

[0175] 9B is a schematic diagram illustrating a side view of a light redirecting film component 50. In this embodiment, the facet angle of each facet 53, defined between the facet normal and the plane normal, is between 40° and 70°, preferably between 47.5° and 62.5°. Advantageously desired positions for off-axis users 45, 47 with high brightness and / or high security factor S may be provided as further described below.

[0176] The facets 53 on either side of the ridge 54 have different facet angles defined between the facet normal and the plane normal. Advantageously, the light 445, 447 is directed towards different off-axis positions with respective angular distributions 455, 457.

[0177] FIG. 9C is a schematic diagram showing a front perspective overview of an alternative light redirecting film component 50 surface suitable for the backlight 20 of FIG. 7A.

[0178] The ridges 54 and facets 53A, 53B include meanderings that provide some light diffusion and increase the size of the angular distributions 455, 457. Advantageously, the uniformity of the display may be increased. The visibility of artifacts resulting from manufacturing defects in the waveguide 1 may be reduced, advantageously improving yield and reducing costs. The visibility of defects from damage in use of the waveguide 1 may be reduced, advantageously increasing lifetime.

[0179] 10 is a schematic graph illustrating polar variations in the brightness output of the backlight 20 of FIG. 7A , operating to direct light to a first user 45 and provide a private image to a second user 47. Such an arrangement is provided by light source 15 without light from light source 17. Advantageously, user 45 sees a high brightness image and user 47 sees a low brightness image. Such an arrangement may be used to provide a low stray light image to passenger 45 for nighttime operation.

[0180] FIG. 11 is a schematic graph illustrating the polar variation in front surface reflectance of the display device 100 arrangement of FIG. 1A resulting from the Fresnel reflectance of a single surface in air.

[0181] Fig. 12 is a schematic graph showing polar variation of visual security level S in a privacy operation mode of the display device 100 of Fig. 1A, the backlight 20 luminance characteristic of Fig. 10, where a first polar controlled retarder 300A includes the transmission characteristic of Fig. 6A, and a second polar controlled retarder 300B has the same prescription as retarder 300A, but the alignment layer is reflected about the horizontal axis. Advantageously, improved symmetry is achieved in the direction orthogonal to the lateral (elevation) direction.

[0182] The security factor S is the value Y measured in nits that is half the illuminance I measured in lux. max The images are presented relative to the front luminance of the display device 100.

[0183] Advantageously, user 45 has a field of view 65 with a security factor S<0.1, which provides high image visibility across the entire display 100. Advantageously, user 47 has a field of view 67 with a security factor S≧1.5 for all image areas and S≧1.8 for some display areas, which provides high image security, with at least some images not visible to user 47 across the entire display area.

[0184] Advantageously, an off-axis privacy display is provided for vehicle passengers 45. The driver 47 may have substantially no visibility of the content of the image data seen by the passengers, such as entertainment content.

[0185] It may be desirable to switch the display 100 so that it is visible to the driver.

[0186] Figures 13A-B are schematic graphs showing polar variations in the luminance output of the backlight 20 of Figure 7A operated to direct light to first and second users 45, 47. Figure 13A illustrates the output from operation of only light source 17, and Figure 13B illustrates the output from operation of both light sources 15, 17.

[0187] The embodiment of Fig. 13A may be used to achieve a low stray light display while providing desired illumination to user 47. The embodiment of Fig. 13B may be used to achieve visibility of the display to both users. Such an embodiment may include a pole controlled delay 300 driven for wide angle operation. In an alternative embodiment of the present disclosure, the pole controlled delay 300 may be omitted.

[0188] FIG. 14 shows polar variations in visual security level S in a dual user operating mode for the display device 100 of FIG. 1A, and a value Y measured in nits which is half the illuminance of a value I measured in lux. max 13B with the front luminance of the display device 100, where the polar controlled retarders 300A, 300B, 300C are driven for high wide angle transmission. Advantageously, high image visibility is achieved over a wide polar range for the user 45, 47.

[0189] It may be desirable to increase the uniformity of brightness across the backlight 20 .

[0190] Figure 15 is a schematic diagram illustrating a side view of an alternative switchable backlight 20 with a waveguide arrangement 11 including two waveguides 1A, 1B arranged in series, a back reflector 3 and a light redirecting film component 50, emitting light in first and second lobe directions 445, 447. Features of the embodiment of Figure 15 that are not discussed in further detail may be assumed to correspond to features with like reference numbers discussed above, including potential variations of features.

[0191] The waveguide arrangement 11 includes a first and a second waveguide.

[0192] The first waveguide 1A comprises opposing first and second light guide surfaces 6A and 8A extending across a plane and arranged to guide light along the light guide 1A, with the second light guide surface 8A arranged to guide light by total internal reflection, and a first input end 2A arranged between the first and second light guide surfaces 6A and 8A, the first input end 2A extending laterally between the first and second light guide surfaces 6A and 8A, wherein at least one first light source 15A is arranged to input light 447 into the first waveguide 1A via the first input end 2A, and the first waveguide 1A is arranged to cause light from the at least one first light source 15A to exit the first waveguide 1A via one of the first and second light guide surfaces 6A and 8A by breaking total internal reflection.

[0193] The second waveguide 1B extends across a plane arranged in series with the first waveguide 1A and comprises opposing first and second light guide surfaces 6B and 8B arranged to guide light along the light guide 1B, where the second light guide surface is arranged to guide light by total internal reflection, and a second input end 2B arranged between and extending laterally between the first light guide surface 6B and the second light guide surface 8B.

[0194] The at least one second light source 15B is arranged to input light 445 into the second waveguide 1B via the second input end 2B, the second waveguide 1B is arranged to output light from the at least one second light source 15B from the second waveguide 1B via one of the first light guide surface 6B and the second light guide surface 8B by breaking total internal reflection, and the first and second waveguides 1A, 1B are oriented such that the at least one first light source 15A and the at least one second light source 15B input light 445, 447 into the first and second waveguides 1A, 1B in opposite directions.

[0195] The backlight apparatus 20 comprises a first waveguide 1A extending across a plane, with opposing first and second light guide surfaces 6A and 8A arranged to guide light along the light guide 1A, with the second light guide surface arranged to guide light by total internal reflection, and a reflector 20 disposed between the first waveguide 1A and the first light guide surface 6A and the second light guide surface 8A. a first waveguide 1A having a first input end 2A extending laterally; and at least one first light source 15A arranged to input light 447 into the first waveguide 1A via the first input end 2A, the first waveguide 1A being arranged to cause light from the at least one first light source 15A to exit the first waveguide 1A via at least one of the first light guide surface 6A and the second light guide surface 8A by breaking total internal reflection; a second waveguide 1B extending laterally between the first light guide surface 6B and the second light guide surface 8B, the second light guide surface being arranged to guide light along the light guide 1B by total internal reflection; and a second input end 2B disposed between the first light guide surface 6B and the second light guide surface 8B; and at least one second light source 15B arranged to input light 445 into the second waveguide 1B, the second waveguide 1B arranged to cause light from the at least one second light source 15B to exit the second waveguide 1B through at least one of the first light guide surface 6B and the second light guide surface 8B by breaking total internal reflection, the first waveguide 1A and the second waveguide 1B being arranged such that the at least one first light source 15A and the at least one second light source 15B input light 445,a second light source 15B oriented to input light from the first waveguide 1A to the second waveguide 1B in opposite directions, 447; and a light redirecting film component 50, the light redirecting film component 50 comprising an input surface 56 extending across a plane and an output surface 58 facing the input surface 56, the input surface 56 being positioned to receive output light from the waveguides 1A, 1B through the light guide surfaces of the first waveguide 1A and the second waveguide 1B by breaking total internal reflection, the input surface 56 comprising an array of elongated prismatic elements 52 each having a pair of elongated facets 53 defining a ridge 54 therebetween, the ridges 54 extending laterally across the plane at a non-zero angle.

[0196] Compared to the embodiment of Figure 7A, the stacked waveguides 1A, 1B of Figure 15 may each provide increased uniformity in the orthogonal lateral direction. Advantageously, display uniformity may be improved for both users 45, 47.

[0197] Figure 16A is a schematic graph illustrating polar variations in luminance output of the backlight 20 of Figure 15 operating to direct light to a first user 45 and provide a private image to a second user 47. Advantageously, the size of the distribution 455 can be reduced and greater efficiency can be achieved.

[0198] We now describe a display including two horizontal alignment layers 419A, 419B for the liquid crystal retarders 301A, 301B of FIG. 1A.

[0199] 16B is a schematic graph showing the polar variation of the transmission of the first pole-controlled retarder 300A, as shown in Table 2, where the angles 617A, 617B are 20° and both surface alignment layers 419A, 419B are arranged to provide a horizontal alignment in the adjacent liquid crystal material 414. Advantageously, a horizontal alignment may provide a faster liquid crystal 414 relaxation time than a vertical alignment, increasing resilience to applied mechanical stress. Additionally, a thinner layer 314 may be provided, reducing manufacturing costs and complexity. [Table 2]

[0200] Fig. 16C is a schematic graph showing polar variation of visual security level S in a privacy mode of operation for the display device 100 of Fig. 1A, where the reflection characteristic of Fig. 11, the transmission characteristic of the first pole-controlled retarder 300A of Fig. 16B, and the transmission characteristic of the second pole-controlled retarder 300B of Fig. 16B are reflected about an axis in the lateral direction. Advantageously, improved symmetry in the elevation direction is achieved.

[0201] Value Y measured in nits is half the illuminance of value I measured in lux max is the front luminance of the display device 100.

[0202] 16C embodiment, the positions of users 45, 47 are shown as, for example, with the displays slightly tilted towards user 47 and at different off-axis angles laterally, so that fields of view 65, 67 are not at the same polar angle. Advantageously, the desired nominal position and tilt angle of the displays can be compensated for to achieve optimal privacy for user 47.

[0203] In an alternative embodiment (exemplary embodiment not provided), each of the surface alignment layers 419A, 419B is arranged to provide a vertical alignment in the adjacent liquid crystal material 414, the surface alignment layers 419A, 419B having a pretilt with a pretilt direction 417 with components 417Ap, 417Bp in the plane of the layer 314 of liquid crystal material 414 that make non-zero acute angles 617A, 617B with respect to the electric vector propagation directions 211, 219, 319 of the display polarizers 210, 218 and additional polarizer 318. Advantageously, such a polar retarder has a wide angle mode with zero drive voltage and therefore reduced power consumption in a mode in which image data from the display is seen by both users 45, 47.

[0204] FIG. 16D is a schematic graph illustrating the polar variation of the luminance output of the backlight 20 of FIG. 15 , which is operated to direct light to first and second users 45, 47, and FIG. 16E is a schematic graph illustrating the polar variation of the visual security level S in a dual user mode of operation for the display device 100 of FIG. 1A , and the value Y measured in nits, which is half the illuminance of the value I measured in lux. max 16D with the front luminance of the display device 100, where the pole-controlled retarders 300A, 300B, 300C are driven for high wide angle transmission.

[0205] Advantageously, high image visibility is provided to both users 45, 47, with the area being further expandable by adding a diffuser in the optical stack 5 of FIG. 1A.

[0206] Next, alternative arrangements for the privacy display are described.

[0207] Fig. 17A is a schematic diagram illustrating a top view of a privacy display 100 for use by a passenger of an automobile 650. Features of the embodiment of Fig. 17A that are not discussed in further detail can be assumed to correspond to features with like reference numbers discussed above, including potential variations of features.

[0208] 4A, the alternative embodiment of FIG. 17A includes a display 100 positioned to provide high image visibility to passengers 45 and high image invisibility to driver 47. Of particular concern with respect to regulatory compliance is the driver 47 attempting to move to the center of the vehicle 650 to view the image data on display 100. It is therefore desirable to provide high image security at a polar location relatively close to the optical axis 199 of display 100.

[0209] FIG. 17B is a schematic graph illustrating polar variation of luminance output for an alternative backlight of FIG. 15 operating primarily to direct light toward passengers. FIG. 17B differs from FIG. 16A in that the output is substantially on-axis in the privacy mode of operation. With reference to FIG. 15, the prisms of turning film components 50 may be adjusted to achieve such illumination for light from light source 15B. The backlight 20 of FIG. 15 may also be arranged with other arrangements of components as illustrated here.

[0210] Figure 17C is a schematic diagram showing a front perspective overview of a switchable privacy display 100 comprising a transmissive spatial light modulator 48. Features of the embodiment of Figure 17C that are not discussed in further detail can be assumed to correspond to features with like reference numbers discussed above, including potential variations of features.

[0211] Compared to the arrangement of FIG. 1A, the alternative arrangement of FIG. 17C differs in several respects.

[0212] In a first point, an additional polarizer 318A is placed on the output side of the display polarizer 218, and a pole-controlled retarder 300A is placed between the output display polarizer 218 and the additional polarizer 318A.

[0213] In a second embodiment, the reflective polarizer 302 is disposed between the display polarizer 218 and the pole-controlled retarder 300A. The electric vector transmission directions of the display polarizer 218, the reflective polarizer 302, and the additional polarizer 318A are parallel. In a public mode of operation, the reflective polarizer 302 is disposed so as not to substantially reflect light for on-axis and off-axis external illumination. Advantageously, no increase in reflectivity is provided. In a privacy mode of operation, light rays passing through the additional polarizer 318 and incident on the reflective polarizer 302 are reflected with high reflectivity for directions substantially parallel to the optical axis 199 (z-direction) but tilted relative to the optical axis 199. Advantageously, a security factor can be increased for off-axis line-of-sight directions, and a low reflectivity can be achieved for primary users closer to the optical axis 199.

[0214] In a third embodiment, a pair of waveguides 1A, 1B and respective oriented light sources 15A, 15B are arranged to provide output illumination in directions 445, 447, respectively. Advantageously, increased brightness and uniformity may be provided compared to the arrangement of Figure 1A.

[0215] Figure 17D is a schematic graph illustrating the polar variation of the transmission of a first pole-controlled retarder with non-rotated alignment layers, i.e., angle 617 is zero across the alignment layers 417A, 417B of the pole-controlled retarder of display 100, and Figure 17E is a schematic graph illustrating the polar variation of the transmission of a second pole-controlled retarder with non-rotated alignment layers, i.e., angle 617 is zero across the alignment layers 417A, 417B of the pole-controlled retarder of display 100.

[0216] FIG. 17F shows polar variations in the visual security level S in the privacy operation mode of the display device of FIG. 17C, and a value Y measured in nits, which is half the illuminance of the value I measured in lux. max 17D-E with the display front luminance.

[0217] FIG. 17G is a schematic graph illustrating the polar variation of the transmission of a first pole-controlled retarder with a rotated alignment layer, and FIG. 17H is a schematic graph illustrating the polar variation of the transmission of a second pole-controlled retarder with a rotated alignment layer, i.e., angle 617 is a non-zero acute angle.

[0218] The angle 617 can be between 10 degrees and −10 degrees from the transmission direction 319 of the additional polarizer 318 across the at least one alignment layer 417A, 417B of the polar-controlled retarder of the display 100. In the illustrative example of Figures 17G-I, the angle 617 is +5 degrees from the transmission direction 319 of the additional polarizer 318 across the at least one alignment layer 417A, 417B of the polar-controlled retarder of the display 100.

[0219] FIG. 17I shows polar variations in the visual security level S in the privacy operation mode of the display device of FIG. 17C, and a value Y measured in nits, which is half the illuminance of the value I measured in lux. max 17G-H with the display front luminance.

[0220] Comparing Figures 17F and 17I illustrates a polar position 448 of light ray 447 as illustrated in Figure 17A. For the unrotated orientation of Figure 17F, the security factor is less than 1.5 at position 448. For the rotated orientation of Figure 17I, the security factor is greater than 1.8. Advantageously, the security factor is increased to a level where the image is not visible to the driver when attempting to view the display. Such an arrangement provides a desirable increase in safety against changes in the position of driver 47 from the nominal seating position.

[0221] It may be desirable to provide light sources 15, 17 in the top and bottom bezels of the display 100 rather than in the left and right bezels.

[0222] Figure 18A is a schematic diagram illustrating a front view of an alternative waveguide arrangement 11, and Figure 18B is a schematic diagram illustrating a rear perspective view of a light redirecting film component 50 for use in a backlight 20 including the waveguide arrangement 11 of Figure 18A. Features of the embodiments of Figures 18A-B that are not discussed in further detail can be assumed to correspond to features with like reference numbers discussed above, including potential variations of features.

[0223] Thus, the backlight device 20 comprises a light guide 1 extending across a plane, the light guide 1 comprising opposing first and second light guide surfaces 6 and 8 arranged to guide light along the light guide 1, the second light guide surface arranged to guide light by total internal reflection, first and second input ends arranged between the first and second light guide surfaces 6 and 8 and extending laterally between the first and second light guide surfaces 6 and 8, at least one light source 15 arranged to input light 445 into the waveguide 1 via the first input end 2 and at least one second light source 17 arranged to input light 445 into the waveguide 1 via the second input end 4, the light guide 1 comprising: a first light source 15 and a second light source 17 that output light from the at least one light source 15 and the at least one light source 17 out of the waveguide 1 through one of the first light guide surface 6 and the second light guide surface 8 by breaking total internal reflection; and a light redirecting film component 50 comprising an input surface 56 arranged to receive light 445, 447 outputting the waveguide 1 through the light guide surface of the waveguide 1 by breaking total internal reflection, the input surface extending across a plane, and an output surface 58 facing the input surface 56, the input surface 56 comprising an array of elongated prismatic elements 52 comprising a pair of elongated facets 53A, 53B defining a ridge 54 therebetween, the ridge 54 extending laterally across the plane at a non-zero angle γ.

[0224] 7A-B and 15, the ridges 54 extend across the plane at a non-zero angle γ to the lateral direction. The ridges 54 extend into the plane at an angle γ of 55° or less from the lateral direction. Such an arrangement can be used with the single waveguide 1 of FIG. 7A or with two stacked waveguides 1A, 1B of FIG. 15.

[0225] Advantageously, the side bezel width of the display is reduced.

[0226] It may be desirable to provide increased brightness reduction to the user 47. Next, an arrangement will be described with first, second and third pole-controlled retarders 300A, 300B, 300C disposed between the polarizer 210 and additional polarizers 318A, 318B and 318C.

[0227] 19A is a schematic graph illustrating the polar variation of the luminance output of the backlight 20 of FIG. 18A , operative to direct light to a first user 45 and provide a private image to a second user 47; FIG. 19B is a schematic graph illustrating the polar variation of the transmission of a first pole-controlled retarder 300A; FIG. 19C is a schematic graph illustrating the polar variation of the front surface reflectance of a display device 100 comprising the backlight 20 of FIG. 18A ; FIG. 19D is a schematic graph illustrating the polar variation of the transmission of a second pole-controlled retarder 300B; FIG. 19E is a schematic graph illustrating the polar variation of the transmission of a third pole-controlled retarder 300C; and FIG. 19F is a schematic graph illustrating the polar variation of the visual security level S in a privacy mode of operation of the display device 100 of FIG. 1A , and a value Y measured in nits which is half the illuminance of a value I measured in lux. max 19A to 19E along with the front luminance of the display device 100.

[0228] Pole controlled delays 300A, 300B, 300C include the exemplary embodiment of Table 1 where angles 617AA, 617AB are 30°, 617BA, 617BB are 20°, and 617CA, 617CB are 40°, respectively. Advantageously, the size of the image blind area increases for all image data (S≧1.8) and user 45 sees an image with high image visibility.

[0229] FIG. 20A is a schematic graph illustrating the polar variation of the luminance output of the backlight 20 of FIG. 15 , which is operated to direct light towards a second user 47, and FIG. 20B is a schematic graph illustrating the polar variation of the visual security level S in a low stray light mode of operation for the display device 100 of FIG. 1A , and the value Y measured in nits, which is half the illuminance of the value I measured in lux. max20A with the front luminance of the display device 100, where the polar controlled retarders 300A, 300B, 300C are driven for high wide angle transmission. Advantageously, the user 47 can be provided with high image visibility over a wide polar range.

[0230] FIG. 21A is a schematic graph illustrating the polar variation of the luminance output of the backlight 20 of FIG. 15 , which is operated to direct light to a first and a second user 45, 47, and FIG. 21B is a schematic graph illustrating the polar variation of the visual security level S in a dual user mode of operation for the display device 100 of FIG. 1A , and the value Y measured in nits, which is half the illuminance of the value I measured in lux. max 21A with the front luminance of the display device 100, where the polar controlled retarders 300A, 300B, 300C are driven for high wide angle transmission. Advantageously, a user 45, 47 can be provided with high image visibility over a wide polar range.

[0231] It may be desirable to provide greater viewing freedom to users 47.

[0232] Figure 22 is a schematic diagram showing a side view of an alternative switchable backlight 20 comprising a waveguide arrangement 11 comprising a waveguide 1 with asymmetric facets 32, 36, a rear reflector 3 and a light redirecting film component 50 and outputting light beams 445, 447 in first and second directions with different angular distributions 455, 457, and Figure 23 is a schematic diagram illustrating a front perspective overview of the light guide 1 of the waveguide arrangement 11 of Figure 22 with microstructures on the first and second sides of the light guide 1.

[0233] Features of the embodiment of FIG. 22 that are not discussed in further detail can be assumed to correspond to features bearing like reference numbers discussed above, including potential variations of features.

[0234] The waveguide 1 is arranged such that light 445, 447 from at least one first light source 15 and at least one second light source 17 exits the waveguide 1 with different angular distributions 455, 457. Compared to the arrangement of Figure 7A, the waveguide 1 comprises a vertical facet 36 instead of the gently sloping facet 32B. A light source 17 is provided at the second end and light escapes through the facet 36 with an increased angular distribution 447 compared to the angular distribution 445.

[0235] Figure 24A is a schematic graph illustrating the polar variation in luminance output of the backlight 20 of Figure 22 operating to direct light to a first user 45 and provide a private image to a second user 47, Figure 24B is a schematic graph illustrating the polar variation in transmission of a first pole-controlled retarder 300A having angles 617AA, 617AB of 30°, Figure 24C is a schematic graph illustrating the polar variation in front reflectance of a display device 100 equipped with the backlight 20 of Figure 22, and Figure 24D is a schematic graph illustrating the polar variation in transmission of a second pole-controlled retarder 300B having angles 617BA, 617BB of 30° and inverted about a horizontally extending axis.

[0236] FIG. 24E illustrates the polar variations of the visual security level S in the privacy mode of operation of the display device 100 of FIG. 1A and the value Y measured in nits, which is half the illuminance of the value I measured in lux. max 24A-D with the front luminance of the display device 100. Advantageously, high image visibility is provided to the user 45 and high image security is provided to the user 47 over a wide polar range.

[0237] Next, other operation modes will be described.

[0238] Figure 25A is a schematic graph illustrating the polar variation of the luminance output of the backlight 20 of Figure 22 operated to direct light to a user 47, and Figure 25B is a schematic graph illustrating the polar variation of the luminance output of the backlight 20 of Figure 22 operated to direct light to users 45, 47, with the pole controlled retarder 300 arranged to provide wide angle transmission. Figure 25A illustrates the luminance distribution of a low stray light mode of operation for user 47, and Figure 25B shows the luminance distribution for dual users 45, 47.

[0239] FIG. 26 shows the polar variations of the visual security level S in the public mode for the display device 100 of FIG. 1A and the value Y measured in nits, which is half the illuminance of the value I measured in lux. max 25B with the front luminance of the display device 100, where the pole-controlled retarder 300 is arranged to be driven for high wide-angle transmission. Advantageously, the freedom of movement of the user 47 is increased compared to FIGS. 13A, 17A, 20A, and 21A.

[0240] An alternative waveguide structure for use in the backlight 20 of FIG. 22 will now be described.

[0241] 27A-B are schematic diagrams showing a front perspective overview of an alternative optical waveguide 1 for the waveguide arrangement 11 of FIG. 22 with microstructures on the same side of the optical waveguide 1. Features of the embodiment of FIG. 27A-B that are not discussed in further detail can be assumed to correspond to features with equivalent reference numbers discussed above, including potential variations of features. Compared to the waveguide of FIG. 23, the waveguide 1 of FIG. 27A-B is provided with a microstructure on a single surface of the waveguide. In other respects, the operating principle is similar. A surface can be provided on a single surface of the waveguide 1, advantageously realizing reduced costs and complexity.

[0242] It may be desirable to provide different outputs to different areas of a display.

[0243] Figure 28 is a schematic diagram showing a top view of several elements of segmented backlight 20. Features of the embodiment of Figure 28 that are not discussed in further detail can be assumed to correspond to features with like reference numbers discussed above, including potential variations of features.

[0244] The first light source 15 comprises first and second portions 15A, 15B and the second light source 17 comprises first and second portions 17A, 17B. The waveguide 1 may be of the type illustrated elsewhere herein or may be a first and second waveguide 1A, 1B as illustrated, for example, in Figure 16B, in which case light sources 15AA, 15AB and light sources 15BA, 15BB are provided at respective ends of the waveguides.

[0245] A light ray 415A propagating in the waveguide 1 is input with a laterally expanding cone. Microstructures on the surfaces 6, 8 of the waveguide 1 adjust the propagation direction of the light ray 415A to achieve some collimation laterally, and thus provide an illumination area 475A with a limited extent in the laterally direction. Such collimation can achieve partial illumination of the backlight in an area 475A determined by the position of the light source along the first input end 2.

[0246] Similarly, light ray 417B propagating in waveguide 1 is input with a laterally expanding cone. A degree of collimation is provided laterally, and thus an illumination area 477B is provided with a laterally limited extent. Such collimation can achieve partial illumination of the backlight in area 477B determined by the position of the light source along input end 4.

[0247] By controlling light sources 15A, 15B and 17A, 17B, the directionality of the output can be different for different regions of the backlight 20. In an illustrative example, in one mode of operation, the left side of the display can be positioned for high image visibility to the driver 47 and passenger 45, and the right side of the display can be provided for a high image security factor for the driver 47 with high image visibility to the passenger 45. In other illustrative modes of operation, the entire display can be positioned to be visible to both occupants, or the entire display can be positioned to be dedicated to the driver.

[0248] The number of light sources 15A-N can be adjusted to increase the number of addressable areas of the display control.

[0249] Next, embodiments for increasing the uniformity of the perceived brightness and security factor across the fields of view 65, 67 will be described.

[0250] Figure 29A is a schematic diagram illustrating a front view of one alignment layer 419B having a pretilt direction 417 with a component 417Bp in the plane of the layer 314 of liquid crystal material 414 that makes a non-zero acute angle 617B with respect to the electric vector transport direction of the polarizer and additional polarizer 318 of the display device 100, which varies across the plane of the alignment layer 419. Features of the embodiment of Figure 29A that are not discussed in further detail may be assumed to correspond to features with like reference numbers discussed above, including potential variations of features.

[0251] 5B, angle 617B varies such that left hand angle 617BL is larger than central angle 617BC which is larger than right hand angle 617BR. Non-zero acute angle 617B therefore has a mean value equal to central angle 617BC and is therefore itself a non-zero acute angle.

[0252] Generally, at least one of the surface alignment layers 419A, h419B has a pretilt having a pretilt direction 417 with components 417Ap, 417Bp in the plane of the layer 314 of liquid crystal material 414 that varies monotonically along a predetermined axis across the surface alignment layer 419 and that makes a non-zero acute angle 617 with respect to the electric vector transmission directions 211, 219, 319 of the display polarizers 210, 218 and the additional polarizer 318.

[0253] Figure 29B is a schematic diagram illustrating pupil formation of a pole-controlled retarder and a graph illustrating the polar variation of transmission with position across the plane of the alignment layer 419. Features of the embodiment of Figure 29B that are not discussed in further detail can be assumed to correspond to features with like reference numbers discussed above, including potential variations of features.

[0254] Illustrated are polar angles 693L, 63C, 63R of points across the display field of view as seen by user 45 at optical window 26A. Angle 617Bp may be provided such that the luminance to user 45 is optimized for each viewing angle. Advantageously, luminance uniformity across display 100 is increased.

[0255] Alternatively, the illuminance provided to the user 47 at the nominal viewing position of viewing window 26B can be minimized to optimize the uniformity of the security factor across window 26B.

[0256] In this disclosure, the optical window 26A is aligned with the display 100 at a window distance Z in the window plane 197, i.e., from the illumination device. w The optical window 26A may also be referred to as an optical pupil. Viewing from a position within the optical window provides a beam of light having common or substantially common optical characteristics from the entire display device 100.

[0257] The use of the term optical window 26 in this embodiment is distinct and different from the use of the term window when used to refer to sheets or panes of other transparent material, such as glass or plastic, for use in house windows, car windows and windshields, and other types of protective windows, which sheets or panes do not contribute to creating the desired viewing area with improved uniformity as described herein.

[0258] Next, pupil illumination of the display device 100 will be described.

[0259] Figure 30A is a schematic diagram illustrating a side view of a pupil-shaped backlight 20 for a first light source 15, and Figure 30B is a schematic diagram illustrating a side view of the operation of a variable tilt facet 53 of a light redirecting film component 50 of the pupil-shaped backlight 20 for a first light source 15. Features of the embodiments of Figures 30A-B that are not discussed in further detail may be assumed to correspond to features with like reference numbers discussed above, including potential variations of features.

[0260] Grazing output light rays 445G from light source 15 are output from waveguide 1 at a cone angle 445 and a substantially uniform output angle across the plane of waveguide 1.

[0261] The prismatic elements 52 of the light redirecting film component 50 are positioned to deflect light 445G exiting the waveguide 1, the deflection varying in at least one direction across the plane.

[0262] Near the top edge of the display, ray 445G has a facet angle β U is reflected by facet 53BU with facet angle α U Surface normal direction n AU 4, resulting in output ray 445U being reflected by total internal reflection at facet 53AU at window distance Z from backlight apparatus 20. wAIn at least one cross-section, the size of the window 26 in the window plane 197A is determined by the angular width of the light cone 455, which may be, for example, by the maximum intensity at half the full width of the angular distribution 455.

[0263] Similarly, near the center of the display, ray 445G has a facet angle β C It is refracted by facet 53BC with facet angle α C Surface normal direction n AC 4C. The output ray 445C is reflected by total internal reflection at facet 53AC of backlight apparatus 20 at window distance Z. wA 197A toward the window 26A at the window plane 197A.

[0264] Similarly, near the bottom edge of the display, ray 445G has a facet angle β D is refracted by facet 53BD with facet angle α D Surface normal direction n AD 4D. The output ray 445D is reflected by total internal reflection at facet 53AD of backlight apparatus 20 at window distance Z. wA oriented toward window 26A in window plane 197A.

[0265] The facet angles α, β vary continuously with position across the length of the light redirecting film component 50. The deflected light rays 445U, 445C, 445D are directed towards a common optical window 26A in front of the backlight apparatus 20.

[0266] The operation of the light redirecting film piece with ridges 54 arranged in a straight line will now be further described.

[0267] Figure 30C is a schematic diagram showing a rear perspective overview of light output from a pupil-like linear light redirecting film component 50 including variable tilt facets 53 of Figures 30A-B. Features of the embodiment of Figure 30C that are not discussed in further detail can be assumed to correspond to features with like reference numbers discussed above, including potential variations of features.

[0268] 30C illustrates that the ridges 54 extend along an array of lines across the plane in which the input face 56 extends. The light redirecting film piece 50 has a rectangular shape across the plane, with the lateral direction being along the major or minor axis of the rectangle.

[0269] The angle of each facet 53, defined between the normal to the facet 53 and the normal to the plane, corresponds to a direction perpendicular to the lateral direction such that the deflection varies in a direction perpendicular to the optical axis 199, which is the normal to the plane.

[0270] The lines are straight and the angle of each facet 53 defined between the normal to the facet 53 and the normal to the plane varies across the array such that the deflection varies in a direction perpendicular to the optical axis 199 which corresponds to a direction perpendicular to the lateral direction.

[0271] The lines of the array have an arithmetic mean adjacent angle projected onto a plane of 0° from the horizontal direction, ie the lines are parallel to the x-axis direction, which in this embodiment is horizontal.

[0272] Thus, light ray 445G is directed by light redirecting film component 50 towards common window 26A. Light rays 445UL, 445CL, 445DL from the top, center and bottom of the left edge region of the light redirecting film are positioned in window 26A at positions corresponding to the lateral position of the left edge region in the lateral direction. Light rays 445UC, 445CC, 445DC from the top, center and bottom of the central region of the light redirecting film are positioned in window 26A at lateral positions corresponding to the lateral position of the central region in the lateral direction. Light rays 445UR, 445CR, 445DR from the top, center and bottom of the right edge region of the light redirecting film are positioned in window 26A at lateral positions corresponding to the lateral position of the right edge region in the lateral direction.

[0273] In the embodiment of Figure 30C, there is no deflection in the lateral direction, and therefore the optical window 26A has an extent in the lateral direction determined by the width of the light redirecting film component 50 and the size of the solid angle of the angular distribution 455, with the width being determined by the size of the solid angle of the angular distribution 455. The size of the optical window 26A at the window plane 197A can also be controlled by a diffusing means, such as a diffuser, in the display's optical stack 5, as illustrated in Figure 1A.

[0274] The embodiment of Figure 30C further illustrates that the common optical window 26A is offset from an optical axis 199 that extends from the center of the light redirecting film piece 50 perpendicular to the plane. Thus, the point 198 where the optical axis 199 intersects the window plane 197A is a distance Z from the point 196 where the light ray 445CC intersects the window plane 197A. OA As will be explained below, off-axis illumination positions can be achieved with increased uniformity across backlight apparatus 20.

[0275] It may be desirable to provide an optical window 26 with a reduced extent in a direction perpendicular to the lateral direction.

[0276] Figure 31A is a schematic diagram illustrating a front perspective view of the operation of facets 53 of a curved light redirecting film component 50 of a pupil-like backlight 20 for light from a first light source 15, and Figure 31B is a schematic diagram illustrating a back perspective view of light output from a curved light redirecting film component 50 including uniform tilt facets 53. Features of the embodiments of Figures 31A-B that are not discussed in further detail may be assumed to correspond to features with like reference numbers discussed above, including potential variations of features.

[0277] Figures 31A-B illustrate an alternative embodiment of the arrangement of Figures 30A-C. In comparison to the arrangement of Figure 30C, the line of ridges 54 is curved across the plane, so that the deflection varies in a direction orthogonal to the optical axis 199 perpendicular to the plane, which corresponds to the lateral direction.

[0278] The curved facets have a surface normal direction n that varies across the width of the light redirecting film 50. AR , n AC , n AL , i.e., the surface normal direction varies laterally along the ridge, such that the light ray 445G from the waveguide 1 is at a distance Z WB , directed towards the common window 26B in the window plane 197B.

[0279] The optical window 26B has a cone width defined by the cone 457 in a direction perpendicular to the lateral direction and has an extent determined by the width of the cone 457 and the height of the light redirecting film component 50, and is therefore perpendicular to the optical window 26A illustrated in FIG. 30C.

[0280] In the embodiment of FIG. 31B, the center of the optical window 26B is shown aligned with the center of the backlight device 20, i.e., the common optical window 26 aligns the optical axis 199 extending from the center of the light redirecting film to a plane. OB is zero and the lines of the array have an arithmetic mean adjacent angle projected onto a plane inclined at 0° from the horizontal direction.

[0281] The direction of the lines in the array is described by the facet peak 54 rotation γ, where γ R is the right rotation of the display, and γ C is the central rotation, γ L is the rotation of the left edge. The arithmetic mean adjacent angle projected onto the plane is the mean rotation across the transverse direction γ.

[0282] Alternatively, the lines of the array may have an arithmetic mean contact angle that is inclined from the horizontal direction by more than 0°. Such an arrangement may be used with a non-zero offset Z OB Advantageously, the position of the nominal window 26B may be set for off-axis illumination with desirable characteristics, as described further below.

[0283] It may be desirable to provide a common optical window at all points across the backlight apparatus 20 .

[0284] 31C is a schematic diagram showing a rear perspective overview of light output from a curved light redirecting film component 50 with variable tilt facets 53 with a common optical window across the lighting device. Features of the embodiment of FIG. 31C that are not discussed in further detail can be assumed to correspond to features with like reference numbers discussed above, including potential variations of features.

[0285] Faceted surfaces 53 are provided to achieve the behavior of light ray 445G as illustrated in both Figures 30B and 31 A. As the angle of each facet 53, defined between the normal of the facet 53 and the normal of the plane, varies across the array, the deflection further varies in a direction perpendicular to the optical axis 199 in a corresponding direction perpendicular to the lateral direction, thereby directing the deflected light towards a further common optical window 26AB in front of the backlight apparatus 20.

[0286] The first-mentioned common optical window 26A and the further common optical window 26B are defined at the same distance in front of the backlight device 20 to provide a common optical window 26AB. Advantageously, improved uniformity of output is achieved across the backlight device 20 from a viewing position within the optical window 26AB.

[0287] FIG. 31D is a schematic diagram illustrating a rear perspective view of light output from a curved light redirecting film component 50 comprising variable tilt facets 53 with first and second different optical window distances 197A, 197B.

[0288] The first-mentioned common optical window 26A and the further common optical window 26B are arranged at different distances Z in front of the backlight device 20. WA , Z WB As further noted above, the offset ZOA may be provided by angular selection of the facets 53, and the offset ZOB may be achieved by selection of the arithmetic mean adjacent angle projected onto the inclined plane of the line formed by the array ridges 54. Advantageously, enhanced uniformity at two different nominal observation distances and angular positions may be achieved.

[0289] The operation of the backlight device 20 in the backlight 20 of the display device 100 will now be described. For the purposes of this description, the backlight 20 will further be referred to as a pupil-shaped backlight, i.e., a backlight providing an optical window 26.

[0290] FIG. 32A is a schematic diagram illustrating a side view of the operation of a light redirecting film component 50 with variable tilt facets 53 in a pupil-like backlight 20. As shown in FIG.

[0291] The light source array 15 is positioned at the bottom edge of the backlight and light rays 445L, 445R are directed into the optical window 26A, which has a lateral extent as described above. In typical operation, the window distance between the backlight 20 and the window plane 197 is positioned to be greater than the normal observer position.

[0292] In an illustrative example, a laptop display with a diagonal size of 14 inches is viewed from a window distance Z of 700 mm. WA while the nominal observer position is at a distance Z of 500 mm. V at the plane 145. The window distance Z WA may be positioned to be at a nominal voyeur distance, which may be, for example, 700 mm, depending on the design of the waveguide 1 and facet 53.

[0293] FIG. 32B is a schematic diagram showing a top view of the operation of a curved light redirecting film component 50 in a pupil-shaped backlight 20, where the user 45 is laterally offset.

[0294] As will be further explained in the illustrative examples below, the arrangement of FIGS. 32A-B advantageously provides improved brightness uniformity across the backlight 20 for at least one of the users 45, 47.

[0295] In operation, the user 45 sees an image with improved uniformity compared to a non-pupillary backlight (i.e., a backlight that does not provide a common optical window 26, in other words, a backlight that provides a common optical window at optical infinity). Thus, the light rays 445L, 445R are directed to the optical window 26 with substantially the same brightness. By increasing the range of positions of the observer 45, the uniformity across the display area can be advantageously improved. A further improvement in the security factor in the privacy mode of operation can be realized by increasing the range of positions of the user 47.

[0296] Features of the embodiments of FIGS. 32A-B that are not discussed in further detail can be assumed to correspond to features bearing like reference numbers discussed above, including potential variations of features.

[0297] FIG. 33 is a schematic diagram showing a side view of the operation of the emissive spatial light modulator of FIG. 3. The aperture 419 is offset by a distance e from each aligned emissive pixel 220, 222, 224. Considering pixel 222, light 445 is directed through aperture 419A to optical window 26A, and light 447 is directed through aperture 419B to optical window 26B. Such an arrangement can provide optical windows 26A, 26B at nominal user 45, 47 locations. Considering FIG. 3, the pole-controlled retarder 300 is arranged in one operating mode to advantageously achieve high image visibility for user 45 and high image security level S for user 47, as described elsewhere herein. Advantageously, an emissive display such as a CSD can be provided.

[0298] Next, the operation of the pole controlled delay circuit of FIGS. 1A and 1B will be described.

[0299] FIG. 34 is a schematic diagram illustrating the propagation of light through the pole-controlled delay 300 of FIG. 1B in a privacy (narrow angle) mode of operation in a side view, and FIG. 35 is a schematic diagram illustrating the propagation of light through the pole-controlled delay 300 of FIG. 1B in a privacy (narrow angle) mode of operation in a side view.

[0300] When the layer 314 of liquid crystal material 414 is driven in the privacy mode of operation, the retarder 300 provides no overall transformation of the polarization component 360 along an axis 400 that is tilted with respect to the normal 199 of the plane of the pole-controlled retarder 300. In this discussion, polarization component refers to the polarization state resulting from the phase and amplitude of two orthogonal components.

[0301] The polarizer 219 provides a linearly polarized component 360 that is incident on the pole-controlled retarder 300. As shown in Figure 5A, the liquid crystal retarder 301 has a surface alignment layer 419B with a pretilt having a pretilt direction 417B with a component 417Bp in the plane of the layer of liquid crystal material 414 that makes a non-zero acute angle 617B with respect to the electric vector propagation direction of the display polarizer 218 and the additional polarizer 318.

[0302] Such a non-zero acute angle 617 provides an axial direction 400 at an acute angle with respect to the normal 199 of the pole-controlled retarder 300, along which substantially no phase difference is provided to the incident polarization component 360, and the transmitted polarization component 362 is the same as the polarization component 360. The additional polarizer 318 transmits the polarization component 360, and high intensity transmission is achieved along the axis 400.

[0303] Considering an axis 402 tilted toward the user 47 at an acute angle orthogonal to the plane of the retarder, the polar controlled retarder 300 further provides an overall transformation of the polarization component 360 into a ray 447 passing along the axis 402. At a minimum, the polarization component 361 is transformed into a linear polarization component 364, which is absorbed by the additional polarizer 318. More generally, the polarization component 361 is transformed into an elliptically polarization component that is partially absorbed by the additional polarizer 318. Thus, the transmittance varies with polar angle, for example in the manner described in FIG. 6A.

[0304] Here, the public operation mode will be described.

[0305] When the liquid crystal retarder 301 is driven so that the molecules of the liquid crystal material 414 are substantially aligned with the optical axis, the retardation of the liquid crystal layer 314 is compensated for by the retardation of the passive retarder 330, resulting in zero or low net retardation for all polar angles of incidence to the pole-controlled retarder.

[0306] Retarder 300 does not provide an overall conversion of polarization component 360 to pass light through orthogonal to the plane of polar retarder 301 or at acute angles to the orthogonal to the plane of polar retarder 301. That is, polarization component 362 is substantially the same as polarization component 360, and polarization component 364 is substantially the same as polarization component 360. Thus, the angular transmission characteristics are substantially uniform across a wide polar range. Advantageously, the display can be switched to a wide viewing angle.

[0307] Other types of switchable privacy displays are now described.

[0308] A display device 100 that can be switched between privacy and public modes of operation comprises an imaging waveguide and an array of light sources, as described in U.S. Patent No. 9,519,153, which is incorporated herein by reference in its entirety. The imaging waveguide images the array of light sources into an optical window that can be controlled to provide high brightness on-axis and low brightness off-axis in the privacy mode, and provides high brightness with a large solid angle cone for public operation.

[0309] As may be used herein, the terms "substantially" and "approximately" provide industry-accepted tolerances for corresponding terms and / or relativities between items. Such industry-accepted tolerances may range from 0 percent to 10 percent and may correspond to, but are not limited to, part values, angles, and the like. Such relativities between items may range from approximately 0 percent to 10 percent.

[0310] While various embodiments according to the principles disclosed herein have been described above, it should be understood that they have been presented by way of example only, and not limitation. Thus, the breadth and scope of the present disclosure should not be limited by any of the above-described exemplary embodiments, but should be defined only in accordance with the claims and their equivalents issued from this disclosure. Moreover, while the above advantages and features are provided in the described embodiments, application of such issued claims to processes and structures that achieve any or all of the above advantages should not be limited.

[0311] In addition, the section headings herein are provided for consistency with suggestions under 37 CFR 1.77 or to provide organizational clues. These headings should not limit or characterize the embodiments described in claims that may be issued from this disclosure. Specifically, by way of example, the headings refer to the "Technical Field," but the claims should not be limited by the language selected under this heading to describe the so-called field. Furthermore, the description of a technology in the "Background" should not be construed as an admission that a particular technology is prior art to any embodiment in this disclosure. Nor should the "Abstract" be considered a feature of the embodiments described in the issued claims. Furthermore, references to the singular "invention" in this disclosure should not be used to assert that there is only a single point of novelty in this disclosure. Multiple embodiments may be described according to the limitations of multiple claims issued from this disclosure, and such claims thus define the embodiments and their equivalents that are protected thereby. In all cases, the scope of such claims should be considered on their own merits in light of this disclosure, but should not be constrained by the headings set forth herein.

Claims

1. 1. A display device, comprising: a spatial light modulator arranged to output spatially modulated light; a display polarizer disposed on one side of the spatial light modulator, the display polarizer being a linear polarizer; an additional polarizer disposed on the same side of the spatial light modulator as the display polarizer, the additional polarizer being a linear polarizer, the display polarizer and the additional polarizer having parallel electric vector transmission directions; at least one pole-controlled retarder disposed between the display polarizer and the additional polarizer; Equipped with The at least one pole controlled delay 1. A display device comprising: a switchable liquid crystal retarder comprising a layer of liquid crystal material and two surface alignment layers disposed adjacent to and on either side of the layer of liquid crystal material, at least one of the surface alignment layers having a pretilt with a pretilt direction with a component in the plane of the layer of liquid crystal material that makes a non-zero acute angle of less than 10 degrees with respect to an electric vector transmission direction of at least one of the display polarizer and the additional polarizer, in at least a portion of the display device, such that a polar direction for maximum transmission is tilted at a non-zero acute angle with respect to normal to a surface of the display device.

2. 2. The display device of claim 1, wherein one of the surface alignment layers is arranged to provide a horizontal alignment in the adjacent liquid crystal material, the one of the surface alignment layers having a pretilt with a pretilt direction with a component in the plane of the layer of liquid crystal material that makes a non-zero acute angle with respect to the electric vector propagation direction of at least one of the display polarizer and the additional polarizer in at least a portion of the display device.

3. 3. The display device of claim 2, wherein the other of the surface alignment layers is arranged to provide a homeotropic alignment in the adjacent liquid crystal material.

4. A display device as described in claim 3, wherein the other of the surface alignment layers has a pretilt having a pretilt direction with a component in the plane of the layer of liquid crystal material that is parallel or perpendicular to the electric vector propagation direction of the display polarizer and the additional polarizer.

5. 3. The display device of claim 2, wherein the other of the surface alignment layers is arranged to provide a horizontal alignment in the adjacent liquid crystal material.

6. 6. A display device as claimed in claim 3 or 5, wherein the other of the surface alignment layers has a pretilt with a pretilt direction with a component in the plane of the layer of liquid crystal material that makes a non-zero acute angle with respect to the electric vector propagation direction of at least one of the display polarizer and the additional polarizer in at least a portion of the display device.

7. 10. The display device of claim 1, wherein each of the surface alignment layers is arranged to provide a homeotropic alignment in the adjacent liquid crystal material.

8. 8. A display device according to claim 1, wherein each of the surface alignment layers has a pretilt having a pretilt direction with a component in the plane of the layer of liquid crystal material that makes a non-zero acute angle with respect to the electric vector propagation direction of at least one of the display polarizer and the additional polarizer in at least a portion of the display device.

9. A display device according to any preceding claim, wherein the at least one pole-controlled delay further comprises at least one passive compensation delay.

10. 10. The display device of claim 9, wherein the at least one passively compensated retarder comprises a passively compensated retarder having an optical axis orthogonal to the plane of the passively compensated retarder.

11. 10. The display device of claim 9, wherein the at least one passive compensation retarder comprises a pair of passive compensation retarders having optical axes in the plane of the pair of passive compensation retarders that intersect.

12. 12. The display device of claim 11, wherein the angle between the optical axes is bisected by the electric vector propagation direction of at least one of the display polarizer and the additional polarizer.

13. 13. A display device as claimed in any one of claims 1 to 12, wherein the at least one of the surface alignment layers has a pretilt having a pretilt direction with a component in the plane of the layer of liquid crystal material that makes the same non-zero acute angle with respect to the electric vector transport direction of the display polariser and the additional polariser at all positions across the surface alignment layer.

14. 13. A display device according to any one of claims 1 to 12, wherein the at least one of the surface alignment layers has a pretilt having a pretilt direction with a component in the plane of the layer of liquid crystal material that varies monotonically along a predetermined axis transverse to the surface alignment layer, and that makes a non-zero acute angle with respect to the electric vector transport direction of the display polarizer and the additional polarizer, in at least a portion of the display device.

15. The display device of claim 14 , wherein the non-zero acute angles have a non-zero acute angle average value.

16. The display device of any one of claims 1 to 15, wherein the display polarizer is an output display polarizer located at the output side of the spatial light modulator.

17. 17. The display device of claim 16, wherein no reflective polarizer is disposed between said output display polarizer and said at least one pole-controlled retarder.

18. A display device according to any one of claims 16 to 17, wherein the spatial light modulator comprises an emissive spatial light modulator arranged to emit the spatially modulated light.

19. 18. The display device of claim 16, further comprising a backlight arranged to output light, the spatial light modulator comprising a transmissive spatial light modulator arranged to receive and spatially modulate the output light from the backlight.

20. 16. The display device of claim 1, further comprising a backlight arranged to output light, the spatial light modulator comprising a transmissive spatial light modulator arranged to receive and spatially modulate the output light from the backlight, and the display polarizer being an input display polarizer arranged at the input side of the spatial light modulator.

21. an output display polarizer disposed on the output side of the spatial light modulator; a further polarizer disposed at the output side of the spatial light modulator, the further polarizer being a linear polarizer having an electric vector transfer direction that is parallel to the electric vector transfer direction of the display polarizer and the further polarizer; 21. The display device of claim 20, further comprising at least one additional pole-controlled retarder disposed between the additional polarizer and the output display polarizer.

22. an additional polarizer disposed on the same side of the spatial light modulator as the additional polarizer outside the additional polarizer, the additional polarizer being a linear polarizer having an electric vector transfer direction that is parallel to the electric vector transfer direction of the display polarizer and the additional polarizer; 10. The display device of claim 1, further comprising at least one additional pole-controlled retarder disposed between the additional polarizer and the further additional polarizer.

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