Optical stacks for privacy displays

Abstract

The present disclosure provides a display device including at least one spatial light modulator and at least one curved viewing angle control element, the at least one curved viewing angle control element including a plurality of retarders arranged between a display polarizer and an additional polarizer of each spatial light modulator. The curvature of the viewing angle control element provides increased brightness uniformity for front users and increased visual security against off-axis snoopers.

Description

Technical Field

[0001] The present disclosure generally relates to optical stacks for privacy displays and low stray light displays. Background Art

[0002] Privacy displays provide image visibility to the primary user, who is typically in an on-axis position, and reduce visibility of the image content to a snooper, who is typically in an off-axis position. Privacy functions can be provided by micro-louver optical films that transmit high brightness from the display in an on-axis direction and transmit low brightness from the display in an off-axis position, however such films are not switchable and the display is limited to privacy functions.

[0003] A switchable privacy display may be provided by control of off-axis optical output. Control of off-axis privacy may be provided by reducing contrast, for example by adjusting liquid crystal bias tilt in an in-plane switching LCD. Control may also be provided by reducing off-axis brightness. Reducing brightness may be achieved by a switchable backlight source of a liquid crystal display (LCD) spatial light modulator. Reducing off-axis brightness may also be provided by switchable liquid crystal retarders and compensating retarders arranged to modulate the input and / or output directional brightness distribution of the spatial light modulator.

[0004] Control may also be provided by increasing the off-axis reflectivity. Increasing the reflectivity may be achieved by a switchable liquid crystal retarder, a compensating retarder arranged to control the polarization of ambient light falling on the reflective polarizer. Summary of the invention

[0005] According to a first aspect of the present disclosure, a display device is provided, which includes: at least one spatial light modulator, which is arranged to output light on an output side; a display polarizer, which is arranged on one side of each spatial light modulator in the at least one spatial light modulator; and a viewing angle control element, which is arranged on the same side of the at least one spatial light modulator as the display polarizer of the at least one spatial light modulator; wherein the viewing angle control element includes: an additional polarizer; and at least one delay plate, which is arranged between the additional polarizer and the display polarizer of the at least one spatial light modulator, the at least one delay plate being capable of simultaneously not introducing a net relative phase shift into an orthogonal polarization component of light transmitted by the display polarizer along an axis along the normal of the at least one delay plate, and introducing a relative phase shift into an orthogonal polarization component of light transmitted by the display polarizer along an axis inclined to the normal of the at least one delay plate; and when observed from the output side, the viewing angle control element is curved with a concave curvature.

[0006] Advantageously, the uniformity of the image seen by a user in front of a display operating in privacy mode may be increased. The uniformity of the visual security level seen by an off-axis snooper may be increased, thereby advantageously reducing image visibility across the width of the display device.

[0007] The viewing angle control element may be curved in a first direction and linear in a second direction orthogonal to the first direction. The display device may have a major axis and a minor axis, and the first direction is the direction of the major axis. Advantageously, the curvature may be conveniently achieved by a low-cost forming method for the viewing angle control element.

[0008] The at least one spatial light modulator may be curved with a concave curvature when viewed from the output side. Advantageously, a user of the display may see the image wrap around.

[0009] The display device may further include at least two spatial light modulators, wherein the spatial light modulators are tiled. At least two of the spatial light modulators may be tilted relative to each other in at least a first direction. Advantageously, the plurality of monitors may be configured to implement privacy protection operation at large image sizes, wherein the privacy protection pattern between two adjacent monitors has a high uniformity.

[0010] The display device may also include at least two viewing angle control elements, wherein at least two viewing angle control elements may be arranged in series. Advantageously, a wide-angle backlight or emissive display may be provided. In the anti-peeping mode of operation, the off-axis brightness and reflectivity may be sufficient to achieve a desired level of visual security. In the public mode of operation, the off-axis brightness may be high enough to achieve high image visibility to multiple display users.

[0011] The curvature of the at least one viewing angle control element in the first direction may be different from the curvature of the at least one spatial light modulator in the first direction. The curvature of the viewing angle control element may be greater than the curvature of the at least one spatial light modulator. Advantageously, the uniformity of the image for the primary user in the anti-peep mode may be increased. Distortion of the image on the spatial light modulator may be reduced or eliminated.

[0012] The spatial light modulator may comprise an emission spatial light modulator arranged to output light, in which case the display polariser may be an output display polariser arranged on the output side of the emission spatial light modulator.Advantageously, the display thickness may be reduced.

[0013] Alternatively, the at least one spatial light modulator may be a transmissive spatial light modulator, in which case the display device may further comprise at least one backlight arranged to illuminate the at least one spatial light modulator.

[0014] Where there are a plurality of spatial light modulators, each of the spatial light modulators may be illuminated by a respective backlight source. Advantageously, each spatial light modulator and its respective backlight source may be provided as an integrated unit. A plurality of off-the-shelf displays may be provided to illuminate the viewing angle control element.

[0015] Where there are multiple spatial light modulators, a single backlight source may be provided to illuminate the multiple spatial light modulators. The at least one backlight source may be curved with a concave curvature when viewed from the output side. Advantageously, image uniformity may also be increased. A spatial light modulator of reduced size may be used to provide a large area display, thereby reducing the overall display cost.

[0016] In the case where the at least one spatial light modulator is a transmissive spatial light modulator, the at least one viewing angle control element may be arranged on the input side of the at least one spatial light modulator between the at least one spatial light modulator and the at least one backlight source. Advantageously, the thickness of the viewing angle control element in front of the spatial light modulator may be reduced.

[0017] In the case where at least one spatial light modulator is a transmissive spatial light modulator or an emitting spatial light modulator, at least one viewing angle control element may be arranged on an output side of the spatial light modulator to receive output light from the spatial light modulator.

[0018] In this case, the reflective polarizer can be arranged between the display polarizer and the additional polarizer. Advantageously, the visual security level of the display device can be increased. A snooper can see the curved reflective polarizer, so that the uniformity of the visual security level is increased.

[0019] The air gap may be arranged between the display polarizer and the additional polarizer; wherein the at least one retarder comprises: an air gap input retarder comprising at least one retarder arranged between the display polarizer and the air gap; and an air gap output retarder comprising at least one retarder arranged between the air gap and the additional polarizer, wherein the air gap input retarder is arranged to provide a phase shift to provide a circularly polarized light component of light transmitted by the display polarizer along an axis normal to the plane of the air gap input retarder in the air gap; and the at least one retarder is capable of simultaneously not introducing a net relative phase shift into an orthogonal polarization component of light transmitted by the display polarizer along an axis normal to the plane of the at least one retarder, and introducing a net relative phase shift into an orthogonal polarization component of light transmitted by the display polarizer along an axis oblique to the normal to the plane of the at least one retarder. The air gap is arranged to achieve the purpose of reducing assembly costs and improving manufacturing yields. Multiple spatial light modulators may be arranged with a single retarder stack and additional polarizers. Image contrast may be optimized for frontal users.

[0020] The display device may also include an additional viewing angle control element, which is arranged on the same side of the spatial light modulator as the initially mentioned viewing angle control element, or, if the spatial light modulator is transmissive, is arranged on the opposite side of the spatial light modulator to the initially mentioned viewing angle control element. Advantageously, the off-axis brightness can be further reduced in anti-peep mode compared to a display including a single additional polarizer. A wide-angle brightness output distribution from the spatial light modulator can be used to achieve the desired level of visual safety. Compared to a collimated backlight, a wide-angle backlight that can be manufactured at a higher yield can be used. The emissive display can have a switchable anti-peep function while achieving a high level of visual safety.

[0021] The display polarizer and the at least one additional polarizer may have parallel electric vector transmission directions. The at least one retarder may include a switchable liquid crystal retarder. The at least one retarder may include a switchable liquid crystal retarder. Advantageously, the display is switchable between a wide angle operating mode and an anti-peep operating mode.

[0022] A plurality of polarity-controlled delay plates may include a switchable liquid crystal delay plate, which includes a liquid crystal material layer. The switchable liquid crystal delay plate may include two surface alignment layers, which are arranged adjacent to the liquid crystal material layer and on opposite sides thereof, each of the surface alignment layers being arranged to provide a vertical alignment in the adjacent liquid crystal material. The liquid crystal material layer of the switchable liquid crystal delay plate may include a liquid crystal material having a negative dielectric anisotropy. The liquid crystal material layer may have a retardation in the range of 500nm to 1000nm, preferably in the range of 600nm to 900nm, and most preferably in the range of 700nm to 850nm for light having a wavelength of 550nm. The plurality of polarity-controlled retarders may further comprise: a passive retarder having an optical axis perpendicular to the plane of the retarder, the passive retarder having a retardation in the range of -300nm to -900nm, preferably in the range of -450nm to -800nm ​​and most preferably in the range of -500nm to -725nm for light having a wavelength of 550nm; or a pair of passive retarder having optical axes crossing in the plane of the retarder, each of the pair of passive retarder having a retardation in the range of 300nm to 800nm, preferably in the range of 500nm to 700nm and most preferably in the range of 550nm to 675nm for light having a wavelength of 550nm. Advantageously, the common mode may have low power consumption. Advantageously, the passive retarder may be provided to match the liquid crystal mode.

[0023] The switchable liquid crystal retarder may include two surface alignment layers, which are arranged adjacent to the liquid crystal material layer and on opposite sides thereof, each of the surface alignment layers being arranged to provide a horizontal alignment in the adjacent liquid crystal material. The liquid crystal material layer of the switchable liquid crystal retarder may include a liquid crystal material having a positive dielectric anisotropy. The liquid crystal material layer may have a retardation in the range of 500nm to 1000nm, preferably in the range of 600nm to 850nm, and most preferably in the range of 700nm to 800nm ​​for light having a wavelength of 550nm. The plurality of polarity-controlled retarders may further comprise: a passive retarder having an optical axis perpendicular to the plane of the retarder, the retarder having a retardation for light having a wavelength of 550 nm in the range of -300 nm to -700 nm, preferably in the range of -350 nm to -600 nm, and most preferably in the range of -400 nm to -500 nm; or a pair of passive retarders having optical axes crossing in the plane of the retarder, each of the pair of passive retarders having a retardation for light having a wavelength of 550 nm in the range of 300 nm to 800 nm, preferably in the range of 350 nm to 650 nm, and most preferably in the range of 450 nm to 550 nm. Advantageously, the display may have increased resilience to applied mechanical stress.

[0024] The backlight source can provide brightness at a polar angle greater than 45 degrees to the normal to the spatial light modulator, i.e., at most 33% of the brightness along the normal to the spatial light modulator, preferably at most 20% of the brightness along the normal to the spatial light modulator, and most preferably at most 10% of the brightness along the normal to the spatial light modulator. Advantageously, no additional additional polarizer may be required to achieve the desired level of visual security against off-axis snoopers. Display thickness, complexity and cost may be reduced.

[0025] According to a second aspect of the present disclosure, there is provided a viewing angle control optical element for application to a display device, the display device comprising a spatial light modulator and a display polarizer arranged on one side of the spatial light modulator, the viewing angle control optical element comprising: an additional polarizer; and at least one delay plate arranged between the additional polarizer and the display polarizer of the at least one spatial light modulator, wherein the at least one delay plate is capable of simultaneously not introducing a net relative phase shift into an orthogonal polarization component of light transmitted by the display polarizer along an axis along a normal to the at least one delay plate, and introducing a relative phase shift into an orthogonal polarization component of light transmitted by the display polarizer along an axis inclined to the normal to the at least one delay plate; and when observed from the output side, the viewing angle control element is curved with a concave curvature.

[0026] Advantageously, an independent viewing angle control element may be provided to achieve a bondless switchable anti-peeping display, and the display including the optical element and the air gap may achieve a high image contrast.

[0027] The viewing angle control element may also include at least one additional delay plate and an additional additional polarizer, wherein the additional additional polarizer is arranged on the output side of the initially mentioned additional polarizer and the at least one additional delay plate is arranged between the initially mentioned additional polarizer and the additional additional polarizer.

[0028] Embodiments of the present disclosure can be used in a variety of optical systems. Embodiments may include or utilize various projectors, projection systems, optical components, displays, microdisplays, computer systems, processors, independent sets of projector systems, visual and / or audio-visual systems, and electrical and / or optical devices. In fact, aspects of the present disclosure can be used with almost any device related to optical and electrical devices, optical systems, demonstration systems, or any device that may include any type of optical system. Therefore, embodiments of the present disclosure can be used for optical systems, devices used in visual and / or optical demonstrations, visual peripherals, etc., and can be used in a variety of computing environments.

[0029] Before discussing the disclosed embodiments in detail, it should be understood that the present invention is not limited in application or formation to the details of the specific arrangements shown, as the present invention is capable of other embodiments. In addition, various aspects of the present disclosure may be described in different combinations and arrangements to define the uniqueness of the embodiments in their own right. In addition, the terminology used herein is for illustrative purposes only and not limiting.

[0030] Directional backlights typically provide control of illumination emitted from substantially the entire output surface by modulating individual LED light sources arranged on the input aperture side of an optical waveguide. Controlling the directional distribution of emitted light can enable single-person viewing for safety functions, where the display can only be viewed by a single observer from a limited range of angles; high electrical efficiency, where illumination is provided primarily within a small angular directional distribution; left-right eye alternating viewing for sequential stereoscopic and autostereoscopic displays; and low cost.

[0031] These and other advantages and features of the present disclosure will become apparent to those of ordinary skill in the art after reading the entire disclosure. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Embodiments are illustrated by way of example in the accompanying drawings, in which like reference numerals refer to like parts, and in which:

[0033] Figure 1is a schematic diagram showing an anti-peeping display device in a perspective front view, the anti-peeping display device comprising two curved spatial light modulators, and a first curved viewing angle control element and a second curved viewing angle control element;

[0034] Figure 2 It is shown in top view Figure 1 A schematic diagram of an anti-peeping display device;

[0035] Figure 3A is a schematic diagram showing an anti-peeping display device in a perspective side view, the anti-peeping display device comprising a spatial light modulator, a first pair of quarter wave plates and a second pair of quarter wave plates, a first switchable retarder stack and a second switchable retarder stack, an additional polarizer and another additional polarizer;

[0036] Figure 3B Shown in expanded view Figure 3A Schematic diagram of the arrangement of polarizers and retarders;

[0037] Figure 4 It is shown in Figure 3A A schematic curve diagram of the output brightness of the anti-peeping display device in the public operation mode changing with the polar direction;

[0038] Figure 5 is a schematic graph showing the variation of output brightness with polar direction in an anti-peeping operation mode of a display including a planar viewing angle control element;

[0039] Figure 6 is a schematic graph showing the variation of output brightness with polar direction in the anti-peeping operation mode of the curved viewing angle control element;

[0040] Figure 7 is a schematic diagram showing the variation of the relative reflectivity of the display with polar direction in the anti-peeping operation mode of the curved viewing angle control element;

[0041] Fig. 8A is a schematic diagram showing an anti-peeping display device in a perspective front view, the anti-peeping display device comprising two planar spatial light modulators, and a first curved viewing angle control element and a second curved viewing angle control element;

[0042] Figure 8B It is shown in top view Fig. 8A A schematic diagram of an anti-peeping display device;

[0043] Fig. 9 is a schematic diagram showing an anti-peeping display in a top view, the anti-peeping display comprising two tilted planar spatial light modulators, and a curved viewing angle control element comprising a first curved viewing angle control element and a second curved viewing angle control element;

[0044] Fig. 10Ais a schematic diagram showing a privacy display in top view, the privacy display comprising two tilted curved spatial light modulators, a single curved backlight, and a first curved viewing angle control element and a second curved viewing angle control element;

[0045] Fig. 10B is a schematic diagram showing a privacy display in top view, the privacy display including two planar spatial light modulators, a single curved collimated backlight, and a curved viewing angle control element;

[0046] Fig.11 is a schematic diagram showing an anti-peeping display in a top view, the anti-peeping display comprising a curved spatial light modulator, a backlight source, and a first curved viewing angle control element and a second curved viewing angle control element, wherein the curvature of the spatial light modulator and the backlight source is smaller than the curvature of the viewing angle control element;

[0047] Fig.12 is a schematic diagram showing a privacy display in top view, the privacy display comprising a curved backlight and a first curved viewing angle control element arranged behind a curved spatial light modulator, and a second curved viewing angle control element arranged to receive light from the spatial light modulator, wherein the curvature of the spatial light modulator, the backlight and the first viewing angle control element is less than the curvature of the second viewing angle control element;

[0048] Fig.13 is a schematic diagram showing a privacy display in top view, the privacy display comprising a curved backlight and first and second curved viewing angle control elements arranged behind a curved spatial light modulator, wherein the curvature of the spatial light modulator is smaller than the curvature of the viewing angle control element and the backlight;

[0049] Fig.14 is a schematic diagram showing a privacy display in top view, the privacy display comprising a curved backlight and a first curved viewing angle control element and a second curved viewing angle control element arranged behind a planar spatial light modulator;

[0050] Fig.15 is a schematic diagram showing a privacy display in top view, the privacy display comprising a curved backlight and a first curved viewing angle control element disposed behind a planar spatial light modulator and a planar viewing angle control element;

[0051] Fig.16 is shown in a perspective side view for FIG. 8A to FIG. 15 A schematic diagram of an angle control element in an anti-peeping display device;

[0052] Fig.17 is a schematic diagram showing, in side view, surface reflection of an anti-peeping display device, the anti-peeping display device comprising a pair of quarter wave plates arranged on opposite sides of an air gap;

[0053] Fig.18A is a schematic diagram showing an anti-peeping display device including a spatial light modulator and a single viewing angle control element in a perspective side view;

[0054] Fig.18B Shown in expanded view Fig.18A Schematic diagram of the arrangement of polarizers and retarders;

[0055] Fig.19A is a schematic diagram showing a directional backlight source in perspective view;

[0056] Fig.19B is a schematic diagram showing a non-directional backlight source in perspective view as before;

[0057] Fig.19C is a schematic curve diagram showing the change of the brightness of the display with the lateral viewing angle under different viewing fields;

[0058] Fig.19D is a schematic diagram showing a switchable directional display device including an imaging waveguide and a switchable liquid crystal retarder in side view;

[0059] Fig.19E is a schematic diagram showing operation of the imaging waveguide in a narrow angle operation mode from a perspective view;

[0060] Fig.19F is shown when used in a display device without a switchable liquid crystal retarder Fig.19E A schematic curve diagram of the output field brightness diagram of ;

[0061] Figure 19G is a schematic diagram showing a switchable directional display device operating in an anti-peeping operation mode in a side view, the switchable directional display device comprising a switchable collimating waveguide and a switchable liquid crystal retarder;

[0062] Fig.19H is a schematic diagram showing the output of a collimating waveguide in top view;

[0063] Fig.19I It is shown Figure 19G A schematic curve diagram of an equal brightness field polar coordinate diagram of a display device;

[0064] Fig. 20 is a schematic diagram showing a display device in top view, the display device including a planar spatial light modulator, a backlight source, and a curved viewing angle control element in a display operating arrangement;

[0065] Fig.21 is a schematic diagram showing a display device in top view, the display device including a planar spatial light modulator, a backlight source, and a flexible viewing angle control element in a folded arrangement;

[0066] Fig.22A is a schematic diagram showing in perspective the illumination of a retardation layer by off-axis light;

[0067] Fig. 22B is a schematic diagram showing in perspective the illumination of the retardation layer by off-axis light in a first linear polarization state of 0 degrees;

[0068] Fig. 22C is a schematic diagram showing in perspective view the illumination of a retardation layer by off-axis light in a first linear polarization state of 90 degrees;

[0069] Fig.22D is a schematic diagram showing in perspective view the illumination of the retardation layer by off-axis light in a first linear polarization state of 45 degrees;

[0070] Fig.23A is a schematic diagram showing in perspective the illumination of a C-plate retarder by off-axis polarized light having a positive elevation angle;

[0071] Fig. 23B is a schematic diagram showing in perspective the illumination of a C-plate retarder by off-axis polarized light having a negative transverse angle;

[0072] Fig.23C is a schematic diagram showing in perspective the illumination of a C-plate retarder by off-axis polarized light having a positive elevation angle and a negative transverse angle;

[0073] Fig.23D is a schematic diagram showing in perspective the illumination of a C-plate retarder by off-axis polarized light having a positive elevation angle and a positive transverse angle;

[0074] Fig.24 It is shown FIG. 23A to FIG. 23D A schematic graph showing the output transmittance of the transmitted light in FIG. 1 as a function of the polar direction;

[0075] Fig.25A is a schematic diagram showing in perspective the illumination of a crossed A-plate retardation layer by off-axis polarized light having a positive elevation angle;

[0076] Fig.25B is a schematic diagram showing in perspective view the illumination of crossed A-plate retardation layers by off-axis polarized light having a negative transverse angle;

[0077] Fig.25C is a schematic diagram showing in perspective view the illumination of crossed A-plate retardation layers by off-axis polarized light having a positive elevation angle and a negative transverse angle;

[0078] Fig.25D is a schematic diagram showing in perspective view the illumination of crossed A-plate retardation layers by off-axis polarized light having positive elevation angles and positive transverse angles; and

[0079] Fig.26 It is shown FIG. 25A to FIG. 25DSchematic graph of the output transmittance of the transmitted light in the image as it changes with the polar direction. DETAILED DESCRIPTION

[0080]

[0046] The terminology associated with optical retarders for the purposes of the present disclosure will now be described.

[0081] In a layer having a uniaxial birefringent material, there is a direction that controls the optical anisotropy, while all directions perpendicular thereto (or at a given angle thereto) have equivalent birefringence.

[0082] The optical axis of an optical retarder refers to the direction of propagation of light rays that do not undergo birefringence in a uniaxial birefringent material. This is different from the optical axis of an optical system, which may be, for example, parallel to the line of symmetry or perpendicular to the display surface along which the principal rays propagate.

[0083] For light propagating in a direction orthogonal to the optical axis, the optical axis is the slow axis, and linearly polarized light with an electric vector direction parallel to the slow axis travels at the slowest speed. The slow axis direction is the direction with the highest refractive index at the design wavelength. Similarly, the fast axis direction is the direction with the lowest refractive index at the design wavelength.

[0084] For a positive dielectric anisotropy uniaxial birefringent material, the slow axis direction is the extraordinary axis of the birefringent material. For a negative dielectric anisotropy uniaxial birefringent material, the fast axis direction is the extraordinary axis of the birefringent material.

[0085] The terms "half wavelength" and "quarter wavelength" refer to the wavelength of the retarder for a design wavelength λ which may typically be between 500 nm and 570 nm. δ In this exemplary embodiment, unless otherwise specified, exemplary retardation values ​​are provided for a wavelength of 550 nm.

[0086] A retarder provides a relative phase shift between two orthogonal polarization components of a light wave incident thereon and is characterized by the amount Γ of relative phase it imparts to the two polarization components; in some contexts, the term "phase shift" is used instead of the word "relative", but it still means a relative phase shift. The relative phase shift is related to the birefringence Δn and thickness d of the retarder by the following equation:

[0087] Γ=2 . π . Δn . d / λ0 Equation 1

[0088] In Equation 1, Δn is defined as the difference between the extraordinary refractive index and the ordinary refractive index, i.e.

[0089] Δn = n e -n o Equation 2

[0090] For a half-wave retarder, the relationship between d, Δn and λ0 is chosen so that the phase shift between the polarization components is Γ = π. For a quarter-wave retarder, the relationship between d, Δn and λ0 is chosen so that the phase shift between the polarization components is Γ = π / 2.

[0091] The term half-wave retarder herein generally refers to light propagating perpendicular to the retarder and perpendicular to the spatial light modulator.

[0092] Some aspects of light propagation through a transparent retarder between a pair of polarizers will now be described.

[0093] The state of polarization (SOP) of light is described by the relative amplitude and phase shift between any two orthogonal polarization components. Transparent retarders do not change the relative amplitude of these orthogonal polarization components, but only act on their relative phase. Providing a net phase shift between orthogonal polarization components changes the SOP, while maintaining the net relative phase maintains the SOP.

[0094] A linear SOP has a polarization component of non-zero amplitude and an orthogonal polarization component of zero amplitude.

[0095] A linear polarizer transmits a unique linear SOP whose linear polarization component is parallel to the electric vector transmission direction of the linear polarizer, and attenuates light having a different SOP.

[0096] A retarder arranged between a linear polarizer and a parallel linear analyzing polarizer that introduces no relative net phase shift provides complete transmission of light, rather than residual absorption within the linear polarizer.

[0097] A retarder that provides a relative net phase shift between the orthogonal polarization components changes the SOP and provides attenuation at the analyzing polarizer.

[0098] In the present disclosure, "A-plate" refers to an optical retarder utilizing a layer of birefringent material whose optical axis is parallel to the plane of the layer.

[0099] The “positive A-plate” refers to a positive birefringent A-plate, that is, an A-plate having a positive Δn.

[0100] In the present disclosure, "C-plate" refers to an optical delay plate using a birefringent material layer, wherein the optical axis of the birefringent material layer is perpendicular to the plane of the layer. "Positive C-plate" refers to a positive birefringent C-plate, i.e., a C-plate with positive Δn. "Negative C-plate" refers to a negative birefringent C-plate, i.e., a C-plate with negative Δn.

[0101] "O-plate" refers to an optical retardation plate using a birefringent material layer, wherein the optical axis of the birefringent material layer has a component parallel to the plane of the layer and a component perpendicular to the plane of the layer. "Positive O-plate" refers to a positive birefringent O-plate, i.e., an O-plate with positive Δn.

[0102] An achromatic retarder may be provided, wherein the material of the retarder has a retardation Δn.d that varies with wavelength λ, i.e.

[0103] Δn . d / λ = κ Equation 3

[0104] where κ is essentially a constant.

[0105] Examples of suitable materials include modified polycarbonates available from Teijin Films.Achromatic retarders may be provided in embodiments of the invention to advantageously minimize color variations between polar viewing directions with low brightness reduction and polar viewing directions with increased brightness reduction, as will be described below.

[0106] Various other terms used in this disclosure in connection with retarders and liquid crystals will now be described.

[0107] The liquid crystal cell has a retardation given by Δn.d, where Δn is the birefringence of the liquid crystal material in the liquid crystal cell and d is the thickness of the liquid crystal cell, which are independent of the alignment of the liquid crystal material in the liquid crystal cell.

[0108] Horizontal alignment refers to the alignment of the liquid crystal in a switchable liquid crystal display, where the molecules are aligned substantially parallel to the substrate. Horizontal alignment is sometimes referred to as planar alignment. Horizontal alignment may typically have a small pretilt angle, such as 2 degrees, so that the molecules at the surface of the alignment layer of the liquid crystal cell are slightly tilted, as will be described below. The pretilt angle is arranged to minimize degeneracy when the cell is switched.

[0109] In the present disclosure, vertical alignment is a state in which rod-like liquid crystal molecules are substantially aligned vertically to the substrate. In discotic liquid crystals, vertical alignment is defined as a state in which the axis of a columnar structure formed by discotic liquid crystal molecules is aligned vertically to the surface. In vertical alignment, the pretilt angle is the tilt angle of molecules close to the alignment layer, and is generally close to 90 degrees, for example, 88 degrees.

[0110] In a twisted liquid crystal layer, a twisted configuration (also called a helical structure or helix) of nematic liquid crystal molecules is provided. The twist can be achieved by a non-parallel alignment of the alignment layer. In addition, cholesteric dopants can be added to the liquid crystal material to destroy the degeneracy of the twist direction (clockwise or counterclockwise) and further control the twist pitch in the relaxed (usually undriven) state. Super twisted liquid crystal layers have a twist greater than 180 degrees. Twisted nematic layers used in spatial light modulators typically have a twist of 90 degrees.

[0111] Liquid crystal molecules having positive dielectric anisotropy switch from a horizontal alignment (such as an A-plate retarder alignment) to a vertical alignment (such as a C-plate or O-plate retarder alignment) under the action of an applied electric field.

[0112] Liquid crystal molecules having negative dielectric anisotropy switch 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) under the action of an applied electric field.

[0113] Rod-shaped molecules have positive birefringence, so that n e >n o , as described in Equation 2. The discotic molecule has negative birefringence, so that n e <n o .

[0114] Positive retardation plates such as A plates, positive O plates, and positive C plates can generally be provided by stretched films or rod-like liquid crystal molecules. Negative retardation plates such as negative C plates can be provided by stretched films or discotic liquid crystal molecules.

[0115] A parallel liquid crystal cell alignment refers to an alignment direction where the horizontal alignment layer is parallel or more usually anti-parallel. For a pre-tilted vertical alignment, the alignment layer may have substantially parallel or anti-parallel components. A hybrid aligned 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 a parallel alignment (e.g., oriented at 90 degrees to each other).

[0116] The transmissive spatial light modulator may also include a retarder between the input display polarizer and the output display polarizer, such as disclosed in U.S. Pat. No. 8,237,876, which is incorporated herein by reference in its entirety. Such a retarder (not shown) is in a different position than the passive retarder of the embodiments of the present invention. Such a retarder compensates for the contrast degradation of the off-axis viewing position, which is different from the brightness reduction effect of the off-axis viewing position of the embodiments of the present invention.

[0117] The privacy mode of operation of a display is one in which the viewer sees low contrast sensitivity such that the image is not clearly visible. Contrast sensitivity is a measure of the ability to distinguish between different levels of brightness in a static image. Inverse contrast sensitivity can be used as a measure of visual safety, as a high visual safety level (VSL) corresponds to low image visibility.

[0118] For a privacy display that provides an image to an observer, visual security can be given as:

[0119] VSL = (Y + R) / (Y – K) Equation 4

[0120] Where VSL is the visual safety level, Y is the brightness of the white state of the display at the perspective of the peeper, K is the brightness of the black state of the display at the perspective of the peeper, and R is the brightness of the reflected light from the display.

[0121] The panel contrast is given by:

[0122] C = Y / K Equation 5

[0123] For high contrast optical LCD modes, the white state transmittance remains substantially constant with viewing angle. In contrast-reduced liquid crystal modes of embodiments of the present invention, the white state transmittance generally decreases as the black state transmittance increases, such that

[0124] Y+K~PL Equation 6

[0125] The visual safety level can then be further given as:

[0126]

[0127] Where the off-axis relative brightness P is typically defined as a percentage of the front brightness L at the peeper's angle, and the display may have an image contrast ratio C, and the surface reflectivity is ρ.

[0128] The off-axis relative brightness P is sometimes referred to as the privacy level. However, such a privacy level P describes the relative brightness of the display relative to the front brightness at a given polar angle, rather than a measure of the privacy appearance.

[0129] The display may be illuminated by a Lambertian ambient illuminance I. Thus, in a completely dark environment, a high contrast display has a VSL of approximately 1.0. As the ambient illuminance increases, the perceived image contrast decreases, the VSL increases and a privacy-protected image is perceived.

[0130] For a typical LCD display, the panel contrast C is higher than 100:1 at almost all viewing angles, making the visually safe level approximately:

[0131] VSL = 1 + I.ρ / (π.PL) Equation 8

[0132] In contrast to privacy displays, ideal wide-angle displays are easily viewed under standard ambient illumination conditions. One measure of image visibility is given by contrast sensitivity (such as Michelson contrast), which is given by:

[0133] M = (I max – I min ) / (I max + I min ) Equation 9

[0134] therefore:

[0135] M = ((Y+R) – (K+R)) / ((Y+R) + (K+R)) = (YK) / (Y+K+2.R) Equation 10

[0136] Therefore, the visual safety level (VSL) is equal to (but not identical to) 1 / M. For this discussion, for a given off-axis relative luminance P, the wide-angle image visibility W is approximated by

[0137] W = 1 / VSL = 1 / (1 + I.ρ / (π.PL)) Equation 11

[0138] Curvature is a property of a curved line, and for the purposes of this disclosure, curvature is the inverse of the radius of curvature.A flat surface has zero curvature.

[0139] A switchable directional display device for use, for example, in a peep-proof display and including a plurality of retarders disposed between a display polarizer and an additional polarizer is described in U.S. Patent No. 10,126,575 and U.S. Patent Publication No. 2019-0086706, both of which are incorporated herein by reference in their entirety. A directional display device further including a reflective polarizer disposed between the display polarizer and the retarders is described in U.S. Patent No. 10,303,030 and U.S. Patent Publication No. 2019-0250458, both of which are incorporated herein by reference in their entirety. A directional display polarizer including a passive retarder disposed between the display polarizer and the additional polarizer is described in U.S. Patent Publication No. 2018-0321553, which is incorporated herein by reference in its entirety.

[0140] Figure 1 1 is a schematic diagram showing an anti-peeping display device 100 in a perspective front view, which includes two curved spatial light modulators 48A, 48B illuminated by backlight sources 20A, 20B, respectively, and a first curved viewing angle control element 360A and a second curved viewing angle control element 360B.

[0141] Primary user 26 observes the display from the output side of spatial light modulator 48A, 48B, which is curved and concave when viewed from the output side. Light 402 is directed from display device 100 to the eyes of observer 26. It is desirable to maximize the uniformity of the brightness directed to user 26 over the area of ​​spatial light modulator 48A, 48B.

[0142] In anti-peeping operation, the display may be viewed by a peep 27. It is desirable to maximize the level of visual safety of light directed from the display device 100 to the peep 27 on the light rays 404.

[0143] Figure 2 It is shown in top view Figure 1Schematic diagram of an anti-peeping display device 100. The viewing angle control elements 360A and 360B provide a restricted light cone 410 for anti-peeping operation. The light cone 410 may, for example, represent the full width at half maximum (FWHM) cone size of the brightness distribution from the display. Light 402 is within the light cone 410, and light 404 is outside these light cones. FIG. 3A to FIG. 3B and Figure 5 The formation of light cone 410 is further described in .

[0144] The curvature of viewing angle control elements 360A, 360B provides a light cone 410 that is tilted at the display edge so that light rays 402 from the display edge remain inside the light cone. Advantageously, display uniformity is increased for user 26 and a visual security level V against snoopers can be increased across the width of display device 100.

[0145] The display device 100 includes: a plurality of spatial light modulators 48A, 48B, which are arranged to output light on the output side of each spatial light modulator 48A, 48B. When viewed from the output side of the corresponding spatial light modulator 48A, 48B, each spatial light modulator 48A, 48B is curved with a concave curvature. The spatial light modulators 48A, 48B are tiled and also tilted relative to each other in a first direction. The display device has a major axis and a minor axis, and the first direction is the direction of the major axis. Typically, for monitor applications in which the monitor is intended for horizontal orientation, the first direction is a horizontal direction.

[0146] Each of the spatial light modulators 48A, 48B is illuminated by a respective backlight source 20A, 20B. Each backlight source 20A, 20B is curved with a concave curvature when viewed from the output side.

[0147] The viewing angle control elements 360A, 360B are arranged to receive output light from the spatial light modulator. The viewing angle control elements 360A, 360B are arranged in series on the output side of the spatial light modulators 48A, 48B. Therefore, the light output from the spatial light modulators 48A, 48B is guided through the first viewing angle control element 360A. The viewing angle control element 360B is arranged to receive light from the viewing angle control element 360B.

[0148] exist Figure 1 In an embodiment, the viewing angle control elements 360A, 360B are curved in a first direction and linear in a second direction orthogonal to the first direction.

[0149] The curvature may generally be cylindrical in only a first direction. The curvature may have a circular profile or may have other profile shapes, for example, the center region may be linear and the outer region may be curved. Advantageously, the curvature may be achieved by attaching the viewing angle control elements 360A, 360B to a curved mechanical alignment fixture. In other embodiments, curvature may be provided that is curved in two directions, for example by forming a substrate surface on a curved mold and applying heat during the bending step.

[0150] The curvature of the viewing angle control element 360A, 360B in the first direction is different from the curvature of the at least one spatial light modulator 48A, 48B in the first direction. Figure 2 , the radius of curvature of the viewing angle control elements 360A, 360B is shown as distance 450. The curved spatial light modulators 48A, 48B are tilted relative to each other and are arranged to have a common radius of curvature 452. The radius 450 is smaller than the radius 452, so that the curvature of the viewing angle control elements 360A, 360B is greater than the curvature of at least one spatial light modulator 48A, 48B. Figures 7 to 9 The operation of the curved viewing angle control elements 360A, 360B is further described.

[0151] The structure of a portion of the display device will now be described.

[0152] Figure 3A is a schematic diagram showing an anti-peeping display device 100 in a perspective side view, the anti-peeping display device including a backlight source 20, a spatial light modulator 48, and a first viewing angle control element and a second viewing angle control element; and Figure 3B Shown in expanded view Figure 3A Schematic diagram of the arrangement of polarizers and retarders.

[0153] The spatial light modulator 48 is a liquid crystal spatial light modulator that includes a display polarizer, namely an input polarizer 210 and an output polarizer 218. The viewing angle control elements 360A, 360B are arranged on the same side of at least one spatial light modulator 48 as the display polarizer of at least one spatial light modulator 48. In FIG. 3 , the viewing angle control element is arranged on the output side of the spatial light modulator 48, and the display polarizer is the output polarizer 218.

[0154] In this embodiment, polarizers 210, 218, 318, 302 (and any other polarizers) are typically linear polarizers, that is, they output linearly polarized light having electric vector transmission directions 211, 219, 319, 303, respectively.

[0155] The viewing angle control elements 360A, 360B each include an additional polarizer 318A, 318B; the plurality of retarders 300A, 300B are disposed between the additional polarizers 318A, 218B and the display polarizer 218 of the spatial light modulator 48. The plurality of retarders 300A, 300B are capable of simultaneously introducing no net relative phase shift into orthogonal polarization components of light passed by the display polarizer 218 along an axis that is normal to the plurality of retarders 300A, 300B, and introducing relative phase shift into orthogonal polarization components of light passed by the display polarizer along an axis that is tilted to the normal to the plurality of retarders 300A, 300B.

[0156] The viewing angle control elements 300A, 300B are arranged in series such that element 300B is arranged to receive light transmitted by element 300A.

[0157] The viewing angle control element 300B also includes a reflective polarizer 302 disposed between the display polarizer and the additional polarizer and also disposed between the additional polarizers 318A, 318B.

[0158] The structure of the display device 100 will now be described in more detail.

[0159] The display device 100 comprises a spatial light modulator 48 arranged to output light 400 ; wherein the spatial light modulator 48 comprises an output polarizer 218 arranged on an output side of the spatial light modulator 48 .

[0160] In the present disclosure, the spatial light modulator 48 may include a liquid crystal display including an input polarizer 210, an output polarizer 218 having substrates 212, 216, a liquid crystal layer 214, and red, green, and blue pixels 220, 222, 224. The backlight 20 may be arranged to illuminate the spatial light modulator 48 and include an input light source 15, a waveguide 1, a back reflector 3, and an optical stack 5 including a diffuser, a light turning film, and other known optical backlight structures. An asymmetric diffuser, which may include, for example, an asymmetric surface relief feature structure, may be provided in the optical stack 5 so that increased diffusion may be provided in the elevation direction compared to the lateral direction.

[0161] In an embodiment of the present invention, the backlight source 20 may be arranged to provide an angular light distribution having reduced brightness for off-axis viewing positions compared to frontal brightness. Typical wide-angle backlight sources have a falloff at higher angles such that the full width at half maximum of the relative brightness may preferably be greater than 40 degrees, more preferably greater than 60 degrees, and most preferably greater than 80 degrees.

[0162] The backlight 20 may also include a switchable backlight arranged to switch the output angular brightness distribution to provide reduced off-axis brightness in the anti-peeping mode of operation and higher off-axis brightness in the wide-angle mode of operation. Such a directional backlight provides some off-axis brightness reduction, advantageously improving front efficiency and reducing display visibility and stray light for off-axis positions.

[0163] The spatial light modulator 48 may alternatively be provided by other display types that provide the output light 400 by emission, such as an organic LED display (OLED) with an output polarizer 218 in the case where the backlight 20 is omitted.

[0164] The spatial light modulator 48 therefore includes an output polarizer 218 arranged on the output side of the spatial light modulator 48. The output polarizer 218 may be arranged to provide light from the pixels 220, 222, 224 of the spatial light modulator 48 with a high extinction ratio.

[0165] The optical stack also includes Figure 1 to Figure 2 The viewing angle control elements 360A and 360B shown in FIG. The viewing angle control elements 360A and 360B may have the configurations described in U.S. Patent No. 10126575 and U.S. Patent Publication No. 2018-0321553, both of which are incorporated herein by reference in their entirety.

[0166] Illustrative examples of viewing angle control elements 360A, 360B will now be given.

[0167] The viewing angle control element 360A includes an additional polarizer 318A disposed on the output side of the output polarizer 218; and a plurality of retarders 300A disposed between the additional polarizer 318A and the output polarizer 218. The electric vector transmission direction 219 of the output polarizer 218 is parallel to the electric vector transmission direction 319A of the additional polarizer 318A.

[0168] A plurality of retarders 300A are arranged between the output polarizer 218 and the additional polarizer 318A. FIG. 3A to FIG. 3B In the embodiment of the invention, the plurality of retarders 300A include a passive retarder 330A and a switchable liquid crystal retarder 301A, but other configurations of at least one retarder may be generally replaced. The retarder 300A does not affect the brightness of light passing through the retarder 300A and the additional polarizer 318A along an axis along the normal to the plane of the retarder 300A, but in at least one of the switchable states of the switchable retarder 301A, the retarder 300A reduces the brightness of light passing through it along an axis inclined to the normal to the plane of the retarder 300A. The principle causing this effect will be described below with reference to FIG. 22A to FIG. 263. More detailed description is given and is caused by the presence or absence of a phase shift introduced by the retarder 300 to light along axes that are at different angles relative to the liquid crystal material of the retarder 300. Similar effects are achieved in all of the devices described below.

[0169] The substrate 312A, 316A of the switchable liquid crystal retarder 301 comprises electrodes arranged to provide a voltage across the layer 314A of liquid crystal material 414. A control system (not shown) is arranged to control the voltage applied on the electrodes of the switchable liquid crystal retarder 301 by the voltage driver.

[0170] FIG. 3A to FIG. 3B Also shown is an air gap 619A provided between the output polarizer 218 of the spatial light modulator 48 and the additional polarizer 318A. It is desirable to provide high contrast for viewing the on-axis image of the switchable privacy display in both the privacy mode of operation and the public mode of operation. In addition, it is desirable to provide an air gap between the spatial light modulator and other components in the optical system to reduce assembly cost and complexity.

[0171] The multiple delay plates also include: an air gap input delay plate 326A, which includes at least one delay plate arranged between the display polarizer 218 and the air gap 619A; and an air gap output delay plate 328A, which includes at least one delay plate arranged between the air gap 619 and the additional polarizer 318.

[0172] The air gap input retarder 326A is arranged to provide a net phase shift to provide a circularly polarized light component of light passed by the display polarizer 218 along an axis that is normal to the plane of the air gap input retarder 326A in the air gap 619. The air gap input retarder and the air gap output retarder advantageously achieve a reduction in reflected light in the air gap 619A between the viewing angle control element 360A and the spatial light modulator 48. Figure 17 to Figure 1 8 describes the principle causing this effect in more detail.

[0173] When combined, the multiple delay plates 326A, 328A, 300A are capable of simultaneously not introducing a net relative phase shift into the orthogonal polarization components of light transmitted by the display polarizer 218 along an axis that is normal to the plane of the multiple delay plates 326, 328, 300, and introducing a net relative phase shift into the orthogonal polarization components of light transmitted by the display polarizer 218 along an axis that is inclined to the normal to the plane of the multiple delay plates 326A, 328A, 300A.

[0174] The viewing angle control element 360B is similar in structure and operation to FIG. 3A to FIG. 3B The viewing angle control element 360A in the implementation scheme.

[0175] The viewing angle control element 360B includes an additional additional polarizer 318B disposed on the output side of the additional polarizer 318A; a reflective polarizer 302 disposed between the additional polarizer 318A and the additional additional polarizer 318B; and a plurality of retarders 300B disposed between the reflective polarizer 302 and the additional additional polarizer 318B. The electric vector transmission direction 303 of the reflective polarizer 302 may be parallel to the electric vector transmission direction 319A of the additional polarizer 318A. The electric vector transmission direction 303 of the reflective polarizer 302 may be parallel to the electric vector transmission direction 219 of the additional polarizer 318A.

[0176] A plurality of retarders 300B are arranged between the reflective polarizer 302 and the additional additional polarizer 318B. FIG. 3A to FIG. 3B In the embodiment of the invention, the plurality of retarders 300B include a passive retarder 330B and a switchable liquid crystal retarder 301B, but can generally be replaced with other configurations of at least one retarder. The retarder 300B does not affect the brightness of light passing through the reflective polarizer 302, the retarder 300B, and the additional polarizer 318B along an axis along the normal to the plane of the retarder 300, but at least in one of the switchable states of the switchable retarder 301, the retarder 300B reduces the brightness of light passing through it along an axis inclined to the normal to the plane of the retarder 300B.

[0177] The substrate 312B, 316B of the switchable liquid crystal retarder 301B comprises electrodes arranged to provide a voltage across the layer 314B of liquid crystal material 414. The control system 352 is arranged to control the voltage applied by the voltage driver 350 on the electrodes of the switchable liquid crystal retarder 301B.

[0178] The display device may be arranged for use in ambient lighting 604 . Hence, the display device 100 for ambient lighting 604 comprises a spatial light modulator 48 arranged to output light 400 .

[0179] FIG. 3A to FIG. 3B Also shown is an air gap 619B provided between the additional polarizer 318A and the reflective polarizer 302.

[0180] The air gap input delay plate 326B includes at least one delay plate arranged between the additional polarizer 318A and the air gap 619B; and the air gap output delay plate 328B, which includes at least one delay plate arranged between the air gap 619B and the reflective polarizer 302.

[0181] The air gap input retarder 326B is arranged to provide a phase shift to provide a circularly polarized light component of light passed by the additional polarizer 318A along an axis normal to the plane of the air gap input retarder 326B in the air gap 619. When combined, the plurality of retarders 326B, 328B are capable of not introducing a phase shift to the polarization component of light passed by the display polarizer 218 along an axis normal to the plane of the plurality of retarders 326B, 328B. The air gap input retarder and the air gap output retarder advantageously achieve a reduction in reflected light in the air gap 619B between the viewing angle control element 360A and the viewing angle control element 360B. Referring now to FIG. Fig.17 The principle causing this effect is described in more detail.

[0182] Not discussed in further detail FIG. 3A to FIG. 3B Features of the embodiments may be assumed to correspond to features having equivalent reference numerals as discussed above, including any potential variations in features.

[0183] Tables 1 and 2 show FIG. 3A to FIG. 3B An exemplary embodiment of an arrangement of .

[0184]

[0185] Table 1

[0186]

[0187] Table 2

[0188] The plurality of retarders 300A, 300B comprises switchable liquid crystal retarders 301 A, 301 B. Further arrangements of the plurality of retarders will now be described.

[0189] In an alternative, the switchable liquid crystal retarder 301A, 301B may include two surface alignment layers, which are arranged adjacent to and on opposite sides of the layer 413A, 413B of liquid crystal material 414 and each arranged to provide a vertical alignment in the adjacent liquid crystal material. The layer 413A, 413B of the liquid crystal material 414 of the switchable liquid crystal retarder 301A, 301B may include a liquid crystal material having a negative dielectric anisotropy. The layer 413A, 413B of the liquid crystal material 414 may have a retardation in the range of 500nm to 1000nm, preferably in the range of 600nm to 900nm and most preferably in the range of 700nm to 850nm for light with a wavelength of 550nm.

[0190] In the case where two surface alignment layers providing vertical alignment are provided, the at least one passive compensating delay plate 330A, 330B may include a delay plate having an optical axis perpendicular to the plane of the delay plate, and the at least one passive delay plate has a delay in the range of -300nm to -900nm, preferably in the range of -450nm to -800nm ​​and most preferably in the range of -500nm to -725nm for light with a wavelength of 550nm.

[0191] Alternatively, in case two surface alignment layers providing vertical alignment are provided, the at least one passive compensating retarder 330A, 330B may comprise a pair of retarder plates having optical axes crossing in the plane of the retarder plates, each of the pair of retarder plates having a retardation in the range of 300nm to 800nm, preferably in the range of 500nm to 700nm and most preferably in the range of 550nm to 675nm for light having a wavelength of 550nm. Advantageously, in this case, an increased field of view in a wide angle operation mode may be provided. Furthermore, zero voltage operation in a wide angle operation mode may be provided, thereby reducing power consumption.

[0192] In another alternative, the switchable liquid crystal retarder 301A, 301B may comprise two surface alignment layers disposed adjacent and on opposite sides of the layer 413A, 413B of liquid crystal material 414 and each arranged to provide a horizontal alignment in the adjacent liquid crystal material. Advantageously, increased resilience to visibility of the flow of liquid crystal material during application of pressure may be achieved compared to a vertical alignment on opposite sides of the liquid crystal.

[0193] The layers 413A, 413B of the liquid crystal material 414 of the switchable liquid crystal retarder 301A, 301B may include a liquid crystal material having a positive dielectric anisotropy. The layers 413A, 413B of the liquid crystal material 414 may have a retardation in the range of 500nm to 900nm, preferably in the range of 600nm to 850nm, and most preferably in the range of 700nm to 800nm ​​for light having a wavelength of 550nm.

[0194] In the case where two surface alignment layers providing horizontal alignment are provided, the at least one passive compensating delay plate 330A, 330B may include a delay plate having an optical axis perpendicular to the plane of the delay plate, and the at least one passive delay plate has a delay in the range of -300nm to -700nm, preferably in the range of -350nm to -600nm and most preferably in the range of -400nm to -500nm for light with a wavelength of 550nm.

[0195] Alternatively, in case two surface alignment layers providing horizontal alignment are provided, the at least one passive compensating retarder 330A, 330B may comprise a pair of retarders having optical axes crossing in the plane of the retarders, each of the pair of retarders having a retardation in the range of 300nm to 800nm, preferably in the range of 350nm to 650nm and most preferably in the range of 450nm to 550nm for light having a wavelength of 550nm. Advantageously, in this case, an increased resilience to the visibility of the flow of the liquid crystal material during the application of pressure may be achieved.

[0196] In another alternative, the switchable liquid crystal retarder 301A, 301B may include two surface alignment layers, which are arranged adjacent to and on opposite sides of the layers 413A, 413B of the liquid crystal material 414, wherein one surface alignment layer is arranged to provide a vertical alignment in the adjacent liquid crystal material and the other surface alignment layer is arranged to provide a horizontal alignment in the adjacent liquid crystal material.

[0197] When the surface alignment layer arranged to provide a horizontal alignment is interposed between the layers 413A, 413B of the liquid crystal material 414 and the compensating delay plates 330A, 330B, the layers 413A, 413B of the liquid crystal material 414 may have a retardation in the range of 700nm to 2000nm, preferably in the range of 1000nm to 1500nm and most preferably in the range of 1200nm to 1500nm for light with a wavelength of 550nm.

[0198] When a surface alignment layer arranged to provide a horizontal alignment is interposed between the layers 413A, 413B of the liquid crystal material 414 and the compensating delay plates 330A, 330B, the at least one passive compensating delay plate 330A, 330B may include a delay plate having an optical axis perpendicular to the plane of the delay plate, and the at least one passive delay plate has a retardation in the range of -400nm to -1800nm, preferably in the range of -700nm to -1500nm and most preferably in the range of -900nm to -1300nm for light with a wavelength of 550nm.

[0199] When a surface alignment layer arranged to provide a horizontal alignment is interposed between the layers 413A, 413B of the liquid crystal material 414 and the compensating delay plates 330A, 330B, the at least one passive compensating delay plate 330A, 330B may include a pair of delay plates having optical axes crossing in the plane of the delay plates, each delay plate in the pair of delay plates having a retardation in the range of 400nm to 1800nm, preferably in the range of 700nm to 1500nm and most preferably in the range of 900nm to 1300nm for light having a wavelength of 550nm.

[0200] When the surface alignment layer arranged to provide a vertical alignment is between the layers 413A, 413B of the liquid crystal material 414 and the compensating delay plates 330A, 330B, the layers 413A, 413B of the liquid crystal material 414 may have a retardation in the range of 500nm to 1800nm, preferably in the range of 700nm to 1500nm and most preferably in the range of 900nm to 1350nm for light with a wavelength of 550nm.

[0201] When a surface alignment layer arranged to provide a vertical alignment is interposed between the layers 413A, 413B of the liquid crystal material 414 and the compensating delay plates 330A, 330B, the at least one passive compensating delay plate 330A, 330B may include a delay plate having an optical axis perpendicular to the plane of the delay plate, and the at least one passive delay plate has a retardation in the range of -300nm to -1600nm, preferably in the range of -500nm to -1300nm and most preferably in the range of -700nm to -1150nm for light with a wavelength of 550nm.

[0202] When a surface alignment layer arranged to provide a homeotropic alignment is interposed between the layers 413A, 413B of liquid crystal material 414 and the compensating retarder 330A, 330B, the at least one passive compensating retarder 330A, 330B may comprise a pair of retarders having optical axes crossing in the plane of the retarders, each of the pair of retarders having a retardation in the range of 400nm to 1600nm, preferably in the range of 600nm to 1400nm and most preferably in the range of 800nm ​​to 1300nm for light having a wavelength of 550nm. Advantageously, in this case, an increased resilience to the visibility of the flow of liquid crystal material during the application of pressure may be achieved.

[0203] Each alignment layer may have a pretilt angle in a pretilt direction, wherein a component in the plane of the liquid crystal layer is parallel or antiparallel or orthogonal to the direction of transmission of the electric vector of the display polarizer. Advantageously, the display may have a narrow viewing angle in the lateral direction and a wide viewing freedom for rotation of the display about a horizontal axis. Such a display may be comfortable to view for a front-facing display user, but difficult to view for an off-axis display user.

[0204] The at least one passive retarder may include at least two passive retarder plates having at least two different orientations of optical axes, the at least two passive retarder plates may have optical axes that cross in the plane of the retarder plates. The field of view of the liquid crystal retarder having a horizontal alignment is increased while providing resilience to visibility of the liquid crystal material flow during application of pressure.

[0205] The pair of passive retarders may have optical axes extending at 45 degrees and 135 degrees, respectively, relative to the direction of electric vector transmission parallel to the electric vector of the display polarizer.The passive retarders may be provided using stretched films to advantageously achieve low cost and high uniformity.

[0206] A switchable liquid crystal retarder 301A, 301B may be provided between the pair of passive retarders. Advantageously, the thickness and complexity of multiple retarders may be reduced.

[0207] A transparent electrode and a liquid crystal alignment layer may be formed on one side of each of the pair of passive delay plates adjacent to the switchable liquid crystal delay plate 301A, 301B; and may also include a first substrate and a second substrate between which the switchable liquid crystal delay plates 301A, 301B are provided, the first substrate and the second substrate each including one of the pair of passive delay plates, wherein each of the pair of passive delay plates has a retardation in the range of 150nm to 800nm, preferably in the range of 200nm to 700nm, and most preferably in the range of 250nm to 600nm for light with a wavelength of 550nm.

[0208] In an alternative, the at least one passive compensating retarder 330A, 330B may include a retarder having an optical axis perpendicular to the plane of the retarder. Advantageously, the thickness and complexity of the passive retarder stack may be reduced.

[0209] The at least one passive compensating retarder 330A, 330B may include two passive retarders having an optical axis perpendicular to the plane of the passive retarders and a switchable liquid crystal retarder 301A, 301B is provided between the two passive retarders. Advantageously, the thickness and complexity of the plurality of retarders may be reduced. Higher frontal efficiency may be achieved in wide angle mode and anti-peep mode, the wide angle mode has a wide field of view and a peeper may not be able to perceive image data from a wide range of off-axis viewing positions.

[0210] The transparent electrode and the liquid crystal alignment layer may be formed on one side of each of the two passive retarders adjacent to the switchable liquid crystal retarders 301A, 301B. A first substrate and a second substrate of the switchable liquid crystal retarders 301A, 301B may be provided therebetween, each of the first substrate and the second substrate including one of the two passive retarders. The two passive retarders may have a total retardation in the range of -300nm to -700nm, preferably in the range of -350nm to -600nm, and most preferably in the range of -400nm to -500nm for light having a wavelength of 550nm.

[0211] In another alternative, the at least one passive compensating retarder 330A, 330B may include a retarder having an optical axis, wherein one component of the optical axis is perpendicular to the plane of the retarder and one component is in the plane of the retarder. Advantageously, the field of view in the wide angle mode may be increased, and a snooper may not be able to perceive image data from a wide range of off-axis viewing positions.

[0212] The components in the plane of the passive retarder may extend at 0 degrees relative to the electric vector transmission direction parallel or perpendicular to the electric vector transmission of the display polarizer. The at least one passive retarder may also include a passive retarder having an optical axis perpendicular to the plane of the passive retarder, or a pair of passive retarder having optical axes crossing in the plane of the passive retarder.

[0213] The delay of the at least one passive compensating delay plate 330A, 330B may be equal in magnitude and opposite in direction to the delay of the switchable liquid crystal delay plates 301A, 301B.

[0214] The switchable liquid crystal retarder 301A, 301B may include a first pretilt angle and a second pretilt angle; and the at least one passive compensating retarder 330A, 330B may include a compensating retarder 330A, 330B having a first pretilt angle and a second pretilt angle, the first pretilt angle of the compensating retarder 330A, 330B being the same as the first pretilt angle of the liquid crystal retarder, and the second pretilt angle of the compensating retarder 330A, 330B being the same as the second pretilt angle of the liquid crystal retarder.

[0215] The switchable liquid crystal retarder 301A, 301B may further comprise electrodes arranged to apply a voltage in order to control the layer 413A, 413B of liquid crystal material 414. The electrodes may be on opposite sides of the layer 413A, 413B of liquid crystal material 414. The display may be switched by control of the liquid crystal layer, thereby advantageously realizing a switchable anti-peep display or other display that reduces off-axis stray light. The display may further comprise a control system arranged to control the voltage applied to the electrodes of the at least one switchable liquid crystal retarder 301A, 301B.

[0216] Now we will use FIG. 3A to FIG. 3B The exemplary embodiments described here are from Figure 1 to Figure 2 Display uniformity of the display structure.

[0217] Figure 4 is shown in Table 3 using the exemplary embodiment and for FIG. 3A to FIG. 3B A schematic curve diagram of the output brightness of a display device in a common operation mode changing with polar direction.

[0218]

[0219] Table 3

[0220] Figure 4 Isoluminance contours are shown that can be achieved with wide angle backlight 20. Viewing angle control elements 360A, 360B are driven with high voltages as shown in Table 1 to provide common mode (wide angle) operation and do not substantially change the field of view of light output from spatial light modulator 48 and backlight 20.

[0221] Polar region 460 shows the field of view of display device 100 for the eye of on-axis user 26, where spatial light modulator 48 and backlight 20 are planar so that all light cones 410 from the display are parallel. The isoluminance lines within polar region 460 show the variation in brightness seen by the user from display device 100.

[0222] Polar region 461 illustrates the field of view of display device 100 for on-axis user 26, where spatial light modulator 48 and backlight 20 have a radius of curvature of 1800 mm around the horizontal direction. The change in edge brightness from about 82% to about 88% (compared to 100% front brightness) at polar position 463 and polar position 464 is not easily discernible to an average user, so curving the spatial light modulator and backlight 20 does not significantly change the brightness uniformity of the image seen by the user.

[0223] Figure 4 Also shown is the field of view in the polar region 465 of user 27 at 2000 mm from the display device 100, which has a radius of curvature of 1800 mm (curvature = 0.55 m), centered at a lateral angle of 45 degrees and an elevation angle of zero degrees. In such a position, user 27 advantageously sees a high brightness image with good brightness uniformity.

[0224] Figure 5 is a schematic graph showing the variation of output brightness with polar direction in an anti-peeping operation mode of a display including a planar viewing angle control element. Figure 4 Thus, the change in edge brightness at pole positions 463 and 464 from about 15% (viewing angle control elements 360A, 360B have no curvature) to about 45% (viewing angle control elements 360A, 360B have a curvature of 0.55 m) is a desirable increase in display uniformity for user 26.

[0225] The snooper 27 can see the polar region 465 with a small lateral extent, since the curvature of the display 100 is similar to the viewing distance of the snooper. Advantageously, the level of visual security against snoopers has a high uniformity.

[0226] with Figure 5 Compared to that shown in , it is expected to further increase the display uniformity.

[0227] Figure 6 3 is a schematic graph showing the change of the output brightness with the polar direction in the anti-peeping operation mode of the curved viewing angle control elements 360A and 360B. Figure 1 In operation of the display device 100, wherein the curvature of the viewing angle control elements 360A, 360B is greater than the desired curvature of the spatial light modulator, and the exemplary embodiment of the planar spatial light modulator 48A, 48B and the viewing angle control elements 360A, 360B has a radius of curvature of 1000 mm. Advantageously, image uniformity is significantly increased, as shown in the polar region 462 for the on-axis user 26, where the brightness uniformity over most of the display area is greater than 60%.

[0228] Figure 7 3 is a schematic diagram showing the variation of the relative reflectivity of the display with polar direction in the anti-peeping operation mode of the curved viewing angle control elements 360A, 360B. The reflectivity is normalized to the maximum reflectivity, and in the implementation, the reflectivity is about 40% considering the polarizer loss, the reflective polarizer reflectivity and the front surface Fresnel reflection.

[0229] Thus, there is low image reflectivity for an on-axis user, i.e., the display corners do not have high reflectivity. However, an off-axis snooper 27 sees high reflectivity over the entire display area, e.g., greater than 30% reflectivity. Advantageously, high visual safety is achieved for all parts of the image area of ​​the snooper's viewing area. Furthermore, as the snooper moves toward a more on-axis position, the brightness can be increased, but the high reflectivity is maintained, so that an increased level of visual safety is achieved away from the optimal pole position.

[0230] Other arrangements of the curved viewing angle control element 360 will now be described.

[0231] Fig. 8A is a schematic diagram showing an anti-peeping display device 100 in a perspective front view, the anti-peeping display device including two planar spatial light modulators 48A, 48B, and a curved viewing angle control element including a first curved viewing angle control element 360A and a second curved viewing angle control element 360B; and Figure 8B It is shown in top view Fig. 8A Schematic diagram of an anti-peeping display device. Not discussed in further detail FIG. 8A to FIG. 8B Features of the embodiments may be assumed to correspond to features having equivalent reference numerals as discussed above, including any potential variations in features.

[0232] and Figure 1 In contrast, the spatial light modulators 48A, 48B may be planar. Advantageously, image distortion on the surface of the curved spatial light modulator may be reduced. For example, due to Figure 1Due to the surface curvature of the spatial light modulator 48, straight lines may be perceived by the display user 360 as being straight rather than curved.

[0233] However, as in Figure 6 to Figure 7 As shown in FIG. 4 , the curved viewing angle control elements 360A, 360B may maintain a cone of light 410 directed toward the primary user 26 such that a high image uniformity is advantageously observed.

[0234] Fig. 9 1 is a schematic diagram showing a top view of an anti-peeping display including two tilted planar spatial light modulators and a curved viewing angle control element including a first curved viewing angle control element and a second curved viewing angle control element. Fig. 9 Features of the embodiments may be assumed to correspond to features having equivalent reference numerals as discussed above, including any potential variations in features.

[0235] The tilted spatial light modulators 48A, 48B may provide a desired multi-display configuration for a typical multi-screen environment while achieving increased uniformity for a center observer 326 in privacy mode.

[0236] An arrangement with a single backlight 20 will now be described.

[0237] Fig. 10A is a schematic diagram showing a privacy display in top view, the privacy display comprising two tilted planar spatial light modulators, a single curved backlight, and a curved viewing angle control element comprising a first curved viewing angle control element and a second curved viewing angle control element; and Fig. 10B 3 is a schematic diagram showing an anti-peeping display in top view, which includes two planar spatial light modulators, a single curved collimated backlight, and a curved viewing angle control element 360.

[0238] exist FIG. 10A to FIG. 10B In FIG. 4 , a single backlight source 20 is provided to illuminate the spatial light modulators 48A, 48B. Fig. 10A shows that the backlight 20 may have a light cone 412 with relatively high brightness decay (but not Lambertian), while Fig. 10B The following is shown FIG. 19I to FIG. 19E A collimated backlight of the type shown has a narrow light cone 412 .

[0239] Advantageously, backlight 20, light cone 412, and viewing angle correction element 360 cooperate to provide increased uniformity for front users in front of the display and provide an increased level of visual security against snoopers. Additionally, the curvature of the spatial light modulator may be independent of the curvature of spatial light modulators 48A, 48B.

[0240] Various arrangements having a single spatial light modulator 48 will now be described.

[0241] Fig.11 is a schematic diagram showing an anti-peeping display in a top view, the anti-peeping display comprising a curved spatial light modulator, a backlight source, and a curved viewing angle control element comprising a first curved viewing angle control element and a second curved viewing angle control element, wherein the curvature of the spatial light modulator and the backlight source is smaller than the curvature of the viewing angle control element; Fig.12 is a schematic diagram showing a privacy display in top view, the privacy display comprising a curved backlight and a first curved viewing angle control element arranged behind a curved spatial light modulator, and a second curved viewing angle control element arranged to receive light from the spatial light modulator, wherein the curvature of the spatial light modulator, the backlight and the first viewing angle control element is less than the curvature of the second viewing angle control element; Fig.13 is a schematic diagram showing a privacy display in top view, the privacy display comprising a curved backlight and first and second curved viewing angle control elements arranged behind a curved spatial light modulator, wherein the curvature of the spatial light modulator is smaller than the curvature of the viewing angle control element and the backlight; Fig.14 is a schematic diagram showing a privacy display in top view, the privacy display comprising a curved backlight and first and second curved viewing angle control elements arranged behind a planar spatial light modulator; and Fig.15 is a schematic diagram showing an anti-peeping display in a top view, the anti-peeping display including a curved backlight and a first curved viewing angle control element arranged behind a planar spatial light modulator and a planar viewing angle control element.

[0242] Not discussed in further detail Figures 11 to 15 Features of the embodiments may be assumed to correspond to features having equivalent reference numerals as discussed above, including any potential variations in features.

[0243] Fig.11 Shows something like Figure 1 An embodiment includes a single spatial light modulator 48 and a backlight source 20, wherein the curvature of the spatial light modulator 48 and the backlight source is different from the curvature of the viewing angle control elements 360A, 360B. Advantageously, the distortion of straight lines on the spatial light modulator 48 is reduced, while improving uniformity in the anti-peep mode. In addition, Fig. 9 Compared with the planar non-tilted spatial light modulators 48A, 48B, the brightness uniformity in the common mode is improved.

[0244] Fig.12 An embodiment is shown in which a viewing angle control element 360A is disposed between the at least one spatial light modulator 48 and the backlight 20. The increased thickness of the curved front element can be advantageously reduced while Figure 3A A reflective front viewing angle control element 360B of the type shown in FIG. 3 may be used to advantageously increase the level of visual safety for off-axis users 27 .

[0245] Figure 13 to Figure 14 The viewing angle control elements 360A, 360B are shown to be arranged between the backlight source 20 and the spatial light modulator 48, which may be as shown in FIG. Fig.13 That is curved or Fig.14 Advantageously, the linearity of the image lines can be provided independently of the uniformity provided to the display user 26 .

[0246] Fig.15 The planar viewing angle control element 360B is shown to be applied in front of the planar spatial light modulator, while the curved viewing angle control element 360A is provided between the curved collimated backlight 20 and the spatial light modulator. Advantageously, the display uniformity can be increased while reducing the thickness of the elements in front of the screen, while utilizing Figure 3A A viewing angle control element 360B of the type shown in FIG. 3 is used to implement switchable reflectivity.

[0247] The viewing angle control elements will now be described.

[0248] Fig.16 is shown in a perspective side view for Figure 3A Schematic diagram of an angle control element in an anti-peeping display device. Fig.16 The features of the embodiments of the present invention may be assumed to correspond to the features having equivalent reference numerals as discussed above, including any potential variations in the features. Viewing angle control elements 360A, 360B may be provided on the spatial light modulator 48, which may be provided with quarter wave plates 328A, 326B, 328B.

[0249] In order to achieve a display front component with different curvatures, it is desirable to provide an air gap between the spatial light modulator 48 and the viewing angle control elements 360A, 360B. Without controlling the reflection, such an air gap will cause a reduction in image contrast due to surface reflections. Such reflections can be reduced by air gap retarders 326, 328. The air gap retarders 326, 328 will now be described. Figure 3A The operation of the air gap input delay plate 326B and the air gap output delay plate 328B at the air gap 619B.

[0250] Fig.17 is a schematic diagram illustrating surface reflections in a portion of an anti-peeping display device in side view, the anti-peeping display device including a pair of quarter-wave plates arranged on opposite sides of an air gap 619B.

[0251] The air gap input retardation plate 326B is arranged on one side of the air gap 619B, and the air gap output retardation plate 328B is arranged on the opposite side of the air gap 619B, and both include quarter wave plates, respectively.

[0252] The first quarter wave plate and the second quarter wave plate of the air gap input delay plate 326B and the air gap output delay plate 328B have crossed optical axes; and the light 400 from the spatial light modulator 48 has a polarization component, which undergoes equal and opposite phase shifts in the crossed first delay plate 326B and the second delay plate 328B.

[0253] In operation, the on-axis ambient light 623 is incident on the reflective polarizer 302, and its polarization component 630 is substantially linear after being transmitted through the passive retarder 330 and the switchable liquid crystal layer 314. The polarization component 630 is parallel to the electric vector transmission direction of the reflective polarizer 302, and is transmitted into the quarter wave plate of the retarder 328B and undergoes a quarter wave phase shift to provide a left circular polarization component 632.

[0254] The quarter wave plate of the retarder 328B provides an opposite phase shift to the transmitted light 623 so that the light is transmitted by the polarizer 218 and absorbed in the viewing angle control element 360A or the spatial light modulator 48.

[0255] For output light 400, the crossed retarders 326B, 328B can also cancel each other, thereby advantageously achieving high output efficiency.

[0256] As shown by ambient light 625, some of the light at the interface of quarter wave plate retarder 326B to air gap 619B is Fresnel reflected where it is phase shifted to provide a right circular polarization component 634 which is incident on quarter wave plate retarder 328B and is converted into a linear polarization component 636 which is reflected at reflective polarizer 302 orthogonal to component 630. This polarization component is phase shifted to output a right circular polarization component 638 which is incident on the quarter wave plate of retarder 326B which is phase shifted into a linear polarization state 640 which is eliminated by display polarizer 218.

[0257] Additionally, as shown by ambient light 627, Fresnel reflections from the interface of the wave plate of retarder 328B are absorbed at the display polarizer 218 in a similar manner.

[0258] Advantageously, a display having high on-axis contrast and low off-axis contrast can be provided while providing an air gap to increase yield and reduce assembly cost and complexity. The retardation varies little with polar angle, allowing the viewing angle control elements 360A, 360B to have a curved shape while maintaining an image with high contrast.

[0259] return FIG. 3A to FIG. 3B The operation of the quarter wave plates 326A, 328A is similar to that in Fig.17 , except that reflective polarizer 302 is omitted and the operation of quarter wave retarders 326A, 326B can be combined with the operation of retarder 300A. Advantageously, a display having high on-axis contrast and low off-axis brightness can be achieved while providing an air gap to increase yield and reduce assembly cost and complexity.

[0260] Fig.18A is a schematic diagram showing an anti-peeping display device including a spatial light modulator and a single viewing angle control element in a perspective side view; and Fig.18B Shown in expanded view Fig.18A Schematic diagram of the arrangement of polarizers and retarders. Features of the embodiments of Figures 18-19 that are not discussed in further detail can be assumed to correspond to features with equivalent reference numerals as discussed above, including any potential changes in the features.

[0261] and FIG. 3A to FIG. 3B 18 to 19 include a single viewing angle control element 360 instead of Fig.16 Independent components 360A, 360B.

[0262] The light redirecting film 926 includes a prism layer having a prism surface 927 arranged on a prism layer supporting substrate 929, which is arranged between the optical waveguide 1 and the spatial light modulator to receive the output light from the optical waveguide 1 and guide the output light through the spatial light modulator 48.

[0263] The prism layer is arranged between the optical waveguide 1 and the prism layer supporting substrate.

[0264] By comparison, in e.g. Figure 4 , a single element 360 can provide relatively high brightness for off-axis viewing directions in the anti-peeping mode of operation. This high brightness will provide undesirably low visual security against off-axis snoopers 27. The light turning film 926 is arranged so that the elongated prism surface 927 is arranged between the prism layer support substrate 929 of the backlight 20 and the waveguide 1. Advantageously, a light cone with low brightness for off-axis viewing positions can be provided, as will be further described below.

[0265] It is desirable to reduce the brightness provided to the off-axis snooper 27 .

[0266] In addition, the backlight source 20 may be a directional backlight source that provides brightness at a polar angle greater than 45 degrees to the normal to the spatial light modulator, and the brightness is at most 30% of the brightness along the normal to the spatial light modulator, preferably at most 20% of the brightness along the normal to the spatial light modulator, and more preferably at most 10% of the brightness along the normal to the spatial light modulator.

[0267] and Figure 3A Compared with the arrangement of Fig.18A In an exemplary embodiment of the invention, the brightness at polar angles greater than 45 degrees to the normal to the spatial light modulator can be up to 18%. Such a backlight source 20 can be provided, for example, by a collimating waveguide 1 provided with surface extraction features that extract from the waveguide surface at angles close to grazing incidence and have narrow lateral angles. Such known collimating waveguides 1 may include lens-like surfaces and prismatic extraction features.

[0268] It is desirable to provide a further reduction in off-axis brightness through directional illumination from spatial light modulator 48. Directional illumination of spatial light modulator 48 by directional backlight 20 will now be described.

[0269] Fig.19A is a schematic diagram showing a directional backlight source 20 in a perspective view, and Fig.19B 2 is a schematic diagram showing a non-directional backlight source 20 in perspective view, any of which may be used in any of the devices described herein. Fig.19A The directional backlight 20 shown provides a narrow cone 450, while Fig.19B The illustrated non-directional backlight 20 provides a wide angular distribution cone 452 of light output rays.

[0270] Fig.19C is a schematic graph showing how brightness changes with lateral viewing angle under various backlight arrangements. Fig.19C The graph of may be a cross-section through the polar field of view distribution described herein.

[0271] A Lambertian backlight has a brightness distribution 846 that is independent of viewing angle.

[0272] Typical wide angle backlights have a falloff 844 at higher angles, such that the full width at half maximum 866 of the relative brightness may be greater than 40 degrees, preferably greater than 60 degrees, and most preferably greater than 80 degrees. In addition, the relative brightness 864 at + / - 45 degrees is preferably greater than 7.5%, more preferably greater than 10%, and most preferably greater than 20%.

[0273] In contrast, directional backlight 20 has a falloff at higher angles such that the full width at half maximum 862 of the relative brightness may be less than 60 degrees, preferably less than 40 degrees, and most preferably less than 20 degrees. In addition, backlight 20 is capable of providing a brightness 868 at a polar angle greater than 45 degrees from the normal to spatial light modulator 48 that is at most 33% of the brightness along the normal to spatial light modulator 48, preferably at most 20% of the brightness along the normal to spatial light modulator 48, and most preferably at most 10% of the brightness along the normal to spatial light modulator 48.

[0274] Scattering and diffraction in the spatial light modulator 48 can degrade the privacy mode operation when the switchable retarder 300 is arranged between the input display polarizer 210 and the additional polarizer 318. In an arrangement where the switchable retarder 300 is arranged between the output display polarizer 218 and the additional polarizer 318, the brightness at polar angles greater than 45 degrees from the normal to the spatial light modulator can be increased compared to an arrangement where the switchable retarder 300 is arranged between the input display polarizer 210 and the additional polarizer 318.

[0275] Advantageously, for Fig.18A arrangement to achieve lower off-axis brightness.

[0276] Fig.19D 1 is a schematic diagram showing a switchable directional display device 100 including a switchable liquid crystal retarder 300 and a backlight source 20 in a side view. Fig.19D The backlight 20 may be used in any of the devices described herein and comprises an imaging waveguide 1 illuminated by an array of light sources 15 through an input end 2 . Fig.19E The following perspective view shows Fig.19D Schematic diagram of the operation of the imaging waveguide 1 in the narrow angle operation mode.

[0277] The imaging waveguide 1 is of the type described in US Pat. No. 9,519,153, which is incorporated herein by reference in its entirety. The waveguide 1 has an input end 2 extending in a lateral direction along the waveguide 1. A light source array 15 is disposed along the input end 2 and inputs light into the waveguide 1.

[0278] The waveguide 1 also has opposing first and second guide surfaces 6, 8, which extend across the waveguide 1 from the input end 2 to the reflective end 4 so as to guide light input at the input end 2 forward and backward along the waveguide 1. The second guide surface 8 has a plurality of light extraction features 12 facing the reflective end 4 and is arranged to deflect at least some of the light that passes through the waveguide 1 and is guided back from the reflective end 4 through the first guide surface 6 in different directions from different input locations across the input end 2, the different directions depending on the input location.

[0279] In operation, light is directed from the light source array 15 through the input end and between the first and second guide surfaces 6, 8 without loss to the reflective end 4. The reflected light is incident on the facet 12 and is output by reflection as light ray 230 or transmitted as light ray 232. The transmitted light ray 232 is directed back through the waveguide 1 by the facets 803, 805 of the back reflector 800. The operation of the back reflector is further described in U.S. Patent No. 10054732, which is incorporated herein by reference in its entirety.

[0280] like Fig.19E As shown, the curved reflective end 4 and the optical power of the facet 12 provide an optical window 26 which is transmitted through the spatial light modulator 48 and has an axis 197 generally aligned with the optical axis 199 of the waveguide 1. A similar optical window 26 is provided by the transmitted light ray 232 reflected by the back reflector 800.

[0281] Fig.19F is shown when used in a display device without a switchable liquid crystal retarder Fig.19E A schematic graph of the output field brightness diagram of .

[0282] Thus for off-axis viewing, the location viewed by snooper 47 may have reduced brightness, for example between 1% and 3% of the center peak brightness at 0 degrees elevation and + / - 45 degrees lateral angle. Further reduction in off-axis brightness is achieved by multiple retarders 301, 330 of embodiments of the present invention.

[0283] Another type of directional backlight having low off-axis brightness will now be described.

[0284] Figure 19G is a schematic diagram showing a switchable directional display device in side view, which includes a backlight source 20 with a switchable collimating waveguide 901, a switchable liquid crystal retarder 300 and an additional polarizer 318. Figure 19G The backlight source 20 may be applied to any of the devices described herein and arranged as follows.

[0285] The waveguide 901 has an input end 902 extending in a lateral direction along the waveguide 901. A light source array 915 is disposed along the input end 902 and inputs light into the waveguide 1. The waveguide 901 also has opposing first and second guide surfaces 906, 908 extending across the waveguide 1 from the input end 2 to the reflective end 4 so as to guide light input at the input end 2 forward and backward along the waveguide 1. In operation, light is guided between the first guide surface 906 and the second guide surface 908.

[0286] The first guide surface 906 may be provided with a lenticular structure 904 including a plurality of elongated lenticular elements 905, and the second guide surface 908 may be provided with a prism-like structure 912 that is tilted and acts as a light extraction feature. The plurality of elongated lenticular elements 905 and the plurality of tilted light extraction features of the lenticular structure 904 deflect input light guided through the waveguide 901 to exit through the first guide surface 906.

[0287] A back reflector 903 , which may be a planar reflector, is provided to direct light transmitted through the surface 908 back through the waveguide 901 .

[0288] Output light rays incident on the prismatic structure 912 and the lenticular elements 905 of the lenticular structure 904 are output at angles close to grazing incidence on the surface 906. A prismatic turning film 926 including facets 927 is arranged to redirect the output light rays 234 through the spatial light modulator 48 and the compensating switchable liquid crystal retarder 300 by total internal reflection.

[0289] Fig.19H Schematic diagram showing the output of collimating waveguide 901 in top view. Prismatic structure 912 is arranged to provide light on lenticular structure 904 at certain incident angles, which are below the critical angle so that light can escape. When incident at the edge of the lenticular surface, the inclination of the surface provides light deflection that causes the light to escape and provides a collimating effect. When incident on position 185 of lenticular structure 904 of collimating waveguide 901, light 234 can be provided by light rays 188a-c and light rays 189a-c.

[0290] Fig.19I It is shown Figure 19G A narrow output light cone can thus be provided, the size of which is determined by structures 904, 912 and turning film 926.

[0291] Advantageously, in areas where a snooper may be positioned at a lateral angle of, for example, 45 degrees or more, the brightness of the output from the display is less, typically less than 2%. It is desirable to achieve a further reduction in output brightness. Such a further reduction is achieved by, for example, Figure 19G The compensating switchable liquid crystal retarder 300 and the additional polarizer 318 shown in FIG. 3A and 3B provide an exemplary embodiment of the present invention. Advantageously, a high performance privacy display with low off-axis brightness can be provided over a wide field of view.

[0292] For a typical snooper 47 position, a directional backlight source such as Fig.19D and Figure 19GThe type described above can achieve an off-axis brightness of less than 1.5%, preferably less than 0.75%, and most preferably less than 0.5% with the plurality of retarders 301, 330 of the embodiments of the present invention. In addition, high on-axis brightness and uniformity can be provided for the primary user 45. Advantageously, a high performance anti-peeping display with low off-axis brightness can be provided over a wide field of view, which can be achieved with the aid of Fig.18A The control system 352 shown switches the high-performance anti-peeping display to the wide-angle mode by controlling the switchable retarder 301 .

[0293] The waveguide 1 of the above-described embodiment can be bent to realize a curved backlight source 20. In an embodiment including a curved concave backlight source 20, for example, as in Figure 5 As shown in the curved viewing angle control implementation shown in , similar improvements in image uniformity and visual safety levels can be achieved.

[0294] It may be desirable to provide a mobile display device having a curved viewing angle control element 360 .

[0295] Fig. 20 is a schematic diagram showing a display device in top view, the display device including a planar spatial light modulator, a backlight, and a curved viewing angle control element in a display operating arrangement; and Fig.21 Schematic diagram showing a display device in top view, the display device including a planar spatial light modulator, a backlight source and a bendable viewing angle control element in a folded arrangement. This arrangement can be applied to foldable devices such as, for example, laptop computers. Fig. 20 In the operating mode shown in FIG. 4 , the flexible member 600 is extended while the center of the viewing angle control element 360 remains in close proximity to the spatial light modulator 48. Fig.21 In the transport mode shown in FIG, the member 600 can be retracted and the element 360 can be folded flat, for example, to the keyboard 602 of a laptop device. Advantageously, the compact display can provide increased uniformity to the front user in the operating mode and can be provided in a thin package in the transport mode.

[0296] The operation of the retarder layer between parallel polarizers for off-axis illumination will now be further described. In the various arrangements described above, at least one retarder is arranged between the reflective polarizer 318 and the additional polarizer 218 in various different configurations. In each case, the at least one retarder is configured so that it does not affect the brightness of light passing through the reflective polarizer 318, the at least one retarder and the additional polarizer 218 along an axis that is normal to the plane of the retarder, but at least in one of the switchable states of the compensating switchable retarder 300, it reduces the brightness of light passing through the reflective polarizer 318, the at least one retarder and the additional polarizer 218 along an axis that is tilted to the normal to the plane of the retarder. A description of this effect will now be given in more detail, the principles of which are generally applicable to all of the arrangements described above.

[0297] Fig.22A 630. A schematic diagram showing illumination of a retarder layer by off-axis light in perspective. Corrective retarder 630 may include a birefringent material represented by an index ellipsoid 632 having an optical axis direction 634 at 0 degrees from the x-axis and having a thickness 631. Normal ray 636 propagates such that the path length in the material is the same as thickness 631. Ray 637 in the yz plane has an increased path length; however, the birefringence of the material is substantially the same as ray 636. By comparison, ray 638 in the xz plane has an increased path length in the birefringent material and additionally has a birefringence different from normal 636.

[0298] Therefore, the retardation of the retarder 630 depends on the angle of incidence of the corresponding light ray and also on the plane of incidence, ie, the light ray 638 in the xz plane will have a different retardation than the normal 636 and the light ray 637 in the yz plane.

[0299] The interaction of polarized light with retarder 630 will now be described. To distinguish from the first and second polarization components during operation of directional backlight 101, the following explanation will refer to third and fourth polarization components.

[0300] Fig. 22B is a schematic diagram showing in perspective the illumination of the retardation layer by off-axis light of a third linear polarization state at 90 degrees to the x-axis, and Fig. 22Cis a schematic diagram showing the illumination of the retarder layer by off-axis light of a fourth linear polarization state at 0 degrees to the x-axis in a perspective view. In such an arrangement, the incident linear polarization state is aligned with the optical axis of the birefringent material represented by the ellipse 632. Therefore, no phase difference is provided between the third orthogonal polarization component and the fourth orthogonal polarization component, and no change is produced in the polarization state of the linearly polarized input for each light ray 636, 637, 638. Therefore, the retarder 630 does not introduce a phase shift into the polarization component of the light transmitted by the polarizer on the input side of the retarder 630 along an axis that is normal to the plane of the retarder 630. Therefore, the retarder 630 does not affect the brightness of the light passing through the retarder 630 and the polarizers (not shown) on each side of the retarder 630. Although FIG. 22A to FIG. 22C Specifically, it relates to a passive retarder 630, but a similar effect is achieved by the retarder in the above-described arrangement.

[0301] Fig.22D 630 is a schematic diagram showing in perspective the illumination of the retarder 630 layer by off-axis light in a linear polarization state of 45 degrees. The linear polarization state can be decomposed into a third polarization component and a fourth polarization component oriented orthogonal to and parallel to the optical axis 634, respectively. The retarder thickness 631 and the material retardation represented by the refractive index ellipsoid 632 can provide a net effect of relatively shifting the phase of the third polarization component and the fourth polarization component incident thereon by half a wavelength in the normal direction represented by the ray 636 with respect to the design wavelength. The design wavelength can be, for example, in the range of 500 nm to 550 nm.

[0302] At the design wavelength and for light propagating normally along ray 636, then at -45 degrees the output polarization may be rotated 90 degrees to a linear polarization state 640. Light propagating along ray 637 may see a phase difference that is similar to, but different from, the phase difference along ray 637 due to the thickness variation, and may therefore output an elliptical polarization state 639 that may have a major axis similar to the linear polarization axis of the output light of ray 636.

[0303] In contrast, the phase difference of the incident linear polarization state along ray 638 can be significantly different, and in particular can provide a lower phase difference. Such a phase difference can provide an output polarization state 644 that is substantially circular at a given tilt angle 642. Thus, retarder 630 introduces a phase shift to the polarization component of light passed by the polarizer on the input side of retarder 630 along the axis corresponding to ray 638 tilted to the normal to the plane of retarder 630. Although Fig.22D A passive retarder 630 is involved, but a similar effect is achieved by the above-mentioned retarder in the switchable state of the switchable liquid crystal retarder corresponding to the anti-peep mode.

[0304] To illustrate the off-axis behavior of the retarder stack, angular brightness control of the C-plates 308A, 308B between the additional polarizer 318 and the output display polarizer 218 will now be described for various off-axis illumination arrangements with reference to the operation of the C-plates between the parallel polarizers 500, 210.

[0305] Fig.23A Schematic diagram showing illumination of a C-plate layer by off-axis polarized light having a positive elevation angle in perspective. An incident linear polarization component 704 is incident on the birefringent material 632 of the retarder 560 in an optical axis direction 507 perpendicular to the plane of the retarder 560 (which is a C-plate). Polarization component 704 sees no net phase difference when transmitted through the liquid crystal molecules, so the output polarization component is the same as component 704. Therefore, maximum transmission is seen through the polarizer 210. Therefore, the retarder 560 has an optical axis 561 perpendicular to the plane of the retarder 560, i.e., the xy plane. The retarder 560 having an optical axis perpendicular to the plane of the retarder includes a C-plate.

[0306] Fig. 23B is a schematic diagram showing in perspective the illumination of a C-sheet layer by off-axis polarized light having a negative transverse angle. Fig.23A As with the arrangement of FIG. 5 , polarization state 704 has no net phase difference and is transmitted at maximum brightness. Thus, retarder 560 does not introduce a phase shift into the polarization component of light that is passed by the polarizer on the input side of retarder 560 along an axis that is normal to the plane of retarder 560. Thus, retarder 560 does not affect the brightness of light that passes through retarder 560 and the polarizers (not shown) on each side of retarder 560. Although FIG. 23A to FIG. 23C Specifically, it relates to a passive retarder 560, but a similar effect is achieved by the retarder in the above-described arrangement.

[0307] Fig.23C is a schematic diagram showing in perspective the illumination of a C-sheet layer by off-axis polarized light having a positive elevation angle and a negative transverse angle. FIG. 23A to FIG. 23B Compared to the arrangement of , polarization state 704 is resolved into eigenstates 703, 705 relative to birefringent material 632, thereby providing a net phase difference when transmitted through retarder 560. FIG. 23A to FIG. 23B The resulting elliptically polarized component 656 is transmitted through polarizer 210 with reduced brightness compared to the light shown in .

[0308] Fig.23D is a schematic diagram showing in perspective the illumination of the C-plate layer by off-axis polarized light having a positive elevation angle and a positive transverse angle. Fig.23CIn a similar manner, polarization component 704 is decomposed into eigenstates 703, 705 that experience a net phase difference and provide an elliptical polarization component 660 that reduces the brightness of the corresponding off-axis light after transmission through the polarizer. Thus, the retarder 560 introduces a phase shift to the polarization component of light passed by the polarizer on the input side of the retarder 560 along an axis that is tilted to the normal to the plane of the retarder 560. Although Fig.23D A passive retarder 560 is involved, but a similar effect is achieved by the above-mentioned retarder in the switchable state of the switchable liquid crystal retarder corresponding to the anti-peep mode.

[0309] Fig.24 It is shown FIG. 23A to FIG. 23D Schematic graph of the output transmittance of the transmitted light in the polar direction. Therefore, the C-plate can provide brightness reduction in the polar quadrant. In combination with the switchable liquid crystal retardation layer 314 described elsewhere herein, (i) the brightness reduction of the C-plate can be eliminated in the first wide-angle operating state, and (ii) an extended polar region of brightness reduction can be achieved in the second anti-peeping operating state.

[0310] To illustrate the off-axis behavior of the retarder stack, angular brightness control of the crossed A-plates 308A, 308B between the additional polarizer 318 and the output display polarizer 218 will now be described for various off-axis illumination arrangements.

[0311] Fig.25A is a schematic diagram showing the illumination of crossed A-plate retardation layers by off-axis polarized light having a positive elevation angle in a perspective view. A linear polarizer 218 having an electric vector transmission direction 219 is used to provide a linear polarization state 704 parallel to the transverse direction on the first A-plate 308A of the crossed A-plates 308A, 308B. The optical axis direction 309A is inclined +45 degrees relative to the transverse direction. The retardation of the retardation plate 308A for the off-axis angle θ1 in the positive elevation direction provides a resulting polarization component 650, which is generally elliptical at output. The polarization component 650 is incident on the second A-plate 308B of the crossed A-plates 308A, 308B, which has an optical axis direction 309B orthogonal to the optical axis direction 309A of the first A-plate 308A. In Fig.25A In the incident plane of θ1, the retardation of the second A-plate 308B for the off-axis angle θ1 is equal to and opposite to the retardation of the first A-plate 308A. Therefore, a net zero retardation is provided for the incident polarization component 704, and the output polarization component is the same as the input polarization component 704.

[0312] The output polarization component is aligned with the electric vector transmission direction of the additional polarizer 318 and is thus efficiently transmitted. Advantageously, substantially no loss is provided to light rays having zero transverse angle components so that full transmission efficiency is achieved.

[0313] Fig.25B Schematic diagram showing illumination of crossed A-plate retardation layers by off-axis polarized light having a negative transverse angle in perspective. Thus, the input polarization component is converted by the first A-plate 308A into an intermediate polarization component 652, which is generally in an elliptical polarization state. The second A-plate 308B again provides retardation equal in magnitude and opposite in direction to the first A-plate, so that the output polarization component is the same as the input polarization component 704, and the light is effectively transmitted through the polarizer 318.

[0314] Thus, the retarders include a pair of retarders 308A, 308B having optical axes that cross in the plane of the retarders 308A, 308B, which in an embodiment of the present invention is the xy plane. The pair of retarders 308A, 308B have optical axes 309A, 309B that extend at 45 degrees relative to the direction of electric vector transmission parallel to the electric vector transmission of the polarizer 318.

[0315] Advantageously, substantially no losses are provided for light rays having a zero elevation angle component so that full transmission efficiency is achieved.

[0316] Fig.25C Schematic diagram showing illumination of crossed A-plate retardation layers by off-axis polarized light having positive elevation angle and negative transverse angle in perspective. Polarization component 704 is converted by first A-plate 308A into elliptical polarization component 654. Resulting elliptical component 656 is output from second A-plate 308B. Input polarizer 318 analyzes elliptical component 656 at reduced brightness compared to the input brightness of first polarization component 704.

[0317] Fig.25D Schematic diagram showing illumination of crossed A-plate retardation layers by off-axis polarized light having positive elevation and transverse angles in perspective. Polarization components 658 and 660 are provided by first A-plate 308A and second A-plate 308B, since the net retardation of the first and second retarders provides no compensation.

[0318] Thus, for light having non-zero lateral angles and non-zero elevation angle components, the brightness is reduced. Advantageously, the display privacy for peepers disposed in the viewing quadrant may be increased without substantially reducing the luminous efficiency for primary display users.

[0319] Fig.26 It is shown FIG. 25A to FIG. 25D Schematic diagram of the output transmittance of the transmitted light in the polar direction. Fig.24 Compared to the arrangement of , the area of ​​reduced brightness is increased for off-axis viewing. However, for off-axis viewing in the first wide-angle mode operating state, the switchable liquid crystal retardation layer 301 may provide reduced uniformity compared to the C-plate arrangement.

[0320] As may be used herein, the terms "substantially" and "approximately" provide industry-accepted tolerances for their corresponding terms and / or relativity between terms. Such industry-accepted tolerances are in the range of 0% to 10% and correspond to, but are not limited to, component values, angles, etc. This relativity between items is in the range of approximately 0% to 10%.

[0321] Although various embodiments according to the principles disclosed herein are described above, it should be understood that these embodiments are shown by way of example only and are not intended to be limiting. Therefore, the breadth and scope of the present disclosure should not be limited by any of the above-described exemplary embodiments, but should only be limited by any claims issued from the present disclosure and their equivalents. In addition, the above-described advantages and characteristic structures are provided in the described embodiments, but the application of these issued claims should not be limited to methods and structures for achieving any or all of the above-described advantages.

[0322] In addition, the section titles of this article are provided to comply with the recommendations of 37CFR 1.77, or to provide organizational clues. These titles should not limit or characterize the one or more embodiments listed in any claims that may arise from this disclosure. Specifically and by way of example, although the title refers to the "technical field", the claims should not be limited by the language selected under this title to describe the so-called field. In addition, the description of the technology in the "background technology" should not be understood as an admission that certain technologies are prior art for any one or more embodiments in this disclosure. "Invention content" is also not to be regarded as a characterization of one or more embodiments described in the claims issued. In addition, any reference to the singular form of "invention" in this disclosure should not be used to argue that there is only a single novel point in this disclosure. Multiple embodiments can be elaborated according to the limitations of multiple claims arising from this disclosure, and such claims therefore limit one or more embodiments and their equivalents protected by them. In all cases, the scope should be considered based on the characteristics of the claims themselves according to this disclosure, and should not be constrained by the titles given herein.

Claims

1. A display device, comprising: at least one spatial light modulator arranged to output light on an output side; a display polarizer disposed on one side of each of the at least one spatial light modulator; and a viewing angle control element disposed on the same side of the at least one spatial light modulator as the display polarizer of the at least one spatial light modulator, The viewing angle control element comprises: Additional polarizer; and at least one retarder arranged between said additional polarizer and said display polarizer of said at least one spatial light modulator, wherein the at least one retarder is capable of simultaneously introducing no net relative phase shift into an orthogonal polarization component of light transmitted by the display polarizer along an axis that is normal to the at least one retarder, and introducing a relative phase shift into an orthogonal polarization component of light transmitted by the display polarizer along an axis that is inclined to the normal to the at least one retarder, and wherein the viewing angle control element is curved with a concave curvature when viewed from the output side, wherein the concave curvature of the viewing angle control element is configured to provide a light cone that is inclined at an edge of the display device so that light from the edge of the display device remains within the light cone. 2 . The display device of claim 1 , wherein the viewing angle control element is curved in a first direction and linear in a second direction orthogonal to the first direction. 3 . The display device according to claim 2 , wherein the display device has a major axis and a minor axis, and the first direction is a direction of the major axis.

4. A display device according to any one of claims 1 to 3, wherein the at least one spatial light modulator is curved with a concave curvature when viewed from the output side. 5 . The display device according to claim 1 , comprising a second viewing angle control element, wherein the viewing angle control element and the second viewing angle control element are arranged in series.

6. The display device according to claim 1 further comprises at least one additional polarizer and at least one additional delay plate, wherein the at least one additional polarizer is arranged on the output side of the at least one spatial light modulator, and the at least one additional delay plate is arranged between the at least one additional polarizer and the additional polarizer.

7. A display device according to claim 1, wherein the concave curvature is curved in a first direction and is linear in a second direction orthogonal to the first direction, wherein the concave curvature of the viewing angle control element in the first direction is different from the curvature of the at least one spatial light modulator in the first direction, wherein the at least one spatial light modulator includes an emission spatial light modulator arranged to output light, and the display polarizer is an output display polarizer arranged on the output side of the emission spatial light modulator, the display polarizer is an output polarizer arranged on the output side of the at least one spatial light modulator, and the viewing angle control element is arranged on the output side of the at least one spatial light modulator.

8. The display device of claim 1, wherein the at least one spatial light modulator is a transmissive spatial light modulator, and the display device further comprises at least one backlight arranged to illuminate the at least one spatial light modulator.

9. The display device of claim 8, wherein the at least one backlight source is curved with a concave curvature when viewed from the output side.

10. The display device of claim 8, wherein the at least one backlight comprises a light guide and an array of light sources, the light guide being arranged to receive light from the array of light sources.

11. The display device according to claim 10, wherein a light-redirecting film including a prism layer arranged on a prism layer supporting substrate is arranged between the light waveguide and the at least one spatial light modulator to receive output light from the light waveguide and guide the output light through the at least one spatial light modulator. 12 . The display device according to claim 11 , wherein the prism layer is arranged between the light waveguide and the prism layer supporting substrate. 13 . The display device according to claim 12 , wherein the prism layer supporting substrate is arranged between the light waveguide and the prism layer.

14. The display device of claim 13, further comprising an additional light turning film, wherein The prismatic surfaces on the light redirecting film and the additional light redirecting film are elongated, and The elongated prismatic surfaces of the light turning film and the additional light turning film are oriented crosswise.

15. A display device according to any one of claims 8 to 12, wherein the at least one backlight source provides brightness at a polar angle greater than 45 degrees with respect to a normal to the at least one spatial light modulator, the brightness being at most 33% of the brightness along the normal to the at least one spatial light modulator.

16. A display device according to any one of claims 8 to 12, wherein the at least one spatial light modulator comprises a plurality of spatial light modulators and the at least one backlight comprises a respective backlight arranged to illuminate each spatial light modulator.

17. The display device according to any one of claims 8 to 12, wherein the at least one spatial light modulator comprises a plurality of spatial light modulators, at least two of the at least one spatial light modulator being illuminated by a single backlight source.

18. A display device according to any one of claims 8 to 12, wherein the display polarizer is an input polarizer arranged on the input side of the at least one backlight source from which light is introduced into the at least one spatial light modulator, and the viewing angle control element is arranged on the input side of the at least one spatial light modulator between the at least one spatial light modulator and the at least one backlight source.

19. The display device according to claim 18, further comprising: a further display polarizer, said further display polarizer being an output polarizer arranged on said output side of said at least one spatial light modulator, a further additional polarizer, said further additional polarizer being arranged on said output side of said at least one spatial light modulator; and At least one further retarder, the at least one further retarder being arranged between the further additional polarizer and the further display polarizer.

20. A display device according to claim 1, wherein the display polarizer is an output polarizer arranged on the output side of the at least one spatial light modulator, and the viewing angle control element is arranged on the output side of the at least one spatial light modulator to receive output light from the at least one spatial light modulator.

21. The display device of claim 20, wherein a reflective polarizer is arranged between the display polarizer and the additional polarizer.

22. A display device according to any one of claims 20 or 21, wherein the display device also includes at least one additional delay plate and an additional additional polarizer, wherein the additional additional polarizer is arranged on the output side of the additional polarizer, and the at least one additional delay plate is arranged between the additional polarizer and the additional additional polarizer.

23. The display device of claim 1, wherein the display polarizer and the additional polarizer have parallel electric vector transmission directions.

24. The display device of claim 1, wherein the at least one retarder comprises a switchable liquid crystal retarder.

25. A viewing angle control optical element for use in a display device, the display device comprising a spatial light modulator and a display polarizer arranged on one side of the spatial light modulator, the viewing angle control optical element comprising: Additional polarizer; and at least one retarder arranged between the additional polarizer and the display polarizer of the spatial light modulator, in The at least one retarder is capable of simultaneously introducing no net relative phase shift into an orthogonal polarization component of light passed by the display polarizer along an axis that is normal to the at least one retarder, and introducing a relative phase shift into an orthogonal polarization component of light passed by the display polarizer along an axis that is oblique to the normal to the at least one retarder, and The viewing angle control optical element is curved with a concave curvature when viewed from an output side of the viewing angle control optical element adapted to output light therefrom, wherein the concave curvature of the viewing angle control optical element is configured to provide a light cone that is inclined at an edge of the viewing angle control optical element so that light from the edge of the viewing angle control optical element remains within the light cone.

26. The viewing angle control optical element according to claim 25, further comprising at least one additional delay plate and an additional polarizer, wherein the additional polarizer is arranged on the output side of the additional polarizer, and the at least one additional delay plate is arranged between the additional polarizer and the additional polarizer.

27. A display device, comprising: at least one spatial light modulator arranged to output light on an output side; a display polarizer disposed on one side of each of the at least one spatial light modulator, the at least one spatial light modulator comprising at least two spatial light modulators, wherein the at least two spatial light modulators are tiled; and a viewing angle control element disposed on the same side of the at least one spatial light modulator as the display polarizer of the at least one spatial light modulator, The viewing angle control element comprises: Additional polarizer; and at least one retarder arranged between said additional polarizer and said display polarizer of said at least one spatial light modulator, wherein the at least one retarder is capable of simultaneously introducing no net relative phase shift into an orthogonal polarization component of light transmitted by the display polarizer along an axis that is normal to the at least one retarder, and introducing a relative phase shift into an orthogonal polarization component of light transmitted by the display polarizer along an axis that is inclined to the normal to the at least one retarder, and wherein the viewing angle control element is curved with a concave curvature when viewed from the output side.

28. A display device, comprising: at least one spatial light modulator arranged to output light on an output side; a display polarizer disposed on one side of each of the at least one spatial light modulator; and a viewing angle control element disposed on the same side of the at least one spatial light modulator as the display polarizer of the at least one spatial light modulator, The viewing angle control element comprises: Additional polarizer; and at least one retarder arranged between said additional polarizer and said display polarizer of said at least one spatial light modulator, wherein the at least one retarder is capable of simultaneously introducing no net relative phase shift into an orthogonal polarization component of light passed by the display polarizer along an axis that is normal to the at least one retarder and introducing a relative phase shift into an orthogonal polarization component of light passed by the display polarizer along an axis that is oblique to the normal to the at least one retarder, and the viewing angle control element is curved with a concave curvature when viewed from the output side, The viewing angle control element is curved in a first direction, the at least one spatial light modulator comprises two spatial light modulators, and the two spatial light modulators are tilted relative to each other in at least the first direction.

29. A display device, comprising: at least one spatial light modulator arranged to output light on an output side; a display polarizer disposed on one side of each of the at least one spatial light modulator; a viewing angle control element disposed on the same side of the at least one spatial light modulator as the display polarizer of the at least one spatial light modulator; and Second viewing angle control element, The viewing angle control element and the second viewing angle control element are arranged in series, and the viewing angle control element comprises: Additional polarizer; and at least one retarder arranged between said additional polarizer and said display polarizer of said at least one spatial light modulator, wherein the at least one retarder is capable of simultaneously introducing no net relative phase shift into an orthogonal polarization component of light passed by the display polarizer along an axis that is normal to the at least one retarder and introducing a relative phase shift into an orthogonal polarization component of light passed by the display polarizer along an axis that is oblique to the normal to the at least one retarder, and the viewing angle control element is curved with a concave curvature when viewed from the output side, The concave curvature of the viewing angle control element is different from the curvature of the at least one spatial light modulator in the first direction.

30. The display device of claim 29, wherein the at least one spatial light modulator is planar.

31. A display device, comprising: at least one spatial light modulator arranged to output light on an output side; a display polarizer disposed on one side of each of the at least one spatial light modulator; and a viewing angle control element disposed on the same side of the at least one spatial light modulator as the display polarizer of the at least one spatial light modulator, The viewing angle control element comprises: Additional polarizer; and at least one retarder arranged between said additional polarizer and said display polarizer of said at least one spatial light modulator, wherein the at least one retarder is capable of simultaneously introducing no net relative phase shift into an orthogonal polarization component of light transmitted by the display polarizer along an axis that is along a normal to the at least one retarder, and introducing a relative phase shift into an orthogonal polarization component of light transmitted by the display polarizer along an axis that is inclined to the normal to the at least one retarder, and wherein the viewing angle control element is curved with a concave curvature when viewed from the output side, wherein the concave curvature of the viewing angle control element is greater than the curvature of the at least one spatial light modulator.

32. A display device, comprising: at least one spatial light modulator arranged to output light on an output side; a display polarizer disposed on one side of each of the at least one spatial light modulator; and a viewing angle control element disposed on the same side of the at least one spatial light modulator as the display polarizer of the at least one spatial light modulator, The viewing angle control element comprises: additional polarizers; and at least one retarder arranged between said additional polarizer and said display polarizer of said at least one spatial light modulator, wherein the at least one retarder is capable of simultaneously introducing no net relative phase shift into an orthogonal polarization component of light passed by the display polarizer along an axis that is normal to the at least one retarder and introducing a relative phase shift into an orthogonal polarization component of light passed by the display polarizer along an axis that is oblique to the normal to the at least one retarder, and the viewing angle control element is curved with a concave curvature when viewed from the output side, wherein the concave curvature of the viewing angle control element is curved in a first direction, and wherein the concave curvature of the viewing angle control element in the first direction is different from a second curvature of the at least one spatial light modulator in the first direction, wherein the display polarizer is an output polarizer arranged on the output side of the at least one spatial light modulator, and the viewing angle control element is arranged on the output side of the at least one spatial light modulator to receive output light from the at least one spatial light modulator, wherein an air gap is arranged between the display polarizer and the additional polarizer, and the at least one retarder comprises: an air gap input retarder comprising at least one retarder disposed between the display polarizer and the air gap; and An air gap output delay plate, the air gap output delay plate comprising at least one delay plate arranged between the air gap and the additional polarizer, the air gap input delay plate being arranged to provide a phase shift to provide a circularly polarized light component of light passed by the display polarizer along an axis along the normal line of the plane of the air gap input delay plate in the air gap, and the at least one delay plate is capable of simultaneously not introducing a net relative phase shift into the orthogonal polarization component of light passed by the display polarizer along the axis along the normal line of the plane of the at least one delay plate, and introducing a net relative phase shift into the orthogonal polarization component of light passed by the display polarizer along the axis along the normal line of the plane of the at least one delay plate.

33. A display device, comprising: at least one spatial light modulator arranged to output light on an output side; a display polarizer disposed on one side of each of the at least one spatial light modulator; and a viewing angle control element disposed on the same side of the at least one spatial light modulator as the display polarizer of the at least one spatial light modulator, The viewing angle control element comprises: Additional polarizer; and at least one retarder disposed between the additional polarizer and the display polarizer of the at least one spatial light modulator, wherein the at least one retarder is capable of simultaneously introducing no net relative phase shift into an orthogonal polarization component of light passed by the display polarizer along an axis that is normal to the at least one retarder and introducing a relative phase shift into an orthogonal polarization component of light passed by the display polarizer along an axis that is tilted to the normal to the at least one retarder, The viewing angle control element is curved with a concave curvature when viewed from the output side, wherein the concave curvature is curved in a first direction and is linear in a second direction orthogonal to the first direction, wherein the concave curvature in the first direction of the viewing angle control element is different from the curvature in the first direction of the at least one spatial light modulator, wherein the at least one spatial light modulator comprises an emission spatial light modulator arranged to output light, and the display polarizer is an output display polarizer arranged on the output side of the emission spatial light modulator, the display polarizer is an output polarizer arranged on the output side of the at least one spatial light modulator, and the viewing angle control element is arranged on the output side of the at least one spatial light modulator.

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