Optical stack for privacy displays

Abstract

A switchable privacy display device includes a spatial light modulator, a light control film, and a polarity-controlled retarder including a plurality of retarders disposed between a display polarizer and an additional polarizer of the spatial light modulator, the display providing high image visibility to off-axis users in a public mode of operation and high image security against off-axis voyeurs in a privacy mode of operation.

Description

[Technical field]

[0001] FIELD OF THE DISCLOSURE This disclosure relates generally to optical stacks for use in privacy and low stray light displays. [Background technology]

[0002] A privacy display provides image visibility to a primary user, typically in an on-axis location, and reduces the visibility of the image content to voyeurs, typically in off-axis locations.

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

[0004] Off-axis privacy control can be provided by contrast reduction, for example by adjusting the liquid crystal bias tilt in an in-plane switching LCD.

[0005] Control can be further provided by off-axis luminance reduction. Luminance reduction can be achieved by a switchable backlight for a liquid crystal display (LCD) spatial light modulator. Off-axis luminance reduction can also be provided by switchable liquid crystal retarders and compensation retarders arranged to modulate the input and / or output directional luminance profile of the spatial light modulator.

[0006] Further control can be provided by increasing the off-axis reflectance, which can be achieved by a switchable liquid crystal retarder, a compensating retarder arranged to control the polarization of the ambient light that strikes the reflective polarizer. Summary of the Invention

[0007] According to a first aspect of the present disclosure, there is provided a display device comprising a spatial light modulator arranged to output spatially modulated light, the spatial light modulator including a display polarizer arranged on one side of the spatial light modulator, the display polarizer being a linear polarizer, an additional polarizer arranged on the same side of the spatial light modulator as the display polarizer, the additional polarizer being a linear polarizer, at least one polarity-controlled retarder arranged between the additional polarizer and the display polarizer, and a light control film arranged in series with the spatial light modulator, the additional polarizer, and the at least one polarity-controlled retarder, the light control film comprising an input surface, an output surface facing the input surface, an array of transmissive regions extending between the input surface and the output surface, and an absorbing region extending at least partially between the transmissive regions and between the input surface and the output surface. Advantageously, the switchable privacy display may comprise areas of increased security factor and areas of increased size of the polar regions where a desired security factor is achieved. In a public operating mode, the image can be made more visible to off-axis users.

[0008] The light control film may have a transmission of 5% or greater over a range of polar angles in the direction in which the array of transmissive regions is repeated, which may be at least 80° wide, at least 90° wide, and up to 130° wide. The absorptive regions of the light control film may have a thickness, t, where t is given by the formula:

number

[0009] The light control film may have a transmittance that may have a profile with a polar angle in a direction in which the array of transmissive regions is repeated with a centerline directed inward toward an optical axis extending forward from the center of the spatial light modulator. The centerline of the profile may be directed to a common point. The light control film may have a transmittance that may have a profile with a polar angle in a direction in which the array of transmissive regions is repeated centered on a normal to the plane of the spatial light modulator at all locations across the light control film. The transmissive regions may be tilted so that an axis defined for each transmissive region between the centers of the apertures on the input and output sides of the transmissive region may be directed inward toward an optical axis extending forward from the center of the spatial light modulator. The axis may be directed to a common point. Advantageously, image brightness uniformity may be increased for the primary display user. Image security uniformity may be increased for off-axis voyeurs.

[0010] The transmissive regions have an axis defined for each transmissive region between the centers of the apertures on the input and output sides of the transmissive region that may be perpendicular to the plane of the spatial light modulator at all locations across the light control film. Advantageously, the light control film can be conveniently tooled at low cost.

[0011] The array of transparent regions can be a one-dimensional array of elongated transparent regions. Advantageously, increased transmission is achieved for a desired level of image security.

[0012] The absorbing regions between the transmissive regions extend between the input and output faces. The light control film can be provided on a supporting substrate. High uniformity in the orientation of the light transmissive regions can be obtained, enhancing the uniformity of the display.

[0013] The display polarizer may be an output display polarizer disposed at the output side of the spatial light modulator. The display device further comprises a reflective polarizer disposed between the output display polarizer and the at least one first polarity controlled retarder, the reflective polarizer being a linear polarizer. A privacy mode may be provided with increased reflectivity for off-axis voyeur positions. Advantageously, in environments with high ambient illumination, the security factor of the image may be increased.

[0014] The light control film can be placed between the reflective polarizer and the spatial light modulator, advantageously increasing the security factor in privacy mode since the reflectivity of the display is not reduced in privacy mode, reducing brightness to an off-axis voyeur.

[0015] The spatial light modulator comprises an emissive spatial light modulator arranged to emit spatially modulated light, and advantageously can be reduced in thickness and cost.

[0016] The display device further comprises a backlight arranged to output light, and the spatial light modulator comprises a transmissive spatial light modulator arranged to receive and spatially modulate the output light from the backlight, and the light control film can be disposed between the backlight and the spatial light modulator. Compared to emissive displays, off-axis brightness can be reduced and security factor can be advantageously increased. A backlight using recycled light can be used to advantageously increase the yield, uniformity, and damage resilience of the backlight.

[0017] The display device further comprises a backlight arranged to output light, and the spatial light modulator comprises a transmissive spatial light modulator arranged to receive and spatially modulate the output light from the backlight, and the light control film can be disposed in front of the spatial light modulator. Reduced scattering of off-axis light can be achieved, and advantageously high angle brightness can be reduced, resulting in an increased security factor.

[0018] The display device further comprises a backlight arranged to output light, and the spatial light modulator comprises a transmissive spatial light modulator arranged to receive and spatially modulate the output light from the backlight, and the display polarizer can be an input display polarizer arranged at the input side of the spatial light modulator. Front surface reflections to a primary front user can be reduced, and image contrast for a front user in bright ambient lighting environments can be advantageously increased.

[0019] A light control film can be placed between the backlight and an additional polarizer to increase scattering and depolarization in the polarized retarder, advantageously achieving reduced off-axis brightness and increased security factor.

[0020] The at least one polarity controlled retarder includes a switchable liquid crystal retarder. The switchable liquid crystal retarder comprises a layer of liquid crystal material and at least one surface alignment layer disposed adjacent to the layer of liquid crystal material. The switchable liquid crystal retarder comprises two surface alignment layers disposed adjacent to and on opposite sides of the layer of liquid crystal material and disposed on respective liquid crystal encapsulation substrates. Advantageously, the switchable privacy display can provide high image security against off-axis voyeurs in a privacy mode and image visibility to off-axis users in a public mode.

[0021] A light control film can be provided on one of the liquid crystal encapsulation substrates. Advantageously, the thickness of the optical stack can be reduced and the flatness of the light control film can be increased to achieve increased uniformity.

[0022] The at least one polarity controlled delay further comprises at least one passive compensation delay Advantageously, the size of the polar area within which desired image security is achieved in privacy mode can be increased.

[0023] The support substrate includes at least one passive compensation retarder of the at least one passive compensation retarder. Advantageously, the thickness of the optical stack can be reduced and the flatness of the light control film can be increased to achieve increased uniformity.

[0024] The embodiments of the present disclosure can be used in a variety of optical systems. The embodiments can include or operate with a variety of projectors, projection systems, optical components, displays, microdisplays, computer systems, processors, self-contained projector systems, visual and / or audiovisual systems, and electrical and / or optical devices. Aspects of the present disclosure can be used with virtually any apparatus related to optical and electrical devices, optical systems, presentation systems, or any apparatus that can include any type of optical system. Thus, the embodiments of the present disclosure can be used in optical systems, devices used in visual and / or optical presentations, visual peripherals, and the like, as well as in numerous computing environments.

[0025] Before proceeding to details of the disclosed embodiments, it should be understood that the disclosure is not limited in its application or construction to the details of the particular arrangements shown, since other embodiments are possible. Moreover, aspects of the disclosure can be described in different combinations and arrangements to define unique embodiments in themselves. Also, the terminology used herein is for purposes of description and not of limitation.

[0026] Directional backlights control the illumination emanating from substantially the entire output face, typically controlled through modulation of independent LED light sources located on the input aperture side of the light guide. By controlling the directional distribution of the emitted light, one can achieve single-person viewing for security features where only one viewer can view the display from a limited range of angles, high electrical efficiency where illumination is provided primarily with a small angle directional distribution, alternating left and right eye displays for time-varying stereoscopic and autostereoscopic displays, and low cost.

[0027] These and other advantages and features of the present disclosure will become apparent to those of ordinary skill in the art upon reading the present disclosure in its entirety. [Brief description of the drawings]

[0028] Embodiments are illustrated by way of example in the accompanying figures, in which like reference numbers indicate similar parts, and in which: [Figure 1] FIG. 1 is a schematic diagram showing a side perspective view of a switchable privacy display device comprising a backlight with crossed brightness enhancement films, a light control film, a transmissive spatial light modulator with input and output display polarizers, a reflective polarizer, a polarity controlled retarder, and an additional polarizer. [Diagram 2] FIG. 2 is a schematic diagram showing the privacy display of FIG. 1 in a side view. [Figure 3A] FIG. 1 is a schematic diagram showing a side perspective view of a switchable privacy display device comprising a backlight with an optical rotatory film, an additional polarizer, a light control film arranged on a passive retarder of a polarity control retarder, a liquid crystal retarder of the polarity retarder, and a transmissive spatial light modulator with input and output polarizers. [Figure 3B] FIG. 1 is a schematic diagram showing a side perspective view of a switchable privacy display device comprising a backlight with a light control film disposed on an optical rotatory film, an additional polarizer, a polarity controlled retarder, and a transmissive spatial light modulator with input and output polarizers. [Figure 4] FIG. 2 is a schematic diagram showing a polarity-controlled retarder and light control film for a switchable privacy display device in a side perspective view, where the support substrate of the light control film is provided by one of a pair of crossed A-plates. [Diagram 5] A schematic diagram showing a side perspective view of a switchable privacy display device comprising an emissive spatial light modulator with an output display polarizer, a light control film, a reflective polarizer, a polarity controlled retarder, and an additional polarizer. [Figure 6]FIG. 1 is a schematic diagram showing a side perspective view of a switchable privacy display device comprising a spatial light modulator with an output display polarizer, a light control film, a polarity controlled retarder, an additional polarizer, and a light control film, the support substrate of which is provided with touch screen detection electrodes. [Figure 7A] A schematic diagram showing a side perspective view of a light control film comprising an array of transmissive regions extending between an input surface and an output surface, and absorbing regions extending at least partially between the transmissive regions and between the input surface and the output surface, where the transmissive regions are parallel. [Figure 7B] A schematic diagram showing a side perspective view of a light control film comprising an array of transmissive regions extending between an input surface and an output surface, and an absorbing region extending at least partially between the transmissive regions and between the input surface and the output surface, wherein the transmissive regions are tapered. [Figure 8] 1 is a schematic graph showing the variation in transmission with lateral angle of a light control film. [Figure 9A] 2 is a schematic diagram showing the operation of the display device of FIG. 1 in a privacy operation mode as viewed from above. FIG. [Figure 9B] 2 is a schematic diagram showing the operation of the display device of FIG. 1 in a public operation mode as viewed from above. FIG. [Figure 10A] 1 is a schematic graph showing the directional variation of luminance of a backlight with crossed brightness enhancement films; [Figure 10B] 1 is a schematic graph showing the directional variation in luminance of a backlight having a light control film with a transmittance of 5% or greater over a polar angle range greater than 96° at all azimuth angles in the direction of transmission of the array of transmissive regions. [Figure 10C] 2 is a schematic graph showing a change in the transmission direction of the polarity controlled delay device of FIG. 1; [Figure 10D] 2 is a schematic graph showing the change in the polarity-controlled retarder and the reflective polarizer of FIG. 1 depending on the reflection direction. [Figure 11] 1 is a schematic graph showing the variation with direction of Fresnel reflection of a single surface in air; [Figure 12] 10A and 10B are schematic graphs showing the variation of luminance with horizontal angle for a display of the type shown in FIG. 1, the backlight profile in FIG. 10A, and the transmission profiles in FIGS. 10B and 10C for a display in a privacy mode of operation. [Figure 13] 10D, with a backlight profile according to FIG. 10A, a transmission profile according to FIG. 10B and FIG. 10C, and a reflection profile according to FIG. 10D, and for a luminance in front of the display, a value Ymax measured in nits which is half the illuminance of value I measured in lux; [Figure 14] 10A is a schematic graph showing the variation of luminance with horizontal angle for a display of the type shown in FIG. 1, the backlight profile in FIG. 10A, and the transmission profile in FIG. 10B of the display in a public mode of operation. [Figure 15] 10B and 11, and for a luminance in front of the display, a value Ymax measured in nits is half the illuminance I measured in lux; [Figure 16] 1 is a schematic graph showing the variation of luminance and transmission with lateral angle for a prior art non-switchable privacy display; [Figure 17] 10B is a schematic graph showing the variation with direction of the security factor S of a conventional non-switchable privacy display having the backlight profile of FIG. 10A, a transmission profile of a light control film with a lateral width of 70° where the transmittance is 5% of the frontal transmittance, and a reflection profile for the luminance in front of the display of FIG. 11, where Ymax is a value measured in nits which is half the illuminance of I measured in lux. [Figure 18]FIG. 1 is a schematic diagram showing a side perspective view of a light control film comprising an array of transmissive regions extending between an input surface and an output surface, and absorbing regions extending at least partially between the transmissive regions and between the input surface and the output surface, wherein the transmissive regions are tapered and sloped such that an axis defined for each transmissive region between the centers of the apertures on the input and output sides of the transmissive regions is directed inward toward an optical axis extending forward from the center of the spatial light modulator. [Figure 19] 19 is a schematic diagram illustrating the operation of the display device of FIG. 1 with the light control film of FIG. 18 in a privacy mode of operation, from a top view. [Figure 20] FIG. 1 is a schematic diagram showing a top view of a display device comprising a curved transmissive spatial light modulator, a curved backlight, a plurality of curved retarders, and a curved light control film. [Figure 21] FIG. 1 is a schematic diagram showing a top view of a display device comprising a curved emissive spatial light modulator, a plurality of curved retarders, and a curved light control film. [Figure 22A] 2 is a schematic diagram illustrating the propagation of output light from the spatial light modulator through the optical stack of FIG. 1 in a privacy mode of operation, from a side view. [Figure 22B] FIG. 2 is a schematic diagram illustrating the propagation of ambient illumination light through the optical stack of FIG. 1 in a top view in a privacy mode of operation. [Figure 23A] 2 is a schematic diagram illustrating the propagation of output light from the spatial light modulator through the optical stack of FIG. 1 in a side view in a public mode of operation. [Figure 23B] 23B is a schematic graph showing the change in output luminance depending on the polarity direction of the transmitted light beam in FIG. 23A. [Figure 23C] FIG. 2 is a schematic diagram illustrating the propagation of ambient illumination light through the optical stack of FIG. 1 in a top view in a public mode of operation. [Figure 23D] 23D is a schematic graph showing the change in reflectance depending on the polarity direction of the reflected light beam in FIG. 23C. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0029] We now explain the terminology associated with optical retarders for the purposes of this disclosure.

[0030] In a layer comprising a uniaxially birefringent material, there is a direction that dominates the optical anisotropy, but all directions perpendicular to it (or at a given angle relative to it) have equivalent birefringence.

[0031] The optical axis of the optical retarder refers to the direction of propagation of light rays in a uniaxially birefringent material where no birefringence occurs, which is different from the optical axis of the optical system, which may be, for example, parallel to a line of symmetry or perpendicular to the display surface through which the chief ray propagates.

[0032] For light propagating perpendicular to the optic axis, the optic axis is the slow axis when linearly polarized light with the electric vector parallel to the slow axis travels at the slowest speed. The slow axis direction is the direction in which the refractive index is highest at the design wavelength. Similarly, the fast axis direction is the direction in which the refractive index is lowest at the design wavelength.

[0033] For uniaxial birefringent materials with positive dielectric anisotropy, the slow axis direction is the extraordinary axis of the birefringent material. For uniaxial birefringent materials with negative dielectric anisotropy, the fast axis direction is the extraordinary axis of the birefringent material.

[0034] The terms half-wave and quarter-wave refer to the design wavelength λ, which may typically be between 500 nm and 570 nm. 0 In this embodiment, unless otherwise specified, exemplary delay values ​​are provided for a wavelength of 550 nm.

[0035] A retarder provides a phase shift between the two perpendicularly polarized components of a light wave incident on it and is characterized by the amount of relative phase it imparts to the two polarization components, Γ, which is related to the birefringence Δn and the retarder thickness d as follows: Γ=2.π.Δn.d / λ 0 formula 1

[0036] In Equation 1, Δn is defined as the difference between the extraordinary and ordinary refractive indices. Δn=n e-n o formula 2

[0037] For half-wave retarders, d, Δn, and λ 0 The relationship between the polarization components is chosen such that the phase shift between them is Γ=π. The quarter-wave retarders, d, Δn, and λ 0 The relationship is chosen such that the phase shift between the polarization components is Γ=π / 2.

[0038] The term half-wave retarder herein typically refers to light propagating perpendicular to the retarder and perpendicular to the spatial light modulator.

[0039] We now describe some aspects of the propagation of light rays through a transparent retarder between a pair of polarizers.

[0040] The state of polarization (SOP) of a beam of light is represented by the relative amplitude and phase shift between any two orthogonally polarized components. A transparent retarder does not change the relative amplitude of these orthogonally polarized components, but only affects their relative phase. Providing a net phase shift between the orthogonally polarized components changes the SOP, while maintaining the net relative phase preserves the SOP. In this description, the SOP may be referred to as the state of polarization.

[0041] A linear SOP has a non-zero amplitude polarization component and an orthogonal polarization component with zero amplitude.

[0042] A linear polarizer transmits a unique linear SOP that has a linear polarization component parallel to the electric vector transmission direction of the linear polarizer and attenuates light with a different SOP.

[0043] An absorbing polarizer is one that absorbs one polarization component of incident light and transmits a second, orthogonal polarization component. An example of an absorbing linear polarizer is a dichroic polarizer.

[0044] A reflective polarizer is a polarizer that reflects one polarization component of incident light and transmits a second orthogonal polarization component. Examples of reflective polarizers that are linear polarizers include multilayer polymer film stacks such as DBEF™ or APF™ manufactured by 3M, or wire grid polarizers such as ProFlux™ manufactured by Moxtek. A reflective linear polarizer may further comprise a cholesteric reflective material and a quarter-wave plate arranged in series.

[0045] A retarder placed between a linear polarizer and a parallel linear analyzing polarizer, which introduces no relative net phase shift, provides perfect transmission of light except for residual absorption in the linear polarizer.

[0046] A retarder, which provides a relative net phase shift between the orthogonal polarization components, changes the SOP and provides attenuation at the analyzing polarizer.

[0047] In this disclosure, "A-plate" refers to an optical retarder that utilizes a layer of birefringent material whose optic axis is parallel to the plane of the layer.

[0048] A "positive A-plate" refers to a positively birefringent A-plate, i.e., an A-plate with a positive Δn.

[0049] In this disclosure, a "C-plate" refers to an optical retarder utilizing a layer of birefringent material whose optic axis is perpendicular to the plane of the layer. A "positive C-plate" refers to a positively birefringent C-plate, i.e., a C-plate with positive Δn. A "negative C-plate" refers to a negatively birefringent C-plate, i.e., a C-plate with negative Δn.

[0050] "O-plate" refers to an optical retarder utilizing a layer of birefringent material whose optic axis has a component parallel to the plane of the layer and a component perpendicular to the plane of the layer. "Positive O-plate" refers to a positively birefringent O-plate, i.e., an O-plate with a positive Δn.

[0051] An achromatic retarder can be provided, the retarder material being provided with a retardation Δn.d that varies with wavelength λ. Δn.d / λ=k Equation 3

[0052] where k is essentially a constant.

[0053] Examples of suitable materials include modified polycarbonates manufactured by Teijin Films, Inc. In this embodiment, an achromatic retarder may be provided to advantageously minimize color shifts between polar angle viewing directions with low luminance degradation and those with increased luminance degradation, as described below.

[0054] Various other terms used in this disclosure in connection with retarders and liquid crystals will now be explained.

[0055] A 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 is independent of the orientation of the liquid crystal material in the liquid crystal cell.

[0056] Uniform alignment refers to the alignment of liquid crystals in a switchable liquid crystal display where the molecules are aligned substantially parallel to the substrates. Uniform alignment is sometimes called planar alignment. Uniform alignment can typically be provided with a small pretilt, such as 2 degrees, so that the molecules at the surface of the alignment layer of the liquid crystal cell are slightly tilted, as explained below. The pretilt is arranged to minimize degeneracy in switching the cell.

[0057] In this disclosure, vertical alignment is the state in which rod-shaped liquid crystal molecules are aligned substantially perpendicular to the substrate. For discotic liquid crystals, vertical alignment is defined as the state in which the axis of the column structure formed by the disc-shaped liquid crystal molecules is aligned perpendicular to the surface. In vertical alignment, the pretilt is the tilt angle of the molecules close to the alignment layer, which is usually close to 90 degrees, and can be, for example, 88 degrees.

[0058] In twisted liquid crystal layers, a twisted configuration (also known as a helical structure or helix) of nematic liquid crystal molecules is provided. The twist can be achieved by non-parallel alignment of the alignment layers. In addition, cholesteric dopants can be added to the liquid crystal material to eliminate the degeneracy of the twist direction (clockwise or counterclockwise) and to further control the pitch of the twist in the relaxed (usually undriven) state. Supertwisted liquid crystal layers have a twist of more than 180 degrees. Twisted nematic layers used in spatial light modulators typically have a twist of 90 degrees.

[0059] Liquid crystal molecules with positive dielectric anisotropy can be switched from a uniform alignment (such as an A-plate retarder alignment) to a perpendicular alignment (such as a C-plate or O-plate retarder alignment) by an applied electric field.

[0060] Liquid crystal molecules with negative dielectric anisotropy can be switched from a vertical alignment (such as a C-plate or O-plate retarder alignment) to a uniform alignment (such as an A-plate retarder alignment) by an applied electric field.

[0061] Since rod-shaped molecules have positive birefringence, N e >N o Since discotic molecules have negative birefringence, n e <n o It is.

[0062] Positive retarders such as A-plates, positive O-plates, and positive C-plates can usually be provided by stretched films or rod-like liquid crystal molecules. Negative retarders such as negative C-plates can be provided by stretched films or discotic-like liquid crystal molecules.

[0063] Parallel liquid crystal cell alignment refers to the alignment direction of the uniform alignment layer being parallel or, more commonly, antiparallel. In the case of a pretilted vertical alignment, the alignment layer may have components that are substantially parallel or antiparallel. A hybrid alignment liquid crystal cell may have one uniform alignment layer and one vertical alignment layer. A twisted liquid crystal cell may be provided by alignment layers that do not have parallel alignment, for example oriented at 90 degrees to each other.

[0064] The transmissive spatial light modulator may further include a retarder between the input and output viewing polarizers, for example as disclosed in U.S. Patent No. 8,237,876, which is incorporated herein by reference in its entirety. Such a retarder (not shown) would be in a different location than the passive retarder of the present embodiment. Such a retarder would compensate for contrast reduction for off-axis viewing positions, which is a different effect than the brightness reduction for off-axis viewing positions of the present embodiment.

[0065] Here, terms relating to the appearance of the privacy display will be explained.

[0066] The private operating mode of a display is one in which the observer sees a low contrast sensitivity so that the image is not clearly visible. Contrast sensitivity is a measure of the ability to distinguish different levels of luminance in a still image. Inverse contrast sensitivity can be used as a measure of visual security, in that a high visual security level (VSL) corresponds to low image visibility.

[0067] For a privacy display that presents an image to a viewer, visual security is obtained as follows. VSL=(Y+R) / (YK) Equation 4

[0068] where VSL is the visual security level, Y is the luminance of the white state of the display at the voyeur's viewing angle, K is the luminance of the black state of the display at the voyeur's viewing angle, and R is the luminance of the reflected light from the display.

[0069] The contrast ratio of the panel is given by: C=Y / K formula 5

[0070] For a high contrast optical LCD mode, the white state transmittance remains substantially constant with viewing angle. In the reduced contrast LCD mode of the present embodiment, the white state transmittance typically decreases as the black state transmittance increases, such that: Y+K~PL Equation 6

[0071] The visual security level is then further obtained as follows: VSL=( C+I.ρ / π.(C+1) / (PL)) formula 7 (C-1)

[0072] where the off-axis relative luminance P is usually defined as a percentage of the frontal luminance, L at the voyeur angle, and the display may have an image contrast ratio C and a surface reflectance ρ.

[0073] The off-axis relative luminance P is also referred to as the privacy level, although such privacy level P describes the relative luminance of a display at a particular polar angle compared to the luminance at the front, and is not a measure of the appearance of privacy.

[0074] The display may be illuminated with a Lambertian ambient illuminance, I. Thus, in a completely dark environment, the VSL of a high-contrast display will be approximately 1.0. As the ambient illuminance increases, the perceived image contrast degrades, the VSL increases, and a private image is perceived.

[0075] For a typical LCD display, the panel contrast C exceeds 100:1 at almost all viewing angles, so the visual security level can be roughly calculated as follows: VSL=1+I.ρ / (π.PL) Equation 8

[0076] The security of the perceived image can be determined from the logarithmic response of the eye, resulting in a security factor S given by: S=log 10 (V) Equation 9

[0077] The desired limits of S were determined as follows: In a first step, a privacy display device was provided. Measurements of the change in privacy level, P(θ) of the display device with polar viewing angles, and the change in reflectance ρ(θ) of the display device with polar viewing angles were made using a photopic measurement instrument. A light source, such as a light box of substantially uniform luminance, was positioned to provide illumination to an observer position at a polar angle greater than 0° relative to the normal to the display device from an illumination area positioned to illuminate the privacy display device along a direction of incidence for reflection. The change in illuminance I(θ) of the substantially Lambertian luminance light box with polar viewing angles was determined by measuring the change in the recorded reflected luminance with polar viewing angles, taking into account the change in reflectance ρ(θ). The measurements of P(θ), r(θ), and I(θ) were used to determine the change in security factor S(θ) with polar viewing angles along the zero elevation axis.

[0078] In a second step, a series of high-contrast images were presented to the privacy display, including (i) small text images with a maximum font height of 3 mm, (ii) large text images with a maximum font height of 30 mm, and (iii) a moving image.

[0079] In the third step, each observer (using vision correction for viewing at 1000 mm if necessary) viewed each of the images from a distance of 1000 m and adjusted the polar coordinate angle at zero altitude until the image was no longer visible with one eye from a location on the display at or near the centerline of the display. The polar positions of the observer's eyes were recorded. From the relationship S(θ), the security factor at that polar position was determined. Measurements were made for a variety of images, a variety of display luminances Y max , was repeated for different light box illuminances I(q=0), different background lighting conditions, and different observers.

[0080] From the above measurements, S<1.0 provides low to no visual security, 1.0≦S<1.5 provides visual security that depends on the contrast, spatial frequency, and temporal frequency of the image content, 1.5≦S<1.8 provides acceptable image invisibility (i.e., no image contrast is observable) for most images and most observers, and S>1.8 provides complete image invisibility for all observers, regardless of image content.

[0081] Compared to privacy displays, the desirable wide-angle displays are easily observed in standard ambient lighting conditions. One measure of image visibility is given by contrast sensitivity, such as the Michelson contrast, given by the following formula: M=(I max -I min ) / (I max +I min ) Equation 10

[0082] So, M=((Y+R)-(K+R)) / ((Y+R)+(K+R))=(YK) / (Y+K+2.R) Equation 11

[0083] Therefore, the visual security level (VSL) is comparable (but not identical) to 1 / M. In this study, for a given off-axis relative luminance P, the visibility W of a wide-angle image is approximated as follows: W=1 / VSL=1 / (1+I.ρ / (π.PL)) Equation 12

[0084] In this study, we consider the desired white point (u w ',v w Output color from (u w '+Δu',v w The color change Δε of λ / (λ′+Δv′) can be determined by the CIELUV color difference metric, assuming a typical display spectral illuminant, as given by: Δε = (Δu '2 +ΔV'2 ) 1 / 2 formula 13

[0085] Catadioptric elements use both refraction and reflection, which can be total internal reflection or reflection from a metallized surface.

[0086] The structure and operation of various directional display devices will now be described. In this description, common elements will have common reference numbers. It should be noted that the disclosure regarding any element applies to each device in which the same or corresponding element is provided. Thus, for the sake of brevity, such disclosure will not be repeated.

[0087] It may be desirable to provide a high level of visual security for a spatial light modulator and / or backlight that provides high brightness at off-axis viewing angles. Here, a switchable privacy display structure is described.

[0088] FIG. 1 is a schematic diagram showing a side perspective view of a switchable privacy display device 100 comprising a backlight 20 with crossed brightness enhancement films 40A, 40B, a light control film 700, a transmissive spatial light modulator 48 with input and output display polarizers 210, 218, a reflective polarizer 302, a polarity control retarder 300 and an additional polarizer 318, and FIG. 2 is a schematic diagram showing a side view of the privacy display 100 of FIG. 1.

[0089] The display device 100 comprises a spatial light modulator 48 arranged to output spatially modulated light. The display device 100 further comprises a backlight 20 arranged to output light, the spatial light modulator 48 comprising a transmissive spatial light modulator 48 arranged to receive and spatially modulate output light from the backlight 20. The spatially modulated light is provided by controllable pixels that modulate the light from the backlight 20. The transmissive spatial light modulator 48 may comprise a liquid crystal display comprising an encapsulation substrate 212, 216 and a liquid crystal layer 214 having red, green, and blue pixels 220, 222, 224. The spatial light modulator 48 has an input display polarizer 210 and an output display polarizer 218 on opposite sides thereof. The output display polarizer 218 is arranged to provide a high extinction ratio for light from the pixels 220, 222, 224 of the spatial light modulator 48. Exemplary polarizers 210, 218 may be absorbing polarizers, such as dichroic polarizers.

[0090] In this embodiment, spatial light modulator 48 includes a display polarizer 218 located on the output side of the spatial light modulator, where display polarizer 218 is a linear polarizer. An additional polarizer 318 is located on the same side of the spatial light modulator as the display polarizer, where additional polarizer 318 is a linear polarizer.

[0091] The backlight 20 will now be further described. The backlight device 20 comprises a back reflector 3 and an illumination device comprising a waveguide 1 and a light source 15. A light ray 412 from the light source 15 is input through the input side 2 and guided in the surfaces 6, 8 of the waveguide 1. The light is output by the extraction features 12 and enters the back reflector 3, which may reflect the light by either scattering or specular reflection back through the waveguide 1 towards crossed brightness enhancement films 40A, 40B arranged to receive the light exiting the first surface 6 of the waveguide 1. In this embodiment, "crossed" refers to a substantially 90° angle between the optical axes of the two retarders in the plane of the retarders.

[0092] Brightness enhancement films 40A, 40B each comprise a prism layer with prism faces 42A, 42B disposed between light guide 1 and spatial light modulator 48 to receive output light from light guide 1. Light rays 412 from the waveguide direct the output light through spatial light modulator 48.

[0093] The prism faces 42A, 42B are elongated and the orientation of the elongated prism faces of the turning film and the further turning film intersect. Light in a direction close to the optical axis 199 is reflected back towards the reflector 3, while light rays 410 that nearly graze the surface 6 are output in the normal direction.

[0094] The optical stack 5 may include diffusers, polarizing films, and other known optical backlight structures. For example, an asymmetric diffuser, which may include asymmetric surface relief features, may be provided in the optical stack 5 with increased diffusion in the elevation direction compared to the lateral direction. Advantageously, image uniformity may be increased.

[0095] Optionally, a reflective polarizer 208 can be provided between the input display polarizer 210 and the backlight 20 to provide recycled light and increase the display efficiency. Advantageously, efficiency can be improved.

[0096] The light-recycling components 3, 40A, 40B, 208 of the backlight 20 achieve mixing of the output light from the waveguides. Such recycling is tolerant to manufacturing defects, and the backlight 20 may be advantageously provided with a larger size, lower cost, and higher brightness uniformity than a collimated backlight, as shown below with reference to FIG. 3A. However, such a backlight provides increased brightness at higher polar angles, which may reduce the security factor in a privacy mode of operation, as described below.

[0097] It would be desirable to provide a highly uniform backlight at low manufacturing costs while achieving a high security factor in privacy mode and a desirable brightness in public operating mode.

[0098] Light control film 700 is disposed between the backlight 20 and the spatial light modulator 48. Light control film 700 comprises an input surface 706, an output surface 708 facing the input surface 706, an array of light transmissive regions 704 extending between the input surface 706 and the output surface 708, and absorptive regions 702 extending between the transmissive regions and between the input and output surfaces.

[0099] The light control film 700 is disposed between the reflective polarizer 208 and the display input polarizer 210 of the backlight 20. The light control film 700 may further comprise a supporting substrate 710. Advantageously, the flatness of the light control film may be increased to achieve increased uniformity. The structure and operation of the light control film are further described below.

[0100] It would be desirable to provide a switchable privacy display. The light control film 700 is disposed in series with the spatial light modulator 48, the additional polarizer 318, and the polarity controlled retarder 300.

[0101] The polarity controlled retarder 300 comprises (i) a switchable liquid crystal retarder 301 comprising a layer of liquid crystal material 314 disposed between transparent encapsulation substrates 312, 316 and disposed between a display polarizer 218 and an additional polarizer 318, and (ii) at least one passive compensation retarder 330.

[0102] The polarizer-controlled retarder 300 is disposed between the additional polarizer 318 and the display polarizer 218. The general principle of operation of the polarizer-controlled retarder 300 disposed between the polarizers 218, 302, 318 is described below with respect to Figures 22A-23D.

[0103] The polarity controlled retarder 300 includes a switchable liquid crystal retarder 301. The switchable liquid crystal retarder 301 comprises a layer 314 of liquid crystal material surface alignment layers 409, 411 disposed adjacent to a layer 314 of liquid crystal material. The switchable liquid crystal retarder 301 comprises two surface alignment layers 409, 411 disposed adjacent to and on opposite sides of the layer of liquid crystal material 314 and disposed on respective liquid crystal encapsulation substrates 312, 316. Further electrodes 413, 415 are arranged to provide a drive voltage across the liquid crystal layer 314. In a privacy mode of operation a first AC voltage is applied by the driver 350 and in a public mode of operation a second AC voltage, which may be zero or a voltage different from the privacy mode, is applied by the driver 350 via the electrodes 413, 415.

[0104] The display device 100 further comprises a reflective polarizer 302 disposed between the output display polarizer 218 and the at least one first polarizer controlled retarder 300, the reflective polarizer 302 being a linear polarizer. The reflective polarizer 302 differs in function and operation from the reflective polarizer 208 described above. The reflective polarizer 302 provides increased frontal reflection and an improved security factor, while the reflective polarizer 208 provides improved backlight recycling efficiency and uniformity.

[0105] In an alternative embodiment (not shown), a further polarizer controlled retarder can be placed between the input polarizer 210 and a further additional polarizer placed between the backlight and the input polarizer 210. In a further alternative embodiment (not shown), a further additional polarizer may be placed between the reflective polarizer 302 and the output polarizer 218. A further polarizer controlled retarder may be placed between the output polarizer 218 and the further additional polarizer. The further additional polarizer and the further additional polarizer controlled retarder may advantageously achieve increased brightness for off-axis users in a public mode of operation, and a narrower switch-on angle for a desirable image security factor in a privacy mode of operation.

[0106] Here, an alternative display structure is shown.

[0107] 3A is a schematic diagram showing a side perspective view of a switchable privacy display apparatus comprising a backlight 20 with an optical rotation film 50, an additional polarizer 318, a light control film 700 disposed on a passive C-plate retarder 330 of a polarity control retarder 300, a liquid crystal retarder 301 of the polarity retarder 300, and a transmissive spatial light modulator 48 with input and output polarizers 210, 218. The display device 100 further comprises a backlight 20 arranged to output light, the spatial light modulator 48 arranged to receive and spatially modulate the output light from the backlight 20, the display polarizer being an input display polarizer 210 disposed at the input side of the spatial light modulator 48.

[0108] 3A shows an alternative to FIG. 1 in which a polarity-controlled retarder 300 is placed between an additional polarizer 318 and the input polarizer 210 of the spatial light modulator 48. The reflective polarizer 302 is omitted. Front reflections from the display 100 are reduced, advantageously achieving increased display contrast at high illumination. Additionally, the thickness of the front surface of the display is reduced, and in embodiments providing a scattering output surface of the polarizer 218, increased image resolution is achieved.

[0109] The light control film 700 is disposed between the additional polarizer 318 and the display polarizer 210. Figure 3A shows another alternative to Figure 1 in which the support substrate 710 of the light control film 700 is omitted and the light control film 700 is provided on a passive retarder 330. Advantageously, thickness and cost can be reduced and uniformity can be maintained.

[0110] In an alternative embodiment (not shown), the light control film 700 can be attached to 312, 316. Advantageously, the thickness can be reduced and flatness of the light control film 700 can be achieved to increase output uniformity.

[0111] FIG. 3A further illustrates an alternative backlight 20 compared to the backlight 20 of FIGS. 1 and 2. In comparison to FIG. 1, the back reflector 3 is a specular reflector and the waveguide has a surface structure arranged to provide output light with an output angle close to grazing the output face 6 of the waveguide 1. As described in FIG. 15, advantageously, such a backlight can achieve a narrower light output solid angle than the light output of the backlight 20 of FIG. 1. Advantageously, the security factor is increased and a privacy display with a narrower switch-on angle for privacy can be provided.

[0112] Features of the embodiment of FIG. 3A that are not discussed in further detail can be assumed to correspond to features bearing like reference numbers discussed above, including potential variations of features.

[0113] FIG. 3B is a schematic diagram showing a side perspective view of a switchable privacy display device 100 comprising a backlight 20 with a light control film 700 disposed on an optical rotation film 50, an additional polarizer 318, a polar retarder 300, and a transmissive spatial light modulator 48 with input and output polarizers 210, 218.

[0114] The light control film 700 is disposed between the backlight 20 and the additional polarizer 318. Residual retardation, scattering, and stray light in the light control film do not reduce the contrast of the polarity controlled retarder for off-axis viewing positions. Advantageously, the security factor against off-axis voyeurs can be increased compared to the arrangement of FIG. 3A.

[0115] 3B illustrates another alternative substrate for the light control film provided by optical rotatory film 50. Advantageously, thickness and cost can be reduced and uniformity can be increased.

[0116] Features of the embodiment of FIG. 3B that are not discussed in further detail can be assumed to correspond to features bearing like reference numbers discussed above, including potential variations of features.

[0117] 4 is a schematic diagram showing a polarity controlled retarder 300 and light control film 700 in a side perspective view for a switchable privacy display device, where the support substrate of the light control film 700 is provided by one of a pair of crossed A-plates 330A, 330B. Compared to the C-plate retarders of Figures 1, 2 and 3A, the A-plate may provide an increased area of ​​high security factor in the liquid crystal mode with uniform alignment of the alignment layers 409, 411.

[0118] A light control film 700 can be provided on the passive retarder 330A. Advantageously, thickness and cost can be reduced and uniformity can be maintained. The polarity control retarder 300 of FIG. 4 can be provided between the additional polarizer 318 and the input polarizer 210 or between the additional polarizer 318 and the output polarizer 218 of the spatial light modulator 48.

[0119] Features of the embodiment of FIG. 4 that are not discussed in further detail can be assumed to correspond to features bearing like reference numbers discussed above, including potential variations of features.

[0120] It may be desirable to use the emissive spatial light modulator 48 to provide a switchable privacy display.

[0121] FIG. 5 is a schematic diagram showing a side perspective view of a switchable privacy display device 100 comprising an emissive spatial light modulator 48 with an output display polarizer 218, a light control film 700, a reflective polarizer 302, a polarity controlled retarder 300 and an additional polarizer 318.

[0122] The emissive spatial light modulator further comprises a quarter wave plate 205 and a display polarizer 218 positioned to reduce the visibility of reflections from the pixel plane 214 of the spatial light modulator 48 .

[0123] The spatial light modulator 48 comprises an emissive spatial light modulator arranged to emit spatially modulated light. The spatial light modulator 48 may be an OLED display or a micro-LED display with an array of self-emissive pixels 220, 222, 224 as compared to the transmissive pixels of FIG.

[0124] The light control film 700 is disposed between the reflective polarizer 302 and the spatial light modulator 48. The light control film 700 is disposed between the reflective polarizer 302 and the display polarizer 218.

[0125] In an alternative embodiment, the emissive spatial light modulator 48 of Figure 5 can be provided by a transmissive spatial light modulator 48 and a backlight 20 as described elsewhere herein. The backlight 20 can provide lower brightness at high polar angles compared to the emission direction of the emissive spatial light modulator 48. Advantageously, the brightness at high angles can be reduced to increase the security factor against off-axis voyeurs in a privacy mode of operation.

[0126] Features of the embodiment of FIG. 5 that are not discussed in further detail can be assumed to correspond to features bearing like reference numbers discussed above, including potential variations of features.

[0127] FIG. 6 is a schematic diagram showing a side perspective view of a switchable privacy display device 100 comprising a spatial light modulator 48 with an output display polarizer 218, a polarity controlled retarder 300, an additional polarizer 318 and a light control film 700 whose supporting substrate is provided with touch screen electrodes.

[0128] The display device 100 further comprises a backlight 20 arranged to output light, the spatial light modulator 48 comprising a transmissive spatial light modulator 48 arranged to receive and spatially modulate the output light from the backlight 20, and a light control film disposed in front of the spatial light modulator 48.

[0129] The electrodes 500 and drivers 452 are disposed on a support substrate 710, with further electrodes 502 and drivers 454 provided on the substrate 510, with a dielectric 501 provided between the substrates 710, 510. A proximate finger 25 can modulate projected magnetic field lines 570, 572 which can be detected to provide touch input. The light control film 700 is separated from the pixel plane 214, which can advantageously reduce moiré. The number of substrates can be reduced, advantageously reducing thickness and cost.

[0130] Features of the embodiment of FIG. 6 that are not discussed in further detail can be assumed to correspond to features bearing like reference numbers discussed above, including potential variations of features.

[0131] Here, the structure and operation of light control film 700 will be described.

[0132] FIG. 7A is a schematic diagram showing a side perspective view of a light control film 700 comprising an input surface 706, an output surface 708 facing the input surface 706, an array of light-transmitting regions 704 extending between the input surface 706 and the output surface 708, and absorptive regions 702 extending between the transmissive regions and partially between the input surface 706 and the output surface 708.

[0133] The array of transmissive regions 704 is a one-dimensional array of elongated transmissive regions 704 that are elongated in the y-axis direction.

[0134] The absorptive regions 702 between the transmissive regions 704 extend between the input face 706 and the output face 708. The light control film 700 is provided on a supporting substrate 710. The substrate 710 can be located on either the input side 706 or the output side 708 of the light control film.

[0135] The light transmissive regions 704 have parallel sides and a surface normal to the plane of the light control film 700 such that the direction of maximum light transmission, e.g., light ray 490, is perpendicular to the plane of the light control film 700. The transmissive regions 704 have an axis 709 defined for each transmissive region 704 between the centers 705, 707 of the apertures 716, 718 on the input and output sides 706, 708 of the transmissive regions 704 that is perpendicular to the plane of the spatial light modulator 48 (the x-y plane) at all locations across the light control film 700.

[0136] In the arrangement of Figure 7A, the light control film 700 has a transmittance having a profile with polar angle in the direction (x-axis) in which an array of transmissive regions centered on a normal to the plane of the spatial light modulator 48 (the x-y plane) is repeated at every position across the light control film.

[0137] 7A, the light absorbing regions 704 do not extend between the input and output sides 706, 708 of the light control film. Rather, a layer of transmissive material 709 may be provided over the light control film. Such a layer may provide support for the light transmitting regions 704 during manufacture.

[0138] Features of the embodiment of FIG. 7A that are not discussed in further detail can be assumed to correspond to features bearing like reference numbers discussed above, including potential variations of features.

[0139] Next, alternative structures for the light control film are described.

[0140] FIG. 7B illustrates a light control film 700 comprising an array of transmissive regions 702 extending between an input face 706 and an output face 708, and absorptive regions 702 extending between the transmissive regions 704 and between the input face 706 and the output face 708, the transmissive regions 704 having a width S of an aperture 716 on the input side. IN is the width S of the opening 718 on the output side 708 OUT7B is a schematic diagram illustrating a side perspective view of a light control film 700 that is tapered so that it is smaller than 0.01 mm. Compared to the light control film 700 of FIG. 7A, such an arrangement can advantageously provide increased luminance uniformity in the on-axis direction, as described further below.

[0141] Features of the embodiment of FIG. 7B that are not discussed in further detail can be assumed to correspond to features bearing like reference numbers discussed above, including potential variations of features.

[0142] We will now discuss the light transmission of the structures of Figures 7A and 7B.

[0143] FIG. 8 is a schematic graph showing the variation in transmission with transverse angle for various light control films 700 in the direction in which light transmitting regions 704 are repeated.

[0144] Under illumination, the structure of FIG. 7A is expected to provide a triangular profile with the angle of incidence at the side angle. That is, the transmission is maximum in the direction 199 perpendicular to the plane of the film 700. At non-zero side angles, some light rays passing through the input aperture 716 of the light transmitting region 704 will be incident on the absorbing region 702, thereby reducing the brightness. In an ideal non-scattering arrangement, such a profile would provide a substantially triangular profile. In reality, some light may be transmitted by the light absorbing region 704. Additionally, scattering, including scattering from diffraction, spreads the light out to provide a modified triangular profile, with the profile becoming somewhat rounded near the axis and near angles where all light would otherwise be absorbed. It is convenient to describe the angular range of polar angles 460 provided by the film using the angle at which the transmission of the light control film 700 falls to 5% of the input illumination. This differs from the transmission of the film compared to the front-on transmission due to the loss of on-axis rays in the light absorbing region 702.

[0145] We now describe a known non-switchable privacy display that is provided by the user by adding a louvre film in front of a conventional spatial light modulator.

[0146] Profile 456 is for a known prior art light control film for use in one type of non-switchable privacy display. Such a profile provides a polar angle range 460 of 66°, which is an angle of 5% transmission. At 45°, brightness is reduced to provide some image security for privacy use. As will be explained further below, such films for use in non-switchable privacy displays provide undesirably low image visibility to off-axis viewers in public operation. Moreover, such films provide approximately 70% frontal transmission, with such loss providing an undesirable loss of brightness and / or increased power consumption.

[0147] Profile 454 is for a different known prior art light control film for use in another type of non-switchable privacy display that provides passive brightness reduction and passive reflectance increase off-axis. Such a profile provides a polar angle range 460 of 72°. At 45°, brightness is reduced and reflectance is increased to improve image security for privacy operation. However, such a film provides undesirable off-axis brightness and off-axis reflectance in public operation.

[0148] Profiles 450, 452 are desirable profiles for embodiments of the present disclosure, but are not desirable profiles for use in non-switchable privacy displays because such profiles provide high brightness at off-axis angles and do not achieve a desirable security factor against off-axis voyeurs.

[0149] Profile 450 is S OUT =S IN7A , the light control film 700 may be conveniently fabricated by exposing a photoresist in collimated light, for example, through a mask.

[0150] Profile 452 is S OUT >S IN 7B, the profile 452 can be provided by a light transmitting region with tapered sides. Advantageously, the profile 452 improves uniformity in the area close to the user's line of sight, improving display uniformity.

[0151] The light control film 700 of the present disclosure may have a transmittance of 5% or greater over a range of polar angles in an orientation where the array of transparent regions is repeated at least 80° wide, and may have a transmittance of 5% or greater over a range of polar angles in an orientation where the array of transparent regions is repeated at least 90° wide.

[0152] Additionally, the light control film 700 may have a transmission of 5% or greater over a range of polar angles in directions where the array of transmissive regions repeats up to 130° wide.

[0153] The absorptive regions 702 of the light control film 700 may have a thickness t, where t is given by the following formula:

number

[0154] In an exemplary embodiment, the light control film 700 as shown in Figure 7A provides a profile 450 with a polar angle range 460 of 98° (where ξ = 0.755) with a transmission of over 15% at 45°. Such a profile advantageously achieves high transmission efficiency from the front.

[0155] In a further exemplary embodiment, the light control film 700 as shown in Figure 7B provides a profile 452 with a polar angle range 460 of 106° (where ξ = 0.799) with a transmission of over 20% at 45°. Such a profile advantageously achieves an extended region of uniform transmission near the on-axis direction. Desirably, the uniformity of the display viewed from the front may be increased compared to profile 450.

[0156] The thickness 706 of layer 700 and the width of louvers 702, 704 are selected to provide absorption at 45 degrees in at least one azimuthal orientation that is between 2% and 30% of the absorption in the direction perpendicular to the light control film, preferably between 4% and 20% of the absorption in the direction perpendicular to the light control film, and most preferably between 6% and 10% of the absorption in the direction perpendicular to the light control film 700.

[0157] An overview of the operation of the displays of Figures 1-6 in the privacy and public modes of operation will now be provided.

[0158] Figure 9A is a schematic diagram illustrating the operation of the display device of Figure 1 in a privacy mode of operation from a top view, and Figure 9B is a schematic diagram illustrating the operation of the display device of Figure 1 in a public mode of operation from a top view. Features of the embodiments of Figures 9A and 9B that are not discussed in further detail may be assumed to correspond to features with like reference numbers discussed above, including potential variations of features.

[0159] A light cone 480 is output from the backlight 20 (or emissive spatial light modulator 48 ) and directed through a light control film 700 with a transmitted light cone 482 that is narrower than cone 480 .

[0160] In Figure 9A, the polarity controlled retarder 300 is positioned to reduce off-axis brightness with cone size 484. A front observer 45 sees light rays 445 from across the display with high brightness and high image visibility. An off-axis voyeur 47 sees light rays 447 from across the display with reduced brightness and improved image security. Some areas of the display close to the voyeur 47 may have undesirably higher brightness.

[0161] In the public mode of operation as shown in FIG. 9B, the cone width 486 increases substantially and both users can see light from the entire display with high image visibility within the transmission cone 482 of the light control film 700 and backlight 20.

[0162] An exemplary embodiment of a switchable privacy display will now be described, in which the field of view 600 seen by user 45 at a plane of 500 mm and 0 degree side angle from a 14 inch landscape display is marked, and the field of view 602 seen by user 47 is shown at 700 mm from the display and a plane with a 45 degree side angle.

[0163] Figure 10A is a schematic graph showing the directional variation in luminance of a backlight 20 with crossed brightness enhancement films as shown in Figure 1. Figure 10B is a schematic graph showing the directional variation in luminance of a backlight with a light control film 700 having a transmittance of 5% or greater over a polar angle range 460 of 100° in the direction in which the array of transmissive regions 704 is repeated (where ξ=0.766).

[0164] Here, an exemplary embodiment of a polarity controlled delay 300 is provided.

[0165] Figure 10C is a schematic graph showing the variation with transmission direction of the polarity-controlled retarder of Figure 1 for an exemplary embodiment of the arrangement, which is shown in Table 1. Figure 10D is a schematic graph showing the variation with direction of reflectance of the polarity-controlled retarder of Figure 1 for an exemplary embodiment of the arrangement, where the display 100 further comprises a reflective polarizer 302. [Table 1]

[0166] Figure 11 is a schematic graph showing the variation with direction of Fresnel reflection of a single surface in air. Such reflection is included in the calculation of the security factor S and image visibility W for both public and privacy modes of operation.

[0167] Further non-limiting alternatives to polarity controlled delay 300 will now be described.

[0168] In one alternative, the switchable liquid crystal retarder 301 may comprise two surface alignment layers disposed adjacent to and on opposite sides of the layer 413 of liquid crystal material 414, each arranged to provide a vertical alignment in the adjacent liquid crystal material. The layer 413 of liquid crystal material 414 of the switchable liquid crystal retarder 301 may comprise a liquid crystal material with negative dielectric anisotropy. The layer 413 of liquid crystal material 414 may have a retardation for light of a wavelength of 550 nm in the range of 500 nm to 1000 nm, preferably in the range of 600 nm to 900 nm, most preferably in the range of 700 nm to 850 nm.

[0169] Where two surface alignment layers providing perpendicular alignment are provided, the at least one passive compensation retarder 330 may comprise a retarder whose optical axis is perpendicular to the plane of the retarder, the at least one passive retarder having a retardation for light of a wavelength of 550 nm in the range of -300 nm to -900 nm, preferably in the range of -450 nm to -800 nm, most preferably in the range of -500 nm to -725 nm.

[0170] Alternatively, if two surface alignment layers providing vertical alignment are provided, the at least one passive compensation retarder 330A, 330B may comprise a pair of retarders with optical axes in intersecting retarder planes, each retarder of the pair having a retardation for light of wavelength 550 nm in the range of 300 nm to 800 nm, preferably in the range of 500 nm to 700 nm, most preferably in the range of 550 nm to 675 nm. Advantageously, in this case, an increased field of view in the wide angle mode of operation may be provided. Furthermore, zero voltage operation in the wide angle mode of operation may be provided, reducing power consumption.

[0171] In another alternative, the switchable liquid crystal retarder 301 may comprise two surface alignment layers disposed adjacent to and on opposite sides of the layer 413 of liquid crystal material 414, each arranged to provide uniform alignment in the adjacent liquid crystal material. Compared to vertical alignment on opposite sides of the liquid crystal, advantageously increased resilience to visibility of flow of the liquid crystal material during application of pressure may be achieved.

[0172] The layer 413 of liquid crystal material 414 of the switchable liquid crystal retarder 301 may comprise a liquid crystal material with positive dielectric anisotropy. The layer 413 of liquid crystal material 414 may have a retardation for light of a wavelength of 550 nm in the range of 500 nm to 900 nm, preferably in the range of 600 nm to 850 nm, most preferably in the range of 700 nm to 800 nm.

[0173] Where two surface alignment layers providing uniform alignment are provided, the at least one passive compensation retarder 330 may comprise a retarder whose optical axis is perpendicular to the plane of the retarder, the at least one passive retarder having a retardation for light of a wavelength of 550 nm in the range of -300 nm to -700 nm, preferably in the range of -350 nm to -600 nm, most preferably in the range of -400 nm to -500 nm.

[0174] Alternatively, if two surface alignment layers providing uniform alignment are provided, the at least one passive compensation retarder 330A, 330B may comprise a pair of retarders with optical axes in the intersecting retarder planes, each retarder of the pair having a retardation for light of wavelength 550 nm in the range of 300 nm to 800 nm, preferably in the range of 350 nm to 650 nm, most preferably in the range of 450 nm to 550 nm. Advantageously, in this case an increase in the restoring force to the visibility of the flow of the liquid crystal material during pressure application may be achieved.

[0175] In another alternative, the switchable liquid crystal retarder 301 may comprise two surface alignment layers disposed adjacent to and on opposite sides of the layer 413 of liquid crystal material 414, one of the surface alignment layers arranged to provide a homeotropic alignment in the adjacent liquid crystal material and the other of the surface alignment layers arranged to provide a uniform alignment in the adjacent liquid crystal material.

[0176] When a surface alignment layer arranged to provide uniform alignment is between the layer 413 of liquid crystal material 414 and the compensation retarder 330, the layer 413 of liquid crystal material 414 may have a retardation for light of a wavelength of 550 nm in the range of 700 nm to 2000 nm, preferably in the range of 1000 nm to 1500 nm, and most preferably in the range of 1200 nm to 1500 nm.

[0177] If a surface alignment layer arranged to provide uniform alignment is between the layer 413 of liquid crystal material 414 and the compensation retarder 330, the at least one passive compensation retarder 330 may comprise a retarder whose optic axis is perpendicular to the plane of the retarder, the at least one passive retarder having a retardation for light of a wavelength of 550 nm in the range of -400 nm to -1800 nm, preferably in the range of -700 nm to -1500 nm, most preferably in the range of -900 nm to -1300 nm.

[0178] Where a surface alignment layer arranged to provide uniform alignment is between the layer 413 of liquid crystal material 414 and the compensation retarders 330A, 330B, the at least one passive compensation retarder 330A, 330B may comprise a pair of retarders having optical axes in the intersecting retarder planes, each retarder of the pair having a retardation for light of a wavelength of 550 nm in the range of 400 nm to 1800 nm, preferably in the range of 700 nm to 1500 nm, most preferably in the range of 900 nm to 1300 nm.

[0179] When a surface alignment layer arranged to provide vertical alignment is between the layer 413 of liquid crystal material 414 and the compensation retarder 330, the layer 413 of liquid crystal material 414 may have a retardation for light of a wavelength of 550 nm in the range of 500 nm to 1800 nm, preferably in the range of 700 nm to 1500 nm, and most preferably in the range of 900 nm to 1350 nm.

[0180] Where a surface alignment layer arranged to provide vertical alignment is between the layer 413 of liquid crystal material 414 and the compensation retarder 330, the at least one passive compensation retarder 330 may comprise a retarder whose optic axis is perpendicular to the plane of the retarder, the at least one passive retarder having a retardation for light of a wavelength of 550 nm in the range of -300 nm to -1600 nm, preferably in the range of -500 nm to -1300 nm, most preferably in the range of -700 nm to -1150 nm.

[0181] If there is a surface alignment layer between the layer 413 of liquid crystal material 414 and the compensation retarders 330A, 330B arranged to provide vertical alignment, the at least one passive compensation retarder 330A, 330B may comprise a pair of retarders having an optical axis in the plane of the intersecting retarders, each retarder of the pair having a retardation for light of a wavelength of 550 nm in the range of 400 nm to 1600 nm, preferably in the range of 600 nm to 1400 nm, most preferably in the range of 800 nm to 1300 nm. Advantageously, in this case an increase in the restoring force to the visibility of the flow of the liquid crystal material during application of pressure may be achieved.

[0182] Each alignment layer may have a pretilt with a pretilt direction with a component in the plane of the liquid crystal layer parallel, anti-parallel or orthogonal to the electric vector transmission direction of the display polarizer. Advantageously, the display may have a narrow lateral viewing angle and a wide viewing freedom for rotation of the display about a horizontal axis. Such a display may be easy to view for a user of a front-on display and difficult to view for a user of an off-axis display.

[0183] The at least one passive retarder may comprise at least two passive retarders with at least two different orientations of the optical axis, which may have optical axes in the planes of the intersecting retarders. The liquid crystal retarders with uniform orientation provide a wider field of view and a restoring force to the visibility of the flow of the liquid crystal material during the application of pressure.

[0184] A pair of passive retarders may have optic axes extending at 45° and 135°, respectively, to an electric vector transmission direction parallel to the electric vector transmission of the display polarizer. The passive retarders may be provided using stretched films to advantageously achieve low cost and high uniformity.

[0185] The switchable liquid crystal retarder 301 may be provided between a pair of passive retarders. Advantageously, the thickness and complexity of multiple retarders may be reduced.

[0186] The transparent electrodes and liquid crystal alignment layers may be formed on one side of each of a pair of passive retarders adjacent the switchable liquid crystal retarder 301, and may further comprise first and second substrates between which the switchable liquid crystal retarder 301 is provided, each of the first and second substrates comprising one of a pair of passive retarders, each of the pair of passive retarders having a retardation for light of a wavelength of 550 nm in the range of 150 nm to 800 nm, preferably in the range of 200 nm to 700 nm, most preferably in the range of 250 nm to 600 nm.

[0187] In one alternative, at least one passive compensation retarder 330 may comprise a retarder having an optical axis perpendicular to the plane of the retarder, which advantageously reduces the thickness and complexity of the passive retarder stack.

[0188] At least one passive compensation retarder 330A, 330B may comprise two passive retarders with optical axes perpendicular to the plane of the passive retarders, and the switchable liquid crystal retarder 301 is provided between the two passive retarders. Advantageously, the thickness and complexity of the multiple retarders may be reduced. High frontal efficiency may be achieved in both the wide-angle and privacy modes, a wide field of view in the wide-angle mode, and a voyeur may not be able to perceive image data from a wide range of off-axis viewing positions.

[0189] A transparent electrode and a liquid crystal alignment layer may be formed on one side of each of the two passive retarders adjacent to the switchable liquid crystal retarder 301. The switchable liquid crystal retarder 301 may be provided on first and second substrates, each of which comprises one of the two passive retarders. The two passive retarders may have a total retardation for light of a wavelength of 550 nm in the range of -300 nm to -700 nm, preferably in the range of -350 nm to -600 nm, most preferably in the range of -400 nm to -500 nm.

[0190] In another alternative, at least one passive compensation retarder 330 may comprise a retarder having an optical axis with a component perpendicular to the plane of the retarder and a component in the plane of the retarder. Advantageously, the field of view in the wide-angle mode is expanded and a voyeur may not be able to perceive image data from a wide range of off-axis viewing positions.

[0191] The in-plane component of the passive retarder may extend at 0° with respect to an electric vector transmission direction parallel or perpendicular to the electric vector transmission of the display polarizer. The at least one passive retarder may further comprise a passive retarder having an optical axis perpendicular to the plane of the passive retarder, or a pair of passive retarders having optical axes in the planes of the intersecting passive retarders.

[0192] The delay of the at least one passive compensation delay 330 may be equal and opposite to the delay of the switchable liquid crystal retarder 301 .

[0193] The switchable liquid crystal retarder 301 may have a first and a second pretilt, and the at least one passive compensation retarder 330 may have a compensation retarder 330 with a first and a second pretilt, where the first pretilt of the compensation retarder 330 is the same as the first pretilt of the liquid crystal retarder, and the second pretilt of the compensation retarder 330 is the same as the second pretilt of the liquid crystal retarder.

[0194] The switchable liquid crystal retarder 301 may further comprise electrodes arranged to apply a voltage to control the layer 413 of liquid crystal material 414. The electrodes may be on opposing sides of the layer 413 of liquid crystal material 414. The display may be switchable by control of the liquid crystal layer, advantageously achieving a switchable privacy display, or other display with reduced off-axis stray light. The display may further comprise a control system configured to control the voltage applied across the electrodes of the at least one switchable liquid crystal retarder 301.

[0195] Here, the output of display 100 having the components shown in FIGS. 10A to 10D will be described.

[0196] Figure 12 is a schematic graph showing the variation of luminance with lateral angle for a display of the type shown in Figure 1, the backlight profile of Figure 10A, and the transmission profiles of Figures 10B and 10C. Profile 430 is the lateral variation of backlight luminance of Figure 10A. Profile 432 is the lateral variation of transmittance of the light control film 700 of Figure 10B. Profile 434 is the variation of the polarity controlled retarder of Figure 10C in the privacy mode of operation. Profile 436 is the resulting profile of the output luminance of the display 100 in the privacy mode of operation.

[0197] FIG. 13 shows a backlight profile of FIG. 10A, a transmission profile of FIG. 10B and FIG. 10C, and a reflection profile of FIG. 10D, with a luminance in front of the display of a value Y measured in nits that is half the illuminance of a value I measured in lux. max 2 is a schematic graph showing the variation with direction of the security factor S in privacy mode for a display of the type shown in FIG. 1, where S is the security factor for a display of the type shown in FIG. A frontal observer 45 has a field of view 600 that provides high image visibility (S<0.1) across the entire display. Advantageously, a bright and easy-to-read image is seen. An off-axis user 47 has a field of view 610 where advantageously all image data is private (S<1.0), and a portion of the display is invisible to all image data (S≧1.8).

[0198] Figure 14 is a schematic graph showing the variation of luminance with lateral angle for a display of the type shown in Figure 1, the backlight profile of Figure 10A, and the transmission profiles of Figures 10B and 10C. Profile 430 is the lateral variation of backlight luminance in Figure 10A. Profile 432 is the lateral variation of transmittance of the light control film 700 in Figure 10B. Profile 434 is the variation of the polarity controlled retarder in the public mode of operation. Profile 436 is the resulting profile of the output luminance of the display 100 in the public mode of operation. The display 100 achieves a 90° angular width 438 where the luminance is 5% or more of the front luminance.

[0199] FIG. 15 shows a backlight profile of FIG. 10A, a transmission profile of FIG. 10B, and a reflection profile of FIG. 11, with a luminance in front of the display of a value Y measured in nits that is half the illuminance of the value I measured in lux. max2 is a schematic graph showing the variation with direction of the security factor S in privacy mode for a display of the type shown in FIG. 1, where S is a square. A frontal observer 45 has a field of view 600 that provides high image visibility (S<0.1) across the entire display. Advantageously, a bright and easy-to-read image is seen. An off-axis user 47 has a field of view 610 where the image data is advantageously invisible (S<1.0). Advantageously, the data is shared by multiple users.

[0200] The operation of a prior art non-switchable privacy display will now be described.

[0201] 16 is a schematic graph showing the variation of luminance and transmittance with horizontal angle for an exemplary prior art non-switchable privacy display. The prior art display may be provided with a backlight with the same luminance profile as in FIG. 10A and a horizontal luminance profile 430. At the output of the display, a prior art light control film with a transmittance of 5% or more over a range of polar angles in a direction where the array of transparent regions is repeated 70° wide is attached by the user. The output luminance profile of the prior art display is shown by profile 437.

[0202] FIG. 17 shows a front reflection profile for the display front luminance of FIG. 11 with the backlight profile of FIG. 10A, a light control film with a width of 70° where the transmittance is 5% of the front transmittance, and a front reflection profile with the display front luminance of FIG. 11, with a value Y measured in nits that is half the illuminance of value I measured in lux. max 1 is a schematic graph showing the variation with direction of the security factor S of a conventional non-switchable privacy display;

[0203] Such a display has a single mode of operation such that the characteristics of the display are fixed. Considering the field of view 610 of an off-axis voyeur, when it is desired to hide off-axis information, such a display achieves a privacy level S>1.0, but some types of image data are visible across the display as S<1.5. Advantageously, for comparison, the present embodiment of FIG. 13 achieves improved image security and image invisibility to off-axis voyeurs.

[0204] Considering an off-axis user's field of view 610, where it is desirable to display off-axis information, however, some types of image data content are not visible across the display as S>1.0 Advantageously, for comparison, the present embodiment of FIG. 15 achieves improved image visibility to off-axis users.

[0205] In other words, the light control film 700 of this embodiment with a transmittance of 5% or more over a range of polar angles in a direction in which the array of transparent regions is repeated 80° wide (ξ>0.643) can achieve improved image visibility in public mode and improved image security in privacy mode compared to conventional displays.

[0206] It would be desirable to increase the uniformity of brightness and security levels of privacy displays.

[0207] Fig. 18 is a schematic diagram showing a side perspective view of a light control film 700 for the display device 100 of this embodiment. Fig. 19 is a schematic diagram showing the operation of the display device of Fig. 1 with the light control film of Fig. 18 in a privacy mode of operation from a top view.

[0208] The light control film 700 comprises an array of transmissive regions 704 extending between an input face 706 and an output face 708, and absorptive regions 702 between the transmissive regions. The absorptive regions 704 extend between the input face 706 and the output face 708, and the transmissive regions 704 are tapered. The transmissive regions 702 are angled such that an axis 709 defined for each transmissive region 704 between centers 705, 707 of the input and output side apertures 716, 718 of the transmissive regions 704 is directed inwardly toward the optical axis 440 that extends forward from the center of the spatial light modulator 48.

[0209] In other words, the light control film 700 has a transmittance having a profile with a polar angle in a direction in which an array of transmissive regions repeats having a centerline 709 directed inwardly toward the optical axis 440 that extends forward from the center of the spatial light modulator 448. The centerline 709 of the profile is directed toward the common point 442.

[0210] The transparent regions 704 are tilted so that an axis 709 defined for each transparent region 704 between the centers 705, 707 of the openings 716, 718 on the input and output sides 706, 708 of the transparent region 704 is directed inward toward an optical axis 709 extending forward from the center of the spatial light modulator 48, the axis being directed toward a common point 442.

[0211] Thus, compared to the arrangement of FIG. 9A, the light cone 482 is tilted towards the front user for image points across the display in the direction in which the transmission regions 704 are repeated. The center of the light cone 482 is directed towards the user 45, thus increasing the uniformity of the image seen, since the roll-off in the profile due to transmission, for example profile 432 of FIG. 14, is less visible or not visible at all. Advantageously, the uniformity of the display is improved. Furthermore, the uniformity of the security factor S is improved, since an off-axis voyeur sees an increased uniformity at low light levels of points across the display, compared to that shown in the field of view 610 of FIG. 13. Advantageously, the security of the image is improved.

[0212] Further, pupil shaping of such light toward point 442 may be achieved by a tapered light transmissive region to achieve improved uniformity of illumination. Such a taper provides a tool that may be pupil shaped without protruding surfaces and may be suitable for replicating light transmissive region 704.

[0213] Features of the embodiments of Figures 18 and 19 that are not discussed in further detail can be assumed to correspond to features bearing like reference numbers discussed above, including potential variations in features.

[0214] Now, an embodiment will be described that includes a curved light control film 700 to improve brightness uniformity and security factor uniformity.

[0215] FIG. 20 is a schematic diagram showing a top view of a display device comprising a curved transmissive spatial light modulator 48, a curved backlight 20, a plurality of curved retarders 300, and a curved light control film 700, and FIG. 21 is a schematic diagram showing a top view of a display device comprising a curved emissive spatial light modulator 48, curved retarders, and a curved light control film 700.

[0216] Light from image points throughout the display 100 is directed by the curvature of each element to a common point 442. The common point 442 may be at the nominal viewing distance to the observer 45, as shown in Figure 20, or alternatively, may be at a different distance. Preferably, the distance is the same as or longer than the nominal viewing distance, as shown in Figure 21.

[0217] Compared to the arrangement of FIG. 9A, the light cones 480, 482, 484 are inclined towards the front user 45 across the display. For example, the changes in the luminance profiles 430, 432, 434 (and the corresponding front reflectance profile when the reflective polarizer 302 is provided) of FIG. 14 are less visible or not visible at all across the display. Advantageously, the uniformity of the display is improved. Furthermore, since an off-axis voyeur sees an increased uniformity of luminance (and uniformity of reflectance when the reflective polarizer 302 is provided) at points across the display device 100 at low light levels, the uniformity of the security factor S is improved compared to that shown by the field of view 610 of FIG. 13. Advantageously, the security of the image is improved.

[0218] Features of the embodiments of Figures 20 and 21 that are not discussed in further detail can be assumed to correspond to features bearing like reference numbers discussed above, including potential variations of features.

[0219] The operating principle of the switchable polarity controlled delay of FIG. 1 will now be described.

[0220] FIG. 22A is a schematic diagram illustrating a side view of the propagation of output light from the spatial light modulator through the optical stack of FIG. 1 in a privacy mode of operation.

[0221] When the layer 314 of liquid crystal material 414 is driven to operate in the privacy mode, the retarder 300 does not provide an overall conversion of polarization component 360 into output ray 400 passing along an axis perpendicular to the plane of the switchable retarder, but does provide an overall conversion of polarization component 361 into passing ray 402 for some polar angle that is acute perpendicular to the plane of the retarder.

[0222] Polarization component 360 from the output polarizer 218 is transmitted by the reflective polarizer 302 and enters the retarder 300. On-axis light has polarization component 362 unchanged from component 360, while off-axis light has polarization component 364 that is transformed by the retarder 300. At a minimum, polarization component 361 is transformed to linear polarization component 364 and absorbed by the additional polarizer 318. More generally, polarization component 361 is transformed to an elliptically polarized component that is partially absorbed by the additional polarizer 318.

[0223] The polar distribution of light transmission shown in Figure 10A modifies the polar distribution of the luminance output of the underlying spatial light modulator 48. If the spatial light modulator 48 comprises a directional backlight 20, the off-axis luminance can be further reduced as described above.

[0224] Features of the embodiment of FIG. 22A that are not discussed in further detail can be assumed to correspond to features bearing like reference numbers discussed above, including potential variations of features.

[0225] Advantageously, a privacy display is provided that has low brightness for off-axis voyeurs while maintaining high brightness for on-axis observers.

[0226] The behavior of the reflective polarizer 302 for light from an ambient light source 604 will now be described for a display operating in privacy mode.

[0227] FIG. 22B is a schematic diagram illustrating the propagation of ambient illumination light through the optical stack of FIG. 1 in a top view in a privacy mode of operation.

[0228] An ambient light source 604 illuminates the display device 100 with unpolarized light. The additional polarizer 318 transmits the light ray 410 perpendicular to the display device 100 with a first polarization component 372 that is a linear polarization component parallel to the electric vector transmission direction 319 of the additional polarizer 318.

[0229] In both operating conditions, polarization component 372 remains unchanged by retarder 300, and as a result, transmitted polarization component 382 is parallel to the transmission axes of reflective polarizer 302 and output polarizer 218, so that ambient light is directed through spatial light modulator 48 and lost.

[0230] In comparison, for light ray 412, the off-axis light is directed through retarder 300 so that polarization component 374 incident on reflective polarizer 302 can be reflected. After passing through retarder 300, such polarization component is reconverted to component 376 and transmitted through additional polarizer 318.

[0231] Thus, when the layer of liquid crystal material 314 is in the second of the two states, the reflective polarizer 302 does not provide reflected light for ambient light rays 410 that pass through the additional polarizer 318 and then through the retarder 300 along an axis perpendicular to the plane of the retarder 300, but provides reflected light rays 412 for ambient light that pass through the additional polarizer 318 and then through the retarder 300 at some polar angle that is acute perpendicular to the plane of the retarder 300, where the reflected light 412 passes back through the retarder 300 and is then transmitted by the additional polarizer 318.

[0232] Thus, the retarder 300 does not provide an overall conversion of the polarization component 380 along an axis perpendicular to the plane of the switchable retarder to ambient light 410 which passes through the additional polarizer 318 and then through the retarder 300, but does provide an overall conversion of the polarization component 372 at some polar angle that is acute perpendicular to the plane of the retarder 300 to ambient light 412 which passes through the absorbing polarizer 318 and then through the retarder 300.

[0233] Thus, the polar distribution of light reflection shown in Figure 10D indicates that the privacy state of retarder 300 can provide high reflectance at typical voyeur positions. Thus, in the privacy mode of operation, the reflectance at off-axis display positions is increased, as shown in Figure 10D, and the brightness of off-axis light from the spatial light modulator is reduced, as shown in Figure 10A.

[0234] In the public mode of operation, the control system 710, 752, 350 is arranged to switch the switchable liquid crystal retarder 301 to a second retarder state in which a phase shift is introduced to the polarization components of light passing along an axis tilted to the normal to the plane of the switchable liquid crystal retarder 301.

[0235] In comparison, the solid angle range 402D may be substantially the same as the solid angle range 402B in the public mode of operation. Such control of the output solid angle ranges 402C, 402D may be achieved by synchronous control of the sets of light sources 15, 17 and at least one switchable liquid crystal retarder 300.

[0236] Advantageously, a privacy mode can be achieved with low image visibility for off-axis display, and a large solid angle coverage can be provided with high efficiency for a public operating mode to share the display image among multiple users and to enhance image spatial uniformity.

[0237] The additional polarizer 318 is disposed on the same output side of the spatial light modulator 48 as the display output polarizer 218, which may be an absorbing dichroic polarizer. The display polarizer 218 and the additional polarizer 318 have electric vector transmission directions 219, 319 that are parallel. As explained below, such a parallel orientation provides high transmission at the central viewing position.

[0238] a switchable liquid crystal retarder 300 comprising a transmissive spatial light modulator 48 arranged to receive output light from the backlight, an input polarizer 210 arranged on an input side of the spatial light modulator between the backlight 20 and the spatial light modulator 48, an output polarizer 218 arranged on an output side of the spatial light modulator 48, an additional polarizer 318 arranged on an output side of the output polarizer 218, a layer 314 of liquid crystal material arranged between the at least one additional polarizer 318 and the output polarizer 318, where the additional polarizer 318 is arranged on the output side of the output polarizer 218, the liquid crystal retarder 300, and a control system 710 configured to synchronously control the light sources 15, 17 and the at least one switchable liquid crystal retarder 300.

[0239] The control system 710 further comprises a control voltage controller 752 arranged to provide control of the voltage driver 350 to effect control of the switchable liquid crystal retarder 301 .

[0240] Features of the embodiment of FIG. 22B that are not discussed in further detail can be assumed to correspond to features bearing like reference numbers discussed above, including potential variations of features.

[0241] Advantageously, a privacy display is provided that has high reflectance to off-axis voyeurs while maintaining low reflectance to off-axis observers. As noted above, such increased reflectance provides enhanced privacy performance of the display in ambient lit environments.

[0242] Here, the public operation mode will be described.

[0243] FIG. 23A is a schematic diagram showing a side view of the propagation of output light from the spatial light modulator through the optical stack of FIG. 1 in a public operating mode, and FIG. 23B is a schematic graph showing the change in output brightness with the polarity direction of the transmitted light beam of FIG. 23A.

[0244] Features of the embodiments of Figures 23A and 23B that are not discussed in further detail can be assumed to correspond to features bearing like reference numbers discussed above, including potential variations of features.

[0245] When the liquid crystal retarder 301 is in the first of its two states, the retarder 300 does not provide an overall conversion of the polarization components 360, 361 into output light passing perpendicular to the plane of the switchable retarder 301 or at an acute angle to the plane of the switchable retarder 301. That is, polarization component 362 is substantially the same as polarization component 360 and polarization component 364 is substantially the same as polarization component 361. Thus, the angular transmission profile of Figure 23B has substantially uniform transmission over a wide polar range. Advantageously, the display can be switched to a wide viewing angle.

[0246] FIG. 23C is a schematic diagram illustrating the propagation of ambient illumination light through the optical stack of FIG. 1 in a top view in a public mode of operation, and FIG. 23D is a schematic graph illustrating the change in reflectance with polarity direction of the reflected light beam of FIG. 23C.

[0247] Thus, when the liquid crystal retarder 301 is in the first of its two states, the retarder 300 does not provide an overall conversion of the polarization component 372 to ambient light 412 which passes through an additional polarizer 318 that is perpendicular to the plane of the retarder 300 or at an acute angle perpendicular to the plane of the retarder 300 and then through the retarder 300.

[0248] In the public mode of operation, the input light ray 412 has a polarization state 372 after being transmitted through the additional polarizer 318. In both the on-axis and off-axis directions, no polarization conversion occurs and thus the reflectance of the light ray 402 from the reflective polarizer 302 is low. The light ray 412 is transmitted by the reflective polarizer 302 and is lost in the display polarizer 218, 210 or the backlight of FIG.

[0249] Features of the embodiments of Figures 23C and 23D that are not discussed in further detail can be assumed to correspond to features bearing like reference numbers discussed above, including potential variations of features.

[0250] Advantageously, the public mode of operation provides high brightness and low reflectance over a wide viewing area, allowing such displays to be conveniently viewed by multiple observers with high contrast.

[0251] Another type of switchable privacy display is now described.

[0252] A display device 100 that can be switched between privacy and public modes of operation comprises an imaging waveguide and an array of light sources, as described in U.S. Patent No. 9,519,153, which is incorporated herein by reference in its entirety. The imaging waveguide images the array of light sources into an optical window that can be controlled to provide high brightness on-axis and low brightness off-axis in the privacy mode, and provides high brightness with a large solid angle cone for public operation.

[0253] As may be used herein, the terms "substantially" and "approximately" provide industry-accepted tolerances for corresponding terms and / or relativities between items. Such industry-accepted tolerances may range from 0 percent to 10 percent and may correspond to, but are not limited to, component values, angles, and the like. Such relativities between items may range from approximately 0 percent to 10 percent.

[0254] While various embodiments according to the principles disclosed herein have been described above, it should be understood that they have been presented by way of example only, and not limitation. Thus, the breadth and scope of the present disclosure should not be limited by any of the above-described exemplary embodiments, but should be defined only in accordance with the claims and their equivalents issued from this disclosure. Moreover, while the above advantages and features are provided in the described embodiments, application of such issued claims to processes and structures that achieve any or all of the above advantages should not be limited.

[0255] In addition, the section headings herein are provided for consistency with suggestions under 37 CFR 1.77 or to provide organizational clues. These headings should not limit or characterize the embodiments described in claims that may be issued from this disclosure. Specifically, by way of example, the headings refer to the "Technical Field," but the claims should not be limited by the language selected under this heading to describe the so-called field. Furthermore, the description of a technology in the "Background" should not be construed as an admission that a particular technology is prior art to any embodiment in this disclosure. Nor should the "Abstract" be considered a feature of the embodiments described in the issued claims. Furthermore, references to the singular "invention" in this disclosure should not be used to assert that there is only a single point of novelty in this disclosure. Multiple embodiments may be described according to the limitations of multiple claims issued from this disclosure, and such claims thus define the embodiments and their equivalents that are protected thereby. In all cases, the scope of such claims should be considered on their own merits in light of this disclosure, but should not be constrained by the headings set forth herein.

Claims

1. 1. A display device, comprising: a spatial light modulator arranged to output spatially modulated light, the spatial light modulator including a display polarizer arranged on one side of the spatial light modulator, the display polarizer being a linear polarizer; an additional polarizer disposed on the same side of the spatial light modulator as the display polarizer, the additional polarizer being a linear polarizer; at least one polarity-controlled retarder disposed between the additional polarizer and the display polarizer; a light control film disposed in contiguous with the spatial light modulator, the additional polarizer, and the at least one polarity-controlled retarder; the light control film comprises an input surface, an output surface facing the input surface, an array of transmissive regions extending at least partially between the input surface and the output surface, and absorptive regions extending at least partially between the transmissive regions and between the input surface and the output surface; The absorptive region of the light control film has a thickness t, where t is expressed by the formula [0010] where S IN is the width of the aperture on the input side of the absorptive region, S OUT is the width of the aperture on the output side of the absorptive region, p is the pitch of the transmissive regions in the direction in which the array of transmissive regions is repeated, and n is the refractive index of the transmissive regions; A display device, wherein ξ is 0.643 or greater.

2. 10. The display device of claim 1, wherein the light control film has a transmission of 5% or greater over a range of polar angles in a direction in which the array of transmissive regions is repeated at least 80 degrees wide.

3. 3. The display device of claim 2, wherein the light control film has a transmission of 5% or greater over a range of polar angles in a direction in which the array of transmissive regions is repeated at least 90 degrees wide.

4. 4. The display device of claim 2 or 3, wherein the light control film has a transmission of 5% or greater over a range of polar angles in a direction in which the array of transmissive regions is repeated up to 130 degrees wide.

5. 2. The display device of claim 1, wherein ξ is greater than or equal to 0.

707.

6. 6. The display device of claim 1, wherein ξ is less than or equal to 0.

906.

7. A display device as described in any one of claims 1 to 6, wherein the light control film has a transmittance having a profile with a polar angle in a direction in which an array of transmissive regions having centerlines directed inward toward an optical axis extending forward from the center of the spatial light modulator is repeated.

8. The display device of claim 7 , wherein the centerlines of the profiles are oriented toward a common point.

9. A display device as described in any one of claims 1 to 6, wherein the light control film has a transmittance having a profile with a polar angle in a direction in which the array of transmissive areas centered on a normal to the plane of the spatial light modulator is repeated at all positions across the light control film.

10. 7. A display device as claimed in any one of claims 1 to 6, wherein the transmissive regions are tilted such that an axis defined for each transmissive region between the centres of the apertures on the input and output sides of the transmissive region is directed inwards towards an optical axis extending forward from the centre of the spatial light modulator.

11. The display device of claim 10 , wherein the axes are oriented toward a common point.

12. 7. The display device of claim 1, wherein the transparent regions have an axis defined for each transparent region between the centers of apertures on the input and output sides of the transparent region that is perpendicular to the plane of the spatial light modulator at all positions across the light control film.

13. A display device according to any preceding claim, wherein the array of transmissive regions is a one-dimensional array of elongated transmissive regions.

14. A display device according to any preceding claim, wherein the absorptive regions between the transmissive regions extend between the input face and the output face.

15. The display device of any one of claims 1 to 14, wherein the light control film is provided on a supporting substrate.

16. A display device according to any preceding claim, wherein the display polariser is an output display polariser arranged at the output side of the spatial light modulator.

17. 17. The display device of claim 16, further comprising a reflective polarizer disposed between the output display polarizer and the at least one first polarity-controlled retarder, the reflective polarizer being a linear polarizer.

18. 20. The display device of claim 17, wherein the light control film is disposed between the reflective polarizer and the spatial light modulator.

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

20. 18. The display device of claim 16 or 17, wherein the display device further comprises a backlight arranged to output light, the spatial light modulator comprises a transmissive spatial light modulator arranged to receive and spatially modulate the light output from the backlight, and the light control film is disposed between the backlight and the spatial light modulator.

21. 17. The display device of claim 16, wherein the display device further comprises a backlight arranged to output light, the spatial light modulator comprises a transmissive spatial light modulator arranged to receive and spatially modulate the light output from the backlight, and the light control film is arranged in front of the spatial light modulator.

22. 16. A display device according to any one of claims 1 to 15, wherein the display device further comprises a backlight arranged to output light, the spatial light modulator comprises a transmissive spatial light modulator arranged to receive and spatially modulate the light output from the backlight, and the display polarizer is an input display polarizer arranged on the input side of the spatial light modulator.

23. 23. The display device of claim 22, wherein the light control film is disposed between the backlight and the additional polarizer.

24. A display device as claimed in any preceding claim, wherein the at least one polarity controlled retarder comprises a switchable liquid crystal retarder.

25. 25. The display device of claim 24, wherein the switchable liquid crystal retarder comprises a layer of liquid crystal material and at least one surface alignment layer disposed adjacent to the layer of liquid crystal material.

26. 26. The display device of claim 25, wherein the switchable liquid crystal retarder comprises two surface alignment layers disposed on respective liquid crystal encapsulation substrates adjacent to and on opposite sides of the layer of liquid crystal material.

27. 27. The display device of claim 26, wherein the light control film is provided on one of the liquid crystal encapsulation substrates.

28. 28. The display device of claim 24, wherein the at least one polarity controlled delay further comprises at least one passive compensation delay.

29. 30. The display device of claim 28, wherein a support substrate comprises at least one of the at least one passive compensation retarder.

Images