Privacy mode backlight, privacy display and method

Abstract

The privacy mode backlight includes a light guide configured to guide light having a predetermined collimation factor orthogonal to the length of the light guide and a plurality of scattering wire elements arranged along the length of the light guide. The scattering wire elements of the plurality of scattering wire elements are configured to scatter a portion of the guided light through an emitting surface of the light guide as emitted light having an illumination beam width determined by the collimation factor in the orthogonal direction. The privacy mode backlight also includes a directional optical diffuser configured to provide directional diffusion of the emitted light in a direction corresponding to the length of the light guide. The directional diffusion can provide uniform illumination in the direction of the length of the light guide. The privacy display also includes an array of light valves configured to modulate the emitted light to provide a private image.

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] none Background Art

[0003] Electronic displays are an almost ubiquitous medium for conveying information to users of various devices and products. The most commonly used electronic displays include cathode ray tubes (CRTs), plasma display panels (PDPs), liquid crystal displays (LCDs), electroluminescent displays (ELs), organic light emitting diodes (OLEDs), and active matrix OLED (AMOLED) displays, electrophoretic displays (EPs), and various displays that employ electromechanical or electrofluidic light modulation (e.g., digital micromirror devices, electrowetting displays, etc.). In general, electronic displays can be classified as either active displays (i.e., displays that emit light) or passive displays (i.e., displays that modulate light provided by another source). Among the most obvious examples of active displays are CRTs, PDPs, and OLED / AMOLEDs. Displays that are typically classified as passive when considering emitted light are LCD and EP displays. Although passive displays often exhibit attractive performance characteristics, including but not limited to inherent low power consumption, they may find their use limited in many practical applications due to their lack of ability to emit light. BRIEF DESCRIPTION OF THE DRAWINGS

[0004] The various features of examples and embodiments according to the principles described herein may be more readily understood by reference to the following detailed description taken in conjunction with the accompanying drawings, in which like reference numerals represent like structural elements, and in which:

[0005] Figure 1 Illustrated is a graphical representation of angular components of a directional light beam having a particular principal angle direction in an example according to an embodiment consistent with the principles described herein.

[0006] Figure 2 Illustrated is a cross-sectional view of a diffraction grating in an example according to an embodiment consistent with the principles described herein.

[0007] Figure 3A Illustrated is a cross-sectional view of a privacy mode backlight in an example of an embodiment consistent with the principles described herein.

[0008] Figure 3B Another cross-sectional view of a privacy mode backlight in an example of an embodiment consistent with the principles described herein is illustrated.

[0009] Figure 3C Illustrated is a top view of a privacy mode backlight in an example of an embodiment consistent with the principles described herein.

[0010] Figure 4A side view illustrating the effect of a directional optical diffuser on the image of a scattering wire element in an example of an embodiment according to principles described herein.

[0011] Figure 5A Illustrated is a cross-sectional view of a privacy mode backlight in an example according to another embodiment consistent with the principles described herein.

[0012] Figure 5B Illustrated is a top view of a privacy mode backlight in an example according to another embodiment consistent with the principles described herein.

[0013] Fig. 6A Illustrated is a cross-sectional view of a mode-switchable display including a privacy mode backlight in an example according to an embodiment consistent with the principles described herein.

[0014] Figure 6B Illustrated is a cross-sectional view of a mode-switchable display including a privacy mode backlight in another example according to an embodiment consistent with the principles described herein.

[0015] Figure 7 A block diagram of a privacy display in an example according to an embodiment consistent with the principles described herein is illustrated.

[0016] Figure 8 A flow chart is illustrated of a method of privacy mode backlight operation in an example of an embodiment consistent with the principles described herein.

[0017] Certain examples and embodiments have other features that are in addition to and in lieu of the features shown in the drawings referenced above. These and other features are described in detail below with reference to the drawings referenced above. DETAILED DESCRIPTION

[0018] A privacy mode backlight is provided according to examples and embodiments of the principles described herein. The privacy mode backlight includes a light guide that guides light as guided light along the length of the light guide, wherein the guided light has a predetermined collimation factor. Moreover, the privacy mode backlight includes a plurality of scattering wire elements that are arranged parallel to each other and spaced apart from each other along the length of the light guide. Each scattering wire element is configured to scatter a portion of the guided light as emitted light through an exit surface of the light guide, and the emitted light has an illumination beam width determined by the collimation factor in a direction orthogonal to the length of the light guide. In addition, the privacy mode backlight includes a directional optical diffuser that is configured to provide directional diffusion of the emitted light in a direction corresponding to the length of the light guide. The directional optical diffuser can be configured to provide a uniform illumination pattern of the emitted light in a direction corresponding to the length of the light guide. For example, the diffusion angle of the directional optical diffuser can be configured to spread the emitted light from each scattering wire element to have an illumination range at the output plane of the privacy mode backlight that is equivalent to the distance between adjacent scattering wire elements of the plurality of scattering wire elements (e.g., center-to-center spacing). Thus, the imaged scattering wire elements may collectively appear to completely fill the length of the light guide with spaces between the imaged scattering wire elements.

[0019] In some embodiments, a privacy mode backlight is included in a display, such as a privacy display configured to provide a private image to a user, wherein the private image is visible only within the illumination beam width along a privacy axis (along the length of the light guide) of the privacy mode backlight. In other embodiments, the privacy mode backlight can be part of a mode-switchable display that is configured to provide a private image during a privacy mode of the mode-switchable display and to provide a shared image during a public mode of the mode-switchable display. In particular, the mode-switchable display can include a wide-angle backlight that is configured to provide wide-angle light during a shared mode, wherein the wide-angle light has a wide-angle illumination beam width, enabling a user to view a shared image over a wider range of angles than the private image. Thus, the mode-switchable display can be configured to selectively display a private image during a private mode and to display a shared image during a shared mode.

[0020] In this document, a beam with a direction is referred to as a "directional beam" and may have a principal angle direction given by the angular components {θ, φ} defined herein. The angular component θ is referred to herein as the "altitude component" or "elevation angle" of the directional beam. The angular component φ is referred to herein as the "azimuth component" or "azimuth angle" of the directional beam. By definition, the elevation angle θ is the angle in the vertical plane (e.g., perpendicular to the plane of the display screen), while the azimuth angle φ is the angle in the horizontal plane (e.g., parallel to the plane of the display screen). Figure 1A graphical representation of the angular components {θ, φ} of a directional light beam 20 having a particular principal angular direction is illustrated in accordance with an example of an embodiment consistent with the principles described herein. Furthermore, the light beam 20 is emitted or emanates from a particular point, as defined herein. That is, by definition, the directional light beam 20 has a central ray associated with a particular origin O, as shown.

[0021] In this document, a "lightguide" is defined as a structure that guides light within the structure using total internal reflection. In particular, a lightguide may include a core that is substantially transparent at the operating wavelength of the lightguide. In various examples, the term "lightguide" generally refers to a dielectric optical waveguide that uses total internal reflection to guide light at the interface between the dielectric material of the lightguide and the material or medium surrounding the lightguide. By definition, the condition for total internal reflection is that the refractive index of the lightguide is greater than the refractive index of the surrounding medium adjacent to the surface of the lightguide material. In some embodiments, in addition to or in place of the refractive index difference mentioned above, the lightguide may also include a coating to further promote total internal reflection. For example, the coating may be a reflective coating. The lightguide may be any of a number of lightguides, including but not limited to one or both of a plate or slab lightguide and a strip lightguide.

[0022] Additionally, herein, the term "plate" when applied to a lightguide in a "plate lightguide" is defined as a layer or sheet of segmented or differentiated planes, which is sometimes referred to as a "plate-like" lightguide. In particular, a plate lightguide is defined as a lightguide that is configured to guide light in two substantially orthogonal directions defined by a top surface and a bottom surface (i.e., opposing surfaces) of the lightguide. Additionally, according to the definition herein, the top surface and the bottom surface are both separated from each other and may be substantially parallel to each other, at least in a differentiated sense. That is, within any small differentiated section of the plate lightguide, the top surface and the bottom surface are substantially parallel or coplanar.

[0023] In some embodiments, the plate light guide may be substantially flat (i.e., confined within a plane), and thus, the plate light guide is a planar light guide. In other embodiments, the plate light guide may be curved in one or two orthogonal dimensions. For example, the plate light guide may be curved in a single dimension to form a cylindrical plate light guide. However, any curvature has a sufficiently large radius of curvature to ensure that total internal reflection is maintained within the plate light guide to guide light.

[0024] In this document, a "diffraction grating" is broadly defined as a plurality of features (i.e., diffraction features) arranged to provide diffraction of light incident on the diffraction grating. In some examples, the plurality of features may be arranged in a periodic manner or a quasi-periodic manner. In other examples, the diffraction grating may be a hybrid periodic diffraction grating comprising a plurality of diffraction gratings, each of the plurality of diffraction gratings having a different periodic arrangement of features. In some examples, the diffraction grating may be substantially periodic in a first direction or dimension and substantially non-periodic (e.g., constant, random, etc.) in another direction across or along the diffraction grating.

[0025] As such, and in accordance with the definitions herein, a "diffraction grating" is a structure that provides diffraction of light incident on the diffraction grating. If light is incident on the diffraction grating from a lightguide, the diffraction or diffraction scattering provided can result in, and is therefore referred to as, "diffraction coupling", because the diffraction grating can couple light out of the lightguide by diffraction. The diffraction grating also redirects or changes the angle of the light by diffraction (i.e., at a diffraction angle). In particular, as a result of diffraction, the light leaving the diffraction grating generally has a propagation direction that is different from the propagation direction of the light incident on the diffraction grating (i.e., the incident light). The change in the propagation direction of light by diffraction is referred to herein as "diffraction redirection". Therefore, a diffraction grating can be understood as a structure comprising diffraction features that diffractively redirect light incident on the diffraction grating and, if the light is incident from the lightguide, the diffraction grating can also diffractively couple light out of the lightguide.

[0026] Additionally, features of a diffraction grating are referred to as "diffraction features" as defined herein, and may be one or more at, in, and on a surface of a material (i.e., at a boundary between two materials). For example, the surface may be below the top surface of the light guide. Diffraction features may include any of a variety of structures that diffract light, including, but not limited to, one or more of grooves, ridges, holes, and protrusions at, in, or on a surface. For example, a diffraction grating may include a plurality of substantially parallel grooves in a surface of a material. In another example, a diffraction grating may include a plurality of parallel ridges rising from a surface of a material. Diffraction features (e.g., grooves, ridges, holes, protrusions, etc.) may have any of a variety of cross-sectional shapes or profiles that provide diffraction, including, but not limited to, one or more of a sinusoidal curve, a rectangular profile (e.g., a binary diffraction grating), a triangular profile, and a sawtooth profile (e.g., a blazed grating).

[0027] According to various examples described herein, a diffraction grating (e.g., a diffraction grating in a plurality of diffraction gratings as described below) can be employed to diffractively scatter or couple light out of a light guide (e.g., a plate light guide) as a light beam. In particular, the diffraction angle θ of or provided by the locally periodic diffraction grating is m It can be given by equation (1) as follows:

[0028]

[0029] where λ is the wavelength of the light, m ​​is the diffraction order, n is the refractive index of the light guide, d is the distance or spacing between the features of the diffraction grating, and θ i is the angle of incidence of the light on the diffraction grating. For simplicity, equation (1) assumes that the diffraction grating is adjacent to the surface of the light guide and that the refractive index of the material outside the light guide is equal to 1 (i.e., n out =1). In general, the diffraction order m is given by an integer (ie, m = ±1, ±2, ...). The diffraction angle θ of the light beam generated by the diffraction grating is m It can be given by equation (1). When the diffraction order m is equal to 1 (ie, m=1), a first-order diffraction or more specifically a first-order diffraction angle θ is provided. m .

[0030] Figure 2 A cross-sectional view of a diffraction grating 30 in an example of an embodiment consistent with the principles described herein is illustrated. For example, the diffraction grating 30 can be located on a surface of the light guide 40. In addition, Figure 2 The diagram shows the incident angle θ i Light beam 50 is incident on diffraction grating 30 . Light beam 50 is the guided light beam within light guide 40 . Figure 2 Also illustrated in FIG. 5 is a directional beam 60 that is diffracted by the diffraction grating 30 and coupled out or scattered due to the diffraction of the incident beam 50. The directional beam 60 has a diffraction angle θ given by equation (1): m (or “primary angular direction” herein). Directed light beam 60 may correspond to a diffraction order “m” of diffraction grating 30 , for example.

[0031] Additionally, according to some embodiments, the diffractive features may be curved and may also have a predetermined orientation (e.g., tilted or rotated) relative to the propagation direction of the light. For example, one or both of the curve of the diffractive features and the orientation of the diffractive features may be configured to control the direction of the light coupled out by the diffraction grating. For example, the primary angular direction of the directional light may be a function of the angle of the diffractive features at the point where the light is incident on the diffraction grating relative to the propagation direction of the incident light.

[0032] Although multiple diffraction gratings are used as illustrative examples in the following discussion, in some embodiments, other components may be used, such as at least one of a micro-reflective element and a micro-refractive element. For example, the micro-reflective element may include a triangular reflector, a trapezoidal reflector, a pyramidal reflector, a rectangular reflector, a hemispherical reflector, a concave reflector, and / or a convex reflector. In some embodiments, the micro-refractive element may include a triangular refractive element, a trapezoidal refractive element, a pyramidal refractive element, a rectangular refractive element, a hemispherical refractive element, a concave refractive element, and / or a convex refractive element.

[0033] According to various embodiments, one or both of the principal angle direction and the angular spread of the directional light beam 60 emerging from the diffraction grating 30 can be determined by the characteristics of the diffraction grating 30, including but not limited to: the size of the diffraction grating 30 (e.g., one or more of the length, width, area, etc.) together with the "grating pitch" or the spacing of the diffraction features and the orientation of the diffraction grating. In some embodiments, the diffraction grating 30 or more generally the scattering element can be considered to be an "extended point light source", that is, a plurality of point light sources distributed across the extent of the diffraction grating 30 or the scattering element, as defined herein. In addition, the directional light beam produced by the diffraction grating or scattering element has a principal angle direction given by the angular components {θ, φ}, as defined herein, and as described above with respect to Figure 1 as described.

[0034] As used herein, a "collimator" is defined as any optical device or apparatus that is substantially configured to collimate light. For example, a collimator may include, but is not limited to, a collimating mirror or reflector, a collimating diffraction grating, a collimating lens, or various combinations thereof. According to various embodiments, the amount of collimation provided by the collimator may vary from one embodiment to another by a predetermined degree or amount. In addition, the collimator may be configured to provide collimation in one or both of two orthogonal directions (e.g., a vertical direction and a horizontal direction). That is, according to some embodiments, the collimator may include a shape or related features that provide collimation of light in one or both of two orthogonal directions.

[0035] As used herein, a "collimation factor," denoted as σ, is defined as the degree to which light is collimated. In particular, as defined herein, the collimation factor defines the angular spread of light rays within a collimated light beam. For example, the collimation factor σ may specify that a majority of the light rays in a collimated light beam are within a particular angular spread (e.g., + / -σ degrees about a center or principal angular direction of the collimated light beam). According to some examples, the light rays of the collimated light beam may have a Gaussian distribution in terms of angle, and the angular spread may be an angle determined at half the peak intensity of the collimated light beam.

[0036] As used herein, a "light source" is defined as a source of light (e.g., an optical emitter configured to generate and emit light). For example, a light source may include an optical emitter, such as a light emitting diode (LED), which emits light when activated or turned on. In particular, as used herein, a light source may be a source of substantially any light or include substantially any optical emitter, including but not limited to one or more of a light emitting diode (LED), a laser, an organic light emitting diode (OLED), a polymer light emitting diode, a plasma-based optical emitter, a fluorescent lamp, an incandescent lamp, and virtually any other source of light. The light generated by the light source may have a color (i.e., may include light of a specific wavelength), or may be a range of wavelengths (e.g., white light). In some embodiments, a light source may include a plurality of optical emitters. For example, a light source may include a group of optical emitters, wherein at least one optical emitter generates light having a color or equivalently a wavelength different from the color or wavelength of light generated by at least another optical emitter of the group. Different colors may include, for example, primary colors (e.g., red, green, blue).

[0037] As used herein, an "angle-preserving scattering feature" or equivalently an "angle-preserving scattering element" is any feature, element, or scatterer that is configured to scatter light in a manner that substantially preserves the angular spread of light incident on the feature, element, or scatterer in the scattered light. In particular, by definition, the angular spread σ of light scattered by the angle-preserving scattering feature is s is a function of the angular spread σ of the incident light (i.e., σ s = f(σ)). In some embodiments, the angular spread of the scattered light σ s is a linear function of the angular spread or collimation factor σ of the incident light (e.g., σ s =a·σ, where a is a proportionality factor). That is, the angular spread σ of light scattered by the angle-preserving scattering feature s It can be roughly proportional to the angular spread or collimation factor σ of the incident light. For example, the angular spread σ of the scattered light s can be substantially equal to the incident light angle spread σ (e.g., σ s ≈σ). A uniform diffraction grating (ie, a diffraction grating having a substantially uniform or constant diffraction feature spacing or grating spacing) is an example of an angle-preserving scattering feature.

[0038] By definition, "wide angle" emitted light is defined as light having a cone angle greater than the cone angle of emitted light used to provide a private confidential image or provided in a private display. In particular, in some embodiments, the wide angle emitted light can have a cone angle greater than about 20 degrees (e.g., >±20°). In other embodiments, the wide angle emitted light cone angle can be greater than about thirty degrees (e.g., >±30°), or greater than about forty degrees (e.g., >±40°), or greater than about fifty degrees (e.g., >±50°). For example, the cone angle of the wide angle emitted light can be greater than about sixty degrees (e.g., for example, >±60°).

[0039] In some embodiments, the wide-angle emitted light cone angle can be defined as being approximately the same as the viewing angle of an LCD computer monitor, LCD tablet, LCD television, or similar digital display device intended for wide-angle viewing (e.g., approximately ±40-65°). In other embodiments, the wide-angle emitted light can also be characterized or described as diffuse light, substantially diffuse light, non-directional light (i.e., lacking any particular or defined directionality), or as light having a single or substantially consistent direction.

[0040] In addition, as used herein, the article "a" is intended to have its ordinary meaning in the patent field, that is, "one or more". For example, "an element" means one or more elements, and, as such, "the element" means "the (one or more) elements" herein. Moreover, references to "top", "bottom", "upper", "lower", "up", "lower", "front", "back", "first", "second", "left" or "right" herein are not intended to be limiting. In this article, when applied to a value, the term "approximately" generally means within the tolerance range of the equipment used to produce the value, or may mean plus or minus 10%, or plus or minus 5%, or plus or minus 1%, unless otherwise expressly specified. In addition, as used herein, the term "substantially" means most, or almost all, or all, or an amount in the range of about 51% to about 100%. Moreover, the examples herein are intended to be illustrative only and are presented for discussion purposes rather than in a limiting manner.

[0041] According to some embodiments of the principles described herein, a privacy mode backlight is provided. Figure 3A Illustrated is a cross-sectional view of a privacy mode backlight 100 in an example of an embodiment consistent with the principles described herein. Figure 3B Another cross-sectional view of a privacy mode backlight 100 is illustrated in an example of an embodiment consistent with the principles described herein. Figure 3CA top view of a privacy mode backlight 100 is illustrated in an example according to an embodiment consistent with the principles described herein. In various embodiments, the privacy mode backlight 100 is configured to emit light having a predetermined illumination beam width as the emitted light 102 .

[0042] As shown, the privacy mode backlight 100 includes a light guide 110. The light guide 110 is configured to guide light as guided light 104 (i.e., guided light beam 104) along the length of the light guide 110. For example, the light guide 110 may include a material (such as a dielectric material) configured to function as an optical waveguide. The dielectric material may have a first refractive index greater than a second refractive index of a medium surrounding the dielectric optical waveguide. For example, the refractive index difference is configured to promote total internal reflection of the guided light 104 according to one or more guided modes of the light guide 110.

[0043] In particular, the light guide 110 can be a flat or plate optical waveguide (i.e., a plate light guide) that includes an extended, substantially flat sheet of optically transparent dielectric material. The substantially flat sheet of dielectric material is configured to guide the guided light 104 using total internal reflection. According to various examples, the optically transparent material of the light guide 110 can include or be made of any of a variety of dielectric materials, including, but not limited to, one or more of various types of glass (e.g., quartz glass, alkali metal aluminosilicate glass, borosilicate glass, etc.) and substantially optically transparent plastics or polymers (e.g., poly(methyl methacrylate) or "acrylic glass", polycarbonate, etc.). In some examples, the light guide 110 can also include a cladding (not shown) on at least a portion of a surface (e.g., one or both of the top and bottom surfaces) of the light guide 110. According to some examples, the cladding can be used to further promote total internal reflection.

[0044] According to various embodiments, the light guide 110 is configured to guide the guided light 104 at a non-zero propagation angle between a first surface 110' (e.g., a "front" or "top" surface or side) and a second surface 110" (e.g., a "back" surface or side) of the light guide 110 according to total internal reflection. In particular, the guided light 104 propagates by reflecting or "bouncing" at a non-zero propagation angle between the first surface 110' and the second surface 110" of the light guide 110. In some embodiments, multiple guided light beams comprising light of different colors can be guided by the light guide 110 as the guided light 104 at corresponding propagation angles among different color-specific non-zero propagation angles.

[0045] As defined herein, a “non-zero propagation angle” is an angle relative to a surface of the light guide 110 (e.g., the first surface 110′ or the second surface 110″). Additionally, according to various embodiments, the non-zero propagation angles are both greater than zero and less than the critical angle for total internal reflection within the light guide 110. For example, the non-zero propagation angle of the guided light 104 may be between approximately ten degrees (10°) and approximately fifty degrees (50°) or, in some examples, between approximately twenty degrees (20°) and approximately forty degrees (40°), or between approximately twenty-five degrees (25°) and approximately thirty-five degrees (35°). For example, the non-zero propagation angle may be approximately thirty degrees (30°). In other examples, the non-zero propagation angle may be approximately 20 degrees, or approximately 25 degrees, or approximately 35 degrees. Moreover, a specific non-zero propagation angle may be selected (e.g., arbitrarily) for a particular implementation, as long as the specific non-zero propagation angle is selected to be less than the critical angle for total internal reflection within the light guide 110.

[0046] In addition, according to various embodiments, the guided light 104 or equivalently the guided light beam 104 provided by coupling light into the light guide 110 can be a collimated light beam. In this document, "collimated light" or "collimated light beam" is generally defined as a light beam in which the rays of the light beam are substantially parallel to each other within the light beam (e.g., the guided light beam 104). Moreover, according to the definition herein, light rays diverging or scattered from the collimated light beam are not considered to be part of the collimated light beam. In some embodiments (not shown), a collimator (such as a lens, a diffraction grating, a reflector, or a mirror, as described above) can be included to collimate light, for example, light from a light source. In other embodiments, the light source itself can include a collimator. The collimated light provided to and guided by the light guide 110 as the guided light 104 can be a collimated guided light beam. In particular, in various embodiments, the guided light 104 can be collimated according to or with a collimation factor σ. In some embodiments, the guided light 104 has a predetermined collimation factor in a width direction orthogonal to the length of the light guide. As shown, the width direction of the privacy mode backlight 100 corresponds to the y-direction and the light guide length or length direction corresponds to the x-direction.

[0047] Figures 3A-3CThe privacy mode backlight 100 shown in also includes a plurality of scattering wire elements 120. According to various embodiments, individual scattering wire elements 120 of the plurality of scattering wire elements are arranged parallel to and spaced apart from each other along the length direction (i.e., the x-direction) of the light guide 110. In particular, according to the definition herein, the plurality of scattering wire elements 120 are separated from each other by a finite (i.e., non-zero) inter-element distance or space, and represent individual different elements along the length of the light guide (i.e., the x-direction, as shown). In addition, according to various embodiments, the plurality of scattering wire elements 120 generally do not intersect, overlap, or otherwise contact each other. As such, each scattering wire element 120 of the plurality of scattering wire elements is generally different and separate from the other scattering wire elements 120, at least in the length or x-direction.

[0048] According to various embodiments, each scattering wire element 120 of the plurality of scattering wire elements is configured to scatter a portion of the guided light 104 as emitted light 102 through an emitting surface (e.g., such as the first surface 110') of the light guide 110. In addition, according to various embodiments, the scattering wire element 120 is configured to provide the emitted light 102 having an illumination beam width γ in a direction orthogonal to a length direction determined by a collimation factor σ of the guided light 104. Figure 3B , the illumination beam width γ in the orthogonal direction (or width direction) is described as an angle in a plane parallel to the y direction. In some embodiments, the scattering element 120 can be a substantially unidirectional scattering element configured to preferentially scatter the guided light 104 in the direction of or toward the emitting surface of the light guide 110. For example, preferential scattering toward the emitting surface is Figure 3A 10 by an arrow pointing to the first surface 110' of the light guide 110. In addition, the scattering element 120 can be an angle preserving scatterer, wherein the illumination beam width γ of the emitted light 102 in the orthogonal or width direction is a linear function of the collimation factor σ of the guided light 104 (e.g., γ=k·σ, where k is a constant scaling factor).

[0049] According to various embodiments, the privacy mode backlight 100 also includes a directional optical diffuser 130. The directional optical diffuser is configured to provide directional diffusion of the emitted light in a direction corresponding to the length of the light guide. In particular, the directional optical diffuser may have a diffuser axis along the length direction of the light guide 110 (i.e., the x direction as shown in the figure). As shown, the directional optical diffuser 130 having a diffuser axis oriented along the length direction is configured to provide directional diffusion of the emitted light 102 in a direction corresponding to the length of the light guide (i.e., the x direction). In various embodiments, the directional diffusion of the emitted light 102 provided by the directional optical diffuser 130 can be configured to effectively expand the apparent size of the scattering line element 120 to provide a uniform or substantially uniform illumination pattern of the emitted light 102 in a direction corresponding to the length of the light guide. In addition, in some embodiments, the directional optical diffuser 130 may provide substantially little or no diffusion in the width direction or the y direction. For example, the directional optical diffuser 130 may be a one-dimensional (1D) optical diffuser. As such, the directional optical diffuser 130 is configured to substantially maintain the illumination beam width of the emitted light 102 in an orthogonal direction (ie, the width or y-direction) to ensure privacy viewing of the privacy mode backlight 100 while providing uniform illumination in or along the length direction.

[0050] For example, the emitted light 102 can have an illumination beam width γ in an orthogonal or y-direction, while the illumination of the emitted light 102 in the x-direction includes a substantially uniform illumination pattern. The uniform illumination pattern can facilitate high resolution of displays employing the privacy mode backlight 100, since each pixel or light valve of the display can be illuminated in a substantially uniform manner.

[0051] In some embodiments, the diffusion angle of the directional optical diffuser 130 is configured to effectively spread the emitted light 102 from each of the plurality of scattering wire elements 120 to have an illumination range at the output plane of the privacy mode backlight 100 that is equivalent to the distance between adjacent scattering wire elements 120 of the plurality of scattering wire elements. For example, the range of the image of the scattering wire elements 120 provided by the diffusion angle of the directional optical diffuser 130 can be equal to or greater than the pitch of adjacent scattering wire elements 120. In other words, the diffusion angle of the directional optical diffuser can be selected so that the image of the scattering wire elements 120 has a range of scattering elements at the output plane that makes the plurality of scattering wire elements 120 appear to be uniform and continuous in the x-direction. As such, the effective light source provided by the privacy mode backlight 100 along the x-direction can appear uniform over the length of the light guide 110 (i.e., along the x-direction). In some embodiments, the effective light source can be equal to the product of the diffusion angle of the directional optical diffuser 130 and the thickness t of the light guide 110 divided by the refractive index of the light guide 110.

[0052] For example, the size of the effective light source LS in the image of the scattering light element 120 can be given by equation (2) with respect to the thickness t

[0053]

[0054] where δn x is the diffusion angle of the directional optical diffuser 130 and n is the refractive index of the light guide 110. In some embodiments, the effective light source size may be equal to or even larger than the pitch or spacing between the scattering wire elements 120 to ensure uniform illumination in the length direction.

[0055] Figure 4 1 illustrates a side view of the effect of directional optical diffuser 130 on the image of scattering wire element 120 in an example of an embodiment according to the principles described herein. In particular, Figure 4 Several scattering wire elements 120 are illustrated, each having a size Δ and a spacing or pitch p. Light 106 scattered from the light guide 110 by the scattering wire elements 120 passes through the directional optical diffuser 130 of the privacy mode backlight 100 as emitted light 102. As shown, the emitted light 102 passing through the directional optical diffuser 130 produces a scattering wire element image 120' of the scattering wire elements 120 at the output plane 100' of the privacy mode backlight 100. In addition, as shown, the diffusion angle of the directional optical diffuser 130 effectively extends the range of the scattering wire element image 120'. In some embodiments, the diffusion angle can be selected or predetermined to sufficiently extend the range of the scattering wire element image 120' so that the scattering wire elements 120 appear at the output plane 100' to be substantially continuous in the x-direction, such as as shown.

[0056] Using a directional optical diffuser 130 to expand the image range of the scattering wire elements 120 or equivalently spread the emitted light 102 from each of the plurality of scattering wire elements 120 can allow for a reduction in the density of the scattering wire elements 120 while still providing uniform illumination. For example, the density of the scattering wire elements 120 can be reduced to less than, and in some examples much less than, one scattering wire element 120 per pixel (such as an integer fraction of each pixel) of a display employing the privacy mode backlight 100. According to some embodiments, this can reduce the complexity of the privacy mode backlight 100, which can increase manufacturing yield and thus can reduce the cost of the privacy mode backlight 100 or a display including the privacy mode backlight 100. According to some embodiments, the directional optical diffuser 130 can include an anisotropic light diffusing layer or film, such as, but not limited to, a holographic optical diffuser configured to provide anisotropic light diffusion.

[0057] In some embodiments, the scattering wire element 120 may be a continuous or substantially continuous scattering structure along the length of the scattering wire element 120 (ie, continuous in the width or y-direction, such as Figure 3B-3C ). In other embodiments, the scattering line element 120 of the plurality of scattering line elements may include an array of individual scattering elements arranged in a line along the length of the scattering line element 120 (i.e., a linear array extending in the width or y direction, as shown). In particular, in some embodiments, adjacent individual scattering elements of the array of individual scattering elements may be separated from each other by gaps.

[0058] Figure 5A Illustrated is a cross-sectional view of a privacy mode backlight 100 in an example according to another embodiment consistent with the principles described herein. Figure 5B FIG. 1 shows a top view of a privacy mode backlight 100 in an example of another embodiment consistent with the principles described herein. Figure 5A-5B As shown in FIG. , the privacy mode backlight 100 and Figures 3A-3C The privacy mode backlight 100 shown in FIG. 1 is substantially similar to FIG. 1 . In particular, Figure 5A-5B A privacy mode backlight 100 is shown including a light guide 110, a scattering wire element 120, and a directional optical diffuser 130. However, in Figure 5A-5B In the embodiments shown in , the scattering wire elements 120 in the plurality of scattering wire elements each include an array of individual scattering elements 122. Additionally, the array of individual scattering elements 122 is arranged as a linear array along the length of the scattering wire elements 120 within the light guide 110, wherein each individual scattering element 122 is separated from adjacent individual scattering elements by a gap. In these embodiments where the individual scattering elements 122 are separated from each other by gaps, the directional optical diffuser 130 can also be configured to provide directional diffusion of the emitted light 202 in an orthogonal direction corresponding to the width direction of the light guide 110.

[0059] Thus, in various embodiments, the directional diffusion provided in the width direction can be configured to provide a uniform illumination pattern of the emitted light 202 in the width direction in addition to the length direction. Note that the diffusion angle of the directional optical diffuser 130 in the width direction can be different from the diffusion angle in the length direction. However, according to various embodiments, the diffusion angle in the width direction and the length and gaps between the individual scattering elements 122 of the scattering line element 120 can still be selected to ensure viewing privacy.

[0060] As previously mentioned above, the scattering line element 120 of the plurality of scattering line elements may include a unidirectional scattering element that is configured to preferentially scatter the guided light 104 in the direction of the emission surface of the light guide 110. For example, the scattering line element 120 of the plurality of scattering line elements may include a diffraction grating. The diffraction grating may be configured to diffract and scatter a portion of the guided light 104 from the light guide 110 as emitted light 102 by diffraction scattering. Notably, the diffraction grating 120 may include a diffraction feature that includes one or both of a groove in the second surface 110" and a ridge on the second surface 110". Additionally, for example, the grooves or the ridges may be tilted to provide unidirectional scattering.

[0061] In other embodiments, the scattering wire element 120 may include reflection islands (partial reflectors) aligned with the diffraction grating 120 adjacent to the scattering wire element 120 opposite to the emitting surface (i.e., the first surface 110'). For example, the reflection islands may be aligned with and have a range or size corresponding to the range or size of the diffraction grating of the scattering wire element 120. More generally, the reflection islands may be patterned in a manner corresponding to the scattering wire element 120. The reflection islands may include a reflective material configured to reflectively redirect light scattered by the scattering wire element 120 in an incorrect direction (i.e., away from the emitting surface) to a direction corresponding to the direction of the emitted light 102. In these embodiments, the scattering wire element 120 including the diffraction grating and the reflection islands may represent a reflection mode diffraction grating. In other embodiments, such as when reflection islands are not employed, the scattering wire element 120 may include a transmission mode diffraction grating defined or implemented on a surface or within the light guide 110.

[0062] In some embodiments, the reflective islands of the scattering wire element 120 may include a metal (e.g., gold, aluminum, silver, etc.) or a polymer-metal combination (e.g., an aluminum polymer film), or even a dielectric layer (e.g., silicon nitride or titanium oxide) configured as a reflector. Moreover, in some embodiments, the reflective islands may be separated from the scattering wire element 120, for example, by an air gap or a gap filled with a dielectric material.

[0063] In some embodiments where the scattering line element 120 includes a diffraction grating, the diffraction grating may include a plurality of diffraction features spaced apart from each other by a diffraction feature spacing (which is sometimes referred to as a "grating spacing") or a diffraction feature or grating spacing configured to provide diffractive outcoupling of the guided light portion. According to various embodiments, the spacing of the diffraction features in the diffraction grating or the grating pitch may be sub-wavelength (i.e., less than the wavelength of the guided light). Note that the diffraction grating may include a plurality of different grating spacings (e.g., two or more grating spacings) or a variable grating spacing or pitch to diffractively scatter out the guided light portion.

[0064] According to some embodiments, the diffraction features of the diffraction grating may include one or both of grooves and ridges spaced apart from each other. The grooves or ridges may include the material of the light guide 110, for example, may be formed in the surface of the light guide 110. In another example, the grooves or ridges may be formed of a material different from the light guide material, for example, a film or layer of another material on the surface of the light guide 110. It is noted that according to some embodiments, grating characteristics (such as grating pitch, groove depth, ridge height, etc.) and / or the density of the diffraction grating along the x-direction may be used to compensate for changes in the intensity of the guided light 104 within the light guide 110 as a function of the propagation distance.

[0065] In some embodiments, the diffraction grating of the scattering line element 120 may be a uniform diffraction grating in which the diffraction feature spacing is substantially constant or unchanging throughout the diffraction grating. In other embodiments, the diffraction grating may include a variable or chirped diffraction grating. By definition, a "chirped" diffraction grating is a diffraction grating that exhibits or has a diffraction feature spacing (i.e., grating pitch) that varies across the range or length of the chirped diffraction grating. In some embodiments, a chirped diffraction grating may have or exhibit a chirp of the diffraction feature spacing that varies linearly with distance. As such, by definition, a chirped diffraction grating is a "linear chirp" diffraction grating. In other embodiments, a chirped diffraction grating may exhibit a nonlinear chirp of the diffraction feature spacing. A variety of nonlinear chirps may be used, including but not limited to exponential chirps, logarithmic chirs, or chirps that vary in another substantially non-uniform or random but still monotonically manner. Non-monotonic chirps may also be employed, such as, but not limited to, sinusoidal chirps or triangular or sawtooth chirps. Combinations of any of these types of chirps may also be employed. Note that in some embodiments described herein, the emitted light 102 may include refraction effects due to the portion of the guided light 104 exiting the light guide 110 at the first surface 110'.

[0066] Although the previous discussion describes the plurality of scattering line elements 120 as or including diffraction gratings 120, in other embodiments, a variety of optical components may be used as scattering line elements 120 to scatter the emitted light 102. For example, the scattering line elements 120 may include micro-reflective elements configured to reflectively scatter a portion of the guided light 104. In another example, the scattering line elements 120 may include micro-refractive elements configured to refract and scatter a portion of the guided light 104 as the emitted light 102. For example, the micro-reflective elements may include triangular mirrors, trapezoidal mirrors, pyramidal mirrors, rectangular mirrors, hemispherical mirrors, concave mirrors, and / or convex mirrors. Note that, according to various embodiments, these micro-reflective and micro-refractive elements may be located on the second surface 110″ of the light guide 110, on the first surface 110′, or between the first surface 110′ and the second surface 110″. Furthermore, the optical feature of the scattering line element 120 may be a “positive feature” of a protruding surface, or it may be a “negative feature” of a concave surface.

[0067] According to some embodiments, the privacy mode backlight 100 may be used as a backlight in a mode-switchable display 100a. Fig. 6A Illustrated is a cross-sectional view of a mode-switchable display 100a including a privacy mode backlight 100, in an example of an embodiment consistent with the principles described herein. Figure 6B 1 shows a cross-sectional view of a mode switchable display 100a including a privacy mode backlight 100 in another example according to an embodiment consistent with the principles described herein. In particular, Fig. 6A The mode-switchable display 100a is shown in or during a privacy mode, and Figure 6B The mode-switchable display 100a is illustrated in or during a wide angle or sharing mode. According to various embodiments, the mode-switchable display 100a is configured to selectively display a private image during a privacy mode and display a shared image during a sharing mode.

[0068] As shown, the mode-switchable display 100a includes a privacy mode backlight 100 configured to provide an emitted light 102, which in turn can be modulated to provide an image having a narrow illumination beam width or an equivalently narrow viewing angle in or during the privacy mode of the mode-switchable display 100a. In particular, in the privacy mode, the guided light provided in the light guide 110 of the privacy mode backlight 100 can be scattered out by the scattering wire element 120 and directed away from the mode-switchable display 100a. The emitted light 102 from the scattering wire element 120 can then be modulated using an array of light valves 140 of the mode-switchable display 100a (described below) to facilitate the display of a private image having a narrow illumination beam width or a narrow viewing angle (e.g., γ). According to various embodiments, the private image can be visible only within a narrower illumination beam width or a narrow viewing angle, thereby allowing a user of the mode-switchable display 100a to view the private image more safely.

[0069] Alternatively, in the shared mode, the mode-switchable display 100a may be dynamically switched (eg, may be switched on demand) to provide a display having a wide or wide angle illumination beam width or equivalently a wide angle viewing angle (eg, ). In particular, the wide-angle illumination beam width during the sharing mode is greater than, and in some embodiments significantly greater than, the narrow illumination beam width of the privacy mode. For example, the wide-angle illumination beam width of the sharing mode may be greater than about twenty degrees (e.g., >±20°), while the narrow illumination beam width of the privacy mode may be, for example, less than about twenty degrees (e.g., <±20°). In another example, the wide-angle illumination beam width of the sharing mode may be greater than about sixty degrees (e.g., >±60°), or greater than about forty degrees (e.g., >±40°), or greater than about thirty degrees (e.g., >±30°), while the narrow illumination beam width of the privacy mode may be less than about thirty degrees (e.g., <±30°), or less than about twenty degrees (e.g., <±20°), or less than about ten degrees (e.g., <±10°), respectively. In some embodiments, the narrow illumination beam width or viewing angle may be less than about one-half (1 / 2) of the wide-angle illumination beam width or less than about one-quarter (1 / 4) of the wide-angle illumination beam width, or even less.

[0070] To provide a wide angle illumination beam width or viewing angle, the mode switchable display 100a further includes a wide angle backlight 150, such as Figure 6A-6Bas shown in . According to various embodiments, the wide-angle backlight 150 is configured to provide wide-angle light 152 during the sharing mode, i.e., emitted light having an illumination beam width corresponding to the wide-angle illumination beam width or viewing angle of the mode-switchable display 100a during the sharing mode. As shown, the wide-angle backlight 150 may be adjacent to a side of the privacy mode backlight 100 opposite to a side adjacent to the light valve array (i.e., the second surface 110"). According to various embodiments, the light guide 110 and the scattering line element 120 may be configured to be transparent to the wide-angle light 152 provided by the wide-angle backlight 150 during the sharing mode. According to various embodiments, the wide-angle backlight 150 may include substantially any planar light source configured to provide wide-angle illumination, including a backlight comprising a light guide and a wide-angle scattering element. In addition, in some embodiments, the shared image may have substantially the same brightness and resolution as the private image.

[0071] like Figure 6A-6B As shown in , the mode-switchable display 100a also includes an array of light valves 140. The array of light valves 140 is configured to modulate light to provide an image displayed by the mode-switchable display 100a. In particular, the light valve array is configured to modulate wide-angle light 152 to provide a shared image during a sharing mode of the mode-switchable display 100a, as shown. In addition, as described above, the array of light valves 140 is configured to modulate the emitted light 102 provided by the privacy mode backlight 100 into a private image during a privacy mode of the mode-switchable display 100a. In various embodiments, any of a variety of different types of light valves may be used as the light valve 140 of the light valve array, including but not limited to one or more of a liquid crystal light valve, an electrophoretic light valve, and a light valve based on electrowetting.

[0072] According to some embodiments, the dimension of the scattering wire element 120 in the length or x-direction of the light guide 110 is comparable to the dimension of the light valve 140. In this document, "dimension" may be defined in any of a variety of ways to include, but not limited to, length, width, or area. For example, the dimension of the light valve 140 may be its length, and the comparable dimension of the scattering wire element 120 may also be the length of the scattering wire element 120. In another example, the dimension may refer to an area such that the area of ​​the scattering wire element 120 may be comparable to the area of ​​the light valve 140.

[0073] In some embodiments, the size of the scattering wire element 120 is comparable to the size of the light valve, such that the diffraction grating size is between about fifty percent (50%) and about two hundred percent (200%) of the light valve size. In other examples, the scattering wire element size is greater than about sixty percent (60%) of the light valve size, or greater than about seventy percent (70%) of the light valve size, or greater than about eighty percent (80%) of the light valve size, or greater than about ninety percent (90%) of the light valve size, and less than about eighty percent (180%) of the light valve size, or less than about sixty percent (160%) of the light valve size, or less than about one hundred and forty percent (140%) of the light valve size, or less than about one hundred and twenty percent (120%) of the light valve size. For example, by "comparable size", the scattering wire element size can be between about seventy-five percent (75%) and about one hundred and fifty percent (150%) of the light valve size. In another example, the size of the scattering wire element can be comparable to the light valve size, wherein the size of the scattering wire element is between about one hundred and twenty-five percent (125%) and about eighty-five percent (85%) of the light valve size. According to some embodiments, the comparable sizes of the scattering wire element 120 and the light valve 140 can be selected to reduce or, in some examples, minimize dark areas between the scattering wire element 120 of the mode-switchable display 100a. Moreover, the comparable sizes of the scattering wire element 120 and the light valve 140 can be selected to reduce and, in some examples, minimize moire fringes associated with the mode-switchable display 100a, for example, the scattering wire element size can be approximately equal to the light valve size.

[0074] Reference again Figure 3A and 3C, the privacy mode backlight 100 may further include a light source 160. According to various embodiments, the light source 160 is configured to provide light to be guided within the light guide 110. In particular, the light source 160 may be positioned adjacent to an entrance surface or end (input end) of the light guide 110. In various embodiments, the light source 160 may include substantially any light source (e.g., for example, a light emitter), including but not limited to an LED, a laser (e.g., a laser diode), or a combination thereof. In some embodiments, the light source 160 may include an optical emitter configured to generate substantially monochromatic light having a narrowband spectrum represented by a specific color. In particular, the color of the monochromatic light may be a primary color of a specific color space or color model (e.g., a red-green-blue (RGB) color model). In other examples, the light source 160 may be a substantially broadband light source configured to provide substantially broadband or polychromatic light. For example, the light source 160 may provide white light. In some embodiments, the light source 160 may include a plurality of different optical emitters configured to provide light of different colors. Different optical emitters may be configured to provide light having different, color-specific, non-zero propagation angles of directed light corresponding to each of the different colors of light.

[0075] In some embodiments, the light source 160 may further include a collimator. The collimator may be configured to receive substantially uncollimated light from one or more of the optical emitters of the light source 160. The collimator is further configured to convert substantially uncollimated light into collimated light. In particular, according to some embodiments, the collimator may provide collimated light that is collimated according to a predetermined collimation factor. Moreover, when optical emitters of different colors are employed, the collimator may be configured to provide collimated light having one or both of different color-specific non-zero propagation angles and different color-specific collimation factors. The collimator is further configured to transmit the collimated light beam to the light guide 110 for propagation as guided light 104, as described above.

[0076] According to some embodiments of the principles described herein, a privacy display is provided. Figure 7 A block diagram of a privacy display 200 in an example of an embodiment consistent with the principles described herein is illustrated. According to various embodiments, the privacy display 200 is configured to display a private image with a narrow viewing angle. In particular, the modulated emission light 202 from the privacy display 200 provides a private image in a limited angular range (i.e., a narrow viewing angle) that can be viewed by the user 200a but cannot be viewed by others (e.g., people outside the limited angular range or the private viewing area). The modulated emission light 202 is Figure 7 2 is shown as a dashed arrow emanating from the privacy display 200 to emphasize its modulation by way of example and not limitation.

[0077] As shown, the privacy display 200 includes a plurality of scattering wire elements 220 distributed along the length of the light guide 210. The plurality of scattering wire elements are configured to scatter the guided light from the light guide 210 in a direction orthogonal to the length of the light guide as emitted light having a predetermined illumination beam width. In some embodiments, the light guide 210 may be substantially similar to the light guide 110 described above with respect to the privacy mode backlight 100. For example, in various embodiments, the light guide may be configured to guide light as a guided light beam based on total internal reflection. In addition, the light guide 210 may be a plate light guide configured to guide light from its light input edge. In addition, the plurality of scattering wire elements 220 may be substantially similar to the scattering wire elements 120 of the privacy mode backlight 100 described above.

[0078] In particular, the guided light may be collimated according to a collimation factor. Additionally, in some embodiments, the predetermined illumination beam width may be determined by the collimation factor of the guided light. More particularly, the collimation factor of the guided light may be specifically selected to achieve the predetermined illumination beam width. In some embodiments, the scattering wire element 220 of the plurality of scattering wire elements may include a scattering element configured to preferentially scatter the guided light in the direction of the emitting surface of the light guide 210. As such, the scattering wire element may be a unidirectional scattering wire element. For example, the scattering wire element may include a reflector or a reflective island, as described above.

[0079] In various embodiments, the scattering wire element 220 may include a diffraction grating or multiple diffraction gratings configured to provide the emitted light 202. In particular, the diffraction grating may be configured to diffract and scatter a portion of the guided light from the light guide 210 as the emitted light 202. In some embodiments, the diffraction grating may be substantially similar to the diffraction grating of the scattering wire element 120 described above. In other embodiments, the scattering wire element 220 may include other scattering elements, including but not limited to micro-reflective elements and micro-refractive elements, as described above with respect to the scattering wire element 120 of the privacy mode backlight 100.

[0080] Figure 7 The privacy display 200 shown in FIG. 1 also includes an array of light valves 230. The array of light valves 230 is configured to modulate the emitted light 202 to provide a private image. In some embodiments, the array of light valves 230 can be substantially the same as the array of light valves 140, as described above with respect to the privacy mode backlight 100.

[0081] According to some embodiments, the size of the scattering wire element 220 of the plurality of scattering wire elements along the length direction of the light guide 210 is comparable to the size of the light valve of the array of light valves 230. For example, in some embodiments, the size of the scattering wire element can be greater than half the size of the light valve and less than twice the size of the light valve.

[0082] According to various embodiments, the privacy display 200 further includes a directional optical diffuser 240, such as Figure 7 As shown in Figure 7 As shown in , the directional optical diffuser is located between the light guide 210 and the array of light valves 230. In various embodiments, the directional optical diffuser is configured to provide directional diffusion of the emitted light 202 in a direction corresponding to the length of the light guide. In some embodiments, the directional optical diffuser 240 can be substantially similar to the directional optical diffuser 130 of the privacy mode backlight 100 described above. In particular, according to various embodiments, the directional diffusion of the directional optical diffuser 240 can provide uniform illumination of the array of light valves in the direction of the light guide length.

[0083] In some of these embodiments ( Figure 7 ), the privacy display 200 may further include a light source. For example, the light source may be configured to provide light to the light guide 210 that is collimated according to a collimation factor to provide a predetermined angular spread of the guided light within the light guide 210. According to some embodiments, the light source may be substantially similar to the light source 160 described above.

[0084] In some embodiments (e.g., Figure 7 ), the privacy display 200 may further include a wide angle backlight 250 positioned adjacent to a side of the light guide 210 opposite to a side adjacent to the light valve array. In some embodiments, the wide angle backlight 250 may be substantially similar to the wide angle backlight 150 of the mode selectable display 100a described above, and the privacy display 200 may be a mode selectable display or operate as a mode selectable display. In particular, the wide angle backlight 250 may be configured to provide wide angle light 252 during a sharing mode of the privacy display 200. Additionally, the light valve array may be configured to modulate the wide angle light 252 to provide a shared image during the sharing mode. According to various embodiments, the shared image may be viewed by multiple users 200b at various different locations within a shared viewing area having a wide angle or a relatively unrestricted range of angles, such as Figure 7 When operating as a mode-selectable display, the light guide 210 and the scattering line element 220 of the privacy display 200 can be configured to be transparent to the wide-angle light 252. In addition, according to some embodiments, the privacy display 200 can be mode-switched between a sharing mode that provides a shared image and a privacy mode that provides a private image.

[0085] According to other embodiments of the principles described herein, a method of privacy mode backlight operation is provided. Figure 8 A flow chart of a method 300 of privacy mode backlight operation in an example of an embodiment consistent with the principles described herein is illustrated. Figure 8As shown in , a method 300 of privacy mode backlight operation includes guiding 310 light in a light guide into collimated guided light having a predetermined collimation factor. According to some embodiments, the light guide can be substantially similar to the light guide 110 described above with respect to the privacy mode backlight 100. In particular, according to various embodiments, the light can be guided according to total internal reflection within the light guide.

[0086] According to various embodiments, the method 300 of privacy mode backlight operation also includes scattering 320 a portion of the collimated guided light from the light guide as emitted light having an illumination beam width. In various embodiments, scattering the collimated guided light portion uses a plurality of scattering wire elements spaced apart from one another along the length of the light guide. In some embodiments, the light guide and the scattering wire elements may be substantially similar to the light guide 110 and the scattering wire elements 120 described above with respect to the privacy mode backlight 100, respectively. In some embodiments, the scattering wire elements of the plurality of scattering wire elements may include unidirectional scattering elements that preferentially scatter the collimated guided light in the direction of the emitted light from the light guide. Additionally, according to various embodiments, the illumination beam width of the emitted light scattered by the plurality of scattering wire elements is determined by a collimation factor, the illumination beam width being in a direction orthogonal to the length of the light guide.

[0087] Figure 8 The method 300 of privacy mode backlight operation shown in also includes diffusing 330 the emitted light in a direction corresponding to the length of the lightguide using a directional optical diffuser. In some embodiments, the directional optical diffuser can be substantially similar to the directional optical diffuser 130 of the privacy mode backlight 100 as described above. In some embodiments, the diffusion angle of the directional optical diffuser spreads out the emitted light from a scattering wire element in the plurality of scattering wire elements to provide an illumination range equivalent to the distance between adjacent scattering wire elements in the plurality of scattering wire elements. In some embodiments, the size of the scattering wire element in the plurality of scattering wire elements can be comparable to the size of a light valve of a light valve array used to modulate the emitted light into a private image displayed by the privacy display.

[0088] In some embodiments (not shown), the method 300 of privacy mode backlight operation further includes modulating the emitted light using an array of light valves to display a private image. The plurality of light valves may be substantially similar to the array of light valves 140 described above with respect to the privacy mode backlight 100.

[0089] In some embodiments (not shown), the method 300 of privacy mode backlight operation may further include providing light to the light guide using a light source. The provided light may be collimated according to a predetermined collimation factor. According to some embodiments, the light source may be substantially similar to the light source 160 described above.

[0090] Thus, examples and embodiments of privacy mode backlights, privacy displays, and methods of privacy mode backlight operation that employ linear scattering elements and directional diffusers have been described. It should be understood that the above examples are merely illustrative of some of the many specific examples that represent the principles described herein. Clearly, many other arrangements can be easily devised by those skilled in the art without departing from the scope defined by the appended claims.

Claims

1. A privacy mode backlight, comprising: a light guide configured to guide light along a length of the light guide as guided light having a predetermined collimation factor in a direction orthogonal to the length of the light guide; a plurality of scattering wire elements arranged parallel to and spaced apart from one another along the length of the light guide, each of the plurality of scattering wire elements being configured to scatter a portion of the guided light out through an emitting surface of the light guide as emitted light having an illumination beam width in the orthogonal direction determined by the predetermined collimation factor; as well as a directional optical diffuser configured to provide directional diffusion of the emitted light in a direction corresponding to the length of the light guide, Wherein the scattering line elements among the plurality of scattering line elements are located at a surface of the light guide opposite to the emitting surface, and the diffusion angle of the directional optical diffuser in the direction corresponding to the length of the light guide multiplied by the thickness of the light guide and divided by the refractive index of the light guide is greater than or equal to the distance between adjacent scattering line elements.

2. The privacy mode backlight of claim 1, wherein the directional diffusion of the emitted light provided by the directional optical diffuser is configured to provide a uniform illumination pattern of the emitted light in the direction corresponding to the light guide length.

3. The privacy mode backlight of claim 2, wherein the diffusion angle of the directional optical diffuser is configured to disperse the emitted light from each of the scattering wire elements to have an illumination range at an output plane of the privacy mode backlight that is equivalent to the distance between adjacent scattering wire elements among the multiple scattering wire elements.

4. The privacy mode backlight of claim 1, wherein the scattering line elements of the plurality of scattering line elements include unidirectional scattering elements configured to preferentially scatter the guided light in the direction of the emitting surface.

5. The privacy mode backlight of claim 1 , wherein the scattering line elements of the plurality of scattering line elements comprise a diffraction grating at a surface of the light guide, the diffraction grating having diffraction features comprising one or both of grooves in the light guide surface and ridges on the light guide surface.

6. The privacy mode backlight of claim 5, wherein the diffraction grating further comprises reflective islands aligned with the diffraction grating, the diffraction grating being adjacent to the diffraction features and opposite the emitting surface, the diffraction grating and the reflective islands in combination representing a reflective mode diffraction grating.

7. The privacy mode backlight of claim 1, wherein a scattering wire element of the plurality of scattering wire elements comprises an array of individual scattering wire elements arranged in a line along a length of the scattering wire element.

8. A privacy mode backlight as described in claim 7, wherein adjacent individual scattering elements of the array of individual scattering elements are separated from each other by gaps, and wherein the directional optical diffuser is also configured to provide directional diffusion of the emitted light in the orthogonal direction corresponding to the width direction of the light guide, and the provided directional diffusion in the width direction is configured to provide a uniform illumination pattern of the emitted light in the width direction.

9. The privacy mode backlight of claim 1, further comprising a light source optically coupled to the light guide and configured to provide light to the light guide to be guided as the guided light having the predetermined collimation factor.

10. A mode-switchable display comprising a privacy mode backlight as described in claim 1, wherein the mode-switchable display also includes an array of light valves, wherein the array of light valves is configured to modulate the emitted light provided by the privacy mode backlight into a private image during a privacy mode of the mode-switchable display, and the private image is selectively visible within the illumination beam width of the privacy mode backlight during the privacy mode.

11. The mode-switchable display of claim 10, wherein the size of the scattering line elements of the plurality of scattering line elements is comparable to the size of the light valves of the light valve array.

12. The mode-switchable display of claim 10 , further comprising a wide-angle backlight adjacent to a side of the light guide that is opposite to a side adjacent to the light valve array, the wide-angle backlight being configured to provide wide-angle light during a sharing mode of the mode-switchable display, the light valve array being configured to modulate the wide-angle light into a shared image during the sharing mode, Wherein the light guide and the scattering wire elements of the plurality of wire elements are configured to be transparent to the wide-angle light, and the mode-switchable display is configured to selectively display the private image during the privacy mode and display the shared image during the sharing mode.

13. A privacy display comprising: a plurality of scattering wire elements distributed along the length of the light guide, the plurality of scattering wire elements being configured to scatter guided light from the light guide into emitted light having a predetermined illumination beam width in a direction orthogonal to the length of the light guide; an array of light valves configured to modulate the emitted light to provide a private image; as well as a directional optical diffuser located between the light guide and the light valve array, the directional optical diffuser being configured to provide directional diffusion of the emitted light in a direction corresponding to the length of the light guide, the directional diffusion providing uniform illumination of the light valve array in the direction of the light guide length, Wherein the scattering line elements among the plurality of scattering line elements are located at a surface of the light guide opposite to the emitting surface, and the diffusion angle of the directional optical diffuser in the direction corresponding to the length of the light guide multiplied by the thickness of the light guide and divided by the refractive index of the light guide is greater than or equal to the distance between adjacent scattering line elements.

14. The privacy display of claim 13, wherein the directed light is collimated according to a collimation factor, the predetermined illumination beam width being determined by the collimation factor of the directed light.

15. The privacy display of claim 13, wherein a scattering line element of the plurality of scattering line elements comprises a scattering element configured to preferentially scatter the guided light out in the direction of an emitting surface of the light guide adjacent the directional optical diffuser.

16. The privacy display of claim 13, wherein a size of a scattering wire element of the plurality of scattering wire elements is comparable to a size of a light valve of the light valve array.

17. The privacy display of claim 13, further comprising a wide angle backlight adjacent a side of the light guide opposite a side adjacent the light valve array and configured to provide wide angle light during a sharing mode, the light valve array configured to modulate the wide angle light into a shared image during the sharing mode, Wherein the light guide and the scattering wire elements of the plurality of wire elements are configured to be transparent to the wide-angle light, and the privacy display can be mode-switched between the sharing mode providing the shared image and the privacy mode providing the private image.

18. A privacy mode backlight operation method, the method comprising: directing the light in the light guide into collimated guided light having a predetermined collimation factor; scattering a portion of the collimated guided light away from the light guide as emitted light having an illumination beam width using a plurality of scattering line elements spaced apart from one another along a length of the light guide; as well as diffusing the emitted light in a direction corresponding to the length of the light guide using a directional optical diffuser, wherein the illumination beam width of the emitted light scattered by the plurality of scattering line elements is determined by the predetermined collimation factor, the illumination beam width is in a width direction orthogonal to the length of the light guide, and Wherein the scattering line elements among the plurality of scattering line elements are located at a surface of the light guide opposite to the emitting surface, and the diffusion angle of the directional optical diffuser in the direction corresponding to the length of the light guide multiplied by the thickness of the light guide and divided by the refractive index of the light guide is greater than or equal to the distance between adjacent scattering line elements.

19. The privacy mode backlight operation method of claim 18, wherein the scattering line elements of the plurality of scattering line elements include unidirectional scattering elements that preferentially scatter the collimated directed light in a direction toward the directional optical diffuser.

20. The privacy mode backlight operation method according to claim 18, characterized in that One or both of the following, wherein the diffusion angle of the directional optical diffuser disperses the emitted light from the scattering wire elements among the plurality of scattering wire elements to provide an illumination range equivalent to the distance between adjacent scattering wire elements among the plurality of scattering wire elements, and wherein the size of the scattering wire elements among the plurality of scattering wire elements is comparable to the size of the light valves of a light valve array used to modulate the emitted light into a private image displayed by the privacy display.

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