HK40003514B - Mode-selectable backlight, method, and display employing directional scattering features - Google Patents

Description

Mode selectable backlighting, method and display with directional scattering

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to U.S. Provisional Patent Application Serial No. 62/404,751, filed October 5, 2016, which is hereby incorporated by reference in its entirety.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

N/A

Background Art

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.). Generally, electronic displays can be classified as active displays (i.e., displays that emit light) or passive displays (i.e., displays that modulate light provided by another source). The most obvious examples of active displays are CRTs, PDPs, and OLED/AMOLEDs. Displays that are typically classified as passive when considering the light emitted are LCDs and EP displays. While passive displays often exhibit attractive performance characteristics, including but not limited to inherently low power consumption, their use may be limited in many practical applications due to their lack of light-emitting capability.

In order to overcome the limitations of passive displays associated with emitted light, many passive displays are coupled to external light sources. The coupled light source can allow these originally passive displays to emit light and essentially act as active displays. An example of such a coupled light source is a backlight. The backlight can be used as a light source (usually a panel backlight) that is placed behind the originally passive display to illuminate the passive display. For example, the backlight can be coupled to an LCD or EP display. The backlight emits light that passes through the LCD or EP display. The emitted light is modulated by the LCD or EP display, and the modulated light is then emitted from the LCD or EP display in turn. Typically the backlight is configured to emit white light. Color filters are then used to convert the white light into the various colors used in the display. For example, the color filter can be placed at the output of the LCD or EP display (less commonly used) or between the backlight and the LCD or EP display.

BRIEF DESCRIPTION OF THE DRAWINGS

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:

FIG. 1A shows a perspective view of a multi-view display in an example of an embodiment consistent with the principles described herein.

1B shows a graphical representation of angular components of light beams having particular principal angle directions corresponding to view directions of a multi-view display, in an example of an embodiment consistent with principles described herein.

2 shows a cross-sectional view of a diffraction grating in an example according to an embodiment consistent with the principles described herein.

3A shows a cross-sectional view of a mode-selectable backlight in an example, according to an embodiment consistent with the principles described herein.

3B shows a plan view of a mode-selectable backlight in an example, according to an embodiment consistent with the principles described herein.

3C shows a perspective view of a mode-selectable backlight in an example, according to an embodiment consistent with the principles described herein.

4A shows a cross-sectional view of a mode-selectable backlight in an example according to another embodiment consistent with the principles described herein.

4B shows a cross-sectional view of the mode-selectable backlight shown in FIG. 4A , according to an example of an embodiment consistent with the principles described herein.

5 shows a cross-sectional view of a portion of a mode-selectable backlight in an example of an embodiment consistent with the principles described herein.

6A shows a cross-sectional view of a portion of a mode-selective backlight including multiple diffraction gratings of a multi-beam element, according to an example of an embodiment consistent with the principles described herein.

6B shows a plan view of the multiple diffraction gratings shown in FIG. 6A , in an example of an embodiment consistent with the principles described herein.

7A shows a plan view of a multi-beam element in an example, according to an embodiment consistent with the principles described herein.

7B shows a plan view of another multi-beam element in an example, according to an embodiment consistent with the principles described herein.

8 shows a cross-sectional view of a portion of a mode-selectable backlight including a multi-beam element, according to an example of another embodiment consistent with the principles described herein.

9 shows a cross-sectional view of a portion of a mode-selectable backlight including a multi-beam element, according to an example of yet another embodiment consistent with the principles described herein.

10 shows a block diagram of a mode-selectable display in an example according to an embodiment consistent with the principles described herein.

11 shows a flowchart of a method of operating a mode-selectable backlight in an example of an embodiment consistent with the principles described herein.

Certain examples and embodiments have other features in addition to and instead of one of the features shown in the above-referenced drawings.These and other features are described in detail below with reference to the above-referenced drawings.

DETAILED DESCRIPTION

Examples and embodiments according to the principles described herein provide a mode-selectable backlight for a mode-selectable display. Embodiments consistent with the principles described herein provide a mode-selectable backlight that employs a light guide configured to provide multiple directional scattering features of emitted light by scattering a portion of the guided light propagating within the light guide away from the light guide. According to various embodiments, by controlling the propagation direction of the guided light during different operating modes, the characteristics of the emitted light can be mode-selected.

For example, during a first operating mode, a first directional scattering feature of the plurality of directional scattering features can be configured to provide a first emitted light from guided light having a first propagation direction within the lightguide. Alternatively, in a second operating mode, a second directional scattering feature of the plurality of directional scattering features can be configured to provide a second emitted light from guided light having a second propagation direction within the lightguide. In some embodiments, the first emitted light can be, but is not limited to, diffuse or unidirectional light. On the other hand, according to various embodiments, the second emitted light provided by the second directional scattering feature is directional, comprising a plurality of directional light beams having different principal directions from one another.

In some embodiments, the diffuse or unidirectional first emitted light can provide a backlight that supports or facilitates display of a two-dimensional (2D) image during a first operating mode. In a second operating mode, the directional beam of the second emitted light can provide a backlight that is configured to support display of a multi-view image (e.g., via a multi-view display), different principal directions corresponding to different view directions of various views of the multi-view image (or equivalently, a multi-view display). Uses of the mode-selectable backlights and mode-selectable displays described herein include, but are not limited to, mobile phones (e.g., smartphones), watches, tablet computers, mobile computers (e.g., laptop computers), personal computers and computer monitors, automotive display consoles, camera displays, and various other mobile and substantially non-mobile display applications and devices.

As used herein, a "two-dimensional display" or "2D display" is defined as a display that is configured to provide substantially the same view of an image regardless of the direction from which the image is viewed (i.e., within a predetermined viewing angle or range of the 2D display). Conventional liquid crystal displays (LCDs) found in smartphones and computer monitors are examples of 2D displays. In contrast, a "multi-view display" is defined as an electronic display or display system that is configured to provide different views of a multi-view image in or from different viewing directions. Specifically, the different views may represent different perspectives of a scene or object of the multi-view image.

FIG1A shows a perspective view of a multi-view display 10 in an example according to an embodiment consistent with the principles described herein. As shown in FIG1A , the multi-view display 10 includes a screen 12 for displaying a multi-view image to be viewed. For example, the screen 12 can be a display screen of a phone (e.g., a mobile phone, a smartphone, etc.), a tablet computer, a laptop computer, a computer display of a desktop computer, a camera display, or an electronic display of substantially any other device.

The multi-view display 10 provides different views 14 of a multi-view image in different view directions 16 relative to a screen 12. The view directions 16 are shown as arrows extending from the screen 12 in various different primary directions (or simply different directions); the different views 14 are shown as shaded polygonal boxes at the endpoints of the arrows (i.e., depicting the view directions 16); and only four views 14 and four view directions 16 are shown, all by way of example and not limitation. Note that although the different views 14 are shown as being above the screen in FIG. 1A , when the multi-view image is displayed on the multi-view display 10, the views 14 actually appear on or near the screen 12. Depicting the views 14 above the screen 12 is merely for ease of illustration and is intended to represent viewing the multi-view display 10 from a respective one of the view directions 16 corresponding to a particular view 14.

As defined herein, a view direction or equivalently a light beam having a direction corresponding to a view direction of a multi-view display generally has a principal angle direction given by an angular component {θ, φ}. The angular component θ is referred to herein as the "elevation component" or "elevation angle" of the light beam. The angular component φ is referred to as the "azimuth component" or "azimuth angle" of the light beam. As defined herein, the elevation angle θ is an angle in the vertical plane (e.g., perpendicular to the plane of the multi-view display screen), while the azimuth angle φ is an angle in the horizontal plane (e.g., parallel to the plane of the multi-view display screen).

FIG1B shows a graphical representation of the angular components {θ, φ} of a light beam 20 having a particular principal direction, or simply "direction," corresponding to a view direction of a multi-view display (e.g., view direction 16 in FIG1A ), according to an example of an embodiment consistent with the principles described herein. Furthermore, light beam 20, as defined herein, is emitted or radiates from a particular point. That is, light beam 20, by definition, has a central ray associated with a particular origin within the multi-view display. FIG1B also shows the light beam (or view direction) point at origin O.

Furthermore, as used herein, the term "multi-view" as used in the terms "multi-view image" and "multi-view display" is defined as a plurality of views representing angular differences between different viewing angles or views comprising a plurality of views. Additionally, as defined herein, the term "multi-view" explicitly includes more than two different views (i.e., a minimum of three views and typically more than three views), as defined herein. Thus, a "multi-view display" as used herein is explicitly distinguished from a stereoscopic display that includes only two different views to represent a scene or image. Note, however, that although a multi-view image and a multi-view display may include more than two views, as defined herein, a multi-view image may be viewed as a stereoscopic image pair (e.g., on a multi-view display) by selecting only two of the multi-view views to be viewed simultaneously (e.g., one view for each eye).

A "multi-view pixel" is defined herein as a "view" pixel or a set of sub-pixels in each of a similar plurality of different views of a multi-view display. Specifically, a multi-view pixel may have individual view pixels corresponding to or representing view pixels in each different view of a multi-view image. Furthermore, according to the definition herein, the view pixels of a multi-view pixel are so-called "directional pixels," where each view pixel is associated with a predetermined view direction of a corresponding one of the different views. Furthermore, according to various examples and embodiments, different view pixels of a multi-view pixel may have equivalent, or at least substantially similar, positions or coordinates in each of the different views. For example, a first multi-view pixel may have individual view pixels located at {x1, y1} in each of the different views of a multi-view image, while a second multi-view pixel may have individual view pixels located at {x2, y2} in each of the different views, and so on.

In some embodiments, the number of view pixels in the multi-view display may be equal to the number of views of the multi-view display. For example, the multi-view pixel array may provide sixty-four (64) view pixels associated with a multi-view display having 64 different views. In another example, the multi-view display may provide an eight by four view array (i.e., 32 views), and the multi-view pixel array may include thirty-two (32) view pixels (i.e., one for each view). Additionally, for example, each different view pixel may have an associated direction (e.g., a beam direction) corresponding to a different one of the view directions corresponding to the 64 different views. Furthermore, according to some embodiments, the number of multi-view pixels in the multi-view display may be substantially equal to the number of "view" pixels (i.e., pixels that make up a selected view) in a view of the multi-view display. For example, if a view includes six hundred and forty by four hundred and eighty view pixels (i.e., a 640×480 view resolution), the multi-view display may have three hundred and seven thousand two hundred (307,200) multi-view pixels. In another example, when a view includes one hundred by one hundred pixels, the multi-view display may include a total of ten thousand (ie, 100×100=10,000) multi-view pixels.

As used herein, a "lightguide" is defined as a structure that uses total internal reflection or "TIR" to guide light within the structure. Specifically, 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 an 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 lieu of the above-mentioned refractive index difference, the lightguide may include a coating to further promote total internal reflection. For example, the coating may be a reflective coating. The lightguide may be any of several lightguides, including but not limited to one or both of a plate or slab lightguide and a strip lightguide.

Furthermore, as used herein, the term "plate" when applied to a lightguide as in a "plate lightguide" is defined as a segmented or differently planar layer or sheet, which is sometimes referred to as a "flat plate" lightguide. Specifically, a plate lightguide is defined as a lightguide 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. Furthermore, according to the definitions herein, the top surface and the bottom surface are both separate from each other and may be substantially parallel to each other, at least in a differential sense. That is, within any distinct subsection of the plate lightguide, the top surface and the bottom surface are substantially parallel or coplanar.

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

As used herein, an "angle-preserving scattering feature" or equivalently an "angle-preserving scatterer" is any feature or scatterer configured to scatter light in a manner that substantially preserves the angular spread of light incident on the feature or scatterer in the scattered light. Specifically, by definition, the angular spread _σs of light scattered by the angle-preserving scattering feature is a function of the angular spread σ of the incident light (i.e., _σs = f(σ)). In some embodiments, the angular spread _σs of the scattered light is a linear function of the angular spread or collimation factor σ of the incident light (e.g., _σs = α·σ, where α is an integer). That is, the angular spread _σs of light scattered by the angle-preserving scattering feature can be substantially proportional to the angular spread or collimation factor σ of the incident light. For example, the angular spread σs of the scattered light can be substantially equal to the angular spread σ of the incident light (e.g., _σs ≈ _σ ). A uniform diffraction grating (i.e., a diffraction grating having a substantially uniform or constant diffraction feature spacing or grating pitch) is an example of an angle-preserving scattering feature. In contrast, Lambertian scatterers or Lambertian reflectors, as well as ordinary diffusers (eg, having Lambertian or nearly Lambertian scattering), are not angle-preserving scatterers according to the definition herein.

In this document, a "diffraction grating" is generally 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 can be arranged in a periodic or quasi-periodic manner. For example, a diffraction grating can include a plurality of features arranged in a one-dimensional (1D) array (e.g., a plurality of grooves or ridges on a material surface). In other examples, a diffraction grating can be a two-dimensional (2D) array of features. For example, a diffraction grating can be a 2D array of bumps on a material surface or holes in a material surface.

Thus, and as defined 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 light guide, this can result in diffraction or diffraction scattering, and is therefore referred to as "diffraction coupling," wherein the diffraction grating can couple light out of the light guide by diffraction. A diffraction grating also redirects or changes the angle of light by diffraction (i.e., at a diffraction angle). Specifically, as a result of diffraction, the light exiting the diffraction grating typically has a propagation direction that is different from the propagation direction of the light incident on the diffraction grating (i.e., the incident light). This change in the propagation direction of light by diffraction is referred to herein as "diffraction redirection." Thus, a diffraction grating can be understood as a structure that includes diffraction features that diffractively redirect light incident on the diffraction grating, and if the light is incident from a light guide, the diffraction grating can also diffractively couple light out of the light guide.

Furthermore, as defined herein, features of a diffraction grating are referred to as "diffraction features" and can be one or more at, in, and on a surface of a material (i.e., a boundary between two materials). For example, the surface can be the surface of a light guide. The diffraction features can include any of a variety of structures that diffract light, including, but not limited to, one or more of grooves, ridges, holes, and bumps at, in, or on a surface. For example, a diffraction grating can include a plurality of substantially parallel grooves in a surface of a material. In another example, a diffraction grating can include a plurality of parallel ridges rising from a surface of a material. The diffraction features (e.g., grooves, ridges, holes, bumps, etc.) can 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 profile, a rectangular profile (e.g., a binary diffraction grating), a triangular profile, and a sawtooth profile (e.g., a blazed grating).

According to various examples described herein, a diffraction grating (e.g., a diffraction grating of a multi-beam element 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. Specifically, the diffraction angle _θm of or provided by a locally periodic diffraction _grating can be given by equation (1):

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 _θi 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., _nout = 1). Typically, the diffraction order m is given by an integer. The diffraction angle _θm of the light beam produced by the diffraction grating can be given by equation (1) for a positive diffraction order (e.g., m>0). For example, first-order diffraction is provided when the diffraction order m is equal to 1 (i.e., m=1).

FIG2 shows a cross-sectional view of a diffraction grating 30 in an example according to an embodiment consistent with the principles described herein. For example, the diffraction grating 30 can be located on a surface of a light guide 40. Additionally, FIG2 shows a light beam 50 incident on the diffraction grating 30 at an incident angle _θi. The incident light beam 50 is a guided light beam within the light guide 40. FIG2 also shows a directed light beam 60 diffractively generated by the diffraction grating 30 and coupled out as a result of the diffraction of the incident light beam 50. The directed light beam 60 has a diffraction angle _θm (or "principal direction" herein) given by equation (1). The diffraction angle _θm can correspond to the diffraction order "m" of the diffraction grating 30.

As used herein, a "directional scattering feature" is defined as a scattering structure that selectively or preferentially scatters light having a particular or predetermined direction of propagation, while not scattering or not substantially scattering light having another or different direction of propagation. For example, a directional scattering feature can be configured to selectively scatter light having a first direction of propagation. Furthermore, a directional scattering feature may not scatter light having a second direction of propagation that is different from the first direction of propagation. Thus, by definition, a directional scattering feature is directionally selective with respect to the direction of light incident on the directional scattering feature. In contrast, Lambertian scattering structures (and similar scattering structures) are generally not directional scattering features because such scattering structures are inherently insensitive to the direction of incident light.

As defined herein, a "multi-beam element" is a structure or element of a backlight or display that generates light comprising multiple light beams. In some embodiments, the multi-beam element can be optically coupled to a light guide of the backlight to provide the multiple light beams by coupling out a portion of the light guided in the light guide. Furthermore, as defined herein, the beams of the multiple light beams generated by the multi-beam element have different principal angular directions from one another. Specifically, as defined herein, a beam in the multiple light beams has a predetermined principal angular direction that is different from another beam in the multiple light beams. Thus, as defined herein, a light beam is referred to as a "directional light beam," and the multiple light beams may be referred to as a "multiple directional light beams."

Furthermore, multiple directional light beams can represent a light field. For example, the multiple directional light beams can be confined to a substantially conical region of space or have a predetermined angular spread including different principal angular directions of the light beams in the multiple light beams. Thus, the predetermined angular spread of the combined directional light beams (i.e., the multiple light beams) can represent a light field.

According to various embodiments, the different principal angular directions of the plurality of various directional light beams are determined by characteristics including, but not limited to, the dimensions (e.g., length, width, area, etc.) of the multi-beam element. In some embodiments, the multi-beam element can be considered an "extended point light source," as defined herein, i.e., a plurality of point light sources distributed across the extent of the multi-beam element. Furthermore, according to the definitions herein, and as described above with respect to FIG. 1B , the directional light beams produced by the multi-beam element have principal angular directions given by the angular components {θ, φ}

As used herein, a "collimator" is defined as substantially any optical device or apparatus configured to collimate light. According to various embodiments, the amount of collimation provided by the collimator can vary from one embodiment to another by a predetermined degree or amount. Furthermore, the collimator can 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 can include a shape that provides collimation of light in one or both of the two orthogonal directions.

As used herein, "collimation factor" is defined as the degree to which light is collimated. Specifically, as defined herein, the collimation factor describes the angular spread of the light rays within a collimated light beam. For example, the collimation factor σ can specify that a majority of the light rays in a collimated light beam are within a particular angular spread (e.g., +/- σ degrees about the center or a particular principal angle of the collimated light beam). According to some examples, the light rays of the collimated light beam can have a Gaussian distribution as a function of angle, and the angular spread is an angle determined by half the peak intensity of the collimated light beam.

As used herein, a "light source" is generally defined as a source of light (e.g., a light emitter configured to generate and emit light). For example, a light source may include a light emitter, such as a light emitting diode (LED) that emits light when activated or turned on. Specifically, as used herein, a light source may be substantially any light source, or include substantially any light 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 light emitter, a fluorescent lamp, an incandescent lamp, and virtually any other light source. 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, the light source may include multiple light emitters. For example, the light source may include a set or group of light emitters, wherein at least one light emitter generates light having a color or equivalent wavelength that is different from the color or wavelength of light generated by at least one other light emitter in the set or group. For example, the different colors may include primary colors (e.g., red, green, blue).

Here, a "view frame" is defined as the area or volume of space in which the image formed by a display or other optical system (e.g., a lens system) is visible and can therefore be viewed. In other words, the view frame defines a location or area in space where the user's eyes can be placed in order to view the image produced by the display or display system. In addition, the view frame is generally large enough to accommodate both eyes of the user. In some embodiments, the view frame can represent a two-dimensional spatial area (e.g., an area with length and width but no substantial depth), while in other embodiments, the view frame can include a three-dimensional spatial area (e.g., an area with length, width, and depth). In addition, although referred to as a "frame," the view frame is not limited to a box with a polygonal or rectangular shape. For example, in some embodiments, the view frame may include a cylindrical spatial area. In other examples, the spatial area can have various other shapes, including but not limited to an elliptical cylinder, a hyperbolic cylinder, and a general ellipsoid.

In addition, as used herein, the articles "a" and "an" are intended to have their ordinary meaning in the patent art, i.e., "one or more". For example, a "directional scattering feature" refers to one or more directional scattering features, and such a "directional scattering feature" refers herein to "(one or more) directional scattering features". In addition, any reference to "top", "bottom", "above", "below", "up", "down", "front", "back", "first", "second", "left" or "right" in this document is not intended to be limiting herein. In this document, the term "about" when applied to a value generally refers to within the tolerance range of the equipment used to produce the value, or may refer to plus or minus 10%, or plus or minus 5%, or plus or minus 1%, unless expressly provided otherwise. In addition, the term "substantially" as used herein refers to an amount in the range of most, or almost all, or all, or about 51% to about 100%. In addition, the examples in this document are intended to be illustrative only and for the purpose of discussion and not as a limitation.

In accordance with some embodiments of the principles described herein, a mode-selective backlight is provided. Figure 3A shows a cross-sectional view of a mode-selective backlight 100 in an example according to an embodiment consistent with the principles described herein. Figure 3B shows a plan view of a mode-selective backlight 100 in an example according to an embodiment consistent with the principles described herein. Figure 3C shows a perspective view of a mode-selective backlight 100 in an example according to an embodiment consistent with the principles described herein. In Figures 3A and 3B, a first operating mode (Mode 1) of the mode-selective backlight 100 is shown in the left half of the figures, and a second operating mode (Mode 2) is shown in the right half, i.e., to the left and right of the dashed lines in Figures 3A-3B, respectively.

3A-3C is configured to provide emitted light 102. The emitted light 102 is configured to have a direction generally away from a surface (e.g., an emitting surface) of the mode-selectable backlight 100. In some embodiments, the emitted light 102 can be used in various applications, such as, but not limited to, illuminating an array of light valves (e.g., light valve 106) in a display application, for example.

In the various operating modes of the mode-selectable backlight 100, the emitted light 102 may have or exhibit different characteristics. For example, as described in more detail below, in a first operating mode, the mode-selectable backlight 100 may provide emitted light 102 having a single or substantially uniform direction. In other embodiments, the emitted light 102' provided in the first operating mode may be diffuse, substantially diffuse, or at least lack any particular or defined directionality. Herein, the emitted light 102 during the first operating mode (Mode 1) may be referred to as "first" emitted light 102' to distinguish it from the light emitted during the other operating modes.

In a second operating mode (Mode 2, as shown) of the mode-selectable backlight 100, the emitted light 102 may include a plurality of directional light beams having different principal angular directions (or simply "different directions") from one another. For example, the plurality of directional light beams may be or represent a light field. According to some embodiments, in or during the second operating mode, the light beams of different principal angular directions of the directional light beams of emitted light 102 may correspond to respective view directions of a multi-view image or a multi-view display.

In some of these embodiments, for example, the directional beam of emitted light 102 can be modulated (e.g., using a light valve 106, as described below) to facilitate displaying information with multi-view or 3D image content. In other embodiments, the different principal directions of the directional beam in the second operating mode can correspond to directions toward a relatively limited spatial region adjacent to or in front of the mode-selectable backlight 100 (e.g., the viewing frame). In these embodiments, for example, the directional beam of emitted light 102 can be modulated (e.g., by a light valve) to provide image content in the viewing frame. Herein, the emitted light 102 during the second operating mode (Mode 2) can be referred to as "second" emitted light 102" to distinguish it from light emitted during other operating modes (such as, but not limited to, the first operating mode).

As shown in Figures 3A-3C, mode-selectable backlight 100 includes a light guide 110. According to some embodiments, light guide 110 can be a plate light guide. Light guide 110 is configured to guide light as guided light 104 along the length of light guide 110. For example, light guide 110 can include a dielectric material configured as an optical waveguide. The dielectric material can have a first refractive index that is greater than a second refractive index of a medium surrounding the dielectric optical waveguide. For example, the difference in refractive index is configured to promote total internal reflection of guided light 104 according to one or more guided modes of light guide 110.

In some embodiments, light guide 110 can be a flat plate or slab optical waveguide comprising an extended, substantially planar, optically transparent sheet of dielectric material. The substantially planar sheet of dielectric material is configured to guide guided light 104 using total internal reflection. According to various examples, the optically transparent material of light guide 110 can include or be composed 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-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, light guide 110 can further 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 light guide 110. According to some examples, the cladding can be used to further promote total internal reflection.

In addition, according to some 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" surface or side) and a second surface 110" (e.g., a "back" surface or side) of the light guide 110 based on total internal reflection. Specifically, the guided light 104 propagates by reflecting or "bouncing" between the first surface 110' and the second surface 110" of the light guide 110 at the non-zero propagation angle. In some embodiments, the guided light 104 may include multiple guided beams of light of different colors, which can be guided by the light guide 110 at a corresponding one of the different color-specific, non-zero propagation angles. Note that for simplicity of illustration, the non-zero propagation angles are not shown in Figures 3A-3C. However, the bold arrows depicting the propagation direction in the various figures show the general propagation direction of the guided light 104 along the length of the light guide.

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"). Furthermore, according to various embodiments, the non-zero propagation angle is greater than zero and less than the critical angle for total internal reflection within the light guide 110. Furthermore, as long as the particular non-zero propagation angle is less than the critical angle for total internal reflection within the light guide 110, the particular non-zero propagation angle may be selected (e.g., arbitrarily) for a particular implementation. In various embodiments, the guided light 104 may be introduced or coupled into the light guide 110 at a non-zero propagation angle.

According to various embodiments, the guided light 104, or equivalently, the guided "beam", produced by coupling light into the light guide 110 can be a collimated beam. As used herein, "collimated light" or a "collimated beam" is generally defined as a beam in which the rays of the beam are substantially parallel to each other within the beam (e.g., the guided beam 104). Furthermore, light rays that diverge or scatter from a collimated beam are not considered to be part of the collimated beam according to the definitions herein. In some embodiments, the mode-selectable backlight 100 can include a collimator, such as, but not limited to, a lens, a reflector or mirror, or a diffraction grating, configured to collimate the light introduced into the light guide 110. In some embodiments, the source of light (e.g., a light source) can include a collimator. In various embodiments, the guided light 104 can be collimated according to a collimation factor or having a collimation factor σ.

According to various embodiments, the mode-selectable backlight 100 further includes first directional scattering features 120. The first directional scattering features 120 are configured to provide first emitted light 102' from guided light 104 having a first propagation direction within the light guide 110. Specifically, the first directional scattering features 120 are configured to preferentially or selectively scatter guided light 104 having the first propagation direction over guided light 104 having other propagation directions. For example, by way of example and not limitation, the first propagation direction may be the x-direction (i.e., aligned with or along the x-axis) as shown in Figures 3A-3C. The thick arrow 103' in the left half of Figures 3A and 3B may represent the first propagation direction of the guided light 104, e.g., during or in the first operating mode (Mode 1). Thus, as shown in Figures 3A-3C, the first directional scattering features 120 are configured to selectively scatter guided light 104 propagating along the x-direction (as indicated by the thick arrow 103') within the light guide 110 over other directions (e.g., the y-direction).

According to various embodiments, guided light 104 having a first propagation direction may be present during a first operating mode (Mode 1) of the mode-selectable backlight 100. Specifically, in some embodiments, guided light 104 having a first propagation direction may be present only during the first operating mode. Thus, selection of the first operating mode may be provided by the presence of guided light 104 having the first propagation direction. For example, turning on a light source that provides guided light 104 having the first propagation direction may select the first operating mode.

In some embodiments, the first emitted light 102' can be diffuse, or at least substantially diffuse, emitted according to a diffuse scattering pattern by the first directional scattering features 120 of the mode-selectable backlight 100. In other embodiments, the first emitted light 102' can be substantially unidirectional light. FIG3A uses broad arrows to depict the diffuse scattering pattern or substantially unidirectional light of the first emitted light 102', for example, to distinguish the directional beam of the second operating mode, as shown. In other embodiments (not shown), the first emitted light 102' can include a directional beam.

According to various embodiments, the first directional scattering feature 120 may include any of a variety of different scattering structures or scatterers configured to provide directional scattering, including but not limited to diffraction gratings, refractive scattering structures (e.g., various prismatic structures), reflective scattering structures (e.g., faceted reflectors), plasma or fluorescent scattering structures (e.g., anisotropic plasma or fluorescent resonators), and various combinations thereof. For example, the orientation or rotation of the diffraction grating and the orientation of the various elements comprising the other scattering structures may be employed to provide directional scattering. According to some embodiments, whether the first emitted light provided by the first directional scattering feature 120 employing such a scattering structure is diffuse, unidirectional, or includes a directional beam depends on the specific characteristics of the first directional scattering feature 120 and the angular spread or collimation factor σ of the guided light 104 having the first propagation direction.

For example, the first directional scattering features 120 may include a diffraction grating on the surface of the light guide 110, the diffraction grating including substantially parallel grooves or ridges. The substantially parallel grooves or ridges may be oriented perpendicular or substantially perpendicular (e.g., including curvature) to the first propagation direction of the guided light 104. When the guided light 104 encounters the diffraction grating of the first directional scattering features 120, a portion of it may be selectively scattered as the first emitted light 102'. The selective scattering is the result of the substantially normal incidence angle or substantially perpendicular orientation of the guided light 104 relative to the diffraction grating orientation.

Furthermore, because a diffraction grating (e.g., that of the first directional scattering features 120) can function as an angle-preserving scattering structure, when the guided light 104 having the first propagation direction has a relatively large collimation factor σ (i.e., a wide angular spread), first emitted light 102' having a correspondingly wide spread can be provided. Thus, the first emitted light 102' provided by the first directional scattering features 120 can be diffuse or substantially diffuse. In contrast, a relatively small collimation factor σ can be used to provide first emitted light 102' having a more restricted angular spread or being substantially unidirectional. For example, the first emitted light 102' can include substantially parallel beams emitted in a direction perpendicular to the surface of the lightguide. In another example, first emitted light 102' that is diffuse or spread over a wide range of angles can be provided by the first directional scattering features 120 comprising a diffraction grating having a random or substantially random grating spacing as a function of distance across the lightguide 110. For example, random grating spacing may be employed with or without guided light 104 having a large collimation factor σ.

In other examples, a refractive or reflective scattering structure having facets aligned to provide directional scattering configured to selectively scatter guided light 104 having a first propagation direction can be used as the first directional scattering feature 120. For example, as with the diffraction grating example above, a relatively large collimation factor σ of the guided light 104 having the first propagation direction can be employed to produce diffuse first emitted light 102', while a relatively small collimation factor σ can produce first emitted light 102' that is substantially unidirectional or has a predetermined direction. For example, a refractive or reflective scattering structure having facets with random slopes can also be used as the first directional scattering feature 120 to provide diffuse first emitted light.

As shown in Figures 3A-3C, the mode-selectable backlight 100 also includes a second directional scattering feature 130. The second directional scattering feature 130 is configured to provide a second emitted light 102" from the guided light 104 having a second propagation direction within the light guide 110. Specifically, the second emitted light 102" is provided by scattering or coupling out a portion of the guided light 104 having the second propagation direction from the light guide 110. As shown in Figures 3A-3C, by way of example and not limitation, the second propagation direction can be in the y-direction (i.e., aligned with or along the y-axis). The arrow 103" in the right half of each figure pointing to the plane of Figure 3A and the thick arrow 103" in Figure 3B show the second propagation direction of the guided light 104. Therefore, as shown in Figures 3A-3C, the second directional scattering feature 130 can be configured to selectively scatter the guided light 104 propagating in the y-direction rather than other directions (for example, the x-direction as shown by the thick arrow 103'), as shown by the thick arrow 103". In addition, the second directional scattering feature 130 is configured not to scatter or at least substantially not to scatter the guided light 104 having the first propagation direction. In this way, the second directional scattering feature 130 does not generate scattered light (i.e., second emitted light 102") during the first operating mode, as shown in the right half of Figure 3A.

As described above, the second emitted light 102" includes multiple directional light beams having different principal axis directions from one another. In this way and by definition, the second directional scattering feature 130 is configured to provide multiple directional light beams having different principal axis directions. On the right side of Figure 3A (Mode 2), the multiple directional light beams of the second emitted light 102" are depicted as separate arrows pointing in different directions to explicitly indicate the different principal axis directions of the directional light beams.

According to various embodiments, the second directional scattering feature 130 may include any of a variety of different scattering structures that provide directional scattering, and may be configured to provide second emitted light 102 including a plurality of directional light beams. Specifically, the scattering structure of the second directional scattering feature 130 may include, but is not limited to, a diffraction grating, a refractive scattering structure (e.g., various prism structures), a reflective scattering structure (e.g., a faceted reflector), a plasma or fluorescent scattering structure (e.g., anisotropic plasma or fluorescent resonator), and various combinations thereof configured to provide directional light beams having different principal angles from each other.

For example, the second directional scattering feature 130 may include a multi-beam diffraction grating or multiple multi-beam diffraction gratings, as defined in U.S. Patent No. 9,128,226 B2 to Fattal et al. In another example, the second directional scattering feature 130 may include a multi-beam element or multiple multi-beam elements. According to various embodiments, the multi-beam element may include one or more of a diffraction grating, a micro-reflective element, and a micro-refractive element, as described in more detail below. As with the first directional scattering feature 120, various orientations or rotations of the scattering structures may be used to provide directional scattering of the second directional scattering feature 130. Similarly, the collimation factor σ of the guided light 104 having the second propagation direction may be used to control the angular spread of the different principal angle directions of the directional light beam generated by the second directional scattering feature 130.

According to various embodiments, guided light 104 having a second propagation direction may be present during a second operating mode (Mode 2) of the mode-selectable backlight 100. In some embodiments, guided light 104 having the second propagation direction may be present only during the second operating mode. Thus, in some embodiments (e.g., Mode 2, as shown), the second directional scattering feature 130 may provide second emitted light 102' from the guided light 104 only during the second operating mode. In other embodiments, the guided light 104 having the second propagation direction may be present during the first and second operating modes. In these embodiments, both the first and second directional scattering features 120, 130 may provide emitted light 102 comprising a combination of the first and second emitted light 102', 102' during the first operating mode, while only the second directional scattering feature 130 provides emitted light 102, 102' only during the second operating mode. As with the first operating mode, mode selection for the second operating mode may be provided by controlling the presence or absence of guided light 104 having one or both of the first and second propagation directions.

Furthermore, by way of example and not limitation, FIG3A shows a first directional scattering feature 120 on a first surface 110′ and a second directional scattering feature 130 on a second surface 110″ of the light guide 110. As shown, the second directional scattering feature 130 is configured to scatter a portion of the guided light 104 having a second propagation direction, which is scattered out through the first surface 110′ to provide second emitted light 102″. Here, the first surface 110′ of the light guide 110 may be referred to as an “emitting” surface. Furthermore, according to various embodiments, the first directional scattering feature 120 may be configured to be transparent or at least substantially transparent to a directional light beam (as second emitted light 102″) scattered by the second directional scattering feature 130. In other embodiments (not shown), the first directional scattering feature 120 may be on the second surface 110″ of the light guide 110, and the second directional scattering feature 130 may be on the first surface 110′.

FIG4A shows a cross-sectional view of a mode-selectable backlight 100 according to an example of another embodiment consistent with the principles described herein. FIG4B shows a cross-sectional view of the mode-selectable backlight 100 shown in FIG4A according to an example of an embodiment consistent with the principles described herein. Specifically, FIG4A shows the mode-selectable backlight 100 in a first operating mode (Mode 1), while FIG4B shows the mode-selectable backlight 100 in a second operating mode (Mode 2). In addition, FIG4A shows a cross-sectional view in the x-z plane, and the cross-sectional view of FIG4B shows a cross-sectional view in the y-z plane.

Figures 4A and 4B show a mode-selectable backlight 100 that includes a light guide 110 configured to guide light (i.e., guided light 104), a first directional scattering feature 120, and a second directional scattering feature 130. However, as shown in Figures 4A-4B, the first directional scattering feature 120 and the second directional scattering feature 130 are located on a common surface of the light guide 110, rather than on opposing surfaces as previously shown in Figure 3A. Specifically, Figures 4A-4B show the first and second directional scattering features 120, 130 on the second surface 110" of the light guide 110. For example, the first directional scattering feature 120 can occupy space between (e.g., around) portions of the second directional scattering feature 130 on the second surface 110". In other embodiments (not shown), the first and second directional scattering features 120, 130 can be together on the first surface 110' of the light guide 110.

As shown in FIG4A , first directional scattering features 120 selectively scatter guided light 104 having a first propagation direction. Guided light 104 is scattered out of light guide 110 as first emitted light 102′. In FIG4A , the first propagation direction is illustrated by thick arrow 103′ parallel to the x-axis, and first emitted light 102′ can be provided by first directional scattering features 120 from guided light 104 as diffuse light having a relatively wide angular range (e.g., greater than 60 degrees). Furthermore, for example, FIG4A can represent a first mode of operation.

4B , the second directional scattering features 130 selectively scatter the guided light 104 having the second propagation direction to provide second emitted light 102″ from the guided light 104, as shown. Specifically, in FIG4B , the second propagation direction is depicted by a thick arrow 103″ parallel to the y-axis. In addition, as indicated by the respective arrows, the second emitted light 102″ includes a plurality of directional light beams having different principal directions from one another. Note that the first directional scattering features 120 in FIG4B do not scatter any guided light 104 having the second propagation direction. As shown, only the second directional scattering features 130 scatter or couple out any guided light 104. For example, FIG4B may represent a first mode of operation.

As described above, during the first operating mode, there can be guided light 104 having both a first propagation direction and a second propagation direction. Thus, in some embodiments, both the first and second directional scattering features 120, 130 can scatter a portion of light from the guided light 104 during the first operating mode. For example, when the first directional scattering features 120 are on the same surface of the light guide 110 as the second directional scattering features 130 (e.g., as shown in Figures 4A-4B), the second directional scattering features 130 can be used to provide second emitted light 102" to effectively "fill in" between areas of emitted light 102 that include the first emitted light 102'. For example, providing emitted light 102 by filling in this manner can produce a more uniform emitted light 102 from the mode-selectable backlight 100 during the first operating mode. However, in the second operating mode, according to these embodiments, the second directional scattering features 130 can be employed alone or exclusively to provide multiple directional beams of second emitted light 102".

According to some embodiments, the mode-selectable backlight 100 may further include a plurality of light sources configured to provide guided light 104 having different propagation directions within the light guide 110. As shown in Figures 3A-3C, the mode-selectable backlight 100 may further include a first light source 140 and a second light source 150. The first light source 140 may be configured to provide guided light 104 having a first propagation direction within the light guide 110. Similarly, the second light source 150 may be configured to provide guided light 104 having a second propagation direction within the light guide 110.

In Figures 3A-3C, a first light source 140 is located on a first side of the light guide 110, and a second light source 150 is located on a second side of the light guide 110 that is orthogonal to the first side. As shown, the first light source 140 is configured to provide guided light 104 having a propagation direction (e.g., a first propagation direction) that is orthogonal to the propagation direction (e.g., a second propagation direction) of the guided light 104 that the second light source 150 is configured to provide. Figure 4A also shows the first light source 140, while Figure 4B shows the second light source 150 of the mode-selectable backlight 100.

In various embodiments, the first and second light sources 140, 150 may comprise substantially any source of light (e.g., a light emitter), including but not limited to one or more light emitting diodes (LEDs) or lasers (e.g., laser diodes). For example, the first and second light sources 140, 150 may each comprise an array of one or more LEDs distributed along the length of a corresponding side of the light guide 110. In some embodiments, one or both of the first and second light sources 140, 150 may comprise a light emitter configured to generate substantially monochromatic light having a narrow-band spectrum represented by a particular color. Specifically, the color of the monochromatic light may be a primary color of a particular color space or color model (e.g., a red-green-blue (RGB) color model). In other examples, one or both of the first and second light sources 140, 150 may comprise a substantially broadband light source configured to provide substantially broadband or multi-color light. For example, the broadband or multi-color light may be white light, and the first and second light sources 140, 150 may be white light sources. In some embodiments, one or both of the first and second light sources 140, 150 may comprise a plurality of different light emitters configured to provide light of different colors or a combination thereof to provide white light.

In some embodiments, one or both of the first and second light sources 140, 150 may further include a collimator (not shown). The collimator can be configured to receive substantially uncollimated light from one or more light emitters of the respective first and second light sources 140, 150 and convert the substantially uncollimated light into collimated light. Specifically, according to some embodiments, the collimator can provide collimated light having a non-zero propagation angle and being collimated according to one or more of a predetermined collimation factor σ. In addition, when light emitters of different colors are employed, the collimator can be configured to provide collimated light having one or both of different, color-specific, non-zero propagation angles and having different color-specific collimation factors. The collimator is also configured to transmit the collimated light to the light guide 110 for propagation as guided light 104, as described above.

In various examples, the collimator can include any of a variety of optical elements configured to collimate light, including but not limited to lenses, reflectors, and diffraction gratings. Another type of collimator that can be employed is a so-called tapered collimator, which includes a portion of a tapered light guide. Collimators that include various combinations of collimating structures can also be used, for example, a collimator that includes a portion of a tapered light guide and a collimating lens or reflector.

In some embodiments, one or both of the first light source 140 and the second light source 150 are configured to provide polarized light as guided light within the light guide. For example, the first and second light sources 140, 150 may include polarized light emitters. In another example, the first and second light sources 140, 150 may include polarizers at the output of the light sources 140, 150 or between the light sources 140, 150 and the light guide 110. According to various embodiments, one or both of the first directional scattering features 120 are configured to provide polarized first emitted light 102', and the second directional scattering feature 130 is configured to provide polarized second emitted light 102". In turn, according to these embodiments, each of the first and second directional scattering features 120, 130 is configured to provide polarized first and second emitted light 102', 102". from the polarized light provided by the first and second light sources 140, 150, respectively. For example, one or both of the first and second directional scattering features 120, 130 may be polarization-maintaining scattering features.

In some embodiments, the mode-selectable backlight 100 further includes a reflector layer 160. As shown in FIG3A , the reflector layer 160 is located near a second surface 110″ opposite the first surface 110′ (i.e., the emitting surface) of the light guide 110. The reflector layer 160 is configured to reflect light in a direction that returns the light toward the first surface 110′ of the light guide 110. For example, the reflector layer 160 can be configured to reflect light resulting from secondary scattering of one or both of the first directional scattering features 120 and the second directional scattering features 130. Secondary scattering is defined herein as scattering in a secondary direction away from the first surface 110′ of the light guide 110. In some embodiments, using the reflector layer 160 to reflect the secondary scattering can enhance the emission efficiency of the mode-selectable backlight 100 by increasing the brightness of the emitted light 102.

The reflector layer 160 may include any of a variety of reflective materials and layers. For example, the reflector layer 160 may include a reflective metal. Reflective metals include, but are not limited to, silver, aluminum, chromium, nickel, copper, and gold, as well as various alloys and combinations thereof. In another example, the reflector layer 160 may include an enhanced specular reflector (ESR), such as, but not limited to, Vikuiti ^™ enhanced specular reflector film available from 3M Optical Systems, St. Paul, MN. In some embodiments (e.g., as shown in FIG. 3A ), the reflector layer 160 may be separated from the second surface 110″ of the light guide 110 by a gap to avoid interference with the total internal reflection of the guided light 104 within the light guide 110. For example, the gap may be filled with air or other low refractive index optical material (e.g., an optical adhesive).

As described above, in some embodiments, the second directional scattering feature 130 may include a multi-beam element 132. Specifically, the second directional scattering feature 130 may include a plurality of multi-beam elements 132. Each multi-beam element 132 in the plurality of multi-beam elements may be configured to provide a plurality of directional light beams having different principal angular directions. In some embodiments, the size of a multi-beam element 132 in the plurality of multi-beam elements is comparable to the size of a light valve of a display employing the mode-selectable backlight 100. Specifically, the size of the multi-beam element 132 may be between approximately fifty percent and approximately two hundred percent of the size of the light valve. By way of example and not limitation, a light valve array 106 that can be used to modulate the emitted light 102 of the mode-selectable backlight 100 is shown in FIG. 3A .

For example, a display employing the mode-selectable backlight 100 may be a mode-selectable multi-view display. The light valve array 106 may be part of the mode-selectable multi-view display. The mode-selectable multi-view display may provide a single-dimensional or two-dimensional (2D) image in a first operating mode of the mode-selectable backlight 100 and provide a multi-view image in a second operating mode. Furthermore, in some embodiments, the principal axis directions of the directional light beams in the plurality of directional light beams correspond to the view directions of different views of the multi-view image.

Here, "size" can be defined in any of a variety of ways, including but not limited to length, width, or area. For example, the size of the light valve 106 can be its length, and the equivalent size of the multi-beam element 132 can also be a length, i.e., the length of the multi-beam element 132. In another example, the size can refer to an area such that the area of the multi-beam element 132 is comparable to the area of the light valve. In yet another example, the size of the multi-beam element 132 can be comparable to the spacing between adjacent light valves (e.g., the center-to-center distance or the inter-light valve spacing). According to some embodiments, for example, the equivalent sizes of the multi-beam element 132 and the light valve 106 can be selected to reduce, or in some examples, minimize, dark areas between views of the multi-view image provided by the mode-selectable multi-view display, while reducing, or in some examples, minimizing, overlap between the views.

In some embodiments (e.g., as shown in Figures 3A-3C), the mode-selectable backlight 100 can include a plurality of multi-beam elements 132 spaced apart from one another along the length of the lightguide. Specifically, the plurality of multi-beam elements 132 are separated from one another by a finite space and represent individual, distinct elements along the length of the lightguide. That is, as defined herein, the plurality of multi-beam elements 132 are spaced apart from one another according to a finite (i.e., non-zero) inter-element distance (e.g., a finite center-to-center distance). Furthermore, according to some embodiments, the plurality of multi-beam elements 132 generally do not intersect, overlap, or otherwise contact one another. In other words, each of the plurality of multi-beam elements 132 is generally distinct and separate from the other multi-beam elements 132.

According to some embodiments, the plurality of multi-beam elements 132 of or within the second directional scattering feature 130 may be arranged in a one-dimensional (1D) array or a two-dimensional (2D) array. For example, the plurality of multi-beam elements 132 may be arranged as a linear 1D array. In another example, the plurality of multi-beam elements 132 may be arranged as a rectangular 2D array or a circular 2D array. Furthermore, in some examples, the array (i.e., a 1D or 2D array) may be a regular or uniform array. Specifically, the inter-element distance (e.g., the center-to-center distance or spacing) between the multi-beam elements 132 may be substantially uniform or constant across the array. In other examples, the inter-element distance between the multi-beam elements 132 may vary across the array and along one or both of the lengths of the light guide 110.

According to various embodiments, multi-beam element 132 can include any of a variety of different types of scattering structures or "scatterers" that are configured to scatter or couple out a portion of guided light 104 from within light guide 110. Furthermore, these different types of scattering structures provide or can be configured (e.g., using orientation) to provide directional scattering to selectively scatter out guided light 104 having a second propagation direction. For example, the different scattering structures can include, but are not limited to, diffraction gratings, micro-reflective elements, micro-refractive elements, or various combinations thereof, each of which can be configured to provide directional scattering.

Specifically, in some embodiments, the multi-beam element 132 may include a diffraction grating configured to diffractively scatter a portion of the guided light 104 having the second propagation direction from the light guide 110 as a plurality of directional beams of second emitted light 102". The diffraction grating of the multi-beam element 132 may include a plurality of diffraction gratings or "sub-gratings". In other embodiments, the multi-beam elements 132 of the plurality of multi-beam elements may include a micro-reflective element configured to reflectively scatter a portion of the guided light 104 having the second propagation direction from the light guide 110 as a plurality of directional beams of second emitted light 102". Furthermore, in other embodiments, the multi-beam elements 132 of the plurality of multi-beam elements may include a micro-refractive element configured to refractively scatter a portion of the guided light 104 having the second propagation direction from the light guide 110 as a plurality of directional beams of second emitted light 102".

FIG5 shows a cross-sectional view of a portion of a mode-selective backlight 100 in an example according to an embodiment consistent with the principles described herein. As shown in FIG5 , the portion of the mode-selective backlight 100 includes a portion of a light guide 110, a portion of a first directional scattering feature 120 on a first surface 110 ′ of the light guide 110, and a portion of a second directional scattering feature 130 on a second surface 110 ″. Furthermore, as shown in FIG5 , the second directional scattering feature 130 includes a multi-beam element 132 implemented using a diffraction grating.

The diffraction grating of multi-beam element 132 is configured to diffractively couple out a portion of guided light 104 having a second propagation direction as multiple directional beams of second emitted light 102″. According to various embodiments, the spacing of the diffraction features in the diffraction grating, or the grating pitch, can be sub-wavelength (i.e., smaller than the wavelength of guided light 104). Moreover, multi-beam element 132, or equivalently the diffraction grating, has a dimension s, as shown in FIG5 , and an orientation of the diffraction features that provides selective scattering of guided light 104 having a second propagation direction (i.e., opposite to guided light 104 having the first propagation direction). FIG5 also shows a portion of reflector layer 160 adjacent to, but spaced apart from, multi-beam element 132. Thick arrow 103″ indicates the second propagation direction in FIG5 .

In some embodiments, the diffraction grating 132 of the multi-beam element can be a uniform diffraction grating having a diffraction feature spacing that is substantially constant or unchanging throughout the diffraction grating. In other embodiments, the diffraction grating is a chirped diffraction grating. By definition, a "chirped" diffraction grating is a diffraction grating that exhibits or has a diffraction feature spacing that varies over the extent or length of the chirped diffraction grating (i.e., the grating spacing). In some embodiments, a chirped diffraction grating can have or display a "chirp" or variation in the diffraction feature spacing that varies linearly with distance. Thus, by definition, a chirped diffraction grating is a "linearly chirped" diffraction grating. In other embodiments, a chirped diffraction grating can display a nonlinear chirp in the diffraction feature spacing. Various nonlinear chirps can be used, including but not limited to exponential chirps, logarithmic chirs, or chirs that vary in another, substantially non-uniform or random, but still monotonic, 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.

In some embodiments, multi-beam element 132, or equivalently, its diffraction grating, may include multiple diffraction gratings. Multiple diffraction gratings may also be referred to as multiple "sub-gratings" of the diffraction grating. The multiple diffraction gratings (or sub-gratings) of multi-beam element 132 may be arranged in a variety of different configurations to selectively scatter or diffractively couple out a portion of guided light 104 as multiple directional light beams. Specifically, the multiple diffraction gratings 122 of multi-beam element 132 may include a first diffraction grating and a second diffraction grating (or equivalently, a first sub-grating and a second sub-grating). The first diffraction grating may be configured to provide a first beam of the multiple directional light beams, while the second diffraction grating may be configured to provide a second beam of the multiple directional light beams. According to various embodiments, the first and second light beams may have different principal directions from each other. Furthermore, according to some embodiments, the multiple diffraction gratings may include a third diffraction grating, a fourth diffraction grating, and so on, each of which is configured to provide a different directional light beam.

In some embodiments, one or more of the plurality of diffraction gratings can provide more than one directional light beam. Furthermore, the different directional light beams provided by the diffraction gratings can have different principal angles along the horizontal axis (e.g., the x-direction or the θ angular component) and the vertical axis (e.g., the y-direction or the φ angular component). Controlling the different principal angles of the respective directional light beams provided by the diffraction gratings can facilitate multi-view displays with either or both horizontal parallax only, full two-dimensional parallax, and variations between horizontal parallax only and full parallax.

FIG6A shows a cross-sectional view of a portion of a mode-selectable backlight 100 including multiple diffraction gratings of a multi-beam element 132, according to an example of an embodiment consistent with the principles described herein. FIG6B shows a plan view of the multiple diffraction gratings shown in FIG6A, according to an example of an embodiment consistent with the principles described herein. For example, the cross-sectional view in FIG6A may represent a bottom row of cross-sections from left to right through the diffraction gratings shown in FIG6B. As shown in FIG6A and 6B, different diffraction gratings have different diffraction grating spacings or diffraction feature spacings than other diffraction gratings of the multiple diffraction gratings. In addition, as shown, some of the diffraction gratings have different grating orientations (i.e., different rotations). The dimensions s of the multi-beam element 132 including the multiple diffraction gratings are shown in both FIG6A and 6B, while the boundaries of the multi-beam element 132 are shown using dashed lines in FIG6B. In FIG6A-6B, the multi-beam element 132 shown may represent a portion of the second directional scattering feature 130 of the mode-selectable backlight 100. By way of example and not limitation, FIG. 6A also illustrates a portion of the light guide 110 and the first directional scattering features 120 .

According to some embodiments, the differential density of diffraction gratings (or sub-gratings) within the plurality of diffraction gratings between different multi-beam elements 132 of the mode-selectable backlight 100 can be configured to control the relative intensities of the plurality of directional light beams diffracted or coupled out by the corresponding different multi-beam elements 132. In other words, the multi-beam elements 132 can have different densities of diffraction gratings (or sub-gratings) therein, and the different densities (i.e., the differential densities of the diffraction gratings) can be configured to control the relative intensities of the plurality of directional light beams. For example, a multi-beam element 132 having fewer diffraction gratings (or sub-gratings) within the plurality of diffraction gratings can produce a plurality of directional light beams (or sub-gratings) having a lower intensity (or beam density) than another multi-beam element 132 having relatively more diffraction gratings. For example, locations within the multi-beam element 132 that lack or are not provided with diffraction gratings (or sub-gratings) can be used to provide a differential density of diffraction gratings (or sub-gratings).

FIG7A shows a plan view of a multibeam element 132a in an example according to an embodiment consistent with the principles described herein. FIG7B shows a plan view of another multibeam element 132b in an example according to an embodiment consistent with the principles described herein. The multibeam elements 132a, 132b shown in FIG7A and 7B together represent a pair of multibeam elements 132. In each multibeam element 132a, 132b of the multibeam element pair, a different plurality of diffraction gratings (or sub-gratings) is shown. Specifically, the first multibeam element 132a of the pair in FIG7A is shown as having a higher density of diffraction gratings (or sub-gratings) than the second multibeam element 132b of the pair. For example, as shown, the second multibeam element 132b has fewer diffraction gratings (or sub-gratings) and more locations without diffraction gratings than the first multibeam element 132a. By way of example and not limitation, Figures 7A-7B also illustrate diffraction gratings having curved diffraction features within the multi-beam elements 132a, 132b.

FIG8 shows a cross-sectional view of a portion of a mode-selectable backlight 100 including a multi-beam element 132, according to an example of another embodiment consistent with the principles described herein. Specifically, FIG8 shows an embodiment of a multi-beam element 132 including micro-reflective elements. Micro-reflective elements used as or in the multi-beam element 132 may include, but are not limited to, reflectors having a reflective material or layer (e.g., a reflective metal) employed therein or reflectors based on total internal reflection (TIR). According to some embodiments, the multi-beam element 132 including micro-reflective elements may be located on a surface of the light guide 110 (e.g., the second surface 110" as shown) or adjacent to a surface of the light guide 110. In other embodiments (not shown), the micro-reflective elements may be located within the light guide 110, between the first and second surfaces 110', 110".

For example, FIG8 shows a multi-beam element 132 comprising a micro-reflective element having reflective facets (e.g., “prismatic” micro-reflective elements) located adjacent the second surface 110″ of the light guide 110. The facets of the illustrated prismatic micro-reflective elements are configured to selectively reflect (i.e., reflectively couple) a portion of the guided light 104 having a second propagation direction out of the light guide 110. For example, the facets may be tilted or slanted (i.e., have an oblique angle) and aligned (i.e., rotationally oriented) relative to the second propagation direction of the guided light 104 to selectively reflect the guided light portion out of the light guide 110. According to various embodiments, the facets may be formed within the light guide 110 using a reflective material, or may be surfaces of a prismatic cavity in the second surface 110″. When a prismatic cavity is employed, in some embodiments, a refractive index variation at the cavity surface may provide reflection (e.g., TIR reflection), or the cavity surface forming the facets may be coated with a reflective material to provide reflection. FIG. 8 also shows a directed beam of second emitted light 102 ″ and a thick arrow 103 ″ indicating a second propagation direction of the guided light 104 .

FIG9 shows a cross-sectional view of a portion of a mode-selectable backlight 100 including a multi-beam element 132, according to an example of yet another embodiment consistent with the principles described herein. Specifically, FIG9 shows the multi-beam element 132 including a microrefractive element. According to various embodiments, the microrefractive element is configured to refractively scatter or couple out a portion of the guided light 104 having the second propagation direction from the light guide 110. 9 , the microrefractive elements are configured to employ refraction (e.g., as opposed to diffraction or reflection) to couple portions of the guided light out of the light guide 110 as a directional beam of second emitted light 102″. The microrefractive elements can have a variety of shapes, including but not limited to hemispherical, rectangular, or prismatic (i.e., shapes having angled facets) having a rotational orientation aligned with the second propagation direction of the guided light 104. According to various embodiments, the microrefractive elements can extend or protrude beyond a surface (e.g., first surface 110′) of the light guide 110, as shown, or can be a cavity in the surface (not shown). Furthermore, in some embodiments, the microrefractive elements can comprise the material of the light guide 110. In other embodiments, the microrefractive elements can comprise another material adjacent to, and in some examples, in contact with, the light guide surface.

In some embodiments, the mode-selectable backlight 100 is configured to be substantially transparent to light in a direction that is orthogonal to the direction of propagation of the guided light 104 through the light guide 110. Specifically, in some embodiments, the light guide 110, the spaced-apart plurality of multi-beam elements 132 of the first directional scattering features 120 and the second directional scattering features 130 can be configured to allow light to pass through the light guide 110 (i.e., through both the first surface 110' and the second surface 110"). For example, transparency can be at least partially facilitated by using diffraction gratings in the first and second directional scattering features 120, 130 because the diffraction gratings are substantially transparent to light propagating orthogonal to the light guide surfaces 110', 110".

According to some embodiments of the principles described herein, a mode-selectable display is provided. The mode-selectable display is configured to emit modulated light as pixels of the mode-selectable display. In a first operating mode, the emitted modulated light may be diffuse or unidirectional to display a two-dimensional (2D) image. In a second operating mode, the emitted modulated light comprises a plurality of emitted modulated directional light beams having directions different from each other. In some embodiments, the emitted modulated directional light beams may preferentially point to a plurality of different view directions of different views to display a multi-view image. Specifically, according to various examples, different modulated, differently pointed directional light beams may correspond to individual pixels of different views (i.e., view pixels) associated with the multi-view image. The different views may provide a "glasses-free" (e.g., autostereoscopic) representation of information in a multi-view image displayed by the mode-selectable display, for example, in the second operating mode. The mode-selectable display may also be referred to herein as a mode-selectable multi-view display.

Figure 10 shows a block diagram of a mode-selectable display 200 in an example of an embodiment consistent with the principles described herein. According to various embodiments, the mode-selectable display 200 is configured to display a 2D image in a first operating mode (mode 1) and to display a multi-view image according to different views in different view directions in a second operating mode (mode 2). Specifically, in the first operating mode, the modulated light 202 emitted by the mode-selectable display 200 as a first modulated emitted light 202' can be diffuse or unidirectional. The first modulated emitted light 202' can represent or be used to display a 2D image. In the second operating mode, the modulated light 202 emitted by the mode-selectable display 200 as a second modulated emitted light 202" includes a modulated directional light beam. The modulated light directional light beam of the second modulated emitted light 202" can represent or be used to display a multi-view image. Specifically, the modulated directional light beam can correspond to view pixels of different views of the multi-view image. The light beams of the modulated emitted light 202" are shown in Figure 10 using arrows with different directions.

The mode-selectable display 200 shown in FIG10 includes a light guide 210. The light guide 210 is configured to guide light as guided light. In some embodiments, the light guide 210 can be substantially similar to the light guide 110 of the mode-selectable backlight 100 described above. For example, the light guide 210 can be a plate light guide.

The mode-selectable display 200 also includes a plurality of light sources 220. The plurality of light sources 220 are configured to provide guided light having different propagation directions within the light guide. Specifically, the guided light is provided in different propagation directions in or during different operating modes of the mode-selectable display 200. In some embodiments, the plurality of light sources 220 can be substantially similar to the first and second light sources 140, 150 described above with respect to the mode-selectable backlight 100.

Specifically, a first light source of the plurality of light sources 220 can be substantially similar to the first light source 140, and a second light source of the plurality of light sources 220 can be substantially similar to the second light source 150. In some embodiments, the first light source 220 of the plurality of light sources can be located on a first side of the light guide 210, and the second light source 220 of the plurality of light sources can be located on a second side of the light guide 210 that is orthogonal to the first side. Furthermore, the first light source 220 can be configured to provide guided light having a propagation direction that is orthogonal, or at least substantially orthogonal, to the propagation direction of the guided light provided by the second light source 220. In some embodiments, the light sources 220 of the plurality of light sources are configured to provide the guided light within the light guide 210 as polarized guided light. For example, the plurality of light sources 220 can include polarized light emitters, or can include a polarizer to polarize the light emitted by the light emitters of the light sources 220.

As shown in FIG10 , the mode-selectable display 200 further includes a plurality of directional scattering features 230 configured to scatter the guided light from the light guide as emitted light 204. According to various embodiments, each directional scattering feature 230 of the plurality of directional scattering features is configured to selectively scatter the guided light having a different propagation direction. In some embodiments, a first directional scattering feature 230 of the plurality of directional scattering features can be substantially similar to the first directional scattering feature 120 described above with respect to the mode-selectable backlight 100. In some embodiments, a second directional scattering feature 230 of the plurality of directional scattering features can be substantially similar to the second directional scattering feature 130 of the mode-selectable backlight 100 described above. Specifically, the emitted light 204 during a selected one of the operating modes includes a plurality of directional light beams having different principal directions from one another. For example, a second directional scattering feature 230 of the plurality of directional scattering features can be configured to provide a plurality of directional light beams, e.g., similar to the directional light beams provided by the second directional scattering feature 130.

The mode-selectable display shown in Figure 10 also includes a light valve array 240. The light valve array 240 is configured to modulate the emitted light as a display image. Specifically, the light valve array 240 is configured to receive the emitted light 204 from the plurality of directional scattering features 230 and generate modulated light 202. In addition, in the first operating mode (mode 1), the light valve array 240 provides a first modulated emitted light 202', and in the second operating mode (mode 2), the light valve array 240 provides a second modulated emitted light 202", as shown. In various embodiments, different types of light valves can be used as the light valves 240 of the light valve array, including but not limited to one or more of liquid crystal light valves, electrophoretic light valves, and electrowetting-based light valves. In some embodiments, the light valve 240 can be substantially similar to the light valve 106 described above with respect to the mode-selectable backlight 100.

In some embodiments, the directional scattering features 230 configured to scatter a plurality of directional scattering features of the guided light during a selected one of the operating modes include a plurality of multi-beam elements. In some embodiments, the multi-beam elements can be substantially similar to the multi-beam elements 132 of the second directional scattering features 130 described above with respect to the mode-selectable backlight 100. For example, the multi-beam elements of the plurality of multi-beam elements can be configured to provide a plurality of directional light beams having different principal angles. Furthermore, for example, the multi-beam elements can have a size that is greater than half the size of the light valves 240 of the light valve array and less than twice the size of the light valves. In various embodiments, the multi-beam elements can include one or more of a micro-refractive element, a diffraction grating, and a micro-reflective element optically coupled to the light guide.

In some embodiments, the plurality of directional scattering features are configured to scatter polarized guided light from the light guide as emitted light 204 having a polarization corresponding to an input polarization of a light valve of the light valve array. The input polarization can be, for example, the input polarization of a liquid crystal cell serving as a light valve 240 of the light valve array. In some embodiments, the polarized guided light can be provided by a polarization light source 220 of the plurality of light sources, and the directional scattering features of the plurality of directional scattering features can be configured to preserve the polarization of the scattering features.

In some embodiments, the different principal directions of the multiple directional beams of emitted light 204 during a selected one of the operating modes may correspond to view directions of views of the multi-view display, and the displayed image may be a multi-view image. Furthermore, during another operating mode other than the selected one of the operating modes, the emitted light may have a diffuse pattern, and the displayed image may correspond to a two-dimensional (2D) image. Thus, the mode-selectable display 200 may be mode-selectable between displaying a 2D image and displaying a multi-view image. In other embodiments, the different principal directions of the multiple directional beams of emitted light during a selected one of the operating modes are directed toward a viewing frame of the mode-selectable display 200. In these embodiments, the mode-selectable display 200 may be configured to be mode-selectable so as to provide a displayed image in a privacy mode in which the displayed image is visible only within the viewing frame.

According to other embodiments of the principles described herein, methods of operating a mode-selective backlight are provided. FIG11 shows a flow chart of a method 300 of operating a mode-selective backlight in an example of an embodiment consistent with the principles described herein. As shown in FIG11 , the method 300 of operating a mode-selective backlight includes guiding 310 light as guided light in a light guide. In some embodiments, the light can be guided 310 at a non-zero propagation angle. Furthermore, the guided light can be collimated according to a predetermined collimation factor. Furthermore, in some embodiments, the guided light can be polarized. According to some embodiments, the light guide can be substantially similar to the light guide 110 described above with respect to the mode-selective backlight 100. Similarly, the guided light can be substantially similar to the guided light 104 also described above.

As shown in FIG11 , the method 300 of operating a multi-view backlight further includes scattering 320 guided light from the light guide as first emitted light using a first directional scattering feature during a first operating mode. According to various embodiments, the guided light has a first propagation direction during the first operating mode. Furthermore, the first directional scattering feature is configured to selectively scatter 320 guided light having the first propagation direction (e.g., opposite to another propagation direction). In some embodiments, the first directional scattering feature can be substantially similar to the first directional scattering feature 120 of the mode-selectable backlight 100 described above.

The method 300 of operating a multi-view backlight shown in Figure 11 also includes scattering 330 guided light from the light guide as second emitted light using a second directional scattering feature during a second operating mode. During the second operating mode, the guided light has a second propagation direction. According to various embodiments, the first and second propagation directions are different. In addition, the second emitted light includes a plurality of directional light beams having different principal directions from each other. In addition, the second directional scattering feature is configured to selectively scatter 330 guided light having a second propagation direction (e.g., opposite to another propagation direction such as the first propagation direction). In some embodiments, the second propagation direction of the guided light can be orthogonal to, or at least substantially orthogonal to, the first propagation direction of the guided light. In addition, in some embodiments, the second directional scattering feature can be substantially similar to the second directional scattering feature 130 described above with respect to the mode-selectable backlight 100.

Specifically, in some embodiments, the second directional scattering feature can include a plurality of multi-beam elements. Each of the plurality of multi-beam elements can be or include one or more of a micro-refractive element, a diffraction grating, and a micro-reflective element optically coupled to a light guide to provide a plurality of directional light beams having different principal angles. In some embodiments, the plurality of multi-beam elements can include a multi-beam element substantially similar to multi-beam element 132 of second directional scattering feature 130 described above.

In some embodiments (e.g., as shown), the method 300 of operating a mode-selectable backlight further includes providing 340 light to a light guide using a plurality of light sources, directing 310 the provided light as guided light. In various embodiments, the plurality of light sources may include a first light source configured to provide guided light having a first propagation direction within the light guide. The first light source may be configured to provide the guided light during the first operating mode. The plurality of light sources may also include a second light source configured to provide guided light having a second propagation direction within the light guide. The second light source may be configured to provide the guided light during the second operating mode. In some embodiments, the first light source may be located on a first side of the light guide, and the second light source may be located on a second side of the light guide that is orthogonal to the first side. The mutually orthogonal side positions of the first and second light sources may facilitate providing the guided light such that the first propagation direction is orthogonal to the second propagation direction. According to some embodiments, the plurality of light sources may be substantially similar to the plurality of light sources 220 of the mode-selectable display 200, and the first and second light sources may be substantially similar to the first and second light sources 140, 150, respectively, of the mode-selectable backlight 100 described above.

As shown in FIG11 , the method 300 for operating a mode-selectable backlight may further include modulating 350 emitted light using light valves of a light valve array. For example, the emitted light may be modulated 350 to display an image. Specifically, during a first operating mode, the light valve array may modulate 350 the first emitted light, and during a second operating mode, the light valve array may modulate 350 the second emitted light. Furthermore, during the second operating mode, the second emitted light comprises a plurality of directional light beams. In some embodiments, different principal directions of the plurality of directional light beams correspond to views of a multi-view display or, equivalently, to view directions of a multi-view image. Thus, during the second operating mode, the displayed image may be a multi-view image. In other embodiments, during the second operating mode, the different principal directions of the plurality of directional light beams of the second emitted light are directed toward a view frame of the displayed image. In these embodiments, the displayed image is displayed in a privacy mode, wherein the displayed image is visible only within the view frame.

In some embodiments, the light valves of the light valve array can be substantially similar to the light valves 240 of the light valve array described above with respect to the mode-selectable display 200. According to some embodiments, the size of the multi-beam element is comparable to the size of the light valves in the light valve array used to modulate the emitted light 350. For example, the multi-beam element can be larger than half the size of a view pixel and smaller than twice the size of a view pixel.

Thus, examples and embodiments of a mode-selectable backlight, a mode-selectable display, and a method of operating a mode-selectable backlight including a first directional scattering feature and a second directional scattering feature have been described. It should be understood that the above examples are merely illustrative of some of the many specific examples that demonstrate the principles described herein. Clearly, those skilled in the art can readily devise numerous other arrangements without departing from the scope of the following claims.

Claims (21)

1. A selectable backlight mode, including: An optical guide, configured to guide light as the light being guided; A first directional scattering feature is configured to provide a first emitted light from the guided light having a first propagation direction within the light guide during a first operating mode, the first emitted light having a diffuse pattern. A second directional scattering feature is configured to provide a second emitted light from the guided light having a second propagation direction within the light guide during a second operating mode. The second emitted light comprises a plurality of directional beams having different principal directions from each other, and the different principal directions correspond to the view directions of different views of a multi-view display employing the mode-selectable backlight. The first propagation direction is different from the second propagation direction. 2. The mode-selectable backlight according to claim 1, wherein the second directional scattering feature includes a plurality of multi-beam elements, each of the plurality of multi-beam elements being configured to provide the plurality of directional beams having different principal directions. 3. The mode-selectable backlight according to claim 2, wherein the size of the plurality of multi-beam elements is between 50% and 200% of the size of the light valve of the multi-view display. 4. The mode-selectable backlight according to claim 2, wherein the multi-beam element of the plurality of multi-beam elements includes one or more of the following: A diffraction grating is configured to diffractically scatter a portion of the guided light having the second propagation direction from the light guide as the plurality of directional beams; A microreflective element configured to reflectively scatter a portion of the guided light having the second propagation direction from the light guide as the plurality of directional beams; and A microrefractive element is configured to refractically scatter a portion of the guided light having the second propagation direction from the light guide as the plurality of directional beams. 5. The mode-selectable backlight according to claim 4, wherein the diffraction grating of the multi-beam element comprises a plurality of diffraction gratings. 6. The mode-selectable backlight according to claim 1, wherein the first directional scattering feature is located at a first surface of the light guide, and the second directional scattering feature is located at a second surface of the light guide opposite to the first surface, the second directional scattering feature being configured to scatter a portion of the guided light having the second propagation direction through the first surface to provide the second emitted light. 7. The mode-selectable backlight of claim 6 further includes a reflector layer adjacent to the second surface, the reflector layer being configured to reflect light emitted by the second directional scattering feature through the second surface of the light guide. 8. The mode-selectable backlight according to claim 1, further comprising: A first light source is configured to provide guided light having the first propagation direction within the light guide; A second light source is configured to provide the guided light having the second propagation direction within the light guide. The first light source is located on the first side of the light guide, and the second light source is located on the second side of the light guide that is orthogonal to the first side. 9. The mode-selectable backlight of claim 8, wherein one or both of the first light source and the second light source are configured to provide polarized light as the guided light within the light guide, one or both of the first directional scattering features are configured to provide polarized first emitted light, and the second directional scattering feature is configured to provide polarized second emitted light, each emitted light originating from polarized light provided by the first light source and the second light source, respectively. 10. A mode-selectable multi-view display, comprising a mode-selectable backlight according to claim 1, the mode-selectable multi-view display further comprising an array of light valves configured to modulate light emitted by the mode-selectable backlight, wherein during a first mode, the light valve array is configured to modulate the first emitted light, and during a second operating mode, the light valve array is configured to modulate the second emitted light of a directional beam comprising the plurality of directional beams, a set of light valves of the array corresponding to a multi-view pixel of the multi-view display during the second operating mode. 11. A mode-selectable display, comprising: An optical guide, configured to guide light; Multiple light sources are configured to provide guided light with different propagation directions within the light guide during different operating modes; Multiple directional scattering features are configured to scatter the guided light out of the light guide as emitted light, each of the multiple directional scattering features being configured to selectively scatter guided light with a different propagation direction; and An array of light valves is configured to modulate the emitted light into the displayed image. The emitted light during a selected operating mode comprises a plurality of directional beams having different principal directions from each other, and wherein, during a selected operating mode, the different principal directions of the plurality of directional beams of the emitted light correspond to the view directions of a view of a multi-view display displaying an image as a multi-view image, or point to the frame of the mode-selectable display, which is a display mode selectable display for providing an image displayed in a privacy mode in which the image displayed is only visible within the frame. 12. The mode-selectable display of claim 11, wherein the directional scattering features of the plurality of directional scattering features configured to scatter guided light during a selected operating mode include: a plurality of multi-beam elements configured to provide the plurality of directional beams having different principal directions and having a size greater than half the size of the light valves of the light valve array and less than twice the size of the light valves. 13. The mode-selectable display of claim 12, wherein the multi-beam element comprises one or more of a microrefractive element, a diffraction grating, and a microreflective element optically coupled to the light guide. 14. The mode-selectable display of claim 11, wherein a first light source of the plurality of light sources is located on a first side of the light guide, a second light source of the plurality of light sources is located on a second side of the light guide orthogonal to the first side, and the first light source is configured to provide guided light having a propagation direction orthogonal to the propagation direction of the guided light provided by the second light source. 15. The mode-selectable display of claim 11, wherein the light sources of the plurality of light sources are configured to provide guided light as polarized guided light within the light guide, and the plurality of directional scattering features are configured to scatter the polarized guided light out of the light guide as emitted light having a polarization corresponding to the input polarization of the light valves of the light valve array. 16. The mode-selectable display of claim 11, wherein, during an operating mode other than the selected operating mode, the emitted light has a diffuse pattern, and the displayed image corresponds to a two-dimensional (2D) image. 17. The mode-selectable display of claim 16, wherein the mode-selectable display is mode-selectable between displaying 2D images and displaying multi-view images. 18. A method for selecting the operating mode of a backlight, the method comprising: The light in the guide light is used as the guided light; During the first operating mode, guided light is scattered from the light guide as a first emitted light using a first directional scattering feature. The guided light has a first propagation direction during the first operating mode, and the first emitted light has a diffusion pattern. During the second operating mode, guided light is scattered from within the photoguide using a second directional scattering feature as a second emitted light, the guided light having a second propagation direction during the second operating mode. The second emitted light comprises a plurality of directional beams having different main directions from each other, and the different main directions correspond to the view directions of the views of the multi-view display, wherein the first propagation direction and the second propagation direction are orthogonal to each other. 19. The method for selective backlighting according to claim 18, wherein the second directional scattering feature comprises a plurality of multi-beam elements, each of the plurality of multi-beam elements being one or more of a microrefractive element, a microreflective element, and a diffraction grating optically coupled to the light guide to provide the plurality of directional beams having different principal directions. 20. The method for selective backlighting according to claim 18, further comprising using a plurality of light sources to provide light as guided light to the light guide to be guided, the plurality of light sources comprising: A first light source is configured to provide guided light having the first propagation direction within the light guide; A second light source is configured to provide guided light having the second propagation direction within the light guide. The first light source is located on the first side of the light guide, and the second light source is located on the second side of the light guide that is orthogonal to the first side. 21. The method of selective backlighting according to claim 18, further comprising modulating emitted light using an array of light valves to display an image, wherein during the first operating mode, the array of light valves modulates the first emitted light, and during the second operating mode, the array of light valves modulates the second emitted light comprising a directional beam of a plurality of directional beams, wherein the image displayed during the first operating mode is a two-dimensional image, and during the second operating mode, the image displayed is a multi-view image.