Patent Description:
Electronic displays are a nearly ubiquitous medium for communicating information to users of a wide variety of devices and products. Among the most commonly found electronic displays are the cathode ray tube (CRT), plasma display panels (PDP), liquid crystal displays (LCD), electroluminescent displays (EL), organic light emitting diode (OLED) and active matrix OLEDs (AMOLED) displays, electrophoretic displays (EP) and various displays that employ electromechanical or electrofluidic light modulation (e.g., digital micromirror devices, electrowetting displays, etc.). In general, electronic displays may be categorized as either active displays (i.e., displays that emit light) or passive displays (i.e., displays that modulate light provided by another source). Among the most obvious examples of active displays are CRTs, PDPs and OLEDs/AMOLEDs. Displays that are typically classified as passive when considering emitted light are LCDs and EP displays. Passive displays, while often exhibiting attractive performance characteristics including, but not limited to, inherently low power consumption, may find somewhat limited use in many practical applications given the lack of an ability to emit light.

To overcome the applicability limitations of passive displays associated with light emission, many passive displays are coupled to an external light source. The coupled light source may allow these otherwise passive displays to emit light and function substantially as an active display. Examples of such coupled light sources are backlights. Backlights are light sources (often so-called 'panel' light sources) that are placed behind an otherwise passive display to illuminate the passive display. For example, a backlight may be coupled to an LCD or an EP display. The backlight emits light that passes through the LCD or the EP display. The light emitted by the backlight is modulated by the LCD or the EP display and the modulated light is then emitted, in turn, from the LCD or the EP display. Often backlights are configured to emit white light. Color filters are then used to transform the white light into various colors used in the display. The color filters may be placed at an output of the LCD or the EP display (less common) or between the backlight and the LCD or the EP display, for example.

<CIT> describes a backlight assembly for use in a transmissive display which includes a light source that illuminates a light chamber. The backlight assembly includes specular reflectors to ensure that the light that exits the light chamber and illuminates a transmissive display positioned adjacent the light chamber. <CIT> describes a backlight which includes a plate light and a collimating reflector to collimate light and direct the collimated light into the plate light guide. <CIT> describes a backlight which includes a light guide and a multibeam diffraction grating at a surface of the light guide.

Various features of examples and embodiments accordance with the principles described herein may be more readily understood with reference to the following detailed description taken in conjunction with the accompanying drawings, where like reference numerals designate like structural elements, and in which:.

Certain examples have other features that are one of in addition to and in lieu of the features illustrated in the above-referenced figures.

Embodiments and examples in accordance with the principles described herein provide dual-direction collimation and display backlighting using the dual-direction collimation. In particular, embodiments of the principles described herein provide dual-direction light collimation that includes collimating light separately in a vertical direction and in a horizontal direction. Moreover, in some embodiments, the light may be collimated in a vertical direction followed by the vertically collimated light being separately collimated in a horizontal direction. In addition, dual-direction collimation described herein provides dual-direction collimated light having a predetermined, non-zero propagation angle in a vertical plane corresponding to the vertical direction.

The dual-direction collimation is provided by a dual-direction collimator comprising a vertical collimator (e.g., vertical collimating reflector) coupled at an output to a horizontal collimator (e.g., horizontal collimating reflector). Light from a light source (e.g., a plurality of LEDs) may be coupled into the dual-direction collimator for dual-direction collimation. The dual-direction collimated light from the dual-direction collimator is coupled into a plate light guide of a backlight used in an electronic display. For example, the backlight may be a grating-based backlight including, but not limited to, a grating-based backlight having a multibeam diffraction grating. In some embodiments, the electronic display may be a three-dimensional (3D) electronic display used to display 3D information, e.g., an autostereoscopic or 'glasses free' 3D electronic display.

In particular, a 3D electronic display may employ a grating-based backlight having an array of multibeam diffraction gratings. The multibeam diffraction gratings may be used to couple light from a light guide and to provide coupled-out light beams corresponding to pixels of the 3D electronic display. For example, the coupled-out light beams may have different principal angular directions (also referred to as 'the differently directed light beams') from one another. According to some embodiments, these differently directed light beams produced by the multibeam diffraction grating may be modulated and serve as 3D pixels corresponding to 3D views of the 'glasses free' 3D electronic display to display 3D information. In these embodiments, the dual-direction collimation provided by the dual-direction collimator may be used to produce output dual-direction collimated light that is substantially uniform (i.e., without striping) within the light guide. In turn, uniform illumination of the multibeam diffraction gratings may be provided, in accordance with the principles described herein.

Herein, a 'light guide' is defined as a structure that guides light within the structure using total internal reflection. In particular, the light guide may include a core that is substantially transparent at an operational wavelength of the light guide. In various examples, the term 'light guide' generally refers to a dielectric optical waveguide that employs total internal reflection to guide light at an interface between a dielectric material of the light guide and a material or medium that surrounds that light guide. By definition, a condition for total internal reflection is that a refractive index of the light guide is greater than a refractive index of a surrounding medium adjacent to a surface of the light guide material. In some embodiments, the light guide may include a coating in addition to or instead of the aforementioned refractive index difference to further facilitate the total internal reflection. The coating may be a reflective coating, for example. The light guide may be any of several light guides including, but not limited to, one or both of a plate or slab guide and a strip guide.

Further herein, the term 'plate' when applied to a light guide as in a 'plate light guide' is defined as a piece-wise or differentially planar layer or sheet, which is sometimes referred to as a 'slab' guide. In particular, a plate light guide is defined as a light guide configured to guide light in two substantially orthogonal directions bounded by a top surface and a bottom surface (i.e., opposite surfaces) of the light guide. Further, by definition herein, the top and bottom surfaces are both separated from one another and may be substantially parallel to one another in at least a differential sense. That is, within any differentially small region of the plate light guide, the top and bottom surfaces are substantially parallel or co-planar.

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

According to various embodiments described herein, a diffraction grating (e.g., a multibeam diffraction grating) may be employed to scatter or couple light out of a light guide (e.g., a plate light guide) as a light beam. Herein, a 'diffraction grating' is generally defined as a plurality of features (i.e., diffractive features) arranged to provide diffraction of light incident on the diffraction grating. In some examples, the plurality of features may be arranged in a periodic or quasi-periodic manner. For example, the plurality of features (e.g., a plurality of grooves in a material surface) of the diffraction grating may be arranged in a one-dimensional (<NUM>-D) array. In other examples, the diffraction grating may be a two-dimensional (<NUM>-D) array of features. The diffraction grating may be a <NUM>-D array of bumps on or holes in a material surface, for example.

As such, and by definition herein, the 'diffraction grating' is a structure that provides diffraction of light incident on the diffraction grating. If the light is incident on the diffraction grating from a light guide, the provided diffraction or diffractive scattering may result in, and thus be referred to as, 'diffractive coupling' in that the diffraction grating may couple light out of the light guide by diffraction. The diffraction grating also redirects or changes an angle of the light by diffraction (i.e., at a diffractive angle). In particular, as a result of diffraction, light leaving the diffraction grating (i.e., diffracted light) generally has a different propagation direction than a propagation direction of the light incident on the diffraction grating (i.e., incident light). The change in the propagation direction of the light by diffraction is referred to as 'diffractive redirection' herein. Hence, the diffraction grating may be understood to be a structure including diffractive features that diffractively redirects light incident on the diffraction grating and, if the light is incident from a light guide, the diffraction grating may also diffractively couple out the light from light guide.

Further, by definition herein, the features of a diffraction grating are referred to as 'diffractive features' and may be one or more of at, in and on a surface (i.e., wherein a 'surface' refers to a boundary between two materials). The surface may be a surface of a plate light guide. The diffractive features may include any of a variety of structures that diffract light including, but not limited to, one or more of grooves, ridges, holes and bumps, and these structures may be one or more of at, in and on the surface. For example, the diffraction grating may include a plurality of parallel grooves in a material surface. In another example, the diffraction grating may include a plurality of parallel ridges rising out of the material surface. The diffractive features (whether grooves, ridges, holes, bumps, etc.) may have any of a variety of cross sectional shapes or profiles that provide diffraction including, but not limited to, one or more of a sinusoidal profile, a rectangular profile (e.g., a binary diffraction grating), a triangular profile and a saw tooth profile (e.g., a blazed grating).

By definition herein, a 'multibeam diffraction grating' is a diffraction grating that produces coupled-out light that includes a plurality of light beams. Further, the light beams of the plurality produced by a multibeam diffraction grating have different principal angular directions from one another, by definition herein. In particular, by definition, a light beam of the plurality has a predetermined principal angular direction that is different from another light beam of the light beam plurality as a result of diffractive coupling and diffractive redirection of incident light by the multibeam diffraction grating. The light beam plurality may represent a light field. For example, the light beam plurality may include eight light beams that have eight different principal angular directions. The eight light beams in combination (i.e., the light beam plurality) may represent the light field, for example. According to various embodiments, the different principal angular directions of the various light beams are determined by a combination of a grating pitch or spacing and an orientation or rotation of the diffractive features of the multibeam diffraction grating at points of origin of the respective light beams relative to a propagation direction of the light incident on the multibeam diffraction grating.

In particular, a light beam produced by the multibeam diffraction grating has a principal angular direction given by angular components {θ, ϕ}, by definition herein. 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, herein. By definition, the elevation angle θ is an angle in a vertical plane (e.g., perpendicular to a plane of the multibeam diffraction grating) while the azimuth angle ϕ is an angle in a horizontal plane (e.g., parallel to the multibeam diffraction grating plane). <FIG> illustrates the angular components {θ, ϕ} of a light beam <NUM> having a particular principal angular direction, according to an example of the principles describe herein. In addition, the light beam <NUM> is emitted or emanates from a particular point, by definition herein. That is, by definition, the light beam <NUM> has a central ray associated with a particular point of origin within the multibeam diffraction grating. <FIG> also illustrates the light beam point of origin O. An example propagation direction of incident light is illustrated in <FIG> using a bold arrow <NUM>.

According to various embodiments, characteristics of the multibeam diffraction grating and features thereof, may be used to control one or both of the angular directionality of the light beams and a wavelength or color selectivity of the multibeam diffraction grating with respect to one or more of the light beams. The characteristics that may be used to control the angular directionality and wavelength selectivity include, but are not limited to, one or more of a grating length, a grating pitch (feature spacing), a shape of the features, a size of the features (e.g., groove or ridge width), and an orientation of the grating. In some examples, the various characteristics used for control may be characteristics that are local to a vicinity of the point of origin of a light beam.

According to various embodiments described herein, the light coupled out of the light guide by the diffraction grating (e.g., a multibeam diffraction grating) represents a pixel of an electronic display. In particular, the light guide having a multibeam diffraction grating to produce the light beams of the plurality having different principal angular directions may be part of a backlight of or used in conjunction with an electronic display such as, but not limited to, a 'glasses free' three-dimensional (3D) electronic display (also referred to as a multiview or 'holographic' electronic display or an autostereoscopic display). As such, the differently directed light beams produced by coupling out guided light from the light guide using the multibeam diffractive grating may be or represent '3D pixels' of the 3D electronic display. Further, the 3D pixels correspond to different 3D views or 3D view angles of the 3D electronic display.

Herein a 'collimating' reflector is defined as a reflector having a curved shape that is configured to collimate light reflected by the collimating reflector (e.g., a collimating mirror). For example, the collimating reflector may have a reflecting surface characterized by a parabolic curve or shape. In another example, the collimating reflector may comprise a shaped parabolic reflector. By 'shaped parabolic' it is meant that a curved reflecting surface of the shaped parabolic reflector deviates from a 'true' parabolic curve in a manner determined to achieve a predetermined reflection characteristic (e.g., a degree of collimation). In some embodiments, the collimating reflector may be a continuous reflector (i.e., having a substantially smooth, continuous reflecting surface), while in other embodiments, the collimating reflector may comprise a Fresnel reflector or Fresnel mirror that provides light collimation. According to various embodiments, an amount of collimation provided by the collimating reflector may vary in a predetermined degree or amount from one embodiment to another. Further, the collimating reflector may be configured to provide collimation in one or both of two orthogonal directions (e.g., a vertical direction and a horizontal direction). That is, the collimating reflector may include a parabolic shape in one or both of two orthogonal directions, according to some embodiments.

Herein, a 'light source' is defined as a source of light (e.g., an apparatus or device that emits light). For example, the light source may be a light emitting diode (LED) that emits light when activated. Herein, a light source may be substantially any source of light or optical emitter including, but not limited to, one or more of a light emitting diode (LED), a laser, an organic light emitting diode (OLED), a polymer light emitting diode, a plasma-based optical emitter, a fluorescent lamp, an incandescent lamp, and virtually any other source of light. The light produced by a light source may have a color or may include a particular wavelength of light. As such, a 'plurality of light sources of different colors' is explicitly defined herein as a set or group of light sources in which at least one of the light sources produces light having a color, or equivalently a wavelength, that differs from a color or wavelength of light produced by at least one other light source of the light source plurality. Moreover, the 'plurality of light sources of different colors' may include more than one light source of the same or substantially similar color as long as at least two light sources of the plurality of light sources are different color light sources (i.e., produce a color of light that is different between the at least two light sources). Hence, by definition herein, a plurality of light sources of different colors may include a first light source that produces a first color of light and a second light source that produces a second color of light, where the second color differs from the first color.

Further, as used herein, the article 'a' is intended to have its ordinary meaning in the patent arts, namely 'one or more'. For example, 'a grating' means one or more gratings and as such, 'the grating' means 'the grating(s)' herein. Also, any reference herein to 'top', 'bottom', 'upper', 'lower', 'up', 'down', 'front', back', 'first', 'second', 'left' or 'right' is not intended to be a limitation herein. Herein, the term 'about' when applied to a value generally means within the tolerance range of the equipment used to produce the value, or may mean plus or minus <NUM>%, or plus or minus <NUM>%, or plus or minus <NUM>%, unless otherwise expressly specified. Further, the term 'substantially' as used herein means a majority, or almost all, or all, or an amount within a range of about <NUM>% to about <NUM>%. Moreover, examples herein are intended to be illustrative only and are presented for discussion purposes and not by way of limitation.

According to some embodiments, a dual-direction optical collimator is provided. <FIG> illustrates a perspective view of a dual-direction optical collimator <NUM> in an example, according to an embodiment of the principles described herein. <FIG> illustrates a top view of a dual-direction optical collimator <NUM> in an example, according to an embodiment of the principles described herein. <FIG> illustrates a cross sectional view of a portion of the dual-direction optical collimator <NUM> illustrated in <FIG>, according to an embodiment of the principles described herein. In particular, the cross section illustrated in <FIG> is indicated in <FIG>. According to various embodiments, the dual-direction optical collimator <NUM> is configured to collimate received light in or with respect to at least two different directions.

In particular, as illustrated in <FIG> and <FIG>, the dual-direction optical collimator <NUM> is configured to receive light <NUM>. In some examples, the light <NUM> received by the dual-direction optical collimator <NUM> may be substantially uncollimated light. For example, the light <NUM> may be provided by and thus be received from a substantially uncollimated light source (not illustrated). In another example, the received light <NUM> may be partially collimated light (e.g., provided by a light source that includes a lens or using some other partial collimation means).

The dual-direction optical collimator <NUM> illustrated in <FIG> is configured to collimate the received light <NUM> and to provide collimated light <NUM> at an output of the dual-direction optical collimator <NUM> (e.g., an output port, an output plane, an output surface, etc.). The collimated light <NUM> provided at the dual-direction optical collimator output is collimated or at least substantially collimated in at least two directions, according to various embodiments. As such, the collimated light <NUM> may be referred to as 'dual-direction' collimated light <NUM>.

In particular, the dual-direction collimated light <NUM> is collimated in two directions that are generally orthogonal to a propagation direction of the dual-direction collimated light <NUM>, by definition herein. Further, by definition, the two collimation directions are mutually orthogonal to one another. For example, the dual-direction collimated light <NUM> may be collimated in or with respect to a horizontal direction (e.g., in an x-y plane) and also in or with respect to a vertical direction (e.g., a z-direction). Herein the dual-direction collimated light <NUM> provided by the dual-direction optical collimator <NUM> is referred to as being both horizontally collimated and vertically collimated or equivalently collimated in both a horizontal direction and vertical direction by way of example and not limitation (i.e., the horizontal and vertical directions may be determined relative to an arbitrary reference frame, for example).

Further according to various embodiments, the dual-direction optical collimator <NUM> is configured to provide the dual-direction collimated light <NUM> at a non-zero propagation angle at the dual-direction optical collimator output. For example, the non-zero propagation angle may be an angle relative to or defined with respect to a horizontal plane of the dual-direction optical collimator <NUM>. As defined herein, the 'non-zero propagation angle' is an angle relative to a plane (e.g., the horizontal or x-y plane) or equivalently to a surface of a light guide, as described herein. In some examples, the non-zero propagation angle of the dual-direction collimated light <NUM> may be between about ten (<NUM>) degrees and about fifty (<NUM>) degrees or, in some examples, between about twenty (<NUM>) degrees and about forty (<NUM>) degrees, or between about twenty-five (<NUM>) degrees and about thirty-five (<NUM>) degrees. For example, the non-zero propagation angle may be about thirty (<NUM>) degrees. In other examples, the non-zero propagation angle may be about <NUM> degrees, or about <NUM> degrees, or about <NUM> degrees. Further, according to some embodiments, the non-zero propagation angle is both greater than zero and less than a critical angle of total internal reflection within a light guide, as described below.

As illustrated in <FIG>, the dual-direction optical collimator <NUM> comprises a vertical collimator <NUM>. The vertical collimator <NUM> is configured to collimate light in a vertical direction (i.e., in a z-direction). <FIG> illustrates a cross sectional view of the vertical collimator <NUM> in an example according to an embodiment of the principles herein. Further <FIG> illustrates the received light <NUM> as an arrow entering the vertical collimator <NUM>, e.g., at an input of the vertical collimator <NUM>. Light exiting the vertical collimator <NUM> as 'vertically' collimated light <NUM>' after being collimated in the vertical direction is also illustrated in <FIG> as another arrow (i.e., dashed-line arrow in both <FIG>). According to various embodiments, the vertical collimator <NUM> may comprise any of a variety of collimator types including, but not limited to, a collimating optical reflector, a collimating lens and a diffraction grating configured to provide collimation.

In particular, as illustrated in <FIG>, the vertical collimator <NUM> may comprise an optical reflector <NUM> having a parabolic shape. The parabolic shape of the optical reflector <NUM> is configured to provide the vertical-direction collimation. In some embodiments, the parabolic shape of the optical reflector <NUM> may have a so-called 'purely' parabolic shape. In other embodiments, the parabolic shape of the optical reflector <NUM> may be adjusted, optimized or otherwise 'shaped' to enhance or tweak collimation characteristics of the optical reflector <NUM>. For example, the parabolic shape of the optical reflector <NUM> may be tweaked as a shaped parabolic reflector to optimize vertical collimation of light <NUM> received from a light source that includes some directional distortion or partial (albeit non-ideal or undesirable) collimation. As such, the optical reflector <NUM> may be referred to as a 'shaped' parabolic reflector <NUM>. Further, the shaped parabolic reflector <NUM> may be shaped or shape-optimized in both the vertical direction (e.g., to control or optimize vertical collimation) and the horizontal direction. For example, in addition to being shaped in the vertical direction, the shaped parabolic reflector <NUM> may be shape-optimized in the horizontal direction to determine or provide control of a distribution (e.g., a width or a spread) of the vertically collimated light <NUM>' in the horizontal direction. Nevertheless, for ease of discussion herein, the optical reflector <NUM> of the vertical collimator <NUM> is generally referred to as having 'a parabolic shape,' whether the optical reflector <NUM> has a purely parabolic shape or is a shaped parabolic reflector <NUM>, unless an explicit distinction is necessary for proper understanding.

According to the invention (e.g., as illustrated in <FIG>), the optical reflector <NUM> of the vertical collimator <NUM> includes a tilt angle (i.e., the optical reflector <NUM> may be tilted at the tilt angle). The tilt angle is configured to provide a non-zero propagation angle of the vertically collimated light <NUM>', and by extension, to provide the non-zero propagation angle (or at least a portion thereof) of the dual-direction collimated light <NUM>. In other words, the optical reflector <NUM> itself may be tilted. In some examples, the tilt angle may be provided by a 'shaping' of the shaped parabolic reflector <NUM> instead of or in addition to an actual or physical tilting of the optical reflector <NUM> itself. In yet another example, the tilt angle may be provided by a shift in a location of the light source that provides the received light <NUM> relative to the focus of a parabola of the optical reflector <NUM>.

<FIG> illustrates a schematic representation of an optical reflector having a tilt in an example, according to an embodiment consistent with the principles described herein. In particular, as illustrated in <FIG>, the optical reflector <NUM> is tilted downward at a tilt angle corresponding to or configured to provide vertically collimated light <NUM>' having a non-zero propagation angle θ'. <FIG> also illustrates a dashed line representing a horizontal plane H from which the non-zero propagation angles θ' are defined. Further, <FIG> illustrates using another (e.g., bold) dashed line an example optical reflector <NUM>' that is not tilted to show the tilt angle θ' of the tilted optical reflector <NUM>. Note, as illustrated, the tilt angle θ' of the tilted optical reflector <NUM> and the non-zero propagation angle θ' are equal to one another, by example and not limitation. Light <NUM> received from a light source in a vicinity of a focus F of the optical reflector <NUM> is illustrated in <FIG> as a pair of diverging light rays (i.e., solid line arrows) incident on the optical reflector <NUM>. Similarly, the vertically collimated light <NUM>' exiting the optical reflector <NUM> is illustrated as a pair of rays (i.e., dashed line arrows) that are substantially parallel to one another. Further, the vertically collimated light rays <NUM>' are illustrated having the non-zero propagation angle θ' provided by the optical reflector tilt angle.

Referring again to <FIG>, the dual-direction optical collimator <NUM> further comprises a horizontal collimator <NUM>. The horizontal collimator <NUM> is configured to collimate light in the horizontal direction (i.e., in a x-y plane, as illustrated) that is substantially orthogonal to the vertical direction (i.e., z-direction, as illustrated). According to various embodiments, the horizontal collimator <NUM> is located to receive the vertically collimated light <NUM>' from the vertical collimator <NUM>. In particular, as illustrated in <FIG>, the horizontal collimator <NUM> is located adjacent to an output of the vertical collimator <NUM>. The horizontal collimator <NUM> is configured to horizontally collimate the vertically collimated light <NUM>' from the vertical collimator <NUM> to provide the dual-direction collimated light <NUM> at an output of the dual-direction optical collimator <NUM>.

<FIG> illustrates a top view of the horizontal collimator <NUM> depicting the vertically collimated light <NUM>' as light rays (i.e., as dashed line arrows) exiting the vertical collimator <NUM> and impinging on the horizontal collimator <NUM>. Light exiting the horizontal collimator <NUM> as the dual-direction collimated light <NUM> (i.e., both horizontally and vertically collimated) is illustrated as a plurality of substantially parallel rays propagating away from the horizontal collimator <NUM>. According to various embodiments, the horizontal collimator <NUM> may comprise any of a variety of collimator types including, but not limited to, a collimating optical reflector, a collimating lens and a diffraction grating configured to provide collimation.

In particular, as illustrated in <FIG> and <FIG>, the horizontal collimator <NUM> may comprise an optical reflector <NUM> having a parabolic shape. The parabolic shape of the optical reflector <NUM> is configured to provide the horizontal-direction collimation. As with the optical reflector <NUM> of the vertical collimator <NUM>, in some embodiments, the parabolic shape of the optical reflector <NUM> of the horizontal collimator <NUM> may have a so-called 'purely' parabolic shape. In other embodiments, the parabolic shape may be adjusted, optimized or otherwise 'shaped' to enhance or tweak collimation characteristics of the optical reflector <NUM>. For example, the parabolic shape of the optical reflector <NUM> may be tweaked as a shaped parabolic reflector to optimize horizontal collimation of the vertically collimated light <NUM>' received from the vertical collimator <NUM>. In particular, the tweaked, shaped parabolic optical reflector <NUM> may be optimized to horizontally collimate some directional distortion or other non-ideal or undesirable collimation artifacts in the vertically collimated light <NUM>'. As such, the optical reflector <NUM> of the horizontal collimator <NUM> may be referred to as a 'shaped' parabolic reflector <NUM>. For ease of discussion herein, the optical reflector <NUM> of the horizontal collimator <NUM> is generally referred to as having 'a parabolic shape,' whether the optical reflector <NUM> has a purely parabolic shape or is a shaped parabolic reflector <NUM>, unless an explicit distinction is necessary for proper understanding.

Further, in some embodiments (not illustrated), the optical reflector <NUM> of the horizontal collimator <NUM>, may include a tilt angle. In some embodiments, the tilt angle may be configured to provide the non-zero propagation angle of the dual-direction collimated light <NUM>. In other embodiments, the tilt angle may be configured to provide a portion of the non-zero propagation angle to augment a portion of the non-zero propagation angle provided by the vertical collimator <NUM>. In other words, the optical reflector <NUM> itself or equivalently a parabolic shape of the optical reflector <NUM>, may be tilted. In some examples, the tilt angle may be provided by a 'shaping' of the shaped parabolic reflector <NUM> instead of or in addition to an actual or physical tilting of the optical reflector <NUM>. In yet another example, the tilt angle may be provided by a shift in a location of the vertical collimator <NUM> relative to the focus of a parabola of the optical reflector <NUM> of the horizontal collimator <NUM>. In addition, when another type of collimator (e.g., a collimating lens or a diffraction grating) is employed, the other collimator type may be 'tilted' to provide the tilt angle, according to various embodiments.

As illustrated in <FIG> and <FIG>, the optical reflector <NUM> of the horizontal collimator <NUM> may be configured to substantially span an output aperture of the dual-direction optical collimator <NUM>. In some embodiments, the horizontal collimator <NUM> is configured to provide the dual-direction collimated light <NUM> having a substantially uniform distribution across the output aperture. In particular, the optical reflector <NUM> may span the output aperture to provide the substantially uniform distribution of the dual-direction collimated light <NUM>.

In some embodiments, the optical reflector <NUM> of the horizontal collimator <NUM> may comprise a plurality of sub-reflectors <NUM>'. In particular, the sub-reflectors <NUM>' may be configured in combination to substantially span the output aperture of the dual-direction optical collimator <NUM>. According to various embodiments, each sub-reflector <NUM>' may comprise a parabolic-shaped reflective surface. For example, the optical reflector <NUM> may be a Fresnel reflector.

<FIG> illustrates a top view of a dual-direction optical collimator <NUM> in an example, according to an embodiment consistent with the principles described herein. In particular, <FIG> illustrates the optical reflector <NUM> of the horizontal collimator <NUM> as a Fresnel reflector having a plurality of sub-reflectors <NUM>'. The vertical collimator <NUM> is illustrated in <FIG> along with the dual-direction collimated light <NUM>.

<FIG> illustrates a top view of a dual-direction optical collimator <NUM> in an example, according to another embodiment consistent with the principles described herein. In particular, <FIG> illustrates the dual-direction optical collimator <NUM> comprising a horizontal collimator <NUM> having a plurality of sub-reflectors <NUM>' along with a plurality of vertical collimators <NUM>. As illustrated in <FIG>, a first sub-reflector <NUM>'a of the horizontal collimator sub-reflector plurality is configured to receive vertically collimated light <NUM>' from a first vertical collimator 110a of the vertical collimator plurality located at a first edge 120a of the horizontal collimator <NUM>. Further, a second sub-reflector <NUM>'b of the horizontal collimator sub-reflector plurality is configured to receive the vertically collimated light <NUM>' from a second vertical collimator 110b of the vertical collimator plurality located at a second edge 120b of the horizontal collimator <NUM>. The second edge 120b is opposite to the first edge 120a in the horizontal plane corresponding to the horizontal direction, as illustrated. Also illustrated in <FIG>, example rays of the dual-direction collimated light <NUM> are illustrated exiting the output aperture of the dual-direction optical collimator <NUM>.

<FIG> illustrates a top view of a dual-direction optical collimator <NUM> in an example, according to yet another embodiment consistent with the principles described herein. In particular, <FIG> illustrates the dual-direction optical collimator <NUM> comprising a horizontal collimator <NUM> having a plurality of sub-reflectors <NUM>' along with a plurality of vertical collimators <NUM>. As illustrated in <FIG>, a first sub-reflector <NUM>'a of the sub-reflector plurality is configured to receive vertically collimated light <NUM>' from a second vertical collimator 110b of the vertical collimator plurality that is located at a second edge 120b of the horizontal collimator <NUM> opposite to the first sub-reflector <NUM>'a. Further, a second sub-reflector <NUM>'b of the sub-reflector plurality is configured to receive vertically collimated light <NUM>' from a first vertical collimator 110a of the vertical collimator plurality that is located at the first edge 120a opposite to the second sub-reflector <NUM>'b, as illustrated in <FIG>. In other words, the sub-reflectors <NUM>'a, <NUM>'b in <FIG> are configured to receive the vertically collimated light <NUM>' from respective opposite edges of the horizontal collimator <NUM>, as compared to the dual-direction optical collimator <NUM> illustrated in <FIG>. Moreover, the dual-direction optical collimator <NUM> of <FIG> is configured to provide the dual-direction collimated light <NUM> to the output aperture of the dual-direction optical collimator <NUM>, as further illustrated in <FIG>.

Although not explicitly illustrated, the dual-direction optical collimator <NUM> may include a sub-reflector plurality having more than two sub-reflectors <NUM>'. Similarly, the vertical collimator <NUM> may comprise a plurality of vertical collimators <NUM> that includes more than two individual vertical collimators <NUM>. For example, each of the two sub-reflectors <NUM>', <NUM>'a, <NUM>'b of <FIG> may be further divided into two or more sub-reflectors (e.g., a plurality of sub-sub-reflectors). Further, the plurality of vertical collimators <NUM> including more than two individual vertical collimators <NUM> may be used to provide vertically collimated light <NUM>' to the more than two sub-reflectors (e.g., one vertical collimator for each sub-sub-reflector). Moreover, different vertical collimators <NUM> may be employed for different colors of received light <NUM> to provide different colors of vertically collimated light <NUM>' to the optical reflector <NUM> (i.e., including sub-reflectors <NUM>') of the horizontal collimator <NUM>.

In particular, any of a number of different sub-reflector/vertical collimator configurations may be employed without departing from the scope of the principles described herein. Moreover, the use of various different sub-reflector/vertical collimator configurations may facilitate scanning of the dual-direction collimated light <NUM> across the output aperture as well as may provide increased brightness (e.g., using multiple light sources) of the dual-direction collimated light <NUM>, according to some embodiments.

In some embodiments, one or both of the vertical collimator <NUM> and the horizontal collimator <NUM> may comprise a substantially optically transparent material. In addition, portions of the dual-direction optical collimator <NUM> between the vertical collimator <NUM> and the horizontal collimator <NUM> as well as between the horizontal collimator <NUM> and the output aperture of the dual-direction optical collimator <NUM> may comprise the substantially optically transparent material, in some embodiments. The optically transparent material may include or be made up of any of a variety of dielectric materials including, but not limited to, one or more of various types of glass (e.g., silica glass, alkali-aluminosilicate glass, borosilicate glass, etc.) and substantially optically transparent plastics or polymers (e.g., poly(methyl methacrylate) or 'acrylic glass', polycarbonate, etc.). For example, one or both of the vertical collimator <NUM> and the horizontal collimator <NUM> may comprise an optically transparent material formed to have parabolic-shaped surface. The parabolic-shaped surface, in turn, may be metalized or otherwise coated with a reflective material to provide the optical reflectors <NUM>, <NUM>, for example. Reflective materials used to coat the parabolic-shaped surface(s) may include, but are not limited to, aluminum, chromium, nickel, silver and gold, for example. Further, the vertical collimator <NUM> is integral to and comprises a material of the horizontal collimator <NUM>. <FIG> illustrates by way of example and not limitation the dual-direction optical collimator <NUM> having integral vertical and horizontal collimators <NUM>, <NUM> formed from a common, optically transparent material.

The material of the dual-direction optical collimator <NUM> serves as a light guide to guide light by total internal reflection. The light guide guides light between the vertical collimator <NUM> and the horizontal collimator <NUM>. <FIG> illustrates vertically collimated light <NUM>' being reflected at an interface between the material of the dual-direction optical collimator <NUM> adjacent to the vertical collimator <NUM> and another material (e.g., air) outside of the material using total internal reflection. The illustrated reflection represents guiding of the vertically collimated light <NUM>' within a portion of the dual-direction optical collimator <NUM> illustrated in <FIG> from the optical reflector <NUM> of the vertical collimator <NUM> in a direction toward the horizontal collimator <NUM> (not shown in <FIG>). In some embodiments (e.g., as illustrated in <FIG>), the material also may extend from the horizontal collimator <NUM> (e.g., the optical reflector <NUM>) to the output aperture. The material is configured as a light guide to guide the vertically collimated light <NUM>' and the dual-direction collimated light <NUM> to the output aperture.

According to some embodiments of the principles described herein, a backlight employing dual-direction collimation is provided. <FIG> illustrates a top view of a backlight <NUM> in an example, according to an embodiment consistent with the principles of the principles described herein. <FIG> illustrates a cross sectional view of a backlight <NUM> in an example, according to an embodiment consistent with the principles of the principles described herein. As illustrated in <FIG>, the backlight <NUM> comprises a dual-direction optical collimator <NUM>.

In some embodiments, the dual-direction optical collimator <NUM> may be substantially similar to the dual-direction optical collimator <NUM> described above. In particular, the dual-direction optical collimator <NUM> comprises a vertical collimator <NUM> and a horizontal collimator <NUM> each of which may be substantially similar to respective ones of the vertical collimator <NUM> and the horizontal collimator <NUM> of the dual-direction optical collimator <NUM>. For example, dashed outlines associated with the dual-direction optical collimator <NUM> in <FIG> may resemble the dual-direction optical collimator <NUM> illustrated in <FIG>. According to various embodiments, the dual-direction optical collimator <NUM> is configured to receive light <NUM>, illustrated in <FIG> (e.g., from a light source <NUM>, described below), and provide dual-direction collimated light <NUM> at an output of the dual-direction optical collimator <NUM>. Further, the dual-direction collimated light <NUM> is provided having a non-zero propagation angle relative to the horizontal x-y plane.

As illustrated in <FIG>, the backlight <NUM> further comprises a plate light guide <NUM> coupled (e.g., optically coupled) to the output of the dual-direction optical collimator <NUM>. The plate light guide <NUM> is configured to receive and to guide the dual-direction collimated light <NUM> at the non-zero propagation angle, as illustrated in <FIG>. According to the invention, the plate light guide <NUM> is further configured to emit a portion of the guided, dual-direction collimated light <NUM> from a surface of the plate light guide <NUM>. In <FIG>, emitted light <NUM> is illustrated as a plurality of rays (arrows) extending away from the plate light guide surface.

In some embodiment, the plate light guide <NUM> may be a slab or plate optical waveguide comprising an extended, planar sheet of substantially optically transparent, dielectric material. The planar sheet of dielectric material is configured to guide the dual-direction collimated light <NUM> from the dual-direction optical collimator <NUM> as a guided light beam <NUM> using total internal reflection. The dielectric material may have a first refractive index that is greater than a second refractive index of a medium surrounding the dielectric optical waveguide. The difference in refractive indices is configured to facilitate total internal reflection of the guided light beam <NUM> according to one or more guided modes of the plate light guide <NUM>, for example.

According to various examples, the substantially optically transparent material of the plate light guide <NUM> may include or be made up of any of a variety of dielectric materials including, but not limited to, one or more of various types of glass (e.g., silica 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, the plate light guide <NUM> may further include a cladding layer on at least a portion of a surface (e.g., one or both of the top surface and the bottom surface) of the plate light guide <NUM> (not illustrated). The cladding layer may be used to further facilitate total internal reflection, according to some examples.

In some embodiments, (e.g., as illustrated in <FIG>), the plate light guide <NUM> may be integral to the dual-direction optical collimator <NUM>. In particular, the plate light guide <NUM> and the dual-direction optical collimator <NUM> may be formed from and thus comprise the same material. For example, the plate light guide <NUM> may be an extension of a light guide extending or connecting between a horizontal collimator and an output aperture of the dual-direction optical collimator <NUM>. In other embodiments (e.g., as illustrated in <FIG>), the dual-direction optical collimator <NUM> and the plate light guide <NUM> are separate and coupling (e.g., one or both of optical coupling and mechanical coupling) thereof is provided by a glue or adhesive layer, another interface material or even air between the output aperture and an input of the plate light guide <NUM>. For example, the dual-direction optical collimator <NUM> may comprise a polymer or plastic material and the plate light guide <NUM> may comprise glass. The dual-direction optical collimator <NUM> and the plate light guide <NUM> may be affixed to one another using a suitable adhesive layer <NUM> (e.g., an optically matched glue), for example as illustrated in <FIG>.

According to some embodiments, the backlight <NUM> may further comprise a light source <NUM>. The light source <NUM> is configured to provide light to the dual-direction optical collimator <NUM>. In particular, the light source <NUM> is located adjacent to (e.g., below, as illustrated in <FIG>) the vertical collimator <NUM> of the dual-direction optical collimator <NUM> and is configured to provide the light <NUM> to an input of the vertical collimator <NUM> as the received light <NUM>. In various embodiments, the light source <NUM> may comprise substantially any source of light including, but not limited to, one or more light emitting diodes (LEDs). In some examples, the light source <NUM> may comprise an optical emitter configured produce a substantially monochromatic light having a narrowband spectrum denoted by a particular color. In particular, 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 some embodiments, the light source <NUM> may comprise a plurality of different optical sources configured to provide different colors of light (i.e., 'different color' optical sources). The different optical sources may be offset from one another, for example. The offset of the different optical sources may be configured to provide different, color-specific, non-zero propagation angles of the dual-direction collimated light <NUM> corresponding to each of the different colors of light, according to some embodiments. In particular, the offset may add an additional non-zero propagation angle component to the non-zero propagation angle provided by the dual-direction collimator <NUM>, for example.

<FIG> illustrates a cross sectional view of a portion of a backlight <NUM> in an example, according to an embodiment consistent with the principles of the principles described herein. For example, the portion of the backlight <NUM> illustrated in <FIG> may be substantially similar to the dual-direction collimator portion illustrated in <FIG>. In particular, <FIG> illustrates a portion of the backlight <NUM> that includes the vertical collimator <NUM> along with the light source <NUM> comprising a plurality of different optical sources. As illustrated in <FIG>, the plurality of different optical sources of the light source <NUM> includes a first optical source <NUM> configured to provide light of a first color (e.g., red light), a second optical source <NUM> configured to provide light of a second color (e.g., green), and a third optical source <NUM> configured to provide light of a third color (e.g., blue). For the example, the first, second and third optical sources <NUM>, <NUM>, <NUM> of the light source <NUM> may respectively comprise a red LED, a green LED and a blue LED. Each of the different optical sources <NUM>, <NUM> and <NUM> of the light source <NUM> is offset from one another, as illustrated.

Specifically, the different optical sources <NUM>, <NUM> and <NUM> are illustrated in <FIG> as being laterally offset from one another in a propagation direction of the vertical collimated light <NUM>'. The offset, in turn, results in the light <NUM> produced by the different optical sources <NUM>, <NUM> and <NUM> having different, non-zero propagation angles upon exiting the vertical collimator <NUM> as vertically collimated light <NUM>'. Since each of the illustrated optical sources <NUM>, <NUM> and <NUM> produces light of a different color, the vertically collimated light <NUM>' comprises three different light beams, each light beam having a different, color-specific, non-zero propagation angle, as illustrated in <FIG>. Note, in <FIG>, different line types (e.g., dashed, solid, etc.) indicate the different colors of light <NUM>, <NUM>'.

According to some embodiments (e.g., as illustrated in <FIG>), the backlight <NUM> may further comprise a multibeam diffraction grating <NUM> at a surface of the plate light guide <NUM>. The multibeam diffraction grating <NUM> is configured to diffractively couple out a portion of the guided, dual-direction collimated light <NUM> from the plate light guide <NUM> as a plurality of light beams <NUM>. The plurality of light beams <NUM> (i.e., the plurality of rays (arrows) illustrated in <FIG>) represents the emitted light <NUM>. In various embodiments, a light beam <NUM> of the light beam plurality has a principal angular direction that is different from principal angular directions of other light beams <NUM> of the light beam plurality.

In some embodiments, the multibeam diffraction grating <NUM> is a member of or is arranged in an array of multibeam diffraction gratings <NUM>. In some embodiments, the backlight <NUM> is a backlight of a three-dimensional (3D) electronic display and the principal angular direction of the light beam <NUM> corresponds to a view direction of the 3D electronic display.

<FIG> illustrates a cross sectional view of a portion of a backlight <NUM> with a multibeam diffraction grating <NUM> in an example, according to an embodiment consistent with the principles described herein. <FIG> illustrates a cross sectional view of a portion of a backlight <NUM> with a multibeam diffraction grating <NUM> in an example, according to another embodiment consistent with the principles described herein. <FIG> illustrates a perspective view of the backlight portion of either <FIG> or <FIG> including the multibeam diffraction grating <NUM> in an example, according to an embodiment consistent with the principles described herein. The multibeam diffraction grating <NUM> illustrated in <FIG> comprises grooves in a surface of the plate light guide <NUM>, by way of example and not limitation. <FIG> illustrates the multibeam diffraction grating <NUM> comprising ridges protruding from the plate light guide surface.

As illustrated in <FIG>, the multibeam diffraction grating <NUM> is a chirped diffraction grating. In particular, the diffractive features 240a are closer together at a second end <NUM>" of the multibeam diffraction grating <NUM> than at a first end <NUM>'. Further, the diffractive spacing d of the illustrated diffractive features 240a varies from the first end <NUM>' to the second end <NUM>". In some embodiments, the chirped diffraction grating of the multibeam diffraction grating <NUM> may have or exhibit a chirp of the diffractive spacing d that varies linearly with distance. As such, the chirped diffraction grating of the multibeam diffraction grating <NUM> may be referred to as a 'linearly chirped' diffraction grating.

In another embodiment, the chirped diffraction grating of the multibeam diffraction grating <NUM> may exhibit a non-linear chirp of the diffractive spacing d. Various non-linear chirps that may be used to realize the chirped diffraction grating include, but are not limited to, an exponential chirp, a logarithmic chirp or a chirp that varies in another, substantially non-uniform or random but still monotonic manner. Non-monotonic chirps such as, but not limited to, a sinusoidal chirp or a triangle or sawtooth chirp, may also be employed. Combinations of any of these types of chirps may also be used in the multibeam diffraction grating <NUM>.

As illustrated in <FIG>, the multibeam diffraction grating <NUM> includes diffractive features 240a (e.g., grooves or ridges) in, at or on a surface of the plate light guide <NUM> that are both chirped and curved (i.e., the multibeam diffraction grating <NUM> is a curved, chirped diffraction grating, as illustrated). The guided light beam <NUM> guided in the plate light guide <NUM> has an incident direction relative to the multibeam diffraction grating <NUM> and the plate light guide <NUM>, as illustrated by a bold arrow in <FIG>. Also illustrated is the plurality of coupled-out or emitted light beams <NUM> pointing away from the multibeam diffraction grating <NUM> at the surface of the plate light guide <NUM>. The illustrated light beams <NUM> are emitted in a plurality of different predetermined principal angular directions. In particular, the different predetermined principal angular directions of the emitted light beams <NUM> are different in both azimuth and elevation (e.g., to form a light field).

According to various examples, both the predefined chirp of the diffractive features 240a and the curve of the diffractive features 240a may be responsible for a respective plurality of different predetermined principal angular directions of the emitted light beams <NUM>. For example, due to the diffractive feature curve, the diffractive features 240a within the multibeam diffraction grating <NUM> may have varying orientations relative to an incident direction of the guided light beam <NUM> within the plate light guide <NUM>. In particular, an orientation of the diffractive features 240a at a first point or location within the multibeam diffraction grating <NUM> may differ from an orientation of the diffractive features 240a at another point or location relative to the guided light beam incident direction. With respect to the coupled-out or emitted light beam <NUM>, an azimuthal component ϕ of the principal angular direction {θ, ϕ} of the light beam <NUM> may be determined by or correspond to the azimuthal orientation angle ϕf of the diffractive features 240a at a point of origin of the light beam <NUM> (i.e., at a point where the incident guided light beam <NUM> is coupled out). As such, the varying orientations of the diffractive features 240a within the multibeam diffraction grating <NUM> produce different light beams <NUM> having different principal angular directions {θ, ϕ}, at least in terms of their respective azimuthal components ϕ.

In particular, at different points along the curve of the diffractive features 240a, an 'underlying diffraction grating' of the multibeam diffraction grating <NUM> associated with the curved diffractive features 240a has different azimuthal orientation angles ϕf. By 'underlying diffraction grating', it is meant that diffraction gratings of a plurality of non-curved diffraction gratings in superposition yield the curved diffractive features 240a of the multibeam diffraction grating <NUM>. Thus, at a given point along the curved diffractive features 240a, the curve has a particular azimuthal orientation angle ϕf that generally differs from the azimuthal orientation angle ϕf at another point along the curved diffractive features 240a. Further, the particular azimuthal orientation angle ϕf results in a corresponding azimuthal component ϕ of a principal angular direction {θ, ϕ} of a light beam <NUM> emitted from the given point. In some examples, the curve of the diffractive features 240a (e.g., grooves, ridges, etc.) may represent a section of a circle. The circle may be coplanar with the light guide surface. In other examples, the curve may represent a section of an ellipse or another curved shape, e.g., that is coplanar with the plate light guide surface.

In other embodiments, the multibeam diffraction grating <NUM> may include diffractive features 240a that are 'piecewise' curved. In particular, while the diffractive feature 240a may not describe a substantially smooth or continuous curve per se, at different points along the diffractive feature 240a within the multibeam diffraction grating <NUM>, the diffractive feature 240a still may be oriented at different angles with respect to the incident direction of the guided light beam <NUM>. For example, the diffractive feature 240a may be a groove including a plurality of substantially straight segments, each segment having a different orientation than an adjacent segment. Together, the different angles of the segments may approximate a curve (e.g., a segment of a circle), according to various embodiments. In yet other examples, the diffractive features 240a may merely have different orientations relative to the incident direction of the guided light at different locations within the multibeam diffraction grating <NUM> without approximating a particular curve (e.g., a circle or an ellipse).

In some embodiments, the grooves or ridges that form the diffractive features 240a may be etched, milled or molded into the plate light guide surface. As such, a material of the multibeam diffraction gratings <NUM> may include the material of the plate light guide <NUM>. As illustrated in <FIG>, for example, the multibeam diffraction grating <NUM> includes ridges that protrude from the surface of the plate light guide <NUM>, wherein the ridges may be substantially parallel to one another. In <FIG> (and <FIG>), the multibeam diffraction grating <NUM> includes grooves that penetrate the surface of the plate light guide <NUM>,wherein the grooves may be substantially parallel to one another. In other examples (not illustrated), the multibeam diffraction grating <NUM> may comprise a film or layer applied or affixed to the light guide surface. The plurality of light beams <NUM> in different principal angular directions provided by the multibeam diffraction gratings <NUM> are configured to form a light field in a viewing direction of an electronic display. In particular, the backlight <NUM> employing dual-direction collimation is configured to provide information, e.g., 3D information, corresponding to pixels of an electronic display.

In accordance with some embodiments of the principles described herein, a three-dimensional (3D) electronic display is provided. <FIG> illustrates a block diagram of a three-dimensional (3D) electronic display <NUM> in an example, according to an embodiment of the principles described herein. According to various embodiments, the 3D electronic display <NUM> is configured to produce modulated, directional light comprising light beams having different principal angular directions and, in some embodiments, also having a plurality of different colors. For example, the 3D electronic display <NUM> may provide or generate a plurality of different light beams <NUM> directed out and away from the 3D electronic display <NUM> in different predetermined principal angular directions (e.g., as a light field). Further, the different light beams <NUM> may include light beams <NUM> of or having different colors of light. In turn, the light beams <NUM> of the plurality may be modulated as modulated light beams <NUM>' to facilitate the display of information including color information (e.g., when the light beams <NUM> are color light beams).

In some embodiments, the modulated light beams <NUM>' having different predetermined principal angular directions form a plurality of pixels of the 3D electronic display <NUM>. In some examples, the 3D electronic display <NUM> may be a so-called 'glasses free' 3D color electronic display (e.g., a multiview, 'holographic' or autostereoscopic display) in which the modulated light beams <NUM>' correspond to pixels associated with different 'views' of the 3D electronic display <NUM>. Modulated light beams <NUM>' are illustrated using dashed line arrows <NUM>' in <FIG>, while the different light beams <NUM> prior to modulation are illustrated as solid line arrows, by way of example.

The 3D electronic display <NUM> illustrated in <FIG> comprises a dual-direction optical collimator <NUM> (abbreviated as 'Dual-Dir. ' in <FIG>). The dual-direction optical collimator <NUM> is configured to provide dual-direction collimated light having both vertical collimation and horizontal collimation. In particular, the vertical and horizontal collimation is with respect to a vertical direction (e.g., z-direction) or a vertical plane (e.g., y-z plane) and a horizontal direction (e.g., x-direction) or a horizontal plane (x-y plane) of the dual-direction optical collimator <NUM>. Further, the dual-direction optical collimator <NUM> is configured to provide the dual-direction collimated light at a non-zero propagation angle relative to the horizontal plane of the dual-direction collimator <NUM>.

In some embodiments, the dual-direction optical collimator <NUM> is substantially similar to the above-described dual-direction optical collimator <NUM>. In particular, the dual-direction collimator <NUM> comprises a vertical collimator and a horizontal collimator. The horizontal collimator is located adjacent to an output of the vertical collimator. Further, the vertical collimator may be substantially similar to the vertical collimator <NUM> and the horizontal collimator may be substantially similar to the horizontal collimator <NUM> described with respect to the dual-direction optical collimator <NUM>, according to some embodiments.

For example, the vertical collimator of the dual-direction collimator <NUM> may comprise an optical reflector having a parabolic shape and a tilt angle. The tilt angle is configured to determine the non-zero propagation angle of the dual-direction collimated light at an output of the dual-direction optical collimator. Further, for example, the horizontal collimator of the dual-direction collimator <NUM> may comprise an optical reflector having a parabolic shape. The optical reflector of the horizontal collimator may be configured to substantially span an output aperture of the dual-direction optical collimator and to provide the dual-direction collimated light with a substantially uniform distribution across the output aperture, for example. In addition, the dual-direction collimator <NUM> may comprise vertical and horizontal collimators arranged in various other configurations including sub-reflectors and multiple vertical collimators, e.g., as described above with respect to the vertical collimator <NUM> and horizontal collimator <NUM> of the dual-direction optical collimator <NUM>.

As illustrated in <FIG>, the 3D electronic display <NUM> further comprises a plate light guide <NUM>. The plate light guide <NUM> is configured to guide the dual-direction collimated light as a guided light beam at the non-zero propagation angle. In particular, the guided light beam may be guided at the non-zero propagation angle relative to a surface (e.g., one or both of a top surface and a bottom surface) of the plate light guide <NUM>. The surface may be parallel to the horizontal plane in some embodiments. According to some embodiments, the plate light guide <NUM> may be substantially similar to the plate light guide <NUM> described above with respect to the backlight <NUM>.

According to various embodiments and as illustrated in <FIG>, the 3D electronic display <NUM> further comprises an array of multibeam diffraction gratings <NUM> located at a surface of the plate light guide <NUM>. According to some embodiments, a multibeam diffraction grating <NUM> of the array may be substantially similar to the multibeam diffraction grating <NUM> described above with respect to the backlight <NUM>. In particular, a multibeam diffraction grating <NUM> of the array is configured to diffractively couple out a portion of the guided light beam as plurality of coupled-out light beams having different principal angular directions and representing the light beams <NUM>. Moreover, the different principal angular directions of light beams <NUM> coupled out by the multibeam diffraction grating <NUM> correspond to different 3D views of the 3D electronic display <NUM>, according to various embodiments. In some embodiments, the multibeam diffraction grating <NUM> comprises a chirped diffraction grating having curved diffractive features. In some embodiments, a chirp of the chirped diffraction grating is a linear chirp.

In some embodiments, the 3D electronic display <NUM> (e.g., as illustrated in <FIG>) further comprises a light source <NUM> configured to provide light to an input of the dual-direction optical collimator <NUM>. In some embodiments, the light source <NUM> may be substantially similar to the light source <NUM> of the backlight <NUM>, described above. In particular, the light source <NUM> may comprise a plurality of different light emitting diodes (LEDs) configured to provide different colors of light (referred to as 'different colored LEDs' for simplicity of discussion). In some embodiments, the different colored LEDs may be offset (e.g., laterally offset) from one another. The offset of the different colored LEDs is configured to provide different, color-specific, non-zero propagation angles of the dual-direction collimated light from the dual-direction optical collimator <NUM>. Further, a different, color-specific, non-zero propagation angle may correspond to each of the different colors of light provided by the light source <NUM>.

In some embodiments (not illustrated), the different colors of light may comprise the colors red, green and blue of a red-green-blue (RGB) color model. Further, the plate light guide <NUM> may be configured to guide the different colors as light beams at different color-dependent propagation angles within the plate light guide <NUM>. For example, a first guided color light beam (e.g., a red light beam) may be guided at a first color-dependent propagation angle, a second guided color light beam (e.g., a green light beam) may be guided at a second color-dependent propagation angle, and a third guided color light beam (e.g., a blue light beam) may be guided at a third color-dependent propagation angle, according to some embodiments.

As illustrated in <FIG>, the 3D electronic display <NUM> may further comprise a light valve array <NUM>. According to various embodiments, the light valve array <NUM> is configured to modulate the coupled-out light beams <NUM> of the light beam plurality as the modulated light beams <NUM>' to form or serve as the 3D pixels corresponding to the different 3D views of the 3D electronic display <NUM>. In some embodiments, the light valve array <NUM> comprises a plurality of liquid crystal light valves. In other embodiments, the light valve array <NUM> may comprise another light valve including, but not limited to, an electrowetting light valve, an electrophoretic light valves, a combination thereof, or a combination of liquid crystal light valves and another light valve type, for example.

In accordance with other embodiments of the principles described herein, a method of dual-direction light collimation is provided. <FIG> illustrates a flow chart of a method <NUM> of dual-direction light collimation in an example, according to an embodiment consistent with the principles described herein. As illustrated in <FIG>, the method <NUM> of dual-direction light collimation comprises collimating <NUM> light in a vertical direction using a vertical collimator to provide vertically collimated light. In some embodiments, the vertical collimator is substantially similar to the vertical collimator <NUM> described above with respect to the dual-direction optical collimator <NUM>. For example, the vertical collimator used in collimating <NUM> light may comprise an optical reflector having a parabolic shape.

The method <NUM> of dual-direction light collimation further comprises further collimating <NUM> the vertically collimated light in a horizontal direction using a horizontal collimator located adjacent to an output of the vertical collimator to produce dual-direction collimated light that is both vertically collimated and horizontally collimated. In some embodiments, the horizontal collimator is substantially similar to the horizontal collimator <NUM> described above with respect to the dual-direction optical collimator <NUM>. For example, the horizontal collimator used in further collimating <NUM> the vertically collimated light may comprise another optical reflector having another parabolic shape. In some embodiments, the horizontal collimator optical reflector may substantially span an output aperture of the horizontal collimator to produce a substantially uniform distribution of the dual-direction collimated light across the output aperture.

The method <NUM> of dual-direction light collimation illustrated in <FIG> further comprises creating <NUM> a non-zero propagation angle in the dual-direction collimated light, wherein the non-zero propagation angle is in a vertical plane corresponding to the vertical direction (or equivalently is an angle relative to a horizontal plane). The non-zero propagation angle may be substantially similar to the non-zero propagation angle described above with respect to the dual-direction optical collimator <NUM>, for example. In particular, according to the invention the non-zero propagation angle is provided by a tilt angle of the optical reflector of the vertical collimator.

In accordance with yet other embodiments of the principles described herein, a method of three-dimensional (3D) electronic display operation is provided. <FIG> illustrates a flow chart of a method <NUM> of 3D electronic display operation in an example, according to an embodiment consistent with the principles described herein. As illustrated in <FIG>, the method <NUM> of 3D electronic display operation comprises providing <NUM> dual-direction collimated light having a non-zero propagation angle. According to various embodiments, the dual-direction collimated light may be provided <NUM> using a dual-direction collimator. The dual-direction collimator may be substantially similar to the dual-direction optical collimator <NUM> described above. In some embodiments, the dual-direction collimated light may be provided <NUM> according to the method <NUM> of dual-direction light collimation, described above. For example, providing <NUM> dual-direction collimated light may employ a vertical collimator followed by a horizontal collimator at an output of the vertical collimator.

The method <NUM> of 3D electronic display operation further comprises guiding <NUM> the dual-direction collimated light in a plate light guide. In particular, the dual-direction collimated light is guided <NUM> at the non-zero propagation angle within the plate light guide. According to some embodiments, the plate light guide may be substantially similar to the plate light guide <NUM> of the backlight <NUM>, as described above.

The method <NUM> of 3D electronic display operation of <FIG> further comprises diffractively coupling out <NUM> a portion of the guided dual-direction collimated light using a multibeam diffraction grating to produce a plurality of light beams. According to some embodiments, the multibeam diffraction grating is located at a surface of the plate light guide. According to various embodiments, diffractively coupling out <NUM> the guided dual-direction collimated light portion is configured to provide the plurality of light beams directed away from the plate light guide in a plurality of different principal angular directions. In particular, the plurality of different principal angular directions corresponds to directions of different 3D views of a 3D electronic display. According to some embodiments, the multibeam diffraction grating is substantially similar to the multibeam diffraction grating <NUM> and the diffractively coupled-out <NUM> light beams of the light beam plurality correspond to the light beams <NUM>, described above with respect to the backlight <NUM> or the light beams <NUM> of the 3D electronic display <NUM>.

According to various embodiments, the method <NUM> of 3D electronic display operation illustrated in <FIG> further comprises modulating <NUM> light beams of the plurality of light beams using an array of light valves. The modulated <NUM> light beams form 3D pixels of the 3D electronic display in the 3D view directions, according to various embodiments. In some embodiments, the array of light valves may be substantially similar to the light valve array <NUM> described above with respect to the 3D electronic display <NUM>.

In some embodiments (not illustrated), the method <NUM> of 3D electronic display operation further comprises providing light to be dual-direction collimated. For example, the light may be non-collimated light provided to a dual-direction optical collimator, such as the dual-direction collimator that may be used in providing <NUM> dual-direction collimated light. The light may be provided using a light source at an input of the vertical collimator, for example. Further, the light source may be substantially similar to the light source <NUM> described above with respect to the backlight <NUM>, in some embodiments.

Claim 1:
A backlight (<NUM>) comprising:
a dual-direction optical collimator (<NUM>,<NUM>) comprising:
a vertical collimator (<NUM>,<NUM>) configured to collimate light in a vertical direction, wherein the vertical collimator (<NUM>) comprises an optical reflector having a tilt angle; and
a horizontal collimator (<NUM>,<NUM>) configured to collimate light in a horizontal direction substantially orthogonal to the vertical direction, the horizontal collimator being located adjacent to an output of the vertical collimator to horizontally collimate vertically collimated light from the vertical collimator to provide dual-direction collimated light at an output of the dual-direction optical collimator, wherein the vertical collimator (<NUM>) is integral to and comprises a material of the horizontal collimator (<NUM>), wherein the material of the dual-direction optical collimator (<NUM>) serves as a light guide configured to guide the vertically collimated light toward the horizontal collimator, and configured to guide the dual-direction collimated light to the output of the dual-direction optical collimator; and
a plate light guide (<NUM>) coupled to the output of the dual-direction optical collimator,
wherein the plate light guide is configured to emit a portion of the guided, dual-direction collimated light from a surface of the plate light guide and wherein the dual-direction optical collimator is configured to provide the dual-direction collimated light at the non-zero propagation angle relative to a horizontal plane corresponding to the horizontal direction, the plate light guide being configured to receive and to guide the dual-direction collimated light at said non-zero propagation angle relative to said surface, the tilt angle of the vertical collimator being configured to provide the non-zero propagation angle of the dual-direction collimated light.