HK1249931B - Dual surface collimator and 3d electronic display employing grating-based backlighting using same - Google Patents

Description

Dual-surface collimator and 3D electronic display using grating-based backlighting

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to U.S. Provisional Patent Application Serial No. 62/214,975, filed September 5, 2015, which is incorporated herein by reference in its entirety.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

not applicable

Background Art

Electronic displays are nearly ubiquitous media for conveying information to users of a wide variety of devices and products. The most common electronic displays are cathode ray tubes (CRTs), plasma display panels (PDPs), liquid crystal displays (LCDs), electroluminescent displays (ELs), organic light emitting diode (OLED) 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. LCD and EP displays are typically classified as passive when considering the light emitted. Passive displays, while often exhibiting attractive performance characteristics, including but not limited to inherently low power consumption, have somewhat limited use in many practical applications due to their lack of ability to emit light.

In order to overcome the applicability limitations of passive displays associated with light emission, many passive displays are coupled to external light sources. The coupled light source can allow these otherwise passive displays to emit light and essentially function as active displays. An example of such a coupled light source is a backlight. A backlight is a light source (often referred to as a "panel" light source) that is placed behind a passive display to illuminate the passive display. For example, a backlight can be coupled to an LCD or EP display. The backlight emits light that passes through the LCD or EP display. The light emitted by the backlight is modulated by the LCD or EP display, and the modulated light is then emitted from the LCD or EP display. 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, a color filter can be placed at the output of the LCD or EP display (uncommon) 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:

FIG1 shows a graphical view of the angular components of a light beam having a particular principal angular direction, according to an example of the principles described herein.

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

3 illustrates a cross-sectional view of a portion of a dual-surface collimator including a curved entrance surface, according to an example of an embodiment consistent with the principles described herein.

4A shows a top view of a backlight in an example, according to an embodiment consistent with the principles described herein.

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

4C shows a cross-sectional view of the alignment between the output aperture of a dual-surface collimator and the input aperture of a plate light guide, according to an example of an embodiment consistent with the principles described herein.

4D shows a cross-sectional view of the alignment between the output aperture of a dual-surface collimator and the input aperture of a plate light guide, according to an example of an embodiment consistent with the principles described herein.

5A shows a cross-sectional view of a portion of a backlight with a multibeam diffraction grating, in an example of an embodiment consistent with the principles described herein.

5B shows a cross-sectional view of a portion of a backlight with a multibeam diffraction grating, in an example of an embodiment consistent with the principles described herein.

5C shows a perspective view of a portion of the backlight of FIG. 5A or FIG. 5B including a multibeam diffraction grating, according to an example of an embodiment consistent with the principles described herein.

6 shows a block diagram of a three-dimensional (3D) electronic display in an example according to an embodiment consistent with the principles described herein.

7 shows a flow chart of a method of bidirectional light collimation in an example of an embodiment consistent with the principles described herein.

8 shows a flow chart of a method of 3D electronic display operation in an example of an embodiment consistent with the principles described herein.

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

DETAILED DESCRIPTION

Embodiments and examples according to the principles described herein provide bidirectional collimation and display backlighting using bidirectional collimation. In particular, embodiments of the principles described herein use a collimator having a curved incident surface and a curved reflective surface to provide bidirectional light collimation. Thus, the collimator is referred to herein as a "dual-surface" collimator. Light entering the dual-surface collimator is refracted at the curved incident surface and reflected back toward the curved incident surface at the curved reflective surface. The reflected light is further reflected or "re-reflected" at the curved incident surface by total internal reflection. The refraction, reflection, and re-reflection of light according to the curved shape of each of the curved incident surface and the curved reflective surface are combined to convert or transform the light entering the dual-surface collimator into bidirectional collimated light at the output of the dual-surface collimator. In addition, the bidirectional collimation described herein can provide bidirectional collimated light having a predetermined, non-zero propagation angle in a vertical plane corresponding to the vertical direction or, equivalently, relative to a horizontal plane.

According to various embodiments, light from a light source (e.g., a plurality of LEDs) can be coupled into a dual-surface collimator at a curved entrance surface for bidirectional collimation. According to some embodiments, the bidirectionally collimated light from the dual-surface collimator can be coupled into a light guide (e.g., a plate light guide) of a backlight used in an electronic display. For example, the backlight can be a grating-based backlight, including but not limited to a grating-based backlight having a multi-beam diffraction grating. In some embodiments, the electronic display can be a three-dimensional (3D) electronic display for displaying 3D information, such as an autostereoscopic or "naked-eye" 3D electronic display.

In particular, a 3D electronic display may employ a grating-based backlight having an array of multi-beam diffraction gratings. The multi-beam diffraction gratings may be used to couple light from a light guide and provide coupled-out light beams corresponding to pixels of the 3D electronic display. For example, the coupled-out light beams may have different principal directions from one another (also referred to as "light beams of different directions"). According to some embodiments, these light beams of different directions generated by the multi-beam diffraction gratings may be modulated and used as 3D pixels corresponding to a 3D view of a "naked-eye" 3D electronic display to display 3D information. In these embodiments, the bidirectional collimation provided by the dual-surface collimator may be used to produce output bidirectional collimated light that is substantially uniform (i.e., without fringes) within the light guide. Furthermore, according to the principles described herein, uniform illumination of the multi-beam diffraction grating may be provided.

In this document, a "lightguide" is defined as a structure that guides light within the structure using total internal reflection. In particular, a lightguide may include a core that is substantially transparent at the operating wavelength of the lightguide. The term "lightguide" generally refers to a dielectric optical waveguide that uses total internal reflection to guide light at the interface between the dielectric material of the lightguide and the material or medium surrounding the lightguide. By definition, the condition for total internal reflection is that the refractive index of the lightguide is greater than the refractive index of the surrounding medium adjacent to the surface of the lightguide material. In some embodiments, the lightguide may include a coating in addition to or as an alternative to the above-mentioned refractive index difference 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 sheet lightguide and a strip lightguide.

Further herein, the term "sheet" as applied to a lightguide as in "sheet lightguide" is defined as a segmented or differently planar layer or sheet, which is sometimes referred to as a "sheet" lightguide. In particular, a sheet 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 in at least a differential sense. That is, within any differentially small segment of the sheet 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 curvature has a sufficiently large radius of curvature to ensure 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) can 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., 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, the plurality of features of the diffraction grating (e.g., a plurality of grooves in a material surface) can be arranged in a one-dimensional (1-D) array. In other examples, the diffraction grating can be a two-dimensional (2-D) array of features. For example, the diffraction grating can be a 2-D array of protrusions on a material surface or holes in a material surface.

Thus, and according to the definitions herein, a "diffraction grating" is a structure that provides diffraction of light incident on the diffraction grating. If light is incident on the diffraction grating from a light guide, the diffraction or diffraction scattering provided can result in and is therefore referred to as "diffraction coupling", because the diffraction grating can couple light out of the light guide by diffraction. A diffraction grating also redirects or changes the angle of light by diffraction (i.e., at a diffraction angle). In particular, due to diffraction, the light leaving the diffraction grating (i.e., the diffracted light) generally has a propagation direction that is different from the propagation direction of the light incident on the diffraction grating (i.e., the incident light). Changing the propagation direction of light by diffraction is referred to herein as "diffraction redirection". Thus, a diffraction grating can be understood as a structure comprising diffraction features that redirects 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, the features of a diffraction grating are referred to as "diffraction features" and can be one or more at a surface, in a surface, and on a surface (i.e., where "surface" refers to a boundary between two materials). The surface can be a surface of a plate 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 protrusions, and these structures can be one or more at a surface, in a surface, and on a surface. For example, a diffraction grating can include a plurality of parallel grooves in the surface of a material. In another example, a diffraction grating can include a plurality of parallel ridges rising from the surface of a material. The diffraction features (whether grooves, ridges, holes, protrusions, etc.) can have any of a variety of cross-sectional shapes or profiles that provide diffraction, including but not limited to a sinusoidal profile, a rectangular profile (e.g., a binary diffraction grating), a triangular profile, and a sawtooth profile (e.g., a blazed grating).

As defined herein, a "multibeam diffraction grating" is a diffraction grating that produces coupled-out light comprising a plurality of light beams. Furthermore, as defined herein, the plurality of light beams produced by the multibeam diffraction grating have different principal angular directions from one another. Specifically, as defined herein, one of the plurality of light beams has a predetermined principal angular direction that is different from another of the plurality of light beams due to diffractive coupling and diffractive redirection of incident light produced by the multibeam diffraction grating. The plurality of light beams may represent a light field. For example, the plurality of light beams may include eight light beams having eight different principal angular directions. For example, the eight light beams (i.e., the plurality of light beams) combined may represent a light field. According to various embodiments, the different principal angular directions of the various light beams are determined by a combination of the grating pitch or spacing and the orientation or rotation of the diffraction features of the multibeam diffraction grating at the origin of the respective light beam relative to the propagation direction of light incident on the multibeam diffraction grating.

In particular, according to the definitions herein, a light beam generated by a multibeam diffraction grating has a principal angular direction given by an angular component. The angular component θ is referred to herein as the "altitude component" or "altitude angle" of the light beam. The angular component is referred to as the "azimuth component" or "azimuth angle" of the light beam. By definition, the altitude angle θ is the angle in the vertical plane (e.g., perpendicular to the plane of the multibeam diffraction grating), while the azimuth angle is the angle in the horizontal plane (e.g., parallel to the plane of the multibeam diffraction grating). FIG1 illustrates the angular components of a light beam 10 having a particular principal angular direction, according to an example of the principles described herein. Furthermore, according to the definitions herein, the light beam 10 is emitted or emanates from a particular point. That is, by definition, the light beam 10 has a central ray associated with a particular origin within the multibeam diffraction grating. FIG1 also illustrates the light beam origin O. An exemplary propagation direction of incident light is illustrated in FIG1 using a thick arrow 12 pointing to the origin O.

According to various embodiments, properties of a multibeam diffraction grating and its features (i.e., diffraction features) can be used to control one or both of the angular directionality of the light beams and the wavelength or color selectivity of the multibeam diffraction grating with respect to one or more light beams. Properties that can be used to control the angular directionality and wavelength selectivity include, but are not limited to, one or more of the following: grating length, grating pitch (feature spacing), feature shape, feature size (e.g., groove width or ridge width), and grating orientation. In some examples, the various properties used for control can be properties that are localized near the origin of the light beams.

Further in accordance with various embodiments described herein, light coupled out of a light guide via a diffraction grating (e.g., a multi-beam diffraction grating) represents a pixel of an electronic display. In particular, a light guide having a multi-beam diffraction grating to generate multiple light beams with different principal directions can be part of a backlight for, or used in conjunction with, an electronic display, such as, but not limited to, a "naked-eye" three-dimensional (3D) electronic display (also known as a multi-view or "holographic" electronic display or an autostereoscopic display). Thus, the light beams of different directions generated by outcoupling guided light from the light guide using the multi-beam diffraction grating can be or represent "pixels" of the 3D electronic display. Furthermore, the 3D pixels correspond to different 3D views or 3D viewing angles of the 3D electronic display.

As used herein, a "collimating" reflector is defined as a reflector having a curved shape that is configured to collimate light reflected by a collimating reflector (e.g., a collimating mirror). For example, a collimating reflector may have a reflective surface characterized by a parabolic curve or shape. In another example, the collimating reflector may comprise a shaped parabolic reflector. "Shaped parabola" means that the curved reflective surface of the shaped parabolic reflector deviates from a "true" parabola in a manner determined to achieve predetermined reflective characteristics (e.g., collimation). In some embodiments, the collimating reflector may be a continuous reflector (i.e., having a substantially smooth, continuous reflective surface), while in other embodiments, the collimating reflector may comprise a Fresnel reflector or Fresnel mirror that provides light collimation. According to various embodiments, the amount of collimation provided by the collimating reflector may vary from one embodiment to another by a predetermined degree or amount. Furthermore, the collimating reflector may be configured to provide collimation in one or both of two orthogonal directions (e.g., vertical and horizontal). That is, according to some embodiments, the collimating reflector may comprise a parabolic shape in one or both of the two orthogonal directions.

As used herein, a "light source" is defined as a light source (e.g., a device or apparatus that emits light). For example, a light source can be a light emitting diode (LED) that emits light when activated. A light source can be essentially any light source or light emitter, including, but not limited to, one or more of the following: 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 a light source can have a color or can include light of a specific wavelength. Thus, a "plurality of different-color light sources" is expressly defined herein as a set or group of light sources, wherein at least one of the light sources 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 source in the plurality of light sources. Furthermore, a "plurality of different-color light sources" can include more than one light source of the same or substantially similar color, so long as at least two of the plurality of light sources are different-color light sources (i.e., generate light of a color that differs between the at least two light sources). Thus, as defined herein, a plurality of different-color light sources can include a first light source that generates light of a first color and a second light source that generates light of a second color, wherein the second color is different from the first color.

Furthermore, 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 grating" refers to one or more gratings, and thus, "grating" herein means "(one or more) gratings". Furthermore, references herein to "top", "bottom", "upper", "lower", "up", "down", "front", "back", "first", "second", "left", or "right" are not intended to be limiting herein. In this document, the term "about" when applied to a value generally means within the tolerance range of the device used to produce the value, or may mean plus or minus 10%, or plus or minus 5%, or plus or minus 1%, unless expressly specified otherwise. Furthermore, the term "substantially" as used herein means most, or almost all, or all, or an amount in the range of about 51% to about 100%. Furthermore, the examples herein are intended to be exemplary only and are provided for discussion purposes and not as limitations.

According to some embodiments of the principles described herein, a dual-surface collimator is provided. FIG2 shows a cross-sectional view of a dual-surface collimator 100 in an example of an embodiment according to the principles described herein. The dual-surface collimator 100 is configured to receive light and collimate the received light in or relative to at least two different directions. In particular, according to some embodiments, the received light can be collimated in both the horizontal and vertical directions.

In particular, the dual-surface collimator 100 is configured to receive light 102 from a light source 104. As shown in FIG2 , according to various embodiments, the light source 104 is external to the dual-surface collimator 100. In some examples, the light 102 from the external light source 104 can be substantially uncollimated light, such as from a light source 104 that produces substantially uncollimated light. In another example, the light 102 can be provided 104 by the external light source as partially collimated light 102. For example, the light source 104 can include a lens or another collimating device to provide the partially collimated light 102. Thus, the light 102 received by the dual-surface collimator 100 can be either uncollimated or partially collimated light.

The illustrated dual-surface collimator 100 is also configured to collimate light 102 received from an external light source 104 using refraction and reflection as described below to produce collimated light 106 and direct the collimated light 106 to an output or output aperture 108 of the dual-surface collimator 100. The output aperture 108 may also be referred to as an output port, output plane, output surface, etc. of the dual-surface collimator 100. According to various embodiments, the collimated light 106 provided at the dual-surface collimator output aperture 108 is generally collimated or at least substantially collimated in at least two directions. Thus, the collimated light 106 may be referred to as "bidirectional" collimated light 106.

In particular, as defined herein, "bidirectional" collimated light 106 is light that is collimated in two directions that are generally orthogonal to the direction of propagation of the bidirectional collimated light 106. Furthermore, as defined herein, the two collimation directions are mutually orthogonal to each other. For example, the bidirectional collimated light 106 can be collimated in the horizontal direction or relative to the horizontal direction (e.g., in a direction parallel to the x-y plane) and also in the vertical direction or relative to the vertical direction (e.g., the z-direction). Thus, by way of example and not limitation, the bidirectional collimated light 106 provided by the dual-surface collimator 100 can be referred to as being horizontally collimated and vertically collimated, or equivalently, as being collimated in both the horizontal and vertical directions (e.g., because the horizontal and vertical directions can be determined relative to an arbitrary reference frame).

In addition, according to various embodiments, the dual-surface collimator 100 is further configured to provide a non-zero propagation angle θ', also described further below, for the bidirectional collimated light 106 at the dual-surface collimator output aperture 108. As defined herein, a "non-zero propagation angle" is an angle relative to a plane (e.g., a horizontal plane or an x-y plane) or equivalently relative to a surface of the light guide (e.g., a surface parallel to the horizontal plane). For example, the non-zero propagation angle θ' can be an angle defined relative to or about the horizontal plane of the dual-surface collimator 100. In some examples, the non-zero propagation angle θ' of the bidirectional collimated light 106 can be between about ten (10) degrees and about fifty (50) degrees, or in some examples, between about twenty (20) degrees and about forty (40) degrees, or between about twenty-five (25) degrees and about thirty-five (35) degrees. For example, the non-zero propagation angle θ' can be about thirty (30) degrees. In other examples, the non-zero propagation angle θ' can be about 20 degrees, or about 25 degrees, or about 35 degrees. Furthermore, according to some embodiments, the non-zero propagation angle θ' is both greater than zero and less than the critical angle for total internal reflection within the light guide, as described below.

As shown in FIG2 , the dual-surface collimator 100 includes an incident surface 110 having a curved shape. The curved incident surface 110 is configured to refract light incident on the incident surface 110 (i.e., incident from the z-direction, as shown). In particular, according to various embodiments, the incident surface 110 can be configured to refract incident light 102 from a light source 104. After being refracted by the incident surface 110, the light becomes refracted light 102′ that propagates through the dual-surface collimator 100.

FIG2 illustrates incident light 102 as an arrow incident on incident surface 110 at an incident point 112 (i.e., the point where the arrow corresponding to the incident light ray intersects incident surface 110). Refracted light 102′, which propagates away from incident point 112 within dual-surface collimator 100, is also illustrated as another arrow in FIG2 . For example, the arrows in FIG2 may represent central light rays 102 and 102′. Typically, incident light 102 includes multiple incident light rays 102, each of which strikes incident surface 110 at a different angle of incidence and at a different point of incidence 112. Refracted light 102′, resulting from the refraction of the multiple incident light rays, generates a similar plurality of refracted light rays 102′ within dual-surface collimator 100 that propagate away from incident point 112. Furthermore, each refracted light ray propagating away from incident surface 110 has a refraction angle determined by the curved shape of incident surface 110 and the angle of incidence of the corresponding incident light ray.

According to various embodiments, the incident surface 110 may include a curvature formed in the surface of the material of the dual-surface collimator 100. For example, the dual-surface collimator 100 may include a material such as, but not limited to, a substantially optically transparent plastic or polymer (e.g., poly(methyl methacrylate) or "acrylic glass," polycarbonate, etc.). In other examples, the dual-surface collimator material in which the curvature of the incident surface 110 is formed may include, but is not limited to, one or more of various types of glass (e.g., quartz glass, alkali aluminosilicate glass, borosilicate glass, etc.).

In some embodiments, the curved shape (or simply "curve") of the incident surface 110 can be configured to spread the light 102 from the light source 104, for example, to uniformly illuminate the reflector surface 120 (described below) of the dual-surface collimator 100 with refracted light 102'. In some embodiments, the curved shape of the incident surface 110 can be configured to differentially refract light incident from multiple different light sources (e.g., light sources generating light of different colors). In some embodiments, the curvature of the incident surface 110 can be configured to partially collimate the refracted light 102', for example, in a direction corresponding to the direction of the bidirectionally collimated light 106 at the dual-surface collimator output aperture 108. In some embodiments, the curved shape of the incident surface 110 can also be configured to modify the virtual position of the light source 104. The modified virtual position can be relative to a focal point of a reflector surface (e.g., reflector surface 120) of the dual-surface collimator 100, described below. According to some embodiments, the incident surface 110 can have a so-called double-curved shape. In this document, a "doubly curved" shape or surface is defined as a shape or surface that is curved in two different directions (e.g., two directions orthogonal to each other). Similarly, a "single curved" shape or surface is defined as a shape or surface that is curved in substantially one direction.

In various embodiments, the particular shape of the curve of the incident surface 110 can be configured (e.g., adjusted, optimized, or otherwise "shaped") to enhance or adjust its refractive properties. For example, the curved shape of the incident surface 110 can have a so-called "shaped cylindrical" profile or a so-called "shaped spherical" profile that is configured or "optimized" to provide target refractive properties (e.g., refraction angles) of the incident surface 110 (e.g., to provide light diffusion, etc.). Furthermore, in some embodiments, the shaped spherical profile can be optimized to address or mitigate characteristics of the light source, including, but not limited to, directional distortion or partial (albeit non-ideal or undesirable) collimation of the incident light 102 generated by the light source 104.

The dual-surface collimator 100 shown in FIG2 also includes a reflector surface 120 opposite the incident surface 110 having another curved surface. As defined herein, "opposite" means that the reflector surface 120 is on or formed in the other surface of the dual-surface collimator material from the incident surface 110. Further, as defined, "opposite" means that the reflector surface 120 is the other surface of the dual-surface collimator material that is positioned to receive the refracted light 102' from the incident surface 110. As an example and not a limitation, FIG2 shows an example of the relative position of the reflector surface 120 relative to the incident surface 110.

According to various embodiments, reflector surface 120 is configured to reflect refracted light 102'. In particular, reflector surface 120 is configured to reflect each refracted light 102' at a reflection point 122. Furthermore, reflector surface 120 is configured to reflect refracted light 102' back toward incident surface 110 as reflected light 102". FIG2 illustrates reflected light 102" as an arrow pointing away from reflector surface 120 toward incident surface 110.

In some embodiments, the curved shape of the reflector surface 120 can have a parabolic or substantially parabolic shape (or profile). In various embodiments, the particular curved shape of the reflector surface 120 (e.g., parabolic shape) can be configured (e.g., adjusted, optimized, or otherwise "shaped") to enhance or adjust its refractive properties. For example, the curved shape of the reflector surface 120 can have a so-called "shaped parabolic" profile that is "optimized" or configured to provide target reflective properties (e.g., reflection angle) of the reflector surface 120 (e.g., to provide light diffusion, etc.). Thus, the curved shape of the reflector surface 120 can vary from one reflection point 122 to another along the reflector surface 120. According to some embodiments, the reflector surface 120 can have a doubly curved shape (e.g., curved in two orthogonal directions). For example, the reflector surface 120 can be a doubly curved, shaped parabolic surface.

According to some embodiments, the reflector surface 120 may be metallized or otherwise coated with a reflective material to provide optical reflection. Thus, according to some embodiments, the reflection point 122 may include a reflective coating. For example, the reflective material used to coat the parabolic surface of the reflector surface 120 may include, but is not limited to, aluminum, chromium, nickel, silver, or gold. In other embodiments, the reflection generated by the reflector surface 120 at the reflection point 122 may be provided by a change in the refractive index between the material of the dual-surface collimator 100 and, for example, but not limited to, air outside the dual-surface collimator 100 (i.e., beyond the reflector surface 120).

In some embodiments, the reflector surface 120 may further include a tilt angle (i.e., the reflector surface 120 may be tilted at a tilt angle). For example, the tilt angle may be configured to provide a non-zero propagation angle θ' of the bidirectional collimated light 106 or a portion thereof. In yet another example, the tilt angle may be provided or further provided by displacing the position of the light source 104 providing the incident light 102 relative to the focus of the curved reflector surface 120 (e.g., as shown by the curved incident surface).

2 and specifically with reference to the incident surface 110, according to various embodiments, the incident surface 110 is further configured to re-reflect the reflected light 102″ toward the output aperture 108 of the dual-surface collimator 100. In particular, the reflected light 102″ may be re-reflected by or at the incident surface 110 according to total internal reflection (TIR). Moreover, the re-reflected light 102″ from the incident surface 110 is re-reflected in a direction toward the output aperture 108 as bidirectionally collimated light 106. It should be noted that according to various embodiments, unlike the reflector surface 120, the incident surface 110 generally does not include a reflective coating. In particular, according to various embodiments, due to the refractive index difference at the boundary between the material of the dual-surface collimator 100 and the material outside the dual-surface collimator 100 (e.g., air), the re-reflection generated by TIR occurs at the inner side 114 of the incident surface 110.

According to various embodiments, the dual-surface collimator 100 is configured such that each of refraction and re-reflection at the incident surface 110, together with reflection at the reflector surface 120, serves to convert the incident light 102 into bidirectional collimated light 106. In particular, according to various embodiments, the curved shapes and relative orientations of the incident surface 110 and the reflector surface 120, in combination, are configured to convert the incident light 102 into bidirectional collimated light 106 at the output aperture 108. Thus, the curvature and orientation of the incident surface 110 and the reflector surface 120 can be substantially arbitrary, so long as the refraction of the incident light 102 resulting from the curved shape of the incident surface 110, the reflection of the refracted light 102′ resulting from the curved shape of the reflector surface 120, and the re-reflection of the reflected light 102″ resulting from the curved shape of the incident surface 110 through TIR provide bidirectional collimated light 106 at the output aperture 108.

According to some embodiments, various bends of the incident and reflector surfaces 110, 120 can be implemented by simultaneous optimization in a simulation of the dual-surface collimator 100. For example, a ray tracing simulation can be used in conjunction with the optimization to adjust or tune the various bends. The optimization can be terminated when the simulated incident light 102 is converted into simulated bi-directional collimated light 106 at the output aperture 108 according to the ray tracing simulation. Furthermore, the various bends or bend shapes can be adjusted or tuned during the optimization to achieve a simulated non-zero propagation angle θ' of the bi-directional collimated light 106, e.g., a non-zero propagation angle relative to the horizontal plane.

In some embodiments, the curvature or curved shape of the incident surface 110 is configured to extend substantially from near an end of the reflector surface 120 to near a surface or boundary representing the output aperture 108 of the dual-surface collimator 100. For example, the curvature of the incident surface 110 can include greater than approximately thirty percent (30%), or greater than approximately fifty percent (50%), or greater than approximately seventy percent (70%), or greater than approximately ninety percent (90%) of the incident surface between the reflector surface 120 and the output aperture 108. For example, FIG. 2 illustrates the curvature of the incident surface extending substantially from near one end of the reflector surface 120 to near one end of the output aperture 108 to represent approximately one hundred percent (100%) of the incident surface 110.

In some embodiments, for example, the curved shape of the incident surface 110 can also be configured to form a cavity that can enclose the light source 104 (e.g., the curved shape can be a concave curved shape). FIG3 shows a cross-sectional view of a portion of a dual-surface collimator 100 including a curved incident surface 110, according to an example of an embodiment consistent with the principles described herein. As shown, the dual-surface collimator 100 contacts the substrate 130, for example, at contact points 130′, 130″ at the ends of the curved incident surface 110 adjacent to the reflector surface 120 and the output aperture 108, respectively. Furthermore, in some examples, the light source 104 is mounted to the substrate. As shown, the curved shape of the incident surface 110 is configured to form a cavity 132 between the curved incident surface 110 and the substrate 130, which is defined by the contact points 130′, 130″. Moreover, the cavity 132 is configured to substantially enclose the light source 104 on the substrate 130. For example, the cavity 132 can enclose the light source 104 to provide protection for the light source 104. In particular, in some embodiments, the light source 104 can include a light emitting diode (LED) mounted to the surface of the substrate 130. For example, enclosing the surface mounted LED by the cavity 132 formed by the curved shape of the incident surface 110 can provide protection, including but not limited to mechanical wear protection and environmental protection (e.g., moisture, debris, etc.).

According to some embodiments of the principles described herein, backlights employing bidirectional collimation are provided. FIG4A shows a top view of a backlight 200 in an example according to an embodiment consistent with the principles described herein. FIG4B shows a cross-sectional view of a backlight 200 in an example according to an embodiment consistent with the principles described herein. FIG4C shows a perspective view of a backlight 200 in an example according to an embodiment consistent with the principles described herein.

As shown in Figures 4A-4C, the backlight 200 includes a dual-surface collimator 210. In some embodiments, the dual-surface collimator 210 can be substantially similar to the dual-surface collimator 100 described above. In particular, in some embodiments, the dual-surface collimator 210 (e.g., as shown in Figure 4B) includes an incident surface 212 and a reflector surface 214, each of which can be substantially similar to a corresponding one of the incident surface 110 and the reflector surface 120 of the dual-surface collimator 100. For example, Figure 4A shows a plurality of reflector surfaces 214 of the dual-surface collimator 210 as viewed from above. For example, each of the plurality of reflector surfaces 214 can be substantially similar to the reflector surface 120. Furthermore, for example, the reflector surfaces 214 shown in Figures 4A-4C can represent a double-curved reflector (e.g., a shaped parabolic reflector). In some examples, the incident surface 212, such as shown in the cross-sectional view of Figure 4B, can be substantially similar to the incident surface 110 of Figure 2. In some embodiments, the incident surface 212 can include a plurality of incident surfaces, wherein each incident surface 212 of the plurality of incident surfaces is configured to direct light to a corresponding reflector surface 214 of the plurality of reflector surfaces. For example, each incident surface 212 of the plurality of incident surfaces can have an independent, double-curved shape (e.g., an independent spherical shape for each incident surface 212). In other embodiments, the incident surface 212 is a substantially continuous curved surface that spans the length of the plurality of reflector surfaces 214. For example, the incident surface 212 can be a single-curved, substantially continuous, cylindrical surface that spans the width of the dual-surface collimator 210 (i.e., in the y-direction, as shown).

4B , according to various embodiments, a dual-surface collimator 210 is configured to receive light 202 (e.g., from a light source 230 described below) and provide bidirectional collimated light 204 at an output 216 of the dual-surface collimator 210. Furthermore, according to various embodiments, the dual-surface collimator 210 is configured to provide the bidirectional collimated light 204 having a non-zero propagation angle relative to a horizontal x-y plane at the dual-surface collimator output 216. In some embodiments, the bidirectional collimated light 204 provided by the dual-surface collimator 210 can be substantially similar to the bidirectional collimated light 106 provided by the dual-surface collimator 100, described above.

The illustrated backlight 200 also includes a plate light guide 220 coupled (e.g., optically coupled) to the output 216 of the dual-surface collimator 210. The plate light guide 220 is configured to receive and guide the bidirectional collimated light 204 at a non-zero propagation angle. In particular, the plate light guide 220 can receive the bidirectional collimated light 204 at an input end of the plate light guide 220, or equivalently, at an input aperture. According to various embodiments, the plate light guide 220 is further configured to emit a portion of the guided, bidirectional collimated light 204 from a surface of the plate light guide 220. In FIG4B , the emitted light is shown as a plurality of light rays (arrows) extending away from the surface of the plate light guide.

In some embodiments, the plate light guide 220 can be a sheet 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 bidirectionally collimated light 204 from the dual-surface collimator 210 as a guided light beam using total internal reflection. The dielectric material can have a first refractive index that is greater than a second refractive index of the medium surrounding the dielectric optical waveguide. The difference in refractive index is configured to promote total internal reflection of the guided light beam according to one or more guided modes of the plate light guide 220.

According to various examples, the substantially optically transparent material of the plate light guide 220 may include or consist of any of a variety of dielectric materials, including, but not limited to, one or more of various types of glass (e.g., silicate 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 220 may further include a cladding layer (not shown) on at least a portion of a surface (e.g., one or both of the top and bottom surfaces) of the plate light guide 220. According to some examples, the cladding layer may be used to further promote total internal reflection.

In some embodiments, (e.g., as shown in FIG4A ), the plate light guide 220 can be integral with the dual-surface collimator 210. In particular, the plate light guide 220 and the dual-surface collimator 210 can be formed from and therefore comprise the same material. For example, the plate light guide 220 can be an extension of the output 216 (or output aperture) of the dual-surface collimator 210. In other embodiments (e.g., as shown in FIG4B ), the dual-surface collimator 210 and the plate light guide 220 are separate, and a layer of adhesive or binder, another interface material, or even air between the output 216 and the input of the plate light guide 220 provides coupling (e.g., one or both of optical coupling and mechanical coupling) between the dual-surface collimator 210 and the plate light guide 220. For example, the dual-surface collimator 210 can comprise a polymer or plastic material, and the plate light guide 220 can comprise glass. The dual-surface collimator 210 and the plate light guide 220 may be secured to each other using a suitable adhesive layer 222 (eg, an optically matching adhesive) therebetween, for example, as shown in FIG. 4B .

According to some embodiments, the backlight 200 may further include a light source 230. The light source 230 is configured to provide light 202 to the dual-surface collimator 210. Specifically, the light source 230 is located near the incident surface 212 of the dual-surface collimator 210 (e.g., as shown below in Figures 4B-4C) and is configured to provide incident light 202 onto the curved shape of the incident surface. In various embodiments, the light source 230 may include substantially any light source, including but not limited to one or more light-emitting diodes (LEDs). In some embodiments, the light source 230 may include an optical emitter configured to generate substantially monochromatic light having a narrowband spectrum represented by a specific color. Specifically, the color of the monochromatic light may be a primary color of a specific color space or color model (e.g., a red-green-blue (RGB) color model). In some embodiments, the light source 230 may include multiple different light sources configured to provide light of different colors. For example, the different light sources may be offset from one another. According to some embodiments, the offset of the different light sources may be configured to provide different, color-specific, non-zero propagation angles of the bidirectionally collimated light 204 corresponding to each of the different colors of light. In particular, for example, the offset can add an additional non-zero propagation angle component to the non-zero propagation angle provided by the dual-surface collimator 210. In some embodiments, the light source 104 and the light source 230 described above with respect to the dual-surface collimator 100 can be substantially similar.

In some embodiments, the vertical range of the output 216 of the dual-surface collimator 210 is greater than the vertical range of the input aperture of the plate light guide 220. According to some embodiments, the alignment between the plate light guide input aperture and the dual-surface collimator output 216 can be configured to adjust the characteristics of the bidirectional collimated light 204 coupled into the plate light guide 220 at the input aperture. For example, the intensity of the bidirectional collimated light 204 coupled into the plate light guide 220 can be adjusted by selecting a particular alignment (i.e., the vertical position of the plate light guide 220 relative to the dual-surface collimator 210). In another example, the relative amounts of various colors of the bidirectional collimated light 204 coupled into the plate light guide 220 can be controlled by the alignment. In particular, when the bidirectional collimated light 204 includes different colors of light at different, color-specific, non-zero propagation angles, aperture alignment can be used to control the relative amounts of each of the different colors depending on these different, color-specific, non-zero propagation angles.

FIG4D illustrates a cross-sectional view of the alignment between the output 216 of the dual-surface collimator 210 and the input aperture 224 of the plate light guide 220, according to an example of an embodiment consistent with the principles described herein. Specifically, FIG4D illustrates that the dual-surface collimator output 216 has a vertical range that is greater than the vertical range of the plate light guide input aperture 224. The bold double-headed arrows indicate adjustment (e.g., up or down) of the alignment between the output 216 and the input aperture 224, respectively. Three extended arrows (e.g., having a solid line, a large dashed line, and a small dashed line) illustrate three different colors of bidirectional collimated light 204 propagating at three different, color-specific, non-zero propagation angles. According to various embodiments, the selection of a specific alignment, or equivalently, a specific vertical position, of the plate light guide input aperture 224 relative to the output 216 of the dual-surface collimator 210 can affect the relative amounts of each of the three different colors of bidirectional collimated light coupled into the plate light guide 220.

In accordance with some embodiments (e.g., as shown in FIG4B ), backlight 200 may further include a multibeam diffraction grating 240 at a surface of plate light guide 220. Multibeam diffraction grating 240 is configured to diffractively couple a portion of the guided, bidirectionally collimated light 204 out of plate light guide 220 as a plurality of light beams 206. The plurality of light beams 206 (i.e., the plurality of light rays (arrows) shown in FIG4B ) represent the emitted light. In various embodiments, a light beam 206 of the plurality of light beams has a principal angular direction that is different from the principal angular directions of other light beams 206 of the plurality of light beams.

In some embodiments, multibeam diffraction grating 240 is a component of or is arranged in an array of multibeam diffraction gratings 240. In some embodiments, backlight 200 is a backlight for a three-dimensional (3D) electronic display, and the principal axis direction of light beam 206 corresponds to the viewing direction of the 3D electronic display.

FIG5A shows a cross-sectional view of a portion of backlight 200 having a multibeam diffraction grating 240, according to an example of an embodiment consistent with the principles described herein. FIG5B shows a cross-sectional view of a portion of backlight 200 having a multibeam diffraction grating 240, according to an example of another embodiment consistent with the principles described herein. FIG5C shows a perspective view of the portion of the backlight of FIG5A or FIG5B including the multibeam diffraction grating 240, according to an example of an embodiment consistent with the principles described herein. By way of example and not limitation, the multibeam diffraction grating 240 shown in FIG5A includes grooves in the surface of the plate light guide 220. FIG5B shows a multibeam diffraction grating 240 including ridges protruding from the surface of the plate light guide.

As shown in Figures 5A-5B, the multibeam diffraction grating 240 is a chirped diffraction grating. In particular, the diffraction features 240a are closer together at the first end 240' of the multibeam diffraction grating 240 than at the second end 240". In addition, the diffraction spacing d of the diffraction features 240a is shown to vary from the first end 240' to the second end 240". In some embodiments, the chirped diffraction grating of the multibeam diffraction grating 240 can have or exhibit a chirp in the diffraction spacing d that varies linearly with distance. Thus, the chirped diffraction grating of the multibeam diffraction grating 240 can be referred to as a "linearly chirped" diffraction grating.

In another embodiment, the chirped diffraction grating of the multibeam diffraction grating 240 can exhibit a nonlinear chirp in the diffraction spacing d. Various nonlinear chirps that can be used to implement a chirped diffraction grating include, but are not limited to, exponential chirp, logarithmic chirp, or chirp that varies in another substantially non-uniform or random, but still monotonic, manner. Non-monotonic chirps can also be employed, such as, but not limited to, sinusoidal chirp or triangular or sawtooth chirp. Combinations of any of these types of chirp can also be used in the multibeam diffraction grating 240.

As shown in FIG5C , the multibeam diffraction grating 240 includes diffractive features 240a (e.g., grooves or ridges) located in, on, or on the surface of the plate light guide 220 that are chirped and curved (i.e., the multibeam diffraction grating 240 is a curved, chirped diffraction grating, as shown). Bidirectionally collimated light 204 guided as guided beams in the plate light guide 220 has an incident direction relative to the multibeam diffraction grating 240 and the plate light guide 220, as indicated by the bold arrows in FIG5A-5C . Also shown are multiple outcoupled or emitted light beams 206 directed away from the multibeam diffraction grating 240 at the surface of the plate light guide 220. The light beams 206 are shown emitted in multiple different predetermined principal angular directions. In particular, the different predetermined principal angular directions of the emitted light beams 206 differ in both azimuth and elevation (e.g., to shape a light field).

According to various examples, both the predefined chirp of the diffractive features 240a and the curvature of the diffractive features 240a can contribute to a corresponding plurality of different predetermined principal angular directions of the emitted light beams 206. For example, due to the curvature of the diffractive features, the diffractive features 240a within the multibeam diffraction grating 240 can have varying orientations relative to the incident directions of the guided light beams within the plate light guide 220. In particular, the orientation of the diffractive features 240a at a first point or location within the multibeam diffraction grating 240 can differ from the orientation of the diffractive features 240a at another point or location relative to the incident direction of the guided light beams. With respect to the outcoupled or emitted light beams 206, the azimuthal component of the principal angular direction of the light beams 206 can be determined by or correspond to the azimuthal orientation angle of the diffractive features 240a at the origin of the light beams 106 (i.e., the point at which the guided light beams are outcoupled). Thus, the varying orientations of the diffractive features 240a within the multibeam diffraction grating 240 produce different light beams 206 having different principal angular directions, at least with respect to their respective azimuthal components.

In particular, at different points along the curvature of the diffractive feature 240a, the "lower diffraction grating" of the multibeam diffraction grating 240 associated with the curved diffractive feature 240a has different azimuthal orientation angles. The "lower diffraction grating" refers to the diffraction grating of multiple non-curved diffraction gratings that, when superimposed, produce the curved diffractive feature 240a of the multibeam diffraction grating 240. Thus, at a given point along the curved diffractive feature 240a, the curvature has a particular azimuthal orientation angle that is substantially different from the azimuthal orientation angle at another point along the curved diffractive feature 240a. Furthermore, the particular azimuthal orientation angle results in a corresponding azimuthal component of the principal direction of the light beam 206 emitted from the given point. In some examples, the curvature of the diffractive feature 240a (e.g., a groove, ridge, etc.) can represent a portion of a circle. The circle can be coplanar with the lightguide surface. In other examples, the curvature can represent a portion of an ellipse or another curved shape, such as coplanar with the lightguide surface.

In other embodiments, the multibeam diffraction grating 240 may include diffractive features 240a that are "segmentally" curved. Specifically, while the diffractive features 240a themselves may not describe a substantially smooth or continuous curve at different points along the diffractive features 240a within the multibeam diffraction grating 240, the diffractive features 240a may still be oriented at different angles relative to the incident direction of the guided beams of the bidirectional collimated light 204. For example, the diffractive features 240a may be grooves comprising a plurality of substantially straight segments, each segment having an orientation different from adjacent segments. According to various embodiments, the different angles of the segments may together approximate a curve (e.g., a portion of a circle). In still other examples, the diffractive features 240a may simply have different orientations relative to the incident direction of the guided light at different locations within the multibeam diffraction grating 240, without approximating a specific curve (e.g., a circle or an ellipse).

In some embodiments, the grooves or ridges forming the diffraction features 240a can be etched, milled, or molded into the surface of the plate light guide. Thus, the material of the multibeam diffraction grating 240 can comprise the material of the plate light guide 220. As shown in FIG. 5B , for example, the multibeam diffraction grating 240 comprises ridges protruding from the surface of the plate light guide 220, wherein the ridges can be substantially parallel to one another. In FIG. 5A (and FIG. 4B ), the multibeam diffraction grating 240 comprises grooves penetrating the surface of the plate light guide 220, wherein the grooves can be substantially parallel to one another. In other examples (not shown), the multibeam diffraction grating 240 can comprise a film or layer applied or affixed to the light guide surface. The multiple light beams 206 provided by the multibeam diffraction grating 240, in different principal angular directions, are configured to form a light field in the viewing direction of an electronic display. In particular, the backlight 200 employing bidirectional collimation is configured to provide information corresponding to pixels of an electronic display, such as 3D information.

According to some embodiments of the principles described herein, a three-dimensional (3D) electronic display is provided. FIG6 shows a block diagram of a three-dimensional (3D) electronic display 300 in an example of an embodiment according to the principles described herein. 3D electronic display 300 is configured to generate directional light comprising light beams having different principal angular directions and, in some embodiments, also having multiple different colors. For example, 3D electronic display 300 can provide or generate multiple different light beams 306 (e.g., as a light field) that emanate from and away from 3D electronic display 300 at different predetermined principal angular directions. Furthermore, different light beams 306 can include light beams 306 having different colors of light. Furthermore, according to some embodiments, light beams 306 of multiple light beams can be modulated into modulated light beams 306′ to facilitate displaying information including color information (e.g., when light beams 306 are colored light beams).

In particular, modulated light beams 306′ having different predetermined principal angles can form multiple pixels of 3D electronic display 300. In some embodiments, 3D electronic display 300 can be a so-called “glasses-free” 3D electronic display (e.g., a multi-view, “holographic,” or autostereoscopic display), where light beams 306′ correspond to pixels associated with different “views” of 3D electronic display 300. By way of example, modulated light beams 306′ are illustrated in FIG6 using dashed arrows, while different light beams 306 prior to modulation are illustrated as solid arrows.

The 3D electronic display 300 shown in FIG6 includes a dual-surface collimator 310 (abbreviated as "dual-surface collimator" in FIG6 ). The dual-surface collimator 310 is configured to provide bidirectional collimated light having vertical collimation and horizontal collimation. In particular, the vertical and horizontal collimations are relative to the vertical direction (e.g., the z-direction) or vertical plane (e.g., the y-z plane) and the horizontal direction (e.g., the x-direction) or horizontal plane (x-y plane) of the dual-surface collimator 310. Furthermore, the dual-surface collimator 310 is configured to provide bidirectional collimated light at a non-zero propagation angle relative to the horizontal plane of the dual-surface collimator 310.

In some embodiments, the dual-surface collimator 310 is substantially similar to the dual-surface collimator 100 described above. In particular, the dual-surface collimator 310 includes a curved incident surface and a curved reflector surface. The curved reflector surface is opposite the curved incident surface, for example, on the opposite side of the material of the dual-surface collimator 310. Furthermore, according to some embodiments, the curved incident surface can be substantially similar to the incident surface 110 having a curved shape, and the curved reflector surface can be substantially similar to the reflector surface 120 having a curved shape described above with respect to the dual-surface collimator 100.

In particular, the curved incident surface of the dual-surface collimator 310 can be configured to refract incident light toward the curved reflector surface. Furthermore, the curved reflector surface can be configured to reflect the refracted light back toward the curved incident surface, and the curved incident surface can also be configured to re-reflect the reflected light from the curved reflector surface toward a plate light guide (e.g., plate light guide 320, described below) to provide bidirectional collimated light. According to some embodiments, the combination of the relative orientation and curved shape of each of the curved incident surface and the curved reflector surface is configured to collimate and redirect the incident light into bidirectional collimated light having a non-zero propagation direction.

In some embodiments, the curved reflector surface comprises a light reflector having a parabolic shape or a substantially parabolic profile. The parabolic shape can be configured to determine or provide a non-zero propagation angle of bidirectional collimated light at the output of the dual-surface collimator. Furthermore, for example, the curved reflector surface of the dual-surface collimator 310 can comprise a light reflector having a parabolic shape. For example, the parabolic shape can be shaped (e.g., by optimization).

As shown in FIG6 , the 3D electronic display 300 further includes a plate light guide 320. The plate light guide 320 is configured to guide bidirectional collimated light as a guided beam at a non-zero propagation angle. In particular, the guided beam can be guided at a non-zero propagation angle relative to a surface of the plate light guide 320 (e.g., one or both of the top and bottom surfaces). The surface can, in some embodiments, be parallel to a horizontal plane. According to some embodiments, the plate light guide 320 can be substantially similar to the plate light guide 220 described above with respect to the backlight 200.

According to various embodiments, and as shown in FIG6 , 3D electronic display 300 also includes an array of multibeam diffraction gratings 330 located at the surface of plate light guide 320. According to some embodiments, the array of multibeam diffraction gratings 330 can be substantially similar to the multibeam diffraction gratings 240 described above with respect to backlight 200. In particular, the array of multibeam diffraction gratings 330 is configured to diffractively couple out portions of the guided light beams as light beams having different principal angles, represented as light beams 306 in FIG6 . Furthermore, according to various embodiments, the different principal angles of light beams 306 coupled out by multibeam diffraction gratings 330 correspond to different 3D views of 3D electronic display 300. In some embodiments, multibeam diffraction gratings 330 include chirped diffraction gratings having curved diffraction features. In some embodiments, the chirp of the chirped diffraction grating is a linear chirp.

In some embodiments, the 3D electronic display 300 (e.g., as shown in FIG6 ) further includes a light source 340 configured to provide light to the input of the dual-surface collimator 310. In some embodiments, the light source 340 can be substantially similar to the light source 230 of the backlight 200 described above. In particular, the light source 340 can include a plurality of different light emitting diodes (LEDs) configured to provide light of different colors (referred to as “different-color LEDs” for simplicity of discussion). In some embodiments, the different-color LEDs can be offset from one another (e.g., laterally offset). The offset of the different-color LEDs is configured to provide different, color-specific, non-zero propagation angles of the bidirectional collimated light from the dual-surface collimator 310. Furthermore, a different, color-specific, non-zero propagation angle can correspond to each of the different colors of light provided by the light source 340.

In some embodiments (not shown), the different colors of light can include red, green, and blue of a red-green-blue (RGB) color model. Furthermore, the plate light guide 320 can be configured to guide the different colors as light beams at different color-dependent non-zero propagation angles within the plate light guide 320. For example, according to some embodiments, a first guided color light beam (e.g., a red light beam) can be guided at a first color-dependent, non-zero propagation angle, a second guided color light beam (e.g., a green light beam) can be guided at a second color-dependent, non-zero propagation angle, and a third guided color light beam (e.g., a blue light beam) can be guided at a third color-dependent, non-zero propagation angle.

As shown in FIG6 , the 3D electronic display 300 may further include a light valve array 350. According to various embodiments, the light valve array 350 is configured to modulate the outcoupled light beams 306 of the plurality of light beams into modulated light beams 306′ to form or serve as 3D pixels corresponding to different 3D views of the 3D electronic display 300. In some embodiments, the light valve array 350 includes a plurality of liquid crystal light valves. In other embodiments, for example, the light valve array 350 may include another type of light valve, including but not limited to an electrowetting light valve, an electrophoretic light valve, a combination thereof, or a combination of a liquid crystal light valve and another type of light valve.

According to other embodiments of the principles described herein, a method for bidirectional light collimation is provided. FIG7 shows a flow chart of a method 400 for bidirectional light collimation in an example of an embodiment consistent with the principles described herein. As shown in FIG7 , the method 400 for bidirectional light collimation includes refracting 410 light incident on and passing through an incident surface of a dual-surface collimator. According to various embodiments, the incident surface has a curved shape. In some embodiments, the incident surface is substantially similar to the incident surface 110 having a curved shape described above with respect to the dual-surface collimator 100. For example, the incident surface can have a curved shape that substantially includes the entire extent of the incident surface. In other examples, the curved shape includes a portion of the extent of the incident surface. Additionally, in various embodiments, the incident surface curved shape can be single-curved or double-curved.

The method 400 for bidirectional light collimation further includes reflecting 420 the refracted light at a reflector surface of the dual-surface collimator. According to various embodiments, the reflector surface has another curved shape. For example, the other curved shape of the reflector surface can be different from the curved shape of the incident surface. In some embodiments, the reflector surface is substantially similar to the curved reflector surface 120 described above with respect to the dual-surface collimator 100. For example, the reflector surface can have a parabolic shape. In another example, the reflector surface can include a double-curved surface.

The method 400 for bidirectional light collimation shown in FIG7 also includes re-reflecting 430 the reflected light at the incident surface using total internal reflection. According to various embodiments, the re-reflected light from re-reflection 430 is directed toward the output aperture of the dual-surface collimator. Furthermore, according to various embodiments, the curved shapes and relative orientations of the incident and reflector surfaces are combined to provide bidirectional collimated light at the output aperture. Furthermore, according to various embodiments, the bidirectional collimated light has a non-zero propagation angle relative to the horizontal plane.

For example, the non-zero propagation angle can be substantially similar to the non-zero propagation angle described above with respect to the dual-surface collimator 100. In some embodiments, the curved shape of the reflector surface includes a parabolic shape with an inclined angle, which is configured to provide or at least partially provide a non-zero propagation angle of bidirectional collimated light. In addition, in some embodiments, the reflector surface can be coated with a reflective coating.

According to other embodiments of the principles described herein, a method of operating a three-dimensional (3D) electronic display is provided. FIG8 shows a flow chart of a method 500 of operating a 3D electronic display in an example of an embodiment consistent with the principles described herein. As shown in FIG8 , the method 500 of operating a 3D electronic display includes providing 510 bidirectional collimated light having a non-zero propagation angle. According to various embodiments, the bidirectional collimated light is provided 510 using a dual-surface collimator. The dual-surface collimator can be substantially similar to the dual-surface collimator 100 described above. In some embodiments, the bidirectional collimated light can be provided 510 according to the method 400 of bidirectional light collimation described above. Moreover, the bidirectional collimated light can be substantially similar to the bidirectional collimated light 106 or 204 described above for the dual-surface collimator 100 or backlight source 200, respectively.

The method 500 of 3D electronic display operation further includes directing 520 bidirectional collimated light in a plate light guide. In particular, the bidirectional collimated light is directed 520 at a non-zero propagation angle within the plate light guide. According to some embodiments, the plate light guide can be substantially similar to the plate light guide 220 of the backlight 200, as described above.

The method 500 of operating a three-dimensional electronic display of FIG8 also includes diffractionally coupling out 530 a portion of the bidirectional collimated light from the plate light guide using a multibeam diffraction grating to generate 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, the diffractionally coupling out 530 a portion of the bidirectional collimated light is configured to provide a 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 correspond to directions of different 3D views of the 3D electronic display. According to some embodiments, the multibeam diffraction grating is substantially similar to the multibeam diffraction grating 240 of the backlight 200, as described above. The diffraction-coupled out 530 beams of the plurality of light beams correspond to the light beams 206 or 306 described above with respect to the backlight 200 or the 3D electronic display 300, respectively.

According to various embodiments, the method 500 of operating a 3D electronic display shown in FIG8 further includes modulating 540 light beams of the plurality of light beams using an array of light valves. According to various embodiments, the modulated light beams 540 form 3D pixels of the 3D electronic display in a 3D viewing direction. In some embodiments, the array of light valves can be substantially similar to the light valve array 350 described above with respect to the 3D electronic display 300.

In some embodiments (not shown), the method 500 of operating a 3D electronic display further includes providing light that is collimated in both directions. For example, the light can be non-collimated light provided to a dual-surface collimator (e.g., a dual-surface collimator that can be used to provide 510 bidirectional collimated light). For example, a light source can be used to provide light at the input of the incident surface of the dual-surface collimator. Furthermore, in some embodiments, the light source can be substantially similar to the light source 230 described above with respect to the backlight 200.

Thus, examples of dual-surface collimators, backlights and 3D electronic displays employing dual-surface collimators, methods of bidirectional collimation, and methods of operating 3D electronic displays employing bidirectional collimation 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 dual-surface collimator, comprising: An incident surface having a curved shape, the incident surface being configured to refract incident light from a light source; and A reflector surface, opposite the incident surface and having another curved shape, is configured to reflect refracted light back toward the incident surface. The incident surface is also configured to reflect reflected light again toward the output aperture of the dual-surface collimator via total internal reflection. The curved shape and relative orientation of the incident surface and the reflector surface are configured to convert the incident light into bidirectional collimated light at the output aperture, the bidirectional collimated light having a non-zero propagation angle relative to the horizontal plane of the dual-surface collimator. 2. The dual-surface collimator of claim 1, wherein the curved shape of the incident surface is configured to modify the virtual position of the light source relative to the focal point of the reflector surface, and the light source is configured to provide light incident on the incident surface. 3. The dual-surface collimator of claim 1, wherein the curvature of the incident surface is configured to extend substantially from the reflector surface to the output aperture of the dual-surface collimator. 4. The dual-surface collimator of claim 1, wherein the incident surface has a concave curvature and is configured to form a cavity to substantially enclose the light source on the substrate. 5. The dual-surface collimator according to claim 1, wherein the curved shape of the reflector surface is coated with a reflective coating. 6. A backlight source comprising the dual-surface collimator according to claim 1, wherein the backlight source further comprises: A plate optical guide coupled to the output aperture of the dual-surface collimator, the plate optical guide having an input aperture configured to receive bidirectional collimated light, the plate optical guide being configured to guide the bidirectional collimated light at a non-zero propagation angle. The plate light guide is further configured to emit a portion of guided bidirectional collimated light from the surface of the plate light guide. 7. The backlight according to claim 6, wherein the vertical range of the output aperture of the dual-surface collimator is greater than the vertical range of the input aperture of the plate light guide, and the alignment between the input aperture of the plate light guide and the output aperture of the dual-surface collimator is configured to adjust the characteristics of bidirectional collimated light coupled to the plate light guide at the input aperture. 8. The backlight source of claim 6, further comprising a light source configured to provide light to the dual-surface collimator, the light source being located near the curved incident surface to provide incident light. 9. The backlight of claim 8, wherein the backlight comprises a plurality of different light sources configured to provide light of different colors, the different light sources being offset from each other, wherein the offset of the different light sources is configured to provide different, color-specific, non-zero propagation angles of bidirectional collimated light corresponding to each of the different colors of light. 10. The backlight source of claim 6, further comprising a multi-beam diffraction grating at the plate light guide surface, the multi-beam diffraction grating being configured to diffractically couple a portion of guided bidirectional collimated light from the plate light guide as a plurality of beams emitted from the plate light guide surface, the beams of the plurality of beams having a principal direction different from the principal direction of the other beams of the plurality of beams. 11. A three-dimensional electronic display comprising the backlight according to claim 10, wherein the three-dimensional electronic display further comprises: An optical valve that modulates the multiple beams, the optical valve being adjacent to the multi-beam diffraction grating. The main direction of the beam corresponds to the viewing direction of the three-dimensional electronic display, and the modulated beam represents a pixel of the three-dimensional electronic display in the viewing direction. 12. A three-dimensional electronic display comprising the dual-surface collimator according to claim 1, wherein the three-dimensional electronic display further comprises: A plate light guide, the plate light guide being configured to guide bidirectional collimated light as a guide beam with a non-zero propagation angle; and An array of multi-beam diffraction gratings on the surface of the plate light guide, the array of multi-beam diffraction gratings being configured to diffractically couple a portion of the output guide beam as multiple coupled output beams having different principal directions corresponding to different three-dimensional views of the three-dimensional electronic display. 13. The three-dimensional electronic display according to claim 12, wherein the array of the multi-beam diffraction gratings comprises a chirped diffraction grating having curved diffraction characteristics. 14. The three-dimensional electronic display according to claim 13, wherein the chirped diffraction grating is a linear chirped diffraction grating. 15. The three-dimensional electronic display according to claim 12, further comprising: A light source, configured to provide incident light to the curved incident surface of the dual-surface collimator; and An array of light valves configured to selectively modulate the coupled output beams of the plurality of coupled output beams into three-dimensional pixels corresponding to different three-dimensional views of the three-dimensional electronic display. 16. The three-dimensional electronic display according to claim 15, wherein the light valve array comprises a plurality of liquid crystal light valves. 17. The three-dimensional electronic display of claim 16, wherein the light source comprises a plurality of different light-emitting diodes configured to provide light of different colors, the different light-emitting diodes being offset from each other, wherein the offset of the different light-emitting diodes is configured to provide different color-specific non-zero propagation angles of bidirectional collimated light, the different color-specific non-zero propagation angles corresponding to each of the different colors of light. 18. The three-dimensional electronic display of claim 17, wherein the vertical range of the output aperture of the dual-surface collimator is greater than the vertical range of the input aperture of the plate light guide, the plate light guide is configured to receive bidirectional collimated light, and the alignment between the input aperture of the plate light guide and the output aperture of the dual-surface collimator is configured to adjust the relative amounts of different colors of light received by the input aperture of the plate light guide according to the different, color-specific, non-zero propagation angles. 19. A method for bidirectional optical collimation, the method comprising: Light is refracted and incident on the incident surface of the double-surface collimator and passes through it, the incident surface having a curved shape; The refracted light is reflected at the reflector surface of the double-surface collimator, the reflector surface having another curved shape; and Total internal reflection is used to reflect the reflected light again at the incident surface, and the reflected light is directed towards the output aperture of the dual-surface collimator. The curved shape and relative orientation of the incident surface and the reflector surface are combined to provide bidirectional collimated light at the output aperture, the bidirectional collimated light having a non-zero propagation angle relative to the horizontal plane of the dual-surface collimator. 20. The method for optical collimation according to claim 19, wherein the curved shape of the reflector surface is coated with a reflective coating. 21. A method for operating a three-dimensional electronic display, comprising the bidirectional optical collimation method according to claim 19, wherein the method for operating the three-dimensional electronic display further comprises: Guide bidirectional collimated light from the output aperture in the plate optical guide with a non-zero propagation angle; A portion of the bidirectional collimated light, diffracted by a multi-beam diffraction grating at the surface of the plate light guide, is output to generate multiple beams oriented away from the plate light guide in multiple different principal directions corresponding to different three-dimensional views of the three-dimensional electronic display; and The beams of the plurality of light beams are modulated using an array of light valves, and the modulated beams form three-dimensional pixels of the three-dimensional electronic display in different three-dimensional viewing directions.