HK1257545B - Grating-based backlight employing reflective grating islands - Google Patents

Description

Grating-based backlight using reflective grating islands

Cross reference to related applications

None.

Statement regarding federally sponsored research or development

None.

Background

Electronic displays are a nearly ubiquitous medium 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 employing electromechanical or electrofluidic light modulation (e.g., digital micromirror devices, electrowetting displays, etc.). In general, electronic displays can be classified as either active displays (i.e., displays that emit light) or passive displays (i.e., displays that modulate light provided by another source). The most common examples of active displays are CRT, PDP and OLED/AMOLED. Displays that are typically classified as passive when considering emitting light are LCD and EP displays. Passive displays, while often exhibiting compelling performance characteristics including, but not limited to, inherently low power consumption, are somewhat limited in their use in many practical applications due to the lack of ability to emit light.

To overcome the limitations of passive displays associated with emitted light, many passive displays are coupled with external light sources. The coupled light sources may allow these otherwise passive displays to emit light and act essentially as active displays. An example of such a coupled light source is a backlight (backlight). Backlights are light sources (typically flat panel light sources) placed behind an otherwise passive display to illuminate the passive display. For example, the backlight may be coupled to an LCD or EP display. The backlight emits light through the LCD or EP display. The emitted light is modulated by the LCD or EP display and then the modulated light is subsequently emitted from the LCD or EP display. The backlight is often configured to emit white light. The white light is then converted to the various colors used in the display using color filters. The color filter may be placed, for example, at the output of the LCD or EP display (less) or between the backlight and the LCD or EP display.

Drawings

Various features of examples and embodiments in 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, in which like reference numerals designate like structural elements, and in which:

figure 1 illustrates, in an example, a cross-sectional view of a diffraction grating according to an embodiment consistent with the principles described herein.

Figure 2A illustrates, in an example, a cross-sectional view of a grating-based backlight according to an embodiment consistent with principles described herein.

Figure 2B illustrates, in an example, a cross-sectional view of a grating-based backlight according to another embodiment consistent with principles described herein.

Figure 3A illustrates, in an example, a cross-sectional view of a reflection grating island according to an embodiment consistent with principles described herein.

Figure 3B illustrates, in an example, a cross-sectional view of a reflection grating island according to another embodiment consistent with principles described herein.

Figure 3C illustrates, in an example, a cross-sectional view of a reflection grating island according to yet another embodiment consistent with principles described herein.

Figure 4A illustrates, in an example, a cross-sectional view of a multibeam diffraction grating, according to an embodiment consistent with principles described herein.

FIG. 4B illustrates, in an example, a perspective view of a multibeam diffraction grating, according to an embodiment consistent with principles described herein.

Fig. 5A illustrates, in an example, a block diagram of a three-dimensional (3D) electronic display according to an embodiment consistent with principles described herein.

Fig. 5B illustrates, in an example, a cross-sectional view of a three-dimensional (3D) electronic display in accordance with an embodiment consistent with principles described herein.

Fig. 6 illustrates, in an example, a flow chart of a method of grating-based backlight operation according to an embodiment consistent with principles described herein.

Some examples may have other features in addition to or in place of those illustrated in the above figures. These and other features are described in detail below with reference to the figures.

Detailed Description

Embodiments in accordance with the principles described herein provide an electronic display backlight using reflective grating islands. In particular, the reflective grating islands employ reflective diffraction gratings to couple light out of the light guide of the backlight. Further, the light may be coupled out of the backlight as a beam of light (i.e., coupled out of the beam of light) that is directed in the view direction of the electronic display. In particular, according to some embodiments, the coupled-out light beams provided by the reflective grating islands are directed in a predefined or predetermined principal angular direction corresponding to the view direction of the electronic display. Further, in some embodiments, multiple coupled-out beams may be provided by the reflective grating islands. In accordance with some embodiments of the principles described herein, the coupled-out light beams may have mutually different principal angular directions. Coupled-out light beams with different principal angular directions (also referred to as "differently directed light beams") may be employed to display information containing three-dimensional (3D) information. For example, the differently directed coupled-out light beams may be modulated and serve as pixels of a 3D or multiview electronic display (e.g., a "glasses-free" or autostereoscopic electronic display).

Here, "light guide" is defined as a structure that uses total internal reflection to direct light within the structure. In particular, the light guide may comprise a core that is substantially transparent at the operating 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 surrounding the light guide. By definition, the condition for total internal reflection is that the refractive index of the light guide is greater than the refractive index of the surrounding medium adjacent to the surface of the light guide material. In some embodiments, the light guide may include a coating in addition to or instead of the above-described refractive index difference to further contribute to total internal reflection. For example, the coating may be a reflective coating. The light guide may be any of several light guides including, but not limited to, one or both of a plate (plate) or slab (slab) light guide and a strip (strip) light guide.

Further, herein, the term "plate" when applied to a light guide as in a "plate light guide" is defined as a segmented or differently planar layer or sheet, sometimes referred to as a "slab" light 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., opposing surfaces) of the light guide. Further, by definition herein, both the top and bottom surfaces are separate from each other and may be substantially parallel to each other in at least a different sense. That is, the top and bottom surfaces are substantially parallel or coplanar within any distinct small region of the plate light guide.

In some embodiments, the plate light guide may 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 may be curved in one or two orthogonal dimensions. For example, the plate light guide may be curved in a single dimension to form a cylindrical plate light guide. However, any curvature has a radius of curvature large enough to ensure that total internal reflection is maintained within the plate light guide to guide the light.

Here, a "diffraction grating" is generally defined as a plurality of features (i.e., diffractive features) arranged so as 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, a diffraction grating may include a plurality of features (e.g., a plurality of grooves in a surface of a material) arranged in a one-dimensional (1D) array. In other examples, the diffraction grating may be a two-dimensional (2D) array of features. For example, the diffraction grating may be a 2-D array of protrusions on or holes in the surface of the material.

Thus, and in accordance with the definition herein, a "diffraction grating" is a structure that provides diffraction of light incident on the diffraction grating. If light is incident from the light guide onto the diffraction grating, the diffraction or diffractive scattering provided may result in, and is therefore referred to as, "diffractive coupling" because the diffraction grating may couple light out of the light guide by diffraction. Diffraction gratings also redirect or change the angle of light by diffraction (i.e., at a diffraction angle). Specifically, as a result of diffraction, light exiting the diffraction grating (i.e., diffracted light of the main beam and the side-beams) generally has a propagation direction different from that of light incident on the diffraction grating (i.e., incident light). The change in the propagation direction of light by diffraction is referred to herein as "diffractive redirection". A diffraction grating may thus be understood as a structure comprising diffractive features that diffractively redirect light incident on the diffraction grating, and if light is incident from the light guide, the diffraction grating may also diffractively couple out light from the light guide.

Further, the features of a diffraction grating are referred to as "diffractive features" according to the definitions herein and may be one or more of at a material surface (i.e., a boundary between two materials), in and on the material surface. For example, the surface may be a surface of a plate light guide, or a surface of a reflective layer on or within the light guide. The diffractive 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 of at, in, and on the surface. For example, the diffraction grating may comprise a plurality of substantially parallel grooves in the surface of the material. In another example, the diffraction grating may include a plurality of parallel ridges that rise from the surface of the material. The diffractive features (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 one or more of sinusoidal profiles, rectangular profiles (e.g., binary diffraction gratings), triangular profiles, and sawtooth profiles (e.g., blazed gratings).

Here, a "reflective" or "reflective" diffraction grating is defined as a grating that both diffracts and reflects incident light. Similarly, "reflective diffraction" is defined as diffraction in a direction corresponding to the light incident side (e.g., of a reflective diffraction grating). Thus, light diffractively scattered by the reflective diffraction grating generally exits or propagates away from the same side of the reflective diffraction grating as the side on which the light is incident (i.e., the incident light side). Conversely, a "transmissive" or "transmissive" diffraction grating is a diffraction grating that diffracts light passing through the transmissive diffraction grating such that the diffracted light generally exits from the side of the transmissive diffraction grating opposite the side on which the light is incident. In some examples, a reflective diffraction grating may include a reflective material or material layer (e.g., a reflective metal) that reflects or at least partially reflects incident light. According to various embodiments, the diffractive features (e.g., ridges or grooves) of a reflective diffraction grating may be one or more diffractive features formed in, on, or adjacent to a surface of a reflective material.

As defined herein, a "multibeam diffraction grating" is a diffraction grating that produces diffractively redirected light (e.g., diffractively coupled out light) comprising a plurality of light beams. The reflective diffraction grating may comprise a multibeam diffraction grating and may likewise be referred to as a reflective multibeam diffraction grating. Further, the plurality of beams produced by the multibeam diffraction grating have mutually different principal angular directions, by definition herein. In particular, by definition, one of the plurality of beams has a predetermined principal angular direction different from another of the plurality of beams as a result of diffractive coupling and diffractive redirection of incident light by the multibeam diffraction grating. The plurality of light beams may represent a light field. For example, the plurality of light beams may comprise eight light beams having eight different principal angular directions. For example, the combined eight light beams (i.e., the plurality of light beams) 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 gap or pitch, and the orientation or rotation of the diffractive features of the multibeam diffraction grating at the origin of the respective light beams relative to the direction of propagation of the light incident on the multibeam diffraction grating.

According to various embodiments described herein, a reflective diffraction grating (e.g., a multibeam diffraction grating) is used to generate coupled-out light that represents pixels of an electronic display. In particular, a light guide having a multibeam diffraction grating to produce a plurality of light beams having different principal angular directions may be part of, or used in conjunction with, an backlight of 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). Thus, the differently oriented light beams produced by coupling out the guided light from the light guide using the multibeam diffraction grating may be or represent "pixels" of the 3D electronic display. Furthermore, as described above, the differently directed light beams may form a light field comprising a direction corresponding to a view direction of the 3D electronic display.

According to various examples described herein, a reflective diffraction grating (e.g., a reflective multibeam diffraction grating) may be used to diffractively scatter or couple light out of a light guide (e.g., a plate light guide) as a light beam. In particular, the diffraction angle θ of the reflective diffraction grating_mOr diffraction angle theta provided by its local periodicity_mCan be given by equation (1):

where λ is the wavelength of the light, m is the diffraction order, n is the refractive index of the material of the reflective diffraction grating on the "incident light" side, d is the distance between the features of the reflective diffraction grating, and θ_iIs the angle of incidence of the light on the reflective diffraction grating. Typically, the diffraction order m is given by an integer. According to various examples, the diffraction angle θ of the light beam produced by the reflective diffraction grating_mCan be given by equation (1) where the diffraction order is a positive number (e.g., m > 0). For example, when the diffraction order m is equal to one (i.e., m ═ 1), first order diffraction is provided.

Fig. 1 illustrates, in an example, a cross-sectional view of a reflective (or reflective) diffraction grating 10 according to an embodiment consistent with the principles described herein. For example, the diffraction grating 10 may be optically coupled to a light guide. Further, FIG. 1 shows the light beam 20 at an incident angle θ_iIncident on the reflective diffraction grating 10. Shown diffractively produced by a reflective diffraction grating 10 and having a diffraction angle theta_m(or principal angular direction) of the light beam 30, as given by equation (1). As shown, the beam 30 corresponds to the diffraction order "m". Further, the incident light side 40 of the diffraction grating 10 is identified.

Herein, a "light source" is defined as a source of light (e.g., an optical emitter configured to generate and emit light). For example, the light source may be a Light Emitting Diode (LED) that emits light when activated. The light source can be substantially any light source 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 light source. The light generated by the light source may be chromatic (i.e., may include light of a particular wavelength), or may be a range of wavelengths (e.g., white light). In some embodiments, the light source may include a plurality of optical emitters. For example, the light source may include a set or group of optical emitters, wherein at least one optical emitter produces light having a color or equivalent wavelength that is different from the color or wavelength of light produced by at least one other optical emitter in the set or group. For example, the different colors may include primary colors (e.g., red, green, blue).

In some embodiments, the light from the light source may be substantially uncollimated light, while in other embodiments, the light may be collimated light. In particular, a collimator may be used to collimate the light. In some embodiments, the light source may comprise a collimator. Herein, a "collimator" is defined as essentially any optical device or apparatus configured to collimate light. For example, the collimator may include, but is not limited to, a collimating mirror or reflector, a collimating lens, and various combinations thereof. In some embodiments, a collimator including a collimating reflector may have a reflective surface characterized by a parabolic curve or shape. In another example, the collimating reflector may comprise a deformed parabolic reflector. By "deformed parabolic" is meant that the curved reflective surface of the deformed parabolic reflector deviates from the "true" parabolic curve in a manner determined to achieve a predetermined reflective characteristic (e.g., degree of collimation). Similarly, the collimating lens may comprise a spherically shaped surface (e.g., a biconvex spherical lens).

In some embodiments, the collimator may be a continuous reflector or a continuous lens (i.e., a reflector or lens having a substantially smooth continuous surface). In other embodiments, the collimating reflector or collimating lens may comprise a substantially discontinuous surface, such as, but not limited to, a fresnel reflector or fresnel lens that provides light collimation. According to various embodiments, the amount of collimation provided by the collimator may vary by a predetermined degree or amount from one embodiment to another. Further, the collimator may be configured to provide collimation in one or both of two orthogonal directions (e.g., a vertical direction and a horizontal direction). That is, according to some embodiments, the collimator may comprise a shape that provides light collimation in one or both of two orthogonal directions.

Herein, "optically coupled" is defined as being positioned or placed to be affected by, or otherwise facilitate, interaction with an optical field (e.g., a light beam). As defined herein, for example, a grating optically coupled to a light guide is positioned or otherwise positioned relative to the light guide such that the grating interacts with (e.g., provides diffraction) light guided within the light guide. For example, the optical coupling grating may be located within the light guide. In another example, the light coupling grating may be located at a surface of the light guide (e.g., positioned to interact with an evanescent optical field of light guided by the light guide).

Also, as used herein, the articles "a" and "an" are intended to have their ordinary meaning in the patent literature, i.e., "one or more". For example, "a grating" means one or more gratings, and likewise, "the grating" means "grating(s)" herein. Moreover, any reference herein to "top," "bottom," "upper," "lower," "front," "rear," "first," "second," "left," or "right" is not intended to be limiting. Herein, the term "about" when applied to a value generally means within the tolerance of the device used to produce the value, or alternatively means plus or minus 10%, or plus or minus 5%, or plus or minus 1%, unless expressly specified otherwise. Further, as used herein, the term "substantially" means mostly or almost entirely or wholly or an amount within the range of about 51% to about 100%. Furthermore, the examples herein are intended to be illustrative only and are presented for purposes of discussion and not as a limitation.

According to some embodiments of the principles described herein, a grating-based backlight is provided. Fig. 2A illustrates, in an example, a cross-sectional view of a grating-based backlight 100 according to an embodiment consistent with principles described herein. Fig. 2B illustrates, in an example, a cross-sectional view of a grating-based backlight 100 according to another embodiment consistent with principles described herein. According to various embodiments, the grating-based backlight 100 is configured to couple out light within the backlight using reflective diffraction as a plurality of emitted or coupled-out light beams 102, the light beams 102 being directed away from a surface of the grating-based backlight 100. In some embodiments, described in more detail below with respect to multibeam diffraction gratings, the coupled-out light beam 102 may be configured to form a light field. The diffractively coupled out light is a portion of the guided light 104 within the grating-based backlight 100. According to various embodiments, the diffraction that provides diffractive coupling of light out of the grating-based backlight 100 is reflective diffraction (i.e., employing a reflective diffraction grating). In fig. 2A-2B, for simplicity of illustration and not for limitation, the guided light is shown as bold arrows 104, indicating the general propagation direction of the guided light 104.

In some embodiments, the grating-based backlight 100 may be a light source or "backlight" for an electronic display. In particular, according to some embodiments in which the light field is generated by the coupled-out light beams 102, the electronic display may be a so-called "glasses-free" three-dimensional (3D) electronic display (e.g., a multiview display or an autostereoscopic display), wherein the grating-based backlight 100 is configured to generate various coupled-out light beams 102, which light beams 102 correspond to or represent pixels associated with different "views" of the 3D display. Further, in some embodiments, the electronic display may modulate the coupled-out light beam 102 (e.g., via a light valve, as described below). For example, modulating different sets of coupled-out light beams 102 directed at different angular directions away from the grating-based backlight 100 may be particularly useful for dynamic 3D electronic display applications. That is, different sets of modulated coupled-out light beams 102 oriented in a particular view direction may represent dynamic pixels of the 3D electronic display corresponding to the particular view direction.

As shown in fig. 2A-2B, the grating-based backlight 100 includes a light guide 110. In some embodiments, the light guide 110 may be a plate light guide 110. The light guide 110 is configured to guide light (e.g., a light beam) as the guided light beam 104. For example, the light guide 110 may include a dielectric material configured as an optical waveguide. 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 promote total internal reflection of the guided light 104, e.g., according to one or more guiding modes of the light guide 110.

According to various embodiments, light is guided by the light guide 110 along the length of the light guide 110. Further, the light guide 110 is configured to guide the guided light beam 104 between a first surface 110' (e.g., a "front" surface or front side) and a second surface 110 "(e.g., a" back "surface or back side) of the light guide 110 at a non-zero propagation angle using total internal reflection. In particular, the guided light beam 104 propagates by reflecting or "bouncing" between the first surface 110' and the second surface 110 "of the light guide 110 at a non-zero propagation angle. In some embodiments, multiple guided light beams 104 comprising different colors of light may be guided by the light guide 110 at respective ones of different color-specific non-zero propagation angles. Note that for simplicity of illustration, non-zero propagation angles are not shown in fig. 2A-2B.

As defined herein, a "non-zero propagation angle" is an angle relative to a surface of the light guide 110 (e.g., the first surface 110' or the second surface 110 "). Further, according to various embodiments, the non-zero propagation angle is greater than zero and less than the critical angle for total internal reflection within the light guide 110. For example, the non-zero propagation angle of the guided light beam 104 may 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 may be about thirty (30) degrees. In other examples, the non-zero propagation angle may be about 20 degrees, or about 25 degrees, or about 35 degrees. Further, a particular non-zero propagation angle may be selected (e.g., arbitrarily) for a particular implementation, so long as the particular non-zero propagation angle is selected to be less than the critical angle for total internal reflection within the light guide 110.

The guided light beam 104 in the light guide 110 may be guided or coupled into the light guide 110 at a non-zero propagation angle (e.g., about 30-35 degrees). For example, one or more of a lens, mirror, or similar reflector (e.g., a tilted collimating reflector) and a prism (not shown) may facilitate coupling light as guided light beam 104 into the input end of light guide 110 at a non-zero propagation angle. Once coupled into the light guide 110, the guided light beam 104 propagates along the light guide 110 in a direction generally away from the input end (e.g., as shown by the bold arrow 104 directed along the x-axis in FIGS. 2A-2B).

Further, according to various embodiments, the guided light beam 104 generated by coupling light into the light guide 110 may be a collimated light beam. Herein, "collimated light" or "collimated beam" is defined as a beam of light in which the rays of the beam are substantially parallel to each other within the beam (e.g., the guided beam 104). Further, light rays that diverge or scatter from the collimated beam are not considered part of the collimated beam, by definition herein. Collimating the light to produce a collimated guided light beam 104 may be provided by a collimator including, but not limited to, a lens or a mirror (e.g., a tilted collimating reflector, etc.).

In some examples, the light guide 110 (e.g., as a plate light guide 110) may be a plate or sheet light guide that includes an extended, substantially planar sheet of optically transparent dielectric material. The substantially flat sheet of dielectric material is configured to guide the guided light beam 104 using total internal reflection. According to various examples, the optically transparent material of the light guide 110 may include or be composed of any of a variety of dielectric materials, including, but not limited to, various types of glass (e.g., quartz glass, alkali aluminosilicate glass, borosilicate glass, etc.), and substantially optically transparent plastics or polymers (e.g., poly (methyl methacrylate) or "acrylic glass," polycarbonate, etc.). In some examples, the light guide 110 may also include a coating layer (not shown) at least a portion of a surface of the light guide 110 (e.g., one or both of the top and bottom surfaces). According to some embodiments, a coating may be used to further promote total internal reflection.

As shown in fig. 2A and 2B, the grating-based backlight 100 also includes a plurality of reflective grating islands 120. The plurality of reflective grating islands 120 are spaced apart from each other, i.e., there is a non-zero space between each of the plurality of reflective grating islands 120. Furthermore, the reflective grating islands 120 are optically coupled to the light guide 110, as described further below. According to various embodiments, a reflection grating island of the plurality of reflection grating islands 120 comprises a reflective diffraction grating (i.e., a reflective diffraction grating). According to various embodiments, the reflective diffraction grating is configured to diffractively couple out a portion of the guided light beam 104 as the coupled-out light beam 102 having the predetermined principal angular direction. In particular, in some embodiments, the plurality of coupled-out light beams 102 may be diffractively coupled out by the reflective diffraction gratings of the reflective grating islands 120. Furthermore, as described below with respect to multibeam diffraction gratings, each of the plurality of coupled-out light beams 102 may have a different principal angular direction than other coupled-out light beams of the plurality of coupled-out light beams.

In some embodiments, the reflective diffraction gratings of the reflection grating islands 120 may comprise diffraction gratings (e.g., dielectric diffraction gratings) adjacent to a layer of reflective material. For example, the diffractive features of a reflective diffraction grating may be formed using a dielectric material or otherwise provided. The diffractive features comprising the dielectric material thus provide a dielectric diffraction grating. Further, the dielectric diffraction grating may be in phaseAdjacent to (e.g., supporting) the layer of reflective material to provide a reflective diffraction grating. The reflective material layer may include, but is not limited to, a reflective metal layer (e.g., gold, silver, aluminum, chromium, nickel, etc.), a reflective mylar film(s) ((R))film), or enhanced reflective film (ESR). For example,ESR can be used as a layer of reflective material. Vikuiti^TMESR is a registered trademark of saint paul 3M company, minnesota.Is a registered trademark of dupont, wilmington, telawa.

In another embodiment, a reflective diffraction grating may include a reflective layer that includes diffractive features formed from or otherwise provided in the reflective layer. For example, the diffractive features of a reflective diffraction grating may comprise a reflective metal (e.g., gold, silver, aluminum, chromium, nickel, etc.) or similar reflective material as described above. In particular, the reflective diffraction grating of the reflective grating island 120 may be a metal diffraction grating (e.g., a metal layer including metal diffractive features). In other examples, diffractive features comprising a reflective material (e.g., a metal) can be supported by or placed adjacent to a reflective layer or film to provide a reflective diffraction grating. The reflective layer or film may be the same material as the material reflecting the diffractive features or a different material from the material reflecting the diffractive features.

Fig. 3A illustrates, in an example, a cross-sectional view of a reflection grating island 120 according to an embodiment consistent with principles described herein. Specifically, as shown in fig. 3A, the reflection grating islands 120 include a dielectric diffraction grating 122 adjacent to a layer of reflective material 124 that combines to provide a reflective diffraction grating. The dielectric diffraction grating 122 may include a plurality of diffractive features 122a of dielectric material. Further, as shown, the dielectric diffractive features 122a are spaced apart from each other by a non-zero distance and are configured to provide diffraction of an incident light beam (e.g., the guided light beam 104 at a non-zero propagation angle). According to various embodiments, the dielectric diffraction grating 122 may be provided on the layer of reflective material 124 (as shown), or located adjacent to but spaced apart from the layer of reflective material 124 (not shown).

Figure 3B illustrates, in an example, a cross-sectional view of a reflection grating island 120 according to another embodiment consistent with principles described herein. As shown in fig. 3B, the reflection grating island 120 includes a plurality of reflective diffractive features 124a at the surface of the layer of reflective material 124 to provide a reflective diffraction grating. In some examples, the reflective diffractive features 124a can be formed from the reflective material layer 124 itself (e.g., as shown). For example, the surface may be patterned by etching the surface or by using nanoimprint lithography to form diffractive features 124a in the surface of the layer of reflective material 124. In another example (not shown), the reflective diffractive features 124a can be provided by depositing and patterning a reflective material (e.g., another reflective material) on a surface of the reflective material layer. In some embodiments, the deposited reflective diffractive features 124a can comprise a different reflective material than the layer of reflective material 124, while in other embodiments, the deposited diffractive features 124a can comprise the reflective material of the layer of reflective material 124, although provided by deposition.

Figure 3C illustrates, in an example, a cross-sectional view of a reflective grating island 120 according to yet another embodiment consistent with principles described herein. As shown in fig. 3C, the reflection grating islands 120 include a reflective diffraction grating that may be provided by a plurality of diffractive features 126 comprising a reflective material. In some embodiments (e.g., as shown), the reflective diffractive feature 126 alone can provide diffraction of an incident light beam (e.g., the guided light beam 104). In other embodiments (not shown), the reflective diffractive features 126 can be further supported by or adjacent to a layer of reflective material (e.g., the layer of reflective material 124). For example, the reflective diffractive features 126 may be adjacent to but spaced apart (by a non-zero distance) from the layer of reflective material to increase the diffraction efficiency of the reflective grating islands 120. Further, although not explicitly listed above, any of a variety of other reflective diffraction gratings may be used as the reflective diffraction grating of the reflective grating islands 120 according to embodiments consistent with the principles described herein. It is also noted that although fig. 3A-3C are illustrated as uniform diffraction gratings, the diffractive features of fig. 3A-3C may be one or both of non-uniformly spaced and non-uniformly shaped in a diffraction grating (e.g., chirped diffraction gratings), according to some embodiments.

According to various embodiments, the plurality of reflective grating islands 120 may be located substantially anywhere in the light guide 110 below the first light guide surface 110' as long as the reflective grating islands 120 are optically coupled to the light guide 110. In particular, in some embodiments, the reflective grating islands 120 may be located in the light guide 110 between the first surface 110' and the second surface 110 ″ of the light guide 110 (e.g., as shown in fig. 2A). For example, the reflective grating islands 120 may be embedded in the dielectric material of the light guide 110. In other embodiments, the reflective grating islands 120 may be located at the second surface 110 "of the light guide 110 (e.g., as shown in fig. 2B). For example, the reflective diffraction grating of the reflective grating island 120 may include diffractive features at the second surface and a layer of reflective material configured to cover or underlie the diffractive features. For example, the diffractive features may comprise one or both of grooves in the second surface 110 "of the light guide 110 and ridges on the second surface 110". Fig. 2B shows a groove in the second surface 110 ". The ridges on the second surface 110 "are not shown, however, the ridges may be implemented by any of the examples shown in fig. 3A-3C, for example. According to various embodiments, for example, as described above with respect to fig. 3A-3C, one or both of the grooves and ridges may comprise the material of the light guide 110 or another material (e.g., a dielectric or reflective material). For example, the grooves may be etched, milled, or molded into the second surface 110 ", or the ridges may be applied, deposited, or otherwise affixed to the second surface 110".

According to various embodiments, the reflective diffraction gratings of the reflection grating islands 120 may comprise multibeam diffraction gratings. The multibeam diffraction grating may be configured to diffractively couple out a portion of the guided light beam 104 as the plurality of coupled-out light beams 102. Furthermore, according to various embodiments, the coupled-out light beams 102 diffractively coupled out by the multibeam diffraction grating have mutually different principal angular directions. Further, the multibeam diffraction grating is configured to operate as a reflective diffraction grating (i.e., a reflective multibeam diffraction grating). For example, by way of example and not limitation, fig. 2A and 2B illustrate a reflective diffraction grating of the plurality of reflective grating islands 120 as a multibeam diffraction grating. Furthermore, fig. 2A and 2B show that the coupled-out light beams 102 from the reflective multibeam diffraction gratings of the reflection grating island 120 have mutually different principal angular directions.

Figure 4A illustrates, in an example, a cross-sectional view of a multibeam diffraction grating 200 according to an embodiment consistent with principles described herein. FIG. 4B illustrates, in an example, a perspective view of a multibeam diffraction grating 200, according to an embodiment consistent with principles described herein. For example, the multibeam diffraction grating 200 shown in fig. 4A-4B may represent a reflective diffraction grating of the reflection grating islands 120 of fig. 2A and 2B. Also shown is a light beam 204 guided by a light guide 210, a multibeam diffraction grating 200 optically coupled to the light guide 210 for receiving an incident guided light beam 204. For example, the light guide 210 and the incident guided light beam 204 may be substantially similar to the light guide 110 and the guided light beam 104 described above.

4A-4B, the multibeam diffraction grating 200 operating as a reflective diffraction grating may be configured to diffractively couple out a portion of the guided light beam 204 as a plurality of coupled-out light beams 202, the coupled-out light beams 202 being directed away from a light-incident side of the multibeam diffraction grating 200 due to reflection diffraction. The plurality of coupled-out optical beams 202 may be substantially similar to, for example, the plurality of coupled-out optical beams 102 described above. In particular, the plurality of coupled-out light beams 202 has a predetermined principal angular direction that is different from the principal angular directions of other coupled-out light beams 202 of the plurality of coupled-out light beams.

According to various embodiments, the multibeam diffraction grating 200 shown in fig. 4A-4B includes a plurality of diffractive features 220, which may represent, for example, one or both of grooves and ridges that are spaced apart from one another. In some embodiments, the diffractive features 220 may be curved, for example, as shown in fig. 4B. The multibeam diffraction grating 200 may be implemented in various embodiments (e.g., as described above) as a reflective diffraction grating of the reflective grating islands 120, including, but not limited to, a dielectric diffraction grating adjacent to a reflective layer (e.g., the dielectric diffraction grating 122 and the reflective material layer 124 of fig. 3A), and reflective diffractive features of a reflective material or reflective diffractive features located at a surface of a reflective layer (e.g., the reflective diffractive features 124a and the reflective material layer 124 of fig. 3B-3C).

As described above, the multibeam diffraction grating 200 is configured to diffractively scatter or diffractively couple out a portion of the guided light beam 204 as a plurality of coupled-out light beams 202 having different predetermined principal angular directions as described above. When the backlight comprising the multibeam diffraction grating 200 is comprised in an electronic display, the different predetermined principal angular directions may for example correspond to different view directions of a 3D or multiview electronic display. Further, according to various embodiments, each of the plurality of coupled-out light beams 202 may have a different predetermined principal angular direction determined by characteristics of the diffractive features of the multibeam diffraction grating 200.

In particular, the diffractive features 220 of the multibeam diffraction grating 200 shown in fig. 4A-4B are configured to provide diffraction (e.g., reflection diffraction) responsible for diffractively coupling a portion of the guided light beam 204 out of the light guide 210. According to some embodiments, the multibeam diffraction grating 200 may be or include a chirped (chirp) diffraction grating. By definition, a "chirped" diffraction grating is a diffraction grating exhibiting or having a diffraction spacing d of diffractive features that varies across the extent or length of the chirped diffraction grating, or having the diffraction spacing d (i.e., diffraction gaps) between the diffractive features, e.g., as shown in fig. 4A-4B (e.g., also as in fig. 2A-2B). Here, different diffraction intervals d are defined and are referred to as "chirps". As a result of the chirp, the portions of the guided light beam that are diffractively coupled out propagate away from the chirped diffraction grating on the chirped diffraction grating of the multibeam diffraction grating 200 at different diffraction angles corresponding to different origins. With a predefined chirp, the chirped diffraction grating is responsible for the coupling out of the plurality of light beams of predetermined and different principal angular directions of the light beams.

In some examples, the chirped diffraction grating of the multibeam diffraction grating 200 may have or exhibit a chirp of the diffraction spacing d that varies linearly with distance. Thus, by definition, a chirped diffraction grating is a "linearly chirped" diffraction grating. Fig. 4A-4B illustrate, by way of example and not limitation, the multibeam diffraction grating 200 as a linearly chirped diffraction grating. In particular, as shown, the diffractive features are closer together at a first end than at a second end of the multibeam diffraction grating 200. Further, as shown, the diffraction spacing d of the diffractive features 220 at the locations shown varies linearly from the first end to the second end.

In another example (not shown), the chirped diffraction grating of the multibeam diffraction grating 200 may exhibit a nonlinear chirp of the diffraction spacing. Various non-linear chirps that may be used to implement the multibeam diffraction grating 200 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 may also be employed such as, but not limited to, sinusoidal chirps or triangular or saw tooth chirps. Combinations of any of these types of chirps may also be employed.

According to some embodiments, the multibeam diffraction grating 200 may include diffractive features 220 that are one or both of curved and chirped. For example, as shown in fig. 4B, the multibeam diffraction grating 200 includes curved and chirped diffractive features 220 (i.e., the multibeam diffraction grating 200 in fig. 4B is a curved, chirped diffraction grating). Also shown in FIG. 4B, at the first end of the multibeam diffraction grating 200, the guided light beam 204 is represented by a bold arrow pointing in an incident direction relative to the multibeam diffraction grating. Also shown is a plurality of coupled-out light beams 202, represented by arrows pointing away from the light-incident side of the multibeam diffraction grating 200. The coupled-out light beams 202 propagate away from the multibeam diffraction grating 200 in a plurality of different predetermined principal angular directions. In particular, the predetermined different principal angular directions of the coupled-out light beams 202 differ from each other in azimuth and elevation, as shown here. According to various examples, both the predetermined chirp of the diffractive features 220 and the curvature of the diffractive features 220 may be responsible for different predetermined principal angular directions of the coupled-out light beam 202.

According to some embodiments of the principles described herein, there is provided an electronic display. In various embodiments, an electronic display is configured to emit modulated light beams as pixels of the electronic display. Further, in various examples, the emitted modulated light beam may preferably be directed toward a viewing direction of the electronic display as a plurality of differently directed light beams. In some examples, the electronic display is a three-dimensional (3D) or multi-view electronic display. According to various examples, different ones of the modulated, differently directed light beams may correspond to different "views" associated with the 3D electronic display. The different views may provide, for example, a "glasses-free" (e.g., autostereoscopic) representation of information displayed by the 3D electronic display.

Fig. 5A illustrates, in an example, a block diagram of a three-dimensional (3D) electronic display 300 according to an embodiment consistent with the principles described herein. Fig. 5B illustrates, in an example, a cross-sectional view of a three-dimensional (3D) electronic display 300 according to an embodiment consistent with the principles described herein. For example, the 3D electronic display 300 shown in fig. 5B may represent an embodiment of the 3D electronic display 300 of fig. 5A. Furthermore, the 3D electronic display 300 may also be referred to as a multi-view display, for example. As shown, the 3D electronic display 300 is configured to emit modulated light beams 302, the modulated light beams 302 representing pixels corresponding to different views associated with different view directions of the 3D electronic display 300.

As shown in fig. 5A and 5B, 3D electronic display 300 includes a plate light guide 310 to guide a light beam, e.g., as shown by the extended arrows in fig. 5B representing guided light beam 306. The guided light beam 306 in the plate light guide 310 is the light source that becomes the modulated light beam emitted by the 3D electronic display 300. According to some embodiments, the plate light guide 310 may be substantially similar to the light guide 110 described above with respect to the grating-based backlight 100. For example, the plate light guide 310 may be a sheet of light guide that is a sheet of flat dielectric material configured to guide light by total internal reflection. The guided light beam 306 may be guided as a light beam at a non-zero propagation angle. Thus, the guided light beam 306 guided by the plate light guide 310 may be substantially similar to the guided light beam 104 of the grating-based backlight 100. For example, according to some embodiments, the guided light beam 306 may be a collimated light beam.

The 3D electronic display 300 shown in fig. 5A-5B also includes an array of reflective grating islands 320. The array of reflective grating islands 320 is optically coupled to the plate light guide 310 (e.g., in or on a surface of the plate light guide 310). The array of reflective grating islands 320 may be substantially similar to the reflective grating islands 120 of the grating-based backlight 100. For example, the reflective grating islands 320 include a reflective diffraction grating. More specifically, according to various embodiments, the reflection grating island 320 includes a reflective multibeam diffraction grating. The reflective multibeam diffraction grating is configured to diffractively couple out a portion of the guided light beam 306 as a plurality of coupled-out light beams 304 having different principal angular directions. Furthermore, according to various embodiments, the different principal angular directions of the coupled-out light beams 304 correspond to respective view directions of different views of the 3D electronic display 300. In some embodiments, the reflective multibeam diffraction grating of the reflection grating island 320 may be substantially similar to the multibeam diffraction grating 200 described above.

Further, in some embodiments, the multibeam diffraction gratings of the reflection grating islands 320 may comprise chirped diffraction gratings. In some examples, the diffractive features (e.g., grooves, ridges, etc.) of the multibeam diffraction grating are curved diffractive features. For example, the curved diffractive features may include curved ridges or grooves (i.e., continuously curved or piecewise curved) and spacings between the curved diffractive features that vary as a function of distance across the multibeam diffraction grating.

As shown in fig. 5A and 5B, 3D electronic display 300 also includes light valve array 330. According to various examples, the light valve array 330 includes a plurality of light valves configured to modulate the coupled-out light beam 304. In particular, the light valves of the light valve array 330 modulate the coupled-out light beam 304 to provide a modulated light beam 302. Modulated light beams 302 represent pixels of different views (i.e., and in different view directions) of 3D electronic display 300. In various examples, different types of light valves in the light valve array 330 may be employed, including but not limited to one or more of Liquid Crystal (LC) light valves, electrowetting light valves, and electrophoretic light valves. As an example, dashed lines are used in fig. 5A to emphasize the modulation of modulated light beam 302.

In some examples (e.g., as shown in fig. 5A-5B), 3D electronic display 300 also includes a light source 340 optically coupled to the input of plate light guide 310. The light source 340 is configured to provide light and, in some embodiments, collimated light to the plate light guide input. In particular, according to some embodiments, the plate light guide 310 is configured to guide collimated light as a collimated light beam at a non-zero propagation angle.

In some embodiments, the light source 340 comprises a light emitter, such as, but not limited to, a Light Emitting Diode (LED) or a laser. For example, the light source 340 may include LEDs of a particular color (e.g., red, green, blue) to provide a single color of light. In some embodiments, light source 340 includes a plurality of light emitters configured to provide light of a plurality of different colors. For example, the light source 340 may include a first LED configured to provide red light, a second LED configured to provide green light, and a third LED configured to provide blue light. According to some embodiments, where different colors of light are provided by the light sources 340, the plate light guide 310 may be configured to direct light beams representing the different colors of light at different color-specific, non-zero propagation angles. For example, when the light source 340 is configured to provide red, green, and blue light, each of the red, green, and blue light may be provided by the light source 340 as a different color collimated beam. Further, the plate light guide 310 may be configured to guide each of the different colored collimated light beams at respective different color-specific non-zero propagation angles. In other embodiments, the light source 340 may be a broadband light source, such as, but not limited to, a fluorescent lamp, and a white or, more generally, a multi-color LED configured to provide broadband light (e.g., white or multi-color light). Further, the light source 340 may include a collimator, such as, but not limited to, any of the collimators described above, to collimate the light from the light source.

According to some embodiments of the principles described herein, a method of grating-based backlight operation is provided. Fig. 6 illustrates, in an example, a flow chart of a method 400 of grating-based backlight operation according to an embodiment consistent with principles described herein. As shown in fig. 6, a method 400 of grating-based backlight operation includes directing 410 a light beam in a light guide. In some embodiments, the light guide and the guided light beam may be substantially similar to the light guide 110 and the guided light beam 104 described above with respect to the grating-based backlight 100. In particular, in some embodiments, the light guide may guide 410 the guided light according to total internal reflection (e.g., as a collimated light beam). Further, the light beam may be guided 410 between the first surface and the second surface of the light guide at a non-zero propagation angle. Further, in some embodiments, the light guide may be a substantially planar dielectric optical waveguide (e.g., a plate light guide).

The method 400 of grating-based backlight operation further includes diffractively coupling out 420 a portion of the guided light beam as a coupled-out light beam using the plurality of reflective grating islands. According to various embodiments, the coupled-out light beam is directed out and away from the first surface of the light guide in a predetermined principal angular direction. Further, the plurality of reflective grating islands are spaced apart from each other and optically coupled to the light guide. Further, according to various embodiments, a reflection grating island of the plurality of reflection grating islands includes a reflective diffraction grating.

In some embodiments, the reflective grating islands for diffractively coupling out 420 a portion of the guided light beam are substantially similar to the reflective grating islands 120 described above with respect to the grating-based backlight 100. Furthermore, the coupled-out light beam may be substantially similar to the coupled-out light beam 102 also described above. For example, the reflective diffraction grating of the reflective grating island may comprise a dielectric grating adjacent to a layer of reflective material. In another example, the reflective diffraction grating may comprise a metal diffraction grating or a diffraction grating having reflective diffractive features.

In some embodiments, the reflective diffraction grating of the reflective grating island may comprise a multibeam diffraction grating. The multibeam diffraction grating may be substantially similar to the multibeam diffraction grating 200 described above. In particular, the multibeam diffraction grating may be configured to diffractively couple out a portion of the guided light beam as a plurality of coupled-out light beams. According to various embodiments, the coupled-out light beams of the plurality of coupled-out light beams may have mutually different principal angular directions. Furthermore, in some embodiments, different principal angular directions of the coupled-out light beams may correspond to respective view directions of different views of a three-dimensional (3D) or multiview electronic display.

In some embodiments (e.g., as shown in fig. 6), the method 400 of grating-based backlight operation further includes coupling out the light beam using a light valve modulation 430. According to various embodiments, the modulated coupled-out light beams may form pixels of an electronic display. In some embodiments (e.g., where a multibeam diffraction grating is used as a reflective diffraction grating), modulating 430 the coupled-out light beam may use multiple light valves to provide modulation of multiple differently oriented coupled-out light beams. Furthermore, the modulated 430 differently directed coupled-out light beams may be directed, for example, in different view directions of the respective view directions of the 3D electronic display.

According to some embodiments, the light valves used to modulate 430 the coupled-out light beams may be substantially similar to the light valves of light valve array 330. For example, the light valve may comprise a liquid crystal light valve. In another example, the light valve may be another type of light valve, including but not limited to one or both of an electrowetting light valve and an electrophoretic light valve, or a combination thereof with a liquid crystal light valve or other type of light valve.

Thus, examples of grating-based backlights employing reflective grating islands, 3D electronic displays, and methods of grating-based backlight operation have been described. It should be understood that the above-described examples are only illustrative of some of the many specific examples and embodiments that illustrate the principles described herein. It should be apparent that numerous other configurations could be readily devised by those skilled in the art without departing from the scope thereof, which is defined by the appended claims.

Claims (21)

1. A grating-based backlight, comprising:

a light guide configured to guide a light beam between a first surface and a second surface of the light guide at a non-zero propagation angle; and

a plurality of reflective grating islands spaced apart from each other and optically coupled to the light guide, a reflective grating island of the plurality of reflective grating islands comprising a reflective multibeam diffraction grating configured to diffractively couple out a portion of the guided light beam as a plurality of coupled-out light beams, the coupled-out light beams of the plurality of coupled-out light beams having mutually different principal angular directions,

wherein coupled-out light beams of the plurality of coupled-out light beams are directed away from the first surface of the light guide in the mutually different principal angular directions.

2. The grating-based backlight of claim 1, wherein the reflective multibeam diffraction grating comprises a dielectric diffraction grating adjacent to a layer of reflective material.

3. The grating-based backlight of claim 1, wherein the reflective multibeam diffraction grating comprises a reflective metal diffraction grating.

4. The grating-based backlight of claim 1, wherein the reflective grating islands are between the first and second surfaces of the light guide.

5. The grating-based backlight of claim 1, wherein the reflective grating islands are at the second surface of the light guide.

6. The grating-based backlight of claim 5, wherein the reflective multibeam diffraction grating of the reflective grating island comprises a diffractive feature at the second surface of the light guide and a layer of reflective material, the diffractive feature comprising one or both of a groove in the second surface of the light guide and a ridge on the second surface of the light guide, and the layer of reflective material on the second surface to cover the diffractive feature.

7. The grating-based backlight of claim 1, wherein the reflective multibeam diffraction grating comprises a chirped diffraction grating.

8. The grating-based backlight of claim 1, wherein the reflective multibeam diffraction grating comprises curved diffractive features spaced apart from one another.

9. The grating-based backlight of claim 1, wherein the different principal angular directions of the coupled-out light beams correspond to respective view directions of different views of a three-dimensional (3D) electronic display.

10. A three-dimensional (3D) electronic display comprising the grating-based backlight of claim 1, the 3D electronic display further comprising:

a light source optically coupled to an input of the light guide, the light source configured to provide collimated light to be directed as a beam of light; and

a light valve configured to modulate an coupled-out light beam of the plurality of coupled-out light beams, the light valve being adjacent to the first surface of the light guide,

wherein the principal angular direction of the coupled-out light beam corresponds to a view direction of the 3D electronic display, the modulated light beam representing a pixel of the 3D electronic display in the view direction.

11. A three-dimensional (3D) electronic display, comprising:

a plate light guide configured to guide a light beam within the plate light guide at a non-zero propagation angle;

a reflective grating island array optically coupled to the plate light guide, a reflective grating island of the reflective grating island array comprising a reflective multibeam diffraction grating configured to diffractively couple out a portion of the guided light beam as a plurality of coupled-out light beams, the plurality of coupled-out light beams having mutually different principal angular directions corresponding to respective view directions of different views of the 3D electronic display; and

a light valve array configured to modulate the coupled-out light beams of the plurality of coupled-out light beams, the modulated coupled-out light beams representing pixels of the different views of the 3D electronic display.

12. The 3D electronic display of claim 11, further comprising: a light source optically coupled to an input of the plate light guide, the light source configured to provide collimated light to the input of the plate light guide, wherein the plate light guide is configured to direct the collimated light as a collimated beam at the non-zero propagation angle.

13. The 3D electronic display of claim 12, wherein the light source comprises a first Light Emitting Diode (LED) configured to provide red light, a second LED configured to provide green light, and a third LED configured to provide blue light, each of the red, green, and blue light provided by the light source as a different color collimated light beam, and wherein the plate light guide is configured to guide each of the different color collimated light beams at a respective different color-specific, non-zero propagation angle.

14. The 3D electronic display of claim 11, wherein the reflective multibeam diffraction grating of the reflective grating island comprises a chirped diffraction grating having curved diffractive features.

15. The 3D electronic display of claim 11, wherein the reflective grating island is between a first surface of the plate light guide and a second surface of the plate light guide, the light valve array being adjacent to the first surface.

16. The 3D electronic display of claim 11, wherein the reflection grating island is at a second surface of the plate light guide opposite the first surface adjacent to the light valve array, and wherein the reflection grating island further comprises a layer of reflective material configured to cover diffractive features of the reflective multibeam diffraction grating, the diffractive features comprising one or both of grooves in the second surface and ridges on the second surface.

17. The 3D electronic display of claim 11, wherein the light valve array comprises a plurality of liquid crystal light valves.

18. A method of grating-based backlight operation, the method comprising:

directing a light beam in a light guide between a first surface and a second surface of the light guide at a non-zero propagation angle; and

diffractively coupling out a portion of the guided light beam as a plurality of coupled-out light beams using a reflective multibeam diffraction grating comprised by a reflective grating island of the plurality of reflective grating islands, the coupled-out light beams of the plurality of coupled-out light beams having mutually different principal angular directions in which the coupled-out light beams of the plurality of coupled-out light beams are directed out of and exit the first surface of the light guide,

wherein the plurality of reflective grating islands are spaced apart from each other and optically coupled to the light guide.

19. The method of grating-based backlight operation of claim 18, wherein the reflective multibeam diffraction grating of the reflection grating island comprises one of a dielectric diffraction grating and a reflective metal diffraction grating adjacent a layer of reflective material.

20. The method of grating-based backlight operation of claim 18, wherein the different principal angular directions of the coupled-out light beams correspond to respective view directions of different views of a three-dimensional (3D) electronic display.

21. The method of grating-based backlight operation of claim 18, further comprising modulating an coupled-out beam of the plurality of coupled-out beams using a light valve, the modulated coupled-out beam forming a pixel of an electronic display.