HK1206091B - Multibeam diffraction grating-based backlighting - Google Patents

Description

Backlighting based on multi-beam diffraction grating

CROSS-REFERENCE TO RELATED APPLICATIONS

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STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

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Technical Field

Electronic displays are an almost ubiquitous medium for conveying information to users of a 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 diodes (OLEDs) and active matrix OLED (AMOLED) displays, electrophoretic displays (EPs), and various displays that employ electromechanical or electrofluidic light modulation (e.g., digital micromirror devices, electrowetting displays, etc.). Generally speaking, electronic displays can be classified as active displays (i.e., displays that emit light) or passive displays (e.g., displays that modulate light provided by another source). The most common examples of active displays are CRTs, PDPs, and OLED/AMOLEDs. Displays that are typically classified as passive when considering the light emitted are LCDs and EP displays. While passive displays often exhibit attractive performance characteristics, including but not limited to inherently low power consumption, their use in many practical applications is limited by their lack of the ability to emit light.

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

BRIEF DESCRIPTION OF THE DRAWINGS

The present application may be more fully understood in conjunction with the following detailed description taken in conjunction with the accompanying drawings, in which like reference numerals represent like parts throughout, and in which:

FIG1 illustrates a schematic diagram of the angular components {θ, φ} of a light beam having a particular principal angular direction, according to an example of the principles described herein.

2A illustrates a perspective view of a multibeam diffraction grating-based backlight, according to an example consistent with the principles described herein.

2C illustrates a cross-sectional view of the multibeam diffraction grating-based backlight shown in FIG. 2A , according to an example consistent with the principles described herein.

2B illustrates a cross-sectional view of a multibeam diffraction grating-based backlight, according to another example consistent with the principles described herein.

3 illustrates a plan view of a multibeam diffraction grating according to another example consistent with the principles described herein.

4 illustrates a block diagram of an electronic display, according to an example consistent with the principles described herein.

5 illustrates a flow chart of a method of operating an electronic display, according to an example consistent with the principles described herein.

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

DETAILED DESCRIPTION

Examples according to the principles described herein provide electronic display backlighting using multi-beam diffraction coupling. Specifically, the backlighting of the electronic display described herein employs a multi-beam diffraction grating. The multi-beam diffraction grating is used to couple light out of a light guide and guide the coupled-out light along a viewing direction of the electronic display. According to various examples of the principles described herein, the coupled-out light guided along the viewing direction by the multi-beam diffraction grating includes a plurality of light beams having different principal axis directions from one another. In some examples, the light beams having different principal axis directions (also referred to as 'differently guided light beams') can be used to display three-dimensional (3-D) information. For example, the differently guided light beams produced by the multi-beam diffraction grating can be modulated and, for example, serve as pixels of a 'glasses-free' 3-D electronic display.

According to various examples, a multibeam diffraction grating generates multiple light beams having a corresponding plurality of different, spatially separated angles (i.e., different principal angular directions). Specifically, each light beam generated by the multibeam diffraction grating has a principal angular direction given by an angular component {θ, φ}. The angular component θ is referred to herein as the 'elevation component' or 'elevation angle' of the light beam. The angular component φ is referred to herein as the 'azimuth component' or 'azimuth angle' of the light beam. By definition, the elevation angle θ is an angle in a vertical plane (e.g., perpendicular to the plane of the multibeam diffraction grating), while the azimuth angle φ is an angle in a horizontal plane (e.g., parallel to the plane of the multibeam diffraction grating). FIG1 illustrates the angular components {θ, φ} of a light beam 10 having a specific principal angular direction, according to an example of the principles described herein. Furthermore, according to the definitions herein, each light beam emanates or emanates from a specific point. That is, by definition, each light beam has a central ray associated with a specific origin in the multibeam diffraction grating. FIG1 also illustrates the beam origin P.

According to various examples, the elevation component θ of the light beam is related to, and in some examples is determined by _, the diffraction angle _θm of the multibeam diffraction grating. Specifically, according to some examples, the elevation component θ can be determined by the diffraction angle _θm local to or at the origin P of the light beam. According to various examples, the azimuthal component φ of the light beam can be determined by the orientation or rotation of features of the multibeam diffraction grating. Specifically, according to some examples, the azimuthal orientation angle _φf of the features near the origin and relative to the propagation direction of light incident on the multibeam diffraction grating can determine the azimuthal component φ of the light beam (e.g., φ= _φf ). Example propagation directions of incident light are illustrated in FIG1 by thick arrows.

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

Herein, a 'diffraction grating' is generally defined as a plurality of features (e.g., diffraction 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 arranged in a one-dimensional (1-D) array (e.g., a plurality of grooves in a material surface). In other examples, a diffraction grating may be a two-dimensional (2-D) array of features. For example, a diffraction grating may be a 2-D array of bumps on a material surface.

As such, 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 provided can result in what is referred to as 'diffraction coupling', as the diffraction grating can couple light out of the light guide by diffraction. A diffraction grating also redirects light or changes the angle of light (i.e., the diffraction angle) by diffraction. In particular, as a result of diffraction, the light leaving the diffraction grating (i.e., the diffracted light) typically has a propagation direction that is different from the propagation direction of the incident light. Here, the change in the propagation direction of light by diffraction is referred to herein as 'diffraction redirection'. Thus, a diffraction grating can be understood as a structure that includes diffraction features that diffractionally redirect light incident on the diffraction grating and, if the light is incident from a light guide, can also diffractionally couple light out of the light guide.

Here, specifically, 'diffraction coupling' is defined as the coupling of electromagnetic waves (e.g., light) across a boundary between two materials as a result of diffraction (e.g., by a diffraction grating). For example, a diffraction grating can be used to couple light propagating in a lightguide out through diffraction coupling across the lightguide boundary. Diffraction coupling substantially overcomes, for example, total internal reflection that guides light within the lightguide to couple out the light. Similarly, 'diffraction redirection' is defined as the redirection or change in the propagation direction of light as a result of diffraction. If diffraction occurs at a boundary between two materials (e.g., a diffraction grating is located at the boundary), then diffraction redirection can occur at the boundary.

Furthermore, herein, by definition, the features of a diffraction grating are referred to as ‘diffractive features’ and can be one or more of at a surface (e.g., a boundary between two materials), in a surface, and on a surface. The surface can be, for example, the surface of a light guide. The diffractive features can include any of a variety of structures that diffract light, including but not limited to grooves, ridges, holes, and protrusions at, in, or on the surface. For example, a multibeam diffraction grating can include a plurality of parallel grooves in a surface of a material. In another example, a diffraction grating can include a plurality of parallel ridges protruding from the surface of a material. The diffractive features (e.g., 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 a rectangular profile, a triangular profile, and a sawtooth profile.

Here, by definition, a 'multibeam diffraction grating' is a diffraction grating that generates multiple light beams. In some examples, the multibeam diffraction grating may be or include a 'chirped' diffraction grating. As described above, the multiple light beams generated by the multibeam diffraction grating may have different principal directions represented by angular components {θ, φ}. Specifically, according to various examples, each light beam may have a predetermined principal direction as a result of diffraction coupling and diffraction redirection of incident light by the multibeam diffraction grating. For example, the multibeam diffraction grating may generate eight (8) light beams in eight different principal directions. According to various examples, as described above, the elevation angle θ of the light beam may be determined by the diffraction angle _θm of the multibeam diffraction grating, while the azimuth angle φ may be associated with the orientation and rotation of a feature of the multibeam diffraction grating at the beam origin relative to the propagation direction of light incident on the multibeam diffraction grating.

According to various examples, the diffraction angle _θm provided by the locally periodic transmissive diffraction grating may be given by the following equation (1):

Wherein λ is the wavelength of light, m is the diffraction order, d is the distance between the features of the diffraction grating, _θi is the angle of incidence of light on the diffraction grating, and n is the refractive index of the material (e.g., liquid crystal) on the side of the diffraction grating (i.e., the 'light incident' side) from which light is incident on the diffraction grating. Equation (1) assumes that the refractive index on the other side of the diffraction grating opposite the light incident side has a refractive index of 1. If the refractive index on the side opposite to the light incident side is not 1, equation (1) can be modified accordingly. Here, according to various examples, the multiple light beams generated by the multi-beam diffraction grating can all have the same diffraction order m.

In addition, herein, a 'light guide' is defined as a structure that uses total internal reflection to guide light within the structure. Specifically, a light guide may include a core that is substantially transparent at the operating wavelength of the light guide. In some examples, the term 'light guide' generally refers to a dielectric light waveguide that provides total internal reflection at the interface between the dielectric material of the light guide and the material or medium surrounding the light guide to guide light. 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 near the surface of the light guide material. In some examples, the light guide may include a coating to supplement or replace the above-mentioned refractive index difference to further promote total internal reflection. The coating may be a reflective coating, for example. According to various examples, the light guide may be any of several light guides, including but not limited to one or both of a plate or slab light guide and a strip light guide.

Additionally, the term 'plate,' as applied to a lightguide as in a 'plate lightguide,' is defined as a piecewise or differentially planar layer or sheet. Specifically, a plate lightguide is defined as a lightguide configured to guide light in two substantially orthogonal directions bounded by the lightguide's top and bottom surfaces. Furthermore, by definition, the top and bottom surfaces are both separate and substantially parallel to each other in a differential sense. That is, within any differentially small region of the plate lightguide, the top and bottom surfaces are substantially parallel or coplanar. In some examples, the plate lightguide can be substantially flat (e.g., confined within a plane), and thus the plate lightguide is a planar lightguide. In other examples, the plate lightguide can be curved in one or two orthogonal dimensions. For example, the plate lightguide can be curved in a single dimension to form a cylindrical plate lightguide. However, in various examples, any curvature has a sufficiently large radius of curvature to ensure that total internal reflection is maintained within the plate lightguide to guide light.

In addition, as used herein, the article 'a' is intended to have its ordinary meaning in patent documents, i.e., 'one or more'. For example, 'a grating' means one or more gratings, and similarly, 'grating' herein means 'one or more gratings'. In addition, any reference herein to 'top', 'bottom', 'above', 'below', 'up', 'down', 'front', 'back', 'left', or 'right' is not intended to be limiting. As used herein, the term 'about', when applied to a value, generally means within the tolerance range of the device used to generate the value, or in some examples, means plus or minus 10%, or plus or minus 5%, or plus or minus 1%, unless expressly stated otherwise. In addition, the examples herein are intended to be illustrative only and are presented for the purpose of discussion and are not to be taken as limiting.

Figure 2A illustrates a perspective view of a multibeam diffraction grating based backlight 100 according to an example consistent with the principles described herein. Figure 2C illustrates a cross-sectional view of the multibeam diffraction grating based backlight 100 illustrated in Figure 2A according to an example consistent with the principles described herein. Figure 2B illustrates a cross-sectional view of a multibeam diffraction grating based backlight 100 according to another example consistent with the principles described herein. According to various examples, the multibeam diffraction grating based backlight 100 is configured to provide a plurality of light beams 102 that are directed away from the multibeam diffraction grating based backlight 100. In some examples, the plurality of light beams 102 form a plurality of pixels of an electronic display. In some examples, the electronic display is a so-called 'glasses-free' three-dimensional (3-D) display (e.g., a multi-view display).

According to various examples, a beam 102 of a plurality of light beams provided by a multibeam diffraction grating-based backlight 100 is configured to have a different principal angular direction than other beams 102 in the plurality of light beams (e.g., see Figures 2B and 2C). Furthermore, the light beam 102 can have both a predetermined direction (principal angular direction) and a narrower angular spread. In some examples, the light beams 102 can be individually modulated (e.g., by a light valve as described below). Individual modulation of the light beams 102 directed in different directions from the multibeam diffraction grating-based backlight 100 can be particularly useful, for example, in 3-D electronic display applications employing thicker light valves.

As shown in Figures 2A-2C, a multibeam diffraction grating-based backlight 100 includes a light guide 110. The light guide 110 is configured to guide light 104 (e.g., from a light source 130). In some examples, the light guide 110 guides the guided light 104 using total internal reflection. For example, the light guide 110 can include a dielectric material configured as an optical waveguide. The dielectric material can have a first refractive index that is greater than a second refractive index of a medium surrounding the dielectric optical waveguide. For example, the difference in refractive index is configured to promote total internal reflection of the guided light 104 according to one or more guiding modes of the light guide 110.

For example, light guide 110 can be a sheet or slab optical waveguide that is an extended, substantially planar sheet of optically transparent material (e.g., as shown in the cross-sections of Figures 2B and 2C and as viewed from the top of Figure 2A). The substantially planar sheet of dielectric material is configured to guide light 104 by total internal reflection. In some examples, light guide 110 can include a cover layer (not shown) on at least a portion of a surface of light guide 110. The cover layer can, for example, be used to further facilitate total internal reflection.

In some examples, the light 104 can be coupled into the end of the light guide 110 to propagate and be guided along the length of the light guide 110. One or more of lenses, mirrors, and prisms (not shown), for example, can facilitate coupling the light into the end or edge of the light guide 110. According to various examples, the optically transparent material of the light guide 110 can 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., polyethylene (methyl methacrylate) or 'acrylic glass', polycarbonate, etc.).

As further illustrated in Figures 2B and 2C, the guided light 104 can propagate in a generally horizontal direction along the light guide 110. The propagation of the guided light 104 is shown from left to right in Figure 2B as several thick horizontal arrows representing various propagating beams in the light guide 110. Figure 2C also shows the propagation of the guided light 104 from right to left as several horizontal arrows. The propagating beams can, for example, represent plane waves of propagating light associated with one or more optical modes of the light guide 110. The propagating beams of guided light 104 can propagate by, for example, 'bouncing' or reflecting off the walls of the light guide 110 at the interface between the material of the light guide 110 (e.g., a dielectric) and the surrounding medium due to total internal reflection.

According to various examples, the multibeam diffraction grating-based backlight 100 further includes a multibeam diffraction grating 120. The multibeam diffraction grating 120 is located on a surface of the light guide 110 and is configured to couple one or more portions of the guided light 104 out of the light guide 110 through or utilizing diffraction coupling. Specifically, the coupled-out portions of the guided light 104 are diffracted and redirected away from the light guide surface as a plurality of light beams 102. As discussed above, according to various examples, each light beam 102 of the plurality of light beams has a different principal angular direction.

Specifically, FIG2C illustrates the plurality of light beams 102 as diverging, while FIG2B illustrates the light beams 102 of the plurality of light beams as converging. Whether the light beams 102 diverge (FIG. 2C) or converge (FIG. 2B) can be determined, for example, by the direction of the guided light 104. In some examples where the light beams 102 diverge, the diverging light beams 102 can appear to emanate from a 'virtual' point (not shown) located at a distance below or behind the multibeam diffraction grating 120. Similarly, according to some examples, the converging light beams 102 can converge to a point (not shown) above or in front of the multibeam diffraction grating 120.

According to various examples, the multibeam diffraction grating 120 includes a plurality of diffraction features 122 that provide diffraction. The provided diffraction results in diffractive coupling of the guided light 104 out of the light guide 110. For example, the multibeam diffraction grating 120 may include one or both of grooves in the surface of the light guide 110 and ridges protruding from the light guide surface 110 as the diffraction features 122. The grooves and ridges may be arranged parallel to each other and, at least at some point, perpendicular to the propagation direction of the guided light 104 to be coupled out by the multibeam diffraction grating 120.

In some examples, the grooves and ridges can be etched, milled, or molded into the surface or applied to the surface. In this way, the material of the multibeam diffraction grating 120 can include the material of the light guide 110. As shown in Figure 2A, the multibeam diffraction grating 120 includes substantially parallel grooves extending through the surface of the light guide 110. In other examples (not shown), the multibeam diffraction grating 120 can be a film or layer applied or attached to the surface of the light guide. The diffraction grating 120 can, for example, be deposited on the surface of the light guide.

According to various examples, the multibeam diffraction grating 120 can be arranged in a variety of configurations at, on, or in the surface of the light guide 110. For example, the multibeam diffraction grating 120 can be one of a plurality of gratings (e.g., multibeam diffraction gratings) arranged in columns and rows across the surface of the light guide. In another example, the plurality of multibeam diffraction gratings 120 can be arranged in groups (e.g., three gratings in a group, each grating in the group being associated with a different color of light), and the groups can be arranged in rows and columns. In yet another example, the plurality of multibeam diffraction gratings 120 can be substantially randomly distributed across the surface of the light guide 110.

According to certain examples, the multibeam diffraction grating 120 can include a chirped diffraction grating 120. By definition, a chirped diffraction grating 120 is a diffraction grating that exhibits or has a diffraction spacing d that varies across the width or length of the chirped diffraction grating 120, as shown in Figures 2A-2C. The varying diffraction spacing d is referred to herein as 'chirp.' Consequently, the guided light 104 diffractively coupled out of the light guide 110 exits _or emerges from the chirped diffraction grating 120 as light beams 102 at different diffraction angles _θm , corresponding to different origins on the chirped diffraction grating 120, e.g., see equation (1) above. Utilizing the chirp, the chirped diffraction grating 120 can generate multiple light beams 102 having different principal angular directions with respect to the elevation component θ of the light beams 102.

In some examples, the chirped diffraction grating 120 can have or exhibit a chirp with a diffraction spacing d that varies linearly with distance. As such, the chirped diffraction grating 120 can be referred to as a 'linearly chirped' diffraction grating. Figures 2B and 2C illustrate the multibeam diffraction grating 120 as, for example, a linearly chirped diffraction grating. As shown, the diffraction features 122 are closer together at the second end 120" of the multibeam diffraction grating 120 than at the first end 120'. Furthermore, the diffraction spacing d of the diffraction features 122 is shown to vary linearly from the first end 120' to the second end 120".

In some examples, when the guided light 104 propagates in a direction from the first end 120' to the second end 120" (e.g., as shown in FIG. 2B ), the light beam 102 generated by coupling the light out of the light guide 110 using the multi-beam diffraction grating 12 including the chirped diffraction grating can converge (i.e., become a converging light beam 102). Alternatively, according to other examples, when the guided light 104 propagates from the second end 120" to the first end 120' (e.g., as shown in FIG. 2C ), a diverging light beam 102 can be generated.

In another example (not shown), the chirped diffraction grating 120 can exhibit a nonlinear chirp of the diffraction spacing d. Various nonlinear chirps that can be used to implement the chirped diffraction grating 120 include, but are not limited to, exponential chirp, logarithmic chirp, and 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 and triangular or sawtooth chirp.

According to certain examples, the diffractive features 122 in the multibeam diffraction grating 120 can have varying orientations relative to the incident direction of the guided light 104. Specifically, the orientation of the diffractive features 122 at a first point in the multibeam diffraction grating 130 can be different from the orientation of the diffractive features 122 at another point. As described above, according to certain examples, the azimuthal component φ of the principal angular directions {θ, φ} of the light beam 102 can be determined by or correspond to the azimuthal orientation angle _{φ f of} the diffractive features 122 at the origin of the light beam 102. In this manner, the varying orientations of the diffractive features 122 in the multibeam diffraction grating 120, at least with respect to their respective azimuthal components φ, produce different light beams 102 having different principal angular directions {θ, φ}.

In some examples, the multibeam diffraction grating 120 can include diffractive features 122 that are curved or arranged in a generally curved configuration. For example, the diffractive features 122 can include one of curved grooves and curved ridges spaced apart from one another along a radius of the curve. FIG2A illustrates a curved diffractive feature 122 that is, for example, a curved, spaced-apart groove. At different points along the curve of the diffractive feature 122, the 'underlying diffraction grating' of the multibeam diffraction grating 120 associated with the curved diffractive feature 122 has different azimuthal orientation angles φ _f . Specifically, at a given point along the curved diffractive feature 122, the curve has a particular azimuthal orientation angle φ _f that is generally different from another point along the curved diffractive feature 122. Furthermore, the particular azimuthal orientation angle φ _f produces a corresponding azimuthal component φ of the principal angle directions {θ, φ} of the light beam 102 emitted from the given point. In some examples, the curve of the one or more diffractive features (e.g., grooves, ridges, etc.) can represent a portion of a circle. The circle can be coplanar with the light guide surface. In other examples, the curve can represent a portion of an ellipse or another curved shape, for example, coplanar with the light guide surface.

In other examples, the multibeam diffraction grating 120 can include diffractive features 122 that are 'segmentally' curved. Specifically, while the diffractive features may not describe a substantially smooth or continuous curve per se, the diffractive features may still be oriented at different angles relative to the incident direction of the guided light 104 at different points along the diffractive features in the multibeam diffraction grating 120. For example, the diffractive features 122 can be grooves comprising a plurality of substantially straight segments, each segment having an orientation different from adjacent segments. According to various examples, the different angles of the segments can together approximate a curve (e.g., a circular segment). See FIG. 3 below. In other examples, the features may simply have different orientations relative to the incident direction of the guided light at different locations in the multibeam diffraction grating 120, rather than approximating a specific curve (e.g., a circle or ellipse).

In some examples, the multibeam diffraction grating 120 can include both differently oriented diffractive features 122 and chirped diffraction spacing d. Specifically, both the orientation and the spacing d between the diffractive features 122 can vary at different points in the multibeam diffraction grating 120. For example, the multibeam diffraction grating 120 can include a curved and chirped diffraction grating 120 having grooves or ridges that are both curved and vary in spacing d as a function of the radius of the curve.

FIG2A illustrates a multibeam diffraction grating 120 including diffractive features 122 (e.g., grooves or ridges) that are each curved and chirped (i.e., a curved, chirped diffraction grating). Example incident directions of guided light 104 are shown in FIG2A by thick arrows. FIG2A also illustrates multiple emitted light beams 102 provided by diffractive coupling as arrows pointing away from the surface of the light guide 110. As shown, the light beams 102 are emitted along multiple different principal angular directions. Specifically, as shown, the different principal angular directions of the emitted light beams 102 differ in azimuth and elevation. Nine separate light beams 102 are depicted in FIG2A by way of example and not limitation. As discussed above, according to certain examples, the chirp of the diffractive features 122 can substantially determine the elevation component of the different principal angular directions, while the curvature of the diffractive features 122 can substantially determine the azimuth component.

FIG3 illustrates a plan view of a multibeam diffraction grating according to another example consistent with the principles described herein. As shown, the multibeam diffraction grating 120 is on the surface of the light guide 110 and includes segmentally curved and chirped diffraction features 122. An example incident direction of the guided light 104 is indicated by a thick arrow in FIG3.

Referring again to Figures 2B and 2C, according to some examples, the multibeam diffraction grating-based backlight 100 may further include a light source 130. Light source 130 may be configured to provide light that, when coupled into light guide 110, is guided light 104. In various examples, light source 130 may be substantially any light source, including, but not limited to, one or more of a light-emitting diode (LED), a fluorescent lamp, and a laser. In some examples, light source 130 may 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 within a specific color range or color model (e.g., a red, green, and blue (RGB) color model). Light source 130 may be a red LED, and the monochromatic light 102 may be substantially red. Light source 130 may be a green LED, and the monochromatic light 130 may be substantially green. Light source 130 may be a blue LED, and the monochromatic light 130 may be substantially blue. In other examples, the light provided by light source 130 may have a substantially broadband spectrum. For example, the light generated by light source 130 may be white light. The light source 130 may be a fluorescent lamp that produces white light. In some examples, the guided light 104 may be light from the light source 130 that is coupled into an end or edge of the light guide 110. For example, a lens (not shown) may facilitate coupling light into the light guide 110 at the end or edge of the light guide 110.

In some examples, the multibeam diffraction grating-based backlight 100 can be substantially transparent. Specifically, according to some examples, both the light guide 110 and the multibeam diffraction grating 120 can be optically transparent in a direction orthogonal to the propagation direction of the guided light in the light guide 110. Optical transparency can, for example, allow an object on one side of the multibeam diffraction grating-based backlight 100 to be seen from the other side.

According to certain examples of the principles described herein, an electronic display is provided. According to various examples, the electronic display is configured to emit modulated light beams as pixels of the electronic display. Furthermore, in various examples, the emitted modulated light beams can be preferably directed as multiple differently directed light beams in a viewing direction of the electronic display. In certain examples, the electronic display is a three-dimensional (3-D) electronic display (e.g., a glasses-free 3-D electronic display). According to various examples, different ones of the modulated, differently directed light beams can correspond to different 'views' associated with the 3-D electronic display. The different 'views' can, for example, provide a 'glasses-free' (e.g., autostereoscopic) presentation of information displayed by the 3-D electronic display.

FIG4 illustrates a block diagram of an electronic display 200 according to an example consistent with the principles described herein. Specifically, the electronic display 200 illustrated in FIG4 is a 3-D electronic display 200 (e.g., a 'glasses-free' 3-D electronic display) configured to emit a modulated light beam 202. The emitted modulated light beam 202 is illustrated in FIG4 as diverging (e.g., as opposed to converging) by way of example and not limitation.

The 3-D electronic display 200 illustrated in FIG4 includes a plate light guide 210 that guides light. The light guided in the plate light guide 210 is the source of light that becomes the modulated light beam 202 emitted by the 3-D electronic display 200. According to some examples, the plate light guide 210 can be substantially similar to the light guide 110 described above for the multibeam diffraction grating-based backlight 100. For example, the plate light guide 210 can be a sheet light waveguide, which is a planar, thin sheet of dielectric material configured to guide light by total internal reflection.

The 3-D electronic display 200 illustrated in FIG4 also includes a multibeam diffraction grating 220. In some examples, the multibeam diffraction grating 220 can be substantially similar to the multibeam diffraction grating 120 of the multibeam diffraction grating-based backlight 100 described above. Specifically, the multibeam diffraction grating 220 is configured to couple a portion of the guided light out as a plurality of light beams 204. Furthermore, the multibeam diffraction grating 220 is configured to direct the light beams 204 along a corresponding plurality of different principal directions. In some examples, the multibeam diffraction grating 220 includes a chirped diffraction grating. In some examples, the diffraction features (e.g., grooves, ridges, etc.) of the multibeam diffraction grating 220 are curved diffraction features. In other examples, the multibeam diffraction grating 220 includes a chirped diffraction grating having curved diffraction features. For example, the curved diffractive features may include curved (ie, continuously curved or segmentally curved) ridges or grooves and a spacing between the curved diffractive features that may vary as a function of distance across the multibeam diffraction grating 220 .

As shown in FIG4 , the 3-D electronic display 200 further includes a light valve array 230. According to various examples, the light valve array 230 includes a plurality of light valves configured to modulate a plurality of differently directed light beams 204. Specifically, the light valves of the light valve array 230 modulate the differently directed light beams 204 to provide modulated light beams 202 as pixels of the 3-D electronic display 200. Furthermore, different light beams in the modulated, differently directed light beams 202 can correspond to different views of the 3-D electronic display. In various examples, different types of light valves can be employed in the light valve array 230, including but not limited to liquid crystal light valves and electrophoretic light valves. The modulation of the light beams 202 is emphasized by dashed lines in FIG4 .

According to various examples, the light valve array 230 employed in a 3-D display can be relatively thick or, equivalently, can be separated from the multibeam diffraction grating 220 by a greater distance. In some examples, the light valve array 230 (e.g., using liquid crystal light valves) can be separated from the multibeam diffraction grating 220 or, equivalently, have a thickness greater than approximately 50 microns. In some examples, the light valve array 230 can be separated from the multibeam diffraction grating 220 or comprise a thickness greater than approximately 100 microns. In other examples, the thickness or separation can be greater than approximately 200 microns. According to various examples of the principles described herein, a relatively thick light valve array 230 or a light valve array 230 separated from the multibeam diffraction grating 220 can be employed because the multibeam diffraction grating 220 provides light beams 204 directed along multiple different principal directions. In some examples, the relatively thick light valve array 230 can be commercially available (e.g., a commercially available liquid crystal light valve array).

In some examples (e.g., as shown in FIG. 4 ), the 3-D electronic display 200 further includes a light source 240. The light source 240 is configured to provide light that propagates in the plate light guide 210 as guided light. Specifically, according to some examples, the guided light is light from the light source 240 that is coupled into the edge of the plate light guide 210. In some examples, the light source 240 is substantially similar to the light source 130 described above for the multi-beam diffraction grating-based backlight 100. For example, the light source 240 can include LEDs of a specific color (e.g., red, green, blue) to provide monochromatic light or a broadband light source, such as, but not limited to, a fluorescent lamp that provides broadband light (e.g., white light).

According to certain examples of the principles described herein, a method of operating an electronic display is provided. FIG5 illustrates a flow diagram of a method 300 of operating an electronic display according to an example consistent with the principles described herein. As shown, the method 300 of operating an electronic display includes guiding 310 light in a light guide. In certain examples, the light guide and the guided light can be substantially similar to the light guide 110 and the guided light 104 described above for the multibeam diffraction grating-based backlight 100. Specifically, in certain examples, the light guide can guide 310 the guided light according to total internal reflection. Furthermore, in certain examples, the light guide can be a substantially planar dielectric light waveguide (e.g., a plate light guide).

The method 300 of operating an electronic display further includes diffractively coupling out 320 a portion of the guided light using a multibeam diffraction grating. According to various examples, the multibeam diffraction grating is located on a surface of the lightguide. For example, the multibeam diffraction grating can be formed as grooves, ridges, etc. in the surface of the lightguide. In other examples, the multibeam diffraction grating can comprise a film on the surface of the lightguide. In some examples, the multibeam diffraction grating is substantially similar to the multibeam diffraction grating 120 described above for the multibeam diffraction grating-based backlight 100. Specifically, the multibeam diffraction grating generates multiple light beams from the portion of the guided light that was diffractively coupled out 320.

The method 300 of operating an electronic display further includes diffractively redirecting 330 the plurality of light beams away from a light-guiding surface. Specifically, one of the plurality of light beams that is diffractively redirected 330 away from the surface has a different principal angular direction than the other light beams in the plurality of light beams. In some examples, each of the plurality of light beams that is diffractively redirected has a different principal angular direction relative to the other light beams in the plurality of light beams. Diffractively redirecting 330 the light beams away from the surface further utilizes a multibeam diffraction grating. According to various examples, utilizing a multibeam diffraction grating to diffractively redirect 330 the plurality of light beams away from the surface along different principal angular directions can be substantially similar to the operation of the multibeam diffraction grating 120 described above for the multibeam diffraction grating-based backlight 100. Specifically, the multibeam diffraction grating can simultaneously or substantially simultaneously diffractively couple out 320 and diffractively redirect 330 the guided light as a plurality of light beams according to the method 300.

In some examples, the method 300 for operating an electronic display further includes modulating 340 light beams from the plurality of light beams using a corresponding plurality of light valves. Specifically, the plurality of light beams redirected 330 in a diffractive manner are modulated 340 by passing through or otherwise interacting with the corresponding plurality of light valves. According to some examples, the modulated light beams can form pixels of a three-dimensional (3-D) electronic display. For example, the modulated light beams can provide multiple views of a 3-D electronic display (e.g., a glasses-free 3-D electronic display).

In some examples, the plurality of light valves used in modulating the plurality of light beams 340 are substantially similar to the light valve array 230 described above for the 3-D electronic display 200. For example, the light valves can include liquid crystal light valves. In another example, the light valves can be another type of light valve, including but not limited to electrowetting light valves and electrophoretic light valves.

Thus, examples of multibeam diffraction grating-based backlights, 3-D electronic displays, and methods of operating electronic displays that employ a multibeam diffraction grating to provide multiple, differently directed light beams have been described. It should be understood that the above examples are merely illustrative of some of the many specific examples that can embody the principles described herein. Clearly, those skilled in the art can readily devise countless other configurations without departing from the scope of the invention as defined by the appended claims.

Claims (16)

1. A backlight based on a multi-beam diffraction grating, comprising: A light guide, which directs light from a light source; and A multi-beam diffraction grating, located on the surface of a light guide, couples out a portion of the guided light using diffraction coupling. This coupled portion of the guided light is directed as multiple beams away from the surface of the light guide, each beam having a different orientation than the other beams. The multi-beam diffraction grating is a curved chirped diffraction grating, and different beams in the multiple beams correspond to different views of the three-dimensional electronic display. 2. The backlight based on a multi-beam diffraction grating according to claim 1, wherein the chirped diffraction grating is a linear chirped diffraction grating. 3. The backlight based on a multi-beam diffraction grating according to claim 1, wherein the multi-beam diffraction grating includes one of mutually spaced curved grooves and curved ridges. 4. The backlight based on a multi-beam diffraction grating according to claim 1 further includes the light source located at the edge of the light guide, wherein the guided light is light from the light source coupled to the edge of the light guide. 5. The backlight based on a multi-beam diffraction grating according to claim 1, wherein the light guide and the multi-beam diffraction grating are substantially transparent in a direction orthogonal to the direction in which the light is to be guided in the light guide. 6. The backlight based on a multi-beam diffraction grating according to claim 1, wherein the multi-beam diffraction grating comprises a chirped diffraction grating having a curved diffraction feature configured to provide principal directions of beams that are at least different from each other in azimuth angle. 7. The backlight based on a multi-beam diffraction grating according to claim 1, wherein the plurality of beams have different main directions configured to form pixels corresponding to different views of the three-dimensional electronic display, the different views being different from each other in both elevation and azimuth angles. 8. An electronic display comprising a backlight based on a multi-beam diffraction grating as claimed in claim 1, wherein the electronic display is a three-dimensional electronic display, and wherein a portion of the guided light to be coupled through the multi-beam diffraction grating is light corresponding to a pixel of the three-dimensional electronic display. 9. The electronic display according to claim 8, further comprising a light valve to modulate one of the plurality of light beams, the multi-beam diffraction grating being located between the light valve and the light guide surface. 10. A three-dimensional electronic display, comprising: A plate light guide directs light from a light source; Multiple multi-beam diffraction gratings, one of which couples a portion of the guided light as multiple beams and directs the beams along corresponding multiple different protagonist directions associated with different views of the three-dimensional electronic display; the multi-beam diffraction grating is a curved chirped diffraction grating; and An array of light valves modulates the differently guided beams among the multiple light beams. The plurality of modulated and differently directed beams represent a plurality of pixels of the three-dimensional electronic display, and the different beams of the modulated and differently directed beams correspond to the different views of the three-dimensional electronic display. 11. The three-dimensional electronic display of claim 10, wherein the multi-beam diffraction grating comprises a chirped diffraction grating having a curved diffraction feature configured to provide a principal direction that is different from each other in both elevation and azimuth angles. 12. The three-dimensional electronic display according to claim 10, wherein the light valve array comprises a plurality of liquid crystal light valves. 13. The three-dimensional electronic display of claim 12, wherein the light valve array has a thickness greater than about 100 micrometers. 14. The three-dimensional electronic display of claim 10, further comprising the light source, wherein the guided light is light from the light source coupled to the light guide edge of the plate. 15. A method for operating an electronic display, the method comprising: Guide light in an optical guide; A portion of the guided light is coupled out in a diffractive manner using a multi-beam diffraction grating on the surface of the light guide to generate multiple beams, one of which has a different principal direction from the other beams. The multi-beam diffraction grating is a curved chirped diffraction grating. The multiple beams are guided away from the light guide surface. Different beams of light that are directed away from the light guide surface correspond to different views of the three-dimensional electronic display. 16. The method of operating an electronic display according to claim 15, further comprising modulating the plurality of light beams using corresponding plurality of light valves, wherein the modulated light beams form pixels associated with the different views of the three-dimensional electronic display.