Patent Description:
Plate light guides, also referred to as slab optical waveguides, are used in a variety of optical and photonic applications. For example, a plate light guide may be employed in a backlight of an electronic display. In particular, the plate light guide may be used to distribute light to pixels of the electronic display. The pixels may be multiview pixels of a multiview display or two-dimensional (2D) pixels of a 2D display, for example. In another example, the plate light guide may be employed as a touch-sensitive panel. Frustrated total internal reflection associated with touching a surface of the plate light guide may be used to detect where and with how much pressure the plate light guide is touched, for example.

In various optical and photonic applications of a plate light guide, light from a light source must be introduced or coupled into the plate light guide to propagate as guided light. Further, in many applications, light introduction or coupling is configured to provide guided light within plate light guide having certain predetermined propagation characteristics. For example, the guided light produced by the light coupling may propagate with a particular or predetermined propagation angle and in a particular or predetermined propagation direction. Further, the guided light or a beam thereof may have a predetermined spread angle(s). For example, the guided light may be a substantially collimated beam of light propagating from an input edge to an output edge of the plate light guide. In addition, the beam of guided light may travel within the plate light guide at a predetermined propagation angle relative to a plane of the plate light guide such that the light beam effectively 'bounces' between a front surface and back surface of the plate light guide.

Among the various light couplers for introducing or coupling light from a light source into a plate light guide are lenses, baffles, mirrors and various related reflectors (e.g., parabolic reflectors, shaped reflectors, etc.) as well as combinations thereof. Unfortunately using such light couplers often requires often exacting manufacturing operations to produce and precisely realize the light coupler such that the desired propagation characteristics of the guided light are obtained. Further, the light coupler manufacturing is often separate from the production of the plate light guide. As a further complication, these separately manufactured light couplers typically must be precisely aligned with and then affixed to the plate light guide to provide the desired light coupling that results in added cost and manufacturing complexity.

<CIT> discloses a dual light guide backlight in which light is guided in a first light guide in a first direction, and light is guided in a second light guide in a second direction. The second light guide includes a redirection coupler configured to redirect the guided light beam from the first light guide into the second light guide. <CIT> discloses a polychromatic backlight which employs a grating coupler to diffractively split and redirect collimated light coupled into a light guide. <CIT> discloses a luminous element that includes a light-guiding device and at least one light entry surface that is coupled to at least one organic light-emitting diode. <CIT> discloses a coherent backlight unit that includes a light source, a light guide plate, and a reflective optical element, where the light source irradiates coherent light to the reflective optical element. <CIT> discloses a display system that comprises an optical waveguide and a light engine, where an incoupling grating of the optical waveguide couples beams from the light engine into an intermediate grating of the waveguide. <CIT> discloses an optical display device which comprises a light guide, an image-generating system, a first diffraction grating by which light that comes from the image-generating system can be coupled into the light guide, and a second diffraction grating, by which the light can be coupled out again from the light guide.

The invention defined by the appended claims may be more readily understood with reference to the following detailed description taken in conjunction with the accompanying drawings, where like reference numerals designate like structural elements, and in which:.

Examples and embodiments in accordance with the principles described herein according to the claimed invention provide light concentration and diffractive coupling of light into a light guide. In particular, light is coupled into the plate light guide using a combination of an optical concentrator and a grating coupler that includes a diffraction grating. Further, the light is coupled in a manner that may transform substantially uncollimated light into guided light within the light guide having predetermined propagation characteristics, according to various examples. For example, the guided light may have a predetermined propagation angle within the light guide. In addition, the guided light within the light guide may have a predetermined spread angle. For example, both of a horizontal spread angle (e.g., parallel to a surface of the plate light guide) of the guided light and a vertical spread angle (e.g., orthogonal to the plate light guide surface) of the guided light may be about zero such that the guided light is a collimated light beam. In another example, guided light having one or both of the horizontal spread angle and the vertical spread angle corresponding to a fan-shaped beam pattern (e.g., a beam having about a thirty degree spread angle to more than about a ninety degree spread angle) may be provided within the light guide.

The coupling of light into a light guide (e.g., a grating-coupled light guide), according to various embodiments of the principles described herein, may be useful in a variety of applications including, but not limited to, a backlight of an electronic display (e.g., a multiview display). Uses of electronic displays employing various embodiments according to the principles described herein include, but are not limited to, mobile telephones (e.g., smart phones), watches, tablet computes, mobile computers (e.g., laptop computers), personal computers and computer monitors, automobile display consoles, cameras displays, and various other mobile as well as substantially non-mobile display applications and devices.

Herein, a 'multiview display' is defined as an electronic display or display system configured to provide different views of a multiview image in different view directions. <FIG> illustrates a perspective view of a multiview display <NUM> in an example, according to an embodiment consistent with the principles described herein. As illustrated in <FIG>, the multiview display <NUM> comprises a screen <NUM> to display a multiview image to be viewed. The screen <NUM> may be a display screen of a telephone (e.g., mobile telephone, smart phone, etc.), a tablet computer, a laptop computer, a computer monitor of a desktop computer, a camera display, or an electronic display of substantially any other device, for example.

The multiview display <NUM> provides different views <NUM> of the multiview image in different view directions <NUM> relative to the screen <NUM>. The view directions <NUM> are illustrated as arrows extending from the screen <NUM> in various different principal angular directions (or simply different directions); the different views <NUM> are illustrated as shaded polygonal boxes at the termination of the arrows (i.e., depicting the view directions <NUM>); and only four views <NUM> and four view directions <NUM> are illustrated, all by way of example and not limitation. Note that while the different views <NUM> are illustrated in <FIG> as being above the screen, the views <NUM> actually appear on or in a vicinity of the screen <NUM> when the multiview image is displayed on the multiview display <NUM>. Depicting the views <NUM> above the screen <NUM> is only for simplicity of illustration and is meant to represent viewing the multiview display <NUM> from a respective one of the view directions <NUM> corresponding to a particular view <NUM>.

A view direction or equivalently a light beam having a direction corresponding to a view direction of a multiview display generally has a principal angular direction given by angular components {θ, φ}, by definition herein. The angular component θ is referred to herein as the 'elevation component' or 'elevation angle' of the light beam. The angular component φ is referred to as the `azimuth component' or `azimuth angle' of the light beam. By definition, the elevation angle θ is an angle in a vertical plane (e.g., perpendicular to a plane of the multiview display screen while the azimuth angle φ is an angle in a horizontal plane (e.g., parallel to the multiview display screen plane).

<FIG> illustrates a graphical representation of the angular components {θ, φ} of a light beam <NUM> having a particular principal angular direction or 'direction' corresponding to a view direction (e.g., view direction <NUM> in <FIG>) of a multiview display in an example, according to an embodiment consistent with the principles described herein. In addition, the light beam <NUM> is emitted or emanates from a particular point, by definition herein. That is, by definition, the light beam <NUM> has a central ray associated with a particular point of origin within the multiview display. <FIG> also illustrates the light beam (or view direction) point of origin O.

Further herein, the term 'multiview' as used in the terms 'multiview image' and 'multiview display' is defined as a plurality of views representing different perspectives or including angular disparity between views of the view plurality. In addition, herein the term 'multiview' explicitly includes more than two different views (i.e., a minimum of three views and generally more than three views), by definition herein. As such, 'multiview display' as employed herein is explicitly distinguished from a stereoscopic display that includes only two different views to represent a scene or an image. Note however, while multiview images and multiview displays include more than two views, by definition herein, multiview images may be viewed (e.g., on a multiview display) as a stereoscopic pair of images by selecting only two of the multiview views to view at a time (e.g., one view per eye).

A `multiview pixel' is defined herein as a set of sub-pixels representing 'view' pixels in each of a similar plurality of different views of a multiview display. In particular, a multiview pixel may have an individual sub-pixel corresponding to or representing a view pixel in each of the different views of the multiview image. Moreover, the sub-pixels of the multiview pixel are so-called 'directional pixels' in that each of the sub-pixels is associated with a predetermined view direction of a corresponding one of the different views, by definition herein. Further, according to various examples and embodiments, the different view pixels represented by the sub-pixels of a multiview pixel may have equivalent or at least substantially similar locations or coordinates in each of the different views. For example, a first multiview pixel may have individual sub-pixels corresponding to view pixels located at {x<NUM>, y<NUM>} in each of the different views of a multiview image, while a second multiview pixel may have individual sub-pixels corresponding to view pixels located at {x<NUM>, y<NUM>} in each of the different views, and so on.

In some embodiments, a number of sub-pixels in a multiview pixel may be equal to a number of views of the multiview display. For example, the multiview pixel may provide sixty-four (<NUM>) sub-pixels in associated with a multiview display having <NUM> different views. In another example, the multiview display may provide an eight by four array of views (i.e., <NUM> views) and the multiview pixel may include thirty-two <NUM> sub-pixels (i.e., one for each view). Additionally, each different sub-pixel may have an associated direction (e.g., light beam direction) that corresponds to a different one of the view directions corresponding to the <NUM> different views, for example. Further, according to some embodiments, a number of multiview pixels of the multiview display may be substantially equal to a number of 'view' pixels (i.e., pixels that make up a selected view) in the multiview display views. For example, if a view includes six hundred forty by four hundred eighty view pixels (i.e., a <NUM> x <NUM> view resolution), the multiview display may have three hundred seven thousand two hundred (<NUM>,<NUM>) multiview pixels. In another example, when the views include one hundred by one hundred pixels, the multiview display may include a total often thousand (i.e., <NUM> x <NUM> = <NUM>,<NUM>) multiview pixels.

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

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

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

According to various embodiments described herein, a grating coupler is used to couple light into the light guide. The grating coupler, by definition herein, includes a diffraction grating in which characteristics and the features thereof (i.e., 'diffractive features') may be used to control one or both of an angular directionality and an angular spread of a light beam produced by the diffraction grating from incident light. The characteristics that may be used to control the angular directionality and the angular spread include, but are not limited to, one or more of a grating length, a grating pitch (feature spacing), a shape of the diffractive features (e.g., sinusoidal, rectangular, triangular, sawtooth, etc.), a size of the diffractive features (e.g., groove or ridge width), and an orientation of the grating. In some examples, the various characteristics used for control may be characteristics that are local to a vicinity of a point of origin of the produced light beam as well as a point or points of incidence of the light on the diffraction grating.

Herein, a 'diffraction grating' is generally defined as a plurality of features (i.e., diffractive features) arranged to provide diffraction of light incident on the diffraction grating. In some examples, the plurality of features may be arranged in a periodic or quasi-periodic manner. For example, the diffraction grating may include a plurality of features (e.g., a plurality of grooves or ridges in a material surface) arranged in a one-dimensional (1D) array. In other examples, the diffraction grating may be a two-dimensional (2D) array of features. The diffraction grating may be a 2D array of bumps on or holes in a material surface, for example.

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

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

According to various examples described herein, a diffraction grating (e.g., a diffraction grating of a multibeam element, as described below) may be employed to diffractively scatter or couple light out of a light guide (e.g., a plate light guide) as a light beam. In particular, a diffraction angle θm of or provided by a locally periodic diffraction grating may be given by equation (<NUM>) as: <MAT> where λ is a wavelength of the light, m is a diffraction order, n is an index of refraction of a light guide, d is a distance or spacing between features of the diffraction grating, θi is an angle of incidence of light on the diffraction grating. For simplicity, equation (<NUM>) assumes that the diffraction grating is adjacent to a surface of the light guide and a refractive index of a material outside of the light guide is equal to one (i.e., nout = <NUM>). In general, the diffraction order m is given by an integer. A diffraction angle θm of a light beam produced by the diffraction grating may be given by equation (<NUM>) where the diffraction order is positive (e.g., m > <NUM>). For example, first-order diffraction is provided when the diffraction order m is equal to one (i.e., m = <NUM>).

<FIG> illustrates a cross sectional view of a diffraction grating <NUM> in an example, according to an embodiment consistent with the principles described herein. For example, the diffraction grating <NUM> may be located on a surface of a light guide <NUM>. In addition, <FIG> illustrates a light beam <NUM> incident on the diffraction grating <NUM> at an incident angle θi. The incident light beam <NUM> may be a guided light beam within the light guide <NUM>. Also illustrated in <FIG> is a directional light beam <NUM> diffractively produced and coupled-out by the diffraction grating <NUM> as a result of diffraction of the incident light beam <NUM>. The directional light beam <NUM> has a diffraction angle θm (or `principal angular direction' herein) as given by equation (<NUM>). The diffraction angle θm may correspond to a diffraction order 'm' of the diffraction grating <NUM>, for example.

Herein, an 'angle-preserving scattering feature' or equivalently an 'angle-preserving scatterer' is any feature or scatterer configured to scatter light in a manner that substantially preserves in scattered light an angular spread of light incident on the feature or scatterer. In particular, by definition, an angular spread σs of light scattered by an angle-preserving scattering feature is a function of an angular spread σ of the incident light (i.e., σs = f(σ) ). In some embodiments, the angular spread σs of the scattered light is a linear function of the angular spread or collimation factor σ of the incident light (e.g., σs = a·σ, where a is an integer). That is, the angular spread σs of light scattered by an angle-preserving scattering feature may be substantially proportional to the angular spread or collimation factor σ of the incident light. For example, the angular spread σs of the scattered light may be substantially equal to the incident light angular spread σ (e.g., σs ≈ σ). A uniform diffraction grating (i.e., a diffraction grating having a substantially uniform or constant diffractive feature spacing or grating pitch) is an example of an angle-preserving scattering feature. In contrast, a Lambertian scatterer or reflector as well as a general diffuser (e.g., having or approximating Lambertian scattering) are not angle-preserving scatterers, by definition herein.

By definition herein, a 'multibeam element' is a structure or element of a backlight or a display that produces light that includes a plurality of light beams. In some embodiments, the multibeam element may be optically coupled to a light guide of a backlight to provide the plurality of light beams by coupling out a portion of light guided in the light guide. In other embodiments, the multibeam element may generate light emitted as the light beams (e.g., may comprise a light source). Further, the light beams of the plurality of light beams produced by a multibeam element have different principal angular directions from one another, by definition herein. In particular, by definition, a light beam of the plurality has a predetermined principal angular direction that is different from another light beam of the light beam plurality. Furthermore, the light beam plurality may represent a light field. For example, the light beam plurality may be confined to a substantially conical region of space or have a predetermined angular spread that includes the different principal angular directions of the light beams in the light beam plurality. As such, the predetermined angular spread of the light beams in combination (i.e., the light beam plurality) may represent the light field.

According to various embodiments, the different principal angular directions of the various light beams of the plurality are determined by a characteristic including, but not limited to, a size (e.g., length, width, area, etc.) of the multibeam element. In some embodiments, the multibeam element may be considered an 'extended point light source', i.e., a plurality of point light sources distributed across an extent of the multibeam element, by definition herein. Further, a light beam produced by the multibeam element has a principal angular direction given by angular components {θ, φ}, by definition herein, and as described above with respect to <FIG>.

Herein a 'collimator' is defined as substantially any optical device or apparatus that is configured to collimate light. According to various embodiments, an amount of collimation provided by the collimator may vary in 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, the collimator may include a shape in one or both of two orthogonal directions that provides light collimation, according to some embodiments.

Herein, a 'collimation factor' is defined as a degree to which light is collimated. In particular, a collimation factor defines an angular spread of light rays within a collimated beam of light, by definition herein. For example, a collimation factor σ may specify that a majority of light rays in a beam of collimated light is within a particular angular spread (e.g., +/- σ degrees about a central or principal angular direction of the collimated light beam). The light rays of the collimated light beam may have a Gaussian distribution in terms of angle and the angular spread may be an angle determined by at one-half of a peak intensity of the collimated light beam, according to some examples.

Herein, a `light source' is defined as a source of light (e.g., an optical emitter configured to produce and emit light). For example, the light source may comprise an optical emitter such as a light emitting diode (LED) that emits light when activated or turned on. In particular, herein the light source may be substantially any source of light or comprise substantially any optical emitter including, but not limited to, one or more of a light emitting diode (LED), a laser, an organic light emitting diode (OLED), a polymer light emitting diode, a plasma-based optical emitter, a fluorescent lamp, an incandescent lamp, and virtually any other source of light. The light produced by the light source may have a color (i.e., may include a particular wavelength of light), or may be a range of wavelengths (e.g., white light). In some embodiments, the light source may comprise a plurality of optical emitters. For example, the light source may include a set or group of optical emitters in which at least one of the optical emitters produces light having a color, or equivalently a wavelength, that differs from a color or wavelength of light produced by at least one other optical emitter of the set or group. The different colors may include primary colors (e.g., red, green, blue) for example.

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

According to the claimed invention, a grating-coupled light guide is provided. <FIG> illustrates a cross sectional view of a grating-coupled light guide <NUM> in an example, according to an embodiment consistent with the principles described herein. <FIG> illustrates a cross sectional view of a grating-coupled light guide <NUM> in an example, according to another embodiment consistent with the principles described herein. The grating-coupled light guide <NUM> is configured to receive and diffractively couple light <NUM> into the grating-coupled light guide <NUM> as guided light <NUM>. For example, the light <NUM> may be provided by a light source <NUM> (e.g. a substantially uncollimated light source), as described in more detail below. According to various examples, the grating-coupled light guide <NUM> may provide a relatively high coupling efficiency. Moreover, the grating-coupled light guide <NUM> may transform the light <NUM> received from the light source <NUM> into guided light <NUM> (e.g., a beam of guided light) having a predetermined spread angle or collimation factor σ within the grating-coupled light guide <NUM>, according to various embodiments.

In particular, a coupling efficiency of greater than about twenty percent (<NUM>%) may be achieved, according to some embodiments. For example, in a transmission configuration (described below), the coupling efficiency of the grating-coupled light guide <NUM> may be greater than about thirty percent (<NUM>%) or even greater than about thirty-five percent (<NUM>%). A coupling efficiency of up to about forty percent (<NUM>%) may be achieved, for example. In a reflection configuration, the coupling efficiency of the grating-coupled light guide <NUM> may be as high as about fifty percent (<NUM>%), or about sixty percent (<NUM>%) or even about seventy percent (<NUM>%), for example.

According to various embodiments, the predetermined spread angle or collimation factor σ provided by and within the grating-coupled light guide <NUM> may yield a beam of guided light <NUM> having controlled or predetermined propagation characteristics. In particular, the grating-coupled light guide <NUM> may provide a controlled or predetermined first spread angle in a 'vertical' direction, i.e., in a plane perpendicular to a plane of a surface of the grating-coupled light guide <NUM>. Simultaneously, the grating-coupled light guide <NUM> may provide a controlled or predetermined second spread angle in a horizontal direction, i.e., in a plane parallel to the grating-coupled light guide surface. Further, the light <NUM> may be received from the light source <NUM> at an angle that is substantially perpendicular to the plane of the grating-coupled light guide <NUM> and then be transformed into the guided light <NUM> having a non-zero propagation angle within the grating-coupled light guide <NUM>, e.g., a non-zero propagation angle consistent with a critical angle of total internal reflection within the grating-coupled light guide <NUM>.

As illustrated in <FIG> and <FIG>, the grating-coupled light guide <NUM> comprises a light guide <NUM>. The light guide <NUM> may be a plate light guide, according to some embodiments. However, herein the term `light guide' is being used for ease of discussion. The light guide <NUM> is configured to guide light along a length or extent of the light guide <NUM> as the guided light <NUM> of the grating-coupled light guide <NUM>.

The illustrated grating-coupled light guide <NUM> further comprises an optical concentrator <NUM>. The optical concentrator <NUM> is configured to concentrate or collimate light to provide concentrated light <NUM>', according to the claimed invention. For example, the light source <NUM> may provide light <NUM> as substantially unconcentrated or uncollimated light <NUM>". The provided unconcentrated or uncollimated light <NUM>" is then concentrated by the optical concentrator <NUM> to provide the concentrated light <NUM>'.

The grating-coupled light guide <NUM> illustrated in <FIG> further comprises a grating coupler <NUM> located at an input of the light guide <NUM>, e.g., located adjacent to an input edge thereof. According to the claimed invention, the grating coupler <NUM> is configured to diffractively redirect the concentrated light <NUM>' into the light guide <NUM> as the guided light <NUM>. The light is diffractively redirected into the light guide <NUM> at a non-zero propagation angle. Further, the guided light <NUM> has a first spread angle and a second spread angle, the first spread angle being and orthogonal to the second spread angle. According to the claimed invention, characteristics of the optical concentrator <NUM> and grating coupler <NUM> are configured in combination to determine the non-zero propagation angle, the first spread angle, and the second spread angle of the guided light <NUM> within the light guide <NUM>.

According to some embodiments, the light guide <NUM> may be a slab or plate optical waveguide comprising an extended, substantially planar sheet of optically transparent, dielectric material that is configured to guide the guided light <NUM> using total internal reflection. For example, the planar sheet of optically transparent dielectric material may have a first refractive index that is greater than a second refractive index of a medium surrounding the dielectric optical waveguide. The difference in refractive indices is configured to facilitate total internal reflection of the guided light <NUM> according to one or more guided modes of the light guide <NUM>. According to various examples, the optically transparent material of the light guide <NUM> may include or be made up of any of a variety of dielectric materials including, but not limited to, one or more of various types of glass (e.g., silica glass, alkali-aluminosilicate glass, borosilicate glass, etc.) and substantially optically transparent plastics or polymers (e.g., poly(methyl methacrylate) or 'acrylic glass', polycarbonate, etc.). In some examples, the light guide <NUM> may further include a cladding layer (not illustrated) on at least a portion of a surface (e.g., one or both of the top surface and the bottom surface) of the light guide <NUM>. The cladding layer may be used to further facilitate total internal reflection, according to some examples.

Further, according to some embodiments, the light guide <NUM> is configured to guide the guided light <NUM> according to total internal reflection at the non-zero propagation angle between a first surface <NUM> (e.g., a 'back' surface or side) and a second surface <NUM> (e.g., a 'front' surface or side) of the light guide <NUM>. In particular, the guided light <NUM> propagates by reflecting or 'bouncing' between the first surface <NUM> and the second surface <NUM> of the light guide <NUM> at the non-zero propagation angle. In some embodiments, a plurality of guided light beams comprising different colors of light may be guided by the light guide <NUM> as the guided light <NUM>, each different color guided light beam of the guided light beam plurality having a different, color-specific, non-zero propagation angles. Note that the non-zero propagation angle is not illustrated in <FIG> for simplicity of illustration. However, a bold arrow depicting a propagation direction <NUM> illustrates a general propagation direction of the guided light <NUM> along the light guide length in <FIG>.

As defined herein, a 'non-zero propagation angle' is an angle relative to a surface (e.g., the first surface <NUM> or the second surface <NUM>) of the light guide <NUM>. Further, the non-zero propagation angle is both greater than zero and less than a critical angle of total internal reflection within the light guide <NUM>, according to various embodiments. For example, the non-zero propagation angle of the guided light <NUM> may be between about ten (<NUM>) degrees and about fifty (<NUM>) degrees or, in some examples, between about twenty (<NUM>) degrees and about forty (<NUM>) degrees, or between about twenty-five (<NUM>) degrees and about thirty-five (<NUM>) degrees. For example, the non-zero propagation angle may be about thirty (<NUM>) degrees. In other examples, the non-zero propagation angle may be about <NUM> degrees, or about <NUM> degrees, or about <NUM> degrees. Moreover, a specific non-zero propagation angle may be chosen (e.g., arbitrarily) for a particular implementation as long as the specific non-zero propagation angle is chosen to be less than the critical angle of total internal reflection within the light guide <NUM>. The non-zero propagation angle may be substantially constant throughout a length of the light guide <NUM>, according to some embodiments.

Regarding the optical concentrator <NUM>, any of a variety of optical structures configured to provide concentration or collimation (e.g., partial collimation) of light may be employed including, but not limited to, a convex or biconvex lens, a parabolic reflector, and a semi-parabolic or shaped reflector. In particular, in some embodiments, the optical concentrator <NUM> comprises freeform optics configured to reduce a spread angle of the light from the light source <NUM>. The freeform optics may be further configured to concentrate the light in a predefined area of a surface of the grating-coupled light guide <NUM>. For example, the predefined area may correspond to an area occupied by the grating coupler <NUM> of the grating-coupled light guide <NUM>. In other embodiments, the optical concentrator <NUM> may comprise a tapered collimator, a catadioptic collimator, or a reflective turning collimator. Some embodiments of the optical concentrator <NUM> may comprise a combination of one or more of the freeform optics, the tapered collimator, the catadioptic collimator, and the reflective turning collimator.

<FIG> illustrates a cross-sectional view of a portion of a grating-coupled light guide <NUM> in an example, according to an embodiment consistent with the principles described herein. In particular, illustrated in <FIG> are the light source <NUM>, the optical concentrator <NUM>, a portion of the light guide <NUM>, and the grating coupler <NUM> located at the input of the light guide portion. Also illustrated are the unconcentrated light <NUM>" provided by the light source <NUM> and the concentrated light <NUM>' provided at an output of the optical concentrator <NUM>. As illustrated, the optical concentrator <NUM> comprises freeform optics <NUM> configured to concentrate the unconcentrated light <NUM>" as the concentrated light <NUM>'. Further, the freeform optics <NUM> of the optical concentrator <NUM> are configured to provide the concentrated light <NUM>' in an area A corresponding to an area occupied by the grating coupler <NUM>, as illustrated. Note that a beam angle γc of the concentrated light <NUM>' is less than a beam angle γu of the unconcentrated light <NUM>" (i.e., γc < γu), as illustrated and by definition.

<FIG> illustrates a cross-sectional view of an optical concentrator <NUM> in an example useful to understand the claimed invention. In particular, <FIG> illustrates the optical concentrator <NUM> comprising a tapered collimator <NUM>. As illustrated, the tapered collimator <NUM> comprises a light guide having tapered sidewalls configured to reflect light by total internal reflection. The total internal reflection in combination with the tapered sidewalls selectively concentrates or collimates light propagating within the tapered collimator <NUM>. Specifically, the unconcentrated light <NUM>" from the light source <NUM> enters a narrow end of the tapered collimator <NUM> and propagates and reflects according to total internal reflection to an output end as the concentrated light <NUM>'. Arrows in <FIG> illustrate light beams of light within the tapered collimator <NUM>.

<FIG> illustrates a cross-sectional view of an optical concentrator <NUM> in an example useful to understand the claimed invention. In particular, <FIG> illustrates the optical concentrator <NUM> comprising a catadioptic collimator <NUM>. As illustrated, the catadioptic collimator <NUM> comprises a first portion 126a configured as a collimating lens to collimate a portion of the unconcentrated light <NUM>" corresponding to an inner beam portion thereof. The catadioptic collimator <NUM> further comprises second portion 126b configured as a collimating reflector to collimate an outer beam portion of the unconcentrated light <NUM>". In <FIG>, arrows illustrate light beams within the unconcentrated light <NUM>". The light beams in the inner beam portion of the unconcentrated light <NUM>" pass through and are concentrated or collimated by refraction in the first portion 126a as a result of the collimating lens, while the light beams of the outer beam portion enter the catadioptic collimator <NUM> and are concentrated or collimated by reflection from the collimating reflector of the second portion 126b. The catadioptic collimator <NUM> may comprise a transparent dielectric material. An outer surface of the second portion 126b may be coated with a reflective material or layer (e.g., a reflective metal) to enhance reflection of the light beams.

<FIG> illustrates a cross-sectional view of an optical concentrator <NUM> in another example useful to understand the claimed invention. In particular, <FIG> illustrates the optical concentrator <NUM> comprising a reflective turning collimator <NUM>. The reflective turning collimator <NUM> comprises a reflective surface 128a configured to reflectively concentrate the unconcentrated light <NUM>" to provide the concentrated light <NUM>'. For example, the reflective surface 128a may be a parabolic or semi-parabolic reflector (e.g., a shaped parabolic reflector). Arrows in <FIG> represent light beams within the reflective turning collimator <NUM> to illustrate light concentration.

Referring again to <FIG> and <FIG>, the grating coupler <NUM> of the grating-coupled light guide <NUM> is configured to couple light <NUM> from the light source <NUM> and optical concentrator <NUM> into the light guide <NUM> using diffraction. In particular, the grating coupler <NUM> is configured to receive the concentrated light <NUM>' from the optical concentrator <NUM> and to diffractively redirect (i.e., diffractively couple) the concentrated light <NUM>' into the light guide <NUM> at the non-zero propagation angle as the guided light <NUM>. As mentioned above, the guided light <NUM> that is diffractively directed or coupled into the light guide <NUM> by the grating coupler <NUM> has controlled or predetermined propagation characteristics (i.e., spread angles), according to various examples.

As noted above, characteristics of the both of the optical concentrator and the grating coupler <NUM> are cooperatively configured to determine the propagation characteristics of the guided light <NUM> or a light beam thereof. The propagation characteristics determined by the optical concentrator <NUM> and grating coupler <NUM> include the non-zero propagation angle, a first spread angle, and a second spread angle of the guided light <NUM>. The `first spread angle,' by definition herein, is a predetermined spread angle of the guided light <NUM> in a plane that is substantially perpendicular to a surface (e.g., the first surface <NUM> or the second surface <NUM>) of the light guide <NUM>. Further, the first spread angle represents an angle of beam spread as the light beam of the guided light <NUM> propagates in a direction defined by the non-zero propagation angle (e.g., beam spread in a vertical plane), by definition herein. The 'second spread angle' is an angle in plane that is substantially parallel to the light guide surface, by definition herein. The second spread angle represents a predetermined spread angle of the guided light beam as the guided light <NUM> propagates in a direction (i.e., in a plane) that is substantially parallel to the light guide surface (e.g., in a horizontal plane).

According to the claimed invention, the grating coupler <NUM> includes a diffraction grating <NUM> having a plurality of spaced-apart diffractive features. The first spread angle and the non-zero propagation angle of the guided light <NUM> may be controlled or determined by a pitch and, to some extent, a lateral shape of the diffractive features of the diffraction grating <NUM>, according to some examples. That is, by selecting a pitch of the diffraction grating <NUM> in a direction corresponding to the general propagation direction of the guided light <NUM>, a diffraction angle of the diffraction grating <NUM> is used to produce the non-zero propagation angle. In addition, by varying the pitch and other aspects of the diffractive features along a length and across a width the diffraction grating <NUM> of the grating coupler <NUM>, the first angular spread of the guided light <NUM> is controlled, i.e., to provide the predetermined first angular spread, according to the claimed invention.

Further, according to the claimed invention, the predetermined second spread angle of the guided light <NUM> may be controlled by a lateral shape or width variation of the diffraction grating <NUM> of the grating coupler <NUM>. For example, a diffraction grating <NUM> that increases in width from a first end toward a second end of the diffraction grating <NUM> (i.e., a fan-shaped grating) may produce a relatively large second spread angle of the redirected, guided light <NUM> (i.e., a fan-shaped optical beam). In particular, according to some embodiments, the predetermined second spread angle may be substantially proportional to an angle of the increase in a width of the diffraction grating <NUM> of the grating coupler <NUM>. In another example, a diffraction grating <NUM> that has relatively little variation in width (e.g., with substantially parallel sides) may provide a relatively small second spread angle of the light beam of guided light <NUM>. A relatively small second spread angle (e.g., a spread angle that is substantially zero) may provide the guided light <NUM> that is collimated or at least substantially collimated in a horizontal direction parallel or coplanar with the light guide surface, for example.

<FIG> illustrates a plan view of a grating coupler <NUM> on a surface of a grating-coupled light guide <NUM> in an example, according to an embodiment consistent with the principles described herein. <FIG> illustrates a plan view of a grating coupler <NUM> on a surface of a grating-coupled light guide <NUM> in an example, according to another embodiment consistent with the principles described herein. In particular, <FIG> illustrates a grating coupler <NUM> having a diffraction grating <NUM> that is fan-shaped, as viewed from a surface (e.g., a top surface or a bottom surface) of the light guide <NUM>. The fan-shaped diffraction grating <NUM> has a width that increases from a first end toward a second end of the diffraction grating <NUM>, where the width increase defines a fan angle ϕ. As illustrated, the diffraction grating fan angle ϕ is about eighty (<NUM>) degrees. The fan-shaped diffraction grating <NUM> may provide a fan-shaped optical beam of guided light <NUM> (e.g., illustrated using bold arrows) having a predetermined second spread angle that is proportional to the fan angle ϕ, according to various examples.

<FIG>, on the other hand, illustrates a grating coupler <NUM> having a rectangular-shaped diffraction grating <NUM> (e.g., having a fan angle ϕ equal to about zero), as viewed from the plate light guide surface. The rectangular-shaped diffraction grating <NUM> may produce a substantially collimated optical beam of guided light <NUM>, i.e., an optical beam of guided light <NUM> having a predetermined second spread angle that is about zero. The substantially collimated optical beam of guided light <NUM> is illustrated using parallel bold arrows in <FIG>. As such, the fan angle ϕ of the diffraction grating <NUM> may be used to control or determine the second spread angle of the guided light <NUM>, according to various embodiments.

According to some embodiments, the grating coupler <NUM> may be a transmissive grating coupler <NUM> (i.e., a transmission mode diffraction grating coupler), while in other examples, the grating coupler <NUM> may be a reflective grating coupler <NUM> (i.e., a reflection mode diffraction grating coupler). In particular, as illustrated in <FIG>, the grating coupler <NUM> may include a transmission mode diffraction grating <NUM>' at a surface of the light guide <NUM> adjacent to the light source <NUM> and optical concentrator <NUM>. For example, the transmission mode diffraction grating <NUM> of the grating coupler <NUM> may be on a bottom (or first) surface <NUM> of the light guide <NUM> and the light source <NUM> may illuminate the grating coupler <NUM> through the optical concentrator <NUM> from the bottom. As illustrated in <FIG>, the transmission mode diffraction grating <NUM>' of the grating coupler <NUM> is configured to diffractively redirect concentrated light <NUM>' that is transmitted or passes through diffraction grating <NUM>.

Alternatively, as illustrated in <FIG>, the grating coupler <NUM> may be a reflective grating coupler <NUM> having a reflection mode diffraction grating <NUM>" at a second surface <NUM> of the light guide <NUM> that is opposite to the surface adjacent to the light source <NUM> and optical concentrator <NUM>. For example, the reflection mode diffraction grating <NUM>" of the grating coupler <NUM> may be on a top (or second) surface <NUM> of the light guide <NUM> and the light source <NUM> may illuminate the grating coupler <NUM> through the optical concentrator and then through a portion of the bottom (or first) surface <NUM> of the light guide <NUM>, as illustrated. The reflection mode diffraction grating <NUM>" is configured to diffractively redirect light <NUM> into the light guide <NUM> using reflective diffraction (i.e., reflection and diffraction), as illustrated in <FIG>.

According to various examples, diffractive grating <NUM> of the grating coupler <NUM> may include grooves, ridges or similar diffractive features of a diffraction grating formed or otherwise provided on or in the surface <NUM>, <NUM> of the light guide <NUM>. For example, grooves or ridges may be formed in or on the light source-adjacent first surface <NUM> (e.g., bottom surface) of the light guide <NUM> to serve as the transmission mode diffraction grating <NUM>' of the transmissive grating coupler <NUM>. Similarly, grooves or ridges may be formed or otherwise provided in or on the second surface <NUM> of the light guide <NUM> opposite to the light source-adjacent first surface <NUM> to serve as the reflection mode diffraction grating <NUM>" of the reflective grating coupler <NUM>, for example.

According to some examples, the grating coupler <NUM> may include a grating material (e.g., a layer of grating material) on or in the plate light guide surface. In some examples, the grating material may be substantially similar to a material of the light guide <NUM>, while in other examples, the grating material may differ (e.g., have a different refractive index) from the plate light guide material. In some examples, the diffractive grating grooves in the plate light guide surface may be filled with the grating material. For example, grooves of the diffraction grating <NUM> of either the transmissive grating coupler <NUM> or the reflective grating coupler <NUM> may be filled with a dielectric material (i.e., the grating material) that differs from a material of the light guide <NUM>. The grating material of the grating coupler <NUM> may include silicon nitride, for example, while the light guide <NUM> may be glass, according to some examples. Other grating materials including, but not limited to, indium tin oxide (ITO) may also be used.

In other examples, either the transmissive grating coupler <NUM> or the reflective grating coupler <NUM> may include ridges, bumps, or similar diffractive features that are deposited, formed or otherwise provided on the respective surface of the light guide <NUM> to serve as the particular diffraction grating <NUM>. The ridges or similar diffractive features may be formed (e.g., by etching, molding, etc.) in a dielectric material layer (i.e., the grating material) that is deposited on the respective surface of the light guide <NUM>, for example. In some examples, the grating material of the reflective grating coupler <NUM> may include a reflective metal. For example, the reflective grating coupler <NUM> may be or include a layer of reflective metal such as, but not limited to, gold, silver, aluminum, copper and tin, to facilitate reflection by the reflection mode diffraction grating <NUM>".

According to various examples, the grating coupler <NUM> (i.e., either the transmissive grating coupler or the reflective grating coupler) is configured to produce a grating spatial phase function that is a difference between an output phase profile of the guided light <NUM> and an input phase profile of the light <NUM> incident from the light source <NUM>. For example, if the light source <NUM> as viewed through the optical concentrator <NUM> approximates a point source at a distance f from the transmissive grating coupler <NUM>, the input phase profile φin of the light may be given by equation (<NUM>) as <MAT> where x and y are spatial coordinates of the transmissive grating coupler <NUM> and λ is wavelength in free space (i.e., a vacuum). The transmissive grating coupler <NUM> may be configured to produce a beam of guided light <NUM> that propagates away from an arbitrary center point (x<NUM> ,y<NUM>) of the grating coupler <NUM> at an angle θ. As such, an output phase profile φout of the guided light <NUM> produced by the transmissive grating coupler <NUM> may be given by equation (<NUM>) as <MAT> where n is an index of refraction of the light guide <NUM>. The grating spatial phase function of the transmissive grating coupler <NUM> may be determined from a difference between equation (<NUM>) and equation (<NUM>). In addition, a horizontal spread angle (e.g., in an x-y plane) may be determined by an envelope function of the diffraction grating <NUM> of the transmissive grating coupler <NUM>, according to various examples. When considering a reflective grating coupler <NUM>, propagation of the light <NUM> through the optical concentrator as wells as both the light source-adjacent first surface <NUM> (e.g., bottom surface) of the light guide <NUM> (i.e., refraction) and through a material of the light guide <NUM> also is taken into account. Further, with a reflective grating coupler <NUM>, optional metallization (e.g., use of metal or a metal layer) may improve grating efficiency (e.g., by effectively eliminating a zero-th order transmitted diffraction order of a diffraction grating of the reflection grating coupler <NUM>).

<FIG> illustrates a cross sectional view of a portion of the grating-coupled light guide <NUM> in an example, according to an embodiment consistent with the principles described herein. <FIG> illustrates a cross sectional view of a portion of the grating-coupled light guide <NUM> in an example, according to an embodiment consistent with the principles described herein. In particular, both <FIG> and <FIG> illustrate a portion of the grating-coupled light guide <NUM> of <FIG> that includes the grating coupler <NUM>. Further, the grating coupler <NUM> illustrated in <FIG> is a transmissive grating coupler <NUM> that includes a transmission mode diffraction grating <NUM>'.

As illustrated in <FIG>, the transmissive grating coupler <NUM> includes grooves (i.e., diffractive features) formed in a bottom (or light source-adjacent) surface <NUM> of the light guide <NUM> to form the transmission mode diffraction grating <NUM>'. Further, the transmission mode diffraction grating <NUM>' of the transmissive grating coupler <NUM> illustrated in <FIG> includes a layer of grating material <NUM> (e.g., silicon nitride) that is also deposited in the grooves. <FIG> illustrates a transmissive grating coupler <NUM> that includes ridges (i.e., diffractive features) of the grating material <NUM> on the bottom or light source-adjacent surface <NUM> of the light guide <NUM> to form the transmission mode diffraction grating <NUM>'. Etching or molding a deposited layer of the grating material <NUM>, for example, may produce the ridges. In some examples, the grating material <NUM> that makes up the ridges illustrated in <FIG> may include a material that is substantially similar to a material of the light guide <NUM>. In other examples, the grating material <NUM> may differ from the material of the light guide <NUM>. For example, the light guide <NUM> may include a glass or a plastic/polymer sheet and the grating material <NUM> may be a different material such as, but not limited to, silicon nitride, that is deposited on the light guide <NUM>.

<FIG> illustrates a cross sectional view of a portion of the grating-coupled light guide <NUM> in an example, according to an embodiment consistent with the principles described herein. <FIG> illustrates a cross sectional view of a portion of the grating-coupled light guide <NUM> in an example, according to an embodiment consistent with the principles described herein. In particular, both <FIG> and <FIG> illustrate a portion of the grating-coupled light guide <NUM> of <FIG> that includes the grating coupler <NUM>, where the grating coupler <NUM> is a reflective grating coupler <NUM> having a reflection mode diffraction grating <NUM>". As illustrated, the reflective grating coupler <NUM> (i.e., a reflection mode diffraction grating coupler) is at or on the second surface <NUM> of the light guide <NUM> opposite the first surface <NUM> that is adjacent to the light source and optical collimator, e.g., light source <NUM> and optical concentrator <NUM> illustrated in <FIG>, (i.e., a light source-opposite second surface <NUM>).

In <FIG>, the reflection mode diffraction grating <NUM>" of the reflective grating coupler <NUM> includes grooves (diffractive features) formed in the light source-opposite second surface <NUM> (e.g., top surface) of the light guide <NUM> to reflectively diffract and redirect incident concentrated light <NUM>' through the light guide <NUM>. As illustrated, the grooves are filled with and further backed by a layer <NUM> of a metal material to provide additional reflection and improve a diffractive efficiency of the illustrated reflective grating coupler <NUM>. In other words, the grating material <NUM> includes the metal layer <NUM>, as illustrated. In other examples (not illustrated), the grooves may be filled with a grating material (e.g., silicon nitride) and then backed or substantially covered by the metal layer, for example.

<FIG> illustrates a reflective grating coupler <NUM> that includes ridges (diffractive features) formed of the grating material <NUM> on the second surface <NUM> of the light guide <NUM> to create the reflection mode diffraction grating <NUM>". The ridges may be etched from a layer of silicon nitride (i.e., the grating material), for example. In some examples, a metal layer <NUM> is provided to substantially cover the ridges of the reflection mode diffraction grating <NUM>" to provide increased reflection and improve the diffractive efficiency, for example.

In some examples, the grating-coupled light guide <NUM> may further comprise the light source <NUM> (e.g., illustrated in <FIG> and <FIG>). As mentioned above, in some examples, the light source <NUM> may be an uncollimated light source <NUM>. For example, the light source <NUM> may be a surface emitting LED chip mounted on a circuit board and configured to illuminate a space adjacent to (e.g., above) the LED chip on the circuit board. In some examples, the light source <NUM> may approximate a point source. In particular, the light source <NUM> may have or exhibit illumination characterized by a broad cone angle. For example, a cone angle of the light source <NUM> may be greater than about ninety (<NUM>) degrees. In other examples, the cone angle may be greater than about eighty (<NUM>) degrees, or greater than about seventy (<NUM>) degrees, or greater than about sixty (<NUM>) degrees. For example, the cone angle may be about forty-five (<NUM>) degrees. According to various examples, a central ray of the light <NUM> from the light source <NUM> after passing through the optical concentrator <NUM> may be configured to be incident on the grating coupler <NUM> at an angle that is substantially orthogonal to a surface of the light guide <NUM>.

In some embodiments, substantially uncollimated light <NUM>" produced by the uncollimated light source <NUM> is substantially collimated by a combination of the optical concentrator <NUM> and the diffractive redirection provided by the grating coupler <NUM> as collimated guided light <NUM>. In other embodiments, the diffractively redirected guided light <NUM> is substantially uncollimated, at least in one direction (e.g., when a fan-shaped beam is produced). In yet other examples, the guided light <NUM> may be substantially collimated by the combination of the optical concentrator <NUM> and the grating coupler <NUM> in first direction (e.g., corresponding to a first spread angle about the non-zero propagation angle) and substantially uncollimated in a second direction (e.g., corresponding to the second spread angle). For example, the optical concentrator in combination with the grating coupler <NUM> may provide a fan-shaped beam in a horizontal direction parallel to the plate light guide surfaces and a substantially collimated beam (i.e., a spread angle equal to about zero) in a vertical direction or plane perpendicular to the light guide surfaces.

In some embodiments of the principles described herein, a grating-coupled light guide system is provided. The grating-coupled light guide system has a variety of uses. For example, the grating-coupled light guide system may be a multiview backlight. The multiview backlight may be employed in a three-dimensional (3D) or multiview display, for example. In another embodiment, the grating-coupled light guide system may be used as a backlight in a privacy display. In yet another embodiment, a portion of the grating-coupled light guide system, such as a light guide of the grating-coupled light guide system, may be employed in a touch-sensitive panel to sense one or both of a location at which the touch panel is touched and a pressure at which the touch is applied using frustrated total internal reflection (FTIR).

<FIG> illustrates a cross sectional view of a multiview backlight <NUM> in an example, according to an embodiment consistent with the principles described herein. <FIG> illustrates a plan view of a multiview backlight <NUM> in an example, according to an embodiment consistent with the principles described herein. <FIG> illustrates a perspective view of a multiview backlight <NUM> in an example, according to an embodiment consistent with the principles described herein. As illustrated, the multiview backlight <NUM> comprises the grating-coupled light guide <NUM> including the light guide <NUM>, the optical concentrator <NUM>, and the grating coupler <NUM>, e.g., illustrated as a transmissive grating coupler <NUM> similar to <FIG>, by way of example and not limitation. Also illustrated in <FIG> are the guided light <NUM> having a collimation factor σ and a propagation direction <NUM> within the light guide <NUM> as well as the light source <NUM>.

The multiview backlight <NUM> illustrated in <FIG> further comprises an array or plurality of multibeam elements <NUM>. According to various embodiments, each multibeam element <NUM> of the multibeam element plurality is configured to scatter from the light guide <NUM> a portion of the guided light <NUM> as a plurality of directional light beams <NUM>. Directional light beams <NUM> of the directional light beam plurality have different principal angular directions from one another, according to various embodiments. Further, the different principal angular directions of the directional light beams <NUM> may correspond to respective different view directions of a multiview display comprising multiview backlight <NUM>, according to some embodiments. In <FIG> and <FIG>, the directional light beams <NUM> are illustrated as a plurality of diverging arrows depicted as being directed way from the second surface <NUM> (front surface) of the light guide <NUM>.

According to various embodiments, multibeam elements <NUM> of the multibeam element plurality may be spaced apart from one another along a length of the light guide <NUM>. In particular, the multibeam elements <NUM> may be separated from one another by a finite space and represent individual, distinct elements along the light guide length. Further the multibeam elements <NUM> generally do not intersect, overlap or otherwise touch one another, according to some embodiments. That is, each multibeam element <NUM> of the multibeam element plurality is generally distinct and separated from other ones of the multibeam elements <NUM>.

According to some embodiments, the plurality of multibeam elements <NUM> may be arranged in either a one-dimensional (1D) array or two-dimensional (2D) array. For example, the plurality of multibeam elements <NUM> may be arranged as a linear 1D array. In another example, the plurality of multibeam elements <NUM> may be arranged as a rectangular 2D array or as a circular 2D array. Further, the array (i.e., 1D or 2D array) may be a regular or uniform array, in some examples. In particular, an inter-element distance (e.g., center-to-center distance or spacing) between the multibeam elements <NUM> may be substantially uniform or constant across the array. In other examples, the inter-element distance between the multibeam elements <NUM> may be varied one or both of across the array and along the length of the light guide <NUM>.

In some embodiments, a size of the multibeam element <NUM> may be comparable to a size of a light valve of a multiview display that employs the multiview backlight <NUM>. Herein, the 'size' may be defined in any of a variety of manners to include, but not be limited to, a length, a width, or an area. For example, the size of a light valve may be a length thereof and the comparable size of the multibeam element <NUM> may also be a length of the multibeam element <NUM>. In another example, size may refer to an area such that an area of the multibeam element <NUM> may be comparable to an area of the light valve. In other examples, the light valve size may be defined as a distance (e.g., a center-to-center distance) between adjacent light valves. For example, the light valves may be smaller than the center-to-center distance between the light valves in the light valve array. The light valve size may be defined as a size corresponding to the center-to-center distance between the adjacent light valves, for example.

In some embodiments, the size of the multibeam element <NUM> is comparable to the light valve size such that the multibeam element size is between about fifty percent (<NUM>%) and about two hundred percent (<NUM>%) of the view pixel size. In other examples, the multibeam element size is greater than about sixty percent (<NUM>%) of the light valve size, or about seventy percent (<NUM>%) of the light valve size, or greater than about eighty percent (<NUM>%) of the light valve size, or greater than about ninety percent (<NUM>%) of the light valve size, and the multibeam element <NUM> is less than about one hundred eighty percent (<NUM>%) of the light valve size, or less than about one hundred sixty percent (<NUM>%) of the light valve size, or less than about one hundred forty (<NUM>%) of the light valve size, or less than about one hundred twenty percent (<NUM>%) of the light valve size. For example, by 'comparable size', the multibeam element size may be between about seventy-five percent (<NUM>%) and about one hundred fifty (<NUM>%) of the light valve size. In another example, the multibeam element <NUM> may be comparable in size to the light valve where the multibeam element size is between about one hundred twenty-five percent (<NUM>%) and about eighty-five percent (<NUM>%) of the light valve size. According to some embodiments, the comparable sizes of the multibeam element <NUM> and the light valve may be chosen to reduce, or in some examples to minimize, dark zones between views of the multiview display, while at the same time reducing, or in some examples minimizing, an overlap between views of the multiview display. <FIG> also illustrate multiview pixels <NUM> along with the multiview backlight <NUM> for the purpose of facilitating discussion. In <FIG>, the multibeam element size is denoted 's' and the light valve size is denoted 'S'.

<FIG> further illustrate an array of light valves <NUM> configured to modulate the directional light beams <NUM> of the directional light beam plurality. The light valve array may be part of the multiview display that employs the multiview backlight <NUM>, for example, and is illustrated in <FIG> along with the multiview backlight <NUM> for the purpose of facilitating discussion herein. In <FIG>, the array of light valves <NUM> is partially cut-away to allow visualization of the light guide <NUM> and the multibeam element <NUM> underlying the light valve array. In various embodiments, different types of light valves may be employed as the light valves <NUM> of the light valve array including, but not limited to, one or more of liquid crystal light valves, electrophoretic light valves, and light valves based on electrowetting.

As illustrated in <FIG>, different ones of the directional light beams <NUM> pass through and may be modulated by different ones of the light valves <NUM> in the light valve array. Further, as illustrated, a light valve <NUM> of the array corresponds to a view pixel, and a set of the light valves <NUM> corresponds to a multiview pixel of the multiview display. In particular, a different set of light valves <NUM> of the light valve array is configured to receive and modulate the directional light beams <NUM> from different ones of the multibeam elements <NUM>, i.e., there is one unique set of light valves <NUM> for each multibeam element <NUM>, as illustrated.

As illustrated in <FIG>, a first light valve set 208a is configured to receive and modulate the directional light beams <NUM> from a first multibeam element 210a, while a second light valve set 208b is configured to receive and modulate the directional light beams <NUM> from a second multibeam element 210b. Thus, each of the light valve sets (e.g., the first and second light valve sets 208a, 208b) in the light valve array corresponds, respectively, to a different multiview pixel, with individual light valves <NUM> of the light valve sets corresponding to the view pixels of the respective multiview pixels, as illustrated in <FIG>.

In some embodiments, a relationship between the multibeam elements <NUM> of the plurality and corresponding multiview pixels (e.g., sets of light valves <NUM>) may be a one-to-one relationship. That is, there may be an equal number of multiview pixels and multibeam elements <NUM>. <FIG> explicitly illustrates by way of example the one-to-one relationship where each multiview pixel comprising a different set of light valves <NUM> is illustrated as surrounded by a dashed line. In other embodiments (not illustrated), the number of multiview pixels <NUM> and multibeam elements <NUM> may differ from one another.

In some embodiments, an inter-element distance (e.g., center-to-center distance) between a pair of adjacent multibeam elements <NUM> of the plurality may be equal to an inter-pixel distance (e.g., a center-to-center distance) between a corresponding adjacent pair of multiview pixels, e.g., represented by light valve sets. For example, as illustrated in <FIG>, a center-to-center distance d between the first multibeam element 210a and the second multibeam element 210b is substantially equal to a center-to-center distance D between the first light valve set 208a and the second light valve set 208b. In other embodiments (not illustrated), the relative center-to-center distances of pairs of multibeam elements <NUM> and corresponding light valve sets may differ, e.g., the multibeam elements <NUM> may have an inter-element spacing (i.e., center-to-center distance d) that is one of greater than or less than a spacing (i.e., center-to-center distance D) between light valve sets representing multiview pixels.

Further (e.g., as illustrated in <FIG>), each multibeam element <NUM> is configured to provide directional light beams <NUM> to one and only one multiview pixel, according to some embodiments. In particular, for a given one of the multibeam elements <NUM>, the directional light beams <NUM> having different principal angular directions corresponding to the different views of the multiview display are substantially confined to a single corresponding multiview pixel, i.e., a single set of light valves <NUM> corresponding to the multibeam element <NUM>, as illustrated in <FIG>. As such, each multibeam element <NUM> of the multiview backlight <NUM> provides a corresponding set of directional light beams <NUM> that has a set of the different principal angular directions corresponding to the different views of the multiview display.

According to various embodiments, the multibeam element <NUM> may comprise any of a number of different scattering structures configured to scatter or couple out a portion of the guided light <NUM>. For example, the different scattering structures may include, but are not limited to, a diffraction grating, a micro-reflective element, a micro-refractive element, or various combinations thereof. Each of these scattering structures may be an angle-preserving scatterer. In some embodiments, the multibeam element <NUM> comprising a diffraction grating is configured to diffractively couple out the guided light portion as the plurality of directional light beams <NUM> having the different principal angular directions. In other embodiments, the multibeam element <NUM> comprising a micro-reflective element is configured to reflectively couple out the guided light portion as the plurality of directional light beams <NUM>, or the multibeam element <NUM> comprising a micro-refractive element is configured to couple out the guided light portion as the plurality of directional light beams <NUM> by or using refraction (i.e., refractively couple out the guided light portion).

<FIG> illustrates a cross sectional view of a portion of a multiview backlight <NUM> including a multibeam element <NUM> in an example, according to an embodiment consistent with the principles described herein. <FIG> illustrates a cross sectional view of a portion of a multiview backlight <NUM> including a multibeam element <NUM> in an example, according to another embodiment consistent with the principles described herein. In particular, <FIG> illustrate the multibeam element <NUM> of the multiview backlight <NUM> comprising a diffraction grating <NUM>. The diffraction grating <NUM> is configured to diffractively couple out a portion of the guided light <NUM> as the plurality of directional light beams <NUM>. The diffraction grating <NUM> comprises a plurality of diffractive features spaced apart from one another by a diffractive feature spacing or a diffractive feature or grating pitch configured to provide diffractive coupling out of the guided light portion. According to various embodiments, the spacing or grating pitch of the diffractive features in the diffraction grating <NUM> may be subwavelength (i.e., less than a wavelength of the guided light).

In some embodiments, the diffraction grating <NUM> of the multibeam element <NUM> may be located at or adjacent to a surface of the light guide <NUM>. For example, the diffraction grating <NUM> may be at or adjacent to the second surface <NUM> of the light guide <NUM>, as illustrated in <FIG>. The diffraction grating <NUM> at light guide second surface <NUM> may be a transmission mode diffraction grating configured to diffractively couple out the guided light portion through the second surface <NUM> as the directional light beams <NUM>. In another example, as illustrated in <FIG>, the diffraction grating <NUM> may be located at or adjacent to the first surface <NUM> of the light guide <NUM>. When located at the first surface <NUM>, the diffraction grating <NUM> may be a reflection mode diffraction grating. As a reflection mode diffraction grating, the diffraction grating <NUM> is configured to both diffract the guided light portion and reflect the diffracted guided light portion toward the second surface <NUM> to exit through the second surface <NUM> as the diffractively coupled-out diffraction light beams <NUM>. In other embodiments (not illustrated), the diffraction grating may be located between the surfaces of the light guide <NUM>, e.g., as one or both of a transmission mode diffraction grating and a reflection mode diffraction grating.

According to some embodiments, the diffractive features of the diffraction grating <NUM> may comprise one or both of grooves and ridges that are spaced apart from one another. The grooves or the ridges may comprise a material of the light guide <NUM>, e.g., may be formed in a surface of the light guide <NUM>. In another example, the grooves or the ridges may be formed from a material other than the light guide material, e.g., a film or a layer of another material on a surface of the light guide <NUM>. In some embodiments, the diffraction grating <NUM> of the multibeam element <NUM> is a uniform diffraction grating in which the diffractive feature spacing is substantially constant or unvarying throughout the diffraction grating <NUM>.

In other embodiments, the diffraction grating <NUM> is a chirped diffraction grating. By definition, the 'chirped' diffraction grating is a diffraction grating exhibiting or having a diffraction spacing of the diffractive features (i.e., the grating pitch) that varies across an extent or length of the chirped diffraction grating. In some embodiments, the chirped diffraction grating may have or exhibit a chirp of the diffractive feature spacing that varies linearly with distance. As such, the chirped diffraction grating is a 'linearly chirped' diffraction grating, by definition. In other embodiments, the chirped diffraction grating of the multibeam element <NUM> may exhibit a non-linear chirp of the diffractive feature spacing. Various non-linear chirps may be used including, but not limited to, an exponential chirp, a logarithmic chirp or a chirp that varies in another, substantially non-uniform or random but still monotonic manner. Non-monotonic chirps such as, but not limited to, a sinusoidal chirp or a triangle or sawtooth chirp, may also be employed. Combinations of any of these types of chirps may also be employed.

In some embodiments, the multibeam element <NUM> or equivalently the diffraction grating <NUM> may comprise a plurality of diffraction gratings. The plurality of diffraction gratings may also be referred to as a plurality of 'sub-gratings' of the diffraction grating <NUM>. The diffraction grating (or sub-grating) plurality may be arranged in a number of different configurations to scatter or diffractively couple out a portion of the guided light <NUM> as the plurality of directional light beams <NUM>. In particular, the plurality of diffraction gratings of the multibeam element <NUM> may comprise a first diffraction grating and a second diffraction grating (or equivalently a first sub-grating and a second sub-grating). The first diffraction grating may be configured to provide a first light beam of the plurality of directional light beams <NUM>, while the second diffraction grating may be configured to provide a second light beam of the plurality of directional light beams <NUM>. According to various embodiments, the first and second light beams may have different principal angular directions. Moreover, the plurality of diffraction gratings may comprise a third diffraction grating, a fourth diffraction grating and so on, each diffraction grating being configured to provide other directional light beams <NUM>, according to some embodiments.

<FIG> illustrates a cross sectional view of a portion of a multiview backlight <NUM> including a multibeam element <NUM> in an example, according to another embodiment consistent with the principles described herein. <FIG> illustrates a cross sectional view of a portion of a multiview backlight <NUM> including a multibeam element <NUM> in an example, according to another embodiment consistent with the principles described herein. In particular, <FIG> illustrate embodiments of the multibeam element <NUM> comprising a micro-reflective element. Micro-reflective elements used as or in the multibeam element <NUM> may include, but are not limited to, a reflector that employs a reflective material or layer thereof (e.g., a reflective metal) or a reflector based on total internal reflection (TIR). According to some embodiments (e.g., as illustrated in <FIG>), the multibeam element <NUM> comprising the micro-reflective element may be located at or adjacent to a surface (e.g., the first surface <NUM>) of the light guide <NUM>. In other embodiments (not illustrated), the micro-reflective element may be located within the light guide <NUM> between the first and second surfaces <NUM>, <NUM>.

For example, <FIG> illustrates the multibeam element <NUM> comprising a micro-reflective element <NUM> having reflective facets (e.g., a 'prismatic' micro-reflective element) located adjacent to the first surface <NUM> of the light guide <NUM>. The facets of the illustrated prismatic micro-reflective element <NUM> are configured to reflect (i.e., reflectively couple) the portion of the guided light <NUM> out of the light guide <NUM>. The facets may be slanted or tilted (i.e., have a tilt angle) relative to a propagation direction of the guided light <NUM> to reflect the guided light portion out of light guide <NUM>, for example. The facets may be formed using a reflective material within the light guide <NUM> (e.g., as illustrated in <FIG>) or may be surfaces of a prismatic cavity in the first surface <NUM>, according to various embodiments. When a prismatic cavity is employed, either a refractive index change at the cavity surfaces may provide reflection (e.g., TIR reflection) or the cavity surfaces that form the facets may be coated by a reflective material to provide reflection, in some embodiments.

In another example, <FIG> illustrates the multibeam element <NUM> comprising a micro-reflective element <NUM> having a substantially smooth, curved surface such as, but not limited to, a semi-spherical micro-reflective element <NUM>. A specific surface curve of the micro-reflective element <NUM> may be configured to reflect the guided light portion in different directions depending on a point of incidence on the curved surface with which the guided light <NUM> makes contact, for example. As illustrated in <FIG>, the guided light portion that is reflectively coupled out of the light guide <NUM> exits or is emitted from the second surface <NUM>, by way of example and not limitation. As with the prismatic micro-reflective element <NUM> in <FIG>, the micro-reflective element <NUM> in <FIG> may be either a reflective material within the light guide <NUM> or a cavity (e.g., a semi-circular cavity) formed in the first surface <NUM>, as illustrated in <FIG> by way of example and not limitation.

<FIG> illustrates a cross sectional view of a portion of a multiview backlight <NUM> including a multibeam element <NUM> in an example, according to yet another embodiment consistent with the principles described herein. In particular, <FIG> illustrates a multibeam element <NUM> comprising a micro-refractive element <NUM>. According to various embodiments, the micro-refractive element <NUM> is configured to refractively couple out a portion of the guided light <NUM> from the light guide <NUM>. That is, the micro-refractive element <NUM> is configured to employ refraction (e.g., as opposed to diffraction or reflection) to couple out the guided light portion from the light guide <NUM> as the directional light beams <NUM>, as illustrated in <FIG>. The micro-refractive element <NUM> may have various shapes including, but not limited to, a semi-spherical shape, a rectangular shape or a prismatic shape (i.e., a shape having sloped facets). According to various embodiments, the micro-refractive element <NUM> may extend or protrude out of a surface (e.g., the second surface <NUM>) of the light guide <NUM>, as illustrated, or may be a cavity in the surface (not illustrated). Further, the micro-refractive element <NUM> may comprise a material of the light guide <NUM>, in some embodiments. In other embodiments, the micro-refractive element <NUM> may comprise another material adjacent to, and in some examples, in contact with the light guide surface.

<FIG> illustrates a block diagram of a grating-coupled display system <NUM> in an example, according to an embodiment consistent with the principles described herein. The grating-coupled display system <NUM> illustrated in <FIG> comprises a light source <NUM> configured to provide light <NUM> in a first direction. In some embodiments, the light source <NUM> may be substantially similar to the light source <NUM> described above with respect to the grating-coupled light guide <NUM>. For example, the light <NUM> provided by the light source <NUM> may be unconcentrated or uncollimated light. Further, the light <NUM> provided in first direction may include a central ray in a z-direction, as illustrated in <FIG>, above.

The grating-coupled display system <NUM> illustrated in <FIG> further comprises a light guide <NUM>. The light guide <NUM> is configured to guide light as guided light <NUM>. The guided light <NUM> has or is guided in a second direction within the light guide <NUM>. The second direction is orthogonal to the first direction, according to various embodiments. In some embodiments, the light guide <NUM> may be substantially similar to the light guide <NUM> of the grating-coupled light guide <NUM>, described above. For example, the light guide <NUM> may be a plate light guide. The second direction may be in an x-direction, for example, as illustrated above in <FIG>.

In <FIG>, the grating-coupled display system <NUM> further comprises an optical concentrator <NUM>, according to various embodiments. The optical concentrator <NUM> is configured to concentrate the light <NUM> received from the light source <NUM> to provide concentrated light <NUM>. In some embodiments, the optical concentrator <NUM> may be substantially similar to the optical concentrator <NUM> of the above-described grating-coupled light guide <NUM>. In particular, according to various embodiments, the optical concentrator <NUM> may comprise one or more of a tapered collimator, a catadioptic collimator, and a reflective turning collimator, as described above with respect to the optical concentrator <NUM>.

As illustrated in <FIG>, the grating-coupled display system <NUM> further comprises a grating coupler <NUM>. The grating coupler <NUM> is configured to diffractively redirect the concentrated light <NUM> into the light guide <NUM> as the guided light <NUM> having the second direction. In some embodiments, the grating coupler <NUM> may be substantially similar to the grating coupler <NUM> described above with respect to the grating-coupled light guide <NUM>. In particular, in some embodiments, the grating coupler <NUM> may comprise one or both of a transmission mode diffraction grating at a surface of the light guide <NUM> adjacent to the light source <NUM> and a reflection mode diffraction grating at a surface of the light guide <NUM> opposite a light guide surface adjacent to the light source <NUM>. According to various embodiments, characteristics of both the optical concentrator <NUM> and grating coupler <NUM> are configured to cooperatively determine a non-zero propagation angle and a predetermined spread angle of the guided light within the light guide.

The grating-coupled display system <NUM> illustrated in <FIG> further comprises an array of light valves <NUM>. The array of light valves <NUM> is configured to modulate light <NUM> emitted from the light guide as a displayed image. According to some embodiments, the array of light valves <NUM> may be substantially similar to the plurality of light valves <NUM> of the above-described multiview backlight <NUM>. For example, light valves <NUM> of the light valve array may include, but are not limited to, one or more of liquid crystal light valves, electrophoretic light valves, and light valves based on electrowetting. Modulated emitted light <NUM>' (e.g., directional light beams) is illustrated as dashed arrows in <FIG> to emphasize modulation by the light valve array.

In some embodiments (not illustrated), the grating-coupled display system <NUM> further comprises an array of multibeam elements optically coupled to the light guide <NUM>. A multibeam element of the multibeam element array is configured to scatter from the light guide <NUM> a portion of the guided light <NUM> as a plurality of directional light beams. Directional light beams of the directional light beam plurality have different principal angular directions from one another, according to various embodiments. In these embodiments, the light emitted by or from the light guide <NUM> and modulated by the array of light valves <NUM> comprises the plurality of directional light beams.

In some embodiments, the multibeam element of the multibeam element array may be substantially similar to the multibeam element <NUM> of the multiview backlight <NUM>, described above. In particular, the multibeam element may comprise one or more of a diffraction grating, a micro-reflective element, and a micro-refractive element. Further, a size of the multibeam element may be greater than one half of a size of a light valve of the light valve array and less than twice the light valve size, in some embodiments. In some embodiments, the different principal angular directions of the directional light beams may correspond to respective view directions a plurality of different views of a multiview display. Thus, the grating-coupled display system <NUM> may be a multiview display and the displayed image may represent a multiview image, in some embodiments.

According to embodiments and examples of the principles described herein, a method of coupling light into a light guide is provided. <FIG> illustrates a flow chart of a method <NUM> of coupling light into a light guide in an example, according to an embodiment consistent with the principles described herein. As illustrated in <FIG>, the method <NUM> of coupling light into a light guide comprises generating <NUM> light using a light source. In some embodiments, the light source is an uncollimated light source and the generated <NUM> light is substantially concentrated or collimated light. For example, the light source used in generating <NUM> light may approximate a point source. In some embodiments, the light source used to generate <NUM> light may be substantially similar to the light source <NUM> described above with respect to the grating-coupled light guide <NUM>.

As illustrated in <FIG>, the method <NUM> of coupling light into a plate light guide further comprises concentrating <NUM> the light from the light source using an optical concentrator. The concentrating <NUM> light by the optical concentrator produces concentrated light. According to some embodiments, the optical concentrator used in concentrating <NUM> light may be substantially similar to the optical concentrator <NUM> of the above-described grating-coupled light guide <NUM>. For example, the optical concentrator may comprise one or more of a tapered collimator, a catadioptic collimator, and a reflective turning collimator. In another example, the optical concentrator comprises a concentrating lens.

The method <NUM> of coupling light into a plate light guide illustrated in <FIG> further comprises coupling <NUM> the concentrated light into the light guide using a grating coupler and guiding <NUM> the coupled light in the light guide at a non-zero propagation angle as guided light. According to various embodiments, the guided light has a first spread angle and a second spread angle, the second spread angle being in a direction orthogonal to the first spread angle. For example, the guided light may include a propagating light beam directed at the non-zero propagation angle by the grating coupler that has a predetermined first spread angle in a plane perpendicular to a surface of the light guide and a predetermined second spread angle in a plane substantially parallel to surface of the light guide. The non-zero propagation angle, the first spread angle, and the second spread angle of the guided light within the light guide are determined by characteristics of both of the optical concentrator and the grating coupler, according to various embodiments.

In some examples, the grating coupler used in coupling <NUM> the light may be substantially similar to the grating coupler <NUM> described above with respect to the grating-coupled light guide <NUM>. In particular, in some examples, the grating coupler includes a transmissive grating at a surface of the light guide adjacent to the light source. In some examples, the grating coupler includes a reflective grating at a surface of the light guide opposite the light source-adjacent surface of the plate light guide.

In some embodiment, the method <NUM> of coupling light into a light guide is used in the operation of an electronic display to display an image or similar information. In particular, according to some examples (not illustrated), the method <NUM> of coupling light into a light guide further comprises scattering out a portion of the guided light from the light guide using a multibeam element that is optically coupled to the light guide to produce a plurality of directional light beams having different principal angular directions from one another. In some embodiments, the multibeam element may be substantially similar to the multibeam element <NUM> of the multiview backlight <NUM>, as described above. Further, in some embodiments (also not illustrated), the method <NUM> of coupling light into a light guide further comprises modulating the plurality of directional light beams using a corresponding plurality of light valves, the modulated light beams forming pixels of a displayed image. For example, the displayed image may be a multiview image and the directional light beams may have directions corresponding to different view directions of the multiview image. Further, the light valves may include liquid crystal light valves. In another example, the light valves may be another type of light valve including, but not limited to, an electrowetting light valve or an electrophoretic light valve.

Claim 1:
A grating-coupled light guide (<NUM>) comprising:
a light guide (<NUM>) configured to guide light (<NUM>);
an optical concentrator (<NUM>) configured to concentrate light (<NUM>") from a light source to provide concentrated light (<NUM>'); and
a grating coupler (<NUM>) at an input of the light guide, the grating coupler configured to diffractively redirect the concentrated light into the light guide at a non-zero propagation angle as guided light having a first spread angle and a second spread angle, wherein the grating coupler comprises a diffraction grating (<NUM>) having diffractive features,
characterized in that characteristics of the optical concentrator and the grating coupler are configured in combination to determine the non-zero propagation angle, the first spread angle, and the second spread angle of the guided light within the light guide, the first spread angle being in a direction orthogonal to the second spread angle, wherein a variation in the pitch of the diffractive features along a length and across a width of the diffraction grating controls the first spread angle, and a variation in a lateral shape or the width of the diffraction grating controls the second spread angle.