Patent Publication Number: US-11041988-B2

Title: Multiview backlighting employing plasmonic multibeam elements

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation patent application of and claims the benefit of priority to International Application No. PCT/US2017/015685, filed Jan. 30, 2017, which is incorporated by reference herein in its entirety. 
    
    
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
     N/A 
     BACKGROUND 
     Electronic displays are a nearly ubiquitous medium for communicating information to users of a wide variety of devices and products. Most commonly employed electronic displays include the cathode ray tube (CRT), plasma display panels (PDP), liquid crystal displays (LCD), electroluminescent displays (EL), organic light emitting diode (OLED) and active matrix OLEDs (AMOLED) displays, electrophoretic displays (EP) and various displays that employ electromechanical or electrofluidic light modulation (e.g., digital micromirror devices, electrowetting displays, etc.). Generally, electronic displays may be categorized as either active displays (i.e., displays that emit light) or passive displays (i.e., displays that modulate light provided by another source). Among the most obvious examples of active displays are CRTs, PDPs and OLEDs/AMOLEDs. Displays that are typically classified as passive when considering emitted light are LCDs and EP displays. Passive displays, while often exhibiting attractive performance characteristics including, but not limited to, inherently low power consumption, may find somewhat limited use in many practical applications given the lack of an ability to emit light. 
     To overcome the limitations of passive displays associated with emitted light, many passive displays are coupled to an external light source. The coupled light source may allow these otherwise passive displays to emit light and function substantially as an active display. Examples of such coupled light sources are backlights. A backlight may serve as a source of light (often a panel backlight) that is placed behind an otherwise passive display to illuminate the passive display. For example, a backlight may be coupled to an LCD or an EP display. The backlight emits light that passes through the LCD or the EP display. The light emitted is modulated by the LCD or the EP display and the modulated light is then emitted, in turn, from the LCD or the EP display. Often backlights are configured to emit white light. Color filters are then used to transform the white light into various colors used in the display. The color filters may be placed at an output of the LCD or the EP display (less common) or between the backlight and the LCD or the EP display, for example. Alternatively, the various colors may be implemented by field-sequential illumination of a display using different colors, such as primary colors. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Various features of examples and embodiments in accordance with the principles described herein may be more readily understood with reference to the following detailed description taken in conjunction with the accompanying drawings, where like reference numerals designate like structural elements, and in which: 
         FIG. 1A  illustrates a perspective view of a multiview display in an example, according to an embodiment consistent with the principles described herein. 
         FIG. 1B  illustrates a graphical representation of angular components of a light beam having a particular principal angular direction corresponding to a view direction of a multiview display in an example, according to an embodiment consistent with the principles described herein. 
         FIG. 2A  illustrates a cross sectional view of a multiview backlight in an example, according to an embodiment consistent with the principles described herein. 
         FIG. 2B  illustrates a plan view of a multiview backlight in an example, according to an embodiment consistent with the principles described herein. 
         FIG. 2C  illustrates a perspective view of a multiview backlight in an example, according to an embodiment consistent with the principles described herein. 
         FIG. 3  illustrates a cross sectional view of a portion of a multiview backlight that exhibits color breakup in an example, according to an embodiment consistent with the principles described herein. 
         FIG. 4  illustrates a graphical representation of color breakup in an example, according to an embodiment consistent with the principles described herein. 
         FIG. 5  illustrates a cross sectional view of a portion of a multiview backlight in an example, according to an embodiment consistent with the principles described herein. 
         FIG. 6  illustrates a cross sectional view of a portion of a multiview backlight in an example, according to an embodiment consistent with the principles described herein. 
         FIG. 7A  illustrates a cross sectional view of a plasmonic multibeam element in an example, according to an embodiment consistent with the principles described herein. 
         FIG. 7B  illustrates a cross sectional view of a plasmonic multibeam element in an example, according to another embodiment consistent with the principles described herein. 
         FIG. 7C  illustrates a top or plan view of a plasmonic multibeam element having a square-shaped multibeam sub-element in an example, according to an embodiment consistent with the principles described herein. 
         FIG. 8A  illustrates a perspective view of a plasmonic resonator according to an example, in an embodiment consistent with the principles described herein. 
         FIG. 8B  illustrates a plan view of another plasmonic resonator according to an example, in an embodiment consistent with the principles described herein. 
         FIG. 9A  illustrates a perspective view of a plasmonic resonator to another example, in an embodiment consistent with the principles described herein. 
         FIG. 9B  illustrates a plan view of another plasmonic resonator according to another example, in an embodiment consistent with the principles described herein. 
         FIG. 10A  illustrates a perspective view of a plasmonic resonator to yet another example, in an embodiment consistent with the principles described herein. 
         FIG. 10B  illustrates a plan view of another plasmonic resonator according to yet another example, in an embodiment consistent with the principles described herein. 
         FIG. 11  illustrates a block diagram of a multiview display in an example, according to an embodiment consistent with the principles described herein. 
         FIG. 12  illustrates a flow chart of a method of multiview backlight operation in an example, according to an embodiment consistent with the principles described herein. 
     
    
    
     Certain examples and embodiments have other features that are one of in addition to and in lieu of the features illustrated in the above-referenced figures. These and other features are detailed below with reference to the above-referenced figures. 
     DETAILED DESCRIPTION 
     Examples and embodiments in accordance with the principles described herein provide multiview backlighting that employs a plasmonic multibeam element. In particular, multiview backlighting embodiments described herein may include a multibeam element comprising a plasmonic material, i.e., a ‘plasmonic’ multibeam element. According to various embodiments, the plasmonic multibeam element is configured to provide emitted light comprising light beams having a plurality of different principal angular directions. The different principal angular directions of the light beams may correspond to different directions of various different views of a multiview display, for example. Further, the light emitted by the plasmonic multibeam element has a color-tailored emission pattern (or a color-tailored ‘plasmonic’ emission pattern) and the light beams include different colors of light consistent with that emission pattern, according to various embodiments. 
     As such, the multiview backlighting employing the plasmonic multibeam element may be configured to provide color backlighting with particular application to color multiview displays. In some embodiments, the color-tailored emission pattern of the plasmonic multibeam element may mitigate, compensate for, or even substantially eliminate various effects associated with color backlighting of color multiview displays including, but not limited to, color break-up. Uses of color multiview displays employing the multiview backlighting using the plasmonic multibeam element 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. 
     Embodiments consistent with the principles described herein provide a multiview backlight (e.g., of a multiview display) having a plasmonic multibeam element (e.g., a plurality or array of plasmonic multibeam elements). According to various embodiments, the plasmonic multibeam element is configured to provide a plurality of light beams. The plurality of light beams includes one or more light beams having different principal angular directions from other light beams of the light beam plurality. As such, the light beams of the light beam plurality may be referred to as ‘directional’ light beams of a plurality of directional light beams. The different principal angular directions of the directional light beams may correspond to angular directions associated with a spatial arrangement of pixels, or ‘view pixels,’ in a multiview pixel of a multiview display, according to some embodiments. 
     Further, the plasmonic multibeam elements of the multiview backlight are configured to provide emitted light comprising light beams that have, include or represent a plurality of different colors of light. For example, the light beam plurality may include light beams representing different colors such as, but not limited to, red (R), green (G), and blue (B) of an RGB color model. The color-tailored emission pattern of the plasmonic multibeam element is configured to provide sets of the different color light beams having substantially similar principal angular directions. For example, the color-tailored emission pattern of the plasmonic multibeam element may provide a set of light beams including light beams of several different colors (e.g., R, G, B) that all have substantially the same principal angular direction that, in turn, corresponds to a direction of one of the view pixels of the multiview display. Another set of different color light beams (e.g., also including R, G, B light beams) provided by the color-tailored emission pattern of the plasmonic multibeam element may have substantially similar principal angular directions corresponding to a direction of a different one of the view pixels. As such, the color-tailored emission pattern of the plasmonic multibeam element may facilitate providing or illuminating each of the view pixels of the multiview pixel with a set of different colors of light (e.g., red, green and blue), according to various embodiments. Further, as is described in more detail below, the color-tailored emission pattern of the plasmonic multibeam element may be configured to mitigate or even substantially compensate for various effects such as color-break up that, for example, may be associated with a finite size of the plasmonic multibeam element. 
     As mentioned above, the plasmonic multibeam element comprises a plasmonic material. Herein, a ‘plasmonic’ material is defined as a material comprising plasmonic scatterers, plasmonic resonators, or more generally plasmonic resonances, that emit light when illuminated by an incident light source or similar stimulus. In particular, light may be emitted due to the presence of surface plasmons excited within the illuminated plasmonic material. As such, the plasmonic material may be substantially any plasmonic resonant material or structure that that supports plasmons or surface plasmons and that scatters or ‘emits’ light by plasmonic scattering or equivalently by plasmonic emission. For example, the plasmonic material may include a plurality of plasmonic nanoparticles (e.g., nanorods, nanospheres, nanocylinders or the like comprising a plasmon-supporting metal or similar material). The plurality of plasmonic nanoparticles may include different types (e.g., different sizes) of plasmonic nanoparticles or plasmonic resonators having respective different colors of plasmonic emission (i.e., different plasmonic resonances that provide different plasmonic emission colors). The plasmonic nanoparticles comprising a plasmon-supporting metal such as, but not limited to, gold, silver, copper or aluminum may be employed as or in the plasmonic material. The plasmonic nanoparticles of the plasmonic material or the plasmonic material as a whole may have a size, a shape, a structure, or be otherwise ‘tuned’ to provide a plasmonic resonance at a frequency consistent with emitting a particular color of light by plasmonic scattering or emission. For example, the plasmonic material configured to emit one or more of red, green and blue light by plasmonic scattering or emission may comprise an aluminum nanorod having a width or thickness of about 50 nanometers (nm) and a length ranging from about 60 nm to about 100 nm. 
     In these various and non-limiting examples, the different types of plasmonic nanoparticles, or other plasmonic materials may be physically arranged, distributed, or spatially offset relative to one another to provide the color-tailored emission pattern. As such, the color-tailored emission pattern may be a result of an arrangement or structure of various different types of plasmonic emitters within the plasmonic material of the plasmonic multibeam element, according to various embodiments. Further, in some embodiments, the plasmonic material may act as a plasmonic source or more particularly a plurality of different plasmonic sources having or providing different colors of emitted light consistent with the color-tailored emission pattern. 
     In some embodiments, the plasmonic material may be configured to be polarization selective, i.e., to selectively interact with light having a predetermined polarization. In particular, plasmonic resonators of the plasmonic material may be configured to selectively emit light by plasmonic emission (i.e., plasmonic scattering) when illuminated by light having a first polarization and to substantially not scatter or emit light when illuminated by another (e.g., an orthogonal) polarization. For example, plasmonic resonators of the plasmonic material may be configured to selectively scatter or emit light by plasmonic scattering or emission when illuminated by incident light having a transverse electric (TE) polarization. In another example, the plasmonic resonators may be configured to selectively interact with and scatter or emit incident light having a transverse magnetic (TM) polarization. In either of these examples, the other polarization (e.g., TM and TE, respectively) of light is substantially not scattered by the plasmonic resonators. That is, there is substantially little or no scattering of TM polarized light by TE selective plasmonic resonators and visa versa. 
     According to various embodiments, a plasmonic material of the plasmonic multibeam element may emit light by plasmonic emission as the plurality of light beams of the different colors determined according to the color-tailored emission pattern. According to some embodiments, the plasmonic multibeam element may be divided into different zones that contain different types of plasmonic material. In particular, the plasmonic multibeam element may comprise a plurality of multibeam sub-elements comprising the different plasmonic material types and therefore exhibiting different plasmonic emission colors from one another, according to some embodiments. A distribution of the different zones or equivalently a distribution of different multibeam sub-elements with in the plasmonic multibeam element may define the color-tailored emission pattern. Further, according to various embodiments, the zones or multibeam sub-elements may be spatially offset from one another in a spatial arrangement corresponding to a spatial arrangement or spacing of color sub-portions or ‘color sub-pixels’ of view pixels in a multiview pixel of the multiview display. As such, herein the plasmonic multibeam element may be referred to as a ‘composite’ multibeam element due to the presence of spatially offset multibeam sub-elements containing the different plasmonic material types or emitters within the plasmonic multibeam element. 
     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. 1A  illustrates a perspective view of a multiview display  10  in an example, according to an embodiment consistent with the principles described herein. As illustrated in  FIG. 1A , the multiview display  10  comprises a screen  12  to display a multiview image to be viewed. The screen  12  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  10  provides different views  14  of the multiview image in different view directions  16  relative to the screen  12 . The view directions  16  are illustrated as arrows extending from the screen  12  in various different principal angular directions; the different views  14  are illustrated as shaded polygonal boxes at the termination of the arrows (i.e., depicting the view directions  16 ); and only four views  14  and four view directions  16  are illustrated, all by way of example and not limitation. Note that while the different views  14  are illustrated in  FIG. 1A  as being above the screen, the views  14  actually appear on or in a vicinity of the screen  12  when the multiview image is displayed on the multiview display  10 . Depicting the views  14  above the screen  12  is only for simplicity of illustration and is meant to represent viewing the multiview display  10  from a respective one of the view directions  16  corresponding to a particular view  14 . 
     A ‘view direction’ or equivalently a light beam having a direction corresponding to a view direction of a multiview display (i.e., a directional light beam) 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 θ is an angle in a horizontal plane (e.g., parallel to the multiview display screen plane).  FIG. 1B  illustrates a graphical representation of the angular components {θ, ϕ} of a light beam  20  having a particular principal angular direction corresponding to a view direction (e.g., view direction  16  in  FIG. 1A ) of a multiview display in an example, according to an embodiment consistent with the principles described herein. In addition, the light beam  20  is emitted or emanates from a particular point, by definition herein. That is, by definition, the light beam  20  has a central ray associated with a particular point of origin within the multiview display.  FIG. 1B  also illustrates the light beam (or view direction) point of origin O. The light beam  20  also represents a directional light beam, herein. 
     Further herein, the term ‘multiview’ as used in the terms ‘multiview image’ and ‘multiview display’ is defined as a plurality of views (e.g., images) representing different perspectives or including angular disparity between views of the view plurality. In addition, the term ‘multiview’ explicitly includes more than two different views (i.e., a minimum of three views and generally more than three views), by some definitions herein. As such, ‘multiview display’ as employed herein may be 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 pixels or ‘view pixels’ representing image pixels in each of a similar plurality of different views of a multiview display. In particular, a multiview pixel has an individual view pixel corresponding to or representing an image pixel in each of the different views of the multiview image. Moreover, the view pixels of the multiview pixel are so-called ‘directional pixels’ in that each of the view 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 view 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 view pixels corresponding to image pixels located at {x 1 , y 1 } in each of the different views of a multiview image, while a second multiview pixel may have individual view pixels corresponding to image pixels located at {x 2 , y 2 } in each of the different views, and so on. 
     In some embodiments, a number of view 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 (64) view pixels associated with a multiview display having 64 different views. In another example, the multiview display may provide an eight by four array of views (i.e., 32 views) and the multiview pixel may include thirty-two (32) view pixels (i.e., one for each view). In yet other examples, a number of views of the multiview display may range substantially anywhere from two or more views and be arranged in substantially any arrangement (e.g., rectangular, circular, etc.). As such, the view pixels in a multiview pixel may have both a similar number and similar arrangement to the number and the arrangement of the views of the multiview display, according to some embodiments. Additionally, each different view pixel generally has an associated direction (e.g., light beam principal angular direction) that corresponds to a different one of the view directions corresponding to the different views (e.g., 64 different views). 
     Further, according to some embodiments, a number of multiview pixels of the multiview display may be substantially equal to a number of pixels (i.e., pixels that make up a selected view) in the various individual views of the multiview display. For example, if a view includes six hundred forty by four hundred eighty pixels (i.e., the view has a 640×480 view resolution), the multiview display may have three hundred seven thousand two hundred (307,200) multiview pixels. In another example, when the views include one hundred by one hundred pixels, the multiview display may include a total of ten thousand (i.e., 100×100=10,000) multiview pixels. 
     In some embodiments, the view pixels in or of a multiview pixel may include portions or sub-portions that correspond to different colors. For example, a view pixel in the multiview pixel may include different color sub-portions or equivalently ‘color sub-pixels,’ by definition herein, that correspond to or that are configured to provide different colors. The color sub-pixels may be light valves (e.g., liquid crystal cells) having particular color filters, for example. In general, a number of color sub-pixels in a multiview pixel is larger than the number of view pixels or equivalently the number of views of the multiview display. In particular, an individual view pixel may include a plurality of color sub-pixels corresponding to or representing the view pixel and having an associated common direction. That is, the color sub-pixels of the plurality collectively represent the view pixel and the view pixel, in turn, has a direction (e.g., a principal angular direction) corresponding to a view direction of a particular view of the multiview image or equivalently of the multiview display. Herein, a size S of a view pixel is defined as a center-to-center spacing (or equivalently an edge-to-edge distance) between adjacent view pixels (see for example,  FIGS. 2A, 3 and 5 , described below). Also, by definition, a size of a color sub-pixel of or within a view pixel is smaller than the view pixel size 5, e.g., a color sub-pixel may have size S/3 when there are three color sub-pixels in a view pixel of size S. Herein, the color sub-pixels may have a size defined either by a center-to-center or edge-to-edge distance between adjacent color sub-pixels within a view pixel. 
     Further, the color sub-pixels may be configured to provide modulated light having wavelengths or equivalently colors associated the colors of or in the multiview image. For example, a first color sub-pixel of the plurality of color sub-pixels may be configured to provide modulated light having a wavelength corresponding to a first primary color (e.g., red). Further, a second color sub-pixel of the plurality of color sub-pixels may be configured to provide modulated light corresponding to a second primary color (e.g., green), and a third color sub-pixel of the plurality of color sub-pixels may be configured to provide modulated light corresponding to a third primary color (e.g., blue). Note that while a red-blue-green (RGB) color model is used as an illustration in this discussion, other color models may be used, according to embodiments consistent with the principles described herein. Also, a view pixel of a multiview pixel may include multiple color sub-pixels, which, therefore, have a smaller size or have a smaller spatial extent than the view pixel, by definition herein. 
     Herein, a ‘light guide’ is defined as a structure that guides light within the structure using total internal reflection or ‘TIR.’ 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. 
     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 light beams by coupling out a portion of light guided in the light guide. 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. 
     By definition herein, a ‘plasmonic multibeam element’ is a multibeam element configured to scatter or emit light by plasmonic emission or equivalently by plasmonic scattering, the emitted light comprising the light beams having the different principal angular directions. In particular, as mentioned above, the plasmonic multibeam element comprises a plasmonic material configured to interact with and scatter a portion of guided light as emitted light. Further, the light that scattered is emitted as a plasmonic emission, according to various embodiments. Herein, both ‘plasmonic emission’ and ‘plasmonic scattering’ are defined as a scattering of light (e.g., a simple elastic scattering of incident light) resulting from a resonant plasmonic interaction between the plasmonic material of the plasmonic multibeam element and incident light, e.g., the guided light. 
     Moreover, as described above, the light beams of the plurality of light beams produced by a plasmonic multibeam element may have the same or substantially the same principal angular direction for different colors corresponding to a spatial arrangement of color sub-pixels of a view pixel in a multiview pixel of a multiview display. These light beams provided by the multibeam element are referred to as emitted light having a ‘color-tailored emission pattern.’ 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 principal angular direction 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. Moreover, the light field may represent a ‘color’ light field with different colors being represented within a set of conical regions of space having substantially the same predetermined angular spread. 
     According to various embodiments, the principal angular direction of the various light beams 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. 1B . Further, a color of the various light beams may be determined by both the color-tailored emission pattern and a distribution of the color sub-pixels of the various view pixels, according to various embodiments. 
     Herein a ‘collimator’ is defined as substantially any optical device or apparatus that is configured to collimate light. For example, a collimator as defined may include, but is not limited to, a collimating mirror or reflector (i.e., a reflective collimator), a collimating lens, prismatic film, or similar refractive structure (i.e., a refractive collimator), or a diffraction grating (i.e., a diffractive collimator), as well as various combinations thereof. The collimator may comprise a continuous structure such as a continuous reflector or a continuous lens (i.e., a reflector or lens having a substantially smooth, continuous surface). In other embodiments, the collimator may comprise a substantially discontinuous structure or surface such as, but not limited to, a Fresnel reflector, a Fresnel lens and the like that provides light collimation. 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 or characteristic 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, e.g., by the collimator. 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 that 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 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., polychromatic or 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. 
     A ‘plasmon’ or more specifically a ‘surface plasmon’ is defined herein as a surface wave or plasma oscillation of a free electron gas at a surface of a plasmon-supporting material (e.g., a noble metal). The surface plasmon also may be considered as a quasiparticle representing a quantization of a plasma oscillation in a manner analogous to the representation of an electromagnetic oscillation quantization as a photon. For example, collective oscillations of a free electron gas in a surface of a noble metal induced by an incident electromagnetic wave at optical frequencies may be represented in terms of surface plasmons. Furthermore, characteristics of an interaction between the surface plasmons and the surface may be characterized in terms of plasmonic modes. In particular, plasmonic modes represent characteristics of surface plasmons in much the same way that electromagnetic oscillations are represented in terms of electromagnetic or optical modes. 
     Surface plasmons and by extension, plasmonic modes, are confined to a surface of a material that supports surface plasmons. For example, an optical signal incident from a vacuum or a dielectric material on a surface of a plasmon-supporting material may excite a surface plasmon. In some cases, the surface plasmon is essentially stationary (e.g., a standing wave) and in other cases, the surface plasmon may propagate along the surface. Plasmon-supporting materials are materials such as, but not limited to, certain organometallics that exhibit a dielectric constant having a negative value real part and metals. Noble metals such as, but not limited to, gold (Au), silver (Ag), aluminum (Al), and copper (Cu) are also plasmon-supporting materials at optical frequencies. 
     As used herein, the article ‘a’ is intended to have its ordinary meaning in the patent arts, namely ‘one or more’. For example, ‘a multibeam element’ means one or more multibeam elements and as such, ‘the multibeam element’ means ‘the multibeam element(s)’ herein. Also, any reference herein to ‘top’, ‘bottom’, ‘upper’, ‘lower’, ‘up’, ‘down’, ‘front’, back’, ‘first’, ‘second’, ‘left’ or ‘right’ is not intended to be a limitation herein. Herein, the term ‘about’ when applied to a value generally means within the tolerance range of the equipment used to produce the value, or may mean plus or minus 10%, or plus or minus 5%, or plus or minus 1%, 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 51% to about 100%. Moreover, examples herein are intended to be illustrative only and are presented for discussion purposes and not by way of limitation. 
     According to some embodiments of the principles described herein, a multiview backlight is provided.  FIG. 2A  illustrates a cross sectional view of a multiview backlight  100  in an example, according to an embodiment consistent with the principles described herein.  FIG. 2B  illustrates a plan view of a multiview backlight  100  in an example, according to an embodiment consistent with the principles described herein.  FIG. 2C  illustrates a perspective view of a multiview backlight  100  in an example, according to an embodiment consistent with the principles described herein. The perspective view in  FIG. 2C  is illustrated with a partial cut-away to facilitate discussion herein only. 
     The multiview backlight  100  illustrated in  FIGS. 2A-2C  is configured to provide a plurality of coupled-out or directional light beams  102  having different principal angular directions from one another (e.g., as a light field). In particular, the provided plurality of directional light beams  102  are coupled or emitted out of and directed away from the multiview backlight  100  in different principal angular directions corresponding to respective view directions of a multiview display, according to various embodiments. In some embodiments, the directional light beams  102  may be modulated (e.g., using light valves, as described below) to facilitate the display of information having 3D content. 
     As illustrated in  FIGS. 2A-2C , the multiview backlight  100  comprises a light guide  110 . The light guide  110  may be a plate light guide  110 , according to some embodiments. The light guide  110  is configured to guide light along a length of the light guide  110  as guided light  104 . For example, the light guide  110  may include a dielectric material configured as an optical waveguide. The dielectric material may have a first refractive index that is greater than a second refractive index of a medium surrounding the dielectric optical waveguide. The difference in refractive indices is configured to facilitate total internal reflection of the guided light  104  according to one or more guided modes of the light guide  110 , for example. 
     In some embodiments, the light guide  110  may be a slab or plate optical waveguide comprising an extended, substantially planar sheet of optically transparent, dielectric material. The substantially planar sheet of dielectric material is configured to guide the guided light  104  using total internal reflection. According to various examples, the material of the light guide  110  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  110  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  110 . The cladding layer may be used to further facilitate total internal reflection, according to some examples. 
     Further, according to some embodiments, the light guide  110  is configured to guide the guided light  104  according to total internal reflection at a non-zero propagation angle between a first surface  110 ′ (e.g., ‘front’ surface or side) and a second surface  110 ″ (e.g., ‘back’ surface or side) of the light guide  110 . In particular, the guided light  104  propagates by reflecting or ‘bouncing’ between the first surface  110 ′ and the second surface  110 ″ of the light guide  110  at the non-zero propagation angle. 
     In some embodiments, the light guide  110  may be configured to ‘recycle’ the guided light  104 . In particular, the guided light  104  that has been guided along the light guide length may be redirected back along that length in another propagation direction  103 ′ that differs from the propagation direction  103 . For example, the light guide  110  may include a reflector (not illustrated) at an end of the light guide  110  opposite to an input end adjacent to the light source. The reflector may be configured to reflect the guided light  104  back toward the input end as recycled guided light. Recycling guided light  104  in this manner may increase a brightness of the multiview backlight  100  (e.g., an intensity of the directional light beams  102 ) by making guided light available more than once, for example, to plasmonic multibeam elements, described below. 
     In  FIG. 2A , a bold arrow indicating a propagation direction  103 ′ of recycled guided light (e.g., directed in a negative x-direction) illustrates a general propagation direction of the recycled guided light within the light guide  110 . Alternatively (e.g., as opposed to recycling guided light), guided light  104  propagating in the other propagation direction  103 ′ may be provided by introducing light into the light guide  110  with the other propagation direction  103 ′ (e.g., in addition to guided light  104  having the propagation direction  103 ). 
     As illustrated in  FIGS. 2A-2C , the multiview backlight  100  further comprises a plasmonic multibeam element  120 . In particular, the multiview backlight  100  of  FIGS. 2A-2C  comprise a plurality of plasmonic multibeam elements  120  spaced apart from one another along the light guide length. As illustrated, the plasmonic multibeam elements  120  of the plurality are separated from one another by a finite space and represent individual, distinct elements along the light guide length. That is, by definition herein, the plasmonic multibeam elements  120  of the plurality are spaced apart from one another according to a finite (i.e., non-zero) inter-element distance (e.g., a finite center-to-center distance). Further the plasmonic multibeam elements  120  of the plurality generally do not intersect, overlap or otherwise touch one another, according to some embodiments. As such, each plasmonic multibeam element  120  of the plurality is generally distinct and separated from other ones of the plasmonic multibeam elements  120 , e.g., as illustrated. 
     According to some embodiments, the plasmonic multibeam elements  120  of the plurality may be arranged in either a one-dimensional (1D) array or two-dimensional (2D) array. For example, the plurality of plasmonic multibeam elements  120  may be arranged as a linear 1D array. In another example, the plurality of plasmonic multibeam elements  120  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 plasmonic multibeam elements  120  may be substantially uniform or constant across the array. In other examples, the inter-element distance between the plasmonic multibeam elements  120  may be varied one or both of across the array and along the length of the light guide  110 . 
     According to various embodiments, a plasmonic multibeam element  120  of the plurality comprises a plasmonic material. The plasmonic multibeam element  120  is configured to provide emitted light (e.g., by plasmonic emission of a surface plasmon) from a portion of the guided light  104  within the light guide  110 . The emitted light provide by the plasmonic multibeam element  120  has a color-tailored emission pattern. The color-tailored emission pattern corresponds to an arrangement of color sub-pixels of a view pixel in the multiview display, according to various embodiments. Further, the emitted light comprises a plurality of directional light beams  102  having different principal angular directions from one another. The different principal angular directions of the directional light beams  102  correspond to respective view directions of a multiview display, in various embodiments. 
     In particular, a portion of the guided light  104  may be scattered or ‘coupled out’ of the light guide  110  by the plasmonic material of the plasmonic multibeam element  120  as or by plasmonic emission. By ‘scattered’ it is meant that the guided light portion stimulates surface plasmons within the plasmonic materials and these surface plasmons, in turn, produce emitted light by plasmonic emission. Further, as is described below in more detail, the plasmonic emission is configured to exhibit the color-tailored emission pattern of the plasmonic multibeam element  120 .  FIGS. 2A and 2C  illustrate the directional light beams  102  of the emitted light as a plurality of diverging arrows depicted as being directed way from the first (or front) surface  110 ′ of the light guide  110 . 
       FIGS. 2A-2C  further illustrate an array of light valves  108  configured to modulate the directional light beams  102  of the coupled-out light beam plurality. The light valve array may be part of a multiview display that employs the multiview backlight, for example, and is illustrated in  FIGS. 2A-2C  along with the multiview backlight  100  for the purpose of facilitating discussion herein. In  FIG. 2C , the array of light valves  108  is partially cut-away to allow visualization of the light guide  110  and the plasmonic multibeam element  120  underlying the light valve array. 
     As illustrated in  FIGS. 2A-2C , different ones of the directional light beams  102  having different principal angular directions pass through and may be modulated by different ones of the light valves  108  in the light valve array. Further, as illustrated, a light valve  108  of the array corresponds to a view pixel  106 ′, and a set of the light valves  108  corresponds to a multiview pixel  106  of a multiview display. In particular, a different set of light valves  108  of the light valve array is configured to receive and modulate the directional light beams  102  from different ones of the plasmonic multibeam elements  120 , i.e., there is one unique set of light valves  108  for each plasmonic multibeam element  120 , as illustrated. In various embodiments, different types of light valves may be employed as the light valves  108  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. 2A , a first light valve set  108   a  is configured to receive and modulate the directional light beams  102  from a first plasmonic multibeam element  120   a , while a second light valve set  108   b  is configured to receive and modulate the directional light beams  102  from a second plasmonic multibeam element  120   b . Thus, each of the light valve sets (e.g., the first and second light valve sets  108   a ,  108   b ) in the light valve array corresponds, respectively, to a different multiview pixel  106 , with individual light valves  108  of the light valve sets corresponding to the view pixels  106 ′ of the respective multiview pixels  106 , as illustrated in  FIG. 2A . Moreover, as described above, in some embodiments each of the light valve sets (e.g., the first and second light valve sets  108   a ,  108   b ) in the light valve array may receive light of different colors corresponding to different color sub-pixels of the light valves in the light valve sets. Thus, in various embodiments the view pixels  106 ′ include color sub-pixels. 
     In some embodiments, a relationship between the plasmonic multibeam elements  120  of the plurality and corresponding multiview pixels  106  (e.g., sets of light valves  108 ) may be a one-to-one relationship. That is, there may be an equal number of multiview pixels  106  and plasmonic multibeam elements  120 .  FIG. 2B  explicitly illustrates by way of example the one-to-one relationship where each multiview pixel  106  comprising a different set of light valves  108  is illustrated as surrounded by a dashed line. In other embodiments (not illustrated), the number of multiview pixels  106  and plasmonic multibeam elements  120  may differ from one another. 
     In some embodiments, an inter-element distance (e.g., center-to-center distance) between a pair of adjacent plasmonic multibeam elements  120  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  106 , e.g., represented by light valve sets. For example, as illustrated in  FIG. 2A , a center-to-center distance d between the first plasmonic multibeam element  120   a  and the second plasmonic multibeam element  120   b  is substantially equal to a center-to-center distance D between the first light valve set  108   a  and the second light valve set  108   b . In other embodiments (not illustrated), the relative center-to-center distances of pairs of plasmonic multibeam elements  120  and corresponding light valve sets may differ, e.g., the plasmonic multibeam elements  120  may have an inter-element spacing (i.e., center-to-center distance ( 1 ) 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  106 .  FIG. 2A  also depicts a size S of a view pixel  106 ′. 
     According to some embodiments (e.g., as illustrated in  FIG. 2A ), each plasmonic multibeam element  120  may be configured to provide directional light beams  102  to one and only one multiview pixel  106 . In particular, for a given one of the plasmonic multibeam elements  120 , the directional light beams  102  having a principal angular direction corresponding to the different colors in a view of the multiview display are substantially confined to a single corresponding multiview pixel  106  and the view pixels  106 ′ thereof, i.e., a single set of light valves  108  corresponding to the plasmonic multibeam element  120 , as illustrated in  FIG. 2A . As such, each plasmonic multibeam element  120  of the multiview backlight  100  may provide a corresponding set of directional light beams  102  that has a principal angular direction and that includes the different colors in one of the different views of the multiview display. That is, the set of directional light beams  102  contains light beams having a common direction and corresponding to each of the different colors in one of the different view directions. The common direction is provided by the color-tailored emission pattern of the plasmonic multibeam element  120 . The common direction may mitigate and, in some examples, substantially eliminate color breakup. 
     Color breakup is an image artifact of color multiview displays that may occur when a directional light beam  102  emanating from a point passes through a view pixel  106 ′ comprising a plurality of color sub-pixels that are spatially displaced or offset from one another. The spatial offset of the color sub-pixels may effectively result in the directional light beam  102  passing through each of the color sub-pixels at a slightly different angle. Thus, the directional light beam  102  exits the color sub-pixels as a plurality of color directional light beams having slightly different directions from one another. The slightly different directions of the color directional light beams exiting the various color sub-pixels produce a concomitant differential displacement or separation of different colors in an image pixel defined by the view pixel  106 ′. The differential separation of the different colors is known as color breakup. 
       FIG. 3  illustrates a cross sectional view of a portion of a multiview backlight  100 ′ that exhibits color breakup in an example, according to an embodiment consistent with the principles described herein. In particular,  FIG. 3  illustrates a portion of an example multiview backlight  100 ′ that includes a multibeam element  120 ′ configured to illuminate a view pixel  106 ′ with a directional light beam  102 . The multibeam element  120 ′ in  FIG. 3  does not have a color-tailored emission pattern (i.e., is not the plasmonic multibeam element  120 , as described above).  FIG. 3  also illustrates the view pixel  106 ′ comprising a plurality of color sub-pixels  107 . The multibeam element  120 ′ and the view pixel  106 ′ each have a comparable size S, i.e., a size s of the multibeam element  120 ′ is about equal to a size S of the view pixel  106 ′ (s  5 ). Further, as illustrated, the color sub-pixels  107  are equally spaced within the view pixel  106 ′. Therefore, since there are three color sub-pixels  107  in the plurality of color sub-pixels  107 , as illustrated, a spacing or distance (e.g., center-to-center spacing) between the color sub-pixels  107  is about one-third of the view pixel size S (S/3). The three, color sub-pixels  107  illustrated in  FIG. 3  may represent three primary colors (e.g., red (R), green (G), and blue (B) of an RGB color model), for example. 
     In  FIG. 3 , the multibeam element  120 ′ acts or serves as an extended point source used to illuminate the color sub-pixels  107  of the view pixel  106 ′, e.g., the color sub-pixels  107  may be color sub-pixels of a light valve that acts as the view pixel  106 ′. A directional light beam  102  emitted by the multibeam element  120 ′ is illustrated as an arrow extending from a center of the multibeam element  120 ′ through the view pixel  106 ′, or more precisely through the color sub-pixels  107  of the view pixel  106 ′. Due to the distance between the color sub-pixels  107 , the directional light beam  102  effectively comprises a plurality of different color directional light beams having slightly different principal angular directions. Three different color directional light beams  102   a ,  102   b ,  102   c  represented by three arrows and corresponding to each of the three different color sub-pixels  107   a ,  107   b ,  107   c  are illustrated in  FIG. 3 , for example. When the view pixel  106 ′ is viewed, the slightly different principal angular directions of different color directional light beams  102   a ,  102   b ,  102   c  representing the different colors of the color sub-pixels  107  result in a shift of the various colors relative to one another. That is, the different colors within the view pixel  106 ′ may appear to be visually shifted with respect to one another resulting in color breakup. 
       FIG. 4  illustrates a graphical representation of color breakup in an example, according to an embodiment consistent with the principles described herein. As illustrated in  FIG. 4 , a typical radiation intensity (I) pattern of light at an output of the view pixel  106 ′ is plotted as a function of angle θ for a selected view direction (e.g., θ 1 ). Curves  109   a ,  109   b , and  109   c  in  FIG. 4  represent different colors of light corresponding to light from a respective one of each of the three example color sub-pixels  107   a ,  107   b ,  107   c  illuminated by the multibeam element  120 ′ illustrated in  FIG. 3 . For example, curve  109   a  may represent red (R) light from a red color sub-pixel  107   a , curve  109   b  may represent green (G) light from a green color sub-pixel  107   b , and curve  109   c  may represent blue (B) light from a blue color sub-pixel  107   c . Note that the principal angular directions of the directional light beams  102  that illuminate the three example color sub-pixels  107   a ,  107   b ,  107   c  in  FIG. 3  are different from one another. Thus, the radiation intensity (I) pattern of the light for the different colors (e.g., R, G, B) is shifted in angle relative to one another as well (e.g., illustrated the angular shift of curves  109   a ,  109   b , and  109   c ), resulting in color breakup. 
     The plasmonic multibeam element  120  having the color-tailored emission pattern may correct for the color breakup by substantially eliminating the slightly different principal angular directions of directional light beams  102  that pass through the different color sub-pixels  107  of the view pixel  106 ′, according to various embodiments. In particular, color-tailored emission pattern of the plasmonic multibeam element  120  may be configured to provide directional light beams  102  of different colors to each of the color sub-pixels  107  where the directional light beams  102  of different colors are substantially parallel to one another due to the color-tailored emission pattern. 
     According to some embodiments, the plasmonic multibeam element  120  may be viewed as a composite multibeam element or equivalently as a composite extended source comprising a plurality of multibeam sub-elements. The plurality of multibeam sub-elements may have different emission colors from one another. In particular, each of the multibeam sub-elements may comprise a different plasmonic material from other multibeam sub-elements of the multibeam sub-element plurality to provide the different plasmonic emission colors. Further, the plurality of multibeam sub-elements may be arranged to provide the color-tailored emission pattern according to the different plasmonic emission colors, in various embodiments. For example, the multibeam elements may be spatially offset from one another within the plasmonic multibeam element  120  to provide the color-tailored emission pattern. 
       FIG. 5  illustrates a cross sectional view of a portion of a multiview backlight  100  in an example, according to an embodiment consistent with the principles described herein. In particular,  FIG. 5  illustrates the plasmonic multibeam element  120  (i.e., as a composite multibeam element) including a plurality of multibeam sub-elements  122 . As illustrated, the plasmonic material of a first multibeam sub-element  122   a  may have or be configured to provide a red plasmonic emission color and a second multibeam sub-element  122   b  have or be configured to provide a green plasmonic emission color. A third multibeam sub-element  122   c , as illustrated, may be configured to provide a blue plasmonic emission color. 
     Also illustrated in  FIG. 5  is a view pixel  106 ′ comprising a plurality of color sub-pixels  107 . The illustrated view pixel  106 ′ has a size S and the color sub-pixels  107  are separated by one another by a distance of about one-third of the view pixel size S (i.e., S/3), as illustrated. In  FIG. 5 , the multibeam sub-elements  122   a ,  122   b ,  122   c  are arranged corresponding to the arrangement of the color sub-pixels  107 . For example, the first or red multibeam sub-element  122   a  having the red plasmonic emission color is arranged corresponding to a location of a first or red (R) color sub-pixel  107   a  of the view pixel  106 ′ and the second multibeam sub-element  122   b  is arranged corresponding to a second or green (G) color sub-pixel  107   b  of the view pixel  106 ′. Further, as illustrated, the third or blue multibeam element  122   c  is arranged corresponding to a location of the third or blue (B) color sub-pixel  107   c  of the view pixel  106 ′. 
     Moreover, in  FIG. 5 , the multibeam sub-elements  122  of the plasmonic multibeam element  120  are spatially offset from one another by a distance (e.g., about S/3) commensurate with a distance between adjacent color sub-pixels  107  of the view pixel  106 ′. As such, an arrangement of the multibeam sub-elements  122  (i.e., both in terms of the arrangement of the colors R, G, B and terms of the distance S/3 between the multibeam sub-elements  122 ) as well as the color-tailored emission pattern of the plasmonic multibeam element  120  corresponds to an arrangement of color sub-pixels  107  (i.e., colors R, G, B and color sub-pixel spacing S/3) of the view pixel  106 ′, as illustrated in  FIG. 5 . 
     According to various embodiments, a size of a multibeam sub-element  122  may be comparable to a size of the view pixel  106 ′. In particular, the multibeam sub-element size may be between fifty percent and two hundred percent of the view pixel size, according to some embodiments. In  FIG. 5 , a multibeam sub-element  122  has a size s that is about equal to the view pixel size S (i.e., s≈S), as illustrated. 
     Further illustrated in  FIG. 5  is a directional light beam  102  comprising a plurality of different color directional light beams  102   a ,  102   b ,  102   c  represented by the three different arrows and corresponding to light beams emitted by each of the three different multibeam sub-elements  122   a ,  122   b ,  122   c , respectively. As illustrated, the three different arrows representing respectively the red (R) color directional light beam  102   a , the green (G) color directional light beam  102   b , and the blue (B) color directional light beam  102   c  emitted by the plurality of multibeam sub-elements  122  are each directed through the corresponding color sub-pixel  107   a ,  107   b ,  107   c . Further, an approximate center or radiation of each of the multibeam sub-elements  122  is spaced to correspond with the spacing (e.g., S/3) of the color sub-pixels  107  in the view pixel  106 ′. As a result, the different color directional light beams  102   a ,  102   b ,  102   c  for each of the different colors of emitted light (i.e., R, G, B) according to the color-tailored emission pattern of the plasmonic multibeam element  120  are substantially parallel to one another (i.e., have substantially the same principal angular directions). Since the different color directional light beams  102   a ,  102   b ,  102   c  provided by the color-tailored emission pattern of the plasmonic multibeam element  120  have substantially the same principal angular directions, the view pixel  106 ′ may be free of color breakup, according to various embodiments. 
     According to various embodiments, the plasmonic material of the plasmonic multibeam element  120  (e.g., in a multibeam sub-elements  122  of the multibeam sub-element plurality) is configured to scatter a portion of the guided light  104  (which may be white light, for example) as the plurality of directional light beams  102  having different colors, e.g., the different color directional light beams  102   a ,  102   b ,  102   c . In some embodiments, the plasmonic material may include various different types of plasmonic structures (e.g., plasmonic nanoparticles) configured to provide different plasmonic emission colors of the color-tailored emission pattern. 
     In particular, the plurality of plasmonic nanoparticles may comprise a first type of plasmonic nanoparticles having one or more of a size, a shape, and a particular choice of plasmon-supporting material, or at least a plasmonic resonance condition of the plasmonic nanoparticles consistent with production of a red plasmonic emission color. The plurality of plasmonic nanoparticles may further comprise a second type of plasmonic nanoparticles having one or more of a size, a shape, and a particular choice of plasmon-supporting material, or at least a plasmonic resonance condition of the plasmonic nanoparticles consistent with production of a green plasmonic emission color. In some embodiments, the plurality of plasmonic nanoparticles further comprises a third type of nanoparticles having one or more of a size, a shape, and a particular choice of plasmon-supporting material, or at least a plasmonic resonance condition of the plasmonic nanoparticles consistent with production of a blue plasmonic emission color. 
     In some embodiments, the plasmonic multibeam element  120  may be located adjacent to a second surface  110 ″ of the light guide  110  opposite a first surface  110 ′. The plasmonic multibeam element  120  may be configured to provide the emitted light comprising the plurality of directional light beams  102  through the first surface  110 ′ of the light guide  110 , for example. In some embodiments, the plasmonic multibeam element  120  further comprises a reflection layer adjacent a side of the plasmonic material opposite a side facing the light guide first surface  110 ′. The reflection layer may be configured to reflect a portion of the emitted light directed away from the first surface  110 ′ and to redirect the reflected emitted light portion back toward the first surface  110 ′ of the light guide  110 , for example. 
       FIG. 6  illustrates a cross sectional view of a portion of a multiview backlight  100  in an example, according to an embodiment consistent with the principles described herein. As illustrated, the portion of the multiview backlight  100  comprises the light guide  110  and the plasmonic multibeam element  120  adjacent to the second surface  110 ″ of the light guide  110  opposite to the first surface  110 ′. The illustrated plasmonic multibeam element  120  includes a plurality of multibeam sub-elements  122   a ,  122   b ,  122   c  and is configured to provide emitted light having the color-tailored emission pattern when illuminated by the guided light  104 . Further, the emitted light comprises the plurality of directional light beams  102 , each directional light beam  102  of the plurality having a different principal angular direction. Moreover, as illustrated, each of the directional light beams  102  includes a plurality of different color directional light beams  102   a ,  102   b ,  102   c . Each of the different color directional light beam  102   a ,  102   b ,  102   c  of a directional light beam  102  has substantially the same principal angular direction as the directional light beam  102 . 
       FIG. 6  further illustrates a reflection layer  124  configured to cover the plasmonic material of the plasmonic multibeam element  120 . The reflection layer  124  may comprise substantially any reflective material including, but not limited to, a reflective metal and an enhanced specular reflector (ESR) film. For example, the reflection layer  124  may be a Vikuiti ESR film manufactured by  3 M Optical Systems Division, St. Paul, Minn., USA. The reflective layer  124  may be electrically isolated from the plasmonic material by an insulating (e.g., dielectric material) layer or spacer (not illustrated), according to some embodiments. 
       FIG. 7A  illustrates a cross sectional view of a plasmonic multibeam element  120  in an example, according to an embodiment consistent with the principles described herein.  FIG. 7B  illustrates a cross sectional view of a plasmonic multibeam element  120  in an example, according to another embodiment consistent with the principles described herein. The plasmonic multibeam element  120  illustrated in  FIGS. 7A and 7B  may be the plasmonic multibeam element  120  illustrated in  FIG. 6 , for example. 
     As illustrated, plasmonic multibeam element  120  comprises a plurality of multibeam sub-elements  122 . A first multibeam sub-element  122   a  of the multibeam sub-element plurality comprises a first plasmonic material having a first (e.g., red) plasmonic emission color and is denoted by a first crosshatch pattern. A second multibeam sub-element  122   b  of the multibeam sub-element plurality comprises a second plasmonic material having a second (e.g., green) plasmonic emission color and is denoted by a second crosshatch pattern. A third multibeam sub-element  122   c  of the multibeam sub-element plurality illustrated in  FIG. 7A-7B  comprises a third plasmonic material having a third (e.g., blue) plasmonic emission color and is denoted by a third crosshatch pattern. 
     The three multibeam sub-elements  122   a ,  122   b ,  122   c  illustrated in  FIGS. 7A-7B  are spatially offset from one another by a distance S/3 commensurate with a similar spacing of corresponding color sub-pixels of a view pixel (not illustrated). For example, the color sub-pixels and spacing thereof may be substantially similar to that illustrated in  FIG. 5 . Further, the three multibeam sub-elements  122   a ,  122   b ,  122   c  each have a size S commensurate with the size of a view pixel (e.g., also substantially similar to that illustrated in  FIG. 5 ). 
     In  FIG. 7A , the plasmonic materials of respective ones of the three multibeam sub-elements  122   a ,  122   b ,  122   c  are mixed with one another in at least a portion of the plasmonic multibeam element  120 . Mixing of plasmonic materials, as illustrated may provide multibeam sub-elements  122  having the size S while still enabling a center-to-center or inter-element spacing of the multibeam sub-elements  122  to be determined by or to be substantially equal to the color sub-pixel spacing (e.g., S/3), for example. In  FIG. 7B , the plasmonic materials of the first, second and third multibeam sub-elements  122   a ,  122   b ,  122   c  overlap one another in adjacent regions of the multibeam sub-elements  122  to provide the center-to-center spacing S/3 therebetween. Note that the illustrated inter-element spacing S/3 in  FIGS. 7A and 7B  is provided by way of example for discussion purposes only. 
     In some embodiments, a shape of the multibeam sub-element  122  of the plasmonic multibeam element  120  is analogous to a shape of a multiview pixel or equivalently, a shape of a set (or ‘sub-array’) of the light valves corresponding to the multiview pixel. For example, the multibeam sub-element  122  may have a square shape when the multiview pixel (or an arrangement of a corresponding set of light valves) is substantially square. In another example, the multiview pixel may have a rectangular shape, i.e., may have a length or longitudinal dimension that is greater than a width or transverse dimension. In this example, the multibeam sub-element  122  corresponding to the rectangular multiview pixel may have an analogous rectangular shape. In yet other examples, the multibeam sub-element  122  and the corresponding multiview pixel may have various other shapes including or at least approximated by, but not limited to, a triangular shape, a hexagonal shape, and a circular shape. 
       FIG. 7C  illustrates a top or plan view of a plasmonic multibeam element  120  having a square-shaped multibeam sub-element  122  in an example, according to an embodiment consistent with the principles described herein. The shape of the square-shaped multibeam sub-element  122  illustrated in  FIG. 7C  may be analogous to the square shape of the multiview pixel  106  comprising a square set of light valves  108  illustrated in  FIG. 2A-2C , for example.  FIG. 7C  also illustrates a set of three multibeam sub-elements  122   a ,  122   b ,  122   c  by way of example and not limitation. As illustrated, the three multibeam sub-elements  122   a ,  122   b ,  122   c  are arranged in a manner corresponding to an arrangement of color sub-pixels  107   a ,  107   b ,  107   c  in a view pixel  106 ′, also illustrated in  FIG. 7C . The color sub-pixels  107   a ,  107   b ,  107   c  in the view pixel  106 ′ of  FIG. 7C  may be arranged in a direction (e.g., from ‘ 107   a ’ to ‘ 107   c ’) of a pixel row of the multiview pixel (e.g., multiview pixel  106  of  FIGS. 2A-2C ), for example. A double-headed arrow signifies the arrangement correspondence in  FIG. 7C . 
     According to other embodiments (not illustrated), any of a variety of arrangements of multibeam sub-elements corresponding to color sub-pixel arrangements including, but not limited to, a triangular arrangement may be employed. Also note that, while a color-order both of the color sub-pixels and the corresponding multibeam sub-elements  122   a ,  122   b ,  122   c  is described herein as generally being red (R) to green (G) to blue (B), this specific color-order arrangement is used for discussion purposes only. In general, substantially any color-order arrangement and, for that matter, also any set of colors may be employed and still be within the scope described herein. For example (not illustrated), the color-order arrangement of the color sub-pixels and corresponding color-order arrangement of the multibeam sub-elements may be green (G) to blue (B) to red (R) or blue (B) to green (G) to red (R), etc., when employing primary colors based on an RGB color model. Further, in general, various embodiments of the plasmonic multibeam elements  120  described herein may be defined or otherwise realized either on or within the light guide  110  using any of a variety of fabrication techniques. For example, the plasmonic material of the plasmonic multibeam element  120  may be configured or defined using an additive process, such as deposition, ink-jet printing, etc. The plasmonic material may comprise plasmonic resonators embedded or suspended in a dielectric matrix (e.g., a high dielectric constant material), in some embodiments. In other embodiments, the plasmonic resonators may be realized in a plasmon-supporting sheet, film or layer, e.g., as an aperture in or through the plasmon-supporting sheet, layer or film. 
     Further, as described above, the plasmonic emission color provided by the plasmonic material of the plasmonic multibeam element  120  may be a function of a plasmonic resonance. In particular, the plasmonic material may comprise a plasmonic resonator that is tuned to resonate at a frequency corresponding to a predetermined plasmonic emission color. Further, the plasmonic material may be polarization selective. As noted above, a variety of nanoparticles and related nanostructures including, but not limited to, nanorods, nanodisks or nanocylinders, nanospheres may be used as plasmonic resonators of the plasmonic material, according to some embodiments. These various nanostructure-based plasmonic resonators may be tuned by selecting a size and, in some embodiments, a shape, to provide a particular plasmonic emission color. Further, various nanostructure-based plasmonic resonators may also provide polarization selectivity when illuminated by incident light. 
       FIG. 8A  illustrates a perspective view of a plasmonic resonator  126  according to an example, in an embodiment consistent with the principles described herein.  FIG. 8B  illustrates a plan view of another plasmonic resonator  126 ′ according to an example, in an embodiment consistent with the principles described herein. As illustrated in  FIG. 8A , the plasmonic resonator  126  comprises a nanorod having a length L and a width or diameter W. The nanorod-based plasmonic resonator  126  may comprise a metal such as, but not limited to, gold, silver, aluminum or copper, for example. The plasmonic resonator  126 ′ illustrated in  FIG. 8B  comprises a nanorod-shaped aperture (i.e., a nanoscale slot) in a plasmon-supporting film  125 , the nanorod-shaped aperture also having length L and width W. The plasmon-supporting film  125  may be a film of plasmon-supporting metal, for example. According to the so-called Babinet principle, the plasmonic resonator  126 ′ having the nanorod-shaped aperture may have similar properties to the nanorod-based plasmonic resonator of  FIG. 8A . According to various embodiments, the plasmonic resonators  126 ,  126 ′ may serve as optical antennas. In particular, both of the plasmonic resonators of  FIGS. 8A and 8B  may be tuned to provide a particular plasmonic emission color by adjusting or selecting the length L. Likewise, the plasmonic resonators of  FIGS. 8A-8B  are polarization selective. For example, the plasmonic resonator illustrated in  FIG. 8A  is polarization selective for TE polarization aligned with the length dimension, e.g., as illustrated in  FIG. 8A  by a double-headed arrow labeled E representing an electric field of the TE illumination. 
       FIG. 9A  illustrates a perspective view of a plasmonic resonator  127  to another example, in an embodiment consistent with the principles described herein.  FIG. 9B  illustrates a plan view of another plasmonic resonator  127 ′ according to another example, in an embodiment consistent with the principles described herein. The plasmonic resonator  127  of the plasmonic multibeam element  120  illustrated in  FIG. 9A  comprises a nanodisk or nanocylinder, while the plasmonic resonator  127 ′ of the plasmonic multibeam element  120  illustrated in  FIG. 9B  comprises a circular aperture in a plasmon-supporting film  125 . The plasmonic resonators  127 ,  127 ′ of  FIG. 9A-9B  may be tuned using a diameter to resonate at a particular frequency (i.e., provide a particular plasmonic emission color). According to some embodiments, the plasmonic resonators  127 ,  127 ′ of  FIGS. 9A-9B  may be substantially polarization independent, e.g., unlike the plasmonic resonators  126 ,  126 ′ of  FIGS. 8A-8B . In particular, the plasmonic resonator  127  may interact equally with light having substantially any electric field orientation, e.g., as indicated by crossed double-headed arrows labeled E in  FIG. 9A . 
       FIG. 10A  illustrates a plan view of a plasmonic resonator  128  to yet another example, in an embodiment consistent with the principles described herein.  FIG. 10B  illustrates a plan view of another plasmonic resonator  128 ′ according to yet another example, in an embodiment consistent with the principles described herein.  FIGS. 10A and 10B  illustrate the plasmonic resonator  128 ,  128 ′ of the plasmonic multibeam element  120  comprising a so-called V-shaped optical antenna. In particular, the plasmonic resonator  128  of  FIG. 10A  comprises linear nanostructures (e.g., nanorods or nanowires) arranged in a ‘V’ shape and the plasmonic resonator  128 ′ of  FIG. 10B  comprises a V-shaped aperture in a plasmon-supporting film  125 . The V-shaped optical antennas may provide anti-symmetric and symmetric polarization selectivity, according to some embodiments. 
     Referring again to  FIG. 2A , the multiview backlight  100  may further comprise a light source  130 . According to various embodiments, the light source  130  is configured to provide the light to be guided within light guide  110 . In particular, the light source  130  may be located adjacent to an entrance surface or end (input end) of the light guide  110 . In various embodiments, the light source  130  may comprise substantially any source of light (e.g., optical emitter) including, but not limited to, one or more light emitting diodes (LEDs) or a laser (e.g., laser diode). In some embodiments, the light source  130  may comprise an optical emitter or plurality of optical emitters configured produce a substantially polychromatic light, such as substantially white light. 
     In some embodiments, the light source  130  may further comprise a collimator configured to couple light into the light guide  110 . The collimator may be configured to receive substantially uncollimated light from one or more of the optical emitters of the light source  130 . The collimator is further configured to convert the substantially uncollimated light into collimated light. In particular, the collimator may provide collimated light having the non-zero propagation angle and being collimated according to a predetermined collimation factor (e.g., collimation factor σ), according to some embodiments. The collimator is further configured to communicate the collimated light beam to the light guide  110  to propagate as the guided light  104 , described above. In other embodiments, substantially uncollimated light may be provided by the light source  130  and the collimator may be omitted. 
     In some embodiments, the multiview backlight  100  is configured to be substantially transparent to light in a direction through the light guide  110  orthogonal to a propagation direction  103 ,  103 ′ of the guided light  104 . In particular, the light guide  110  and the spaced apart plurality of plasmonic multibeam elements  120  allow light to pass through the light guide  110  through both the first surface  110 ′ and the second surface  110 ″, in some embodiments. Transparency may be facilitated, at least in part, due to both the relatively small size of the plasmonic multibeam elements  120  and the relative large inter-element spacing (e.g., one-to-one correspondence with multiview pixels  106 ) of the plasmonic multibeam element  120 . Further, the plasmonic multibeam elements  120  may reemit light propagating orthogonal to the light guide surfaces  110 ′,  110 ″, according to some embodiments. 
     In some embodiments, the multiview backlight  100  is configured to emit light (e.g., as the plurality of directional light beams  102 ) that varies as a function of distance along a length of the light guide  110 . In particular, the plasmonic multibeam elements  120  (or of the multibeam sub-elements  122 ) along the light guide  110  may be configured to provide the emitted light having an intensity that varies as a function of distance along the light guide in a propagation direction  103 ,  103 ′ of the guided light  104  from one plasmonic multibeam element  120  to another. Varying the intensity of the emitted light may compensate for or mitigate a variation (e.g., a decrease) in an intensity of the guided light  104  along a length of the light guide  110  due to incremental absorption of the guided light  104  during propagation, for example. In some embodiments, a density of the plasmonic material is a function of a location of the plasmonic multibeam element  120  along the light guide  110  and the plasmonic material density is configured to vary an intensity of the emitted light provided by the plasmonic multibeam element  120  as a function of distance along the light guide  110  in a propagation direction  103 ,  103 ′ of the guided light  104 . In other words, the emitted light intensity as a function of distance may be provided or controlled by varying the density of the plasmonic material of individual plasmonic multibeam elements  120  of the plurality. In some embodiments, the plasmonic material density is defined as a density of the plasmonic structures within the plasmonic material. In other embodiments, the plasmonic material density used to control the emitted light intensity may be varied by incorporating gaps or holes in the plasmonic material of the plasmonic multibeam elements  120 . In these embodiments, the term ‘density’ may be defined as a coverage density of the plasmonic material across the plasmonic multibeam element  120 . 
     In accordance with some embodiments of the principles described herein, a multiview display is provided. The multiview display is configured to emit modulated light beams as pixels of the multiview display. Further, the emitted modulated light beams may comprise light beams representing a plurality of different colors (e.g., red, green, blue of an RGB color model). According to various embodiments, the emitted modulated light beams, e.g., including the different colors, may be preferentially directed toward a plurality of viewing directions of the multiview display. In some examples, the multiview display is configured to provide or ‘display’ a 3D or multiview image. Moreover, the multiview image may be a color multiview image. For example, the multiview image may represent in color a 3D scene displayed on a mobile device such as, but not limited to, a mobile telephone, tablet computer, or the like. Different ones of the modulated, different color and differently directed light beams may correspond to individual pixels of different ‘views’ associated with the multiview image, according to various examples. The different views may provide a ‘glasses free’ (e.g., an ‘automultiscopic’) representation of information in the color multiview image being displayed by the multiview display, for example. 
       FIG. 11  illustrates a block diagram of a multiview display  200  in an example, according to an embodiment consistent with the principles described herein. The multiview display  200  is configured to display a multiview image (e.g., color multiview image) according to different views in corresponding different view directions. In particular, modulated directional light beams  202  emitted by the multiview display  200  are used to display the multiview image and may correspond to pixels of the different views (i.e., view pixels), including color sub-pixels in each of the different views that are associated with different colors. The modulated directional light beams  202  are illustrated as arrows emanating from multiview pixels  210  in  FIG. 11 . Dashed lines are used for the arrows depicting the directional modulated light beams  202  emitted by the multiview display  200  to emphasize the modulation thereof by way of example and not limitation. 
     The multiview display  200  illustrated in  FIG. 11  comprises an array of the multiview pixels  210 . The multiview pixels  210  of the array are configured to provide a plurality of different views of the multiview display  200 . According to various embodiments, a multiview pixel  210  of the array comprises a plurality of view pixels configured to modulate a plurality of directional light beams  204  and produce the modulated directional light beams  202 . In some embodiments, the multiview pixel  210  is substantially similar to a set of light valves  108  of the array of light valves  108 , described above with respect to the multiview backlight  100 . In particular, a view pixel of the multiview pixel  210  may be substantially similar to the above-described light valves  108 . That is, a multiview pixel  210  of the multiview display  200  may comprise a set of light valves (e.g., a set of light valves  108 ), and a view pixel of the multiview pixel  210  may comprise a plurality of light valves of the set. Further, the view pixel may comprise color sub-pixels, each color sub-pixel representing a light valve (e.g., a single light valve  108 ) of the set of light valves, for example. 
     The multiview display  200  illustrated in  FIG. 11  further comprises a light guide  220  configured to guide light. The guided light within the light guide  220  may comprise white light, for example. In some embodiments, the light guide  220  of the multiview display  200  may be substantially similar to the light guide  110  described above with respect to the multiview backlight  100 . 
     As illustrated in  FIG. 11 , the multiview display  200  further comprises an array of plasmonic multibeam elements  230 . A plasmonic multibeam element  230  of the element array comprises a plasmonic material. The plasmonic multibeam element  230  of the element array is configured to provide emitted light from guided light. The emitted light has a color-tailored emission pattern and comprises the plurality of directional light beams  204 , according to various embodiments. In some embodiments, the plasmonic multibeam element  230  of the element array may be substantially similar to the plasmonic multibeam element  120  of the multiview backlight  100 , described above. In particular, the color-tailored emission pattern may correspond to an arrangement of color sub-pixels of a view pixel in the view pixel plurality of the multiview pixels  210 . 
     Further, the plasmonic multibeam element  230  of the element array is configured to provide the plurality of directional light beams  204  to a corresponding multiview pixel  210 . Light beams  204  of the plurality of directional light beams  204  have different principal angular directions from one another, according to various embodiments. In particular, the different principal angular directions of the directional light beams  204  correspond to different view directions of the different views of the multiview display  200 , and each of the view directions includes different colors along a corresponding principal angular direction. Moreover, owing to the color-tailored emission pattern, the different colors of directional light beams  204  corresponding to a common view direction may be substantially parallel to one another, according to various embodiments. 
     According to some embodiments, the plasmonic multibeam element  230  may comprise a plurality of multibeam sub-element substantially similar to the multibeam sub-elements  122 , described above. In particular, the plasmonic multibeam element  230  may comprise a plurality of multibeam sub-elements (not separately illustrated in  FIG. 11 ) having different plasmonic emission colors from one another. Each of the multibeam sub-elements may comprise a different plasmonic material from other multibeam sub-elements of the multibeam sub-element plurality to provide the different plasmonic emission colors. Further, the plurality of multibeam sub-elements may be arranged to provide the color-tailored emission pattern according to the different plasmonic emission colors. In other embodiments, one or more of the multibeam sub-elements may comprise a substantially non-plasmonic material and act or serve as diffuser of scatter in conjunction with other ones of the multibeam sub-elements that include the plasmonic materials. 
     According to some embodiments, a size of the multibeam sub-element is comparable to a size of a view pixel of the view pixel plurality. The comparable size of the multibeam sub-element may be greater than one half of the view pixel size and less than twice the view pixel size, for example. Further, the multibeam sub-elements may be spatially offset from one another by a distance commensurate with (e.g., about equal to) a distance between adjacent color sub-pixels of the view pixel, according to some embodiments. 
     In some embodiments, the plasmonic material of the plasmonic multibeam element  230  or equivalently the multibeam sub-element(s) comprises a plurality of plasmonic nanoparticles. A plasmonic emission color of the plasmonic material may be a function of a distribution of different types of the plasmonic nanoparticles within the plasmonic material, for example. A distribution of types may include a distribution based on a size of the plasmonic nanoparticles. Other characteristics of the plasmonic nanoparticles such as, but not limited to, a choice of plasmon-supporting material or metal, and a plasmonic resonance condition may also be to control the plasmonic emission color, in some examples. 
     In some embodiments, an inter-element or center-to-center distance between multibeam sub-elements of the plasmonic multibeam element  230  may correspond to an inter-pixel distance between color sub-pixels of the view pixel in the multiview pixels  210 . For example, the inter-element distance between the multibeam sub-elements may be substantially equal to the inter-pixel distance between the color sub-pixels. Further, there may be a one-to-one correspondence between the multiview pixels  210  of the multiview pixel array and the plasmonic multibeam elements  230  of the element array. In particular, in some embodiments, the inter-element distance (e.g., center-to-center) between the plasmonic multibeam elements  230  may be substantially equal to the inter-pixel distance (e.g., center-to-center) between the multiview pixels  210 . As such, each view pixel in the multiview pixel  210  may be configured to modulate a different one of the plurality of light beams  204  provided by a corresponding plasmonic multibeam element  230 . Further, each multiview pixel  210  may be configured to receive and modulate the light beams  204  from one and only one plasmonic multibeam element  230 , according to various embodiments. 
     As described above, the plurality of light beams  204  may include different colors, and the plasmonic multibeam elements  230  may direct a color-tailored emission pattern that includes the plurality of light beams  204  to corresponding color sub-pixels of view pixels in multiview pixels  210 . Further, the principal angular directions of the different colors in a particular view direction of the multiview display  200  may be aligned (i.e., the same), eliminating or substantially eliminating spatial color separation or color breakup, according to various embodiments. 
     In some embodiments (not illustrated in  FIG. 11 ), the multiview display  200  may further comprise a light source. The light source may be configured to provide the light to the light guide. According to some embodiments, the light source may be substantially similar to the light source  130  of the multiview backlight  100 , described above. For example, the light provided by the light source may comprise white light. 
     In accordance with other embodiments of the principles described herein, a method of multiview backlight operation is provided.  FIG. 12  illustrates a flow chart of a method  300  of multiview backlight operation in an example, according to an embodiment consistent with the principles described herein. As illustrated in  FIG. 12 , the method  300  of multiview backlight operation comprises guiding  310  light along a length of a light guide. According to some embodiments, the light guide may be substantially similar to the light guide  110  described above with respect to the multiview backlight  100 . In some examples, the guided light may be collimated according to a predetermined collimation factor σ. 
     As illustrated in  FIG. 12 , the method  300  of multiview backlight operation further comprises emitting  320  light by plasmonic emission from the guided light using an array of plasmonic multibeam elements. According to various embodiments, the emitted light comprises a plurality of directional light beams having different principal angular directions corresponding to respective different view directions of a multiview display. Further, the directional light beams have or represent different colors of light (e.g., red, green, blue). In some embodiments, the plasmonic multibeam elements may be substantially similar to the plasmonic multibeam elements  120  of the multiview backlight  100  described above. For example, a plasmonic multibeam element of the array may comprise a plasmonic material and have a color-tailored emission pattern. The color-tailored emission pattern may correspond to an arrangement of color sub-pixels of a view pixel in the multiview display, for example. 
     Further, in some embodiments, the plasmonic multibeam element may comprise a plurality of multibeam sub-elements spatially offset from one another by a distance corresponding to a distance between the color sub-pixels. The plasmonic material within a multibeam sub-element may emit a different color of emitted light from other multibeam sub-elements of plasmonic multibeam element to provide the color-tailored emission pattern from the guided light. 
     In some embodiments (not illustrated), the method  300  of multiview backlight operation further comprises providing light to the light guide using a light source. The provided light may be collimated according to a collimation factor to provide a predetermined angular spread of the guided light within the light guide. In some embodiments, the light source may be substantially similar to the light source  130  of the multiview backlight  100 , described above. For example, the provided light may comprise white light. 
     In some embodiments (e.g., as illustrated in  FIG. 12 ), the method  300  of multiview backlight operation further comprises optionally modulating  330  the emitted light using light valves configured as a multiview pixel of a multiview display. In various embodiments, the emitted light comprises the plurality of directional light beams, as discussed above. As such, modulating  330  also modulates the plurality of directional light beams. According to some embodiments, a light valve of a plurality or array of light valves corresponds to a color sub-pixel of a view pixel within the multiview pixel. 
     Thus, there have been described examples and embodiments of a multiview backlight, a method of multiview backlight operation, and a multiview display that employ a plasmonic multibeam element having a color-tailored emission pattern to provide directional light beams corresponding to a plurality of different views of a multiview image. It should be understood that the above-described examples are merely illustrative of some of the many specific examples that represent the principles described herein. Clearly, those skilled in the art can readily devise numerous other arrangements without departing from the scope as defined by the following claims.