BACKLIGHT HAVING GLOBAL MODE MIXER, MULTI-VIEW BACKLIGHT

Abstract

The embodiments disclosed herein include a light guide plate configured to guide light along a length of a light guide. The light guided along the length of the light guide propagates in at least two directional modes, a first directional mode and a second directional mode. The light guided in the first directional mode has one or both of a lateral component that is greater than the lateral component of the light guided in the second directional mode and a longitudinal component that is less than the longitudinal component of the light guided in the second directional mode. Also included is a global mode mixer. The global mode mixer extends along the length of the light guide and is configured to convert a portion of the light guided in the first directional mode to the second directional mode. The scattering element preferentially scatters the light in the second directional mode out of the light guide.

Description

[Technical field]

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS none

[0002] STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT none [Background technology]

[0003] Light can propagate within a waveguide configured as a light guide, such as a light guide plate, and as it propagates along the waveguide, the light can be extracted from the waveguide for use as an illumination source. Such waveguides configured as light guides can be used as light sources, for example, for certain types of electronic displays. Summary of the Invention

[0004] In general, electronic displays can be classified as either active displays (i.e., displays that emit light) or passive displays (i.e., displays that modulate light provided by another light source). The most prominent examples of active displays include cathode ray tubes (CRTs), plasma displays (PDPs), and organic light emitting diodes (OLEDs) / active matrix organic light emitting diodes (AMOLEDs). Displays that are typically classified as passive when considering emitting light are liquid crystal display (LCD s ) displays and electrophoretic (EP) displays. Passive displays often exhibit attractive performance characteristics, including but not limited to, inherently low power consumption, but their inability to emit light can make them somewhat limited in many practical applications.

[0005] Passive displays can be coupled to an external light source. The coupled light source allows these otherwise passive displays to emit light and essentially function as an active display. An example of such a coupled light source is a backlight. A backlight can function as a light source (often a panel backlight) placed behind a passive display to illuminate the otherwise passive display. For example, a backlight can be coupled to an LCD or EP display. The backlight emits light that passes through the LCD or EP display. The amount of light coupled from the backlight into the LCD or EP display can determine the brightness and efficiency of the display.

[0006] This disclosure includes the following [1] to

[22] . [1] A flat backlight, a light guide plate configured to guide light as guided light along a length of the light guide plate; a global mode mixer extending along a length of the light guide plate, the global mode mixer configured to convert a portion of the light directed in a first directional mode to light directed in a second directional mode; a scattering structure configured to preferentially scatter the light guided in the second directional mode out of the light guide plate as radiation, A flat backlight, wherein the light guided in the first directional mode has one or both of a horizontal component that is greater than the horizontal component of the light guided in the second directional mode and a vertical component that is less than the vertical component of the light guided in the second directional mode. [2] The flat backlight of [1] above, wherein the global mode mixer is configured to convert the guided light portion of the first directional mode into guided light of the second directional mode, which includes one or both of a decrease in a horizontal component of the guided light portion and an increase in a vertical component of the guided light portion. [3] The flat backlight according to [1], wherein the global mode mixer is disposed on a surface of the light guide plate. [4] The flat backlight according to [3], wherein the scattering structure is disposed on a surface of the light guide plate opposite to a surface on which the global mode mixer is disposed. [5] The flat backlight of [1], wherein the global mode mixer comprises a diffraction grating extending across the width of the light guide plate and along the length of the light guide plate, the diffractive features of the diffraction grating being aligned parallel to the direction of propagation of the guided light along the length of the light guide plate. [6] The flat backlight of [1], wherein the global mode mixer includes a reflective element having reflective facets aligned parallel to a direction of propagation of the guided light along a length of the light guide plate. [7] The flat backlight of [1], wherein the scattering structure includes an array of scattering elements spaced apart from one another along the length of the light guide plate, and the global mode mixers are distributed between each spaced apart scattering element of the array of scattering elements. [8] The flat backlight of [7], wherein each scattering element of the array of scattering elements includes a plurality of scattering sub-elements, and the global mode mixers are further distributed within the scattering element and between each of the plurality of scattering sub-elements. [9] The flat backlight of [7], wherein each scattering element of the array of scattering elements comprises a multi-beam element, each of the multi-beam elements configured to scatter the guided light out of the light guide plate in the second directional mode as radiation comprising a directional light beam having a direction corresponding to a view direction of a view of a multi-view image.

[10] The flat backlight of [9], wherein each of the multi-beam elements includes one or more of a diffraction grating, a micro-reflective element, and a micro-refractive element.

[11] A multi-view display comprising the flat backlight of [9] above, further comprising an array of light valves configured to modulate the directional light beams of the emitted light to provide the multi-view image, the multi-beam elements having a size of 25% to 200% of the size of the light valves of the array of light valves.

[12] A multi-view backlight, comprising: A light guide plate configured to guide light as guided light; an array of multi-beam elements arranged along a length of the light guide plate, each of the multi-beam elements configured to scatter the guided light out of the light guide plate as radiation comprising directional light beams having directions corresponding to different view directions of a multi-view image; and global mode mixers distributed among the multibeam elements of the array of multibeam elements, the global mode mixers configured to convert light directed according to a first directivity mode into light directed according to a second directivity mode; A multi-view backlight, wherein each multi-beam element is configured to preferentially scatter output light directed according to the second directivity mode relative to light directed according to the first directivity mode.

[13] The light guided according to the first directional mode, a lateral component of light directed according to the second directivity mode that is greater than the lateral component; and a light having a longitudinal component smaller than the longitudinal component of the light guided according to the second directional mode, or both; 13. The multi-view backlight of claim 12, wherein the global mode mixer is configured to convert light guided according to the first directional mode into light guided according to the second directional mode, the second directional mode comprising one or both of a reduction in a lateral component and an increase in a vertical component of the guided light.

[14] The multi-view backlight of

[12] , wherein the global mode mixer is disposed on a surface of the light guide plate and the array of multi-beam elements is disposed adjacent to the surface on which the global mode mixer is disposed.

[15] The multi-view backlight of

[12] , wherein the global mode mixer comprises a diffraction grating extending across the width of the light guide plate and along the length of the light guide plate between each multi-beam element of the array of multi-beam elements, the diffractive features of the diffraction grating being aligned parallel to the direction of propagation of the guided light along the length of the light guide plate.

[16] The multi-view backlight of

[12] , wherein the global mode mixer comprises one or both of the reflective and refractive elements, the reflective elements having reflective facets aligned parallel to the propagation direction of the guided light along the length of the light guide plate, and the global mode mixer extends across the lateral width of the light guide plate and along the length of the light guide plate between each multibeam element of the array of multibeam elements.

[17] A multi-view display comprising the multi-view backlight of

[12] above, further comprising an array of light valves configured to modulate the directional light beams of the emitted light to provide the multi-view image, the multi-beam elements having a size of 25% to 200% of the size of the light valves of the array of light valves.

[18] A method for operating a flat backlight, comprising: directing light as guided light along a length of a light guide plate in a propagation direction; converting a portion of the light guided in the first directional mode into light guided in a second directional mode using a global mode mixer extending along a length of the light guide plate; and scattering the guided light out of the light guide plate using a scattering structure to provide emitted light, the scattering structure preferentially scattering light guided in the second directional mode; the light directed in the first directional mode has one or both of a lateral component that is greater than a lateral component of the light directed in the second directional mode and a longitudinal component that is less than a longitudinal component of the light directed in the second directional mode. How a flat backlight works.

[19] A method of operating a flat backlight as described in

[18] above, wherein the global mode mixer converts the guided light portion of the first directional mode into guided light of the second directional mode, which includes one or both of a reduction in a horizontal component of the guided light portion and an increase in a vertical component of the guided light portion.

[20] The global mode mixer, a diffraction grating extending across a lateral width of the light guide plate and along the length of the light guide plate, diffractive features of the diffraction grating being aligned parallel to the direction of propagation of the guided light along the length of the light guide plate;

[18] A method of operating a flat backlight as described above, comprising: one or both of a reflective element having reflective facets aligned parallel to the propagation direction of the guided light along the length of the light guide plate.

[21] A method of operating a flat backlight as described in

[18] above, wherein the scattering structure includes an array of scattering elements spaced apart from one another along a length of the light guide plate, and the global mode mixer is distributed among the spaced apart scattering elements of the array of scattering elements.

[22] The method of operating a flat backlight described in

[18] above, wherein the scattering structure includes an array of multi-beam elements, each of which scatters the guided light out of the light guide plate in the second directional mode as emitted light including a directional light beam having a direction corresponding to a view direction of a view of a multi-view image, and the method of operating the flat backlight further includes the step of modulating the directional light beam of the emitted light to provide the multi-view image. Various features of examples and embodiments according to the principles described herein can be more readily understood by reference to the following detailed description in conjunction with the accompanying drawings, in which like reference numerals indicate like structural elements, and in which: [Brief description of the drawings]

[0007] [Figure 1] FIG. 1A illustrates a diagrammatic representation of angular components of a light beam having a directional mode in one example, according to an embodiment consistent with principles described herein.

[0008] FIG. 1B shows a graph of the lateral and longitudinal components of two exemplary directional modes described herein.

[0009] [Figure 2A] 1 shows a cross-sectional view of a planar backlight having scattering structures and a global mode mixer in one example according to an embodiment consistent with principles described herein.

[0010] [Figure 2B-C]FIG. 2B shows a perspective view of a planar backlight having scattering structures and a global mode mixer in one embodiment consistent with principles defined herein.

[0011] [FIG. 2C] A plan view of a planar backlight having scattering structures and a global mode mixer in one embodiment consistent with principles described herein.

[0012] [Figure 3A] 1 shows a cross-sectional view of a multi-view display having a scattering structure and a global mode mixer in one embodiment consistent with principles described herein.

[0013] [Figure 3B-C] [Figure 3B] A plan view of a multi-view display having scattering structures and a global mode mixer in one embodiment consistent with principles described herein.

[0014] [Figure 3C] A perspective view of a multi-view display having scattering structures and a global mode mixer in one embodiment consistent with principles described herein.

[0015] [Figure 4] [FIG. 4A] A cross-sectional view of a portion of a planar backlight including a multi-beam element shaped as a diffraction grating and a global mode mixer disposed within a planar waveguide, consistent with principles described herein.

[0016] [Figure 4B] Shows a cross-sectional view of a portion of a planar backlight including multi-beam elements formed as diffraction gratings, positioned on either side of a planar waveguide, as well as a global mode mixer, consistent with principles described herein.

[0017] [Figure 4C] Shows a cross-sectional view of a portion of a planar backlight including a multi-beam element formed as a diffraction grating and a global mode mixer arranged on the same side of a planar waveguide consistent with principles described herein.

[0018] [Diagram 5] 1 shows a plan view of a scattering element having multiple scattering sub-elements and a global mode mixer disposed in the open area between the scattering sub-elements according to one embodiment consistent with principles described herein.

[0019] [Figure 6] 1 shows a flowchart of a method of operating a planar backlight consistent with principles disclosed herein. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0020] Particular examples and embodiments have other features in addition to, or in place of, certain features shown in the above-referenced drawings, and these and other features are described in detail below with reference to the above-referenced drawings.

[0021] In accordance with the principles described herein, examples and embodiments provide a planar waveguide configured to guide light in multiple directional modes. The light guide plate includes a global mode mixer disposed along a length of the light guide plate. The global mode mixer is configured to convert a portion of the light guided in a first directional mode into light guided in a second directional mode. The directional mode can have a vertical component and a horizontal component. By converting a portion of the light guided in the first directional mode into light guided in the second directional mode, the global mode mixer can improve the light extraction efficiency of the light guide. Such light guides can be used, for example, to produce brighter or more efficient backlights for passive displays.

[0022] A "light guide" is defined herein as a structure that uses total internal reflection to guide light within its structure. In particular, a light guide may include a core that is substantially transparent at its operating wavelength. In various examples, the term "light guide" generally refers to a dielectric light guide that uses total internal reflection to guide light at the interface between the dielectric material of the light guide and the material or medium that surrounds the light guide. By definition, a condition for total internal reflection is that the refractive index of the light guide is greater than the refractive index of the surrounding medium adjacent to the surface of the light guide material. In some embodiments, the light guide may include a coating in addition to or instead of the refractive index difference mentioned above to further promote total internal reflection. The coating may be, for example, a reflective coating. The light guide may be any of a number of light guides, including, but not limited to, a light guide plate or one or both of a slab light guide and a strip light guide.

[0023] Further, the term "plate" as applied to a light guide, such as a "light guide plate", is defined herein as a piecewise or differentially flat layer or lamina, sometimes referred to as a "slab" light guide. In particular, a light guide plate is defined as a light guide configured to guide light in two substantially orthogonal directions bounded by a top and bottom surface (i.e., opposing surfaces) of the light guide. Further, as defined herein, these top and bottom surfaces are separated from one another and may be substantially parallel to one another, at least in a differential sense. That is, within any differentially small section of the light guide plate, the top and bottom surfaces lie in substantially parallel planes or are coplanar.

[0024] In some embodiments, the light guide plate is substantially flat (i.e., confined to a plane) and the light guide plate is a planar light guide. In other embodiments, the light guide plate can be curved in one dimension, or in two orthogonal dimensions. For example, the light guide plate can be curved in one dimension to form a cylindrically shaped light guide plate. However, any curvature has a sufficiently large radius of curvature to ensure that total internal reflection is maintained within the light guide plate to guide the light.

[0025] As used herein, the term "directional mode" refers to the direction of propagation of a light beam, or more generally, the direction of propagation of light propagating or guided within a light guide. In general, light propagating within a light guide in a directional mode can be described by multiple orthogonal components, including a longitudinal component, a transverse component, and a vertical component. For example, using a Cartesian coordinate system, the longitudinal component can be the component of light propagating in the x-direction within the light guide. The transverse component can be the component of light propagating in the y-direction within the light guide. The perpendicular vertical component can be the component of light propagating in the z-direction of the light guide.

[0026] Furthermore, as used herein, the article "a" is intended to mean its ordinary meaning in the patent art, i.e., "one or more". For example, "a scattering element" means one or more scattering elements, and thus, as used herein, "the scattering element(s)" means "particular scattering element(s)". Also, any reference herein to "top", "bottom", "upper", "lower", "upward", "downward", "front", "back", "first", "second", "left", or "right" is not intended to be limiting. As used herein, the term "about", when applied to a value, unless otherwise specified, typically means within the tolerance of the equipment used to generate the value, or ±10%, or ±5%, or ±1%. Furthermore, as used herein, the term "substantially" means the majority, or nearly all, or all, or an amount in the range of about 51% to about 100%. Furthermore, the examples herein are intended to be illustrative only and are presented for purposes of illustration and not limitation.

[0027] 1A shows a diagrammatic representation of the angular components of a light beam having a directional mode in one embodiment according to principles described herein. Light having a directional mode is represented by a vector that depicts the direction of propagation.

[0028] Furthermore, by definition, light guided in a light guide in a directional mode is constrained to the relationship given by equation (1).

number

[0029] As light propagates through a light guide, it may propagate in many different directional modes. For example, light in a particular directional mode may propagate along the length of the light guide in the x-direction and include a transverse component in the y-direction and a longitudinal component in the z-direction.

[0030] FIG. 1B illustrates a diagrammatic representation of directional modes within a light guide in one example, in accordance with an embodiment consistent with principles described herein. In particular, FIG. 1B illustrates the directional modes plotted in the yz plane, showing a conceptual diagram of three different directional modes: a first directional mode 101, a second directional mode 102, and a third directional mode 103. Light propagating or guided in the first directional mode 101 has a first transverse component (n y ) and the first vertical component (n z) The light propagating or guided in the second directional mode 102 may include light having a second transverse component (n y ) and the second vertical component (n z 1B, the first directional mode 101 may include light having a first transverse component (n y ) is the second transverse component (n y ) is larger than the first longitudinal component (n z ) is the longitudinal component (n z ) is smaller than

[0031] As described in more detail herein, embodiments of a global mode mixer according to the principles described herein are configured to convert light in one directional mode, or light propagating in one directional mode, into light in another directional mode, or light propagating in another directional mode. mode The mixer can convert light in or having the third directional mode 103 to light in or having the fourth directional mode 104 by interacting with light propagating in the third directional mode 103. FIG. 1B illustrates the conversion of the third directional mode 103 to the fourth directional mode 104 using curved arrows. According to some embodiments, the fourth directional mode 104 can exhibit better or more desirable properties than the third directional mode 103. For example, when light is propagating in the fourth directional mode 104, the light can exhibit more preferential interaction with the scattering structure of the light guide compared to the third directional mode, as described in more detail herein. Thus, the mode conversion provided by the global mode mixer can be used to scatter light propagating within the light guide by the scattering structures or to improve the scattering efficiency in the fourth directional mode 104 compared to that which would be achieved for light propagating in the third directional mode 103.

[0032] 2A-2C, various views of a planar backlight 200 are shown. Although various embodiments of the concepts disclosed herein are described in relation to a backlight, those skilled in the art will appreciate that the global mode mixer and methods disclosed herein are not limited to use in backlights, and more specifically, in multi-view backlights, as described in more detail below. The planar backlight 200 may include a light guide plate 210 configured to direct light along the length of the light guide plate. A global mode mixer 220 may extend along the length of the planar waveguide. In FIGS. 2B and 2C, a global mode mixer 220 is shown. 220 is represented by a series of lines arranged across the width of the planar backlight and along the length of the light guide plate 210. 220 2A, the global mode mixer 220 can be located on the top surface of the light guide plate 210, or even within the light guide plate, as described in more detail below. The global mode mixer 220 can convert a portion of the light guided within the light guide plate 210 (as indicated by the arrows) from light guided in a first directional mode to light guided in a second directional mode. The light guided in the first directional mode can be converted to light guided in a second directional mode. directional 2A , the light guide plate 210 has a lateral component greater than the lateral component of the light guided in the first mode, and a vertical component less than the vertical component of the light guided in the second mode. The planar backlight 200 can also be accompanied by a scattering structure including a plurality of scattering elements 231 formed on or within the light guide plate 210. The scattering elements 231 of the scattering structure are configured to scatter or couple out the light propagating within the light guide as emitted light 202, as represented by the arrows. In FIG. 2A , the scattered out light is shown using arrows as emitted light 202, or equivalently, as a scattered out or coupled out light beam.

[0033] In some embodiments, as shown in more detail in connection with Figures 3A-3C, the planar backlight 200 is configured as a multi-view backlight that can provide multiple scattered output light beams or directional light beams as emitted light 202 (e.g., as a light field) having different principal angular directions. In particular, according to various embodiments, the multiple scattered output light beams or directional light beams of the provided emitted light 202 can be scattered away from the multi-view backlight in different principal angular directions corresponding to respective viewing directions of the multi-view display. In some embodiments, the directional light beams of the emitted light 202 can be modulated (e.g., using light valves, as described below) to aid in the display of information having three-dimensional (3D) or multi-view content. Also shown in Figure 3A are an array of multi-view pixels 206 and light valves 208, which are described in more detail below.

[0034] FIG 2A illustrates a cross-sectional view of an example flat backlight 200 according to an embodiment consistent with principles described herein. FIG 3A illustrates a cross-sectional view of a multi-view display having a scattering structure and a global mode mixer according to an embodiment consistent with principles described herein. The multi-view display of FIG 3A-3C uses an example flat backlight 200 as shown in FIG 2A-2C. Note that in FIG 2A and FIG 3A, common reference numbers refer to the same structures unless otherwise indicated.

[0035] As shown in Figures 2A and 3A, the flat backlight 200 comprises a light guide plate 210. The light guide plate 210 is configured to guide light as guided light 204 along the length of the light guide plate 210. According to various embodiments, the guided light 204 propagates along the length of the light guide in multiple directional modes, including a first directional mode and a second directional mode. The light guide plate 210 can include a dielectric material configured as a light guide. The dielectric material can have a first refractive index that is greater than a second refractive index of a medium surrounding the dielectric light guide. This refractive index difference is configured to promote total internal reflection of the guided light 204 according to, for example, one or more guiding or directing modes of the light guide plate 210.

[0036] In some embodiments, the light guide plate 210 can be a slab or planar light guide (i.e., a light guide plate) that comprises a substantially planar sheet of an optically transmissive dielectric material. The substantially planar sheet of dielectric material is configured to direct the guided light 204 (or a guided light beam) using total internal reflection. According to various embodiments, the optically transmissive material of the light guide plate 210 can include or be composed of any of a variety of dielectric materials, including, but not limited to, one or more of various types of glasses (e.g., silica glass, alkali aluminosilicate glass, borosilicate glass, etc.). In some embodiments, the light guide plate 210 can further include a cladding layer (not shown) on at least a portion of a surface (e.g., one or both of the top and bottom surfaces) of the light guide plate 210. According to some embodiments, the cladding layer can be used to further promote total internal reflection.

[0037] Furthermore, according to some embodiments, the light guide plate 210 is configured to guide the guided light 204 (e.g., a guided light beam) between a first surface 210′ ​​(e.g., a “front” surface or face) and a second surface 210″ (e.g., a “back” surface or face) of the light guide plate 210 according to total internal reflection at a non-zero propagation angle. In some embodiments, a plurality of guided light beams including light of different colors can be guided by the light guide plate 210 at different color-specific respective non-zero propagation angles. It should be noted that light propagating within the light guide plate 210 can propagate along different directions within the light guide plate 210, which define directional modes of light propagation within the light guide plate 210. Light propagating in each of these different directional modes has a longitudinal component (n x ), the horizontal component (n y ), and the vertical component (n z ).

[0038] The guided light 204 in the light guide plate 210 can be coupled into the light guide plate 210 at a non-zero propagation angle (e.g., about 30 degrees to 35 degrees). In some embodiments, coupling structures, such as, but not limited to, lenses, mirrors or similar reflectors (e.g., tilted collimating reflectors), diffraction gratings and prisms (not shown), and various combinations thereof, can facilitate coupling the light into the input end of the light guide plate 210 as guided light 204 at a non-zero propagation angle. In other embodiments, the light can be directly coupled into the input end of the light guide plate 210 without or substantially without the use of a coupling structure (i.e., using direct or "butt" coupling). When coupled into the light guide plate 210, the guided light 204 is configured to propagate along the light guide plate 210, with a substantial component propagating generally away from the input end (e.g., as shown by the bold arrows indicating a direction along the x-axis in FIG. 3A ). On the mark However, light within light guide plate 210 can propagate in a number of different directional modes, each of which has a longitudinal component (n x ), the horizontal or y-direction component (n y), and the vertical or z-direction vertical component (n z ) is understood to be defined as

[0039] The light coupled into the light guide plate 210 can be a collimated light beam according to certain exemplary implementations of the principles disclosed herein. In this specification, "collimated light" or "collimated light beam" is generally defined as a beam in which the rays of the light beam are substantially parallel to each other within the light beam (e.g., the guided light 204). Furthermore, according to the definition herein, the rays that diverge or are scattered from the collimated light beam are not considered to be part of the collimated light beam. In some embodiments, the flat backlight 200 can include a collimator (e.g., a tilted collimating reflector), such as a lens, a reflector, or a mirror, as described above, for example, to collimate the light from the light source. In some embodiments, the light source includes a collimator. In this case, the collimated light provided to the light guide plate 210 is the collimated light of the guided light 204.

[0040] As used herein, "collimation factor" is defined as the degree to which light is collimated. Specifically, as defined herein, the collimation factor defines the angular spread of rays in a collimated light beam. For example, the collimation factor σ may specify that the majority of rays in a collimated light beam are within a certain angular spread (e.g., ±σ degrees around the central angle or main angular direction of the collimated light beam). According to some embodiments, the rays of a collimated light beam may have a Gaussian distribution with respect to angle, and the angular spread may be an angle determined at half the peak intensity of the collimated light beam.

[0041] As shown in Figures 2A-2C and 3A-3C, the flat backlight 200 further comprises a scattering structure 230. According to some embodiments, the scattering structure 230 can be disposed on the first surface 210' of the light guide plate 210. For example, Figures 2A and 3A show the scattering structure 230 on the first surface 210'. In other embodiments, the scattering structure 230 can be disposed on the second surface 210'' of the light guide plate 210. In yet other embodiments, the scattering structure 230 can be located between the first surface 210' and the second surface 210'' in the light guide plate 210. According to various embodiments, the scattering structure 230 is configured to preferentially scatter the light guided in the second directional mode out of the light guide plate 210 as the emitted light 202.

[0042] The scattering structure 230 may include an array of scattering elements 231 distributed along the length of the light guide plate 210, for example along the first surface 210′, or the second surface 210″, or within the light guide plate 210. As described in more detail below, the scattering elements 231 that make up the scattering structure 230 may include multiple scattering sub-elements (not shown).

[0043] The scattering elements 231 of the scattering structure 230 may be separated from one another by a distance, which may define separate boundaries for each element along the length of the light guide. That is, as defined herein, the scattering elements 231 of the scattering structure 230 are spaced apart from one another according to a finite (non-zero) inter-element distance (e.g., a finite center-to-center distance). Furthermore, according to some exemplary implementations, the multiple scattering elements 231 generally do not intersect, overlap, or touch one another. That is, each of the multiple scattering elements 231 is generally distinct and separated from the others of the scattering elements 231 according to these implementations. In another implementation, scattering elements arranged continuously along the length of the light guide plate 210 may be used in the scattering structure (not shown). When light propagates through the light guide plate 210, the guided light includes light propagating in both a first directional mode and a second directional mode. The guided light 204 in the first directional mode can have, for example, one or both of a lateral component that is greater than a lateral component of the light guided in the second directional mode and a vertical component that is less than a vertical component of the light guided in the second directional mode. In various embodiments, the scattering elements 231 of the scattering structure 230 can be configured and arranged such that the scattering elements 231 preferentially scatter light in the second directional mode out of the light guide plate 210, as described above.

[0044] As shown in Figures 2A and 3A, the planar backlight 200 further comprises a global mode mixer 220. According to various embodiments, the global mode mixer 220 is configured to convert a portion of the guided light 204 guided in or having a first directional mode to a guided light 204 having or being guided in a second directional mode. In particular, as the light propagates in the light guide plate 210 in the propagation direction, the guided light 204 interacts with the global mode mixer 220, which converts the guided light 204 from the first directional mode to light in the second directional mode. In some embodiments, the global mode mixer 220 can be positioned along the length of the light guide plate 210 such that a portion of the guided light 204 in the first directional mode is converted to the second directional mode as the light propagates along the length of the light guide plate 210. According to some embodiments, the global mode mixer 220 can be used to convert light having a first directional mode to light having a second directional mode by either or both reducing the transverse component of the guided light portion and increasing the longitudinal component of the guided light portion.

[0045] In some embodiments, the global mode mixer 220 can be disposed on a surface of the light guide plate 210 opposite the side of the light guide plate 210 on which the scattering structures 230 are disposed. For example, in FIG. 3A, the global mode mixer 220 is shown on the second surface 210″ of the light guide plate 210, while the scattering structures 230 are located on the first surface 210′ ​​as shown. In other embodiments, such as those shown in FIGS. 2A-2C, the global mode mixer 220 and the scattering structures 230 can be located on the same surface of the light guide plate 210. In still other embodiments, the global mode mixer 220 can be located or disposed internally between the surfaces of the light guide plate 210, as described in more detail below.

[0046] According to some embodiments, the global mode mixer 220 includes multiple mode mixer elements 221 spaced apart along the length of the light guide plate 210. In some embodiments, there can be an equal number of mode mixer elements 221 as scattering elements 231. Alternatively, there can be a different number of mode mixer elements 221 than scattering elements 231, as shown in FIG. 3A. Although the mode mixer elements 221 are shown as separate elements, it should be understood that the global mode mixer 220 can be implemented as a continuous structure along the length of the light guide plate 210, as shown in FIGS. 2A-2C. Although not shown, global mode mixers 220 can be disposed on both the first surface 210' and the second surface 210'' of the light guide plate 210. As discussed above, the global mode mixer 220 can be disposed on both the first surface 210' and the second surface 210'' of the light guide plate 210. To In addition to or instead of one or both of the first surface 210' and the second surface 210'' of the light guide plate 210, a global mode mixer 220 may also be disposed between the first surface 210' and the second surface 210'' of the light guide plate 210, as shown in FIG. 4A.

[0047] While FIG. 3A shows one exemplary embodiment of the global mode mixer 220 located opposite the scattering elements 231 of the scattering structure 230, in another embodiment the global mode mixer 220 can be located between the scattering elements 231 of the scattering structure 230, for example as shown in FIGS. 2A-2C. In this embodiment, a plurality of scattering elements 231 can be arranged in an array on one surface of the light guide plate 210, and the global mode mixers 220 can be distributed along the length of the light guide plate 210. According to another embodiment, the global mode mixers 220 can be located within scattering sub-elements (not shown) of individual scattering elements 231 of the scattering structure 230. This type of embodiment is described in more detail in relation to FIG. 5.

[0048] In some embodiments, the global mode mixer 220 may be implemented as or may include a diffraction grating. In some embodiments, the diffraction grating may extend across the width and along the length of the light guide. When the global mode mixer 220 is implemented as one or more diffraction gratings, the diffractive features of the diffraction grating may be aligned parallel to the direction of propagation of the guided light along the length of the light guide. The arrangement of the diffraction gratings may be such that multiple diffraction gratings are spaced apart at regular intervals along the length of the light guide.

[0049] In other embodiments, the global mode mixer 220 can be implemented as a reflective element having reflective facets aligned parallel to the direction of propagation of the guided light along the length of the light guide plate. The reflective element can include, for example, a microreflector. Alternatively, the global mode mixer 220 can be implemented as a refractive element, such as a microrefractor. In yet other implementations, the global mode mixer 220 can be implemented as a combination of refractive, reflective, and diffractive elements.

[0050] According to some embodiments, the scattering elements 231 may be arranged in either a one-dimensional (1D) array or a two-dimensional (2D) array. For example, the scattering elements may be arranged in a linear 1D array. In another example, the scattering elements may be arranged in a rectangular 2D array or a circular 2D array. Examples of such multi-view backlights are shown in Figures 3B and 3C. Furthermore, the array (i.e., 1D or 2D array) may be a regular or uniform array, or may be an irregular array. In particular, if the array is regular or uniform, the inter-element distance (e.g., center-to-center distance or spacing) between the scattering elements 231 may be substantially uniform or constant across the array. The array If is irregular, the inter-element distance between the scattering elements may vary across the array or along the length of the light guide plate 210. That is, the inter-element distance may vary across and along the length of the light guide plate 210.

[0051] According to various embodiments, the scattering elements 231 of the scattering structure 230 may include a multibeam element. The multibeam element may be configured to scatter and output the guided light at the wavelength. As defined herein, a "multibeam element" is a structure or element of a backlight or display that generates light comprising multiple directional light beams. In some embodiments, the multibeam element may be optically coupled to a light guide of a backlight (e.g., the light guide plate 210 of the planar backlight 200) to provide multiple directional light beams by coupling out portions of the light guided within the light guide. In other embodiments, the multibeam element may generate light (e.g., may comprise a light source) that is emitted as a light beam. Furthermore, each light beam of the multiple directional light beams generated by the multibeam element has a different principal angular direction from each other, as defined herein. In particular, by definition, a directional light beam in the multiple light beams may have a different principal angular direction from each other, as defined herein. directional Another in the light beam directional The directional light beams may have a predetermined principal angular direction different from the light beam. Furthermore, the multiple directional light beams may represent a light field. For example, the multiple directional light beams may be confined to a substantially cone-shaped spatial region or may have a predetermined angular spread that includes different principal angular directions of the light beams in the multiple light beams. Thus, the predetermined angular spread of the combined directional light beams (i.e., the multiple light beams) may represent a light field.

[0052] According to various embodiments, the different principal angular directions of the various directional light beams are determined by, but not limited to, the size (e.g., length, width, area, etc.) of the multibeam element. In some embodiments, the multibeam element can be considered as an "extended point source" according to the definitions herein, i.e., multiple point sources distributed over the extent of the multibeam element. According to various examples, the multibeam element can include one or more of a diffraction grating, a micro-reflective element, or a micro-refractive element. An example of a diffraction grating according to some examples is shown in Figures 4A-4C.

[0053] As used herein, a "diffraction grating" is generally defined as a plurality of features (i.e., diffractive features) arranged to provide diffraction of light incident on the diffraction grating. In some embodiments, the features can be arranged in a periodic or quasi-periodic manner. For example, a diffraction grating can include a plurality of features (e.g., a plurality of grooves or ridges in a surface of a material) arranged in a one-dimensional (1D) array. In other embodiments, a two-dimensional (2D) array of features can be a diffraction grating. For example, a 2D array of protrusions or holes in a surface of a material can be a diffraction grating.

[0054] Thus, and as defined herein, a "diffraction grating" is a structure that provides diffraction of light incident on the diffraction grating. When light is incident on the diffraction grating from a light guide, the diffraction grating can diffract light out of the light guide, and the resulting diffraction or diffraction scattering can be referred to as "diffractive coupling". The diffraction grating also redirects or changes the angle of light by diffraction (i.e., at the diffraction angle). In particular, as a result of diffraction, the light exiting the diffraction grating generally has a different propagation direction than the propagation direction of the light that entered the diffraction grating (i.e., the incident light). The change in the propagation direction of light by diffraction is referred to herein as "diffractive redirection". Thus, a diffraction grating can be understood as a structure that includes diffractive features that diffractively redirect light incident on the diffraction grating, and when light is incident from a light guide, the diffraction grating can also diffractively couple light out of the light guide.

[0055] Further, as defined herein, the features of a diffraction grating are referred to as "diffractive features" and may be present in, on, or at one or more of a material surface (i.e., at the interface between two materials). The surface may be, for example, a surface of a light guide. The diffractive features may include any of a variety of features that diffract light, including, but not limited to, one or more of grooves, ridges, holes, and protrusions in or on the surface. For example, the diffraction grating may include a plurality of substantially parallel grooves in the material surface. In another example, the diffraction grating may include a plurality of parallel ridges rising from the material surface. The diffractive features (e.g., grooves, ridges, holes, protrusions, etc.) may include one or more of a sinusoidal profile, a rectangular profile (e.g., a binary diffraction grating), a triangular profile, and a sawtooth profile (e.g., a blazed diffraction grating). However, the diffractive features may have any of a variety of cross-sectional shapes or profiles that result in diffraction, including, but not limited to, the above.

[0056] According to various embodiments described herein, a diffraction grating (e.g., a diffraction grating of a multi-beam element as described below) can be used to diffract light from a light guide (e.g., a light guide plate) and scatter or couple it out as a light beam. In particular, the diffraction angle θ m , or the diffraction angle θ provided by a locally periodic diffraction grating m is given by equation (2) as follows:

number

[0057] 4A-4C show cross-sectional views of a portion of a planar backlight 200 including a multi-beam element 232 formed as a diffraction grating, as well as a global mode mixer 220 disposed at various locations in or on the light guide plate 210. As shown in FIGS. 4A-4C, the scattered output directional light beam of emitted light 202 is depicted as a number of diverging arrows directed away from the first (or front) surface 210′ ​​of the light guide plate 210. Furthermore, according to various embodiments, the size of the multi-beam element 232 may correspond to the size of a light valve 208 of a multi-view display (or equivalently, a sub-pixel in a multi-view pixel of a multi-view display), as described herein. A multi-view pixel 206 is shown in FIGS. 3A-3C along with the planar backlight 200 for ease of illustration. This “size” may be defined in a variety of ways, including, but not limited to, length, width, or area.

[0058] In some embodiments, the size of the multibeam element corresponds to the size of the light valve such that the size of the diffraction grating is between about twenty-five percent (25%) and about two hundred percent (200%) of the size of the light valve. In other embodiments, the size of the multibeam element is in a range that is greater than about fifty percent (50%) of the size of the light valve, or greater than about sixty percent (60%) of the size of the light valve, or greater than about seventy percent (70%) of the size of the light valve, or greater than about eighty percent (80%) of the size of the light valve, as well as less than about one hundred eighty percent (180%) of the size of the light valve, or less than about one hundred sixty percent (160%) of the size of the light valve, or less than about one hundred forty (140%) of the size of the light valve, or less than about one hundred twenty percent (120%) of the size of the light valve. According to some embodiments, the corresponding sizes of the multibeam element and the light valve can be selected to reduce, and in some embodiments minimize, dark zones between the views of a multiview display. Furthermore, ,Ma The corresponding sizes of the multi-beam elements and light valves can be selected to reduce, and in some embodiments minimize, overlap between views (or view pixels) of a multi-view display or a multi-view image displayed by the multi-view display.

[0059] FIG. 3A to FIG. 3C are also , release Radiation 202 Multiple An array of light valves 208 is shown configured to modulate a directional light beam. The array of light valves may be part of a multi-view display, for example, using a planar backlight 200 configured as a multi-view backlight, and is shown in Figures 3A-3C for ease of explanation herein. In Figure 3C, the array of light valves 208 is partially cut away for illustration purposes only, to reveal the underlying light guide plate 210, global mode mixer scattering element 231, and mode mixer element 221.

[0060] As shown in Figures 3A-3C, individual ones of the directional light beams of emitted light 202 having different principal angular directions can be modulated by passing through individual ones of the light valves 208 in the array of light valves. Further, as shown, the light valves 208 in the array correspond to sub-pixels of a multi-view pixel 206, and a set of light valves 208 corresponds to a multi-view pixel 206 of a multi-view display. In particular, individual sets of light valves 208 in the array of light valves are configured to receive and modulate directional light beams from corresponding ones of the scattering elements 231 configured as multi-beam elements. That is, as shown, there can be a unique set of light valves 208 for each scattering element 231. In various embodiments, various types of light valves can be used as the light valves 208 in the array of light valves, including, but not limited to, one or more of liquid crystal light valves, electrophoretic light valves, and electrowetting-based light valves.

[0061] As shown in FIG. 3A , the first set of light valves 208a is configured to receive and modulate a directional light beam of emitted light 202 from a first scattering element 231a. Additionally, the second set of light valves 208b is configured to receive and modulate a directional light beam of emitted light 202 from a second scattering element 231b. Thus, in this embodiment, each of the sets of light valves in the array of light valves (e.g., the first set of light valves 208a and the second set of light valves 208b) are configured to receive and modulate a directional light beam of emitted light 202 from a different scattering element 231 (e.g., First and second Each of the light valves 208 in the set of light valves corresponds to a sub-pixel of a respective multi-view pixel 206, as shown in FIG. 3A.

[0062] It should be noted that the size of a subpixel of a multi-view pixel 206 may correspond to the size of a light valve 208 in a light valve array, as shown in FIG. 3A. In other embodiments, the size of the light valve or the size of the subpixel may be defined as the distance (e.g., center-to-center distance) between adjacent light valves in an array of light valves. The size of a subpixel may be defined, for example, as either the size of the light valve 208 or a size corresponding to the center-to-center distance between the light valves 208.

[0063] In some example implementations, the relationship between the scattering elements 231 and the corresponding multiview pixels 206 (i.e., sets of subpixels and corresponding sets of light valves 208) can be a one-to-one relationship. That is, there can be an equal number of multiview pixels 206 and scattering elements 231. Figure 3B illustrates an example of a one-to-one relationship, with each multiview pixel 206 (and corresponding subpixels) including a different set of light valves 208 surrounded by dashed lines. In other embodiments (not shown), the number of multiview pixels 206 and the number of scattering elements 231 can be different from each other.

[0064] In some embodiments, the inter-element distance (e.g., center-to-center distance) between pairs of the plurality of scattering elements 231 can be equal to the inter-pixel distance (e.g., center-to-center distance) between pairs of corresponding multi-view pixels 206 represented, for example, by the sets of light valves. For example, as shown in FIG. 3A, the center-to-center distance between the first scattering element 231a and the second scattering element 231b is substantially equal to the center-to-center distance D between the first set of light valves 208a and the second set of light valves 208b. In other embodiments (not shown), the relative center-to-center distances of pairs of scattering elements 231 and corresponding light valve sets may be different. For example, the scattering elements 231 can have an inter-element spacing (i.e., center-to-center distance d) that is either greater than or less than the spacing (i.e., center-to-center distance D) between the sets of light valves that represent the multi-view pixel 206.

[0065] In some embodiments, the shape of the scattering element 231 is similar to the shape of the multiview pixel 206, or equivalently, similar to the shape of the set of light valves 208 (or "subarray") that corresponds to the multiview pixel 206. For example, the scattering element 231 can have a square shape, and the multiview pixel 206 (or the corresponding array of sets of light valves 208) can be substantially square. In another example, the scattering element 231 can have a rectangular shape; that is, it can have a length or longitudinal dimension that is greater than its width or lateral dimension. In this example, the multiview pixel 206 (or equivalently, the array of sets of light valves 208) that corresponds to the scattering element 231 can have a similar rectangular shape. FIG. 3B shows a top, or plan, view of a square scattering element 231 and a corresponding square multiview pixel 206 that includes a square set of light valves 208. In yet another embodiment (not shown), the scattering elements 231 and corresponding multi-view pixels 206 have a variety of shapes, including, but not limited to, triangular, hexagonal, and circular, or at least approximating these.

[0066] Moreover, according to some embodiments (e.g., as shown in FIG. 3A ), each scattering element 231 is configured to provide a directional light beam of emitted light 202 to one and only one multi-view pixel 206. In particular, for a given one of the scattering elements 231, the directional light beams of emitted light 202 having different principal angular directions corresponding to different views of the multi-view display are substantially limited to a single corresponding multi-view pixel 206 and its sub-pixels, i.e., a single set of light valves 208 corresponding to the scattering element 231, as shown in FIG. 3A . Thus, each scattering element 231 of the planar backlight 200 provides a corresponding set of directional light beams of emitted light 202 having a different set of principal angular directions corresponding to different views of the multi-view display (i.e., the set of directional light beams of emitted light 202 includes light beams having directions corresponding to each of the different view directions).

[0067] As shown in FIGS. 4A-4C and according to various embodiments, the scattering elements of the scattering structure can include a multibeam element 232. In some embodiments, the multibeam element 232 can comprise a diffraction grating (e.g., as shown in FIGS. 4A-4C). In some embodiments, one or more (e.g., each) of the multibeam elements 232 can comprise multiple diffraction gratings. The multibeam element 232, or more specifically, the multiple diffraction gratings of the diffractive multibeam element 232, can be located on or adjacent to a surface of the light guide plate 210 or between the respective surfaces of the light guide. In other embodiments, the multibeam element 232 can be located between the first surface 210′ ​​and the second surface 210″ of the light guide plate 210.

[0068] FIG. 4A shows a cross-sectional view of a portion of a planar backlight 200 including a multi-beam element 232 formed as a diffraction grating, as well as a mode mixer element 221 of a global mode mixer 220 disposed within a light guide plate 210. Here, the light guide plate 210 can be fabricated such that the global mode mixer is disposed between a first surface 210' of the light guide plate and a second surface 210'' of the light guide plate. The mode mixer element 221 is configured to convert light of a first directional mode into light of a second directional mode, which is preferentially scattered out of the light guide plate 210 by scattering it with the multi-beam element 232 or another multi-beam element (not shown) of the scattering element. In FIG. 4A, the emitted light 202 scattered out of the light guide plate 210 is indicated by a directional arrow.

[0069] 4B illustrates a cross-sectional view of a portion of a planar backlight 200 including a multi-beam element 232 and a portion of a global mode mixer 220 in one example, according to an embodiment consistent with principles described herein. As shown in FIG. 4B, the multi-beam element 232 is at a first surface 210' of the light guide plate 210. Moreover, the multi-beam element 232 illustrated in FIG. 4B includes a plurality of diffraction gratings, for example and not by way of limitation. When placed at the first surface 210' of the light guide plate 210, the diffraction grating of the plurality of gratings can be, for example, a transmission mode diffraction grating configured to diffractively couple out the guided light portion as emitted light 202 or a directional light beam via the first surface 210'. The multibeam element 232 can be configured to preferentially scatter light directed in a second directional mode (e.g., second directional mode 102 as described above) out of the light guide 210 as directional light beams or emitted light 202, including directional light beams having directions corresponding to the view directions of the views of the multi-view image, as described in more detail below. The portion of the global mode mixer 220 shown in FIG. 4B is shown extending along the underside of an entire segment of the light guide 210. It will be appreciated that the global mode mixer 220 according to this embodiment may extend along substantially the entire length of the underside of the light guide 210.

[0070] 4C shows a cross-sectional view of a portion of a planar backlight 200 including a multi-beam element 232 formed as a diffraction grating, as well as a portion of a global mode mixer 220 with a mode mixer element 221 disposed on the same side of the light guide plate 210 as the multi-beam element 232. In this embodiment, the global mode mixer 220 includes a multi-beam element 232 5 and 6. The scattering structure includes a global mode mixer element 221 arranged to be distributed in the region between the spaced apart scattering elements, such as a scattering element 222. Other configurations and arrangements of global mode mixers and elements of the scattering structure are shown in FIG. 5 and discussed elsewhere, such as in connection with the embodiments described below.

[0071] When placed on the second surface 210'', the gratings constituting the multi-beam element 232 can be, for example, reflection mode gratings. As a reflection mode grating, the grating is configured to diffract the guided light portions and reflect the diffracted guided light portions towards the first surface 210' so that the guided light portions exit the first surface 210' as diffractively coupled out diffracted light beams. In other embodiments (not shown), the gratings can be placed between the surfaces of the light guide plate 210, for example, as one or both of a transmission mode grating and a reflection mode grating. It should be noted that in some embodiments described herein, the principal angular direction of the coupled out light beam entails the effect of refraction due to the coupled out light beam exiting the light guide plate 210 at the light guiding surface. For example, FIG. 4C illustrates, by way of example and not limitation, the refraction (i.e., bending) of the coupled out light beam of the emitted light 202 due to the change in refractive index as the coupled out light beam crosses the first surface 210'.

[0072] According to some embodiments, the diffractive features of the diffraction grating can include one or both of spaced apart grooves and ridges. The grooves or ridges can be comprised of the material of the light guide plate 210 and can be formed, for example, on the surface of the light guide plate 210. In another example, the grooves or ridges can be formed on the surface of the light guide plate 210 in a material other than the light guide material, for example, a film or layer of another material.

[0073] In some embodiments, the grating is a uniform grating, with a substantially constant or invariant spacing of the diffractive features across the entire grating. In other embodiments, the grating is a chirped grating. By definition, a "chirped" grating is a grating that exhibits or has a diffractive spacing of the diffractive features (i.e., grating pitch) that varies across its range or length. In some embodiments, a chirped grating has or can exhibit a chirp in the spacing of the diffractive features that varies linearly with distance. By definition, such a chirped grating is a "linearly chirped" grating. In other embodiments, a chirped grating can exhibit a non-linear chirp in the spacing of the diffractive features. A variety of non-linear chirps can be used, including, but not limited to, exponential chirp, logarithmic chirp, or another substantially non-uniform or irregular but monotonically varying chirp. Non-monotonic chirps can also be used, such as, but not limited to, sinusoidal chirp, triangular or sawtooth chirp. Any combination of these types of chirps can also be used.

[0074] According to various embodiments, the diffraction grating is a multi-combined output light beam. M and Then, the guided wave 204 In particular, the multiple gratings of the multi-beam element 232 can include a first grating and a second grating, as shown in more detail in connection with FIG.

[0075] The first grating can be configured to provide a first light beam of the plurality of scattered outputs or combined light beams as the emitted light 202, while the second grating can be configured to provide a second light beam of the plurality of scattered outputs or combined light beams as the emitted light 202. According to various embodiments, the first and second light beams can have different principal angular directions. Further, according to some embodiments, the plurality of gratings can include a third grating, a fourth grating, etc., each grating configured to provide a different combined light beam. In some embodiments, one or more gratings of the plurality of gratings can provide two or more combined light beams.

[0076] 5 illustrates a plan view of a scattering element 231, including a global mode mixer element 222, according to an embodiment consistent with principles described herein. The scattering element 231 may include multiple scattering sub-elements 233, including, for example, a first scattering sub-element 233a and a second scattering sub-element 233b. The multiple scattering sub-elements 233 may be arranged to scatter light from a surface of the light guide plate 210 (e.g., First and second 210′, 210″) or may be disposed inside the light guide plate 210. According to a particular embodiment, the scattering element 231 may be a multi-beam element, which may include multiple gratings. The scattering sub-elements 233, such as 233a and 233b, may be independent of each other and exhibit different grating characteristics. In FIG. 5, the size s of the scattering element 231 is shown, and the boundaries of the scattering element 231 are shown with dashed lines. When the scattering element 231 is a multi-beam element including multiple gratings, each grating may have one or more of the characteristics described above. For example, one or more of the gratings of the multiple gratings may be chirped, while other gratings are not chirped.

[0077] The scattering element 231 may have multiple scattering sub-elements 233 and may also include open areas without scattering sub-elements. A global mode mixer element 222 may also be disposed within such open areas without scattering sub-elements such that a global mode mixer is disposed at least partially within the scattering element 231 of the planar backlight. Some or all of the scattering sub-elements 233 may have curved diffractive features. Those skilled in the art will recognize that a variety of structures may be used to define the scattering sub-elements in or on the surface, including, for example, grooves, ridges, holes, and protrusions.

[0078] According to some embodiments, the scattering elements 231 may be configured to control the relative intensities of the multiple directional light beams of emitted light 202 combined out by each different scattering element 231. 231 Inside of A differential density of the scattering sub-elements 233 can be configured. In other words, the scattering element 231 can have scattering sub-elements 233 therein at various densities, and the various densities (i.e., differential density of the scattering sub-elements) can be configured to control the relative intensity of the multiple combined output light beams (e.g., 202). In particular, a scattering element 231 having fewer scattering sub-elements 233 in the multiple scattering sub-elements can generate multiple combined output light beams with a lower intensity (or beam density) than another scattering element 231 having a relatively larger number of scattering sub-elements 233. A differential density of the scattering sub-elements 233 can be provided using, for example, a location in the diffractive multi-beam element corresponding to the global mode mixer element 222 shown in FIG. 5. Although the entire area of ​​the scattering element 231 is shown as being occupied by either the scattering sub-elements 233 or the global mode mixer element 222, it should be understood that some areas in the scattering element may not include either structure.

[0079] Due to the differential density of the scattering sub-elements 233 within the scattering element, some free space remains within the scattering element 231. A global mode mixer can be placed within the remaining free space by using a differential spacing technique such that some or all of the free space remains open among the separately spaced scattering sub-elements 233 within the scattering element. Figure 5 shows an example of placing a global mode mixer in the area between the scattering sub-elements 233 of the scattering element 231.

[0080] Referring again to FIG. 3A, the flat backlight 200 may further comprise a light source 250. According to various embodiments, the light source 250 is configured to provide light guided within the light guide plate 210. In particular, the light source 250 may be located adjacent to an input surface or end (input end) of the light guide plate 210. In various embodiments, the light source 250 may comprise substantially any light source (e.g., light emitter), including, but not limited to, a light emitting diode (LED), a laser (e.g., a laser diode), or a combination thereof. In some embodiments, the light source 250 may comprise a light emitter configured to generate substantially monochromatic light having a narrowband spectrum exhibited by a particular color. In particular, the color of this monochromatic light may be a primary color of a particular color space or color model (e.g., red-green-blue (RGB) color model). In other examples, the light source 250 may be a substantially broadband light source configured to provide substantially broadband or polychromatic light. For example, the light source 250 may provide white light. In some embodiments, the light source 250 can include a plurality of different light emitters configured to provide light of different colors. The different light emitters can be configured to provide light having different color-specific non-zero propagation angles of the guided light corresponding to each of the different colors of light. According to various embodiments, the spacing and other scattering characteristics of the scattering features (e.g., periodicity of the scattering features, such as protrusions, holes, lattices, etc.) and the orientation of such features with respect to the propagation direction of the guided light can correspond to different colors of light. In other words, the scattering element 231 can be composed of different scattering elements of a plurality of scattering elements that can be tuned for different colors of the guided light, for example.

[0081] In some embodiments, the light source 250 may further comprise a collimator. The collimator may be configured to receive substantially uncollimated light from one or more of the light emitters of the light source 250. The collimator may further be configured to convert the substantially uncollimated light into collimated light. In particular, according to some embodiments, the collimator may provide collimated light having a non-zero propagation angle and collimated according to a predefined collimation factor. Furthermore, when light emitters of different colors are used, the collimator may be configured to provide collimated light having different color-specific non-zero propagation angles and / or having different color-specific collimation factors. The collimator may further be configured to transmit the collimated light beam to the light guide plate 210 for propagation as the guided light 204 described above.

[0082] In some embodiments, the planar backlight 200 is configured to be substantially transmissive to light passing through the light guide plate 210 in a direction perpendicular (or substantially perpendicular) to the propagation direction of the guided light 204. In particular, in some embodiments, the light guide plate 210 and the spaced apart scattering elements 231 (e.g., diffractive multi-beam elements) of the scattering structures 230 allow light to pass through the light guide plate 210 via both the first surface 210' and the second surface 210''. Transmittance can be facilitated, at least in part, by both the relatively small size of the scattering elements 231 and the relatively large inter-element spacing of the scattering structures 230 (e.g., one-to-one correspondence with the multi-view pixels 206). Furthermore, according to some embodiments, the scattering elements 231 of the scattering structures 230 are arranged in a manner that is substantially perpendicular to the propagation direction of the guided light 204. First and second It may be substantially transparent to light propagating perpendicular to the surfaces 210', 210''.

[0083] According to some embodiments of the principles described herein, a multi-view display is provided. The multi-view display is configured to emit modulated light beams as pixels of the multi-view display. The emitted modulated light beams have different principal angular directions (also referred to herein as "differently directed light beams"). Furthermore, the emitted modulated light beams can be preferentially directed to multiple view directions of the multi-view display. In a non-limiting example, the multi-view display can include views having a number of view directions corresponding to four-by-eight (4×8) or eight-by-eight (8×8). In some examples, the multi-view display is configured to provide or "display" a 3D image or a multi-view image. According to various examples, each of the modulated and differently directed light beams can correspond to individual pixels of different "views" associated with the multi-view image. These different views can, for example, provide a "glasses-free" (e.g., autostereoscopic) representation of information in the multi-view image displayed by the multi-view display.

[0084] FIG. 6 illustrates a flow chart of a method of operating a flat backlight consistent with principles disclosed herein. The method of operating a flat backlight can include the step 610 of directing light as guided light generally along a length of a light guide. The guided light can include at least a first directional mode and a second directional mode. As the light is directed along the length of the light guide, a portion of the light directed in the first directional mode is converted to light in the second directional mode in step 620 using a global mode mixer that extends along the length of the light guide. The method of operating a flat backlight can further include the step 630 of preferentially scattering light out of the light guide using a scattering structure to provide emitted light. The scattering structure is configured to preferentially scatter light propagating in the second directional mode out of the light guide. The light directed in the first directional mode can have one or both of a lateral component that is greater than the lateral component of the light directed in the second directional mode and a vertical component that is less than the vertical component of the light directed in the second directional mode. According to various embodiments, the global mode mixer converts the guided light portion of the first directional mode into guided light of a second directional mode, which includes one or both of a reduction in a transverse component of the guided light portion and an increase in a longitudinal component of the guided light portion.

[0085] When used in this method of operating a planar backlight, the global mode mixer can be implemented as a diffraction grating. In such an embodiment, the diffraction grating can extend along the length and across the width of a light guide, such as a light guide plate. In such a case, the diffractive features of the diffraction grating are aligned parallel to the propagation direction of the guided light along the length of the light guide plate. Instead of or in combination with the diffractive features, the global mode mixer can perform mode mixing using a reflective element having reflective facets aligned parallel to the propagation direction of the guided light along the length of the light guide plate. The method can further include using a scattering structure including an array of scattering elements spaced apart along the length of the light guide. In such a method, the conversion of light from a first directional mode to a second directional mode can be performed using a global mode mixer disposed between each spaced apart scattering element of the scattering elements.

[0086] Other aspects of the exemplary method can include use of a scattering structure including an array of multi-beam elements, each of which can scatter the guided light out of the light guide in the second directional mode as emitted light including a directional light beam having a direction corresponding to a view direction of a view of the multi-view image, and the method of operating the planar backlight further includes modulating the directional light beam of emitted light to provide the multi-view image. [Explanation of symbols]

[0087] 101 First directional mode 102 Second directional mode 103 Third directional mode 104 4th directional mode 200 Flat Backlight 202 Synchrotron Radiation 204 Waveguide Light 206 Multiview Pixels 208 Light bulb 208a First set of light valves 208b Second set of light valves 210 Light guide plate 210' First Surface 210'' Second Surface 220 Global Mode Mixer 221 mode mixer element 222 Global Mode Mixer Element 230 Scattering structure 231 Scattering Elements 231a First scattering element 231b Second scattering element 232 Multi-Beam Element 233 Scattering Sub-Elements 233a First scattering sub-element 233b Second scattering subelement 250 light source 302 Light Beam 304 Waveguide 322 Multi-beam elements 610 Guiding light along a light guide 620 Converting light from a first directional mode to a second directional mode 630 Preferentially scattering light of a second mode xx direction yy direction zz direction nx vector component ny vector components nz vector components D Center distance d Center distance S size

Claims

1. A flat backlight, comprising: a light guide plate configured to guide light along a length of the light guide plate as guided light; a global mode mixer extending along a length of the light guide plate, the global mode mixer configured to convert a portion of the light directed in a first directional mode to light directed in a second directional mode; a scattering structure configured to preferentially scatter the light guided in the second directional mode out of the light guide plate as radiation, the light directed in the first directional mode has one or both of a lateral component that is greater than a lateral component of the light directed in the second directional mode and a longitudinal component that is less than a longitudinal component of the light directed in the second directional mode; the scattering structure includes an array of scattering elements spaced apart from one another along a length of the light guide plate, the global mode mixers being distributed between each spaced apart scattering element of the array of scattering elements; A planar backlight, wherein each scattering element of the array of scattering elements includes a plurality of scattering sub-elements, and the global mode mixers are further distributed within the scattering element and between each scattering sub-element of the plurality of scattering sub-elements.

2. 2. The flat backlight of claim 1, wherein the global mode mixer is configured to convert the guided light portion of the first directional mode into guided light of the second directional mode, the second directional mode including one or both of a decrease in a horizontal component of the guided light portion and an increase in a vertical component of the guided light portion.

3. The planar backlight of claim 1 , wherein the global mode mixer is disposed on a surface of the light guide plate.

4. The planar backlight of claim 3 , wherein the scattering structures are disposed on a surface of the light guide plate opposite to a surface on which the global mode mixer is disposed.

5. 2. The flat backlight of claim 1, wherein the global mode mixer comprises a diffraction grating extending across the lateral width of the light guide plate and along the length of the light guide plate, diffractive features of the diffraction grating being aligned parallel to the propagation direction of the guided light along the length of the light guide plate.

6. The planar backlight of claim 1 , wherein the global mode mixer comprises a reflective element having reflective facets aligned parallel to a direction of propagation of the guided light along a length of the light guide plate.

7. 2. The flat backlight of claim 1 , wherein each scattering element of the array of scattering elements comprises a multi-beam element, each of the multi-beam elements configured to scatter the guided light out of the light guide plate in the second directional mode as emitted light comprising a directional light beam having a direction corresponding to a view direction of a view of a multi-view image.

8. The planar backlight of claim 7 , wherein each of the multi-beam elements includes one or more of a diffraction grating, a micro-reflective element, and a micro-refractive element.

9. 8. A multi-view display including a planar backlight as described in claim 7, further including an array of light valves configured to modulate the directional light beams of the emitted light to provide the multi-view image, the multi-beam elements having a size of the array of light valves between 25% and 200% of the size of the light valves.

10. 1. A multi-view backlight, comprising: A light guide plate configured to guide light as guided light; an array of multi-beam elements arranged along a length of the light guide plate, each of the multi-beam elements configured to scatter the guided light out of the light guide plate as radiation comprising directional light beams having directions corresponding to different view directions of a multi-view image; and global mode mixers distributed among the multi-beam elements of the array of multi-beam elements, the global mode mixers configured to convert light directed according to a first directional mode into light directed according to a second directional mode; each multi-beam element is configured to preferentially scatter output light directed according to the second directivity mode relative to light directed according to the first directivity mode; A multi-view backlight, wherein the global mode mixer is disposed on a surface of the light guide plate, and the array of multi-beam elements is disposed adjacent to the surface on which the global mode mixer is disposed.

11. The light guided according to the first directional mode comprises: a transverse component of light guided according to the second directional mode that is greater than a transverse component; and a light having a longitudinal component smaller than the longitudinal component of the light guided according to the second directional mode, or both; 11. The multi-view backlight of claim 10, wherein the global mode mixer is configured to convert light guided according to the first directional mode into light guided according to the second directional mode, the second directional mode including one or both of a reduction in a lateral component and an increase in a vertical component of the guided light.

12. 11. The multi-view backlight of claim 10, wherein the global mode mixer comprises a diffraction grating extending across a lateral width of the light guide plate and along the length of the light guide plate between each multibeam element of the array of multibeam elements, diffractive features of the diffraction grating aligned parallel to a direction of propagation of the guided light along the length of the light guide plate.

13. 11. The multi-view backlight of claim 10, wherein the global mode mixer comprises one or both of a reflective element and a refractive element, the reflective element having reflective facets aligned parallel to a propagation direction of the guided light along a length of the light guide plate, and the global mode mixer extends across a lateral width of the light guide plate and along the length of the light guide plate between each multibeam element of the array of multibeam elements.

14. 11. A multi-view display including a multi-view backlight as claimed in claim 10, further comprising an array of light valves configured to modulate the directional light beams of the emitted light to provide the multi-view image, the multi-beam elements having a size of the array of light valves between 25% and 200% of the size of the light valves.

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