Patent Description:
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 active displays. 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.

<CIT> discloses a backlight unit and a display device. The backlight unit includes at least one light source unit and a light guide plate. The light source unit provides collimated light.

<CIT> discloses a backlight module and a display device. The backlight module includes a light source and a light guide plate and a polarizing beam-splitting clement configured to convert the parallel rays into a first polarized ray and a second polarized ray.

Examples and embodiments in accordance with the principles described herein provide backlighting employing polarization-preserving scattering with application to electronic displays. In various embodiments consistent with the principles described herein, a polarized backlight employing a polarization-preserving scattering feature is provided. A light source is employed to provide polarized light to the polarized backlight. The polarization-preserving scattering feature is configured to provide emitted light that preserves or at least substantially preserves a polarization of light generated by the light source. In some embodiments, the emitted light is configured to match a polarization of a light valve array configured to modulate the emitted polarized light as modulated polarized light representing pixels of a display. This may obviate a need for a polarizing element such a polarizing film at either an input to the light valve array or an output of the polarized backlight, in some embodiments.

According to various embodiments, the polarization-preserving scattering feature includes a polarization-preserving scattering element that may comprise one or both of a diffractive grating and any of various microprism structures to scatter out guided polarized light as emitted polarized light. In particular, the polarization-preserving scattering feature may comprise a plurality of polarization-preserving scattering elements spaced apart from one another and having a density within the polarization-preserving scattering feature configured to control an intensity of the emitted light. The polarized backlight may further comprise a collimator configured to collimate light communicated to the light guide. The polarization-preserving scattering feature may further provide angle-preserving scattering in some embodiments. As such, the polarization-preserving scattering feature may also be an angle-preserving scattering feature configured to preserve a spread angle or 'collimation factor' of the polarized guided light in the emitted light. This may eliminate the need for a collimator element at the output of the polarized backlight, in some embodiments.

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

Herein, 'polarized light' is defined as light having a predetermined or predefined polarization. In some embodiments, the predetermined polarization is a linear polarization having selectively oriented polarization components. In particular, the polarized light may have a predetermined polarization comprising a first polarization component and a second polarization component. The first polarization component may be a transverse electric (TE) polarization component, while the second polarization component may be a transverse magnetic (TM) polarization component. In some embodiments, the TE component may be selectively oriented to be parallel to a surface of a light guide.

Herein, a 'light guide' is defined as a structure that guides light within the structure using total internal reflection. In particular, the light guide may include a core that is substantially transparent at an operational wavelength of the light guide. 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.

Herein, a 'polarization-preserving scattering feature' or equivalently a 'polarization-preserving scatterer' is defined as any feature or scatterer configured to scatter light in a manner that substantially preserves in scattered light a polarization or at least a degree of polarization of the light incident on the feature or scatterer. In some embodiments, light may comprise a polarized portion and an unpolarized portion. By definition, therefore, a degree of polarization of light is a measure of the polarization of light, and specifically, the fraction of light that is polarized. In some embodiments, the degree of polarization of light may be given by equation (<NUM>) as: <MAT> where V is the degree of polarization, Ip is an intensity of the polarized portion of the light, and In is an intensity of the unpolarized portion of the light. Accordingly, a 'polarization-preserving scattering feature' may be further defined as any feature or scatterer where a degree of polarization of a light incident on the feature or scatterer is substantially equal to the degree of polarization of the scattered light.

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

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

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

Herein, a 'microprism structure' is generally defined as a structure comprising a microprism or a plurality of microprisms having an inclined sidewall(s) and configured to refractively scatter light incident on the microprism structure. If the light is incident on the microprism structure from a light guide, the microprism structure may be understood as a structure comprising a microprism or a plurality of microprisms configured to refractively couple out or scatter out light from the light guide. In some embodiments, the microprism structure can comprise a first microprism layer and a second microprism layer disposed adjacent to and separated by a gap from the first microprism layer. Herein therefore, a 'microprism layer' is defined as a plurality of microprisms disposed or arrayed in or on a material layer of film. In some embodiments, microprisms of the first and second microprism layers may have inclined sidewalls with complimentary slopes. The inclined sidewalls of the second microprism layer may be configured to reflect light at an interior surface of the sidewalls to provide emitted light. In some embodiments, the microprisms of the first and second microprism layers may include curved microprisms.

According to various embodiments, the microprism structure may comprise an inverted microprism element. By definition herein, an 'inverted microprism element' is a microprism having a truncated conical shape with an input aperture, an inclined sidewall, and an output aperture that is larger than the input aperture. In particular, the input aperture is configured to receive light and the inclined sidewall is configured to reflect the light received through the input aperture, whereas the output aperture is configured to emit the reflected light. Thus, the input aperture is a portion of the inverted microprism element comprising an optical connection between the inverted microprism element and the light guide, and configured to receive extracted or coupled-out light from the light guide. The inclined sidewall comprises an interior surface of the inverted microprism element that is configured to reflect light. In some embodiments, the inclined sidewall may comprise a reflective layer or reflective material (e.g., a reflective material layer on an exterior surface of the sidewall). The reflective layer may be configured to provide or enhance reflection at the interior surface of the inverted microprism element. The reflected light is emitted from the output aperture of the inverted microprism element.

Herein a 'collimator' is defined as substantially any optical device or apparatus that is configured to collimate light. According to various embodiments, an amount of collimation provided by the collimator may vary in a predetermined degree or amount from one embodiment to another. Further, the collimator may be configured to provide collimation in one or both of two orthogonal directions (e.g., a vertical direction and a horizontal direction). That is, the collimator may include a shape in one or both of two orthogonal directions that provides light collimation, according to some embodiments.

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

Herein, 'angle-preserving scattering' is defined as scattering of light in a manner that substantially preserves in scattered light a collimation factor of incident light. That is, 'angle-preserving scattering' comprises scattering of light in a manner that substantially preserves an angular spread of light incident on a feature or scatterer. In particular, by definition, an angular spread σs of light scattered by an angle-preserving scattering feature is a function of an angular spread σ of the incident light (i.e., σs = f(σ) ). In some embodiments, the angular spread σs of the scattered light is a linear function of the angular spread or collimation factor σ of the incident light (e.g., σs = a·σ, where a is an integer). That is, the angular spread σs of light scattered by an angle-preserving scattering feature may be substantially proportional to the angular spread or collimation factor σ of the incident light. For example, the angular spread σs of the scattered light may be substantially equal to the incident light angular spread σ (e.g., σs ≈ σ). A uniform diffraction grating (i.e., a diffraction grating having a substantially uniform or constant diffractive feature spacing or grating pitch) is an example of an angle-preserving scattering feature.

Further, as used herein, the article 'a' is intended to have its ordinary meaning in the patent arts, namely 'one or more'. For example, 'a polarization-preserving scattering feature' means one or more a polarization-preserving scattering features and as such, 'the polarization-preserving scattering feature' means 'polarization-preserving scattering feature(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 <NUM>%, or plus or minus <NUM>%, or plus or minus <NUM>%, unless otherwise expressly specified. Further, the term 'substantially' as used herein means a majority, or almost all, or all, or an amount within a range of about <NUM>% to about <NUM>%. 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 polarized backlight is provided. <FIG> illustrates a cross-sectional view of a polarized backlight <NUM> in an example, according to an embodiment consistent with the principles described herein. <FIG> illustrates a plan view of a polarized backlight <NUM> in an example, according to an embodiment consistent with the principles described herein. <FIG> illustrates a perspective view of a polarized backlight <NUM> in an example, according to an embodiment consistent with the principles described herein. The illustrated polarized backlight <NUM> may be used for backlighting in an electronic display including, but not limited to, a backlit display, for example. According to various embodiments and as described below, the polarized backlight <NUM> may comprise a light guide <NUM>, a polarization-preserving scattering feature <NUM>, and a light source <NUM>.

The polarized backlight <NUM> illustrated in <FIG> is configured to provide coupled-out or emitted light <NUM> having a predetermined polarization. As such, the emitted light <NUM> may be emitted polarized light, according to various embodiments. The emitted light <NUM> is directed away from a surface (e.g., a first surface <NUM>' of the light guide <NUM>) of the polarized backlight <NUM>, as illustrated. The emitted light <NUM> may be employed to illuminate or serve as an illumination source for an electronic display. In particular, the emitted light <NUM> may be modulated (e.g., using light valves, as described below) to facilitate the display of information (e.g., images) by the electronic display, for example.

As illustrated in <FIG>, the polarized backlight <NUM> comprises a light source <NUM>. According to various embodiments, the light source <NUM> is configured to provide polarized light to be guided within the light guide <NUM>, as described below. In particular, the light source <NUM> may be located adjacent to an entrance surface or end (input end) of the light guide <NUM>. In various embodiments, the light source <NUM> may comprise substantially any source of light (e.g., optical emitter) including, but not limited to, a light emitting diode (LED), a laser (e.g., laser diode) or a combination thereof. In some embodiments, the light source <NUM> may comprise an optical emitter <NUM> configured to produce a substantially monochromatic light having a narrowband spectrum denoted by a particular color. In particular, the color of the monochromatic light may be a primary color of a particular color space or color model (e.g., a red-green-blue (RGB) color model). In other examples, the light source <NUM> may be a substantially broadband light source configured to provide substantially broadband or polychromatic light. For example, the light source <NUM> may provide white light. In some embodiments, the light source <NUM> may comprise a plurality of different optical emitters configured to provide different colors of light. The different optical emitters <NUM> may 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.

In embodiments noted above, the light source <NUM> is configured to emit polarized light. In some embodiments, the light source <NUM> may comprise an optical emitter <NUM> configured to produce polarized light. That is, the optical emitter <NUM> may be configured to emit light having a predetermined polarization. In some embodiments, the optical emitter <NUM> is configured to provide light comprising a transverse electric (TE) polarization component. In other embodiments, the optical emitter <NUM> is configured to provide light comprising a transverse magnetic (TM) polarization component. In some embodiments, the light source <NUM> may comprise an optical emitter <NUM> configured to emit unpolarized or non-polarized light. In these embodiments, the light source <NUM> may further comprise a polarizing element or polarizer (not shown) disposed between the optical emitter <NUM> and an output of the light source <NUM>, the polarizing element configured to polarize the unpolarized or non-polarized light provided by the optical emitter <NUM> of the light source <NUM>. For example, the polarizing element may be configured to receive unpolarized light and selectively transmit a portion of the received light in which transverse electric (TE) polarization component is selectively oriented. In this way, the light emitted by the light source <NUM> is polarized light regardless of embodiment.

As illustrated in <FIG>, the polarized backlight <NUM> further comprises a light guide <NUM>. The light guide <NUM> may be a plate light guide, according to some embodiments. The light guide <NUM> is configured to guide light along a length of the light guide <NUM> as guided light <NUM>. In particular, the light guide <NUM> is configured to guide the polarized light provided by the light source <NUM> as a guided 'polarized' light <NUM>. For example, the light guide <NUM> may include a dielectric material configured as an optical waveguide. The dielectric material of the optical waveguide 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 polarized light <NUM> according to one or more guided modes of the light guide <NUM>. In <FIG>, a general propagation direction <NUM> of the guided polarized light <NUM> is indicated by bold arrows.

In some embodiments, the dielectric optical waveguide of the light guide <NUM> may be a slab or plate optical waveguide comprising an extended, substantially planar sheet of optically transparent, dielectric material. According to various examples, the optically transparent, dielectric material of the light guide <NUM> may include or be made up of any of a variety of dielectric materials including, but not limited to, one or more of various types of glass (e.g., silica glass, alkali-aluminosilicate glass, borosilicate glass, etc.), one or more substantially optically transparent plastics or polymers (e.g., poly(methyl methacrylate) or 'acrylic glass', polycarbonate, etc.) or a combination thereof. In some embodiments, the light guide <NUM> may further include a cladding layer (not illustrated) on at least a portion of a surface (e.g., one or both of a top surface and a bottom surface) of the light guide <NUM>. The cladding layer may be used to further facilitate total internal reflection, according to some examples.

According to some embodiments, the light guide <NUM> is configured to guide the guided polarized light <NUM> according to total internal reflection at a non-zero propagation angle between a first surface <NUM>' (e.g., 'front' surface or side) and a second surface <NUM>" (e.g., 'back' surface or side) of the light guide <NUM>. In particular, the guided polarized light <NUM> may propagate by reflecting or 'bouncing' between the first surface <NUM>' and the second surface <NUM>" of the light guide <NUM> at the non-zero propagation angle (albeit in the propagation direction <NUM> indicated by the bold arrows).

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

In some embodiments, the guided polarized light <NUM> may be collimated or equivalently may be a collimated light beam (e.g., provided by a collimator <NUM>, described below). Herein, a 'collimated light' or 'collimated light beam' is generally defined as a beam of light in which rays of the light beam are substantially confined to a predetermined or defined angular spread within the light beam (e.g., the guided polarized light <NUM>). Further, rays of light that diverge or are scattered from the collimated light beam are not considered to be part of the collimated light beam, by definition herein. Moreover, the guided polarized light <NUM> may be collimated according to or having a collimation factor σ, in various embodiments.

In some embodiments, the light guide <NUM> may be configured to 'recycle' the guided polarized light <NUM>. In particular, the guided polarized light <NUM> that has been guided along the light guide length may be redirected back along that length in another propagation direction that differs from (e.g., is opposite to) the propagation direction <NUM>. For example, the light guide <NUM> may include a reflector (not illustrated) at an end of the light guide <NUM> opposite to an input end or entrance edge adjacent to the light source. The reflector may be configured to reflect the guided polarized light <NUM> back toward the entrance edge as recycled guided light. Alternatively (e.g., as opposed to recycling guided light), guided polarized light <NUM> propagating in the other propagation direction may be provided by introducing light into the light guide <NUM> with the other propagation direction (e.g., in addition to guided polarized light <NUM> having the propagation direction <NUM>). Recycling guided polarized light <NUM> or alternatively providing guided polarized light <NUM> in the other propagation direction may increase a brightness of the polarized backlight <NUM> (e.g., an intensity of the light beams of the emitted light <NUM>) by making guided light available to be scattered out of the polarized backlight <NUM> more than once, for example, e.g., by polarization preserving scatterers and angle-preserving scatterers described below.

According to various embodiments, the light guide <NUM> has a polarization-preserving scattering feature <NUM>. The polarization-preserving scattering feature <NUM> is configured to scatter a portion of the guided polarized light <NUM> out of the light guide <NUM> as the emitted light <NUM>. In some embodiments (e.g., as illustrated), the polarization-preserving scattering feature <NUM> comprises a plurality of polarization-preserving scatterers. In particular, individual polarization-preserving scatterers of the polarization-preserving scattering feature <NUM> may be discrete structures, elements or features that are spaced apart from one another, each discrete structure being configured to scatter or couple-out a different portion of the guided polarized light <NUM> in a polarization-preserving manner. In various embodiments, the polarization-preserving scattering feature <NUM> may comprise any of a variety of different structures or features that provide or are configured to produce polarization-preserving scattering including, but not limited to, a diffraction grating, a reflective structure, and a refractive structure (e.g., a microprism structure, as described below) as well as various combinations thereof. Further, the polarization-preserving scattering feature <NUM> may also provide angle-preserving scattering and thus may comprise an angle-preserving scatterer or also be an angle-preserving scattering feature, according to various embodiments.

Referring to <FIG>, the polarization-preserving scattering feature <NUM> may comprise a plurality of polarization-preserving scattering elements <NUM>' spaced apart from one another one or both of across a width and along a length of the light guide. In particular, the polarization-preserving scattering elements <NUM>' may be separated from one another by a finite space and represent individual, distinct elements along the light guide length. That is, by definition herein, polarization-preserving scattering elements <NUM>' 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 polarization-preserving scattering elements <NUM>' generally do not intersect, overlap or otherwise touch one another, according to some embodiments. That is, each polarization-preserving scattering element <NUM>' of the plurality is generally distinct and separated from other ones of the polarization-preserving scattering elements <NUM>'.

In various embodiments, the plurality of polarization-preserving scattering elements <NUM>' may be arranged in a variety of configurations that are one or more of at, on and in the surface (e.g., the first surface <NUM>' or the second surface <NUM>") of the light guide <NUM>. For example, polarization-preserving scattering elements <NUM>' may be arranged in columns and rows across the light guide surface (e.g., as an array). In another example, a plurality of polarization-preserving scattering elements <NUM>' may be arranged in groups and the groups may be arranged in rows and columns. In yet another example, illustrated in <FIG>, the plurality of polarization-preserving scattering elements <NUM>' may be distributed substantially randomly across the surface of the light guide <NUM>.

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

In some embodiments, a spatial density of polarization-preserving scattering elements within the plurality of polarization-preserving scattering elements <NUM>' is configured to control an intensity of the emitted light <NUM>, as illustrated in <FIG>. In particular, the spatial density may be a function of distance from the light source <NUM>. That is, an inter-element distance (e.g., center-to-center distance or spacing) between the polarization-preserving scattering elements <NUM>' may be varied or modulated across a length or a width of the light guide <NUM> or both as a function of distance from the light source <NUM>. In some embodiments, the spatial density grows with the distance from the light source <NUM>. That is, the inter-element distance between polarization-preserving scattering elements <NUM>' diminishes with distance from the light source <NUM>. Accordingly, polarization-preserving scattering elements <NUM>' are spaced further apart near the light source <NUM>, and spaced closer together when further from the light source <NUM>. The spatial density of polarization-preserving scattering elements <NUM>' may vary with distance from the light source <NUM> according to a variety of patterns. In some embodiments, the spatial density may be varied linearly with the distance from the light source <NUM>. In other embodiments, the spatial density may be varied non-linearly with the distance from the light source <NUM>. For example, the variation of the spatial density based on the polarization-preserving scattering element's distance from the light source <NUM> may be exponential, logarithmic, or other substantially non-uniform or random but still monotonic manner. Non-monotonic density variations such as, but not limited to, a sinusoidal variation or a triangular or sawtooth variation, may also be employed, as well as combinations of any of these variations.

Further, an intensity of the emitted polarized light increases with the spatial density of polarization-preserving scattering elements <NUM>'. The increased intensity may reflect a coupling efficiency of the polarization-preserving scattering elements, according to some embodiments. That is, for a given intensity of guided polarized light coupled out by a polarization-preserving scattering element, elements with smaller inter-element distance may produce emitted light of higher intensity than elements with larger inter-element distance. Further, in some embodiments, an intensity of the guided polarized light <NUM> propagated through the light guide <NUM> decreases with distance from the light source <NUM>. In such embodiments, a spatial density of polarization-preserving scattering elements <NUM>' increases with distance from the light source to compensate for the diminishing intensity in the guided polarized light and couple out light of substantially equal intensity. In embodiments, therefore, the spatial density of the polarization-preserving scattering elements <NUM>' may be varied or modulated to produce a substantially uniform intensity of emitted light across the light guide.

Referring to <FIG>, the polarization-preserving scattering elements <NUM>' of the polarization-preserving scattering feature <NUM> may comprise a diffraction grating <NUM>. The diffraction grating <NUM> is configured to scatter or couple out a portion of the guided polarized light <NUM> from the light guide <NUM> by or using diffractive coupling (also referred to as 'diffractive scattering'), according to various embodiments. The portion of the guided polarized light <NUM> may be diffractively coupled out by the diffraction grating <NUM> through the light guide surface (e.g., through the first surface <NUM>' of the light guide <NUM>). Further, the diffraction grating <NUM> is configured to diffractively couple or scatter out the portion of the guided polarized light <NUM> as the emitted light <NUM>. The emitted light <NUM> is directed away from the first surface <NUM>' of the light guide <NUM>, according to various examples. In particular, the coupled-out portion of the guided polarized light <NUM> is diffractively redirected away from the light guide surface by the diffraction grating <NUM> as the emitted light <NUM>.

The diffraction grating <NUM> may be located on either the first surface <NUM>' (e.g., 'front' surface or side) or the second surface <NUM>" (e.g., 'back' surface or side) of the light guide <NUM>. On the first surface <NUM>', the diffraction grating operates in a transmission mode, as described above. That is, the diffraction grating <NUM> is configured to diffractively redirect guided polarized light <NUM> that is transmitted or passes through diffraction grating <NUM> as emitted light. The emitted light <NUM> is directed away from the first surface <NUM>' of the light guide, as described above. Alternatively, the diffraction grating may be located on the second surface <NUM>" (not illustrated). In this configuration, the diffraction grating operates in a reflection mode. The reflection mode diffractive grating is configured to diffractively redirect guided polarized light <NUM> into the light guide <NUM> using reflective diffraction (i.e., reflection and diffraction). The diffractively redirected light is emitted from the first surface <NUM>' as emitted light <NUM>.

According to various embodiments, the diffraction grating <NUM> comprises a plurality of diffractive features <NUM>' that diffract light (i.e., provide diffraction). The diffraction is responsible for the diffractive coupling of the portion of the guided polarized light <NUM> out of the light guide <NUM>. For example, the diffraction grating <NUM> may include one or both of grooves in a surface of the light guide <NUM> and ridges protruding from the light guide surface that serve as the diffractive features <NUM>'. The grooves and ridges may be arranged parallel or substantially parallel to one another and, at least at some point, perpendicular to a propagation direction of the guided polarized light <NUM> that is to be coupled out by the diffraction grating <NUM>. As illustrated in <FIG>, a diffraction pattern of the diffraction grating <NUM> is depicted as alternating black and white bands representing diffractive features of the diffraction grating <NUM>, e.g., one or both of grooves and ridges in a surface of the light guide <NUM>.

In some examples, the diffractive features may be etched, milled or molded into the surface or applied on the surface. As such, a material of the diffraction grating <NUM> of the polarization-preserving scattering feature <NUM> may include a material of the light guide <NUM>. As illustrated in <FIG>, for example, the diffraction gratings <NUM> comprise substantially parallel grooves formed in the surface of the light guide <NUM>, by way of example and not limitation. In another example (not illustrated), the diffraction gratings <NUM> may comprise substantially parallel ridges that protrude from the light guide surface. In yet other examples (also not illustrated), the diffraction gratings <NUM> may be implemented in or as a film or layer applied or affixed to the light guide surface.

In some embodiments, diffraction grating <NUM> of the polarization-preserving scattering feature <NUM> may comprise curved diffractive features <NUM>" or diffractive features arranged to approximate a curve. As illustrated in <FIG>, the diffractive features are curved diffractive features, by way of example and not limitation. In particular, as shown in <FIG>, concentric black and white curved lines may represent concentric curved diffractive features (e.g., both of concentric curved ridges and concentric curved grooves) on or in the light guide surface. In some embodiments, the curved diffractive features of the diffraction grating <NUM> may be represented by semicircles (i.e., may be semicircular curved diffractive features), while in other embodiments, another substantially non-circular curve may be employed to realize the curved diffractive features.

According to various embodiments, the polarization-preserving scattering elements <NUM>' of the polarization-preserving scattering feature <NUM> may comprise a microprism structure <NUM>, e.g., as illustrated in <FIG>. The microprism structure <NUM> of <FIG> comprises a plurality of microprisms <NUM> configured to refractively scatter light incident on the microprism structure <NUM>. As illustrated in <FIG>, the microprism structure <NUM> may be disposed adjacent the light guide <NUM>. In particular, the microprism structure <NUM> may be in contact with a surface (e.g., the first surface <NUM>') of the light guide <NUM>, in some embodiments. For example, the microprism structure <NUM> may be partially formed in a surface (e.g., the first surface <NUM>') of the light guide <NUM>, as illustrated in <FIG>. The microprism structure <NUM> is thus configured to refractively scatter out of the light guide <NUM> a portion of the guided polarized light <NUM> as the emitted light <NUM>.

In some embodiments, the microprism structure <NUM> may comprise a first microprism layer and a second microprism layer disposed adjacent to and separated by a gap from the first microprism layer. In other embodiments, the microprism structure may comprise an inverted microprism element. For example, as illustrated in <FIG>, the microprism structure <NUM> comprises a first microprism layer 124a and a second microprism layer 124b. The first microprism layer 124a is configured to refractively couple out of the light guide <NUM> a portion of the guided polarized light <NUM>. For example, the first microprism layer 124a may locally defeat total internal reflection such that the guide polarized light portion is able to escape or leak out of the light guide <NUM> (e.g., as illustrated in <FIG> by an extended arrow that is depicted exiting the light guide <NUM> through a surface or facet of the first microprism layer 124a). The refractively coupled-out light is subsequently scattered out as emitted light <NUM> by the second microprism layer 124b using reflection, as will be described further below.

In various embodiments, the first microprism layer 124a comprises a plurality of substantially parallel elongated ridges or microprisms <NUM>, each microprism <NUM> being separated from an adjacent microprism <NUM> by an intervening region or groove <NUM>'. That is, a microprism <NUM> of the first microprism layer 124a may comprise an elongated microprism <NUM> situated between two substantially parallel grooves <NUM>'. Thus the first microprism layer 124a comprises a plurality of alternating microprisms <NUM> and grooves <NUM>'. In some examples, the microprisms <NUM> may be raised up from or protrude above a surface of the first microprism layer 124a or equivalent the first surface <NUM>' of the light guide <NUM>. Alternatively, a pair of closely-spaced, parallel grooves <NUM>' may be formed or otherwise provided in the surface of the first microprism layer 124a (or the light guide first surface <NUM>') to form a microprism <NUM> between the grooves <NUM>'.

In accordance with various embodiments, a microprism <NUM> of the first microprism layer 124a may have inclined or sloped sidewalls <NUM>" that join as an apex to form the microprism <NUM> having a substantially triangular cross-section, as illustrated in <FIG>. That is, the first microprism layer 124a may comprise a microprism <NUM> having a triangular cross-sectional profile. In other embodiments (not illustrated), the microprism <NUM> of the first microprism layer 124a may have a sawtooth cross-sectional profile. In yet other embodiments, the microprism <NUM> of the first microprism layer 124a may have a pyramid structure (not illustrated). The pyramid-shaped microprism <NUM> may be raised up from a surface of the first microprism layer 124a. In some embodiment, the pyramid may be formed by grooves carved into the surface of the first microprism layer 124a. That is, the microprism <NUM> of the first microprism layer 124a may be formed by two normally intersecting pairs of closely spaced, substantially parallel grooves having inclined sidewalls. In such embodiments, the first microprism layer 124a thus comprises an array of pyramid microprisms. The microprism layer may comprise an array of microprisms <NUM> having a variety of other shapes such as, but not limited to, a rectangular, pentagonal, or other polygonal or non-polygonal prism or pyramid.

According to various examples, the first microprism layer 124a is disposed adjacent a surface of the light guide <NUM>. In some embodiments, the first microprism layer 124a may be in contact with the first surface <NUM>' of the light guide <NUM>. In some of these embodiments, the first microprism layer 124a may be integrally formed with or in the surface <NUM>' of the light guide <NUM>, e.g., as shown in <FIG>. This is the case in embodiments where the microprisms are formed with grooves <NUM>' provided into the surface of the first microprism layer 124a and therefore of the light guide <NUM>. In such embodiments, the microprisms <NUM> may comprise a material of the light guide <NUM>. In other embodiments, the first microprism layer 124a may be a layer adjacent or affixed to a surface of the light guide <NUM>. In these embodiments, the microprism <NUM> or the first microprism layer 124a, as a whole, may also comprise that includes either a material of the light guide <NUM> or a different material having substantially the same optical properties has the light guide <NUM>. In particular, the first microprism layer 124a and microprisms <NUM> thereof may comprise material having a dielectric material with the same refractive index as the light guide <NUM>.

According to various embodiments, the microprism structure <NUM> may comprise a second microprism layer 124b. The second microprism layer 124b is configured to scatter out the refractively coupled out guided light portion provided by the first microprism layer 124a using reflection. The second microprism layer 124b is disposed adjacent the first microprism layer 124a and is separated therefrom by a gap <NUM>', as illustrated in <FIG>. In some embodiments, the second microprism layer 124b is disposed on top of first microprism layer 124aand faces the first microprism layer 124a such that the gap <NUM>' is provided between microprisms <NUM> of the first microprism layer 124a and complementary microprisms <NUM> of the second microprism layer 124b. In particular, the second microprism layer 124b may be substantially similar to the first microprism layer 124a such that sloped or inclined sidewalls <NUM>" of microprisms <NUM> of the first and second microprism layers 124a, 124b have complimentary slopes.

According to various embodiments, the inclined sidewalls <NUM>" of the microprisms <NUM> of the second microprism layer 124b are configured to reflect the refractively coupled-out guided light portion at an interior surface of the inclined sidewalls <NUM>" to provide the emitted light <NUM>, e.g., as illustrated in <FIG>. Accordingly, a microprism <NUM> of the first microprism layer 124a may be disposed inside an intervening region or groove of the second microprism layer 124b or between adjacent microprisms <NUM> thereof, such that the gap <NUM>' separates respective inclined sidewalls <NUM>" of the microprisms <NUM> of the first and second microprism layers 124a, 124b.

According to various embodiments, the gap <NUM>' comprises a medium having a dielectric material with a refractive index that is less than a refractive index of the respective first and second microprism layers 124a, 124b. As discussed above, in some embodiments, the first microprism layer 124a and the light guide <NUM> may comprise the same material or dielectric material having substantially the same refractive index. Accordingly, the gap <NUM>' may comprise a medium having a dielectric material with a refractive index that is lower than a refractive index of the light guide <NUM> and first microprism layer 124a. For example, the gap <NUM>' between the first and second microprism layers 124a, 124b may comprise air or a similar low refractive index material. The lower refractive index of material within the gap <NUM>' provides a condition for total internal reflection within the light guide and the first microprism layer 124a. Further, the greater refractive index of microprisms <NUM> in the second microprism layer 124b relative to that of the gap <NUM>' provides an optical boundary between the microprisms <NUM> thereof and the gap <NUM>' to support total internal reflection of the refractively coupled-out guided light portion at an interior surface of the inclined sidewalls <NUM>", as illustrated in <FIG>. In some examples, the gap <NUM>' may extend between an entirety of the opposing surfaces of the first microprism layer 124a and the second microprism layer 124b and further may have a substantially uniform separation or width throughout.

In some embodiments, the first and second microprism layers 124a, 124b may comprise curved microprisms or microprisms arranged to approximate a curve. A plan view in Figure 3C illustrates curved microprisms <NUM>. As illustrated, the curved microprisms <NUM> may represent microprisms of the first microprism layer 124a at the surface of the light guide <NUM>. Similarly, the curved microprisms <NUM> in <FIG> may represent microprisms <NUM> of the second microprism layer 124b that are complementary to the microprisms <NUM> of the first microprism layer 124a. In particular, as described above, microprisms <NUM> of the first and second microprism layers 124a, 124b may have inclined sidewalls with complimentary slopes. As a result, in these embodiments, microprisms <NUM> of the second microprism layer 124b may also be curved. Microprisms <NUM> of the first or second microprism layers 124a, 124b may have a concentric curve with a center of curvature. In some embodiments, the curved microprisms <NUM> may be semicircular, while in other embodiments another substantially non-circular curve may be employed to realize the curved microprisms <NUM>.

According to the other embodiments, the microprism structure <NUM> of the polarization-preserving scattering feature <NUM> may comprise an inverted microprism element. An example of a microprism structure <NUM> comprising an inverted microprism element <NUM> is illustrated in <FIG>. As illustrated, the inverted microprism element <NUM> has a truncated conical shape with an input aperture <NUM>, an inclined sidewall <NUM>, and an output aperture <NUM>. In some embodiments, the microprism structure <NUM> may comprise a plurality of inverted microprism elements <NUM>, e.g., as illustrated in <FIG>.

According to various embodiments, the inverted microprism element <NUM> is configured to couple out or more generally receive a portion of the guided polarized light <NUM>. In particular, the inverted microprism element <NUM> is configured to receive the guided polarized light <NUM> at or through the input aperture <NUM> and to provide or 'emit' light comprising the guided polarized light reflected by the inclined sidewall(s) <NUM> of the inverted microprism element at the output aperture <NUM> as the emitted light <NUM>. In some embodiments, the inverted microprism element <NUM> may have a shape resembling or substantially similar to a truncated cone, a truncated pyramid, and various other multi-sided structures, according to various embodiments. Further, a specific shape of the inverted microprism element <NUM> as well as a predetermined slope angle of the inclined sidewalls <NUM> thereof may be configured to control a shape or an intensity as well as other aspects of the emitted light <NUM>.

In various embodiments, the inverted microprism element <NUM> may be disposed adjacent to a surface of the light guide <NUM>, e.g., the first surface <NUM>' as illustrated. In some embodiments, the inverted microprism element <NUM> may extend from and be in direct contact with the first surface <NUM>' of light guide <NUM>. Further, in some embodiments, a material of the inverted microprism element <NUM> may be substantially similar to a material of the light guide <NUM>. For example, the inverted microprism element <NUM> may be integral to and comprise a material of the light guide <NUM>. The inverted microprism element <NUM> may be formed in or from a material (e.g., a surface material) of the light guide <NUM>, for example. In other embodiments, the inverted microprism element <NUM> may be provided separately from the light guide <NUM> and then subsequently positioned adjacent or attached thereto to provide contact with the first surface <NUM>' (e.g., top surface) of the light guide <NUM>. In these embodiments, the inverted microprism element <NUM> may either comprise light guide material or another optical material, for example.

As mentioned above, the inverted microprism element <NUM> has an input aperture <NUM>. In particular, a portion of the guided polarized light <NUM> may be extracted or coupled out at an optical connection between the inverted microprism element <NUM> and the light guide <NUM>. A portion of the inverted microprism element <NUM> at the optical connection may be referred to as the input aperture <NUM> of the inverted microprism element <NUM>. The input aperture <NUM> is thus configured to receive a portion of the extracted or coupled-out portion of the guided polarized light <NUM>.

As is also mentioned above, the inverted microprism element <NUM> further comprises an inclined sidewall <NUM>, the inclined sidewall <NUM> having an inclination angle. In various embodiments, the inclined sidewall <NUM> has an interior surface configured to reflect light. Thus, the inverted microprism element <NUM> is configured to receive coupled-out polarized light <NUM> at an input or input aperture <NUM>, and to reflect the received light at an interior surface of the inclined sidewall <NUM>. In some examples, the inclined sidewall <NUM> of the inverted microprism element <NUM> may be substantially flat. In other examples, the inclined sidewall <NUM> may comprise a curve. Some example inverted microprism elements <NUM> may comprise combinations of flat and curved inclined sidewalls <NUM>. Other varieties of shapes for the inclined sidewall <NUM> or interior surface thereof may also be used. Further, a specific shape or predetermined slope of the inclined sidewall <NUM> may be configured to control a shape, intensity, or other aspect of the emitted light <NUM>. In some embodiments, the inclined sidewall <NUM> may further comprise a reflective layer or reflective material (e.g., a reflective material layer on an exterior surface of the inclined sidewall <NUM>). The reflective layer may be configured to provide or enhance reflection at the interior surface of the inverted microprism element <NUM>. Alternatively, reflection at the interior surface of the inclined sidewalls may be provided by total internal reflection, obviating a need for the reflective layer, in other embodiments.

As mentioned above, the inverted microprism element <NUM> also has an output or output aperture <NUM>. The output aperture <NUM> is configured to emit light from the inverted microprism element as the emitted light <NUM>. In particular, the output aperture <NUM> is configured to provide as the emitted light the guided polarized light <NUM> received through the input aperture <NUM> and reflected on the inclined sidewall <NUM> of the inverted microprism element <NUM>. The output aperture <NUM> may have any of a variety of different shapes including, but not limited to, a square shape, a circular shape and a triangular shape. An aspect ratio (e.g., a length vs. width) of the output aperture <NUM> is generally less than about three-to-one (i.e., a length that is less than three times a width), according to various embodiments.

According to some embodiments, the polarized backlight <NUM> may further comprise a collimator. The collimator may be located between the light source <NUM> and the light guide <NUM>, for example. In other examples, the light source <NUM> may comprise the collimator. <FIG> illustrates a plan view of a portion of the polarized backlight <NUM> including a collimator <NUM> in an example, according to an embodiment consistent with the principles described herein. As illustrated, the collimator <NUM> is disposed between the light source <NUM> and the light guide <NUM> of the polarized backlight <NUM>. According to various embodiments, the collimator <NUM> is configured to collimate the polarized light generated by the light source <NUM> to provide collimated polarized light. The collimator <NUM> is further configured to communicate the collimated polarized light to the light guide <NUM>. In particular, the collimator <NUM> may be configured to receive substantially uncollimated light from one or more of the optical emitters <NUM> of the light source <NUM>. The collimator <NUM> is further configured to convert the substantially uncollimated light into collimated light. The collimator <NUM> may provide collimated polarized light having the non-zero propagation angle and being collimated according to a predetermined collimation factor σ, according to some embodiments. The collimator is further configured to communicate the collimated polarized light beam to the light guide <NUM> to propagate as the guided polarized light <NUM>, described above.

In some embodiments (e.g., as illustrated in <FIG>), the collimator <NUM> may be a 'tapered' collimator <NUM>. The tapered collimator <NUM> illustrated in <FIG> comprises a light guide having a sidewall taper such that an input end <NUM> of the tapered collimator <NUM> is generally narrower than an output end <NUM> of the tapered collimator <NUM>. In particular, a width dimension of the tapered collimator <NUM> increases or 'tapers' from the input end <NUM> to the output end <NUM> as a result of the sidewall taper. Herein, as illustrated in <FIG>, the 'width dimension' or simply 'width' is defined as a dimension in a direction corresponding to a width of the light guide <NUM>. The light guide 'width', in turn, is defined as a dimension along or corresponding to a plane that is substantially orthogonal to the general propagation direction the guided polarized light <NUM>. The width of the light guide <NUM> may also be substantially perpendicular to a height or thickness of the light guide <NUM>, in some embodiments.

According to various embodiments, the input end <NUM> of the tapered collimator <NUM> is adjacent to and configured to receive light from the light source, e.g., the light source <NUM>, as illustrated. The light source <NUM> may be configured to provide substantially uncollimated light, for example. The output end <NUM> of the tapered collimator <NUM> is adjacent to and configured to provide the collimated light to the light guide <NUM> of the polarized backlight <NUM>. As illustrated, collimated light from the tapered collimator <NUM> is provided at an input or entrance edge 110a of the light guide <NUM>.

According the various embodiments, the polarization-preserving scattering feature <NUM> of the polarized backlight <NUM> is further configured to provide angle-preserving scattering of the guided polarized light <NUM>. The angle-preserving scattering is configured to preserve a collimation factor σ of the guided polarized light portion in the emitted light <NUM>. That is, the angle-preserving scattering is configured to preserve an angular spread of light incident on the polarization-preserving scattering feature <NUM> in the emitted light <NUM>. In some embodiments, angle-preserving scattering may be provided by individual discrete structures or features such as the diffraction grating, microprism, or inverted microprism element of the polarization-preserving scattering feature <NUM>, as described above. Further, each discrete structure may be configured to scatter out or couple out a different portion of the guided light in an angle-preserving manner. Thus an angular spread of the emitted light <NUM> is determined by a characteristic of the angle-preserving scattering of the polarization-preserving scattering feature <NUM>.

In some embodiments, the polarization-preserving scattering feature <NUM> having angle-preserving scattering is configured to provide emitted light <NUM> having the angular spread characterized by a predetermined subtended angle γ. The emitted light <NUM> may thus be substantially confined within the predetermined subtended angle γ or angular spread. Further, the angular spread is a function of the collimation factor of the guided polarized light <NUM>. In particular, the angular spread is proportional to the collimation factor of the guided polarized light <NUM>, according to some embodiments. For example, the predetermined subtended angle γ of the angular spread (or equivalently the 'angular spread') may be given by equation (<NUM>) as: <MAT> where σ is the collimation factor of the guided polarized light <NUM> and f(·) represents a function such as, but not limited to, a linear function of the collimation factor σ. For example, the function f(·) may be given as γ = a · σ, where a is an integer.

<FIG> further illustrate an array of light valves <NUM> configured to modulate the emitted light <NUM>. The light valve array may be part of a backlit display that employs the polarized backlight <NUM>, for example, also illustrated in <FIG> for the purpose of facilitating discussion herein. In <FIG>, the array of light valves <NUM> is partially cut away to allow visualization of the light guide <NUM> and the polarization-preserving scattering feature <NUM> underlying the light valve array. In various embodiments, different types of light valves may be employed as the light valves <NUM> of the light valve array including, but not limited to, one or more of liquid crystal light valves, electrophoretic light valves, and light valves based on electrowetting.

The array of light valves <NUM> is configured to modulate the emitted light <NUM>. In particular, emitted light <NUM> from the polarization-preserving scattering feature <NUM> on the light guide <NUM> may pass through and be modulated by individual light valves <NUM> of the plurality of light valves or the light valve array. In some embodiments, the emitted light <NUM> is modulated as pixels of a displayed image. In some embodiments, a polarization of the emitted light <NUM> is configured to match a polarization of the light valves <NUM>. In particular, the polarization-preserving scattering feature <NUM> of the polarized backlight <NUM> used in a backlit display may be configured to couple out of the light guide <NUM> emitted light <NUM> that matches a polarization of the light valves <NUM>. Modulated emitted light <NUM> is illustrated in <FIG> as dashed arrows to emphasize modulation thereof.

In accordance with other embodiments of the principles described herein, a method for polarized backlight operation is provided. <FIG> illustrates a flow chart of a method <NUM> of polarized backlight operation in an example, according to an embodiment consistent with the principles herein. As illustrated in <FIG>, the method <NUM> of polarized backlight operation comprises providing <NUM> polarized light using a light source. The light source is configured to emit polarized light to be guided within the light guide. That is, the light source is configured to provide light having a predetermined polarization. In some embodiments, the predetermined polarization may be a transverse electric (TE) polarization. Thus, the light provided by the light source may have a transverse electric (TE) polarization component selectively oriented, for example. In other embodiments, the predetermined polarization may be a transverse magnetic (TM) polarization. In some embodiments, the light source may be substantially similar to the light source <NUM> described above with respect to the polarized backlight <NUM>. For example, the light source may comprise an optical emitter configured to emit polarized light having the predetermined polarization. In other examples, the light source may comprise an optical emitter generating non-polarized light in combination with a polarizer disposed at an output of the optical emitter to provide polarized light.

The method <NUM> of polarized backlight operation further comprises guiding <NUM> the polarized light in a propagation direction along a length of a light guide as guided polarized light, as illustrated in <FIG>. The polarized light may be guided at a non-zero propagation angle using a light guide <NUM> that is substantially similar as that described above with respect to the polarized backlight <NUM>. The polarized light propagates along the light guide using total internal reflection within the light guide, according to various embodiments.

The method <NUM> of polarized backlight operation further comprises scattering <NUM> a portion of the guided polarized light out of the light guide as emitted polarized light using a polarization-preserving scattering feature optically coupled to the light guide. According to various embodiments, the portion of the guided polarized light is scattered <NUM> out in a manner that substantially preserves in scattered light a degree of polarization of the light incident on the polarization-preserving scattering feature. As such, a polarization of the emitted polarized light is determined by a polarization of the guided polarized light. Further, the polarization-preserving scattering feature may provide angle-preserving scattering, according to some embodiments. In these embodiments, an angular spread of the emitted polarized light is determined by an angular spread or collimation factor of the guided polarized light.

In some embodiments, the polarization-preserving scattering feature employed in scattering <NUM> a portion of the guided polarized light out of the light guide may be substantially similar to the polarization-preserving scattering feature <NUM>, described above with respect to the polarized backlight <NUM>. For example, the polarization-preserving scattering feature used may comprise various polarization-preserving scattering elements including, but not limited to, a diffraction grating, a microprism structure and an inverted microprism element as well as various combinations thereof that are configured to provide polarization-preserving scattering. In some embodiments, the diffraction grating may be substantially similar to the diffraction grating <NUM>, the microprism structure may be substantially similar to the microprism structure <NUM>, and the inverted microprism may be substantially similar to the inverted microprism <NUM>, also described above with respect to the polarization-preserving scattering feature <NUM>.

In particular, in some embodiments, scattering <NUM> the guided polarized light portion out of the light guide as emitted polarized light comprises diffractive scattering, the polarization-preserving scattering feature comprising a diffraction grating. In some embodiments, the diffraction grating comprises a plurality of diffraction gratings arranged across a width and along the length of the light guide. In some embodiments, the diffraction grating may comprise curved diffractive features.

In some embodiments, scattering <NUM> the guided polarized light portion out of the light guide as emitted polarized light comprises refractive scattering, the polarization-preserving scattering feature comprising a microprism structure having an inclined sidewall. In particular, the microprism structure may comprise a microprism or a plurality of microprisms configured to refractively scatter <NUM> out of the light guide guided polarized light incident on the microprism structure. The microprism structure may comprise a first microprism layer and a second microprism layer, in some embodiments. Microprisms of the first and second microprism layers may have complementary inclined sidewalls, for example. In other embodiments, the microprism structure may comprise an inverted microprism element having a truncated conical shape with an input aperture, an inclined sidewall, and output aperture. In some embodiments, the microprism structure may comprise curved microprisms.

In some embodiments, scattering <NUM> the guided polarized light portion out of the light guide further comprises controlling an intensity of the emitted polarized light using a spatial density of plurality of polarization-preserving scattering elements of the polarization-preserving scattering feature distributed across a width and a length of the light guide. For example, the spatial density of polarization-preserving scattering elements may be increased as a function of distance from the light source to provide a substantially uniform intensity of the emitted polarized light. That is, the spatial density may compensate for a general decrease in available guided polarized light within the light guide as the distance from the light source increases, for example.

In some embodiments (not illustrated), the method <NUM> of polarized backlight further comprises collimating the polarized light provided by the light source using a collimator between the light source and the light guide to provide collimated guided polarized light within the light guide. The collimator may comprise a tapered collimator that is substantially similar to the tapered collimator <NUM> described above with respect to polarized backlight <NUM>, in some embodiments.

In some embodiments, as mentioned above, scattering <NUM> the guided polarized light portion out of the light guide as emitted polarized light further comprises preserving or substantially preserving a collimation factor of the guided light in the emitted polarized light using the polarization-preserving scattering feature that is also an angle-preserving scattering feature. In particular, the angle-preserving scattering comprises scattering in a manner that substantially preserves in the emitted polarized light a collimation factor of guided polarized light. That is, the angle-preserving scattering may comprise scattering of the guided polarized light in a manner that substantially preserves an angular spread or collimation factor thereof. The angle-preserving scattering may be provided by any of the scattering features described above, including the diffractive gratings and microprism structures, according to various embodiments.

In accordance with some embodiments of the principles described herein, a backlit display <NUM> is disclosed. <FIG> illustrates a block diagram of a backlit display <NUM> in an example, according to an embodiment consistent with the principles described herein. According to various embodiments, the backlit display <NUM> employs polarization-preserving scattering to provide emitted polarized light <NUM> that preserves a polarization of light generated by within the backlit display <NUM>. Further, a polarization of the emitted polarized light <NUM> is configured to match a polarization of the light valve array used to modulate the emitted polarized light as pixels or modulated polarized light <NUM> of a displayed image. The backlit display <NUM> may further employ angle-preserving scattering to preserve a collimation factor of the generated light in the emitted polarized light <NUM>, in some embodiments.

As illustrated in <FIG>, the backlit display <NUM> comprises a polarized light source <NUM> configured to provide polarized light. That is, the light source <NUM> is configured to provide light having a predetermined polarization. For example, the provided polarized light may comprise a transverse electric (TE) polarization component that is selectively oriented. In some embodiments, the polarized light source <NUM> may be substantially similar to the light source <NUM> described above with respect to polarized backlight <NUM>.

The backlit display <NUM> illustrated in <FIG> further comprises a light guide <NUM> configured to guide the polarized light as guided polarized light. According to various embodiments, the light guide <NUM> may be configured to guide the polarized light using total internal reflection. Further, the polarized light may be guided at a non-zero propagation angle by or within the light guide <NUM>. In some embodiments, the light guide may be substantially similar to the light guide <NUM> of the polarized backlight <NUM>, described above. In particular, the light guide <NUM> may comprise a slab of dielectric material. As such, the light guide <NUM> may be a plate light guide.

As illustrated, the light guide <NUM> further comprises a polarization-preserving scattering feature <NUM> at a surface of the light guide <NUM>. The polarization-preserving scattering feature <NUM> is configured to scatter a portion of the guided polarized light out of the light guide as emitted polarized light <NUM>. In some embodiments, the polarization-preserving scattering feature <NUM> of the light guide <NUM> may be substantially similar to the polarization-preserving scattering feature <NUM> of the above-described polarized backlight <NUM>. For example, the polarization-preserving scattering feature <NUM> may comprise various polarization-preserving scattering elements including, but not limited to, a diffraction grating, a microprism structure and an inverted microprism element as well as various combinations thereof that are configured to provide polarization-preserving scattering. In particular, the polarization-preserving scattering feature <NUM> may comprise one or both of a diffraction grating configured to diffractively scatter the guided polarized light portion out of the light guide <NUM> and a microprism structure configured to refractively scatter the guided polarized light portion out of the light guide <NUM>. In some embodiments, the diffraction grating may be substantially similar to the diffraction grating <NUM>, while the microprism structure may be substantially similar to either of the microprism structure <NUM> or the inverted microprism <NUM>, also described above with respect to the polarization-preserving scattering feature <NUM>. In some embodiments, the diffraction grating may comprise curved diffractive features, while the microprism structure may comprise curved microprisms, in some embodiments.

The light guide <NUM> further comprises a light valve array <NUM> configured to modulate the emitted polarized light <NUM> to provide the modulated polarized light <NUM> representing pixels of a displayed image. In some embodiments, the light valve array <NUM> may comprise a liquid crystal valve or more particularly a plurality of liquid crystal light valves. Further, according to some embodiments, a polarization of the emitted polarized light <NUM> may be configured to match a polarization of the light valve array <NUM>.

As mentioned above, in some embodiments, the polarization-preserving scattering feature <NUM> of the light guide <NUM> of the backlit display <NUM> may provide angle-preserving scattering of the guided polarized light. For example, the angle-preserving scattering may be provided by the diffraction grating or microprism structures as described above with respect to the polarized backlight <NUM>. The angle-preserving scattering may preserve a collimation factor of the guided polarized light in the emitted polarized light <NUM>, in some embodiments.

Claim 1:
A polarized backlight comprising:
a light source (<NUM>) configured to provide polarized light to an input end of a light guide (<NUM>);
wherein the light guide is configured to guide the polarized light in a propagation direction along a length of the light guide as guided polarized light; and
a scattering feature (<NUM>) optically coupled to the light guide, the scattering feature being configured to scatter a portion of the guided polarized light out of the light guide as emitted polarized light,
characterized in that
said scattering feature is polarization-preserving,
wherein a polarization of the emitted polarized light is the polarization of the guided polarized light.