Patent Description:
This application claims the benefit of priority to <CIT>.

The present invention relates generally to display techniques for high dynamic range images, and in particular, to compact displays for local dimming.

Dynamic range is the ratio of intensity of the highest luminance parts of an image scene and the lowest luminance parts of a scene. For example, the image projected by a video projection system may have a maximum dynamic range of <NUM>:<NUM>.

The human visual system is capable of recognizing features in scenes which have very high dynamic ranges. For example, a person can look into the shadows of an unlit garage on a brightly sunlit day and see details of objects in the shadows even though the luminance in adjacent sunlit areas may be thousands of times greater than the luminance in the shadow parts of the scene. To create a realistic rendering of such a scene can require a display having a dynamic range in excess of <NUM>:<NUM>. The term "high dynamic range" (HDR) means dynamic ranges of at least <NUM>:<NUM>.

Conventional display technology, using direct-lit local dimming (as an example, described by <CIT>, "Locally Dimmed Display,"), is capable of rendering images in a manner that faithfully reproduces high dynamic ranges. This is accomplished by independent modulation of light sources, as well as modulation by one or more liquid crystal panels, for improved contrast. However, a direct-lit panel <NUM> cannot do so in a form factor sufficiently thin for many applications (e.g., a cellular telephone display). As shown in <FIG>, the width <NUM> of a direct-lit panel stacks the light sources, liquid crystal panel, and intervening optics (such as, a diffusion layer).

As an alternative to direct-lit panels, edge-lit technology (as an example, described in <CIT>, "Edge Lit LED based Locally Dimmed Display," ) is employed with mixed results. As shown in <FIG>, an edge-lit panel <NUM> is thinner by not stacking a light source, and width <NUM> driven by the liquid crystal panel, light guide, and any intervening optics (not shown). That said, edge-lit panel <NUM> suffers from noticeably reduced HDR performance because light source modulation is row dependent and light intensity decreases along the length of the light guide (e.g., non-uniformity as a function of distance from the light source).

Accordingly, a need exists for a compact (e.g., thin) local dimming display capable of reproducing a wide range of light intensities.

<CIT> describes an illumination device having a partially transmissive front reflector, a back reflector, and a cavity between them. At least one light injector including a baffle and a light source is disposed in the cavity. The light injector is capable of injecting partially collimated light into the cavity. The output area of the illumination device can be increased by disposing light injectors progressively within the cavity, without sacrificing uniformity of the light emitted through the output area.

<CIT> describes an illumination device with first and second reflecting sheets. Each of the first reflecting sheets is provided so as to cover the opposite surface of a corresponding lightguide which is opposite to a light exit surface of the corresponding lightguide. Each of the second reflecting sheets is provided on the opposite surface of a corresponding first reflecting sheet which is opposite to a surface thereof facing a corresponding lightguide, over a corresponding first gap, wherein each of the first gaps is defined between adjacent two of the lightguides that do not to overlap each other. Each of the second reflecting sheets covers a region where no first reflecting sheet is provided in the corresponding first gap and extends over the adjacent two of the lightguides.

<CIT> describes a light-emitting apparatus including a plurality of adjacent, overlapping light-guide plates formed of substantially transparent material and a plurality of light sources. Each of the light-guide plates has first and second ends, one or more substantially transparent surfaces through which light is emitted, and one or more reflective surfaces to redirect light within the light-guide plate. Where first and second light-guide plates are adjacent, the first end of the first light-guide plate underhangs the second end of the second light-guide plate, and is positioned opposite a primary light-emitting side of the apparatus. The plurality of light sources are optically coupled to the first ends of the light-guide plates so as to illuminate the interiors of the light-guide plates.

<CIT> describes a plurality of aligned backlight blocks. Each block includes light sources and a unit light guide plate for guiding light from the light sources to the side of a liquid crystal panel. Unit diffusion patterns are formed in a zigzag alignment on the unit light guide plate and another diffusion pattern is formed on the back of the unit light guide plate. One side of the unit light guide plate is defined as a light entrance surface. LEDs as the light sources are aligned along the light entrance surface.

<CIT> describes a display apparatus including a display panel, a light source and a plurality of a light guiding plate. The light guiding plate includes light incident, counter, light emitting and rear surfaces. The counter and rear surfaces are respectively opposite to the light incident and light emitting surfaces. The light emitting surface includes an ineffective light emitting area making contact with the light incident surface and an effective light emitting area connecting the ineffective light emitting area with the counter surface. The counter surface of a first light guiding plate is disposed overlapping the light incident surface of a second light guiding plate along a first direction, so that the rear surface partially overlaps with the effective light emitting area of the second light guiding plate, and the light guiding plates collectively form a light guiding plate array along the first direction.

<CIT> describes a display comprising a light source and an image display panel disposed in an optical path from the light source. The light source comprises a primary light source for illuminating a re-emission material which comprises at least a first nanophosphor material for, when illuminated by light from the primary light source, re-emitting light in a first wavelength range different from the emission wavelength range of the primary light source. The image display panel comprises a first filter having a first narrow passband or a first narrow absorption band, the first narrow passband or first narrow absorption band being aligned or substantially aligned with the first wavelength range. The combination of a narrow wavelength range emitted by the first nanophosphor material and the narrow passband or narrow absorption band of the filter allows a display with high efficiency and a high NTSC ratio to be obtained.

Techniques are provided for a high dynamic range panel that includes an array of light sources illuminating a corresponding array of light guides. A light source of the array illuminates a first light guide. The light source directly underlies, such as in a cavity, a second light guide that is adjacent to the first light guide. The light source does not extend below a bottom side of either the first light guide or the second light guide to reduce thickness of the panel.

In an example, not part of the claimed invention, an apparatus includes a first light source to illuminate a first light guide with blue or ultraviolet light. The first light source is within a cavity formed by at least the first light guide and a second light guide. A second light source illuminates the second light guide with the blue or ultraviolet light. The second light guide is adjacent to the first light guide. The first light guide includes a sloped surface generating a broad spectrum light (e.g., white light) from the blue or ultraviolet light. The first light source does not extend beyond the cavity.

As another example of the present disclosure, not part of the claimed invention, an apparatus includes an array of light sources respectively illuminating an array of light guides. A first light source of the array of light sources directly underlies a first light guide illuminated by a second light source in the array. The first light source does not extend below a bottom side of the first light guide. The first light guide includes a multi-faceted reflective layer that directs light to a different direction.

In an aspect of the present invention, an apparatus for a display includes a first group of primary light sources to illuminate in a first direction a first light guide with a first light. The first light guide directs the first light to a second direction perpendicular to the first direction. The first group of primary light sources are disposed within a cavity of a second light guide. Both the second light guide and the cavity are coupled to the first light guide in the first direction in a tile assembly without overlapping the first light guide. A second group of primary light sources illuminates in the first direction the second light guide with a second light. The second light guide has a sloped surface to direct the second light to the second direction. The cavity underlies the sloped surface in a direction opposite to the second direction. The second light guide is adjacent to the first light guide. The first group of primary light sources underlies in the second direction the second light guide. The first and second light guides each may include a multi-faceted reflective layer to direct light to the second direction. The first group of primary light sources does not extend below a bottom side of the second light guide.

Example possible embodiments, which relate to HDR displays used for televisions, computer displays, tablets, PDAs, mobile cellular telephones, advertising displays or the like, are described herein. In other instances, well-known structures and devices are not described in exhaustive detail, in order to avoid unnecessarily occluding, obscuring, or obfuscating the present invention.

<FIG> illustrates an exemplary HDR panel <NUM>. HDR panel <NUM> is a two dimensional array of pixel elements (e.g., <NUM> x <NUM>; <NUM> x <NUM>; <NUM> x <NUM>; <NUM> x <NUM>; <NUM> x <NUM>), each pixel element includes at least a light source optically coupled to a light guide (i.e., an optical waveguide, such as optical fiber) in this example. Each light source is independently controllable for fine local dimming, or a subset of these light sources can be controlled in concert for coarse local dimming. Further, the spatial resolution of HDR panel <NUM> need not be the same, <NUM>:<NUM>, as other optical elements, such as a liquid crystal panel (not shown). For example, the spatial resolution of HDR panel <NUM> can be <NUM>:<NUM>, <NUM>:<NUM>, <NUM>:<NUM> or less of the liquid crystal panel. In other words, a single light source of the backlight can be used to reproduce multiple pixels in an area of a display.

For improved compactness of panel <NUM>, light sources are disposed within cavities underlying adjacent light guides. Light source <NUM> illuminates light guide <NUM>, but it is placed in a cavity <NUM> of adjacent light guide <NUM>. Light guide <NUM> is meanwhile illuminated by light source <NUM>. Cavity <NUM> is an arbitrarily shaped void, hollow, opening, or the like sufficiently large to hold, completely or partially, light source <NUM>. In a specific embodiment, a cavity is form fitting to partially encapsulate a light source (e.g., cavity closely follows, at least in part, the contours of the light source). For simplicity, surface <NUM> of light guide <NUM> defines size and shape of cavity <NUM>. Further details relating to surface <NUM> are described more fully below in connection with <FIG>.

In one example, light source <NUM> is physically mounted to light guide <NUM>. This can be accomplished by a form factor housing both light source <NUM> and light guide <NUM>. Light source <NUM> is can behoused with adjacent light guide <NUM>. These structures containing one light guide and a one or more light sources (e.g., one white LED, three LED sources for red green blue, or the like), referred hereinafter as a "tile assembly," provide benefits beyond compactness, such as a modular design.

Light guides (e.g., <NUM>, <NUM>) can be glass, polymer, semiconductor, plastic, or the like whether as slab, planar, rib, strip, segmented, or fiber structure. Light guides <NUM>, <NUM> direct electromagnetic waves in the optical spectrum (e.g., light with a wavelength between about <NUM> to <NUM> nanometers) or a subset of the optical spectrum. Light guide <NUM> guides at least the desired wavelength(s) associated with light source <NUM>.

Since light source <NUM> provides lateral illumination of light guide <NUM>, light guide <NUM> is configured to reflect light in an outwards direction through a display's optical stack and ultimately to a viewer. In an implementation of the present invention, a surface of a light guide, such as surface <NUM> of light guide <NUM>, is reflective. A reflective layer can be deposited (including by chemical vapor deposition), applied or affixed to, or under, to light guide <NUM> at surface <NUM>. The reflective layer provides a specular reflection surface or diffuse reflection surface, depending on desirability. Example materials for the reflective layer include one or more of: metals (e.g., aluminum, gold, silver, copper, brass, mercury, nickel or the like), polished metals, paint (e.g., white paint, glossy paint, matte paint), optically reflective silicone, water, and plastic. The reflected light from light guide <NUM> can be further processed by subsequent elements in the optical stack. In <FIG>, an optional layer <NUM>, overlaid on one or more light guides, can diffuse the light for improved uniformity or alter the point spread function for less or more contribution to adjacent pixels.

Light source <NUM> can be a light-emitting diode (LED), organic light-emitting diode (OLED), active matrix organic LED, light-emitting electrochemical cell, field-induced electroluminescent polymer, cold cathode lamp, cold cathode fluorescent lamp, laser, phosphor coated LED, quantum dot coated LED, incandescent bulb, or any suitable source of electromagnetic waves of an appropriate wavelength, preferably thinner than the light guides. A combination of light sources of differing technologies can be employed in panel <NUM>. In other words, light sources <NUM> and <NUM> can both be LEDs, but they need not be the same (e.g., as a specific embodiment, light source <NUM> can be an OLED, and light source <NUM> can be quantum dot coated LED).

In an example of the present invention, light sources <NUM>, <NUM> produce a broad spectrum light (e.g., white light) to illuminate light guides <NUM>, <NUM>. Color can be imparted to the light exiting light guides <NUM>, <NUM> by several techniques. For example, subsequent color filters in the optical path can be used to produce each of the primary colors, such as red, green and blue. Specifically, a liquid crystal panel (not shown in <FIG>) with subpixel color filters can be used.

A matrix array of quantum dot subpixel areas in the optical stack above a light guide can also convert light respectively to individual primary colors, e.g., red, blue, green and/or yellow. When light sources <NUM>, <NUM> produce blue and/or ultraviolet light, surface <NUM> can optionally be a layer of quantum dots (i.e., semiconductor nanocrystals, when under excitation, emit light dependent on its size and shape) to generate broad spectrum light later imparted with color by filtering. Alternatively, the layer of quantum dots can be within, above, or below surface <NUM>. As another example, the light guides can reflect blue or ultraviolet light to the subsequent optical stack, which can include a quantum dot layer of a matrix of red light generating, green light generating, and blue light generating areas of quantum dots. If the appropriate blue light is directly generated by light sources <NUM>, <NUM>, then the blue light generating area can be replaced with either a transparent filter or no filter at all (e.g., a cut-out to pass light, without alteration).

As described above, light sources (e.g., light source <NUM>) are positioned wholly within a cavity <NUM> formed by an adjacent light guide (e.g., light guide <NUM>). Light source <NUM> is completely within cavity <NUM>. For a thinner tile assembly, a light source should not extend below the lowest (bottom) side <NUM>, relative to an optical stack of a display device, of either its corresponding light guide or its adjacent light guide. Similarly, the light source should not extend above the highest (top) side <NUM> of either its corresponding light guide or its adjacent light guide To the extent the light source extends above or below the light guides, thickness of the tile assembly is enlarged.

<FIG> illustrate simplified cross-sectional views of exemplary HDR panels, according to embodiments of the present invention. <FIG> shows a linear surface <NUM>. The slant angle of linear surface <NUM> can range from about <NUM>° to about <NUM>°, preferably about <NUM>° to about <NUM>°, and more preferably about <NUM>° to about <NUM>°. In another embodiment, surface <NUM> can vary non-linearly. The desired point spread function (PSF, a measure of the degree of spreading of a point object) of the reflected light, as well as sizing of cavity <NUM>, will influence acceptable slant angles. In an example, cavity <NUM> is sufficiently ample to house light source <NUM>, whether light source <NUM> is integrated as a tile assembly with light guide <NUM> or as a standalone light source device. Such an arrangement reduces thickness <NUM>, compared to stacking an entire thickness of a light guide plus height of a light source.

Referring to <FIG>, light guides include multi-faceted, convex or concave, reflection surfaces <NUM> and <NUM>, although reflection surfaces can be smoothed to avoid sharp angles. The angle and number of facets (e.g., two, three, four, five, six, seven or more facets) influence the PSF of the reflected light. In some instances, PSF that spread beyond one pixel area it is preferable. This increased PSF size reduces blocking artifacts associated with abrupt illumination changes at pixel boundaries. <FIG> shows an undulating surface <NUM>, which can be any waveform, such as sinusoidal, square, triangle, sawtooth or the like, or combinations of the foregoing. The waveform can be either uniform or non-uniform in frequency or amplitude. For example, about a proximal start of surface <NUM> can have a higher frequency than about the distal end of surface <NUM>. It should be appreciated, based on the teachings herein, that surfaces <NUM>, <NUM>, and <NUM> can vary with height, depth, and/or length (in all three dimensions). In other words, one side of a reflective surface (e.g., left side) can differ from its opposite side (e.g., right side) or its center. In an example, a reflecting surface in three dimensions can vary with azimuth, elevation, or both.

As depicted in the figures, the proximal start <NUM>, <NUM> of reflection surfaces <NUM> and <NUM> is disposed away by a length <NUM> from illuminating light sources. Length <NUM> can substantially range from about <NUM>% to about <NUM>% of the length of the entire light guide, but preferably <NUM>% to <NUM>%. Likewise, the distal end of reflection surfaces <NUM> and <NUM> need not abut the end of the light guide, nor coincide with a top surface (e.g., <NUM>) of the light guide - in other words, surfaces <NUM>, <NUM> can be less than thickness <NUM>. These considerations can also apply to reflective surface <NUM> of <FIG>.

In <FIG>, instead of a single light source (e.g., white, blue or UV LED) for each light guide, primary light sources are arranged as a group <NUM>. Group <NUM> is collectively housed, partially or wholly, in cavity <NUM>. In other words, the primary light sources share a single light guide per group.

<FIG> illustrates a simplified cross-sectional view of exemplary HDR panels, according to another embodiment of the present invention. In this example, a group <NUM> of primary light sources illuminates two opposite facing light guides <NUM> and <NUM>. Fewer light sources are needed, thus saving on bill of materials (BoM) cost, but reducing resolution for local dimming control. This implementation can earn further BoM savings by using group <NUM> to illuminate four or more light guides organized radially about group <NUM>. In this scenario, an "expanded tile assembly," as a single module, can include group <NUM> and its plurality of illuminated light guides.

<FIG> illustrates exemplary groups <NUM>, <NUM>, <NUM> of primary light sources, according to an embodiment of the present invention. Groups <NUM>, <NUM> and <NUM> can be applied to the embodiments described above in connection with <FIG> and <FIG>. Groups <NUM> and <NUM> are illustrated to show three primary light sources <NUM>, <NUM>, and <NUM>; however, there can be two, four, <NUM> or more primaries in an HDR panel. For example, an HDR panel can implement any one of RGB, RGB + yellow, RGB + white, or RGB + yellow + cyan.

For a three dimensional (3D) rendering panel utilizing spectral separation, group <NUM> includes six primary light sources. A viewer wears spectrally sensitive glasses such that different components of the illuminated light are directed to the viewers' left and right eyes. As an example, a first red primary is perceived in a viewer's left eye, but a second red primary (spectrally different from the first) is filtered by the left eye lenses of the 3D glasses. For the right eye, the second red primary is perceptible, but not the first. Accordingly, group <NUM> includes two sets of primaries that do not overlap spectrally. Additional details about 3D spectral separation as used for cinema projection are described in <CIT>.

<FIG> illustrates a tile assembly <NUM> for subpixel resolution, according to an example not part of the claimed invention. A plurality of light sources (e.g., <NUM>, <NUM>, and <NUM> or more) emanating a display's primary colors are coupled to respective light guides (e.g., <NUM>, <NUM>, and <NUM>). For example, light source <NUM> can be a red LED, light source <NUM> can be a green LED, and light source <NUM> can be a blue LED. The light output from light guides <NUM>, <NUM>, and <NUM> provide subpixel color modulation by the backlight, as well as further modulation by a liquid crystal display (not shown). This tile assembly avoids the use of color filters in the optical stack and quantum dots. It should be appreciated that the resulting spatial resolution of the HDR panel comprising an array of tile assemblies <NUM> can be less than, equal to, or greater than other optical components, such as the liquid crystal panel.

<FIG> illustrate an exemplary HDR display. The structures depicted in <FIG> can be applied to one or more of the embodiments described above for <FIG>, <FIG>, <FIG>, and <FIG>, as would be readily apparent by a person skilled in the art benefiting from the teachings of this specification. It will also be apparent that one or more of the depicted layers in <FIG> are optional. For example, if the tile assembly <NUM> includes quantum dots, then quantum dot layer <NUM> can be omitted.

<FIG> illustrates an exemplary HDR display with a compact design, according to an embodiment not part of the claimed invention.

Light sources (such as white LEDs, RGB LED groups, etc.) are mounted along the edges of an LCD display. The light sources are tiled as closely as possible in two dimensions along the edge of the display, essentially creating a low-resolution backlight.

The light is directed to the desired location behind the LCD display. First, the light sources emit light into a planar light guide. The light is transmitted along the light guide either by total internal reflection (TIR) or by reflective boundaries. Eventually, light is reflected upwards through a diffuser and LCD. As illustrated in <FIG>, the light sources transmit light at <NUM> degrees to the light guide to allow for the light guides to be very thin (order of um). The light is reflected along the light guides using an angled reflector or TIR. Alternatively, the LEDs could emit light directly into the light guide.

The backlight optics can be tiled or continuous across the display, with light being emitted along both top and bottom, or left and right edges. Instead of reflecting the light upwards towards the LCD as described above for <FIG>, a top surface of the light guide could be diffused if using TIR, or the reflector could be terminated to eject light from the light guide in the desired location.

This specification often refers to colors, such as blue, ultraviolet, red, green, etc. Without limiting the generality of the teachings herein, light colors can be within about the following ranges for one or moreexamples of the present disclosure:.

In the foregoing specification, possible embodiments of the invention have been described with reference to numerous specific details that may vary from implementation to implementation. Thus, the sole and exclusive indicator of what is the invention, and is intended by the applicants to be the invention, is the appended set of claims.

The specification and drawings are, accordingly, to be regarded in an illustrative rather than a restrictive sense.

Claim 1:
An apparatus (<NUM>) for a display, the apparatus (<NUM>) comprising:
a first group of primary light sources (<NUM>; <NUM>; <NUM>; <NUM>) to illuminate in a first direction a first light guide (<NUM>) with a first light, the first light guide (<NUM>) directing the first light to a second direction perpendicular to the first direction, the first group of primary light sources (<NUM>; <NUM>; <NUM>; <NUM>) disposed within a cavity (<NUM>) of a second light guide (<NUM>), both the second light guide (<NUM>) and the cavity (<NUM>) coupled to the first light guide (<NUM>) in the first direction in a tile assembly without overlapping the first light guide (<NUM>);
a second group of primary light sources (<NUM>; <NUM>; <NUM>; <NUM>) to illuminate in the first direction the second light guide (<NUM>) with a second light, the second light guide (<NUM>) having a sloped surface configured to direct the second light to the second direction, the cavity (<NUM>) underlying the sloped surface (<NUM>) in a direction opposite to the second direction.