WO2012097004A1

WO2012097004A1 - Color separating light guide for edge-lit lcd backlights

Info

Publication number: WO2012097004A1
Application number: PCT/US2012/020835
Authority: WO
Inventors: Michael J. Little
Original assignee: Little Michael J
Priority date: 2011-01-10
Filing date: 2012-01-10
Publication date: 2012-07-19

Abstract

An apparatus to deliver light to the sub-pixels of each pixel in a liquid crystal display includes two or more light distribution assemblies. Each assembly includes a manifold coupled to a plurality of light guiding channels. Each manifold is configured to receive light from a source and evenly distribute it to the plurality of light guiding channels, which are configured to deliver light to corresponding sub-pixel locations. Light from each light distribution assembly is prevented from mixing with light from one or more of the other light distribution assemblies in the apparatus. This abstract is provided to comply with rules requiring an abstract that will allow a searcher or other reader to quickly ascertain the subject matter of the technical disclosure. It is submitted with the understanding that it will not be used to interpret or limit the scope or meaning of the claims.

Description

KLT-OOl/PCT

COLOR SEPARATING LIGHT GUI DE FOR EDGE-LIT LCD BACKLIGHTS

CROSS-REFERENCE TO RELATED APPLICATIONS This application is related to provisional application number 61/431 , 141 , to Michael John Little, entitled "COLOR SEPARATING LIGHT GUIDE FOR EDGE-LIT LCD BACKLIGHTS", filed on January 10, 201 1 , the entire disclosures of which are incorporated herein by reference.

FIELD OF THE INVENTION

Embodiments of the present invention relate generally to full-color liquid crystal displays (LCDs) and more specifically to a backlight illumination system that separately distributes each of the primary colors to the LCD sub-pixels by means of an interdigitated thin waveguide network, eliminating the need for integrating color filters into the LCD.

BACKGROUND OF THE INVENTION

Due to their thinness and low power consumption, LCDs have become the dominant display technology for a wide range of applications including but not limited to mobile cellular phones, computer monitors and large screen televisions. In each of these applications, LCDs create color images with an array of pixels wherein each pixel consists of 3 sub-pixels; one for modulating each of the primary colors, red, green and blue. This approach for producing color images with a LCD is referred to as the spatial color method.

In the majority of color LCDs, a backlight that produces white light is used to illuminate a planar matrix array of liquid crystal optical elements or pixels known as a Liquid Crystal Panel. Each pixel is further divided into three sub-pixels, one for each of the primary colors. At each sub- pixel of a Liquid Crystal Panel, an absorptive color filter is incorporated that restricts the transmission of each sub-pixel to only one of the primary colors. By individually controlling the transmitted intensity of each of the primary colors, full color images can be produced.

Traditionally, the LCD backlight consists of an array of either cold cathode fluorescent lamps

(CCFLs) or LEDs that are mounted directly behind the Liquid Crystal Panel to produce the white light illumination. This approach for mounting sources for the backlight directly behind the Liquid Crystal Panel is referred to as direct-lit illumination and significantly adds to the thickness of the LCD. KLT-OOl/PCT

Market data has repeatedly demonstrated that reduced LCD thickness is an important feature in the eyes of consumers. To produce the thinnest possible LCDs, manufacturers have developed edge-lit illumination technology; an illumination system wherein the light sources are mounted at the edge of the display instead of directly behind the LCD panel. Due to its thinness, this edge-lit illumination approach is strongly preferred over the traditional direct-lit illumination system.

Edge-lit illumination systems use a thin light guide plate to bring illumination from the edge mounted sources and distribute it uniformly over the area of the display. In operation, white light from the CCFL or LED sources is injected along one or more of the edges of a thin lightguide plate. The light guide plate uses total internal reflection from its upper and lower surfaces to guide the light and broadcast it uniformly over the 2 dimensional area of the display.

With both direct-lit and edge-lit LCDs, color filters within the Liquid Ciystal Panel are required to separate the white light into the 3 primary colors; this enables each of the primary colors to be modulated separately. However, to spectrally separate the incoming white light into the 3 primary colors, each of the color filters must absorb >2/3 of the incident white light. For example, at the sub-pixel with a red filter, all of the green and blue light is absorbed, while at the green sub-pixel, all of the red and the blue light are absorbed. Similarly, at the blue sub-pixel, all of the red and green light is absorbed. Thus, for each of the sub-pixels, each of the color filters absorbs in excess of 66% of the white light produced by the LCD backlight. This high optical absorption by the color filter is a primary reason for the very poor optical efficiency of LCDs; typically less than 10% of the light generated by the backlight is transmitted to the viewer. Thus, the color filter is a major impediment to significantly lowering the power consumption of color LCDs. In addition, the fabrication of the color filters is an expensive component of the Liquid Crystal Panel assembly.

One method for producing LCD color images that avoids the cost and optical absorption of color filters is temporal color modulation, often referred to as color sequential. With the temporal color method, the pixels are not divided into sub-pixels; all of the display pixels are sequentially illuminated with one single color at a time at a frequency above the flicker frequency of the human eye. The relatively slow switching speed of LCDs remains a major hurdle to overcome to enable the use of the temporal color architecture in LCDs. While the temporal color method is significantly less costly to manufacture and avoids the optical absorption inherent in the color filters, the spectral range of colors it can produce is significantly less than can be realized with the spatial color method. The poor color rendering capabilities of the temporal color method has limited its use to only the very least demanding display applications. Thus, spatial color systems with their necessary color filters are strongly preferred by consumers and dominate the marketplace.

Referring now to FIG. 1 , a typical spatial color type of Liquid Crystal Display 10 is composed of 2 major sub-assemblies; a backlight assembly 30 and a Liquid Crystal Panel 20 that modulates the illumination produced by the backlight, which may be located outside a viewing area of the Liquid Crystal Display 10. Fabricated within the sandwich-like Liquid Crystal Panel 20 is a color filter layer 28 composed of red 28a, green 28b, and blue 28 color filters. However, to produce images with a broader spectral gamut, some Liquid Crystal Panels 20 are known to be subdivided into more than just 3 primary colors for example the Sharp Corporation Quadron system.

Referring again to FIG. 1 , the typical backlight sub-assembly 30 consists of a light source 60 and several additional layers 40 aimed at improving the angular distribution of the emerging illumination and improving the efficiency with which light is extracted from the backlight. In a typical direct-lit backlight configuration, the light source 60 is positioned directly behind the Liquid Crystal Panel 20. In this example an array of cold cathode fluorescent lamps (CCFLs) 62 is depicted. However due to their higher optical efficiency and broader spectral gamut, arrays of LEDs positioned directly below the Liquid Crystal Panel 20 are used as alternative light sources for direct illumination systems .

An alternative light source arrangement for LCDs illustrated in FIG. 2a, known as edge-lit illumination, enables LCDs to be significantly thinner than with the direct-lit arrangement. In the edge-lit arrangement, the array of CCFLs is replaced with an edge-mounted light source 54 and a light guide plate 52. In FIG. 2a a single CCFL lamp is illustrated, however, more than one light source can be mounted along more than one perimeter edge. The output of the edge-mounted light source 54 is distributed over the area of the display with a thin light guide plate 52. The operation of an edge-lit illumination arrangement is most easily described with the aid of FIG. 2b. Light source 54 is coupled into the light guide plate 52 which acts as a planar waveguide; total internal reflection from the upper 52a and lower 52b surfaces the light guide plate 52 together with end reflector 56 prevent the light rays 53 from escaping from the light guide plate. Surface texture patterns are incorporated in either the upper surface 52a or the lower surface 52b, or both, and provide sites for the illumination 55 to emerge from the light guide plate 52. The surface texturing patterns are typically carefully designed and positioned to take advantage of the multiple back and forth paths across the light guide plate 52 that are needed to produce very uniform illumination 55 along the entire length and breadth of the light guide plate. A CCFL source is illustrated in FIG. 2; however, LED sources are also known and, in most cases are the preferred edge mounted sources.

In LCDs, white light illuminates the Liquid Crystal Panel whether it comes from a direct-lit or and edge-lit illumination arrangement. FIG. 3 schematically illustrates an edge-lit light guide plate 52 illuminating the color filters of two pixels (27a and 27b) of a Liquid Crystal Panel. White light 55 is incident on the color filters (red-28a, green-28b, and blue-28c). As described earlier each color filter absorbs >66% of the incident white light. Since the production of illumination by the backlight is the primary source of power consumption in LCDs, the absorption of such a large fraction of the backlight illumination substantially increases the power needed to generate a particular level of LCD brightness.

A number of innovations have been developed to avoid the large power consumption associated with color filters. Examples of the innovations aimed at eliminating the optical absorption of the color filters include: (1) US Patent 4,686,519 of Yoshida which describes the use of a color separating prism along with one or more arrays of microlenses, (2) Patent 4,799,050 of Prince which describes the use of an array of color phosphor stripes along with a microlens array, (3) Patent 7,320,531 of West et al. which describes the use of an array of colored LEDs and (4) US Patent 7,488,087 of Cernasov which describes the use of multiple layers of stacked light guides. However, while these innovations do eliminate the need for color filters they are limited to use in direct-lit illumination arrangements where the light source is positioned directly behind the

Liquid Cry^sta' Panel ; thus they do not provide a solution for edge-lit illumination arrangements which enable thinner LCDs.

An example a of prior art innovation that aims to eliminate the LCD color filters but is suitable for edge-lit illumination arrangements is US Patent 6, 151 ,166 of Matsushita et al. In US Patent 6,151 ,166, Matsushita et al. describe an innovation wherein a thin diffraction grating coupled with a thin microlens array separates the white light illumination into narrow bands of primary colors that illuminate each sub-pixel. Importantly, this approach produces the desired narrow bands of primary colors without the optical absorption suffered with conventional color filters. Additional examples of similar types of innovation can be found in US Patent 7,580,083 of Jung, and US Patent 6,665,027 of Gunn et al. However, in all of the designs of this type of innovation, additional optical elements such as microlens arrays, diffraction gratings and arrays of micro- prisms must be added to the existing light guide plates. Additionally, the very fine structural details that are required for these types of innovations as well as their overall complexity make them both costly and difficult to manufacture. An example of another type of prior art innovation that aims to eliminate the LCD color filters and is also suitable for edge-lit illumination arrangements is US Patent 6,791 ,636 of Paolini et al. In US 6,791 ,636, a faceted light guide plate directs the red, green and blue illumination coming from edge mounted red, green and blue light sources to the Liquid Crystal Panel. In this approach, an array of facets is incorporated on the surface of the light guide; each one of the facets must be precisely angled to reflect light from one specific light source to a specific sub- pixel within the Liquid Crystal Panel. This design restricts the illumination to one single pass from its source to its destination and thereby loses the benefit of multiple back and forth paths within the light guide plate which is critical to enabling the light guide plates to provide a very uniform level of illumination across the display as well as be very efficient. Thus, there is a need for a method that does not require additional components to provide a color-filterless solution for LCDs with edge-lit illumination systems.

SUMMARY OF THE INVENTIO

In view of the foregoing, there is a need for a method that will eliminate the need for color filters in LCDs yet facilitate the formation of images with excellent color fidelity in the thinnest possible configuration yet not require components in addition to the light guide plate or high frequency temporal color switching. The present invention meets this need with a light guide plate design that separately delivers the red, green, and blue primary colors to their respective sub-pixels without mixing them to form white light. With this approach, color filters with their high optical absorption and high cost are not required nor are additional optical components or layers, thereby substantially reducing the cost while simultaneously improving the power efficiency of color LCDs by 2x-3x. In addition, the present invention is suitable for fabricating LCDs with the thinnest possible configurations.

BRIEF DESCRIPTION OF THE DRAWINGS Objects and advantages of the invention will become apparent upon reading the following detailed description and upon reference to the accompanying drawings in which:

FIG. 1 illustrates the construction of a typical prior art LCD.

FIG. 2 illustrates a prior art edge-lit backlight source.

FIG. 3 illustrates a prior art light guide coupling white light into the color filters. FIG. 4 illustrates an embodiment of the light guiding channels in relation to the sub-pixels.

FIGs. 5a-5b illustrate an overview of an embodiment of the light distribution assemblies.

FIG. 6 illustrates an exploded view of an example of an embodiment of the light distribution assemblies with staggered color light sources.

FIGs. 7a-7b illustrate other examples of embodiments of the light distribution assemblies. FIGs. 8a-8b illustrate an example of an embodiment of the light distribution assemblies with multiple groups of RGB LEDs.

FIGs. 9a-9b illustrate another example of an alternative manifold arrangement of the present invention.

FIGs. 10a- 10b illustrate an embodiment with a manifold arrangement suitable for displays with narrow display bezels.

FIGs. 1 la, 1 lb, and I l c illustrate another embodiment with a manifold arrangement suitable for displays with narrow display bezels.

FIG. 12 illustrates an example of a multi-section embodiment of the present invention. FIGs. 13a-13b illustrate light guiding channels mechanically constrained to remain in their desired relative positions with a low refractive index material.

FIG. 14 illustrates an alternative method of providing mechanical stability of the relative positions of the light guiding channels. FIGs. 15a-l 5b illustrate the use of the thermoforming method to fabricate the light guiding channels.

FIGs. 16, 16b, 16c, and 16d illustrate an alternative method of fabricating the light guide channels using embossing and subsequent backfilling of the embossed channels.

FIGs. 1 7a, 17b, and 17c illustrate an alternative method of fabricating light guide channels using a printing method

FIG. 18 illustrates a method of fabricating the channelized light guide device that partitions it into separate input manifold and light guide channels components

DETAILED DESCRIPTION OF THE SPECIFIC EMBODIMENTS

Light guide plates used in edge-lit LCD illumination systems are planar waveguide structures; light launched into the light guide plate is trapped by total internal reflection between the faces of the light guide plate. Conventionally, a single continuous light guide plate extends over the entire area of the display. This is a simple and efficient way to deliver a common illumination to all of the pixels of the display. However, this single continuous light guide plate is incapable of separately delivering the primary colored illumination to each of the sub-pixels of the LCD. In an embodiment of the present invention, conceptually illustrated in FIG. 4, an apparatus may separately deliver the individual primary colored illumination to the Liquid Crystal Panel and thereby eliminate the need for color filters. The figure shows a magnified view of two pixels each with three subpixels. Two pixel rows 127 are shown with three subpixel columns 128. Distinct channels 159 use waveguide design principles to subdivide the heretofore light guiding area into separate light guiding channels each capable of carrying and isolating individual primary colored illumination. Each light guiding channel is composed of a core made of a transparent material with a relatively high index of refraction while being surrounded by a KLT-OOl/PCT cladding material of relatively low index material. The material used for the core of the waveguide can be any of a number of high index materials such as poly(l -naphthyl

methacrylate) (n = 1.64), poly(pentabromobenzyl methacrylate) (n = 1.71) or preferably polyetherimide (n= 1.68). The cladding material surrounding the sides of the core material may also be selected from a number of low index of refraction materials; preferred materials are polymethylmethacrylate (PMMA) (n = 1 .49) and air (n = 1 .00). Embodiments of the present invention are anticipated wherein one or more of the sides of the core material of waveguide channels 159 have interfaces with a low index polymer such as PMMA while one or more of the . remaining sides have air interfaces. In FIG. 4, the light guiding channel 159 is shown to be divided into a series of adjacent channels 159-R, 159-G, and 159-B, each separated by a narrow gap occupied with a low index of refraction material such as PMMA or air. For convenience, in FIG 4 and subsequent figures, the gap between channels is depicted with air as the low index cladding material.

With the geometry depicted in FIG. 4, each channel acts as an independent waveguide; trapping the light within it by the total internal reflection mechanism. Independent light streams of the 3 primary colors 153-R, 153-G and 153-B are launched into the separate channels 159-R, 159-G and 159-B of the light guiding channel 159. The light sources from which the light streams are launched may be located outside a viewing area of a Liquid Crystal Panel. Surface texturing features may be incorporated into the upper or lower surface, or both, of each of the light guiding channels 159-R, 159-G and 159-B to enable an individual primary color to illuminate the respective sub-pixels 128d of the Liquid Crystal Panel (for simplicity none of the well-known texturing features are illustrated in FIG. 4). Importantly, the sub-pixels 128d of the Liquid Crystal Panel have no color filter and yet the display panel can create full color images by independently modulating each of the primary colors. While FIG. 4 depicts a light guide channel designed for illumination with 3 primary colors, embodiments of the present invention are anticipated that are suitable for fewer or more than 3 component colors.

FIG. 5a is a downward view of an entire light distribution system 152 while FIG. 5b is a side view of the system. Referring now to FIG. 5a, the light distribution system 152 may be composed of one or more light distribution assemblies, each having 2 main sections; a manifold 158 which brings light from the individual light sources 154-R, 154-G, and 154-B and injects it into section 159 which contains the array of light guiding channels 159-R, 159-G, and 159-B. The transition between sections 158 and 159 occurs outboard of the boundary of the edge of the viewable area of the liquid crystal display, one edge of which is indicated by dashed line 160. The 3-dimensional design of a light distribution system 152 is more easily described with the aid of FIG. 6. The light distribution system 152 is composed of 2 main sections; (1) section 159 which contains all of the primary color light guiding channels 159-R, 159-G, and 159-B and (2) a manifold 158 that brings light from the light sources 154-R, 154-G and 154-B and injects it into the primary color light guiding channels in section 159. For purposes of explanation FIG. 6 depicts the three primary color light distribution assemblies 152-R, 152-G and 152-B of light distribution system 152 as though there were vertical and horizontal offsets between them. Using primary color light guiding assembly 152-R as an example for the other primary color light guiding channels which are similar in structure, if not identical; within section 159-R is an array of waveguide channels with a periodicity of P and a width of W, where W is always < (P/3). Importantly, this geometry allows all of the light guide channels 159-R, 159-G, and 159-B to be in the same plane within section 159 and therefore be a thin planar structure beneath the footprint of the viewable area of the display.

Within the planar section 159 there are no instances of the color light guiding channels crossing over each other. However, since each primary color light source must illuminate multiple of its respective light guiding channels, a cross-over network is required to interdigitate the color channels in the planar section 159. This cross-over is necessarily a 3-dimensional structure and is accomplished in the manifold section 158. Section 158 is in effect a distribution manifold composed of two sub-sections; an expansion section 158a and a distribution network 158b. In the expansion section 158a, illumination from light source 154-R expands laterally to uniformly illuminate each of the entrances to the distribution network 158b which in turn routs the individual colors to its respective waveguide channels 159-R.

While the manifold 158 depicted in FIG. 6 employs funnel shapes for sections 158a and 158b, other embodiments or combinations of embodiments such as those schematically illustrated in FIG. 7 are anticipated. In the manifold illustrated in FIG. 7a the width of the expansion section 158a is essentially equal to the sum of the widths of the light guiding channels W that are to be illuminated with a particular light source of that particular color. Thus, at the junction of section 158a and 158b the gaps between adjacent channels are nearly zero while at the junction of section 158b and section 159 the gaps between adjacent channels is (P - W). In an alternative embodiment depicted in FIG. 7b, the expansion section 158a is as wide as or wider than the full width of the waveguide channels 159. In this instance, at the junction of section 158a and 158b the gaps between adjacent channels are (P - W). Also depicted in FIG. 7b is the mounting of the light sources 154-R, 154-G, and 154-B on an edge that is at right angles to the light guiding channels 159 as opposed to being mounted on an edge directly opposite the entrances to the light guiding channels 159.

Referring back to FIG. 5, while there are no instances of one color light guiding channels crossing over another within section 159, however, within the manifold section 158 there are multiple instances of color crossovers. For example, to obtain in-plane alternating color channels of red, green, and blue, a green and blue light guiding channel must be interleaved between each pair of adjacent red light guiding channel. The embodiment illustrated in FIG s 5 through 1 1 utilize some form of vertical offset in the manifold section 158 to accomplish the needed crossovers. One embodiment of the vertical offset used to accommodate the color crossovers in section 158 is shown in FIG. 5b.

FIGs. 8a-8b illustrate another embodiment of the manifold section 158 which can accommodate one or multiple sources of each color. In this embodiment, as with the embodiment schematically illustrated in FIG. 6, some or all of the light sources can be mounted in more than one plane. In FIG. 8b the light sources 154-R, 154-G, and 154-B are depicted to be staggered in a longitudinal direction however, it is anticipated that the light sources 154-R, 154-G, and 154-B could be inline vertically without any longitudinal stagger. FIGs. 9a-9b illustrate yet another embodiment of the manifold section 158 configuration wherein this geometry can accommodate light sources 154-R, 154-G, and 154-B being mounted in a single plane with or without a lateral offset in one or more directions. In this example, among others, both the manifolds and the light guiding channels may be substantially in the same plane. FIG. 10a is a downward looking illustration of an embodiment of the present invention wherein vertical crossovers in the manifold section 158 are avoided by staggering the extension of the light guiding channels 159 to a point where they turn downward out of the plane of the light guide channels. A side view of this geometry is illustrated in FIG. 10b. While in FIG. 10b an angled transition from vertical to horizontal is illustrated, smooth rounded transitions are also possible. This type of folded manifold geometry is especially suitable for LCDs which require that the LCD bezels widths beyond the viewable edge of the display to be as narrow as possible.

An alternative embodiment of the narrow bezel folded manifold geometry is schematically illustrated in FIG. 1 l a and 1 lb. FIG. 1 l a is a downward looking view of the light distribution system 152. As with the embodiment just described, downward thrusting staggered extensions of the light guiding channels 159 avoid the color crossovers in section 158 of the manifold. In this embodiment, the channel extensions 158b make an additional 90° turn before joining the distribution manifold 158a. This type of geometry enables the light sources to be mounted in a plane offset from, but parallel to that of the light guiding channels 159. The offset light sources can be mounted underneath the display as illustrated in FIG. 1 lb or they can be mounted outboard of the display area as shown in FIG. 1 lc either below the plane of the light guide channels 159 as depicted in the drawing or above it.

Yet another embodiment of the present invention, illustrated schematically in FIG. 12, can be configured to illuminate an LCD from more than one perimeter edge. In this embodiment the light distribution system 152 is capable of uniformly illuminating a large display area.

The arrangement illustrated in FIG. 12 can also provide multiple zones where the illumination intensity of one zone can be adjusted to be different than the illumination intensity of any of the other zones. This feature enables the present invention to be compatible with multi-zone backlight dimming that is frequently used in LCDs for reducing the power consumption of LCD as well as extending the dynamic range of the LCD's contrast, commonly referred to as local dimming.

While a particular manifold arrangement is indicated in FIG. 12, the use of other manifold arrangements such as those previously discussed is anticipated. Also in FIG. 12, 8 independently KLT-OOl/PCT addressable zones (A-H) are illustrated; however, configurations are anticipated with fewer or more than 8 zones.

Embodiments of the channelized light guide can be fabricated with any of the manufacturing methods currently being used to manufacture light guide plates; injection molding and die cutting with embossing are presently the most widely used methods to make light guide plates. In addition to the injection molding and embossing methods, new manufacturing methods such as thermoforming and printing, may also be used to fabricate the channelized waveguides described herein. The waveguides can be molded with a high index polymer

With injection molding, after the waveguide channel cores are molded with a high index polymer, the gaps between adjacent channel cores would be filled, or partially filled, with a low index polymer, having a lower refractive index than the material of the channels 159. The low index polymer would serve both as the optical cladding for the waveguide cores as well as provide the mechanical rigidity necessary to lock all of the waveguide channels into their precise relative positions. An example of this type of embodiment is illustrated in FIGs. 13a and 13b. In FIG. 13a the low index of refraction polymer material 162 partially or completely fills the gaps between the high index waveguide channels 159. An alternate embodiment shown in FIG. 13b illustrates the low index material filling the gaps and cladding the lower side of the waveguide channels 159 to provide additional mechanical support of the waveguide channels.

One method for manufacturing the channelized waveguide is to stack three sheets of the previously die-cut light guide material as was illustrated in FIG. 6. One die cut sheet for each of the three primary colors. In that portion of each of the sheets that corresponds to area under the viewable area of the display 159 each sheet has been die-cut to remove 2/3 of material between the color waveguide channels. The die-cutting operation would also form the light injection structures 158a and the light distribution manifold 158b. When stacked, the light distribution manifold 158 provides the desired 3-dimensional cross-over network in the area that is outboard of the viewable area of the display (for example the areas outside of the areas A-H of FIG. 12) while in the area that corresponds to area under the viewable area of the display, the 3 color waveguide channels would intcrdigitatc and all would lie in a common plane. As illustrated in FIG. 14, mechanical stability can be provided to the waveguide channels by laminating a low KLT-OOl/PCT index polymer 162 to either the bottom or the top of the stacked but interdigitated waveguide channels thereby mechanically locking all of the waveguide channels into their precise relative positions.

New manufacturing methods such as thermoforming could be used to implement embodiments of the channelized waveguide design. Referring to FIG. 1 5a parallel strands of polymer waveguides 163 each consisting of a core of high index polymer material and a cladding of a low index polymer material are aligned with the parallel molding channels of a thermoforming mold 164. The assembly is heated and pressed together with a sheet of polymer material 162,

preferably of a low index of refraction. The thermoforming machine compresses the polymer waveguides 163 into the parallel mold channels resulting in a structure schematically illustrated in FIG. 15b. As indicated in FIGs. 15a and 15b, the initial cross-sectional shape of the parallel mold channels have the desired shape of the core of the waveguide channels but the strands of the polymer waveguides 163 may have a different cross-sectional shape than that of the mold channels. A subsequent shaving or polishing operation would remove the optical cladding from the upper surface of the waveguide channels to enable light to be extracted from the waveguide channels. After de-molding, the thermoformed structure is the same as that which was shown in FIG. 14.

As illustrated in FIG. 16, the embossing process followed by a backfilling process can also be used to fabricate embodiments of the channelized light guide disclosed herein. An embossable material with a low index of refraction 162 is embossed to form waveguide channels. A material with a high index of refraction 165 is subsequently backfilled into the prepared waveguide channels to form the waveguide core. An optional top layer of a low index of refraction material can be added to cover the structure. Although rectangular waveguide core cross-sections 159 are shown in FIG. 16, other geometries, such as round, with specific optical benefits are anticipated. Printing methods can also be used to manufacture embodiments of the channelized light guide disclosed herein. As schematically illustrated in FIG. 17a, a sheet of low index of refraction polymer material such as PMMA would be used as the substrate 162. FIG. 17b illustrates Gravurc or other printing methods being used to print the high index of refraction material that would form the cores of the parallel waveguide channels 165 onto the surface of the low index substrate 162. The waveguide channels 165 may be made of a material having a higher refractive index than the substrate 162. With this approach, the bottom side of the cores of the parallel waveguide channels would have an interface with the low index substrate polymer 162 while the remaining sides (sidewalls) would have air interfaces. Surface texturing features that provide sites for the illumination to escape from the waveguide channels could be incorporated as part of the printing process or embossed later. An optional additional printing step shown in FIG. 17c could fill the gaps between the cores of the waveguide channels with a material having lower refractive index than the waveguide channels 165 to produce waveguide cores that are clad on all but the upper surface with a low index of refraction polymer. This alternative construction has the advantage that the surface is planarized and amenable to additional printing or processing steps. The waveguide channels 165 may also be sandwiched between the lower refractive index substrate 162 and a sheet of material 162a having a lower refractive index than the channels as shown in FIG. 17c.

Multi-layer printing technology would be used to form the color crossover networks in the input structure region. In this embodiment the input structure region of the common substrate contains a 3-dimensional patterned layer of alternating low index and high index polymers.

The descriptions of the embodiments of the current invention that are shown in FIGs. 5a through I lc include implementations in which the manifolds 158 that couple the input light into each of the respective waveguide channels 159 are integral with or fabricated in or on a common substrate with the waveguide channels. An alternate embodiment, which is the preferred embodiment, is to accomplish these two distinct functions separately. The embodiments of the present invention illustrated in FIGs. 13 through 17 anticipate the possibility of separating the fabrication of the waveguide channel structures from the input manifold structures. FIG. 18 illustrates an example of separately fabricating the light guide channels 159 from the input manifold 158. For simplicity in FIG. 18, the entire manifold structure 158 is not depicted, only the cross-over portion that enables the individual colors to be interleaved in a single plane is shown. It is anticipated that any of the other input structure geometries discussed in conjunction with FIGs. 5 through 1 1 can be implemented in this separate input structure embodiment. This partitioning of the system into the separate functions enables optimal fabrication technology to be used for each function, independent of the constraints that one function necessarily imposes on the other when the fabrication of the entire unit is completed with a common substrate. For example, fabricating the large 2-dimensional areas of thin sheets of waveguide channels is most easily accomplished with printing and embossing types of processes whereas the 3-dimensional cross-over networks necessary for implementing the input manifold are best accomplishes with injection molding for example. This approach also enables the possibility of creating alignment and attachment features that are built-in to the input manifold structure that can precisely position and attach the light sources to the input manifold.

Claims

WHAT IS CLAIMED IS

1. An apparatus to deliver light to the sub-pixels of each pixel in a liquid crystal display comprising:

two or more light distribution assemblies, each light distribution assembly comprising; a manifold coupled to a plurality of light guiding channels; wherein the manifold is configured to receive light from a source and distribute it to the plurality of light guiding channels; wherein each of the light guiding channels is configured to deliver light to corresponding sub-pixel locations in the liquid crystal display;

wherein light from each light distribution assembly is prevented from mixing with light from one or more of the other light distribution assemblies in the apparatus.

2. The apparatus of claim 1 wherein the light guiding channels include textured features manufactured onto the surface of the light guiding channels, wherein the textured features are configured to deliver light to corresponding sub-pixel locations.

3. The apparatus of claim 1 wherein each light distribution assembly is configured to deliver a different color of light to its corresponding sub-pixels.

4. The apparatus of claim 1 wherein each light guiding channel has a core made from a material having an index of refraction and a cladding made from a different material with a lower index of refraction than the core.

5. The apparatus of claim 1 wherein the distribution assemblies receive light of a specific color from a backlighting source.

6. The apparatus of claim 1 wherein the distribution assemblies receive colored light from a backlighting source located outside a viewing area of a liquid crystal display.

7. The apparatus of claim 1 , wherein the manifolds and the light guiding channels are

configured to be located in substantially the same plane.

8. The apparatus of claim 1 , further comprising two or more light sources of different

colors, wherein each of the two or more light sources is configured to couple light to the

manifold of a corresponding one of the two or more light distribution assemblies which deliver the colored light to the corresponding color subpixels.

9. A method of forming an apparatus to deliver colored light to the sub-pixels of each pixel in a liquid crystal display, the method comprising.

coupling one or more manifolds to one or more corresponding pluralities of light guiding channels; wherein each of the two or more manifolds is configured to receive light from a source and evenly distribute it to the plurality of light guiding channels; wherein each of the light guiding channels is configured to deliver colored light to corresponding sub- pixel locations, wherein colored light from each light distribution assembly is prevented from mixing with colored light from one or more of the other light distribution assemblies in the apparatus.

10. The method of claim 9, further comprising:

providing reinforcement to each plurality of light guiding channels by at least partially filling the gaps between the light guiding channels with material having a lower index of refraction than a material of the light guiding channels.

1 1 . The method of claim 9, further comprising embossing or printing on a surface of the light guiding channels a patterned design configured to scatter light from the light guiding channels to the sub-pixel locations without mixing colors.

12. The method of claim 9 further comprising laminating a material with a lower index of refraction than the light guiding channels to either the top or bottom surfaces of the light guiding channels.