Patent Abstract:
A system for illuminating a reflective display or other material from a planar front device and a method of manufacture thereof. The system includes a light guide plate that conducts light from an edge light source across the face of a reflective display. Micro lenses are formed on the inner or outer surface of the light guide and direct the light conducted in the light guide toward the display. A stepped index layer is formed on the surface of light guide plate containing the micro lenses. The stepped index layer has an index of refraction lower than an index of refraction of the light guide plate to assist in the total internal reflection of light injected into the light guide plate. A top layer protective coat or touch screen can be laminated to the outside of the light guide plate.

Full Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims benefit of U.S. Provisional Application No. 61/525,641, filed Aug. 19, 2011, which is hereby incorporated by reference. 
    
    
     FIELD OF THE INVENTION 
     The present invention generally relates to planar front illumination systems for the illumination of reflective materials and displays, and more particularly to a light guide plate that conducts light from an edge light source across the face of a reflective display. 
     BACKGROUND OF THE INVENTION 
     In contrast to backlit displays (e.g., a backlit transmissive Liquid Crystal Display, LCD), where light is projected through one or more filters or shutters to create an observable image, a reflective display (e.g., an electrophoretic display, EPD) relies on light reflected off of a reflective surface to generate an image. Typically, reflective displays make use of the ambient light present in the environment where the display is used. Planar front illumination systems have been used for many years to augment the ambient light so that reflective displays can be used in darker environments. Typical planar front light illumination systems are made of clear materials and are attached to the front of reflective electronic displays. Front lights provide supplemental illumination to the face of the display when the reflected ambient light is insufficient to create an observable image. 
     An ideal front light illumination system would be able to efficiently and uniformly direct the light from a supplemental light source toward the display while not emitting stray light toward the environment or user. This ideal front light illumination system passes all of the reflected light to the user without optical loss or optical artifacts. Further, such an ideal front illumination system would be unobtrusive under ambient lighting, i.e., maintaining the contrast, brightness and image quality of the underlying display. In addition, such an ideal front light is also low cost, thin, lightweight, easily manufactured, compatible with touch technologies and widely available. 
     One common type of front light illumination system includes a light guide plate constructed with numerous microscopic optical surface features. Each of these optical surface features incrementally redirects a small portion of the light inside the light guide plate using reflection or refraction. Ideally, these optical surfaces extract and distribute the luminous flux within the light guide plate uniformly over the surface of the reflective display. To achieve reflection or refraction without mirrored surfaces (which would be costly and/or difficult to produce), optical engineers carefully construct the critical features and angles of the micro optical surface features to reliably and predictably reflect or refract despite the often poor collimation (i.e., the wide distribution of ray angles) of the source illuminators (e.g., LEDs or fluorescent tubes). The refractive and reflective feature of an optical interface is strongly dependent on the relative indices of refraction of the materials on either side of the interface. To maximize the reflective and refractive power of these micro optical features, the micro optical features are usually exposed directly to air to maximize the refractive index difference. 
       FIG. 1  shows a front illumination system with microscopic optical surface features. This system comprises a reflective display  100 , a light source  101  and a light guide plate  102 . The light guide plate has optical features  103  formed on the outer facing surface of the front illumination system. The light source  101  is typically comprised of one or more cold cathode fluorescent lights (CCFLs) or one or more LEDs suitably arranged to produce moderately collimated light  104  directed into a light injection surface of the light guide plate  102 . 
     Common additional features known in the art (not shown) include a reflective housing for the light source, surface treatments on the light source  101  and the injection area of the light guide plate  102 , and films or mixing plates inserted between the light source  101  and light guide plate  102  that improve coupling efficiency, uniformity, manufacturability, optical performance and cost. Such additions are applicable to the present invention as well to achieve similar advantageous effects. 
     The light guide plate  102  has nominally coplanar light guiding surfaces (top and bottom of  102  in  FIG. 1 ). A substantial portion of the light  104  injected into light guide plate  102  remains within the light guide plate  102  due to the well-known optical effect of total internal reflection (TIR). Light guide plate  102  has a plurality of micro optic features  103  on its outer surface that redirect a portion of the guided rays  107  downward at each micro optic feature  103 . Ideally, the injected light  104  is uniformly redirected and distributed across the entire surface of the reflective display  100 . To achieve uniformity, the density, height, angle, pitch and shape of the micro optic features  103  and the thickness or shape of the light guide plate  102  is modulated across the breadth and width of the light guide plate  102  to account for the diminished light flux as a function of distance from the light source  101 . 
     The incrementally redirected light  107  illuminates the reflective display  100  creating reflected rays  109  that can be seen by a user (the user, not shown, is above the front illumination systems as illustrated herein). 
     A typical front illumination system is usually only activated when the ambient light  108  falling on the display from external sources is insufficient for the user to perceive an image from the reflective display  100 . When ambient illumination  108  is strong enough and consequently the front illumination source is not needed, the front illumination system should be as unobtrusive as possible. Specifically, the front light system should not create unusual reflections, image artifacts or stray light paths that degrade the appearance of the underlying display. 
       FIG. 2  shows a prior art back illumination system comprising a transmissive display  200 , a light source  201  and a light guide plate  202 . Light guide plate  202  has printed white dots  203  on the outer surface farthest from the display  200 . The light source  200  injects light  204  into the light guide plate  202 , which is then substantially guided by total internal reflection in a lateral direction in the light guide plate  202 . A plurality of small white dots  203  is screen or inkjet printed, etched, stamped, burned, or molded (among the many conventional methods well known in the art of backlight design) on the outer surface of the light guide plate  202  to act as scattering centers that redirect the guided light in a diffuse scattering pattern  207  towards the transmissive display  200  and ultimately toward the viewer (ray  209 ). The density, color, scattering effects and/or sizes of the dots  203  is conventionally varied as a function of position to account for non-uniformity of the light source and to compensate for the consumption of guided light flux as a function of distance from the light source  201 . As is known in the art, additional films  208  are conventionally placed between the back light and the transmissive display (e.g. diffusers and light redirecting films, polarization recycling films, etc.) to improve the optical efficiency, contrast, viewing angle and uniformity of the overall display. 
     The refractive and reflective feature of an optical interface between two clear materials (e.g. plastic and air) is strongly dependent on the relative indices of refraction of the materials on either side of the interface. To optimize the light guiding (via total internal reflection) and light extraction (via scattering, reflection or refraction) behaviors, the micro optical features are usually exposed directly to air to maximize the refractive index difference. 
     SUMMARY OF THE INVENTION 
     The front illumination systems of the prior art that rely on air interfaces, while improving the refracting and reflecting effects, create a number of substantial difficulties that are solved by the present invention. First, air gaps between optical elements over a wide area are difficult to mechanically construct while maintaining thinness and optical quality. If the front illumination system is integrated with a touch panel function, the front face must be sufficiently rigid so that it can maintain the air gap under worst case user finger pressure. Air gaps, due to the high relative index of refraction change, also can create substantial unwanted reflections unless costly anti-reflection coatings are used at each interface. 
     Second, if air gaps are formed on films that are subsequently laminated to a light guide plate (i.e., an embedded air gap), these air gaps are difficult to control in production as the lamination adhesive can be displaced into the air gaps or grooves, modifying the behavior of the light extraction phenomena and creating uniformity problems. An inherent tradeoff in adhesion strength versus optical quality and feature size is introduced that may not provide satisfactory solutions. Furthermore, air pressure and humidity vary widely (sometimes quickly, e.g., on an aircraft) and condensation, contamination and pressure related effects (if sealed) can create engineering, production and user difficulties. 
     Further, since the source light is usually poorly collimated, stray light leakage can be inadvertently directed toward the viewer, significantly increasing the brightness of the black level and thus degrading contrast. Such stray light leakage, even if not directed to the viewer, e.g., if exported at a highly acute angle from the front surface of the display system, can still result in poor electro-optical efficiency, which can negatively impact the battery life of mobile devices. 
     Additionally, controlling the quality of the micro optical features created in a molding process can be challenging as the light guide plate is made thinner and lighter. 
     Another concern associated with the prior art systems is that mechanical damage, e.g., scratches, may extract light from the light guide plate causing them to be especially highlighted when the front light is activated. Additional mechanical barriers between the light guide plate and the user are often required to prevent scratch highlighting, increasing thickness of the front illumination system and degrading optical performance of the display system. 
     Front light illumination system design forces a number of compromises where optical design goals, e.g. minimizing ambient reflections and image artifacts. are optimized at the expense of some other constraints, e.g., the cost of anti-reflection coatings and thickness of the system. 
     The front illumination system of the present invention addresses a number of the aforementioned limitations and forced compromises in the art, enabling a fully laminated, thin, light, economical, uniform, mechanically robust, efficient, highly transparent, low artifact, low leakage front illumination system. 
     The system of the present invention includes a light guide plate that conducts light from an edge light source across the face of a reflective display. Micro lenses are formed on the inner or outer surface of the light guide. The micro lenses direct the light conducted in the light guide toward the display. A layer having a lower index of refraction is formed on the surface of the light guide plate having the micro lenses. This layer is also known as a stepped index layer and assists in substantially confining the injected light in the light guide plate by total internal reflection. This structural configuration provides a fully laminated front illumination system with a buried light guide layer. In a preferred embodiment, the micro lenses are formed as concave or convex structures in or on the surface of the light guide plate. In another embodiment, a touch screen can be laminated inside protective layers either above or below the light guide plate. 
     The planar front illumination system of the present invention can be fully laminated with no air gaps and no air pockets in order to maximize ruggedness and minimize internal surface reflections that can degrade optical performance. The system simplifies integration of reflective displays with touch sensor. The system is thin and light. The system maximizes the light directed inward toward the display while minimizing stray light in all other directions. The system generates substantially uniform illumination over a large area and minimizes display and illumination related artifacts such as Moire, ghosting and pressure sensitivity. The system is efficiently and inexpensively produced. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       For the purposes of illustrating the present invention, there is shown in the drawings a form which is presently preferred, it being understood however, that the invention is not limited to the precise form shown by the drawing in which: 
         FIG. 1  depicts a prior art front illumination system for a reflective display with micro optic features on the front face of a light guide plate; 
         FIG. 2  illustrates a prior art back illumination system for a transmissive display utilizing a printed dot pattern light guide plate; 
         FIG. 3  illustrates a planar front illumination system of the present invention with convex micro lenses formed on the inner face of a light guide plate; 
         FIG. 4  depicts a planar front illumination system of the present invention with convex micro lenses formed on the inner face of a light guide plate with a laminated outer protective sheet; 
         FIG. 5  illustrates a planar front illumination system of the present invention with concave micro lenses formed on the inner face of a light guide plate; 
         FIG. 6  depicts a planar front illumination system of the present invention with concave micro lenses formed on the inner face of a light guide plate with a laminated outer protective sheet; 
         FIG. 7  depicts a planar front illumination system of the present invention with concave micro lenses formed on the outer face of a light guide plate with a laminated outer protective sheet; and 
         FIG. 8  illustrates a planar front illumination system of the present invention with convex micro lenses formed on the outer face of a light guide plate with a laminated outer protective sheet. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The following abbreviations are utilized in the following description, which are intended to have the meanings provided as follows: 
     CCFL—cold cathode fluorescent light 
     EPD—electrophoretic display 
     LCD—liquid crystal display 
     LGP—light guide plate 
     LED—light emitting diode 
     OCA—optically clear adhesive 
     OLED—organic light emitting diode 
     PC—polycarbonate 
     PET—polyethylene terephthalate 
     PMMA—poly methyl methacrylate 
     TIR—total internal reflection. 
       FIG. 3  illustrates an embodiment of the present invention including a reflective display or material  300 , a light source  301  and a light guide plate  302 . A plurality of convex micro lenses  303  is formed on the inner surface of the light guide plate  302 , the surface closest to the reflective display  300 . The light source  301  and light guide plate  302  are coupled as is well known in the art to achieve efficient, uniform and reproducible light injection  304  into the light guide plate  302 . Laterally propagating rays  305  are confined within the light guide plate  302  by, in part, the TIR effect  306  from the inner surface of the light guide plate  302  at the interface to a stepped index layer  310 . The stepped index layer  310  has an index of refraction that is lower than that of the light guide plate  302 . In a preferred embodiment, the stepped index layer  310  is a clear adhesive layer that has a lower index of refraction than the light guide plate  302  in order to support total light guiding by TIR. The outer optical interface of the light guide plate  302  in the embodiment illustrated in  FIG. 3  is to air (above plate  302  in  FIG. 3 ). This interface also provides for TIR of guided rays  305 . Although air can be used as the stepped index layer, it is preferred to use some other material, such as the above described clear adhesive layer. 
     The term “stepped index” is borrowed from the fiber optic technology and is distinguished from other indexes such as “graded index” fiber which has a smooth index peak that confines a single mode in order to keep propagation speed very uniform). In a fiber structure, a cylindrical inner core of high index material is cladded with a lower index material to achieve TIR for light propagating down the length of the cylinder. In contrast to the use in fiber structures, the present invention uses its stepped index layer to confining light in only one dimension and leaves the light to freely propagate freely in the other two dimensions. In a fiber, the light is confined in two dimensions and can freely propagate in only one dimension. 
     Micro lenses  303  formed on the light guide plate  302  perform a light extraction function in which a portion of the incident guided rays  305  are refracted and/or reflected  307  toward the reflective display  300 . The reflective display  300  reflects the extracted light  307  and incident ambient light  308  toward the viewer (not shown) as rays  309 . These reflected rays  309  pass through the light guide plate  302 , optical adhesive layer  310  and micro lenses  303  with only small reflection and refraction effects. 
     In one embodiment of the present invention, the areal density of the micro lenses  303 , with respect to the surface area of the surface of light guide plate  302 , is varied within the light guide plate  302  to compensate for light source nonuniformity and variations in the optical flux in the light guide plate  302  as a function of position in order to present a substantially uniform light source to the display. In a preferred embodiment of the present invention, the density of the micro lenses  303  is increased farther from the light source  301  to achieve a more uniform flux  307  over the length of light guide plate  302 . In a further embodiment, the micro lens  303  density is adjusted near edges of the light guide plate  302  to account for side and opposing surface reflections and optical losses in order to achieve a more uniform extracted light field  307 . The areal density of the micro lenses  303  can range from near zero, &lt;1% by area, to very high, nearly 100%, depending on the non-uniformity of the light flux and the extraction efficiency of the micro lenses  303 . 
     The density of the micro lenses  303  can be simulated to get an initial areal density, and then empirically tuned during the manufacturing process, e.g., fabricating a light guide plate  302  with a specific areal density of micro lenses  303 , measuring the uniformity of the light on the display  300  and repeating this process, changing the density over many cycles to optimize the uniformity of the light flux 
     In a further embodiment of the present invention, the area of each micro lens  303  is kept substantially smaller than the underlying reflective display  300  unit pixel area so that the micro lenses  303  do not objectionably distort the underlying pixels (not shown in  FIG. 3 ). 
     In a further embodiment of the present invention, the height and profile of each micro lens  303  is engineered, e.g., by making substantially microscopically smooth edges and profile transitions, to allow the optical adhesive  310  to uniformly coat and fill all spaces around micro lenses  303  to prevent microscopic air bubbles from being trapped or forming after some post-manufacturing environmental exposure, e.g., exposure to low external air pressure at high altitudes, heat and/or humidity. 
     In a further embodiment, the convex shape of micro lenses  303  is tuned to the refractive indices of the light guide plate  302  and the optically clear adhesive layer  310  to optimize uniformity of the extracted light, manufacturing yield, tooling complexity and material cost by making the optical reflection and refractive effects insensitive to manufacturing and material variations. 
     In a further embodiment, the micro lenses  303  are made sufficiently small e.g., 50 microns or less, and spaced sufficiently closely together and sufficiently elevated above the image plane of display  300  so that the extracted light  307  reaching the display  300  image plane is substantially spatially uniform. 
     In a still further embodiment, the micro lenses  303  are designed to minimize direct reflection from ambient illumination  308  and to minimize distortion of the reflected image  309  through refraction by, for example, constraining the maximum angle of the micro lenses  303  relative to the light guide plate  302 . The micro lens  303  shape, micro lens  303  edge geometry, OCA  310  index of refraction, and OCA  310  softness, i.e., the ability to flow around the micro lens  303  shape, contribute to the contrast, brightness, clarity, and overall optical performance of he combined display system. By balancing the multiple demands on the micro lens  303  shape in accordance with the present teachings, one skilled in the art can minimize the perceived degradation of the reflective display  300  performance, e.g., contrast, brightness, clarity, caused by the front illumination system of the present invention. 
     A large number of materials are available for constructing the present invention. Light guides  302  typically have substantially flat surfaces and are commonly constructed of PMMA or PC plastic, although any optically clear material, e.g., glass, with an index of refraction that is higher than the surrounding material, e.g., air or vacuum above and the OCA  310  below the light guide plate  302  in  FIG. 3 . Similarly, the light source  301  can assume many forms and be made from many materials. For example a CCFL, an OLED or one or more LED lamps coupled to a light bar or mixing plate may be used within the present teachings as the light source  301 . One or more sides of the light guide plate  302  may have injecting surfaces with one or more light sources  301 . For simplicity, only one light source is shown in the figures but as is well known in the art, the number and positions of light sources, e.g., placed at one or more edges or corners, can be varied given system constraints on cost, light uniformity, brightness, mechanical boundaries, form factor, etc. Other light sources (e.g., incandescent lamps, lasers, vacuum fluorescent tubes) could be used. 
     The optical interfaces and surfaces of the components of the present invention can be coated, shaped, processed, textured or modified by the inclusion or application of specialized films so as to achieve any number of standard desirable changes in properties. These films can be used to improve light confinement, improve light guide injection uniformity, reduce stray reflections, improve light source  301  to light guide plate  302  coupling efficiency, improve light guide plate  302  to reflective display  300  interface or reduce the thickness and weight of the system. Such additions and modifications are well known in the art of illumination design and are available at the discretion of the designer to achieve the desired balance between cost, performance, yield, etc., without detracting from the scope of the present teachings. 
     Many options are available for fabricating micro lenses  303  on the light guide plate  302 . In one embodiment, the micro lenses  303  are printed using, e.g., an industrial inkjet printer and a clear UV cured polymer ink. Such printers can directly apply small, e.g., 30 microns or less, clear polymer dots precisely, rapidly and inexpensively onto the light guide plate. 
     In another embodiment, micro lenses  303  can be formed on the surface of the light guide plate  302  by an injection molding process when the light guide plate  302  is manufactured. In this process, a metal mold is tooled with precise micro lens indentations and plastic is injected into the mold creating convex lenses  303  at each metal mold indentation. 
     Micro lenses  303  can also be hot stamped, molded, mechanically embossed, engraved, chemically etched and/or created lithographically on the light guide plate  302 . Substituting such alternative techniques for creating micro lenses  303  on the inner surface of a front illumination light guide plate  302  are known to those skilled in the art and are included in the scope of the present teachings. 
     The exact shape of the micro lenses  303  can be substantially changed within the present teachings, e.g., circular, hemispherical, triangular, square, rectangular or oval shapes among others are all possible. In addition or in the alternative, lensing lines, segments or traces could be substituted for the round micro lenses  303  illustrated in  FIG. 3 . 
     In one embodiment of the present invention, the light guide plate  302  and the stepped index layer  310 , e.g., an optically clear adhesive layer, can be manufactured as a unit, for later incorporation in the assembly of a completed device having a light source  301  and a display  300 . 
     In an alternative embodiment, stepped index layer  310 , with an index of refraction lower than the light guide plate  302  can be co-extruded with the light guide  302  to achieve both protection and light confinement by TIR within in the light guide plate  702 . 
       FIG. 4  shows a further embodiment of the present invention comprising a reflective display or material  400 , a light source  401  and a light guide plate  402 . A plurality of convex micro lenses  403  is formed on the inner surface of the light guide plate  402 , the surface closest to the reflective display  400 . The light source  401  and light guide plate  402  are coupled as is well known in the art to achieve efficient, substantially uniform and reproducible light injection  404  into the light guide plate  402 . Laterally propagating rays  405  are confined within the light guide plate  402  by a TIR effect from the inner surface of the light guide plate  402  at the interface to a stepped index layer  410 . In a preferred embodiment, the stepped index layer  410  is a clear adhesive layer that has a lower index of refraction than the light guide plate  402  in order to support TIR light guiding. 
     An outer clear protective sheet  412  is laminated to the top of light guide plate  402  with an additional stepped index layer  411  disposed between the protective sheet  412  and the light guide plate  402 . In a preferred embodiment, the stepped index layer is an optically clear adhesive layer that has a lower index of refraction than the light guide plate  402 . This upper optical interface of light guide plate  402  also supports light guiding of the transversely travelling rays  405  by TIR. 
     In an alternative embodiment, a protective layer  412  with an index of refraction lower than the light guide plate  402  can be coextruded with the light guide plate  402  to achieve both protection and light confinement by TIR within the light guide plate  402 . In this embodiment, no adhesive layer is required and the protective layer  412  acts as the stepped index layer. 
     The micro lenses  403  of the embodiment illustrated in  FIG. 4  perform the same light extraction function as the micro lenses  303  described above with respect to  FIG. 3 . Further, all of the above description with respect to the manufacture and variations in the micro lenses  303  applies equally to the micro lenses  403 . 
     Micro lenses  403  formed on the light guide plate  402  perform a light extraction function in which a portion of the incident guided rays  405  are refracted and/or reflected  407  toward the reflective display  400 . The reflective display  400  reflects the extracted light  407  and incident ambient light  408  toward the viewer (not shown) as rays  409 . The incident  408  and reflected rays  409  pass through the protective sheet  412 , optical adhesives  410   411 , light guide plate  402  and micro lenses  403  with only small reflection and refraction effects. 
       FIG. 5  shows a further embodiment of the present invention comprising a reflective display or material  500 , a light source  501  and a light guide plate  502 . A plurality of concave micro lenses  503  is formed on the inner surface of the light guide plate  502 , the surface closest to the reflective display  500 . The light source  501  and light guide plate  502  are coupled as is well known in the art to achieve efficient, substantially uniform and reproducible light injection  504  into the light guide plate  502 . Laterally propagating rays  505  are confined within the light guide plate by TIR from the inner surface of the light guide plate  502  at the interface to a stepped index layer  510 . In a preferred embodiment, the stepped index layer  510  is a clear adhesive layer that has a lower index of refraction than the light guide plate  502  in order to support TIR. 
     Micro lenses  503  on the light guide plate  502  perform a light extraction function in which a portion  507  of the incident guided rays  505  are refracted and/or reflected by the lenses  503  and are directed toward the reflective display  500 . The reflective display  500  reflects the extracted light  507  and incident ambient light  508  toward the viewer (not shown) as rays  509 . These reflected rays pass through the light guide plate  502 , stepped index layer  510  and micro lenses  503  without substantial losses or distortions. 
     All of the above description with respect to the variations in the micro lenses  303  applies equally to the micro lenses  503 . 
     Concave micro lenses  503  can be formed on the surface of the light guide plate  502  by an injection molding process when the light guide plate  502  is manufactured. In this process, a metal mold is tooled with precise micro lens bumps and plastic is injected into the mold creating concave lenses at each metal mold bump. Numerous other processes known in the art can be adapted to create concave lens shapes, including hot stamping, etching, photolithography, sandblasting, mechanical engraving or drilling and laser engraving. 
       FIG. 6  shows a further embodiment of the present invention comprising a reflective display or material  600 , a light source  601  and a light guide plate  602 . A plurality of concave micro lenses  603  is formed on the inner surface of the light guide plate  602 , the surface closest to the reflective display  600 . The light source  601  and light guide plate  602  are coupled as is well known in the art to achieve efficient, uniform and reproducible light injection  604  into the light guide plate  602 . Laterally propagating rays  605  are confined within the light guide plate  602  by TIR from the inner surface of the light guide plate  602  at the interface to a stepped index layer  610 . In a preferred embodiment, the stepped index layer  610  is a clear adhesive layer that has a lower index of refraction than the light guide plate  602  in order to support TIR light guiding. An outer clear protective sheet  612  is laminated to the light guide plate  602  with an intervening stepped index layer  611 . In a preferred embodiment, stepped index layer  611  is an optically clear adhesive with a lower index of refraction than the light guide plate  602  in order to support light guiding by TIR. 
     In an alternative embodiment, a protective layer  612  with an index of refraction lower than the light guide plate  602  can be coextruded with the light guide plate  602  to achieve both protection and light confinement by TIR within in the light guide plate  602 . In this embodiment, no adhesive layer is required and the protective layer  612  acts as the stepped index layer. 
     Micro lenses  603  on the light guide plate  602  perform a light extraction function as described above with respect to  FIG. 5  in regard to concave micro lenses  503 . Further, all of the above description with respect to the variations in the micro lenses  303  applies equally to the micro lenses  603 . 
     Micro lenses  603  formed on the light guide plate  602  perform a light extraction function in which a portion of the incident guided rays  605  are refracted and/or reflected  607  toward the reflective display  600 . The reflective display  600  reflects the extracted light  607  and incident ambient light  608  toward the viewer (not shown) as rays  609 . The incident  608  and reflected rays  609  pass through the protective sheet  612 , optical adhesives  610   611 , light guide plate  602  and micro lenses  603  without substantial losses or distortions. 
       FIG. 7  shows a further embodiment of the present invention comprising a reflective display or material  700 , a light source  701  and a light guide plate  702 . A plurality of concave micro lenses  703  is formed on the outer surface of the light guide plate  702 , the surface that is farthest from the reflective display  700 . The light source  701  and light guide plate  702  are coupled as is well known in the art to achieve efficient, substantially uniform and reproducible light injection  704  into the light guide plate  702 . Laterally propagating rays  705  are confined within the light guide plate  702  by the TIR effect from the inner surface of the light guide plate  702  at the interface to a stepped index layer  710 . In a preferred embodiment, the stepped index layer is an optically clear adhesive layer that has a lower index of refraction than the light guide plate  702  in order to support TIR light guiding. 
     An outer clear protective sheet  712  is laminated to the top of light guide plate  702  with an additional stepped index layer  711 . In a preferred embodiment, the stepped index layer  711  is an optical adhesive layer that has a lower index of refraction than the light guide plate  702 . This upper optical interface of light guide plate  702  also supports light guiding of the transversely travelling rays  705  by TIR. 
     In an alternative embodiment, protective layer  712  with an index of refraction lower than the Light guide plate  702  can be co-extruded with the light guide  702  to achieve both protection and light confinement by TIR within in the light guide plate  702 . In this embodiment, no adhesive layer is required and the protective layer  712  acts as the stepped index layer. 
     Micro lenses  703  formed on the light guide plate  702  perform a light extraction function in which a portion  707  of the incident guided rays  705  are refracted and/or reflected toward the reflective display  700 . The extracted rays  707  pass through the light guide  702  and the clear adhesive layer  710  to the reflective display  700 . Reflective display  700  reflects the extracted light  707  and the ambient light  708  toward the viewer as rays  709 . These reflected rays  709  pass through the clear areas of light guide plate  702  and micro lenses  703  with only small reflection and refraction effects. 
     All of the above description with respect to the manufacture of the concave micro lenses  503  and the variations in the micro lenses  303  apply equally to the micro lenses  703 . 
       FIG. 8  shows a further embodiment of the present invention comprising a reflective display or material  800 , a light source  801  and a light guide plate  802 . A plurality of convex micro lenses  803  is formed on the outer surface of the light guide plate  802 , the surface that is farthest from the reflective display  800 . The light source  801  and light guide plate  802  are coupled as is well known in the art to achieve efficient, uniform and reproducible light injection  804  into the light guide plate  802 . Laterally propagating rays  805  are confined within the light guide plate  802  by the TIR effect from the inner surface of the light guide plate  802  at the interface to a stepped index layer  810 . In a preferred embodiment, the stepped index layer  810  is a clear adhesive layer that has a lower index of refraction than the light guide plate  802  in order to support TIR light guiding. 
     An outer clear protective sheet  812  is laminated to the top of light guide plate  802  with an additional stepped index layer  811 . In a preferred embodiment, the stepped index layer  811  is an optically clear adhesive layer that preferably has a lower index of refraction than the light guide plate  802 . This upper optical interface of light guide plate  802  also supports light guiding of the transversely travelling rays  805  by total internal reflection. 
     In an alternative embodiment, a protective layer  812  with an index of refraction lower than the light guide plate  802  can be coextruded with the light guide plate  802  to achieve both protection and light confinement by TIR within in the light guide plate  802 . In this embodiment, no adhesive layer is required and the protective layer  812  acts as the stepped index layer. 
     Micro lenses  803  formed on the light guide plate  802  perform a light extraction function in which a portion  807  of the incident guided rays  805  are refracted or reflected toward the reflective display  800 . The extracted rays  807  pass through the light guide  802  and the clear adhesive layer  810  to the reflective display  800 . Reflective display  800  reflects the extracted light  807  and the incident ambient light  808  toward the viewer (not shown) as rays  809 . These reflected rays  809  pass through the light guide plate  802 , optical adhesives  810   811 , protective sheet  812  and micro lenses  803  without substantial losses or distortions. 
     Further, all of the above description with respect to the manufacture and variations in the micro lenses  303  apply equally to the micro lenses  803   
     In the above embodiments of the present invention, the protective sheets  412 ,  612 ,  712  and  812  respectively provide a layer of mechanical separation between the light guiding layers  402 ,  602 ,  702  and  802  and the user so that mechanical marks, or surface contamination, e.g., scratches, gouges, oil, dirt, water, fingerprints, dust, etc. do not create inadvertent light extraction toward the user. Further, the protective sheets  412 ,  612 ,  712  and  812  can support additional layers and surface treatments that enhance the performance, e.g., anti-glare/haze, anti-reflection, anti-fingerprint, anti-scratch, hardcoat or other enhancements. If these additional layers are applied directly to the light guide plates  402 ,  602 ,  702  and  802 , they would possibly degrade the light guide confinement performance and adversely affect contrast, brightness or other display performance criteria under ambient or front lighted conditions. 
     In an additional embodiment of the present invention, the light guide plates  302 ,  402 ,  502 ,  602 ,  702  and  802  are fabricated from polycarbonate with an index of refraction of approximately 1.585, and the optical adhesive layers  310 ,  410 ,  411 ,  510 ,  610 ,  611 ,  710 ,  711 ,  810  and  811  are made of a low index optical adhesive with an index of refraction between 1.32 and 1.50. In an alternative embodiment of the present invention, the light guide plates  302 ,  402 ,  502 ,  602 ,  702  and  802  are fabricated from PMMA with an index of refraction of approximately 1.49 and the optical adhesive layers  310 ,  410 ,  411 ,  510 ,  610 ,  61 ,  710 ,  711 ,  810  and  811  are made of a low index optical adhesive with an index of refraction between 1.32 and 1.45. Those skilled in the art will recognize the wide variety of light guide materials and adhesive laminating materials that can be substituted within the general framework of the present teachings to create the conditions for sufficient confinement by TIR within the light guide plates  302 ,  402 ,  502 ,  602 ,  702  and  802 . 
     Those skilled in the art will also recognize that the protective layers  412 ,  612 ,  712  and  812  can be used as a substrate for integrating a fully laminated touch sensor onto the top of the display system. Such laminated touch sensors are well known in the art, e.g., projected capacitance, surface capacitance, and infrared, among others. The lamination of such a touch sensor as, or in addition to, the top protective layers  412 ,  612 ,  712  and  812  are within the scope of the present invention. 
     The light sources  301 ,  401 ,  501 ,  601 ,  701  and  801  are only shown as firing from a single edge to simplify the drawings. In practice, these light sources  301 ,  401 ,  501 ,  601 ,  701  and  801  can inject light from any or all edges and/or from one or more corners of the light guide plates  302 ,  402 ,  502 ,  602 ,  702  and  802 . A string of LEDs or point light sources arranged linearly along one or more edges of the light guide plate  302 ,  402 ,  502 ,  602 ,  702  and  802  can also constitute the light source  301 ,  401 ,  501 ,  601 ,  701  and  801  within the present invention. 
     Although the present invention has been described in relation to particular embodiments thereof, many other variations and other uses will be apparent to those skilled in the art. It is preferred, therefore, that the present invention be limited not by the specific disclosure herein, but only by the gist and scope of the disclosure.

Technology Classification (CPC): 8