Abstract:
A display device includes: an array of color pixels each color pixel including a plurality of individually addressable subpixels for emitting different colored light; and a fiber optic faceplate arranged adjacent the array of color pixels, with one fiber for each color pixel.

Description:
FIELD OF THE INVENTION 
   The present invention relates to light emitting color display devices and more particularly to color display having fiber optic faceplates. 
   BACKGROUND OF THE INVENTION 
   Digital imaging displays use individual addressable picture subpixels or pixels to display imagery and data on the displays. These pixels are designed to meet a variety of objectives for a product and for manufacturing processes. For example, pixel layout density, process design rules, interconnect cross-talk, and power distribution are all concerns for imaging displays. The displays are also designed to match the needs of the human visual system. 
   Typical pixel layouts used in digital imaging displays are shown in  FIGS. 2 and 3 . Referring to  FIG. 2 , a prior art stripe pattern of alternating red  10 , green  12 , and blue  14  light emitting pixel columns are interspersed with non-light emitting areas. A typical design attempts to reduce the amount of non-light emitting area to increase the amount of light that can be emitted from the device. The ratio between the light emitting area and the non-light emitting area is called the fill factor. Referring to  FIG. 3 , a prior art delta pattern is illustrated in which alternate rows  22  and  24  of the stripes of  FIG. 2  are placed out of phase. 
   Digital imaging displays using the pixel layouts illustrated in  FIGS. 2 and 3  can be found in various display technologies. In particular, they may be applied in organic light emitting diode (OLED) displays. OLED displays have many advantages as a flat-panel display device and are useful in optical systems. 
   It is well known in the art to use fiber-optic subpixels in conjunction with display devices to transport the light from a display to a different location. Conventionally, fiber subpixels or faceplates are placed above the cover of a display, for example an LCD or OLED device. Sakai et al. describe a tiled display application in U.S. Pat. No. 5,465,315, issued Nov. 7, 1995, using fiber arrays in conjunction with LCD displays. However, most fiber subpixels or light pipes have a circular cross-section. This circular cross-section does not match the typical, rectangular shape of pixels causing light loss in coupling from a display to a fiber for applications in which a single fiber or light pipe is associated with pixels or subpixels. In the best case, only 78% of the light from a square pixel enters a circular light fiber centered on, and touching, a square pixel, as shown in FIG.  4 . Referring to  FIG. 4 , a circle  30  is shown superimposed above a square  32  circumscribing it. If the fibers are made larger, so as to cover a greater portion of the area of the pixel (as shown in  FIG. 5 , which illustrates a square  32  circumscribed by a circle  40 ), the density of pixels is reduced. Rectangular pixels with larger aspect ratios become progressively worse. The situation is exacerbated when the fill factor of the display is taken into account. Any non-light emitting area located within the fiber area is effectively wasted and increases the cost of the fiber. If the fibers are made very small so that many fibers are associated with every pixel, costs also increase and the fill factor of the device is replicated on the viewing surface. Moreover, fiber plates with many small subpixels are more expensive than arrays of larger plastic light pipes. If single, larger fibers are associated with an entire conventional three-color pixel, the fill factor and light coupling are even more problematic. 
   JP07028050 entitled “Image Display Device” describes an image displaying device where many dot-shaped pixels are arranged two-dimensionally and a filter consisting of optical fibers is arranged on the display optical path of the image displaying device. It is also known to create hexagonal pixel shapes as described in, for example, JP 7261166 A. 
   In all of these designs, one or more fibers or light pipes are associated with a single pixel subpixel of one color. Hence, the fiber subpixels associated with each color component of a pixel must be small relative to the pixel size. 
   There is a need therefore for an improved color display design with improved coupling to an optical fiber faceplate. 
   SUMMARY OF THE INVENTION 
   The need is met according to the present invention by providing a display device that includes: an array of color pixels each color pixel including a plurality of individually addressable subpixels for emitting different colored light; and a fiber optic faceplate arranged adjacent the array of color pixels, with one fiber for each color pixel. 
   ADVANTAGES 
   The present invention has the advantage that it increases the efficiency of display devices having optical fiber faceplates. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a diagram illustrating a circular three-color pixel having pie-shaped subpixels according to one embodiment of the present invention; 
       FIG. 2  illustrates a prior art striped pattern for flat-panel displays; 
       FIG. 3  illustrates a prior art delta pattern for flat-panel displays; 
       FIG. 4  is a diagram showing a circular light pipe having a diameter equal to the side of a square pixel; 
       FIG. 5  is a diagram showing a circular light pipe having a diameter equal to the diagonal of a square pixel; 
       FIG. 6  is a side view of a display device having a fiber optic faceplate; 
       FIG. 7  illustrates a hexagonal pixel according to one embodiment of the present invention; 
       FIG. 8  illustrates an octagonal pixel according to one embodiment of the present invention; 
       FIG. 9  illustrates a cruciform pixel according to one embodiment of the present invention; and 
       FIG. 10  illustrates a rectilinear pixel with smaller features according to one embodiment of the present invention. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   Referring to  FIG. 1 , one embodiment of the present invention is shown. In  FIG. 1 , the pixel geometry consists of a circular light-emitting, three-color pixel  50  with three subpixels  51 R, G, and B within a square pixel area  52  wherein each subpixel is a different color. Although the subpixels are shown having equal sizes, they may be of different sizes. Any necessary circuitry, for example power and control connections and transistors are located around the pixel  50 , for example in the corners of the square area  52 . Referring to  FIG. 6 , a display device  57  includes an array  55  of pixels  50 , configured according to the present invention, located in close alignment with light pipes or optical fibers  58  in a fiber optic faceplate  59  located over the array of pixels  50  to convey the light to a preferred location. The array of pixels  50  may form a two-dimensional regular array as is well known for traditional displays. 
   In practice, tolerance limitations of manufacturing processes require that the active area of subpixels have a gap  53  between them as illustrated in FIG.  1 . The degree of separation is specified by the tolerances of the manufacturing process. 
   Some manufacturing processes or display layout geometries can be further constrained in the shapes and orientation of features that are supported. In an alternative embodiment of the present invention, subpixels can be limited to shapes having straight edges. For example, a hexagonal shaped pixel can be utilized as shown in FIG.  7 . Each of the three colored subpixels  51 R, G, B is a rhombus that together, forms a hexagonal pixel  50  within a square pixel area  52 . The pixel  50  is shown with gaps between the subpixels  51 . In this example, it is straightforward to make the three subpixels  51  the same size, since the hexagonal shape of pixel  51  is readily divided into three identical portions. 
   In an alternative embodiment, an octagonal shape can be utilized as shown in FIG.  8 . Octagonal pixel shapes may be preferred since they have edges at 45 degrees to the vertical and horizontal, thus improving the display quality for diagonal lines. The pixel  50  comprises the three color subpixels  51 R, G, B as shown within a square pixel area  52 . In an octagon, the central rectangle includes one half of the area while the two side subpixels include the other half of the area. Hence, in order to make the three subpixels the same size, the central rectangle has an edge smaller than the edge of the octagon and the side subpixels include some of the central area. 
   In a further alternative embodiment, the features of the pixel are rectilinear. Rectilinear shapes are easier to lay out and are more compatible with conventional interconnect and electronic component structures, such as those found in an active matrix display. Referring to  FIG. 9 , a pixel  50  has three components  51 , a central rectangle and two side subpixels whose aspect ratio is approximately the inverse of the central rectangle. The pixel  50  represents the active, light-emitting area of the pixel, the square  52  represents the entire pixel area, including any non-light emitting elements such as wiring, transistors and capacitors (not shown) within the square  52 . As shown in  FIG. 9 , the light emitting area is largely included within a circle  56  circumscribed by the square  52  so that a light fiber with a circular cross-section placed in close proximity to the pixel  50  will transmit nearly all of the light emitted by the pixel  50 . At the same time, the pixel area  52  and light emitting subpixels  51  have rectilinear boundaries, thereby enhancing the manufacturability of the display. The relative widths and heights of the subpixels  51 R, G, B may be altered to suit differing fill factors, color intensities or lifetimes of the color components or materials. 
   Given, as an example, a 50% fill factor in a square layout, one half of the overall pixel area  52  is filled with equal sized light emitting subpixels  51 . In this case, if the pixel edge is designated h and the width of the vertical component is x, then the area of subpixel  51 G is hx. The area of subpixels  51 R and B are the same and equal to the area of  51 G. For convenience in design, we can arbitrarily set the height of subpixels  51 R and B to one half that of subpixel  51 G and the width of the square area  52  equal to the height. Therefore, hx=(h/2)((h/2)−x). Solving for x yields x=h/6. Therefore, for a configuration in which the fill factor is 50%, the three color subpixels are of equal size and half the height of the central subpixel, the central subpixel is h by h/6 and the two side subpixels are h/2 by h/3. All have the same area: h 2 /6. In this configuration, the present invention improves the light coupling area from 39% to nearly 100%. Moreover, the fill factor of the viewed side of the array of light pipes can be, for example, 78% if the circular pipes are touching, while the fill factor of the display device itself is only 39%. This improvement is not possible if many small fibers are used in a traditional face-plate. 
   The configuration of  FIG. 9  provides large rectilinear feature sizes. If smaller feature sizes and tolerances can be achieved in a manufacturing process, the shape of the light emitting pixel  50  can become more circular, thus enhancing the coupling of light from the light emitting pixel to the fiber. For example,  FIG. 10  illustrates a rectilinear layout that is more nearly circular but has smaller rectilinear features. In  FIG. 10 , the subpixels have stepped edges  70 . The exact configuration of the edges will depend on the various factors cited above. 
   It is also known to provide fiber optic faceplates with light pipes having rectangular cross sections. In such a case, the pixel and subpixels can be rectangularly shaped. 
   A wide variety of configurations using the present invention are possible. Different fill factors may be used, the colors may change position or relative size, the horizontal and vertical components can be exchanged, the ratio of height of the horizontal components to the vertical may be changed. In particular, the subpixels may be of different sizes to accommodate differences in efficiency or lifetimes of the materials comprising the different colored subpixels. 
   The present invention can applied to emissive displays made of OLED materials, either top- or bottom-emitting (emitting light from the cover or the substrate). The fiber optic faceplate can comprise the cover or substrate of the OLED display device. 
   The invention may be employed in a device that includes Organic Light Emitting Diodes (OLEDs) which are composed of small molecule or polymeric OLEDs as disclosed in but not limited to U.S. Pat. No. 4,769,292, issued Sep. 6, 1988 to Tang et al., and U.S. Pat. No. 5,061,569, issued Oct. 29, 1991 to VanSlyke et al. Many combinations and variations of organic light emitting displays can be used to fabricate such a device. 
   The invention has been described in detail with particular reference to certain preferred embodiments thereof, but it will be understood that variations and modifications can be effected within the spirit and scope of the invention. 
   Parts List 
   
     
       
             
             
             
           
         
             
                 
                 
             
           
           
             
                 
               10 
               red pixel 
             
             
                 
               12 
               green pixel 
             
             
                 
               14 
               blue pixel 
             
             
                 
               22 
               row of stripes 
             
             
                 
               24 
               row of stripes 
             
             
                 
               30 
               circle 
             
             
                 
               32 
               square 
             
             
                 
               40 
               circle 
             
             
                 
               50 
               color pixel 
             
             
                 
               51R 
               red subpixel 
             
             
                 
               51G 
               green subpixel 
             
             
                 
               51B 
               blue subpixel 
             
             
                 
               52 
               square pixel area 
             
             
                 
               53 
               gap 
             
             
                 
               55 
               pixel array 
             
             
                 
               56 
               circle 
             
             
                 
               57 
               display device 
             
             
                 
               58 
               light pipe or optical fiber 
             
             
                 
               59 
               fiber optic faceplate 
             
             
                 
               70 
               stepped edges