Abstract:
A back-light assembly for uniformly illuminating large area displays. The back-light assembly includes a uniformly thin waveguide, a reflector and a plurality of light sources evenly distributed along the display area between the waveguide and the reflector. Prismatic facets are provided along the lower surface of the waveguide for effectively coupling light emitted from light sources into the waveguide.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention relates generally to back-light systems for uniform illumination of large area displays. More particularly the invention concerns collimating back-light systems for displays such as liquid crystals displays and micro-electromechanical light valve displays. 
         [0003]    2. Discussion of the Prior Art 
         [0004]    Back-light assemblies provide a planar light source for transmissive displays. More common light sources used in display back-lighting are cold cathode fluorescent lamps and light emitting diodes. 
         [0005]    Based on arrangements of light sources the back-light systems may be grouped either “edge-lit” or “direct-lit”. In direct-lit, back-light&#39;s plural light sources are evenly distributed along the display area and each of the light sources directly illuminates a small segment of the display. In order to achieve relatively uniform illumination the light sources are placed at a great distance from the display panel. This increases the depth of the display. Additionally, diffractive optical components and diffusers are placed between the light sources and the display panel. Each light source must align with the diffractive optical components. 
         [0006]    The only positive feature of direct-lit systems is that light sources and associated heat is evenly distributed along the display area. 
         [0007]    Edge-lit back-light systems comprise a light source, a thin, rectangular optical waveguide, a reflector or a diffuser at the back of optical waveguide and prism films mounted between the waveguide and the display panel. 
         [0008]    The primary limitation of edge-lit back-lights is its incapability of illuminating a large size display. Efficient light coupling and concentrated heat generated from the light sources limit the size of the edge-lit back-lights. 
       SUMMARY OF THE INVENTION 
       [0009]    It is an object of the present invention to provide a homogenized, collimated and highly efficient back-light assembly for uniform illumination of large area display. 
         [0010]    Another object of this invention is to provide a back-light assembly of the aforementioned character that exhibits an efficiency of greater than ninety-five percent. 
         [0011]    It is another object of this invention to provide a back-light assembly that effectively overcomes the limitations of prior art direct-lit and edge-lit back-light systems. 
         [0012]    It is another object of this invention to provide a back-light assembly that exhibits highly efficient light coupling between the light sources and the waveguide of the assembly. 
         [0013]    It is another object of this invention to provide a back-light assembly of the character described in the preceding paragraphs that is easily scalable for displays of different sizes. 
         [0014]    The foregoing as well as other objects of the invention will be achieved by the novel back-light assembly illustrated in the accompanying drawings and described in the specification that follows. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0015]      FIG. 1  is a generally perspective view of one form of the back-light assembly of the present invention. 
           [0016]      FIG. 2  is a side-elevation view of the back-light system shown in  FIG. 1 . 
           [0017]      FIG. 3  is a side-elevation view of an alternate form of the back-light assembly of the invention. 
           [0018]      FIG. 4  is a greatly enlarged view of the area designated in  FIG. 3  as  4 - 4 . 
           [0019]      FIG. 5  is a side-elevation view of still another form of back-light assembly of the invention. 
           [0020]      FIG. 6  is a greatly enlarged view of the area designated in  FIG. 5  as  6 - 6 . 
       
    
    
     DESCRIPTION OF THE INVENTION 
       [0021]    Referring to the drawings and particularly to  FIGS. 1 and 2 , one form of the back-light assembly of the invention for uniformly illuminating displays such as liquid crystal displays and micro-electromechanical light valve displays is there shown and generally designated by the numeral  14 . This embodiment of the invention comprises an optical waveguide  16  that has an upper, generally flat surface  18 , a first side surface  20 , a second side surface  22  and a specially configured lower surface  24 . Surface  24  uniquely includes a plurality of upwardly inclined optically flat first facets  26  with specularly reflective coatings and a plurality of downwardly inclined optically flat second facets  28 . 
         [0022]    As best seen in  FIG. 2  of the drawings, the first light-reflecting facets  26  are here inclined upwardly at an angle of between about two degrees and about fifteen degrees with respect to the plane of the upper surface  18  of the optical waveguide. The second light coupling facets  28  are inclined downwardly at a relatively steep angle of between about fifty degrees and about ninety degrees with respect to the plane of the upper surface  18 . As illustrated in the drawings, alternating facets  26  and  28  form generally V-shaped grooves that extend along lower surface  24  of the waveguide between sides  20  and  22 . Back-light assembly  14  also includes a light reflector panel  32  that is spaced-apart from the lower surface  24  of the optical waveguide. 
         [0023]    Disposed between reflector panel  32  and lower surface  24  of the waveguide is a plurality of transversely spaced-apart light sources  34 . In this first embodiment of the invention, light sources  34  comprise side-mounted light emitting diodes having 120 degree emission angles that emit light in the direction of X-axis (see  FIG. 2 ). It is to be understood that light sources  34  can be of various types including cold cathode fluorescent lamps with side-mounted reflectors the character of which presently is described. 
         [0024]    Referring to  FIG. 2  of the drawings, it is to be noted that certain of the light rays  36  that are generated by the light sources  34  enter into the waveguide  16  directly from the light coupling facets  28 . Additionally, depending on the angles that light rays  36  reflect from light-reflecting facets  26  and the upper surface of reflector panel  32 , and also enter the waveguide  16  from the light coupling facets  28 . Inside the waveguide  16  light rays  36  propagate in the X-axis direction by total internal reflections from the major upper surface  18  and light-reflecting facets  26 . As indicated in  FIG. 2 , certain of the upwardly inclined light-reflecting facets  26  cause the light rays to exit the waveguide. 
         [0025]    More particularly, the light rays exit the waveguide from the upper surface  18  when the light rays strike the upper surface at less than the critical angle. 
         [0026]    Turning next to  FIGS. 3 and 4 , an alternate form of the back-light assembly of the invention is there illustrated and generally designated by the numeral  40 . This latest embodiment is similar in some respects to the embodiment shown in  FIGS. 1 and 2  of the drawings and like numbers are used in  FIGS. 3 and 4  to identify like components. As indicated in  FIG. 3 , back-light assembly  40  here comprises an optical waveguide  16 . An important feature of this second embodiment of the back-light assembly of the invention resides in the provision of a plurality of spaced-apart micro-prisms  56  that are disposed proximate lower surface  24  of the waveguide  16 . As indicated in  FIGS. 3 and 4  of the drawings, each micro-prism  56  has a first facet  56   a  optically coupled to a selected one of the light-reflecting facets  26 . In a similar fashion, a second facet  56   b  is optically coupled to a selected one of the downwardly inclined facets  28 . Each micro-prism  56  also includes a light coupling third facet  56   c  that interconnects the first and second facets  56   a  and  56   b . To form the micro-prisms  56 , a UV hardening liquid polymer may be filled into the V-shaped grooves with approximately the same refractive index as the waveguide  16 . 
         [0027]    Back-light assembly  40  also includes a light reflector panel  32  that is spaced-apart from the light coupling third facets  56   c  of the micro-prisms  56 . 
         [0028]    Disposed between reflector panel  32  and the third facets  56   c  is a plurality of transversely spaced-apart light sources  34 . As in the first embodiment of the invention, light sources  34  comprise side-mounted light emitting diodes having 120 degree emission angles that emit light in the direction of the X-axis (see  FIG. 3 ). 
         [0029]    Referring to  FIG. 3  of the drawings, it is to be noted that certain of the light rays  36  that are generated by the light sources  34  enter into micro-prism from the light coupling third facets  56   c.    
         [0030]    Additionally, depending on the angles that light rays  36  reflect from the upper surface of reflector panel  32  and enter into micro-prism from the light coupling third facets  56   c.    
         [0031]    Inside of the micro-prisms  56  light rays propagate in X-axis direction by total internal reflections from facets  56   a  and  56   c  and enter the waveguide  16  from facets  28 . 
         [0032]    Inside the waveguide  16  light rays  36  propagate in the X-axis direction by total internal reflections from the major upper surface  18  and light-reflecting facets  26 . As indicated in  FIG. 2 , certain of the upwardly inclined light-reflecting facets  26  cause the light rays to exit the waveguide. 
         [0033]    More particularly, the light rays exit the waveguide from the upper surface  18  when the light rays strike the upper surface at less than the critical angle. 
         [0034]    Referring now to  FIG. 5 , still another form of the back-light assembly of the invention is there illustrated and generally designated by the  60 . This latest embodiment is similar in many respects to the embodiment shown in  FIGS. 3 and 4  of the drawings and like numbers are used in  FIG. 5  to identify like components. The main differences between this third embodiment of the invention and that shown in  FIGS. 3 and 4  reside in the provision of a different type of light source and in the addition of a prism film  70  that is positioned adjacent the upper surface of the waveguide  16 . 
         [0035]    As before, the back-light assembly  60  here comprises an optical waveguide  16  that includes an upper, generally flat surface  18 , a first side surface  20 , a second side surface  22  and a specially configured lower surface  24  that is identical to the lower surface described in connection with the embodiment of  FIGS. 3 and 4 . 
         [0036]    Like the embodiment in  FIGS. 3 and 4 , this third embodiment of the invention includes a plurality of spaced-apart micros-prisms  56  that are disposed proximate lower surface  24  of the waveguide  16  and are identical in construction and operation to the micro-prisms described in connection with the second embodiment of the invention. 
         [0037]    Back-light assembly  60  also includes a light reflector panel  32  that is spaced-apart from the third facets  56   c  of the micro-prisms  56 . 
         [0038]    Disposed between reflector panel  32  and the third facets  56   c  is a plurality of transversely spaced-apart cold cathode fluorescent lamps  62  having side-mounted reflectors  64  (see  FIG. 6 ). 
         [0039]    As indicated in  FIG. 5  of the drawings, certain of the light rays  36  that are generated by the light sources  62  enter into micro-prism from the light coupling third facets  56   c . Additionally, depending on the angles that light rays  36  reflect from the upper surface of reflector panel  32  and enter into micro-prism from the light coupling third facets  56   c . Inside of the micro-prisms  56  light rays propagate in X-axis direction by total internal reflections from facets  56   a  and  56   c  and enter the waveguide  16  from facets  28 . 
         [0040]    As before, inside the waveguide  16  light rays  36  propagate in the X-axis direction by total internal reflections from the major upper surface  18  and light-reflecting facets  26 . As indicated in  FIG. 2 , certain of the upwardly inclined light-reflecting facets  26  cause the light rays to exit the waveguide. More particularly, the light rays exit the waveguide from the upper surface  18  when the light rays strike the upper surface at less than the critical angle. 
         [0041]    As previously mentioned, an important feature of this latest form of the invention is the prism film  70  that is positioned adjacent the upper surface  18  of the waveguide. As has been seen in  FIG. 5 , prism film  70  is comprised of a planar upper surface  72  and a plurality alternating prismatic facets  74   a  and  74   b  that function to redirect the light exiting the waveguide  16  at an angle approximately perpendicular to the upper surface  72  of the prism film  70 . Light directed towards the normal is most effective for display panels such as liquid crystal displays. 
         [0042]    Having now described the invention in detail in accordance with the requirements of the patent statutes, those skilled in this art will have no difficulty in making changes and modifications in the individual parts or their relative assembly in order to meet specific requirement or conditions. Such changes and modification may be made without departing from the scope and spirit of the invention, as set forth in the following claims.