Abstract:
An optical wave-guide device is provided between a light source and a lower diffuser for deflecting and reflecting the light passing through the optical wave-guide device so that the light is consistently diffused through the lower diffuser without creating any blind area among light sources to effectively solve the prior art problem of displaying bright bands and dark bands on the LCD.

Description:
BACKGROUND OF THE INVENTION 
     (a) Field of the Invention 
     The present invention is related to an improved structure of a LCD optical wave-guide device, and more particularly to a backlight module free of dark bands and bright bands. 
     (b) Description of the Prior Art 
     As illustrated in  FIG. 1  of the accompanying drawings for a sectional view of the structure of a backlight module for an LCD of the prior art, the backlight module is essentially comprised of a reflector mask  10 , multiple light sources  20 , a diffuser plate  30 , a lower diffuser sheet  40 , a prism  50 , a reflective polarizing sheet or an upper diffuser  60  and a protector sheet  70  arranged in sequence from inside out. Wherein, the light sources  20  may be each a light tube in the shape of a stripe, U-shape or other continuous curve arranged at a proper spacing between the reflector mask  10  and the diffuser plate  30  and the light emitted by each of the light sources  20  provide the display effects by the LCD. Therefore, the diffuser plate  30  functions to diffuse the light passing through it to correct the dark bands and the bright bands created on the LCD due to the absence of light produced at each spacing between two abutted sources  20 . 
     Whereas the diffuser plate  30  functions only to help achieve the even diffusion for light passing through it, it has a limited efficiency in correcting the phenomenon of the bright bands and the dark bands observed on the LCD. An improvement is made for certain backlight modules by extending the distance between the light source  20  and the diffuser plate  30  in the hope of widening the scope of each of those light sources  20  entering into the diffuser plate  30  to achieve the purpose of reducing the dark bands. However, the structural design for such an improvement not only provides limited effects but also results in a backlight module which must be made thicker thereby failing the compact requirements in the current LCD market. 
     Furthermore, some other backlight modules seek to provide extinction (dispersion) on the surface of the diffuser plate by printing on the diffuser plate with ink containing SiO 2  or TiO 2  to achieve the purpose of reducing the dark bands. Again, the extinction process not only increases the production cost of the diffuser and the complexity of the manufacturing process, but also relates to a passive solution to reduce the dark bands on LCD since the extinction occurs only after the light lands on the surface of the diffuser. 
     SUMMARY OF THE INVENTION 
     The primary purpose of the present invention is to provide an improved structure of an optical wave-guide device to effectively solve the problem of the bright bands and dark bands on the LCD and reduce the spacing between light sources and a lower diffuser sheet to make the backlight module thinner for the meeting compact requirements of the current LCD market by replacing the diffuser plate with an optical wave-guide device. To achieve the purpose, the optical wave-guide device is provided between light sources and a lower diffuser sheet for the light passing through the optical wave-guide device to be properly refracted and reflected to evenly diffuse via the lower diffuser sheet thereby providing an active solution. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a sectional view of the structure of a backlight module of the prior art. 
         FIG. 2  is a sectional view of a backlight module of a first preferred embodiment of the present invention. 
         FIG. 3  is a sectional view showing that the surface of the optical wave-guide device of the present invention is embossed on the surface facing a lower diffuser sheet. 
         FIG. 4  is a sectional view showing that the surface of the optical wave-guide device of the present invention is embossed on the surface facing multiple light sources. 
         FIG. 5  is a sectional view a sectional view showing that the surface of the optical wave-guide device of the present invention is embossed on the surface facing away the lower diffuser sheet. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring to  FIG. 2 , a first preferred embodiment of the present invention backlight module having a reflector mask  10 , multiple light sources  20 , a diffuser plate  30 , a lower diffuser sheet  40 , a prism  50 , a reflective polarizing sheet (or an upper diffuser)  60  and a sheet  70  arranged in sequence from inside out. Wherein, the light sources  20  may be shaped as a light tube in a stripe shape, U-shape or other continuously curved shape. The light sources are preferably arranged at a proper spacing between the reflector mask  10  and the lower diffuser sheet and the light emitted by each of the light sources  20  provide the display effects for the LCD. 
     At least one optical wave-guide device  80  is separately provided between those light sources  20  and the lower diffuser sheet  50 . The optical wave-guide device  80  is made into a plate and provided with multiple recesses  81 , each accommodating a respective light source  20 . The light emitted from each light source  20  passes through the optical wave-guide device  80  and is refracted and reflected to, thereby, be evenly diffused via the lower diffuser sheet. As a result this preferred embodiment provides an active means to eliminate the bright bands and dark bands which otherwise would be formed between any two abutted light sources  20 . Furthermore, replacing the diffuser plate of the prior art with the optical wave-guide device  80  reduces the spacing between the light source  20  and the lower diffuser sheet to further advantageously reduce the thickness of the backlight module. 
     The optical wave-guide device  80  may be made of plastic materials including but not limited to Polycarbonate (PC), or Polymethyl methacrylate (PMMA), or Polyethylene Terephthalate (PET) in a white or transparent stick structure; or transparent plastic materials, e.g. PC or PMMA added with diffusion agent (such as SiO2 or TiO2) in a white mat stick structure so to produce the optical wave-guide device  80  with various refraction effects for the selection of the proper optical wave-guide device  80  depending on the spacing between the backlight module and the light source  20 . 
     Now referring to  FIG. 3 , at least one surface of the optical wave-guide device  80 , is locally or entirely distributed with embossment  82  on the surface facing the lower diffuser sheet  40  in accordance with a second preferred embodiment of the present invention; or on the surface of the recess  81  where the optical wave-guide device  80  is facing the light source  20  as illustrated in  FIG. 4  in accordance with a third preferred embodiment; or on the surface of the optical wave-guide device  80  facing away from the lower diffuser sheet  40  as illustrated in  FIG. 5  in accordance with a fourth embodiment. The embossment forms at least one straight line or curve (or the combination of both) in the form of V-, U-, or C-shaped cut for the convex of the embossment  82  to create a converging effect so as to evenly distribute the lights from the light source  20  diffusing from the concave portion of each embossment  82 , to thereby effectively solve the problem of bright bands and dark bands observed with prior art LCD&#39;s. Alternatively, the same effects can be achieved by having at least one surface of the optical wave-guide device  80  locally or entirely matted, or printed with ink, or distributed with concave and convex points in either round, rectangular, diamond or polygonal form. 
     The preferred embodiments of the present invention provide an improved structure of a backlight module to reduce the spacing between light sources and diffuser plate, and thereby reduce the thickness of the backlight module allowing the production of a more compact LCD. It should be noted that the specification and drawings are provided to describe the preferred embodiments of the present invention and do not in any way limit the present invention. Therefore, any structure, device, and/or characteristics similar or equivalent to that of the present invention shall be deemed as falling within the scope of the purpose and claims made by the present invention.