Abstract:
The present invention relates to an apparatus for mixing light beams, which has at least one cholesteric liquid crystal (CLC) layer disposed between a reflective plate and an upper plate so as to form two mixing areas. Because the cholesteric liquid crystal (CLC) layer has a property of reflecting narrow band-circular polarized light, the light beams emitted from a plurality of light source are mixed in the two mixing areas. As a result, the height of the mixing area is reduced, and the color-mixing performance is raised.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     The present invention relates to an apparatus for mixing light beams and a backlight module having the same, particularly to an apparatus having two mixing areas by utilizing at least one cholesteric liquid crystal (CLC) layer.  
         [0003]     2. Description of the Related Art  
         [0004]      FIG. 1  shows a schematic view of a conventional direct-type backlight module. The direct-type backlight module  1  is used in a liquid crystal display and comprises a diffusion plate  10 , a plurality of light emitting diodes (LEDs)  11 ,  12 ,  13  and a reflector  14 .  
         [0005]     The diffusion plate  10  is a transparent substrate doped with diffusion particles therein or thereon. The diffusion plate  10  has a top surface  101  and a bottom surface  102 , wherein the bottom surface  102  is an illuminated surface for receiving the incident light beams from the light emitting diodes (LEDs)  11 ,  12 ,  13  and reflected by the reflector  14 . The light emitting diodes (LEDs)  11 ,  12 ,  13  are the light source of the direct-type backlight module  1  and are disposed on the reflector  14 . The light emitting diodes (LEDs)  11 ,  12 ,  13  comprise a red LED  11 , a green LED  12  and a blue LED  13 , wherein the red LED  11  emits a red light beam  15 , the green LED  12  emits a green light beam  16  and the blue LED  13  emits a blue light beam  17 . The reflector  14  is used for reflecting the light beams  15 ,  16 ,  17 .  
         [0006]     In the direct-type backlight module  1 , since the light sources are LEDs of different colors, it is necessary to mix the light beams  15 ,  16 ,  17  into a white light beam. According to a conventional way for mixing light beams, as shown in  FIG. 1 , a space  18  formed between the diffusion plate  10  and the reflector  14  is a mixing area. The light beams  15 ,  16 ,  17  are mixed in the space  18  naturally to become a white light beam. Unfortunately, such conventional way needs large space  18 , which is not suitable for the liquid crystal display that is becoming smaller in size and lighter in weight. Additionally, the light beams  15 ,  16 ,  17  are not uniformly mixed. In order to overcome the above-mentioned shortcoming, U.S. Pat. Nos. 6,139,166 and 6,604,839 B2 and US. Pub. No. 2004/0061810 disclose various apparatuses for mixing light beams. However, such apparatuses are complex, bulky and expensive.  
         [0007]     Consequently, there is an existing need for a novel and improved apparatus for mixing light beams to solve the above-mentioned problem.  
       SUMMARY OF THE INVENTION  
       [0008]     One objective of the present invention is to provide an apparatus for mixing light beams, which has two mixing areas by utilizing at least one cholesteric liquid crystal (CLC) layer. As a result, the height of the mixing area is reduced, and the color-mixing performance is raised.  
         [0009]     Another objective of the present invention is to provide an apparatus for mixing light beams, which has at least one cholesteric liquid crystal (CLC) layer. Because the cholesteric liquid crystal has a property of reflecting narrow band-circular polarized light, the apparatus can be used in a backlight module that has light source of LEDs so as to raise the color-mixing performance of the LEDs.  
         [0010]     Still another objective of the present invention is to provide an apparatus for mixing light beams, comprising: a reflective plate, a receiving plate, a first light source, a second light source, a first cholesteric liquid crystal (CLC) layer, a second cholesteric liquid crystal (CLC) layer and an upper plate. The reflective plate is used for reflecting light beams. The receiving plate is disposed above the reflective plate and apart from the reflective plate by a first space. The first light source is used for emitting a first light beam. The second light source is used for emitting a second light beam. The first cholesteric liquid crystal (CLC) layer is disposed on the receiving plate, and the polarized reflection and property of transmittance of the first cholesteric liquid crystal (CLC) layer correspond to the first light beam. The second cholesteric liquid crystal (CLC) layer is disposed on the receiving plate, and the polarized reflection and property of transmittance of the second cholesteric liquid crystal (CLC) layer correspond to the second light beam. The upper plate is disposed above the receiving plate and apart from the receiving plate by a second space, whereby the first light beam and the second light beam are mixed in the first space and the second space. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0011]      FIG. 1  shows a schematic view of a conventional direct-type backlight module; and  
         [0012]      FIG. 2  shows a schematic view of an apparatus for mixing light beams according to the present invention. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0013]      FIG. 2  shows a schematic view of an apparatus for mixing light beams according to the present invention. The apparatus  2  is used in a backlight module of a liquid crystal display. The apparatus  2  comprises a reflective plate  21 , a receiving plate  22 , a first light source  23 , a second light source  24 , a first cholesteric liquid crystal (CLC) layer  25 , a second cholesteric liquid crystal (CLC) layer  26  and an upper plate  27 .  
         [0014]     The reflective plate  21  is used for reflecting light beams and changing the polarization direction of the light beams. The receiving plate  22 , for example, a lens or other transparent mechanisms, is disposed above the reflective plate  21 . It should be noted that the interior or surface of the receiving plate  22  might be doped with diffusion particles. The space between the receiving plate  22  and the reflective plate  21  is defined as a first mixing area  28 .  
         [0015]     The first light source  23  is used for emitting a first light beam  29  having a first wavelength. The second light source  24  is used for emitting a second light beam  30  having a second wavelength. In the embodiment, the first light source  23  is a red LED, the first light beam  29  is red light beam, the second light source  24  is a green LED, and the second light beam  30  is green light beam. It is understood that the apparatus may further comprise light source of other color, for example, a third light source  32  that is a blue LED for emitting blue third light beam  33 .  
         [0016]     In the embodiment, the first light source  23 , the second light source  24  and the third light source  32  are disposed in the first mixing area  28 , which forms a direct-type backlight module. Alternatively, if the first light source  23 , the second light source  24  and the third light source  32  are disposed outside the first mixing area  28 , they form a side-edge backlight module.  
         [0017]     The first cholesteric liquid crystal (CLC) layer  25  is disposed on the receiving plate  22  by adhering or coating. The polarized reflection and property of transmittance of the first cholesteric liquid crystal (CLC) layer  25  correspond to the first wavelength of the first light beam  29 . That is, the first cholesteric liquid crystal (CLC) layer  25  is used for partially reflecting the first light beam  29 . The second cholesteric liquid crystal (CLC) layer  26  is disposed on the first cholesteric liquid crystal (CLC) layer  25 . The polarized reflection and property of transmittance of the second cholesteric liquid crystal (CLC) layer  26  correspond to the second wavelength of the second light beam  30 . That is, the second cholesteric liquid crystal (CLC) layer  26  is used for partially reflecting the second light beam  30 . Additionally, if there is the third light source  32 , it is necessary to add a third cholesteric liquid crystal (CLC) layer  34  disposed on the second cholesteric liquid crystal (CLC) layer  26 . The polarized reflection and property of transmittance of the third cholesteric liquid crystal (CLC) layer  34  correspond to the third wavelength of the third light beam  33 . That is, the third cholesteric liquid crystal (CLC) layer  34  is used for partially reflecting the third light beam  33 .  
         [0018]     The upper plate  27  is disposed above the receiving plate  22  and the space between the upper plate  27  and the receiving plate  22  is defined as a second mixing area  31 . The upper plate  27  is a transparent substrate, or its interior or surface may be doped with diffusion particles. The upper plate  27  has a top surface  271  and a bottom surface  272 , wherein the bottom surface  272  is an illuminated surface for receiving the incident light beams from the light sources  23 ,  24 ,  32  and reflected by the reflector  21 . It should be noted that if the apparatus  2  is applied to a backlight module, the upper plate  27  is a diffusion plate.  
         [0019]     The operation of the apparatus  2  is as follows. When the first light beam  29  passes through the receiving plate  22  and enters the first cholesteric liquid crystal (CLC) layer  25 , it is split into two orthogonal circularly polarized lights, one of which is left-handed circularly polarized light (light  291 ) and the other is right-handed circularly polarized light (light  292 ), then in the embodiment, the light  291  (left-handed circularly polarized light) passes through the first cholesteric liquid crystal (CLC) layer  25 , the second cholesteric liquid crystal (CLC) layer  26  and the third cholesteric liquid crystal (CLC) layer  34 , and then enters the second mixing area  31 .  
         [0020]     The light  292  (right-handed circularly polarized light) is reflected to the first mixing area  28 , and is then reflected by the reflective plate  21  to become a left-handed circularly polarized light (light  293 ). The light  293  is like the light  291  that can pass through the first cholesteric liquid crystal (CLC) layer  25 , the second cholesteric liquid crystal (CLC) layer  26  and the third cholesteric liquid crystal (CLC) layer  34 , and then enters the second mixing area  31 .  
         [0021]     In the same way, when the second light beam  30  passes through the receiving plate  22  and the first cholesteric liquid crystal (CLC) layer  25 , and enters the second cholesteric liquid crystal (CLC) layer  26 , it is split into two orthogonal circularly polarized lights, one of which is left-handed circularly polarized light (light  301 ) and the other is right-handed circularly polarized light (light  302 ), then in the embodiment, the light  301  (left-handed circularly polarized light) passes through the first cholesteric liquid crystal (CLC) layer  25 , the second cholesteric liquid crystal (CLC) layer  26  and the third cholesteric liquid crystal (CLC) layer  34 , and then enters the second mixing area  31  so as to mix with the light  291 .  
         [0022]     The light  302  (right-handed circularly polarized light) is reflected to the first mixing area  28  so as to mix with the light  292 , and then the light  302  is reflected by the reflective plate  21  to become a left-handed circularly polarized light (light  303 ). The light  303  is like the light  301  that can pass through the first cholesteric liquid crystal (CLC) layer  25 , the second cholesteric liquid crystal (CLC) layer  26  and the third cholesteric liquid crystal (CLC) layer  34 , and then enters the second mixing area  31 .  
         [0023]     According to the present invention, there are two mixing areas  28 ,  31  for light beams to proceed mixing so that the height of mixing area is reduced hugely, and the total height of the apparatus  2  is also reduced. Additionally, since high color-mixing performance can be achieved by utilizing several cholesteric liquid crystal (CLC) layers, the manufacture cost is low.  
         [0024]     While several embodiments of the present invention have been illustrated and described, various modifications and improvements can be made by those skilled in the art. The embodiments of the present invention are therefore described in an illustrative but not restrictive sense. It is intended that the present invention may not be limited to the particular forms as illustrated, and that all modifications which maintain the spirit and scope of the present invention are within the scope as defined in the appended claims.