Abstract:
Light beam splitting and combining system integrate some optic elements into the interfaces of two sets of prisms. Films for reducing stray color beams are coated the interfaces. Two sides of bigger prisms are faced to each other. Another side of each bigger prism is attached to the hypotenuse side of one small prism. A dichroic mirror and PBS are coated on those interfaces. Modulators are parallel to and positioned on the sides of the small prisms and a third side of one bigger prism. Such a system may be applied to a projector.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention relates to a light beam splitting and combining system and method thereof, and more especially, to a light beam splitting and combining system and method thereof applied to a projector. 
         [0003]    2. Background of the Related Art 
         [0004]    Reflective liquid crystal display (RLCD) has gradually played an important role with the low price of liquid crystal display. Generally, RLCD is classified into on-axis and off-axis types. The on-axis RLCD, for example, four-cube type of IBM (trademark of International Business Machines Corporation), Philips (trademark of Royal Philips Electronics of the Netherlands) prism, color corner and color cube types, has difficulties in the contrast, polarized devices and colors enhancements. 
         [0005]      FIG. 1  is a schematic diagram illustrating four-cube type for light beam splitting and combining system in accordance with one prior art. In combination of polar beam splitters  110 , 112 , 114  and X-prism  116 , white light beam emitted from a light source module  12  is divided into three monochromatic light beams and then modulated by three RLCDs  120 , 122  and  124  for loading image data and then integrated into color image light. 
         [0006]      FIG. 2  is a schematic diagram illustrating Philips prism type for light beam splitting and combining system in accordance with one prior art. Two total Internal Reflection (TIR) prisms  210 ,  212 , waveguide polarizing beam splitter (WPBS)  214 , RLCDs  220 , 222  and  224  are used to constitute a light beam splitting and combining system. 
         [0007]      FIG. 3  is a schematic diagram illustrating a color cube type for a light beam splitting and combining system in accordance with one prior art. Four polarizing beam splitters (PBSs)  310 ,  312 ,  314 ,  316 , three color selectors  330 ,  332 ,  334 , and RLCDs  320 ,  322 ,  324  are combined to form light beam splitting and combining system. 
         [0008]    The prior light beam splitting and combining system aforementioned, there is stray light in those monochromatic light beams. The existence of stray light has influences on the brightness of dark field and contrast. Furthermore, the many amounts of elements and complex design of optic path increase the difficulties in assembly, alignment and requirement of high accuracy. 
       SUMMARY OF THE INVENTION 
       [0009]    The present invention provides a light beam splitting and combining system and method. Some optical elements are directly formed on the interfaces of other optical devices to enhance the high accuracy of alignment. 
         [0010]    The present invention further provides a light beam splitting and combining system and method. One or more coatings utilized may disperse other stray light under the transmission of the required light, so as to prevent the stray light from entering into the system and reduce heat generation. 
         [0011]    The present invention further provides a light beam splitting and combining system and method. Two sets of prisms of different dimensions are utilized associated with surface treatment to reduce the amount of optical devices in the system. 
         [0012]    Accordingly, one embodiment of the present invention provides a light beam splitting and combining system and method integrating some optical elements, such as dichroic mirror and PBS, into the interfaces of two sets of prisms. Films for reducing stray color beams are coated the interfaces. Two sides of bigger prisms are opposite attached to each other. Another side of each bigger prism is attached to the hypotenuse side of one small prism. A dichroic mirror and PBS are coated on those interfaces. Modulators are parallel to and positioned on the sides of the small prisms and the third side of one bigger prism. Such a system may be applied to a projector. 
         [0013]    Accordingly, a method of splitting and combining light beams is provided therein. A first light beam of a first polarity is provided with a first, a second and a third monochromatic light beams of a first polarity. The first light beam is divided into the first monochromatic light beam and a second light beam in which the second light beam includes the second and the third monochromatic light beams of the first polarity. The first monochromatic light beam is modulated into the first monochromatic light of a second polarity different from the first polarity. The second light beam is polarized to generate the second monochromatic light beam of the second polarity and the third color light beam of the first polarity. The second monochromatic light beam of the second polarity is also modulated to generate a third light beam which includes the second monochromatic light beam of the first polarity. The third monochromatic light beam of the first polarity is modulated to generate a fourth light beam which includes the third monochromatic light beam of the second polarity. The third light beam, fourth light beam and modulated first monochromatic light beam are polarized to generate a fifth light beam which includes the first, second and third monochromatic light beams all of the second polarity. 
     
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0014]      FIG. 1  is a schematic diagram illustrating four-cube type for light beam splitting and combining system in accordance with one prior art; 
           [0015]      FIG. 2  is a schematic diagram illustrating Philip prism type for light beam splitting and combining system in accordance with one prior art; 
           [0016]      FIG. 3  is a schematic diagram illustrating color cube type for light beam splitting and combining system in accordance with one prior art; 
           [0017]      FIG. 4A  is a schematic diagram illustrating a light beam splitting and combining system in accordance with one embodiment of the present invention; 
           [0018]      FIG. 4B  is a schematic diagram illustrating a light beam splitting and combining system in accordance with another one embodiment of the present invention; 
           [0019]      FIG. 5  is a schematic diagram illustrating a light beam splitting and combining system in accordance with another embodiment of the present invention; and 
           [0020]      FIG. 6  is a schematic diagram illustrating the transmission of coating used in one embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0021]    The features of the present invention are illustrated in association with the following figures. It is noted that the optic paths are drew for clarification. Those who know the knowledge in the field should understand all the paths are performed according to fundamental optical knowledge. 
         [0022]      FIG. 4A  is a schematic diagram illustrating a light beam splitting and combining system in accordance with one embodiment of the present invention. A light beam splitting and combining system  10  mainly includes a first prism  40  and a second prism  42  in an identical dimension, and a third prism  44  and a fourth prism  46  in another identical dimension. Each prism aforementioned has a first side, a second side and a third side. In one embodiment, two polar beam splitters  28  and  22  are respectively formed on the respective one sides of the first prism  40  and second prism  42  by a coating method and then respectively attached to the first sides of the third prism  44  and the fourth prism  46 . Furthermore, the first prism  40  and the second prism  42  are attached to each other with the respective second sides by a method of, such as UV adhesive, after a dichroic mirror  38  is formed respectively on one second side of the first prism  40  or the second prism  42 . 
         [0023]    Next, a modulator  32  is positioned on the third side of the first prism  40  and a color selector  34  is positioned on the third side of the second prism  42 . Similarly, another modulator  30  and a color selector  26  are respectively positioned on the second and third sides of the third prism  44 . Furthermore, another modulator  24  is positioned on the third side of the fourth prism  46 . A dichroic mirror  20  (in  FIG. 4A ) or a double mirror  21  (in  FIG. 4B ) is positioned between the third prism  44  and fourth prism  46 , such as the position of angle bisector, which is aligned with the dichroic mirror  38 . 
         [0024]    Accordingly, one of features of the present invention is to utilize some optical thin film devices directly formed on the interfaces of the prisms, so as to simplify the alignment step for the light beam splitting and combining system  10  and meet the accuracy requirement. Furthermore, the optical thin film devices formed by the interface treatment may occupy less space so as to be applied to portable equipment. Furthermore, the arrangement of the optical devices in the embodiment of the present invention provides a simplified an optic path to reduce the problem of the stray light and enhance the color contrast. One exemplary optic path is illustrated as follows. 
         [0025]    Referring to  FIG. 4A  and  FIG. 4B  continuously, a light source module  12  outputs different monochromatic light beams  62 ,  64  and  66  with same polarity, such as S polarity. The monochromatic light beams  62 ,  64  and  66  (viewed as the first light beam) firstly penetrates through a dichroic mirror  20  or double mirror  21  and then are divided into a reflected light beam  63  and a transmission light beam  65  (viewed as the second light beam). One of the reflecting light beams  63  and transmission light beam  65  may include two color light beams. In the embodiment, the transmission light beam  65  is provided with the monochromatic light beams  64  and  66 , and the reflected light beam  63  includes the monochromatic light beam  62 . Next, the reflected light beam  63  is reflected by a polar beam splitter  22  (to change the optic path of the reflected light beam  63 ) and then incident to a modulator  24  to generate a monochromatic light  63   a  with loaded image data. Of the different polarity from the reflected light beam  63  of one, the monochromatic light  63   a  may transmit through the PBS  22  and then be reflected by the dichroic mirror  38 . It is noted that, when the double mirror  21  is utilized, the monochromatic light beams  62 ,  64  and  66  may be generated in different optic paths by a plurality of light source module and incident to the light splitting and combining system from the two sides of the double mirror  21 . 
         [0026]    On the other hand, still shown in  FIG. 4A  and  FIG. 4B , the transmission light beam  65  including the monochromatic light beams  64  and  66  penetrates through the color selector  26  to convert the monochromatic light beam  66  into the monochromatic light beam  66   a  of different polarity and keep the monochromatic light beam  64  of the primary polarity. Of the different polarities, the monochromatic light beam  66   a  is separated from the monochromatic light beam  64  by the polar beam splitter  28 . In the embodiment, the monochromatic light beam  66   a  penetrates through the polar beam splitter  28  and is modulated by another modulator  32  to be converted into a monochromatic light beam  66   b  (viewed as the third light beam) with loaded data. It is noted that the polarities of the monochromatic light beam  66   b  and the monochromatic light beam  66  are identical. On the other hand, the monochromatic light beam  64  of the primary polarity is reflected by the polar beam splitter  28  and then incident to a modulator  30  to generate the monochromatic light beam  64   a  (viewed as the fourth light beam) with loaded image data. With the different directions of polarity and different colors, the monochromatic light beam  64   a  may be transmitted through the polar beam splitter  28  and the dichroic mirror  38  and then parallel to the monochromatic light  63   a  reflected by the dichroic mirror  38 . On the other hand, the modulated monochromatic light beam  66   b  penetrates through the polar beam splitter  28  (to change the optic path thereof) and then transmits the dichroic mirror  38  to align with the monochromatic light beam  64   a  and monochromatic light  63   a . It is noted that the polarity of the monochromatic light beam  66   b  is different from the ones of the monochromatic light beam  64   a  and the monochromatic light  63   a.    
         [0027]    Finally, shown in  FIG. 4A  and  FIG. 4B , a color selector  34  may convert the polarities of the monochromatic light beam  64   a  and monochromatic light  63   a  into the same polarity as the monochromatic light beam  66   b , as well as reversely, to become the color image data for a lens module (not shown on the drawing) through a polarizer  36 . In one embodiment, the monochromatic light beam  62  is a green light beam of S polarity, monochromatic light beam  64  is a blue light beam of S polarity and the monochromatic light beam  66  is a red light beam of S polarity. For the associated modulators, the modulator  24  is a green reflective liquid crystal display (RLCD), the modulator  30  is a blue RLCD and the modulator  32  is a red RLCD. Next, the dichroic mirrors  20  and  38  may permit of the reflection of green light and the transmission of red and blue light. Furthermore, the PBS  22  is same as the polar beam splitter  28 . Alternatively, the dichroic mirror  21  may be changed for the light source in the different incident direction. Shown in  FIG. 5 , the dichroic mirror  50  may permit of the transmission of green light and the reflection of red and blue light. Other optical devices in  FIG. 5  are same as the ones in  FIG. 4A  and  FIG. 4B . For light beam, the reflected light beam  63  includes the monochromatic light beams  64  and  66 , and the transmission light beam  65  includes the monochromatic light beam  62 . 
         [0028]    It is noted that one of features of the present invention may reduce heat generated by optic system. Shown on  FIG. 6 , in one embodiment, the coating film for the dichroic mirror is provided with the low transmission in the wavelength range of 490 to 590 nm. It is advantageous that yellow light beam with the wavelength of 570 nm may be outside of the light beam splitting and combining system  10  for reducing heat generated by the entrance of yellow light beam to prevent the leakage of dark field. Thus, a whole optic path is simplified with the use of the dichroic mirror associated with PBS. Furthermore, optic thin film devices are utilized for reducing alignment step, improving the accuracy of the system and reducing the manufacture cost. Furthermore, the yellow light beam is reflected away to reduce heat effect on the dark field. 
         [0029]    Accordingly, one embodiment of the present invention provides a light beam splitting and combining system for a projector. Each prism is provided with a first side, a second side and a third side. A first dichroic mirror is attached between the second side of a second prism and the second side of a first prism. A first polar beam splitter is attached between the first side of the first prism and the first side of a third prism. A second polar beam splitter is attached between the first side of the second prism and the first side of a fourth prism. A first color selector is adjacent to the third side of the third prism. A second color selector is adjacent to the third side of the second prism. A first modulator is positioned on the third side of the first prism and opposite parallel to the first color selector. A second modulator is adjacent to the second side of the third prism and opposite parallel to the second color selector. A third modulator is adjacent to the third side of the fourth prism. A second dichroic mirror is positioned between the third side of the third prism and the second side of the fourth prism. 
         [0030]    Accordingly, one embodiment of the present invention provides a method of splitting and combining light beams. A first light beam includes a first, a second and a third monochromatic light beams of a first polarity. The first light beam is divided into the first monochromatic light beam and a second light beam. The second light beam includes the second and the third monochromatic light beams of the first polarity. The first monochromatic light beam is modulated into the first monochromatic light; of a second polarity different from the second polarity. The second light beam is polarized to generate the second monochromatic light beam of the second polarity and the third color light beam of the first polarity. The second monochromatic light beam of the second polarity is modulated to generate a third light beam which includes the monochromatic light beam of the first polarity. The third monochromatic light beam of the first polarity is modulated to generate a fourth light beam which includes the third monochromatic light beam of the second polarity. The third light beam, fourth light beam and modulated first monochromatic light beam are polarized to generate a fifth light beam which includes the first, second and third monochromatic light beams all of the second polarity. 
         [0031]    Although the present invention has been explained in relation to its preferred embodiment, it is to be understood that other modifications and variation can be made without departing the spirit and scope of the invention as hereafter claimed.