Abstract:
A digital light-processing projection apparatus includes a light source, a beam splitter module and an optical combiner module. The beam splitter module is used in conjunction with an optical combiner module that includes combiners and a plurality of prisms. The beam splitter module comprises a beam splitter element for splitting the beam into a plurality of color lights that pass through the respective prisms separately. The polarization direction of each color light when separated in the beam splitter module is equal to the polarization direction of each respective color light when colour combination in the combiner module.

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to a digital light-processing projection apparatus and a beam splitter module used in conjunction with the projection apparatus, and especially relates to the design of the digital light-processing projection apparatus and a beam splitter element of the beam splitter module. 
   2. Descriptions of the Related Art 
     FIG. 1  is a schematic view of a digital light-processing projection apparatus disclosed in ROC (Taiwan) Patent Application No. 093101928, which was filed by the assignee of the subject application on 29 Jan. 2004. The digital light-processing projection apparatus comprises an optical combiner module  200 , a light source  300 , a beam splitter module  400 , a plurality of Digital Micro-mirror Devices (DMDs)  500 R,  500 G,  500 B, and a projection lens  600 . 
   A light beam W is emitted from the light source  300 , passes through a rod integrator  310  and enters the beam splitter module  400 , which in turn, splits the light beam W into three primary colour lights R, G, B. Dichroic mirrors  402 ,  404  split colour lights R, G and colour light B, respectively. Colour lights R, G, B then enter the optical combiner module  200  by respective condenser lenses  406 ,  408 ,  410  and reflection mirrors  412 ,  414 ,  416 ,  418 ,  420  and  422 . Colour light B is reflected onto incident plane  242   a , while colour light G is reflected onto incident plane  232   a . Colour light R, G, B are reflected onto the respective DMDs  500 R,  500 G,  500 B by respective air gaps in Total Internal Reflection (TIR) prisms  220   a ,  230   a ,  240   a , from which they are subsequently reflected and pass through the respective TIR prisms  220   a ,  230   a ,  240   a . The projection lens  600  is disposed in the light paths of the respective colour lights R, G, B after the optical combiner module  200 . Back focal length  550  is the back focal length of the digital light-processing projection apparatus. 
   As shown in  FIG. 2A , which illustrates a spectrum curve diagram of the colour light R in the beam splitter module  400 . Curve S 1  represents the spectrum of S-polarized light when the incident angle of colour light R is 45 degrees. Curve P 1  represents the spectrum of P-polarized light when the incident angle of colour light R is 45 degrees. Curve S 2  represents the spectrum of S-polarized light when the incident angle of colour light R is 52 degrees. Curve P 2  represents the spectrum of P-polarized light when the incident angle of colour light R is 52 degrees. 
   Referring to  FIG. 2B , which illustrates a spectrum curve diagram of the colour light R in the optical combiner module  200 . Curve S 3  represents the spectrum of S-polarized light when the incident angle of colour light R is 45 degrees. Curve P 3  represents the spectrum of P-polarized light when the incident angle of colour light R is 45 degrees. Curve S 4  represents the spectrum of S-polarized light when the incident angle of colour light R is 52 degrees. Curve P 4  represents the spectrum of P-polarized light when the incident angle of colour light R is  52  degrees. 
   Now referring to  FIGS. 2A and 2B , as shown in curves S 1 , P 1 , S 3  and P 3 , when the wave length of S-polarized light of colour light R is greater than 570 nm, the S-polarized light of colour light R starts to reflect, while the P-polarized light of colour light R does not reflect until the wave length thereof is greater than 600 nm and the rate of reflection is close to 100%. In other words, the S-polarized light is more suitable for reflection regardless of light splitting or combining. 
   After two reflections of fold mirrors, the S-polarized light of red light is converted to the P-polarized light. As for curve S 1 , when the S-polarized light of colour light R in the beam splitter module  400  enters the optical combiner module  200 , the curve spectrum becomes curve P 3 . 
   Given above, when the wave length of the S-polarized light of colour light R in the beam splitter module  400  is between 570 nm and 600 nm, the light will be transmitted in the optical combiner module  200 , which in turn, results in light loss. The same also applies to colour lights B and G. If light loss occurs, the intensity of images by the projection lens is reduced, which in turn, affects the quality and effects of projected images. 
   SUMMARY OF THE INVENTION 
   Accordingly, it is an object of the present invention to provide a digital light-processing projection apparatus and a beam splitter module to make the direction of image plane of each split polarized light be equal to that of each polarized light of the respective colour light during light combining in the optical combiner module so light loss can be avoided. 
   The present invention provides a beam splitter module used in conjunction with an optical combiner module. The optical combiner module comprises a combiner; and a plurality of prisms. The combiner comprises at least one pared-corner, and one side of the prisms is disposed adjacent to the pared-corner. The beam splitter module comprises a beam splitter element for splitting a light beam into a plurality of colour lights passing through the respective prisms separately. Wherein the polarization direction of each colour light split by the beam splitter module is equal to that of each respective polarization of colour light during light combination in the optical combiner module. 
   The other object of the present invention is to provide a digital light-processing projection apparatus. The projection apparatus comprises a light source, a beam splitter module, an optical combiner module, a plurality of Digital Micro-mirror Devices (DMDs) and a projection lens. 
   The beam splitter module comprises a beam splitter element disposed in the light path of the light beam emitted from the light source, wherein the beam splitter module splits the light beam into a plurality of colour lights. 
   The optical combiner module is disposed at an intersection of the plurality of colour lights after the light splitter module. The optical combiner module comprises a combiner and a plurality of prisms. The combiner comprises at least one pared-corner, and one side of the prisms is disposed adjacent to the pared-corner. 
   The plurality of DMDs are disposed in the light paths of the respective colour lights after the optical combiner module. The plurality of colour lights are reflected onto the DMDs by the respective prisms and are subsequently reflected by the respective DMDs to pass through the respective prisms, wherein the direction of image plane of each polarized light of the respective colour light split by the beam splitter module is equal to that of each respective polarized light of colour light during light combining in the optical combiner module. 
   Other objects, advantages and novel features of the present invention will be drawn from the following detailed description of preferred embodiments of the present invention with the accompanying drawings, in which: 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  illustrates a schematic view of a digital light-processing projection apparatus disclosed in ROC (Taiwan) Patent Application No. 093101928; 
       FIG. 2A  illustrates a spectrum curve diagram of the colour light R in a beam splitter module in  FIG. 1 ; 
       FIG. 2B  illustrates another spectrum curve diagram of the colour light R in a optical combiner module in  FIG. 1 ; 
       FIG. 3  illustrates an exploded view of a preferred embodiment of a digital light-processing projection apparatus according to the present invention; 
       FIG. 4A  illustrates a schematic view of a preferred embodiment of a beam splitter element according to the present invention; 
       FIG. 4B  illustrates a schematic view of a rod integrator according to the present invention; 
       FIG. 5A  illustrates a perspective view of a preferred embodiment of an optical combiner module according to the present invention; 
       FIG. 5B  illustrates a transparent schematic view of the optical combiner module in  FIG. 5A ; 
       FIG. 6A  illustrates a perspective view of a combiner in  FIG. 5A ; 
       FIG. 6B  illustrates a transparent schematic view of the combiner in  FIG. 5A ; 
       FIG. 7A  illustrates a perspective view of a total internal reflection prism in  FIG. 5A ; 
       FIG. 7B  illustrates a transparent schematic view of the total internal reflection prism in  FIG. 5A ; 
       FIG. 7C  illustrates a side view of the total internal reflection prism in  FIG. 5A ; and 
       FIG. 8  illustrates a spectrum curve diagram of a colour light B 0  in a preferred embodiment of a beam splitter element. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENT 
     FIG. 3  illustrates a preferred embodiment of a digital light-processing projection apparatus  1  according to the present invention. The projection apparatus  1  comprises a light source  340 , a rod integrator  350 , a beam splitter module  330 , an optical combiner module  320 , a plurality of Digital Micro-mirror Devices (DMDs)  361 ,  362 ,  363 , and a projection lens  360 . 
   A light beam X is emitted from the light source  340 , which usually comprises, for example but not limited to, a metal-halide lamp (MHL) or an ultra-high performance (UHP) lamp, which can provide high brightness and high colour saturation white light. The light beam X becomes uniform by rod integrator  350  then enters the beam splitter module  330 . The beam splitter module  330  splits the light beam X into three primary colour lights, i.e., red light R 0 , green light G 0  and blue light B 0 , which subsequently enter the optical combiner module  320 . The optical combiner module  320  receives red light R 0 , green light G 0  and blue light B 0  from the beam splitter module  330  and forms images on DMDs  361 ,  362 ,  363 . After the optical combiner module  320 , three colour images are projected by the projection lens  360 . The following paragraphs describe each element of the digital light-processing projection apparatus in order. 
   The beam splitter module  330  comprises a beam splitter element  331  and reflection mirrors  332 ( a )˜( i ). Red light R 0  and blue light B 0  are reflected towards different directions (e.g., left and right, up and down, respectively) by the beam splitter module  331  while green light G 0  passes through it. 
     FIG. 4A  illustrates a schematic view of a preferred embodiment of the beam splitter  331  according to the present invention. Preferably, the beam splitter element  331  is an X-plate. The inside of the beam splitter element  331  is disposed with optical coating FR and optical coating FB. The red light R 0  of the light beam X is reflected by the optical coating FR. The blue light B 0  of the light beam X is reflected by the optical coating FB. Nevertheless, the green light G 0  is unaffected and passes through the beam splitter element  331  directly. 
     FIG. 4B  illustrates a schematic view of the rod integrator  350 . The rod integrator  350  has an output end having a length a 1  and a width a 2 . In the preferred embodiment, the ratio of the length a 1  and width a 2  is 16:9, and the length a 1  is perpendicular to the horizontal direction. In the beam splitter element  331 , the direction of reflection of the red light R 0  reflected by the optical coating FR is, for example, parallel to the length a 1 , or beneath the beam splitter element  331  (e.g., from the bottom of the beam splitter element  331 ). The direction of reflection of the blue light B 0  reflected by the optical coating FB is, for example, parallel to the length a 1 , or above the beam splitter element  331  (e.g., from the top of the beam splitter element  331 ). Nevertheless, the arrangement of the above mentioned upwardly and downwardly reflected blue light and red light is only one of the possible embodiments. 
     FIG. 5A  illustrates a perspective view of a preferred embodiment of an optical combiner module according to the present invention, while  FIG. 5B  illustrates a transparent schematic view of the optical combiner module in  FIG. 5A . The optical combiner module  320  of the embodiment comprises a combiner  322  and a plurality of prisms  323 ,  324 ,  325  adjacent to the combiner  322 . Although three prisms  323 ,  324 ,  325  are used in the embodiment, the number of prisms used in the present inventions is not limited to three. In addition, the prisms  323 ,  324 ,  325  adjacent to the combiner  322  can be integrated to the combiner  322  by any means either directly or indirectly. 
   The reflection mirrors  332 ( a )˜( i ) are utilized to continuously reflect the three primary lights R 0 , G 0  and B 0  to the optical combiner module  320 . For instance, the reflection mirrors  332 ( a )˜( c ) continuously reflect the red light R 0  to the prism  323 , the reflection mirrors  332 ( d )˜( f ) continuously reflect the blue light B 0  to the prism  324 , and the reflection mirrors  332 ( g )˜( i ) continuously reflect the green light G 0  to the prism  325 . 
     FIGS. 6A and 6B  illustrate a perspective view and a transparent schematic view of the combiner in  FIG. 5A , respectively. In the embodiment, the combiner  322  comprises at least one pared-corner C. Although three pared-corners C are used in the embodiment, the number of pared-corners is not limited to three and can actually depend on what is required. 
   The combiner  322  of the embodiment can be an X-prism or other optical element capable of optically combining. Taking the X-prism as an example, the inside of the prism can have two optical coatings FR′, FB′, where FR′ can reflect a light having a wave length of red light, and FB′ can reflect a light having a wave length of blue light. In addition, the above mentioned X-prism is substantially a regular hexahedron, which usually has four sides  322   b , a top surface  322   a , a bottom surface  322   c  and three lean surfaces  322   d . The top surface  322   a  and the bottom surface  322   c  are adjacent to the side  322   b , respectively. A portion of the lean surfaces  322   d  is adjacent to the top surface  322   a  and one of the sides  322   b , while the other portion of the lean surfaces  322   d  is adjacent to the bottom surface  322   c  and one of the sides  322   b . The shape of lean surfaces  322   d  of the pared-corners C of the combiner  322  is, for example, a regular triangle. 
   Referring to  FIGS. 5A ,  5 B,  6 A and  6 B, one side of the prisms  323 ,  324 ,  325  is disposed adjacent to the pared-corner C of the combiner  322  so that the volume of the optical combiner module  320  can be effectively reduced. 
     FIGS. 7A ,  7 B and  7 C illustrate a perspective view, a transparent schematic view and a side view of a total internal reflection (TIR) prism in  FIG. 5A . The prisms  323 ,  324 ,  325  of this embodiment can be, for example, TIR prisms. The TIR prism  323  is described in more detail as an example as follows. 
   TIR prism  323  comprises a first prism  321  and a second prism  329 . The first prism  321  comprises a first light incident plane  321   a , a first contact surface  321   b  and a first light exit plane  321   c . The second prism  329  comprises a second contact surface  329   a  and a second light exit plane  329   b . In addition, inside the TIR prism  323 , the second light exit plane  329   b  of the second prism  329  has, for example, a transparent region A and a light-shielding region M, where the light-shielding region M is used to filter spurious lights. 
   Referring to  FIG. 7C , inside the TIR prism  323 , an air gap  321   e  is formed between a portion of the first contact surface  321   b  and the second contact surface  329   a , while the other portion of the first contact surface  321   b  is disposed adjacent to one of the lean surfaces  322   d  of the combiner  322 , and the second light exit plane  329   b  is disposed adjacent to one of the sides  322   b.    
   Now referring to  FIGS. 5B and 7C , in the embodiment, the TIR prism  323  is, for example, a red light TIR prism, the TIR prism  324  is, for example, a blue light TIR prism, and the TIR prism  325  is, for example, a green light TIR prism, where the red light TIR prism  323  and the blue light TIR prism  324  are disposed at opposite sides of the combiner  322 . Each side  323   a ,  324   a ,  325   a  of the TIR prisms  323 ,  324 ,  325  is on a first plane (not shown in the figures), the top surface  322   a  of the combiner  322  is on a second plane (not shown in figures), and an angle between the first plane and the second plane is about 45 degrees. 
   A blue light reflecting coating is further disposed inside the red light TIR prism  323 . The blue light reflecting coating is disposed, for example, on the first contact surface  321   b  of the first prism  321 , or on the second contact surface  329   a  of the second prism  329 , to filter spurious lights other than blue light. In addition, for example, a red light reflecting coating is disposed inside the blue light TIR prism  324  to filter spurious lights other than red light. 
   Digital Micro-mirror Devices (DMDs)  361 ,  362 ,  363  are disposed in the light paths of the respective colour lights R 0 , G 0 , B 0  after the optical combiner module  320 . The colour lights R 0 , G 0 , B 0  are reflected onto the respective DMDs  361 ,  362 ,  363  by the respective air gaps of the TIR prisms  323 ,  324 ,  325 , from which they are subsequently reflected by the respective DMDs  361 ,  362 ,  363  to pass through the respective TIR prisms  323 ,  324 ,  325 . The projection lens  360  is disposed in the combined light path after the optical combiner module  320 . 
   When colour lights R 0 , G 0 , B 0  are combined in the combiner, compared the combined light beam with the light beam X at the output end of the rod integrator  350 , during the transmission of colour lights, the image plane of the combined light beam is that of the light beam X rotated by 90 degrees. For example, when the light beam X passes through the rod integrator  350 , the length is perpendicular to the ground, while the width is parallel to the ground. To suit a viewer&#39;s viewing effects, the length of the combined light beam is parallel to the ground, while the width thereof is perpendicular to the ground, and the ratio of the length to the width is 16:9. 
   Now referring to  FIG. 8 , which illustrates a spectrum curve diagram of colour light B 0  in the beam splitter module  330 . When the incident angle of colour light B 0  is 45 degrees, curve S 5  represents the spectrum of S-polarized light thereof, while curve P 5  represents the spectrum of P-polarized light thereof. When the incident angle of colour light B 0  is 52 degrees, curve S 6  represents the spectrum of S-polarized light thereof, while curve P 6  represents the spectrum of P-polarized light thereof. 
   After the optical combiner module  330 , contrary to the prior art, the S-polarized and P-polarized lights of the colour light B 0  will not come into the situation where the directions of image planes of the S-polarized and P-polarized lights thereof are different. This is to say, during combining of the colour light B 0 , no lights having a certain wave length will be transmitted because they are not reflected. Therefore, in the optical combiner module  320 , the spectrum curve of the colour light B 0  does not change. In other words, the direction of S-polarized light of the split colour light B 0  is equal to that of S-polarized light of the combined colour light B 0 . Similarly, for colour lights R 0  and G 0 , the directions of S-polarized lights are the same when both separation and combination of the colour lights. Therefore, no light loss occurs. 
   From the above. it is clear that when using the digital light-processing projection apparatus and the beam splitter module according to the present invention, each colour light will have no light loss so that the quality of the projected images at the last stage is ensured. Due to the configuration of tight contacts between prisms, the light path of each colour light is shortened, and the size of the digital light-processing projection apparatus becomes more compact when manufactured, which is more acceptable to the users and therefore enhances competitiveness in the market. 
   While the invention has been described in terms of several preferred embodiments, those persons skilled in the art will recognize that the invention can still be practiced with modifications, within the spirit and scope of the appended claims.