Abstract:
A projection display apparatus includes a light source configured to supply light; a polarizing beam splitter for splitting light from the light source into two different polarization state lights; two reflective light panels of which each has a color filter embedded therein and respectively modulates the two polarization state lights so as to simultaneously produce red, green and blue image lights; and a projection lens receiving these color image lights and then projecting them onto a viewing surface so as to form a full-color image.

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   This invention generally relates to projection display apparatus, and more particularly to a projection display apparatus with two reflective light panels each having a color filter embedded therein. 
   2. Description of the Related Art 
   In a projection display system, a liquid crystal display (LCD) panel is used as a modulator for modulating light from a light source so that a projection lens can project the modulated light onto a display screen to form an image. The LCD panel used in such a projection display system mainly includes two types, i.e. a transmissive type and a reflective type. 
   A reflective type of LCD panel known as a liquid crystal on silicon (LCOS) panel recently receives an attention due to its small size and high resolution and arrangement of reflective LCD elements on a silicon backplane. LCoS panels have a number of significant advantages over other types of reflective LCD panels. For example, crystalline silicon can be used to form active matrix elements of the LCoS panels. The silicon backplane can also be used to form the TFT drivers and other functional circuitry, using well-known and efficient semiconductor manufacturing techniques. Moreover, a larger percentage of the active area can be used for processing video information for display. 
   In an LCoS projection display system, a single-panel projector and a three-panel projector has been used to achieve a full color. To achieve full color using a white light source, color management systems are needed for partitioning the spectrum into red, green, and blue, either temporally or spatially. In temporal or time sequential color management systems, only a single LCoS panel is needed for producing a full color by sequential colors. In spatial or multi-path color management systems, three LCoS panels are needed and respectively used for each of the primary colors. 
   For the single-panel systems, overall system cost and size can be small but there exists a color break-up problem. For the three-panel systems, the optical architecture can easily deliver the high lumen output required for large area projection displays but is complex. Therefore, a two-panel system is used so as to overcome the disadvantages in above-mentioned systems. In addition, the two-panel system incorporates the attractive aspects of above-mentioned systems, including high optical throughput and a small size and cost close to these of the single-panel system. 
   Referring to  FIG. 1 , it shows a schematic view of a conventional projection display apparatus  100 . The projection display apparatus  100  comprises a white light source  102  configured to supply light  103 , a first clean-up polarizer.  104 , a color switch  106 , a polarizating beam splitter  108 , a reflective panel  110 , and a projection lens  112 . The color switch  106  is an electronically switchable spectral filter for generating a red, green, and blue color light  114  sequentially. The polarizating beam splitter  108  receives the single color light  114  and then reflects the single color light  114  to the reflective panel  110 . The reflective panel  110  modulates the single color light  114  for changing the polarity of the single light  114  and reflects the modulated single color light  114  so as to pass through the polarizating beam splitter  108 . The projection lens  112  receives the modulated single color light  114  from the polarizating beam splitter  108  and then projects the modulated single color light  114 . 
   However, the aforementioned projection display apparatus  100  must project red, green, blue colors sequentially so as to form a full color image: Therefore, the circuit designs are complicated and synchronization is difficult between the color switch  106  and the reflective panel  114 . Besides, the use of the color switch  106  and its related circuits increase the overall cost of the projection display apparatus  100 . 
   Accordingly, the present invention provides a novel two-panel projection display apparatus having simple controlled circuits and lower manufacturing cost. 
   SUMMARY OF THE INVENTION 
   It is an object of the present invention to provide a two-panel projection display apparatus having simple controlled circuits and lower manufacturing cost. 
   In order to achieve the above object, the present invention provides a projection display apparatus including a light source configured to supply light; a polarizing beam splitter for splitting light from the light source into two different polarization lights; two reflective light panels each having a color filter embedded therein and respectively modulates the two polarization lights so as to simultaneously generate red, green and blue image lights; and a projection lens receiving these color image lights and then projecting them onto a viewing surface so as to form a full-color image. 
   According to one aspect of the present invention, the two reflective light panels used in the projection display apparatus respectively have a single-color and a two-color filters embedded therein for producing red, green and blue image lights simultaneously so as to achieve a full color image. 
   According to the other aspect of the present invention, the projection display apparatus can achieve a fill color image by utilizing fewer electronic and optical elements so as to reduce the overall cost. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Other objects, advantages, and novel features of the present invention will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings. 
       FIG. 1  is a schematic view of a conventional projection display apparatus with two LCoS panels. 
       FIG. 2  is a schematic view of a projection display apparatus with two reflective light panels according to one embodiment of the present invention. 
       FIG. 3  is a cross-sectional view of a LCoS panel having a color filter embedded therein according to the present invention. 
       FIG. 4  is a schematic view of a projection display apparatus with two reflective light panels according to another embodiment of the present invention. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
   Now referring to  FIG. 2 , it shows a schematic view of a projection display apparatus  200  with two reflective light panels according to one embodiment of the present invention. The projection display apparatus  200  comprises a polarizating beam splitter  202  which reflects S-polarization light in a transverse direction and which allows P-polarization light to pass directly therethrough. The polarizating beam splitter  202  has a light input side  202   a,  a first split-light side  202   b  adjacent to the light input side  202   a  orthogonally, a second split-light side  202   c  opposite to the light input side  202   a  and a light output side  202   d  opposite to the first split-light side  202   b.  A light source  203  is configured to supply white light  203   a  toward the polarizating beam splitter  202 . A P-state polarizer  204  is disposed adjacent to the light input side  202   a,  allows P-polarization light to pass directly therethrough, and absorbs S-polarization light. A first Green/Magenta color selector  206  is disposed between the P-state polarizer  204  and the light input side  202   a,  and converts the polarization state of magenta light that passes therethrough. A first reflective light panel  208  is disposed adjacent to the first split-light side  202   b  while a second reflective light panel  210  is disposed adjacent to the second split-light side  202   c.  A second Green/Magenta color selector  212  is disposed adjacent to the light output side  202   d.  An S-state polarizer  214  is disposed adjacent to one side of the second Green/Magenta color selector  212  opposite to the light output side  202   d,  and prevents P-polarization light from passing therethrough. A projection lens  216  receives light that passes through the S-state polarizer  214 . When the first and second reflective light panels  208 ,  210  are in a display state, they modulate and convert the polarization state of light that is incident thereon, and reflect the modulated light in an opposite direction. In the following paragraphs, the operation of the projection display apparatus  200  of the present invention will be described in greater detail with the first and second reflective light panels  208 ,  210  in the display state. In addition, each of a pair of quarter wavelength plates  218 ,  220  is disposed between the polarizating beam splitter  202  and a respective one of the first and second reflective light panels  208 ,  210  for enhancing the image contrast quality. 
   According to the projection display apparatus of the present invention, the first and second reflective light panels  208 ,  210  are preferably LCoS panels each having a color filter embedded therein.  FIG. 3  shows a cross-sectional view of an LCoS panel  50  according to the projection display apparatus of the present invention. The LCoS panel  50  comprises a glass substrate  52 , a silicon backplane  54  and an LC layer  56  disposed therebetween. The silicon backplane  54  has a plurality of electrodes  58  disposed thereon, and the glass substrate  52  has a color filter  60  and an ITO layer  62  disposed thereon, wherein the color filter  60  is disposed between the glass substrate  52  and the ITO layer  62 . The color filter  60  comprises a plurality of color sub-pixels  60   a  for filtering color light therethrough. For this embodiment, the color filter embedded in the first reflective light panel  208  is a red-blue color filter comprising red and blue sub-pixels, and that embedded in the second reflective light panel  210  is a green color filter only comprising green sub-pixels. 
   Each of the first and second Green/Magenta color selector  206 ,  212 , such as the ColorSelect filter products commercially available from ColorLink Co., is used to convert the polarization state of a predetermined color component. In this preferred embodiment, the first Green/Magenta color selector  206  is used to convert P-polarization magenta light that passes therethrough into S-polarization magenta light and to allow green light to pass therethrough. The second Green/Magenta color selector  212  is used for converting the polarization states of the P-polarization blue and red lights (magenta light) that pass therethrough into S-polarization and allowing green light to pass therethrough. 
   When white light  203   a  is provided to the P-state polarizer  204 , only P-polarization white light passes therethrough and reaches the first Green/Magenta color selector  206 . The first Green/Magenta color selector  206  separates the P-polarization white light into S-polarization magenta light  222  and P-polarization green light  224 . When the polarizating beam splitter  202  receives the S-polarization magenta light  222  and the P-polarization green light  224  from the first Green/Magenta color selector  206 , it reflects the S-polarization magenta light  222  toward the first reflective light panel  208  and allow the P-polarization green light  224  to pass directly therethrough. The S-polarization magenta light  222  and the P-polarization green light  224 , then, respectively reach the first reflective light panel  208  and the second reflective light panel  210 . 
   When the first and second reflective light panels  208 ,  210  are in the display state, the S-polarization magenta light  222  is modulated by the first reflective light panel  208 , and the polarization state of the magenta light  222  is changed to P-polarization. The P-polarization magenta light  222  is then reflected by the first reflective light panel  208  and passes through the red-blue color filter embedded in the first reflective light panel  208  so as to generate P-polarization red image light  226  and P-polarization blue image light  228 . The P-polarization red image light  226  and P-polarization blue image light  228  then pass directly through the polarizating beam splitter  202  so as to reach the second Green/Magenta color selector  212 . The second Green/Magenta color selector  212  converts the polarization states of both the P-polarization red image light  226  and the P-polarization blue image light  228  to S-polarization, and then the S-polarization red image light  226  and blue image light  228  pass through the S-state polarizer  214  and reach the projection lens  216  for being projecting on a projection screen (not shown). On the other hand, the P-polarization green light  224  is modulated by the second reflective light panel  210 , and the polarization state of the P-polarization green light  224  is changed to S-polarization. The S-polarization green light  224  then is reflected by the second reflective light panel  210  and pass through the green color filter embedded in the second reflective light panel  210  so as to generate S-polarization green image light  230 . The S-polarization green image light  230  is then transmitted toward the polarizating beam splitter  202  and further reflected by the polarizating beam splitter  202  to pass in sequence through the second Green/Magenta color selector  212 , the S-state polarizer  214  and finally reach the projection lens  216 . When the green image light  230  is projected by the projection lens  216 , it cooperates with the red image light  226  and blue image light  228  so as to form a full color image on the projection screen (not shown). 
   Now referring to  FIG. 4 , it shows a schematic view of a projection display apparatus  400  with two reflected light panels according to another embodiment of the present invention. Unlike the projection display apparatus  200 , the projection display apparatus  400  can achieve a full color image without the P-state polarizer  204  and the first Green/Magenta color selector  206  used in the projection display apparatus  200 . 
   The projection display apparatus  400  similarly comprises a polarizating beam splitter  402 , a light source  403 , a first reflective light panel  408 , a second reflective light panel  410 , a Green/Magenta color selector  412 , a S-state polarizer  414 , a projection lens  416 , a first quarter wavelength plates  418  and a second quarter wavelength plates  420 . 
   Similarly, the first and second reflective light panels  408 ,  410  are preferably LCoS panels each having a color filter embedded therein, and the color filter embedded in the first reflective light panel  408  is a red-blue color filter and that embedded in the second reflective light panel  410  is a green color filter. 
   When the light source  403  supplies unpolarized white light  403   a,  including at least S-polarization white light  422  and P-polarization white light  424 , to the polarizating beam splitter  402 , the polarizating beam splitter  402  reflects the S-polarization white light  422  toward the first reflective light panel  408  and allows the P-polarization white light  424  to pass directly therethrough. The S-polarization white light  422  and the P-polarization white light  424 , then, respectively reach the first reflective light panel  408  and the second reflective light panel  410 . 
   When the first and second reflective light panels  408 ,  410  are in the display state, the S-polarization white light  422  is modulated by the first reflective light panel  408 , and the polarization state of the S-polarization white light  422  is changed to P-polarization. The P-polarization white light  422  is then reflected by the first reflective light panel  408  and passes through the red-blue color filter embedded in the first reflective light panel  408  so as to generate P-polarization red image light  426  and P-polarization blue image light  428 . The P-polarization red image light  426  and P-polarization blue image light  428  then pass directly through the polarizating beam splitter  402  so as to reach the second Green/Magenta color selector  412 . The second Green/Magenta color selector  412  converts the polarization states of both the P-polarization red image light  426  and the P-polarization blue image light  428  to S-polarization, and then the S-polarization red image light  426  and blue image light  428  pass through the S-state polarizer  414  and reach the projection lens  416  for being projecting on a projection screen (not shown). On the other hand, the P-polarization white light  424  is modulated by the second reflective light panel  410 , and the polarization state of the P-polarization white light  424  is changed to S-polarization. The S-polarization white light  424  then is reflected by the second reflective light panel  410  and pass through the green color filter embedded in the second reflective light panel  410  so as to generate S-polarization green light image  430 . The S-polarization green image light  430  is then transmitted toward the polarizating beam splitter  402  and further reflected by the polarizating beam splitter  402  to pass in sequence through the second Green/Magenta color selector  412 , the S-state polarizer  414  and finally reach the projection lens  416 . When the green image light  430  is projected by the projection lens  416 , it cooperates with the red image light  426  and blue image light  428  so as to form a full color image on the projection screen (not shown). 
   According to the projection display apparatus  400  of the present invention, the white light  403   a  applied to the polarizating beam splitter  402  can be unpolarized such that optical elements used for polarizing the white light  403   a  are eliminated, and therefore the overall cost of the projection display apparatus  400  can be reduced. In addition, the light source  403  can supply white light mixed with some blue or red while the size of each red sub-pixel and that of each blue sub-pixel on the red-blue color filter are proportionally designed. For example, if the light source  403  supplies white light mixed with some blue, the size of each blue sub-pixel is designed to be smaller than that of each red sub-pixel so as to generate balanced blue image light and red image light. 
   It should be noted that the red-blue color filter and the green color filter respectively embedded in the reflective light panel  408 ,  410  can be alternatively substituted by a blue-green color filter and a red color filter, or a green-red color filter and a blue color filter, such that red, blue and green image lights can be generated by the reflective light panel  408 ,  410  simultaneously and projected by the projection lens  416  to form a full color image. 
   While the foregoing descriptions and drawings represent the preferred embodiments of the present invention, it should be understood that various additions, modifications and substitutions may be made therein without departing from the spirit and scope of the principles of the present invention as defined in the accompanying claims. One skilled in the art will appreciate that the invention may be used with many modifications of form, structure, arrangement, elements, and components. The presently disclosed embodiments are therefore to be considered in all respects as illustrative and not restrictive, and the scope of the invention should be defined by the appended claims and their legal equivalents, not limited to the foregoing descriptions.