Abstract:
A triple-lens type projection display includes a source for generating a white primary beam output, a first beam splitter for splitting the white primary beam output into a first color component and a secondary beam output, a second beam splitter for splitting the secondary beam output into a second color component and a third color component, first, second and third light modulators for modulating the first, second and third color components, respectively, a first projection lens for receiving the first color component from the first light modulator, a second projection lens for receiving the second color component from the second light modulator, and a third projection lens for receiving the third color component from the third light modulator. Each of the first, second and third color components has a respective optical path length that is measured from the first beam splitter to a respective one of the first, second and third light modulators. The optical path lengths of the first, second and third color components are equal.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates to a projection display, more particularly to a triple-lens type projection display with uniform optical path lengths for different color components. 
     2. Description of the Related Art 
     Referring to FIG. 1, a conventional triple-lens type projection display  1  is shown to comprise a light source  11 , a light filter  12  downstream of the light source  11  for removing ultraviolet rays and infrared rays from a light beam generated by the light source  11  to thereby obtain a white primary beam output, a first expansive lens  141  downstream of the light filter  12 , a first beam splitter  131  downstream of the first expansive lens  141  to split the primary beam output from the first expansive lens  141  into a first color component and a secondary beam output, a second expansive lens  142  downstream of the first beam splitter  131 , a second beam splitter  132  downstream of the second expansive lens  142  to split the secondary beam output from the second expansive lens  142  into second and third color components, and a third expansive lens  143  downstream of the second beam splitter  132 . The first, second and third color components are generally primary color components, such as red, green and blue. The first color component from the first beam splitter  131  passes sequentially through a first focusing lens  151 , a first polarizer  161 , and a light-modulated first light valve  171  before being received by a first projection lens  181 . The second color component from the second beam splitter  132  passes sequentially through a second focusing lens  152 , a second polarizer  162 , and a light-modulated second light valve  172  before being received by a second projection lens  182 . The third color component from the third expansive lens  143  is reflected by a mirror  133  so as to pass sequentially through a third focusing lens  153 , a third polarizer  163 , and a light-modulated third light valve  173  before being received by a third projection lens  183 . The first, second and third projection lenses  181 ,  182 ,  183  are disposed on a common plane, and project light onto a display screen  19  for showing an image on the latter. 
     It is noted that, while the distances of the first, second and third projection lenses  181 ,  182 ,  183  from the respective one of the first and second beam splitters  131 ,  132  and the mirror  133  are equal, the distance of the second beam splitter  132  from the light source  11  is longer than that of the first beam splitter  131 , and that the distance of the mirror  133  from the light source is longer than that of the second beam splitter  132 . There is thus a need to install the expansive lenses  141 ,  142 ,  143  to compensate for the differences in the optical path lengths traveled by the different color components. 
     However, because three expansive lenses  141 ,  142 ,  143  are needed for the three focusing lenses  151 ,  152 ,  153 , the conventional projection display  1  involves a relatively large number of essential components. In addition, the expansive lenses  141 ,  142 ,  143  can introduce edge distortion to the image  191  shown on the plane of the light valves, as shown in FIG.  2 . 
     SUMMARY OF THE INVENTION 
     Therefore, the main object of the present invention is to provide a triple-lens type projection display with uniform optical path lengths for different color components, thereby eliminating the need for expansive lenses as required in the aforesaid prior art. 
     According to this invention, a triple-lens type projection display comprises: 
     a source for generating a white primary beam output; 
     a first beam splitter for splitting the white primary beam output into a first color component and a secondary beam output; 
     a second beam splitter for splitting the secondary beam output into a second color component and a third color component; 
     first, second and third light modulators for modulating the first, second and third color components, respectively; 
     a first projection lens for receiving the first color component from the first light modulator; 
     a second projection lens for receiving the second color component from the second light modulator; and 
     a third projection lens for receiving the third color component from the third light modulator. 
     Each of the first, second and third color components has a respective optical path length that is measured from the first beam splitter to a respective one of the first, second and third light modulators. The optical path lengths of the first, second and third color components are equal. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Other features and advantages of the present invention will become apparent in the following detailed description of the preferred embodiments with reference to the accompanying drawings, of which: 
     FIG. 1 illustrates a conventional triple-lens type projection display; 
     FIG. 2 illustrates a distorted image on the light valves, generated by the expansive lenses, and shown on the projection display of FIG. 1; 
     FIG. 3 is a perspective view of the first preferred embodiment of a triple-lens type projection display according to this invention; 
     FIG. 4 is a schematic top view of the first preferred embodiment; 
     FIG. 5 is a schematic side view of the first preferred embodiment; 
     FIG. 6 is a perspective view of the second preferred embodiment of a triple-lens type projection display according to this invention; 
     FIG. 7 is a schematic top view of the second preferred embodiment; 
     FIG. 8 illustrates a light valve, a polarization beam splitter and a projection lens of the second preferred embodiment; 
     FIG. 9 is a schematic top view of the third preferred embodiment of a triple-lens type projection display according to this invention; 
     FIG. 10 is a schematic top view of the fourth preferred embodiment of a triple-lens type projection display according to this invention; 
     FIG. 11 illustrates a light valve and a projection lens of the fourth preferred embodiment; 
     FIG. 12 is a schematic top view of the fifth preferred embodiment of a triple-lens type projection display according to this invention; and 
     FIG. 13 illustrates a light valve and a projection lens of the sixth preferred embodiment of a triple-lens type projection display according to this invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring to FIGS. 3,  4  and  5 , the first preferred embodiment of a triple-lens type projection display  2  according to this invention is shown to comprise a light source  21 , a light filter  22  downstream of the light source  21  for removing ultraviolet rays and infrared rays from a light beam generated by the light source  21  to thereby obtain a white primary beam output, an integrated lens set including a pair of spaced apart integrated lenses  23  downstream of the light filter  22  to ensure uniformity of the primary beam output, a polarizing or P/S converter  24  downstream of the integrated lens set  23 , a first beam splitter  251  downstream of the P/S converter  24  to split the primary beam output from the P/S converter  24  into a first color component that travels along a first optical path  201  and a secondary beam output that travels along a second optical path  202  transverse to the first optical path  201 , a first mirror  261  to direct the first color component along the first optical path  201  to travel along a third optical path  203  that is parallel to the second optical path  202 , a second beam splitter  252  to split the secondary beam output along the second optical path  202  into a second color component that travels along a fourth optical path  204  transverse to the second optical path  202  and in a direction opposite to the first optical path  201  and into a third color component that travels along a fifth optical path  205  parallel to the second optical path  202 , a second mirror  262  to direct the second color component along the fourth optical path  204  to travel along a sixth optical path  206  that is parallel to the second optical path  202 , a third mirror  263  to direct the third color component along the fifth optical path  205  to travel along a seventh optical path  207  that is transverse to both the first and second optical paths  201 ,  202 , and a fourth mirror  264  downstream of the third mirror  263  to direct the third color component along the seventh optical path  207  to travel along an eighth optical path  208  that is parallel to the fifth optical path  205 . The third, sixth and eighth optical paths  203 ,  206 ,  208  are transverse to a common vertical plane, and form three vertices of an imaginary triangle on the common vertical plane. The third and sixth optical paths  203 ,  206  further traverse a horizontal line on the common vertical plane. 
     The first, second and third color components are generally primary color components, such as red, green and blue. The first color component along the third optical path  203  passes sequentially through a first focusinglens  291  and a light-modulated first light valve  271  before being received by a first projection lens  281 . The second color component along the sixth optical path  206  passes sequentially through a second focusing lens  292  and a light-modulated second light valve  272  before being received by a second projection lens  282 . The third color component along the eighth optical path  208  passes sequentially through a third focusing lens  293  and a light-modulated third light valve  273  before being received by a third projection lens  283 . The first, second and third light valves  271 ,  272 ,  273  are thus disposed on the common vertical plane traversed by the third, sixth and eighth optical paths  203 ,  206 ,  208 . 
     The first, second and third light valves  271 ,  272 ,  273  are transmissive liquid crystal light valves. As is known in the art, the first, second and third projection lenses  281 ,  282 ,  283  project light onto a display screen (not shown) for showing an image on the latter. 
     In the preferred embodiment, the first, fourth and seventh optical paths  201 ,  204 ,  207  have equal path lengths (P 1 =P 4 =P 7 ). The third optical path  203  has a path length (P 3 ) equal to the sum of the path lengths (P 2 , P 6 ) of the second and sixth optical paths  202 ,  206 . The path length (P 6 ) of the sixth optical path  206  is equal to the sum of the path lengths (P 5 , P 8 ) of the fifth and eighth optical paths  205 ,  208 . 
     Thus, the path length for the first color component, measured from the first beam splitter  251  to the first focusing lens  291 , is equal to P 1 +P 3 =P 1 +P 2 +P 6 =P 4 +P 2 +P 6 . The path length for the second color component, measured from the first beam splitter  251  to the second focusing lens  292 , is equal to P 2 +P 4 +P 6 . The path length for the third color component, measured from the first beam splitter  251  to the third focusing lens  293 , is equal to P 2 +P 5 +P 7 +P 8 =P 2 +P 4 +P 6 . 
     In view of the uniform path lengths for the different color components, there is no need to use the expansive lenses as required in the aforesaid conventional projection display  1 , thereby eliminating the edge distortion effect that is introduced to the image shown on the plane of the light valves. 
     Referring to FIGS. 6,  7  and  8 , the second preferred embodiment of a triple-lens type projection display  3  according to this invention is shown to comprise a light source  31 , a light filter (not shown) downstream of the light source  31  for removing ultraviolet rays and infrared rays from a light beam generated by the light source  31  to thereby obtain a white primary beam output, an integrated lens set including a pair of spaced apart integrated lenses (not shown) downstream of the light filter to ensure uniformity of the primary beam output, a polarizing or P/S converter (not shown) downstream of the integrated lens set, a first beam splitter  321  downstream of the P/S converter to split the primary beam output from the P/S converter into a first color component that travels along a first optical path  301  and a secondary beam output that travels along a second optical path  302  transverse to the first optical path  301 , a second beam splitter  322  to split the secondary beam output along the second optical path  302  into a second color component that travels along a third optical path  303  parallel to the first optical path  301  and into a third color component that travels along a fourth optical path  304  parallel to the second optical path  302 , and a mirror  33  to direct the third color component along the fourth optical path  304  to travel along a fifth optical path  305  that is parallel to the first optical path  301 . The first, third and fifth optical paths  301 ,  303 ,  305  are transverse to a common vertical plane, and traverse a horizontal line on the common vertical plane. 
     The first, second and third color components are generally primary color components, such as red, green and blue. The first color component along the first optical path  301  passes through a first focusing lens (not shown), a first polarization beam splitter  361  and a light-modulated first light valve  341  before being received by a first projection lens  351 . Particularly, as shown in FIG. 8, incident light with S-polarization  371  from the first focusing lens is directed by the first polarization beam splitter  361  to the first light valve  341 . The first light valve  341 , which is a reflective light valve, reflects light back to the first polarization beam splitter  361 . The reflected light with P-polarization  372  is subsequently directed by the first polarization beam splitter  361  to the first projection lens  351 . 
     The second color component along the third optical path  303  passes through a second focusing lens (not shown), a second polarization beam splitter  362  and a light-modulated second light valve  342  before being received by a second projection lens  352 . The second focusing lens, the second polarization beam splitter  362  and the second light valve  342  operate in a manner similar to the first focusing lens, the first polarization beam splitter  361  and the first light valve  341 . 
     The third color component along the fifth optical path  305  passes through a third focusing lens (not shown), a third polarization beam splitter  363  and a light-modulated third light valve  343  before being received by a third projection lens  353 . The third focusing lens, the third polarization beam splitter  363  and the third light valve  343  operate in a manner similar to the first focusing lens, the first polarization beam splitter  361  and the first light valve  341 . 
     Like the previous embodiment, light from the first, second and third projection lenses  351 ,  352 ,  353  are projected on a display screen (not shown) for showing an image on the latter. 
     In the second preferred embodiment, the first optical path  301  has a path length (P 1 ) equal to the sum of the path lengths (P 2 , P 3 ) of the second and third optical paths  302 ,  303 . The path length (P 3 ) of the third optical path  303  is equal to the sum of the path lengths (P 4 , P 5 ) of the fourth and fifth optical paths  304 ,  305 . Thus, with reference to a common vertical plane upon which the first and second beam splitters  321 ,  322  and the mirror  33  are disposed, the first projection lens  351  is farther from the common vertical plane than the second projection lens  352 , and the second projection lens  352  is farther from the common vertical plane than the third projection lens  353 . 
     The path length for the first color component, measured from the first beam splitter  321  to the first focusing lens, is equal to P 1 . The path length for the second color component, measured from the first beam splitter  321  to the second focusing lens, is equal to P 2 +P 3 =P 1 . The path length for the third color component, measured from the first beam splitter  321  to the third focusing lens, is equal to P 2 +P 4 +P 5 =P 2 +P 3 =P 1 . The different color components thus have uniform path lengths in the second preferred embodiment of this invention. 
     The third preferred embodiment of a triple-lens type projection display  4  according to this invention is shown in FIG.  9 . Unlike the second preferred embodiment, the projection display  4  comprises a source  41  for providing a white primary beam output, a first beam splitter  421  downstream of the source  41  to split the primary beam output from the source  41  into a first color component that travels along a first optical path  401  and a secondary beam output that travels along a second optical path  402  transverse to the first optical path  401 , a first mirror  431  to direct the first color component along the first optical path  401  to travel along a third optical path  403  parallel to the second optical path  402 , a second beam splitter  422  to split the secondary beam output along the second optical path  402  into a second color component that travels along a fourth optical path  404  parallel to the second optical path  402  and into a third color component that travels along a fifth optical path  405  transverse to the second optical path  402  and in a direction opposite to the first optical path  401 , and a second mirror  432  to direct the third color component along the fifth optical path  405  to travel along a sixth optical path  406  that is parallel to the second optical path  402 . 
     The first, second and third color components are generally primary color components, such as red, green and blue. The first color component along the third optical path  403  passes through a first focusing lens (not shown), a first polarization beam splitter  461  and a light-modulated!first light valve  441  before being received by a first projection lens  451  in a manner similar to the second preferred embodiment. 
     The second color component along the fourth optical path  404  passes through a second focusing lens (not shown), a second polarization beam splitter  462  and a light-modulated second light valve  442  before being received by a second projection lens  452  in a manner similar to the second preferred embodiment. 
     The third color component along the sixth optical path  406  passes through a third focusing lens (not shown), a third polarization beam splitter  463  and a light-modulated third light valve  443  before being received by a third projection lens  453  in a manner similar to the second preferred embodiment. 
     Like the previous embodiments, light from the first, second and third projection lenses  451 ,  452 ,  453  are projected on a display screen (not shown) for showing an image on the latter. 
     In the third preferred embodiment, the sum of the path lengths (P 1 , P 3 ) of the first and third optical paths  401 ,  403  is equal to the sum of the path lengths (P 2 , P 4 ) of the second and fourth optical paths  402 ,  404 . The path length (P 4 ) of the fourth optical path  404  is equal to the sum of the path lengths (P 5 , P 6 ) of the fifth and sixth optical paths  405 ,  406 . The first, second and third projection lenses  451 ,  452 ,  453  are thus arranged in a triangular formation with respect to a common horizontal plane. 
     The path length for the first color component, measured from the first beam splitter  421  to the first focusing lens, is equal to P 1 +P 3 =P 2 +P 4 . The path length for the second color component, measured from the first beam splitter  421  to the second focusing lens, is equal to P 2 +P 4 . The path length for the third color component, measured from the first beam splitter  421  to the third focusing lens, is equal to P 2 +P 5 +P 6 =P 2 +P 4 . 
     The different color components thus have uniform path lengths in the third preferred embodiment of this invention. 
     FIGS. 10 and 11 illustrate the fourth preferred embodiment of a triple-lens type projection display  5  according to this invention. The projection display  5  is based upon the second preferred embodiment, and includes a light source  51 , first and second beam splitters  521 ,  522 , and a mirror  53  which cooperate to form three color components in three different optical paths having uniform optical path lengths. 
     Unlike the second preferred embodiment, there is no polarization beam splitter between a light valve and a projection lens for each color component. Particularly, with reference to FIG. 11, incident light  571  of the first color component impinges upon a light-modulated first light valve (DMD)  541 , which is a digital reflective light valve, at an angle relative to the plane of the first light valve  541 . Reflected light  572  from the first light valve  541 , which is transverse to the plane of the first light valve  541 , is provided directly to a first projection lens  551 . 
     Like the first color component, the second color component is received by a second projection lens  552  via a digital reflective second light valve  542 , whereas the third color component is received by a third projection lens  553  via a digital reflective third light valve  543 . 
     FIG. 12 illustrates the fifth preferred embodiment of a triple-lens type projection display  6  according to this invention. The projection display  6  is based upon the third preferred embodiment, and includes a light source  61 , first and second beam splitters  621 ,  622 , and first and second mirrors  631 ,  632  which cooperate to form three color components in three different optical paths having uniform optical path lengths. 
     Unlike the third preferred embodiment, there is no polarization beam splitter between a light valve and a projection lens for each color component. Instead, the first color component is received by a first projection lens  651  via a digital reflective first light valve  641  in a manner similar to the fourth preferred embodiment. Likewise, the second color component is received by a second projection lens  652  via a digital reflective second light valve  642 , whereas the third color component is received by a third projection lens  653  via a digital reflective third light valve  643 . 
     FIG. 13 illustrates a light valve  71  and a projection lens  72  of the sixth preferred embodiment of a triple-lens type projection display according to this invention. Unlike the fourth and fifth preferred embodiments, the light valve  71  is an inclined reflective liquid crystal light valve. Incident light  73  impinges upon the light valve  71  at an angle relative to the plane of the latter. Reflected light  74  from the light valve  71 , which also forms an angle with the plane of the latter, is provided directly to the projection lens  72 . The projection lens  72  is thus staggered with respect to the light valve  71  to result in a flatter arrangement as compared to the light valve and projection lens set of the fourth and fifth preferred embodiments. 
     While the present invention has been described in connection with what is considered the most practical and preferred embodiments, it is understood that this invention is not limited to the disclosed embodiments but is intended to cover various arrangements included within the spirit and scope of the broadest interpretation so as to encompass all such modifications and equivalent arrangements.