Abstract:
A projection display apparatus has at least two dichroic reflecting surfaces, a wavelength plate, a polarizing beam splitter, and two reflection-type liquid crystal display devices. The first dichroic reflecting surface separates a polarized light beam into light beams of two different wavelength ranges. The wavelength plate rotates the polarization plane of the light beam of the first wavelength range. The second dichroic reflecting surface integrates together the light beam of the first wavelength range after the rotation of its polarization plane and the light beam of the second wavelength range. The polarizing beam splitter reflects one and transmits the other of the light beams of the first and second wavelength ranges after the integration by the second dichroic reflecting surface. The reflection-type liquid crystal display devices modulate and reflect the light beams reflected from and transmitted through the polarizing beam splitter, respectively. The polarizing beam splitter transmits the light beam coming from the first reflection-type liquid crystal display device and reflects the light beam coming from the second reflection-type liquid crystal display device so as to integrate together those two light beams.

Description:
This application is based on applications Nos. H10-076104 and H10-077377 filed in Japan, the content of which is hereby incorporated by reference. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a projection display apparatus employing eflection-type liquid crystal display devices. 
     2. Description of the Prior Art 
     Conventionally, various display apparatuses of the so-called projection type have been proposed. For example, Japanese Laid-Open Patent Application H2-74903 proposes an arrangement that employs an optical system in which illumination light is separated into beams of different colors and these beams are integrated together by a color integration system including a polarizing beam splitter, a liquid crystal display device, and a cross-dichroic prism. Japanese Laid-Open Patent Application H8-122772 describes, as prior art, an arrangement that employs an optical system composed of three reflection-type liquid crystal display devices, a polarizing beam splitter, and two dichroic mirrors. This Japanese Laid-Open Patent Application H8-122772 proposes an arrangement that employs an optical system composed of three reflection-type liquid crystal display devices and a polarizing beam splitter. 
     However, the above-mentioned optical system including a cross-dicliroic prism is unduly expensive, because the cross-dichroic prism itself is expensive. The above-mentioned optical system having three reflection-type liquid crystal display devices, a polarizing beam splitter, and two dichroic mirrors requires that the two dichroic mirrors be disposed between the polarizing beam splitter and the reflection-type liquid crystal display devices. This makes the back focal length, i.e. the distance from the projection lens to the reflection-type liquid crystal display devices, unduly long, and thus makes the f-number of the projection lens unduly large, making it impossible to obtain satisfactory brightness. 
     The above-mentioned optical system proposed in Japanese Laid-Open Patent Application H8-122772 lets unpolarized light enter the polarizing beam splitter, and therefore suffers from flare caused in the projected image by unused polarized-light components. Moreover, this optical system discards the P-polarized light component included in the green component and the S-polarized light component included in the red and blue components without using them for image formation, and thus suffers from inefficient use of the light source. 
     SUMMARY OF THE INVENTION 
     An object of the present invention is to provide an inexpensive, compact, and efficient projection display apparatus having a simple structure and offering high contrast and high quality in the projected image. 
     To achieve the above object, according to one aspect of the present invention, a projection display apparatus is provided with: a first dichroic reflecting surface for separating a polarized light beam into a light beam of a first wavelength range and a light beam of a second wavelength range; a wavelength plate for rotating a polarization plane of the light beam of the first wavelength range; a second dichroic reflecting surface for integrating together the light beam of the first wavelength range after rotation of its polarization plane and the light beam of the second wavelength range; a first polarizing beam splitter for reflecting one and transmitting the other of the light beams of the first and second wavelength ranges after integration by the second dichroic reflecting surface; a first reflection-type liquid crystal display device for modulating and reflecting a light beam reflected from the first polarizing beam splitter; and a second reflection-type liquid crystal display device for modulating and reflecting a light beam transmitted through the first polarizing beam splitter. Here, the first polarizing beam splitter transmits a light beam coming from the first reflection-type liquid crystal display device and reflects a light beam coming from the second reflection-type liquid crystal display device so as to integrate together those two light beams. 
     According to another aspect of the present invention, an illumination optical system is provided with: separating means for separating a light beam from a light source into a light beam of a first wavelength range and a light beam of a second wavelength range; processing means for optically processing the light beam of the first or second wavelength range; and separating/integrating means for separating a light beam of a third wavelength range from the light beam of the second wavelength range and integrating together a portion of the light beam of the second wavelength range that remains after separation of the light beam of the third wavelength range and the light beam of the first wavelength range. 
     According to still another aspect of the present invention, a projection display apparatus is provided with: a first dichroic reflecting surface for separating a source light beam into a light beam of a first wavelength range and a light beam of a second wavelength range; a dichroic polarizing beam splitter that transmits the light beams of the first and second wavelength ranges shone onto it from different directions from each other; a first reflection-type liquid crystal display device for modulating and reflecting one of the light beams of the first and second wavelength ranges transmitted through the dichroic polarizing beam splitter; and a second reflection-type liquid crystal display device for modulating and reflecting the other of the light beams of the first and second wavelength ranges transmitted through the dichroic polarizing beam splitter. Here, the dichroic polarizing beam splitter transmits a light beam coming from the first reflection-type liquid crystal display device and reflects a light beam coming from the second reflection-type liquid crystal display device so as to integrate together those two light beams. 
     Alternatively, a projection display apparatus is provided with: a first dichroic reflecting surface for separating a source light beam into a light beam of a first wavelength range and a light beam of a second wavelength range; a dichroic polarizing beam splitter that reflects the light beams of the first and second wavelength ranges shone onto it from different directions from each other; a first reflection-type liquid crystal display device for modulating and reflecting one of the light beams of the first and second wavelength ranges reflected from the dichroic polarizing beam splitter; and a second reflection-type liquid crystal display device for modulating and reflecting the other of the light beams of the first and second wavelength ranges reflected from the dichroic polarizing beam splitter. Here, the dichroic polarizing beam splitter reflects a light beam coming from the first reflection-type liquid crystal display device and transmits a light beam coming from the second reflection-type liquid crystal display device so as to integrate together those two light beams. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     This and other objects and features of the present invention will become clear from the following description, taken in conjunction with the preferred embodiments with reference to the accompanied drawings in which: 
     FIG. 1 is a diagram schematically showing a first embodiment of the invention; 
     FIG. 2 is a diagram schematically showing a second embodiment of the invention; 
     FIG. 3 is a diagram schematically showing a third embodiment of the invention; 
     FIGS. 4A to  4 D are diagrams showing the transmittance characteristic of the polarizing beam splitters; 
     FIG. 5 is a diagram schematically showing a fourth embodiment of the invention; 
     FIG. 6 is a diagram schematically showing a fifth embodiment of the invention; 
     FIGS. 7A to  7 E are diagrams showing the transmittance characteristic of the polarizin beam splitters; 
     FIG. 8 is a graph showing a practical example of the transmittance characteristic (film characteristic); and 
     FIG. 9 is a graph showing another practical example of the transmittance characteristic (film characteristic). 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a diagram schematically showing a first embodiment of the invention. In FIG. 1, reference numeral  1  represents a white light source; reference numeral  2  represents a reflector, disposed so as to surround the white light source  1 , for reflecting the light emitted from the white light source  1 ; and reference numeral  3  represents a polarization converter, disposed above the white light source  1 , for converting the light from the white light source  1  into light polarized on a predetermined polarization plane. In this embodiment, it is assumed that the light from the light source is used after being converted into S-polarized light with respect to the mirrors, prisms, and other optical elements used. 
     This polarization converter  3  is composed of a polarizing beam splitter  4  for internally reflecting the S-polarized light component, indicated by the broken-line arrow S, and transmitting the P-polarized light component, indicated by the solid-line arrow P, in such a way that they both pass therethrough, and a half-wave plate  5  for rotating the polarization plane of the transmitted P-polarized light component so as to convert it into S-polarized light. The components noted thus far constitute an illumination optical system. Although not shown, it is customary to additionally use an integrator optical system to minimize unevenness of the illumination light of this illumination optical system. 
     Moreover, in FIG. 1, reference numerals  101  and  102  represent dichroic mirrors; reference numerals  201  and  202  represent polarizing beam splitters; reference numeral  206  represents a dichroic prism; reference numerals  301  to  303  represent reflection-type liquid crystal display devices (slantly hatched rectangles); reference numeral  401  represents reflecting mirrors; reference numerals  501  to  503  represent polarizing plates (horizontally or vertically hatched rectangles); reference numerals  601  to  603  represent band-pass filters (dot-filled rectangles); and reference numeral  701  represents half-wave plates (plain rectangles). 
     As shown in FIG. 1, the illumination light (a white light beam), composed of the light coming directly from the white light source  1  and the light reflected from the reflector  2 , first passes through the polarization converter  3 , which transmits the S-polarized light component and converts the P-polarized light component into S-polarized light, and then reaches the dichroic mirror  101 . Here, out of the now wholly S-polarized white light beam, only the blue (B) component is transmitted, and the other, green (G) and red (R), components are reflected. The B component transmitted through the dichroic mirror  101  is then reflected from one of the reflecting mirrors  401 , has its polarization plane rotated by the half-wave plate  701  so as to be converted into P-polarized light, has its polarization direction aligned by the polarizing plate  501 , and then reaches the dichroic mirror  102 . 
     On the other hand, in a similar manner, the G and R components reflected from the dichroic mirror  101  are then reflected from the other of the reflecting mirrors  401 , have their polarization direction aligned by the polarizing plate  502 , and then reach the dichroic mirror  102 . Here, the P-polarized B component is transmitted and the S-polarized G component is reflected so that these two components are integrated together. The S-polarized R component is transmitted and thereby separated from the other components. 
     This S-polarized R component is then reflected from the polarizing beam splitter  202 , has its wavelength range trimmed by the band-pass filter  602 , and then illuminates the pixels on the reflection-type liquid crystal display device  302 . Here, at every moment, those pixels which are used for screen display are turned on so that the S-polarized R component incident on those pixels is reflected after being converted into P-polarized light, and those pixels which are not used are turned off so that the same component incident on those pixels is reflected intact as S-polarized light. The R component reflected from the reflection-type liquid crystal display device  302  reaches the polarizing beam splitter  202  again. Here, only the P-polarized light component of the R component is transmitted. The transmitted component then has its polarization direction aligned by the polarizing plate  503 , has its polarizing plane rotated by the half-wave plate  701  so as to be converted into S-polarized light, and is then reflected from the dichroic prism  206 . 
     On the other hand, the P-polarized B component and the S-polarized G component integrated together by the dichroic mirror  102  reach the polarizing beam splitter  201 . Here, the P-polarized B component is transmitted, and the S-polarized G component is reflected. These components then have their wavelength ranges trimmed by the band-pass filters  601  and  603 , respectively, and then illuminate the pixels on the reflection-type liquid crystal display devices  301  and  303 , respectively. On the reflection-type liquid crystal display device  301 , at every moment, those pixels which are used for screen display are turned on so that the P-polarized B component incident on those pixels is reflected after being converted into S-polarized light, and those pixels which are not used are turned off so that the same component incident on those pixels is reflected intact as P-polarized light. The B component reflected from the reflection-type liquid crystal display device  301  reaches the polarizing beam splitter  201  again. 
     On the reflection-type liquid crystal display device  303 , at every moment, those pixels which are used for screen display are turned on so that the S-polarized G component incident on those pixels is reflected after being converted into P-polarized light, and those pixels which are not used are turned off so that the same component incident on those pixels is reflected intact as S-polarized light. The G component reflected from the reflection-type liquid crystal display device  303  reaches the polarizing beam splitter  201  again. Here, the S-polarized B component is reflected and the P-polarized G component is transmitted so that these two components are integrated together. 
     These S-polarized B component and P-polarized G component integrated together reach the dichroic prism  206 , through which they both are transmitted so as to be integrated together with the previously mentioned S-polarized R component. In this way, the components of three primary colors are integrated together, which are then directed to a projection optical system (not shown). Note that, instead of the dichroic prism  206  for reflecting the R component and transmitting the G and B components, it is possible to use a dichroic mirror for the same purposes. 
     FIG. 2 is a diagram schematically showing the second embodiment of the invention. The illumination optical system shown in FIG. 2 is the same as that shown in FIG.  1 . Reference numerals  101  and  104  represent dichroic mirrors; reference numerals  202  and  204  represent polarizing beam splitters; reference numeral  205  represents a dichroic prism; reference numerals  301  to  303  represent reflection-type liquid crystal display devices (slantly hatched rectangles); reference numeral  401  represents reflecting mirrors; reference numerals  501  to  503  represent polarizing plates (horizontally or vertically hatched rectangles); reference numerals  601  to  603  represent band-pass filters (dot-filled rectangles); and reference numeral  701  represents half-wave plates (plain rectangles). 
     As shown in FIG. 2, the illumination light (a white light beam), composed of the light coming directly from the white light source  1  and the light reflected from the reflector  2 , first passes through the polarization converter  3 , which transmits the S-polarized light component and converts the P-polarized light component into S-polarized light, and then reaches the dichroic mirror  101 . Here, out of the now wholly S-polarized white light beam, only the blue (B) component is transmitted, and the other, green (G) and red (R), components are reflected. The B component transmitted through the dichroic mirror  101  is then reflected from one of the reflecting mirrors  401 , has its polarization plane rotated by the half-wave plate  701  so as to be converted into P-polarized light, has its polarization direction aligned by the polarizing plate  501 , and then reaches the dichroic mirror  104 . 
     On the other hand, in a similar manner, the G and R components reflected from the dichroic mirror  101  are then reflected from the other of the reflecting mirrors  401 , have their polarization direction aligned by the polarizing plate  502 , and then reach the dichroic mirror  104 . Here, the P-polarized B component is transmitted and the S-polarized R component is reflected so that these two components are integrated together. The S-polarized G component is transmitted and thereby separated from the other components. 
     This S-polarized G component is then reflected from the polarizing beam splitter  202 , has its wavelength range trimmed by the band-pass filter  603 , and then illuminates the pixels on the reflection-type liquid crystal display device  303 . Here, at every moment, those pixels which are used for screen display are turned on so that the S-polarized G component incident on those pixels is reflected after being converted into P-polarized light, and those pixels which are not used are turned off so that the same component incident on those pixels is reflected intact as S-polarized light. The G component reflected from the reflection-type liquid crystal display device  303  reaches the polarizing beam splitter  202  again. Here, only the P-polarized light component of the G component is transmitted. The transmitted component then has its polarization direction aligned by the polarizing plate  503 , has its polarizing plane rotated by the half-wave plate  701  so as to be converted into S-polarized light, and is then reflected from the dichroic prism  205 . 
     On the other hand, the P-polarized B component and the S-polarized R component integrated together by the dichroic mirror  104  reach the polarizing beam splitter  204 . Here, the P-polarized B component is transmitted, and the S-polarized R component is reflected. These components then have their wavelength ranges trimmed by the band-pass filters  601  and  602 , respectively, and then illuminate the pixels on the reflection-type liquid crystal display devices  301  and  302 , respectively. 
     On the reflection-type liquid crystal display device  301 , at every moment, those pixels which are used for screen display are turned on so that the P-polarized B component incident on those pixels is reflected after being converted into S-polarized light, and those pixels which are not used are turned off so that the same component incident on those pixels is reflected intact as P-polarized light. The B component reflected from the reflection-type liquid crystal display device  301  reaches the polarizing beam splitter  204  again. 
     On the reflection-type liquid crystal display device  302 , at every moment, those pixels which are used for screen display are turned on so that the S-polarized R component incident on those pixels is reflected after being converted into P-polarized light, and those pixels which are not used are turned off so that the same component incident on those pixels is reflected intact as S-polarized light. The R component reflected from the reflection-type liquid crystal display device  302  reaches the polarizing beam splitter  204  again. Here, the S-polarized B component is reflected and the P-polarized R component is transmitted so that these two components are integrated together. 
     These S-polarized B component and P-polarized R component integrated together reach the dichroic prism  205 , through which they are transmitted so as to be integrated together with the previously mentioned S-polarized G component. In this way, the components of three primary colors are integrated together, which are then directed to a projection optical system (not shown). Note that, instead of the dichroic prism  205  for reflecting the G component and transmitting the R and B components, it is possible to use a dichroic mirror for the same purposes. 
     FIG. 3 is a diagram schematically showing a third embodiment of the invention. In FIG. 3, reference numeral  1  represents a white light source; 
     reference numeral  2  represents a reflector, disposed so as to surround the white light source  1 , for reflecting the light emitted from the white light source  1 ; and 
     reference numeral  3  represents a polarization converter, disposed by the side of the white light source  1 , for converting the light from the white light source  1  into light polarized on a predetermined polarization plane. As noted earlier, in this embodiment, it is assumed that the light from the light source is used after being converted into S-polarized light. The illumination optical system shown in FIG. 3 is the same as those shown in FIGS. 1 and 2. 
     Moreover, in FIG. 3, reference numerals  101  to  103  represent dichroic mirrors; reference numeral  201  represents a polarizing beam splitter; reference numeral  203  represents a dichroic polarizing beam splitter; reference numerals  301  to  303  represent reflection-type liquid crystal display devices (slantly hatched rectangles); reference numeral  401  represents a reflecting mirror; reference numeral  501  represents a polarizing plate (a vertically hatched rectangles); reference numerals  601  to  603  represent band-pass filters (dot-filled rectangles); and reference numeral  701  represent half-wave plates (plain rectangles). 
     As shown in FIG. 3, the illumination light (a white light beam), composed of the light coming directly from the white light source  1  and the light reflected from the reflector  2 , first passes through the polarization converter  3 , which transmits the S-polarized light component and converts the P-polarized light component into S-polarized light, and then reaches the dichroic mirror  101 . Here, out of the now wholly S-polarized white light beam, only the blue (B) component is transmitted, and the other, green (G) and red (R), components are reflected. 
     The B component transmitted through the dichroic mirror  101  is then reflected from the reflecting mirror  401 , has its polarization plane rotated by the half-wave plate  701  so as to be converted into P-polarized light, and then reaches the dichroic mirror  103 . On the other hand, the G and R components reflected from the dichroic mirror  101  reach the dichroic mirror  102 . Here, the S-polarized G component is reflected and the S-polarized R component is transmitted so that these two components are separated from each other. The S-polarized G component then reaches the dichroic mirror  103 . Here, The S-polarized G component is reflected and the P-polarized B component is transmitted so that these two components are integrated together. 
     The S-polarized R component transmitted through the dichroic mirror  102  then has its polarization plane rotated by the half-wave plate  701  so as to be converted into P-polarized light, has its polarization direction aligned by the polarizing plate  501 , reaches the dichroic polarizing beam splitter  203  so as to be transmitted therethrough, has its wavelength range trimmed by the band-pass filter  602 , and then illuminates the pixels on the reflection-type liquid crystal display device  302 . Here, at every moment, those pixels which are used for screen display are turned on so that the P-polarized R component incident on those pixels is reflected after being converted into S-polarized light, and those pixels which are not used are turned off so that the same component incident on those pixels is reflected intact as P-polarized light. The R component reflected from the reflection-type liquid crystal display device  302  reaches the dichroic polarizing beam splitter  203  again. Here, only the S-polarized light component of the R component is reflected. 
     On the other hand, the P-polarized B component and the S-polarized G component integrated together by the dichroic mirror  103  reach the polarizing beam splitter  201 . Here, the P-polarized B component is transmitted and the S-polarized G component is reflected. These components then have their wavelength ranges trimmed by the band-pass filters  601  and  603 , respectively, and then illuminate the pixels on the reflection-type liquid crystal display devices  301  and  303 , respectively. 
     On the reflection-type liquid crystal display device  301 , at every moment, those pixels which are used for screen display are turned on so that the P-polarized B component incident on those pixels is reflected after being converted into S-polarized light, and those pixels which are not used are turned off so that the same component incident on those pixels is reflected intact as P-polarized light. The B component reflected from the reflection-type liquid crystal display device  301  reaches the polarizing beam splitter  201  again. 
     On the reflection-type liquid crystal display device  303 , at every moment, those pixels which are used for screen display are turned on so that the S-polarized G component incident on those pixels is reflected after being converted into P-polarized light, and those pixels which are not used are turned off so that the same component incident on those pixels is reflected intact as S-polarized light. The G component reflected from the reflection-type liquid crystal display device  303  reaches the polarizing beam splitter  201  again. Here, the S-polarized B component is reflected and the P-polarized G component is transmitted so that these two components are integrated together. 
     These S-polarized B component and P-polarized G component integrated together reach the dichroic polarizing beam splitter  203 , through which they both are transmitted so as to be integrated together with the previously mentioned S-polarized R component. In this way, the components of three primary colors are integrated together, which are then directed to a projection optical system (not shown). 
     In the arrangement shown in FIG. 3, what corresponds to the elements  202  and  206  in the arrangement shown in FIG. 1, or what corresponds to the elements  202  and  205  in the arrangement shown in FIG. 2, is realized by the use of a single element. This makes the arrangement shown in FIG. 3 more inexpensive than those shown in FIGS. 1 and 2. Note that the first to third embodiments described above are all designed to have the same back focal length (i.e. the distance from the projection optical system to the reflection-type liquid crystal display device) or all of the color components. 
     FIGS. 4A to  4 D are diagrams showing the transmittance characteristic, for the wavelength ranges of the individual color components, of the polarizing beam splitters employed in the first to third embodiments, with FIGS. 4A to  4 D showing the transmittance characteristic of the polarizing beam splitters  201  to  204 , respectively. In these diagrams, a broken line indicates P-polarized light, and a solid line indicates S-polarized light. As shown in FIG. 4A, the polarizing beam splitter  201  is designed to transmit almost 100% of the P-polarized light within the wavelength ranges of the B and G components and reflect almost 100% of the S-polarized light within the wavelength ranges of the B and G components. 
     As shown in FIG. 4B, the polarizing beam splitter  202  is designed to transmit almost 100% of the P-polarized light within the wavelength ranges of the G and R components and reflect almost 100% of the S-polarized light within the wavelength ranges of the G and R components. 
     As shown in FIG. 4C, the dichroic polarizing beam splitter  203  is designed to transmit almost 100% of the P-polarized light within the wavelength ranges of the B, G, and R components, transmit almost 100% of the S-polarized light in the wavelength range of the B component, and reflect almost 100% of the S-polarized light within the wavelength ranges of the G and R components. 
     As shown in FIG. 4D, the polarizing beam splitter  204  is designed to transmit almost 100% of the P-polarized light within the wavelength ranges of the B, G, and R components and reflect almost 100% of the S-polarized light within the wavelength ranges of the B, G, and R components. 
     The polarizing beam splitters described above each employ a prism-type polarizing element called a MacNeile polarizing element. The various characteristics of these polarizing beam splitters are achieved by laying layers of two different refractive indices alternately over one another. 
     FIG. 5 is a diagram schematically showing a fourth embodiment of the invention. In FIG. 5, reference numeral  1  represents a white light source; reference numeral  2  represents a reflector, disposed so as to surround the white light source  1 , for reflecting the light emitted from the white light source  1 ; and reference numeral  3  represents a polarization converter, disposed by the side of the white light source  1 , for converting the light from the white light source  1  into light polarized on a predetermined polarization plane. In this embodiment, it is assumed that the light from the light source is used after being converted into P-polarized light with respect to the mirrors, prisms, and other optical elements used. 
     This polarization converter  3  is composed of a polarizing beam splitter  4  for internally reflecting the S-polarized light component, indicated by the broken-line arrow S, and transmitting the P-polarized light component, indicated by the solid- line arrow P, in such a way that they both pass therethrough, and a half-wave plate  5  for rotating the polarization plane of the S-polarized light component that has passed therethrough so as to convert it into P-polarized light. The components noted thus far constitute an illumination optical system. Although not shown, it is customary to additionally use an integrator optical system to minimize unevenness of the illumination light of this illumination optical system. 
     Moreover, in FIG. 5, reference numerals  101  and  102  represent dichroic mirrors; reference numerals  201   a  and  203   a  represent dichroic polarizing beam splitters; reference numeral  202   a  represents a polarizing beam splitter; reference numerals  301  to  303  represent reflection-type liquid crystal display devices (slantly hatched rectangles); reference numeral  401  represents reflecting mirrors; reference numerals  501  to  503  and  507  represent polarizing plates (horizontally or vertically hatched rectangles); reference numerals  601  to  603  represent band-pass filters (dot-filled rectangles); reference numeral  701  represents half-wave plates (plain rectangles); and reference numeral  6  represents a relay optical system for compensating the optical path length. 
     As shown in FIG. 5, the illumination light (a white light beam), composed of the light coming directly from the white light source  1  and the light reflected from the reflector  2 , first passes through the polarization converter  3 , which transmits the P-polarized light component and converts the S-polarized light component into P-polarized light, and then reaches the dichroic mirror  101 . Here, out of the now wholly P-polarized white light beam, only the blue (B) component is transmitted, and the other, green (G) and red (R), components are reflected. 
     The B component transmitted through the dichroic mirror  101  is then reflected from the first reflecting mirror  401 , passes through the relay optical system  6 , is further reflected from the second and then third reflecting mirror  401 , has its polarization direction aligned by the polarizing plate  503 , and then reaches the dichroic polarizing beam splitter  203   a . Here, the P-polarized B component is transmitted. This component is then transmitted through the dichroic polarizing beam splitter  201   a , has its wavelength range trimmed by the band-pass filter  601 , and then illuminates the pixels on the reflection-type liquid crystal display device  301 . 
     On the reflection-type liquid crystal display device  301 , at every moment, those pixels which are used for screen display are turned on so that the P-polarized B component incident on those pixels is reflected after being converted into S-polarized light, and those pixels which are not used are turned off so that the same component incident on those pixels is reflected intact as P-polarized light. The B component reflected from the reflection-type liquid crystal display device  301  reaches the dichroic polarizing beam splitter  201 a again. Here, the S-polarized B component is transmitted, which is then reflected from the dichroic polarizing beam splitter  203   a.    
     On the other hand, the G and R components reflected from the dichroic mirror  101  reach the dichroic mirror  102 . Here, the P-polarized R component is transmitted and the P-polarized G component is reflected so that the two components are separated from each other. The P-polarized R component then has its polarization plane rotated by the half-wave plate  701  so as to be converted into S-polarized light, has its polarization direction aligned by the polarizing plate  502 , is reflected from the polarizing beam splitter  202   a , has its wavelength range trimmed by the band-pass filter  602 , and then illuminates the pixels on the reflection-type liquid crystal display device  302 . 
     Here, at every moment, those pixels which are used for screen display are turned on so that the S-polarized R component incident on those pixels is reflected after being converted into P-polarized light, and those pixels which are not used are turned off so that the same component incident on those pixels is reflected intact as S-polarized light. The R component reflected from the reflection-type liquid crystal display device  302  reaches the polarizing beam splitter  202   a  again. Here, only the P-polarized R component is transmitted, which then has its polarization plane rotated by the half-wave plate  701  so as to be converted into S-polarized light, and is then transmitted through the dichroic polarizing beam splitter  203   a.    
     The P-polarized G component separated by the dichroic mirror  102  has its polarization direction aligned by the polarizing plate  501 , and then reaches the a dichroic polarizing beam splitter  201   a . Here, the P-polarized G component is transmitted, which then has its wavelength range trimmed by the band-pass filter  603 , and then illuminates the pixels on the reflection-type liquid crystal display device  303 . 
     On the reflection-type liquid crystal display device  303 , at every moment, those pixels which are used for screen display are turned on so that the P-polarized G component incident on those pixels is reflected after being converted into S-polarized light, and those pixels which are not used are turned off so that the same component incident on those pixels is reflected intact as P-polarized light. The G component reflected from the reflection-type liquid crystal display device  303  reaches the dichroic polarizing beam splitter  201   a  again. Here, the S-polarized G component is reflected, which is then further reflected from the dichroic polarizing beam splitter  203   a.    
     Finally, the R, G, and B components, now all S-polarized, are integrated together by the dichroic polarizing beam splitter  203   a . In this way, the components of three primary colors are integrated together, which then have their polarization direction aligned by the polarizing plate  507 , and are directed to a projection optical system (not shown). 
     FIG. 6 is a diagram schematically showing a fifth embodiment of the invention. In FIG. 6, reference numeral  1  represents a white light source; reference numeral  2  represents a reflector, disposed so as to surround the white light source  1 , for reflecting the light emitted from the white light source  1 ; and reference numeral  3  represents a polarization converter, disposed by the side of the white light source  1 , for converting the light from the white light source  1  into light polarized on a predetermined polarization plane. In this embodiment, it is assumed that the light from the light source is used after being converted into S-polarized light with respect to the mirrors, prisms, and other optical elements used. 
     This polarization converter  3  is composed of a polarizing beam splitter  4  for internally reflecting the S-polarized light component, indicated by the broken-line arrow S, and transmitting the P-polarized light component, indicated by the solid-line arrow P, in such a way that they both pass therethrough, and a half-wave plate  5  for rotating the polarization plane of the transmitted P-polarized light component so as to convert it into S-polarized light. The components noted thus far constitute an illumination optical system. Although not shown, it is customary to additionally use an integrator optical system to minimize unevenness of the illumination light of this illumination optical system. 
     Moreover, in FIG. 6, reference numerals  101  and  102  represent dichroic mirrors; reference numeral  204   a  represents a dichroic polarizing beam splitter; reference numerals  202   a  and  205   a  represent polarizing beam splitters; reference numerals  301  to  303  represent reflection-type liquid crystal display devices (slantly hatched rectangles); reference numeral  401  represents reflecting mirrors; reference numerals  502  and  504  to  506  represent polarizing plates (horizontally or vertically hatched rectangles); reference numerals  601  to  603  represent band-pass filters (dot-filled rectangles); reference numeral  701  represents a half-wave plate (a plain rectangle); and reference numeral  6  represents a relay optical system for compensating the optical path length. 
     As shown in FIG. 6, the illumination light (a white light beam), composed of the light coming directly from the white light source  1  and the light reflected from the reflector  2 , first passes through the polarization converter  3 , which transmits the S-polarized light component and converts the P-polarized light component into S-polarized light, and then reaches the dichroic mirror  101 . Here, out of the now wholly S-polarized white light beam, only the blue (B) component is transmitted, and the other, green (G) and red (R), components are reflected. 
     The B component transmitted through the dichroic mirror  101  is then reflected from the first reflecting mirror  401 , passes through the relay optical system  6 , is further reflected from the second reflecting mirror  401 , has its polarization direction aligned by the polarizing plate  505 , and then reaches the polarizing beam splitter  205 a. Here, the S-polarized B component is reflected. 
     This component is then further reflected from the dichroic polarizing beam splitter  204   a , has its wavelength range trimmed by the band-pass filter  601 , and then illuminates the pixels on the reflection-type liquid crystal display device  301 . 
     On the reflection-type liquid crystal display device  301 , at every moment, those pixels which ate used for screen display are turned on so that the S-polarized B component incident on those pixels is reflected after being converted into P-polarized light, and those pixels which are not used are turned off so that the same component incident on those pixels is reflected intact as S-polarized light. The B component reflected from the reflection-type liquid crystal display device  301  reaches the dichroic polarizing beam splitter  204   a  again. Here, the P-polarized B component is reflected, which is then transmitted through the polarizing beam splitter  205   a.    
     On the other hand, the G and R components reflected from the dichroic mirror  101  reach the dichroic mirror  102 . Here, the S-polarized R component is transmitted and the S-polarized G component is reflected so that the two components are separated from each other. The S-polarized R component then has its polarization direction aligned by the polarizing plate  502 , is reflected from the polarizing beam splitter  202   a , has its wavelength range trimmed by the band-pass filter  602 , and then illuminates the pixels on the reflection-type liquid crystal display device  302 . 
     Here, at every moment, those pixels which are used for screen display are turned on so that the S-polarized R component incident on those pixels is reflected after being converted into P-polarized light, and those pixels which are not used are turned off so that the same component incident on those pixels is reflected intact as S-polarized light. The R component reflected from the reflection-type liquid crystal display device  302  reaches the polarizing beam splitter  202   a  again. Here, only the P-polarized R component is transmitted, which then has its polarization direction aligned by the polarizing plate  506 , has its polarization plane rotated by the half-wave plate  701  so as to be converted into S-polarized light, and is then reflected from the polarizing beam splitter  205   a.    
     The S-polarized G component separated by the dichroic mirror  102  has its polarization direction aligned by the polarizing plate  504 , and then reaches the dichroic polarizing beam splitter  204   a . Here, the S-polarized G component is reflected, which then has its wavelength range trimmed by the band-pass filter  603 , and then illuminates the pixels on the reflection-type liquid crystal display device  303 . 
     On the reflection-type liquid crystal display device  303 , at every moment, those pixels which are used for screen display are turned on so that the S-polarized G component incident on those pixels is reflected after being converted into P-polarized light, and those pixels which are not used are turned off so that the same component incident on those pixels is reflected intact as S-polarized light. The G component reflected from the reflection-type liquid crystal display device  303  reaches the dichroic polarizing beam splitter  204   a  again. Here, the P-polarized G component is transmitted, which is then further transmitted through the polarizing beam splitter  205   a.    
     Finally, the G and B components, now P-polarized, and the R component, now S-polarized, are integrated together by the polarizing beam splitter  205   a . In this way, the components of three primary colors are integrated together, which are then directed to a projection optical system (not shown). Note that the fourth and fifth embodiments described above are both designed to have the same back focal length (i.e. the distance from the projection optical system to the reflection-type liquid crystal display device) for all of the color components. 
     FIGS. 7A to  7 E are diagrams showing the transmittance characteristic, for the wavelength ranges of the individual color components, of the polarizing beam splitters employed in the fourth and fifth embodiments, with FIGS. 7A to  7 E showing the transmittance characteristic of the polarizing beam splitters  201   a  to  205   a , respectively. In these diagrams, a broken line indicates P-polarized light, a and a solid line indicates S-polarized light. As shown in FIG. 7A, the dichroic polarizing beam splitter  201   a  is designed to transmit almost 100% of the P-polarized light within the wavelength ranges of the B and G components, transmit almost 100% of the S-polarized light within the wavelength range of the B component, and reflect almost 100% of the S-polarized light within the wavelength range of the G component. 
     As shown in FIG. 7B, the polarizing beam splitter  202   a  is designed to transmit almost 100% of the P-polarized light within the wavelength ranges of the G and R components and reflect almost 100% of the S-polarized light within the wavelength ranges of the G and R components. 
     As shown in FIG. 7C, the dichroic polarizing beam splitter  203   a  is designed to transmit almost 100% of the P-polarized light within the wavelength ranges of the B, G, and R components, transmit almost 100% of the S-polarized light in the wavelength range of the R component, and reflect almost 100% of the S-polarized light within the wavelength ranges of the G and B components. 
     As shown in FIG. 7D, the dichroic polarizing beam splitter  204   a  is designed to transmit almost 100% of the P-polarized light within the wavelength range of the G component, reflect almost 100% of the P-polarized light within the wavelength range of the B component, and reflect almost 100% of the S-polarized light within the wavelength ranges of the B and G components. 
     As shown in FIG. 7E, the polarizing beam splitter  205   a  is designed to transmit almost 100% of the P-polarized light within the wavelength ranges of the B, G, and R components and reflect almost 100% of the S-polarized light within the wavelength ranges of the B, G, and R components. 
     The polarizing beam splitters described above each employ a prism-type polarizing element called a MacNeile polarizing element. The various characteristics of these polarizing beam splitters are achieved by laying layers of two different refractive indices alternately over one another. 
     FIGS. 8 and 9 are graphs showing practical examples of the transmittance characteristic (film characteristic) of the polarizing beam splitters. FIG. 8 shows a characteristic that corresponds to the dichroic polarizing beam splitter  201   a . In this graph, the broken line indicates P-polarized light and the solid line indicates S-polarized light. The characteristic shown in FIG. 8 is obtained by forming 17 coating film layers between glass prisms (regarded as the 0th and 18th layers) in such a way that the individual layers have refractive indices and optical film thicknesses (nd/λ 0 ) as listed in Table 1. Note that, here, the reference wavelength λ 0  is assumed to be 865.8356 nm. 
     FIG. 9 shows a characteristic that corresponds to the dichroic polarizing beam splitter  203   a . In this graph, the broken line indicates P-polarized light and the solid line indicates S-polarized light. The characteristic shown in FIG. 9 is obtained by forming 17 coating film layers between glass prisms (regarded as the 0th and 18th layers) in such a way that the individual layers have refractive indices and optical film thicknesses (nd/λ 0 ) as listed in Table 2. Note that, here, the reference wavelength X, is assumed to be 650.9595 nm. 
     
       
         
               
               
               
             
           
               
                 TABLE 1 
               
               
                   
               
               
                   
                   
                 Optical Film 
               
               
                   
                   
                 Thickness 
               
               
                 Layer 
                 Refractive Index 
                 (nd/λ 0 ) 
               
               
                   
               
             
             
               
                 18 
                 1.62 
                   
               
               
                 17 
                 1.62 
                 0.125 
               
               
                 16 
                 2.05 
                 0.214 
               
               
                 15 
                 1.385 
                 0.393 
               
               
                 14 
                 2.05 
                 0.178 
               
               
                 13 
                 1.385 
                 0.307 
               
               
                 12 
                 2.05 
                 0.255 
               
               
                 11 
                 1.385 
                 0.262 
               
               
                 10 
                 2.05 
                 0.183 
               
               
                 9 
                 1.385 
                 0.391 
               
               
                 8 
                 2.05 
                 0.183 
               
               
                 7 
                 1.385 
                 0.262 
               
               
                 6 
                 2.05 
                 0.255 
               
               
                 5 
                 1.385 
                 0.307 
               
               
                 4 
                 2.05 
                 0.179 
               
               
                 3 
                 1.385 
                 0.393 
               
               
                 2 
                 2.05 
                 0.214 
               
               
                 1 
                 1.62 
                 0.125 
               
               
                 0 
                 1.62 
               
               
                   
               
             
          
         
       
     
     
       
         
               
               
               
             
           
               
                 TABLE 2 
               
               
                   
               
               
                   
                   
                 Optical Film 
               
               
                   
                   
                 Thickness 
               
               
                 Layer 
                 Refractive Index 
                 (nd/λ 0 ) 
               
               
                   
               
             
             
               
                 18 
                 1.62 
                   
               
               
                 17 
                 1.62 
                 0.125 
               
               
                 16 
                 2.05 
                 0.249 
               
               
                 15 
                 1.385 
                 0.270 
               
               
                 14 
                 2.05 
                 0.133 
               
               
                 13 
                 1.385 
                 0.314 
               
               
                 12 
                 2.05 
                 0.240 
               
               
                 11 
                 1.385 
                 0.345 
               
               
                 10 
                 2.05 
                 0.199 
               
               
                 9 
                 1.385 
                 0.236 
               
               
                 8 
                 2.05 
                 0.199 
               
               
                 7 
                 1.385 
                 0.345 
               
               
                 6 
                 2.05 
                 0.240 
               
               
                 5 
                 1.385 
                 0.314 
               
               
                 4 
                 2.05 
                 0.133 
               
               
                 3 
                 1.385 
                 0.270 
               
               
                 2 
                 2.05 
                 0.249 
               
               
                 1 
                 1.62 
                 0.125 
               
               
                 0 
                 1.62