Patent Publication Number: US-2009237616-A1

Title: Projection type image display device

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a projection type image display device using a reflective spatial light modulation element. 
     2. Description of the Related Art 
       FIG. 1  is a block diagram illustrating a conventional projection type image display device disclosed in a patent document 1 (Japanese Unexamined Patent Application Publication No. 2007-3809). 
     In  FIG. 1 , white light emitted from a light source  1  goes through a light pipe (rod integrator)  2 , and then enters a cross dichroic mirror  4  through a condenser lens  3 . 
     The light source  1  is a lamp such as a metal halide lamp and emits intense white light. The light pipe  2  guides white light having entered from the light source  1 . The guided white light is reflected on the inner surface of the light pipe  2  several times, which equalizes the illumination distribution of the guided white light, and then exits. 
     The cross dichroic mirror  4  is composed of two dichroic mirrors  4   a  and  4   b  combined crisscross. One dichroic mirror  4   a  reflects blue light B and the other dichroic mirror  4   b  reflects red/green light RG. The blue light B reflected on the dichroic mirror  4   a  is reflected on a mirror  5  to polarize, and then enters a reflective polarizing plate  7  through a relay lens  6 . The blue light B is converted into p-polarized light by the reflective polarizing plate  7 , goes through as polarized blue light PB, and enters a reflective spatial light modulation element  8 . 
     On the other hand, the red/green light RG reflected on the dichroic mirror  4   b  is reflected on a mirror  9  to polarize, and then enters a dichroic mirror  10 . The dichroic mirror  10  transmits red light R from the red/green light RG and reflects green light G. The red light R having gone through the dichroic mirror  10  enters a reflective polarizing plate  12  through a relay lens  11 . The red light R is converted into p-polarized light by the reflective polarizing plate  12 , goes through as polarized red light PR, and enters a reflective spatial light modulation element  13 . 
     In contrast, the green light G reflected on the dichroic mirror  10  enters a reflective polarizing plate  15  through a relay lens  14 . The green light G is converted into p-polarized light by the reflective polarizing plate  15 , goes through as polarized green light PG, and enters a reflective spatial light modulation element  16 . 
     The polarized blue light PB, the polarized red light PR and the polarized green light PG having entered the reflective spatial light modulation elements  8 ,  13  and  16  are modulated by image signal input into the reflective spatial light modulation elements  8 ,  13  and  16  and are polarized-and-modulated into s-polarized light, and then emitted to the reflective polarizing plates  7 ,  12  and  15  as polarized-and-modulated blue light SMB, polarized-and-modulated red light SMR and polarized-and-modulated green light SMG. 
     The polarized-and-modulated blue light SMB, the polarized-and-modulated red light SMR and the polarized-and-modulated green light SMG are reflected by the reflective polarizing plates  7 ,  12  and  15 , and enter a crossdichroic prism  17  which forms a color combine optical system. The crossdichroic prism  17  is a cubic prism in which four triangular prisms  17   a - 17   d  are jointed, wherein dichroic coatings are formed on joint surfaces of respective triangular prisms  17   a - 17   d . Here, joint surfaces of the triangular prisms  17   a  and  17   b  are defined as a plane a and joint surfaces of the triangular prisms  17   c  and  17   d  are defined as a plane a′. Also, joint surfaces of the triangular prisms  17   a  and  17   d  are defined as a plane b and joint surfaces of the triangular prisms  17   b  and  17   c  are defined as a plane b′. Two planes a-a′ and b-b′ formed by the four dichroic coatings  17   a - 17   d  are cruciately crossed at the center of crossdichroic prism  17 . 
     One plane b-b′ reflects the entering polarized-and-modulated blue light SMB toward the side of projection lens  18 , transmits the entering polarized-and-modulated red light SMR, and transmits the entering polarized-and-modulated green light SMG and emits it toward the side of projection lens  18 . The other plane a-a′ reflects the entering polarized-and-modulated red light SMR toward the side of projection lens  18 , transmits the entering polarized-and-modulated blue light SMB, and transmits the entering polarized-and-modulated green light SMG and emits it toward the side of projection lens  18 . 
     Thus, the polarized-and-modulated blue light SMB, the polarized-and-modulated red light SMR and the polarized-and-modulated green light SMG having exited the crossdichroic prism  17  are combined in space and then enter the projection lens  18 . The projection lens  18  causes the combined light having entered to be focused on a screen not shown to display an enlarged image on the screen. 
     The light source of the conventional projection type image display device uses very bright white light as illuminating light, which needs to cool the light source using a large cooling fun at a time of the projection because high heat is generated on the light source itself. As the result, it has a problem that the whole device increase in size, noise occurs due to rotation sound of the cooling fan, and life cycle of the light source itself is relatively shortened. 
     Also, the conventional projection type image display device has a problem that the whole device increases in size and weight because it is configured to arrange various optical parts at certain positions between the condenser lens  3  and the crossdichroic prism  17  on respective optical paths of color lights R, G and B in order to project an image in higher contrast and higher brightness. 
     SUMMARY OF THE INVENTION 
     The present invention is invented in order to solve the above-described problems, and has an object to provide a space-saving and lightweight projection type image display device capable of reducing noise using a small and low-heat-generating light source and projecting a projection image in low color blurring, high contrast and high fineness. 
     The present invention provides a projection type image display device that has the configuration of (1) to (4) described below, in order to solve the above-described problems. 
     (1) A projection type image display device comprising: a light source that emits lights with three different wavelengths; a polarizing plate that transmits a first linear polarized light therethrough and reflects a second linear polarized light from among the lights entering; a color separation and combine means that, when the first linear polarized light transmitted through the polarizing plate enters, separates the first linear polarized light into three separated lights according to the wavelengths and emits as three separated linear polarized lights in three different directions and, when lights with the different wavelengths enter from respective directions opposed to the three different directions, combines the lights with the different wavelengths and emits as a combined modulated-and-polarized light toward a direction opposed to the entering direction of the first linear polarized light; three reflective spatial light modulation elements that are arranged on respective optical paths of the three separated linear polarized lights emitted in the three different directions, and light-modulates and reflects the separated linear polarized lights entering; and a projection means that enlarges and projects the second linear polarized light reflected by the polarizing plate from among the combined modulated-and-polarized light light-modulated by the three reflective spatial light modulation elements and combined by the color separation and combine means, wherein the color separation and combine means includes a first color separation filter and a second color separation filter arranged so as to be inclined at about 45 degrees with respect to light entering, and the first color separation filter and the second color separation filter meet a condition that a phase difference between a phase of a polarized light component parallel to an entrance surface and a phase of a polarized light component orthogonal to the polarized light component parallel to the entrance surface is equal to or less than 15 degrees in the respective wavelengths of the three separated linear polarized lights. 
     (2) The projection type image display device according to (1), wherein the first color separation filter and the second color separation filter meet 
       (cos 2  θ+sin 2 θ*   e   −iα ) 2 /(sin θ*cos θ−sin θ*cos θ* e   −iα ) 2 ≧2500, 
     where an angle formed between the first linear polarized light and a polarized light parallel to the entrance surface is θ and the phase difference is α. 
     (3) The projection type image display device according to (1), wherein the color separation and combine means is a crossdichroic mirror in which the first color separation filter and the second color separation filter are orthogonal to each other. 
     (4) The projection type image display device according to (1), wherein the color separation and combine means comprises: a first polarizing beam splitter that reflects a first color component light and transmits a second color component light and a third color component light therethrough from among lights entering; and a second polarizing beam splitter that, when the second color component light and the third color component light enter, reflects the second color component light and transmits the third color component light therethrough. 
     According to the projection type image display device of the present invention, it employs an illumination means that combines a red light R, a green light G and a blue right B with narrow wavelength bands emitted from a light source of respective color lights of red-green-blue RGB, and can well prevent unnecessary polarization rotation of image light generated by a combine optical system to obtain a projection image in high contrast, low color blurring and high fineness and realize the reduction in size and weight. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a block diagram that illustrates a conventional projection type image display device. 
         FIG. 2  is a block diagram that illustrates a first embodiment of a projection type image display device of the present invention. 
         FIG. 3  is a block diagram in which A portion of  FIG. 2  is enlarged. 
         FIG. 4  is an explanatory diagram that illustrates lights entering a crossdichroic prism and polarizing axes of the lights. 
         FIG. 5A  and  FIG. 5B  are graphs each of which shows wavelength selectivity on joint surfaces of triangular prisms forming the crossdichoroic prism. 
         FIG. 6  is an explanatory diagram that illustrates the relation between an entrance polarizing axis and a polarizing angle. 
         FIG. 7  is an explanatory diagram that illustrates the relation between a phase difference of dichroic coating and a contrast. 
         FIG. 8  is a table that shows a layered structure of the dichroic coating. 
         FIG. 9  is a block diagram that illustrates a second embodiment of the projection type image display device of the present invention. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     First Embodiment 
     A first embodiment of a projection type image display device of the present invention will be described below, with reference to  FIG. 2  and  FIG. 3 . In the description, the same symbol is assigned to the same component part as that described previously. 
     The projection type image display device of the present embodiment includes an illumination means (illumination unit)  100 , a polarizing plate  22 , a color separation and combine means (crossdichroic prism)  23 , three reflective spatial light modulation elements  24 ,  25  and  26 , and a projection means (projection lens)  27 . 
     The illumination unit  100  includes a three color light source  19  ( 19   a ,  19   b  and  19   c ) of red-green-blue RGB, three dichroic mirrors  20  ( 20   a ,  20   b  and  20   c ), a collective lens  21 , a light pipe  2  and a condenser lens  3 . 
     The light source  19  is composed of a red light source  19   a  which is a semiconductor light source for emitting red light R with a narrow wavelength band in which wavelength is within the range of 600 nm to 700 nm, a green light source  19   b  which is a semiconductor light source for emitting green light G with a narrow wavelength band in which wavelength is within the range of 480 nm to 600 nm, and a blue light source  19   c  which is a semiconductor light source for emitting blue light B with a narrow wavelength band in which wavelength is within the range of 400 nm to 480 nm, and is a red-green-blue light emitting diode (LED) for example. The red light source  19   a , the green light source  19   b  and the blue light source  19   c  do not produce high heat in light emitting state, in comparison with the light source  1  illustrated in  FIG. 1 , because they are semiconductor light sources. 
     Lights emitted from the light source  19  enter the dichroic mirrors  20  which are inclined at about 45 degrees with respect to respective light axes and arranged in parallel with one another. 
     Here, the dichroic mirrors  20  are composed of a red dichroic mirror  20   a , a green dichroic mirror  20   b  and a blue dichroic mirror  20   c  arranged corresponding to the red light source  19   a , the green light source  19   b  and the blue light source  19   c.    
     Also, the dichroic mirrors  20  are configured to reflect lights from the semiconductor light sources for respective colors. 
     The three dichroic mirrors  20  respectively reflect red, green and blue lights R, G and B entering from the respective light sources  19   a - 19   c  to bend light axes at 90 degrees, and are composed of the dichroic mirrors  20   a - 20   c  for combining red, green and blue lights R, G and B. Red-green-blue light RGB combined in the dichroic mirrors  20   a - 20   c  enters the collective lens  21  as illumination light W. The collective lens  21  collects the entering illumination light W toward the light pipe  2  and emits it. 
     The light pipe  2  is formed in a polygonal column shape or a substantially multi-sided pyramid shape in which an inner wall is composed of mirrors. In this embodiment, the light pipe  2  is formed in a hollow truncated pyramid structure in which four mirrors are joined in a longitudinal direction. The illumination light W which exited the collective lens  21  has been collected, and enters the light pipe  2  from an entrance side of the light pipe  2  and is reflected on the inner wall surface of the light pipe  2  several times, which has the function that uniforms the illumination distribution and the luminance distribution of light flux in a direction orthogonal to an light axis at an exit side of the light pipe  2  and then emits it. 
     It is noted that the entering light may be guided using total reflection on glass as the light pipe  2 . 
     The illumination light W having gone through the light pipe  2  is diffusion light and is turned into collective light by going through the collective lens  3 . The illumination light W turned into the collective light enters the polarizing plate  22 . 
     An optical path of illumination light which exited the collective lens  3  will be described using  FIG. 3 . 
     The polarizing plate  22  is a reflective polarizing plate so-called “wire grid” and is arranged to be inclined at about 45 degrees with respect to a light axis of the illumination light W. The illumination light W entering the polarizing plate  22  is in a random state where the polarizing state is irregular, and the polarizing plate  22  transmits only p-polarized light of the illumination light W and emits it as polarized illumination light PW toward the crossdichroic prism  23 . 
     It is noted that, at the stage before the illumination light W enters the polarizing plate  22 , the illumination light W may be polarization-converted into the p-polarized light by a well-known polarization conversion element or the like and then enter the polarizing plate  22  as the polarized illumination light PW with the p-polarized light. 
     The crossdichroic mirror  23  is a quadratic prism in which two side surfaces of respective four triangular prisms  23   a - 23   d  are jointed. Dichroic coatings which are color separation filters are formed on four abutting surfaces of the triangular prisms  23   a - 23   d . Here, an abutting surface of the triangular prisms  23   a  and  23   b  are defined as a plane c and an abutting surface of the triangular prisms  23   c  and  23   d  are defined as a plane c′. Also, an a butting surface of the triangular prisms  23   a  and  23   d  are defined as a plane d and an abutting surface of the triangular prisms  23   b  and  23   c  are defined as a plane d′. Two continuous planes c-c′ and d-d′ formed by four dichroic coatings are cruciately crossed at the center of crossdichroic prism  23 . 
     Dichroic coatings forming one continuous plane c-c′ of the crossdichroic prism  23  have wavelength selectivity that reflects a blue (B) light component of entering light (polarized illumination light PW), and transmits a green (G) light component and a red (R) light component of entering light and emits them. Dichroic coatings forming the other continuous plane d-d′ of the crossdichroic prism  23  have wavelength selectivity that reflects a red (R) light component of entering light, and transmits a green (G) light component and a blue (B) light component of entering light and emits them. 
     More specifically, the dichroic coatings forming one continuous plane c-c′ of the crossdichroic prism  23  carry out wavelength separation of blue polarized light PB from the entering polarized illumination light PW and reflects the blue polarized light PB toward the side of the reflective spatial light modulation element for blue (B) light  26 , and as well carry out wavelength separation of green polarized light PG and red polarized light PR from the polarized illumination light PW and transmit and emit them. 
     The dichroic coatings forming the other continuous plane d-d′ of the crossdichroic prism  23  carry out wavelength separation of red polarized light PR from the entering polarized illumination light PW and reflects the red polarized light PR toward the side of the reflective spatial light modulation element for red (R) light  24 , and as well carry out wavelength separation of green polarized light PG and blue polarized light PB from the polarized illumination light PW and transmit and emit them. 
     Thereby, the red polarized light PR enters the reflective spatial light modulation element for red (R) light  24 , the green polarized light PG enters the reflective spatial light modulation element for green (G) light  25 , and the blue polarized light PB enters the reflective spatial light modulation element for blue (B) light  26 . 
     The red polarized light PR, the green polarized light PG and the blue polarized light PB entering the reflective spatial light modulation elements for respective color lights  24 ,  25  and  26  are modulated based on image signals input from outside, and emitted to the dichroic coatings forming the planes c-c′ and d-d′ as polarized-and-modulated red light SMR, polarized-and-modulated green light SMG and polarized-and-modulated blue light SMB. 
     The dichroic coatings forming one plane c-c′ of the crossdichroic prism  23  reflect and emit toward the side of the polarizing plate  22  the polarized-and-modulated blue light SMB entering from the reflective spatial light modulation element for blue (B) light  26 , transmit and emit toward the side of the polarizing plate  22  the polarized-and-modulated green light SMG entering from the reflective spatial light modulation element for green (G) light  25 , and transmit the polarized-and-modulated red light SMR entering from the reflective spatial light modulation element for red (R) light  24 . 
     The dichroic coatings forming the other plane d-d′ of the crossdichroic prism  23  reflect and emit toward the side of the polarizing plate  22  the polarized-and-modulated red light SMR entering from the reflective spatial light modulation element for red (R) light  24 , transmit and emit toward the side of the polarizing plate  22  the polarized-and-modulated green light SMG entering from the reflective spatial light modulation element for green (G) light  25 , and transmit the polarized-and-modulated blue light SMB entering from the reflective spatial light modulation element for blue (B) light  26 . 
     At this time, in the crossdichroic prism  23 , the polarized-and-modulated blue light SMB, the polarized-and-modulated red light SMR and the polarized-and-modulated green light SMG are combined on one plane c-c′ and the other plane d-d′ of the crossdichroic mirror  23  and exit as polarized-and-modulated white light SW. 
     Thus, the polarized-and-modulated white light SW having exited the crossdichroic mirror  23  enters the polarizing plate  22  again, and an s-polarized light component of the polarized-and-modulated white light SW generated by modulation is reflected by the polarizing plate  22  and exits as projection light PL. The projection light PL having exited the polarizing plate  22  enters the projection lens  27  which is the projection means. The projection lens  27  causes the projection light PL having entering from the polarizing plate  22  to be focused on a screen not shown to display an enlarged image on the screen. 
     Here, the relation between light entering the crossdichroic mirror  23  and contrast will be described. 
     Light entering coating surfaces of dichroic coatings of the four triangular prisms  23   a - 23   d  of the crossdichroic prism  23  goes through the polarizing plate  22  which is a wire grid polarizing plate, to be turned into linear polarized light, before entering. A polarizing axis of the linear polarized light is defined as an entrance polarizing axis. 
     At this time, a polarizing axis of p-polarized light is parallel to a plane formed by entering light and reflecting light, and a polarizing axis of s-polarized light is orthogonal to the plane formed by the entering light and the reflecting light. 
     This causes an angle between the polarizing axis of p-polarized light and the entrance polarizing axis to differ according to an angle of an entering light beam which enters a coating surface of the crossdichroic prism  23 . For example, as shown in  FIG. 4 , entering light A and entering light B are linear polarized lights which have the same entrance polarizing axes. When the entering light A of which a traveling direction of light beam is parallel to XZ-plane and in which the entrance polarizing axis is coincident with a polarizing axis of p-polarized light is reflected on a coating surface, a polarizing direction of the entrance polarizing axis is kept to be coincident with the polarizing axis of p-polarized light without rotating. However, when the entering light B, entering the coating surface of the crossdichroic prism  23  at an angle (θ) relative to the coating surface in Y-direction, of which a traveling direction of light beam is no parallel to XZ-plane and in which the entrance polarizing axis is not coincide with a polarizing axis of p-polarized light is reflected on the coating surface, a polarizing direction of the entrance polarizing axis rotates so that the linear polarized light is turned into elliptically polarized light. 
     Further, in a case where spectroscopic characterization of dichroic coatings of the crossdichroic prism  23  causes a phase difference (a) between s-polarized light and p-polarized light to occur in wavelength of entering light, an entrance polarizing direction rotates. For example, in a case of the LED light source  19  employed in this embodiment, when a wavelength of the red light source  19   a  is 630 nm, a wavelength of the green light source  19   b  is 530 nm, and a wavelength of the blue light source  19   c  is 460 nm, the phase difference (α) between s-polarized light a 1  and p-polarized light a 2  has a large value as shown in  FIG. 5A  which is more than about 100 degrees at 630 nm, about 180 degrees at 530 nm, or 50 degrees at 460 nm. This causes an entrance polarizing axis of light entering the dichroic coatings of the crossdichroic prism  23  to rotate largely. 
     At this time, polarized components (s-polarized lights) which are modulated in the reflective spatial light modulation elements for respective color lights  24 ,  25  and  26  are reflected by the polarizing plate  22 , and then enlarged by the projection lens  27  to be projected on a screen not shown as an image. On the other hand, polarized components (p-polarized lights) which are not modulated in the reflective spatial light modulation elements for respective color lights  24 ,  25  and  26  go through the polarizing plate  22 , and then returns to the side of the light source  19 . At this time, polarized light is changed on the dichroic coatings of the crossdichroic mirror  23 . When the polarized light (p-polarized light) not modulated is turned into s-polarized light, the polarized light is reflected, which projects the polarized components not modulated on the screen. This deteriorates contrast of image. 
     In other words, the difference between phase changes due to the difference between polarizing directions prevents an image portion to be projection-replicated at simple black from being replicated at simple black, and allows another color to run at a boundary edge of the image portion. As the result, this deteriorates contrast of image at the area. 
     Here, in a case where we assume that a polarization state of entering light is described as (J x , J y )=(1, 0) using Jones Vector as shown in  FIG. 6 , an angle (angle of deflection) between a polarizing axis of entering light and a polarizing axis of p-polarized light is θ, and a phase difference (α) between s-polarized light and p-polarized light occurs on a dichroic coating, Jones Vector (J x′ , J y′ ) of light emitted from a coating surface is described as the following eq.1. 
     
       
         
           
             
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     At this time, contrast (C) is described as the following eq.2. 
         C =(cos 2  θ+sin 2    θ*e   −iα ) 2 /(sin θ*cos θ−sin θ*cos θ* e   −iα ) 2    
     Further,  FIG. 7  shows a relation between a phase difference (α) and contrast when angles of deflection (θ) are 10 degrees or 20 degrees. 
     According to eq.2 and  FIG. 7 , when θ= 0  or α=0, contrast (C) reaches an infinity value. 
     When an image is projected by the projection type image display device, even if a projection place is a bright place, the image is recognized if contrast (C) is equal to or more than 500:1. 
     Therefore, it is requested in a dichroic coating and an optical system of the crossdichroic prism  23  that an angle of deflection (θ) and a phase difference (α) meets the following eq.3. 
       (cos 2  θ+sin 2    θ*e   −iα ) 2 /(sin θ*cos θ−sin θ*cos θ* e   −iα )≧500 
     Namely, as shown in  FIG. 7 , for example, in a case where an angle of deflection (θ) is 10°, when a phase difference (α) is equal to or less than 15°, contrast is equal to or more than 500:1. Also, if a phase difference (α) between s-polarized light and p-polarized light is decreased by coating design of dichroic coatings of the crossdichroic prism  23 , deterioration of contrast can be prevented. Further, even if the angle of deflection (θ) increases, the deterioration of contrast (C) can be prevented by relatively decreasing the phase difference (α). 
     Next, as an example, a case that each dichroic coating of the crossdichroic prism  23  is formed using a silicon dioxide SiO 2  coating and a titanium dioxide TiO 2  coating in 22 layers laminated structure will be described. 
     In this example, the coating design is carried out under the assumption that wavelengths of the red light source  19   a , the green light source  19   b  and the blue light source  19   c  as the LED light source  19  are 630 nm, 530 nm and 460 nm. 
       FIG. 8  illustrates a layer structure and a coating thickness of each layer used in the example. As shown in  FIG. 8 , a SiO 2  coating with low refractive index and a TiO 2  coating with high refractive index are alternately laminated, and the coating thickness of each layer is adjusted to a certain value. 
     A characteristic of the crossdichroic prism  23  using the dichroic coatings formed in the above structure is shown in  FIG. 5B . In  FIG. 5B , s-polarized light is indicated in a 3  and p-polarized light is indicated in a 4 . 
     In  FIG. 5B , a phase difference (α) between the s-polarized light a 3  and the p-polarized light a 4  emitted from the LED light sources  19   a ,  19   b  and  19   c  is about 0 in all wavelengths. 
     As this result, the projection type image display device of this example can improve contrast (C). 
     In the first embodiment, the dichroic coatings forming the plane c and the plane d in the four abutting surfaces (the plane c, the plane c′, the plane d and the plane d′) of the crossdichroic prism  23  may have wavelength selectivity such that the dichroic coating forming the plane c reflects a blue (B) light component of entering light (polarized illumination light PW) and transmits a green (G) light component and a red (R) light component of entering light and emits them, the dichroic coating forming the plane d reflects a red (R) light component of entering light and transmits a green (G) light component and a blue (B) light component and emits them, the dichroic coating forming the plane c′ reflects a blue (B) light component of entering light (polarized illumination light PW) and transmits a green (G) light component and emits it, and the dichroic coating forming the plane d′ reflects a red (R) light component of entering light and transmits a green (G) light component and emits it. 
     Second Embodiment 
     As another embodiment, a projection type image display device using two polarizing beam splitters instead of the crossdichroic prism in  FIG. 2  will be described. 
     A projection type image display device in  FIG. 9  shows only a portion corresponding to the A portion of  FIG. 2 , and the other portions are omitted because the other portions are common to those of  FIG. 2 . 
     The projection type image display device of the second embodiment includes a polarizing plate  22 , and a first polarizing beam splitter  31  and a second polarizing beam splitter  32  which are set among the three reflective spatial light modulation elements  24 ,  25  and  26  as the color separation and combine means, instead of the crossdichroic prism  23 . 
     Dichroic coatings are formed in the first polarizing beam splitter  31  and the second polarizing beam splitter  32 , so as to be arranged to be inclined at about 45 degrees with respect to respective entering lights. 
     The first polarizing beam splitter  31  has wavelength selectivity that reflects a blue (B) light component of entering light, and transmits a green (G) light component and a red (R) light component of entering light and emits them. 
     The second polarizing beam splitter  32  has wavelength selectivity that reflects a red (R) light component of entering light, and transmits a green (G) light component of entering light and emits it. 
     The illumination light W, which is combined to be white light by being emitted from the light source  19  and reflected by the dichroic mirror  20 , enters the polarizing plate  22  through the collective lens  21 , the light pipe  2  and the collective lens  3 , and then exits as the polarized illumination light PW with the p-polarized light. The polarized illumination light PW having exited the polarizing plate  22  enters the first polarizing beam slitter  31 , and wavelength separation is carried out by the first polarizing beam splitter  31  such that blue polarized light PB is reflected toward the side of the reflective spatial light modulation element for blue (B) light  26 , and green polarized light PG and red polarized light PR go through and then exit. 
     The green polarized light PG and the red polarized light PR having gone through the first polarizing beam splitter  31  enters the second polarizing beam splitter  32 . 
     Wavelength separation is carried out with respect to the green polarized light PG and the red polarized light PR entering the second polarizing beam splitter  32  by the second polarizing beam splitter  32  such that the red polarized light PR is reflected toward the side of the reflective spatial light modulation element for red (R) light  24 , and the green polarized light PG is reflected toward the side of the reflective spatial light modulation element for green (G) light  25 . 
     The red polarized light PR, the green polarized light PG and the blue polarized light PB entering the reflective spatial light modulation element for blue (B) light  26 , the reflective spatial light modulation element for red (R) light  24  and the reflective spatial light modulation element for green (G) light  25  are modulated based on image signals input from outside and reflected as polarized-and-modulated red light SMR, polarized-and-modulated green light SMG and polarized-and-modulated blue light SMB, in the respective reflective spatial light modulation elements  24 ,  25  and  26 . 
     The polarized-and-modulated red light SMR and the polarized-and-modulated green light SMG enters the second polarizing beam splitter  32  and are combined and exit. The polarized-and-modulated blue light SMB enters the first polarizing beam splitter  31 , is combined with the polarized-and-modulated red light SMR and the polarized-and-modulated green light SMG entering from the second polarizing beam splitter  32 , and exits the second polarizing beam splitter  32  as polarized-and-modulated white light SW. 
     The polarized-and-modulated white light SW emitted from the second polarizing beam splitter  32  enters the polarizing plate  22 , and an s-polarized light component of the polarized-and-modulated white light SW generated by modulation is reflected by the polarizing plate  22  and exits as projection light PL. The projection light PL having exited the polarizing plate  22  enters the projection lens  27  which is the projection means. The projection lens  27  causes the projection light PL having entering from the polarizing plate  22  to be focused on a screen not shown to display an enlarged image on the screen. 
     Since lights entering the first polarizing beam splitter  31  are red polarized light PR, green polarized light PG and blue polarized light PB as well as the crossdichoric prism  23  of the first embodiment, it is necessary to adjust a phase difference according to wavelengths of polarized lights of three colors. However, in the second embodiment, since lights entering the second polarizing beam splitter  32  are red polarized light PR and green polarized light PG, it is only necessary to adjust a phase difference according to wavelengths of polarized lights of two colors. Therefore, coating design of dichroic coating to be used in the second polarizing beam splitter  32  is easier than that to be used in the first polarizing beam splitter  31 . 
     In the second embodiment, although  FIG. 9  illustrates the dichroic coating of the first polarizing beam splitter  31  and the dichroic coating of the second polarizing beam splitter  32  such that they are arranged to be substantially parallel to each other, they may be arranged to be substantially perpendicular to each other.