Abstract:
A prism structure that includes: a plurality of liquid crystal devices each include a liquid crystal panel and a light emitting-side optical element, and generate an image light through modulation of any of a plurality of color lights in accordance with image information; and a cross dichroic prism that combines the image lights coming from the liquid crystal devices. In the prism structure, each of the liquid crystal devices further includes: a fixture member that is fixed to the cross dichroic prism; a retention member that keeps hold of the liquid crystal panel, and is fixed to the fixture member; and a light emitting-side optical element retention member that keeps hold of the light emitting-side optical element, and is rotation-adjustable about an illumination axis. The light emitting-side optical element retention member is rotation-adjusted about the illumination axis before fixation to the retention member.

Description:
BACKGROUND 
     1. Technical Field 
     The present invention relates to a prism structure and a projector. 
     2. Related Art 
       FIG. 8  is a diagram showing a system of a general type provided to a projector. In the accompanying drawings and descriptions below, a z axis is along the traveling direction of lights, an x axis is vertical to the z axis and parallel to the paper surface of  FIG. 8 , and a y axis is vertical to both the z axis the paper surface of  FIG. 8 . 
     As shown in  FIG. 8 , a projector  1000   a  is configured to include an illumination device  100 , a color separation light guiding system  200 , three liquid crystal devices  400   a R,  400   a G, and  400   a B, a cross dichroic prism  500   a,  and a projection system  600 . Specifically, the color separation light guiding system  200  separates a light coming from the illumination device  100  into three color lights of red, green, and blue. The liquid crystal devices  400   a R,  400   a G, and  400   a B each generate an image light through modulation of, in accordance with image information, the three color lights as results of separation by the color separation light guiding system  200 . The cross dichroic prism  500   a  combines the image lights generated by those three liquid crystal devices  400   a R,  400   a G, and  400   a B. The projection system  600  projects the image light as a result of combination in the cross dichroic prism  500   a  onto a projection surface such as screen SCR. 
     In recent years, such a projector is often provided with a prism structure, which is a combination unit that includes the entire or part of components of liquid crystal devices, and a cross dichroic prism. The components of liquid crystal devices are exemplified by a liquid crystal panel, a light emitting-side polarizer, and others. For an exemplary projector of such a type, refer to Patent Document 1 (JP-A-10-10994 (FIG. 7)). 
       FIG. 9  is a diagram for illustrating such a prism structure  550   b.    
     As shown in  FIG. 9 , in the prism structure  550   b,  a liquid crystal panel  410   b R specifically for red lights is retained by a liquid crystal panel retention frame  412   b R in its concave portion. A cross dichroic prism  500   b  is affixed with a fixture frame  440   b R on its light incident-side surface. The fixture frame  440   b R is screwed with an intermediate frame  450   b R. 
     The liquid crystal panel  410   b R is put into the temporarily-screwed state through insertion and engagement of pins into each corresponding hole of the liquid crystal panel retention frame  412   b R. The pins are each protruding from the corner of the intermediate frame  450   b R. While being in the temporarily-screwed state, the liquid crystal panel  410   b R is positioned by a pair of wedges  418   b R and  418   b R being pushed between the liquid crystal panel  410   b R and the liquid crystal panel retention frame  412   b R. These wedges  418   b R and  418   b R are eventually adhered for fixation to the fixture frame  440   b R. Although not shown, other liquid crystal panels  410   b G and  410   b B are similarly subjected to such positioning and fixation so that the liquid crystal panels  410   b R,  410   b G, and  410   b B are all positioned with precision. 
     The problem here is that, however, such a prism structure  550   b  requires a number of components including the fixture frame  440   b R, the intermediate frame  450   b R, the liquid crystal panel retention frame  412   b R, the wedges  418   b R and  418   b R, and others. Assembling such many components also requires a lot of work and makes the processes complicated, and thus reducing the manufacturing cost is not that easy. 
     In consideration of the above, the inventor of the present invention has filed an application for the prism structure that can solve the above problems (JP-A-2005-234124). 
       FIG. 10  is a diagram for illustrating a prism structure  550   c  in the above related art. The prism structure  550   c  (partially not shown) is a combination unit with a part of components of liquid crystal devices  400   c R,  400   c G, and  400   c B (partially not shown), and a cross dichroic prism  500   c  (not shown). The components here include a liquid crystal panel  410   c R, and a light emitting-side polarizer  430   c R. This prism structure  550   c  is configured to include a fixture member  440   c R and a retention member  450   c R. The fixture member  440   c R is provided with a stand-up piece d 1  each at both ends, and has the C-shaped cross section. The retention member  450   c R is provided with a stand-up piece each at both ends, and also has the C-shaped cross section. The stand-up pieces d 1  and d 1  of the fixture member  440   c R are so assembled as to slide in contact with the stand-up pieces d 2  and d 2  of the retention member  450   c R. 
     In the prism structure  550   c  of such a configuration, after the fixture member  440   c R is combined together with the retention member  450   c R for fixation, the liquid crystal panel  410   c R is attached and fixed to the cross dichroic prism  500   c.  This accordingly reduces the number of components required to attach the liquid crystal panel  410   c R to the cross dichroic prism  500   c,  i.e., only the fixture member  440   c R, and the retention member  450   c R. As a result, the assembly procedure is simplified so that the manufacturing cost can be reduced. 
     The issue is that, with the prism structure  550   c,  the process remains complicated to dispose the light emitting-side polarizer  430   c R with a right angle with respect to the liquid crystal panel  410   c R and the cross dichroic prism  500   c.  This is due to the configuration that the light emitting-side polarizer  430   c R is glued with adhesive to a light emitting-side surface d 3  of the retention section  450   c R. 
     The recently-popular liquid crystal device in a projector includes a viewing angle compensation plate or a second light emitting-side polarizer between a liquid crystal panel and a light emitting-side polarizer. This is aimed to increase the viewing angle characteristics, the contrast characteristics, and others. Similarly to the above-described case with the light emitting-side polarizer, such viewing angle compensation plate and second light emitting-side polarizer both fail in implementing a predetermined viewing angle or contrast if they are not correctly angled with respect to the liquid crystal panel and the cross dichroic prism. 
     The related art of JP-A-2005-234124 presents no description, not in the specification or in the accompanying drawings, about how to correctly angle the viewing angle compensation plate or the second light emitting-side polarizer with respect to the liquid crystal panel  410   c R, the cross dichroic prism  500   c,  and others. 
     SUMMARY 
     An advantage of some aspects of the invention is to provide a prism structure of a configuration capable of easing the process of correctly angling the light emitting-side optical elements such as a light emitting-side polarizer, a viewing angle compensation plate, or a second light emitting-side polarizer, with respect to a liquid crystal panel and a cross dichroic prism. Another advantage of some aspects of the invention is to provide a projector including such a prism structure, and being with a wider viewing angle or a higher contrast. 
     A first aspect of the invention is directed to a prism structure that includes: a plurality of liquid crystal devices each include a liquid crystal panel and a light emitting-side optical element, and generate an image light through modulation of any of a plurality of color lights in accordance with image information; and a cross dichroic prism that combines the image lights coming from the liquid crystal devices. In the prism structure, each of the liquid crystal devices further includes: a fixture member that is fixed to the cross dichroic prism; a retention member that keeps hold of the liquid crystal panel, and is fixed to the fixture member; and a light emitting-side optical element retention member that keeps hold of the light emitting-side optical element, and is rotation-adjustable about an illumination axis. The light emitting-side optical element retention member is rotation-adjusted about the illumination axis before fixation to the retention member. 
     As such, according to the prism structure of the first aspect of the invention, the light emitting-side optical element retention member keeping hold of the light emitting-side optical element is subjected to rotation adjustment about the illumination axis before fixation to the retention member. Accordingly, the light emitting-side optical element can be correctly angled with respect to the liquid crystal panel and the cross dichroic prism. 
     According to the prism structure of the first aspect of the invention, angling the light emitting-side optical element can be implemented with such a considerably simple process that the light emitting-side optical element retention member is subjected to rotation adjustment about the illumination axis before fixation to the retention member. 
     As such, the prism structure of the first aspect of the invention can be of a configuration capable of easing the process of correctly angling a light emitting-side optical element with respect to a liquid crystal panel and a cross dichroic prism. 
     In the prism structure of the first aspect of the invention, preferably, the retention member is provided with a circular guiding hole for rotation adjustment of the light emitting-side optical element, and the light emitting-side optical element retention member is provided with a pin that can be inserted into the guiding hole. 
     Such a configuration enables to subject the light emitting-side optical element retention member to rotation adjustment about the illumination axis by moving the pin provided to the light emitting-side optical element retention member along the guiding hole of the retention member. This favorably leads to the smooth implementation of fixing the light emitting-side optical element retention member to the retention member after rotation adjustment about the illumination axis. 
     In the prism structure of the first aspect of the invention, preferably, the light emitting-side optical element retention member is subjected to rotation adjustment while being pushed against the retention member before attachment fixation to the retention member. 
     Such a configuration favorably controls the tilt of the light emitting-side polarizer with respect to the illumination axis so that the chromatic aberration due to the tilt is prevented from occurring. 
     In the prism structure of the first aspect of the invention, preferably, the light emitting-side optical element retention member is provided with a hold section for holding the retention member, and the light emitting-side optical element retention member is subjected to rotation adjustment while being pushed against the retention member by elasticity of the hold section before attachment fixation to the retention member. 
     The light emitting-side optical element retention member may be pushed against the hold section using a specific hold jig configured by a spring member. Alternatively, the above-described configuration is capable of easing, to a further degree, the process of fixing the light emitting-side optical element retention member to the retention member after rotation adjustment about the illumination axis. 
     In the prism structure of the first aspect of the invention, preferably, the liquid crystal devices are each further provided with a light emitting-side polarizer that is attached to the cross dichroic prism, and the light emitting-side optical element retention member is a viewing angle compensation plate. 
     With such a configuration, by using the prism structure of the invention to a projector, the resulting projector can have a wider viewing angle. 
     In the prism structure of the first aspect of the invention, preferably, the liquid crystal devices are each further provided with a light emitting-side polarizer that is attached to the cross dichroic prism, and the light emitting-side optical element is a second light emitting-side polarizer. 
     With such a configuration, by using the prism structure of the invention to a projector, the resulting projector can have a higher contrast. 
     In the prism structure of the first aspect of the invention, preferably, the retention member keeps hold of the light emitting-side optical element with a space both from the liquid crystal panel and the light emitting-side polarizer. 
     By spacing the light emitting-side optical element from a light emitting-side polarizer and a liquid crystal panel both being a heat-producing member, the resulting configuration is not susceptible to heat that much, and becomes ready for projectors of high brightness. 
     In the prism structure of the first aspect of the invention, preferably, the light emitting-side optical element is a light emitting-side polarizer. 
     With such a configuration, by using the prism structure of the invention to a projector, the resulting projector can have a higher contrast. 
     A second aspect of the invention is directed to a projector that includes: an illumination device; a color separation light guiding system that separates an illumination light coming from the illumination device into a plurality of color lights; a prism structure that emits an image light as a result of modulation and combination of the color lights coming from the color separation light guiding system in accordance with image information; and a projection system that projects the image light emitted from the prism structure. In the projector, the prism structure is the prism structure of the invention. 
     According to the projector of the invention, by including the prism structure of the invention as above, the projector can have a wider viewing angle or a higher contrast. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       A prism structure and a projector of the invention will be described below based on illustrated embodiments. 
         FIG. 1  is perspective view for illustrating a prism structure  550  of a first embodiment. 
         FIG. 2  is a diagram for illustrating both a retention member  450 R and a light emitting-side optical element retention member  462 R for use in the first embodiment. 
         FIGS. 3A and 3B  are both a diagram for illustrating the effects and advantages of the prism structure  550  of the first embodiment. 
         FIGS. 4A to 4C  are all a diagram for illustrating the effects and advantages of the prism structure  550  of the first embodiment. 
         FIGS. 5A to 5C  are all a diagram for illustrating the effects and advantages of the prism structure  550  of the first embodiment. 
         FIG. 6  is a diagram for illustrating a prism structure  550 A of a second embodiment. 
         FIGS. 7A to 7C  are all a diagram for illustrating both the retention member  450 R and the light emitting-side optical element retention member  462 R for use in the third embodiment; 
         FIG. 8  is a diagram showing a general system of a projector. 
         FIG. 9  is a diagram for illustrating a prism structure  550   b.    
         FIG. 10  is a diagram for illustrating a prism structure  550   c.    
     
    
    
     DESCRIPTION OF EXEMPLARY EMBODIMENTS 
     First Embodiment 
       FIG. 1  is a perspective view for illustrating a prism structure  550  of a first embodiment.  FIG. 2  is a diagram for illustrating both a retention member  450 R and a light emitting-side optical element retention member  462 R for use in the first embodiment. 
     Note here that, in  FIG. 1 , a light emitting-side optical element retention member in a liquid crystal device  400 G is not fully shown at its hold section. 
     As shown in  FIG. 1 , the prism structure  550  of the first embodiment is configured to include liquid crystal devices  400 R,  400 G, and  400 B for red lights, green lights, and blue lights, respectively, and a cross dichroic prism  500 . The liquid crystal device  400 R is provided with a liquid crystal panel  410 R, and a viewing angle compensation plate  460 R serving as a light emitting-side optical element. The liquid crystal device  400 R generates image lights through modulation of red lights in accordance with image information. The liquid crystal devices  400 G and  400 B serve similarly to the liquid crystal device  400 R. The cross dichroic prism  500  combines the image lights generated by the liquid crystal devices  400 R,  400 G, and  400 B. 
     The liquid crystal devices  400 R,  400 G, and  400 B are sharing basically the same configuration. Therefore, the configuration of the liquid crystal device  400 R for red lights is described in detail below. 
     As shown in  FIG. 1 , the liquid crystal device  400 R is provided with a fixture member  440 R, a retention member  450 R, and a light emitting-side optical element retention member  462 R. Specifically, the fixture member  440 R is fixed to the cross dichroic prism  500 . The retention member  450 R keeps hold of the liquid crystal panel  410 R, and is fixed to the fixture member  440 R. The light emitting-side optical element retention member  462 R keeps hold of the viewing angle compensation plate  460 R, and serves as a light emitting-side optical element retention member that is rotation-adjustable about an illumination axis. The liquid crystal device  400 R is also provided with a light emitting-side polarizer  430 R, and a second light emitting-side polarizer  432 R. The light emitting-side polarizer  430 R is affixed to the cross dichroic prism  500  on its light incident-side surface. The second light emitting-side polarizer  432 R is affixed to the retention member  450 R on its light emitting-side surface d 3  using a double-faced tape T. The liquid crystal panel  410 R is retained by a liquid crystal panel retention frame  412 R in its concave portion. 
     In the prism structure  550  of the first embodiment configured as such, the light emitting-side optical element retention member  462 R is subjected to rotation adjustment about an illumination axis before fixation to the retention member  450 R. As shown in  FIG. 2 , the retention member  450 R is provided with a circular guiding hole  452 R for rotation adjustment of the viewing angle compensation plate  460 R, which is combined to the light emitting-side optical element retention member  462 R to be a piece therewith. The light emitting-side optical element retention member  462 R is provided with a pin  466 R that can be inserted into the guiding hole  452 R formed to the retention member  450 R (refer to  FIGS. 3A to 4C ). 
       FIGS. 3A to 5C  are all a diagram for illustrating the effects and advantages of the prism structure  550  of the first embodiment.  FIG. 3A  is a front view showing the state that the light emitting-side optical element retention member  462 R is inserted into the retention member  450 R.  FIG. 3B  is a side view showing the state that the light emitting-side optical element retention member  462 R is inserted into the retention member  450 R.  FIG. 4A  is a front view showing the state of rotation adjustment made in the left direction after insertion of the light emitting-side optical element retention member  462 R into the retention member  450 R.  FIG. 4B  is a front view showing the state before rotation adjustment but after insertion of the light emitting-side optical element retention member  462 R into the retention member  450 R.  FIG. 4C  is a front view showing the state of rotation adjustment made in the right direction after insertion of the light emitting-side optical element retention member  462 R into the retention member  450 R.  FIG. 5A  is a top view showing the state that the prism structure  550  is cooled.  FIG. 5B  is a cross sectional view cut along a line A 1 -A 1  of  FIG. 5A , and  FIG. 5C  is a partially enlarged view of a main component of  FIG. 5A . 
     In the prism structure  550  of the first embodiment, as shown in  FIGS. 4A to 4C , the light emitting-side optical element retention member  462 R that keeps hold of the viewing angle compensation plate  460 R is subjected to rotation adjustment about an illumination axis before fixation to the retention member  450 R. This accordingly angles correctly the viewing angle compensation plate  460 R with respect to the liquid crystal panel  410 R and the cross dichroic prism  500 . 
     What is more, with the prism structure  550  of the first embodiment, such an angle operation can be implemented with a considerably simple process of subjecting the light emitting-side optical element retention member  462 R to rotation adjustment about an illumination axis before fixation to the retention member  450 R. 
     As such, the prism structure  550  of the first embodiment can be of a configuration capable of easing the process of correctly angling the viewing angle compensation plate  460 R with respect to the liquid crystal panel  410 R and the cross dichroic prism  500 . 
     As shown in  FIG. 2 , in the prism structure  550  of the first embodiment, the retention member  450 R is provided with a circular guiding hole  452 R for rotation adjustment of the viewing angle compensation plate  460 R. As shown in  FIGS. 3A and 3B  the light emitting-side optical element retention member  462 R is provided with a pin  466 R that can be inserted into the guiding hole  452 R of the retention member  450 R. 
     As such, as shown in  FIGS. 4A to 4C , according to the prism structure  550  of the first embodiment, the light emitting-side optical element retention member  462 R can be subjected to rotation adjustment about an illumination axis through movement of the pin  466 R thereof along the guiding hole  452 R of the retention member  450 R. It is possible to rotate and adjust the light emitting-side optional element retention member  462 R about the illumination axis and lead to the smooth implementation of fixing the light emitting-side optical element retention member  462 R to the retention member  450 R after rotation adjustment about the illumination axis. 
     As shown in  FIGS. 2 to 3B , in the prism structure  550  of the first embodiment, the light emitting-side optical element retention member  462 R is provided with a hold section  464 R for holding the retention member  450 R. The light emitting-side optical element retention member  462 R is subjected to rotation adjustment while being pushed against the retention member  450 R by elasticity of the hold section  464 R before attachment fixation to the retention member  450 R. 
     With such a prism structure  550  of the first embodiment, the process can be eased to a further degree to fix the light emitting-side optical element retention member  462 R to the retention member  450 R after rotation adjustment about an illumination axis. 
     What is better, the light emitting-side optical element retention member  462 R is pushed against the light emitting-side surface d 3  of the retention member  450 R by elasticity of the hold section  464 R so that the tilt of the viewing angle compensation plate  460 R is controlled with respect to the illumination axis, thereby preventing the chromatic aberration due to the tilt from occurring. 
     In the prism structure  550  of the first embodiment, as shown in  FIG. 1 , the liquid crystal device  400 R is further provided with a light emitting-side polarizer  430 R that is affixed to the cross dichroic prism  500 . As shown in  FIGS. 5A to 5C , the retention member  450 R keeps hold of the viewing angle compensation plate  460 R with a space both from the liquid crystal panel  410 R and the light emitting-side polarizer  430 R. This is applicable also to the remaining liquid crystal devices  400 G and  400 B. 
     As such, the prism structure  550  of the first embodiment enables to space the viewing angle compensation plate  460 R from the light emitting-side polarizer  430 R and the liquid crystal panel  410 R both being a heat-producing member. Therefore, the resulting configuration is not susceptible to heat that much, and becomes ready for projectors of high brightness. Moreover, in the prism structure  550  of the first embodiment, a path is formed between the light emitting-side polarizer  430 R and the second light emitting-side polarizer  432 R, and between the viewing angle compensation plate  460 R and the liquid crystal panel  410 R for cooling air Air to flow therethrough. The resulting configuration is protected from heat to a further degree, and becomes ready for projectors of much higher brightness. 
     In the prism structure  550  of the first embodiment, the light emitting-side optical element is the viewing angle compensation plate  460 R as described above. Accordingly, by using the prism structure  550  of the first embodiment to a projector, the resulting projector can have a wider viewing angle. 
     Second Embodiment 
       FIG. 6  is a diagram for illustrating a prism structure  550 A of a second embodiment. 
     Note here that, in  FIG. 6 , a light emitting-side optical element retention member in a liquid crystal device  400 AG is not fully shown at its hold section. 
     The prism structure  550 A of the second embodiment shares basically the same configuration as the prism structure  550  of the first embodiment. As shown in  FIG. 6 , the difference from the prism structure  550  of the first embodiment lies in that a liquid crystal device  400 AR includes no second light emitting-side polarizer. Other liquid crystal devices  400 AG and  400 AB have the similar configuration as the liquid crystal device  400 AR. 
     As such, the prism structure  550 A of the second embodiment is different from the prism structure  550  of the first embodiment in the respect that no second light emitting-side polarizer is provided. However, the light emitting-side optical element retention member  462 R is subjected to rotation adjustment about an illumination axis before fixation to the retention member  450 R. Accordingly, the viewing angle compensation plate  460 R is correctly angled with respect to the liquid crystal panel  410 R and the cross dichroic prism  500 . 
     What is more, with the prism structure  550 A of the second embodiment, such an angle operation can be implemented with a considerably simple process of subjecting the light emitting-side optical element retention member  462 R to rotation adjustment about an illumination axis before fixation to the retention member  450 R. 
     As such, similarly to the prism structure  550  of the first embodiment, the prism structure  550 A of the second embodiment has a configuration capable of easing the process of correctly angling the viewing angle compensation plate  460 R with respect to the liquid crystal panel  410 R and the cross dichroic prism  500 . 
     Other than that, the prism structure  550 A of the second embodiment takes the similar configuration to the prism structure  550  of the first embodiment so that the same effects as those of the prism structure  550  of the first embodiment are observed therein. 
     Third Embodiment 
       FIGS. 7A to 7C  are all a diagram for illustrating the retention member  450 R and a light emitting-side polarizer retention member  462 BR for use in a third embodiment. Specifically,  FIG. 7A  is a front view showing the state that the light emitting-side polarizer retention member  462 BR is inserted into the retention member  450 R.  FIG. 7B  is a side view showing the state that the light emitting-side optical element retention member  462 BR is inserted into the retention member  450 R.  FIG. 7C  is a front view showing the state that a hold jig  470 R is removed after the light emitting-side optical element retention member  462 BR is inserted into the retention member  450 R. 
     A prism structure  550 B of the third embodiment (not shown) shares basically the same configuration as the prism structure  550  of the first embodiment. As shown in  FIGS. 7A to 7C , the difference from the prism structure  550  of the first embodiment lies in that the light emitting-side optical element retention member  462 BR includes no hold section. 
     As such, the prism structure  550 B of the third embodiment is different from the prism structure  550  of the first embodiment in the respect that the light emitting-side optical element retention member includes no hold section. However, the light emitting-side polarizer retention member  462 BR is subjected to rotation adjustment about an illumination axis before fixation to the retention member  450 R. Accordingly, the viewing angle compensation plate  460 R is correctly angled with respect to the liquid crystal panel  410 R (not shown) and the cross dichroic prism  500  (not shown). 
     What is more, with the prism structure  550 B of the third embodiment, such an angle operation can be implemented with a considerably simple process of subjecting the light emitting-side optical element retention member  462 BR to rotation adjustment about an illumination axis before fixation to the retention member  450 R. 
     As such, similarly to the prism structure  550  of the first embodiment, the prism structure  550 B of the third embodiment has a configuration capable of easing the process of correctly angling the viewing angle compensation plate  460 R with respect to the liquid crystal panel  410 R and the cross dichroic prism  500 . 
     In the prism structure  550 B of the third embodiment, the light emitting-side optical element retention member  462 BR is subjected to rotation adjustment while being pushed against the retention member  450 R by elasticity of the hold jig  470 R that is provided to hold the retention member  450 R before attachment and fixation to the retention member  450 R. 
     With such a prism structure  550 B of the third embodiment, the process can be eased to a further degree to fix the light emitting-side optical element retention member  462 BR to the retention member  450 R after rotation adjustment about an illumination axis. 
     What is better, the light emitting-side optical element retention member  462 BR is pushed against the light emitting-side surface d 3  of the retention member  450 R by elasticity of the hold jig  470 R so that the tilt of the viewing angle compensation plate  460 R is controlled with respect to the illumination axis, thereby preventing the chromatic aberration due to the tilt from occurring. 
     After the process of attaching and fixing the light emitting-side polarizer retention member  462 BR to the retention member  450 R, as shown in  FIG. 7C , the hold jig  470 R can be removed from the prism structure. 
     Other than that, the prism structure  550 B of the third embodiment takes the similar configuration as the prism structure  550  of the first embodiment so that the same effects as those of the prism structure  550  of the first embodiment are observed therein. 
     As such, the prism structure and the projector of the invention are described based on the embodiments above. The invention is not surely restrictive to those embodiments, and it is understood that numerous other modifications and variations can be devised without departing from the scope of the invention. For example, the following modifications are possible. 
     In the prism structures  550 ,  550 A, and  550 B of the above embodiments, exemplified is a case of using a viewing angle compensation plate as a light emitting-side optical element. The invention is not surely restrictive thereto, and alternatively, a second light emitting-side polarizer or a light emitting-side polarizer may be an option for the light emitting-side optical element. With this being the case, by using the prism structure of the invention to a projector, the resulting projector can have a high contrast. 
     The entire disclosure of Japanese Patent Application No. 2005-076857, filed Mar. 17, 2005 is expressly incorporated by reference herein.