Dichroic prism and projection display apparatus

Abstract

The invention provides a dichroic prism capable of reducing displacements of projection pixels of colors caused by chromatic aberration of magnification. A dichroic prism is formed in the shape of a quadrangular prism as a whole by joining four rectangular prisms together. A red reflecting dichroic plane and a blue reflecting dichroic plane intersect to form substantially an X shape along junction surfaces of the prisms. The red reflecting dichroic plane is convex-shaped by partly changing the thickness of an adhesive layer for connecting the rectangular prisms together. Accordingly, since a red beam can be guided to a projection optical system while being enlarged, it is possible to reduce a projection image of the red beam to be projected onto a projection plane via the projection optical system. This makes it possible to reduce relative displacements of projection pixels of color beams caused by chromatic aberration of magnification.

1. A dichroic prism, comprising:
 four prisms that are joined together, each of the four prisms having a triangular cross-section and joint surfaces; and  
 a first dichroic plane and a second dichroic plane, the first dichroic plane and the second dichroic plane intersecting so as to form approximately an X shape along the joint surfaces of the four prisms, the first dichroic plane and the second dichroic plane having different reflectance characteristics, at least the first dichroic plane being at least one of concave shape and convex shape.  
 
     
     
       2. The dichroic prism according to  claim 1 , the first dichroic plane being inclined symmetrically relative to a line of intersection of said first dichroic plane and the second dichroic plane. 
     
     
       3. The dichroic prism according to  claim 1 , further including an adhesive layer joining the prisms, the four prisms each being a rectangular prism with a right vertical angle, and the first dichroic plane is made to be at least one of concave shape and convex shape by adjusting a thickness of the adhesive layer. 
     
     
       4. The dichroic prism according to  claim 1 , at least one of the four prisms having at least one of an acute vertical angle and an obtuse vertical angle, and the first dichroic plane is made to be at least one of concave shaped and convex shaped by using the prism having the at least one of an acute vertical angle and an obtuse vertical angle. 
     
     
       5. A projection display apparatus for projecting image to a projection plane and having the dichroic prism claimed in  claim 1 , comprising:
 a light source that emits a light beam;  
 color separation means for separating the light beam emitted from said light source into color beams of at least two colors;  
 modulation means for modulating the separated color beams according to image information, the dichroic prism synthesizing the color beams modulated by said modulation means; and  
 a projection optical system that enlarges and projects the synthesized beams onto the projection plane.  
 
     
     
       6. The projection display apparatus according to  claim 5 , the modulation means being of a reflective type, and the dichroic prism also functioning as the color separation means. 
     
     
       7. The dichroic prism according to  claim 2 , further including an adhesive layer joining the prisms, the four prisms each being a rectangular prism with a right vertical angle, and the first dichroic plane is made to be at least one of concave shaped and convex shaped by adjusting a thickness of the adhesive layer. 
     
     
       8. The dichroic prism according to  claim 2 , at least one of the four prisms having at least one of an acute vertical angle and an obtuse vertical angle, and the first dichroic plane is made to be at least one of concave shape and convex shape by using the prism having the at least one of an acute vertical angle and an obtuse vertical angle. 
     
     
       9. A projection display apparatus for use with a projection plane and having the dichroic prism claimed in  claim 2 , comprising:
 a light source that emits a light beam;  
 color separation means for separating the light beam emitted from said light source into color beams of at least two colors;  
 modulation means for modulating the separated color beams according to image information, the dichroic prism synthesizing the color beams modulated by the modulation means; and  
 a projection optical system that enlarges and projects the synthesized beams onto the projection plane.  
 
     
     
       10. The projection display apparatus according to  claim 9 , the modulation means being of a reflective type, and the dichroic prism also functioning as the color separation means. 
     
     
       11. A projection display apparatus for use with a projection plane and having the dichroic prism claimed in  claim 3 , comprising:
 a light source that emits a light beam;  
 color separation means for separating the light beam emitted from said light source into color beams of at least two colors;  
 modulation means for modulating the separated color beams according to image information, the dichroic prism synthesizing the color beams modulated by the modulation means; and  
 a projection optical system that enlarges and projects the synthesized beams onto the projection plane.  
 
     
     
       12. The projection display apparatus according to  claim 11 , the modulation means being of a reflective type, and the dichroic prism also functioning as the color separation means. 
     
     
       13. A projection display apparatus for use with a projection plane and having the dichroic prism claimed in  claim 4 , comprising:
 a light source that emits a light beam;  
 color separation means for separating the light beam emitted from said light source into color beams of at least two colors;  
 modulation means for modulating the separated color beams according to image information, the dichroic prism synthesizing the color beams modulated by the modulation means; and  
 a projection optical system that enlarges and projects the synthesized beams onto the projection plane.  
 
     
     
       14. The projection display apparatus according to  claim 13 , the modulation means being of a reflective type, and the dichroic prism also functioning as the color separation means. 
     
     
       15. A method of manufacturing a dichroic prism, comprising the steps of:
 joining four prisms together, each of the four prisms having a triangular cross-section and joint surfaces; and  
 forming a first dichroic plane and a second dichroic plane into approximately an X shape along the joint surfaces of the four prisms, the first dichroic plane and the second dichroic plane having different reflectance characteristics, at least the first dichroic plane being at least one of concave shape and convex shape.  
 
     
     
       16. The method according to  claim 15 , further including the step of inclining the first dichroic plane symmetrically relative to a line of intersection of the first dichroic plane and the second dichroic plane. 
     
     
       17. The method according to  claim 15 , further including the step of forming the first dichroic plane into at least one of a concave shape and a convex shape by adjusting a thickness of an adhesive layer that joins the prisms. 
     
     
       18. The method according to  claim 15 , further including the step of forming the first dichroic plane into at least one of a concave shape and a convex shape by using at least one of the four prisms that has at least one of an acute vertical angle and an obtuse vertical angle. 
     
     
       19. A projector that protects an image, comprising:
   a plurality of modulators that modulates color beams according to image information;        a dichroic prism that synthesizes the color beams modulated by the modulator, the dichroic prism including four prisms that are joined together, each of the four prisms having a triangular cross - section and point surfaces, and two dichroic planes intersecting so as to form approximately an X shape along the joint surfaces of the four prisms and having different reflectance characteristics, at least one of the two dichroic planes having one of a concave shape and a convex shape; and        a projection optical system that enlarges and projects a synthesized beam synthesized by the dichroic prism.      
     
     
       20. The projector according to  claim 19 , the first dichroic plane being inclined symmetrically relative to a line of intersection of said first dichroic plane and the second dichroic plane.  
     
     
       21. The projector according to  claim 19 , further including an adhesive layer joining the prisms, the four prisms each being a rectangular prism with a right vertical angle, and the first dichroic plane is made to be at least one of concave shape and convex shape by adjusting a thickness of the adhesive layer.  
     
     
       22. The projector according to  claim 19 , at least one of the four prisms having at least one of an acute vertical angle and an obtuse vertical angle, and the first dichroic plane is made to be at least one of concave shaped and convex shaped by using the prism having the at least one of an acute vertical angle and an obtuse vertical angle.  
     
     
       23. The projector according to  claim 19 , the modulator being of a reflective type.  
     
     
       24. The projector according to  claim 19 , further comprising:
   a power source;        an interface circuit;        a control circuit; and        an outer casing that accommodates the plurality of modulators, the dichroic prism, the power source, the interface circuit, and the control circuit.