Dichroic prism, prism unit, and projection display apparatus

Abstract

At least one of four rectangular prisms in a dichroic prism is made longer than the other rectangular prisms. Parts of the rectangular surfaces of the long rectangular prisms partially protrude from the rectangular surfaces of the other rectangular prisms in the longitudinal direction. The protruding parts of the rectangular surfaces of the long rectangular prisms are not provided with a dichroic film. Such a construction makes it possible to prevent return light, which returns from the light emitting surface side of the dichroic prism and the dichroic prism, from emitting again from the light emitting surface.

1. A dichroic prism comprising:
 four rectangular prisms, each rectangular prism having rectangular surfaces bonded to rectangular surfaces of adjacent rectangular prisms, a first surface part of at least one of said four rectangular prisms protruding from the rectangular surfaces of other ones of said rectangular prisms, said first surface part being provided with a light diffusing layer for diffusing light, and  
 a dichroic film formed on a second surface part of said at least one rectangular prism, said second surface part not protruding from said rectangular surfaces of said other ones of said rectangular prisms.  
 
     
     
       2. The dichroic prism according to  claim 1 , said first surface part being provided with a light diffusing layer for diffusing light. 
     
     
       3. The dichroic prism according to claim  2    1 , said light diffusing layer being an adhesive layer. 
     
     
       4. The dichroic prism according to claim  2    1 , said light diffusing layer being a ground glass layer. 
     
     
       5. A dichroic prism comprising:
 four rectangular prisms, each rectangular prism having rectangular surfaces bonded to rectangular surfaces of adjacent rectangular prisms, a first surface part of a first rectangular prism pair composed of two adjoining rectangular prisms of said four rectangular prisms protruding from a rectangular surface of a second rectangular prism pair in a longitudinal direction, and  
 a dichroic film formed on a second surface part of said first rectangular prism pair, said second surface part not protruding from said rectangular surfaces of said second rectangular prism pair of said rectangular prisms.  
 
     
     
       6. The dichroic prism according to  claim 5 , said two adjoining rectangular prisms in said first rectangular prism pair being in a state shifted from each other in the longitudinal direction so that they form a step. 
     
     
       7. A prism unit, comprising:
 a dichroic prism composed of four rectangular prisms, each rectangular prism having rectangular surfaces bonded to rectangular surfaces of adjacent rectangular prisms, a first surface part of at least one of said four rectangular prisms protruding from the rectangular surfaces of other ones of said rectangular prisms, and a dichroic film formed on a second surface part of said at least one rectangular prism, said second surface part not protruding from said rectangular surfaces of said other ones of said rectangular prisms, said first surface part being provided with a light diffusing layer for diffusing light; and  
 a prism stand for mounting said dichroic prism thereon, said prism stand having a step that matches a step of said dichroic prism.  
 
     
     
       8. The prism unit according to  claim 7 , said first surface part being provided with a light diffusing layer for diffusing light. 
     
     
       9. The prism unit according to claim  8    7 , said light diffusing layer being an adhesive layer. 
     
     
       10. The prism unit according to claim  8    7 , said light diffusing layer being a ground glass layer. 
     
     
       11. A projector, comprising:
 an illumination optical system for emitting illumination light;  
 colored light separation means for separating the illumination light into lights of three colors;  
 three light modulation means for modulating the three colored lights based on a given image signal;  
 a dichroic prism composed of four rectangular prisms, each rectangular prism having rectangular surfaces bonded to rectangular surfaces of adjacent rectangular prisms, a first surface part of at least one of said four rectangular prisms protruding from the rectangular surfaces of other ones of said rectangular prisms, and a dichroic film formed on a second surface part of said at least one rectangular prism, said second surface part not protruding from said rectangular surfaces of said other ones of said rectangular prisms, said first surface part being provided with a light diffusing layer for diffusing light; and  
 a projection optical system for projecting the lights synthesized by said dichroic prism.  
 
     
     
       12. The projector according to  claim 11 , said first surface part being provided with a light diffusing layer for diffusing light. 
     
     
       13. The projector according to claim  12    11 , said light diffusing layer being an adhesive layer. 
     
     
       14. The projector according to claim  12    11 , said light diffusing layer being a ground glass layer. 
     
     
       15. A prism unit, comprising:
 a dichroic prism composed of four rectangular prisms, each rectangular prism having rectangular surfaces bonded to rectangular surfaces of adjacent rectangular prisms, a first surface part of a first rectangular prism pair composed of two adjoining rectangular prisms of said four rectangular prisms protruding from a rectangular surface of a second rectangular prism pair in a longitudinal direction, and a dichroic film formed on a second surface part of said first rectangular prism pair, said second surface part not protruding from said rectangular surfaces of said second rectangular prism pair of said rectangular prisms; and  
 a prism stand for mounting said dichroic prism thereon, said prism stand having a step that matches a step of said dichroic prism.  
 
     
     
       16. The prism unit according to  claim 15 , said two adjoining rectangular prisms in said first rectangular prism pair being fixed in a state shifted from each other in the longitudinal direction so that they form the step of said dichroic prism. 
     
     
       17. A projector, comprising:
 an illumination optical system for emitting illumination light;  
 colored light separation means for separating the illumination light into lights of three colors;  
 three light modulation means for modulating the three colored lights based on a given image signal;  
 a dichroic prism composed of four rectangular prisms, each rectangular prism having rectangular surfaces bonded to rectangular surfaces of adjacent rectangular prisms, a first surface part of a first rectangular prism pair composed of two adjoining rectangular prisms of said four rectangular prisms protruding from a rectangular surface of a second rectangular prism pair in a longitudinal direction, and a dichroic film formed on a second surface part of said first rectangular prism pair, said second surface part not protruding from said rectangular surfaces of said second rectangular prism pair of said rectangular prisms; and  
 a projection optical system for projecting the lights synthesized by said dichroic prism.  
 
     
     
       18. The projector according to  claim 17 , said two adjoining rectangular prisms in said first rectangular prism pair being fixed in a state shifted from each other in the longitudinal direction so that they form a step. 
     
     
       19. A projection display method, comprising:
 emitting an illumination light;  
 separating the illumination light into lights of three colors;  
 modulating the three colored lights based on a given image signal;  
 synthesizing the lights using a dichroic prism composed of four rectangular prisms, each rectangular prism having rectangular surfaces bonded to rectangular surfaces of adjacent rectangular prisms, a first surface part of at least one of said four rectangular prisms protruding from the rectangular surfaces of other ones of said rectangular prisms, and a dichroic film formed on a second surface part of said at least one rectangular prism, said second surface part not protruding from said rectangular surfaces of said other ones of said rectangular prisms; and  
 projecting the lights synthesized by said dichroic prism.  
 
     
     
       20. A projection display method, comprising:
 emitting an illumination light;  
 separating the illumination light into lights of three colors;  
 modulating the three colored lights based on a given image signal;  
 synthesizing the lights using a dichroic prism composed of four rectangular prisms, each rectangular prism having rectangular surfaces bonded to rectangular surfaces of adjacent rectangular prisms, a first surface part of a first rectangular prism pair composed of two adjoining rectangular prisms of said four rectangular prisms protruding from a rectangular surface of a second rectangular prism pair in a longitudinal direction, and a dichroic film formed on a second surface part of said first rectangular prism pair, said second surface part not protruding from said rectangular surfaces of said second rectangular prism pair of said rectangular prisms; and  
 projecting the lights synthesized by said dichroic prism.  
 
     
     
       21. A method for assembling a dichroic prism that includes a first rectangular prism including two first side surfaces making a right angle therebetween, a second rectangular prism including two second side surfaces making a right angle therebetween, a third rectangular prism including two third side surfaces making a right angle therebetween, and a fourth rectangular prism including two fourth side surfaces making a right angle therebetween, a height of the first rectangular prism being larger than the third rectangular prism, a height of the second rectangular prism being larger than the fourth rectangular prism, the method comprising:
   forming a first dichroic film only on a first part of one first side surface;        forming the first dichroic film only on a first part of one second side surface;        forming a second dichroic film on the other second side surface;        forming the second dichroic film on one third side surface;        bonding the one first side surface on which the first dichroic film is formed with one fourth side surface on which no dichroic film is formed so that a second part of the one first side surface on which no dichroic film is formed protrudes from the one fourth side surface;        bonding the one second side surface on which the first dichroic film is formed with the other third side surface on which no dichroic film is formed so that a second part of the one second side surface on which no dichroic film is formed protrudes from the other third side surface;        bonding the other first side surface on which no dichroic film is formed with the other second side surface on which the second dichroic film is formed; and        bonding the one third side surface on which the second dichroic film is formed with the other fourth side surface on which no dichroic film is formed.     
     
     
       22. The method for assembling a dichroic prism according to  claim 21 , further includes:
   forming the second dichroic film only on a first part of the other second side surface, and        bonding the other first side with the other second side surface so that a second part of the other second side surface on which no dichroic film is formed protrudes from the other first side surface.     
     
     
       23. The method for assembling a dichroic prism according to  claim 21 , further including forming a light diffusing layer on the second part of the one first side surface and on the second part of the one second side surface. 
     
     
       24. The method for assembling a dichroic prism according to  claim 23 , the forming a light diffusing layer including forming a light diffusing layer that is an adhesive layer. 
     
     
       25. The method for assembling a dichroic prism according to  claim 23 , the forming a light diffusing layer including forming a light diffusing laser that is a ground glass layer.