Patent ID: 6533427
Filing Date: 2003-03-18
Classification: G02B

Abstract:
An illuminating device adapted to provide a light output to a projection display, said illuminating device comprising:a light source for generating output light that converges at a focal point; a light guiding pipe aligned with said light source along an optical axis, said light guiding pipe having a reflective surrounding wall surface that defines a passage, said passage having a light input end proximate to said light source, and a light output end distal from said light source, said focal point being coincident with a plane of said light input end such that the output light from said light source can enter into said passage via said light input end, can be guided by said surrounding wall surface toward said light output end, and can exit from said passage via said light output end; a quarter-wavelength plate and a reflective polarizer disposed in sequence relative to said passage of said light guiding pipe such that the light that travels in a direction from said light input end to said light output end of said light guiding pipe passes through said quarter-wavelength plate before reaching said reflective polarizer; said reflective polarizer allowing light of a first polarization state to pass therethrough and reflecting light of a second polarization state back into said passage of said light guiding pipe via said light output end; and a reflector mounted on said light guiding pipe at said light input end of said passage, said reflector having an outer surface that faces said light source, an inner surface that faces said light output end of said passage, and a through-hole that extends through said outer and inner surfaces of said reflector and that is centered at said focal point to permit entry of the output light from said light source into said passage; said reflector reflecting the light that travels in said light guiding pipe in a direction from said light output end to said light input end back to said light output end; wherein the light of the second polarization state that was reflected by said reflective polarizer is converted into the light of the first polarization state when passing through said quarter-wavelength plate for a second time.