Beam splitting prism system for color television

Claim 1

A beam splitting prism system for a color television device for splitting an incident light beam into partial light beams in each of a first, second, and third of three different spectral regions, comprising: A. first and second beam splitting prisms, each forming an identical isosceles right triangle in cross-section, each triangle being formed by first and second faces of equal given lengths and a longer third face of the respective prism, B. a first dichroic coating situated between and optically adjacent to the third face of both prisms, whereby the prisms are placed to form a square in cross-section, with the respective first faces on opposite sides of the square and with the respective second faces on the other opposite sides of the square, C. means for providing light from all spectral regions to the first face of the first prism, D. a first doubly refractive coating optically adjacent to the second face of the first prism, E. a second dichroic coating optically adjacent to the first doubly refractive coating on the side of the first doubly refractive coating remote from the first prism, F. a second doubly refractive coating optically adjacent to the first face of the second prism, G. a third dichroic coating optically adjacent to the second doubly refractive coating on the side of the second doubly refractive coating remote from the second prism, wherein the first dichroic coating comprises means for transmitting light in a first spectral region to the first face of the second prism, for reflecting light in a second spectral region to the second face of the first prism, and for transmitting a first part of the light in the third spectral region to the first face of the second prism and for reflecting the remaining second part of the light in the third spectral region to the second face of the fIrst prism depending on the orientation of a polarization plane of the incident light relative to an incident plane, whereby substantially all of the light from all three spectal regions reaches either the first face of the second prism or the second face of the first prism by traversing the prism system via a path equal to said given length. wherein the first doubly refractive coating and the second dichroic coating comprise means for transmitting the light in the second spectral region out from the second face of the first prism and for reflecting the second part of the light in the third spectral region to and out from the second face of the second prism, and wherein the second doubly refractive coating and the third dichroic coating comprise means for transmitting the light in the first spectral region out from the first face of the second prism and for reflecting the first part of the light in the third spectral region to the first dichroic coating, which in turn reflects said first part to and out from the second face of the second prism, whereby both the first part and the second part of the light in the third spectral region reach the second face of the second prism after passing along a path equal to twice said given length.