Bandpass filter to reduce thermal impact of dichroic light shift

Abstract

A color splitting prism assembly ( ) comprised of three prisms. Each a dichroic filter at an interface ( ) between a first and second of the three prisms reflects a first primary color component of a white light beam passing through the prism assembly. The first primary color component is directed to a first modulator ( ). The remaining portions of the white light beam enter a second prism ( ) and strike a second dichroic filter at the interface between ( ) the second and third prisms. The second dichroic filter separates a second primary color component from the white light beam leaving a third primary color component to travel through the third prism ( ) to a third modulator. The second primary color component of the white light beam is directed to a second modulator ( ). Light modulated by the first and third modulators travels through the prisms at a slightly different angle than the unmodulated light and therefore reacts differently upon striking the first dichroic filter for the second time. Portions of the light modulated by the first and third modulator travel toward the second modulator ( ). An additional filter on or near the exit face ( ) of the second prism ( ) prevents light in the first and third primary color components from reaching the second modulator ( ) and heating the second modulator ( ). The light rejected by the additional filter is dispersed by ground glass surfaces of the color splitting prism assembly.