Ultra-bright light engine for projection displays
View Patent ↗A projector incorporating a prism and a plurality of light valves for modulating light that passes though the prism, wherein the color splitting-converging prism includes a dichroic coating having multiple layers of high and low index of refraction and ¼ wavelength thickness at each desired angle of incidence for reducing dichroic shift and thereby minimizing light loss.
1. For use in a projector incorporating a light engine with color-splitting converging prism, said prism having at least two prism elements wherein a first prism element comprises a red dichroic coating and a second prism element comprises a blue dichroic coating, the improvement comprising application of red and blue dichroic coatings to said respective prism elements, said coatings being characterized by respective dichroic shifts less than first and second predetermined amounts, for minimizing light loss and thereby increasing light throughput.
2. The improvement of claim 1 , wherein said first and second predetermined amounts are 65 nm and 35 nm, respectively.
3. The improvement of claim 1 , wherein said coatings consist of stacks of alternating layers of high and low index of refraction with layer thicknesses equivalent to ¼ wavelength at specific angles of incidence.
4. The improvement of claim 3 , wherein said coatings comprise 20 to 30 of said layers.
5. The improvement of claim 1 , wherein said dichroic coatings comprise alternating layers of TiO 2 and SiO 2 .