Thin film dichroic color separation filters for color splitters in liquid crystal systems

An optical filter is provided for use in color projection display imaging systems which utilize liquid crystal light valves for image modulation. The optical filter is a dichroic coating which separates light into different colors. The optical filter is located on a light transmissive surface of a color splitting device such as a Philips prism. The optical filter is formed from layers of at least two different dielectric materials including a high refractive index material, such as zirconium oxide and a low refractive index material such as aluminum oxide. The low refractive index material has an average refractive index of no less than about 1.6. The high refractive index material has an average refractive index which is sufficiently greater than the average refractive index of the low refractive index such that the average refractive index of the high refractive index material divided by the average refractive index of the low refractive index material yields a ratio that is greater than about 1.2 and less than about 1.55.