Patent ID: 7359020

Claim:
An optical device comprising a pair of substantially identical crossed sheet polarizer packages, each package comprising an integrated combination of an absorbing layer and a compensator placed on at least one side of said absorbing layer, wherein the compensator comprises a biaxial plate with effectively constant values of retardation over wavelength, (n y0 -n x0 )d/λ and (n z0 -n x0 )d/λ, across a wavelength range of 450-650 nm, such that for either (n y0 -n x0 )d/λ and (n z0 -n x0 )d/λ, the values at any two wavelengths within the range of 450-650 nm differ by no more than ±20% from each other, and for all wavelengths in the range of 450-650 nm, (n y0 -n x0 )d/λ is a value selected from within 0.5±0.1 and (n z0 -n x0 )d/λ is a value selected within 0.1±0.07, wherein n x0 =an index of refraction with respect to an x axis placed parallel to the transmission axis of the absorbing layer; n y0 =an index of refraction with respect to a y axis; n z0 =an index of refraction with respect to a z axis; d =plate thickness; and λ=wavelength.