Patent ID: 6906764

Claim:
A reflective cholesteric filter comprising: a substrate; a polarization separation layer laminated onto to said substrate; and an auxiliary polarization separation layer laminated onto said polarization separation layer, wherein said polarization separation layer has a function to separate at least part of non-polarized incident light into two circularly polarized lights, the rotational directions of which are mutually opposite, one being reflected and another being transmitted, further wherein said polarization separation layer is a liquid crystal having cholesteric characteristics, a helical axis of liquid crystal molecules thereof being formed so as to traverse said liquid-crystal layer in a thickness direction, a thickness of said liquid-crystal layer being smaller than a thickness required to reflect one of said incident right or left circularly polarized light components at a selective reflection wavelength with maximum reflectivity, the number of molecular helix pitches in a part in which the selective reflection wavelength of said liquid-crystal layer in said polarization separation layer is between 1 and 10 pitches, so that said circularly polarized light component is reflected thereby with a reflectivity that is less than said maximum reflectivity, said other left or right circularly polarized light component being transmitted therethrough, said auxiliary polarization separation layer is a liquid crystal having cholesteric characteristics, a helical axis of liquid crystal molecules thereof being formed so as to traverse said liquid-crystal layer in a thickness direction, and a thickness of said liquid-crystal layer being smaller than a thickness required to reflect said other circularly polarized light components at a selective reflection wavelength with maximum reflectivity, and the number of molecular helix pitches in a part in which the selective reflection wavelength of said liquid-crystal layer in said polarization separation layer is between 1 and 10 pitches, so that said other circularly polarized light component is reflected thereby with a reflectivity that is less than said maximum reflectivity, said one circularly polarized light component being transmitted therethrough.