Patent ID: 7826138

Claim:
A dichroic mirror for a projection device comprising: a substrate; a first film stack deposed on the substrate and having a structure represented by a first formula: (2HL) n ; and a second film stack deposed on the first film stack and having a structure represented by a second formula: (0.325H0.65L0.325H) m ; wherein ‘2HL’ and ‘0.325H0.65L0.325H’ respectively represent a double-layer sub-structure of the first film stack and a sandwiched sub-structure of the second film stack, ‘n’ and ‘m’, which are integers, respectively represent the number of repetitions of the double-layer sub-structures and sandwiched sub-structures, ‘H’ and ‘L’ respectively represent a high refractive index layer and a low refractive index layer, both of which have a height equal to ¼ of a reference wavelength of the dichroic mirror, and ‘2’, ‘0.325’ and ‘0.65’ are height coefficients.