Patent ID: 7227691

Claim:
A multi-bandpass filter comprising; a substrate transparent to an object light; and a thin film superimposed layer portion formed by at least mirror layers and cavity layers out of mirror layers, cavity layers and matching layers, comprising two kinds of dielectrics with different refractive indices, superimposed on the substrate as one unit, an optical film thickness thereof being a quarter of a reference wavelength, to form a plurality of Fabry-Perrot interferometer structures, wherein the thin film superimposed layer portion has a structure represented by a fundamental formula of superimposition: [M 0 C 1 M 1 . . . C i M i (T)] k or [M 0 C 1 M 1 . . . C i M i ] k (where i and k are integers not less than 2), when films of the dielectrics are represented by X and Y; the mirror layers are represented by M; the cavity layers are represented by C; and the matching layer is represented by T, where M is a single layer, optical film thickness of films thereof being odd times of a quarter of the reference wavelength, or an alternating layer represented by [(2p+1)X, (2 q +1)Y, . . . ] of different dielectrics X and Y (where p, q, . . . are zero or a positive integer respectively); C is a single layer, optical film thickness of films thereof being even times of a quarter of the reference wavelength, or an alternating layer represented by [(2r)Y, (2s)X, . . . ] of different dielectrics X and Y (where r, s, . . . are zero or a positive integer respectively); T is a single layer, optical film thickness of films thereof being odd times of a quarter of the reference wavelength.