Patent ID: 7289268

Claim:
An optical filter formed by a substrate and a thin film that is formed on the substrate, wherein the thin film is formed by laminating low refractive index layers whose refractive index is relatively low alternatingly from the substrate side with high refractive index layers whose refractive index is relatively high, and wherein the thin film is provided with a first laminated portion, a second laminated portion that is adjacent to the first laminated portion, and a third laminated portion that is adjacent to the second laminated portion, and wherein in the first laminated portion, the refractive indices of the high refractive index layers become gradually higher approaching the substrate, in the second laminated portion, the refractive indices of the high refractive index layers are substantially equal to the highest refractive index of the high refractive index layers constituting the first laminated portion, and in the third laminated portion, the refractive indices of the high refractive index layers become gradually lower from the second laminated portion side, and wherein the refractive indices of the low refractive index layers constituting the first through third laminated portions are substantially equal to the refractive index of the substrate, and an absolute value of a refractive index gradient of the high refractive index layers constituting the first laminated portion is different from an absolute value of a refractive index gradient of the high refractive index layers constituting the third laminated portion.