Patent ID: 7324283
Filing Date: 2008-01-29
Classification: G02B

Abstract:
1. An optical filter formed by a substrate and a thin film that is formed on the substrate, wherein the thin film is provided with laminated portions having predetermined refractive index profiles, and wherein the refractive index profiles are 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 refractive index profiles are represented by a first laminated portion, a second laminated portion that is laminated on the substrate side of the first laminated portion, and a third laminated portion that is laminated on the substrate side of 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 side, 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 approaching the substrate side, and wherein an optical thickness of the high refractive index layers and an optical thickness of the low refractive index layers are different from each other, wherein the refractive indices of the low refractive index layers are substantially equal to the refractive index of the substrate.