Patent ID: 9588266
Date: 2017-03-07
CPC Classifications: G02B

Claim:
1. An optical filter comprising: a light-transmitting substrate; and a light-absorbing gradient refractive index thin film consisting of a thin film having no interface in the whole inner part thereof, and wherein the refractive index and an extinction coefficient continuously change by a change in film composition so that the refractive index is close to the refractive index of the substrate toward the substrate side in a film thickness direction thereof, wherein the light-absorbing gradient refractive index thin film, in the film thickness direction, comprises: (1) a first region where a spectral transmission characteristic of a visible wavelength region increases approaching a long wavelength side based on the changes of the refractive index and the extinction coefficient; and (2) a second region, which is located in a region different from the first region in the film thickness, and where the spectral transmission characteristic of the visible wavelength region decreases approaching the long wavelength side based on the changes of the refractive index and the extinction coefficient, and wherein the changes of the refractive index and the extinction coefficient per film thickness of the light-absorbing gradient refractive index thin film decrease approaching the interface of the light-absorbing gradient refractive index thin film on the side of the substrate so that the refractive index of the light-absorbing gradient refractive index thin film is close to the refractive index of the substrate.