Patent ID: 9513417
Filing Date: 2016-12-06
CPC Classification: G02B,G03B

Claim Text:
1. An optical filter comprising: a light-transmitting substrate; a gradient refractive index thin film with a refractive index change in the film thickness direction formed on the substrate; and an anti-reflection structure formed on the gradient refractive index thin film, wherein the gradient refractive index thin film has a light absorption property and a gradient refractive index property such that the refractive index change comprises plural changing points, each of which has an increase and a decrease of the refractive index, wherein the gradient refractive index thin film has a gradient refractive index property comprising plural local maximum value points, at each of which the refractive index turns to reduction after increase, as the plural changing points in the refractive index change, wherein the gradient refractive index thin film has a gradient refractive index property in that, of the plural local maximum value points, the local maximum value point nearest to the substrate is the global maximum value point of the refractive index change, and wherein the gradient refractive index thin film comprises, in the film thickness direction thereof: (a) a region where a spectral transmission characteristic of a visible wavelength region increases as approaching a long wavelength side; and (b) a region where the spectral transmission characteristic of the visible wavelength region decreases as approaching the long wavelength side.