Patent ID: 7372075

Claim:
An optical substrate comprising: a transparent substrate; a low refractive index layer, whose refractive index is lower than that of the transparent substrate, disposed over the transparent substrate; and a solgel film disposed over the low refractive index layer, a relationship between the surface roughness of the low refractive index layer, represented by Ra1, and that of the solgel film over the low refractive index layer, represented by Ra2, being defined as Ra1>Ra2, said solgel film having in its infrared absorption spectrum an absorption A of 1107±2 cm−1 in wave number attributable to Si—O—C, an absorption B of 1070±2 cm−1 in wave number attributable to Si—O—Si, and an intensity ratio A/B between the absorption A and the absorption B ranging from 0.5 to 1.0.