Patent ID: 7864425

Claim:
A diffractive optical element comprising: a substrate made of a first material and having a diffraction grating pattern formed on its surface; and a protective film made of a second material and covering the diffraction grating pattern, wherein the first material comprises a first resin; the second material is a composite material that comprises a second resin and first inorganic particles dispersed in the second resin and containing at least zirconium oxide, has a refractive index at the d line n COMd of not less than 1.60 and an Abbe's number Î½ COM of not less than 20, and satisfies a relationship n COMd â‰§1.8âˆ’0.005 Î½ COM (2); the weight ratio of the first inorganic particles to the composite material as a whole is not less than 50 wt % and not more than 85 wt %; the diffraction grating pattern has a depth of not more than 20 Î¼m; and the diffractive optical element has a first-order diffraction efficiency of not less than 85% at a wavelength of 400 to 700 nm.