Patent ID: 7755834

Claim:
An optical head device, comprising: a light source, configured to emit light having three different wavelengths of λ 1 =405 nm band, λ 2 =660 nm band and λ 3 =780 nm band; an objective lens, configured to converge at least part of the light to a recording layer of an optical recording medium; a photo detector, configured to detect light reflected from the optical recording medium; and a wavelength-selective diffraction element, configured such that the light having a three wavelengths is incident on the wavelength-selective diffraction element as incident light, the wavelength-selective diffraction element comprising: a transparent substrate; a concavo-convex part, formed on the transparent substrate such that concave portions and convex portions are alternately extended in one direction, and comprised of a first material which is optically isotropic; and a filling part, filling at least the concave portions and comprised of a second material which is optically isotropic, wherein: the first material and the second material have no absorbance with respect to the three different wavelengths of the incident light, the first material and the second material have a same refractive index with respect to light having the wavelength of λ 1 or a same refractive index with respect to light having the wavelengths of λ 2 and λ 3 , the first material and the second material have different refractive indices with respect to light having the remaining wavelength of the three different wavelengths of the incident light.