Patent ID: 7710849

Claim:
An optical head device, comprising: a plural-wavelength light source capable of selectively emitting a single light beam among a plurality of light beams of different wavelengths; an objective lens for focusing emitted light from the plural-wavelength light source onto an optical recording medium; a photodetector for receiving reflected light from the optical recording medium; a light separating element for separating the emitted light from the plural-wavelength light source and the reflected light from the optical recording medium; and a diffractive optical element provided between the plural-wavelength light source and the light separating element, the diffractive optical element branching the emitted light from the plural-wavelength light source into a plurality of light beams; a first magnification control element provided between the plural-wavelength light source and the light separating element so as to alter magnification of the objective lens in an outward path in accordance with a wavelength of incident light; and a second magnification control element provided between the light separating element and the photodetector so as to alter magnification of the objective lens in an inward path in accordance with a wavelength of incident light, wherein the light separating element includes a polarizing beam splitter which guides the emitted light from the diffractive optical element to the optical recording medium and also guides the reflected light from the optical recording medium to the photodetector, and among a plurality of the light beams of different wavelengths making incidence to the polarizing beam splitter, at least two light beams are linearly polarized light with a same polarization direction.