Patent ID: 7801009

Claim:
An optical head device comprising a light source, a diffractive element for branching light exiting from the light source into at least three light fluxes including a main beam that is transmitted without being diffracted and two sub-beams that are diffracted, an objective lens for converging the three light fluxes on a recording surface of an optical disc, and a light detector for receiving the light converged on the recording surface of the optical disc by the objective lens and reflected by the optical disc and photoelectric converting the light to an electrical signal; wherein the diffractive element is divided into a first diffraction grating region formed with a first diffraction grating, a second diffraction grating region formed with a second diffraction grating having a phase differing by substantially 180 degrees from the first diffraction grating, and a central region sandwiched by the first diffraction grating region and the second diffraction grating region; wherein the central region is divided into a plurality of divided regions by a virtual dividing line; and wherein the central region has phases or grating vectors different from the first diffraction grating region and the second diffraction grating region, and the divided regions divided by the dividing line are formed with diffraction gratings having different phases and grating vectors from each other.