Optical pickup device with diffraction device

Abstract

An optical pickup device in which a main beam and a pair of sub-beams are used and a diffraction device is disposed between a recording medium and a light receiving device such as a photodetector is disclosed. The diffraction device comprises first to third diffraction regions. The second and third regions receive light beams from the recording medium which are substantially identical in amount to each other. The light receiving device comprises a first to a fourth light receiving regions. The first and second light receiving regions are juxtaposed, and separated by a line. The main beam which has been diffracted by the first diffraction region is focused onto said line. The main beam which has been diffracted by the second diffraction region is focused onto the first light receiving region. The main beam which has been diffracted by the third diffracting region is focused onto the second light receiving region. The sub-beams which have been diffracted by the diffraction device are focused onto the third and fourth light receiving regions, respectively. Alternatively, the diffraction device comprises an area where one or more diffraction regions are formed. The farthest point of the area at the side of the light receiving device is separated from the optical axis by a predetermined distance, to prevent the first order diffracted beam from entering the optical system disposed between the diffraction device and a recording medium.