Optical pickup device keeping coincident the optical axes of the objective lens and of the recording/reproducing beam

摘要

An optical pickup device for an optical recording disk having an information recording surface comprises an objective lens for converging a light beam emitted from a light source onto the information recording surface of the disk so as to form a beam spot thereon along an information track of the disk. At least one light detecting unit comprised of a plurality of photodetectors is provided for the detection of focus and tracking errors and the detection of the position of the optical axis of the objective lens. Each of the photodetectors is able to receive a light beam reflected by the information recording surface of the disk and to produce an output signal which is proportional to the amount of the light beam incident thereon. At least two photodetectors of the light detecting unit are separated from each other through a separation line which is optically parallel to a tangent to the information track of the disk so that a differential signal corresponding to the difference between the levels of the output signals produced by the two photodetectors can be obtained as a lens position detection signal which is used for the detection of position of the optical axis of the objective lens in relation to the photodetectors.