OPTICAL PICKUP DEVICE AND FOCAL ERROR DETECTING METHOD

摘要

PROBLEM TO BE SOLVED: To provide an optical pickup device which is hardly influenced by a truck crossing noise or an optical disk thickness error and in which both a 3-beam mode and a DPD mode can be used, and to provide a focal error detecting method. SOLUTION: The optical pickup device which detects the focal error of a light beam is provided with: an optical element for detecting a focal error which has four divided regions of the first quadrant to the fourth quadrant divided by two parting lines which extend in the extension direction of a truck and in the direction perpendicular to the extension direction on the plane perpendicular to the optical path of a return light beam and which splits the return light beam into at least four light beams while imparting astigmatism in the direction rotated mutually by 90 degrees around the optical path to the return light beam which passes through the adjacent regions of the same side divided by the parting lines; and a photodetector which has a contour corresponding to the parting line in the image surface where the light beam becomes circular in each optical system to which astigmatism is imparted, and which has a light receiving element consisting of two light-receiving regions divided by two parting lines extended approximately parallel to one of the contours.