Patent ID: 6967908

Claim:
An optical pickup device for detecting a focus error of a light beam, having an irradiation optical system for focusing the light beam to form a spot on a track extending in an information recording surface of an optical recording medium, and a light detection optical system for leading return light reflected back from the spot to a photodetector, said optical pickup device comprising: a focus error detecting optical element having four sections of first through fourth quadrants quadrisected around the center of an optical path of the return light along two division lines extending corresponding to a track extending direction and a direction perpendicular to the track extending direction respectively, the four sections disposed on a plane substantially perpendicular to the optical path of the return light, wherein the four sections provide astigmatism for the return light passing through the sections contiguous to said division lines so that the astigmatism in directions are rotated by 90° from each other about the optical path, while separating the return light into at least four paths; and a photodetector which has at least four spaced light receiving elements for receiving the separated return light each of which has contour lines corresponding to said division lines and is comprised of two light receiving areas divided by a bisect line extending substantially in parallel with one of the contour lines, wherein said bisect line of said spaced light receiving element extends corresponding to the direction perpendicular to the track extending direction.