Optical head having focus error detection and tracking error detection sensors arranged on substantially the same plane

摘要

Light reflected from an information recording surface is branched into first and second substantially parallel beams. The first beam is directed to a focus error detection system and the second beam is directed to a tracking error detection system. The photodetector includes light receiving sections for the two detection systems. The light receiving sections include Light receiving surfaces and are housed in a single package. A substantially flat plate is placed either in the focus error detection system or in the tracking error detection system, serving to shorten the optical path so as to create a difference in optical path length to the light receiving surfaces between the two detection systems, thereby enlarging the light spot on the light receiving sections for the tracking error detection system. A cylindrical lens placed in the tracking error detection system serves as astigmatism generating and to make the light spot on the light receiving section in the tracking error detection system to be enlarged in one direction. The light receiving surfaces of one detection system have division lines substantially perpendicular to that of the other detection system. The perpendicular division lines are effective in eliminating an inherent problem encountered in the prior art optical head that adjustment of the tracking error detection system affects the adjustment of the focus error detection system.