Optical pick-up apparatus

摘要

An optical pick-up apparatus using the knife edge method to detect focus errors is arranged so that the sub-spot (Ss1) which gives rise to the sub-beam (Bs1) which is intercepted in the detection optical system by the knife edge (11) to a lesser extent is positioned on the optical disc (2) ahead of the main spot in the recording direction. The sub-spot (Ss2) giving rise to the detection sub-beam (Bs2) which is intercepted by the knife edge in the detection optical system to a greater extent is located on the disc behind the main spot relative to the recording direction. In this manner an imbalance in the amount of light from each sub-beam reflected by the knife edge to the tracking error photodetector is compensated for by an imbalance in the reflectivities of the non-recorded portion ahead of the main beam and the recorded portion behind the main beam. <IMAGE>