| 摘要 |
PURPOSE:To prevent the interference of a tracking error component with a focusing error signal by providing a photodetector with a tracking error detecting light receiving part and a focusing error detecting light receiving part. CONSTITUTION:The return beam which is cut to a half by a knife edge 13 forms a semicircular spot across light receiving areas 21a and 21b of a tracking error detecting light receiving part 21 of a photodetector 20 at the time of focusing an optical disk D, and outputs of light receiving areas 21a and 21b are subtracted to detect the tracking error signal by the push-pull method. The semicircular spot is mainly formed on a light receiving area 22b of a focusing error detecting light receiving part 22 when the distance between the optical disk D and an objective lens 11 is too short, and this spot is formed on a light receiving area 22a when said distance is too long, and outputs of light receiving areas 22a and 22b are subtracted to detect the focusing error signal by the knife edge method. |
