| 摘要 |
PURPOSE:To detect a tracking error accurately without the effect of the inclination of a disk by casting the luminous flux of the wavefront aberration of an odd function on the disk, and operating the output different of a photodetector which is divided with a boundary line in the radial direction. CONSTITUTION:A parallel planar plate 9 which imparts the wavefront aberration of an odd function on luminous flux is provided between a laser light source 1 and a collimator lens 2 in the inclined pattern. A photodetector 7 has a light receiving region which is bisected with a boundary line in the radial direction of the disk as a boundary. When the luminous flux having astigmatism in the direction of + or -45 deg. is cast, the distribution of the amount of the light in the photodetector 7 caused by a tracking error becomes asymmetric in the radial and tangential directions. Therefore, when the output difference between two regions of the photodetector 7 is operated, the tracking error can be detected. When a mirror 3 is inclined, the spot on the photodetector 7 is moved along the boundary line, and the error signal is not affected. |
