| 摘要 |
PURPOSE:To improve the efficiency of light utilization and to reduce weight by using photodetecting elements for error detection which receive the imaging light by a knife edge method and detect a focus error by the signals thereof and detecting a tracking error by the difference in the detecting signals. CONSTITUTION:The focus position does not coincide with the photodetectors 21, 22 and a difference arises in the levels of the output signals of photodetecting surfaces 21a, 21b and 22a, 22b when a laser beam is not focused at an optical disk 6. The focus detection can, therefore, be detected by the signals of the photodetectors 21, 22. The total sum of the incident signal light to the photodetectors 21, 22 varies according to the direction of a deviation when the focusing light of the laser beam deviates in position from the tracks of the disk 6. The tracking error can be detected by the difference in the signal light. The photodetectors which can detect the focus error and the tracking error are commonly used in such a manner, by which the efficiency of light utilization is improved and the photodetecting surfaces are formed smaller to reduce the weight. |
