| 摘要 |
PURPOSE:To realize both the focus control and the tracking control through a simple optical system, by using a detecting system comprising a split prism and two sets of 2-split photodetectors put close to each other. CONSTITUTION:When a disk gets out of focus, an image formed by the light flux passed through a wedge-shaped prism 7a gets out of the bordr between detectors A and B to produce a difference between the light volumes to be made incident to those detectors A and B. In the same way, a difference is also produced to the light volumes which are made incident to the detectors A and B through a wedge-shaped prism 7b. The signals of adverse codes to each other are detected at the disk position centering on an in-focus position by an operation of A-B+D-C. When the bit center gets out of the spot light center, the signals of adverse codes to each other are obtained at the bit position, i.e., the track position centering on a coincident state between the bit cetner and the spot light center due to an operation of A+B-C-D as well as the diffraction of the bit. |
