| 摘要 |
PURPOSE:To obtain tracking and focusing signals, by splitting a reflected light from a disc into a transmitted light and a reproduced light at a hologram element, and detecting the split lights at photodetectors. CONSTITUTION:A light reflected on a disc 7 passes through a lens 6, a 1/4 wavelength plate 5 and a polarizing prism 4 and is made incident to a hologram element 20, from which a transmitted and a reproducing light are obtained. The transmitted light is a far field image of a pit image recorded on the disc 7 and photodetected at a two-split photodetector 9, where a tracking signal is obtained. A focusing signal can be obtained by photodetecting a reproduced image at a 4-split photodetector 12. |
