| 摘要 |
PURPOSE:To decrease the number of component parts and to miniaturize the titled optical head together with simple constitution by using a 4-split photodetector which receives the light transmitted through a prism and reflected by a light separating element. CONSTITUTION:The beams radiated from a laser light source are turned into parallel beams by a collimator lens 12 and made incident on a prism 13 through a light separating element, e.g., a polarized beam splitter 14. These beams are set in the same direction by the prism 13 and condensed on a recording medium 17 in the form of minute spots through a focusing lens 16. The beams reflected by the medium 17 travel back along an optical path and are made incident on the prism 13. Then the beams made incident on the reflecting surface of the prism 13 at an angle approximate to a critical angle when they pass through the prism and polarized by 90 deg. by the splitter 14 to be made incident on a photodetector 18 after passing through the prism 13. Thus just a single 4-split detector 1 can detect a focus error and all information signals as long as a push-pull method is applied for detection of a track error. Then it is possible to decrease the number of component parts and to realize a compact optical head. |
