| 摘要 |
PROBLEM TO BE SOLVED: To provide the optical head having a good C/N by separating plural return light beams reflected on discoid recording media by a light beam separating surface in common use as a light beam branching surface and guiding them onto the same optical axis. SOLUTION: A linearly polarized light beam emitted from a semiconductor laser 1 is transmitted through a grating 3 and is branched into a main beam and two bub- beams, and these beams are converted into parallel light beams by a collimator lens 2 to be incident upon a optical prism 4, and then they are converted into a light beam having an intensity distribution of approximately circularity. Then, this light beam is branched by the light beam branching surface 4b into a reflected light beam to be incident upon an object lens 5 and a transmission light beam to be incident upon an objective lens 6, and the transmission light beam is made parallel to the reflected light beam by a reflecting surface 4f. Return light beams reflected by disks 11 and 12 are branched into reflected light beams and transmission light beams respectively and are separated from refracted light beams by the light beam separating surface 4b, and they are incident upon a photodetector 9, where a focus error is detected by the so-called astigmatic method. Based on this focus error signal, an object lens holder 7a is driven in the focusing direction. |
