| 摘要 |
PURPOSE:To obtain a stable servo control signal and light information signal by forming a concave lens which magnifies the reflected light from a disk and spots the same onto a photodetector in such a manner that the disk side is convex and the photodetector side is concave. CONSTITUTION:The light of a semiconductor laser 1 is condensed by an objective lens 3 onto the disk 4 and the reflected light thereof is detected through lenses 13, 16 by the photodetector 7. The disk side of the concave lens 13 which magnifies the light spot on the element is formed convex and the element side thereof is formed concave. Mapping direction 8, 9 of tracks and the virtual line perpendicular thereto in a spot diagram on the element 7 can be decreased in spherical aberration by constituting the lens 13 as negative meniscus lens and, therefore, said lines coincide with division lines 10a, 10b. The stable servo control signal and light information signal from which the false focus error by a tracking error and disk distortion is eliminated are thus obtd. |
