| 摘要 |
PURPOSE:To obtain a stable servo control signal and light information signal by forming one face of a concave lens which magnifies the reflected light from a disk and spots the same onto a photodetector to an aspherical face. CONSTITUTION:Light from 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 a photodetector 7. The one face of the concave lens 13 which magnifies the light spot on the element is formed to the aspherical face. Mapping directions 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 the aspherical concave lens 13 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. |
