| 摘要 |
PROBLEM TO BE SOLVED: To enhance light availability, to reduce spherical aberration and to facilitate manufacture and assembly of parts by using an objective lens of a prescribed shape. SOLUTION: The objective lens 20, a light splitter 60 and a detection lens 40 are arranged on an optical path between a disk 30 and a photodetector 90, and a light source 80 is placed on a branching optical path. An intermediate area A2 having an outside diameter smaller than a whole effective diameter for a light passing area is formed on one side surface of the objective lens 20, and a central area A1 on the inside of the area A2, and a peripheral area A3 on the outside are formed respectively. The areas A1 and A3 are optimized in their curvatures for a thin DVD, and the curvature of the area A2 is optimized for a thick CD. The photodetector 90 is designed so that the light arrives at only the central area A1 and the intermediate area A2 so that the light of a far axial area doesn't arrive when information is reproduced from the CD. |
