| 摘要 |
PROBLEM TO BE SOLVED: To record/reproduce disks with different thicknesses without mechanically switching objective lenses by dividing and making incident a light beam from a light source to/on plural pieces of objective lenses arranged on the same lens holder. SOLUTION: When the thick disk 12 is arranged selectively, the light beam outgoing from a semiconductor laser 21 is made incident on a prism 23 with a beam splitter through a grating lens 28 and a collimate lens 22, and passes through the joint surface of the prism 23 to be focused on the disk 12 by the objective lens 1a. On the other hand, when the thin disk 13 is arranged selectively, the light beam outgoing from the semiconductor laser 21 is made incident on the prism 23 through the lenses 28, 22, and is reflected by the surface opposite to the joint surface of the prism 23 and the joint surface of a parallelogram prism to be focused on the disk 13 by the objective lens 1b. Thus, the necessity that the objective lenses 1a, 1b are switched dynamically according to the disks 12, 13 with different thicknesses is eliminated, and a switch means is eliminated. |
