| 摘要 |
<P>PROBLEM TO BE SOLVED: To condense a light beam up to a diffraction limitation on information media (optical disk) with different substrate thicknesses by utilizing hologram lens whose transmitted light has also sufficient intensity, in an optical head unit. <P>SOLUTION: In designing an objective lens, the objective lens is designed so that it is divided into a plurality of areas, at least a first area and a second area, based on the distance between the incident light and the optical axis in the passage area of the light entering the objective lens used for an optical head, and that the light passing through the first area is focused onto an optical disk having the transparent substrate thickness t2. And it is designed so that the light passing through the second area focuses onto an optical disk having the transparent substrate thicknesses of t1 and t2 (t2<t1) by having an annular zone with concavo-convex shape. Here, the annular zone is constituted in the concentric circle shape about the optical axis of the objective lens, and is integrally formed on a surface where the curvature of the objective lens is large, or the radius of curvature is small. This suppresses the aberration produced by the incline to the optical axis. <P>COPYRIGHT: (C)2004,JPO |
