| 摘要 |
<P>PROBLEM TO BE SOLVED: To suppress spherical aberration even when numerical aperture NA is enlarged with respect to an optical disk whose mass-productivity is excellent and an optical disk having a multilayer recording layer without tightening tolerance of the thickness of a light transmission layer. <P>SOLUTION: A lens group 29 located on the light source 21 side among a plurality of lens groups 29, 30 constituting a coupling lens 25, is made a fixed lens group, while the lens group 30 located on the objective lens 27 side is made a driving lens group which can be driven in the direction of the optical axis. Only the driving lens group 30 is drive-controlled to emit a non-parallel light flux, and thereby spot spherical aberration and chromatic aberration on the surface of the optical disk 2 resulting from the difference in thickness of the light transmission layers, error or variation in a light source wavelength or the like can be canceled. <P>COPYRIGHT: (C)2005,JPO&NCIPI |
