| 摘要 |
<P>PROBLEM TO BE SOLVED: To provide an objective optical element capable of dealing with an optical media having different substrate thicknesses by using a plurality of wavelengths and also capable of dealing with optical media of not only a single layer but also of a multilayer. <P>SOLUTION: The optical element is divided into a plurality of areas. As for a DVD, the absolute value of a spherical aberration SA of the optical element is increased in proportion to separation from an optical axis, and different codes are assigned for every adjacent area. On the other hand, the absolute value of the aberration is made to be equal to or smaller than a specified value by providing an optical path difference imparting structure to an aperture area required for forming an conversion spot on a CD. <P>COPYRIGHT: (C)2005,JPO&NCIPI |
