| 摘要 |
<P>PROBLEM TO BE SOLVED: To provide an optical pickup optical system which forms a good spot by preventing decrease in diffraction efficiency, and suppresses the change of spherical aberration resulting from minute change of a laser beam, in order to establish compatibility to an existing optical disk or a new standard optical disk, when a diffraction structure is used. <P>SOLUTION: This optical pickup optical system 10 has compatibility at least in two kinds of optical disks of which the specification differs, and has at least an optical element 11 which has a phase shift surface on one surface. The phase shift surface 11a has a first region 11ai which focuses each laser beam on a recording surface of a corresponding optical disk. The region has at least one ring zone structure having a ring zone group of which the amount of optical path length addition to a first laser beam when a refraction surface located inside is made reference is almost that of two wave lengths, and a return level difference section of which the amount of optical path length addition to the first laser beam when the refraction surface located inside is made reference is that of almost three wave lengths in the opposite direction to a level difference of the ring zone group. <P>COPYRIGHT: (C)2006,JPO&NCIPI |
