| 摘要 |
<P>PROBLEM TO BE SOLVED: To solve such an unavoidable problem that formerly a detection system using an in-line type DPP (differential push-pull) system is disclosed as a system detecting a tracking error signal for a plurality of kinds of optical disks of which the track pitches are different, but differential push-pull signal amplitude is deteriorated substantially in a visual field property when displacement of an objective lens or the like occurs. <P>SOLUTION: Such a diffraction grating is provided that a branching means is divided into at least three regions of first, second, and third, and the prescribed periodic structure is provided in respective regions, the first region is arranged between the second region and the third region, also, in the second region, periodic structure having a phase being different by 90° from a phase of periodic structure provided in the first region is provided, while in the third region, periodic structure having a phase being different by 180° from a phase of periodic structure provided in the second region is provided. <P>COPYRIGHT: (C)2009,JPO&INPIT |
