Kenya NAKAI, Masahisa SHINODA and Kazuo MORI

Advanced Technology R & D Center, Mitsubishi Electric Corp. 1, Zusho-Baba, Nagaokakyo City, Kyoto 617-8550, Japan

(Received January 30, 2003; Accepted May 26, 2003)

In an error detection optical system for optical pick-ups using a parallel plane type half mirror, influence on the differential phase detection (DPD) signal by a coma aberration was simulated. The coma aberration deforms the spot profile on the photodetector and influences the DPD signal level characteristics and the offset characteristics with respect to the objective lens shift. In the 4-segment-type DPD, the coma aberration caused by a half mirror 2.75 mm thick hardly affects the DPD signal if the photodetector is not misaligned. On the other hand, the 2-segment-type DPD has a small offset variation with respect to the objective lens shift and a large variation of the DPD signal level against the misalignment of the photodetector in comparison with the 4-segment-type DPD when there is no coma aberration. In the presence of a coma aberration, however, these variations of the 2-segment-type DPD are suppressed by choosing a pair of elements without the coma apex part of the spot.

Key words: optical disc, optical pick-up, half mirror, differential phase detection, astigmatic aberration, coma aberration