[OPTICAL REVIEW Vol. 17, No. 4 (2010) 360-366]
© 2010 The Japan Society of Applied Physics

Dependence of Tracking Error Characteristics on Objective Lens Shift for In-Line-Type Differential Push–Pull Methods Using Segmented Gratings

Masahisa SHINODA, Kenya NAKAI, and Nobuo TAKESHITA

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

(Received December 24, 2009; Accepted April 14, 2010)

In this paper, we present the validity of in-line-type differential push–pull methods using segmented gratings with respect to the radial shift of an objective lens by numerical calculation for the first time. In these differential push–pull methods, the segmented gratings for generating sub spots are divided into two to four regions each with a specific phase value and a width. Tracking error signals are calculated with respect to the objective lens shift under parameter conditions of the widths of the segmented regions. The obtained results show that the grating of the simpler configuration with two regions reveals good compatibility between DVD-R and DVD-RAM compared with those with three or four regions.

Key words: optical pickup head, tracking error detection, differential push–pull method, segmented grating, digital versatile disc, Blu-ray disc