Dependence of tracking error characteristics of in-line-type differential push-pull methods on arrangement error of segmented gratings

We present the validity of in-line-type differential push-pull methods using segmented gratings with respect to arrangement errors by numerical calculation for the first time. In these differential push-pull methods, the segmented gratings for generating subspots are divided into more than two regions, each with a specific width and a specific phase value, and are ideally arranged on the optical axis. We calculate tracking error signals in these methods with respect to the arrangement errors against the optical axis under parameter conditions of the widths of the segmented regions of the gratings. The obtained results show that the grating with a simpler configuration with two regions reveals good compatibility between DVD-recordable (DVD-R) and DVD-random access memory (DVD-RAM) compared with those with three or four regions, when the arrangement error is less than 10% of the radius of the incident laser beam.