In-Line-Type Differential Push-Pull Methods for Tracking Error Detection

The validity of in-line-type differential push-pull (DPP) methods for digital versatile disc-recordable (DVD-R) and digital versatile disc-random access memory (DVD-RAM) is presented by numerical calculation. In these methods, segmented gratings which are divided into two or three regions each with a specific phase value and a width are used to generate subspots on the optical disk. 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 relationship between the signal characteristics and grating types becomes clear in both cases of DVD-R and DVD-RAM.