Method and apparatus for composite tracking servo system with track offset correction and rotary optical disc having at least one correction mark for correcting track offset

摘要

A composite wobbled tracking servo system uses a rotary optical disc which has a header field and a data field alternately arranged along the direction of rotation to provide a sector, and which includes pregrooves formed in at least the data field and at least one pair of wobbled track marks disposed in the header field in a relation wobbled relative to the center of a track. A light spot is directed toward and onto the optical disc to detect a push-pull tracking error signal from the reflection of the light spot diffracted by the pregroove, and a wobbled tracking error signal is detected from the reflection of the light spot traversing the wobbled track marks. The push-pull tracking error signal is corrected on the basis of the wobbled tracking error signal to attain the tracking control with higher accuracy, thereby eliminating an undesirable track offset attributable to tilting or eccentricity of the optical disc.