Abstract: The present inventions are related to systems and methods for transferring information to and from a storage medium, and more particularly to systems and methods for positioning a sensor in relation to a storage medium. For example, an apparatus for determining a sensor position is disclosed that includes discrete Fourier transform calculators operable to process input data to yield a magnitude response of the input data at each of a number of candidate frequencies, a comparator operable to compare the magnitude responses to yield a winning candidate frequency, a servo controller operable to process at least one servo field in the input data to identify a position of a sensor based on the at least one servo field, and a servo frequency synthesizer operable to establish a frequency of operation in the servo controller based at least in part on the winning candidate frequency.

Abstract: When using an optical disc medium that includes pit trains having their widths narrower than a diffraction limit, it is difficult to detect a tracking error signal and take a tracking-servo control while increasing pit density in a direction orthogonal to a pit-train extension direction. Information pit trains are arranged spirally or concentrically and formed in a structure in which their depths are changed periodically at a pitch radially along the optical disc medium, so that the tracking error signal can be obtained by push-pull detection of diffraction light from the structure.