Optical data storage readout with quadrant pupil detection

A novel detection scheme that uses combinations of quadrant signals derived in a pupil of the optical system is described for optical storage devices. The signals arise because of an asymmetry in the reflected light distribution when the focused spot scans data with a nonzero tracking offset. Theoretical and scalar diffraction characterization indicates that the signals may be useful for improved data density by reducing intertrack interference (cross talk). The signals may also be useful for providing a tracking error signal.