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Dependence of Differential Phase Detection Signals on Astigmatism in a Focused Spot

We have simulated the differential phase detection (DPD) signal characteristics in the presence of astigmatism in the focused spot of an optical pickup for a DVD player. Both DPD signals generated from four elements and two elements of a four-segment photo-diode have been simulated. The DPD signal level and the offset level depend on the direction of astigmatism and the type of detection. In the two-element detection, astigmatism of 45 deg against the tangential direction of an optical disk deteriorates the DPD signal characteristics more severely than that of 0 deg along the tangential direction.