Crosstalk cancellation using differential wax-wane focus servo technique

We present studies of crosstalk cancellation using the differential wax-wane focus servo technique. A scalar diffraction model is employed to accurately predict its performance. The measured wavefront is implemented in the diffraction model, and excellent agreement between experimental and modeling results is achieved. With measured system aberration, the tracking crosstalk is reduced from 0.7 µm in a single channel to less than 0.1 µm in the optimized differential channel. Comparisons to the astigmatic and pupil obscuration focus error detection techniques are given. Without any aberration, the differential wax-wane technique has a tracking crosstalk amplitude of 0.04 µm compared to about 0.25 µm in other techniques.