Synthetic complex superresolving pupil filter based on double-beam phase modulation.

To take advantage of phase-only filters to reduce reflected stray light, two phase plates are used in a synthetic complex superresolving pupil filter to get a small spot for laser direct writing. The amplitude modulation in a conventional complex superresolving pupil filter (CCSPF) is substituted by an equivalent phase modulation. The equivalence between the proposed filter and a CCSPF is established for a general design. The effectiveness of the proposed filter was proven through experiments to obtain a small main lobe width of 0.86 times the size of the airy spot.