Duel-layer optical scanner with non-periodic phase structure element of birefringent material for different wavefront aberration compensation of orthogonally polarized radiation beams

摘要

An optical scanning device for scanning a dual-layer optical record carrier with dual orthogonally polarized radiation beams. The device having a spherical aberration compensation optical subsystem including a switchable liquid crystal cell of birefringent material for altering different optical paths lengths provided by a phase structure of stepped annular zones.