Polarization-invariant grating based on a photoaligned liquid crystal in an oppositely twisted binary configuration

We demonstrate a polarization-invariant liquid-crystal (LC) grating in an oppositely twisted and mutually orthogonal configuration. The polarization-invariant LC grating with high diffraction efficiency is fabricated using a single-masking process with two-step exposure of a linearly polarized ultraviolet light. It is found that the zeroth- and the first-order diffracted beams are linearly polarized and perpendicular to each other irrespective of the incident polarization for the phase retardation of m pi (m=integer).