Superperiodic Liquid-Crystal Metasurfaces for Electrically Controlled Anomalous Refraction

Optical liquid-crystal metasurfaces self-assemble on polymer layers locally processed with a digitally controlled focused ion beam. We expand their functionality by introducing superperiodic design consisting of parallel stripes of various widths inducing different liquid crystal alignment. We optimize the design to achieve strongly asymmetric light diffraction effectively resulting in efficient anomalous refraction. By implementing the optimal patterns of different periodicity, assembling a liquid crystal cell, and assessing its diffractive properties, we experimentally confirm the deflection of normally incident light into a particular oblique direction with 60% efficiency. Applying AC voltage of several volts amplitude across the liquid crystal reversibly straightens its orientation, suppresses the refraction, and reroutes light into the direct transmission. Time-resolved measurements reveal that the switching between refracting and transmitting states occurs within a few milliseconds in both directions.