Superperiodic Liquid-Crystal Metasurfaces for Electrically Controlled Anomalous Refraction

Abstract

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.

Review of Metasurfaces and Metadevices: Advantages of Different Materials and Fabrications

“…The orientation of the anisotropic liquid crystals can be both electrically and thermally controlled. The optical properties of a metasurface can be thus modified [142][143][144][145]. Although the efficiency is presently not favorable, the technique exhibits promise.…”

Tunable Metasurfaces: The Path to Fully Active Nanophotonics

“…[ 110 ] The Mie resonances of the metasurface interact differently depending on the orientation of the LCs, resulting in an absolute transmission modulation of 53% at a driving voltage of 20 V. Beam steering applications have also been demonstrated. [ 111 ] Using an computational inverse design method, beam steering at a working wavelength of 1550 nm of up to 114°, with diffraction efficiency into the ±1 orders of 78% between the on and off states, has been proposed (Figure 4b). [ 112 ] To ensure that the grating structures exhibits the desired beam switching into the ±1 diffraction orders with high efficiency, an adjoint‐based optimization method was used for the inverse design.…”

Vanadium Dioxide for Dynamically Tunable Photonics

“…Therefore, distinct optical properties can be realized by manipulating the polarization of the incident light. This has been proven through the use of electrically tunable polarizers [23,24] and liquid crystals (LCs) [25–27] . This has also been extended to vectorial holography [28,29] to produce different images through the use of an electrical bias to control both the input and output polarization states of the light.…”