Effect of Alignment on a Liquid Crystal/Split-Ring Resonator Metasurface

A metasurface comprising a two-dimensional array of split-ring resonators with resonance frequencies in the near-infrared region is fabricated and embedded in a uniformly aligned liquid crystal. The change of the dielectric permittivity in proximity to the plasmonic structure by the replacement of air with the liquid crystal results in a decrease in resonance frequencies. The resonance shift can be attributed to the interaction of the evanescent field of the excited resonant plasmon modes with the liquid crystal. This shift in resonance frequency is found to depend on the liquid-crystal alignment and to vary for different modes. Also, the resulting effects of changes in temperature or applied external electric field on the metasurface depend on the liquid-crystal alignment and may differ from mode to mode. These observations indicate that the characteristic frequencies of the resonant split-ring resonator modes may depend on different evanescent field components interacting with the liquid crystal. Consequently, certain design rules should be taken into account for the development of tunable metasurfaces based on liquid crystals.