Efficient visible light modulation based on electrically tunable all dielectric metasurfaces embedded in thin-layer nematic liquid crystals

Mingyu Sun,Xuewu Xu,Xin’An Liang,Yuanjin Zheng,Xiao Wei Sun,Vytautas Valuckas,Arseniy I Kuznetsov,Ramón Paniagua-Domínguez

doi:10.1038/s41598-019-45091-5

Abstract

All-dielectric metasurfaces have attracted attention for highly efficient visible light manipulation. So far, however, they are mostly passive devices, while those allowing dynamic control remain a challenge. A highly efficient tuning mechanism is immersing the metasurface in a birefringent liquid crystal (LC), whose refractive index can be electrically controlled. Here, an all-dielectric tunable metasurface is demonstrated based on this concept, operating at visible frequencies and based on TiO2 nanodisks embedded in a thin LC layer. Small driving voltages from 3~5 V are sufficient to tune the metasurface resonances, with an associated transmission modulation of more than 65%. The metasurface optical responses, including the observed electric and magnetic dipole resonance shifts as well as the interfacial anchoring effect of the LC induced by the presence of the nanostructures, are systematically discussed. The dynamic tuning observed in the transmission spectra can pave the way to dynamically tunable metasurface devices for efficient visible light modulation applications.

Highlights

Metasurfaces are two-dimensional spatial arrangements of sub-wavelength scatters engineered to manipulate the incoming wavefront[1]
We demonstrate a transmission-type, Liquid crystals (LC)-based tunable metasurface based on titanium dioxide (TiO2) nanoantennas efficiently operating in the visible spectral range
The metasurfaces were fabricated from 190 nm thick amorphous TiO2 films deposited on commercially available ITO-coated soda lime glass substrates using electron-beam lithography (EBL) followed by inductively-coupled plasma reactive ion etching (ICP-RIE)

Summary

Introduction

Metasurfaces are two-dimensional spatial arrangements of sub-wavelength scatters engineered to manipulate the incoming wavefront[1]. At optical frequencies, where this strategy cannot work, one can e.g. introduce mechanically deformable meta-atoms or substrates and possibly use MEMS to tune their resonances[29,30,31,32,33] or change the dielectric environment of the metasurface using birefringence crystals[34], graphene[35], gated semiconductors[36], phase change materials[37] or electro-optical polymers[48] to name a few. Most of the LC-based high-index dielectric metasurfaces reported used silicon as meta-atoms, showing large tunability of the supported electric and magnetic dipole resonances in the near-IR frequency range under external thermal[34,43,44] and electrical control[45]. We demonstrate a transmission-type, LC-based tunable metasurface based on titanium dioxide (TiO2) nanoantennas efficiently operating in the visible spectral range. We study the influence of the anchoring effect induced by the nanoantennas on the LC anisotropy through theoretical and experimental investigations, which is related to the morphology and material composition of the meta-atoms, affecting the LC molecule alignment direction

Methods

Results

Conclusion