Hybrid Photonic Metamaterials Coupled with Liquid Crystals at Nanoscale

^{Nano-electro-mechanical system (NEMS) under study. (a) Artistic impression of a mechanically reconfigurable zigzag metasurface (cross-section) infiltrated with a liquid crystal. Red and blue arrows indicate the directions of electrically induced displacements for the nanobridges baring opposite potentials. (b) SEM image of the fabricated metasurface. Scale bar corresponds to 2 μm. (c and d) Close-up view of the areas marked in panel (b) with green and purple boxes, respectively. Images were taken with SEM at 52° to the normal and color-coded to enhance the contrast between gold (yellow) and silicon nitride (gray). Scale bar corresponds to 300 nm.}

Photonic metamaterials (MMs) is a novel class of nano-structured artificial media with optical properties not found, or superior, to those exhibited by natural materials. Nowadays, the scientific efforts are focused on development of active and tunable MMs, a generation of artificial photonic media with dynamically, on demand controlled, optical properties. We have created tunable MMs by functionalising their fabric with liquid crystals (LCs), where the MM properties were tuned by changing the LC optical anisotropy with external electric field.

The spectral tuning of hybrid LC-MM systems of up to 10% in the optical part of the spectrum using electric field was achieved, a goal that posed a significant challange before, due to strong anchoring of LC molecules to the surface of nano-structures [1]. In order to increase the tunability of LC-MM systems even further, we made MM framework mechanically re-configurable and, for the first time, employed elastic properties of LCs to control the MM movement at the nanoscale [2]. The resulting hybrid nano-electro-mechanical systems (NEMS) were free from stiction and the robust control of nano-scopic actuations in such systems was achieved for the entire range of structurally allowed displacements. We experimentally demonstrated the full potential of electrically controlled LCs for tuning photonic MMs, and also introduced a novel type of NEMS, which are elastically coupled to and controlled by LCs.

^{1. O. Buchnev , N. Podoliak , M. Kaczmarek , N. I. Zheludev, and V. A. Fedotov, Electrically controlled nanostructured metasurface loaded with liquid crystal: toward multifunctional photonic switch, Adv. Optical Mater. 3, 674–679 (2015)
https://doi.org/10.1002/adom.201400494}

^{2. O. Buchnev, N. Podoliak, T. Frank, M. Kaczmarek, L. Jiang, and V. A. Fedotov, Controlling stiction in nano-electro-mechanical systems using liquid crystals, ACS Nano 10, 11519–11524 (2016)
https://doi.org/10.1021/acsnano.6b07495}