Broadband terahertz polarization conversion using a planar toroidal metamaterial

Abstract

The development of metamaterial-based photonic components has acquired a significant interest in technological developments at terahertz frequencies. The manipulation of the state of polarization is an important parameter in optical devices. In this study, we have investigated, both numerically and experimentally, a toroidal excitation-based metamaterial that is capable of converting terahertz from its linearly polarized state to an orthogonally polarized state over a broad spectrum. The meta-molecule unit of the proposed geometry is comprised of a pair of resonators connected to each other having a split gap in each arm. We have studied both the horizontal and vertical components of transmission for numerous in-plane rotations of the proposed geometry. A multipolar analysis confirms a significant contribution of the toroidal component. Polarization conversion of nearly 40% is observed over a broad spectrum of 1.19–2.5 THz. Such a broadband cross-polarization converter could have remarkable implications for the development of terahertz toroidal metamaterial devices.