Linear polarization conversion at the theoretical limit using a Toroidal metasurface

Metasurface enables controlling the light properties at will by structuring sub-wavelength unit elements. Among feasible applications, polarization control plays a vital role in communication, quantum optics, and imaging. Due to the Joule loss issue, the polarization conversion efficiency for the plasmonic metasurfaces operating at NIR region is usually lower than 10% [1]. In this work, we innovate a metasurface design to enhance the polarization conversion efficiency [2]. A S-shaped plasmonic metasurface with a toroidal dipole-quadrupole coupling response is used to push the polarization conversion efficiency to 22.9% that is very close to the theoretical conversion limit 25% [3].