Highly efficient ultrathin broadband quarter-waveplate based on plasmonic metasurface

In this paper, highly efficient broadband ultrathin quarter-wave plate is proposed to perform circular-to-linear and linear-to-circular polarization conversion using a plasmonic metasurface. The reported design has three diagonally coupled L-shaped resonators whose responses interact constructively with high power conversion efficiency of 97.95% normalized to the input power. Additionally, the achieved bandwidth is 2.6 times greater than that of previous designs. Further, the power of the undesired polarization state is nearly zero over the whole operation bandwidth. Such characteristics are mainly due to the anisotropy of the proposed unit cell, which produces collective resonance. This concept can be generally used with other structures to boost anisotropy, and is not limited to the suggested polarization converter. The reported quarter-wave plate is also insensitive to large deviation from the optimum geometry. Furthermore, the introduced structure is very flexible to work in different frequency regimes starting from mid-wavelength infrared regime up to the visible range based on the unit cell dimensions.