Bi-functional dynamic tunable absorber and highly robust polarisation converter for graphene-based metasurface

Abstract

In this study, a graphene-based metasurface structure with bi-functional dynamically tunable absorber and highly robust polarisation converter is proposed. The device primarily consists of two functional tiers. The top tier of cyclically patterned graphene and the back of a fully reflective gold mirror, which are separated by an intermediate tier of SiO2 dielectric to form a typical sandwich structure. The proposed device is numerically calculated by finite element method (FEM), and the equivalent R-L-C circuit model is built to validate the calculated results. The proposed reflective-type circularly to circularly polarisation converter (RCCPC) has a wide operating band of 0.8 THz (2.12 THz to 2.92 THz) and can obtain near unity polarisation conversion rate (χPCR). It is worth noting that the device is also immune to structural parameter deviations. In addition, due to the excited charge of monolayer graphene has the cyclotron property in a static magnetic field, the cross-polarised component of the polarisation converter can be increased by applying a vertical magnetic field, which provides a feasible method to improve the energy conversion rate of the device. At the same time, the device can also serve as a narrowband dual channel absorber, with 95 % absorption effect. In addition, the tunability of graphene is based on the correlation between conductivity and Fermi energy. As the Fermi energy changes, the working frequency of the device is shifted, realizing the dynamic tunable absorber and polarisation converter. It is believed that these findings provide a way to implement a variety of novel multifunctional photonic device, including polarisation imaging, electromagnetic energy absorption, and integrated photonic devices.