Dual tunable terahertz polarization conversion enabled by Double-Layer Graphene Metasurface

Tunable manipulation on the polarization states of electromagnetic waves is the greatly significant and largely desired fields including information encryption of electromagnetic waves, photodetection, and optical microscope. However, such tunability is usually limited by narrow-working bandwidth. In this paper, we propose a novel design of a dynamic tunable multi-function Double-Layer Graphene Metasurface (DLGM) in THz frequency range, assisted by the graphene plasmon resonance (GPR), which enables to realize dynamic tunable polarization states in the same frequency, and achieve polarization conversion in a broadband frequency range. Moreover, by tuning the Fermi level at different times in each layer of graphene, our design can be applied in time-domain encryption of electromagnetic waves since the frequency range of polarization conversion (circular polarization) as well as the polarization states at specific frequency can be controlled at different times corresponding to the Fermi level. Finally, the mechanism of the phase difference induced by GPR is revealed in our proposed design and our numerical calculation shows such polarization conversion can cover broader THz region compared with previous results.