Dual-frequency tunable unidirectional reflectionless propagation in non-Hermitian graphene plasmonic waveguide system

Abstract We theoretically investigate a dynamically tunable unidirectional reflectionlessness phenomenon by applying external voltage in a graphene plasmonic waveguide system based on far-field coupling among three resonators. The system consists of three wing-shaped resonators, which are side-coupled to a graphene plasmonic ribbon waveguide. Based on the temporal coupled-mode theory (TCMT) and numerical simulation, the dual-frequency unidirectional reflectionless phenomenon is studied. The reflections for forward incidence are zero at 34.34 THz and 35.83 THz, while the reflections for backward incidence are close to 33.13% and 21.13%, respectively. The contrast ratio between the forward and backward reflections is almost 1. Besides, the non-Hermitian scattering matrix of our proposed structure is proposed to verify the existences of double exceptional points, and the tunable unidirectional reflectionless phenomenon is also achieved by changing the Fermi level of graphene.