▎ 摘　　要

In this paper, the design process of a novel three-port graphene-based circulator in terahertz (THz) and infrared frequencies is presented. This new structure consists of three 120 degrees rotational symmetry branches of graphene-based single-mode waveguides coupled to a cavity resonator at the center. To achieve the nonreciprocity response in this structure, the anisotropic property of the graphene has been utilized in the cavity resonator. Owing to the low insertion loss, wide bandwidth (similar to 15%), small footprint (similar to subwavelength dimension), and simple configuration of our design, it is superior to other structures reported in the literature. The propagation loss of the graphene in the waveguide and energy loss in the graphene patch resonator have been efficiently controlled, and insertion loss is maintained near similar to 1.8 dB. Also, due to the extremely confined hybrid surface plasmon polariton modes and large wavenumber (similar to 120k(0)) of these modes, the proposed configuration has a very small footprint. For verification of the method of design, two circulators at 17 THz and 33 THz are designed in this paper, and the reported results demonstrate the excellent performance of the presented configuration. The structures were simulated using the finite element method by commercial COMSOL Multiphysics electromagnetic solver, while the graphene is considered as a surface sheet that carries surface current density. (C) 2018 Optical Society of America