Three-port graphene-based electromagnetic circulator in the terahertz and infrared frequency ranges with a very low loss and wideband response

Abstract

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° 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 (∼15%), small footprint (∼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 ∼1.8 dB. Also, due to the extremely confined hybrid surface plasmon polariton modes and large wavenumber (∼120k0) 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.