Controllable graphene W-shaped three-port THz circulator

Abstract

We propose a new graphene-based THz circulator. It consists of a circular graphene resonator and three graphene nanoribbon waveguides of W-geometry placed on a dielectric substrate. Surface plasmon-polariton waves propagate in the waveguides. The nanoribbon excites in the resonator dipole resonance. Nonreciprocity of the device is defined by nonsymmetry of the conductivity tensor of the magnetized graphene. Numerical simulation example present a circulator which operates at a central frequency of 7.5 THz has the bandwidth 4.25% for isolation −15 dB, insertion loss −2.5 dB. Applied DC magnetic field is 0.56 T and Fermi energy of graphene ϵF=0.15 eV. The frequency band of the circulator can be enlarged at the expense of higher DC magnetic field and its central frequency of operation can be tuned by varying resonator radius, nanostrips width, distance between the resonator and the waveguide. Fermi energy allows one to control dynamically the circulator responses.