Dynamically Controllable Terahertz Graphene Y-Circulator

A new type of the graphene-based three-port circulator for the terahertz (THz) region is suggested and analyzed theoretically. The cross section of the component presents a three-layer structure consisting of the layers of graphene, silica, and silicon. The in-plane figure of the circulator consists of a circular graphene resonator and three waveguides symmetrically connected to it. The resonator is magnetized normally to its plane by a dc magnetic field. The working principle of the device is based on the dipole resonance of the magnetized graphene resonator. The numerical simulations are fulfilled by a full-wave computational program. For the analysis of the circulator, the analytical temporal coupled mode theory and circuit theory are also used. Numerical calculations demonstrate the isolation greater than -15 dB and the insertion loss better then -3 dB within the bandwidth of about 7.4% and the central frequency of 5.38 THz. At this frequency, the minimum of the insertion losses is -2.65 dB, and the maximum of isolation is -40 dB. The biasing dc magnetic field is 0.45 T, and the Fermi energy is EF = 0.15 eV. In our example, the diameter of the graphene resonator is 1.2 μm which corresponds to 0.0215λ
₀
where λ
₀
is the operating wavelength in the free space. The influence of geometrical and physical parameters of the circulator on its characteristics is discussed. The frequency band can be enlarged at the expense of higher dc magnetic field. The central frequency of the circulator can be adjusted by the Fermi energy of graphene through the electrostatic gating, and it allows one to control dynamically the circulator responses.