Multifunctional resonant graphene four-port for THz and far IR regions

A new multifunctional resonant device for THz and far-infrared regions based on surface plasmon-polariton graphene resonator and waveguides is suggested and analyzed in this paper. The device consists of a circular graphene resonator and four nanoribbons serving as waveguides. Every waveguide is front-coupled to the resonator with a small gap between them. The waveguides are oriented with the angle 90∘ between them. The graphene elements are deposited on a dielectric substrate. The Fermi energy of graphene can be dynamically varied by applying an electrical potential difference between the graphene and a thin polysilicon layer which acts as an electrode. The resonator can work with dipole and quadrupole resonant modes. They are used to provide the functions of tunable band-pass filter, tunable power divider and switch. Using the scattering matrix description of the four-port, the circuit theory representation and full-wave analysis, we show that for the central frequency 14.52 THz the parameters of the developed device are as follows: the Q-factor due to use of resonant structure is (6÷8), the matching in the pass-band with return loss of − 17 dB and low insertion loss of about − 1.0 dB. The component provides a tunability of the central frequency and the power ratio between the three output ports can be projected in a wide range. In the OFF regime, the transmission coefficients to output ports are lower than − 42 dB.