Circuit Modeling of the Modulator Based on a Plasmonic Waveguide

An electro-plasmonic modulator is modeled in this study based on a lossy plasmonic waveguide. The waveguide contains a graphene sheet sandwiched between two silicon dioxide layers. The switch operation is carried out using a pair of gates on the upper and lower sides of the waveguide. The fundamental mode of the waveguide, the characteristic impedance, and circuit elements are calculated by considering the losses when varying the Fermi level of graphene sheet. Especially, the loss of waveguide and the loss of discontinuity of graphene sheet conductivity are considered in this research. The transmission line elements for the plasmonic waveguide including a series inductor, a series resistor, a parallel capacitor, and a parallel conductor are calculated for different Fermi levels and frequencies. Thereafter, the discontinuity effect is investigated in the graphene conductivity. Its complex scattering matrix is extracted by considering the losses and the method of lines is used to solve the Maxwell's equations at the left and right borders for the first time. With the use of this circuit model, the transmission coefficient of the modulating device is monitored at several middle infrared wavelengths and at a few gate lengths and is compared with the Comsol simulation results.