Design and simulation of a compact graphene-based plasmonic D flip-flop

In this paper, a compact graphene-based plasmonic D flip-flop is presented where the graphene waveguides are sandwiched between two SnO2 layers. The structure includes two input ports CLK and D, and two output ports Q and Q'. The input signals transmit through the waveguides and interfere with other signals. A portion of input signal D appears at port Q, and another portion interferes with the incoming signal from port CLK then is guided toward port Q'. The commercial Lumerical software is used to solve Maxwell’s equations and simulate the propagation of terahertz waves. The finite difference time domain method is used to calculate the electric and magnetic components of waves throughout the structure. The structure is studied at the transverse magnetic mode, and the perfectly matched layer is assumed at boundaries. The wavelength is assumed from 12.7 µm to 13.1 µm, and the area of the structure is 0.83 µm2. The small area of the designed flip-flop is an essential feature for use in optical integrated circuits. The contrast ratio of outputs Q and Q' is about 7.3 dB and 13 dB, respectively which is more than the previous work. In comparison to the last work which had one port for signal Q, two output ports for signals Q and Q' are designed in this work. This feature is needed for employing the flip-flop at sequential circuits.