Improving the performance of nanostructure multifunctional graphene plasmonic logic gates utilizing coupled-mode theory

Nanostructure ring resonators are suitable devices for photonic integrated circuits. A nano-scale multifunctional logic device based on plasmon-induced transparency (PIT) is presented here. This device consists of a pair of hexagonal ring resonators coupled with two parallel metal-insulator-metal (MIM) waveguides. According to the coupled-mode theory, the appropriate detuning between the resonances wavelengths of two resonators acts as the key factor to achieve the PIT phenomenon. For this purpose, the PIT phenomenon for several metals utilized in MIM waveguides is studied. Also, graphene has been employed as the replacement for the metal under the hexagonal ring resonator and its parallel waveguides. However, the interaction of light with graphene as a 2D material is weak, by varying the dimensions of waveguides, rings, and their distances, and also, incident light wavelength and graphene chemical potential, we have achieved the desired couplings in the structure. Finite-difference-time-domain (FDTD) simulations confirm that "1" and "0" logic states which represent the high and low levels of the optical power can be achieved at the through and drop ports by changing the refractive index. It has been demonstrated that the proposed structure implements the function of logical operations including XOR and XNOR, simultaneously.