Enhancing third harmonic generation using a mid-infrared graphene plasmonic waveguide

In this paper, based on the nonlinear property of graphene and placing a layer of graphene on a suitable substrate, a plasmonic waveguide is created to produce the third harmonic of the input light. The role of different parameters of monolayer graphene in the resonance property and the nonlinear conductivity of graphene are determined. Thus, the resonant frequency of the proposed structure is adjusted in the Terahertz range. In this paper, for the first time, a graphene-based nonlinear plasmonic waveguide is proposed to produce a third harmonic of the input signal. It is shown that by changing the electrochemical potential (mu(cg)) of graphene, the resonance behavior of the structure can be adjusted for optimizing the third harmonic generation which is based on nonlinear properties of the monolayer graphene. The FDTD method is applied to numerically simulate and analyze the proposed structure in the Terahertz and mid-infrared wavelengths ranges. Our simulations show an increase of more than six-order of magnitudes higher third harmonic generation can be observed in the proposed structure with respect to the simple structure. Using high quality graphene samples and Si3N4 dielectric waveguide improved the performance of the proposed structure if compared with a structure using graphene on a flat substrate. The outcome of this work can be used to develop a range of important applications such as new frequency generation, signal processing, spectroscopy, chemical sensing and switches in the terahertz frequency range.