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Broadband generation of terahertz waves via infrared frequency nondegenerate parametric down-conversion by nonlinear graphene arrays

To analyze the terahertz (THz) wave generation by the mid-infrared (MIR) frequency nondegenerate parametric downconversion (NPDC) process in graphene nanoribbon arrays (GNAs) the nonlinear simulations using the perturbation method for solving the nonlinear diffraction problems were performed. First, we find the resonant frequencies of surface plasmon polaritons (SPP) modes in GNAs using the calculated multimode linear absorption spectra of incident waves with s-, p-polarization. Then we select the graphene ribbon sizes to satisfy the excitation condition of the SPP modes in the MIR frequency range. We choose the frequencies of pump and signal waves equal to resonant frequencies of the fundamental and high order SPP modes of GNA, respectively. It is shown that the efficiency of the THz wave generation via frequency NPDC of MIR to THz by nonlinear graphene arrays increases by several orders of magnitude when the frequency of signal and pump waves are close to the resonant SPP mode frequencies.