Abstract
The possibility of the tunable terahertz (THz) wave generation by the mid-infrared (MIR) frequency down-conversion (DC) and the up-conversion (UC) of MIR to near-IR (NIR) via the nonlinear wave-mixing in graphene ribbon metasurfaces (GRMs) are numerically investigated using the perturbation method for solving the nonlinear diffraction problems. First, we designed the linear spectral properties of GRMs to support resonances of surface plasmon polaritons (SPP) modes in the MIR range by choosing the pump and signal frequencies equal to resonant frequencies of the fundamental and higher-order SPP modes, respectively. The results of numerical simulations of tuned nonlinear transmission spectra, i.e. the normalized powers of generated THz waves at the combination frequency <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$f_{3}=2f_{1}-f_{2}$</tex> or the intensity of the emitted NIR waves at the combination frequency <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$f_{3}=2f_{1}+f_{2}$</tex> for various values of chemical potential µc in the GRMs are obtained for the normally incident pump and signal waves with <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$s$</tex> - and <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$p$</tex> -polarization. The enhancement of efficiency of broadband THz wave generation by the MIR frequency DC and the MIR to NIR UC is shown to be several orders in magnitude upon decreasing the value of the chemical potential in the resonantly excited GRMs.
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