Nonlinear frequency conversions via weak surface polaritonic wave breaking in a hybrid plasmonic waveguide.

Material design and input field properties limit high-harmonic excitation efficiency of surface-plasmon polaritons (SPPs) in a nanoscopic device. We remedy these limitations by developing a concept for a plasmonic waveguide that exploits spatiotemporal control of a weak surface polaritonic field to create efficient four-wave mixing (FWM) and periodic phase singularities. Our configuration comprises four-level double -type atomic medium (4 As) doped in a lossless dielectric situated above a negative-index metamaterial (NIMM) layer. We report the coherent excitation and propagation of the multiple surface polaritonic shock waves (SWs) and establish the highly efficient frequency combs by surface polaritonic wave (SPW) breaking. Consequently, multiple FWM and periodic plasmonic phase singularity patterns generate through nonlinear self-defocusing control commensurate with the plasmonic noise within the atomic electromagnetically induced transparency (EIT) window. Our work introduces SW formation within the subwavelength scale and generates efficient nonlinear frequency conversion, thereby opening prospects for designing fast optical modulators and nonlinear plasmonic gates.