Efficient Second Harmonic Generation via Plasmonic-Photonic Mode Matching in Hybrid Waveguide.

Hybrid nonlinear plasmonic waveguides, characterized by a small mode area and large nonlinear susceptibility, present an intriguing and practical platform for the minimization of nonlinear photonic devices. Nevertheless, the intrinsic Ohmic loss associated with surface plasmon polaritons (SPPs) and modal dispersion imposes constraints on the effective interaction length and, consequently, the ultimate efficiency of nonlinear processes. In this study, we demonstrate an efficient second harmonic generation (SHG) within a hybrid plasmonic waveguide by leveraging SPP-like modes at the fundamental wave and photonic-like modes at the SHG under phase matching conditions. The presence of photonic-like modes significantly reduces the SHG losses, while the SPP-like modes improve the modal overlap, resulting in SHG conversion efficiency up to 8.5% W cm in a 55 μm-long waveguide. Our findings offer new avenues for the minimization of nonlinear photonic devices on a chip.