Highly Efficient Phase-Matched Third Harmonic Generation From Mid-IR to Near-IR Regions Using an Asymmetric Plasmonic Slot Waveguide

We theoretically propose an asymmetric plasmonic slot waveguide (APSW) with a thin silicon nanocrystal (Si-nc) layer and a thinner silicon layer that fills the bottom and the top of the metallic slot region to increase third-harmonic generation (THG) efficiency. The needed modal phase-matching condition is satisfied with properly mode dispersion engineering by exploiting the waveguide geometrical parameters. Combining the asymmetric waveguide structure and the high third-order susceptibility of the nonlinear materials, efficient phase-matched THG from mid-infrared (IR) to near-IR regions is realized. Then, the THG performance was further improved by increasing the silicon slot width wherein the THG nonlinear coefficient as large as 21452 is achieved. The corresponding THG efficiency comes up to 0.5% at a waveguide length of 9.3 with a pump power of 1 W.