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
$\hbox{m}^{-1} \cdot \hbox{W}^{-1}$
is achieved. The corresponding THG efficiency comes up to 0.5% at a waveguide length of 9.3
$\mu\hbox{m}$
with a pump power of 1 W.