Enhanced Green Light Emission from a Silicon-Based Metal-Encapsulated Nanoplasmonic Waveguide

Integrated silicon plasmonic circuitry is becoming integral for communications and data processing. One key challenge in implementing such optical networks is the realization of optical sources on silicon platforms, due to silicon's indirect bandgap. Here, we present a silicon-based metal-encapsulated nanoplasmonic waveguide geometry that can mitigate this issue and efficiently generate light via third-harmonic generation (THG). Our waveguides are ideal for such applications, having strong power confinement and field enhancement, and an effective use of the nonlinear core area. This unique device was fabricated, and experimental results show efficient THG conversion efficiencies of η = 4.9 × 10^-4, within a core footprint of only 0.24 μm². Notably, this is the highest absolute silicon-based THG conversion efficiency presented to date. Furthermore, the nonlinear emission is not constrained by phase matching. These waveguides are envisioned to have crucial applications in signal generation within integrated nanoplasmonic circuits.