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.