Mid-infrared supercontinuum generation in a low-loss germanium-on-silicon waveguide

We experimentally demonstrate supercontinuum (SC) generation in a germanium-on-silicon waveguide. This waveguide exhibits propagation loss between 1.2 dB/cm and 1.35 dB/cm in the 3.6 μm-4.5 μm spectral region for both transverse electric (TE) and transverse magnetic (TM) polarizations. By pumping the waveguide with ∼200 fs pulses at 4.6 μm wavelength, we generate a mid-infrared (IR) SC spanning nearly an octave from 3.39 μm to 6.02 μm at the -40 dB level. Through numerical analysis of the evolution of the SC, we attribute the current limit to further extension into the mid-IR mainly to free-carrier absorption.