  Broadband mid-infrared light sources are highly desired for wide-ranging
applications that span free-space communications to spectroscopy. In recent
years, silicon has attracted great interest as a platform for nonlinear optical
wavelength conversion in this region, owing to its low losses (linear and
nonlinear) and high stability. However, most research in this area has made use
of small core waveguides fabricated from the silicon-on-insulator platform,
which suffer from high absorption losses of the silica cladding, limiting their
ability to generate light beyond 3 ${\mu}$m. Here we design and demonstrate a
compact silicon core, silica clad waveguide platform that has low losses across
the entire silicon transparency window. The waveguides are fabricated from a
silicon core fibre that has been tapered to engineer the mode properties to
ensure efficient nonlinear propagation in the core with minimal interaction of
the mid-infrared light with the cladding. These waveguides exhibit many
benefits of fibre platforms, such as high coupling efficiency and power
handling capabilities, allowing for the generation of mid-infrared
supercontinuum spectra with high brightness and coherence spanning almost two
octaves (1.6-5.3 ${\mu}$m).
