… However, for longer wavelength applications that exist in the mid-infrared (MIR), such as
sensing of molecular vibrations in the 3-15 μm wavelength range requires a different
waveguide platform [1]. This is due to SiO2, which is not optically transparent and therefore
causes large waveguide losses. An alternative platform that has been suggested is Ge-on-Si.
This is an excellent candidate since both Si and Ge are broadly transparent over the full MIR. …
This represent an exciting perspective for MIR integrated silicon photonic sensing chips. …

Germanium-on-silicon waveguides are designed, fabricated and characterized with a novel
near-field infrared spectroscopy technique that allows on-chip investigation of the in-
coupling efficiency. On-chip propagation along bends and straight sections up to 0.8 mm is
demonstrated around λ= 6 μm.