Penadés, J SolerSánchez-Postigo, ANedeljkovic, MOrtega-Moñux, AWangüemert-Pérez, J GXu, YHalir, RQu, ZKhokhar, A ZOsman, ACao, WLittlejohns, C GCheben, PMolina-Fernández, IMashanovich, G Z2023-01-252023-01-252018http://hdl.handle.net/10668/12136In this Letter, we report suspended silicon waveguides operating at a wavelength of 7.67 μm with a propagation loss of 3.1±0.3  dB/cm. To our knowledge, this is the first demonstration of low-loss silicon waveguides at such a long wavelength, with loss comparable to other platforms that use more exotic materials. The suspended Si waveguide core is supported by a sub-wavelength grating that provides lateral optical confinement while also allowing access to the buried oxide layer so that it can be wet etched using hydrofluoric acid. We also demonstrate low-loss waveguide bends and s-bends.enAttribution 4.0 Internationalhttp://creativecommons.org/licenses/by/4.0/research article29443996open access10.1364/OL.43.0007951539-4794https://doi.org/10.1364/ol.43.000795