Ge-on-Si waveguides for sensing in the molecular fingerprint regime

Low loss, single mode, Ge-on-Si rib waveguides are used to demonstrated optical sensing in the molecular fingerprint region of the mid-infrared spectrum. Sensing is carried out using two spin-coated films, with strong absorption in the mid-infrared. These films are used to calibrate the modal overlap with an analyte, and therefore experimentally demonstrate the potential for Ge-on-Si waveguides for mid-infrared sensing applications. The results are compared to Fourier transform infrared spectroscopy measurements. The advantage of waveguide spectroscopy is demonstrated in terms of the increased optical interaction, and a new multi-path length approach is demonstrated to improve the dynamic range, which is not possible with conventional FTIR or attenuated total reflection (ATR) measurements. These results highlight the potential for Ge-on-Si as an integrated sensing platform for healthcare, pollution monitoring and defence applications. Published by The Optical Society under the terms of the Creative Commons Attribution 4.0 License. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI.