Mid-IR sensing platform for trace analysis in aqueous solutions based on a germanium-on-silicon waveguide chip with a mesoporous silica coating for analyte enrichment

A novel platform based on evanescent wave sensing in the 6.5 to 7.5 mu m wavelength range is presented with the example of toluene detection in an aqueous solution. The overall sensing platform consists of a germanium-on-silicon waveguide with a functionalized mesoporous silica cladding and integrated microlenses for alignment-tolerant back-side optical interfacing with a tunable laser spectrometer. Hydrophobic functionalization of the mesoporous cladding allows enrichment of apolar analyte molecules and prevents strong interaction of water with the evanescent wave. The sensing performance was evaluated for aqueous toluene standards resulting in a limit of detection of 7 ppm. Recorded adsorption/desorption profiles followed Freundlich adsorption isotherms with rapid equilibration and resulting sensor response times of a few seconds. This indicates that continuous monitoring of contaminants in water is possible. A significant increase in LOD can be expected by likely improvements to the spectrometer noise floor which, expressed as a relative standard deviation of 100% lines, is currently in the range of 10(-2) A.U. (C) 2020 Optical Society of America under the terms of the OSA Open Access Publishing Agreemen

Silicon-based photonic integrated circuits for the mid-infrared

AbstractSilicon-based photonic integrated circuits (PICs) operating in the mid-infrared wavelength range are presented. Firstly, it is shown that the operation of the SOI-based waveguide circuits can be pushed beyond the telecom window till a wavelength of 4μm. Ge-on-Si based PICs are demonstrated for operation beyond 4μm wavelength. Low-loss waveguides and integrated spectrometers are reported for both the waveguide platforms. We also present our results on efficient thermo-optic phase shifters for germanium waveguide circuits