Fiber-Coupled Substrate-Integrated Hollow Waveguides: An Innovative Approach to Mid-Infrared Remote Gas Sensors.

In this study, an innovative approach based on fiberoptically coupled substrate-integrated hollow waveguide (iHWG) gas cells for the analysis of low sample volumes suitable for remote broad- and narrow-band mid-infrared (MIR; 2.5-20 μm) sensing applications is reported. The feasibility of remotely addressing iHWG gas cells, configured in a double-pass geometry via a reflector, by direct coupling to a 7-around-1 mid-infrared fiber bundle is demonstrated, facilitating low-level hydrocarbon gas analysis. For comparison studies, two iHWGs with substrate dimensions of 50×50×12 mm (L × W × H) and geometric channel lengths of 138 mm and 58.5 mm, serving as miniature light guiding gas cells, were fiber-coupled to a Fourier transform infrared (FT-IR) spectrometer enabling broadband MIR sensing. In addition to the fundamental feasibility of this concept, the achievable sensitivity towards several gaseous hydrocarbons and the reproducibility of assembling the fiber-iHWG interface were investigated.