Suitability of single-mode fluoride fibers for evanescent-wave sensing

An investigation of the suitability of monomode fluoride glass fibers for the sensing of fluid concentration by evanescent wave absorption in the mid-infrared spectral region is reported. The test system consisted of a HeNe laser ((lambda) equals 3.39 micrometers ), a polished semi- coupler, and a cooled PbSe detector. Evanescent wave absorption in isopropanol was measured for a range of cladding overlayer thicknesses. Results are in broad agreement with the predictions of a theoretical model based on a planar waveguide structure under similar conditions. Calculations based on this model indicate that more elaborate sensor designs are required in order to achieve sufficient sensitivity for the sensing of gaseous species.