Fluoride glass optical waveguides (ZBLAN) were coupled to a Fourier Transform Infrared Analyzer (FTIR) to execute remote IR chemical sensing. These fibers were used passively for only signal transmission, and the sensing was accomplished by direct or evanescent absorption of the fundamental modes corresponding to the desired chemical species. Due to the poor chemical and physical durability of fluoride glass, a crystal optrode (ZnSe) was used for evanescent wave absorption to isolate the fibers from the sensing environment. Several different types of chemical mixtures were studied to show the flexibility and limitations of such a system: 1) methane gas concentration in nitrogen using the C-H absorption at 3.31 um, 2) alcohol concentration in water using the C-H absorption at 3.36 um, and 3) water concentration in 1,4 dioxane using the 0-H fundamental stretching mode at 2.9 um. The last mixture proved to be the most difficult to analyze due to the low transmission of the fluoride fiber system in the 2.9 um region.
Steven J Saggese,
Mahmoud R Shahriari,
George H Sigel,
"Fluoride Fibers For Remote Chemical Sensing", Proc. SPIE 0929, Infrared Optical Materials IV, (18 July 1988); doi: 10.1117/12.945858; https://doi.org/10.1117/12.945858