Te-​based glass fiber for far-​infrared biochemical sensing up to 16 μm

International audienceChalcogenide glass fibers are very suitable to carry out mid-​infrared spectroscopy by Fiber Evanescent Wave Spectroscopy (FEWS)​. Nowadays, selenide glasses are used for FEWS, but the reachable domain is limited in the infrared to typically 12 μm. Te-​rich glasses, due to their heavy atomic weight, are better for far-​infrared sensing but they crystallize easily and until now that was difficult to prepare operational optical fibers from such glasses. In this work, Te-​Ge-​AgI highly purified glasses have been prepared and successfully drawn into optical fiber. The minimum of attenuation is 3 dB​/m around 10 μm, which is up to now the lowest value ever measured for Te-​based fiber. Overall, such fibers open the sensing window up to 16 μm against 12 μm so far. Then, for the first time, tapered telluride fibers with different diameters at the sensing zone were obtained during the fiber drawing process. Chloroform and butter were used to test the fiber infrared sensing ability, and the sensitivity has been greatly enhanced as the sensing zone fiber diameter decreases. Finally, the new protocol of telluride glass preparation allows shaping them into efficient functional fibers, opening further in the mid-​infrared which is essential for chemical spectroscopy