Chalcogenide fibers for infrared sensing

Optical sensors based on chalcogenide glass fibers transparent in the mid infrared (MIR) spectral range from 2 to 16 μm (4000 to 625 cm^-1) have been developed in order to analyse biological and chemical samples. These sensors are based on the Fiber Evanescent Wave Spectroscopy (FEWS) principle. Indeed, most of the molecules have their functional groups absorption bands in the mid infrared region and the fibers are able to detect the characteristic vibrations these of molecules. First, fibers have been developed in the frame of large-scale projects such the DARWIN mission in order to permit the detection of CO₂ at 15 μm. A large activity was focused on the synthesis of Te-Ge-Se glasses, containing no more than 3% of Se but stable enough to draw fibers transmitting light until 16 μm. Then, single mode fibers have been successfully fabricated thanks to a new preform molding process. Finally, the growing need for sensors able to detect diseases in the medical domain or polluting molecules in the environmental area led us to develop very stable Te-Ge-AgI low loss fibers. These fibers have been implemented in FEWS experiments permitting detection of biomolecules, like sugars and lipids and emerging pollutants like benzene, and chloroform, in the spectral domain extending from 2 to 16 μm. To our knowledge, it is the first time that spectra are collected on such a wide range of wavelengths.