Infrared sulfide fibers for all-optical gas detection

A review of our work on all-optical gas sensors is presented with an emphasis on the development of both new infrared (IR) sources and IR to visible converters. Many radicals spectroscopic signatures associated to gases of interest are in the 2.5 -15 μm spectral range (4000-350 cm-1). This spectral domain matches rare-earth ions emissions when embedded into chalcogenide glasses which are well- known for having low phonon energies. We present here results concerning the development of IR sources and IR to visible converters based on rare earth doped chalcogenide fibers. The development of all-optical gas sensors in the 3 to 5 µm spectral range is described showing IR signal conversion into visible light using specific excited state absorption mechanisms in rare earth doped materials. This wavelength conversion enables the use of silica fibers to transport the “gas” signal over large distances considerably increasing the scope of possible applications. An example of all-optical sensor using this photon conversion is presented in the case of CO2 detection. The implementation of this type of sensor for different gases such as methane is finally discussed. This all-optical sensor can be typically used over a kilometer range, with sensitivity around hundreds of ppm with cost effective detection heads, making this tool suitable for field operations. Finally, the photon conversion at the heart of this all-optical sensor is discussed as a general mean to detect infrared radiations avoiding the use of infrared detectors for a large span of applications.