Silica hollow-core anti-resonant fiber for harsh environment mid-infrared sensing applications

Mid-infrared absorption spectroscopy is nowadays considered as a routine analysis and sensing tool providing highly discriminatory information on organic and inorganic molecules. The specific needs of the transport, aerospace or energy industries may involve applications for which the spectroscopic sensor has to withstand high temperatures. This paper reports the design and fabrication of a silica hollow-core anti-resonant fiber with 8 non touching capillaries primarily designed for mid-infrared CO_x sensing inside engines. Numerical and analytical simulations performed to ensure fiber transparency in the 4-5 µm region are reported. Optical transmission between 3.9 µm and 4.7 µm is observed and demonstrate attenuation below 1 dB/m for single capillary ring fibers in this range. A preliminary scheme for CO₂ sensing using a quantum cascade laser operating in one of the fiber’s transmission windows (λ=4.3 µm) is depicted.