Optical fibers based on special pure Ge20Se80 and Ge26As17Se25Te32 glasses for FEWS

Abstract For middle infrared fiber-optic evanescent wave spectroscopy, the single-index Ge20Se80 and Ge26As17Se25Te32 glass fibers are fabricated by a crucible method. The background optical loss in the Ge20Se80 fiber is 1.5 dB/m in the 5–7.8 μm spectral range (minimum is 0.9 dB/m at 7.1 μm), and that in the Ge26As17Se25Te32 fiber is 1 dB/m in the range of 5.5–8.5 μm (minimum is 0.65 dB/m at 6.6 μm). On the basis of these chalcogenide glass fibers, the middle infrared sensors with the different geometry of sensitive zone (straight, U-shaped form, one loop, two loops) are manufactured. By the example of diesel fuel, it is shown that when passing from the straight section of the sensitive zone to the double loop, the integrated intensity of the absorption bands increases by an order of magnitude. The method of regression analysis was applied to plot a calibration dependence for the additive concentration in diesel fuel in the range of 0.1–1 vol% using a U-shaped fiber sensor. The possibility of using the luminescent Pr(3+)-doped chalcogenide fiber as the source of mid-IR radiation for recording the absorption spectra of substances absorbing in the spectral range 4–5 μm is demonstrated.