2016, Habisreuther, Tobias, Elsmann, T., Graf, A., Schmidt, M.A.

Strain sensor designs and strain measurements based on single-crystal sapphire fibers with inscribed first-order fiber Bragg gratings for applications up to 600 °C are presented. We report on all the details of two different sensor designs; for instance, we show that the resolution of multimode sapphire fiber Bragg grating (SFBG) strain sensors is about l / l = ¼ 10-5 (10 µstrain), which is comparable with state-of-the-art high-temperature sensors. We apply our sensors for the determination of the thermal expansion coefficients of high-temperature steel alloys, showing a good match to known values. Hence, we believe that SFBG sensors may represent a promising alternative to currently used non-optic-based strain-detecting devices.