1200°C high-temperature distributed optical fiber sensing using Brillouin optical time domain analysis

In this paper, up to 1100 degrees C and 1200 degrees C high-temperature distributed Brillouin sensing based on a GeO2-doped single-mode fiber (SMF) and a pure silica photonic crystal fiber (PCF) are demonstrated, respectively. The Brillouin frequency shift's (BFS) dependence on temperatures of the SMF and PCF agrees with a nonlinear function instead of a linear function, which is mainly due to the change of the acoustic velocity in a silica fiber. BFS hopping is observed in both kinds of fibers between 800 degrees C-900 degrees C in the first annealing process, and after that, the BFS exhibits stability and repeatability with a measurement accuracy as high as +/- 2.4 degrees C for the SMF and +/- 3.6 degrees C for the PCF. The BFS hopping is a highly temperature-dependent behavior, which means that a high temperature (>800 degrees C) would accelerate this process to reach a stable state. After BFS hopping, both the SMF and PCF show good repeatability for temperatures higher than 1000 degrees C without annealing. The process of coating burning of a silica fiber not only introduces a loss induced by micro-bending, but also imposes a compressive stress on the bare fiber, which contributes to an additional BFS variation at the temperature period of the coating burning (similar to 300 degrees C-500 degrees C). (C) 2016 Optical Society of America