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

An up to 1100°C and 1200°C high-temperature distributed Brillouin sensing based on a GeO2-doped single mode fiber (SMF) and a pure-silica photonics crystal fiber (PCF) are demonstrated, respectively. We found that the BFS dependence on temperature of SMF and PCF agrees well with an exponential function instead of a linear function, which is mainly attributed by the change of the acoustic velocity in a silica fiber. A Brillouin frequency shift (BFS) hopping is observed in both kinds of fiber between 800°C–900°C in the first annealing process and after that the BFS exhibits the stability and repeatability with a measurement accuracy as high as ±1.42°C for SMF and ±2.6°C for PCF, respectively. The BFS hopping is a highly temperature-dependent behavior, which means that a high-temperature (> 800°C) would accelerate the process of BFS hopping to reach a stable state and after BFS hopping, both SMF and PCF shows good repeatability from 1000°C to 1100°C and 1000°C to 1200°C without annealing. The process of coating burning of 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 coating burning (272°C–564°C).