Fig. 1. Experimental setup of BOTDA. (C, coupler; PC, polarization controller; EOM, electro-optic modulator; DC, direct current; AFG, arbitrary function generator; MG, microwave generator; PS, polarization scrambler; EDFA, erbium-doped fiber amplifier; FUT, fiber under test; FBG, fiber Bragg grating; PD, photodetector; OSC, oscilloscope)

Fig. 2. (a) Distributed high temperature measurement results of 50 m long SMF sensing fiber; (b) Comparison of the first and second measurement results; (c) Comparison and difference of the second and third measurement results; (d) Brillouin gain spectrum measured after annealing in the temperature range of 25-1100 ℃

Fig. 3. (a) Distributed measurement results of Brillouin frequency shift on photonic crystal fiber; (b) Comparison diagram of the first and second BFS measurements; (c) Comparison and the difference between the second and third measurements; (d) Brillouin gain spectrum measured after the first annealing in the range of 36-1200 ℃

Fig. 4. (a) Investigation of BFS hopping; (b) Comparison of two measurements under temperature region of BFS hopping

Fig. 5. (a) BFS results of 5 measurements at a single sensing point in steps of 50 ℃ from 100 ℃ to 1000 ℃; (b) Comparison diagram of BFS difference between two adjacent measurements with temperature change; (c) Comparison diagram of temperature coefficient from room temperature to 90 ℃ before and after annealing