Fig. 1. Time-frequency relationship of the OCC probe wave.

Fig. 2. (a) BLSs obtained from a 70 ns pulse (purple short dash–dot) and a 40 ns pulse (pink dashed line), resulting in the differential BLS (black line). (b) Simulated differential BLS (black line), measured differential BLS (red dots), and intrinsic BLS (blue dashed line) based on the DPP technique.

Fig. 3. Operation principle of how to employ the PCA algorithm to compute the fiber intrinsic BFS from the measured Brillouin signal in the OCC-BOTDA scheme.

Fig. 4. Experiment setup scheme of fast long-range BOTDA based on the OCC technique and Brillouin loss scheme. MG, microwave generator.

Fig. 5. (a) Brillouin time traces of the 70 ns (black curve) and 40 ns (red curve) pump pulses. (b) Brillouin time trace of the differential signal (blue curve). (c) BLSs obtained from (a) and (b). (d) The 40 and 70 ns pump pulses at the input end and the output end of the FUT.

Fig. 6. Measured BLS and the fitting result based on the PCA and QLS fitting methods: (a) PCA fitting result and (b) QLS fitting result at 1 km, (c) PCA fitting result and (d) QLS fitting result at 60 km, (e) PCA fitting result and (f) QLS fitting result at 100 km in the oven.

Fig. 7. 100 km sensing fiber BFS results of two algorithms: black curve is the QLS fitting result; red curve is the PCA fitting result.

Fig. 8. Temperature measurement in the last 268 m of the sensing fiber and the top view of the sensing fiber 3D Brillouin loss spectra (inset).