Fig. 1. Schematic diagram of Brillouin gain spectrum measurement for BOCDA

Fig. 2. Working principle of BOCDA system^[47]. (a) Distribution of pump-probe beat spectrum near correlation peak (CP); (b) structure of BOCDA signal

Fig. 3. Experimental setup of sine-FM BOCDA system and distribution of Brillouin gain^[33]. (a) Experimental setup; (b) distribution of Brillouin gain

Fig. 4. Schematic illustration and experimental setup of BOCDA based on beat lock-in detection^[44]. (a) Schematic illustration; (b) experimental setup

Fig. 5. Schematic illustrations of differential measurement for BOCDA^[50]. (a) Construction of Signal 1 with ordinary pump wave; (b) construction of Signal 2 with phase-modulated pump wave; (c) differential measurement by analyzing the difference of Signal 1 and Signal 2

Fig. 6. Diagrams of BOCDA system using multiple correlation peaks. (a) Diagram of BOCDA system connecting different optical fibers^[57]; (b) diagram of BOCDA system with pump-probe switching^[59]

Fig. 7. Schematic diagrams of BOCDA system based on temporal gating. (a) Schematic illustration of temporal gating^[60]; (b) modulation scheme for BOCDA system based on double modulation and temporal gating^[50]

Fig. 8. Schematic illustration of modulation of BOCDA system with time-domain data processing^[62]

Fig. 9. Development process of Sine-FM BOCDA syetem

Fig. 10. Schematic diagram of phase-coded BOCDA^[40]

Fig. 11. Experimental setup of phase-coded BOCDA based on PRBS and distribution of Brillouin gain^[40]. (a) Experimental setup; (b) distribution of Brillouin gain of heated section

Fig. 12. Schematic diagram of phase modulation based on PSK^[66]

Fig. 13. Generation of phase-coded short optical pulse source and BFS distribution measured by short-pulse BOCDA^[67]. (a) PRBS phase-coded short optical pulse source generated by MLLD; (b) measured BFS distribution near 2 mm long fiber section

Fig. 14. Simulated acoustic wave density fluctuations and output signal power^[42]. (a) Simulated normalized magnitude |Q(z,t)| of stimulated acoustic wave density fluctuation; (b) simulated output signal power |A_s(z=0,t)|²

Fig. 15. Schemetic illustration of incoherent sequence compression and Brillouin gain of output signal^[43]. (a) Schemetic illustration; (b) Brillouin gain of output signal

Fig. 16. Results of double-pulse pair analysis^[77]. (a) Measurement results of output signal; (b) result of subtraction between two traces

Fig. 17. Measured normalized steady-state and transient Brillouin gains^[79]. (a) Measured normalized steady-state Brillouin gain; (b) measured normalized transient Brillouin gain

Fig. 18. Development process of phase-coded BOCDA syetem

Fig. 19. Experimental setup of BOCDA system based on ASE source, and distribution of measured BFS^[80]. (a) Experimental setup; (b) distribution of measured BFS

Fig. 20. Autocorrelation curve of chaotic laser^[83]

Fig. 21. Experimental setup of chaos-based BOCDA^[83]

Fig. 22. Distributed temperature sensing measurement results^[83]. (a) Distribution of BGS along FUT; (b) distribution of BFS along FUT

Fig. 23. Characteristic diagrams of chaotic laser in three typical states^[45]. (a) RF spectra; (b) autocorrelation traces; (c) correlation peaks with Gauss fitting

Fig. 24. Distributed strain sensing measurement results of broadband chaos-based BOCDA system^[45]. (a) Distribution of BGS along FUT; (b) distribution of BFS along FUT

Fig. 25. Autocorrelation characteristics of chaotic pump and measurement result of distributed temperature sensing^[86]. (a) Autocorrelation characteristics of chaotic pump light with and without amplitude pulse modulation; (b) measurement result of distributed temperature sensing

Fig. 26. Development process of broadband source-based BOCDA syetem