Fig. 1. Simulation results of COTDR intensity curves. (a) I and Q components obtained by analog I/Q demodulation and by Hilbert transform; (b) intensity curves at different detection frequencies

Fig. 2. Flow chart of proposed optimization algorithm

Fig. 3. MF-COTDR sensing system and experimental scheme. (a) MF-COTDR sensing system; (b) schematic of pulse modulation scheme; (c) beat signal and PSD of P and S polarization in MF-COTDR system

Fig. 4. Test results of FUT dynamic strain spatiotemporal intensity for different phase demodulation algorithms. (a) Without frequency diversity; (b) MFD; (c) MFOD

Fig. 5. Analysis results of time-frequency characteristics. (a) Temporal domain response caused by PZT disturbance at 1025 m at five detection frequencies; s1, MFD, and MFOD demodulation of (b) temporal domain waveform and (c) PSD; (d) SNR calculation results of the whole optical fiber link

Fig. 6. Test results of frequency response. (a) Temporal domain waveform and (b) STFT of linear chirp signal; (c) spatiotemporal intensity map and (d) PSD of 5 Hz sin signal

Fig. 7. Response results of 5 Hz sin signal under different peak voltages