Fig. 1. Schematic of sensor unit of grating array

Fig. 2. System schematics. (a) DAS system with grating array; (b) low-cost perimeter system

Fig. 3. Interference principles of systems. (a) DAS system; (b) low-cost perimeter system

Fig. 4. Schematic of frequency response test bench

Fig. 5. Demodulation effect of the system on 10 Hz vibration. (a) Time domain; (b) FFT spectrum

Fig. 6. Demodulation effect of the system on 20 Hz vibration. (a) Time domain; (b) FFT spectrum

Fig. 7. Demodulation effect the system on 50 Hz vibration. (a) Time domain; (b) FFT spectrum

Fig. 8. Demodulation effect of the system on 60 Hz vibration. (a) Time domain; (b) FFT spectrum

Fig. 9. Demodulation effect of the system on 80 Hz vibration. (a) Time domain; (b) FFT spectrum

Fig. 10. Effect of the system on 90 Hz vibration demodulation. (a) Time domain; (b) FFT spectrum

Fig. 11. System linearity test results

Fig. 12. Schematics of wall test environment. (a) Place where people knock; (b) place where optical cable is laid

Fig. 13. Time domain diagram of original knock signal

Fig. 14. Time domain diagram of knock signal after high-pass filtering

Fig. 15. STFT spectrum of knock signal

Fig. 16. Schematic of girth-vibration fiber optic cable hanging network experiment

Fig. 17. Data processing block diagram of perimeter system