Journal
SENSORS
Volume 16, Issue 5, Pages -Publisher
MDPI
DOI: 10.3390/s16050681
Keywords
fiber optics sensors; remote sensing and sensors; scattering measurement; optical time domain reflectometry
Funding
- International Science and Technology Cooperation Program of China [2014DFA11170]
- National Natural Science Foundation of China [61475128]
- Key Grant Project of Chinese Ministry of Education [313049]
- Fundamental Research Fund for the Central Universities [2682014RC22]
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Phase-sensitive optical time domain reflectometry (Phi-OTDR) attracts much attention due to its capability of telling the type and position of an intrusion simultaneously. In recent decades, coherent Phi-OTDR has been demonstrated to realize long-distance detection. For coherent Phi-OTDR, there are three typical demodulation schemes in the reported studies. However, they still cannot realize real-time monitoring to satisfy practical demands. A simple and effective demodulation method based on self-mixing has been put forward to demodulate the beat signal in coherent Phi-OTDR. It not only saves a local electrical oscillator and frequency locked loop, but also demodulates the beat signal without residual frequency. Several vibrations with different frequency were separately applied at the same location of a 42.5 km fiber. The spatial resolution of 10 m and frequency response range from 8 Hz to 980 Hz have been achieved. The precise location with signal-to-noise ratio of 21.4 dB and broadband measurement demonstrate the self-mixing scheme can demodulate the coherent Phi-OTDR signal effectively.
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