8 March 2014 OTDR and OFDR for distributed multi-parameter sensing
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The drive for high spatial resolution (millimeters) distributed fiber sensors has renewed the interest in optical frequency domain reflectrometry (OFDR) systems. Because millimeters equivalent spatial resolution in optical time domain reflectrometry (OTDR) systems would require a data acquisition card with a bandwidth of 10 GHz and a sampling rate of tens of G Samples/s, such a digitizer or data acquisition card plus the pulse generator and detection system will make a distributed sensors very expensive, while a tunable laser with a wide tuning range can provide millimeters resolution with short sensing range (<100m). We developed a high precision temperature (0.1°C) and strain (1μ strain) resolution and 2.5mm spatial resolution over 180m range by auto and cross-correlation of OFDR in PMF. The dual modes of PMF allow the discrimination of the temperature and strain with distinct dependency. The application of this sensor for internal crack detection of concrete beam has been demonstrated. For distributed dynamic measurement, the upper frequency is limited by the repetition rate of the laser pulse in sensing fiber; in addition the weak Rayleigh scattering signal demands many averaging to improve SNR. The continuous wavelet transform approach has been introduced in phase OTDR sensor system to suppress random noise, and multiple vibration disturbances have been measured simultaneously for power generator monitoring. For the high frequency vibration detection, the coherent detection combined with polarization diversity scheme is implemented.
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Xiaoyi Bao, Xiaoyi Bao, Wenhai Li, Wenhai Li, Zengguang Qin, Zengguang Qin, Liang Chen, Liang Chen, "OTDR and OFDR for distributed multi-parameter sensing", Proc. SPIE 9062, Smart Sensor Phenomena, Technology, Networks, and Systems Integration 2014, 906202 (8 March 2014); doi: 10.1117/12.2045807; https://doi.org/10.1117/12.2045807

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