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Abstract
Phase-sensitive optical time-domain reflectometry (Φ-OTDR) has attracted numerous attention due to its superior performance in detecting the weak perturbations along the fiber. Relying on the ultra-sensitivity of light phase to the tiny deformation of optical fiber, Φ-OTDR has been treated as a powerful technique with a wide range of applications. It is fundamental to extract the phase of scattering light wave accurately and the methods include coherent detection, I/Q demodulation, 3 by 3 coupler, dual probe pulses, and so on. Meanwhile, researchers have also made great efforts to improve the performance of Φ-OTDR. The frequency response range, the measurement accuracy, the sensing distance, the spatial resolution, and the accuracy of event discrimination, all have been enhanced by various techniques. Furthermore, lots of researches on the applications in various kinds of fields have been carried out, where certain modifications and techniques have been developed. Therefore, Φ-OTDR remains as a booming technique in both researches and applications.-
Keywords:
- optical fiber sensors /
- Ф-OTDR /
- phase demodulation /
- application research
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References
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Figure 1.
The setup of DVS-Φ-OTDR system based on direct detection.
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Figure 2.
The setup of DAS-Φ-OTDR system with different demodulation methods.(a) Heterodyne detection + IQ phase demodulation. (b) Heterodyne detection + Hilbert transform phase demodulation. (c) Direct detection + phase demodulation based on a 3×3 coupler. (d) Direct detection + phase demodulation based on PGC.
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Figure 3.
Operation principle of Φ-OTDR based VSP monitoring system. (a) Zero-offset VSP. (b) Walk-away VSP.
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Figure 4.
(a) Normalized strain (green curve) recorded during an Mb ~6.2 (USGS) earthquake (Kota Ternate, Indonesia, 2015-03-17 22:12:28 UTC, 1.669°N; 126.522°E, 44 km depth) superimposed with the normalized velocity record (red curve) from the broadband station RAH (80 m from the optical cable). (b) Zoom-view from (a) showing a good phase correspondence between seismometer velocity record and DAS strain records at a 20s period. (c) Short record (6 s) of strain phases from a local earthquake trapped in the fault damage zone. Waves inside and outside the fault zone have different apparent velocities. Figures reproduced from ref.98, under a Creative Commons Attribution 4.0 International License.
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Figure 5.
(a) Stacked DAS beam trace (black) filtered to various bands between 0.02 and 1 Hz compared with amplitude-normalized particle velocity from a broadband seismometer rotated into the mean azimuth of the DAS array (red). (b) Separation of ocean and seismic waves in the first quadrant of the logarithmic space of the Φ-OTDR signal frequency-wave number domain. Figures reproduced from ref.101, under a Creative Commons Attribution 4.0 International License.
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Figure 6.
Ambient noise based, cross-correlation computed between all Φ-OTDR traces of the cable with respect to one arbitrary trace (at position ~11.5 km) showing several geological features. Figure reproduced from supplementary material of ref.98 under a Creative Commons Attribution 4.0 International License.
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Figure 7.
Experimental site layout. Figure reproduced from ref.103, under a Creative Commons Attribution 4.0 International License.
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Figure 8.
Fiber cable layout and operation principle of 1D-CNN. Figure redrawn after ref.192.
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Figure 9.
An illustration of the railway safety monitoring experiments. Figure reproduced from ref.108, under the OSA Open Access Publishing Agreement.
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Figure 10.
Fiber cable layout alongside railways. Figure redrawn after ref.113.
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Figure 11.
Integration of Φ-OTDR system in the DWDM communication network. Figure reproduced with permission from ref.116, IEEE.
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Figure 12.
Experimental setup for discharge detection with two acoustic transducers attached to the 40 kV joint. (Figure redrawn after ref. 119)
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Figure 13.
Fiber deployment inside or outside electrical cable. (Figure redrawn after ref. 120)
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Figure 14.
(a) Fiber coil transducer deployment on the GIS device. (b) Detected discharge signal of transducer #1, #2 and #3 at pulse repetition rate of 10 kHz. Figure reproduced from ref. 121, under a Creative Commons Attribution 4.0 International License.
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Figure 15.
(a) Φ-OTDR system configuration. (b) Tree infestation sensing results. (Figure reproduced from ref.182, under a Creative Commons Attribution 4.0 International License.
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Figure 16.
(a) Cross section of the MCF. The circled fiber cores were selected for bending direction analysis. (b) Fiber bending direction analysis in the x-y-ε space. The x-yplane corresponds to one cross section of the MCF. Figure reproduced from ref.181, under the OSA Open Access Publishing Agreement.
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Figure 17.
(a) Operation principle of the Φ-OTDR based solar irradiance sensing system. (b) Temperature difference between the black and reference fiber vs. the applied solar irradiance. Figure reproduced from ref.183, under a Creative Commons Attribution 4.0 International License.
