9 May 2018 Cost-effective laser source for phase-OTDR vibration sensing
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Self-injection locking, an efficient method to improve the spectral performance of semiconductor lasers without active stabilization, has already demonstrated its high potential for operation with single-longitude-mode fiber lasers. Recently, we have demonstrated significant line-narrowing (more than 1000 times) of the conventional low-cost DFB laser locked to an external fiber optic ring resonator. However, dynamical behavior of such a laser exhibits mode-hopping making its applications for distributed acoustic sensing rather questionable. In order to explore capacity of the injection locked laser for a phase-OTDR, we have designed a simple configuration of the injection locking DFB laser and applied it for detection and localization of perturbations with a phase-OTDR based distributed vibration sensor. The conventional DFB laser locked at critical coupling regime through fiber optic ring resonator of 3.75 m length (Free Spectral Range is 54.5 MHz) delivers CW mode-hoping free radiation with a linewidth of about ~5.0 kHz, i.e. ~200 times narrower than the linewidth of free-running laser. In combination with the moving differential processing algorithm such a laser is capable to provide high SNR distributed measurements of vibrations and dynamic strain perturbations. The fiber under test comprises three sections of standard single mode fiber, with a total length of ~4.5 km. Perturbations have been locally implemented into the test fiber at two positions using a shaker and a piezoelectric stretcher, respectively. In the first case, perturbations of the fiber induced by the shaker at a frequency of 815 Hz have been recognized as a peak in the recorded and processed traces with a signalto- noise ratio (SNR) of 12 dB over a 10 m resolution cell. In the second case, dynamical strain induced by the fiber stretcher over 40 m at a frequency of 3 kHz is shown in a similar pronounced peak with a signal-to-noise ratio (SNR) of 11 dB. These signatures are similar to the results obtained with a commercial 1 kHz linewidth laser employed with the same phase- OTDR setup. We believe that proposed solution could be a basis for development of a cost-effective phase-sensitive OTDR for distributed sensing specified for the distance up to tens of kilometers.
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C. A. López-Mercado, C. A. López-Mercado, J. Jason, J. Jason, V. V. Spirin, V. V. Spirin, J. L. Bueno Escobedo, J. L. Bueno Escobedo, M. Wuilpart, M. Wuilpart, P. Mégret, P. Mégret, D. A. Korobko, D. A. Korobko, I. O. Zolotovskiy, I. O. Zolotovskiy, A. A. Fotiadi, A. A. Fotiadi, } "Cost-effective laser source for phase-OTDR vibration sensing", Proc. SPIE 10680, Optical Sensing and Detection V, 106802S (9 May 2018); doi: 10.1117/12.2307683; https://doi.org/10.1117/12.2307683

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