Enhanced range of the dynamic strain measurement in phase-sensitive OTDR with tunable sensitivity.

Phase-sensitive optical time domain reflectometry (Phi-OTDR) realizes quantitative measurement of the dynamic strain employing phase demodulation. Unfortunately, it is difficult to measure the large dynamic strain with the conventional Phi-OTDR due to the restriction of the unwrapping algorithm. In this work, an approach based on two-wavelength probe is proposed and demonstrated to improve the measurable range of the dynamic strain in Phi-OTDR. By utilizing the difference between the two phases acquiring with two different lasers, the large dynamic strain can be recovered. In experiments, dynamic strains with peak values from 10.32 u epsilon to 24.08 u epsilon are retrieved accurately, which cannot be recovered with the conventional Phi-OTDR. Moreover, the tunable sensitivity is also demonstrated through adjusting the wavelengths of the probe. With the increment of the wavelength interval from 9.06 nm to 23.06 nm, the normalized sensitivity increases from 0.4 to 1 accordingly. That agrees well with the theoretical prediction. Foreseeably, the proposed method will extend the scope of application fields for Phi-OTDR, which requires large dynamic strain recognition. (C) 2019 Optical Society of America under the terms of the OSA Open Access Publishing Agreement