Acquiring the large phase jumping beyond pi with phase unwrapping
assisted by auxiliary light in PHI-OTDR
Abstract
The absolute difference (phase jumping) between two adjacent phases
should be less than pi in order to accurately recover the phase signal
with traditional phase unwrapping algorithm, which limits the capability
of quantitative measurement for traditional PHI-OTDR. In this article, a
new process of phase unwrapping with an auxiliary light in coherent
PHI-OTDR is proposed, so the resolvable phase jumping is extended to a
larger value beyond pi and the capability of phase unwrapping is
improved. In this PHI-OTDR system, wrapped differential phases between a
reference position and the subsequent positions of fiber are firstly
acquired for all probe light pulses. And wrapped differential phases of
interleaving pulse sequence are unwrapped using the traditional phase
unwrapping algorithm. Then, positions where the differential phases are
correctly unwrapped are obtained from the discontinuously linear profile
of the phase change curves of the original probe light. Based on these
positions, the information of perturbation can be correctly retrieved.
In experiment, the new process of phase unwrapping with the auxiliary
for PHI-OTDR is executed and a perturbation signal which induces a
maximum phase jumping of 3.7154 rad is well reconstructed. More
experimental results all demonstrate the validity of the proposed
method.