Detection-Localisation-Identification of Vibrations over Long Distance SSMF using Coherent Phase-OTDR

We propose a novel interrogation technique for Distributed Acoustic Sensing (DAS) and demonstrate the detection and recognition of multiple vibration events over 50km of SSMF. A differential-phase optical time-domain reflectometry (diff-Phi OTDR) approach is used with the transmission of a continuous laser modulated with polarization-multiplexed orthogonal binary sequences and the reception of the backscattered signal through a polarization-diversity coherent mixer in a self-homodyne configuration. The detection of the full optical field vector and the use of an ultra-narrow-linewidth laser source enhance the sensitivity of the interrogating solution. A comparison of the experimental results to a simulation model is developped to better understand the noise limits. A low-complexity localization technique based on a multi-resolution approach is also presented. Major results include the identification of an engine noise, paving the way for numerous smart-city/industrial monitoring applications over deployed telecom fibers.