Polarization-relevance noise compensation for an Φ-OTDR based optical communication network maintenance system

Optical network is the backbone of modern data communication. The relevant maintenance technologies are of fundamental importance if the reliability of optical communication network is required. However, traditional monitoring and diagnosing methods such as the Rayleigh back-scattering (RBS) based optical time-domain reflectometry (OTDR) and coherent OTDR (COTDR) are only suitable for static measurement. That means they cannot make early warning before serious failure is actually occurred. Recently, phase-sensitive OTDR (Φ-OTDR) has attracted more and more attentions for its high sensitivity and distributed vibration detection ability. Monitoring technology based on Φ-OTDR could capture disturbance event through vibrating field, which can preserve the optical communication fibre from being destroyed even when the threat event has not directly contacted with the network yet. Unfortunately, those installed telecommunication fibres have small but significant birefringence. Once any of the disturbance events leads to a local birefringence change, the polarization evolution of the Rayleigh back-scattering signal will be disturbed along the following fibre, which will result in the generation of polarization-relevance noise (PRN) and the failure of multi-point vibration events identification. An orthogonal-SOP pulse pair (OSPP) method has been proposed to compensate the polarization-dependence of Φ-OTDR, making the sensing technology purely phase-sensitive. Experimental result has shown that a noise suppression ratio of 8.2dB could be achieved. The proposed method can reduce PRN influence on Φ-OTDR without complicating the sensor scheme, which extends the potential of Φ-OTDR technology in optical communication network maintenance system.