Real time dynamic strain monitoring of optical links using the backreflection of live PSK data

摘要

A major cause of faults in optical communication links is related to unintentional\udthird party intrusions (normally related to civil/agricultural works) causing fiber breaks or\udcable damage. These intrusions could be anticipated and avoided by monitoring the dynamic\udstrain recorded along the cable. In this work, a novel technique is proposed to implement realtime\uddistributed strain sensing in parallel with an operating optical communication channel.\udThe technique relies on monitoring the Rayleigh backscattered light from optical\udcommunication data transmitted using standard modulation formats. The system is treated as a\udphase-sensitive OTDR (ΦOTDR) using random and non-periodical non-return-to-zero (NRZ)\udphase-shift keying (PSK) pulse coding. An I/Q detection unit allows for a full (amplitude,\udphase and polarization) characterization of the backscattered optical signal, thus achieving a\udfully linear system in terms of ΦOTDR trace coding/decoding. The technique can be used\udwith different modulation formats, and operation using 4 Gbaud single-polarization dual PSK\udand 4 Gbaud dual-polarization quadrature PSK is demonstrated. As a proof of concept,\uddistributed sensing of dynamic strain with a sampling of 125 kHz and a spatial resolution of\ud2.5 cm (set by the bit size) over 500 m is demonstrated for applied sinusoidal strain signals of\ud500 Hz. The limitations and possibilities for improvement of the technique are also discussed.