Distributed acoustic sensing based on pulse-coding phase-sensitive OTDR

Phase-sensitive optical time-domain reflectometry (Φ-OTDR), which utilizes the phase information of Rayleigh scattered lightwave inside optical fiber, could turn a fiber cable into a massive sensor array for distributed acoustic sensing (DAS), i. e., an emerging infrastructure for Internet of Things. Given a certain fiber length, there are trade-offs among the sensing bandwidth, the sensitivity and the spatial resolution. In this paper, the concept of linearization and Golay pulse-coding for heterodyne Φ-OTDR are proposed and experimentally verified for the first time. Firstly we gave a full theoretical treatment on how an intensity-coded yet phase-retrieved Φ-OTDR can be built up as a fully linear system, therefore a significant enhancement of signal to noise ratio becomes viable and the sensing bandwidth keeps equal the four-times averaging case. Secondly in the proof-of-concept experiment, submeter gauge length and nano-strain resolution were realized with 10 km sensing range, in other words, more than ten thousand sensitive sensing units were realized along the fiber. This work makes a significant step towards high-performance DAS with orders-of-magnitude performance enhancement.