Dynamic Measurements of 1000 microstrains using Chirped-pulse Phase Sensitive Optical Time Domain Reflectometry (CP-PhiOTDR)

Abstract

This work demonstrates the capabilities of Chirped pulse, phase-sensitive optical time domain reflectometry (CP-PhiOTDR) to measure large dynamic strains. Benefitting from the use of incoherent detection and single shot measurements, this technique can sample the fiber under test at rates limited only by the fiber length. Yet, for large strains it relies on incremental measurements, where each trace is cross-correlated with its predecessor to determine the relative change of strain. The individual increments are then integrated to provide the strain at the spatial point of measurement. Here, a 4 m section (out of a 210 m spool) was subjected to longitudinal vibration by a mechanical shaker. With a pulse repetition rate of 200 kHz, we present, for the first time to our knowledge, Rayleigh backscattering based distributed measurements of large and fast dynamic strains: from 150 µepsilon at a vibration frequency of 400 Hz to 1190 µepsilon (peak to peak) at 50 Hz over long single-mode fibers. Along with a detailed description of the implemented data processing, we also discuss some of the associated limitations.