Dynamic Measurements of 1000 Microstrains Using Chirped-Pulse Phase-Sensitive Optical Time-Domain Reflectometry

Hari Datta Bhatta,Maria R Fernandez-Ruiz,Andres Garcia-Ruiz,Moshe Tur,Miguel Gonzalez-Herraez,Hugo F Martins,Luis Costa

doi:10.1109/jlt.2019.2928621

Hari Datta Bhatta, Maria R Fernandez-Ruiz + Show 5 more

Open Access

https://doi.org/10.1109/jlt.2019.2928621

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Abstract

This paper extends the capabilities of chirped-pulse phase-sensitive optical time-domain reflectometry to the measurement of large dynamic strains over hundreds of meters of standard single-mode fiber. Benefitting from single-shot strain measurements, this technique has already demonstrated dynamic strains of the order of submicrostrains with a sensitivity of picostrains-per-root-Hertz. Yet, for large dynamic strains, it relies on the accumulation of incremental measurements, where each trace is cross correlated with its predecessor to determine the relative change of strain. However, practical time records of measured high slew-rate applied perturbations contain disturbing outliers. We then detail and analyze a post-processing strategy to mitigate this limitation. Through this strategy, we are able to achieve for the first time (to our knowledge) high signal-to-noise Rayleigh-backscattering-based distributed measurements of large and fast dynamic strains of a longitudinally vibrating 4 m section at the end of 210 m of a single-mode fiber: from peak to peak 150-1190 με at vibration frequency of 400 Hz and 50 Hz, respectively.

Highlights

D ISTRIBUTED fiber optic sensors are currently of immense importance as they are capable of efficiently monitoring bridges, buildings, aircrafts and trains/railway tracks, preventing leakage and theft from oil and gas pipelines, and providing cost-effective perimeter protection [1]–[3].Manuscript received January 27, 2019; revised May 23, 2019 and June 26, 2019; accepted July 3, 2019
Δt is estimated from the two sub-traces by one of the common methods for time delay estimation [38], most frequently by the relatively fast cross-correlation of the two signals, hopefully resulting in a single distinctive peak whose horizontal location gives the value of Δt
The temporal density of outliers tends to grow with the signal slew rate, eventually limiting the performance envelope of this sensing method. As long as these outliers are rare and temporally isolated, they can be effectively eliminated by median filtering the individual strain differences, as demonstrated below

Summary

INTRODUCTION

D ISTRIBUTED fiber optic sensors are currently of immense importance as they are capable of efficiently monitoring bridges, buildings, aircrafts and trains/railway tracks, preventing leakage and theft from oil and gas pipelines, and providing cost-effective perimeter protection [1]–[3]. While Raman-based technologies, in general, are not suitable for strain sensing [1], Brillouin sensors are sensitive to both temperature and strain, and perform well along standard single-mode fibers [4] They are truly distributed and can reach tens of kilometers at the expense of very long measurement time. The paper presents and analyzes an innovative median-based post-processing strategy in an attempt to mitigate this limitation Through this strategy, we were able to achieve for the first time (to our knowledge) high signal-to-noise, Rayleigh-based distributed measurements of large and fast dynamic strains of a longitudinally vibrating 4 m section at the end of 210 m of a single mode fiber from 150 με (peak-to-peak) at a vibration frequency of 400 Hz to 1190 με at 50 Hz. Preliminary results of this work were presented at [37].

The Principle of the Technique

Adjustments Necessary for the Measurement of Large Dynamic Strains

THE EXPERIMENTAL SETUP

Outliers

The Measurement of Large Dynamic Strains

CONCLUSIONS