Dynamic Strain Measurement Using Small Gain Stimulated Brillouin Scattering in STFT-BOTDR

Bo Li,Jize Yan,Linqing Luo,Kenichi Soga,Yifei Yu

doi:10.1109/jsen.2017.2657119

Abstract

A distributed dynamic strain measurement is demonstrated using small gain stimulated Brillouin scattering (SBS) in Brillouin optical time domain reflectometry based on the short-time Fourier transform algorithm. The input power limits, frequency uncertainties for given pulse durations, fiber lengths, and the number of averaging are calculated. The output signal power and the signal-to-noise ratio of the system output are enhanced by SBS. It is found that the signal processing is faster and requires fewer averaging to achieve dynamic sensing performance along the fiber under test. A 60-Hz vibration on a 6-m fiber section at the end of a 935-m fiber is detected with the spatial resolution of 4 m with a sampling rate of 2.5 kS/s.

Highlights

I N RECENT years, structural health monitoring (SHM) is becoming critical in structural and geotechnical engineering applications [1]
The dynamic strain measurement by Brillouin optical time-domain reflectometry (BOTDR) is experimentally verified with 60Hz vibration frequency on a shaker
The spatial sampling resolution is set to 0.4m by setting the step of Short-time Fourier transform (STFT), which means that there is a Brillouin frequency shift (BFS) result along the fiber in every 0.4m

Summary

Introduction

I N RECENT years, structural health monitoring (SHM) is becoming critical in structural and geotechnical engineering applications [1]. Distributed fiber optic sensing technology, as an effective method of SHM, has the advantages of long sensing distance, distributed sensing information and small sensor size [2]. Rayleigh and Brillouin based distributed fiber optic sensors have been developed to monitor distributed temperature and strain information for decades [3]–[5]. Phase-sensitive optical time domain reflectometry (phase-OTDR), the most studied Rayleigh based dynamic system, has been proved to be capable of detecting strain vibration as accurate as 0.08με [7]. It can only give relative strain between two strain conditions [8], [9]. Phase-OTDR has a limited strain range of as low as 2 με [8], and its linearity between phase and strain is sensitive to the intrinsic phase of the fiber [7], [8]

Methods

Results

Conclusion