Analysis of Phase-Shift Pulse Brillouin Optical Time-Domain Reflectometry.

Tsuneo Horiguchi,Yuki Masui,Mohd Zan

doi:10.3390/s19071497

Abstract

Distributed strain and temperature can be measured by using local Brillouin backscatter in optical fibers based on the strain and temperature dependence of the Brillouin frequency shift. The technique of analyzing the local Brillion backscatter in the time domain is called Brillouin optical time domain reflectometry (BOTDR). Although the best spatial resolution of classic BOTDR remains at around 1 m, some recent BOTDR techniques have attained as high as cm-scale spatial resolution. Our laboratory has proposed and demonstrated a high-spatial-resolution BOTDR called phase-shift pulse BOTDR (PSP-BOTDR), using a pair of probe pulses modulated with binary phase-shift keying. PSP-BOTDR is based on the cross-correlation of Brillouin backscatter and on the subtraction of cross-correlations obtained from the Brillouin scatterings evoked by each phase-modulated probe pulse. Although PSP-BOTDR has attained 20-cm spatial resolution, the spectral analysis method of PSP-BOTDR has not been discussed in detail. This article gives in-depth analysis of the Brillouin backscatter and the correlations of the backscatters of the PSP-BOTDR. Based on the analysis, we propose new spectral analysis methods for PSP-BOTDR. The analysis and experiments show that the proposed methods give better frequency resolution than before.

Highlights

Brillouin scattering occurs via the interaction of light with acoustic waves in a medium; this interaction causes a frequency shift, called a Brillouin frequency shift (BFS), due to the Doppler effect
We have derived an expression for the complex spectrum obtained by the high-spatialBOTDR called PSP-Brillouin optical time domain reflectometry (BOTDR), and have explained the principle of PSP-BOTDR theoretically
We have proposed the use of new spectra—a real part and an imaginary the complex spectrum

Summary

Introduction

Brillouin scattering occurs via the interaction of light with acoustic waves in a medium; this interaction causes a frequency shift, called a Brillouin frequency shift (BFS), due to the Doppler effect. A recent article reported the dependency of the BFS for guided acoustic-wave Brillouin scattering (GAWBS) on the mechanical impedance of substances outside the cladding of optical fibers [2]. Based on the BFS characteristics and spatially-resolved BFS measurement techniques, various types of distributed fiber-optic strain and temperature sensors based on Brillouin scatterings have been reported. They include fiber sensors using backward stimulated Brillouin scattering (SBS) and spontaneous. SBS-based sensors need to access both ends of the fiber to transmit counter propagating pump and probe lights through the fiber, which makes it difficult to apply

Methods

Results

Conclusion