Brillouin Frequency Shift of Fiber Distributed Sensors Extracted from Noisy Signals by Quadratic Fitting

Abstract

It is a basic task in Brillouin distributed fiber sensors to extract the peak frequency of the scattering spectrum, since the peak frequency shift gives information on the fiber temperature and strain changes. Because of high-level noise, quadratic fitting is often used in the data processing. Formulas of the dependence of the minimum detectable Brillouin frequency shift (BFS) on the signal-to-noise ratio (SNR) and frequency step have been presented in publications, but in different expressions. A detailed deduction of new formulas of BFS variance and its average is given in this paper, showing especially their dependences on the data range used in fitting, including its length and its center respective to the real spectral peak. The theoretical analyses are experimentally verified. It is shown that the center of the data range has a direct impact on the accuracy of the extracted BFS. We propose and demonstrate an iterative fitting method to mitigate such effects and improve the accuracy of BFS measurement. The different expressions of BFS variances presented in previous papers are explained and discussed.

A Novel Method of Spectra Processing for Brillouin Optical Time Domain Reflectometry

“…Brillouin reflectometry, in which the accuracy of deformations and temperatures determining depends on the accuracy of detecting the Brillouin gain spectra (BGS) [1] (preferably with the maximum signal-to-noise ratio (SNR)) and determining the frequency coordinate of its maximum value (Brillouin frequency shift (BFS)), is no exception. A lot of works [2][3][4][5] have been devoted to the sources of noise of the BGS and methods for their suppression.…”

Контроль Волс Методом Бриллюэновской Рефлектометрии: Проблемы И Возможные Решения

“…Что касается второй задачи (повышение достоверности сигнала сенсора), то точность системы в случае бриллюэновской рефлектометрии напрямую зависит от качества определения BFS. Исследованиям источников шумов, методов шумоподавления и получения более точных данных о BGS и BFS посвящены многочисленные работы [9][10][11][12][13][14][15][16][17][18][19][20]. Условно можно выделить два основных подхода к получению реального значения BFS.…”

Recent Advances in Brillouin Optical Time Domain Reflectometry

“…In 2018, Zheng et al deduced a new formula for estimating BFS measurement, allowing for both the data length of fitted points and the center deviation of the data range relative to the real frequency peak. Based on the above analysis, they proposed an iterative fitting method to improve the BFS measurement accuracy and enhance the SNR of the BOTDR system [81]. Besides, three different formulas of BFS standard deviation were respectively deduced in [79,80,81] and listed in Table 2 by considering different influence parameters.…”