Abstract
We propose and demonstrate a dynamic Brillouin optical fiber sensing based on the multi-slope assisted fast Brillouin optical time-domain analysis (F-BOTDA), which enables the measurement of a large strain with real-time data processing. The multi-slope assisted F-BOTDA is realized based on the double-slope demodulation and frequency-agile modulation, which significantly increases the measurement range compared with the single- or double- slope assisted F-BOTDA, while maintaining the advantage of fast data processing and being suitable for real-time on-line monitoring. A maximum strain variation up to 5000με is measured in a 32-m fiber with a spatial resolution of ~1m and a sampling rate of 1kHz. The frequency of the strain is 12.8Hz, which is limited by the rotation rate of the motor used to load the force on the fiber. Furthermore, the influence of the frequency difference between two adjacent probe tones on the measurement error is studied theoretically and experimentally for optimization. For a Brillouin gain spectrum with a 78-MHz width, the optimum frequency difference is ~40MHz. The measurement error of Brillouin frequency shift is less than 3MHz over the whole measurement range (241MHz).
Highlights
Brillouin optical fiber sensing has attracted great interest since 1990s [1]
Peled and coauthors proposed a frequency-agile method based on a pre-programming of arbitrary wave generators (AWG) to realize fast BOTDA (F-BOTDA), where a 100-Hz strain was measured with 1-m spatial resolution over a 100-m fiber [18]
A high-spatial-resolution F-BOTDA based on differential double-pulse and second-order sideband modulation was proposed by our group, where a measurement of 50-Hz vibration with the spatial resolution of 20cm in a 50-m polarization maintaining (PM) fiber was realized [22]
Summary
Brillouin optical fiber sensing has attracted great interest since 1990s [1]. Excellent researches have been carried out to extend the sensing range [2,3,4,5,6] and improve the spatial resolution [7,8,9,10,11,12]. The BFS is demodulated via curve fitting in the frequency-scanning methods above It is time-consuming and generally takes much more time than data acquisition, especially for the long range sensing, which makes them not suitable for the real-time on-line monitoring, even though high efficient compiled programing techniques (such as C and Cpp) are employed in curve fitting algorithms. We propose a dynamic distributed Brillouin sensing based on multi-slope assisted fast BOTDA, which is capable of extending the measurement scale significantly. This method employs a frequency-agile method to generate a multi-tone probe wave, which forms multiple slopes of BGS in the FUT and extends the measurement range of strain from single slope to several slopes. The measurement error of the BFS is less than 3MHz over the whole measurement range (241MHz)
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