A dynamic distributed Brillouin optical fiber pressure sensor based on frequency agility technology is proposed, and the performance of dynamic and static pressure sensing is experimentally demonstrated. A set of frequency-agile pump pulse sequences with single pulse duration of 250 ns are generated by an arbitrary waveform generator. The interval of the frequency sweep pulse sequence is 30 μs, the maximum repetition frequency is 18.2 kHz, and the average is 64 times. Double-coated single-mode fiber (SMF) is used as the sensing fiber to enhance the pressure sensitivity of Brillouin frequency shift (BFS), which the outer coating diameter is 3000 μm. The BFS pressure sensitivity of -3.32 MHz/MPa is achieved in the pressure range of 0-24 MPa, which is about 4.5 times that of SMF. The measurement time of the proposed optical fiber pressure sensing system is only 3.52 ms. Furthermore, the dynamic pressure measurement experiment is carried out, and the continuous measurement of the dynamic range of 6-0 MPa is achieved, and the dynamic distributed pressure measurement ability of the sensing system is verified.
A high resolution distributed dynamic strain sensing has been proposed and experimentally demonstrated based on the combination of Brillouin and Rayleigh scattering. The proposed scheme employs the same set of frequency-scanning optical pulses modulated through the frequency-agile technique for fast measurements. The Brillouin optical time domain analyzer (BOTDA) technology is used to provide absolute measurement benchmarks, while the phase-sensitive optical time domain reflectometer (φ-OTDR) technology is used to capture relative strain changes in details. Two groups of 100 Hz vibrations with different amplitude (300 nε and 250 nε) have been measured under two different absolute strains (1173.9 με and 525.3 Με), which allows for dynamic absolute strain measurement with a high resolution of 8.4 nε.
In view of the limitations of the traditional Brillouin optical time domain analysis (BOTDA) system such as low sampling rate, large transmission and storage space, a fast BOTDA scheme based on compressed sensing technology has been proposed to realize the random frequency sampling of Brillouin gain spectrum (BGS). The proposed scheme uses a data-adaptive sparse base obtained by the principle component analysis algorithm to realize the sparse representation of Brillouin spectrum. Then, it can be reconstructed successfully with orthogonal matching-pursuit algorithm. Compared with the traditional uniform spectrum sampling with a step size of 4 MHz, the proposed compressed sampling scheme can recover the BGS using 30% of the frequency. With fewer sampling frequencies, compressed sensing technology can improve the sensing performance of traditional fast BOTDA, including increasing the sampling rate by 3.3 times and reducing the amount of data storage by 70%.
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