In practical engineering applications, the real-time monitoring of structural physical field is very important, which requires overall performance improvements on the Brillouin optical fiber sensing, including fast measurement, quick data demodulation and small amount of data storage. A novel Brillouin optical time-domain analysis (BOTDA) scheme has been proposed based on compressed sensing and pattern recognition algorithms, which paves the way for the real time Brillouin optical fiber sensing. In order to test the sensing performance, the Brillouin gain spectrum is measured by the traditional fast BOTDA, where the frequency step and span are 4 MHz and 500 MHz, respectively. By employing the proposed algorithms, the strain information is directly obtained with only 35% of the full data, verifying the feasibility of real-time measurements.
Two types of fast Brillouin optical time-domain reflectometry (BOTDR) for dynamic strain measurements have been proposed and experimentally demonstrated based on the frequency-agile technology. Using the frequency-agile modulated reference wave, the spontaneous Brillouin gain spectrum (BGS) is fast scanned in the frequency domain. Then, the spontaneous BGS can be reconstructed in the time domain by employing the band-pass filter and envelope detection. The frequency-agile technology enables two fast frequency-modulation methods, optical frequency sweeping and optical chirp chain modulation. Based on these two methods, the proposed fast BOTDR allows for a distributed, one-end-access and dynamic strain measurements. Besides, the sensing performance is investigated with different experiment parameters. The dynamic strain with dozens of Hertz vibrating frequency is successfully measured for both fast BOTDR schemes, which shows the proposed fast BOTDR a bright prospect.
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%.
We propose and demonstrate a novel fast Brillouin optical time-domain analysis system using the coefficient K spectrum which is defined as the ratio of phase-shift and gain of Brillouin amplification, where K features linear response, immune to the variation of pump power and a wide measure range. For a 30ns-square pump pulse, the frequency span of K spectrum can reach up to 200MHz. In dynamic strain experiment, a multi-slope assisted K-BOTDA with the measured strain of 5358.3με and the vibration frequency of 6.01Hz and 12.05Hz are demonstrated.
A dynamic distributed Brillouin optical fiber sensing based on dual-modulation is proposed, in which the scanning of the Brillouin gain spectrum (BGS) is implemented by the combination of a single-frequency modulation and a frequency-agility modulation. The frequency of the single-frequency modulation is a little less than the Brillouin frequency shift of the fiber (∼10.8 GHz for silica fiber), while the tuning range of the frequency-agility modulation is required to cover only several-hundred MHz for the scanning of BGS, which can significantly reduce the bandwidth requirement for the arbitrary waveform generator and ultimately reduce the cost of dynamic Brillouin sensors. With a 30-m fiber, a 11.8-Hz strain is measured. The spatial resolution and the sampling rate are 1 m and 200 Hz, respectively.
We propose and demonstrate a dynamic Brillouin optical fiber sensing based on the multi-slope analysis, which features a large measurement range of strain and the capability of real-time data processing. The multi-slope analysis is realized by using the frequency-agility modulation and it can significantly increase the measurement range compared with the single-slope analysis, while maintaining the advantage of fast data processing time and suitable for real-time monitoring. In experiment, we performed a measurement of strain up to 5000 με with the frequency of 13 Hz by using a six-slope analysis.
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