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Three-dimensional vibration frequency spectra for the sensing fiber ranging from 10.37km to10.65km at the working frequency points of 10.815GHz (a), 10.831GHz (b), 10.845GHz (c) and 10.865GHz (d).
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A BOTDA sensing scheme combined frequency sweeping and slope-assisted techniques is proposed and experimentally demonstrated for simultaneously temperature and strain-induced vibration sensing. In this scheme, during sweeping Brillouin gain spectrum (BGS) for temperature measurement, we simultaneously perform FFT to the time-domain traces whose pro...
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Citations
... This method can transform the BFS into the signal intensity without involving the scanning frequency, thereby possessing the advantages of high sampling frequency and simple operation. Meanwhile, the measurement range of the dynamic strain in this technique strongly depends on the bandwidth of the BGS (approximately 40 MHz), being limited to less than 1000 µε in the SMF [14]. In 2017, a vector BOTDA system combined with a multi-SA method and the FAT has been introduced, enabling one to detect the dynamic strain up to 5372.9 µε [15]. ...
In this Letter, a method for measuring large dynamic strain via slope-assisted Brillouin optical time domain reflectometry (SA-BOTDR) is proposed. A linear artificial slope created by a frequency equalizer is used instead of the traditional slope of the Brillouin gain spectrum (BGS) as the linear response region between the Brillouin frequency shift (BFS) and signal intensity. This method makes the strain measurement range independent of the bandwidth of the BGS. The large dynamic strain with a maximum value of 3108 µε and the spatial resolution of 5 m along the ∼1.94-km single-mode fiber (SMF) are obtained by means of the proposed technique. Meanwhile, a strong linear relationship is also established between the signal strength and strain at the vibration frequencies of 10.3 and 13.1 Hz. The maximum measured errors of vibration frequency are 0.5 Hz@10.3 Hz and 0.8 Hz@13.1 Hz.
... SA method utilizes slopes of BGS to translate the change of Brillouin frequency shift (BFS) into the change of signal intensity under a fixed frequency of reference light (work frequency) and can accomplish sampling process without frequency scanning. However, strain sensing range of SA method depends on the bandwidth of the intrinsic BGS of the sensing fiber, which is about 40 MHz in SMF@1550nm [16], and the corresponding strain range is below 1000 µε. Zhou et al. proposed a vector SA-BOTDA system and realized dynamic strain measurement with the maximum strain of 2467.4 µε by single SA method. ...
A slope-assisted Brillouin optical time domain reflectometry system with large dynamic strain range was proposed and demonstrated using graded-index multi-mode fiber (GI-MMF) as sensing fiber. Analysis of the simulated and experimental results indicated that the Brillouin gain spectrum in GI-MMF could be broadened by controlling the coupling efficiency of optical and acoustic modes. The coupling efficiency could be controlled by adjusting lateral offset between single mode fiber (SMF) and GI-MMF. The system realized the maximum strain dynamic measurement of 3000 µɛ with the spatial resolution of 5 m along ∼1 km GI-MMF, and exhibited significant linear relationship between signal intensity and strain at vibrational frequency of 7.83 and 15.47 Hz. The measured error of vibration frequency was less than 0.2 and 1.5 Hz, respectively. The measured strain range of this system was more than three times that of traditional systems based on SMF and could be achieved at relatively low cost.
... Investigators have proposed a variety of slope-assisted Brillouin time-domain sensing systems, such as SA-BOTDA [24,[29][30][31][32][33][34][35][36][37][38][39][40][41], SA-BOTDR [42], and slope-assisted Brillouin dynamic grating (BDG) sensor [43][44][45]. ...
Brillouin-based fiber-optic sensing has been regarded as a powerful distributed measurement tool for monitoring the conditions of modern large civil and geotechnical structures, since it provides continuous environmental information (e.g., temperature and strain) along the whole fiber used for sensing applications. In the past few decades, great research efforts were devoted to improve its performance in terms of measurement range, spatial resolution, measurement speed, sensitivity, and cost-effectiveness, of which the slope-assisted measurement scheme, achieved by exploiting the linear slope of the Brillouin gain spectrum (BGS), have paved the way for dynamic distributed fiber-optic sensing. In this article, slope-assisted Brillouin-based distributed fiber-optic sensing techniques demonstrated in the past few years will be reviewed, including the slope-assisted Brillouin optical time-domain analysis/reflectometry (SA-BOTDA/SA-BOTDR), the slope-assisted Brillouin dynamic grating (BDG) sensor, and the slope-assisted Brillouin optical correlation domain analysis/reflectometry (SA-BOCDA/SA-BOCDR). Avenues for future research and development of slope-assisted Brillouin-based fiber-optic sensors are also prospected.
... Integration of distributed temperature and vibration fiber optic sensing systems are becoming a pressing requirement in the industrial infrastructure monitoring [1,2]. Especially in the oil and gas pipelines security monitoring applications, the function of distributed temperature detection of small region, early warning of explosion or fire disaster as well as a wide vibration response bandwidth is vitally important. ...
Distributed fiber optic sensor for multi-parameter measurements plays a crucial role in various applications. In this work, distributed temperature/vibration fiber optic sensor with high precision and wide bandwidth is proposed and experimentally demonstrated. To improve the signal-to-noise ratio (SNR) and sensitivity of the system, the backscattering enhanced optical fiber (BEOF) is employed to provide strong and stable sensing signal. With the assistance of the coherent phase detection, a high precision measurement of phase can be achieved. In addition, the wavelet packet decomposition algorithm is put forward to effectively discriminate the quasi-static temperature and dynamic vibration signals. In the experiment, wide bandwidth vibration signal from 0.01Hz to 20kHz can be successfully detected. Owing to the high sensitivity of the system, the local temperature change within the range of only 10cm can be captured with high precision of 0.095°C. Besides, the system has a good capability of fast response to the external temperature variation where the response time is less than 0.3 seconds, which is meaningful for the early warning of centimeters-level sized fire source in the special oil and gas pipelines monitoring applications.
... Another commonly used method for dynamic measurement is slope-assisted BOTDA (SA-BOTDA), which takes advantage of the Brillouin gain variations of the probe wave for fast demodulation of the strain [15,16]. For example, a slope-assisted BOTDA sensing scheme has been proven to obtain two vibrations with the frequency of 7.00 Hz and 10 Hz in 10.6km sensing fiber with 3m SR [17]. However, this scheme employs the short pump pulse as the conventional scheme, and the SR is still limited by the pulse width. ...
Gain-profile tracing (GPT) is a useful strategy of distributed sensing in BOTDA technique for achieving high spatial resolution, which has not been used for the dynamic strain measurement previously. In this paper, we propose a modified gain-profile tracing (MGPT) technique for fast dynamic strain measurement while maintaining the advantage of high spatial resolution. This technique is based on a modified pump pulse modulation scheme and the slope-assisted demodulation method. The time consumption using MGPT technique for a single pump pulse measurement of dynamic strain is less by 25% than the conventional GPT technique. The spatial resolution of our BOTDA system using MGPT technique is 50cm and maximal frequency of dynamic strain detection could be up to 53.5 Hz for 248m sensing length. In the experiments, we measure two vibration events spacing 50 cm with the frequency of 14.0 Hz and 17.0 Hz in a 248 m single-mode fiber. The proposed method is a potential real-time dynamic alternative for distributed structural health monitoring.
... In recent years, several sweeping-free adaptations of classical BOTDA have been proposed for dynamic measurements, such as slope-assisted BOTDA [8][9][10] and BOTDA based on multiple probe and pump pulse pairs [11,12]. However, these methods suffer either a limited measurement range or poor frequency granularity. ...
A spatial resolution improvement scheme for the digital optical frequency comb (DOFC)-based single-shot Brillouin optical time domain analysis (BOTDA) by utilizing multiple pump pulses is demonstrated. Assisted by four pump pulses, the spatial resolution can be improved by four times without decreasing the detection resolution. The response time, and the spatial resolution of our scheme over 10 km fiber, are 0.1 ms and 12.5 m. Distributed temperature and strain measurements are carried out with detection resolutions of 1.6°C and 44 μ ϵ , respectively, and the capability of dynamic measurement of this proposed BOTDA is also demonstrated by probing a vibration with frequency up to 1.2 kHz.
... Compared to spontaneous Brillouin scattering, the BGS was detected with an extremely high SNR [18]. In the past decade, another application has been widely used for enhancing signals in longitudinal distributed sensing with intense signal and better spatial resolution [19][20][21][22]. However, for the two mentioned above, a high-cost microwave generator is needed to control the modulator to shift and sweep the frequency of a probe light. ...
We propose and demonstrate a modified frequency sweep-free pump-probe technique, called staring pump-probe technique (SPPT) for Brillouin signal measurement based on stimulated Brillouin scattering (SBS). The SPPT retains the advantages of conventional pump-probe technique, and employs a simple device and low-cost measurement system. Moreover, the Brillouin gain/loss spectrum (BGS/BLS) can be reconstructed without frequency-sweep, thus greatly improving the measurement speed. In this paper, an approximate flat-top spectrum broadened probe light is introduced through distributed feedback laser by direct modulation. The BGS/BLS is reconstructed with the enhanced signal-noise ratio of approximately 21 dB/23 dB. This technique has a potential application for some Brillouin scattering involved Brillouin frequency shift measurement.
... These methods eliminate the Brillouin frequency shift (BFS) cross-sensitivity between temperature and static strain. Slope-assisted method, based on stimulated Brillouin scattering interaction between two counter propagating optical pulses, permits dynamic strain or low frequency vibration to be measured by Brillouin optical time-domain analysis (BOTDA) schemes [22][23][24][25][26][27]. For the purpose of sensing temperature and strain-induced vibration simultaneously, a BOTDA scheme combined frequency sweeping and slope-assisted techniques was proposed [27]. ...
... Slope-assisted method, based on stimulated Brillouin scattering interaction between two counter propagating optical pulses, permits dynamic strain or low frequency vibration to be measured by Brillouin optical time-domain analysis (BOTDA) schemes [22][23][24][25][26][27]. For the purpose of sensing temperature and strain-induced vibration simultaneously, a BOTDA scheme combined frequency sweeping and slope-assisted techniques was proposed [27]. Two vibration events and one temperature point are clearly identified. ...
We demonstrate a cost-effective distributed fiber sensing system for the multi-parameter detection of the vibration, the temperature, and the strain by integrating phase-sensitive optical time domain reflectometry (φ-OTDR) and Brillouin optical time domain reflectometry (B-OTDR). Taking advantage of the fast changing property of the vibration and the static properties of the temperature and the strain, both the width and intensity of the laser pulses are modulated and injected into the single-mode sensing fiber proportionally, so that three concerned parameters can be extracted simultaneously by only one photo-detector and one data acquisition channel. A data processing method based on Gaussian window short time Fourier transform (G-STFT) is capable of achieving high spatial resolution in B-OTDR. The experimental results show that up to 4.8kHz vibration sensing with 3m spatial resolution at 10km standard single-mode fiber can be realized, as well as the distributed temperature and stress profiles along the same fiber with 80cm spatial resolution.
We present a distributed fiber sensor capable of discriminating between temperature and strain while performing low-noise, dynamic measurements. This was achieved by leveraging recent advances in Brillouin and Rayleigh based fiber sensors. In particular, we designed a hybrid sensor that combines a slope-assisted Brillouin optical time domain analysis system with a Rayleigh-scattering-based frequency scanning optical time domain reflectometry system. These sub-systems combine state-of-the-art sensitivity with the ability to perform both dynamic and quasi-static measurements. This enabled a hybrid system capable of temperature/strain discrimination with a quasi-static temperature resolution of 16 m°C and a strain resolution of 140 nɛ along 500 m of single mode fiber with 5 m spatial resolution. In contrast to previously reported techniques, this approach also enabled dynamic measurements with a bandwidth of 1.7 kHz and temperature (strain) noise spectral density of 0.54 m°C/√Hz (4.5 nɛ/√Hz) while temperature/strain cross-sensitivity was suppressed by at least 25 dB. This represents a dramatic improvement in measurement speed and sensitivity compared with existing techniques capable of temperature/strain discrimination in standard single mode fiber.
Short-time Fourier transform (STFT) algorithm with Lorentzian fitting is popular in distributed Brillouin optical fiber sensors to acquire Brillouin frequency. However, STFT often suffers from the trade-off between Brillouin frequency measurement resolution and computation complexity. To lower the complexity of Brillouin frequency analysis and speedup measurement, a novel method based on instantaneous frequency (IF) analysis is proposed. The instantaneous Brillouin frequency can be obtained through the instantaneous phase change between two adjacent samples in time domain. The requirement on spectral resolution is therefore greatly relaxed, significantly reducing computation complexity and lowering measurement time cost. A Brillouin optical time-domain reflectometry (BOTDR) scheme is demonstrated with a spatial resolution of 1.2 m over 5 km sensing fiber. For an average count of 4096 over measurements, experiments show that IF algorithm can reduce computation complexity by 122 times at a standard deviation (STD) of 0.5065MHz for BFS estimation which is comparable to the standard deviation obtained through STFT in conjunction with Lorentzian fitting.
