Since the phase-sensitive optical time-domain reflectometry (Ф-OTDR) concept was proposed in 1993
Opto-Electronic Advances, Volume. 6, Issue 7, 230063(2023)
The cornerstone of fiber-optic distributed vibration/acoustic sensing: Ф-OTDR
Fiber-optic distributed vibration/acoustic sensing (DVS/DAS) technology achieves breakthrough performance and explores broad cornerstone industrial applications.
Background
Since the phase-sensitive optical time-domain reflectometry (Ф-OTDR) concept was proposed in 1993
In the recent work
Figure 1.
Principle
The article first analyzes the sensing principles of DVS-Ф-OTDR based on Raleigh backscattering intensity demodulation and DAS-Ф-OTDR based on phase demodulation. The article focuses on comparing and discussing DAS phase demodulation technologies, including IQ demodulation based on heterodyne detection, Hilbert transform scheme based on heterodyne detection, direct detection method based on 3×3 coupler, and direct detection method based on phase-generated carrier technology. Recently, S. Liu et al. proposed a fast generation method of phase orthogonal signals in the digital domain. By using the phase difference of beat signals between adjacent spatial sampling channels, the fast demodulation of vibration is realized, which greatly reduces the computational complexity of the Φ-OTDR phase demodulation process
Figure 2.
Performances
Ф-OTDR enables distributed measurements of vibration, dynamic strain, etc., which can usually be evaluated by several technical parameters, mainly including sensing distance, signal-to-noise ratio, sensitivity, frequency response range, spatial resolution, and event recognition capability. This review article provides a detailed and valuable summary and analysis of the recent progress in improving key parameters of Ф-OTDR in recent years.
Φ-OTDR uses the very weak backscattered light in fiber as the signal. With the increase in the sensing distance, the signal decays exponentially, which renders long-distance measurement difficult. In 2014, F. Peng et al. proposed to apply heterodyne detection and first-order bidirectional Raman amplification to Φ-OTDR, increasing the sensing distance to 131.5 km
SNR is the key parameter that determines the performance of Φ-OTDR. It not only determines the sensing distance, but also the sensitivity and accuracy. On the one hand, SNR can be improved by increasing the signal strength by amplifying the optical power of the probe and compensating the fiber transmission loss, and suppressing the system noise. Some methods have also been proposed to suppress low-frequency noise
The spatial resolution of Φ-OTDR refers to the shortest distance between distinguishable events. It reflects the spatial recognition and positioning capabilities and is related to probe pulse width, photodetector sampling rate, acquisition card, and so on.
In order to solve the problem that Φ-OTDR systems can locate external interference but cannot distinguish different types of intrusion events, pattern recognition algorithms for Φ-OTDR signal post-processing have been widely studied in recent years
Applications
Through appropriate optical configurations, Φ-OTDR can measure vibration, dynamic strain or temperature distribution over long distances with high spatial resolution. This capability makes Φ-OTDR widely applicable in different scenarios. This review summarizes the recent developments of Φ-OTDR in various application fields, including geological exploration, perimeter monitoring, traffic sensing, partial flow monitoring, and other applications
Figure 3.
An ultra-sensitive distributed fiber-optic sensing seismometer called uDAS, independently developed by Optical Science and Technology (Chengdu) Ltd. of China National Petroleum Corporation (CNPC), based on coherent detection and multi-frequency modulation method proposed by the Chinese researchers
Some cases apply Φ-OTDR to new application scenarios, such as detecting pest infections, while others introduce special fibers or advanced post-processing algorithms to convert the measurement of target physical parameters into vibration detection, strain or temperature changes along the sensing fiber, such as gas concentration levels and fiber bending directions. These novel applications have demonstrated that Φ-OTDR systems are promising tools applicable to various scenarios with enormous potential.
Future
Future research would focus on exploring new operating principles, developing key devices, improving system performance, and expanding application areas of Φ-OTDR. In terms of operating principles, developing new light sources such as optical frequency combs and special sensing fibers including uwFBG arrays, fs-lasing enhanced fibers, or multicore fibers will further improve the performance of Φ-OTDR. In terms of data interpretation methods, advanced signal processing methods in artificial intelligence and computer science can be adopted. In practical engineering applications, it is necessary to develop practical interpretation algorithms that are based on unsupervised learning. In addition, Φ-OTDR will also be applied to more fields such as determining the event features and locations of underground activities or airborne aircraft and so on.
[1] HF Taylor, CE Lee. Apparatus and method for fiber optic intrusion sensing. U. S. Patent(1993).
[2] KL Xie, YJ Rao, ZL Ran. Distributed optical fiber sensing system based of Rayleigh scattering light φ-OTDR using single-mode fiber laser with high power and narrow linewidth. Acta Opt Sin, 28, 569-572(2008).
[3] T Liu, H Li, T He, CZ Fan, ZJ Yan et al. Ultra-high resolution strain sensor network assisted with an LS-SVM based hysteresis model. Opto-Electron Adv, 4, 200037(2021).
[4] YJ Rao, ZN Wang, HJ Wu, ZL Ran, B Han. Recent advances in phase-sensitive optical time domain reflectometry (Ф-OTDR). Photonic Sens, 11, 1-30(2021).
[5] SQ Liu, FH Yu, R Hong, WJ Xu, LY Shao et al. Advances in phase-sensitive optical time-domain reflectometry. Opto-Electron Adv, 5, 200078(2022).
[6] SQ Liu, LY Shao, FH Yu, WH Lin, DR Xiao et al. Accelerating the phase demodulation process for heterodyne Φ-OTDR using spatial phase shifting. Opt Lett, 48, 1048-1051(2023).
[7] F Peng, H Wu, XH Jia, YJ Rao, ZN Wang et al. Ultra-long high-sensitivity Φ-OTDR for high spatial resolution intrusion detection of pipelines. Opt Express, 22, 13804-13810(2014).
[8] ZN Wang, JJ Zeng, J Li, MQ Fan, H Wu et al. Ultra-long phase-sensitive OTDR with hybrid distributed amplification. Opt Lett, 39, 5866-5869(2014).
[9] D Wang, J Zou, Y Wang, BQ Jin, Q Bai et al. Distributed optical fiber low-frequency vibration detecting using cross-correlation spectrum analysis. J Lightwave Technol, 38, 6664-6670(2020).
[10] Q Yuan, F Wang, T Liu, Y Liu, YX Zhang et al. Compensating for influence of laser-frequency-drift in phase-sensitive OTDR with twice differential method. Opt Express, 27, 3664-3671(2019).
[11] Q Yuan, F Wang, T Liu, YX Zhang, XP Zhang. Using an auxiliary Mach–Zehnder interferometer to compensate for the influence of laser-frequency-drift in Φ-OTDR. IEEE Photonics J, 11, 7100209(2019).
[12] SQ Liu, LY Shao, FH Yu, WJ Xu, MI Vai et al. Quantitative demodulation of distributed low-frequency vibration based on phase-shifted dual-pulse phase-sensitive OTDR with direct detection. Opt Express, 30, 10096-10109(2022).
[13] C Zhang, NM Zou, JY Song, S Tong, YY Yao et al. Digital signal processing and application of Φ-OTDR system. Opto-Electron Eng, 50, 220088(2023).
[14] FH Yu, SQ Liu, LY Shao, WJ Xu, DR Xiao et al. Ultra-low sampling resolution technique for heterodyne phase-OTDR based distributed acoustic sensing. Opt Lett, 47, 3379-3382(2022).
[15] FH Yu, LY Shao, SQ Liu, WJ Xu, DR Xiao et al. Data reduction in phase-sensitive OTDR with ultra-low sampling resolution and undersampling techniques. Sensors, 22, 6386(2022).
[16] WJ Xu, FH Yu, SQ Liu, DR Xiao, J Hu et al. Real-time multi-class disturbance detection for Φ-OTDR based on YOLO algorithm. Sensors, 22, 1994(2022).
[19] YJ Rao, ZL Ran, KL Xie. Method for enhancing performance of fiber-optic distributed sensing system with subcarrier wave technique. CN Patent(2009).
[20] YJ Rao, ZL Ran, JZ Li. Fiber-optic disturbance detection method and apparatus. CN Patent(2012).
Get Citation
Copy Citation Text
Yunjiang Rao. The cornerstone of fiber-optic distributed vibration/acoustic sensing: Ф-OTDR[J]. Opto-Electronic Advances, 2023, 6(7): 230063
Category: Research Articles
Received: Apr. 23, 2023
Accepted: Apr. 27, 2023
Published Online: Sep. 25, 2023
The Author Email: