Current Status and Future of Research and Applications for Distributed Fiber Optic Sensing Technology

Significance The construction scale of large-scale infrastructure in China has ranked first in the world for many years. Meanwhile, due to construction quality, using environment, natural disasters, and other factors, serious accidents occur frequently. Distributed optical fiber sensing technologies employ optical fibers as signal transmission medium and sensing units to realize continuous distributed measurement of external parameters along the optical fiber. Therefore, it is the most potential non-destructive monitoring technology for large-scale infrastructure health monitoring in real time. However, distributed fiber optic sensing technologies still face various challenges such as reliability, low cost, and intelligence as they move toward the market. Progress At present, distributed optical fiber sensing technologies that have caught extensive attention and research include optical time-domain reflectometer, coherent optical time-domain reflectometer, phase-sensitive optical timedomain reflectometer, optical frequency-domain reflectometer, Raman optical time-domain reflectometer, Brillouin scattering optical time-domain reflectometer, Brillouin optical time-domain analyzer, and optical interferometry. We focus on introducing their working principles, system basic structures, development history, current status, and major research institutions and manufacturers at home and abroad. Based on detailing the application requirements, principles, and methods of distributed optical fiber sensing technologies in communication system monitoring, power system monitoring, coal geology monitoring, oil and gas exploration, transportation field, transportation pipeline monitoring, aerospace equipment monitoring, and perimeter security, we provide several typical application cases. Conclusions and Prospects The future main directions of development are listed: 1) Multi-mechanism integration system. Single sensing parameters make it difficult to represent the true state of the measured object, which can result in false reports and missed reports. Simultaneous measurement of multiple parameters can provide multidimensional and more comprehensive information, thereby more accurately identifying fault events. The key point of the fusion-type distributed optical fiber sensing technology is to employ different scattering lights to respond to different events in the optical fiber to achieve multi-parameter sensing. 2) Specialty sensing fiber cable technology. By changing the fiber material, structure, and packaging, specialty optical fiber cables can overcome the limitations of distributed sensors based on ordinary single-mode optical fibers, and obtain engineering applications in specific sensing parameters and performance in specific fields and scenarios. 3) Sensing signal processing and intelligent perception technology. Due to the weak intensity of scattered light compared to incident light, distributed sensing systems are limited by signal-to-noise ratio. This affects the measurement accuracy, monitoring distance, response speed, spatial resolution, and other key indicators of distributed sensing systems. Signal processing techniques to analyze and enhance collected data are important means to improve the performance of sensing systems. 4) Communication-sensing fusion system. Technologies such as wavelength division multiplexing, polarization diversity, and coherent detection from optical communication systems are applied to distributed fiber optic sensing systems. Additionally, existing optical fiber communication systems can be adopted for synchronous sensing. These are crucial steps towards the practical applications of distributed fiber optic sensing systems. 5) Distributed shape sensing technology. Leveraging distributed fiber optic sensing technology for shape sensing is an important development direction. 6) Ocean state monitoring based on existing optical cables. Existing undersea optical communication networks are employed as sensing networks to achieve intelligent perception of the surrounding environment of the cables. This enables large-scale online monitoring and early warning capabilities with relatively low investment, thus providing rapid and accurate assurance for managing major maritime incidents and maritime disaster risks.