Dynamic Distributed Brillouin Optical Fiber Sensing Based On Optical Frequency-agile Technology

In recent years the fiber sensor technology develops rapidly, and it has already been widely used in many areas such as national defense and military, disaster monitoring and civil structural health monitoring. Now the fiber sensor technology attracts the attention of many researchers. The fiber is not only the transmitting channels for signal but also the sensing part of the sensors. So the fiber sensors can realize the distributed sensing. It has many advantages over other methods, which are resistance to electromagnetic interference, strong corrosion resistance, small volume, light weight, high resolution and high sensitivity. Brillouin optical time domain analysis technology is a representative of the Brillouin distributed sensing that features high spatial resolution, long sensing distance and good signal to noise ratio.The conventional Brillouin optical time domain system need a long time to measure the fiber`s Brillouin gain spectrum. So the system can only operate in the stable environment. In this paper we investigate on dynamic Brillouin optical fiber sensing to expand its application. We propose a novel scheme for dynamic distributed Brillouin fiber sensing, which realizes strong feasibility and real-time on-line monitoring. The contents are as follows:Firstly, we utilize the arbitrary waveform generator to generate the frequency-agile microwave, while the modulator is working on the second-order sideband operating model to generate the optical frequency-agile signal. After filtered by fiber Bragg grating the lower second-order sideband is generated as probe wave to measure the Brillouin gain spectrum rapidly. So we can realize the dynamic Brillouin fiber sensing using the optical frequency-agile modulation.Secondly, we propose the multi-slope algorithm which is based on double-slope demodulation and frequency-agile modulation. The multi-slope algorithm enables the measurement of a large strain with real-time data processing.Finally, we utilize the dynamic Brillouin optical time domain analysis system to make fiber vibration experiment. We employ the multi-slope algorithm to process the data. We can get the best frequency interval in multi-slope algorithm after the analysis of the fitting error. We also investigate the influence of Brillouin gain spectrum`s width on muli-slope algorithm to improve the precision of algorithm.