Ultra-fast BOTDA Sensing System Based On Digital Optical Frequency Comb And Multiple Pump Pulses

The sensing technology based on Brillouin optical time domain analysis(BOTDA)has the characteristics of long distance,continuous and distributed measurement.It can provide high precision temperature and strain sensing on the fiber of dozens of kilometers,which means that the BOTDA sensing technology is especially suitable for structural health monitoring of some large civil engineering and buildings.For the conventional BOTDA technology,because of the need for frequency scanning to obtain the Brillouin gain spectrum(BGS)and the Brillouin frequency shift(BFS)in the sensing process,the time of measurement is generally long.With the continuous in-depth study of scholars,the BOTDA technology is developing towards faster measurement speed and other directions,and the fast BOTDA sensing technology that can realize dynamic measurement has attracted wide attention.Aiming at the long measurement time of the conventional BOTDA technology,and based on the research of different BOTDA technologies,an ultra-fast BOTDA sensing system based on digital optical frequency comb(DOFC)and multiple pump pulses is proposed for the first time.With the proposed sensing system,the BGS and the BFS distribution needed for sensing can be obtained without frequency sweeping,and thus the measurement time of the system can be greatly shortened.And the spatial resolution of this DOFC-based BOTDA sensing system can be improved by times without decreasing the detection accuracy.Through the theoretical analysis,the specific system construction and the corresponding experimental tests,the research achievements of this sensing system are as follows:1.The proposed sensing system can obtained a 0.1ms respond time and a 12.5m spatial resolution simultaneously over 10 km sensing fiber,and the spatial resolution of 12.5m is the highest index in the same type of technology.2.On the premise of obtaining the above two indexes,the detection accuracy of the sensing system are 1.6°C for temperature and 44?? for strain respectively,and the maximum measurement deviation are about 0.3°C of temperature and less than 10?? of strain.Compared with the same type of technology,our sensing system can provide a higher precision detection of temperature and strain.3.Due to the ultra-fast response speed,the proposed sensing system can realize a dynamic measurement with the vibration frequency up to 1.2 kHz.All the results show that the proposed BOTDA sensing system based on the DOFC and the multiple pump pulses can realize a long distance,high precision and ultra-fast sensing process,which is also expected to become one of the key technologies for real-time dynamic measurement in the future.