Study On Recovery Characteristics Of Radiated BOTDR System

As a distributed optical fiber sensing technology,Brillouin optical time domain reflectometer(BOTDR)has many advantages such as anti-electromagnetic interference,light weight and small size,so it is widely used in large-scale ground structures.Health monitoring field.Researchers in the aerospace field are also beginning to consider introducing this technology into the structural monitoring of spacecraft.However,there is space radiation in the working environment of the spacecraft,which will lead to the deterioration of the performance of the BOTDR system.Therefore,it is necessary to study the performance of the BOTDR system in a radiation environment through experiments.Radiation can cause color center structure defects in the fiber,resulting in deterioration of its sensing performance.However,the color center is not permanent and can be self-healing.Therefore,the performance change of the optical fiber in the radiation environment is actually the result of the continuous generation and repair of the color center.Usually the ground simulated space radiation experiment does not consider the effect of the recovery effect on the performance of the sensing fiber.If the recovery characteristics are introduced into the performance variation model of the fiber in the radiation environment,the evaluation model of the damage of the BOTDR system in the radiation environment will be greatly improved,thereby reducing the redundancy design of the BOTDR system in the spacecraft.In order to study the radiation recovery characteristics of the BOTDR system,three commercial single-mode G.652.D fibers,1km long-fly,1km Corning and 1.5km Fujikura are used as sensing fibers for the BOTDR system.It was placed in a Co60 radiation field to receive gamma radiation with a radiation rate of 1.42 Gy/min and a total dose of 200 Gy.After the radiation is stopped,40 ns of pulsed light is used as the probe light,and the BOTDR system is tested for recovery performance of up to 1001 h.The results show that the recovery effect after 200Gy radiation has little effect on Brillouin frequency shift and stress coefficient,but the recovery of fiber induced loss in the first 200h is very obvious.The anti-radiation performance of the three samples was verified from high to low in order of Changfei,Corning and Fujikura.The final induced losses of Changfei,Corning and Fujikura after absorbing 200Gy radiation are 1.12dB/km,1.25dB/km and 1.52dB/km,respectively.After that,the performance of the BOTDR system under different pulse width detection light was studied.The results show that increasing the pulse width can effectively increase the signal-to-noise ratio of the system,thus suppressing the deterioration of the BOTDR system caused by radiation.In the process of radiation recovery,the change of the pulse width of the light source has less influence on the Brillouin frequency shift and loss coefficient..Finally,the performance of the BOTDR system based on Golay complementary sequence modulation source in the radiation recovery process is studied.The results show that the longer coding length can significantly improve the signal-to-noise ratio of the BOTDR system,thus reducing the uncertainty of the Brillouin frequency shift in the radiation recovery process.When a monitoring scene with high event sensitivity and low spatial resolution is required,a larger pulse width is a better choice than an encoding technique,and when the spatial resolution of the BOTDR system is required,compared to the boosting Detecting the pulse width of the light,using a longer coding length or boosting the source power without exciting the stimulated Brillouin scattering can effectively improve the performance of the BOTDR system during radiation recovery.In summary,this paper designs a BOTDR system radiation recovery experiment using three sample fibers as the sensing fiber.The radiation recovery effect was verified and the effects of radiation recovery effects on the performance of the BOTDR system were analyzed.The performance of BOTDR system with different pulse width and BOTDR system with Golay complementary sequence in radiation recovery process are analyzed.The above research results are of great significance for modifying the radiation model of the BOTDR system and then promoting it to the aerospace field.