Development Of Intrusion Sensor System On BOTDR Distributed Optical Fiber

In the distributed optical fiber sensing system of brillouin optical time domain reflection(BOTDR),the backscattering signal's frequency is changed when temperature and strain is changed,it can realize the long distance measurement of temperature and strain by demodulated the frequency of backscattering signal.BOTDR sensing system has widely future application,such as fire prediction and security intrusion detection.Nowadays,it adopts frequency sweep method to acquire backscattering signal.However,the method mentioned above,it takes long time to acquire signal,the signal is week and noise is large.Based on the in-depth study of the Brillouin scattering principle,it had adopted edge filter to change frequency signal into energy output.And then,Brillouin frequency information is rapidly demodulated.By detecting the output signal energy of edge filter,intrusion behavior around sensing fiber had been detected rapidly with high responsibility.The detailed researches in this article are as follow:(1)The principle of Brillouin distributed optical fiber sensor had been analyzed in detail.It mainly includes,the relationship between Brillouin frequency shift and the temperature,strain,the related characteristics of Brillouin frequency shift,the traditional method of acquisition and processing in the scattering signal in BOTDR.It lays a theoretical foundation for the subsequent development of the BOTDR system.(2)The distributed intrusion sensing system device had been designed.According to the technical indexes of the main part of the system,a continuous light source,optical amplifier(EDFA)and chopper circuit had been designed.Finally,the performance of them had been tested.The test shows,the precision of current control reaches 0.06 mA,and the stability of the laser is 0.02%,and the relative error of temperature control is 0.09%.The most reasonable parameter had been varied,including EDFA,laser driving current and setting temperature,that keeps light wavelength and optical power stable It makes Brillouin distributed sensing in a state of spontaneous Brillouin scattering.(3)The key modules and the overall performance of the system had been verified by experiments,simulation experiments of temperature and strain based on the edge filter had been designed.Experimental results show that,the geophone output increased 0.29 mV when the optical fiber temperature increases with every 5.When temperature changes from 45 ?C to 80 ?C,the actual amount of frequency shift was equal to theoretical value converted by edge filter.The theory frequency shift is 42 MHz and the actual value is 42.9MHz.So,the actual value is consistent with the actual value.Finally,the effectiveness of the edge filter method in obtaining the temperature of the optical fiber is verified.At the same time,the temperature in the optical fiber can be measured according to the output voltage value.In strain experiment,the actual frequency shift coefficient is 3.3%/MHz and the theory is 3%.so the difference between them is very small.At the same time,it can be calculated position of simulated intrusion by the sampling time,which provides a new method to acquire Brillouin fiber sensor signal,proved reliability of edge filter method Finally,it had verified the feasibility of this scheme.