Distributed Optical Fiber Vibration Detection And Location System Based On Linear Sagnac

Owing to the outstanding advantages of long distance monitoring,corrosion resistance,and immunity to electromagnetic interference,distributed optical fiber technology have been widely applied in the fields of perimeter security and health monitoring of pipelines,dams,and bridges,by measuring the parameters such as vibration,temperature,and strain,etc.Among them,vibration monitoring is in a great need for many practical applications.For instance,in the field of perimeter security,the intrusion detection usually rely on manual patrol or cameras.However,these traditional methods suffer from the short monitoring distance and high maintenance cost.Hence,there is a strong need for a new long distance monitoring vibration sensor.In the field of health motoring of pipeline,which is usually hundreds of thousands of kilometers and buried in the underground,manual patrols have inevitable drawbacks due to the high cost,low efficiency and poor reliability.Fortunately,the advent of distributed optical fiber vibration sensing technology reduces the labor cost and improves working efficiency.Distributed optical fiber vibration sensing technology has become the preferred scheme for long distance monitoring due to the characteristics of low price,high efficiency and good performance,etc.In this paper,a distributed optical fiber vibration sensing system based on linear Sagnac is proposed.The vibration signal is firstly sensed by the fiber,and then acquired and finally displayed.An embedded phase modulation module is designed to simulate the vibration signal,and the software is implemented in LabVIEW to detect and locate the vibration.Moreover,a location optimization algorithm based on multilevel null-frequency is proposed.In summary,this paper mainly including the following researching aspects:(1)The sensing mechanism of linear Sagnac distributed optical fiber vibration detection system is studied and the theoretical model is analyzed.(2)Linear Sagnac distributed optical fiber vibration detection system is established,and the vibration detection method and positioning principle is introduced.(3)In order to solve the problems of traditional vibration excitation methods,an embedded phase modulation module including hardware and software is designed by combing the embedded technology and piezoelectric ceramic technology for sensor commissioning and calibration.(4)Data acquisition software based on LabVIEW is designed,as well as the bottom driver and user interface,for vibration real time acquisition.(5)The traditional position theory and algorithm based on the first nullfrequency of the linear Sagnac vibration sensing system is analyzed,and a location optimization algorithm based on multilevel null-frequency is proposed.The experimental results verifies that the positioning accuracy can be improved by reasonable use of the multilevel null-frequencies.Based on the optical fiber sensing technology,linear Sagnac distributed optical fiber vibration detection system is able to be applied in long distance monitoring in complex environment to observe the entire sensor link in real time and improve the automation level of vibration detection.