Analysis Of Positioning Accuracy And Research Of Polarization Control On Mach-zehnder Distributed Opticial Fiber Sensing System

Optical fiber sensing technology has the advantage of safe and reliable,anti-electromagnetic interference and long distance distributed sensing,so it has become a researching hot spot in secure field. Optical fiber sensing technology commonly includes fiber grating technology, optical time domain reflection technology, Michelson interference technology, Sagnac ring technology and dual Mach-Zehnder(DMZ) interference technology.The structure of the optical fiber sensing system based on the DMZ interferometer structure is simple,the demodulation technology easy to realize,and it has important application value in the field of perimeter security. In this paper, the factors that affect the accuracy of positioning the disturbance signal in the system are analyzed, and the polarization of adjusting method is proposed to reduce the polarization fading effect of optical path.Distributed optical fiber sensing system on DMZ, uses the external intrusion disturbance to cause the phase change of the interference signal, and the delay signal is interpolated by the mutual correlation operation. The results of the positioning calculation are affected by the frequency of the signal, the data sampling parameters and the correlation between the two signals. In this paper, the above factors for theoretical and experimental analysis. The main research contents are as follows:(1) Combining the Cramer-Rao lower bound formula, the relationship of the frequency of the disturbance signal and the received data sampling parameter with the positioning error is analyzed and discussed. Aiming at the contradiction between the length of the sampled data and the computation time, the high frequency band data is used to locate the calculation,and the efficiency of the localization algorithm is improved. The influence of the method on the positioning result is analyzed. Aiming at the problem that the two-way received signal correlation is degraded by the polarization fading effect, the method of adjusting the optical path polarization state of the system using the feedback signal contrast as the feedback parameter is studied. Combining the traversal algorithm and the simulated annealing algorithm, the modified simulated annealing algorithm is designed, and validating the practicability of the algorithm in system detection.(2) Based on the VS software platform, the positioning calculation program and the polarization control algorithm program are completed. The experimental results show that the contrast of the received signal can be greater than 0.9, and the average time of the polarization control algorithm is about 6 seconds. At the sensing distance of 1 km,the network is sampled at 800 meters, the sampling frequency is 10MHz, When the data length is 50K, the positioning accuracy is 42.74 meters, and the calculation time is about 94 milliseconds. At the same time,the accuracy of the disturbance signal location and the real-time performance of the algorithm are ensured.