Research And Modularization Of Polarization Control Method For Dual Mach-zehnder Fiber Disturbance System

The Dual Mach-Zehnder fiber disturbance system has been widely used because of its simple structure,high sensitivity and long distance positioning.But in actual use of the system,the polarization fading caused by the defects of the optical fiber and the external environment may reduce the positioning accuracy.In this paper,the polarization theory of light was researched,the polarization change model of the system was established,and the influence of polarization fading on the positioning was analyzed.An FPGA-based polarization control method was proposed,it achieved the polarization state adjustment based on the feedback value of the two optical signals,and combined with the improved harmony search(IHS)algorithm.Besides,the use of FPGA instead of the computer as the control core of system improves the data processing speed,reduces the polarization control time,thereby facilitating the miniaturization of the polarization control instruments.On the basis of summarizing the development status at home and abroad,this paper mainly carries out the following four aspects of innovation work:1.The polarization change model of the sensing system is established based on sensing positioning principle of the Dual Mach-Zehnder fiber optic disturbance system.Quantitative analysis of the influence of polarization fading on the detection and positioning performance using Jones matrix.A fast polarization control is proposed,in the method,a polarization feedback mechanism is built on the sensing fiber,the polarization state in the fiber is quickly adjusted by the polarization controller and the phase modulator based on the use of FPGA as the control core.2.The modularization design idea is used to complete the instrumentation of the polarization control system.The power module,configuration module,AD conversion module,clock module and drive circuit module of the FPGA hardware board system are designed.The FPGA board,polarization controller,and phase modulator form a new type of polarization control system that miniaturizes the instrument3.According to the polarization control structure,an improved harmony search(IHS)polarization control algorithm is proposed.it achieved the quickly polarization state adjustment based on the feedback value of the two optical signals.Based on the FPGA parallel hardware structure,combined with the pipeline,interception processing,RAM processing and other technologies,compress the running time of the algorithm and improve the processing speed.4.Tested the prototype,the waveforms and positioning accuracy of the signals before and after the introduced of the polarization control system were compared and analyzed.The experimental results show that the system can improve the consistency of the phase and amplitude of the two signals,reduce the effect of polarization fading on the positioning accuracy of the system.The polarization control time is about 781 ms,which satisfies the real-time requirements of the system.