Research On Phase Closed Loop Control And Stabilization Technology Of Photo-elastic Modulation

The photo-elastic modulator(PEM)has the advantages of wide spectral window,high frequency,high efficiency,large area and light aperture,so the PEM is the core of the Fourier transform spectrometer with wide spectral range,high sensitivity and high speed and other.It has broad application prospects in environmental monitoring,deep space exploration,national defense and security and biomedical fields.Due to the disturbance of external environment and the heat dissipation of itself,the work of the PEM is unstable and the optical path difference fluctuates.It becomes the biggest constraint factor for the high accuracy and high stability of the PEM Fourier transform spectrometer.Firstly,this paper analyzes the basic principle of the PEM,and establishes the dynamic model of heat exchange.The driving voltage phase is the same as the current phase of the PEM.Design the PEM stabilization system based on phase closed loop control according to the phase relation.Secondly,the hardware circuit of the system is designed,including power supply circuit,detector circuit,high voltage driver circuit,laser drive circuit,FPGA and its surrounding circuit,digital phase locked circuit.The design of enhanced DDS square wave generation module,data acquisition module,reference signal generation module,digital phase-locked algorithm module and FPGA data communication module are implemented in FPGA by using Verilog language.In host computer,the data transmitted to the host computer through FPGA interface is processed through by LabVIEW,and the working frequency of the system is modulated by analyzing the feedback signal.Finally,test each module of the system,through the experimental platform to test the PEM optical path difference stability,obtained the optical path difference can stable for a long time,the maximum fluctuation amplitude is 2.14%,and the removal of stable system the optical path difference of the maximum fluctuation amplitude is 53.1%,which proves that the system can greatly improve the stability of PEM,and keep the optical path difference stable for long time.