Research On Accurate Calibration And Closed-Loop Control Of Photo-Elastic Modulator

As a high-quality factor opto-electrical coupling device,the photo-elastic modulator has advantages such as high modulation frequency,large aperture,and wide spectral range,which are important in polarization modulation and analysis.It is widely used in spectroscopic measurement,polarized microscopy imaging,energetic material research,and biosensing.However,in practical applications,the increased strain amplitude and significant thermal dissipative effect of PEM greatly affect the measurement accuracy and long-term stability of testing systems that use PEM as a modulator.Therefore,precise calibration and stable control of PEM are key to achieving high-precision polarization measurement using PEM.Based on the analysis of the development status of PEM control systems and lock-in technology at home and abroad,this study designs a PEM precise calibration and closed-loop control system using a feedback optical path.A centralized calibrated feedback optical path is designed at positions away from the center of PEM to achieve precise calibration of phase delay and closed-loop stability control.The main research contents of this study are as follows:Firstly,starting from the composition of PEM,the calibration and working principle of the photo-elastic modulatorare analyzed.The factors that affect the system’s instability are explored by establishing its vibration and heat exchange models.Based on this,the PEM precise calibration and closed-loop stability control system are theoretically designed,and the preliminary design of the experimental plan is completed.Secondly,using FPGA as the core,the high-voltage driving circuit based on LC resonance,detector circuit,FPGA peripheral circuit,and power supply circuit are designed to complete the photoelectric conversion and signal processing of the modulated optical signal.Simulations and experimental verifications are conducted.Thirdly,the FPGA program design is completed,including Direct Digital Synthesizer and ADC sampling,and the accurate extraction of multiplier signal is realized by digital phase locking algorithm,and the design of closed-loop stability control system based on duty cycle adaptive adjustment is completed to realize the accurate calibration and long time stability control of PEM.Finally,a test platform for the PEM precise calibration and closed-loop control system is built.The experimental results show that,within 60 minutes of calibration time,after feedback control,the standard deviation of the phase delay of the central detection position in the half-wave state is 0.0016 rad,and the maximum deviation does not exceed 0.62%,and the phase delay standard deviation of the edge calibration position is 0.0019 rad,and the maximum deviation does not exceed 0.53%.The relative deviation between the calibrated value and the measured value of the central phase delay of the feedback optical path at the edge of the PEM does not exceed 0.56%.Accomplished precise calibration and sustained control of PEM,providing reliable ideas for the application of PEM in high-tech fields.