Research On Double Closed Loop Stabilization And Control Technology Of Of Photoelastic Modulation

With the rapid development of science and technology, in the national security, air monitoring, space exploration, bioengineering and other high-tech areas, spectral measurements increasingly attention. In the various existing for spectroscopic measurements of the spectrometer, with the advantages of high operating frequency, wide range of spectral bands, responsive and accurate make the photoelastic modulation Fourier transform spectrometer with photoelastic modulation interferometer as the core has significant advantages in the application of space wide. Photoelastic modulator working state cannot stably for a long time, the modulation effect is severely limited by its own thermal effect and the environment. So how to overcome photoelastic modulator instability problem, convenient and accurate control it, ensure the stability of the modulation effects and can according to the needs output modulation optical path difference is the difficulties of the development of photoelastic modulation Fourier transform spectrometer must crossed.At first, the thesis analyzes the composition and modulation principle of photoelastic modulator and to build dynamic model of the optical crystal for analyze the frequency drift caused by the thermal dissipation in the process. Use obtained the relationship between the resonant frequency and phase difference and The effect of frequency drift on optical path difference modulation effect as based to design the scheme of the stability and control system of the photoelastic modulation.Secondly, the hardware system is designed with FPGA as the control core, the system is composed of feedback collection and conversion, voltage regulation, A/D feedback, optical path difference detection, DA conversion and so on modules. And the design of frequency automatic tracking program based on the design of DDS signal generator and digital phase detector is realized, as well as the design of optical path difference detection program for feedback the effect of modulation optical path difference, the design of automatic voltageregulation system for compensation the effect of modulation optical path difference and A/D feedback control program for driving voltage monitoring, there is also the design of the data transmission program for the wavelength calibration is performed for Spectral restoration for the collected interference signal. So as to realize the control of the photoelastic modulator work stably and output the modulation optical path difference we need, and to prepare for subsequent data processing and spectral inversion.Finally the system modules were tested, and photoelastic modulation stability and control system experiment platform and PEM-FTS comprehensive test experiment platform is built, were used to test the performance of the whole system, the modulation effect of system is stable for a long time in the state under the large optical path difference modulation.