The Research Of High-speed Data Processing Technology Of The Photo-elastic Modulation Fourier Transform Spectral Reconstruction

The technology of the photo-elastic modulation Fourier transform spectrometer (PEM-FTS) with high speed, wide spectrum and high sensitivity has potential application in the transient spectral detecting fields such as aerospace detection, environmental monitoring, biological medicine, industrial production and so on. As the core technology and unit the elasto-optical modulator has high modulation frequency and its modulated optical path difference is nonlinear,which result in the problem in the data processing technology of photo-elastic modulation.Wherefore, how to realize high-speed sampling and storage of elasto-optical modulation interference signal, to caculate accurately transient maximum optical path difference of elasto-optical modulation Fourier transform interferometer and how to make spectral reconstruction, calibration fast and accurate are the important science problems need to be solved.Based on the technology of spectral reconstruction data processing in the Fourier transform spectrometer and the principle of the photo-elastic modulation Fourier transform interferometer, the paper makes research to high speed data processing technology of PEM-FTS, develops the high-speed data processing platform of PEM-FTS.First, the study on the data processing technology in the Fourier transform spectral recovery is researched. Based on the Fourier transform spectral theory, the operating principle, the resolution and the sampling method in the time modulation Fourier transform spectrometer are analyzed; In order to suppression the spectral leakage, decrease the phase distort, the technology of truncation and phase correction are studied, and based on Forman and Mertz methods the interferogram symmetrization phase correction method is put forward. In the method the phase shift spectrum is estimated by the high resolution interferogram, and the phase-corrected technology of the rebuilt spectrum is realized in the frequency domain. It shows from experiment that the method decreased the complexity of the algorithm and has the comparativity high accuracy in rebuilt spectrum. Second, based on the principle of photo-elastic modulator Fourier transform interferometer, the dynamic model is built. In view of high speed and the nonlinearity of interference signal in the photo-elastic interferometer, the interference signal is high-speed sampled by the equal time intervals, and the transient maximum optial path difference is calculated by zero-crossing counting of laser’s interference signal when the laser is used as reference source, to accomplish the spectral reconstruction and the wavelength calibration of rebuilt spectrum.Third, according to the phase nonlinearity of the photo-elastic modulator interference signal, the nonuniform discrete Fourier transform algorithm, the D-R algorithm and the nonuniform fast Fourier transform algorithm based on Fourier transform matrix are analyzed, the accelerated nonuniform fast Fourier transform algorithm is put forward. In the method the Fourier coefficient is estimated by convolution arithmetic of kernel function to realize the uniform data interpolation. It is verified that the algorithm can rebuild the laser spectrum and blackbody spectrum fast and accurately when choose Gaussian kernel function and set parameters reasonablely.Last, based on FPGA+DSP framework, it sets up an elasto-optical modulation high-speed data process platform. Using high speed ADS4245ADC and DDR3dynamic RAM to realize the high speed sampling and storage of interference signal, it realizes the data processing in the spectral reconstruction based on DSP. In order to verify the performance of the platform, the complete spectrum test system is set up, using the known narrow-band laser and infrared blackbody with different temperature as radiation source to rebuild their spectrum, and the expected result is obtained.