高分辨率傅里叶变换光谱仪分束器补偿器的厚度匹配设计

Thickness Matching Design Between Splitter and Compensatorfor High Spectral Resolution Fourier Transform Spectrometer

应用于航天遥感领域的高光谱分辨率傅里叶变换光谱仪,多采用分束器补偿器的方案实现分光。由于光学器件的加工误差,实际应用的分束器与补偿器厚度并不能达到理想的完全匹配,当分束器与补偿器的厚度不匹配时,由于厚度误差引入的光程差会在视场内产生干涉条纹,进而影响光谱仪的调制度并降低其信噪比。为满足航天遥感高信噪比的要求,需要根据性能要求对分束器与补偿器的厚度误差范围进行限制,即分束器补偿器厚度匹配设计。通过理论分析方法建立了引入厚度匹配误差的附加光程差计算公式,以及视场范围内的光谱仪干涉信号强度计算公式,并通过Zemax建模仿真直观显示了由于分束器与补偿器厚度匹配误差导致的视场内干涉条纹信号,给出了光谱仪调制度随厚度匹配误差增加而下降的变化曲线。分析了视场范围在厚度不匹配条件下对调制度影响的增强效果,发现扩展光源的入射角变动受视场角影响,入射角变动越大导致光程差变化量越大,进而引起调制度的下降越大;分析了光源波数与计量激光波数不同条件下,由于器件折射率变化导致的色散效应对厚度不匹配影响的增强效果,发现厚度不匹配误差越大色散相位差越大,要恢复明确相位需要限制厚度不匹配误差使其引起的色散相位差小于2π。通过理论分析,建立了分束器补偿器厚度匹配设计准则,提出先通过光谱仪光谱范围和计量激光器参数限制分束器补偿器厚度不匹配误差,再导入光谱仪设计参数计算厚度不匹配误差与调制度关系曲线,根据调制度要求进一步限制厚度不匹配误差。通过该设计准则,可以提出傅里叶变换光谱仪的分束器补偿器厚度不匹配公差范围,指导分束器与补偿器的工程设计。

The high spectral resolution Fourier transform spectrometer used in the aerospace field mostly adopt the scheme with a beam splitter and compensator for light splitting.However,for the machining error,the thickness between splitter and compensator cannot match perfectly,and the matching error wound impact the interferometer modulation value which is an important parameter of the instrument SNR(Signal Noise Ratio).For the requirement of high SNR,the matching error(ME)between splitter and compensator must be limited,which means thickness matching design.Firstly,the impact caused by the thickness matching under different situation was analyzed with theoretical analysis,and then the formulas of additional optical path difference(OPD)and signal intensity are given.Secondly,the interference signal caused by ME is visually displayed with Zemax simulation and it can be obviously observed that the modulation value decreases with the increase ME.Furtherly,the view field of the extended light source will cause oscillation in the incidence angle of non-central light of field,which can increase the variance range of OPD and enhance the influence on modulation with ME.Beyond that,for the wave number difference between the light source and metering laser,the dispersion effect will be introduced into the spectrometer system and the ME will enhance the influence on the signal with dispersion effect.For phase retrieval requirement,the ME must be limited to ensure that the dispersion phase difference is no more than 2π.Finally,based on the theoretical analysis,the design principle of the thickness matching between splitter and compensator was summarized,and it provided a design method for the tolerance analysis of the interferometer,which will improve the performance of the Fourier transform spectrometer.