基于微梯形弹光晶体的大光程差PEM研究

摘要

针对目前基于弹光调制器（photoelastic modulator ，PEM ）的傅里叶变换光谱测量技术（PEM‐FTS）的光谱分辨率低，并且PEM调制光程差有限、多次反射对入射光斑大小要求高且光能利用率低等缺点。提出一种基于微梯形八角结构弹光晶体的大光程差PEM方法。通过改进弹光晶体结构，使其为微梯形八角结构，两个通光面略微成一定夹角，该结构PEM不仅可以有效提高PEM 调制的最大光程差，而且对入射光斑要求较小。理论推导分析了该PEM的最大调制光程差，并推导得出任意角、任意位置入射时 PEM 的最大调制光程差公式；通过多物理场耦合仿真软件COMSOL Multiphysics 4.3a对PEM 的振动模态和应力分布进行分析；结合PEM 的最大调制光程差和光能利用率，分析了寻找最佳入射角的方法。设计加工该PEM ，其中弹光晶体选用硒化锌晶体，压电晶体选用压电石英晶体。采用波长为632.8 nm的氦氖激光进行实验分析，实验结果显示，在相同驱动电压下，该PEM的最大调制光程差是普通PEM的19.25倍，与理论仿真的相对误差为1.3％。%Existing Photoelastic Modulator (PEM) ,whose optical path difference (OPD) is small ,has strict requirements on the inci‐dent spot size and is poor in the aspect of light use efficiency under multiple reflections .What’s more ,Photoelastic Modulator based Fourier transform spectrometer (PEM‐FTS ) spectral resolution is relatively poor .Because there are these disadvantages in the PEM , this paper presents a method of large optical path difference whose PEM is based on micro trapezoidal photoelastic crystals .By improving the structure of photoelastic crystal ,the PEM becomes micro trapezoidal octagonal structure .And two transmission surfaces are changed slightly into a certain angle .Therefore ,the PEM improved can not only increase the optical path difference of the PEM ,but also have less requirements on the incident spot size .Firstly ,a detailed analysis of the maximum modulation optical path difference was made in this paper .Secondly ,the equation of maximum optical path difference was deduced under any angle and any position of incident light ,vi‐bration displacement and stress distribution of PEM are analyzed by the way of COMSOL Multiphysics 4.3a .Again ,a method was ana‐lyzed to find the best angle of incidence ,combining with maximum optical path difference and energy efficiency .Then the large OPD’s PEM is designed and processed ,including two parts :photoelastic crystal and piezoelectric crystal .Moreover ,ZnSe crystal is used as photoelastic crystal ,and piezoelectric quartz crystal is used as piezoelectric crystal .With experiment analyzed by 632.8 nm He‐Ne laser , the results show that under the same driving voltage ,the optical path difference of the PEM improved is about 19.25 times bigger than the normal PEM ,and the relative error is 1.3% .