消偏振二维二元闪耀光栅设计

Design of polarization-independent two-dimensional binary blazed grating

为减小成像光谱仪的偏振敏感度并提高其定量化探测精度,提出一种透射式消偏振二维二元闪耀光栅。它在两个正交方向上都具有周期性槽形单元,每个槽形单元包含7个子周期。每个子周期的介质占空比在两个方向上是独立的,可同时调制TE和TM偏振态的等效折射率,以此优化光栅偏振特性。本文将等效介质理论拓展到二维情况,设计了以熔石英为基底,工作波段为0.6~0.8μm的高衍射效率消偏振二维二元闪耀光栅。光栅两正交方向周期分别为3.31μm和0.473μm。仿真结果表明,在参考波长0.7μm处TE和TM偏振态衍射效率分别为79.5%和79.6%,0.6~0.8μm波段范围内TE和TM偏振态衍射效率均高于70%,偏振敏感度低于2.6%。与一维二元闪耀光栅相比,二维二元闪耀光栅具有高衍射效率、低偏振敏感度和易制作的优势。所得结论可用于指导实际应用中透射式二元闪耀光栅的设计,可望在光栅型高光谱成像仪中得到应用。

In order to reduce imaging spectrometer’s polarization sensitivity and improve its quantitative measurement accuracy of target’s spectral radiance,a transmission polarization-independent two-dimensional binary blazed grating was proposed.It consists of periodical groove units in both orthogonal directions and there contains7 sub-periods within one groove unit.Duty cycles of sub-periods are independent in two orthogonal directions,so that the effective index of both TE and TM polarizations can be modulated simultaneously,and the grating’s polarization property can be optimized.Through extending the effective medium theory to the two-dimensional pattern,a two-dimensional binary blazed grating with polarization-independent high efficiency on fused silica substrate was designed for wavelength range from 0.6 to 0.8μm.The grating periods in two orthogonal directions are 3.31μm and 0.473μm,respectively.Simulation results show that,for normal incident light,diffraction efficiencies of TE and TM polarizations at reference wavelength 0.7μm are 78.4%and 78.3%,respectively.Within wavelength range from 0.6 to 0.8μm,diffraction efficiencies of TE and TM polarizations are both above70%and the degree of polarization is below 2.6%.Compared with one-dimensional binary blazed grating,the two-dimensional grating has the advantages of high diffraction efficiency,low degree of polarization and easier manufacture.It is expected to be used in grating-type imaging spectrometers.