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对用于光栅优化设计初值估计的简化模式法(SMM)进行了修正。考虑介质光栅的反射对透射率的影响,从多层膜等效的角度结合模式理论,推导出介质光栅的透射效率公式,实现了对SMM的修正。计算结果表明,与SMM相比,修正后的方法与严格耦合波(RCWA)的计算偏差大大缩小,TE和TM波都小于2%。因此相对于只能提供设计参数优化初值的SMM,该方法可对光栅参数进行优化;与RCWA相比,该方法将透射光栅的衍射效率表达成模式的相位差偏移和光栅与空气导纳之差引起的反射,更直观地展示了光栅衍射的物理过程。基于此修正的简化模式法(MSMM),优化设计了一个双端口光栅分束器,该光栅在1020~1100nm波段,TE波和TM波的0级和-1级透射效率都在50%左右,具有较好的分束效果。
A simplified pattern method (SMM) for initial estimate of grating optimization design was revised. Considering the influence of dielectric grating reflection on transmittance, the transmission efficiency formula of dielectric grating is deduced from the perspective of multi-layer film equivalent and the correction of SMM is achieved. The calculated results show that compared with the SMM, the calculated deviation of the modified method and the strict coupled wave (RCWA) is greatly reduced, and both the TE and the TM wave are less than 2%. Compared with RCWA, this method expresses the diffraction efficiency of the transmission grating as the mode shift of the phase difference and the grating and air admittance The reflection caused by the difference shows the physical process of grating diffraction more intuitively. Based on the modified simplified mode method (MSMM), a dual-ported grating splitter is optimized. The transmission efficiencies of the 0th order and the -1st order of the TE wave and the TM wave in the 1020-1100 nm band are about 50% Has better beam splitting effect.