In this paper, an enhanced polarization-independent two-layer five-port grating with covering layer is proposed. The rigorous coupled-wave analysis (RCWA) is used to predict grating parameters. In addition, the total efficiency of the polarization-independent five-port grating with covering layer can exceed 80% with the good uniformity of 1.97% for TE and TM polarization. The inherent coupling mechanism and the electric field energy distribution of the gratings are explained well under TE and TM polarization by the simplified mode method (SMM) and the finite element method (FEM). According to the reported five-port gratings, the proposed transmission five-port grating with a covering layer has good uniformity for TE and TM polarization. Moreover, the grating can be protected and the groove of the grating can be kept clean by adding a covering layer during the actual fabrication. At the same time, the fabrication errors of the two-layer five-port diffraction grating are further considered. Therefore, the numerically simulated five-port grating with covering layer has a wide application prospect in precision displacement measurement and holographic projection imaging.

中文翻译：

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带覆盖层的增强型偏振无关两层五端口光栅

在本文中，提出了一种增强的偏振无关的两层五端口带覆盖层光栅。严格耦合波分析（RCWA）用于预测光栅参数。此外，具有覆盖层的与偏振无关的五端口光栅的总效率可以超过80%，对于TE和TM偏振均具有1.97%的良好均匀性。通过简化模式法（SMM）和有限元法（FEM）很好地解释了在TE和TM极化下光栅的固有耦合机制和电场能量分布。根据报道的五端口光栅，所提出的具有覆盖层的透射五端口光栅对于TE和TM偏振具有良好的均匀性。而且，在实际制作过程中，通过增加覆盖层可以保护光栅，保持光栅凹槽的清洁。同时，进一步考虑了两层五端口衍射光栅的制造误差。因此，数值模拟的带覆盖层五端口光栅在精密位移测量和全息投影成像中具有广泛的应用前景。