In this paper, we report a two-layer five-port diffraction grating by a polarization-independent design under normal incidence. To be different from conventional five-port gratings, initially, we design a novel two-layer grating with operation in transmission. Next, we firstly design a polarization-independent grating with five-port splitting output. On the one hand, the accurate grating vector parameters are optimized using rigorous coupled-wave analysis (RCWA) approach. On the other hand, the inherent coupling mechanism happened in the grating region can be well explained by employing simplified modal method (SMM). More importantly, all reported conventional five-port beam splitter gratings were designed based on polarization dependent. Although they could obtain high diffraction efficiency for TE or TM polarization, it requires more complicated and time-consuming fabrication processes in practical grating applications. Thus, this work can open up a possible thought for designing polarization-independent multi-port beam splitter diffraction gratings.

中文翻译：

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正交入射下具有五端口分光输出的偏振无关两层光栅

在本文中，我们报告了一种在垂直入射下通过偏振无关设计的两层五端口衍射光栅。为了与传统的五端口光栅不同，我们最初设计了一种新型的具有透射操作的两层光栅。接下来，我们首先设计了一个具有五端口分光输出的偏振无关光栅。一方面，使用严格的耦合波分析 (RCWA) 方法来优化精确的光栅矢量参数。另一方面，光栅区域内发生的固有耦合机制可以通过简化模态方法（SMM）很好地解释。更重要的是，所有报道的传统五端口分束器光栅都是基于偏振相关设计的。虽然它们可以获得高的 TE 或 TM 偏振衍射效率，在实际光栅应用中，它需要更复杂和耗时的制造工艺。因此，这项工作可以为设计偏振无关的多端口分束器衍射光栅开辟可能的思路。