A compact and ultra-wideband multimode interferometer (MMI)-based polarization beam splitter (PBS) is designed in a silicon-on-insulator (SOI) platform. A sub-wavelength grating (SWG) structure is employed in the multimode region to reduce the overall length of the structure and also increase its operating bandwidth. Instead of using the beat-length difference to separate the transverse electric (TE) and transverse magnetic (TM) polarized waves, the TM waves are directly coupled to the output bar port through an interconnecting waveguide, while the TE polarized waves are transmitted to the cross port by the self-imaging process. This substantially reduces the length of the PBS and the overall footprint can be as small as 4.8 × 21 µm 2 . The proposed device exhibits the extinction ratio of more than 15 dB in a 250 nm wavelength range (1.38–1.63 µm) and more than 12 dB in the 350 nm wavelength range (1.3–1.65 µm) for the TE and TM polarizations, respectively. In addition, the insertion loss remains below 1.2 dB for both the TE and TM polarization in a broad wavelength range from 1.38 to 1.54 µm. The proposed PBS can be fabricated by a single-step etching process on an SOI wafer. Moreover, our simulations show the robustness of the PBS performance to the fabrication errors’.

中文翻译：

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基于亚波长光栅多模干涉耦合器的紧凑型超宽带偏振分束器的设计与仿真

在绝缘体上硅 (SOI) 平台中设计了一种基于紧凑型超宽带多模干涉仪 (MMI) 的偏振分束器 (PBS)。在多模区采用亚波长光栅 (SWG) 结构以减少结构的总长度并增加其工作带宽。不是使用拍长差来分离横电 (TE) 和横磁 (TM) 极化波，而是将 TM 波通过互连波导直接耦合到输出棒端口，而 TE 极化波传输到通过自成像过程跨端口。这大大减少了 PBS 的长度，并且总占地面积可以小到 4.8 × 21 µm 2 。所提出的器件在 250 nm 波长范围 (1.38–1. 63 µm) 和 350 nm 波长范围 (1.3–1.65 µm) 中的 TE 和 TM 偏振超过 12 dB。此外，在 1.38 至 1.54 µm 的宽波长范围内，TE 和 TM 极化的插入损耗保持在 1.2 dB 以下。所提出的 PBS 可以通过单步蚀刻工艺在 SOI 晶片上制造。此外，我们的模拟显示了 PBS 性能对制造错误的鲁棒性。