Chang Li-Min, Liu Lei, Gong Yuan-Hao, Tan Man-Qing, Yu Yu-De, Li Zhi-Yong
Appl Opt. 2018 Feb 1;57(4):678-683. doi: 10.1364/AO.57.000678.
The polarization dependence of a directional coupler (DC) based on asymmetric cross-slot waveguides is investigated. Due to structural birefringence, the coupling behaviors of the quasi-TE and quasi-TM modes in the DC vary with the waveguide geometry. A polarization-independent directional coupler (PIDC) and polarization beam splitter (PBS) are proposed by tailoring the ratio of the coupling length for quasi-TE and quasi-TM modes. The simulated results show that the coupling lengths of the designed PIDC and PBS are 8 and 28.25 μm, respectively. Both the PIDC and PBS show an insertion loss (IL) <0.7 dB on a bandwidth over 100 nm. The extinction ratios are ∼20 dB for PIDC and ∼14 dB for PBS. The fabrication-error tolerance of the practical devices is also discussed. In this study, we employ a commercial software tool for finite difference eigenmode and three-dimensional finite difference time domain methods to perform the numerical simulations.
研究了基于非对称交叉狭缝波导的定向耦合器（DC）的偏振依赖性。由于结构双折射，DC中准TE模和准TM模的耦合行为随波导几何结构而变化。通过调整准TE模和准TM模的耦合长度比，提出了一种偏振无关定向耦合器（PIDC）和偏振分束器（PBS）。模拟结果表明，所设计的PIDC和PBS的耦合长度分别为8μm和28.25μm。PIDC和PBS在超过100nm的带宽上均表现出插入损耗（IL）<0.7dB。PIDC的消光比约为20dB，PBS的消光比约为14dB。还讨论了实际器件的制造误差容限。在本研究中，我们使用商业软件工具进行有限差分本征模和三维有限差分时域方法来进行数值模拟。
