Li Shuyi, Cai Lifeng, Gao Dingshan, Dong Jianji, Hou Jin, Yang Chunyong, Chen Shaoping, Zhang Xinliang
Opt Express. 2020 Nov 9;28(23):35395-35412. doi: 10.1364/OE.409981.
The focusing apodized subwavelength grating coupler (F-ASGC) has advantages of high coupling efficiency, small footprint and simple fabrication process, which make it a popular component for chip-scale coupling and testing of integrated optical circuit. However, the design of F-ASGC based on effective medium theory lacks accuracy, causing the drawbacks of peak wavelength deviation and performance degradation. In this work, we propose a deterministic design method of F-ASGC. Our grating coupler is formed by assembling various subwavelength grating units according to their complex effective indexes. The complex effective indexes of these grating units are accurately obtained by the weak form calculation. Then combining with transformation optics, we strictly analyze the F-ASGC for the first time. The simulation results show that the deterministically designed F-ASGC has high coupling efficiency of -2.51 dB, 3 dB bandwidth of 51 nm, and accurate central wavelength of 1553.1 nm. And we also fabricated it on the commercial SOI wafer. The measured maximum efficiency is -3.10 dB, the 3 dB bandwidth is 55 nm, and the central wavelength is 1551.5 nm.
聚焦变迹亚波长光栅耦合器（F-ASGC）具有耦合效率高、占用面积小和制作工艺简单等优点，这使其成为集成光路芯片级耦合和测试的常用组件。然而，基于有效介质理论的F-ASGC设计缺乏准确性，导致出现峰值波长偏差和性能下降等缺点。在这项工作中，我们提出了一种F-ASGC的确定性设计方法。我们的光栅耦合器是通过根据各种亚波长光栅单元的复有效折射率来组装而成的。这些光栅单元的复有效折射率通过弱形式计算精确获得。然后结合变换光学，我们首次对F-ASGC进行了严格分析。仿真结果表明，确定性设计的F-ASGC具有-2.51 dB的高耦合效率、51 nm的3 dB带宽以及1553.1 nm的精确中心波长。并且我们还在商用SOI晶圆上制作了它。测量得到的最大效率为-3.10 dB，3 dB带宽为55 nm，中心波长为1551.5 nm。
