利用不同占空比的亚波长结构剪裁光栅槽的等效折射率来改变光栅的衍射特性实现衍射输出光束与单模光纤之间的模式匹配，通过优化埋氧化层厚度和集成底部金反射镜，可以改善光栅耦合器弱的方向性，从而设计出用于SOI波导与光纤之间高效率耦合的光栅耦合器。采用本征模展开方法，模拟了光栅耦合器随剪裁的光栅槽等效折射率变化的相关特性，在SOI波导和单模光纤之间对波长为1550 nm的光获得了最高93.1%的耦合效率，3dB带宽为82 nm。

A high-efficiency grating coupler is designed to couple a planar waveguide and a single-mode fiber. An improvement in fiber coupling efficiency is obtained by using nonuniform diffraction gratings whose grating grooves consist of subwavelength structures with different duty cycle, which can better match the diffracted field profile to that of the Gaussian fiber mode. By optimizing the thickness of the buried oxide layer and integrating a gold bottom mirror, the directionality of SOI grating coupler can be increased. The coupler is optimized using eigenmode expansion-based simulations. A peak coupling eficiency of 93.1% at 1550 nm and 3 dB bandwidth of 82 nm are achieved.