We propose a broadband high-efficiency grating coupler for perfectly vertical fiber-to-chip coupling. The up-reflection is reduced, hence enhanced coupling efficiency is achieved with the help of a Fabry-Perot-like cavity composed of a silicon nitride reflector and the grating itself. With the theory of the Fabry-Perot cavity, the dimensional parameters of the coupler are investigated. With the optimized parameters, up-reflection in the C-band is reduced from 10.6% to 5%, resulting in an enhanced coupling efficiency of 80.3%, with a 1-dB bandwidth of 58 nm, which covers the entire C-band. The minimum feature size of the proposed structure is over 219 nm, which makes our design easy to fabricate through 248 nm deep-UV lithography, and lowers the fabrication cost. The proposed design has potential in efficient and fabrication-tolerant interfacing applications, between off-chip light sources and integrated chips that can be mass-produced.

中文翻译：

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宽带高效光栅耦合器，可通过法布里-珀罗型腔增强完美垂直光纤到芯片的耦合。

我们提出了一种宽带高效光栅耦合器，用于完美的垂直光纤到芯片耦合。减少向上反射，因此借助于由氮化硅反射器和光栅本身组成的法布里-珀罗型腔，可以提高耦合效率。利用法布里-珀罗腔的理论，研究了耦合器的尺寸参数。通过优化的参数，C波段的向上反射率从10.6％降低到5％，从而使耦合效率提高了80.3％，而1-dB带宽为58 nm，覆盖了整个C波段。所提出结构的最小特征尺寸超过219 nm，这使我们的设计易于通过248 nm深紫外光刻来制造，并降低了制造成本。