Broadband High-Efficiency Grating Couplers for Perfectly Vertical Fiber-to-Chip Coupling Enhanced by Fabry-Perot-like Cavity.

Zan Zhang,Zanyun Zhang,Lin Zhang,Bing Bai,Hongda Chen,Tianxi Gao,Xiaobo Xu,Wenping Gu,Chuantong Cheng,Beiju Huang

doi:10.3390/mi11090859

Abstract

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.

Highlights

Benefitting from mature complementary metal-oxide-semiconductor (CMOS) technology, various photonic devices have been demonstrated based on low loss silicon-on-insulator (SOI) waveguides, showing great promise for electronic-photonic integrated circuits, high-density photonic integrated circuits (PICs), and three-dimensional (3D) photonic integration [1,2,3,4,5]
Much effort has been devoted to the design and optimization of Grating couplers (GCs) [10,11,12,13] for interfacing between single mode fiber and silicon photonic chips
In conclusion, we have presented a broadband high-efficiency perfectly vertical GC, with minimum featmuirneimIsniuzemcolnafecragluteusriroetnhs,aiznwe2ela1hr9ganevrmeth.parBneys2et1na9tkenidnmga

Summary

Introduction

Benefitting from mature complementary metal-oxide-semiconductor (CMOS) technology, various photonic devices have been demonstrated based on low loss silicon-on-insulator (SOI) waveguides, showing great promise for electronic-photonic integrated circuits, high-density photonic integrated circuits (PICs), and three-dimensional (3D) photonic integration [1,2,3,4,5]. The Si3N4 layer and the grating together form a Fabry-Perot-like cavity, and obtain a reduced reflection around the resonant wavelength. Combined with the Equations (1)–(4), as long as D and H are carefully designed to make sure that R1 = R2 and φ = mπ for the desired wavelength, the Fabry-Perot-like cavity will be under resonance, reduced reflection and enhanced CE will be achieved

Design and Optimization

Findings

Conclusions