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

• Published in: Micromachines (Basel) Vol. 11; no. 9; p. 859
• Main Authors: Zhang, Zan, Huang, Beiju, Zhang, Zanyun, Cheng, Chuantong, Bai, Bing, Gao, Tianxi, Xu, Xiaobo, Gu, Wenping, Zhang, Lin, Chen, Hongda
• Format: Journal Article
• Language: English
• Published: MDPI 17.09.2020; MDPI AG
• Subjects: Communication; Fabry-Perot cavity; grating coupler; photonic integrated circuit; silicon photonics
• ISSN: 2072-666X; 2072-666X
• DOI: 10.3390/mi11090859

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.