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Published on: July 18, 2015
Efficient broadband normal-incidence grating coupler on a lithium niobate-silicon nitride platform
Chengkai Jiang1, Zhilin Ye1,2, Jiachang Liang1
1National Laboratory of Solid State Microstructures, Key Laboratory of Intelligent Optical Sensing and Manipulation, and College of Engineering and Applied Sciences, Nanjing University, Nanjing 210093, China.
Abstract:
Thin-film lithium niobate (TFLN) is driving the development of next-generation optoelectronic technologies. Grating couplers are key components in TFLN photonic integrated circuits; however, achieving high-efficiency and broadband normal-incidence coupling remains challenging. In this work, we propose a lithium niobate-silicon nitride dual-layer vertical grating coupler, in which lithium niobate serves as the guiding layer, while an underlying silicon nitride grating is designed to suppress the second-order back-reflection under normal incidence. Simulations predict a coupling efficiency of -1.61 dB and a 3-dB bandwidth of 66 nm. The grating coupler was fabricated using the DUV wafer-scale process, and experimental results show a - 3.09 dB coupling efficiency and a 62-nm 3-dB bandwidth. The present work will pave the way for vertical fiber interconnects, high-density packaging, and wafer-level testing on the TFLN platform.
