A High-Efficiency Wideband Grating Coupler Based on Si3N4 and a Silicon-on-Insulator Heterogeneous Integration Platform

To fully utilize the advantages of Si3N4 and Silicon-On-Insulator to achieve a high-efficiency wideband grating coupler, we propose and numerically demonstrate a grating coupler based on Si3N4 and a Silicon-On-Insulator heterogeneous integration platform. A two-dimensional model of the coupler was established and a comprehensive finite difference time domain analysis was conducted. Focusing on coupling efficiency as a primary metric, we examined the impact of factors such as grating period, filling factor, etching depth, and the thicknesses of the SiO2 upper cladding, Si3N4, silicon waveguide, and SiO2 buried oxide layers. The calculations yielded an optimized grating coupler with a coupling efficiency of 81.8% (−0.87 dB) at 1550 nm and a 1-dB bandwidth of 540 nm. The grating can be obtained through a single etching step with a low fabrication complexity. Furthermore, the fabrication tolerances of the grating period and etching depth were studied systematically, and the results indicated a high fabrication tolerance. These findings can offer theoretical and parameter guidance for the design and optimization of high-efficiency and broad-bandwidth grating couplers.