Design and optimization of a high-efficiency uniform Si3N4 grating coupler using parameter sweeping and comprehensive performance analysis

Silicon (Si) grating couplers are widely used in photonic applications; however, they suffer from limitations such as high propagation losses and limited bandwidth. In contrast, silicon nitride (Si 3 N 4 ) has attracted increasing interest due to its low optical losses, broader bandwidth, and compatibility with CMOS fabrication processes. These advantages make Si 3 N 4 an attractive platform for developing compact, high-performance photonic integrated circuits, particularly for applications in telecommunications, sensing, and other advanced technologies. In this manuscript, we propose a novel grating coupler device architecture entirely based on Si 3 N 4 materials. The design features a uniform grating, which simplifies fabrication by eliminating the need for apodization, and incorporates a bottom reflector to enhance coupling efficiency by reducing downward optical losses. A two-dimensional model of the coupler was developed, and detailed finite-difference time-domain (FDTD) simulations were conducted. Through parametric sweeps, optimal values were determined for key parameters including grating period, etch depth, cladding thickness, incident angle, Si 3 N 4 thickness, buried oxide layer thickness, source position, and fill factor. The optimized design achieved a coupling efficiency of 76.41 % (−1.1685 dB) at a wavelength of 1550 nm, with a 1 dB bandwidth of 60.31 nm and a 3 dB bandwidth of 95.83 nm. A comparative analysis between efficiencies provided by metal and perfect reflectors was also performed to assess real-world loss factors. The proposed structure exhibits a high tolerance to fabrication, maintaining consistent performance despite variations in its structural parameters. The proposed uniform grating design offers performances comparable to more complex alternatives while being easier to fabricate, making it a practical and efficient solution for Si 3 N 4 -based grating couplers in modern photonic applications.