Numerical Calculation of Grating Couplers Based on SiN-Loaded LNOI

Lithium niobate on insulator is a promising photonic platform that combines electro-optical properties with a high refractive index contrast, enabling miniaturization of photonic integrated circuits. However, coupling between optical fibers and thinfilm waveguides remains challenging, as conventional processes often require direct etching of lithium niobate on insulator. Such fabrication steps can introduce additional optical losses, complexity, and variability. In this study, a silicon nitride-loaded lithium niobate on insulator-based grating coupler is proposed as an alternative, leveraging the optical and mechanical characteristics of silicon nitride. Through detailed finite element method simulations, design parameters were optimized, leading to a transmission efficiency of fifty percent at a wavelength of 1.55 μm with a bandwidth of 90 nm. Comparative evaluations indicate that this design achieves performance comparable to directly etched lithium niobate on insulator structures, while offering greater fabrication tolerance and simplified processing. Future experimental investigations are expected to validate its potential for telecommunications and light detection and ranging applications.