Lithium Niobate-Based Single-Mode Rib Waveguide: Design and Parameter Optimization

In photonic integrated circuits (PICs), singlemode waveguides play a critical role in ensuring low-loss and stable light transmission. Owing to its remarkable electro-optic, piezoelectric, and nonlinear optical properties, lithium niobate $\left(\mathrm{LiNbO}_{3}, \mathrm{LN}\right)$ has emerged as a prominent material for integrated photonic systems. Recently, the development of the lithium niobate on insulator (LNOI) platform has enabled LN to achieve high refractive index contrast and compatibility with silicon-based fabrication processes. In this study, geometric parameter optimization was carried out to achieve single-mode operation in a rib waveguide. The optimization process utilized the particle swarm optimization (PSO) algorithm, where the width and height of the waveguide was analyzed based on the effective refractive index ($\boldsymbol{n}_{\text {eff }}$) obtained via the Eigenmode Solver in Lumerical MODE. The results indicate that this approach not only ensures single-mode propagation but also enhances light confinement and guiding efficiency. Consequently, this work presents a systematic method for designing high-performance rib waveguides for LNOI-based electro-optic modulators and other photonic components.