Exploration of TFLN pedestal waveguides for high-speed modulation applications

Abstract

Lithium niobate has been the material of choice for high-speed modulation due to its large electro-optic coefficient. However, traditional bulk LN devices suffer from weak optical confinement and large footprints, hindering high-density integration. To address this, the Thin-Film Lithium Niobate (TFLN) platform has emerged as a compact solution, though standard etching techniques often introduce scattering losses due to sidewall roughness. In this work, we present a numerical analysis of a TFLN pedestal waveguide operating at visible wavelengths (λ=633 nm). Through 2D modal analysis, we identify an optimized core cross-section (W=0.6μm,H=0.25μm) for robust single-mode TE operation. Furthermore, using Copper (Cu) electrodes, we demonstrate a critical resonant coupling regime at narrow gaps (⪅0.25μm). We establish a minimum electrode-to-waveguide separation of 0.3 μm to avoid metal-induced absorption while ensuring efficient modulation performance.