10th U6+ Consortium of African Universities International Conference

Efficient second-harmonic generation (SHG) in thin-film lithium niobate-on-insulator (TFLNOI) waveguides requires accurate phase matching between interacting optical modes. Conventional approaches such as quasi-phase matching (QPM) achieve high efficiency but require complex periodic domain engineering, while modal phase matching (MPM) is highly sensitive to fabrication imperfections and lacks post-fabrication tunability. This research presents the design and simulation of a compact electro-optically tunable TFLNOI ridge waveguide for efficient SHG. The waveguide structure was modeled and optimized using the wave optic and electrostatics modules in COMSOL Multiphysics. Modal analysis was carried out to determine the propagation constants and effective refractive indices of the interacting modes. Phase matching was achieved through modal dispersion engineering between the fundamental TM00 mode at 1550 nm and the second-harmonic TM01 mode at 775 nm. Electro-optic tuning based on the Pockels effect was introduced using integrated indium tin oxide (ITO) and gold electrodes to dynamically control the phase mismatch. Simulation results showed strong optical confinement of approximately 88 %, low optical propagation loss of , and high normalized conversion efficiency of . The optimized structure achieves phase-matching wavelength sensitivities of 0.216 nm/V and 0.25 nm/V with respect to ridge height and width variations respectively. Electro-optic tuning successfully restored high conversion under fabrication-induced ridge-width deviation of ±10 nm using CMOS compatible voltages. The findings demonstrate that electro-optically tunable modal phase matching provides a compact, fabrication-tolerant, and dynamically controllable alternative to conventional QPM-based TFLNOI devices. The proposed structure is therefore promising candidate for integrated nonlinear photonics, optical signal processing, frequency conversion, and tunable photonic systems.