Comparative optical coupling and propagation analysis of Al 0.3 Ga 0.7 N and GaN straight and circularly bent waveguides for visible-light communication applications

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Abstract Integrated III-nitride waveguides are promising platforms for visible-light photonic integrated circuits owing to their wide bandgap, optical transparency, and compatibility with visible-wavelength operation. In this work, a comparative numerical investigation of straight, 90°, and 180° circularly bent Al₀.₃Ga₀.₇N and GaN waveguides is carried out using COMSOL Multiphysics. An equivalent optical dipole excitation source is employed to analyze dipole-to-waveguide coupling and guided-wave propagation characteristics. The influence of waveguide width, propagation length, and dipole-to-waveguide separation distance on the normalized optical response is systematically investigated. The results show that waveguide widths below approximately 3 µm exhibit unstable optical behavior due to weak modal confinement and enhanced near-field interactions. Comparative analysis further indicates that Al₀.₃Ga₀.₇N waveguides exhibit smoother and more consistent optical response under bent waveguide conditions, whereas GaN waveguides provide stronger optical confinement in straight-waveguide configurations. The study highlights the influence of refractive-index contrast and waveguide geometry on optical coupling and propagation behavior, providing useful design guidelines for the development of future III-nitride visible-light photonic integrated systems.

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