Tunable Narrow-Linewidth Si₃N₄ External-Cavity Semiconductor Laser Based on an Asymmetric Bezier Triple-Ring Resonator

This paper presents an AI-assisted design of a tunable narrow-linewidth external cavity laser based on an asymmetric Bezier cascaded triple-ring resonator. To address the high bending loss, limited quality factor, and footprint–loss trade-off in conventional external cavity ring resonators, asymmetric Bezier waveguide bends are introduced and optimized using particle swarm optimization, enabling smoother mode evolution and reducing bend loss. On this basis, this paper constructs a triple-ring-coupled external cavity structure to further enhance the mode-selection capability and filtering performance of the resonant cavity. Simulation results indicate that the asymmetric Bezier resonator optimized using particle swarm optimization can effectively reduce cavity loss and improve the resonator quality factor while maintaining a compact device footprint. Theoretical analysis indicates that the designed laser based on the proposed external cavity can achieve a linewidth of approximately 390 Hz. This work provides a feasible approach for designing high-performance, low-loss, and narrow-linewidth-integrated lasers, and is of significance for the development of integrated photonic laser sources.