In-Loop Fabrication-Robust Inverse Design of Silicon Photonic Waveguide Bends

This paper presents a constrained multi-objective inverse design method for silicon photonic waveguide bends that include fabrication robustness within the optimization loop. Instead of a post-facto manufacturability check, up to 13 morphological variants per candidate design (erosion, dilation, opening, and closing at 20, 60, and 100 nm radii) are generated and their transmission spectra are co-optimized. The objective function is a weighted softmin, CVaR tail-risk minimization, spectral flatness enforcement, and hard gates on worst-case performance, with a three-stage lambda schedule and multi-start initialization. Applied to a 90-degree bend on 220 nm SOI, the method obtains 0.90 nominal C-band transmission with a worst-case variant transmission of 0.82, reducing the nominal-to-worst drop from 0.42 (post-hoc baseline) to 0.08. CVaR and compound morphological operations contribute independently significant robustness gains, confirmed by ablation experiments. All results are presented in a 2D effective-index approximation.