Phase-Aware Interconnect Routing for Photonic Waveguides via Nonlinear Optimization

We present a phase-aware interconnect routing framework for photonic waveguides based on nonlinear optimization, in which routing paths are treated as continuous geometric entities subject to curvature and fabrication constraints. By formulating waveguide routing as a geometry-constrained optimization problem, the proposed approach enables automatic generation of compact routing layouts while indirectly regulating routing-induced phase variations through curvature-aware design, without relying on circuit-scale full-wave electromagnetic optimization. The proposed framework is experimentally validated through the design and fabrication of an O-band arrayed waveguide grating (AWG)–based wavelength filter circuit on a silicon nitride (SiN) photonic platform. In comparison to a reference design based on a conventional box layout, the proposed routing method produces smoother curvature distributions along the arrayed waveguide arms and achieves lower insertion loss under a stringent minimum bend-radius condition. In particular, robust interferometric performance is maintained even for a minimum bend radius of $R_{\min }=50 \,{\mu }\mathrm{m}$, which highlights the effectiveness of suppressing abrupt curvature variations in mitigating routing-induced residual interference. The proposed routing framework is not limited to AWG-based circuits, and it is applicable to a broad class of photonic integrated circuits that require precise control of path-dependent phase or latency. This offers a practical foundation for scalable layout generation in advanced photonic integrated systems by providing a systematic and automation-friendly approach to curvature-constrained and phase-aware routing.