Methodology for Topological Interface Engineering in 2D Photonic Crystals

Topological photonics offers a robust platform for controlling light, with applications such as backscattering‐immune edge‐transport and slow‐light propagation. A comprehensive and automated framework is presented for the design and characterization of symmetry‐protected interface modes in 2D photonic crystals. The main tool in this approach is an iterative band‐connection algorithm that ensures symmetry consistency across the Brillouin zone, enabling reliable reconstruction of bands even near degeneracies. Complementing this, a data‐driven symmetry classification method is introduced that constructs comparator functions directly from eigenmode data, removing the need for predefined symmetry operations or irreducible representations. These tools are particularly suited for generative or parametrized geometries where symmetries may vary. Using this framework, example structures exhibiting obstructed atomic limits, characterized by Wannier center displacements and mode inversions, are identified. The tradeoffs between interface mode dispersion and bulk bandgap size are analyzed, and how the number of photonic crystal periods at the interface governs the emergence and robustness of topological modes is shown. Finally, the scalability of this approach across material platforms and operating wavelengths, including the telecommunication range, is demonstrated. These contributions enable physically grounded and fully automated design of topological photonic interfaces, paving the way for large‐scale exploration and optimization of complex photonic structures.