3D finite-element modeling of topological photonics in germanium

We investigated the photonic properties of topological lattices specifically designed to open a terahertz photonic bandgap in a germanium matrix. An extensive analysis based on three-dimensional finite element method enabled the identification of the requirements in terms of vertical height and lateral dimensions of the Ge motifs to suitably vary the bulk gap between 41 and 65 THz. Furthermore, by interfacing topologically distinct domains, we were able to observe the emergence of non-trivial edge modes that remain stable at a constant frequency despite the varying geometry of the unit cells. These findings provide valuable insights for designing resilient and effective photonic devices based on topological photonic crystals, and open new avenues for the realization of advanced quantum technologies in the THz regime.