Reconstruction of topological boundary modes in non-Hermitian photonic crystals

We propose a non-Hermitian kagome-honeycomb photonic crystal platform for investigating the reconstruction of topological boundary and localized modes under the combined influence of lattice symmetry and non-Hermiticity modulation. The composite lattice supports both pseudospin and valley degrees of freedom, enabling pseudospin-related edge transport and valley-dependent boundary propagation within a single photonic structure. In finite hexagonal configurations, spatially distributed gain and loss modulation leads to complex eigenfrequency spectra in which bulk, edge, corner, and modulation-induced transition states can be distinguished by their field localization and non-Hermitian spectral responses. Reducing structural symmetry lifts the degeneracy of originally equivalent corner states and introduces transition states localized along the modulated region. We further show that geometric displacement breaks inversion symmetry and lifts the degeneracy between the upper- and lower-interface edge states. Consequently, the two branches separate in both the real and imaginary frequency spectra, accompanied by changes in local energy-flow patterns. As the gain–loss modulation strength increases, the corner modes gradually extend toward the adjacent boundaries and evolve into edge-like distributions. These results clarify how non-Hermiticity and crystalline-symmetry control jointly reshape topological modes, providing a route toward tunable boundary-mode selection in photonic crystals.