Tailoring coupled topological corner states in photonic crystals via symmetry breaking induced by defects

Abstract

In this paper, we present an effective approach to tailor the optical properties of coupled corner states in photonic crystal (PhC) supercell arrays by symmetry breaking. Defects are strategically introduced into unit cells to break the in-plane C4v symmetry, and numerical simulations confirm the preservation of the band gap and two-dimensional Zak phases, in spite of the presence of defects. Notably, the size of defects is demonstrated to play a significant role in tuning the eigenfrequencies, quality (Q) factors, and band structures of the coupled corner states. Furthermore, these defects exhibit the ability to transform topological dark states into bright states, enabling efficient excitation by external plane waves and polarization-dependent Q factors. The resonant origin of the coupled corner states is comprehensively elucidated using a multipole decomposition analysis. This study further releases the potential of the topological light-matter interaction, holding significant implications for the design and advancement of topological photonic devices with on-demand tunability and multifrequency regions for various applications such as lasing, sensing, and quantum information processing. Published by the American Physical Society 2024