High Q-factor fano resonance via coupling of topological corner states and waveguides for enhanced optical sensing

Recent advancements in topological photonics with the distinctive sharp, asymmetric and high-Quality factor Fano resonance bring wide applications in sensing and optical switching. This study presents a novel approach for constructing a resilient sensor based on topological resonance. The proposed structure was contracted based on coupling between topological corner state (TCS) and conventional waveguide to obtain Fano resonance mode with an extraordinary quality factor (Q-factor). The waveguide process provides a well-defined propagating mode, while the TCS is a localized mode that is topologically protected against structure perturbations. The designed sensor exhibits high robustness toward defects and changes in the background refractive index. For optical sensing, the proposed sensor achieves a high sensitivity value of 394.2nm/RIU, high Q-factor >10⁷, exceptional figure of merit (FOM) value of >10⁷, and has an ideal detection limit value of 10^-7 RIU. Our work paves the way for a new paradigm in sensing, enabling the development of ultracompact on-chip nanophotonic devices with unprecedented sensitivity and control. © 2025 Elsevier Ltd