Dynamic manipulation of Goos-Hänchen shifts empowered by phase-change quasi-BIC metasurfaces

Dynamic manipulation of the Goos-Hänchen (GH) shift is crucial for photonic applications such as information storage and ultrasensitive sensing. However, most previously reported GH shift enhancements rely on resonance effects or quasi-bound states in the continuum (quasi-BICs), which typically require passive adjustment of structural parameters. Herein, we achieve dynamic evolution of BICs by actively adjusting the excitation power density of the pump light incident upon the phase-change materials (PCMs). By regulating the crystalline phase through the excitation power density of the pump light, two off-Γ points, each bearing a -1 topological charge, gradually approach the Γ point carrying a + 1 topological charge and subsequently merge, giving rise to the annihilation of topological charges. Assisted by controllable quasi-BICs with high reflectance, the value of the GH shift can be flexibly controlled. Based on the enhanced GH shifts by quasi-BICs, we further design an ultrasensitive sensor with a sensitivity exceeding 1 × 10³λ/RIU, reaching a maximum value of 2.9 × 10⁴λ/RIU. This study reveals the tremendous application potential of PCMs in BIC-related optical research, and provides a novel technical route for the dynamic control of optical devices.