Tunable dual quasi-bound states in the continuum in metasurfaces based on phase-change materials

Tunable metasurfaces, with their dynamic control over light–matter interactions, are increasingly important and attractive for various photonic applications. In this work, we present a dual-band tunable metasurface by leveraging quasi-bound states in the continuum (QBICs) based on TE₂₁ and TE₂₂ modes, achieved by incorporating a phase-change material (PCM) layer on a silicon-based metasurface. By introducing an asymmetric slit to break symmetry and utilizing GeTe PCM, we demonstrate simultaneous control over QBIC resonances through thermal modulation. The crystallization of GeTe leads to a substantial shift in resonance wavelengths exceeding 200 nm while retaining high Q-factors. Our design enables dynamic spectral control, offering new capabilities for multi-band filters, tunable resonators, and compact photonic devices. The findings underscore the potential of PCM enhanced QBIC metasurfaces for advanced applications in reconfigurable optics, adaptive imaging, and efficient light–matter interaction in nanophotonics.