Topology-preserving multilevel tuning of a quasi-BIC vortex microlaser with phase-change Sb2S3 metasurfaces

Dynamic reconfiguration of bound-state-in-the-continuum (BIC) microlasers typically involves mode hopping or angle switching, which compromises mode consistency and beam topology. Here, we demonstrate a phase-change Sb2S3 nanodisk metasurface microlaser that enables nonvolatile multilevel wavelength programming while preserving the same symmetry-protected quasi-BIC lasing mode and surface-normal emission. The device exhibits vertical lasing with a linewidth of ∼0.4 nm and Q-factors exceeding 3000. By laser writing of amorphous, intermediate, and crystalline states, the lasing wavelength is tuned from 881 to 889 nm without optical-mode switching or beam steering. Polarization-resolved far-field measurements together with interference analysis confirm vortex-beam emission with a conserved topological charge (q = −1) throughout the programmed tuning sequence. These results establish Sb2S3 quasi-BIC metasurfaces as a compact platform for programmable structured-light microlasers and integrated photonic systems.