Dirac‐Point‐Assisted Topological Charge Exchange in Dual‐Wavelength BIC Vortex Microlasers

On‐chip lasers that emit wavelength‐multiplexed structured light are important in integrated photonics. Bound states in the continuum (BICs) provide high‐quality resonances with radiation topology, enabling vortex lasing at multiple wavelengths. However, the topological charges of the symmetry‐protected BICs at the Γ‐point are constrained by lattice symmetry, whereas creating Dirac‐point degeneracies between photonic bands can redistribute polarization singularities. The connection between momentum‐space topology reconstruction and topological charge exchange of dual‐wavelength vortex emission remains underexplored. Here, we demonstrate a dual‐wavelength BIC vortex microlaser in a Lieb‐lattice photonic crystal. Numerical calculations reveal that, during continuous structural parameter tuning, the topological reconstruction is accompanied by the emergence of Dirac points, while the topological charges associated with the Γ‐point BIC modes are exchanged. Experimentally, room‐temperature dual‐wavelength lasing operation is realized, with far‐field polarization and self‐interference measurements revealing the transformation of topological singularities between two BIC modes. This work connects momentum‐space BIC topology reconstruction with coherent vortex lasing, offering an active route toward compact and tunable structured‐light sources.