Low-threshold vortex lasing in three-dimensional cavities via flatband bound states in the continuum
Bound states in the continuum (BICs) offer a robust route toward high-Q resonators and topological structured-light generation. While optically pumped BIC lasers have advanced significantly, realizing electrically pumped vortex lasers remains challenging due to conflicting requirements for optical confinement and carrier injection. Here, we demonstrate an electrically pumped vector vortex laser based on a photonic crystal-guiding layer-distributed Bragg reflector (PC-GL-DBR) heterostructure. The photonic crystal slab precisely tailors the symmetry and dispersion of BIC modes, including a flatband BIC state, while an intermediate guiding layer enables optical mode engineering without directly patterning the multiple-quantum-well active region, preserving efficient carrier injection and strong optical confinement. Under optical pumping, the device achieves single-mode lasing with a Q of 9700, a threshold of 0.129 kW/cm$^2$, and a side-mode suppression ratio of 26 dB. Crucially, room-temperature electrically pumped vortex lasing is achieved with a low turn-on voltage of 1.8 V, a threshold current density of 0.13 kA/cm$^2$, and a cavity Q of 8600, successfully preserving the characteristic vector-vortex emission of the topological BIC state. These results establish a practical route toward electrically driven BIC vortex lasers for integrated structured-light sources and topological photonics.