Chiral lasing enabled by strong coupling

Chiral quasi-bound states in the continuum are spin-dependent high-<i>Q</i> resonances in meta-photonic structures that are realized by perturbing symmetry-protected optical states by engineering in-plane and out-of-plane asymmetries, and they support chiral lasing in the vertical direction. Here, we explore the coupling between two resonances in a chiral metasurface and introduce a mechanism for high-purity chiral laser emission. We reveal that two resonances with nearly orthogonal polarizations become strongly coupled in an engineered chiral metasurface. The inherent phase difference of the resonances, associated with the coherent destruction on the decay channel, can endow high-<i>Q</i> factor and maximize chirality to one of the hybrid modes. We verify this approach experimentally by measuring transmission spectra, angle-resolved photoluminescence, and laser emission. We believe that this mechanism allows breaking restrictions on conventional chiral quasi-BIC lasing, enabling the realization of chiral emission at any designed direction.