Observation of chiral emission enabled by collective guided resonances.

A simple yet insightful question is whether it is possible to arrange optical resonances in such a way that their collective response differs from that of the individual constituents. Here, inspired by the collective oscillation of spatially localized modes and Fourier duality between real and momentum spaces, we demonstrate a chiral emission of collective guided modes by leveraging the omnidirectional hybridization of individual guided resonances within a photonic crystal slab. Specifically, we encircle a uniform photonic crystal with isotropic boundaries and hybridize discrete bulk guided resonances into a series of collective modes owing to the scatterings of the boundaries. This results in a chiral spiral vortex emission in real space. By using asymmetric pumping to lift the chiral symmetry, we then achieve stable single-mode lasing oscillation of the spiral collective mode and confirm the nature of vortex emission through polarization-resolved imaging and self-interference patterns, thus demonstrating a vivid example of collective oscillations in the momentum space.