Orbital chiral lasing in twisted bilayer metasurfaces

Chirality is a fundamental concept in physics that underpins various phenomena in nonlinear optics, quantum physics, and topological photonics. Althoughthe spin of a photon naturally brings chirality, orbital angular momentum canalso become chirally active in the structures with a broken mirror symmetry.Here, we observe orbital chiral lasing from a twisted bilayer photonic structure leveraging its inherent structural chirality. Specifically, we design andfabricate a Moire-type optical structure by bonding and rotating two separatesemiconductor membrane metasurfaces. We achieve single-mode lasing overa broad spectral range of 250 nm by optically pumping the twisted structure.The lasing emission exhibits orbital chiral characteristics, arising from helicaland non-Hermitian couplings between clockwise and counter-clockwise rotating collective guided resonances, confirmed by polarization-resolved imagingand self-interference patterns. Our results provide the first observation oforbital chiral lasing in twisted photonics, and they can contribute to diverseapplications of chiral light in diagnostics, optical manipulation, and communication with light.