Chiral orbital lasing in a twisted bilayer metasurface.

Chirality is a fundamental concept in physics, core to many phenomena in nonlinear optics, quantum physics and topological photonics. Photons are intrinsically chiral when carrying spin angular momentum, whereas orbital angular momentum can induce chirality when photons interact with structures with broken mirror symmetry. Here, we observe orbital chiral lasing from a twisted bilayer photonic structure, by leveraging its inherent structural chirality. We design and fabricate a Moiré-type optical structure consisting of two semiconductor membrane metasurfaces. By optically pumping the twisted bilayer, we achieve single-mode lasing over a broad spectral range of 250 nm. The lasing emission exhibits chiral orbital characteristics, arising from helical and non-Hermitian couplings between collective guided resonances rotating clockwise and counterclockwise and confirmed by polarization-resolved imaging and self-interference measurements. The observed chiral orbital lasing from a twisted photonic structure can contribute to diverse applications of chiral light in diagnostics, optical manipulation and communication with light.