Integrated vortex soliton microcombs

Synergistic control of the frequency and orbital angular momentum (OAM) of light offers new opportunities for the generation of spatio-temporal optical waveforms and optical metrology. However, their physical realizations are typically bulky and complex owing to challenges in creating, manipulating and detecting mutually coherent, high-dimensional OAM states. Here we achieve combined control over the frequency and the OAM of a comb structure on a photonic chip. Dissipative optical solitons are formed in a nonlinear ring microresonator and emitted owing to engraved angular gratings, with each comb line carrying a distinct OAM. The beam of such a vortex soliton microcomb manifests dynamically revolving, double-helical intensity profiles. The one-to-one correspondence between the OAM and frequencies features a high extinction ratio of over 18.5 dB, enabling precision spectroscopy of optical vortices. Our work provides an integrated solution for realizing coherent light sources that are multiplexed in the spatial and frequency domains, with the potential to establish a new approach to the generation of high-dimensional structured light. Nonlinear microring resonators can generate a vortex soliton microcomb, that is, a frequency comb with each comb line carrying a distinct orbital angular momentum.