Integrated optical vortex microcomb

The exploration of physical degrees of freedom of light with infinite dimensionality, such as orbital angular momentum (OAM) and frequency, has profoundly reshaped the landscape of modern optics, with representative photonic functional devices including optical vortex emitters and frequency combs. In nanophotonics, whispering gallery mode microresonators naturally support applications based on the OAM of light and have been employed as on-chip emitters of monochromatic optical vortices. On the other hand, whispering gallery mode microresonators can serve as a highly efficient non-linear optical platform for producing light at different frequencies, that is, microcombs. Here we combine optical vortices and microcombs by demonstrating an optical vortex comb on a III-V integrated non-linear ring microresonator. The angular grating-dressed non-linear microring simultaneously emits spatiotemporal light springs consisting of 50 OAM modes, with each frequency of the microcomb carrying a distinct OAM value. We also experimentally generate optical pulses with time-varying OAM by carefully endowing the spatiotemporal light springs with a specific intermodal phase relation. We expect our work to favour the development of integrated non-linear and quantum photonics for exploring fundamental optical physics and advancing photonic quantum technology. Microring-based vortex combs with each comb line carrying a distinct orbital angular momentum generate light springs with time-varying orbital angular momenta.