  The explorations of physical degrees of freedom with infinite
dimensionalities, such as orbital angular momentum and frequency of light, have
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
orbital angular momentum of light and have been demonstrated as on-chip
emitters of monochromatic optical vortices. On the other hand, whispering
gallery mode microresonators serve as a highly efficient nonlinear optical
platform for producing light at different frequencies - i.e., microcombs. Here,
we interlace the optical vortices and microcombs by demonstrating an optical
vortex comb on an III-V integrated nonlinear microresonator. The
angular-grating-dressed nonlinear microring simultaneously emits spatiotemporal
light springs consisting of 50 orbital angular momentum modes that are each
spectrally addressed to the frequency components (longitudinal whispering
gallery modes) of the generated microcomb. We further experimentally generate
optical pulses with time-varying orbital angular momenta by carefully
introducing a specific intermodal phase relation to spatiotemporal light
springs. This work may immediately boost the development of integrated
nonlinear/quantum photonics for exploring fundamental optical physics and
advancing photonic quantum technology.
