We theoretically investigate the potential of the extreme mode-confinement waveguides for single-photon sources. Confining light far below the diffraction limit in a V-groove GaAs-on-insulator waveguide, we enhance the Purcell factor by a factor of eight.

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 emitters1-3 and frequency combs4-6. In nanophotonics, whisper gallery mode microresonators naturally support orbital angular momentum of light7 and have been demonstrated as on-chip emitters of monochromatic optical vortices8. On the other hand, whisper gallery mode microresonators serve as a highly-efficient nonlinear optical platform for producing light at different frequencies - i.e., microcombs9. 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 up to 50 orbital angular momentum modes that are each spectrally addressed to the frequency components ((longitudinal whispering gallery modes) of the generated microcomb. We further show that the integrated vortex comb with varied orbital angular momenta distributed across different frequencies exhibits unprecedented advantages in the synthesis of spatio-temporal optical pulses with time-varying orbital angular momenta. This work may immediately boost the development of integrated nonlinear/quantum photonics for exploring fundamental optical physics and advancing photonic quantum technology.

We propose an extreme dielectric confinement bullseye microcavity for single-photon emission and theoretically show the nanometer-scale light confinement enables a Purcell factor of 87, which is four times larger than that of standard bullseye microcavities.