Orbital angular momentum assisted spin-directional coupling

Spin-directional coupling is associated with the quantum spin-Hall effect of photons, which has attracted much attention over the past few years. Here, we report orbital angular momentum (OAM) assisted spin-directional coupling and its reversal in a silicon nitride (SiN
_x
) photonic integrated circuit. SiN
_x
microring resonators with angular grating have been designed and realized to emit high purity circularly polarized OAM beam. In addition, utilized as an OAM receiver, photonic spin-controlled unidirectional excitation of whispering-gallery modes in ring resonator is also observed, coupling the left-hand and right-hand circularly polarized OAM beam to different channel waveguide, respectively. Our results exemplify a very promising waveguide-based OAM device such as a robust OAM assisted spin-directional coupler and may open up many new capabilities in emerging applications of on-chip chiral photonics and quantum optics.