Chiral spontaneous emission propagation based on a honeycomb photonic crystal slab

We propose the direction-tunable chiral photonic propagation of spontaneous emission based on magnetic helicity and finite-size effect in a topological honeycomb photonic crystal slab. The chiral edge state channels are excited by emitters with magnetic polarization due to the $C_6$ symmetry, where their propagation directions are tuned by the emitter's position on the magnetic helicity pattern. Meanwhile, the finite size of the honeycomb photonic crystal brings chirality oscillation, which also decides the chirality of photonic propagation. This method of controlling chiral transport in two-dimensional designs can be extended to a three-dimensional silicon-based photonic crystal slab containing a silver split ring resonator as the emitter providing spontaneous emission, which is convenient to fabricate via existing nanotechnology. Moreover, we show the magnetic Purcell effect with chiral transport in the three-dimensional topological PC slab structure. Our research reduces the threshold of on-chip photonic transmission under topological protection, which is helpful for single-photon sources, photonic integrated chip manufacturing, and quantum information processing.