Cascade Enhancement\nand Efficient Collection of Single\nPhoton Emission under Topological Protection

High emission rate, high collection efficiency, and immunity\nto\n defects are the requirements of implementing on-chip single photon\nsources. Here, we theoretically demonstrate that both cascade enhancement\nand high collection efficiency of emitted photons from a single emitter\ncan be achieved simultaneously in a topological photonic crystal containing\na resonant dielectric nanodisk. The nanodisk excited by a magnetic\nemitter can be regarded as a large equivalent magnetic dipole. The\nnear-field overlapping between this equivalent magnetic dipole and\nedge state enables achieving a cascade enhancement of single-photon\nemission with a Purcell factor exceeding 4 × 10<sup>3</sup>.\nThese emitted photons are guided into edge states with a collection\nefficiency of more than 90%, which is also corresponding to quantum\nyield due to topological antiscattering and the absence of absorption.\nThe proposed mechanism under topological protection has potential\napplications in on-chip light–matter interactions, quantum\nlight sources, and nanolasers.