Modular nanophotonic design of an on-chip quantum dot single-photon source with waveguided resonant optical excitation

A key element for on-chip quantum photonic systems is a reliable source of on-demand, indistinguishable, waveguided single photons that can be seamlessly integrated with photonic circuits. While epitaxial semiconductor quantum dots have the potential to fulfill such needs, optical excitation that is resonant with the quantum dot ensures maximum single-photon indistinguishability. To date, a majority of waveguided quantum dot sources that allowed resonant excitation have relied on free-space excitation beams. Free-space excitation requires significant experimental overhead, especially if multiple sources need to be addressed. waveguided resonant excitation, in contrast, has not been extensively explored, and yet enables simplified, plug-and-play operation of single and even multiple sources on chip. Here, we show design steps for what we believe to be a novel, modular nanophotonic structure that, relying on inversely designed components, allows waveguided resonant quantum dot excitation with high single-photon waveguide collection efficiencies (> 85 %) and low multi-photon probability (<10^-3), many favorable trade-off possibilities, and reasonable robustness to quantum dot positioning.