Near-unity efficiency in ridge waveguide-based, on-chip single-photon sources

TL;DR

This paper presents a numerical design for a highly efficient on-chip single-photon source using a ridge waveguide with a quantum dot, achieving near-unity coupling efficiency through optimized cavity and taper design.

Contribution

The study introduces a novel design approach combining finite element simulations and taper optimization to significantly improve on-chip single-photon source efficiency.

Findings

Achieved 97.7% coupling efficiency with a Purcell factor of 38.6.

Optimized taper design reduces mode mismatch and enhances efficiency.

Source properties remain robust under fabrication imperfections.

Abstract

We report a numerical design procedure for pursuing a near-unity coupling efficiency in quantum dot-cavity ridge waveguide single-photon sources by performing simulations with the finite element method. Our optimum design which is based on a 1D nanobeam cavity, achieves a high source efficiency $\epsilon_{xy}$ of 97.7$\%$ for an isotropic in-plane dipole, together with a remarkable Purcell factor of 38.6. Such a good performance is mainly attributed to the high index contrast of GaAs/SiO$_2$ and a careful cavity design achieving constructive interference and low scattering losses. Furthermore, we analyze the bottleneck of the proposed platform, which is the mode mismatch between the cavity mode and the Bloch mode in the nanobeam. Accordingly, we present the optimization recipe of an arbitrarily high-efficiency on-chip single-photon source by implementing a taper section, whose high smoothness is beneficial to gradually overcoming the mode mismatch, and therefore leading to a higher Purcell factor and source efficiency. Finally, we see good robustness of the source properties in the taper-nanobeam system under the consideration of realistic fabrication imperfections on the hole variation.