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

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 εxy 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/SiO2 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.

GaAs-on-insulator ridge waveguide nanobeam cavities with integrated InAs quantum dots

“…However, holes that are too small may not provide an adequate photonic bandgap for sufficient reflection. To overcome this limitation, the mirror sections in this design are composed of a number of elliptical periodic holes etched into the GaAs waveguide to form a 1D DBR [21]. Notably, the right mirror section has fewer holes compared to its left counterparts, facilitating the directional coupling of photons into the right waveguide section.…”

“…Moving the dipole to align it with one of the antinodes will enhance the emission of the dipole due to the increased light-matter interaction, as shown in figure 2(c). Assuming that the distance from the dipole to the DBR is d and the period of the antinode in figure 2(c) is a, as in the previous method introduced in [21], the cavity length can simply be twice the distance from the dipole to the DBR, which will excite the odd-order longitudinal mode. That is, the cavity length is 2d.…”

“…Building on this foundation, the integration of two 1D distributed Bragg reflectors (DBRs) to form a nanobeam cavity further underscored the improved coupling efficiency achieved through careful cavity parameter design. This advancement was theoretically investigated on both the GaAs/AlGaAs [20] and GaAs-on-insulator (GaAsOI) platforms [21]. The latter, characterized by its high refractive index contrast that obviates the need for deep etching, combined with stronger optical confinement, theoretically enables near-unity coupling efficiency through careful cavity parameter design [21].…”

“…This advancement was theoretically investigated on both the GaAs/AlGaAs [20] and GaAs-on-insulator (GaAsOI) platforms [21]. The latter, characterized by its high refractive index contrast that obviates the need for deep etching, combined with stronger optical confinement, theoretically enables near-unity coupling efficiency through careful cavity parameter design [21]. Building on these works, we systematically explore on-chip nanobeam cavities with InAs QDs as single-photon emitters, covering design, fabrication, and experimental characterization.…”