A broadband high-brightness single photon source using a quantum dot embedded double solid immersion lens

Abstract

A single photon source (SPS) is an important component for quantum information technology. Among the candidates, S PSs based on epitaxial quantum dot (QD) reported excellent properties of quantum yield, Fourier-transform limited linewidth, multiphoton suppression, and indistinguishability. Despite these good properties, QD itself has poor extraction efficiency of photons to air from high index semiconductor. Micro-pillar and bull’s eye structures greatly improved the brightness. However, due to their high Q-factors, it is challenging to fabricate the SPSs since spectral matching of QD emission and the resonance of the structure is very difficult. In this presentation, we report deterministically fabricated bright and broadband SPS with a double solid immersion lens (SIL) structure on a gold reflector. With finite-difference time-domain simulation, the optimized double SIL structure is expected to provide 88% of maximum brightness in 0.5 NA and more than 80% of brightness in the range of 65 nm. For deterministic fabrication, we find a QD in micro-photoluminescence measurement and cure photoresist at the QD position at low temperature. For two-photon absorption curing, we match the wavelength of the searching and curing laser to reduce the aberration effect. Also, we could perfectly match the beam path by coupling the two lasers into the same single-mode fiber. We fabricated GaAs SIL structure with the cured pattern by an isotropic wet etching process. The second polymer SIL covered the GaAs SIL to complete the double SIL structure. Experimentally, we obtained brightness of 51.6% and g(2)(0)=0.014 in non-resonant excitation with a GaAs SIL structure larger than the optimized one. The presented structure is highly efficient yet easy to fabricate without using e-beam lithography and dry etching equipment, which can pave the way to practical use of SPSs.