Contents 1. Introduction
Photonic quantum information applications often require an ideal single photon source (SPS) with on-demand single photon emission into a desired quantum channel and indistinguishability of the generated photons. Further specifications then include high repetition rate (GHz range), tunable wavelength, electronic trigger, and photon emission into a Gaussian mode for fiber coupling. Among various candidates to realize an ideal SPS, semiconductor quantum dots (QD) have demonstrated excellent progress so far [1]. However, all of the aforementioned criteria have not yet met simultaneously in a QD device. One of the major challenges, inter alia, remains the overall collection efficiency of the emitted photon into a single mode fiber (SMF). Several schemes have been proposed to overcome this challenge where nanophotonics structures including micropillar cavities [2], [3], Bragg gratings [4] and photonic nanowires [5] were used. Nevertheless, due to directionality of the emitted photon, reflection at the high refractive index boundary, very high numerical aperture (NA) of the output mode and loss in the optical components, overall collection efficiency at the SMF is very low compared to the theoretical limit. In this work, we design a complete scheme for high efficiency light coupling from an InP/InAsP quantum dot to a single mode fiber (Fig. 1a). The QD is embedded in a tapered nanowire (NW) waveguide (QD-NW) [6] where the geometry of the NW is optimized to have Gaussian output mode along with relatively low NA. A lithographically defined alignment structure is designed to house the collection fiber, where a graded index multimode fiber lens (GRIN-lens) in combination with a SMF is designed for high efficiency coupling of light from the nanowire into the fiber.
