Highly Efficient Photon Coupling Devices Utilizing a Nanofiber Tip

Abstract

Efficient coupling of photons from a single-photon source to the single-mode optical fiber is necessary for quantum cryptography and quantum information technology. Nanoemitters such as quantum dots, NV centers in nanodiamonds, and atoms are employed as a single-photon source. A typical method to collect photons from a nanoemitter is to use a lens with high numerical aperture (NA). However, further coupling of the photons collected by a lens to a single-mode optical fiber reduces the actual coupling efficiency. Recently the uses of silica nanofibers to collect light from a nanoemitter have been proposed and demonstrated[1-4]. A nanofiber is adiabatically connected to a standard single-mode optical fiber through a tapered region with low losses. In previous studies, photons from a nanoemitter are coupled to the guided mode of a nanofiber through the evanescent field around the nanofiber surface. In this study, we propose a new method utilizing a nanofiber tip to collect light from a nanoemitter to a nanofiber. We numerically simulated the coupling efficiency of light into the nanofiber when a point dipole source is located in the vicinity of a tip of nanofiber. Figure (a) depicts the simulation geometry. Figure (b) shows the dependence of the coupling efficiency on the nanofiber radius. Simulations are performed for radial and axial polarizations of the source. Up to 38% of the light radiated by a source is coupled to the fundamental guided mode of the nanofiber. Therefore these devices utilizing a nanofiber tip can be applied to efficient singlephoton sources.