Efficient Channeling of Fluorescence Photons from Single Quantum Dots into Guided Modes of Optical Nanofiber

We experimentally demonstrate the efficient channeling of fluorescence photons from single $q$ dots on optical nanofiber into the guided modes by measuring the photon-count rates through the guided and radiation modes simultaneously. We obtain the maximum channeling efficiency to be $22.0(\pm 4.8)\%$ at a fiber diameter of 350 nm for the emission wavelength of 780 nm. The results may open new possibilities in quantum information technologies for generating single photons into single-mode optical fibers.

Figure 1

Schematic diagram of the experimental setup. Inset shows the optical nanofiber and microscope system. OL, BS, FM, and FL denote objective lens, beam splitter, flipper mirror, and filter, respectively. SMF, FC, and MMF denote single-mode fiber, fiber coupler, and multimode fiber, respectively. LD, APD, and OMA denote laser diode, avalanche photodiode, and optical multichannel analyzer, respectively.

Figure 2

Observed fluorescence photon-count rate by scanning the focusing point along the nanofiber. Origin of the horizontal axis corresponds to the center of the nanofiber. Inset shows an expanded profile of a peak marked by an arrow. Gray solid curve shows a Gaussian fitting with a width of $1.5\mu \mathrm{m}$ FWHM.

Figure 3

(a) Typical fluorescence photon-count rate from a single $q$ dot as a function of time. Black (upper) and red (lower) traces correspond to fluorescence photon-count rates observed through guided and radiation modes, respectively. (b) Histograms for the count rates plotted for guided and radiation modes. The right side black (left side red) histograms correspond to the guided (radiation) modes. Fittings by Gaussian profiles are drawn by gray solid curves. Adjusted $R^2$ for the fittings are estimated to be 0.85 and 0.86 for the right side black and left side red histograms, respectively.

Figure 4

Channeling efficiency as a function of fiber size parameter ($k_{0}a=2\pi a/\lambda$). Red solid curve denotes the theoretical prediction. Measured values are marked by black squares with error bars.