Better single-photon source couples QD to waveguide

Single-photon sources have been successfully developed by coupling a single quantum dot (QD) to a photonic-crystal nanocavity.

Nov 1st, 2008

Single-photon sources have been successfully developed by coupling a single quantum dot (QD) to a photonic-crystal nanocavity (see www.laserfocusworld.com/articles/257230); however, these nanocavity single-photon sources operate over a narrow bandwidth established by the high quality factor of the cavity and, because the photons have to be coupled out of the cavity, the efficiency of these device is low. But researchers at the Technical University of Denmark (Lyngby, Denmark) and Universität Würzburg (Würzburg, Germany) have overcome these limitations by coupling a single QD to the mode of a photonic-crystal waveguide (PCW).

A PCW is formed by omitting a line of holes within a photonic-crystal slab. The slab is fabricated using electron-beam lithography and etching steps that create a 150-nm-thick gallium arsenide membrane with a single layer of indium arsenide QDs at its center. A pulsed Ti:sapphire laser excites the QDs within the PCW. Spontaneously emitted photons couple to the radiative modes and are collected by a CCD sensor and avalanche photodiode. When efficient coupling to the PCW matches the excited state of the QD, faster decay rates are observed for emitted photons. The β-factor, or QD coupling efficiency into the PCW, reaches 0.89 using the PCW approach. Such enhanced coupling improves the efficient channeling of single photons with an improved operating bandwidth of 20 nm for a 960 nm emission wavelength. Contact Toke Lund-Hansen at tolh@fotonik.dtu.uk or Peter Lodahl at pel@fotonik.dtu.dk.

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