Doubly resonant photonic antenna for single infrared quantum dot imaging   at telecommunication wavelengths
  Colloidal Quantum dots (CQDs) are nowadays one of the cornerstones of modern photonics as they have led to the emergence of new optoelectronic and biomedical technologies. However, the full characterization of these quantum emitters is currently restricted to the visible wavelengths and it remains a key challenge to optically probe single CQDs operating in the infrared spectral domain which is targeted by a growing number of applications. Here, we report the first experimental detection and imaging at room temperature of single infrared CQDs operating at telecommunication wavelengths. Imaging was done with a doubly resonant bowtie nano-aperture antenna (BNA) written at the end of a fiber nanoprobe, whose resonances spectrally fit the CQD absorption and emission wavelengths. Direct near-field characterization of PbS CQDs reveal individual nanocrystals with a spatial resolution of 75 nm (lambda/20) together with their intrinsic 2D dipolar free-space emission properties and exciton dynamics (blinking phenomenon). Because the doubly resonant BNA is strongly transmissive at both the CQD absorption and emission wavelengths, we are able to perform all-fiber nano-imaging with a standard 20 % efficiency InGaAs avalanche photodiode (APD). Detection efficiency is predicted to be 3000 fold larger than with a conventional circular aperture tip of the same transmission area. Double resonance BNA fiber probes thus offer the possibility of exploring extreme light-matter interaction in low band gap CQDs with current plug-and-play detection techniques, opening up new avenues in the fields of infrared light emitting devices, photodetectors, telecommunications, bio-imaging and quantum information technology. 
Zhihua Xie, Miguel Suarez, Mathieu Mivelle, Roland Salut, Jean-Marc   Merolla and Thierry Grosjean
physics.optics