Investigation into the coupling of quantum dots to photonic crystal nanocavities at telecommunication wavelengths

Abstract

Recently, the emission of single photons with emission wavelength in the 1.3 µm telecommunication window was demonstrated for InAs quantum dots. This makes them strong candidates for applications such as quantum cryptography, and in a longer term, quantum computing. However, efficient extraction of the spontaneous emission from semiconductors still represents a major challenge due to total internal reflection at the semiconductor/air interface. In particular, single photon sources based on quantum dots are plagued by low extraction efficiency and poor coupling to single-mode fibers, typically on the order of 10-3 10-4, which prevents their application to quantum communication. To seek a solution to this problem, this thesis work explores the integration of quantum dots, with emission at 1.3 µm, in photonic crystal microcavities. Photons emitted in a mode of the cavity are funneled out of the semiconductor, and thus bypass the total internal reflection. In addition, the modified density of electromagnetic states in the cavity affects the emission lifetime of a weakly coupled emitter: in resonance, we assist to an increase of the emission rate, known as the Purcell effect, that would allow faster data transmission. Photonic crystal microcavities conveniently address this objective as they provide modes with the required small volumes and high quality factors. They also allow the engineering of the farfield pattern of the cavity modes, and thus of the collection efficiency. In the following pages, after brie y reviewing single photon emitters, the Purcell effect, and photonic crystal cavities, we present our results on the coupling of quantum dots to photonic crystal cavities. We report on the different strategies we used to control the tuning between the cavity mode and the quantum dot emission frequency. We also show our efforts in improving the collection of coupled photons by engineering the shape of the microcavity. Finally, we present our time-resolved measurements demonstrating the Purcell effect under optical and electrical operation.