Colloidal Quantum Dot Integrated Light Sources for Plasmon Mediated Photonic Waveguide Excitation

We operate micron-sized CdSe/CdS core shell quantum dot (QD) clusters deposited onto gold patches as integrated light sources for the excitation of photonic waveguides. The surface plasmon mode launched by the QD fluorescence at the top interface of the gold patches are efficiently coupled to photonic modes sustained by titanium dioxide ridge waveguides. We show that, despite a large effective index difference, the plasmonic and the photonic modes can couple with a very high efficiency provided the vertical offset between the two kinds of waveguides is carefully controlled. Based on the effective index contrast of the plasmonic and the photonic modes, we engineer in-plane integrated hybrid lenses. The hybrid lenses are obtained by shaping the contact interface between the plasmonic and the photonic waveguides. We demonstrate a 2-fold enhancement of the coupling efficiency for tapers equipped with a hybrid lens. Our results are expected to be useful for the development of low-cost, integrated light sources deployed in photonic circuits.