Simulation of the gap plasmon coupling with a quantum dot

Active control of plasmon propagation via coupling to Quantum Dots (QDs) is a hot topic in nano-photonic research. When a QD is excited it acts like a dipole emitter. If this excited QD is placed near a metallic waveguide structure, it can decay either radiatively into bulk electromagnetic radiation, non-radiatively into heating of the metal or, of interest to this project, into a plasmon mode (γpl). By altering the position of the QD it is possible to optimise the decay into the plasmon mode. In this paper we present a system with a QD placed within the vicinity of a single mode Gap Plasmon Waveguide (GPW). First, we constructed a 2D finite element modelling simulation to find γpl using COMSOL MULTIPHYSICS for symmetric GPW structures with varying width (w) of the gap and distance of the QD to the waveguide surface (d). We then constructed a 3D model to calculate total rate of spontaneous emission of a QD (γtot) and determine spontaneous emission β factor, which is the ratio between γpl and all possible decay channels. It is shown that the decrease in width of the gap results in much larger β factor. As the gap width decreases, fraction of modal power in the metal increases slowing down the plasmon mode resulting in an enhancement in coupling efficiency. The optimized β factor for a square metallic slot waveguide is estimated up to 80%.

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