Spontaneous emission (SE) of a Quantum emitter depends mainly on the transmission strength between the upper and lower energy levels as well as the Local Density of States (LDOS)<sup></sup>. When a QD is placed in near a plasmon waveguide, LDOS of the QD is increased due to addition of the non-radiative decay and a plasmonic decay channel to free space emission<sup>[2-4]</sup>. The slow velocity and dramatic concentration of the electric field of the plasmon can capture majority of the SE into guided plasmon mode (Г<sub>pl</sub> ). This paper focused on studying the effect of waveguide height on the efficiency of coupling QD decay into plasmon mode using a numerical model based on finite elemental method (FEM). Symmetric gap waveguide considered in this paper support single mode and QD as a dipole emitter. 2D simulation models are done to find normalized Г<sub>pl</sub> and 3D models are used to find probability of SE decaying into plasmon mode ( β) including all three decay channels. It is found out that changing gap height can increase QD-plasmon coupling, by up to a factor of 5 and optimally placed QD up to a factor of 8. To make the paper more realistic we briefly studied the effect of sharpness of the waveguide edge on SE emission into guided plasmon mode. Preliminary nano gap waveguide fabrication and testing are already underway. Authors expect to compare the theoretical results with experimental outcomes in the future.
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 (γ<sub>pl</sub>). By altering the position of the QD it is possible to optimise the decay into the plasmon mode.<p> </p>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 γ<sub>pl</sub> 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 (γ<sub>tot</sub>) and determine spontaneous emission β factor, which is the ratio between γ<sub>pl</sub> 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%.