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%.
The interaction of Au particles with few layer graphene is of interest for the formation of the next generation of sensing devices <sup>1</sup>. In this paper we investigate the coupling of single gold nanoparticles to a graphene sheet, and multiple gold nanoparticles with a graphene sheet using COMSOL Multiphysics. By using these simulations we are able to determine the electric field strength and associated hot-spots for various gold nanoparticle-graphene systems. The Au nanoparticles were modelled as 8 nm diameter spheres on 1.5 nm thick (5 layers) graphene, with properties of graphene obtained from the refractive index data of Weber 2 and the Au refractive index data from Palik 3. The field was incident along the plane of the sheet with polarisation tested for both s and p. The study showed strong localised interaction between the Au and graphene with limited spread; however the double particle case where the graphene sheet separated two Au nanoparticles showed distinct interaction between the particles and graphene. An offset was introduced (up to 4 nm) resulting in much reduced coupling between the opposed particles as the distance apart increased. Findings currently suggest that the graphene layer has limited interaction with incident fields with a single particle present whilst reducing the coupling region to a very fine area when opposing particles are involved. It is hoped that the results of this research will provide insight into graphene-plasmon interactions and spur the development of the next generation of sensing devices.
The properties of ellipsoidal nanowires are yet to be examined. They have likely applications in sensing, solar
cells, microelectronics and cloaking devices. Little is known of the qualities that ellipse nanowires exhibit as we
vary the aspect ratio with different dielectric materials and how varying these attributes affects plasmon
coupling and propagation. It is known that the distance a plasmon can travel is further if it is supported by a
thicker circular nanowire, while thinner nanowires are expected to be able to increase QD coupling.
Ellipsoidal nanowires may be a good compromise due to their ability to have both thin and thick dimensions.
Furthermore it has been shown that the plasmon resonances along the main axis of an ellipsoidal particle is
governed by the relative aspect ratio of the ellipsoid, which may lead to further control of the plasmon.
Research was done by the use of COMSOL Multiphysics by looking at the fundamental plasmon mode
supported by an ellipsoidal nanowire and then studying this mode for various geometrical parameters,
materials and illumination wavelength. Accordingly it was found that ellipsoidal nanowires exhibit a minimum
for the wavenumber and a maximum for the propagation distance at roughly the same dimensions -
Highlighting that there is an aspect ratio for which there is poor coupling but low loss. Here we investigate
these and related attributes.
The design of structures capable of producing strong electric near-fields has become an active area of plasmonics
research with applications including sensor technology, surface enhanced Raman scattering and plasmon solar cells. The
purposeful design of plasmonic systems is complicated by the problem of finding analytical solutions to Maxwell's
equations. Recently we developed a theory, based on a simplification of the boundary element method (BEM), for
modeling the interaction between plasmonic nanoparticles mediated by their evanescent electric fields. The theory makes
extensive use of "electrostatic" resonances in which the nanoparticle system is taken to be much smaller than the
wavelength of the exciting radiation. The key result is an expression describing the "electrostatic" coupling between
arbitrarily-shaped particle pairs, expressed in terms of their resonant eigenmodes. Simple analyses of two and three
particle systems predict the formation of "dark modes" in which the dipole scattering cross section becomes small but the
evanescent electric fields remain large.
The propagation of surface plasmons in thin films is important for a number of technologies and has found applications
in chemical and biological sensing. There is growing interest in the use of surface plasmons coupled with optical systems
for high density photonic devices. While the analysis of the properties of surface plasmons at a metal-dielectric interface
is straightforward, it becomes increasingly more difficult as the number of surfaces is increased, as in a multi-layer thin
film structure. In this paper we discuss recent developments in mathematical methods for studying the properties of
surface plasmons in multi-layer thin film structures of the metal-insulator-metal (MIM) type. The films may consist of a
large number of layers creating MIMIM... structures that determine the allowed modes of the surface plasmons. The
mathematical formulation is based on a matrix method that yields the eigenvalues (dispersion relation) and the
eigenfunctions (mode profiles) associated with the surface plasmons. The method is used to analyze modes in a number
of structures. In particular it is shown that modes in structures that contain an optically resonant film can have dispersion
curves that cross one another and that changing the resonances in the film can lead to switching of the surface plasmon