Plasmonic Waveguides : Design and Comparative Study

Sammanfattning: Although photonics offers an attractive solution to the speed limitation of electronics, reducing the size of bulky photonic components is one of the major issues towards the implementation of photonic integrated circuits. Plasmonic circuits, which tightly confine electromagnetic waves at the metal-dielectric interface, can be a potential solution to this problem. Despite an excessive amount of papers published in the field, there exist an inconsistency in terms of the measure of plasmonic modal properties, especially their mode size. In this thesis work, several representative plasmonic structures are studied and there modal characteristics are cross-compared. Confinement has been calculated using several definitions in order to measure their figure of merits consistently. In addition, we propose a plasmonic waveguide, which achieves both deep sub-wavelength scale confinement and relatively long propagation. The waveguide consists a metal nanowire on top of a high index dielectric strip which can be made of Germanium. The hybridization of dielectric mode and cylinder plasmon polariton mode leads to localization of the mode energy in the nanoscale gap. This structure outperforms existing plasmonic waveguides in terms of gure of merit, which makes the waveguide particularly useful in high density photonic integrated circuits. This thesis also investigates optical forces due to the enhanced gradient field in plasmonic waveguides. Gradient forces and trapping forces are calculated using Maxwell's stress tensor for dierent hybrid waveguides, among which the forces with the proposed waveguide structure are found to be the largest.