Theory of nonlinear and amplified surface plasmon polaritons

Abstract

This thesis presents a study of Surface Plasmon Polaritons (SPPs) in hybrid metal-dielectric waveguides. The embedding of metal in nanostructured photonic components allows for manipulating and guiding light at the subwavelength scale. Such an extreme confinement enhances the nonlinear response of the dielectric medium, which is important for applications in optical processing of information, but is paid in terms of considerable ohmic loss in the metal. It is, however, possible to embed externally pumped active inclusions in the dielectric in order to compensate for the metal loss. A novel perturbative theory for Maxwell equations is introduced and applied to various nonlinear metal-dielectric structures, deriving the propagation equation for the optical field. The nonlinear dispersion law for amplified SPPs, filamentation and dissipative plasmon-soliton formation have been studied, revealing intrinsic core and tail instabilities that prevent solitons to propagate over long distances. Stable propagation of plasmon-solitons can be achieved in insulator-metal-insulator structures with active and passive interfaces. The active SPP is coupled with the passive SPP, which absorbs the perturbations destabilising the zero background of the soliton. Theoretical modelling of optical propagation in metal-dielectric stacks predicts a modified two-band structure, allowing for gap/discrete plasmon-soliton formation. Loss and nonlinear parameters in subwavelength nanowire waveguides are evaluated and compared to the results obtained by other research groups. In all calculations, particular attention is paid in considering boundary conditions accounting for loss and nonlinear corrections, which contribute to the propagation equation with a surface term that becomes significant in the subwavelength regime.EThOS - Electronic Theses Online ServiceGBUnited Kingdo