Design and Analysis of Plasmonic Couplers with Enhanced Performance

Abstract

The capability of plasmonics-based devices to avoid the diffraction limit commonly found in the sub wavelength devices has attracted the attention of researchers now a days. As a result of the demand of plasmonics-based devices the necessity of a plasmonic coupler has also increased to make these plasmonic-based devices compatible with the existing non-plasmonic devices. In this thesis, efficient coupling of light between the dielectric waveguide and plasmonic waveguide of metal-dielectricmetal (MDM) type has been investigated theoretically in three dimensions. A novel nano-plasmonic semi-elliptical structure of silicon (Si) has been used as a coupler that connects these waveguides. Finite Integration Technique (FIT) has been deployed for the investigation. A theoretical coupling efficiency of ∼78% at optical communication wavelength (1550 nm) has been achieved through numerical simulations. Later on, an air gap was inserted between the dielectric waveguide and the plasmonic waveguide which has improved the efficiency to ∼85% near 1550 nm. The dependency of coupling efficiency has been investigated by varying the curvature of the semi-elliptical coupler, the air gap width between the two waveguides, and the width of the air gap of MDM (Ag-Air-Ag) waveguide, and an optimal dimension of the proposed structure has been determined. A number of performance parameters like coupling efficiency, reflection coefficient, return loss, and voltage standing wave ratio (VSWR) have been analyzed with the obtained optimal dimensions for both of the cases. A broad range of operating frequency, tolerance to angular and air gap misalignment and excellent agreement to a demonstrated experimental coupler has made the proposed coupler distinctive