Theory of surface modes in structured plasmonic arrays

Metamaterials can provide many different functionalities and striking optical properties, whereby the optical control often comes from metallic building blocks which exhibit plasmonic resonances in the optical and infra-red frequency regimes. However, one of the major obstacles in the use of metallic elements is the overcoming of the losses in plasmonic structures. In this thesis, we consider how mode hybridisation can be used to circumvent these losses using cut-wire plasmonic arrays coupled to photonic slab waveguides. The resulting hybrid modes can have low loss characteristics and we investigate how the geometric parameters of the structure can be used to control the transmission and dispersion properties. We then investigate finite arrays finding they can support modes with extremely high quality factors (Q∼ 4000), which is highly unusual in plasmonic systems, and that the individual loss mechanisms can be controlled via the geometry. In the second part of the thesis we consider another type of surface mode, the spoof SPP. Theoretical methods for describing spoof SPPs in perfectly conducting materials are well established, enabling the design of an arbitrary spoof plasma frequency. However, for dispersive materials there have been a lack of theoretical studies. We begin by considering first how small changes to the spoof plasmon geometry affect the characteristics of spoof SPP waves, adapting the coupled mode method to slanted geometries and even right-angled triangular indentations, a structure not normally associated with spoof SPPs. We then develop a formalism based on the coupled mode method allowing the dispersion of real metal spoof SPPs to be understood and tuned, thus enabling control of the optical spoof SPP characteristics via both the geometry and the incorporated materials. This method also enables an in depth look at the modal losses which occur once dispersive materials are incorporated into the spoof plasmon dispersion relation and vary drasticallywith the groove width.Open Acces