Novel on-chip plasmonic devices

Abstract

Abstract Surface plasmon polaritons (SPP) – shortly called plasmonics – have recently attracted a lot of researchers due to their potential applications in a wide range of fields including physics, biology and engineering. However, there are severe limitations to the utilization of plasmonics in practical applications due the high propagation losses of SPP. Additionally, the extremely short skin-depth of the metal used in guiding the SPP reduces the coupling efficiency between plasmonic waveguides. In this dissertation we propose novel devices that adopt engineering mechanisms to address the drawbacks of plasmonic guided waves. Compatibility with the widely spread silicon photonic platform is also investigated. The proposed devices rely on the exceptional capabilities of plasmonics to confine light beyond the diffraction limit. Contrary to conventional dielectric waveguides, the light is concentrated inside the lower refractive index medium in plasmonic waveguide. This effect is extremely useful in applications of electro-optical modulation or sensing where the active medium is of low refractive index. Thus, we focus on these applications introducing two high performance electro-optical modulators and a gas sensor. An electro-optical modulator based on an asymmetric hybrid plasmonic waveguide is introduced. The proposed modulator consists of two non-identical hybrid plasmonic waveguides (HPW) vertically coupled through an ultra-thin metal spacer. Each HPW has three main layers in a metal-oxide-semiconductor structure. The lower HPW employs an additional layer of conducting oxide that acts as the active material for electro-optical modulation. A detailed analysis is performed to study the supported modes in the on and off states of the modulator. It is established that the low loss symmetric super-mode guided by the modulator is easily excited by butt coupling to a standard silicon waveguide. The switching mechanism proposed is based on breaking the symmetry of the waveguide and introducing losses resulting in a high extinction ratio while keeping the insertion loss ultra-low.