EO Modulators using Plasmonic Waveguides

Optical modulators are key components in the design of high speed optical communication systems. In particular, Electro Optic Mach-Zehnder modulators (EO MZM) realized in LiNbO3 ere a well established and reliable solution in long haul communication suitable to encode both analog and digital information. Even though the operating principle is the linear electro-optic effect (Pockels Effect), these devices are considered interferometers since they exploit the interference between two phase shifted light beams to obtain an amplitude modulation. The appealing feature of LiNbO_3 MZM is the possibility to obtain a good trade off between the need to have low loss, low driving voltages broad bandwidth and low chirp, while a big drawback is the large footprint (cm ^2) that poses a severe limitation when compact and performing devices are need \cite{Haffner1}. In the search of a valid alternative to LiNbO3 MZM, when very small dimensions are required, Plasmonic POH Modulators emerged as promising devices ideally capable of providing a large bandwidth (>100GHz), small energy consumption ( 25fJ/b) and a very small voltage-length product (40Vmum) with a footprint of the order of few mum^2. In these structure Metal-Insulator-Metal (MIM) waveguides are integrated on SOI wafer, light propagates as surface plasmons at the metal-insulator interfaces making possible to achieve sub-wavelength field confinement (main cause of the small dimensions). In this thesis work a study of a Plasmonic Mach-Zehnder modulators is proposed. Starting from the analysis of the basic Electro Optic Mach-Zehnder modulator structure, then a block model developed in a MICROWAVE CAD environment is proposed, it gives the possibility to design and optimize the driver and modulator within the same circuit environment\cite{Pirola}. The last part focuses on the description of waves propagation through plasmonic structures and proposes simulation results obtained integrating the electric characteristics of plasmonic structures in the block model previously described.