Optical components based on high index materials

This thesis is part of a Ph.D. project: ”Optical components based on high index materials”, carried out at COM at the Technical University of Denmark. The project has focused on the material and optical characterization of silicon rich nitride (SRN) thin films and waveguides, with the goal of developing efficient and reliable fabrication methods for submicron optical components for use in high-speed optical telecommunications. Some of the results are described in more detail in previously published papers. The work has been divided into three parts: thin film characterization, cleanroom fabrication, and analysis waveguide components. The thin film characteristics and the cleanroom fabrication strongly influence the performance of optical waveguide components. Hence, the thin film properties and waveguide fabrication have been developed and reoptimized for the best optical performance. The first part of the work is material and optical characterization of the thin films. It consists of determination of stoichiometry, chemical composition, and optical loss of SRN film films. Most of this part of the work was performed at the Universität der Bundeswehr München, Germany, and the University of Twente, the Netherlands. The second part is fabrication of optical submicron structures in SRN films. The cleanroom fabrication was optimized in such a way as to minimize the optical losses in the waveguide structures and maximize the overall production efficiency. A process has been developed for processing submicron structures with UV-photolithography and reactive ion etching. The components have vertical sidewalls with a roughness small enough not to induce scattering losses. The processing steps are optimized so as to produce a reliable processing sequence for making low loss single mode waveguide components. The third part is an analysis of SRN waveguides and components. The main focus has been on minimizing the optical losses resulting from the production of waveguide structures in the SRN thin films. New and yet unpublished results show that a process optimization and a reduction of the number of particles has reduced the propagation loss to a degree where no extra loss is induced, compared to the losses in the thin film itself. In addition, the performance of a ring resonator has been investigated. It was possible to achieve a free spectral range that is larger than the channel spacing in wavelength division multiplexing (WDM) systems. This allows for the selection of a single wavelength band within the complete telecommunication C-band (1530 - 1570 nm).