Wavelength division multiplexing (WDM) is the currents tep in the development of optical telecommunication. The emphasis of the project is to explore the exisiting photonic technology to realize integrated optical structures for WDM systems. Two methods of fabricting silica on silicon buried channel waveguides are presented: a conventional method and direct UV writing. It is shown that an optimized three layer glass structure yields directly UV written waveguides with low insertion losses. Integrated optical structures have been designed and fabricated. The impact of process variations on the performance and crosstalk characteristics of thes devices have been studied theoretically and compared with experimental results. Wavelength insensitive devices and structures with low sensistivity towards process variations have been identified. The possibility of wideband couplers have been experimentally confirmed. The design and implementation of Bragg gratings are described. The fabrication and characterization of a 2x2 optical add-drop mulitplexer and a frequency to intensity conferter are presented. Trimming of optical components have been addressed. It was found, that thermal trimming offers a simple way of adjusting center frequencies opt optical filters to a grid. The draw-back is that the components need to be temperature stabilized. UV trimming have ben used to permanently change the refractive index in selected areas of a device. In this way, a novel way of trimmin arrayed waveguide gratings have been demonstrated. Finally, the characterization of the fabricated devices is reviewed. The polarization properties of the fabricated devices are investigated. An examination of the impact of crosstalk on measured bit errors rates have been performed.