Sol-gel processing is becoming one of the cheapest and most versatile methods For the fabrication of passive and active planar waveguides for integrated optics, in particular for the silica-on-silicon type. The present paper focuses on some recent work in our group on both passive and active (Er3+-doped) silica-titania inorganic and hybrid waveguides, considering in detail their densification behaviour, structure and optical properties. Recent advanced topics, such as nanocrystalline active waveguides prepared by by sol-gel method, are also addressed. The main results to be presented will deal first with the structural evolution during the densification of inorganic and hybrid silica-titania waveguides. Then, the fluorescence behaviour of active waveguides, doped with Er3+ ions, will also be described. And finally silver co-doped nanocrystalline waveguides, will be considered in detail, with particular emphasis on, firstly, the influence of preparation conditions on optical properties such as the visible and infrared absorption spectra. including the characterization of the surface plasmon resonances of the silver nanoparticles by visible spectroscopy as well as the 1.5 mum fluorescence lifetime and, secondly, the nature of the chemical environment of the erbium and silver ions, before the thermally induced nanocrystallite precipitation and during the course of film densification.
