Germania sol-gel waveguides for optical amplifiers

Sol-gel is one of the possible production techniques of silica-on-silicon integrated optical devices, combining low cost with a great flexibility. In the frame of a European project, we have investigated the application of the sol-gel technique for the realization of an erbium-doped optical amplifier. In particular we developed GeO2-SiO2-Al2O3 sol-gel waveguides doped with Er. The material was optimized in terms of heat treatments, Al2O3 co- doping content and Er doping level. RBS measurements showed that well densified films could be obtained heating the coatings at 700 degrees C in O2 flux. Waveguide properties were tested measuring the propagation losses at 840 nm. In the planar waveguide pumped at 980 nm, erbium showed fluorescence around 1530 nm with up to 6.5 ms. In order to achieve lateral confinement, the planar waveguides were co-doped with Na2O and channel waveguides were fabricated by ion exchange. The feasibility of sodium-silver and sodium-potassium ion exchange was demonstrated. The influence of the process parameters on passive and active optical properties of the films was studied and straight channel waveguides with Gaussian mode profiles were obtained by the sodium-silver route.