Erbium-activated silica-titania planar waveguides

A sol gel processing has been developed to prepare passive and erbium-activated SiO2-TiO2 planar waveguides by a dip-coating technique. The starting solution was obtained by mixing tetraethylorthosilicate (TEOS), ethanol, deionized water and hydrochloric acid as a catalyst. Titanium isopropoxide (TiPOT) was used as TiO2 precursor. Silica-titania films were obtained by dip-coating, with a dipping rate of 70 mm/min, using cleaned pure v-SiO2 slabs as substrates. Some parameters such as H2O content, intermediate and final thermal treatments, and the molar ratio TiO2/SiO2 were modified during the preparation of the solution in order to minimize the final content of residual hydroxyl groups and the phase separation between silica and titania. Raman and luminescence spectroscopies, and attenuation coefficient measurements were used to check the structural and optical properties of the waveguides as a function of the parameter which was modified. We found that the composition to obtain acceptable optical and spectroscopic properties was 93SiO2-7TiO2 with a molar ratio H2O/TEOS=2. With these parameters we produced planar waveguides which have a single propagating mode at 632.8 nm with a refractive index of 1.48. The room temperature photoluminescence spectrum of the 4I13/2?4I15/2 transition of the Er3+ ions in a 93SiO2-7TiO2 planar waveguide activated by 1 mol % Er/(Si+Ti) shown a spectral width, measured at 3 dB from the maximum of the intensity, of 51 ? 2 nm. The decay curve of the luminescence from the 4I13/2 metastable state of the Er3+ ions in the same waveguide exhibited a single exponential profile with a lifetime of about 7 ms. The preparation of waveguides which suffer a single propagating mode at 1.5 ?m is in progress.