Erbium-doped sol-gel materials for optical applications

Abstract

A new chemical nanotechnological route for the preparation of fully densified doped SiO2 coatings with thicknesses in the low µm-range on Si- and siO2-wafers has been developed. Beside pure SiO2 coatings, that might be useful as a buffer layer on silicon, silicate layers with increased refractive index are needed for planar waveguide application. Therefore, a synthesis for the preparation of nano particulate sols was developed, thus allowing the incorporation of dopands lika Al"O3, PbO and Er2O3 for passive and active layers. Alumina was incorporated for the improvement of the Erbium solubility in active components. The coating sols consist of an organic binder, dissolved in a suspension of nanoscaled silica particles (10nm in diameter) and dopands and were applied on si- and SiO2-wafers by spin coating. After removal of the binder at 500°C, investigated by IR-spectroscopy, highly porous (nD=1.23) but transparent doped silica layers were obtained. The densification of the layers was examined by measuring the refractive index by ellipsometry as a function of the densification temperature. Completely densified layers with thicknesses between 1.7 µm (doped SiO2) and 6.5 µm (doped SiO2) were obtained at temperatures between 1000°C (doped SiO2) and 1100 °C(pure SiO2). The layer thickness andunevenness was determined by interferometric measurements. The optical loss of Al2O3 and PbO doped layers was measured by prism coupling, the Er2O3 doped layers with Er3+ concentrations of up to 2.5 mole % show fluorescence around 1500 nm with a fluorescence lifetime of about 3.6 ms.