Spectroscopic assessment of silica-titania and silica-hafnia planar waveguides.

Silicate glasses remain the most investigated systems for optical planar waveguides, since they offer a reasonable solubility for rare-earth ions, they are transparent in the near-infrared-visible region and they are compatible with integrated optics (IO) technology. In the last decade, various technologies have been employed for the fabrication of silica (SiO2)-based IO components and a broad variety of silicate glass systems have been investigated. Besides the SiO2-titania (TiO2) system, which has been widely studied, it has recently been shown that SiO2-hafnia (HfO2) could be a further viable system for 1.5 µm applications. This paper compares spectroscopic results, in particular infrared and Raman spectra, in order to assess the structural and optical properties of erbium-activated SiO2-TiO2 and SiO2-HfO2 planar waveguides, prepared by two different techniques: rf sputtering and the sol-gel method. Particular attention is devoted to the homogeneity of the material structures obtained in each case.