Optical nanocomposite planar waveguides doped with rare-earth and noble metal elements

The present paper is focused on multilayer Er3+-doped silica-titania planar waveguides, co-doped with silver, which were prepared by spin-coating on silica glass, or buffered single crystal silicon substrates. The single layer thickness (~0.4 µm) and refractive index (~1.60–1.63) were measured by spectroscopic ellipsometry at 715 nm. The thickness of the waveguides (measured by mechanical profilometry) was ~1 µm and their optical propagation losses were measured at different laser wavelengths (488 nm, 514 nm and 633 nm), exhibiting an approximately Rayleigh-like behavior. The thermal precipitation of silver nanocrystallites was achieved, both in air and under a controlled atmosphere (dry nitrogen) and these were characterized by visible absorption spectroscopy, which clearly showed the development of a plasmon absorption band near 415 nm, by X-ray diffraction (XRD) and Transmission Electron Microscopy (TEM). The Er3+metastable level lifetimes for the emission at ca. 1.54 µm were found to be ca. 4–6 ms, for Er3+concentrations varying between 0.2–2.0 mol% (or ~(0 4–4 4) ×1020 ions/cm3), but no significant variation was observed with the Ag concentration added (up to 2.5 mol%).