Comparative study of Ag–Na thermal and field-assisted ion exchange on Er-doped phosphate glass

Silver-sodium ion-exchanged waveguides on a new erbium-doped phosphate glass have been fabricated and characterized. Thermal diffusion and field-assisted ion exchanges have been investigated and compared. A simple yet effective method to reconstruct the refractive index profile from the measured effective indexes, obtained by the in-lines spectroscopy with prism-coupling technique, has been successfully adopted. The optical parameters describing the waveguide properties, namely the refractive index variation, the diffusion coefficient and, for the field-assisted ion exchanges, the drift velocity, have been calculated and correlated with the fabrication parameters. Thermal diffusion is more reproducible while the field-assisted process provides a step-like index and better confinement by an appropriate control. Straightforward guidelines have been outlined for choosing appropriate diffusion time, temperature and melt composition to fabricate active waveguides compatible with optical fibers. (C) 2001 Elsevier Science B.V. All rights reserved.