Rare-earth-doped oxide glasses for integrated optical amplifiers and lasers

Oxide glasses have been used since long time to host a number of active compounds, first of all rare-earth (RE) ions, for optical amplification and lasing. The growing request of integrated optical amplifiers and lasers at 1.5 micron for telecom systems has stimulated the search for better Er3+-doped glasses and more efficient guiding structures, able to provide a large optical gain in the C band. Oxide glasses, despite their higher phonon energies, are still more convenient than non-oxide glasses for the development of practical devices: silicate glasses, in particular, are considered an excellent solution, due to their chemical robustness and adaptability to different waveguide fabrication processes. They present, however, the drawback of a narrow emission bandwidth (e.g. from 15 to 30 nm). Tellurite glasses, on the other hand, are gaining increasing attention because the emission band of Erbium in these glasses is exhibiting a bandwidth larger than 60 nm. Here we present the experimental results we obtained so far in these two classes of glass. We prepared a set of five silicate glasses, all having the same base composition (soda-lime-silicate type), but containing different percentages of trivalent Erbium and Ytterbium ions. Several samples of tellurite glasses, with different base composition and doped with various Erbium concentrations, were also investigated. Spectroscopic properties of all these glasses were tested; Judd-Ofelt analysis was carried out on most of the samples, and radiative lifetimes were compared with experimental lifetimes of the metastable level of Erbium in the different glasses. The ion-exchange process was used to fabricate optical waveguides in the glasses. Results were very good in silicate glasses, where an optical gain of 1,5 dB/cm could be measured in channel waveguides. In tellurite glasses, on the contrary, we produced good planar waveguides, but we have not yet been able to fabricate channel waveguides, due to chemical weakness of the glass itself and to consequent surface damage occurring during the etching steps in the patterning process.