Towards a high-performance optical gain medium based on bismuth and aluminum co-doped germanate glass

In this paper we present the development process of glass based on bismuth and aluminum co-doped germanate (GAB) glass. We found the addition of PbO to this glass (GAPB glass) increased the quantum efficiency (QE). Excitation of GAPB glass at 808 nm produced emission peaking at 1230 nm with a width of 260 nm, indicating the glass may be useful as a broadband optical amplifier covering the second telecommunications window. The composition of each component of the GAPB glass has been optimized for the QE and lifetime of this emission to produce an optimized composition of 87.4GeO2–6Al2O3–6PbO–0.6Bi2O3 (% molar) which had a QE of 67%. However, this composition had a phase separation tendency which would make the glass unsuitable for fibre fabrication. Next we tried adding various quantities of a variety of glass additives including SiO2, LiO, ZnO and SrCO3. All these additives reduced the QE, and all except SiO2 produced a transparent glass in the appropriate quantity. The quantity of these additives which gave a transparent glass and their QE’s were LiO: 10% and 6%, ZnO: 10% and 43%, SrCO3: 5% and 27%, respectively. Therefore the optimized composition for QE and transparency was 74.4GeO2–10ZnO–6Al2O3–6PbO–0.6Bi2O3.