Abstract

Work on rare earth-doped fiber lasers and amplifiers has focused on silica and fluorozirconate glasses primarily because fiber synthesis techniques are better developed for these compositions. Because pure silica is a poor host for rare earth ions the use of codopants is critical to controlling device properties. The addition of A1₂O₃ significantly increases the solubility of rare earths, preventing clustering and its associated inefficiency. Al₂O₃-codoping also substantially increases the gain bandwith of silica Er³⁺-doped fiber amplifiers (EDFAs) by providing a broad emission spectrum more typical of a fluoride of fluorophosphate glass. For Er³⁺-doped silica, cross sections at 1500 nm are sensitive to codopants primarily through changes in the shape of the absorption and emission bands. While codopants can enhance the efficiency of EDFAs pumped at 800 nm, significant improvement can only be obtained by going to other glasses such as fluorophosphates. Composition has less influence on performance when exciting at 980 or 1480 nm, the latter pump band suffering from an inherent noise penalty of 1-2 dB. The strong 1060-nm transition of Nd³⁺ has a lower small-signal gain efficiency than ER³⁺, regardless of host. The weaker 1300-nm transition suffers additionally from excited state absorption, a process that is sensitive to composition.

© 1991 Optical Society of America