On the multiplicity of Bismuth active centres in germano-aluminosilicate preform

Spatially resolved optical spectroscopy of Bismuth-doped germano-aluminosilicate fibre preform prepared by modified chemical vapor deposition (MCVD) reveals the existence of two subnetworks accommodating the active centres connected to Bismuth doping: a pure silica subnetwork and an aluminosilicate one. Even at low Bismuth doping level for which laser generation in the fibre has been demonstrated, two kinds of optical centres in a silica subnetwork can be identified. At least one of these centres is able to inhibit the laser generation in aluminosilicate fibres at high Bismuth doping levels. We discuss the technological issues for improving the efficiency of Bi-doped fibre lasers in the spectral range of 1150-1500 nm. (C) 2010 Elsevier B.V. All rights reserved.