Existence of intrinsic ‘background loss’ in rare-earth doped fibres: drawbacks and usefulness

Abstract

Estimates are given of the intrinsic multiphonon absorption of trivalent rare earth (RE) in glasses. The Letter shows that the orders of magnitude of 1.5 dB/km in ZBLAN glass and 3.5 dB/km in silica glass as far as 2000 cm−1 from an electronic transition can contribute to what is generally called the ‘background loss’ and could explain why fibre lasers and amplifiers can be pumped outside usual electronic RE transitions.