The past two years has seen the emergence, within research laboratorie
s, of an optical device - the praseodymium-doped fluoride fibre amplif
ier (PDFFA) - which if viable could find early application within exis
ting optical fibre communications systems, as its spectral characteris
tics make it ideally suited to present day 1.3 mum networks. It is thi
s compatibility with existing technology that makes the PDFFA a key el
ement, with the potential to radically influence network upgrade strat
egy. As in the case of its predecessor, the erbium-doped fibre amplifi
er, it removes many of the barriers to full network utilisation which
are imposed by power budget. As such, it is already clear that a fully
developed PDFFA will have a critical role to play in the evolutionary
route from present day networks, with their mix of copper and fibre,
to the ultimate goal of a fully integrated optical 'ether' capable of
supporting the diversity of services which the future is likely to hol
d. This paper describes the application of amplifiers in optical fibre
networks, and the reasons for current interest in 1.3 mum fibre ampli
fiers. The operating principles of fibre amplifiers are then described
in simple terms, together with the specific features of importance to
1.3 mum fibre amplifiers. Detailed experimental measurements of curre
nt laboratory based 1.3 mum fibre amplifiers are then presented in ord
er to give an indication of the present state-of-the-art in this techn
ology. Finally, a realistic assessment of the likely performance impro
vements that will be obtained in the near future is presented.