TOWARDS A PRACTICAL 1.3 MU-M OPTICAL-FIBER AMPLIFIER

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.