Optical fibre amplifiers

摘要

During the 1980s there has been increasing interest in rare-earth doped, single mode fibres for devices and sensors, of which the most exciting results have been achieved with erbium doped fibre amplifiers (EDFA). Great progress has been made since the first EDFA was reported by Mears in 1987. A gain of 26dB was achieved whereas 46.5dB has now been demonstrated. High speed, direct detection in fibre based transmission systems has allowed bit rates and transmission distances to be markedly increased. For example, use of twelve 1.48µm laser diode pumped EDFAs as power amplifiers has allowed transmission of 1.2 Gbit/s over more than 900km of fibre. The power penalty arising from dispersion and the presence of the EDFAs was only 0.6dB at 10 BER, with no observed error floor due to accumulated noise. A number of similar systems have also been demonstrated with alternative pump sources and device configurations. Thus the compatibility of EDFAs with long-haul communications systems has clearly been demonstrated. However, simultaneous improvement in manufacture and design of doped fibres has been essential. Here, the techniques for manufacture of such fibres are described and design criteria for optimal performance outlined. First, however, the advantages of EDFAs are summarised