Prospects for 1.3µm amplifiers

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Description/Abstract

Current status and future prospects for a practical 1.3µm fibre amplifier are reviewed. Summary:
The optical amplifier became a realistic prospect for telecommunications after the demonstration of the erbium doped fibre amplifier (EDFA), operating at 1.5µm. in 1987. Subsequent demonstrations of the diode-pumped device led to the first commercial products in 1990 and installation of optically amplified systems followed in 1993. However much of the installed base of fibre is designed for 1.3µm operation and thus the early success of the EDFA spurred the search for a 1.3µm fibre amplifier. First efforts focused on neodymium (Nd3+) and a diode pumped device exhibiting 10dB gain for 50mW of pump power was demonstrated in a ZBLAN fibre in 1991. However the performance of Nd3+ is limited in several respects, the most important of which, signal excited state absorption (ESA) limits the operating wavelength to more than 1.32µm. longer than ideal for zero dispersion in telecoms systems. Further the performance is fundamentally limited by the low branching ratio of the 1.3µm transition relative to competing transitions such as the 1.06µm emission. Techniques to completely suppress the build up of amplified spontaneous emission at 1.06µm have been proposed but, as yet, none has been demonstrated.