Abstract

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 [1]. Subsequent demonstrations of the diode-pumped device [2] led to the first commercial products in 1990 and installation of optically-amplified systems followed in 1993. However, 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 [3]. However, performance of Nd³⁺ in ZBLAN 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. Current research shows that alternative fluoride glasses can allow operation down to ~ 1310nm, which appears to be adequate for most installed systems which have a dispersion zero around 1315nm. Care must also be taken to suppress the large amplified spontaneous emission which results from the more-favoured 1.06µm transition [4].

© 1995 Optical Society of America