The EDFA: past, present and future

Summary form only given, as follows. More than thirteen years have elapsed since the first experimental demonstration of a high-gain erbium doped fibre amplifier. Since then the aggregate bandwidth of optical fibres has increased dramatically with the deployment of WDM systems. Back in 1986 a bandwidth of 4 THz seemed fantastic, yet recent lab demonstrations in Japan have pushed the EDFA bandwidth close to the limit. Hybrid EDFA/Raman and novel dopant amplifiers offer a further order of magnitude in bandwidth, but further gains are only possible with more efficient coding methods and multiple deployment of fibres. The use of concatenated EDFAs in WDM systems raises issues of gain tilt and longer term stability. As a result, a number of research groups, including that of the author, are investigating dynamic spectral equalisation techniques for WDM channel management. The paper reviews the history and certain topics of current interest in EDFA research and look forward to further developments in the twenty-first century.