Abstract

Recently, L-band EDFAs for WDM systems are very attractive because the transmission capacity in C-band is gradually becoming insufficient and L-band is a potential candidate to extend the capacity by all means. A successful L-band EDFA design for WDM systems requires a flat gain spectrum and low noise figure. Moreover, gain-clamped characteristics are also indispensable for the reason that in WDM systems, the channel gains are required to be constant even though the operating conditions, such as the total input signal power, can vary significantly. The transient (dynamic) response is another issue that needs to be considered as large dynamic gain excursion can lead to errors at the receiver and degrade system performance. It has been shown that gain-clamping EDFAs using optical feedback can provide stable gain performance.^1–3 However, the noise figure is also degraded due to the decreased gain and different distribution of the upper state population along the EDF. Furthermore, dynamic gain excursions and transient times become worse in L-band EDFAs as a result of the EDF length.^4–5

© 2002 Optical Society of America