Abstract

The erbium-doped-fiber amplifier (EDFA) is attractive for wavelength-division-multiplexing (WDM) networks owing to its high gain, low noise, and low cross talk. The 3-dB-gain bandwidth of EDFA’s is typically 3-8 nm but can be increased to ~30 nm with appropriate techniques.¹ However, in these cases the gain band is not flat, exhibiting a small ripple (~±1 dB). When combined with wavelength-dependent losses in the transmission fiber and optical components in the link, such variations limit the number of amplifiers that can be cascaded before a significant difference in signal levels develops between channels. Ideally, the signal levels should be actively² or passively compensated after each amplifier to equalize all channels.

© 1993 Optical Society of America