Gain enhancement in gain-shifted erbium-doped fiber amplifiers for WDM applications

Utilization of amplified spontaneous emission (ASE) for gain enhancement in gain-shifted erbium-doped fiber amplifier (GS-EDFA) is analyzed. It is shown that in a multiwavelength regime, gain enhancement as high as 5 dB can be achieved when the counterpropagating ASE is used to invert an unpumped first stage of a two-stage GS-EDFA. We present design criteria for flat gain operation and noise penalty minimization of two-stage GS-EDFAs determined for multiwavelength operation in the 1580-nm wavelength band. The analysis is based on an application of a comprehensive large-signal numerical model which takes into consideration propagation of signal, pump and both the downstream and upstream ASE powers.