Main issues associated with EDFA designs are as follows:
1. The first issue is the flat gain. As EDFAs do not amplify all wavelengths through them the same; thus, the gain is not exactly flat.
2. The second issue is the pump power-sharing. The pump power is shared by all wavelengths in the link. Therefore the more the wavelengths, the lesser power per wavelength will be available. However, as wavelengths can get drop but not added, or some wavelengths get lost due to failures, EDFAs will amplify few wavelengths more.
These two issues can be mitigated by properly engineering the WDM system and by dynamic gain control.
3. The third issue is not as simple and is addressed differently. When engineering a fiber-optic path, it should be remembered that optical noise sources are cumulative and that the ASE of EDFAs introduces noise that degrades the signal to noise ratio (SIN). Although a strong optical signal launched into the fiber could overcome this, near the zero-dispersion wavelength region, four-wave mixing would become dominant, and it would degrade the SIN ratio.