Design of gain-shifted erbium-doped fibre amplifiers for WDM applications

Design criteria for gain-shifted erbium-doped fibre amplifiers (GS-EDFAs) determined for multiwavelength operation in the 1580 nm wavelength band are presented. To achieve a flat gain profile and low noise figure, special care must be taken when selecting erbium-doped fibre (EDF) length, pump power and pumping configuration. The design criteria are based on the results of computer analysis performed with the aid of a comprehensive large-signal numerical model which takes into account time variation effects in an erbium-doped fibre amplifier. It follows from the performed analysis that flat gain spectrum in the wavelength range 1570 to 1605 nm can be achieved with co-, counter-, and unsymmetrical bidirectional pumping configuration. Unidirectional pumping requires, however, more pump power than the unsymmetrical bidirectional scheme. In order to achieve low noise figure the codirectional part of pump power must be much higher that the counterdirectional one. Surviving channel power excursions in a 16-channel WDM network containing six GS-EDFAs have been found comparable to those in a similar network with conventional 1550 nm EDFAs