AbstractFilters and isolators placed within the EDFA's can be used to increase the gain , and decrease the noise figure. By use of an accurate model the placement of the filters and isolators are optimized. The optimization are performed for situations with pump lasers emittiing at O.98O.tm and 1.48Otm and signal wavelengths at either the emission cross section peak near 1.530p.m or at the silica loss minimum around 1.550pm. 1 IntroductionErbium fibre amplifiers with optimum gain design i.e EDFA's with the erbium confinedwithin the core, high numerical aperture and cutoff wavelengths around 1tm1'2 can today be produced with pump efficiencies near 10dB/mW.3 Even though this is a tremendous improvement compared with the situation for a couple of years ago most of the pump photons are still lost to amplify spontaneous radiated emission captured by thefibre core. One of the most promising candidates with respect to improve the pump efficiency is arecently published amplifier configuration in which the signal passes the Er-fibre twice