Abstract: An optical fibre amplifier (50) comprises a SiO.sub.2 --Al.sub.2 O.sub.3 --GeO.sub.2 single-mode optical fibre (52) doped with E.sub.r.sup.3+. It is pumped by 1.55 .mu.m and 1.47 .mu.m optical sources (54 and 56) whose optical outputs are combined by an optical coupler (58) and are then coupled to the fibre (52) by a further optical coupler (50). A source of optical signals to be amplified (62) is also coupled to the fibre (52) by the further coupler (60). The E.sub.r.sup.3+ ions provide a three-level lasing scheme with a fluorescence peak at about 1.53 .mu.m. Low noise amplification of optical signals in the long-wavelength tail of the fluorescence spectrum with suppressed ASE at the fluorescence spectrums peak wavelength is obtained as follows. The 1.47 .mu.m pump provides some low noise amplification of the optical signal but preferentially amplifies the 1.55 .mu.m pump source. The resultant 1.55 .mu.