An optical signal amplifier comprises a Semiconductor Optical Amplifier SOA used as semiconductor Amplified Spontaneous Emission ASE source. This SOA produces optical pumping seed which has to be amplified to get a large pump power. With such large pump power, it will be possible to counteract the loss in a fiber link of optical signals transmitted through it by applying said amplified pumping seed as Raman amplification on the optical signals. The invention further relates to a method for amplifying an optical signal comprising the combination of a semiconductor ASE source together with a high-power pump source. Latter will be used to amplify optical pumping seed to be produced by the semi-conductor ASE source. Accordingly, the obtained amplified pumping seed will be used to act as a Raman amplification of optical signals.