Abstract : Relative intensity noise of lasers running at 1550 nm is studied. The two, three and four levels models for studying both statical and intensity noise laser behavior are presented and compared. Semiconductor laser model is also detailed. Experimental results on relative intensity noise of distributed feedback fiber lasers are presented. A Relative Intensity Noise measurement technic allowing the observation of very low value of noise (-170dB.Hz−1 for 1 mW) is detailled. The intensity noise of an original laser structure developed at the Laval University of Québec is also detailled. The influence of optical injection of semi-conductor lasers experimentally shows a reduction of intensity noise due to external pertubations at low frequency. Theoretical investigations indicate a noise transfer of intensity noise to the slave laser near the relaxation frequency of the master one.