The erbium doped fiber amplifier (EDFA) is presently the key element of a long distance transmission. Experimental results of noise characteristics (1 Hz <EQ f <EQ 500 kHz) of an Er3+ erbium doped fiber amplifier pumped by 1.48 micrometers laser diode are reported in this paper. Several kinds of noise generated in EDFAs (1/f(alpha ) noise, 1 <EQ (alpha) <EQ 3; hopping noise, quantum noise) are very troublesome in the various applications of the EDFA. These noise levels impede to improve the optical coherence and the signal to noise ratio. Several studies have been made in order to introduce the low and medium frequency noise for transmitters but nothing yet concerning the EDFA. This communication deals with optical noise simulations of an EDFA. The output noise depends on the amplified spontaneous emission (ASE) power because no input signal is applied. Thanks to a noise simulation, we have been able to deduce the internal gain G of the doped fiber and the spontaneous emission factor nsp. The correlation between the monitoring photocurrent noise, the output noise and the input noise of the amplifier are given in order to show the influence of the pump laser on the EDFA output and input.© (1995) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.