Noise figure limit of L-band EDFAs

Erbium-cloped fiber amplifiers (EDFAs) with high gain generally degrade the signal-to-noise ratio by at least 3 dB. In the conventional wavelength band, noise figures close to the so-called quantum limit can be obtained by strong pumping. Due to their lower average population in the metastable level, this limit is not reached by amplifiers designed for the longwavelength band (L-band). In this paper, the lower noise figure limit is determined for such amplifiers. It has been found that the noise figure for typical gain values of about 30dB can be very close to the quantum limit, whereas significantly larger noise figure values result for small amplifier gains. The lower limit decreases with increasing gain if the gain values are beyond 5 dB. In addition, the results reveal that low temperatures yield better noise figure.