Noise Characteristics of the EDFA in Gain Saturation Regimes

Abstract

Though erbium-doped fiber amplifiers (EDFA) are very attractive candidates for optical transmissions, one of their important characteristics is the noise properties. These amplifiers generate low noise levels and corresponding noise figures are close to the quantum limit[l,2]. However, a number of applications, such as CATV and transoceanic links, will be highly sensitive to excess noise above this limit. Up to now, noise figures have been experimentally [1,3,4] and theoretically studied in several conditions, such as small-signal or highly-pumped amplifiers[2,5]. But when looking at the behavior of the noise figure in various signal regimes as a function of the amplifier working point, important variations appear [6]. This indicates a highly complex reciprocal influence of the different propagating beams through the amplifying medium. In this paper, we study the noise properties of the EDFA, especially in the transition from small-signal regimes to saturated gain ones. Theoretical results are shown to explain experimental observations.