Spectral Dependence of Gain Saturation and Effect of Inhomogeneous Broadening in Erbium-Doped Aluminosilicate Fiber Amplifiers

Abstract

As erbium-doped fiber amplifiers (EDFA) [1-3] promise to play a major role in optical fiber communications [4], the optimization of the amplifier pumping efficiency and saturation power is becoming an important issue. In the large-signal regime, the effect of inhomogeneous gain broadening [5] results in gain hole-burning, which reduces both efficiency and power extraction. It was shown that aluminosilicate Er:glass has an advantageously large (26nm) homogeneous gain bandwidth [6] with comparatively small (11.5nm) inhomogeneous component [7]. On the other hand, for germanosilicate Er:glass inhomogeneous saturation is observed at relatively low signal powers [8]. Theoretical models evolved so far [6,9] assumed homogeneous broadening and therefore cannot be used for an in-depth study of saturation effects in these two types of fiber amplifiers. In this paper, the spectral dependence of gain saturation in an aluminosilicate EDFA is studied experimentally and theoretically. A theoretical model representing, to our knowledge, the first attempt to model both homogeneous and inhomogeneous gain saturation in EDFA’s, is presented. A second model using the same parameters but assuming completely homogeneous broadening is used for comparison. The calculated signal and amplified spontaneous emission (ASE) spectra are then compared to experimental data. It is observed that the strong spectral dependence of gain saturation is quite well described by the homogeneous model. However, the inhomogeneous model is seen to provide a more detailed description of the changes in the ASE spectrum.