Signal output power and noise in erbium-doped fiber power amplifiers

The quantum conversion efficiency (QCE) and noise figure of erbium-doped fiber power amplifiers have been investigated experimentally. Under 980 nm co-directional pumping, efficiencies up to 89% were achieved. Very good agreement of the measured QCE, gain and noise figure with those predicted by a numerical model using only measured input parameters was obtained. The model was utilized to analyze the influence of fiber waveguide design, erbium confinement, signal wavelength and the signal input level on the QCE and noise figure for power amplifiers pumped at 980 nm or 1480 nm. Increasing the NA from 0.15 to 0.25 was found to increase the QCE by up to 52%, and decreasing the confinement factor from 1.0 to 0.5 produced up to an 18% increase of QCE. The noise figure is predicted to be up to 3 dB higher for pumping at 1480 nm than for pumping at 980 nm, and up to 2 dB higher for a signal wavelength of 1532 nm than for one at 1555 nm. As the signal input level increases, the QCE saturates and the noise figure begins to increase. This leads to a pump-power dependent optimum input signal level if both QCE and noise figure are a consideration.?