Optimization of Tandem 980-nm Single-Pump Recycled Erbium Amplifier Configurations

Abstract

In this paper we study the design and performance of 980-nm single-pumped tandem recycled erbium amplifier pump (REAP) configurations. These configurations feature high gain (>40 dB) and low noise figure (3 dB) using an isolator incorporated in the amplifier length to block backward-traveling amplified spontaneous emission from degrading the amplifier performance. In particular, we investigate theoretically the trade-offs between gain and noise figure and their dependency on fiber length, signal level, and pump power. First, using the ratio between first-stage length and total amplifier length as a figure of merit, we determine the optimum position of the isolator to achieve a combination of high gain and low noise figure, for constant levels of pump power in the small signal regime. Then, we calculate the amplifier performance for applications as power booster, in-line amplifier, and preamplifier. Since the REAP topology is especially attractive as a preamplifier, we further establish the dependency of gain and noise figure as a function of second-stage active fiber length and pump power level. Finally, we contrast the performance of two different REAP configurations and show good agreement between our experimental data and simulations.