Optimum configuration for high-power low-noise-figure erbium-doped fiber amplifiers for lightwave CATV applications

Abstract We theoretically investigate various 980-nm-pumping configurations for simultaneously achieving high-power, low-noise-figure erbium-doped fiber amplifiers (EDFAs) acted as power amplifiers and in-line amplifiers for lightwave analog cable-television (CATV) applications. The target of saturated output power and noise figure is ≥100 mW and ≤5 dB, respectively. Those configurations considered include single-stage and two-stage designs in dual-forward, dual-backward, and bidirectional pumping schemes, each with and without the midway optical isolator. The bidirectional pumping scheme includes the forward-and-backward, and the backward-and-forward cases. A total of nine configurations are examined and compared in this paper. We find that the midway isolator for all amplifier configurations operated at large input signal level (>0 dBm) in CATV analog systems did not contribute to noise figure reduction, but the additional insertion loss reduced the output power. This is quite opposite to the case for an amplifier operated at small input signal power in the digital systems. From both system power budget and carrier-to-noise ratio (CNR) points of view, among all configurations, the single-staged forward-and-backward bidirectional pumping scheme without using inter-staged components is the best amplifier configuration to offer the highest output power with fairly low noise figure and highly satisfied CNR performance. It is also the simplest scheme with the shortest required EDF length. This conclusion provides the configuration selection of designing both power and in-line amplifiers for AM CATV lightwave systems.