Pump Configuration and Length Optimization of Erbium-doped Fiber Amplifier for Low Noise and High Power Operation

In a ultra-long system with cascaded erbium-doped fiber amplifiers(1) (EDFAs), in order to keep a signal-to-noise ratio (SNR) as high as possible, EDFA(2) having high output power and low noise is highly required as a post-amplifier or as an in-line-amplifier. Such an EDFA is also important for optical pre-amplifiers with large dynamic ranges. Although Way et al. reported a low noise figure (NF) in a saturation region under the condition of sufficiently high pump power(3), the relationship between lowering the NF and optimizing the gain of EDFA was not clear. In this paper, we report that an EDFA having both a high output power (+15dBm) and a low NF (6dB) can actually be realized using 1.48μm pump LDs when the EDFA length is optimized to give a maximum gain for large signal power. In addition, we also show that there is a remarkable difference between forward and backward pump in terms of NF characteristics of EDFA in a deep saturation.