Double-path erbium-doped fiber amplifier with enhanced noise figure characteristics

Summary form only given. Efforts paid to various pump schemes such as forward, backward and bidirectional pumping have made significant contributions to highly reliable erbium-doped fiber amplifiers (EDFAs) with high gain and low noise figure characteristics. Reflective type EDFAs by using a mirror and an optical isolator were proposed to achieve a better utilization of wasted pump energy. Therefore, this double-path EDFA doubled the gain coefficient compared to that of single-path ones. However, its noise figure was worse than that of single-path EDFAs. Using a 3 nm bandpass filter (BPF) between the EDF and mirror to remove the amplified spontaneous emission (ASE) improved the noise performance. However, the BPF scheme is not suitable for wavelength division multiplexing (WDM) optical communications since the BPF simultaneously filtered out other WDM signals outside its transmission band.