A comparative analysis of doubled-pass erbium doped fiber amplifiers considering different signal-return schemes

In this work, an experimental comparative analysis of doubled-pass erbium doped fiber amplifiers with different signal-return is presented. The amplifier per formancewas investigated in terms of gain and noise figure as the signal under amplification was reflected back towards the er bium doped fiber by a mirror, filter, or circulator ar rangement. Also, a semiconductor laser under single-facet optical injection locking was tried as an equivalent reflexiveelement. In par ticular, the regenerative character istics provided by the injection locking processwere able to provide considerably high gain and low noise figure levels for the amplifier, especially for considerably low input signal power.