Uni- and bi-directional feedbacks regenerative EDFA operating below threshold

In this paper, the performance of unidirectional and bi-directional regenerative erbium-doped fiber amplifier (EDFA) operating below laser oscillation threshold is compared. The experimental results show that the unidirectional system bas a higher gain and a lower noise figure than that of the bidirectional system. Resonant-amplification characteristic of regenerative amplifier is observed at low input signal for both schemes.