Abstract

Fiber amplifiers are used in transmission systems with gain-clamping techniques to avoid unexpected situations such as sudden changes in incoming power due to unstable factors. The O-band bismuth-doped fiber amplifier (BDFA) has developed rapidly in recent years and has been reported in transmission cases, but its application in clamping is still relatively rare. In past work, we have investigated the clamping effect of a BDFA under a coupler ring cavity under different pumping schemes, while in this work we further improved the structure by replacing the coupler with a circulator to comparatively investigate the limit range of gain stabilization. The experimental results demonstrate that, when the loop loss is 0 dB, the BDFA exhibits nearly identical gain-clamping performance, including flat range and maximum float, with both structures. However, as the loss increases, the circulator structure exhibits a wider gain flatness range than the coupler structure. With pump power of 1 W and VOA loss of 0 dB, the BDFA achieves a maximum gain float of 0.42 dB in the coupler configuration and 0.56 dB in the circulator configuration over an ultra-wide input range of ${-}15\; {\rm dBm}$ to 9 dBm. In addition, the gain flat range under the circulator structure is 3 dB wider than the coupler structure when the VOA loss is 10 dB. Therefore, with the pursuit of a balance between the higher average gain and the widest flat range, it is most advantageous to consider the circulator in the ring cavity. This work gives a valuable reference for the application of the O-band BDFA in gain clamping.

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