Bismuth-doped fiber amplifier with controlled gain and extended bandwidth based on tunable gain clamping

The study of gain clamping in broadband bismuth-doped fiber amplifiers (BDFA) not only helps to solve the gain instability problem due to the variation of the number of optical multiplexing channels but also is an effective way to extend the amplifier's operating bandwidth to improve the communication capacity. In this paper, we illustrate the advantages of linear cavity gain clamping through simulation. Using simulation to guide the experiments, we propose a BDFA with tunable linear-cavity gain clamping and incorporate a variable optical attenuator (VOA) in the linear cavity to enhance the flexibility of gain control. The gain-clamping is utilized to generate a control laser and act on the BDF together with the external pumping to achieve multi-wavelength pumping without excessive pumping sources. In addition, we investigate the gain and noise figure (NF) of the BDFA with respect to pump, signal, wavelength, and VOA loss. A 6 dB gain bandwidth of 115 nm is achieved when the VOA loss is 0 dB. The gain float is less than 0.2 dB over the input signal range of -26.5 dBm to 7 dBm. This work extends the operating bandwidth of the BDFA and makes the amplifier more tolerant to variations in signal power in the channel.