LAUSR

A Widely flatness gainbandwidth with double pass parallel hybrid fiber amplifier is experimentally demonstrated in this study. The proposed design combines serial erbium–Raman fiber amplifier in one branch and Raman fiber amplifier in the second branch. Multiple Raman pump units with a maximum power of 800 mW (250 mW of 1410 nm, 225 mW of 1480 nm, and 325 mW of 1495 nm) are utilized. Pump recycling technique is applied to achieve acceptable pumping efficiency. A maximum flatness gain bandwidth of 80 nm (1525–1605 nm) and average gain level of 22.5 dB are obtained at a small input signal power of $$-25$$  dBm and optimum pump power values. While, a wider flatness gain of 90 nm (1520–1610 nm) and average gain level of 11.5 dB are achieved at a large input signal power of $$-5$$  dBm.