O+E Band BDFA with Flattop 116 nm Gain Bandwidth Pumped with 250 mW at 1256 nm. - Aleksandr Khegai; Yan Ososkov; Sergei Firstov; Konstantin Riumkin; Sergey Alyshev; Alexander Kharakhordin; Alexey Lobanov; Alexey N. Guryanov; Mikhail Melkumov (OFC, 2021)