Stable and broadband Er-doped superfluorescent fibre sources using double-pass backward configuration

Er-doped superfluorescent fibre sources (SFSs) pumped near 980 nm in double-pass backward configuration are characterised experimentally for the first time. By properly adjusting erbium doped fibre lengths, SFSs can have pump-power insensitive mean wavelength operations with broader linewidths and better pump efficiencies than those in the commonly adopted single-pass backward configuration