A low-noise and gain-flattened amplifier composed of a silica-based and a fluoride-based Er3+-doped fiber amplifier in a cascade configuration

We propose a novel low noise and gain-flattened Er3+-doped fiber amplifier (EDFA) with a cascade configuration for wavelength division multiplexing (WDM) signals, In this configuration, a 1480-nm pumped fluoride-based EDFA is joined to a 980-nm pumped silica-based EDFA through an optical isolator, By adjusting the silica-based Er3+-doped fiber length in the silica-based EDFA, we realized an excellent flat gain EDFA with a gain excursion of less than 0.9 dB and noise figure of 5.7 +/- 0.2 dB, and a low noise EDFA with a noise figure of 5 +/- 0.2 dB and a gain excursion of less than 1.4 dB, for 8 channel WDM signal in the 1532-1560-nm wavelength region.