Wide-Range Variable Gain Fiber Amplifier With Erbium-Doped Fiber Switching

A variable gain erbium-doped fiber amplifier (EDFA) with a wide gain range and a small noise figure (NF) variation is analyzed numerically and demonstrated experimentally. The EDFA can change the total erbium-doped fiber length by selecting six combinations of three EDFs with optical switches (SWs). The numerical calculation of the NF and the pump power using the analytical model of an EDFA indicates that such a variable gain EDFA has an advantage over a conventional multi-stage EDFA in terms of NF variation and required pump power. These characteristics are demonstrated by constructing a variable gain EDFA that employs SWs and variable optical attenuators (VOAs) integrated on a silica-based planar lightwave circuit (PLC). The variable gain EDFA exhibits a smaller NF variation of 1.2 dB for the 24-dB variable gain range than conventional two- and four-stage EDFAs, which have NF variations of 12.6 and 2.0 dB, respectively, for the same variable gain range. The power consumption of these EDFAs is also discussed by comparing the operating electric power of the SWs and VOAs with that of the pump laser.