Static analysis of gain control for a few-mode erbium-doped fiber amplifier employing pump power adjustment.

In mode-division multiplexing (MDM) optical transmission systems and MDM networks, the gain must be kept nearly constant even when the input signal power of the few-mode (FM), erbium-doped fiber amplifier (EDFA) changes. This paper investigates controllability of the gain in a 4-LP mode EDFA, whose EDF has signal modes of L P 01, L P 11, L P 21, and L P 02 or L P 01, L P 11, L P 21, and L P 31, by using analytical and full models. The results of calculation using the analytical model and a gain simulation using the full model show that the gain can be kept almost constant with an error less than 0.25 dB simply by adjusting the L P 01 pump power of the EDFA with signal modes of L P 01, L P 11, L P 21, and L P 31. This result suggests that it is possible to control the gain simply by adjusting the pump power in FM-EDFAs where all signal modes have a radial mode number of one.