Optical Amplifier With Rotationally Symmetrical Pump Modes for Enhanced Mode Multiplexing

Multimode erbium-doped fiber amplifiers are promising candidates for the realization of cost- and energy-efficient long-haul transmission for mode-division multiplexing. Mode-dependent gain in such amplifiers is a potential source of signal quality degradation and should be avoided. We show by numerical simulations that gain values and noise figures for the signal modes exhibit an angular dependence if the amplifier is pumped with the LP₂₁ mode. In order to avoid this angular dependence, we propose to use pump modes with a rotationally symmetric intensity distribution, such as the TE₀₁ mode. Our simulation results show that pumping with this mode completely removes the angular dependence and optimizes gain and noise figure values for the signal modes.