Spectral efficiency of information transfer by erbium-doped fiber amplifiers in the unsaturated gain regime

The results of numerical simulation of the ultimate spectral efficiency of information transfer by erbium-doped fiber amplifiers in the S and C bands in the regime of unsaturated gain are presented. The cases of co-and counterpropagating pumps are analyzed in terms of the three-level and quasi-two-level schemes. It is shown that, for the peak gain in the range 12–24 dB and a signal-to-noise ratio at the entrance equal to 20 dB, the ultimate efficiency lies in the range 5.5–7.5 bit s^?1 Hz^?1 for the S band and 5.6–7.2 bit s^?1 Hz^?1 for the C band.