The gain characteristics of an erbium-doped fiber amplifier pumped in the 800 nm band have been investigated in detail. The fiber has a dual shape core and the erbium ions are doped only in the inner core to improve the pumping efficiency. The most efficient pumping wavelength is around 820 nm which is determined by the trade off between the decrease in excited state absorption and the decrease in the absorption coefficient. This pumping wavelength makes it possible to achieve an optical gain as high as 40 dB. The noise figures of Er3+-doped fiber amplifiers pumped in the 800 nm band are 4-5 dB in the 1.5 μm signal wavelength region.
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