Detailed characterization of a high-gain, low differential modal gain and low gain flatness integrated FM-EDFA for...

In this paper, an integrated few-mode erbium-doped fiber amplifier (FM-EDFA), with high gain, low differential modal gain (DMG), and low gain flatness for multi-wavelength amplification, is constructed using homemade weakly-coupled ring-core few-mode erbium-doped fiber (FM-EDF) and low insertion-loss passive components. The gain characteristics of the FM-EDFA for multi-wavelength amplification are analyzed in detail and compared with single-wavelength amplification. The experimental results demonstrate that, although multi-wavelength amplification in different modes has an impact on the gain characteristics, through simple LP₀₁ core pumping only, all guided modes can achieve a gain higher than 22.4 dB when simultaneously amplifying 8 wavelength channels. The DMG is less than 1.179 dB, the minimum DMG across the C-band is as low as 0.168 dB, and the wavelength gain flatness is less than 3.232 dB. Furthermore, when the three-signal mode is multiplexed for amplification, the DMG can be stabilised at less than 2 dB. The constructed FM-EDFA can achieve gain equalization in multi-wavelength amplification across the C-band, which has essential practical applications in long-haul WDM-MDM transmission systems.