Wavelength-independent low-DMG EDFA for C-band Inline WDM-MDM Signal Amplification

The co-multiplexing of the wavelength and mode in a WDM-MDM system can significantly enhance the transmission capacity, surpassing the Shannon limit of the SMF-based system. The erbium-doped fiber amplifier (EDFA) can ensure the loss compensation, and is an indispensable part of the transmission system. However, realizing the gain equalization between different wavelengths and modes poses a challenge for the WDM-MDM EDFA. Herein, a practical WDM-MDM EDFA is constructed employing the self-developed gain-equalized few-mode EDF and high coupling efficiency side-pump coupler, which can not only realize the loss compensation but also balanced signal gains across various wavelength-mode groups. Low gain differences can be obtained at any wavelength position in the whole C-band. Additionally, the active fiber is directly fused with the passive transmission fiber, enhancing the system stability. The gain characteristics under single wavelength-, single mode- and wavelength-mode co-multiplexing are comprehensively tested. When applying in a dual-wavelength dual-mode system, the gains of all signals at 1550 nm are higher than 18.5 dB, the gain difference is below 1 dB.