Gain Characteristics of Few-Mode EDFA with Different Pump

Few-mode erbium-doped fiber amplifier (FM-EDFA) is a key device to achieve power compensation in long-haul mode division multiplexing (MDM) optical system. The gain characteristics of FM-EDFA are related to the number of modes and multiplexing mode selection. In this paper, the gain characteristics of four modes and six modes FM-EDFA with various mode combinations and different wavelengths are analyzed in single and dual-pump cases. The results show that when the azimuthal-dependent pump is selected, different degenerate mode (odd and even mode) multiplexing will arise DMG. In the replacement of different degenerate modes at the same modal order, the DMG of signal modes LP_11o,s and LP_21o,s is 1 dB (single-pump: LP_01,p) while the DMG between signal modes LP_11e,s and LP_21e,s is 8 dB (dual-pump: LP_01,p+LP_11e,p). Compared with single-wavelength amplification, both the overall gain and the DMG decrease in the multi-wavelength case. The above conclusions can provide a theoretical basis for the selection of FM-EDFA in the wavelength division multiplexing (WDM)-MDM system.