Modal Superposition and Gain Competition in Clad-Pump Few-Mode EDFA

The clad-pump few-mode erbium-doped fiber amplifier (FM-EDFA) is independent to the pump mode selection and it shows much potential to construct an all-fiber scheme due to the natural allfiber interconnect. In the case of cladding-pump, we utilize the mode superposition theory to expound the modal gain competition under different modes multiplexing in the FM-EDFA. It is found that, at the same multiplexed signal mode number, both the modal gain and the differential modal gain (DMG) are relatively immune to the different degenerate signal mode selection. With the growing number of multiplexing modes, there is a fiercer modal gain competition and thus, compared with four modes multiplexing, the highest gain is reduced by 1.594 dB in the case of six modes multiplexing. The DMG is reduced by 0.45 dB due to the competitive balance. The modal superposition and gain competition theory specialized for clad-pump are helpful for erbiumdoped fiber design and FM-EDFA scheme optimization.