A practical in-line FM-EDFA based on cladding pumping for MIMO-free MDM amplification and transmission

Abstract

The amplification of the long-haul mode division multiplexing (MDM) transmission systems is currently mainly implemented by three steps due to the lack of high-performance in-line few-mode erbium-doped fiber amplifiers (FM-EDFA): firstly, the multiplexed signals need to be demultiplexed. Secondly, multiple single-mode EDFAs are used to amplify the modes separately. Finally, the signals are re-multiplexed into the few-mode fiber for transmission. The multi-stage multiplexing and demultiplexing bring significant complexity and additional modal crosstalk, resulting in degraded transmission performance. To address this issue, an in-line FM-EDFA based on cladding pumping is proposed for simultaneous amplification and transmission in MDM systems. The direct connection of the in-line FM-EDFA to the transmission FMFs reduces the need for mode multiplexing/demultiplexing devices, which provides excellent stability and applicability for MDM transmission systems. The experimental results show that the modal gains of in-line FM-EDFA can reach 21 dB with a differential modal gain (DMG) of less than 0.9 dB. Moreover, the in-line FM-EDFA is applied for simultaneous amplification and transmission in a weakly-coupled MDM system with MIMO-free direct detection. The modal crosstalk of the in-line FM-EDFA is less than −11 dB. Therefore, the in-line cladding-pumped FM-EDFA provides good integration to the fiber links, showing much potential in practical long-haul transmission systems.