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

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 inline 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.

Automated summary

The amplification of long-haul mode division multiplexing (MDM) transmission systems is currently achieved through three steps, which can result in complexity and degraded transmission performance. To address this issue, this paper proposes an in-line few-mode erbium-doped fiber amplifier (FM-EDFA) based on cladding pumping, which enables simultaneous amplification and transmission in MDM systems. Experimental results demonstrate that the in-line FM-EDFA has excellent performance and shows great potential for practical long-haul transmission systems.