Ultralow noise and SCL wideband few-mode amplification and transmission based on second-order few-mode distributed Raman and first-order single-mode lumped Raman

Transmission with few-mode fiber (FMF) is one of the most promising methods for increasing single fiber capacity, with urgent demands for low-noise and wideband amplification. In this work, we experimentally demonstrate a few-mode hybrid Raman amplifier (FM-HRA) based on a second-order few-mode distributed Raman amplifier (FM-DRA) cascaded with a lumped Raman amplifier (LRA). The few-mode hybrid amplification with a 100-nm bandwidth (1520 to 1620 nm), covering the S + C + L bands, is realized using a weakly-coupled FMF with a transmission length of 100 km and a dispersion compensating fiber (DCF). The maximum on-off gains for three modes (LP01, LP11, and LP21) are 22.6, 25.1, and 25.5 dB, and the average on-off gains over 100-nm bandwidth are 19.6, 21.4, and 21.3 dB, respectively. The differential modal gain (DMG) is less than 2.9 dB. The effective noise figure (NF) of the three modes is lower than −1.1 dB over 100-nm bandwidth, and the lowest effective NF is −6.8 dB, which is close to the effective NF of FM-DRA. This means HRA can fully utilize the advantages of ultralow noise of DRA and high gain of LRA. The MIMO-less transmission experiment demonstrates the highest data rate of 56 Gbps for LP01 mode. This work features pure Raman amplification with high gain, ultralow noise, and wideband. The configuration of high-order DRA in FMF and first-order LRA in DCF also offers the benefits of better pump power utilization and dispersion compensation. •Experiment demonstrates a few-mode hybrid Raman fiber amplifier.•Amplification bandwidth is 100 nm (1520 to 1620 nm), covering the S + C + L bands.•The effective noise figure (NF) is lower than −1.1 dB, and the lowest NF is −6.8 dB.