Second-order few-mode distributed Raman amplifier for mode-division multiplexing transmission

We first experimentally demonstrate a second-order few-mode distributed Raman amplifier with 4 dB mode-equalized gain. The noise figure improvement of the LP
₀₁
and LP
₁₁
modes are respectively 1.1 dB and 0.9 dB compared with first-order Raman amplification scheme.