Dual-polarization NFDM transmission using distributed Raman amplification and NFT-domain equalization

Transmission systems based on the nonlinear Fourier transform (NFT) can potentially address the limitations in transmission reach and throughput set forth by the onset of Kerr-induced nonlinear distortion. Whereas this technique is at a preliminary research stage, a rapid progress has been shown over the past few years leading to experimental demonstrations of dual-polarization systems carrying advanced modulation formats. The lossless transmission required by the NFT to ensure the theoretical validity of the scheme is a fairly strong requirement considering practical transmission links. Here, we address it by using optimized distributed Raman amplification to minimize the power variations to approx. 3 dB over 200 km, thus approaching the lossless transmission requirement. Additionally we experimentally evaluate the improvement provided by equalization schemes applied to the signals in the nonlinear Fourier domain. By combining distributed Raman amplification and nonlinear-Fourier-domain equalization we show transmission reaches for dual-polarization nonlinear frequency division multiplexing (NFDM) systems transmitting both two eigenvalues (8 bit/symbol) up to 2200 km and three eigenvalues (12 bit/symbol) up to more than 600 km at hard-decision (HD) and soft-decision (SD) forward error correction (FEC) threshold, respectively.