All-Raman unrepeatered transmission of 1.28 Tbit/s (32×40 Gbit/s) over 240 km conventional 80-μm2 NDSF employing bi-directional pumping

A total of 32 channels of 40 Gbit/s CS-RZ ETDM signals have been successfully transmitted over an unrepeatered span of 240 km conventional 80-μm² NDSF employing all-Raman amplification and bi-directional pumping. No large-effective-area fibres, hybrid transmission lines, or intraspan remotely pumped EDFAs were used. Up to 65 dB span loss, out of a total span loss of 93.8 dB, has been compensated. Individual channel Q-factors between 12.5 dB and 14.5 dB, at a PRBS pattern length of 2³¹-1, were achieved without using FEC. Bi-directional pumping with pump laser RINs around -140 dB/Hz has allowed an average OSNR improvement by 6 dB in the transmission fibre, compared to either counter-pumping or co-pumping alone. This highlights the prospect of possible performance enhancement in high bit rate multiple long-span systems by bi-directionally pumped distributed Raman amplification, as compared to counter-pumping only, or unrepeatered transmissions with additional adoption of fibre effective area management and remote pumping.