The limitation of conventional long-haul fibre communication network has been identified to be the inter-channel interference resulted from the linear signal multiplexing scheme — wavelength division multiplexing. In this KER, non-linear frequency-division multiplexing based on the non-linear Fourier transform is proposed and experimentally verified as a potential solution to tackle the capacity limit of the current optical fibre network. With the non-linear signal multiplexing scheme, different users are, in theory, interference-free, and hence, have a monotonically increasing channel capacity.

We exploited a novel b-modulation scheme using dual-polarisation non-linear Fourier transform for information transmission in the long-haul optical fibre channel. The q_c- and b-modulated dual-polarisation (DP) non-linear frequency-division multiplexing (NFDM) systems were compared in terms of Q-factor, correlation of sub-carriers, joint and individual entropy. The b-modulated DP-NFDM system shows 1 dB Q-factor improvement over q_c-modulated DP-NFDM system due to a weaker correlation of sub-carriers and less effective noise. Finally, the b-modulated system was optimised for higher data rate, achieving a record net data rate of 400~Gbit/s (spectral efficiency of 7.2 bit/s/Hz) over 12×80 km of standard single mode fibre, amplified by Erbium-doped fibre amplifier.