Phase-conjugated twin waves for communication beyond the Kerr nonlinearity limit

Kerr nonlinearity imposes a limit on the achievable transmission performance and capacity of optical fibre communication links. We show that the nonlinear distortions of a pair of phase-conjugated twin waves are essentially anticorrelated, so cancellation of signal-to-signal nonlinear interactions can be achieved by coherently superimposing the twin waves at the end of the transmission line. We demonstrate that by applying this approach to fibre communication, nonlinear distortions can be reduced by >8.5 dB. In dispersive nonlinear transmission, the nonlinearity cancellation additionally requires a dispersion-symmetry condition that can be satisfied by appropriately predispersing the signals. By using these techniques we succeed in transmitting a 400 Gb s superchannel over 12,800 km of fibre. We further show a connection between the nonlinearity cancellation and a nonlinear noise squeezing effect. The concept of using phase-conjugated twin waves to suppress nonlinear interactions may prove beneficial in other physical systems governed by the nonlinear Schrödinger equation.