Mitigation of Nonlinear Impairment by Coherently Superimposing CAP Sideband Signals

We propose to utilize the Hermitian symmetry of carrier-less amplitude phase (CAP) signals to mitigate distortion caused by fiber nonlinearity. The upper and lower frequency sidebands of CAP signals constitute phase-conjugated twin waves. Hence, coherent superposition of the two sidebands at the receiver can improve signal-to-noise ratio and compensate nonlinear impairment. We experimentally demonstrate that this scheme can improve the Q factor by ~1.6 dB after 80-km transmission. When the fiber length is extended to 240 km, the Q factor still exceeds the 7% hard decision forward error correction threshold by ~0.4 dB, showing potential application of the scheme for access and metro networks.