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Compensating for intercarrier nonlinear distortion allows launching higher power into the transmission fiber and it leads to an increase in the transmission distance. Numerical calculations show that the launch power is increased by 10 dB and the maximum transmission distance is more than tripled, when the optical repeater spacing of 80 km, dispersion-shifted fiber, and signal format of 10 Gb/s nonreturn-to-zero are assumed. It is experimentally demonstrated that waveform distortion due to the four-wave mixing (FWM) among different carriers in wavelength-division multiplexing (WDM) becomes deterministic by phase-locking optical carriers and that FWM distortion can be compensated at 5 Gb/s with three-channel condition by employing DSP at the transmitter or receiver.

We propose a novel optical orthogonal frequency-division multiplexing (OFDM) transmission, where the frequency spacing of subchannels is less than the symbol rate. We show experimentally that the novel OFDM transmission achieves an optical SNR (OSNR) sensitivity level and dispersion tolerance roughly equivalent to those of the conventional OFDM. We also show the influence of chromatic dispersion from the transmission channel on the OFDM signal. The chromatic dispersion causes a desynchronization of the symbol timing between subchannels and breaks the frequency orthogonality in OFDM. We confirm experimentally that it is possible to mitigate the signal degradation due to the chromatic dispersion by optimizing the symbol timing and orthogonally polarizing the subchannels to the neighboring subchannels.