Pre-spread RZ pulse transmission for reducing intra-channel nonlinear interactions

In high bit-rate systems over 40 Gbit/s, intra-channel nonlinear interactions yield a serious impairment for extending a transmissible distance. They yield not only timing jitters mainly arising from intra-channel cross-phase-modulation (XPM) but also ghost pulse generation and amplitude fluctuation from intra-channel four-wave-mixing (FWM). A solution for such obstacles is to use a strongly dispersion-managed (DM) soliton whose pulse width comes back to the input value after every period of dispersion variation. In this paper, we propose a novel design of the system in which widely spread RZ pulses are transmitted throughout the system except just after the transmitter and just before the receiver. The intra-channel XPM is drastically reduced and we can then extend the transmissible distance. We also show that a wider spread spectrum with narrower input pulse helps to suppress the intra-channel FWM and it gives a trade-off relation between the transmissible distance and spectral efficiency