Abstract

Intra-channel (IC) FWM is one of the major limiting factor for dispersion-managed (DM) bit-overlapped return-to-zero transmission at high bit-rates > 40 Gb/s [1,2]. ICFWM manifests itself by generation of shadow (’’ghost”) pulses in the middle of the "zero” time slots due to FWM between spectral components within a single channel. We have developed a path-average theory of ICFWM that describes initial growth and slow long-scale evolutions of FWM components. At high bit rates of 40 Gb/s and more carrier pulses periodically experience large spreading in time with corresponding reduction of the nonlinear effects. Variations of signal parameters over one period then can be averaged out (see details and notations in [3]). Spectral power distribution for long enough bit pattern consists from few narrow peaks around the central carrier frequency [1]. The main side peaks are spectral components of input signal (in a single channel) at ω± separated by Δω = |ω₀ - ω_| = |ω₊ − ω₀| = 2π/ΔT (here ΔT is the bit time) from the central carrier frequency ω₀- Amplitudes of the side peaks decay very fast, therefore, we assume that the main contribution to FWM at the carrier frequency ω₀ is generated by the process ω₊ + ω_ → 2ω₀. Note that a reasonable part of the pattern energy is concentrated in these three modes (the rest is in the low-amplitude background). Resonance interaction of these modes leads to generation of the FWM component at ω₀. Considered model obviously is very simplified and effectively it estimates only the maximum of the background growth at the zero time slots, without specification of the ghost pulses that occur in time domain.

© 2000 IEEE