IMPULSE-RESPONSE OF CROSS-PHASE MODULATION FILTERS IN MULTISPAN TRANSMISSION-SYSTEMS WITH DISPERSION COMPENSATION

As shown by Chiang et al. (1996), cross-phase modulation on each chann el of a wavelength-division-multiplexed transmission system can be vie wed as a phase modulation, where the modulating signal is the sum of t he input intensities of all the other copropagating channels, each fil tered by a low-pass filter, whose bandwidth decreases with the walk-of f parameter. We give an explicit expression of the impulse response of such filter in the general case of dispersion mapped transmission sys tems. We show by simulation that this filter, in intensity-modulated t ransmission systems, gives an optimal prediction of the signal phase e ven when the underlying assumption of negligible envelope distortion u pon which its derivation is based is strongly violated. As an applicat ion, we show an analytical evaluation of the spectral broadening induc ed by XPM in multi-span compensated systems. (C) 1998 Academic Press.