IMPACT OF MODULATION FREQUENCY ON CROSS-PHASE MODULATION EFFECT IN INTENSITY MODULATION DIRECT-DETECTION WDM SYSTEMS

The impact of modulation frequency on the cross-phase modulation (XPM) effect in intensity modulation (IM) -direct detection wavelength-divi sion multiplexing systems is investigated theoretically and numericall y. A simple expression for the XPM-induced IM is derived, verified by simulation and its validity range is presented. The dependence of XPM- induced IM on the fiber length, fiber dispersion, channel separation a nd pump modulation frequency is assessed. It is shown that at very low frequency the walkoff effect has almost no influence on the XPM-induc ed IM efficiency which increases with the square of the frequency; at higher frequency the IM efficiency can be reduced significantly by the walkoff and scales linearly with modulation frequency.