Determination of FWM products in unequal-spaced-channel WDM lightwave systems

Recently, unequal-spaced channel-allocation techniques have been studied an d analyzed to reduce four-wave-mixing (FWM) crosstalk in high-capacity, lon g-haul wavelength-division multiplexing (WDM) transmission systems. It will be helpful to system designers if there exists a fast tool to measure the strength of FWM crosstalk in such WDM systems. In this paper, we develop tw o algorithms, using Frequency Difference Triangles and Frequency Difference Squares, that can determine the total numbers of FWM signals falling onto the operating band and each channel, respectively, of unequal-spaced WDM sy stems. By knowing these two numbers, one can adjust the system parameters, such as minimum channel spacing, in order to keep a good balance on the adv erse effects of FWM crosstalk and interchannel interference, or avoid the a ssignment of channels at locations with the most severe crosstalk.