A serious issue for WDM systems is the presence of resonant four wave mixing (FWM) terms, as a result of interactions between different channels. FWM presents a major source of non-linear cross talk. In multichannel systems, third order distortion mechanisms generate third order cross harmonics and a gamut of cross products. These cross products cause the most problems since they often fall near or on top of the desired signals .So the best solution is to avoid the FWM generation from early design stages. This paper describes the sources of FWM in WDM systems. In order to test the FWM generation with different frequency ranges, and different bit rates, different layout has been designed and strategies for getting around this limitation have been proposed. The experiments have been tested both on low and high bit rates, using optical signals with different frequency ranges. Proposed are solutions to avoid FWM for both low rate and high rate optical communication systems