To use the available bandwidth in optical communication systems different multiplexing techniques are adopted, so that multiple users can access and use the bandwidth efficiently. The most common techniques are frequency division multiplexing, time division multiplexing, optical code division multiplexing, wave length division multiplexing and dense wavelength division multiplexing. Absolute Polar Duty Cycle Division Multiplexing over wave length division multiplexing technique is another technique which increases the channel count from other conventional existing systems. However, AP-DCDM-WDM system faces the non-linearities as like the other conventional system which affects the spectral efficiency. There is a need to study the effect of non linearities, especially effect of four wave mixing on this technique, to make this technique more efficient and powerful by taking suitable measures against the non-linearities.