Abstract: Optical wavelength converters are very important devices in optical (DWDM) systems. Among numerous wavelength technologies (FWM) in optical fibres is attractive. Because it offers strict transparency to amplitude, frequency and phase. They also have the ability to convert multiple wavelengths simultaneously and to invert optical spectra. Four wave mixing conversion efficiency depends upon fibre non-linearity. The effects of fibre non-linearity play a decisive role in the design and performance of modern optical communication links. So, it is important to measure the nonlinear promising technique for determining fiber non-linearity (γ). This study investigates a way of estimating fibre non-linearity through four-wave mixing process.