Thank you saja
I think you input power is low to observe the FWM effects clearly.increase your laser power on each cw laser and as taiwo said you can decrease the channel spacings.But your cw laser freq. Should be matched to wdm mux in order to get the desired output.Every time you change the spacings ,you will have to match it with mux.you can increase the value of gamma to increase the non linear efferctsthat depends upon effective area and non linear coefficient of fiber.you can get help from some research articles on the same topic,there are many articles on this particuler topic that i have studied.illet me know if you will need that.