INTENSITY dependent phenomena in optical guided waves have attracted a great deal of interest in the recent past because of their potential use in nonlinear optical devices like optical switches, nonlinear directional couplers, etc., these devices are needed for all optical processing [1]–[3]. Optical fiber is one of the most promising nonlinear media because of its high power density and long interaction length. Ultrafast all optical switching with power of 14 W was demonstrated in 48 cm long single mode fiber [4].