In this study we investigate an all-optical switching node which can be controlled via transient grating formed by interference of two Gaussian beams. This design considers 3-D architecture of switching fabrics, real profile of Gaussian beams and nonlinearity for fast switching time requirements. Four Wave Mixing (FWM) is applied in the evanescent field region of waveguide to estimate the reflection angle and the efficiency of switching node. The effect of the formed grating on the propagation of mode is analysed by coupled mode theory and co-directional mode coupling coefficient is found by using Distributed Feedback Laser approach. A method for overall diffraction efficiency is proposed and optimization parameters for better efficiency are described.