Silicon on Insulator and directional optical coupler based AND, OR, NOR and NAND gates are designed in this paper. The Silicon On Insulator (SOI) waveguide with high effective indices is used as primary material. All the logic gates are analyzed with all the Boolean possibilities. The overall wafer size for the design is maximum μm × μm achieved. The operating wavelength for the all optical gates is chosen 1500 nm. All the Boolean functions are satisfying its functionalities even though reduction of overall wafer size. All the analysis perform with finite differentiation time domain (FDTD) method.