Optical switch is a passive device that is very important in optical network communication system. It is used to switch an optical signal from one port to another one. The optical switch is fabricated using fiber optics or slab waveguide to becomes directional fiber coupler and Mach–Zehnder Interferometer (MZI). It's coupling region is disturbed by DC voltage. The different voltage between the electrodes will change the refractive index of the material, and as a result, the coupling coefficient will be changed. A directional fiber coupler switch is promising an easier technique and much cheaper that the other one. It consists of two or more single mode fibers joined by fusion method, and the output power be able to switch by adjusting the applied voltage. However, MZI is a good optical switch since it gives high efficiency, faster switching time, and less voltage requires to switch optical power.