Although a fiber coupler is widely used in application and numerous methods have been researched, several phenomena still occur in the optical fiber, where power in fiber couplers not only depends on the waveguides, but also the power parameters. A matrix transfer method is used to model phenomena for several junctions. An optical switch, the fabricated fusion directional coupler, enables the routing of optical data signals without the need for conversion to electrical signal, independent of data rate and protocol. Therefore, an applied voltage is designed to control and drive parametric changes of device. The coupled mode theory, Pockel effect and the empirical equation are simulated by MATLAB software. The determination of each switching characteristic is important to realize the functional operation. This model can be compared to the switching experiment and control the voltage through the coupling parameters. This book consists of two volumes describing the directional single mode fiber coupler and to design optical switch.