Over the past two decades, a mechanism process to obtain Single Mode Fiber (SMF) coupling has emerged as a visible means for fiber optic communication. Generally, the process is always described at initial input and output result, whereas the source waves transmitting along the coupled fibers have not been fully understood. Although modeling of fiber coupling provides good understanding of the process, but experimentally the determination of the coupling range has not been clearly established. In applications optical fiber coupling is used to control and to apply power propagation from one fiber to another by splitting it as a junction. However, the coupling fiber fabrication is complicated especially at the junction. This may be due to the fact that at coupling region some parameters are affected by the structural and geometrical fiber itself. This book experimentally describes the better behavior and operation of fiber couplers at different side of measurements. Models are also proposed, and compared to experiment.