Coaxial optical fiber coupling

The main purpose of this work is to demonstrate and physically explain the operation of coaxial directional coupling. Two approaches have been used to explain the behavior of the coaxial couplers. Mode coupling theory and normal mode interference have been successfully employed in the design of such couplers. Experimental observation of switching and beatlength was in agreement with the theory. Such fibers, when designed as couplers are multimoded supporting at least three modes. However, it is possible for such fibers to be single moded.