Multi-core fibers can be realized with all-glass fiber technology or alternatively as photonic crystal fibers containing air holes. In the first case, one may fabricate an all-glass preform which contains multiple cores, or combine multiple single-corporate forms to a branch from which the fiber is drawn (bunch fiber). For photonic crystal fibers, no special extension of the fabrication technology is required; one can simply assemble a more complex bundle of rods and/or tubes to obtain a preform with multiple cores. Multicore fiber (MCF) refers to an optical fiber that contains multiple cores or light guiding cores within a single strand of optical fiber. It
