2 - Technologies

In optical communication links, it is the optical fiber that provides the transmission channel. The fiber consists of a solid cylinder of transparent material, the core, surrounded by a cladding of similar material. Light waves propagate through the core in a series of plane wave fronts, or modes - the simple light ray path used in elementary optics is an example of a mode. For this propagation to occur, the refractive index of the core must be larger than that of the cladding. There are two basic structures that have this property: step-index fibers with two different refractive index values for core and cladding and graded-index fibers providing a continuous transition of refractive index from core to cladding. There are multimode fibers that allow a great number of modes to propagate and single-mode fibers that only allow one mode to propagate. The propagation in the fibers can be described with the effective refractive index, which depends on both core and cladding refractive indices, as well as on the type and thickness of the fiber.