These cables are made up of glass or plastic fibers. Its sources are LED or laser diodes. It uses light beam to transmit the signals. Firstly, the signal converted in to light signal from electrical signal. It has core and cladding, core is under the cladding. The refractive index of cladding is lower than that of core.Coating the cladding is a protective coating consisting of plastic, it is called the Jacket.