The core of a conventional optical fiber is the part of the fiber that guides the light. The core is surrounded by a medium with a lower index of refraction, typically a cladding of a different glass, or. A fiber optic cable consists of five basic components: the core, the cladding, the coating, the strengthening fibers, and the cable jacket. The ability of a hair-thin strand of glass to move massive amounts of data instantly across continents is rooted in the precise engineering of its internal.