Optical fibers used for lighting are similar to the fibers used in high speed communication. The only difference is how the cable is optimized for light rather than data. The fibers consist of a core that transmits the light and an outer sheathing that traps the light inside the core of the fiber.
Side-emitting fiber optic lighting cable has a rough edge between the core and the sheathing to disperse the light out of the core along the length of the fiber optic cable to create a consistent lighted look similar to neon light tubes.
Fiber optic cable can be made of glass, just like communications fibers, or plastic. If the fibers are glass, they are usually very small diameter and many are bundled together in one jacketed cable to provide enough light transmission.