Comparing the size of fiber optics to a penny. Fiber optics are used for transmitting data in the form of light. They are usually made from flexible glass that has a high refractive index. Each fiber consists of a core with an outer protective layer (cladding) that has a lower refractive index than the core. Light traveling through the fiber is contained within the core because of total internal reflection at the core/cladding boundary. This allows data to be transmitted over long distances with little information loss. Magnification x20