Fiber optics. Female technician holding fiber optic cables. Optical fibers are made from flexible glass that has a high refractive index. Each fiber is then coated with an outer protective layer that has a low refractive index. The light beams that emerge from the end of each fiber have been completely internally reflected. The light may thus travel along the entire cable with little or no absorption. Bundles of optical fibers may be used to carry images, or high volumes of data such as telephone conversations.