As we mentioned previously, both coaxial and twisted pair cables use a copper wire to transmit a signal in the form of voltage. In contrast, fiber optic cables use a signal made up of light. The light is generated by either an LED or a laser. Fiber optic networks provide high speed, long-distance connectivity that is resistant to EMI.
A fiber optic cable consists of either a single glass strand or multiple glass strands surrounded by an outer jacket, as shown in the following diagram. Each glass strand comprises a hollow central core that the light travels down and a glass cladding layer that prevents the light from escaping by reflecting it back into the core:
Figure 8.16: Fiber optic cable: 1) Core 2) Cladding 3) Buffer 4) Jacket
The preceding diagram can be found at https://commons.wikimedia.org/wiki/File:Singlemode_fibre_structure...