Question:How are optical fibers actually used to carry signals?
Flashes or light are sent along the fiber to signify the 1's of a digital signal and the spaces between the flashes represent the 0's.
The flashes are usually called pulses.
Light sources can be turned on and off very rapidly so that the sending of a series of on and off flashes can happen very quickly in addition to the fact that they reach their destination at the speed of light.
Remember: Optical fibers guide light because the light experiences a series of Total Internal Reflections as it travels along the glass.