One of the primary information sources we used on Fiber Optics is Understanding Fiber Optics, Second Edition, by Jeff Hecht.
A fiber optic is nothing but a cable (see also: Coaxial Cable) made of Glass about the diameter of a human hair. It is made from ultra-pure silica glass,
which is nearly 200,000 times more pure than ordinary window glass. All it is
capable of doing is carrying Light. That requires the communications to take place in a Digital format, either the light is on (a value of 1) or it is off (a value of 0).
To learn more about Fiber Optics pursue the following:
Fiber Optics - History
Fiber Optic Types
Fiber Optics - How and Why it Evolved
Microwave Communications - Fiber Optics Versus Microwave