To understand why the world has shifted to optical transmission requires an explanation of the shift from metal to glass. First of all, light traveling in a glass fiber is immune to electrical interference. Plus, it does not radiate anything because the entire signal remains contained in the cable. Also, fiber is less bulky than other cables, and the signal travels longer distances.

With advances in technology, the cost has become very low, and a huge amount of information can be transmitted on a single fiber strand. Sending more information on metal wire means sending it a shorter distance. Fiber, however, seems to have infinite capacity.

The technology was first explored in 1966; indeed, the pioneers of the optical network discovered its possibilities more than 30 years ago. It was necessary to turn a signal into '1s' and '0s', prove the propagation along the fiber, and, of course, design the fiber itself.

A fiber is a tube of glass, as thin as a hair (see Figure 1). It is made of two types of glass: the inner tube is very small and maintains the flow of the light, and the outside cladding prevents the light from escaping. At present, we have many variants of optical fiber optimized for different rates of transmission and distances.

Figure 1. Fiber Strand: Very Thin Core and Large Cladding to Keep the Light Inside