Fiber Optic Cable

An alternative to copper wire are flexible glass fibers that transmit information. By using a laser or light-emitting diode (LED) to transmit a pulse of light from one end of the fiber, a light-sensitive receiver at the other end can receive that pulse. Networks that use glass fibers are commonly called fiber optic networks.

Pulses of light move through a glass fiber at the speed of light (the fasted possible transmission speed). Other factors aside, fiber optic networks offer the highest bandwidth of any communication media.

Optical fibers have several advantages over copper wire, including:

  • Glass fibers are made from silica (i.e., sand), which—unlike copper—is inexpensive and almost unlimited in supply.
  • Because they use light and not electricity, glass fibers do not cause or suffer from the electromagnetic interference problems of copper.
    A glass fiber can carry a pulse of light much farther than copper wire can carry an electromagnetic signal.
  • Light can encode more information than electricity, giving glass fibers much higher bandwidth than copper wire. To illustrate, a single glass fiber the width of a human hair can carry more information than the (copper) transatlantic cable.

So why does anyone still use copper?

The main answer is that fiber optic cable is very expensive to install; in fact, most of the cost is in the installation!

One key difficulty is that connecting two glass fibers is more difficult than connecting two copper wires. To connect two copper wires, you simply twist them together. By contrast, you can't just twist two glass fibers together. Instead, the fibers must be connected using a special connector that (hopefully) bonds the fibers together seamlessly.

More precisely, light refracts when it passes from one medium to another, and unless the two glass fibers being connected are bonded without a seam, the seam may represent a change of medium. Thus, light crossing a connection with a seam may refract, and the refraction can cause the light pulse to change in frequency or wavelength. Since the light pulse represents information, such changes will change the information being transmitted across the connection. The chief disadvantage of glass fiber is thus the difficulty of connecting two fibers in such a way that the light passes through the connection unaltered.

Finally, fiber optic cable is also more fragile than copper cable and difficult to bend. Thus, it can sometimes be difficult to find a path for the cable.

Previous Page Next Page


 

 

 


This chapter was written by Jeff Nyhoff and Joel Adams. Copy editing by Nancy Zylstra
©2005 Calvin College, All Rights Reserved

If you encounter technical errors, contact rit@calvin.edu.