Fiber Optic cable employs photons for the transmission of digital signals. A fiber optic cable consists of a strand of pure glass a little larger than a human hair. Photons pass through the glass with negligible resistance. The glass is so clear that, according to Michael Coden of Codenoll Technologies Corporation (a major fiber vendor), “a 3-mile-thick fiber optic window would give you the same view as a 1/8-inch-thick plate glass window.” The optic core of fiber optic cable is pure silicon dioxide. It makes for good tricks. You can wrap it around yourself, then shine a light in one end and see that light on the other end. Copper cable, on the other hand, is subject to problems with attenuation, capacitance, and crosstalk.

Fiber optic cable is resistant to electromagnetic interference and generates no radiation of its own. This last point is important in locations where high levels of security must be maintained. Copper wire radiates energy that can be monitored. In contrast, taps in fiber optic cable are easily detected. fiber optic cable also extends to much longer distances than copper cable.

Information is transmitted through fiber optic cable by pulsing laser light. The electronic 1s and 0s of computers are converted to optically coded 1s and 0s. A light-emitting diode on one end of the cable then flashes those signals down the cable. At the other end, a simple photodetector collects the light and converts it back to electrical signals for transmission over copper cable networks.

Cable Construction

Figure 1-A illustrates the fiber optic cable structure. The core is the transparent glass (or plastic) component of the cable. Light shines through it from one end to the other. The cladding, which is a glass sheath that surrounds the core, is a key component. Like a mirror, it reflects light back into the core. As light passes through the cable, its rays bounce off the cladding in different ways as shown in Figure 1-B.

A “dopant” is added to the core to actually make it less pure than the cladding. This changes the way the core transmits light. Because the cladding has different light properties than the core, it tends to keep the light within the core. Because of these properties, fiber optic cable can be bent around corners and can be extended over distances of up to 100 miles.

The types of fiber optic cable are listed here:

Cable specifications list the core and cladding diameters as fractional numbers. For example, the minimum recommended cable type for FDDI (Fiber Distributed Data Interface) is 62.5/125 micron multimode fiber optic cable. That means the core is 62.5 microns and the core with surrounding cladding is a total of 125 microns.

Optical Cable Types

The following cable types are available from Optical Cable in Roanoke, Virginia. They are listed here as a representative sample of the cable types available from various manufacturers.