In the past few years, several major improvements have been made in the use of optical fiber communications. In earlier discussions regarding the use of SONET (see Chapter 3) and SDH (see Chapter 4), the issue of bandwidth surfaced. Not only does the issue of bandwidth keep coming up, but more significant is the problem of just how quickly we consume all the bandwidth that is made available. No matter how much or how fast we improve our spectrum availability, newer applications crop up that literally eat up all the capacity available to us. The carriers have installed fiberoptic cables as the backbone to link their interoffice networks. This creates a mainstay in their communications infrastructure. Using standard time-division multiplexing (TDM), their standard is to carry between 2.488 and 9.953 gigabits per second (Gbps) on a single fiber. The revolution to high-bandwidth applications and the explosive use of the Internet have created capacity demands that exceeded the traditional TDM limits. TDM only can operate within the spectrum of the silicon that drives current technologies. What was once considered an inexhaustible amount of capacity when fiberoptics was first introduced has literally vaporized. The depletion of the excess capacity we once had drove a new demand for more bandwidth. To meet this demand, the use of wave-division multiplexing (WDM) surfaced.

To solve the problem, the use of frequency-division multiplexing (FDM) with our light-based systems became a topic of research. What ensued was the ability to introduce various wavelengths...