Chapter List

Overview

Optical fiber is a remarkable communication medium compared to other media such as copper or free space. An optical fiber provides low-loss transmission over an enormous frequency range of at least 25 THz even higher with special fibers which is orders of magnitude more than the bandwidth available in copper cables or any other transmission medium. For example, this bandwidth is sufficient to transmit hundreds of millions of phone calls simultaneously, or tens of millions of Web pages per second. The low-loss property allows signals to be transmitted over long distances at high speeds before they need to be amplified or regenerated. It is due to these two properties of low loss and high bandwidth that optical fiber communication systems are so widely used today.

As transmission systems evolved to longer distances and higher bit rates, dispersion became an important limiting factor. Dispersion refers to the phenomenon where different components of the signal travel at different velocities in the fiber. In particular, chromatic dispersion refers to the phenomenon where different frequency (or wavelength) components of the signal travel with different velocities in the fiber. In most situations, dispersion leads to broadening of pulses, and hence pulses corresponding to adjacent bits interfere with each other. In a communication system, this leads to the overlap of pulses representing adjacent bits. This phenomenon is called Inter-Symbol Interference (ISI). As systems evolved...