Overview

The authors decided to collect a slew of rules, in a single chapter, devoted to the degradation of the optical signal. Many of these are fiber related as they deal with the propagation of light down a long fiber. These rules deal with the purely optical effects of dispersion, four-wave mixing, and other nonlinear effects that occur when sending an optical pulse down a length of fiber. Thus, these rules do not address the important issue of amplitude noise generation, which is covered in Chap. 8. They also do not speak to signal degradation as a result of connectors, switches, amplifiers, or other network elements.

The phenomena described in this chapter manifest themselves as an increase in the length of a data pulse or a decrease in optical signal or in signal quality, and/or the generation of noise. The effects we include may affect the signal-to-noise ratio (SNR) of the system. They can also appear as an increase in noise at one wavelength due to the presence of a signal in another channel. An example would be four-wave mixing of dense wavelength division multiplexing (DWDM) signals. Temporal lengthening of a pulse as a result of differential group delay (DGD) may cause one pulse to mix with its neighbor, affecting the basic SNR.

Dispersion results when there are different speeds in the fiber for different modes. In multimode fibers, both chromatic and intramodal dispersion (different propagation speeds for different modes) can occur. This phenomenon generally limits the length of high-data-rate...