n include impurities in the optical fiber that result in disper- sion of the components of a signal as well as such nonlinear effects as four-wave mixing, modulation instability, and self-phase and cross-phase modulation. Signal distortion resulting from signal dispersion can be limited by selecting purer fiber as well as by using a compensating device with a polarity opposite to that of the transmission fiber. Although such tech- niques reduce dispersion, they do not reduce the effect of nonlinear phenomena that can also adversely affect the performance of an optical transmission system. Concerning nonlinear effects, four-wave mixing (FWM) occurs when multiple wavelengths are transmitted over a com- mon fiber. Modulation instability results from the interaction between an optical signal and an optical amplifier. When multiple wavelengths are transmitted on a common fiber, modulation instability results in individual wavelengths mixing, generating new, unwanted wavelengths. Those unwanted wavelengths can both interfere with the original sig- nals as well as mask a portion of their power, making it harder on the receiver to discriminate the correct signal from the unwanted wave- lengths. Two additional nonlinear effects are self-phase and cross-phase modulation. Self-phase modulation represents a term used to describe the broadening of light pulses as they flow down a fiber. In a WDM or DWDM system, a similar effect is referred to as cross-phase modulation. In an effort to counter the effects of dispersion and nonlinear phe- nomena, several optical fiber manufacturers developed new products. One such product was a so-called non-zero-dispersion-shifted large-effective- Chapter Six area fiber (LEAF) developed by Corning. This so-called LEAF optical fiber has a low dispersion coupled to a large effective area Aeff The effective area represents the average area of a fiber in which optical power is transmitted. For example, when using single-mode fiber, the effective area is approximately equivalent to the fiber core a