 field trials using lasers operating at 40 Gbits/s were in progress. At the same time work was proceeding to extend transmission rates to 40 Gbits/s, work was also progressing to add more wavelengths to a DWDM system. To illustrate the potential growth in the transmission capacity of a single optical fiber, let's examine the use of evolving 128- and 256-channel DWDM systems. At 10 Gbits/s per channel, a 128-chan- nel system provides a composite transmission capacity of 1.28 Tbits/s! Yes, that's 1.28 trillion bits per second, a transmission capacity suffi- cient to carry all data, voice, and video generated by every person on the planet as recently as approximately 1991. If we sharpen our pens and perform a simple computation, we note that the transmission capacity of a single optical fiber has increased by a factor of 1.28 Tbits/s to 5.12 Tbits/s, or approximately 474,000 times from AT&T's FT3C lightwave system introduced during 1983. Note that this repre- sents an increase in transmission capacity of over six magnitudes! If we consider the possible near-term availability of 256-channel sys- items, with each channel operating at 40 Gbits/s, the capacity of a single Fiber in the WAN optical fiber may appear to resemble a science fiction fantasy. For exam- ple, with 256 channels, each operating at 40 Gbits/s, the composite capacity of a single optical fiber becomes 10.24 Tbits/s. Instead of being science fiction, the increase in the transmission capacity of optical fiber is a reality. However, this increase resulted from three technological advances. Those advances include the manu- facture of better-quality glass fibers, the development of fiber Bragg gratings, and the availability of optical amplifiers, three topics that we now focus on. ADVANCES IN OPTICAL FIBER The transmission of multiple wavelengths with high levels of optical power can result in several non- linear phenomena that can adversely affect the performance of a trans- mission system. Some of the factors that can adversely impact optical transmissio