Optical Networks: A Practical Perspective - Part 14. This book describes a revolution within a revolution, the opening up of the capacity of the now-familiar optical fiber to carry more messages, handle a wider variety of transmission types, and provide improved reliabilities and ease of use. In many places where fiber has been installed simply as a better form of copper, even the gigabit capacities that result have not proved adequate to keep up with the demand. The inborn human voracity for more and more bandwidth, plus the growing realization that there are other flexibilities to be had by imaginative use of the fiber, have led people. | 100 Propagation of Signals in Optical Fiber called higher-order solitons. A brief quantitative discussion of soliton propagation in optical fiber appears in Section . The significance of solitons for optical communication is that they overcome the detrimental effects of chromatic dispersion completely. Optical amplifiers can be used at periodic intervals along the fiber so that the attenuation undergone by the pulses is not significant and the higher powers and the consequent soliton properties of the pulses are maintained. Solitons and optical amplifiers when used together offer the promise of very high-bit-rate repeaterless data transmission over very large distances. By the combined use of solitons and erbium-doped fiber amplifiers Section repeaterless data transmission at a bit rate of 80 Gb s over a distance of 10 000 km has been demonstrated in the laboratory NSK99 . The use of soliton pulses is key to the realization of the very high bit rates required in OTDM systems. These aspects of solitons will be explored in Chapter 12. The main advantage of soliton systems is their relative immunity to fiber dispersion which in turn allows transmission at high speeds of a few tens of gigabits per second. On the other hand in conventional on-off-keyed systems dispersion can be managed in a much simpler manner by alternating fibers with positive and negative dispersion. We encountered this in Section and we will study this further in Chapter 5. Such systems when using special pulses called chirped RZ pulses can also be viewed as soliton systems albeit of a different kind and we discuss this in the next section. Dispersion-Managed Solitons Solitons can also be used in conjunction with WDM but significant impairments arise when two pulses at different wavelengths overlap in time and position in the fiber. Such collisions which occur frequently in the fiber add timing jitter to the pulses. Although methods to overcome this timing jitter have been .
