Solitons in Optical Fiber Communication Systems (Book Chapter)

To understand why optical solitons are needed in optical fiber communication systems, we should consider the problems that limit the distance and/or capacity of optical data transmission. A fiber optic transmission line consists of a transmitter and a receiver connected with each other by a transmission optical fiber. Optical fibers inevitably have chromatic dispersion, losses (attenuation of the signal) and nonlinearity. Dispersion and nonlinearity can lead to the distortion of the signal. Since the optical receiver has a finite sensitivity, the signal should have high enough level to achieve "error-free" performance of the system. On the other hand, by increasing the signal level one also increases the nonlinear effects in the fiber. In order to compensate for the fiber losses in a long distance transmission, one has to periodically install optical amplifiers along the transmission line. By doing this , a new source of erroes is introduced into the system - an amplifier spontaneous emission noise. (Note that even ideal optical amplifiers inevitably introduce spontaneous emission noise).