Chapter 5 - Optical Solitons

Abstract

Publisher Summary The word soliton refers to special kinds of wave packets that can propagate undistorted over long distances. Solitons have found applications in the field of fiber-optic communications. This chapter focuses on the study of pulse propagation in optical fibers—in the regime in which both the group-velocity dispersion (GVD) and the self-phase modulation (SPM) are considered simultaneously. It reviews the phenomenon of modulation instability and shows that propagation of a continuous-wave (CW) beam inside the optical fibers is inherently unstable because of the non-linear phenomenon of SPM, and leads to the formation of a pulse train in the anomalous-dispersion regime of optical fibers. The chapter explains that the modulation instability can be interpreted in terms of a four-wave-mixing process that is phase-matched by SPM. Physically, the energy of two photons from the intense pump beam is used to create two different photons. The case in which a probe is launched together with the intense pump wave is known as the induced modulation instability. Even when the pump wave propagates by itself, modulation instability can lead to spontaneous breakup of the CW beam into a periodic pulse train. The chapter explains that perturbations include fiber losses, amplification of solitons, and noise introduced by optical amplifiers. Higher-order non-linear effects such as self-steepening and intrapulse Raman scattering are the focus of conclusion of the chapter.