Introduction

This chapter provides a succinct overview of the various nonlinear effects that can occur when a light field propagates in an optical fibre. Given that nonlinear fibre optics is a very mature research field, it has been covered in much detail by many previous reviews and monographs. The reader is particularly referred to Agrawal (2007) for a treatment that combines a review of both theory and experiments in a way that is simultaneously accessible and technically comprehensive. Other monographs that contain valuable material and references to the original literature include Taylor (2005) and Alfano (2006). In this treatment we provide only a brief introduction to the major concepts, placing particular emphasis on effects that play an important role in supercontinuum generation. Where appropriate, these effects will be discussed in more detail in other chapters. We do, however, treat the numerical modelling of nonlinear pulse propagation in more depth than is usually found in the literature.

Modelling nonlinear pulse propagation

The propagation of an electromagnetic wave or pulse depends on the medium in which it propagates. In vacuum a pulse can propagate unchanged. When propagating in a medium, however, an electromagnetic field interacts with the atoms, which generally means that the pulse experiences loss and dispersion. The latter effect occurs because the different wavelength components of the pulse travel at different velocities due to the wavelength dependence of the refractive index. In an optical waveguide, the total dispersion has an additional component due to the light confinement called waveguide dispersion, which cannot be neglected.