Introduction

This chapter begins the second part of the book, dealing with fundamental principles of non-linear optics and light polarization. These notions are essential to understanding the interactions between the electric field and matter, and in particular with dielectric materials in glass-based optical fibers and more generally in every dielectric waveguide. Nowadays, optical communication requires a deep understanding of several engineering disciplines to reach optimum transmission performance, and basic concepts of non-linear optics as well as light polarization must be mastered by every engineer working in this fascinating field.

Section 4.2 briefly reviews the Maxwell equations and the constitutive relationships, focused on dielectric and diamagnetic materials, widely used in optical communication. Section 4.3 introduces the dielectric polarization field from a macroscopic point of view, introducing the series expansion model and related higher-order polarization components. The usual linear polarization is only a first-order approximation of the interaction between the applied electric field and the material response. The linear dielectric susceptibility and dielectric permittivity are then generalized to account for higher-order interactions, introducing the formalism of tensor quantities, with interesting dual representations in time and frequency domains. Section 4.4 translates the concepts introduced in the preceding section to common macroscopic properties of the dielectric medium, justifying several assumptions quite often made as postulates.