Introduction

In Chapter 1 we discussed wave propagation in isotropic media in, which the velocity of propagation of an electromagnetic wave is independent of the direction of propagation. In this chapter we will discuss wave propagation in anisotropic media in which the velocity of propagation, in general, depends on the propagation direction and also on the state of polarization and one observes the phenomenon of double refraction. Anisotropic media form the basis of a large number of polarization devices such as quarter wave and half wave plates, the Soleil–Babinet compensator, the Wollaston prism, etc. Their study is also very important for understanding various light modulators based on the electrooptic effect (see Chapter 15).

In Sec, 3.2 we will discuss the phenomenon of double refraction and in Sec. 3.3 we will discuss some important polarization devices based on anisotropic media. Sees. 3,4–3.7 will discuss the electromagnetics of anisotropic media. In Sec. 3.8 we will introduce the index ellipsoid and show how from the index ellipsoid one can obtain the velocities of propagation and the polarizations of the two waves which can propagate along any given direction.

Double refraction

If we place a crystal of calcite or quartz on a point marked on a piece of paper, we will, in general, observe two images of the point. This phenomenon is referred to as double refraction or birefringence. This happens because when a ray enters the crystal it splits up, in general, into two rays which propagate along different directions and which are orthogonally polarized.