Magneto-optic materials have unique physical properties that offer the opportunity of constructing devices with many special functions not possible from other photonic devices. The most significant of these properties are that the linear magneto-optic effect can produce circular birefringence and that, unlike other optical effects in dielectric media, it is nonreciprocal. All practical magneto-optic devices exploit one or both of these two properties. Important applications of these devices include polarization control, optical isolation, optical modulation, and magneto-optic recording. The basic principles of magneto-optic effects, as well as the functions of various magneto-optic devices based on these effects, are considered in this chapter.

Magneto-optic effects

Because magneto-optic effects are intimately connected to the magnetic properties of materials, we first briefly summarize the fundamental magnetic properties of materials. To a certain degree there is a parallelism between the electric and the magnetic properties of materials, but this parallelism is not complete. We shall pay attention to the similarities and differences between these properties in order to gain an appreciation of the uniqueness of magneto-optic devices.

Following the similarity between (1.1) and (1.2), a magnetic susceptibility tensor, χm, analogous to the electric susceptibility tensor χ can be defined to describe the magnetization induced by a magnetic field.