Although discovered over 150 years ago, it was not until the 1970's that materials were developed that enabled magneto-optic (Faraday) effect devices of practical sizes. These developments are: magneto-optic materials with high Verdet constants, and the rare-earth magnet materials, capable of extremely high magnetic fields.

The magneto-optic effect has enabled development of equipment used in diverse laser applications, from industrial use to fiber-optic telecommunications.

The principle of operation of optical isolators and circulators is described herein, as well as descriptions of critical components in such equipment, such as the polarizers and the magnets.