Applications of magneto-optics in ring laser gyroscopes

Magneto-optical elements can be used to provide the frequency bias needed to prevent lock-in in ring laser gyroscopes by introducing a differential phase shift between counterpropagating beams. Some of the magneto-optical and magnetic requirements are noted and the various magneto-optical elements developed to satisfy these requirements are discussed. A number of magnetic metals and alloys as well as transparent magnetic garnets are described in terms of the properties needed to evaluate their magneto-optical performance. Fe, MnBi and garnets with high Faraday rotation appear to be the best candidates, and magneto-optic mirrors based on these have received industry attention. To reduce the optical loss to acceptable levels it is necessary to incorporate the magnetic metal mirrors into multilayer dielectric-magnetic thin film composites. A general scattering matrix method for handling multilayer composites which incorporate either an opaque or transparent magnetic film is described. It is based on the methods of Hunt. Typical results are shown for a number of Fe and garnet based multilayer mirrors.