Chapter 3 - Epitaxial Garnet Films for Nonreciprocal Magneto-Optic Devices

Abstract

The Faraday effect in magnetic garnets is the basis for many unique nonreciprocal devices including magneto-optic isolators. Bismuth-doped rare earth iron garnets, initially developed for magnetic bubble applications, are extensively developed for thick- and thin-film magneto-optic applications. Garnet compositional design and liquid phase epitaxial growth have been adapted to these new requirements. Properties such as optical absorption, temperature, and wavelength dependence of Faraday rotation, index of refraction, and magnetic and optical anisotropy can be controlled to a high degree to satisfy device design requirements. The development of nucleation-induced coercivity has even permitted the elimination of the bias magnet in thick-film devices. Thin-film waveguide devices are extensively investigated, but not commercialized. The most important task in practical waveguide device design and manufacture is control of material birefringence; this is accomplished by a variety of innovative material and device solutions. Further developments offer hope for integration of garnet magneto-optic elements into fiber optic systems and semiconductor devices. The current commercial nonreciprocal devices are all based on bulk or thick-film technology. The process of thin-film growth and parameter optimization is well understood and materials can be designed and grown to fit most device requirements. However, thin-film devices are likely to achieve importance in applications where an integrated wave-guide solution is required.