Development of Hexaferrite Films for Integrated Optical Waveguide Isolators

Northeastern University, Boston MA

Investigators

Abstract

The magneto-optical and optical properties of thick films of hexagonal ferrites (hexaferrites) will be developed to meet the emerging need for integrated optical isolators for broad-band telecommunication systems. Comparisons between barium hexaferrite, the prototypical uniaxial hexaferrite, and yttrium iron garnet (YIG), the prototypical garnet composition used as the basis for developing all presently used magneto-optic materials, shows that barium hexaferrite possesses a significantly higher Curie temperature and larger Faraday rotation than YIG. In addition, the optical absorption mechanisms and spectral dependence appear to be the same for both materials. Thus, there is a strong premise for believing that the substituted hexaferrite films to be developed here may have superior magneto-optical properties and temperature stability compared to present-day bismuth-substituted garnets. In addition, the strong uniaxial anisotropy inherent in oriented hexaferrite films may allow fabrication of self-biased, magnetically-saturated, waveguide isolators that can be incorporated into integrated optoelectronic devices. As of yet, no one has measured hexaferrite films of sufficient thickness for magneto-optical applications. This program builds upon our successful development of thick epitaxial hexaferrite films for milimeter-wavelength applications, and will systematically measure the structural, magnetic, optical and magneto-optical properties of both pure and substituted hexaferrite films. Techniques for film lift-off will also be developed to simplify the fabrication of integrated devices. Particular emphasis will be placed on developing films having high Faraday rotation and good thermal stability, and on designing and testing optical waveguide isolators that use the uniaxial anisotropy of hexaferrites to eliminate external magnets.