Investigation of magneto-optical properties for optical fiber based devices

Abstract

The digital traffic increased manifold over the years with increasing number o f users of the internet irom home based PCs to large businesses and research organizations. Electronic switching is a mature and sophisticated technology; however, the optical signals require conversion to electronic form in order to be switched. All optical switching eliminates the optical-electronic-optical conversions. Advances in all optical technologies coupled with rapidly rising demands for network bandwidths are fueling an increasing amount of research in the field o f optical switching. Some o f the current technologies are micro-electro-mechanical-systems technology and electro-optic teclmology. However the former technique is slow with switching times in the order of milliseconds and the latter method although fast is expensive. Magneto-optical materials have been successfully used in optical devices such as isolators and circulators; however, they have overall led to very few optical fiber based applications especially in optical communications. The emphasis of this thesis is the investigation of Faraday rotation for small beam sizes that are compatible with standard single mode and multimode optical fibers. Rare earth iron garnet films suitable for optical communication wavelengths in the 1310 nm and 1550 nm range were used due to their high magneto-optical figures o f merit, which is the ratio of optical absorption to Faraday rotation. The Faraday rotation for an optical beam size that is comparable to the domain width o f the given magnetic material is different than the linear Faraday rotation expected for a large beam size. For the first time the nonlinearity of the Faraday rotation for a small optical beam size has been experimentally studied. The Stoner-Wohlfarth astroid model predicts very well the observed Faraday rotation. This abrupt transition is generally sought after in the design of devices especially switching devices. This work e). tends the application o f magneto-optical materials to all fiber devices which includes high speed switches as well as interferometers. A Mach-Zehnder interferometer (MZI) based on Faraday rotation is proposed and experimentally implemented, which in the current framework the device is an on/off switch. The simple construction and operation o f the Mach-Zehnder interferometer (MZI) makes it suitable for application in photonic integrated circuits. Thus interferometric configuration