Materials issues in the layers required for integrated magneto-optical isolators
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Materials issues in the layers required for integrated magneto-optical isolators Luis J. Cruz-Rivera1, Sang-Yeob Sung2, Jessie Cassada2, Mariza R. Marrero-Cruz2, and Bethanie J H Stadler2, 1Stanford University, Stanford CA 94305, 650-497-6908, U. S. A., 2University of Minnesota, Minneapolis MN 55455, 612-626-1628, U. S. A. ABSTRACT The development of integrated optical isolators is critical to the functional integration of optical devices and systems. This work will primarily elucidate a methodology to grow, by a semiconductor compatible process, the critical active material in monolithically integrated magneto-optical isolators; yttrium iron garnet (YIG: Y3Fe5O12). Reactive radio frequency (RF) sputtering was used to grow YIG on MgO, which is a promising buffer layer material for optical devices. The chemical, structural, optical, magneto-optical and magnetic properties of the resulting films have been studied by various techniques including energy dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD), Faraday rotation measurements and vibrating sample magnetometry (VSM). Low forward powers (lower limit of 12.3 W/cm2) grew YIG nuclei in an amorphous matrix and the number of these nuclei increased with increasing forward power. At powers exceeding 19W/cm2 film cracking occurred. The films with YIG had strong in-plane magnetizations with small coercive fields. Optical cladding layers compatible with YIG films have been grown through plasma enhanced chemical vapor deposition (PECVD) and thin film permanent magnets for biasing have been grown and optimized.
INTRODUCTION Currently, nonreciprocal devices, such as isolators and circulators are strictly bulk components. The integration of such devices is critical to the technological progression of photonic systems. However, integrated nonreciprocal devices are following a slow development trajectory despite their expected impact to the telecommunications industry by enabling the integration of complete optical subsystems [1]. Magneto-optics uniquely enables the production of nonreciprocal components, which are the basis for polarization rotation, nonreciprocal phase shifting, and mode conversion [2]. Traditionally MO garnet films for bulk components have been grown by liquid phase epitaxy, thus excluding growth onto semiconductors given the epitaxial requirements of this technique [3]. This study’s focus centers on the growth and characterization of YIG films on a semiconductor buffer layer (MgO) without the use of a substrate heater. Recently several attempts have been made to integrate diode lasers, optical fibers and waveguides structures with magneto-optic (MO) films [4,5]. Of all materials studied, yttrium iron garnet (YIG) is the best Faraday medium for isolators in the visible and near infrared regions. [6]. Bismuth and other elemental substitutions into the dodecahedral sites of the garnet structure strongly enhance the MO effect. [7]. The Bi:Y substitution has an upper limit of approximately 5:1 that, when approached, decreases the thermal expansion misma
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