Abstract
A magneto-optical isolator is indispensable for optical fiber communication to protect active devices from unwanted reflections. A ferrite garnet such as yttrium iron garnet (YIG) is typically used because of its transparency and relatively large magneto-optic effect for near-infrared light (~0.8 eV). However, a YIG film must be epitaxially grown on a garnet substrate, which makes it difficult to integrate optical isolators with other photonic devices. In a literature, a cobalt ferrite has specific peak of magneto-optic effect at the infrared wavelength.We then propose and design an ultra-compact magneto-optical isolator with cobalt ferrite on silicon photonic circuits. The isolator is based on a Mach-Zehnder interferometer of silicon optical waveguide fabricated on a silicon-on-insulator wafer. A cobalt ferrite film is partially deposited on the interferometer arms. In our design, the length of the nonreciprocal phase shifter is about 35μm which is on tenth of the case with Ce:YIG. We deposited cobalt ferrite films on buffer layer by a sputtering deposition. A (400)-oriented CoFe2O4 film was fabricated on FeO/Fe buffer layer to achieve low material loss.
