Waveguide Optical Isolators for Integrated Optics

Waveguide optical isolators are investigated for an application to integrated optics. A nonreciprocal loss shift isolator has the advantage of high compatibility with optical active devices. The interferometric waveguide optical isolator that uses nonreciprocal phase shift brought about by the first-order magneto-optic effect is applicable to a variety of waveguide platforms. In a silicon-on-insulator (SOI) waveguide, the low refractive index of buried oxide layer enhances the magneto-optic phase shift, which contributes to reduce the device size of isolator. We developed the surface activated direct bonding technique to integrate a magneto-optic garnet crystal onto dissimilar crystals. The performance of SOI waveguide optical isolator was demonstrated with an optical isolation of 21 dB at a wavelength of 1559 nm.