Application of Wafer Direct Bonding Technique to Optical Nonreciprocal Devices

A wafer direct bonding technique enables one to integrate dissimilar crystals like a magnetooptic garnet on Si and III-V semiconductors, which facilitates fabrication of optical nonreciprocal devices on commonly used waveguide platforms. The surface-activated direct bonding technique is described, focusing on the change of surface roughness due to the surface activation process with oxygen or argon plasma irradiation. The interferometric waveguide optical isolator that uses magnetooptic nonreciprocal phase shift is fabricated by directly bonding a magnetooptic garnet onto a silicon rib waveguide. An isolation of 21 dB is obtained at a wavelength of 1.56 μm. The interferometric optical isolator can be modified to a waveguide optical circulator. The calculated performance of the waveguide optical circulator is also shown in this paper.