Compact Mach–Zehnder Interferometer Ce:YIG/SOI Optical Isolators

We demonstrate an optical isolator integrated with a silicon-on-insulator waveguide platform realized by the adhesive bonding of a Ce:YIG/SGGG die on top of a Mach-Zehnder interferometer (MZI). The design is based on the different nonreciprocal phase shifts (NRPS) experienced by both arms of the interferometer, which have different waveguide widths. Simulation of NRPS versus silicon waveguide width is shown for a few different benzocyclobutene bonding layer thicknesses for a particular silicon waveguide thickness and Ce:YIG/SGGG stack. Variations of NRPS as a function of MZI arm lengths with bonded stack on top of MZI are measured. Optical isolation of 11 dB is experimentally obtained for a device with a footprint of 1.5 mm × 4 μm.