We fabricate a Mach-Zehnder interferometer-based optical isolator using a silicon-wire waveguide with magneto-optic garnet cladding using direct bonding techniques. Using Si-wire waveguides, the size of the device is greatly reduced from that of our previous device. We investigate surface-activated direct bonding with nitrogen plasma treatment, which shows better bonding results than oxygen plasma treatment. A large magneto-optic phase shift of 0.8π and an optical isolation of 18 dB are obtained at a wavelength of 1322 nm.

An optical isolator for transverse electric (TE) polarized light is demonstrated by adhesive bonding of a ferrimagnetic garnet die on top of a 380 nm thick silicon waveguide circuit. Polarization rotators are implemented in the arms of a nonreciprocal Mach-Zehnder interferometer to rotate the polarization to transverse magnetic in the nonreciprocal phase shifter regions. Calculation of the nonreciprocal phase shift (NRPS) as a function of bonding layer thickness experienced by the TM mode in the interferometer arms is presented, together with the simulation of the robustness of the polarization rotator. Experimentally, 32 dB isolation is measured at 1540.5 nm wavelength using a magnetic field transverse to the light propagation directions. This paves the way to the cointegration of laser diodes and optical isolators on a silicon photonics platform.

We demonstrate a silicon Mach–Zehnder interferometer (MZI) based magneto-optical isolator having an 8 nm bandwidth for more than 20 dB isolation. The operational bandwidth of the isolator is determined by the wavelength dependence of a reciprocal phase difference provided by the asymmetric path length of the MZI. Although a shorter path length requires precise control of the waveguide dimensions, we achieve wider-bandwidth operation.

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