Fig. 1. Schematic of the experimental setup. The CW or CCW modes of the microsphere are probed by switching the opposite propagating lights through a 2 × 2 optical switcher. The bias magnetic field is perpendicular to the equator of the YIG microsphere. FPC, fiber polarization controller; DSO, digital oscilloscope; PD, photodetector. B stands for the magnetic field. Insets: the packaged Si₃N₄ waveguide and microring with the fiber lenses and the schematic cross-section view of the bus waveguide after depositing the SiO₂ for protection.

Fig. 2. Typical transmission spectra of the (a) TM- and (b) TE-polarized lights before or after the YIG microsphere touches the Si₃N₄ waveguide. The YIG microsphere has a diameter of 1000 µm with a bias magnetic field of about 50 mT.

Fig. 3. (a) Transmission evolution of the 1000-µm-diameter microsphere as the magnetic field intensity increases. (b) The variation of the wavelength separation with the increase of the magnetic field intensity for microspheres with different diameters.

Fig. 4. Realization of isolation in the 1000-µm-diameter YIG microsphere with a bias magnetic field of about 70 mT.