Fig. 1. Illustration of the fabrication flow of the microrings.

Fig. 2. (a) Optical microscope image of the fabricated microring. (b) Magnified scanning-electron-microscope (SEM) image of the fabricated microring. (c) The SEM image shows that a small slit is cut through the microring with a focused ion beam. (d) The optical microscope image of the ridge waveguide on other LNOI chips for coupling of the microring.

Fig. 3. (a) Experimental setup for mode characterization. (b) Optical micrograph of the waveguide coupled with the microring. (c) The measured transmission spectrum. (d) and (e) Q factors of the modes fitted by Lorentz-shape curves; insets: the corresponding field distributions of the modes, where the direction presents the radial direction.