Fig. 1. Process flow of fabricating an on-chip LN racetrack resonator integrated with Cr microelectrodes. (a), (b) Patterning the Cr thin film into a stripe mask using femtosecond laser microfabrication. (c) Etching of the LNOI layer by chemo-mechanical polishing. (d), (e) Selective removal of the stripe Cr mask on the LN racetrack resonator using femtosecond laser ablation. (f) Reducing the thickness of LN racetrack resonator by a post chemo-mechanical polishing, which leads to the smooth top surface on the LN waveguide.

Fig. 2. (a) Top view optical micrograph of the on-chip LN racetrack resonator integrated with Cr electrodes. Zoom-in optical micrographs of the (b) curved and (c) straight waveguides. (d) Distributions of the optical (TE) field and electrical field overlapping each other simulated using COMSOL. The arrows indicate the direction of the electric field.

Fig. 3. (a) Picture of the LN racetrack resonator integrated with Cr electrodes. (b) Zoom-in image of the LN racetrack resonator integrated with Cr electrodes. (c) Schematic of the experimental setup for characterizing the Q factor and tunability of the device.

Fig. 4. (a) Transmission spectrum of the LN ractrack resonator. (b) The Lorentz fitting (red curve) reveals a loaded Q factor of 1.4×106, corresponding to an intrinsic Q factor of 2.8×106 as measured at the 1547.93 nm wavelength; the linewidth of 1.1 pm is shown in inset.

Fig. 5. (a) Calculated effective index n_eff and (b) group index n_g of the optical mode in Fig. 2(d) for the wavelength range between 1550 and 1600 nm.

Fig. 6. (a) Resonance wavelength continuously red shifts with the increasing voltage. (b) The linear fit reveals an electrical tuning rate of ∼0.46 pm/V and indicates that the tuning range spans over a full FSR.