Fig. 1. (a) Optical microscope image of a microring cavity with the nearby coupling bus waveguide on thin-film lithium tantalate. (b) Scanning electron microscopy (SEM) image of the straight part of the bus waveguide. (c) Simulated cross-sectional optical modal profiles in the straight part of the bus waveguide and in the microring cavity. (d) Cross-sectional SEM image of the straight part of the bus waveguide. (e) Measured AFM image of the coupling region between the microring cavity and the bus waveguide. (f) Measured surface roughness profile of an etched region of thin-film lithium tantalate.

Fig. 2. (a) SEM image of a fabricated grating coupler. (b) Zoomed-in SEM image of the region marked with white box in (a). The grating pitch and etched trench width are labeled with p and t, respectively. (c) Measured normalized transmission spectra of grating couplers with different t/p, where p is fixed at 1.175 μm.

Fig. 3. (a) Broad-range normalized transmission spectrum of a microring cavity with a ring radius r=100  μm. (b)–(d) Zoomed-in normalized transmission spectra showing the resonances at the wavelengths of 1571.597, 1573.387, and 1575.183 nm, respectively.

Fig. 4. Broad-range normalized transmission spectrum of a microring cavity with a ring radius r=80  μm. The insets show the zoomed-in spectra of resonances at the wavelengths of 1595.250, 1597.577, 1599.917, 1602.267, and 1604.629 nm.

Fig. 5. (a) Normalized transmission spectra of a lithium tantalate microring cavity measured with a tunable semiconductor laser under different optical powers at a fixed sweep rate of 1 nm/s. The optical power in the bus waveguide varied from −21.08 to −8.13  dBm. (b) Frequency shift of the resonance as a function of intracavity optical power based on the measured data in (a).