Fig. 1. Dependence of refractive index change (normalized to its maximum) on θS and θO.

Fig. 2. (a) Cross-section rendering of the AO modulator. Note that dimensions are not to scale and the actual SAW of this implementation propagates more deeply in the substrate. (b) and (c) Schematic layouts of MZI- and resonator-type AOMs. Light (green arrows) is coupled to/from the chip by grating couplers. An SAW is launched by the split IDT, and its amplitude is enhanced in the cavity formed by the reflectors (acting as acoustic mirrors). Drawings are conceptual renderings and not to scale. The acoustic cavity (black dashed line) is much larger than the MZI and RT resonators (1.2  mm×5.7  mm for MZI and 2.4  mm×6.2  mm for the RT).

Fig. 3. Dependence of the (a) first and (b) second derivative of transmission T with respect to ϕ on a and r.

Fig. 4. Microscope pictures of (a) MZI- and (b) resonator-type AOMs. (c) SEM image of the photonic waveguide (tilted view). (d) SEM image of the IDT region (top view).

Fig. 5. (a) Measurement setup for characterizing AOM. PC, polarization controller; RF SG, RF signal generator; DUT, device under test; EDFA, erbium-doped fiber amplifier; PD, photodetector; SA, spectrum analyzer. (b) Detected modulation power (normalized to the maximum) of the first harmonic when the frequency of RF SG is swept. The Q factor of the acoustic cavity is 1800. (c) Measured (triangle) and theoretical (solid line) first, second, and third harmonic signals as functions of the square root of the driving power from the RF SG when the frequency is fixed at 111.725 MHz. All are normalized to the maximum first harmonic modulation power of −34  dBm. (d) Ratio of first to third harmonic signals (log scale) as a function of the square root of the input power from RF SG. peff and ap are extracted to be 0.053 and 0.073 rad/√mW, respectively.

Fig. 6. (a) Transmission of the RT resonator for a broad wavelength range. (b) Measured (blue circle) and Lorentzian fit (red) transmission of one of the resonances around 1601.53 nm. Inset: mode profile of the fundamental TE-like mode.

Fig. 7. (a) Measured (triangle) and theoretical (solid line) first and seconnd harmonic signals as functions of the square root of the driving power from RF SG. All are normalized to the maximum first harmonic modulation power of −71.4  dBm. The reason for the modulated power being lower in the resonator-type AOM than in the MZI-type AOM is that the EDFA is not used in the measurement of the RT resonator. Inset: transmissions of RT resonator when Pe is off (blue), 8 dBm (green), and 15 dBm (red). (b) Measured (green circle) and theoretical (green dash) first harmonic signal as the laser wavelength is swept around the resonance of the RT. The maximum modulation is located at the highest slope of the transmission curve. (c) The gain of the resonator-type AOM relative to MZI-type AOM as a function of the square root of the driving power.

Fig. 8. Displacement components (a) uz and (b) uy. The scale bar is 5 µm. Strain field S3=∂uz/∂z and S2=∂uy/∂y in the (c) z′ and (d) y′ direction. Both S3 and S2 are normalized to the maximum of S3. The LN thin film surface is at y′=0.

Fig. 9. Refractive index ellipsoid of LN. x–y–z are crystalline principle coordinates. kSAW is in the x–z plane and rotates by angle θS with respect to z. θO is the relative angle between kopt and kSAW.

Fig. 10. Primary (blue) and effective (red) photo-elastic coefficient tensor elements (a) p21−p26 and (b) p31−p36.

Fig. 11. (a) Extracted a and r from the transmission spectra of resonator at three power levels (Pe is off, 8 dBm, and 15 dBm). The black line is the linear fitting of a. (b) The first (green) and second (orange) derivative of T with respect to ϕ, respectively.