Fig. 1. AO devices based on thin-film AlScN photonic platform. (a) Schematic diagram of AO devices for intramodal AO modulation (bottom) and intermodal AO modulation (top). (b) Cross-sectional view of the device. It consists of an AlScN ridge waveguide with a width (W) and an etching depth of 220 nm, along with the aluminum IDTs. (c) Numerical simulation results of the normalized electric field and strain field profiles.

Fig. 2. Characterization of AlScN film. (a) XRD 2θ pattern indicates that the AlScN film is deposited along the c-axis-oriented (0002). (b) Rocking curve of the 0002 AlScN peak has an FWHM of 1.84°. (c) Measured refractive index n (black line) and extinction coefficient k (red line) as a function of optical wavelength. (d) AFM image of the ridge waveguide.

Fig. 3. Intramodal AO modulation based on an AlScN straight waveguide. (a) Micrograph of the fabricated AO modulator. (b) Schematic diagram of ω−k space showing the phase matching condition. (c) Schematic diagram of the setup used to characterize the AO modulators. (d) Electrical reflection coefficient S11 as a function of RF frequency Ω/2π. (e) RF frequency response of the measured modulation efficiency. (f) Modulation efficiency versus optical wavelength, with the RF frequency fixed at Ω/2π=2.36  GHz. (g) Modulation efficiency versus RF power in the range of 15 to 25 dBm. The blue and red lines result from the linear fitting.

Fig. 4. Intramodal AO modulation with enhanced modulation efficiency based on an AlScN spiral waveguide. Micrographs of the intramodal AO modulator at various levels of detail are shown in (a) and (b). (c) Electrical reflection coefficient S11 as a function of RF frequency Ω/2π. (d) RF frequency response of the modulation efficiency for the AO modulator. (e) Modulation efficiency versus optical wavelength, with the RF frequency fixed at Ω/2π=2.36  GHz. (f) Modulation efficiency versus RF power in the range of 15 to 25 dBm.

Fig. 5. Intermodal AO modulation in a multi-mode AlScN waveguide. (a) Schematic diagram of ω−k space showing the intermodal AO modulation phase matching condition. (b) In the forward direction, the probe light (blue) travels through the device without alteration. (c) In the backward direction, the intermodal AO modulation is phase matched, such that the probe light is partly converted to the TE00 mode and is output in port 2 (red). (d) Micrograph of the fabricated intermodal AO modulator. The zoomed-in images below show details of the ADC, IDTs, and grating couplers. (e) Normalized optical transmission of the device without being RF driven. (f) Electrical reflection coefficient S11 as a function of RF frequency for IDTs with pitch D=0.94  μm. The conversion efficiency of the IDTs at the RF drive frequency Ω/2π of 2.89 GHz is 17.9%. (g) Modulation efficiency versus RF power in the range of 15 to 25 dBm. The blue line results from linear fitting indicating the linear relationship between the modulation efficiency and RF power. (h) Modulation efficiency versus optical wavelength. The blue dots (forward) and red dots (backward) represent the measured data.

Fig. 6. Normalized finite element simulation results of AO overlap for the process of (a) intramodal AO modulation and (b) intermodal AO modulation, respectively.

Fig. 7. (a) Micrograph of IDTs with pitch Λ=1.1  μm. (b) Schematic diagram of the equivalent circuit model. Measured wideband (c) real part of impedance and (d) imaginary part of impedance with fitting curve (red line) as functions of frequency. Measured narrowband (e) real part and (f) imaginary part of admittance with fitting curve (red line) as functions of RF frequency.

Fig. 8. Response of the non-reciprocity AO modulator, where AO coupling occurs over 18  μm×200  μm regions spaced along a total length of L=17.1  mm. (a) Coupling strength as a function of position z. The resulting modulation response is shown in (b).