Fig. 1. Schematic illustration of the wafer-scale PPLN optical waveguides featuring segmented micro-heaters. Insets: (a), (b) recovered QPM spectrum (b) after thermal tuning with segmented heating powers (a). (c) Broadened QPM spectrum due to thickness variation before thermal tuning.

Fig. 2. Simulated QPM spectra with (right column) and without (left column) segmented thermal tuning in the cases of (a)–(d) linearly increasing film thickness and (e)–(h) realistic thickness profile. (a), (e) Local QPM wavelengths along the TF-PPLN waveguides (red) compared with the target QPM wavelength (blue). (c), (g) Corresponding simulated QPM spectra (red) in comparison with the ideal QPM spectrum (blue). (b), (f) Local QPM wavelength distributions after the center QPM wavelengths in each section are aligned by the segmented micro-heaters. (d), (h) Corresponding recovered QPM spectra by the micro-heaters.

Fig. 3. (a) Fabricated 4-inch LNOI wafer patterned with finger electrodes for periodic poling. (b) Wafer after periodic poling and patterning of optical waveguides. (c) Final cleaved TF-PPLN chip wire-bonded to a PCB. (d)–(f) Cross-sectional schematics of the fabrication process flow, specifically, (d) high voltage poling; (e) optical waveguide formation using RIE; and (f) fabrication of the segmented micro-heaters. (g) Close-up microscope image of the fabricated segmented micro-heaters. Scale bar: 250 μm. (h) Measured QPM wavelength as a function of increasing heating power.

Fig. 4. (a)–(c) Measured SHG intensities as functions of pump wavelengths for a 6 mm TF-PPLN waveguide before applying tuning currents (a), after optimization of the heater powers (b), and with an arbitrary set of tuning parameters (c). (d)–(f) DC powers applied to each segmented micro-heater for the scenarios in (a)–(c), respectively.

Fig. 5. (a), (b) Measured SHG intensities as functions of pump wavelengths for a 1 cm TF-PPLN waveguide before (a) and after (b) applying tuning currents. (c) DC powers applied to each segmented micro-heater for the scenario in (b).