Fig. 1. (a) Fabrication steps of the periodically poled LNOI ridge waveguide. (b) Geometric schematic of the LNOI ridge waveguide cross section. (c) Schematic of the electrode structure on the ridge waveguide. (d) SEM image of the sidewall surface of the ridge waveguide after poling.

Fig. 2. (a) Image of the inverted domain structure of the LNOI ridge waveguide recorded using the confocal SH microscopy. (b) Simulated electric field distribution at the waveguide surface viewing from the top. (c) Simulated transverse electric field profile.

Fig. 3. Schematic experimental setup

Fig. 4. Schematic of the inverted domain with triangular shape in the locally periodically poled LNOI ridge waveguide.

Fig. 5. (a) Measured (black dots) and theoretical (red line) wavelength tuning curves for SHG in the nonlinear waveguide. (b) Quadratic power dependence of the SH wave on the FW. The black dots and the red line are the measured data and the fitting curve, respectively.