Ferroelectric-domain-engineered thin-film lithium niobate (TFLN) holds significant potential for applications in quantum optics and nonlinear photonics. In periodically
poled x-cut TFLN ridge waveguides, however, achieving complete depth-wise domain inversion
within the ridge waveguide remains a critical challenge. In this work, we propose a high-temperature-assisted poling technique combined with a SiO2 cladding layer for lithium niobate
ridge waveguides. The introduction of a SiO2 overlayer enhances the uniformity of the electric field distribution within the ridge structure, enabling the formation of depth-penetrating
ferroelectric domains. Meanwhile, elevated-temperature poling reduces both the resistivity of
the SiO2 layer and the coercive field of lithium niobate, thereby facilitating effective domain
inversion in the waveguide region under appropriate applied voltages. By optimizing the poling temperature and external voltage conditions, periodic ferroelectric domain structures with
high depth uniformity and well-defined periodicity were experimentally achieved. The proposed technique provides a viable route toward the fabrication of high-performance nonlinear
photonic chips based on TFLN.
