Abstract:

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.

Key words: thin-film lithium niobate, ridge waveguide, ferroelectric domain inversion, insulated cladding layer, high-temperature electric-field poling