Electro-Optic Properties of a One-Dimensional Topological Photonic Crystal Cavity Based on c-Axis BaTiO3 Thin Film

To meet the demand for compact, low-power on-chip electro-optic modulators for high-density photonic integration in the post-Moore era, this paper proposes an on-chip integrated electro-optic modulation structure that combines an embedded waveguide–electrode configuration with a c-axis-oriented BaTiO3 crystal thin film and a one-dimensional Si3N4 topological photonic crystal. The proposed structure tunes the equivalent refractive index by means of periodic rectangular holes patterned in a Si3N4 loaded-strip waveguide, and constructs two one-dimensional photonic crystal systems with opposite topological invariant signs under the Su–Schrieffer–Heeger (SSH) model. When the two systems are spliced, a localized topological interface state resonance is formed within their common band gap, thereby enhancing optical field confinement. An embedded electrode configuration is further introduced to improve the electric field distribution within the BaTiO3 crystal thin film, and the electro-optic modulation performance is improved by optimizing key parameters, including the rectangular hole dimensions, lattice constant, number of periods, electrode embedding depth, and the Si3N4 waveguide height. The results show that the proposed structure yields a narrow-linewidth topological interface state near 1550 nm and achieves an equivalent resonant-wavelength tuning efficiency of approximately 300 pm/V at a modulation voltage of 10 V, with a modulation region only 61 μm long. The structure substantially shortens the device dimensions and provides a feasible design scheme for realizing ultra-compact, high-efficiency on-chip electro-optic modulators.