The renaissance of ferroelectric barium titanate in integrated photonics: Growth, properties and devices

Ferroelectric barium titanate (BaTiO 3 , BTO) is attracting renewed attention as an electro-optic platform for integrated photonics as conventional devices face intrinsic limits in bandwidth, energy efficiency and linearity. Compared with lithium niobate and semiconductor materials, BTO combines large Pockels coefficients with the possibility of epitaxial integration on silicon, enabling compact and energy-efficient phase shifters. This review surveys recent advances in BTO from epitaxial growth and electro-optic characterization to integrated devices. Epitaxial growth on oxide-insulator substrates and on silicon is discussed with emphasis on how strain state, crystallographic orientation and domain configuration influence the electro-optic response. Electro-optic tensor formalisms are then used to relate direct optical metrology to device-based extractions. In particular, Sénarmont-type measurements combined with structural probes provide a practical means to compare reported coefficients and to link epitaxial strain and domain structure to electro-optic properties from films to devices. On this basis, representative BTO-based photonic devices such as Mach–Zehnder interferometers, micro-ring resonators and plasmonic modulators are reviewed, together with selected examples that illustrate their operating performance. Taken together, these developments suggest that continued progress in scalable epitaxy, device co-design and standardized electro-optic benchmarking could establish BTO as a practical platform for high-speed, low-energy and reconfigurable integrated photonic systems with broad prospects for future applications.