Thermo-optic coefficient of single-crystal thin-film barium titanate on insulator

We report the thermo-optic coefficient (TOC) of single-crystalline barium titanate (BTO) thin film on dysprosium scandate (DSO) at 1550 nm, determined using both prism coupler measurements and an integrated thermo-optic Mach–Zehnder interferometer (TO MZI). The prism coupler, combined with temperature-dependent Sellmeier fitting, yielded an intrinsic TOC of (1.095 ± 0.002) × 10 −5 K −1 . The TO MZI, analyzed through wavelength shift measurements and COMSOL thermal simulations, provided an effective TOC of (1.100 ± 0.035) × 10 −5 K −1 . The close agreement (approximately 0.5% deviation) validates both approaches and offers a reliable reference for designing BTO-based TO photonic devices, enabling accurate thermal tuning, phase control, and multiphysics simulation in integrated photonic systems.