Strategic measurement for the axis orientation and electro-optic coefficient of BaTiO₃ crystal thin film grown on MgO...

BaTiO₃ crystal thin film has been investigated to realize electro-optic (EO) devices due to its ultrahigh EO effect, but not much research has been focused on the correct axis orientation and EO coefficient. In this Letter, with a BaTiO₃ crystal film grown by pulse laser deposition technique on ⟨100⟩ MgO crystal substrate, an embedded device configuration having the two-step etched waveguide/electrode scheme is designed to reach a high optic-electrical field interaction efficiency, and a 45° outside electric field with an in-plane axis is set to fit the possibility of the a-axis or c-axis orientation of the BaTiO₃ crystal film. Then, through a poling process to the sample, the 1π, 2π, and 3π EO modulations of linear polarization are implemented at 4.9, 9.3, and 11.8 V, respectively, and a decremental voltage period is found. Thereby, a c-axis oriented BaTiO₃ crystal film is determined, so that the nonlinear modulation equation is exploited. Finally, with an overlap of 1π, 2π, and 3π modulations, the coherent EO coefficient r₅₁ and birefringence of 606 pm/V and -0.0215 are obtained, resulting in one (Vπ)²L value of 68 (V²·mm).