Fabrication and characterization of epitaxial Ba₀.₇Sr₀.₃TiO₃ thin films for optical waveguide applications

Abstract

The optical properties of barium strontium titanate (Ba ₀.₇Sr₀.₃TiO₃; BST) thin films are described. The BST thin films were epitaxially grown upon MgO (001) substrates by pulsed laser deposition. The crystallographic properties of the BST thin films were examined by x-ray diffraction. The BST thin films were highly optically transparent in the visible region. The optical waveguide properties were characterized by a prism coupling technique. An inverse-WBK method was employed to determine the refractive-index profile along the thickness of the BST films. Optical losses were measured by a moving fiber method, and the optical losses were found to be 0.93 dB/cm for the TE₀ mode and 1.29 dB/cm for the TM₀ mode at 1550 nm. Electro-optic (E-O) properties were measured by a phase-modulation detection method at 632.8 nm, and the BST films exhibited a predominantly quadratic E-O effect with a quadratic E-O coefficient of 6.64 × 10⁻¹⁸ m²/V².