Electro-optical properties of BaTiO₃-SrTiO₃ multilayer thin films for waveguide modulators

Optical properties of ferroelectric BaTiO3 (BTO) and paraelectric SrTiO3 (STO) multilayer structures were investigated as a possible material choice for thin-film electro-optic devices. It has been demonstrated that dielectric properties can be enhanced by optimizing the stacking periodicity of BTO-STO superlattices, and in this work, it was studied how the shifts in permittivity are transferred to the optical properties. BTO-STO superlattices with stacking periodicity varying between 27 Å and 1670 Å were grown on MgO substrates by pulsed laser deposition. In X-ray diffraction patterns, periodic satellite peaks were observed indicating the formation artificial superlattices. The evolution of electro-optic response with varying stacking periodicity was analyzed by ellipsometric transmission method. The electro-optic response reached a maximum at a stacking periodicity of 105 Å corresponding the individual layer thickness of 13 unit cells. The suitability of superlattices, and also single layer BTO thin films, in planar optical devices were evaluated by fabricating and characterizing Mach-Zehnder waveguide modulators. (23 refs.