Ridge waveguide using highly oriented BaTiO3 thin films for electro-optic application

In this work, 750 nm-thick BaTiO3 thin films with highly (0 0 1) preferred orientation were grown on single crystal MgO substrates by RF-sputtering. Hydrogen silsesquioxane (HSQ) resist material based ridge waveguides, which were fabricated on BaTiO3 thin films, were formed by e-beam lithography. Au electrodes were deposited on top of the BaTiO3 films beside the waveguide. Propagation losses of the BaTiO3 ridge waveguide were 3–5 dB/cm in transverse electric polarization. The measured electrooptic coefficient value (r51) was 110 pm/V, which is three times larger than the electrooptic coefficient (r33 = 30.8 pm/V) of single crystal LiNbO3. SiO2 strip waveguide formed by HSQ exhibited light propagation with loss lower than 5 dB/cm. This result demonstrates potential possibility of creating highly oriented and/or epitaxially grown BaTiO3 waveguides and optical components on oxide substrates.