Dresden 2003 – wissenschaftliches Programm

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DS: Dünne Schichten

DS 23: Elektrische und optische Eigenschaften II

DS 23.5: Vortrag

Donnerstag, 27. März 2003, 16:15–16:30, GER/38

Electro-optic Mach-Zehnder modulators based on polycrystalline BaTiO₃ thin films on MgO — •Adrian Petraru, Jürgen Schubert, Martin Schmid, and Christoph Buchal — Institut für Schichten und Grenzflächen (ISG1-IT), Forschungszentrum, 52425 Jülich, Deutschland

BaTiO₃ is an attractive material for electrooptical devices in thin film technology due to its large electro-optic coefficients and its high transparency in the visible and near infrared range. The integration of these devices on Si is desirable, but the very different thermal expansion coefficients of the isolating layer and of the BaTiO₃ film make this a difficult task. The replacement of the epitaxial BaTiO₃ layer by a polycrystalline layer simplifies a potential integration considerably, because the deposition temperature can be lowered and the optical separation layer to the substrate could be replaced by an amorphous SiO₂ layer. We present a waveguide Mach-Zehnder optical modulator based on polycrystalline BaTiO₃ thin film deposited on MgO substrates. The films were grown at relatively low temperature (400 ^∘C) by pulsed laser deposition at an oxygen pressure of 2x10⁻³ mbar. They are still highly transparent with an estimated waveguide propagation loss of 4 dB/cm at 633 nm wavelength. Although polycrystalline, the BTO is still birefringent with n_o= 2.316 and n_e = 2.301. Ridge waveguides have been formed by ion beam etching. Using 3 mm long electrodes with a spacing of 10 µm, a V_π voltage of 14 V was obtained at 633 nm wavelength. This is half of the observed effective electro-optic coefficient measured at epitaxial BTO films. At 1.5 µm wavelength similar results were observed.