Optische und elektrooptische Eigenschaften von BaTiO$_{3}$-Dünnschichtwellenleitern

The growth in the field of optical communication drives the high interest in integrationof photonic devices. The development of a thin film technology of photonic materials isa prerequisite for this integration. BaTiO$_{3}$ shows high transparency and interesting electroopticproperties. Therefore, it is a very interesting material for optical applications.Preceding research demonstrated the possibility to produce epitaxial, single crystallineBaTiO$_{3}$ thin films on MgO by pulsed laser deposition. The films showed smooth surfacesand promising optical properties. Usually, the films are c-axis oriented, the orientationof the longer c-axis is perpendicular to the surface. Under modified deposition conditionsit is also possible to grow a-axis oriented films.The main objective of this work is the analysis of the optical and electrooptical propertiesof these films. The interdependencies of film and deposition parameters were studied. Amanufacturing process for electrooptic phase modulators was developed and electroopticmodulation could be demonstrated.In particular, a closer investigation of the lattice parameters yielded a broad distribution.The values were mainly in between the values for the bull. crystals a-axis and c-axis.Deposition with reduced laser power or the application of an in-situ anneal step resultedin a reduction of the lattice parameters. This may be attributed to a reduced numberof oxygen vacancies in the film. Refractive index measurements show a correspondingdependency on laser power or an anneal step. All measured refractive index values arelower than the bull. ordinary index. The variations of the in-plane values are smaller inall cases probably due to the clamping of the in-plane axis by the substrate.The index dispersion of a film can be described by single oscillator Sellmeier equations,like the bulk crystal behaviour. Measurements of the optical attenuation of thin filmplanar waveguides gave very good values down to < 2 dB/cm for 633 nm.A fabrication process for phase modulators was succesfully developed. Single mode ridgewaveguides (width: 2 $\mu$m, ridge height: 50-100 nm, film thickness: 1 $\mu$m) were fabricatedby ion beam etching using an etch mask structured by photolithography.With the phase modulators among crossed polarizers, modulation signals could be measured. The corresponding plots leads to the conclusion of a partial polarization of thefilms by means of creation of a-axis domains in the c-axis oriented film. The evaluationof the modulation signals gave values for an effective r5i-coefficient of 60-20 pm/V. Thedecreasing values for increasing electric field may be attributed to the increasing amountof a-domains in the waveguide generated by the field