Investigation of the effect of ferroelectric domain structure and dynamics on the electro-optic properties of polydomain epitaxial barium titanate thin films

The dependence of the electro-optic (EO) properties on the field-dependent domain structure in epitaxial polydomain BaTiO3 thin films was investigated. Models of both the field-dependent electronic polarization and the EO response and their dependence on domain structure were developed. The agreement of these models with measured polarization and EO data demonstrates their efficacy. The measured domain structure and remnant polarization were both in agreement with those predicted by the polarization model. The hysteretic EO response was well described by a model based on the E-field dependent intrinsic electro-optic response and the E-field dependent domain structure. In the model of the hysteretic EO response, the functional form of the field-dependent domain structure was that of the field-dependent polarization due to ferroelectric switching (Pferro (E)). Effects due to 90° domain switching were incorporated into the model by inclusion of elasto-optic contributions to the optical response.; Measurements of the effective electro-optic coefficient were made in waveguide and transmission geometries under both in-plane <110> and <100> E-fields. The field dependence of the electro-optic response (reff) for both <110> and <100> E-fields is dominated by the r51-contributing domains. The <110> field act to pole these domains, resulting in larger effective electro-optic coefficient (reff) values and a hysteretic response whereas a <100> field does not pole these domains, resulting in a lower reff and no hysteresis. Average effective electro-optic coefficient (reff) values at 633 nm under <110> and <100> fields were 247 and 5.6 pm/V, respectively. Average reff values at 1550 nm under <110> and <100> fields were 132 and 14 pm/V, respectively.; Domain dynamics were studied as a function of the applied bias based on the assumption of a distribution of relaxation times within the film. The distribution of relaxation times is tentatively attributed to a distribution of domain sizes. The transient 90° domain relaxation was examined as a function of the poling field. The time response was well described by the Koulraush-Williams-Watts function, with the relaxation time constant linearly proportional to the poling field. The transient amplitude likewise increased with the poling field.