Investigation of Electro-optic Properties of Barium Titanate Epitaxial Thin Films, Photonic Crystals and Modulators

Electro-optic (EO) materials and devices, in which their optical properties can be changed by an external electric field, are widely used in optical communication systems. BaTiO3, a ferroelectric material with one of the highest EO coefficients, is a promising material for ultra-wide bandwidth and low drive voltage devices. In this investigation, the frequency, temperature and field dependence of the EO effect in BaTiO3 epitaxial thin films was studied. At low frequency, nucleation and growth of ferroelectric domains affect the EO properties. The transient EO response was analyzed for different external fields and temperatures using the Kohlrausch-Williams-Watts (KWW) kinetic model. Domain reversal in a polydomain thin film is achieved by polarization switching processes showing a broad distribution of switching times. The activation field and activation energy for domain switching were analyzed from the switching behavior. Activation field and activation energy are comparable to bulk BaTiO 3, indicating that a similar kinetically limiting process is present. A depolarization field is present that affects the domain dynamics by increasing the activation field required for domain switching.;The electro-optic properties of BaTiO3 photonic crystals (PhCs) were investigated over the spectral region from 1300 to 1800 nm. Simulation, fabrication and measurement of a hexagonal PhC using a Si3N 4/BaTiO3/MgO multilayer structure were conducted. The 2-D finite-difference time-domain (FDTD) simulation of the PhC optical transmission shows a wide stop band of 60 nm centered at 1550 nm. A stop band in the measured transmission spectrum was observed that was attributed to the slow light effect due to the enhanced optical index. Analysis of the EO response of the PhC modulator indicates that ideal phase velocity matching was achieved. EO response to 50 GHz was measured. For a 3 mm long modulator containing a 33 µm PhC, the 3 dB bandwidth of 17 GHz and the half-wave voltage of 5.3 V were measured. Simulation indicates that a device length below 1 mm potentially enables EO modulation at sub-terahertz frequencies. The PhC structure significantly reduces the footprint of the EO modulator, enabling device integration on silicon for Si photonics.