D. J. Towner

Electrooptic modulation up to 40 GHz in a barium titanate thin film waveguide modulator.

The high frequency operation of a low-voltage electrooptic modulator based on a strip-loaded BaTiO3 thin film waveguide structure has been demonstrated. The epitaxial BaTiO3 thin film on an MgO substrate forms a composite structure with a low effective dielectric constant of 20.8 at 40 GHz. A 3.9 V half-wave voltage with a 3.7 GHz 3-dB bandwidth and a 150 pm/V effective electrooptic coefficient is obtained for the 3.2mm-long modulator at 1.55 ?m. Broadband modulation up to 40 GHz is measured with a calibrated detection system. Numerical simulations indicate that the BaTiO3 thin film modulator has the potential for a 3-dB operational bandwidth in excess of 40 GHz through optimized design.

Low-voltage, polarization-insensitive, electro-optic modulator based on a polydomain barium titanate thin film

A BaTiO3 thin-film electro-optic waveguide modulator with a half-wave voltage-interaction length product (VπL) of 1.1Vcm at 1.55-μm wavelength is demonstrated. The half-wave voltage and the measured effective electro-optic coefficient are 3.3V and 162pm∕V, respectively. The half-wave voltage increases less than 10% over a temperature range of 23–90°C. Polarization-independent electro-optic modulation was observed and attributed to the polydomain structure of the BaTiO3 film. The unique combination of large electro-optic coefficient and polarization independence illustrates how engineered domain structures in ferroelectric thin films can enable properties and performance unachievable in bulk single crystals.

Relative dielectric constant of epitaxial BaTiO3 thin films in the GHz frequency range

The relative dielectric constant of epitaxial BaTiO3 thin films deposited on MgO was determined over the frequency range from 0.05 to 40.05 GHz. Coplanar stripline waveguides were formed on the BaTiO3 films and the dielectric constant was determined by matching the reflection (S11-) parameter by measurement with that by simulation. The dielectric constants were ∼2200 and ∼500 at <1 and 40 GHz, respectively. The frequency response of the dielectric constant is well described by a Curie–von Schweidler power law with an exponent of 0.29. The effective index of the coplanar stripline structure on the BaTiO3 film and MgO substrate was 3.6.

Low-loss electrooptic BaTiO/sub 3/ thin film waveguide modulator

A strip-loaded electrooptic waveguide modulator based on an epitaxial BaTiO/sub 3/ thin film was fabricated and characterized for the first time. The strip-loaded waveguide structure greatly improves waveguide propagation and polarization-dependent loss performance. A propagation loss of 1.1 dB/cm and polarization dependent loss of 0.1 dB/cm were measured. The electrooptic waveguide modulator exhibited a half-wave voltage-interaction length product of 4.5 V /spl middot/ cm at a wavelength of 1542 nm. The measured effective electrooptic coefficient of the as-grown BaTiO/sub 3/ waveguide modulator was 38 pm/V. The experimental results indicate that a strip-loaded thin film waveguide modulator is suitable for photonic applications.

Microstructure and strain in thin ferroelectric BaTiO3 films epitaxially grown on MgO substrates

High-resolution x-ray diffraction and high-resolution scanning electron microscopy have been applied to characterize BaTiO 3 films of different thicknesses, metal-organic chemical vapour deposition grown on MgO substrates. We found a strong correlation between the strain state of the films and the amount of specific material discontinuities, the latter serving as an effective channel of strain relaxation. The results obtained are explained by considering the structural misfit arising at the interface between in-plane oriented 90° domains.

Nanosecond-Scale Domain Dynamics in BaTiO 3 Probed by Time-Resolved X-Ray Diffraction

The pulsed synchrotron radiation from the Advanced Photon Source at Argonne National Laboratory was used to stroboscopically measure the dynamic response of BaTiO 3 ferroelectric films, in situ, under the application of a high-frequency electric field. The time-dependent lattice d -spacings measured in the frequency range, 25-1300 MHz, demonstrated both periodicity and attenuation features which were attributed to domain dynamics. Drastic (two order of magnitude) reduction of the relaxation time (i.e., attenuation increase) was found with increasing electric field frequency. Experimental findings are analyzed in terms of hindering of domain wall motion by generated deformation waves.

Velocity Matching in BaTiO3 Thin Film Electrooptic Waveguide Modulators

Near velocity-matched coplanar strip electrodes for high-speed BaTiO3 thin film electro-optic modulators are achieved. The velocity mismatch between optical wave and microwave is 2%. Microwave loss and impedance of the electrodes are measured.