Abstract
High-quality BaTiO3 epitaxial thin films on MgO substrates have been grown by pulsed-laser deposition. Both, c-axis and a-axis BaTiO3 orientations were studied. Mach–Zehnder optical waveguide modulators with a fork angle of 1.7° have been fabricated by ion-beam etching. The waveguides are of the ridge type, the BaTiO3 thickness is 1 μm, the ridge step 50 nm, and the width 2 μm. Light was coupled into the waveguides from optical fibers. The BaTiO3 waveguide propagation losses are 2–3 dB/cm. Electrodes of 3 mm length were deposited besides the waveguides. Electro-optic modulation has been demonstrated with Vπ=6.3 V at 632 nm wavelength and Vπ=9.5 V at 1550 nm wavelength for the a-axis samples, and with Vπ=8 V at 632 nm wavelength and Vπ=15 V at 1550 nm for the c-axis samples. Theoretical modelling of the Mach–Zehnder modulators for both crystalline orientations of the BaTiO3 films gave the Pockels coefficients r51=80 pm/V for the c-axis film and an effective Pockels coefficient reff=734 pm/V for the a-axis films at 632 nm wavelength.
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