Ferroelectric BaTiO3 thin-film optical waveguide modulators

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 1.7degrees have been fabricated by ion-beam etching. The waveguides are of the ridge type, the BaTiO3 thickness is 1 mum, the ridge step 50 nm, and the width 2 mum. 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 V-pi=6.3 V at 632 nm wavelength and V-pi=9.5 V at 1550 nm wavelength for the a-axis samples, and with V-pi=8 V at 632 nm wavelength and V-pi=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 r(51)=80 pm/V for the c-axis film and an effective Pockels coefficient r(eff)=734 pm/V for the a-axis films at 632 nm wavelength. (C) 2002 American Institute of Physics.