Ferroelectric BiFeO3 thin-film optical modulators

High quality epitaxial BiFeO3 (BFO) thin films have been grown on (001) SrTiO3 substrate by magnetron sputtering. Both a-axis and c-axis BFO orientations were studied. Prism coupler results reveal that the c-axis and a-axis refractive indices of the BFO thin films were 2.721 and 2.653 at 632.8 nm; the corresponding propagation losses were 4.3 and 4.6 dB/cm, respectively. An electrooptic (EO) modulator based on such BFO film has been demonstrated with a fast switching time t = 3.8 mu s at 632.8 nm for the a-axis orientation and t = 3.4 mu s for the c-axis orientation. Moreover, these BFO films gave the Pockels coefficient r(eff) = 19.3 pm/V for the c-axis orientation and r(eff) = 15.9 pm/V for the a-axis orientation at 632.8 nm. Such an anisotropic refractive index and linear EO behaviors are attributed to the epitaxial strain and stripe domain structure in the BFO thin films with mixed phases. This study illustrates the suitability of the BFO thin films for EO modulators and optical switches beyond their current extensive spintronic and memory applications. Published by AIP Publishing.