Linear electro-optic effect in strontium barium niobate

We report a first-principles study of the linear electro-optic or Pockels effect in Sr_xBa_1-xNb₂O₆ (SBN). SBN is an attractive material for building electro-optic modulators in silicon photonics, as it has one of the highest known Pockels coefficients and can be integrated on Si. We investigate the microscopic mechanism behind the giant Pockels effect and find that the optical phonon contribution dominates the electro-optic response. We identify the phonon modes that have a significant contribution to the Pockels response and discuss the microscopic origin of the response. In addition, we analyze the contribution of the converse piezoelectric effect to the Pockels response. We find good agreement when comparing our results to available experiment.