  An electro-optic modulator offers the function of modulating the propagation
of light in a material with electric field and enables seamless connection
between electronics-based computing and photonics-based communication. The
search for materials with large electro-optic coefficients and low optical loss
is critical to increase the efficiency and minimize the size of electro-optic
devices. We present a semi-empirical method to compute the electro-optic
coefficients of ferroelectric materials by combining first-principles
density-functional theory calculations with Landau-Devonshire phenomenological
modeling. We apply the method to study the electro-optic constants, also called
Pockels coefficients, of three paradigmatic ferroelectric oxides: BaTiO3,
LiNbO3, and LiTaO3. We present their temperature-, frequency- and
strain-dependent electro-optic tensors calculated using our method. The
predicted electro-optic constants agree with the experimental results, where
available, and provide benchmarks for experimental verification.
