There is a Chi2 material built-in to FDTD, however this is not used for simulating the Pockels effect since we can't create a DC field in FDTD. Instead, you can calculate the static E fields, calculate the refractive index as a function of position based on the E field, then import this index data into FDTD to do your simulation. You can use the spatial (n,k) material object for this:
Spatial (n,k) data - Simulation object – Ansys Optics
There is an example of a similar workflow here, for FEEM instead of FDTD:
 Thin Film Lithium Niobate Electro-Optic Phase Modulator – Ansys Optics
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