Longitudinal Pockels cell as a vertical ferroelectric Pb(Zr0.53Ti0.47)O3 (PZT) thin film capacitor was fabricated by pulsed laser deposition technique onto the both side polished YAlO3 + 1% Nd2O3 single crystal substrate. At first, conducting La0.5Sr0.5CoO3 (LSCO) 100 nm thick layer was deposited as an atomic template for 1 m thick PZT film. Epitaxial quality (exceptional c-axis orientation and coherent in-plane texture) of PZT/LSCO/Nd:YAlO3 (001) heterostructure has been confirmed by x-ray diffraction. On the top, semitransparent 100 nm thick Au electrode was deposited by thermal evaporation. Intensity of the chopped 670 nm polarized laser radiation transmitted through the Au/PZT/LSCO/Nd:YAlO3 cell was measured using lock-in amplifier. Special precautions were employed to get reproducible transmittance vs. temperature scans up to 400 °C. Phenomenon of critical opalescence (scattering of the light with critical fluctuations of polarization) was observed in the vicinity of Curie temperature at 208 °C. Modulation of the transmitted light as high as 3% was achieved applying 20 V (200 kV/cm) across the capacitive cell, whereas the voltage tunability measured at 1 kHz from C-V characteristics was about 70%.