Linear longitudinal electro-optic effect in oxygen octahedra ferroelectrics

Abstract Electro-optic half-wave voltages have been calculated for a longitudinal geometry in crystals of point group symmetry mm2 (orthorhombic) and 4mm (tetragonal). The solution for an arbitrary direction of light propagation and parallel electric field is given. The predicted minimal longitudinal half-wave voltages range from 194 V in KNbO3, 100 V in Sr0.75Ba0.25Nb2O6 and 40 V in BaTiO3 to 9 V in KTal-x Nb x O3. The angular, wavelength and temperature dependences of the half-wave voltage have been determined. In KNbO3 measurements of the minimal longitudinal half-wave voltage at room temperature reach (195 ± 8) V and (118 ± 7) V with red (Λ = 633 nm) and blue light (Λ = 458 nm) respectively. At–40°C, close to the orthorhombic-rhombohedral phase transition, the half-wave voltage for red light reduces to (135 ± 6) V. From the measurements we determine a negative sign of the electro-optic coefficient r 42 = – 380 pm/V. The possibility of spatial light modulation by the longitudinal electro-optic effect is discussed.