Linear Electro-Optic Effect in Ferroelectric KTN

The low-frequency linear electro-optic coefficients have been measured in ferroelectric KTN (KTax Nb1−xO3) as a function of temperature. A measurement of the field-induced retardation shows that the half-wave voltage is about one 100th of that for KDP and about one half that for BaTiO3. The half-wave voltage increases from about 20 V at 3°C below the Curie point to approximately 115 V at 40°C below the Curie point. The possibility of tailoring the Curie point by varying the Ta-to-Nb ratio therefore makes KTN attractive for light modulation and deflection.An ac technique was developed to determine the electro-optic coefficient r42. This coefficient is extremely large, showing the expected increase towards the orthorhombic transition temperature but it is not useful for modulation or deflection.