Measurement of the electro-optic coefficient of Bi12GeO20 (BGO), Bi12TiO20 (BTO) crystals

The coexistence of optical activity, field-induced linear birefringence, piezoelectric and photoelastic effects in photorefractive materials such as Bi12GeO20 and Bi12TiO20 renders the measurement of their electro-optic coefficients quite complex. Analytic expressions are given for the ellipticity and the orientation of the emerging light vibration when linearly polarized light is incident normally on the crystal. The ellipticity is a function of the electric-field-induced linear birefringence and hence of the electro-optic coefficient of the crystal. Therefore measurement of the ellipticity as a function of electric field applied across the crystal leads to a value of the electro-optic coefficient r41. Experimental results are given.