Electrooptic voltage sensor: birefringence effects and compensation methods.

Crystals of Bi(4)Ge(3)O(12)from two different sources exhibited linear birefringences of 1.7 x 10(-5)-5.4 x 10(-5)5 (or, phase retardations of 1.3-4.1 degrees /cm) at a wavelength of 830 nm. These birefringences, however, are sensitive to temperature. The temperature variation of the birefringence dB/(B(0)dT) normalized by the room temperature birefringence B(0) was -1 to -7 x 10(-3)/ degrees C. The effects of the temperature dependent birefringence and the birefringence induced by pressure on an electrooptic voltage sensor were measured and quantitatively compared to the predictions. To remove the temperature dependent birefringences, the crystals were annealed over two days. The birefringences were reduced to about half of their original values after a first annealing process, but the values remained unchanged after a second annealing process. To eliminate the effects of the birefringences, a compensation method was used. After applying this compensation method to an electrooptic voltage sensor, the temperature stability of the sensor was improved to +/-0.75% from +/-7.0% in the temperature range between -2 and 65 degrees C, and the pressure stability was improved to +/-0.2% from +/-2% under pressure as high as 1 x 10(5) N/M(2).