Optical dc voltage measurement based on ac voltage modulation of elliptically polarized light using BGO crystals

Abstract

This paper deals with the theoretical analysis and experimental investigation of a new optical dc voltage measuring system, in which two Pockels cells are located between a polarizer and an analyzer, and ac voltage is applied to one cell while dc voltage for measuring is applied to the other. Supposing a slight elliptical polarization at zero applied voltage when linearly polarized light is passed through the Pockels cells without optical activity, a theoretical analysis of the measuring system is carried out. It is found that the light intensity variation in the system can be compensated by dividing the ac normal component V(ω0) of the output by the second harmonic component V(2ω0), and that V(ω0)/V(2ω0) is linearly proportional to the applied dc voltage, but is not equal to zero at zero applied dc voltage. Experiments using Bi4Ge3O12 (BGO) crystals longitudinally modulated with ac and dc voltages showed that the characteristics of the dc component and V(ω0) and V(2ω0) of the output agreed well with the calculated results. By slightly rotating the y–z surface of the BGO about the x axis, it was determined that the phase difference caused by spontaneous birefringence in the BGO could be decreased to zero and that a linear dc voltage dependence of V(ω0)/V(2ω0) passing through the origin could be obtained at zero apparent elliptical polarization. © 1998 Scripta Technica. Electr Eng Jpn, 122(3): 10–18, 1998