The electro-optic voltage transducer (EOVT)
exploits the Pockels effect in a cylinder-shaped
BGO crystal (Bi4Ge3O12), which has cubic crystal
symmetry. The full voltage is applied between the
two end faces of the crystal. The light doublepasses
the electro-optic material. At voltages in the
several 100 kV range the field-induced
birefringence causes a differential optical phase
shift between two orthogonal polarizations
corresponding to several wave periods. The
waveform of the applied voltage is unambiguously
reconstructed from two output signals in quadrature.
The crystal orientation (cylinder axis along a [1,0,0]-
direction) is such that only the field components
parallel to the light path give rise to an electro-optic
phase shift. Hence, the sensor measures the line
integral of the field and is insensitive to external
perturbations of the field distribution or to fields from
neighbouring electric phases.