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An optical voltage sensor is presented which can be used for the measurement of dc voltage by use of a Pockels crystal associated with a pulse-controlled electrooptic quarter waveplate. The measurand dc voltage signal is converted into the amplitude of an ac pulse-modulated voltage-sensing signal. Therefore, the output sensing signal is immune to electromagnetic interference owing to the applications of pulse modulation and lock-in amplifying techniques. In addition, the voltage-sensing signal is obtained from a single light path and free from light intensity fluctuations. The dc voltage of ±0.4 to ±180 V has been measured with 1.8% nonlinear error.