PURPOSE: To detect the voltage or electric field of a high frequency range, by providing a light receiving circuit detecting a low-frequency.
CONSTITUTION: A modulator 21 contains a light source and not only DC voltage but also AC voltage of single frequency fc are applied to said light source. As a result, light having intensity wherein the AC component of single frequency fc is superposed to a DC light component is emitted to an optical voltage or electric field sensor 1. The light incident on the sensor 1 is modulated by the voltage applied to the Pockels element 4 of the sensor 1 to be emitted to a light receiving circuit 22. The light incident on the circuit 22 is photoelectrically converted by a photo detector 23 to be given to a filter 24 when only a component of difference frequency fm-fc of the frequency fc and the frequency fm of voltage or an electric field is taken out and subsequently given to a condenser 25 to remove the component corresponding to DC light. The difference frequency component is amplified by an amplifier 26 and, as a result, applying voltage or an electric field is detected. By this method, the voltage or electric field of a high frequency range can be detected.
YOSHIKAWA HIROSHI
MIYAMOTO TOSHIHARU
