An optical voltage and current sensor with electrically switchable quarter waveplate

An optical sensor is proposed which can perform the simultaneous measurements of voltage and current through single light path. This novel optical sensor makes use of an electrically switchable quarter waveplate to produce an alternating polarized light whose state of polarization alternately changes between linear and circular polarizations. By the use of the alternately polarized light and polarization multiplexing, we can simultaneously measure ac voltage and ac current through single light path. In addition, the output voltage and current sensing signals are free from the fluctuation of light intensity and have an enhanced immunity to electromagnetic interference due to the application of square wave modulation and lock-in amplification. The ac voltage and ac current with industrial frequency have been experimentally measured with good linearity within the ranges of 0.2–235 V and 0.05–10 A.