WLI high voltage optical fiber sensor systems with compensation for optical power fluctuations

Two versions of opto-electronic signal processors applied to demodulating the output signal of a White Light interferometry (WLI) based optical sensor, designed to measure ac high voltages, are presented. Both processors incorporate schemes to compensate optical power fluctuations caused by changes of attenuations and losses in components of the optical fiber sensor systems. The strategy adopted in the first signal processor is based on the precise detection of the peaks and valleys values present in the output signal of a modulated recover interferometer, which signal contains desired information about the ac high-voltage applied to a specially designed Pockels cell used as sensor interferometer. The second signal processor uses a reference sample of the optical power delivered in the output of the sensor interferometer to normalize the output signal of an unmodulated recover interferometer. Prototypes for both signal processors were developed and subjected to tests conducted to measure ac high voltages up to 110 kV(pp) and to verify the stability of the measurements under conditions of optical power attenuations up to -8.66 dB introduced in the link.