Improvements in difference-over-sum normalization method for Faraday effect magnetic field waveforms measurement

Abstract

This paper presents a detection method for arbitrary magnetic induction and electric current waveform measurement that uses two orthogonally polarized light beams for sensing the Faraday rotation. A procedure is proposed for setting the maximum sensitivity for a sensor with a Faraday crystal that possesses optical activity. Accuracy improvement is achieved by using YVO 4 beam displacer instead of polarising prism. The results of the optical magnetic field and corresponding electric current measurements are presented and compared to current measurement by shunt. The Verdet constant of the Faraday crystal is determined and calibration of the sensing system is performed.

High-Dynamic and High-Precise Optical Current Measurement System Based on the Faraday Effect

“…Equation (5) shows that the obtained signal depends on the beam power P 0 . A common method to get a signal independent of P 0 is the difference-over-sum computation [8]. The beam is split into a s-and a p-polarized beam using, e.g., a polarizing beam splitter.…”

“…The first error source is drifts in the gains k 1 and k 2 . Equation (8) shows that the difference over sum computation is only influenced by the ratio of these gains. Hence, only a drift in the ratio k = (k 2 /k 1 ) results in an error.…”

Mitigation of Output Fluctuations due to Residual State of Input Polarization in a Compact Current Sensor

“…Optical current sensors based on light polarization have attracted great interest for many years [1][2][3]. The use of these devices is reported to be advantageous since they do not suffer from hysteresis and saturation, as conventional current transformers [4], and can respond linearly in a wider band, making it possible to accurately measure high order harmonics of the electrical system.…”

“…Some issues have been addressed for optical current sensors. The design of optical sensors with two orthogonal polarization outputs allows, by means of the application of the difference-over-sum of the signals, the reduction of the effects of optical source instabilities as well as the effects of unwanted birefringence [1,3]. In [5] the use of a temperature-dependent birefringent plate in the Faraday sensor head allows, by the measurement of its retardation, the compensation for the temperature dependence of the Verdet constant.…”

Compensation of Verdet Constant Temperature Dependence by Crystal Core Temperature Measurement

“…Circular birefringence reduces sensitivity but can be used for temperature compensation, as will be shown in this paper. The Δ/Σ measurement technique provides normalization to the light source intensity across the whole spectrum and can be realized in both free space and measurement head [15]. …”