Influence of polarization-dependent crosstalk on scale factor in the in-line Sagnac interferometer current sensor

The scale factor of the in-line Sagnac interferometer current sensor associated with the polarization-dependent crosstalk introduced by optical devices is theoretically investigated. The variations of output pigtail polarization crosstalk of the Ti-indiffused LiNbO₃ phase modulator and polarization crosstalk of the polarization-maintaining (PM) delay optical fiber with the temperature can lead to the scale-factor error. The whitelight interferometry is utilized to measure the pigtail polarization crosstalk of the phase modulator. The variation of the scale factor with the temperature has been tested over a range from-40°C to 60°C experimentally. The results confirm the influence of output pigtail polarization crosstalk of phase modulator and polarization crosstalk of the PM delay optical fiber on the scale factor. To ensure the scale factor error to be within ±0.2%, the output pigtail polarization crosstalk of phase modulator and polarization crosstalk of the PM delay optical fiber should not exceed-30 dB for the current sensor operating in the outdoor environment.