This paper presents theoretical and experimental results showing the effects of linear and circular birefringence on the sensing coil of an in-line Sagnac interferometer current sensor. Linear birefringence induces local scale factor variations along the length of the sensing coil which can be suppressed with circular birefringence. We show that by winding the sensing coil with tension in a helix configuration, these variations may be effectively reduced to zero for ordinary single mode fiber. In our opinion, this method of implementation overcomes the need to use annealed fiber in the sensing coil.
Shayne X. Short, Josiel U. de Arruda, Alexandr A. Tselikov, and James N. Blake, "Elimination of Birefringence Induced Scale Factor Errors in the In-Line Sagnac Interferometer Current Sensor," J. Lightwave Technol. 16, 1844- (1998)