We analyze scale factor errors associated with integrating imperfect quarter-waveplates into loop and in-line Sagnac interferometer fiber-optic current sensors. We show that relatively large imperfections in the quarter-waveplates can be tolerated in the loop version when the birefringence axes of the two quarter-waveplates are oriented 45 with respect to each other. For the in-line version, we demonstrate an electronic signal processing scheme that desensitizes the scale factor to imperfections in the quarter-waveplate.
Shayne X. Short, Alexandr A. Tselikov, Josiel U. de Arruda, and James N. Blake, "Imperfect Quarter-Waveplate Compensation in Sagnac Interferometer-Type Current Sensors," J. Lightwave Technol. 16, 1212- (1998)