The scale factor of optic-fiber current sensor is nonlinearized because of the linear birefringence and the imperfection of
quarter wave plate (QWP). In this paper, we analyze the effects of birefringence and show that modified scale factor
performs better by using Faraday rotate mirror (FRM) and harmonic division method. The scale factor error associated
with integrating imperfect quarter wave plate is also analyzed. Moreover, a certain linear birefringence may be helpful to
compensate for deviation of QWP's alignment.