Identification the differences of phase and group birefringence of different polarization-maintaining fibers with Brillouin dynamic grating and Sagnac interferometer

Measurement of the birefringence of polarization-maintaining fiber (PMF) make difference for fiber optical gyro (FOG) improvement. In this work, the phase birefringence and group birefringence of four kinds of different commercial gyro-used PMFs are theoretically calculated by finite element method and experimentally measured by Brillouin dynamic grating (BDG) and Sagnac method. The difference between the phase birefringence and group birefringence in shape-induced PMFs are confirmed by comparing the calculation and experiment results; and BDG is proved to be a distributed measurement of phase birefringence, while Sagnac is for group birefringence average measurement. From this work, it can be found that when concerning the polarization properties of FOGs, BDG should be used to measure the phase birefringence rather than the Sagnac and group birefringence.