Research on the Birefringence Distribution of the Fiber Coil With Quadrupole Symmetrical Winding Method

As the core component of the fiber optic gyroscope, the fiber coil has been the focus of research. In the field of fiber coil environmental adaptability research, researchers are calculating environmental errors, such as thermally-induced errors and magnetic-induced errors. They approximated the refractive index and birefringence of the fiber coil to an average value. However, the values of birefringence changes by the different bending radius of the fibers in the different layers, which would greatly reduce the accuracy of the environment error model. Therefore, in this paper, a birefringence distribution model of the fiber coil is proposed for the first time based on the quadrupole symmetrical winding pattern. Firstly, we qualitatively analyze the birefringence of Panda-type polarization-maintaining fiber, and then the fiber coil winding law is established through detailed analysis of the standard quadrupole symmetric winding method. Secondly, we use the finite element method to analyze the force of the single-layer fiber, and obtain the change law of the refractive index of polarization-maintaining fiber. The mathematical model of the birefringence distribution is established and simulated. Finally, we use optical coherence domain polarization measurement technology to detect the distributed polarization crosstalk of the fiber coil. The data is obtained by using the white light interferometer that is consistent with the simulation. The result proves the correctness of the theory. Moreover, an experimental platform for Sagnac loop is built, and the interference optical power is measured by the optical spectrum analyzer. Compared with the equivalent radius method, the accuracy of model is improved by 91.48% at 1310nm.The method proposed in this paper will greatly promote the research on the environmental adaptability of fiber optic gyroscope.