Theoretically speaking, the fiber with a circular core should not produce birefringence, and the polarization state of the fiber will not change during propagation. However, in practice, during the production process, conventional optical fibers will be subjected to external forces and other reasons, which will cause the optical fiber to be uneven in thickness or bent, which will cause birefringence. When the optical fiber is affected by any external interference, such as wavelength, bending degree, temperature, etc., the polarization state of light will become disordered when it is transmitted in a conventional optical fiber.
The application of polarization-maintaining fiber can solve this problem of polarization state change, but it does not eliminate the birefringence phenomenon in the fiber, but eliminates it by designing the fiber geometry to generate stronger birefringence The effect of stress on the polarization state of incident light.
How does PM fiber affect the birefringence in the fiber? During the drawing process of polarization-maintaining fiber, when linearly polarized light is transmitted along one characteristic axis of the fiber, part of the optical signal will be coupled into another characteristic axis perpendicular to it, which will eventually cause a decrease in the polarization extinction ratio of the outgoing polarized light signal, thereby affect the birefringence effect.
