Polarization maintaining fiber

Because the light wave propagating in the optical fiber has the property of electromagnetic wave, in addition to the basic single mode of light wave, there are essentially two orthogonal modes of electromagnetic field (TE, TM) distribution. Generally, because the cross-section structure of the optical fiber is circular symmetry, the propagation constants of the two polarization modes are equal, and the two polarized lights do not interfere with each other. However, in fact, the optical fiber is not completely circular symmetry. For example, if there is a curved part, there will be a combination factor between the two polarization modes, which is irregularly distributed on the optical axis. The dispersion caused by this change of polarized light is called polarization mode dispersion (PMD). For cable TV, which mainly distributes images, the impact is not great, but for some businesses with special requirements for UWB in the future, such as:

① When heterodyne detection is used in coherent communication, and the polarization of light wave is required to be more stable;

② When the input and output characteristics of optical machines are related to polarization;

③ When making polarization maintaining optocouplers and polarizers or depolarizers, etc;

④ Making optical fiber sensors using light interference,

Where the polarization wave is required to remain constant, the fiber that has been improved to keep the polarization state unchanged is called polarization maintaining fiber (PMF), or fixed polarization fiber.