In fiber optics, polarization-maintaining optical fiber (PMF or PM fiber) is a single-mode optical fiber in which linearly polarized light, if properly launched into the fiber, maintains a linear polarization during propagation, exiting the fiber in a specific linear polarization. In fiber optics, polarization-maintaining optical fiber (PMF or PM fiber) is a single-mode optical fiber in which linearly polarized light, if properly launched into the fiber, maintains a linear polarization during propagation, exiting the fiber in a specific linear polarization. In fiber optics, polarization-maintaining optical fiber (PMF or PM fiber) is a single-mode optical fiber in which linearly polarized light, if properly launched into the fiber, maintains a linear polarization during propagation, exiting the fiber in a specific linear polarization state; there is. Polarisation-maintaining fibers (PM fibers) are used in specific applications where the polarisation effect (maintaining signal polarisation state) plays a major role and directly influences the functionality of the whole system. PM fibres are typically used in interferometers, sensing solutions. In polarization-maintaining single-mode fibers (PM fibers), the fiber symmetry is broken by integrating stress elements into the fiber cladding. The. Thorlabs offers both PANDA and Bow-Tie Single Mode Polarization-Maintaining (PM) fiber. These two fibers are named based on the stress rods used.