This polarization-maintaining fiber is optimized for fiber optic gyroscope (FOG) applications. It is designed for optimal performance over a wide temperature range and with a small coil radius. 5 dB at -60 °C are typical for this fiber. Stress rods run parallel to the fiber's core and apply stress that creates birefringence in the fiber's core, allowing polarization-maintaining. 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. In polarization-maintaining single-mode fibers (PM fibers), the fiber symmetry is broken by integrating stress elements in the fiber cladding. The light is then guided in two perpendicular principle states of polarization with different propagation constants – the fast and the slow axis. The linear. Polarization-maintaining single- mode fibers (PM fibers) are rotation-ally non-symmetric because of inte-grated stress elements, for example, that break the degeneracy of the two principle states of polarization (SOP). The two fiber types were compared in terms of.