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 little or no cross-coupling of optical
power between the two polarization
modes. Such fiber is used in special applications where preserving polarization is essential.