Polarization-maintaining optical fiber

Image of the cross section of a polarization-maintaining optical fiber patch cord, taken with an illuminated microscopic viewer called a fiberscope. The two small, eye-like circles are the stress rods and the tiny circle between them is the core. The larger circle surrounding them is the cladding, usually 125 microns in diameter.

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.