Polarization-maintaining optical fiber

In telecommunication, a polarization-maintaining optical fiber (PM) is an optical fiber in which the polarization planes of lightwaves launched into the fiber are maintained during propagation with little or no cross-coupling of optical power between the polarization modes.

Note 1: Cross sections of polarization-maintaining optical fibers range from elliptical to rectangular.

Note 2: Polarization-maintaining optical fibers are used in special applications, such as in fiber optic sensing and interferometry. Synonym: polarization-preserving (PP) optical fiber.

Source: from Federal Standard 1037C and from MIL-STD-2196[?]