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. Thorlabs' Polarization-Maintaining (PM) Optic Circulators are non-reciprocating, unidirectional, three-port devices that are used in a wide range of optical setups. Available with a center wavelength of 1064, 1310 (O-Band), or 1550 nm (C-Band), these circulators are fast axis blocked and hence are. Polarization-maintaining fibers are applied in devices where the polarization state cannot be allowed to drift, e. as a result of temperature changes. Examples are fiber interferometers, fiber-optic gyroscopes and certain fiber lasers. This capability is not a marketing claim—it is a measurable performance requirement in many photonics systems where polarization drift can translate into signal fading, phase.