Polarization-maintaining optical fibers are used in special applications, such as in fiber optic sensing, interferometry and quantum key distribution. They are also commonly used in telecommunications for the connection between a source laser and a modulator, since the modulator requires polarized light as input. They are rarely used for long-distance transmission, because PM fiber is expensive. OverviewIn, polarization-maintaining optical fiber (PMF or PM fiber) is a single-mode in which , if properly launched into the fiber, maintains a linear polarization during,. In an ordinary (non-polarization-maintaining) fiber, different polarization modes have the same nominal due to the fiber's circular symmetry. in such a fiber, or bending. Polarization-maintaining fibers work by intentionally introducing a systematic linear in the fiber, so that there are two well defined polarization modes which propagate along the fiber with very distinct phase velo.
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