Polarization-maintaining and dispersion-compensating fibers
Optical fibers for telecommunications

As already mentioned, a rotationally symmetrical waveguide does not retain the polarization of the electromagnetic waves propagating through it, since there is no preferred direction (in electromagnetics, this is the notion of mode degeneracy). In long-distance transmission, this property is not a problem, as the receiver will recover the polarization from the received signal when it carries information: this is the case in systems using modulation schemes based on two orthogonal carriers.

In other applications, however, such as fiber amplifiers or lasers, it is necessary to transport a signal without changing its polarization: this is the purpose of polarization-maintaining fibers (PMF). A polarization-maintaining fiber...