Unless it is compensated, which is polarization mode dispersion pdf, this ultimately limits the rate at which data can be transmitted over a fiber. In an ideal optical fiber, the core has a perfectly circular cross-section.
The signal that is transmitted over the fiber is randomly polarized, i. In a realistic fiber, however, there are random imperfections that break the circular symmetry, causing the two polarizations to propagate with different speeds.
In this case, the two polarization components of a signal will slowly separate, e. The symmetry-breaking random imperfections fall into several categories.