When optic pulse propagates in a fiber it always experience small environment disturbance of it polarization state. Is any pulse stable polarization that hardly can be destroyed ? If such a state exist, pulse polarization have to develope to that from any other state and be stable.
In Conventional Single Mode Fibers, due to change of refractive index along the fiber in x-y direction, where the two state of polarized light propagate, the two polarized modes experience different phase velocity. If the z is the propagation direction, say, at z=L, the two polarized modes, under polarization mode dispersion (PMD), would lag each other, resulting in spread in time of the propagating pulse with a particular input polarization.
To avoid this effect, polarization-maintaining fiber (PMF) could be a remedy, of course for a short distance applications, such as sensors. Polarizing optical fibers, such as D-shape fiber also can be used to maintain polarized pulses.
Hi Arkadiy,
you can find interesting information on the evolution of the polarization state along an optical fiber in the publication attached to this message.
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