When light passes through matter, power losses occur. One of the causes of this is polarization dependent loss
(PDL). Since almost all optical materials affect the polarization of light, the PDL attenuation of optical
fiberschanges with the polarization state of the propagating light waves. The polarization-dependent attenuation results from the maximum difference in light transmission in an optical waveguide, under all possible polarization states. Polarization can be caused by strong or less strong absorption
, by bending of the optical waveguide, by different optical density
and by mode reflection. To avoid polarization-dependent losses, there are polarization-maintaining fibers in which linearly polarized light maintains the initial polarization while passing through the optical waveguide.