Polarization-dependent loss and its effect on the signal-to-noise ratio in fiber-optic systems

We study the effect of polarization-dependent loss (PDL) on the signal-to-noise ratio in fiber-optic systems. We show that in most cases of interest PDL-induced penalties result primarily from the coupling of noise generated with a polarization state orthogonal to that of the signal into the signals' state of polarization. This mechanism sets a limit to the improvement that can be expected to result from the periodic use of dynamic gain equalizers along the link.