Combined PMD-PDL effects on BERs in simplified optical systems: an analytical approach

A new analytical evaluation of polarization-induced error probability for optical systems consisting of both PMD and PDL is presented. Using a simplified model containing a lumped PMD-PDL fiber, an amplifier with ASE noise, an idealized optical filter, and an electrical filter with integrate-and-dump response, a closed-form of the probability density of the filtered current is obtained. This allows us to evaluate the BER affected by the PMD and PDL. Based on this, two polarization related effects, i.e., the PMD and PDL directional coupling and the polarization-induced intersymbol interference (ISI), are studied. We show that the PMD and PDL directional coupling can be strongest when the PMD vector perpendicularly correlates with both the PDL vector and the input signal polarization in the 3D Stokes space. Besides, its impact on bit-error-rate (BER) strongly depends on the PDL value. We also find that, for an optical system with realistic parameters, the impact of polarization-induced ISI on the BER is mostly caused by the two closest neighbors of the desired bit. Related with these two polarization effects is the PMD value fluctuation. Large PMD value variation can play an overwhelming role in impairing the optical performance.