A deterministic broad-band polarization-dependent loss compensator

Polar decomposition of the transmission matrix allows lumped polarization-dependent loss (PDL) followed by lumped polarization mode dispersion (PMD) compensation at the receiver's end. Thus, we propose in this paper, the architecture of a broad-band PDL compensator in a feed-forward compensation scheme. This module consists of three stages. Stage 1 and 2 are the frequency-dependent polarization rotators that align all the different PDL vectors into the {1,0,0} direction in Stokes space. Stage 3 eliminates both the PDL magnitude and the frequency dependence in the isotropic attenuation by introducing different frequency-dependent variable attenuation to the linear horizontal and vertical polarizations. By applying the known Mueller transformations of the PDL compensator to the monitored polarimetric data, we show that the composite PMD spectrum can be deduced for subsequent broad-band PMD compensation.

I. Introduction

The deployment of optical amplifiers in lightwave systems has significantly increased the number and variety of optical components distributed along the link. As a result, small polarization effects, such as polarization-dependent loss (PDL) [1]–[5], associated with the individual components accumulate to produce noticeable performance degradation. These optical components include optical isolators, add/drop filters, switches, wavelength-division multiplexing (WDM) multiplier, and couplers, which could have PDL up to 0.3 dB. Although the PDL of the individual component is relatively constant in time and frequency, when they interact with polarization mode dispersion (PMD) presented in the fiber, the global PDL becomes frequency-dependent and time-varying on the same time-scale as PMD. This makes the compensation of both PMD and PDL [6], [7] particularly challenging.