Improved phase delays for optical compensation of polarization-mode dispersion

We present numerical simulations of the average frequency dependence of the differential phase delays (DPDs) that are introduced by polarization-mode dispersion (PMD) between the signal components transmitted in the two principal states of polarization of the fiber. Our study confirms that the first-order approximation of frequency-independent DPDs is valid for fibers that normally do not require PMD compensation. However, for fibers with larger mean differential group delays (DGDs), the first-order approximation tends to overestimate the mean DPDs for any given DGD. Based on our numerical results, we derive closed-form approximations for the frequency and group-delay dependence of the mean DPD conditioned on a given DGD and show that these more accurate DPDs may significantly improve the performance of optical PMD compensators.