Abstract

Polarization Mode Dispersion (PMD) was proven to limit the upgrade of numerous 10 Gb/s systems to 40 Gb/s. When considering 160 Gb/s transmission, it is clear that upgrade requires higher order PMD compensation. PMD results from the birefringence of transmission fibers, which breaks the degeneracy of the two modes of the so called ‘single mode’ fiber. Random time fluctuating differential propagation velocity and cross coupling along the optical path leads to signal distortions and system impairments. To the first order, it acts as a dual path fading channel, i.e., the fiber presents special polarizations along which the pulse remains polarized but propagates at different speeds. These states are called Principal States of Polarization (PSP), they arrive separated by a Differential Group Delay (DGD). Because fiber’s birefringence (axis and strength) varies with frequency, this is a rather crude approximation, as signal bandwidth increases. In fact, both DGD and PSP are frequency dependent parameters. This is one possible definition of PMD higher order, where DGD variation is called Polarization Chromatic Dispersion (PCD) and PSP variation leads to depolarization. PCD’s impact is usually negligible in comparison with de-polarization.

© 2002 Optical Society of America