Polarization mode dispersion is a physical phenomenon in optical fiber hatcauses light pulses to spread in time. If the amount of spread （dispersion） is excessive

adjacent light pulses will overlap and interfere with each other. This interference willmanifest itself as an increased bit error rate as the receiver may be unable to discernadjacent bits from each other. As the bit spacing decreases

as in high data-rate transmis-sions such as 10Gbit/s （OC-192

STM-64） or 40Gbit/s （OC-768

STM-256）

excessive PMD willseverely impact network operation. This paper will explain how these negative effects can beminimized or eliminated through proper PMD measurement and compensation.