We describe a method of characterizing high-order polarization mode dispers
ion (PMD). Using a new expansion to approximate the Jones matrix of a polar
ization-dispersive medium, we study the length dependence of high-order PMD
to the fourth order. A simple rule for the asymptotic behavior of PMD for
short and long fibers is found. It is also shown that, in long fibers (simi
lar to 1000 km), at 40 Gbits/s the third- and fourth-order PMD may become c
omparable to the second-order PMD. (C) 2000 Optical Society of America OCIS
codes: 060.0060, 060.2400, 060.4510.