The fluctuation of polarization mode dispersion (PMD) due to environme
ntal change is an important issue for fiber-optic communication system
s. We measure the time evolution of PMD for installed aerial and burie
d cables and for a spooled fiber in a temperature controlled chamber.
The results show that PMD fluctuates much more rapidly for aerial cabl
es than for buried cables. The magnitude of PMD is different for the t
hree fibers and our results also show that the magnitude of PMD fluctu
ation depends on the magnitude of the PMD.