Field measurements of polarization mode dispersion

Polarization mode dispersion (PMD) measurements are presented for a sample of installed optical fibers. High PMD values are fairly common, with 9 of t he 71 fibers having PMD coefficients above 0.3 ps / km(1/2). The results ar e analyzed in terms of the age of the fibers and the type of cabling. Measu rements are presented for a number of concatenated fiber links, and the res ults show that the PMD value of the link is approximately equal to the squa re root of the sum of the squares of the PMD values of the individual fiber s.