Measurement of local beat length and differential group delay in installed single-mode fibers

We present beat length and polarization mode dispersion (PMD) measurements performed on installed fibers. Results regard three different kinds of fibers: standard step index, dispersion shifted and nonzero dispersion (NZD). After a historical comparison with standard differential group delay measurement collected four years ago on the same fibers, we perform a spatial-resolved measurement of the beat length by analyzing the state of polarization of the backscattered field. We compare PMD properties of different fibers and calculate the statistical distribution of the beat length. The differential group delay (DGD) and the beat length statistics depend strongly on fiber type and on fiber position along the link. The influence of the beat length on the DGD is also discussed.