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

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