Study of variation of the laplacian parameter of DGD time derivative with fiber length using measured DGD data

Temporal and spectral DGD measurements were made on different combinations of three 95-km fibers within a slotted-core, direct-buried, standard single-mode fiber-optic cable over long time periods to characterize DGD variability. From this data we observed that DGD varies slowly over time but rapidly over wavelength. We also observed that the DGD variation with time becomes more rapid for longer length fibers. The DGD time derivative data obtained from the measured DGD data showed good agreement with a Laplacian distribution. We observed that the Laplacian parameter, which dictates the Laplacian pdf of DGD time derivative, seems to converge to a lower value as the fiber length is increased. This observation, which needs further verification, if true, would greatly simplify the system outage analysis due to first-order PMD on long-haul optical fiber links.