Measurement of distributions of differential Group delay in a recirculating loop with and without loop-synchronous scrambling

Using the Jones matrix eigenanalysis and Poincare´ arc methods, we measured the differential group delay (DGD) in a recirculating loop for arbitrary fiber realizations and for different round trips. The measurement uncertainty was less than 2.0 ps in most cases. With this capability, we measured the DGD distribution with and without loop-synchronous polarization scrambling. We found that the DGD distribution can be influenced by the slow drift of fiber realization in the loop.