Field and laboratory measurements of polarization mode dispersion in optical fibres

摘要

In this dissertation, the PMD measurements of field and laboratory optical fibre will be discussed. In the laboratory, temperature cycling of different configurations of fibre were tested. It is shown that the environmental temperature plays a significant role in determining the behaviour of PMD. The PMD of all fibres tested showed changes in the PMD when the environmental temperature was changing, but remained constant for constant temperatures. This is explained by the structure and thermal coefficients of the materials used to make up the fibres. It is found that the temperature gradient has a large effect on the magnitude of the PMD fluctuations. Field measurements were conducted on buried and aerial cable. It is shown that the PMD of aerial cables shows a higher degree of scatter than the PMD of buried cables. The scatter seen in the PMD can be attributed to changing environmental temperature as well as movement of the cable. The PMD of the deployed fibre is in all cases found to be considerably higher than the PMD of laboratory fibre. Age of the fibre, deployment conditions and installation procedures are believed to be responsible for the higher value. Long term monitoring of the PMD is also found to be critical when testing fibres. Over- or underestimations of the average PMD are often made in the field due to only a limited number of readings being taken. Having a large test ensemble of input states of polarization is shown to increase the accuracy of the results. For aerial cables, movement of the cable has the same effect as scrambling the input SOP and hence the results will be more accurate. Buried cables on the other hand show little movement and hence only one input SOP is often tested. Scrambling the input SOP will therefore increase the accuracy of these results.