Electrical and Electronic Engineering - Theses
Permanent URI for this collection
Search Results
1 - 1 of 1
-
ItemAn evaluation of system penalties from polarisation mode dispersion( 2007)Polarisation mode dispersion (PMD) arises from the polarisation properties of an optical signal interacting with the non-degenerate polarisation modes of an optical fibre. When an optical signal is launched into a fibre, the power is split between the polarisation modes. The amount of power contained in each mode depends on the relationship between the launch state of polarisation and the axes of the fibre's polarisation modes. Assuming that some optical power is contained in each polarisation mode, the difference in propagation constants between the modes causes pulse broadening to data bits contained within an optical signal. The inter-symbol interference that results from PMD-induced pulse broadening is the first-order manifestation of PMD. However, in deployed optical systems, the coordinate axes of the fibre's polarisation modes vary with length, and are sensitive to mechanical stresses and temperature variations. The resulting all-order PMD causes more complicated signal distortions, which are stochastic in nature. This thesis investigates the impact of first- and all-order PMD in optical systems using the PMD-induced system penalty. To achieve this, tools are first developed to aid the investigation. Firstly, a novel channel characteristic is introduced, for monitoring PMD-induced penalties. Secondly, the channel characteristic is used to develop a new theoretical framework, to interrelate different methods for monitoring PMD to the PMD-induced penalty. The techniques investigated include degree of polarisation, RF spectral power monitoring and eye closure. The framework is confirmed experimentally, and then used to demonstrate that the novel channel characteristic is the most practical method for monitoring PMD-induced penalties. Finally, the impact of the penalty measurement is recognised as a factor that influences the PMD-induced penalty. As a result, a new theoretical basis is derived to quantify the differences between the various methods of measuring system penalties, including eye closure penalties, Q-penalties, power penalties and optical signal-to-noise ratio penalties. This basis is also experimentally verified. In the second half of the thesis the tools that have been developed are used to experimentally investigate the system impact of first- and all-order PMD on two different systems. The first system does not employ PMD compensation, while the second system is compensated for PMD, using a maximum likelihood sequence estimation-based electronic equaliser. In both cases, the work extends previous investigations of PMD-induced penalties, by investigating the impact of first- and all-order PMD over many launch states of polarisation. The results from the study of PMD-induced penalties in the PMD uncompensated system are used to derive a new PMD-induced penalty model, which is then critically compared to existing models. The new model is shown to better represent both first- and all-order PMD-induced system penalties. The impact of all-order PMD in the two optical systems is reported in detail, and it is shown that in most circumstances first-order PMD is the dominant cause of system penalty. In addition, the results provide experimental evidence for previous simulation based studies of all-order PMD, and some new findings are reported.