Researches On Adaptive Technology Of Compensation For Polarization Mode Dispersion

Polarization Mode Dispersion (PMD) causes pulse broadening because of the difference in speed between two polarized modes in optical fiber communication systems. It limits the upgrading of bit rates and span of relay distance. Solving PMD is the key to realizing optical long-haul transmissions systems and becomes one of the most important considerations. The difficulty of solving PMD lies in its randomness of differential group delay (DGD) between the principal states of polarization (PSP) and the change in PSP with time and wavelength. Tasks done in the thesis are of three aspects. Firstly, a mathematical description of PMD is given and optical pulse broadening and eye patterns closing are observed with different set-ups of experiments. A prototype of PMD compensation system for a 10Gbit/s transmission system emulated by two sections of DGD is set up. The relation between electrical power and DGD is established and ways of extracting feedback control signals for PMD compensation are shown. Calculations for the transmission matrix of a polarization controller are performed and are useful for a control algorithm of compensation.Secondly, experiments of dynamic compensation are well done for PMD of 10Gbit/s pseudo random sequences. The eye patterns with/without compensation are compared and results are shown to be good. Receiving sensitivity of the prototype is measured and deterioration caused by simulator is well compensated for by using our compensation system.Finally, degree of polarization (DOP) as feedback signal for PMD compensation is investigated theoretically and experimentally. A mathematical relation between DOP and DGD is derived based on optical coherent matrix. Theoretical calculations and experiments for optical transmissions of Gaussian pulse are done and compared, showing a fine fit between them for both non-return to zero (NRZ) and return to zero (RZ) codes of 10Gbit/s under certain conditions. Other factors affecting DOP are also mentioned in the thesis.