Study On Polarization Mode Dispersion Compensation With Different Formats In High-speed Optical Communication System

Optical fiber communication system is the main part in a modern high-speed communication link. Polarization mode dispersion (PMD) is considered as a ultimate limiting factor in the long-distance optical fiber communication systems. The study on fiber's PMD compensation is a solution to overcome the limitations posed by PMD. PMD compensation can eliminate the impairment of optical signal transmission performance; decrease the impact of the link; cut the cost for the long-distance optical fiber communication. Different modulation formats have various tolerant effects to PMD, which is one of the key issues in high-speed communication systems. The adaptive PMD compensation with different modulation formats is investigated by numerical simulation. The impact of PMD in single- and multi-channel is analyzed in this paper.The effect of different modulation formats is studied and compared by numerical simulation for multi-stage PMD compensators under the degree of polarization (DOP) of single state of polarization (SOP) feedback signal in a 40-Gb/s fiber-optic communication system. The particle swarm optimization (PSO) algorithm is used as the feedback control algorithm. The PMD is produced including first and second-order PMD. The correlation between DOP and bit error rate (BER) for return-to-zero (RZ), non-return-to-zero (NRZ), carrier-suppressed return-to-zero (CSRZ) and chirp return-to-zero (CRZ) format is obtained. Results show that the two-stage PMD compensator has better performance for RZ and NRZ format under the DOP of single SOP feedback signal regarding the relationship of the compensated BER, DOP and PMD. The three-stage PMD compensator with many degrees of freedom (DOF) does not apply effectively to the higher-order PMD theoretically. The BER will increase when the DOP gets into the sub-maximum value. So the two-stage PMD compensator has better performance in terms of less DOF. And the effect of compensation is not ideal for CSRZ and CRZ format due to the weak correlation between DOP and BER.A novel PMD compensation scheme, that two WDM channels share one PMD compensator at receiver, is proposed for wavelength-division-multiplexing (WDM) system. The different modulation formats with multi-stage PMD compensators is performed and compared under RZ format and NRZ format in 40-Gb/s WDM optical fiber communication system. The PSO algorithm is used as a control method in WDM systems. The compensated DOP value of RZ and NRZ format has increased valid. The PSO algorithm is proposed and implemented successfully in adaptive multi-stage PMD compensation in a 40-Gb/s optical WDM system. The three-stage PMD compensator can resolve the influence of second-order PMD completely in WDM system. The compensated eye diagrams indicate that the three-stage PMD compensator takes the best efficiency in both the two channels for RZ and NRZ format.