Investigation And Simulation On The Nonlinear Impairments In Coherent Optical OFDM System

Coherent Optical Orthogonal Frequency Division Multiplexing (COOFDM) is an important modulation technique which will be adopted in the next generation of optical transmission network, because of its unique advantage in the application of ultra-long haul and high speed transmission system.For example, by utilizing the characteristic of multi-carriers sharing the channel,the dynamic allocation of communication bandwidth can be implemented, then complex service configuration and effective resource optimization will be supported.What is more, such type of system can apply flexible digital signal processing algorithm to compensate the chromatic dispersion, mitigating the urge for precise optical chromatic dispersion compensation and reducing the cost of the system construction and operation.However, there is limit on the performance in such system. The major reason for such limit originates from the nonlinearity in the optical fiber, which is more severe than that in the traditional system, due to compact distribution of sub-carriers.In the ultra-long transmission system, the nonlinear impairments may accumulate along the transmission length, severely degrading the quality of the signal.Although there are previous literatures studying this type of impairments,no accurate model is proposed to describe the mechanism and impact. Thus,under the support of the National Science Foundation, this thesis makes profound investigation on the problems above and acquires some innovations.The relevant achievements have been published on some international journal: and.The Major achievements are listed as followThe first, based on the nonlinear Schrodinger equation and considering the specific waveform of CO-OFDM, a more accurate model to describe the nonlinear impairments is acquired, and an upper-limit of SNR is offered.The Second, based on the nonlinear impairments model derived, the unique characteristics in CO-OFDM system is pointed out that the data correlation will enhance such type of impairments.What is more, a quantized standard to evaluate data correlation in CO-OFDM is proposed, and the feasibility is investigated that this standard is used as the optimization indicator in the equalization algorithm.The third, Designing the simulation system on the CO-OFDM system and the detail verification is carried out. On the matlab based CO-OFDM platform of our laboratory. The 4 X 80 km CO-OFDM simulation system is built. The power level is varied to verify the validation of our theoretical derivation.The simulation result shows that, the result of the theoretical derivation is consistent with most practical communication system.