| Research on transmission system with high rate,large capacity,long distance is becoming hotter in the field of optical communication in recent years.Coherent optical frequency division multiplexing?CO-OFDM?system has been well developed as it has the advantages of high spectral efficiency,large capacity and high transmission rate under polarization multiplexing.However,some problems still exist in the system that need to be solved.What's more,the researches are mostly based on simulation analysis so far.This paper mainly focuses on the estimation and compensation of transmitter IQ imbalance and phase noise,meanwhile the experimental platform of CO-OFDM system is established.The main contents of this paper are as follows:?1?A novel pilot structure is proposed for CO-OFDM system to compensate phase noise and transmitter IQ imbalance.The simulation results show that the proposed algorithm increases the transmission rate from 20Gb/s to 50Gb/s.With IQ imbalance of 3dB,15?and 0linewidth after 640km transmission at 50Gb/s,the OSNR penalty of the proposed algorithm is reduced by about 6dB when the BER is 1×10-3;when the linewidth is 120kHz,BER is 1×10-3,the OSNR of proposed algorithm is 26dB,the amplitude and phase imbalance tolerance of the proposed algorithm is 3.5dB and 25?,respectively.The BER of comparison algorithm can not achieve 1×10-33 under the same condition.?2?Two low-overhead pilot structures combined with orthogonal basis expansion-based method are proposed for PDM CO-OFDM system to compensate phase noise and transmitter IQ imbalance,which can achieve better performance.The simulation results show that the OSNR of the proposed methods are 24dB and 22dB when the BER is 1×10-33 with IQ imbalance of 3dB,15?at each polarization and 100kHz linewidth after 480km transmission at80Gb/s.With same OSNR,the BER is increased by an order of magnitude at 100Gb/s transmission rate.It proves that the proposed methods can reduce the overhead of pilot as well as adapt to the transmission with high rate.?3?Establishment of the experimental platform of CO-OFDM system.The structure of the CO-OFDM experimental platform is analyzed in details,then the parameters are set properly to achieve effective transmission,and conventional algorithms are adopted for signal processing to test the time-domain signals and the frequency spectrum with respect to each procedure.Currently an effective transmission with 96.6km transmission distance at 12Gb/s can be achieved,which can be used to verify the compensation effect of the proposed pilot structure. |
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