| In recent years,with the development of cloud services,broadband video,file sharing and other big data services,resulting in the explosive growth of optical information traffic in the short-and medium-range,which covering data center networks,access networks and metropolitan area networks.However the existing scheme for the short-and medium-range optical communication(intensity modulation/direct detection,IM/DD)has been difficult to meet the future demand growth.Therefore,a new scheme at low cost and complexity is urgently needed to improve the communication capacity.Among them,Kramers-Kronig coherent optical receivers can demodulate quadrature amplitude modulation(QAM)modulation format signal only with the intensity information detected by one photodetector(PD),which is a candidate for the next generation of short-and medium-range optical fiber communication system.Therefore,this dissertation focuses on the Kramers-Kronig(KK)coherent optical receiving system,and carries out related research and innovation work.The main contents are as follows:Firstly,the principle of eliminating signal-signal beat interference(SSBI)by KK algorithm is draw from the full-field recovery theory.Furthermore,to describe the physical mechanism of KK algorithm which recovers the phase of signal from its intensity clearly,the minimum phase signal condition and the relationship between amplitude and phase of the signal are deduced from the signal analyticity.Then,the basic composition of KK coherent optical communication system is briefly described,and the part which is different from coherent optical communication is described in detail.In order to optimize the performance of KK receivers in the practical application,and make the cost and complexity of the system as low as possible,it is necessary to systematically analyze the relevant parameters which affects the performance of KK coherent optical communication system.Therefore,in the third chapter of this dissertation,the main parameters affecting the performance of KK receiver are analyzed and optimized.Including: Transmitter parameters: carrier signal power ratio,the interval between continuous wave and signal(protection bandwidth);Channel dispersion;Receiver parameters: optical filter bandwidth and receiver bandwidth,oversamplingfactor.The results of this part can be used as a reference for the practical application of KK coherent optical communication system.In order to further improve the spectral efficiency of KK receiver,polarization multiplexing schemes for KK receiver is studied.The combination of Stokes vector receiver and KK algorithm can realize polarization multiplexing.Based on this,a demodulation scheme based on Stokes vector statistical information is proposed,which is transparent to the dispersion and signal modulation format.The simulation results show that the estimated rotation rate of polarization state is up to 10 Mrad/s,which meets the requirements of short-and medium-range optical communication.And the BER performance remains unchanged after 200 km optical fiber transmission.In addition,for SVR receiver with relatively complex structure,this dissertation further studies a polarization division multiplexed systems with carrier wave added at the transmitter,and the signal is received with only two PDs.The scheme cascaded KK algorithm and linear iteration filter is proposed to restore the full field of the signal,which can realize the polarization multiplexing of QAM modulation signal.Compared with the SVR-KK scheme,the complexity of the receiver is greatly reduced.Through simulation analysis,this scheme can effectively eliminate intra-polarization SSBI and interpolarization SSBI,and recover the full-field of the signal.Compared with the original scheme,the proposed scheme has a greater improvement in BER performance.The above research is expected to provide solutions and technical sercices for the next generation of ultra-high-speed,high-capacity,low-cost short-and medium-range optical fiber communication systems. |
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