Research On Techniques Of Modulation And Demodulation Of High-speed Coherent Optical Fiber Communication

With the rising of high-quality data services, the requirement for the capability ofbandwidth of transmission system is growing. Considering the demand for wideningbandwidth, as well as to reducing the consumption and cost per bit, high-speed coherentoptical fiber modulation and demodulation techniques can be a solution.This thesisfocuses on the research of modulation and demodulation subsystem in high-speedcoherent optical fiber communication system, with the purpose of putting forward ahighly effective and practical scheme for high-speed coherent fiber communicationsystem. It mainly does research and simulation on phase modulation self-coherentdemodulation technology. The thesis mainly focuses on investigations of opticalmodulation and demodulation research. And it does research and simulation on phasemodulation self-coherent demodulation technology. The work can be divided into threeparts.1.The status of domestic and foreign research is compared to indicate high sensitivityand high dispersion tolerance for coherent optical fiber techniques. The performancesof various modulation schemes are compared. The frequency modulation, due to thecomplexity of its structure, is not suitable for the current communication system. Thephase modulation, compared with the above mentioned two modulation schemes, hasan simpler structure and a better transmission characteristic, and can be upgradedsmoothly in the present system, thus it is the most suitable modulation scheme forhigh-speed optical fiber communication.2.The phase modulation self-coherent demodulation system is analyzed,withcalculation of the system performances of BPSK and DQPSK under an ideal situation.When the communication rate is10Gbit/s and BPSK receiver power is-43.4dBm, theBER of system is10^-9. Further more, when the communication rate is10Gbit/s andDQPSK receiver power is-37.8dBm, the BER of system is10^-9. For the self-coherentdemodulation of the BPSK modulation system, when the Mach-Zehnderinterferometer delay arm error is less than1%of the total length, changes in thesystem bit error rate are less than5%. For DQPSK modulation system, when delay arm error does not exceed0.8%of the total length, changes in the system bit errorrate are less than5%. For BPSK systems, the BER is better than10^-9only if the laserlinewidth less than10MHz when the communication rate is10Gbit/s. For DQPSKsystems, the BER is better than10^-9only if the laser linewidth less than3MHz whenthe communication rate is10Gbit/s. The impact on the system of power distributionerror is analyzed. The3dB coupler proved the best choice for the system. For theBPSK system, when the power allocation error is less than30%, changes in thesensitivity are less than3dB.3.In the thesis a simulation model for the BPSK modulation self-coherent demodulationis established. Through this simulation model the author finds that, whencommunication rate is low, the performance of this simulation system consists withthe theoretical value; when it is high, the deviation is about1.9dB.Through thesimulation of laser linewidth and Mach-Zehnder delay error, it is found that thesimulation value consists with the theoretical value, free from the effects ofcommunication speed. Through the simulation of PIN responsiveness and modulatorphase shift, it is found that the simulation value of system performance.