Study On The Influence Of Atmospheric Turbulence On The Performance Of Coherent Optical Communication Systems

Because of the higher receiver sensitivity and being immune to the backgroundnoise, the space coherent optical communication system has a competitive advantagein the high-speed and long-haul communication and is the development direction ofthe space optical communication. However the refractive-index fluctuations inducedby the atmospheric turbulence will lead to the random variations of the amplitude andphase of the optical signal. Compared to the direct detection system, the coherentdetection system is not only affected by the amplitude fluctuations but also affectedby the phase fluctuations evidently. So there is an important significance toinvestigate the influence of the atmospheric turbulence on the space coherent opticalcommunication. However most of the former theory models of the space coherentoptical communication system are based on the plane wave transmission model, butthe plane wave model can not approximate the Gaussian optical beam model in theuplink and some other situations. So it is necessary to develop the Gaussian opticalbeam model of the space coherent optical communication under the influence of theatmospheric turbulence and investigate the influence of the atmospheric turbulenceeffects.The dissertation summarizes the research significance, the research progress, thekey techniques of the space coherent optical communication system and the researchprogress of the influence of the atmospheric turbulence on the performance of thespace coherent optical communication system. The turbulence characteristic of theatmospheric channel is introduced, including the atmospheric refractive-indexstructure parameter model, the power spectrum models for refractive-indexfluctuations and the atmospheric turbulence effectsThe dissertation analyzes the plane wave theory model for the space coherentoptical communication system under the influence of the atmospheric turbulence, andbased on the plane wave theory model, the Gaussian optical beam theory model forthe space coherent optical communication system under the influence of theatmospheric turbulence is built and the probability density function of the signal-to-noise ration of the system is derived. Using the plane wave theory model,for the horizontal transmission coherent optical communication link, the influence ofthe scintillation index, the phase variance and the phase compensation technique onthe bit-error rate of the system is investigated and the receiver aperture diameter isoptimized, the influence of aperture averaging including the atmospheric turbulenceinner scale and outer scale on the bit-error rate and the optimum receiver aperturediameter is investigated. Using the Gaussian optical beam theory model, for thehorizontal transmission coherent optical communication link, the influence of thescintillation index, the phase variance and the phase compensation technique on thebit-error rate of the system is investigated and the transmitting optical beam radius,the local oscillator optical beam radius and the receiver aperture diameter areoptimized. Using the Gaussian optical beam theory model, for the ground-to-satellitecoherent optical communication uplink, the influence of beam wander on the bit-errorrate of the system and the optimum receiver aperture diameter is investigated, thetransmitting optical beam radius and the receiver aperture diameter are optimized fordifferent zenith angles and wavelengths, and one conclusion is concluded that in theground-to-satellite uplink the influence of the phase fluctuation on the performance ofthe system is little and the phase compensation technique is not needed to use. Usingthe Gaussian optical beam theory model, for the satellite-to-ground coherent opticalcommunication downlink, the influence of the aperture average and the phasecompensation technique on the bit-error rate of the system and the optimum receiveraperture diameter is investigated.The research results in the dissertation supply the theory basic for the design of thefree space coherent optical communication system and have the direction significanceand the reference worth.