Research On The Impact Of Optical Axis Deviation On The Performance Of Two-way Atmosphere Laser Communication Systems

Atmospheric laser communication has been widely used in 5G mobile communication technology,battlefield rapid network communication,extension of inter-building local area networks,and earthquake relief emergency communication due to its advantages of high communication rate,good confidentiality,and strong anti-interference capability.However,the performance of the two-way atmospheric laser communication system is affected by the transmitting and receiving optical axis deviation of the communication terminal due to various factors such as system mounting error,optical axis detection error and platform vibration.In order to study the impact of optical axis deviation on the performance of atmospheric laser communication systems and its improvement methods,a high dynamic range optical axis deviation detection method and an optical fibre coupling efficiency model under the influence of received optical axis deviation are investigated.On the basis of this,a composite channel model is established by combining the optical fiber coupling efficiency model under the influence of the received optical axis deviation,which provides a theoretical basis for analyzing the performance of the bi-directional atmospheric laser system.The main research elements are as follows:(1)The effects of transmitting optical axis deviation,receiving optical axis deviation,path loss and random fluctuations in light intensity on laser transmission are investigated for atmospheric laser communication links.The optimal beam divergence angle for a given transmitting optical axis deviation is given.At the same time,the optical axis deviation of the two-way communication system and its causes are investigated.(2)An integral infinite logarithmic ratio algorithm is proposed to address the problem of the random fluctuations of the detection signal caused by the flicker effect of atmospheric turbulence,which leads to the need for a higher dynamic range of the optical axis deviation detection system.Based on this,the signal-to-noise ratio parameter is introduced,and an integral infinite logarithmic ratio algorithm based on the signal-to-noise ratio is proposed,which improves the dynamic range while guaranteeing the accuracy of optical axis deviation detection under low signal-to-noise ratio conditions.Then,the coupling efficiency under the influence of the received optical axis deviation is studied,and a model of the coupling efficiency is established under the atmospheric turbulence conditions where the received optical axis deviation follows the Rice distribution,revealing the influence of the received optical axis bias error and random jitter on the coupling efficiency.(3)The performance of a two-way laser communication link under the influence of the deviations of the optical axis was investigated.The joint channel gain models were established combining transmitting optical axis deviation,receiving optical axis deviation,path loss and random fluctuation of optical intensity with and without transmitting and receiving optical axis deviation.The effects of transmit and receive optical axis random jitter,communication distance and atmospheric structure refractive index constants on channel gain and communication performance were analyzed in the absence of deviation between the transmit and receive optical axis.In the case of deviation between the transmit and receive optical axis,the effect of the deviation between the transmit and receive optical axis on the channel gain and communication performance of the two-way communication link was analyzed.(3)The calculation of the performance of a two-way atmospheric laser communication link under the influence of optical axis deviation is investigated.A composite channel model is developed by combining transmitting optical axis deviation,receiving optical axis deviation,path loss and random fluctuation of optical intensity in the case of transmitting and receiving optical axis deviation.The effects of transmit and receive optical axis random jitter,communication distance and atmospheric structure refractive index constants on channel gain,average bit error rate,outage probability and average capacity are investigated in the absence of bias between transmit and receive optical axes.The effect of transmit and receive optical axis deviations on channel gain,average BER,outage probability and average capacity of a two-way communication link is investigated in the presence of deviations between the transmit and receive optical axes.(4)A nano-displacement testbed was built to verify the optical axis deviation detection performance of the integral infinite logarithmic ratio algorithm and the signalto-noise ratio-based integral infinite logarithmic ratio algorithm.Experimental validation of the theoretical model of channel gain and system performance for the8.9km urban two-way atmospheric laser link was carried out.The channel gain and system performance were calculated from optical power samples at the receiver end to verify the correctness of the theoretical model.