在星地链路的空间相干光通信系统中,大气湍流、跟踪误差会影响系统的混频效率和误码率.根据混频效率公式分别推导了大气湍流强度和跟踪误差与系统混频效率的关系并进行仿真计算.计算结果表明,混频效率随跟踪误差和大气湍流强度的增加而降低,其中当跟踪误差大于12 μrad或湍流强度超过10-16时,混频效率趋近零.建立了大气湍流下带跟踪误差的光混频效率及误码率的数学模型,并计算了不同情况下的混频效率.在跟踪误差小于2 μrad时大气湍流是混频效率的主要影响因素,当跟踪误差继续增大时跟踪误差起主导作用.根据传统相干光通信系统参量取值估算得最大混频效率约为67.8%,当误码率为10-9时系统接收灵敏度为17 photon/bit.

In the free space coherent optical communication system of satellite-ground link,atmosphere turbulence and tracking error will affect the mixing efficiency and the bit error rate.According to the mixing efficiency formula,both the relationship between system mixing efficiency and atmosphere turbulence intensity and the relationship between system mixing efficiency and tracking error were derived and simulatied.The results show that the mixing efficiency will decrease with the increasing of tracking error and atmosphere turbulence intensity.When the tracking error is greater than 12 μrad or turbulence intensity exceeds 10-16,the mixing efficiency is close to 0.An optical mixing efficiency model and a bit error rate model were built in atmosphere turbulence with tracking error,and the homodyne efficiency with different conditions was calculated.Atmosphere is the significant factor of mixing efficiency when tracking error is less than 2 μrad.Then,the tracking error will be as the leading factor with it increasing.According to the reference values of traditional coherent communication system,the maximum of mixing efficiency is about 67.8%,and the system receiving sensitivity is 17 photon/bit when the error rate is 10-9.