以加载QPSK调制信号的轨道角动量(OAM)光束为传输载波, 以多个相位屏模拟大气湍流, 研究不同大气湍流强度下OAM复用态的串扰情况。通过对复用光束光强和相位研究, 得出在OAM复用态光强受到湍流影响时会发生明显的闪烁现象, 光功率分散, 相位发生旋转弯曲, 且湍流强度越大, 受到的影响越大。选用螺旋谱分析不同湍流强度下各OAM复用态之间的弥散程度, 当大气湍流强度增加时, OAM态之间的弥散程度增加, 且较强湍流会导致OAM复用态失真。同时, 考虑OAM复用态之间的模式串扰以及每路携带信息的OAM态因大气信道引起的混合噪声而造成的码间干扰, 对比研究了不同大气湍流强度下系统误码率随传输距离的变化, 结果表明: 系统误码率随传输距离的增长而增大, 强湍流之下光束误码率会随着传输距离增长到一定程度后趋于平稳, 弱湍流之下光束误码率会随着传输距离的增长而增大。

The orbital angular momentum(OAM) beam loaded with the QPSK modulated signal was used as the transmission carrier to research the crosstalk of OAM multiplexed state under different atmospheric turbulence intensity, atmospheric turbulence was simulated by several phase screens. The study of the intensity and phase of the beam showed that there was obvious flickering phenomenon, when the light intensity of OAM multiplexed state was affected by turbulence. The greater the turbulence intensity, the greater impact was. The spiral spectrum was used to analyze the OAM multiplexed state dispersion degree between different turbulence intensity. With the increase of turbulence intensity, dispersion degree between OAM states increased, and the strong turbulence led to the OAM multiplexed state beam distortion. Meanwhile, considering the mode crosstalk between OAM multiplexed state and the inter-symbol interference of OAM states of each carrying information by the mixed noise model caused by atmospheric channel. The bit error rate(BER) changing with propagation distance under different atmospheric turbulence intensity was comparatively studied. The results show that the system BER increases with the increase of the propagation distance. Under strong turbulence the error rate of the light beam tends to be stable as the transmission distance increases to some extent. Under the weak turbulence the error rate of the light beam increases with the increase of the transmission distance.