Crosstalk analysis of orbital angular momentum-multiplexed state under atmospheric turbulence

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.