Theoretical and experimental investigation on the performance of heterodyne detection system affected by the beam mode of partially coherent beams in atmospheric turbulence

The mathematical model of the effect of beam mode (It contains fundamental mode and other higher orders mode) on the heterodyne efficiency of heterodyne detection system was established, and the effect of beam mode on the performance of heterodyne detection system was theoretically investigated for partially coherent GSM beam in slant atmospheric turbulence conditions. The results show that the inner scale of turbulence has a greater effect on the heterodyne efficiency and normalized M2. (It is used to evaluate beam quality.) The larger the mode orders are, the lower the proportion of the fundamental mode and heterodyne efficiency are. Finally, the changes of beam mode caused by turbulence was obtained by a heterodyne detection system in an experiment investigating optical communication at a distance of 1.3 km. The results of this experiment verified that the mode orders are increased by turbulence effect and the beam mode increases with an increase in the turbulence intensity, resulting in a decrease in the corresponding the peak-to-peak value of the IF signal.