实验研究了光轨道角动量(OAM)光束的短距离自由空间传输特性。在实验装置中使用数字微镜器件(DMD)产生 OAM光束, 传输距离为室内 0～50 m。在接收端使用空间光束模场分析仪测量传输后的 OAM光束光强分布, 实验研究了不同传输距离下 OAM光束的模场展宽效应, 并通过干涉法研究了传输对 OAM光束相位分布特性的影响。在接收端使用一个单路 Sagnac干涉仪对传输后 OAM光束的各阶模式进行分离检测, 实验研究了不同距离下传输导致的 OAM光束能量从产生的模式向临近各阶模式的迁移再分配。使用局部加热的方法模拟较强的大气湍流扰动, 实验研究了较强湍流对 OAM光束模式特性的影响。实验结果表明, 在湍流扰动下, OAM光束的拓扑荷值越大传输后模式纯度的劣化越严重。

The short-distance free-space transmission characteristics of the optical orbital angular momentum (OAM) beam were experimentally studied. The transmission distance is 0～50 m indoors. A digital micromirror device (DMD) was used in the experimental setup to generate the OAM beam. At the receiver, a spatial beam analyzer was used to measure the intensity pattern of the OAM beam. The beam broadening effect of the OAM beam at different trans- mission distances was studied. The phase pattern of the OAM beam was studied by the interferometric method. At the receiver, a single path Sagnac interferometer (SPSI) was used to separate and detect the intensity of modes of the OAM beam. The effects of energy migration from the sending mode to the sideband modes of the OAM beam were studied. A heater was used to generate the strong turbulence to simulate the influence to the OAM beam mode transmission characteristics.The experimental results show that the OAM beam with large mode topological charge has more deterioration of the mode purity after transmission in the strong turbulence.