带有螺旋相位分布的波束都具有轨道角动量(Orbital Angular Momentum, OAM), 其螺旋相位取决于OAM态拓扑荷数。理论分析了叠加涡旋光束的相位及光场分布, 然后将叠加态涡旋光束的相位分布图加载到空间光调制器上产生了多态涡旋光束,讨论了不同拓扑荷数叠加时光场衍射图的分布情况。实验结果表明, 叠加态的涡旋光束光场衍射图随着叠加光束拓扑荷数的正负以及数值而呈一定规律性变化, 即当叠加的两束光拓扑荷数为异号时, 衍射产生的光斑数为两束光拓扑荷数绝对值之和; 当叠加的两束光拓扑荷数为同号时, 衍射产生的光斑数为两束光拓扑荷数之差的绝对值。通过此性质可以检验涡旋光束的拓扑荷数, 为叠加涡旋光束在自由空间光复用通信系统的拓扑荷数检测提供了新的方法。

The beam with helical phase distribution has Orbital Angular Momentum(OAM), whose helical phase depends on the topological charge of OAM state. The phase distribution and the light field distribution of the superposition vortex beams were analyzed theoretically, and then the phase distribution pattern was loaded onto the spatial light modulator to generate the superposition vortex beams. The light of the field diffraction pattern with different topological charges superposition was discussed. The experimental results show that the optical field diffraction pattern of the superposition state varies regularly with the positive and negative values of the superposition of the beam topological charge and the numerical value, namely when the superposition of two optical topological charges is different symbol, the number of diffraction spots is the sum of the absolute values of the two optical topological charges; when the superposition of two optical topological charges is same symbol, the number of diffraction spots is the absolute value of the difference between the two optical topological charges. By this property, the topological charge of the vortex beam can be detected, which provides a new method for the topological charge detection of the superposed vortex beams in the free space optical communication system.