光束偏移对轨道角动量信息传输系统的影响

研究了拉盖尔-高斯光束轨道角动量信息传输系统在未对准时轨道角动量谱的变化.采用数学推导和数值仿真的方法，得到在任意传播距离处，接收系统轴与光轴分别出现横向偏移、角向倾斜，以及两者同时存在时光束的表达式，并分析和比较了几种情况下螺旋谱的变化特征.研究表明，两种偏移量的增加会增加螺旋谱的弥散，而弥散现象与两者偏移方向无关.在传输起点，横向偏移和角向倾斜均会引起螺旋谱的对称弥散.然而，随着传输距离的增加，横向偏移时螺旋谱的弥散程度逐渐减小，而角向倾斜时螺旋谱弥散程度逐渐增加.角向倾斜时螺旋谱始终保持对称分布，而横向偏移引起的弥散螺旋谱呈非对称分布，且经过一定距离后得到稳定的螺旋谱分布.当两者同时存在时，光束螺旋谱的弥散程度随着距离的增加逐渐增加到一个最大值，之后平缓地下降.并进一步得出了横向偏移与角向倾斜对弥散度的影响是不独立的.关键词：拉盖尔-高斯光束螺旋谱横向偏移角向倾斜

Influences of misaligned optical beam carrying orbital angular momentum on the information transfer

An analysis of the orbital angular momentum of an optical beam misaligned with respect to a receiver during propagation in the information transfer is investigated. The analytical expressions of Laguerre-Gaussian beams laterally displaced， angularly deflected and simultaneously misaligned in both ways are derived, and the features of the spiral spectrum in these cases are studied. It is shown that both parallel displacement and angular tilt will lead to the spread of the spiral spectrum, which is independent of the misalign direction. The larger the misalign, the more serious the spectrum spread. However, with the increasing of the propagation distance, the degree of the spread for the laterally displacement is decreasing gradually, while that for the angular tilt is increasing. In the angular tilt case, the spread of the spiral spectrum always keeps symmetric during propagation, while in the case of lateral displacement, the spiral spectrum is asymmetric, and goes to a stable state. The spiral spectrum is also investigated for the case with simulataneous lateral misalignment and angular tilt, and we conclude that the effects of both misaligns on the spectrum are related with one another.