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摘要: 本文采用分步相位屏方法来仿真椭圆涡旋光束在海洋中的实际传输情况,并对椭圆涡旋光束在海洋湍流中的传输光强和闪烁因子进行了仿真。研究发现,椭圆涡旋光束在海洋传输过程中,光斑会发生明显的旋转,同时光斑会产生暗核且暗核个数与光束的拓扑荷数相等。一个拓扑荷数为m的相位奇点会分裂成m个拓扑荷数为1的相位奇点,并且海洋湍流越强,光斑受到的干扰越严重。研究还发现,在较弱的海洋湍流中,随着传输距离的增加,椭圆涡旋光束的闪烁因子会低于高斯光束和涡旋光束的闪烁因子,而且在远距离处拓扑荷数越大闪烁因子降低越明显,同时也发现,传播一段距离后涡旋光束的闪烁因子会低于高斯光束的闪烁因子。在较强湍流中,椭圆涡旋光束的闪烁因子会交叠在一起。对于不同强度的海洋湍流,随着均方温度耗散率的增大,椭圆涡旋光束的轴上点闪烁因子也增大。在同一传输距离处,束腰宽度越小的椭圆涡旋光束闪烁因子越小。Abstract: The propagation and scintillation index of elliptical vortex beams propagating in oceanic turbulence were simulated using a step-by-step phase screen method.It was found that the beam spot rotates significantly when an elliptical vortex beam transmits through the oceanic turbulence and dark cores are produced, whose number is equal to the topological charge of the beam. A phase singularity with the topological charge m splits into m phase singularities with 1 unit of topological charge and as oceanic turbulence is made stronger, the beam spot experiences greater distortion. It was also found that with an increment in propagation distance, the scintillation index of the elliptical vortex beam is lower than that of the Gaussian beam and the vortex beam in weaker ocean turbulence.Likewise, it was found that the scintillation index reduces more evidently with a larger topological charge when the elliptical vortex beam propagates over a longer distance and that the scintillation index of the vortex beam is lower than that of Gaussian beam after a given transmission distance. In stronger oceanic turbulence, the scintillation indices of the elliptical vortex beams overlap. For oceanic turbulence of different strength, the on-axis scintillation index of the elliptical vortex beam increases with an increment in the rate of dissipation of the mean-square temperature. At a constant propagation distance, a smaller elliptical vortex beam waist width corresponds to a smaller scintillation index.
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图 1 m=2时不同椭球率的椭圆涡旋光束的光强分布和相应的相位分布,其中(a)、(b)、(c)的椭球率分别为1、2、5/6,(d)、(e)、(f)为其相应的相位分布
Figure 1. Intensity distributions and phase distributions of elliptical vortex beams with m=2 under different ellipsoid ratios, where (a), (b) and (c) have ellipsoid ratios of 1, 2 and 5/6 respectively, and (d), (e) and (f) are corresponding phase distributions
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