【摘要】 携带轨道角动量的涡旋光束作为传输信息的载体能有效提高信息传输效率,然而在传输过程中受大气湍流影响轨道角动量会发生串扰.基于螺旋谱分析理论,推导得到了聚焦拉盖尔高斯光束在各向异性大气湍流中传输时的螺旋谱解析表达式,并对比分析不同湍流和光束参数对聚焦与非聚焦拉盖尔高斯光束接收功率的影响,最后利用多相位屏法进行模拟验证.结果表明:随着传输距离、湍流强度、拓扑荷数的增大以及湍流内尺度、光束波长的减小,接收功率减小,轨道角动量串扰增大;接收孔径到达一定值时对轨道角动量串扰的影响非常小;聚焦光束比非聚焦光束的轨道角动量串扰要小.这些结果将对提高自由空间光通信的质量有一定意义.更多还原

【Abstract】 Vortex beams with orbital angular momenta with different mode numbers are mutually orthogonal to each other, which makes it possible to improve the information transmission efficiency in space optical communication system. Nevertheless, the implementation of this strategy is limited by the orbital angular momentum crosstalk caused by atmospheric turbulence. Focused Laguerre-Gaussian vortex beams are less affected by atmospheric turbulence due to their lager intensity density. Consequently, focused LaguerreGaussian vortex beams can be used as the carriers to reduce the orbit angular momentum crosstalk and increase the channel capacity of information transmission. In this paper, based on the spiral spectrum analysis theory,the analytical expression of spiral spectrum of focused Laguerre Gaussian beam propagating in anisotropic atmospheric turbulence is derived. The influences of turbulence and beam parameters on the received power of focused and unfocused Laguerre Gaussian beam are investigated via numerical calculations. Finally, the multiphase screen method is used for verificating the simulation. The research findings are as follows. First, with the increase of transmission distance, turbulence intensity and topological charge, the receiving power of orbital angular momentum decreases, that is, the orbital angular momentum crosstalk turns more serious. Second, the larger the turbulence inner-scale, anisotropy index and beam wavelength are, the smaller the orbital angular momentum crosstalk is. Third, when the receiving aperture reaches a certain value, its influence on the orbit angular momentum crosstalk is very small. Fourth, different parameters have different effects on crosstalk, and the orbit angular momentum crosstalk of the focused vortex beam is less than that of the unfocused vortex beam. Therefore, in the vortex optical communication, the focused vortex beams can be used as the signal light to reduce the crosstalk between the orbit angular momentum modes, and thus improving the communication quality. These results have some theoretical reference values for reducing crosstalk in free-space optical communication.更多还原