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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.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 Laguerre-Gaussian 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 multi-phase 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.
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Keywords:
- atmospheric turbulence /
- focus vortex beam /
- orbital angular momentum crosstalk /
- multi-phase screen method
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图 1 聚焦LG光束真空中传输不同距离的光强分布
Fig. 1. Intensity distribution of the focused LG beam propagating at different distances in vacuum
图 2 LG光束(a)、聚焦LG光束(b)在湍流中传输不同距离时的螺旋谱分布
Fig. 2. Spiral spectrum distribution of LG beam (a) and focused LG beam (b) at different distances in turbulence
图 3 不同波束参数下LG、聚焦LG光束在湍流中的接收功率 (a)波长; (b)拓扑荷数; (c)束腰半径; (d)接收孔径
Fig. 3. Receiving power of LG and focused LG beams in turbulence under different beam parameters: (a) Wavelength; (b) topological charge; (c) waist radius; (d) receiving aperture.
图 4 不同湍流参数下LG、聚焦LG光束在湍流中的接收功率 (a)距离; (b)湍流强度; (c)湍流内尺度; (d)各向异性系数
Fig. 4. Receiving power of LG and focused LG beams in turbulence under different turbulence parameters: (a) Distance; (b) turbulence intensity; (c) turbulence internal scale; (d) anisotropy coefficient.
图 5 多相位屏法模拟聚焦LG光束在湍流中传输示意图
Fig. 5. Multiphase screen method to simulate the propagation of focused LG beam in turbulence
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[1] Gibson G, Courtial J, Padgett M, Vasnetsov M, Pas'ko V, Barnett S, Franke-Arnold S 2004 Opt. Express 12 5448
Google Scholar
[2] Dikmelik Y, Davidson F M 2005 Appl. Opt. 44 4946
Google Scholar
[3] Anguita J A, Neifeld M A, Vasic B V 2008 Appl. Opt. 47 2414
Google Scholar
[4] Dogariu A, Amarande S 2003 Opt. Lett. 28 10
Google Scholar
[5] Tyler G A, Boyd R W 2009 Opt. Lett. 34 142
Google Scholar
[6] Ji X L, Lv B D 2005 Opt. Commun. 251 231
Google Scholar
[7] 黎芳, 唐华, 江月松, 欧军 2011 物理学报 60 014204
Google Scholar
Li F, Tang H, Jiang Y S, Ou J 2011 Acta Phys. Sin. 60 014204
Google Scholar
[8] Cheng M, Zhang Y, Zhu Y, Gao J, Dan W, Hu Z 2015 Opt. Laser Tech. 67 20
Google Scholar
[9] 柯熙政, 谌娟, 杨一明 2014 物理学报 63 150301
Google Scholar
Ke X Z, Chen J, Yang Y M 2014 Acta Phys. Sin. 63 150301
Google Scholar
[10] Zhu Y, Zhang Y, Li Y, Hu Z D 2016 Int. J. Mod. Phys. B 30 1650193
Google Scholar
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Google Scholar
[12] X uY, Zhang Y X 2019 Opt. Commun. 438 90
Google Scholar
[13] 仓吉, 张逸新, 徐建才 2009 光子学报 38 2122
Cang J, Zhang Y X, Xu J C 2009 Acta. Phot. Sin. 38 2122
[14] 吴逢铁, 马亮, 张前安, 郑维涛, 蒲继雄 2012 物理学报 61 014202
Google Scholar
Wu F T, Ma L, Zhang Q A, Zheng W T, Pu J X 2012 Acta Phys. Sin. 61 014202
Google Scholar
[15] 罗亚梅, 高曾辉, 唐碧华, 吕百达 2014 物理学报 15 154201
Google Scholar
Luo Y M, Gao Z H, Tang B H, Lv B D 2014 Acta Phys. Sin. 15 154201
Google Scholar
[16] 仓吉, 张逸新 2009 光子学报 38 1277
Cang J, Zhang Y X 2009 Acta. Phot. Sin. 38 1277
[17] Torner L, Torres J, Carrasco S 2005 Opt. Express 13 873
Google Scholar
[18] Zhang T, Liu Y D, Wang J, Liu P, Yang Y 2016 Opt. Express 24 20507
Google Scholar
[19] Toselli I 2014 J. Opt. Soc. Am. A. Opt. Image Sci. Vis. 31 1868
Google Scholar
[20] Wu G H, Tong C M, Cheng M J, Peng P 2016 Chin. Opt. Lett. 14 080102
Google Scholar
[21] Xu J, Gao J, Zhu Y, Zhang L, Zhang Y 2014 Optik 125 280
Google Scholar
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