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基于广义的Huygens-Fresnel原理和非Kolmogorov谱模型,推导了无线光通信系统中径向分布部分相干高斯-谢尔模型阵列光束在非Kolmogorov大气湍流中传输时瑞利区间z_R和湍流距离z_T的解析表达式,对瑞利区间和湍流距离随湍流参量和光束参量的变化情况进行了数值分析.结果表明:不论是相干还是非相干合成,径向分布部分相干高斯-谢尔模型阵列光束的z_R和z_T均随湍流广义指数α的增大非单调变化,当α=3.11时,z_R和z_T取最小值,此时阵列光束扩展最大;相干合成比非相干合成的光束扩展要小,但其受湍流的影响更大;对于相干合成而言,径向分布半径r0越大,合成光束的z_R和z_T就越大,而非相干合成的z_R和z_T不受r0的影响;不论是相干还是非相干合成,阵列子光束数目对合成光束的z_R和z_T没有影响;当光束相干参量β足够小或波长λ足够大时,大气湍流对阵列光束z_R的影响可以忽略. 相似文献
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建立了超高斯光束的相干叠加的数学模型,对比了光束间距为1 cm、超高斯阶数为12条件下25束高斯光束相干叠加与非相干叠加时的光强分布,发现相干合成的峰值光强为非相干叠加的峰值光强的近10倍,且光束质量也得到大大提高,有利于提高能量的利用率。分析了多种条件下相干合成的光强分布特性,结果表明:随机相位差小于十分之一波长时,相位差的变化对相干合成效果影响不大;当超高斯阶数大于10时对相干合成的峰值光强影响较小;随着相干发射阵列光束间距的增大,相干合成光强迅速减小,光束质量变差。得到了传输距离分别为10 m,100 m,1 km和5 km下的光强分布,表明合成的峰值光强随着传输距离的增加而由小变大,最后随着传输距离的进一步增大而衰减。最后得到了不同传输距离处的环围功率比。 相似文献
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采用积分变换的技巧,推导出了径向分布高斯列阵光束通过湍流大气传输的二阶矩束宽和远场发散角的解析公式,并详细研究了大气湍流对光束扩展和方向性的影响.研究表明,相干合成情况下,子光束数N越小、径向分布半径r0越大,列阵光束扩展受湍流影响越小.相干较非相干合成时列阵光束的扩展小,但非相干合成时列阵光束扩展受湍流的影响比相干合成时的小.特别地,N足够小或r0足够大时,相干与非相干合成列阵光束的远场束宽相等.另一方面,还给出了相干和非相干合成径向分布高斯列阵
关键词:
径向分布高斯列阵光束
大气湍流
相干和非相干合成
二阶矩束宽 相似文献
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研究了湍流对离轴列阵高斯光束相干与非相干合成的影响.推导出了相干合成光束的传输方程.采用二阶矩束宽、桶中功率和参数β作为光束质量评价参数比较了离轴列阵高斯光束通过湍流大气的相干与非相干合成,并对主要结果给予了合理的物理解释.研究表明:一方面,不论是相干合成还是非相干合成,湍流都使得合成光束扩展、峰值光强下降,并且子光束数越多,合成光束受湍流影响就越小.另一方面,非相干合成光束较相干合成光束受到湍流的影响要小.
关键词:
相干与非相干合成
湍流大气
离轴列阵高斯光束 相似文献
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引入部分相干余弦-高斯光束,推导出部分相干余弦-高斯光束通过近轴ABCD光学系统的传输公式和M2因子,研究了部分相干余弦-高斯光束通过像散透镜的传输特性.结果表明,部分相干余弦-高斯光束的M2因子与部分相干余弦-高斯光束的空间相干参量和离心参量有关,但与透镜的像散系数无关.适当选取空间相干参量,离心参量或像散系数,在几何焦面处可得到类高斯、平顶和空心等不同的光强剖面,实现部分相干余弦-高斯光束的空间整形. 相似文献
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引入部分相干余弦-高斯光束,推导出部分相干余弦-高斯光束通过近轴ABCD光学系统的传输公式和M2因子,研究了部分相干余弦-高斯光束通过像散透镜的传输特性.结果表明,部分相干余弦-高斯光束的M2因子与部分相干余弦-高斯光束的空间相干参量和离心参量有关,但与透镜的像散系数无关.适当选取空间相干参量,离心参量或像散系数,在几何焦面处可得到类高斯、平顶和空心等不同的光强剖面,实现部分相干余弦-高斯光束的空间整形. 相似文献
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Analytical expressions for the effective radius of curvature, R, of Hermite–Gaussian (H–G) array beams propagating in free space for both coherent and incoherent combinations are derived. It is shown that for the two types of beam combination a minimum of the effective radius of curvature, Rmin, appears as the propagation distance z increases. For the coherent combination, R is larger than that for the incoherent combination. The position zmin where the effective radius of curvature reaches its minimum is further away from the source plane for the coherent combination than that for the incoherent combination. For the two types of beam combination, R and zmin increase with increasing beam number, increasing beam separation distance, increasing waist width, and decreasing beam order and wavelength. In particular, the R of single H–G beams is always smaller than that of H–G array beams; the R of Gaussian array beams is always larger than that of H–G array beams. 相似文献
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建立了矩形阵列高斯光束合成模型,采用数值模拟方法计算了光束间距、单元光束特性以及阵列结构等参数对非相干合成和同相位相干合成的远场峰值强度及光束质量的影响,描述了非同相位相干合成可能产生的结果,讨论了同轴与非同轴合成,相干与非相干合成的特点。结果表明:非相干和同相位相干合成时的光束质量随着单元光束的增多而变差,并且随着光束间距与单元光束束腰之比的增大而下降;而非同相位相干合成的结果较为复杂,可能产生完全相消干涉,合成光束“重心”离轴及束腰位置偏移等现象。分析认为:同轴合成可以获得最佳的光束质量,是值得采用的合成方式。此外,同轴相干合成优于非相干合成的充分条件是将单元光束之间的相位差控制在(-π/4,π/4)以内。 相似文献
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Yongzhong Li Liejia Qian Daquan Lu Dianyuan Fan Shuangchun Wen 《Optics & Laser Technology》2007,39(5):957-963
Beam combining of fiber array with hexagonal ring distribution is studied in detail. The theoretical analysis and numerical calculation results are given to illustrate the propagation properties of the resulting beam through free space. A comparison between the coherent and the incoherent case shows that high peak irradiance and good beam quality for coherent combining can be obtained in the far field. The effect of phase errors and the beam quality M2 factor are also studied. Results indicate that the element numbers should be increased to achieve high power and the space between adjacent elements should be reduced to maintain good beam quality, which is basically the same for both coherent and incoherent beam combining. 相似文献
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Analytical propagation expression of a radial Airy array beam in coherent and incoherent combination passing through paraxial ABCD system is derived, and used to investigate the effect of combination scheme, array orientation and initial phase of Airy beamlet on propagation dynamics of the resulting beam in free space, where optical spot array and vortex array with different shapes are also found, respectively. And then taking four-beamlet Airy array beam in same array orientation as an example, square optical spot array obtained in focal field can be used for simultaneous trapping multiple Rayleigh particles with relative refractive index larger than 1. The transverse gradient forces serving as restore forces tend to push particles at different initial positions to their individual optical spot center. The analysis of trapping stability indicates that larger input peak intensity of Airy beamlet and smaller particle size are benefit to trapping particle owing to many deeper potential wells. Vortex array produced by coherent combined Airy array beam in this paper is expected to be useful for simultaneous trapping microparticles with relative refractive index smaller than 1. 相似文献
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Propagation properties of off-axis Hermite--cosh--Gaussian beam combinations through a first-order optical system 下载免费PDF全文
Based on the Collins integral formula, the analytic expressions of propagation of
the coherent and the incoherent off-axis Hermite--cosh--Gaussian (HChG) beam
combinations with rectangular symmetry passing through a paraxial first-order
optical system are derived, and corresponding numerical examples are given and
analysed. The resulting beam quality is discussed in terms of power in the bucket
(PIB). The study suggests that the resulting beam cannot keep the initial intensity
shape during the propagation and the beam quality for coherent mode is not always
better than that for incoherent mode. Reviewing the numerical simulations of
Gaussian, Hermite--Gaussian (HG) and cosh--Gaussian (ChG) beam combinations
indicates that the Hermite polynomial exerts a chief influence on the irradiance
profile of composite beam and far field power concentration. 相似文献