Hui Xiaonnan, Zheng Shilie, Zhang Weite, Jin Xiaofeng, Chi Hao, Zhang Xianmin
Opt Express. 2016 Mar 7;24(5):5423-5430. doi: 10.1364/OE.24.005423.
The topological charge of an electromagnetic vortex beam depends on its wavefront helicity. For mixed vortex beams composed of several different coaxial vortices, it is significant to investigate the local topological charges. Fourier transform based methods are restrained by the uncertainty principle and cannot achieve high angular resolution and mode resolution simultaneously. In this paper, an analysis method for local topological charges of vortex beams is presented based on the empirical mode decomposition (EMD). From EMD, the intrinsic mode functions (IMFs) can be obtained to construct the bases of the electromagnetic wave, and each local topological charge can be respectively defined. With this method the local value achieves high resolution of both azimuth angle and topological charge, meanwhile the amplitudes of each orbital angular momentum (OAM) modes are presented as well. The simulation and experimental results confirm the validity of the EMD based method.
电磁涡旋光束的拓扑电荷取决于其波前螺旋度。对于由几个不同同轴涡旋组成的混合涡旋光束，研究局部拓扑电荷具有重要意义。基于傅里叶变换的方法受到不确定性原理的限制，无法同时实现高角分辨率和模式分辨率。本文提出了一种基于经验模态分解（EMD）的涡旋光束局部拓扑电荷分析方法。通过EMD，可以获得本征模态函数（IMF）来构建电磁波的基函数，并分别定义每个局部拓扑电荷。利用该方法，局部值在方位角和拓扑电荷上都实现了高分辨率，同时还给出了每个轨道角动量（OAM）模式的幅度。仿真和实验结果证实了基于EMD方法的有效性。
