Wuhan National Laboratory for Optoelectronics, School of Optical and Electronic Information, Huazhong University of Science and Technology, Wuhan, 430074, Hubei, China.
Shenzhen Institute of Huazhong University of Science and Technology, Shenzhen, 518000, China.
Sci Rep. 2017 Jun 21;7(1):3990. doi: 10.1038/s41598-017-04380-7.
Orbital angular momentum (OAM) modes are another mode basis to represent spatial modes. There have been increasing interests in exploiting OAM modes in specialty fibres. In this paper, we present a comprehensive characterisation of OAM modes in conventional graded-index multimode fibre (MMF). 1) We synthesise the circularly polarized OAM modes by properly combining two fold degenerate cylindrical vector modes (eigenmodes) and analyse the total angular momentum, i.e. spin angular momentum and orbital angular momentum. 2) We divide all the OAM modes of the conventional graded-index MMF into 10 OAM mode groups with effective refractive index differences between different mode groups above 10 enabling low-level inter-group crosstalk. 3) We study the chromatic dispersion, differential group delay, effective mode area, and nonlinearity for each OAM mode group over a wide wavelength ranging from 1520 to 1630 nm covering the whole C band and L band. 4) We discuss the performance tolerance to fibre ellipticity and bending. 5) We further address the robustness of performance against fibre perturbations including the core size, index contrast and the imperfect index profile of the practically fabricated MMFs. The obtained results may provide theoretical basis for further space-division multiplexing applications employing OAM modes in conventional graded-index MMF.
轨道角动量 (OAM) 模式是另一种表示空间模式的模式基础。在特种光纤中利用 OAM 模式的兴趣日益增加。在本文中，我们全面表征了常规渐变折射率多模光纤 (MMF)中的 OAM 模式。1）我们通过适当组合两个折叠简并圆柱矢量模式（本征模式）来合成圆偏振 OAM 模式，并分析总角动量，即自旋角动量和轨道角动量。2）我们将常规渐变折射率 MMF 中的所有 OAM 模式分为 10 个 OAM 模式组，不同模式组之间的有效折射率差大于 10，从而实现低水平的组间串扰。3）我们研究了每个 OAM 模式组在从 1520nm 到 1630nm 的宽波长范围内的色散、差分群延迟、有效模式面积和非线性，涵盖了整个 C 波段和 L 波段。4）我们讨论了对光纤椭圆度和弯曲的性能容限。5）我们进一步讨论了性能对光纤扰动的鲁棒性，包括芯径、折射率对比度和实际制造的 MMF 的不完善折射率分布。所得到的结果可能为在常规渐变折射率 MMF 中利用 OAM 模式进行进一步的空分复用应用提供理论基础。
