涡旋光纤的理论研究与设计

发布时间：2018-03-24 13:03

本文选题：轨道角动量　切入点：光学涡旋　出处：《北京交通大学》2017年硕士论文

【摘要】：光纤通信容量的需求日益增长,而标准单模光纤的传输容量受到了香农极限的限制,空分复用成为了一种有效提高光纤通信容量的方式。涡旋光束具有相位或偏振奇点,其波前相位是螺旋形状分布。作为具有相位奇点的一种涡旋光束,具有轨道角动量(OAM,Orbital angular momentum)的模式在理论上有无限多的正交基,利用其正交性作为复用机制,可以有效地提升光纤的传输容量。在光纤中稳定传输OAM模式需要解决光纤中模式简并的问题,即把同一标量LP模式组内的矢量模式进行简并分离,获得可以在光纤中长距离稳定传输的涡旋模式。本文针对光纤中矢量模式简并分离的问题,基于对阶跃型光纤结构、空气芯光纤结构和倒抛物线折射率分布结构这三种光纤模式特性的对比分析,提出了倒抛物线环形芯结构光纤,并对其进行了系统的分析。首先,综合分析了倒抛物线型结构的纤芯层参数对模式特性的影响,在一定范围内对于LP11模式组与LP21模式组来说,矢量模式的有效折射率会随着纤芯半径的减小而依次截止,模式间的有效折射率差会在纤芯半径趋于截止的临界值附近达到最大值。模式间的有效折射率差与纤芯的倒抛物线特征参数存在复杂的依赖关系。之后,在倒抛物线型纤芯结构的外侧增加了高折射率层和低折射率层,并分析了各个参数对模式特性的影响。得到的最优参数使得该光纤结构可以实现较大的有效折射率差,同时可以保证较大的有效模场面积。在波长为1550nm处,LP11模式组的有效折射率差最高可达到7.2×10-4,LP21模式组的有效折射率差可达到3.1×10-4,有效地实现了矢量模式的简并分离。最后,利用得到的倒抛物线环形芯光纤结构仿真生成了OAM光束,计算表明其纯度可达到0.982。本文的结论对涡旋光纤的设计及制造具有重要的指导意义。
[Abstract]:The demand for optical fiber communication capacity is increasing day by day, and the transmission capacity of standard single-mode fiber is limited by Shannon's limit. Space division multiplexing has become an effective way to increase the optical fiber communication capacity. The vortex beam has phase or polarization singularity. As a vortex beam with phase singularity, the mode with orbital angular momentum (OAM) has infinite orthogonal bases in theory, and its orthogonality is used as a multiplexing mechanism. The stable transmission of OAM mode in optical fiber needs to solve the problem of mode degeneracy, that is, to degenerate the vector mode in the same scalar LP mode group, and to separate the vector mode in the same scalar LP mode group. In this paper, the vector mode in fiber is degenerate and separated, and the structure of step fiber is used to solve the problem that the vector mode can be propagated over a long distance and stably in optical fiber. Comparing and analyzing the structure of air core fiber and the structure of inverted parabola refractive index distribution, the inverted parabola annular core structure fiber is proposed and systematically analyzed. The influence of the core layer parameters of inverted parabola structure on the mode characteristics is analyzed synthetically. For the LP11 mode group and the LP21 mode group, the effective refractive index of the vector mode will end with the decrease of the core radius within a certain range. The effective refractive index difference between modes will reach the maximum near the critical value when the core radius tends to close. There is a complex dependence between the effective refractive index difference between the modes and the characteristic parameters of the inverted parabola of the core. A high refractive index layer and a low refractive index layer are added to the outer side of the inverted parabola core structure, and the influence of each parameter on the mode characteristics is analyzed. The optimum parameters obtained make the fiber structure achieve a large effective refractive index difference. At the same time, the large effective mode field area can be guaranteed. The maximum effective refractive index difference of LP11 mode group at wavelength of 1550nm is 7.2 脳 10 ~ (-4) 渭 m LP21 mode group, and the effective refractive index difference of LP21 mode group can reach 3.1 脳 10 ~ (-4), which effectively realizes the degenerate separation of vector mode. The OAM beam is generated by the structure simulation of the inverted parabola ring core fiber. The calculation shows that the purity of the optical fiber can reach 0.982.The conclusion in this paper is of great significance for the design and manufacture of the vortex fiber.
【学位授予单位】：北京交通大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TN929.11;TN253

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