具有多层结构的轨道角动量模式光纤的模式特性研究

发布时间：2018-10-18 12:51

【摘要】：携带轨道角动量的光束拥有许多奇异的特性,比如:螺旋型的波前相位和圆环型的光强分布等,基于这些特性,携带轨道角动量的光束在许多领域都有巨大的应用价值。在光通信方面,光波的轨道角动量被认为是除了幅度、相位、波长和偏振外的一种新的调制自由度,有望为光纤信道复用提供一个新的纬度。本论文在结合多种轨道角动量模式传输波导的研究分析下,设计了一种具有多层结构的轨道角动量模式光纤,并利用一款有限元仿真软件COMSOL Multiphysics对其进了行模拟仿真,验证了轨道角动量模式在该多层结构的轨道角动量模式光纤中的稳定性及走离长度。取得以下工作成果:1)通过研究该多层结构的轨道角动量模式光纤的模式有效折射率之差,矢量模的2π走离长度和10ps走离长度,发现:该多层结构的轨道角动量模式光纤能够支持比较多的轨道角动量模式稳定传输,至少支持60个轨道角动量模式,拓扑荷数可从1到15。同时,部分模式的10ps走离长度能够达到10km以上。2)通过研究该光纤的第四层介质的厚度和折射率与模式有效折射率之差,2π走离长度和10ps走离长度的关系,发现:当增大第四层介质的厚度时,会增加所支持的轨道角动量模式的数量;当增大第四层介质的折射率时,会增加所支持的轨道角动量模式的数量,而且会增大模式有效折射率之差,提高轨道角动量模式的稳定性。但是伴随着第四层介质的厚度和折射率的增大的同时,大多数模式的2π走离长度和10ps走离长度也会减小。3)通过研究基于该多层结构的轨道角动量模式光纤的定向耦合器,发现:当两个光纤的第四层之间的间距为1μm时,模式HE_(10,1)、EH_(8,1)、HE_(11,1)和EH_(9,1)的耦合长度都小于6mm,当间距增大时,模式的耦合长度呈增大的趋势。总的来说,本文提出并研究了一种新型多层结构的轨道角动量模式光纤,发现具有五层结构的光纤能够支持60个轨道角动量模式的稳定传输,并具有良好的模式稳定性指标。该结果比参考文献中的三层结构的光纤多支持24个轨道角动量模式,这表明该五层结构的轨道角动量模式光纤对于模式复用更为有利。
[Abstract]:Beams carrying orbital angular momentum have many strange properties, such as helical wavefront phase and toroidal intensity distribution. Based on these characteristics, orbital angular momentum beams have great application value in many fields. In optical communication, orbital angular momentum of optical wave is considered as a new modulation degree of freedom besides amplitude, phase, wavelength and polarization, which is expected to provide a new latitude for fiber channel multiplexing. In this paper, a kind of orbital angular momentum mode optical fiber with multilayer structure is designed, and a finite element simulation software COMSOL Multiphysics is used to simulate it. The stability and walking length of orbital angular momentum mode in the multilayer orbital angular momentum mode fiber are verified. The results are as follows: 1) the difference of the effective refractive index of the orbital angular momentum mode fiber, the 2 蟺 walk length of vector mode and the 10ps walk length of the multilayer structure are studied. It is found that the multilayer orbital angular momentum mode fiber can support more stable orbital angular momentum modes, at least 60 orbital angular momentum modes, and the topological charge number can range from 1 to 15. At the same time, the 10ps walk length of partial mode can reach above 10km. 2) by studying the difference between the thickness and refractive index of the fourth layer of the fiber and the effective refractive index of the mode, the relationship between the walk length of 2 蟺 and the walk length of 10ps is studied. It is found that when the thickness of the fourth layer medium is increased, the number of supported orbital angular momentum modes will be increased, and when the refractive index of the fourth layer medium is increased, the number of supported orbital angular momentum modes will increase. Moreover, the difference of the effective refractive index of the mode will be increased, and the stability of the orbital angular momentum mode will be improved. However, with the increase of the thickness and refractive index of the fourth layer medium, the 2 蟺 walk length and the 10ps walk length of most modes will also decrease. 3) the directional coupler of orbital angular momentum mode fiber based on the multilayer structure is studied. It is found that when the distance between the fourth layers of the two fibers is 1 渭 m, the coupling lengths of the mode HE_ (10 ~ 1), EH_ (8 ~ 1), HE_ (11 ~ 1) and EH_ (9 ~ 1) are all less than 6 mm. When the spacing increases, the coupling length of the mode increases. In general, a novel multilayer orbital angular momentum mode fiber is proposed and studied. It is found that the fiber with five layers structure can support the stable transmission of 60 orbital angular momentum modes and has good stability index. The results support 24 orbital angular momentum modes more than the three-layer optical fibers in the reference, which indicates that the orbital angular momentum mode fibers with this five-layer structure are more favorable for mode multiplexing.
【学位授予单位】：深圳大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TN253

【参考文献】