光纤和硅基波导的3模复用解复用器的研究

发布时间：2018-04-06 05:41

本文选题：模式复用　切入点：锥形光纤　出处：《北京交通大学》2017年硕士论文

【摘要】：模分复用系统利用少模光纤来应对单模光纤面临的香农极限问题,将模式作为传输信道,能够成倍的增加光通信系统的传输容量。模式复用解复用器作为模分复用系统的重要器件,能够实现基模与高阶模的相互转换,同时将多个模式复用/分离进入一个或多个波导。本文结合国内外的研究现状,基于理论分析及仿真结果,分别对光纤型和波导型的模式复用解复用器进行研究。本文的主要工作如下:(1)从光纤和矩形波导出发,研究光在两种不同结构波导中传输的模式特性,并对波导中传输的模式进行仿真和分析。同时对波导中传输的模式正交性以及利用耦合模理论对波导间各个模式发生耦合及转换进行了详细的推导。(2)介绍一种锥形光纤型三模式(解)复用器,它能够同时实现模式转换以及模式(解)复用。利用COMSOL软件对该器件进行仿真分析,得到该器件分别实现模式复用和解复用时输入端及输出端的光场分布图。提出通过计算复用器输出端光场与标准模式场的重叠积分值以及解复用器各个输出端口光功率比值得到该器件实现模式复用/解复用的效率,并且分析了改变器件结构对实现模式(解)复用效率的影响。结果表明:当复用器拉锥长度为3.88 cm时实现模式复用的效果最好,输出端的三个模斑与其对应的标准模式场的相似度分别为0.8991、0.6834、0.5080;改变拉锥长度对LP01模向LP01、LP11a模的转换没有太大的影响,但是对LP01模向LP11b模的转换影响较大;解复用器长度为3.8931 cm时实现解复用的效果最好,各个模式经过转换后在输出端对应的端口光强为最大。(3)利用FDTD(Finite Difference Time Domain)算法分别对条形波导和脊型波导两种结构下的模分复用解复用器进行设计及仿真,得到了器件内实现模式复用解复用时的光场传输图,通过计算解复用器输出端各个端口输出的能量比值得到损耗以及串扰,并且讨论了改变器件结构及工作波长对串扰的影响。结果表明:两种结构下的模分复用解复用器的损耗均小于1dB,串扰均低于-20dB;在1.55μm波长处满足相位匹配条件,模式转换的效率最高,串扰也最小;当耦合区域内波导间隙增大,串扰最低点的波长会向着大于1.55μm处移动。根据仿真结果,对条形波导模分复用解复用器进行了 SOI硅片的工艺制作、测试及分析。最后将两种结构下的器件进行对比,发现脊型波导实现模式转换时所需要的耦合长度小于条形波导,但是脊型波导结构下的模分复用解复用器的串扰要高于条形波导结构。
[Abstract]:Mode division multiplexing system uses small mode optical fiber to deal with the Shannon limit problem faced by single mode optical fiber. Using mode as transmission channel, the transmission capacity of optical communication system can be increased exponentially.As an important device in mode division multiplexing system, mode multiplexing demultiplexer can realize the interconversion between the base mode and the higher order mode, and at the same time, multiple modes are multiplexed / separated into one or more waveguides.In this paper, based on the theoretical analysis and simulation results, the mode multiplexing demultiplexer based on optical fiber and waveguide is studied in combination with the current research situation at home and abroad.The main work of this paper is as follows: (1) based on optical fiber and rectangular waveguide, the mode characteristics of light propagation in two waveguides with different structures are studied, and the modes of transmission in waveguides are simulated and analyzed.At the same time, the mode orthogonality of transmission in waveguide and the coupling and conversion of each mode between waveguides are deduced in detail by using coupling mode theory. A tapered fiber type three-mode (demultiplexer) is introduced.It can realize both pattern conversion and pattern demultiplexing.The COMSOL software is used to simulate and analyze the device, and the light field distribution diagram of the input and output end of the device for mode multiplexing and demultiplexing is obtained respectively.It is proposed that the efficiency of mode multiplexing / demultiplexing can be obtained by calculating the overlapping integral between the output field and the standard mode field of the multiplexer and the optical power ratio of each output port of the demultiplexer.The effect of changing the device structure on the efficiency of mode demultiplexing is also analyzed.The results show that the mode reuse is the best when the length of the multiplexer is 3.88 cm.The similarity between the three speckles at the output end and their corresponding standard mode fields is 0.8991U 0.6834n0.5080.The change of the taper length has no great effect on the conversion from LP01 mode to LP01 LP11a mode, but has a great effect on the conversion from LP01 mode to LP11b mode.When the demultiplexer length is 3.8931 cm, the demultiplexing effect is the best.After each mode is converted, the corresponding port light intensity at the output end is maximum. The FDTD(Finite Difference Time domain algorithm is used to design and simulate the mode division multiplexing demultiplexer with two kinds of structures, stripe waveguide and ridge waveguide, respectively.The optical field transmission diagram of demultiplexing in the device is obtained. The loss and crosstalk are obtained by calculating the energy ratio of the output ports of the demultiplexer. The effects of changing the device structure and the working wavelength on the crosstalk are discussed.The results show that the loss of the demultiplexer is less than 1 dB and the crosstalk is lower than -20 dB, the mode conversion efficiency is the highest and the crosstalk is minimum when the wavelength is 1.55 渭 m.The wavelength at the lowest point of crosstalk will move towards more than 1.55 渭 m.According to the simulation results, the fabrication, test and analysis of the SOI wafer for the strip waveguide mode division multiplexing demultiplexer are carried out.Finally, it is found that the coupling length of the ridge waveguide is smaller than that of the strip waveguide, but the crosstalk of the demultiplexer is higher than that of the strip waveguide.
【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

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