可调谐的铌酸锂光波导模分复用器研究

发布时间：2018-09-01 07:51

【摘要】：随着互联网技术的发展,人们对光通信系统传输容量的需求越来越大,但传统单模光纤传输技术因为容量限制问题最终将无法满足人们的需求。而模分复用技术引入了空间正交模式作为一个新的自由度,能够在很大程度上提高光通信系统的传输容量,而备受关注。模分复用器/解复用器是模分复用系统的重要组成部分,其中基于平面光波导结构的模分复用器/解复用器则具有结构灵活,材料众多,易于实现可调谐特性,易于与光纤耦合等优点。一方面,可调谐特性可以调整器件的耦合中心波长,降低器件的制作难度。另一方面,可调谐特性还可用于实现模式开关或模式路由。目前,光波导器件的调谐方式主要有利用热光效应实现的热光调谐和利用电光效应实现的电光调谐。由于热光调谐的速度较慢,因此在高速应用的情况下,电光调谐是一个不错的选择。为实现电光调谐特性,应采用电光材料来制作波导器件,而电光系数较大的铌酸锂晶体材料不失为最好的选择。当前,铌酸锂光波导的制作工艺主要有钛扩散和退火质子交换。其中退火质子交换工艺可以通过匹配退火和质子交换参数来调整波导的折射率,其可控因素更多。本论文提出采用退火质子交换工艺来实现一种基于非对称定向耦合器结构的可调谐的铌酸锂光波导模分复用器,由于该器件在电场作用下,其工作的中心波长及相应的耦合效率均可以基于电光效应进行调谐,因此该器件除了作为普通的模分复用器使用外,更重要的是可以用作可调谐的宽带模式开关,从而极大地增大了该器件应用的灵活性。论文首先采用有效折射率分析方法,结合MATLAB仿真软件求解出铌酸锂光波导的色散曲线,继而得出理论上可满足相位匹配条件的单模波导和双模波导的尺寸范围。在此基础上,利用退火质子交换工艺来制作铌酸锂单模以及双模光波导,使用棱镜耦合仪来测量波导的折射率,根据测量结果分析了质子交换和退火对波导折射率的影响,并得到实验上大致满足相位匹配条件的单模波导和双模波导尺寸。进一步地,根据以上分析,设计器件的大致结构,并采用BPM仿真软件对波导非对称定向耦合器结构进行仿真分析,从而得出理论上可达到完全耦合时器件的耦合间距、耦合长度以及其他参数。结合以上分析,设计合理的光波导结构以及相应电极结构参数。其次,根据以上分析设计的参数制作了相应的波导及电极掩膜版,并研究了交换及退火参数对相位匹配条件的影响,同时也研究了低损耗光波导的制作工艺及高质量电极的制作工艺。接下来,根据这些工艺参数研制了本论文所提出的可调谐的铌酸锂光波导模分复用器。最后,对制作成功的器件进行了测试及分析。主要测试的参数包括器件的传输光谱、近场输出以及插入损耗等。测试结果表明器件不仅实现了模分复用器的功能,更实现了耦合效率及中心波长均可调谐的宽带模式开关功能。其中电光调谐的灵敏度约为5 nm/V,且当工作波长为1562 nm,调谐电压为9 V时,隔离度可达27 dB。
[Abstract]:With the development of Internet technology, the demand for transmission capacity of optical communication system is increasing, but the traditional single-mode fiber transmission technology can not meet the demand of people because of the capacity limitation. The spatial orthogonal mode is introduced into the mode division multiplexing technology as a new degree of freedom, which can greatly improve the optical communication. The mode division multiplexer/demultiplexer is an important part of the mode division multiplexing system, in which the mode division multiplexer/demultiplexer based on planar optical waveguide structure has many advantages, such as flexible structure, numerous materials, easy to realize tunable characteristics, easy to couple with optical fiber and so on. On the other hand, tunable characteristics can also be used to realize mode switching or mode routing. At present, the main tuning methods of optical waveguide devices are thermo-optic tuning using thermo-optic effect and electro-optic tuning using thermo-optic effect. Therefore, electro-optic tuning is a good choice for high-speed applications. In order to achieve electro-optic tuning characteristics, electro-optic materials should be used to fabricate waveguide devices, while lithium niobate crystals with large electro-optic coefficients are the best choice. The annealed proton exchange process can adjust the refractive index of waveguides by matching annealing and proton exchange parameters, which has more controllable factors.In this paper, a tunable LiNbO_3 optical waveguide mode division multiplexer based on asymmetric directional coupler structure is proposed. The central wavelength and the corresponding coupling efficiency can be tuned based on the electro-optic effect, so the device can be used as a tunable broadband mode switch in addition to the ordinary mode division multiplexer, which greatly increases the flexibility of the device. Methods The dispersion curves of LiNbO_3 waveguides were solved by MATLAB simulation software, and the size ranges of single-mode waveguides and dual-mode waveguides which can satisfy the phase-matching conditions theoretically were obtained. The influence of proton exchange and annealing on the refractive index of waveguides is analyzed according to the measured refractive index, and the sizes of single-mode waveguides and dual-mode waveguides which satisfy the phase matching condition are obtained experimentally. Furthermore, according to the above analysis, the general structure of the device is designed, and the structure of the waveguide asymmetric directional coupler is improved by BPM simulation software. The coupling distance, coupling length and other parameters can be obtained by simulation analysis. Combining with the above analysis, the reasonable optical waveguide structure and corresponding electrode structure parameters are designed. Secondly, the corresponding waveguide and electrode mask are fabricated according to the above analysis and design parameters, and the switching and switching are studied. The influence of annealing parameters on the phase matching condition is also studied. The fabrication process of low loss optical waveguide and the fabrication process of high quality electrode are also studied. Then, a tunable LiNbO_3 optical waveguide mode division multiplexer is developed according to these parameters. Finally, the fabricated devices are tested and analyzed. The parameters to be tested include the transmission spectrum, near-field output and insertion loss of the device. The test results show that the device not only realizes the function of the mode division multiplexer, but also realizes the broadband mode switching function with tunable coupling efficiency and central wavelength. When the harmonic voltage is 9 V, the isolation can reach 27 dB..
【学位授予单位】：电子科技大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TN929.1

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