【作者】 王燕；

【导师】 郑建成（Kin Seng Chiang）；

【作者基本信息】 电子科技大学 ， 光学工程， 2016， 硕士

【摘要】 定向耦合器与基于定向耦合器的集成光学器件广泛用于光纤通信系统中光信号传输与处理,是波分复用器、光矩阵开关、分插复用器、滤波器、功率混合／分配器、调制器等集成光学器件的基本组成单元。利用不同空间模式作为独立信道传输光信号的模分复用技术是近年为了提升光纤通信系统传输容量而提出的一门新技术。模式转换器与模式复用／解复用器是模分复用系统中不可或缺的核心器件。以定向耦合器作为基本单元的模式转换器与模式复用／解复用器,具有结构简单、制作成本低、制作材料多样等优点,对模分复用技术的研究具有重要意义。本文以模分复用技术为背景,以光栅辅助定向耦合器为基本结构,提出了一种侧壁长周期光栅辅助聚合物波导定向耦合器。该定向耦合器由一个单模波导与支持三个空间模式的少模波导组成；其目标是实现单模波导与少模波导基模之间的耦合,同时要求单模波导基模与少模波导的高阶模不发生耦合：侧壁长周期光栅位于少模波导内侧,用于补偿少模波导与单模波导基模之间的模式折射率差；该定向耦合器制作材料为聚合物,芯层与包层材料分别为EpoCore与EpoClad。论文对提出的侧壁长周期光栅辅助聚合物波导定向耦合器进行了仿真工作,并进行了实物制作,从理论与实验两个角度证明了该方案的可行性。从模式复用技术的角度出发,本文提出的侧壁长周期光栅辅助聚合物波导定向耦合器实现了模式复用／解复用器中基模信道的复用／解复用。论文的主要工作如下：(1)从耦合模理论出发,分析了对称定向耦合器、非对称定向耦合器、光栅辅助定向耦合器的基本工作原理。(2)对提出的侧壁长周期光栅辅助聚合物波导定向耦合器进行了建模与仿真工作,确定了定向耦合器的各项设计参数,如单模波导与少模波导的宽度、厚度、两者之间的间距、光栅周期、光栅深度、耦合长度等。(3)在实验中通过旋涂、光刻、显影、固化等工艺步骤,成功制作了符合设计参数要求的侧壁长周期光栅辅助定向耦合器实验室原型器件。(4)所制作的侧壁长周期光栅辅助聚合物波导定向耦合器的测试与分析,测试了器件的红外近场光斑,测量了所制作的定向耦合器的光谱特性及其热调谐特性,测量了单模波导与少模波导基模的传输损耗,以及侧壁长周期光栅对少模波导基模引起的额外损耗,最后对器件的性能进行了分析讨论。更多还原

【Abstract】 Directional coupler and integrated optical device based on directional coupler is widely used to transmit and process optical signals in optical fiber communication system, it is the basic composition unit of a wavelength division multiplexer, an optical matrix switch, an add-drop multiplexer, a filter, a power mixer/distributor, a modulator, etc. Mode division multiplexing technology, which uses individual spatial modes as independent optical signal channel to transmit optical signals, is a new technology proposed in recent years, to improve transmission capacity of optical fiber communication system. Mode converter and mode multiplexer/demultiplexer are indispensable core components in mode division multiplexing system. Mode converter and mode multiplexer/demultiplexer with directional coupler as basic unit have advantages of simple structure, low production cost, material variety, and so on. It is of great significance for the research of mode division multiplexing technology.On the background of the mode division multiplexing technology, with grating assisted directional coupler as the basic structure, a kind of sidewall long-period grating assisted polymer waveguide directional coupler has been put forward in this dissertation. The proposed directional coupler consists of a single-mode waveguide and a few-mode waveguide which supports three spatial modes. The objective of the proposed directional coupler is to achieve the coupling between the fundamental modes of the single-mode waveguide and the few-mode waveguide, while the fundamental mode of the single-mode waveguide will not couple with the high order modes in the few-mode waveguide. The sidewall long-period grating along the inner side of the few-mode waveguide is used to compensate for the mode refractive index difference of the fundamental modes between the few-mode waveguide and the single-mode waveguide. The directional coupler is made from polymer materials, EpoCore and EpoClad, both are used as core layer and cladding layer, respectively. To find the optimal device parameters, simulation works have been done for the proposed sidewall long-period grating assisted polymer waveguide directional coupler, then device samples have been fabricated and characterized, and the results prove the feasibility of the scheme in theory and in experiment. From the point of mode division multiplexing technology, the sidewall long-period grating assisted polymer waveguide directional coupler proposed in this dissertation has realized the multiplex/demultiplex of fundamental mode channel in the mode division multiplexer/demultiplexer. The main work is as follows:(1) From the perspective of coupled mode theory, the basic working principles of the symmetrical directional coupler, the asymmetric directional coupler, and the grating assisted directional coupler was analyzed.(2) Simulation works were done to determine all the design parameters of the proposed sidewall long-period grating assisted polymer waveguide directional coupler, such as the widths, the thicknesses of the single-mode waveguide and the few-mode waveguide, and the gap between the single-mode waveguide and the few-mode waveguide, the grating period, the grating depth, the coupling length, and so on.(3) By the process steps of spin-coating, lithography, development, and curing, sample of the sidewall long-period grating assisted directional coupler, which meets the requirements of the design parameters, was fabricated.(4) To characterize the fabricated devices, the output infrared near-field pattern, the optical spectral characteristics, and the thermal tuning characteristics of the fabricated sidewall long-period grating assisted polymer waveguide directional coupler were measured. Moreover, the propagation losses of the fundamental modes of the single-mode waveguide and the few-mode waveguide were measured by cutback method, respectively. Also the additional loss caused by the sidewall long-period grating was measured for the fundamental mode of the few-mode waveguide.更多还原