有机聚合物热光光可变衰减器的研究

【作者】 李鹰；

【导师】 江晓清；

【作者基本信息】 浙江大学 ， 微电子与固体电子学， 2004， 硕士

【摘要】 在波分复用（WDM）光通信网络中，多信道间的功率均衡和调整需要具有良好特性的光可变衰减器（VOA），这些特性包括：低功耗、低插入损耗、偏振无关、易于集成以及大波长范围内的通带平坦性。在已有的VOA器件中，热光波导器件具有电光器件无法比拟的偏振无关性，驱动功率也较微电机械（MEMS）器件小的多。聚合物波导以其优良的材料特性成为近年来热光VOA的研究重点。本文首先综述了目前用于VOA设计和制作的最新技术，扼要介绍了几种用于光通信波段的聚合物，举例并比较了几种典型的热光VOA设计。 本文先以埋入式沟道波导为例，建立了二维稳态热传导方程模型，用分离变量法推导了方程解，并用MathCAD2000在波导截面上绘出了二维温度分布图和受到热光效应影响的折射率分布图。这种方法克服了模拟软件在热场分析上的不足，是对现有文献多数采用一维温度分布作为热光器件分析的有力补充，也避免了傅立叶变换法的复杂形式，为后面分析热光效应对器件衰减性能和功耗的影响打下了基础。 本文提出一种新型聚合物热光可变光衰减器（VOA）的设计。器件采用聚合物作为波导材料，以抛物型轮廓过渡区连接单模波导和展宽的多模波导。采用局部标准模理论，解释了两个最低阶模式沿着过渡区传播时的相互耦合。对于表征局部标准模之间功率耦合的两个重要的参数Δβ_ij（模式传播常数差）和C_ij（模式耦合系数），推导了用器件结构参数表达的近似公式，然后根据功率耦合的需求，在常见的三种不同轮廓的过渡区之间进行了比较，得出了抛物形轮廓过渡区能够使光束在最短尺寸内以最低损耗通过波导的结论。 除此之外，还提出了附加旁路多模波导的改进方案，以改善阵列VOA之间的串扰。采用RSoft公司的BeamPROP^TM软件埋入式沟道波导热光VOA进行了模拟。软件模拟比较了两组经过优化的反射泄漏型热光VOA的衰减性能，其中波长均匀性较好的一组在电极温升30℃时达到最大衰减为26.8dB，计算功耗为25mW，衰减最大时PDL＜0.2dB，此时在C波段内衰减波动为2dB。加入的旁路吸收波导和多模区间距为零时最大衰减对应的温度为60℃，衰减增加了20dB以上，功耗也增加了1倍，插入损耗比间距为1，2μm时增加约0.4dB，比没有旁路波导时插入损耗增加了约ldB。有间距以后衰减增加值明显不如没有间距。本文还分析了四个VOA组成的阵列，VOA之间的串扰可以降至SOdB以下。 本文还分析了基于Mach一Zehnder千涉仪的热光VOA，根据衰减与温度升高的关系，再利用己经计算出的温度场分布公式，可以直接计算相应功耗下的器件衰减，指出了文献中用电极温升计算衰减的错误。得到的MZI型VOA衰减最大可达50dB，只需3mw，但是对温度变化非常敏感。在此基础上，进一步分析了带有3dB定向祸合器的MZ型热光VOA的衰减特性和器件藕合参数的关系，并给出了单个VOA和衰减波谱更平坦的级联VOA之间的特性对比。 作者经过反复的工艺实验，确定了聚合物波导涂膜和固化、三层金属电极蒸发和腐蚀等新工艺的参数，并得到了聚合物紫外固化、等离子体刻蚀等新工艺的初步数据。最后作者采用倒脊形结构研制了热光VOA芯片样品，测出明显的热光效应，最大衰减达10dB，功耗约为300mw，本文给出了测试和分析结果，对实验和模拟结果的差异也作出了解释，提出了改进措施，为器件更深一步研究奠定了基础。更多还原

【Abstract】 In Wavelength Division Multiplexing(WDM) optical communication networks, power equalization and adjustment between channels demand Variable Optical Attenuator(VOA) be capable of providing low power consumption, low insertion loss, polarization independence, integration compatibility and flatness in a wide wavelength range. Among the presented VOAs, thermo-optic type owns superior polarization dependence upon electro-optic one, and thermo-optic VOA can be driven with much lower power than Micro-electro-mechanic System(MEMS). Recently, polymeric waveguides became attractive due to its advanced characteristics. The article overviewed first of all the latest techniques realizing VOA, then briefly introduced several polymers used on optical communications. Furthermore, a few typical thermo-optic VOA designs were illustrated and compared.The article set up 2-dementional steady heat conduction model and equations based on buried channel waveguide, and solved the equations by separating variables method. Using MathCAD, 2-D temperature distribution and the influenced refractive index distribution by thermo-optic effect were plotted in waveguide section area. This equation solving method overcomes the shortcomings of simulation software on thermal field analysis, strongly complements the commonly used 1-D temperature distribution to analyze thermo-optic devices in literature. The results avoids complicated form of solutions provided by Fourier Transform method, and thereafter lend itself to analyze the influence of thermo-optic to attenuation characters and power consumption in waveguide.The article introduced a novel thermo-optic VOA based on organic polymer, which used a parabolic profile transition to connect single-mode waveguide and multi-mode waveguide. To illustrate the superiority of this type of transition, the author adapted the Local Normal Mode(LNM) based on couple-mode theory to explain the coupling between two lowest order modes along the transition. For the two important parameters, propagation constants difference between the two modes Apy and mode coupling coefficient Cy, which denoting power coupling between LNMs, the approximation expressions using structure parameters were worked out. Then the author compared three typical different transitions according to the demanding of power coupling, at last concluded that the parabolic-type transition can transport the light in shortest length with lowest loss. Besides this, a bypass multi-mode waveguide were used to improve attenuation efficiency and reduce power consumption. Based on buried channel structure, the simulation software BeamPROP?produced by Rsoft Corp shows some better results than the original device: attenuation range over 20 higher, insertion loss merely 1dB higher and the calculated power consumption is only 25mW. The crosstalk between arrayed VOAs wasalso considered, the best result is -50dB. Simulations shows that the wavelength dependence and polarization dependence are respectively 2dB and 0.2dB.Apart from these, the Mach-Zehnder type VOA was analyzed too. The author deduced directly the relation between attenuation and power consumption, which corrects the faults in literature, utilizing the relation between attenuation and temperature rise and the already presented temperature distribution. From these results, MZ-type VOA based on two 3dB directional couplers was studied further, the characters comparison between single and cascaded MZ-type VOA were given.The reflection leakage VOA don’t depend on high temperature stability as MZ-type need, while the latter own much lower power consumption than the former. In a word, the two type of VOA both have valuable applicability and potential market.The author have done numerous processing to work out new processing such as polymer coating and cure and triple-layer-metal film vaporing. Other new processing, polymer ultra-violet(UV) cure and inductively-coupled plasma(ICP) etching were studied.At last, the author developed thermo-optic VOA sample chip in reverse ridge struc更多还原