【作者】 梁磊；

【导师】 张大明；

【作者基本信息】 吉林大学 ， 微电子学与固体电子学， 2014， 博士

【摘要】 光开关及其阵列在光通信网络中具有重要的应用，如微光机电系统(MOEMS)光开关、液晶光开关等。与上述光开关相比，波导光开关由于没有机械移动部件，因而在可靠性方面具有明显优势和潜在应用价值。在波导光开关中，热光开关体积小、可扩性强、稳定性好，是光开关领域的研究热点之一。响应时间和功耗是热光开关的主要性能指标，研制响应速度快、功耗低的热光开关一直是人们追求的目标。近年来，为了加快响应时间并降低功耗，人们相继报道了Si/SiO2热光开关和全聚合物热光开关。硅材料具有大的导热系数，因此Si/SiO2热光开关响应速度快，但是其开关功耗一般较高。为了解决无机波导热光开关功耗大的缺点，虽然人们研究了各种类型的波导结构(如悬浮型波导结构)，但是，器件的制作工艺相当复杂，而且实验效果不是十分理想。与无机材料热光开关相比，聚合物热光开关具有功耗低和制作工艺简单的优势，其缺点是响应时间较长，一般为ms量级。鉴于上述两类热光开关的优缺点，为了使器件兼具低的功耗和快的响应速度，人们研究了一类有机/无机混合结构的热光开关。本文利用聚合物材料SU-8和聚甲基丙烯酸甲酯(PMMA)分别作为芯层和上包层、无机材料SiO2作为下包层、Si材料作为衬底，制备了多种有机/无机混合结构热光开关。一方面，由于SU-8材料的热光系数较大(1.8×10-4K-1)，这可降低器件的驱动功率；另一方面，由于PMMA(n3=1.4798@1550nm)与SU-8(n1=1.5742@1550nm)间的折射率差较大，上包层可以制作的较薄，这将加快电极产生的热量向芯层的传导速率，同时由于SiO2材料的导热系数较大，这也将加快芯层中热量的散失，这些都有利于缩短器件的上升和下降时间。本文的主要工作和创新点如下：1、从麦克斯韦方程出发，得到电磁场全矢量、半矢量、标量本征方程和边界条件，利用有限差分法推导出它们的有限差分形式，将此方法应用到矩形波导和脊形波导的模式分析中，并将三个有限差分法的计算结果做了对比；从横向亥姆赫兹方程出发得到三层平板波导光场强度分布的解析形式和模式有效折射率，并将其应用到有效折射率法中，推导出矩形和脊形波导的模式有效折射率；采用解析法和有限差分法对二维狭缝(slot)波导模式作了分析，采用半矢量有限差分法对三维狭缝波导作了分析；推导固体热传导方程的一般形式和稳态形式，并利用合适的差分网格推导出稳态热传导方程的有限差分形式。2、针对聚合物材料有热光系数大、导热系数小、制备工艺简单和成本低的特点，而无机材料具有热光系数相对较小、导热系数大、制备工艺相对复杂且成本相对较高的特点，提出了有机无机复合波导结构，制备了不同类型的马赫-曾德尔干涉仪(MZI)型热光开关：1)采用湿法腐蚀工艺，充分利用有机无机材料的优点，分别以聚合物材料SU-8和PMMA为波导的芯层和上包层，以无机材料SiO2为下包层，制备了1×1MZI热光开关。通过优化设计，确定波导上下包层厚度的理论最佳值，分别为3μm和2μm。利用数字计算方法给出了热光开关光场和热场的分布。对制备好的热光开关在1550nm下进行了测试，从不同波导尺寸热光开关的稳态特性测试可以看出，在波导横截面最佳尺寸为2.5μm×2.5μm时，开关的驱动功率仅为4mW，消光比高达29.6dB。从开关的动态特性测试可以看出，开关10-90%的上升时间73.5μs，90-10%的下降时间为96.5μs。2)与1×1MZI热光开关采用相同的湿法腐蚀工艺和同样的波导结构体系，制备了有机无机复合波导1×2多模干涉(MMI)MZI热光开关。通过测试得到此热光开关的开关功率是9.6mW，在交叉态的串扰是-23dB，上升和下降时间分别为264μs和444μs。3)为了利于波导之间的耦合，采用ICP刻蚀工艺制备了脊形波导1×2定向耦合器(DC)MZI热光开关。通过测试得到此器件的开关功率是10.7mW，在交叉态和直通态的串扰分别是-11.5dB和-23dB，器件1端口10%-90%上升时间是170μs，90%-10%下降时间是560μs，2端口10%-90%上升时间是200μs，90%-10%下降时间是560μs。4)同样利用了脊形波导的耦合，为了减少S型波导对3-dB耦合器耦合系数的影响，优化了其尺寸。通过ICP刻蚀工艺制备了2×2DC-MZI热光开关，测试得到器件的功耗为7.2mW，在交叉态和直通态的串扰分别是-22.8dB和-26.5dB。两个输出端口在ON状态下总的纤纤损耗分别为14.5dB和16.2dB。纤纤插入损耗包括两个单模光纤与波导的耦合损耗和器件上的传输损耗，通过截断法可测得波导的传输损耗约为2.0dB cm-1。3、研究了有机无机复合波导1×1MZI和2×2DC-MZI热光开关的容噪特性，提出容噪特性测试法。对于消光比高达32.6dB的1×1MZI热光开关，忽略了温度变化和开关引起的电压波动，假设通信系统可接受的最小消光比ERm in大于10dB时,器件所能允许的最大噪声幅值允许量是1.1V。对于在交叉态和直通态的串扰分别是-22.8dB和-26.5dB的2×2DC-MZI热光开关，当叠加了一个频率为2KHz、峰峰值为2.5V的方波噪声信号，开关最小的消光比大约为11.3dB，当叠加一个频率为5kHz、峰峰值为2.5V的方波噪声信号时，开关的最小消光比增加到24.1dB。通过进一步的测试发现，当噪声频率相同时，热光开关最小消光比随着噪声峰峰Vn oise的增大而减小；当噪声幅值相同时，热光开关最小消光比随着频率的增大而减小。但是当噪声频率足够大时，器件的最小消光比变化不大，证明器件达到了其噪声截止频率。4、提出了一种有机无机复合波导2×2全内反射热光开关。当从1端口输入时，开关在交叉态和直通态的串扰分别为-24dB和-26dB；当从2端口输入时，开关在交叉态和直通态的串扰分别为-25.7dB和-26.3dB；开关在大于26dB时的功耗约为100mW。通过优化波导结构尺寸，器件的功耗降低到59.7mW，在交叉态和直通态下的串扰分别为-27.6dB和-35dB。当拓扑的全内反射开关阵列是阻塞型的，需要2N11个2×2全内反射开关级联而成；当拓扑的全内反射开关阵列是榕树型无阻塞N×N开关阵列，需要N2个2×2全内反射开关级联。5、针对一般MZI热光开关光谱很窄的缺点，提出了一种宽光谱热光开关。此器件含有一个由相位发生器(PGC)和两个DC组成3-dB耦合器，它与传统3-dB耦合器不同，随着波长的漂移相位差会产生漂移，而这种漂移在一定范围内能补偿热光调制区因波长漂移产生的相位漂移。模拟结果显示，所设计的宽光谱热光开关的两个输出端口在110nm的波长范围内，消光比都大于30dB。而传统的MZI型热光开关的输出功率谱只有50-60nm，也就是说，本文设计的宽光谱热光开关的光谱比传统MZI型热光开关宽了近一倍。更多还原

【Abstract】 Optical switch and array have important applications in optical communicationnetworks, such as Micro-opto-electro-mechanical Systems (MOEMS) switch, liquidcrystal optical switch, and so on. Compared with these optical switches, the opticalswitch using waveguide has obvious advantages and potential applications, because ithas no mechanical moving parts, so it is more reliable. Thermo-optical switch is oneof the hot areas of the waveguide switch, it has some advantages of small size,scalability, good stability. Response time and power consumption are keyperformance of thermo-optical switch, and developing a thermo-optical switch withfast response, low power consumption is very important.In recent years, in order to speed up response time and reduce powerconsumption, Si/SiO2thermo-optic switch and polymer thermo-optical switch havebeen reported. Silicon has a large thermal conductivity, therefore, Si/SiO2thermo-optical switch has faster response, but its switching power consumption isgenerally higher. Although in order to solve the shortcoming about large powerconsumption in inorganic waveguide optical switch, various of waveguide structuresof thermo-optical swiches have been studied, such as a suspended phase armwaveguide, the fabricating process is extremely complex, and the experimental resultsare not very satisfactory. Compared with inorganic materials thermo-optical switch,polymer thermo-optical switch has low power consumption and simple fabricatingprocess, but it has slower response time of milliseonds.In order to fabricate a switch with low power consumption and fast responsespeed, the advantages of both organic and inorganic have been used. In this paper, thepolymeric materials of SU-8and polymethyl methacrylate (PMMA) as the core andthe upper cladding layer of the waveguides, respectively, an inorganic material ofSiO2were used as the lower cladding layer of the waveguides on the Si substrate, we fabricated varieties of organic/inorganic hybrid thermo-optical switches. On the onehand, SU-8has larger thermal-optical coefficient of1.8×10-4K-1, which can reduce thedriving power of the device, on the other hand, the refractive index differencebetween PMMA (n3=1.4798@1550nm) and SU-8(n1=1.5742@1550nm) is bigenough. The upper cladding layer was fabricated as thin as2μm, which could speedup the heat conduction between electrode and the core, and because of the largethermal conductivity of SiO2, which would accelerate heat dissipation of the core, onthis way, it was conducive to shorten the rise and fall time of the device. The mainwork and innovation of this paper is as follows:1、The full vector, half-vector, scalar eigenvalue equations and their boundaryconditions were obtained from the Maxwell’s equations, and their derive their finitedifference equations were also ratiocinated by finite difference method. The opticalfield intensity distribution and the mode effective refractive index of three-slabwaveguide had been resolved from the horizontal Helmholtz equation. Utilizing theanalytical method of solving three-slab waveguide mode, the effective refractiveindex of the rectangular waveguide was obtained combining with effective indexmethod, in addition, all-vector, semi-vector and scalar finite difference method werealso analysised for comparing. The analytical method of ridge waveguide was same asrectangular waveguide. Using the analytical method and semi-vectorial finitedifference method, two-dimensional slot waveguide modes were analyzed, and usingsemi-vectorial finite difference method, three-dimensional slot waveguide wasanalyzed. Heat conduction equation in general form and steady form and their finitedifference form were ratiocinated.2、Polymer has some characteristices such as big thermo-optical coefficient, lowthermal conductivity, simple fabricating process and low cost, while the inorganicmaterial has a relatively small thermo-optical coefficient, big thermal conductivitycoefficient, relatively complex preparation process and high cost. So the organic-inorganic composite waveguide structure was proposed, and different types ofMach-Zehnder interferometer (MZI) thermo-optical switch was fabricated:1) Makinguse of the advantages of organic and inorganic materials,1×1MZI thermo-optical switch was fabricated by wet etching process. The core, upper cladding and undercaladding of the waveguide were SU-8, PMMA and SiO2, respectively. Thethickneses of upper and lower cladding were3μm and2μm by theoretical optimizing,respectively. Calculating with finite difference method, the light field and the heatdistribution of the optical switch was obtained. The driving power was only4mWand the extinction ratio was up to29.6dB at1550nm, the rise time and fall time were73.5μs and96.5μs, respectively.2)1×2organic-inorganic hybrid waveguidemultimode interferometer (MMI) MZI thermo-optical switch was proposed. Theswitch power is9.6mW, and the crosstalk is-23dB, the rise time and fall time were264μs and444μs, respectively.3)1×2organic-inorganic hybrid waveguidedirectional coupler (DC) MZI thermo-optical switch was proposed. The switch poweris10.7mW, and the crosstalks under bar state and cross state were-11.5dB and-23dB. The rise time and fall time of port1were170μs and560μs, and the rise time andfall time of port2were200μs and560μs.4)2×2organic-inorganic hybrid waveguideDC-MZI thermo-optical switch was proposed. The switch power is7.2mW, and thecrosstalks under bar state and cross state were-22.8dB and-26.5dB.3、 In order to study the capacity of noise tolerance characteristics oforganic-inorganic hybrid waveguide thermo-optical switch, a driving-noise-tolerantmethod was proposed on1×1MZI thermo-optical switch and2×2DC-MZIthermo-optical switch. When ignored the changes caused by temperature fluctuations,a1×1MZI device with a extinction ratio up to32.6dB was chooseed to study thedriving-noise-tolerant characteristic. Experimental results showed that when theacceptable minimum extinction ratio was bigger than10dB, the maximum allowablenoise amplitude was1.1V. For2×2DC-MZI thermo-optical switch, which crosstalkwere-22.8dB and-26.5dB on cross state and bar state, respectively. When a squarewave noise signal with a frequency of2KHz and a peak-peak value of2.5V wassuperimposed on driving signal, the smallest extinction ratio was about11.3dB.When a square wave noise signal with a frequency of5KHz and a peak-peak value of2.5V was superimposed on driving signal, the smallest extinction ratio was about24.1dB. The minimum extinction ratio increased with the increasing of peak-peak value of noise. When the noise amplitude was immovable, the minimum extinctionratio increased with the decreasing of frequency. However, when the frequency of thenoise is large enough, the change of the minimum extinction ratio almost did notchange, it was proved the device is insensitive to high frequency signals.4、An organic-inorganic hybrid total internal reflection2×2switch was porposed.When the signal input from input port1, the crosstalk were-24dB and-26dB oncross state and bar state, respectively. When the signal input from input port2, thecrosstalk were-25.7dB and-26.3dB on cross state and bar state, respectively. Thepower consumption of the switch was about100mW when the extinction ratio wasgreater than26dB. By optimizing the size of the device, the power consumption wasreduced to59.7mW, the crosstalk on cross state and bar state were-27.6dB and-35dB, respectively. When the total internal reflection switch matrix is blocking, itrequires2×(N-1)-1total internal reflection2×2switches. When the total internalreflection switch matrix is non-blocking, it requiresN2total internal reflection2×2switches.5、 As the general MZI switch usually has very narrow spectrum, Athermo-optical switch with broad spectrum was proposed. A3-dB coupler composedby phase-generating coupler (PGC) was used to replace general DC3-dB coupler,which phase difference was also changed with the wavelength drift, and thischaracteristic could compensate the drift of modulation region. Simulation resultsshowed that the two output ports of designed models had a wavelength range of110nm, in which the extinction ratio was greater than30dB.更多还原