【作者】 张小贝；

【导师】 黄德修； 张新亮；

【作者基本信息】 华中科技大学 ， 光学工程， 2009， 博士

【摘要】 随着光纤通信技术的发展，光通信网络需要不断地提高工作性能和降低运营成本，其核心技术在于光波导器件的微型化、集成化和规模化，与此同时未来全光网络迫切需要能够实现多种功能的新型光波导器件，例如能同时实现光学滤波器、延迟线、缓存器和各种全光信号处理的基本单元，通过大规模集成该单元在一个衬底上实现功能强大的光子学“片上系统”。微环谐振器(简称微环)满足了上述两个要求，其微纳米量级的尺寸非常适于大规模单片紧密集成，同时能实现包括滤波器、延迟线、缓存器、激光器、路由器、波长复用／解复用器、光开关、调制器、波长转换器、码型转换、逻辑门和传感器等功能单元，功能非常强大，因此微环已成为光纤通信和集成光学领域的研究热点之一。本论文以光学滤波器、延迟线和缓存器为应用背景，在微环器件设计、少量微环、微环阵列和失谐微环结构等领域开展了理论研究工作，并对微环激光器进行了初步的实验研究。概括全文的研究成果和贡献，可以总结为如下几个方面：(1)研究了微环的理论基础，包括光波导的模式理论和耦合模理论，以及本论文用到的全矢量模式匹配法和时域有限差分(FDTD)数值计算方法，并推导了全通型和上下载型微环的参量模型，最后给出了简要分析和表征参量的定义。(2)对全通型微环的脉冲响应特性进行了解析法和分段模型法的比较研究，两种方法在脉冲宽度逐渐增大的情况下逐渐与理论延迟相符合。提出了一种参量模型和数值FDTD法相结合的微环谱线快速算法，仅仅计算光波在微环中传输3／4圈即可得到微环的谱线。采用全矢量模式匹配法和耦合模理论相结合的方式设计了工作波段在1．55μm的硅基跑道型微环，也设计了工作波段在850nm的聚合物矩形微环，该结构含有两个多模干涉器(MMI)和四个空气槽反射镜，采用Fimmwave／Fimmprop、OptiFDTD软件包和参量模型相结合的方法进行了数值模拟，实现了下载端20dB的消光比。(3)解析研究了三种少量微环的特性。推导了串联双微环的谱线和延迟的解析模型，首次发现在串联微环谱线和延迟都不简并的情况下，谱线和延迟的峰值频率不重合的特性，且损耗对谱线和延迟的影响可以等效为环-波导耦合系数的增大。推导了串联三微环的解析模型，在非简并态下次谐振峰频率和纹波凹陷频率与相等耦合系数近似线性相关，当损耗增大时，这两个特征频率逐渐靠近并重合。首次提出了基于3×3耦合器的双微环结构，推导了解析模型，并给出了该结构四种类型的详细理论分析，其中前两种类型具有耦合谐振器诱导透明(CRIT)的特性，第三种类型在两个下载端实现了均等分束功能，最后一种类型在两个下载端分别实现了一阶和二阶滤波器。(4)系统研究了微环阵列的模型、传输特性和两个特例。建立了微环阵列的六单元与模拟退火优化算法模型，该模型能分析任意耦合系数、微环尺寸和直波导腔长，同时能根据目标谱线合理优化耦合系数矩阵。研究了奇数行微环阵列的谱线在横向和纵向耦合系数渐变以及行数和列数增大情况下特性的改善，首次系统地研究了偶数行微环阵列的传输特性，由于直波导腔的前馈作用，该结构的谱线中出现大量的零点。提出了2×2微环阵列，其谱线随着耦合系数呈现了丰富的演化特性，谱线涵括了单、双、三和四个谐振峰，采用FDTD数值模拟了谱线，验证了解析理论的正确性，并提出了半对称模式的概念用来解释单谐振峰特性。最后解析研究了3×2微环阵列的谱线，通过箱状滤波特性的优化设计，实现了旁瓣抑制比大于10dB、通带纹波抑制比小于0．1dB和通带带边陡峭系数小于1dB的箱状滤波器，且该滤波器的半高全宽在一定范围内是可调整的。(5)全面研究了基于失谐微环结构的慢光效应。首先分析了并联失谐双微环的微环失谐量、耦合系数和损耗对慢光的影响，当耦合系数过小时，延迟存在非简并态，并研究了非对称参量如直波导腔失谐量、非对称微环损耗和非对称微环耦合系数导致的非对称透明特性。接着分析了并联失谐多微环结构中直波导腔相位作用的重要性、多信道峰值不一致和多信道峰值频率漂移的现象。最后提出了一种新颖的并联失谐双微环耦合谐振光波导以实现多信道慢光，基于切比雪夫第二类多项式给出了解析模型，并对多信道延迟特性进行了分析，随着微环数的增大，最外侧信道的延迟逐渐退化为双谐振峰。(6)实验研究了微环激光器的电学和光学特性，首先对器件测试的关键部分和平台进行了简要介绍，然后给出了微环激光器的测试结果，为基于微环激光器的缓存器研究建立了工作基础。更多还原

【Abstract】 With the development of fiber-optic communication technologies,high-performanceand low-cost are both desirable for optical communication networks.The core technologyincludes small-size optical waveguide devices with the potentials for integrations.Inaddition,optical waveguide devices with various functions such as optical filters,delaylines,buffers and other kinds of basic units for all optical signal processing are becomingmore important for the realization of future all-optical networks.Therefore,powerfulon-chip photonic systems which are fabricated by integrating these optical waveguidedevices with large dimensions on a single substrate are required.The microring resonator is a suitable candidate to meet these two requirements.It hasthe capability to realize the functions of optical filters,delay lines,buffers,lasers,routers,wavelength multiplexers/demultiplexers,switches,modulators,wavelength converters,format conversion,logic gates,and sensors,etc.Moreover,its small size is very suitable forintegration with large dimensions.Thus microring resonators have become one of the hotresearch topics in fiber-optic communication and integrated optics.This thesis is dedicatedto the research on the applications of optical filters,delay lines and buffers,which focuseson fields such as device design,microring resonators with small numbers,microringresonator arrays and detuning microring resonator structures.Furthermore,some primaryexperiments have been carried out based on microring lasers.In summary,major researchachievements and contributions are as the following:(1)The background theory for microring resonators is reviewed,including the modetheory and coupled mode theory of optical waveguides.The full vectorial film modematching method and finite difference time domain (FDTD)method are also described.Theparameter models of both all-pass and add-drop microring resonators are derived,withsome brief analysis and definitions of characterization parameters presented.(2)Comparative study of the analytical method and section model is carried out for thepulse response of all-pass microring resonators.It is found that simulation results have agood agreement with the theoretical ones when the pulse width becomes larger.A simpleand fast method which consist of both the parameter model and FDTD method is proposed.By using this method,spectra can be calculated within the 3/4 round-trip of lightpropagation in the microring resonator.Based on the full vectorial film mode matchingmethod and coupled mode theory,a silicon racetrack microring resonator is designed working around 1.55μm.Finally,a polymer rectangular microring resonator is alsodesigned working at 850nm,which consists of two multimode interferences (MMI)andfour air trenches.The numerical simulation is performed by the combinations ofFimmwave/Fimmprop,OptiFDTD and the parameter model,and the simulated extinctionratio at the drop port is around 20dB.(3)Three kinds of microring resonators with small numbers are analytically studied.The analytical models of both the spectrum and delay of serried-cascaded dual microringresonators are derived,respectively.Their peak frequencies are found to be differentwithout mode degenerations.The loss results in the same effect as the increase in thering-bus coupling coefficient.After that,the analytical model of series-cascaded triplemicroring resonators is derived.The frequencies of the outer peak and ripple notch arefound to increase nearly linearly with the identical coupling coefficients.Finally,dualmicroring resonators coupled via 3×3 couplers are proposed with analytical models derivedand detailed investigations presented.The first two types show a property ofcoupled-resonator-induced transparency (CRIT),while the third type achieves identicalintensities at two drops and the fourth type realizes the first and second order filters at twodrop ports.(4)The model,transmission characteristics and two special cases of microringresonator arrays are theoretically studied.The model of microring resonator arrays is basedon six transfer cells and the simulated annealing algorithm,which is suitable for analyzingarbitrary coupling coefficients,resonator sizes and straight waveguide lengths.In addition,it can optimize the matrix of coupling coefficients for a specified target spectrum.By usingthe model,odd row microring resonator arrays are studied in forms of variations oftransverse and longitudinal coupling coefficients and the increase in row and columnnumbers for spectral improvements.The row microring resonator arrays are investigated inmore detail for the first time.There are lots of zero transmissions in spectra due to thefeedforward effects of straight waveguide cavities.The 2×2 microring resonator array isproposed and the resultant spectra show a variety of shapes including one,two,three andfour peaks,as the coupling coefficients change.This analytical model is validated by usingFDTD simulations,.A semi-symmetrical mode concept is proposed to explain thephenomenon of the single resonance peak.Finally,the spectrum of the 3×2 microringresonator array is investigated analytically.Under the optimal design process of box-likefiltering characteristics,the filter with the side lobe larger than 10dB,the passband ripplesmaller than 0.1dB and the roll-off coefficient of passband edge smaller than l dB are achieved,with the full width at half maximum adjustable in some range.(5)The slow light effect of detuning microring resonator structures is analyzed.Firstly,the effects of resonator detuning,coupling coefficients and loss on the slow light effect areinvestigated.The delay is found to become two peaks under small coefficients.Theasymmetrical parameters such as nonzero straight waveguide cavity detuning,asymmetricalresonator loss and asymmetrical coupling coefficients are studied as the reasons ofasymmetrical.transparent properties.Then the phase effects of straight waveguide cavitiesin the parallel detuning multiple microring resonators are pointed out,with different peakvalues and shifted peak frequencies of multi-channels studied.Finally,a novel twocascaded stages of microring coupled-resonator optical waveguides for multi-channel slowlight is proposed,with the analytical model based on Chebyshev polynomials of the secondkind.Then multi-channel delay properties are studied.Delays of outer channels becomedegenerated as the number of microring resonators increases.(6)The electrical and optical properties of microring lasers are experimentally studied.Firstly,key parts of device measurements and the platform are described briefly.Thenmeasurements of microring lasers are implemented,which is a fundamental start for futureresearches on microring lasers based buffers.更多还原