【作者】 杨柳；

【导师】 何赛灵； 戴道锌；

【作者基本信息】 浙江大学 ， 测试计量技术及仪器， 2009， 博士

【摘要】 器件小型化的研究一直是集成光电子器件的发展方向之一。利用强限制光波导结构是实现器件小型化设计的一种非常有效的途径。微环谐振器（MRR）是集成光电子回路的重要组成单元,它可以实现光无源/有源器件的众多功能,因此MRR的相关研究至关重要。本论文围绕SOI（Silicon-on-insulator）和SU-8两种材料,研究了两种强限制光波导结构:SOI纳米线光波导和SU-8脊型光波导,在此基础上,对基于强限制光波导的小型化MRR及其热光特性进行了深入的理论和实验研究。集成光电子器件的理论基础是光波导电磁场理论及其数值计算方法。在此,给出了包括有限差分方法（FDM）、光束传输方法（BPM）及时域有限差分方法（FDTD）等的分析求解过程,并将其应用到光波导器件的分析研究中。本文利用分步FDTD方法对透镜光纤（TLF）与SOI纳米线光波导的端面耦合系统进行了分析:考虑到光纤的旋转对称性结构,我们采用旋转体FDTD方法对磨锥TLF和拉锥TLF的聚焦特性进行了分析,把三维问题转化为二维问题,节省了计算资源,提高了计算效率。计算结果表明拉锥TLF具有较强的聚焦特性,但是相对于磨锥TLF,其传输损耗比较大。因为SOI纳米线光波导不具备旋转对称性,所以对光纤-波导耦合系统的特性分析,我们使用了标准的三维FDTD方法。仿真结果显示拉锥TLF光斑小,与Si纳米线光波导的耦合效率高;但是耦合系统总的损耗（耦合损耗与TLF传输损耗之和）与磨锥TLF耦合时计算出的总的损耗相差不多。在热传导理论基础上建立了光波导的热学分析模型,提出了亚微米宽的新型热电极,并把它应用到SOI脊型纳米线光波导上。利用自建的热学分析模型,对该光波导结构进行了数值分析,并与传统的掩埋型光波导进行了热学性能的比较。结果显示,具有新型热电极的SOI脊型纳米线光波导结构所需电极功耗低,约为后者的1/10,响应速度快,约为后者的2倍。不仅如此,其加工工艺简单（仅需一次光刻工艺）,制作成本可大大降低。在此基础上,我们对该光波导结构进行了光学性能优化,并利用MRR结构设计出一种超小型、低功耗（5mW）、大范围可调（20nm）的热光可调谐滤波器。对SOI超小型光波导器件的制作工艺进行了总结,并给出了新型热电极下的SOI脊型纳米线光波导热光器件的工艺流程。对SU-8脊型光波导（空气为波导的上包层）的制作工艺进行了研究,并对两种制作工艺（纳米压印技术和直接紫外光刻技术）进行了比较。后者工艺简单,对于我们设计的SU-8光波导结构（微米量级）仍然能够提供足够的工艺容差,因此本文中关于SU-8光器件的制作都是利用直接紫外光刻技术完成的,器件表征结果显示利用该技术能够制作出低损耗的SU-8光波导及器件,如小型化多模干涉（MMI）耦合器、MRR等。利用SU-8脊型光波导结构,通过在MMI区域引入二次曲线锥形结构,设计出一种基于GI（General Interference）干涉机制的小型化2×2 MMI耦合器,并利用直接紫外光刻技术,完成了该器件的制作,测试结果显示该器件具有损耗低、均匀性好、带宽大等优点。把小型化2×2锥形MMI耦合器引入到MRR耦合区,研制出了小型化的MRR器件,对其光学性能,包括光谱响应、偏振相关特性等进行了表征,并对其热光效应进行了实验研究,测试结果显示温度升高100℃,其谐振波长漂移量将超过10nm,该性质对于研制大范围可调谐的滤波器件十分有利。针对SU-8脊型光波导的强限制作用及MRR的谐振增强效应,我们对MRR的热光非线性效应进行了探索性实验研究,通过对测试结果的分析,我们得到了SU-8材料对红外光的吸收系数约为0.179 cm^-1,为实现全光控制提供了一定基础。更多还原

【Abstract】 Miniaturization is one of the research directions for integrated opto-electronic devices.A very effective method to develop compact or ultracompact devices is using strongly-confined optical waveguides.Microring resonators（MRRs）become indispensable elements for photonic integrated circuits because of their strong flexibility and functionality.Therefore, researches on MRRs are very important.In this thesis,two kinds of strongly-confined optical waveguides are involved,namely,SOI（Silicon-on-insulator）nanowire waveguides and SU-8 ridge waveguides.Compact MRRs based on these strongly-confined optical waveguides and their thermal performances are studied theoretically and experimentally.Optical lightwave theory and numerical methods build up the basis of integrated optics. Here,various numerical methods,including finite-difference method（FDM）,beam propagation method（BPM）,finite-difference time domain（FDTD）method,are introduced and applied to analyze and design various photonic devices.In this thesis,two-step FDTD method is utilized to analyze the butt-coupling between tapered lens fibers（TLFs）and a SOI rib waveguide.Two types of TLFs are considered,namely,a tapered-cladding TLF and a tapered-core TLF.The BOR（or radial）FDTD is first used to simulate light focusing for two types of TLFs.It is shown that the tapered-core TLF has a smaller focus spot size and a larger transmission loss than the tapered-cladding TLF.The butt-coupling between a TLF of either type and a SOI rib waveguide is then simulated by a 3D FDTD method.The tapered-core TLF has a smaller coupling loss to the SOI rib waveguide but a similar total loss（the sum of the coupling loss and the transmission loss）,as compared with the tapered-cladding TLF.According to the heat conduction theory,thermal modeling of optical waveguides is presented.Based on this thermal modeling,a photonic SOI ridge wire with a submicron metal heater is proposed.Its thermal analysis is presented and compared with the conventional buried optical waveguide.The simulation indicates that the power consumption of the proposed SOI waveguide structure is almost less than 1/10 of the latter,and the response time is about half of that of the latter.This proposed structure also helps reduce the manufacture cost,because only one photolithography process is needed.Furthermore,optical performances of this structure are optimized,and an ultracompact widely tunable thermooptical（TO）MRR filter is designed.The calculation shows that the designed MRR has a wide tuning range of about 20nm with a low heating power of 5mW.The fabrication processes for SOI based ultracompact optical waveguides and devices are summarized.Here also present the manufacturing processes for the thermooptical devices based on the photonic SOI ridge wire with a submicron metal heater.We conduct researches on fabrication arts of SU-8 ridge waveguides and devices.Two kinds of technologies are compared,i.e.,nanoimprint lithography and direct ultraviolet（UV）photolithography.The latter is easier and is still able to provide enough fabrication tolerance for our designed SU-8 optical waveguides（several microns）.Therefore,in this thesis,SU-8 based photonic devices are all developed by direct UV photolithography technology,which are proved effective by low loss optical waveguides and devices,e.g.,small multimode interference（MMI）coupler, MRR,etc.A2×2 tapered MMI coupler is designed and fabricated by using air-cladded SU-8 ridge waveguides,which are effective in reducing the device size and improving the self-imaging quality.The parabolically tapered MMI section is used to reduce further the size of the MMI coupler.The measurement results show that the fabricated 2×2 tapered MMI coupler has relatively small excess loss and nonuniformity for both polarizations in a broad wavelength range.Introducing this 2×2 tapered MMI coupler into MRR coupling region,we develop a compact MRR device.Its optical performances are characterized.TO effect of such MMI-based MRR are studied experimentally and the measurement results indicate that the resonant wavelength will shift over 10nm when the temperature is increased by 100℃.This is useful for developing TO devices with a wide tuning range.Considering the strong light confinement of SU-8 based air cladded ridge waveguides and the resonance enhancement of MRR structure,the last experiment presented in the thesis is carried out to explore the thermal nonlinearity of SU-8 polymer.The measurement results are analyzed and the infrared light absorption coefficient of SU-8(about 0.179cm^-1)is obtained,which establishes the basis for the future work involved in all-optical communication.更多还原