【作者】 杨一粟；

【导师】 任晓敏；

【作者基本信息】 北京邮电大学 ， 电磁场与微波技术， 2010， 硕士

【摘要】 本工作围绕亚波长光栅(SWG)展开,这种衍射光学元件周期长度小于入射光波长,只有零级衍射波才可以传导,其余的高级次衍射波均为倏逝波。SWG可视为一种特殊薄膜,其折射率为具有周期分布折射率的光栅层的平均折射率,调整SWG结构参数,使折射率在一定范围内连续可变。对入射光波长或入射角等物理量的微小的变化,SWG的衍射波的强度会发生突变。论文研究了工作在光通信C波段的InP基SWG,SWG周期小于1.55μm,采用电子束光刻(EBL)工艺实现精确加工以满足设计指标。建立SWG分析模型,利用导模共振异常效应,将SWG设计成高性能反射谐振滤波器,将其集成到通信用谐振腔增强型光探测器(RCEPD)中。通过提升RCE PD性能,有助于推动光纤通信系统、网络的升级。主要研究工作和创新点如下：1.对具有一维、二维周期分布的SWG(简称：1D-SWG, 2D-SWG),以及具有分布布喇格反射镜(DBR)堆栈膜系的SWG的衍射特性进行研究,理论分析方法是严格耦合波分析法(RCWA),时域有限差分方法(FDTD)和平面波展开法(PWE)。其中RCWA是严格的解析分析法,精度高,计算速度快。FDTD作为数值方法,用计算时间和计算空间的代价弥补RCWA的不足,便于对有限周期分布的SWG结构分析,RCWA与FDTD综合使用保证仿真结果可靠性又可提高计算效率。PWE方法可从能带的角度分析SWG的滤波本质。2.编写程序实现上述理论分析,可对SWG的衍射效率以及集成了SWG的RCE PD性能的分析,与已有文献的结果进行对比,验证了可靠性。可以分析SWG衍射效率、光探测器中光场分布、量子效率、串扰衰减、冲击响应、脉冲响应、阶跃响应和频率响应。3.提出将SWG与InP系DBR集成,使SWG具有宽带滤波效果,以便适应工作在光通信C波段的InP材料系。RCWA与FDTD互补使用,用PWE进行能带分析,研究一维、二维周期分布的SWG,以及具有分布布喇格反射镜(DBR)堆栈膜系的SWG的衍射特性与其周期、厚度、占空比等参数的关系。对于2D-SWG综合RCWA、FDTD方法设计出反射率高于99%、波长区间在1.47μm～1.59μm、峰值反射率大于99.9%的反射式滤波器。4.提出将SWG以反射式谐振滤波器的形式应用于InP系材料构成的RCE PD中。该种光探测器工作在C波段,用于WDM光通信系统解复用光接收机。理论分析探测器中光场分布、量子效率、串扰衰减、冲击响应、脉冲响应、阶跃响应和频率响应。设计的RCE PD类型如下：1)具有一个一维周期分布的SWG；2)具有一个二维周期分布的SWG；3)具有两个一维周期分布的SWG。5.重点针对便于工艺实现的具有一个2D-SWG的RCE PD,通过研究其内部呈现驻波效应的光场,指导吸收层位置的设置。理论分析表明SWG的引入使InP系材料反射镜所需的介质层数小于10对,有望解决InGaAsP/InP系DBR反射率低、反射带宽窄的问题,器件量子效率超过90%。台面尺寸为30μm×30μm的具有一个1D-SWG的RCE PD 3dB带宽仿真结果为15GHz。6.在实验上,与外单位合作,采用外延技术、EBL技术以及感应耦合等离子体(ICP)刻蚀技术,制备出InP基SWG结构,可以满足具有优化性能所需要的SWG的尺寸：SWG厚度265nm,周期为1.4μm,占空比为33%,粗糙起伏的平均高度从150nm减小到40nm左右。7.设计并制备了针对具有SWG结构的半导体光探测器光刻掩膜版图,为配合SWG的结构,引入方形台面,加入了小尺寸倒”T”型对准标记和光栅掩膜层。8.与他人合作,进行纳米线制备测试工作,完成了关于制备纳米线所需的Au-Ga合金纳米颗粒的原子力显微镜(Atomic Force Microscopy:AFM)测试,测试表明在不同的Au薄膜溅射厚度条件下,纳米颗粒密度分别为1.64×1010cm-2,1.26×1010cm-2,2.2×109cm-2,扫描电子显微镜(Scanning Electron Microscopy:SEM)测试表明GaAs纳米线的平均长度分别为5.2μm,5.3μm,6.3μm,密度大于109cm-2。9.根据微栅尺寸和SEM测试结果估算了透射电子显微镜(Transmission Electron Microscopy:TEM)测试所用GaAs纳米线样品面积只需1cm2。用TEM测得了直径分别为24nm,68nm和168nm的GaAs纳米线样品的形貌。分析纳米线样品属于面心立方体结构,为闪锌矿结构的单晶,生长方向为[111]方向。更多还原

【Abstract】 The work focuses on subwavelength grating (SWG) which is a kind of important diffractive optical elements.SWG takes an important role in the family of gratings and gives rise to propagation of only the zero-reflected and zero-transmitted diffraction orders as its period is smaller than the incident wavelength.SWG can be considered as a special film whose refractivity is equal to the average refractivity of the grating layer where the refractivity is periodically modulated in space.By modifying SWGs’structure,the refractivity can be tuned continuously. Besides,SWGs’diffraction field may have sharp change when the incidence light wavelength or the structure has small change.This is due to guide mode resonance (GMR) phenomena.In this dissertation, InP based SWGs that work in the C band of optical communication are designed.SWG period is smaller than 1.55μm. Electron beam lithography is adopted to fabricate surface pattern in nano scale.Reliable analyzing models are set up for different SWGs.Utilize GMR to realize reflection resonance filters in C band. SWGs are integrated into resonant cavity enhanced photodetectors (RCE PD) for optical communication system. The reasons of chosing RCE PDs as an application of SWGs are as following.RCE PDs can realize the full absorption of multi-reflected lightwave in the resonance cavity with thin (several hundreds of nanometer) absorption layer which guarantees the ability of high speed signal processing and high quantum efficiency. Make it a good candidate for wavelength-demultiplex receiving application in optical fiber communication systems and networks. The research work and innovations mainly include the followings.1.Analyze SWGs by rigorous coupled-wave analysis (RCWA), plane wave-expansion(PWE) method and finite difference time domain (FDTD) method. SWG types are including SWG with 1D period distribution(1D-SWG),SWG with 2D period distribution (2D-SWG) and SWG (1D-SWQ 2D-SWG) with DBR stacks. RCWA is an analytical method which is accurate and has high calculation speed. FDTD is a numerical method which can analyze SWG with finite period numbers at the cost of calculation time and memory space.RCWA and FDTD are compensated with each other for analyzing.And PWE can reveal the essence of performance of SWGs by energy band graph.2. Program to analyze SWGs by RCWA, FDTD and PWE respectively and to analyze the performances of RCE PDs with SWG filters.Results are verified by published conclusions.Programs can analyze SWGs’diffraction efficiency and RCE PDs’light field distribution,quantum efficiency, cross-talk attenuation,step response, Gauss pulse response, impulse response and frequency response.3.Design InP based SWGs that work in the C band of WDM system. DBR is integrated with SWGs to realize broadband reflection. The influences of SWGs’period length, thickness,duty cycle on its diffraction feature are studied in detail.With DBR,2D-SWGs’reflectivity is higher than 99% from 1.47μm to 1.59μm. Its peak reflectivity is higher than 99.9% in C band.4.Design InP based RCE PD with SWG filters that works in C band of WDM system. Propose three kinds of RCE PD for WDM system demultiplex receiver with single 1D-SWG, single 2D-SWG and double 1D-SWGs respectively.5.Simulation for RCE PD with single 2D-SWG reveals that 1)light field distribution in the RCE PD shows stand wave effects that can be used to decide where to set the absorption layer; 2) with high cross-talk attenuation coefficient,devices’quantum efficiency is higher than 90%;3) compared with pure DBR in RCE PD,the total numbers of reflector’s layers are no more than 10 pairs of InGaAsP/InP DBR; And 3dB bandwidth is 15Gb for 1D-SWG RCE PD whose square top mesa area is 30μm×30μm.6.Fabricate InP based SWGs by Electron Beam Lithography (EBL) and Inductively Coupled Plasma (ICP) etching. SWGs are designed according to the following optimization guidelines.SWG’s thickness is 265nm. Period is 1.4μ. Duty cycle is 33%.The average bottom roughness of SWG is reduced to 40nm after optimizing ICP conditions.7.Design and fabricate the lithography pattern mask of RCE PD with SWG. "T" style small location mark and square grating protection mask is designed for SWGs.RCE PD’s top mesa is square.8.Take part in the work of GaAs nanowire growth.Test nano morphology of Au-Ga alloy nano-particles and nanowires by Atomic Force Microscopy (AFM) and Scan Electron Microscopy (SEM) respectively.The densities of Au-Ga nano particles are 1.64×1010cm-2, 1.26×1010cm-2,2.2×109cm-2 for different thicknesses of Au film.SEM tests reveal that the length of nanowires are 5.2μm,5.3μm,6.3μm with densities larger than 109cm-2 for different nano-particles.9.GaAs nanowires are tested by Transmission Electron Microscopy (TEM).In the part of TEM sample preparation, the paper calculates the size of nanowire sample as lcm2 by SEM testing results and micro-grid holder parameters.TEM tests reveal that nanowires’diameter are 24nm, 68nm and 168nm. Nanowires grow in the[111]direction and pure zinc blend FCC lattice is discovered.更多还原