二维光子晶体耦合腔阵列的慢波效应研究

设计了一种六角晶格二维光子晶体耦合腔阵列,平面波展开法计算能带表明,处于禁带中的耦合缺陷腔模的色散曲线在光子晶体平面内所有k矢量方向更加平坦.模拟了横电波沿ΓK方向的透射谱.与光子晶体单缺陷腔相比,耦合腔阵列结构的缺陷腔模透射率提高三个量级以上,而群速度降低一个量级,得到0.007c的结果.该慢波效应在构造微型可调谐光延迟器和低阈值光子晶体激光器等方面具有潜在的应用前景. 关键词： 光子晶体 耦合腔阵列 慢波 透射率     

基于二维光子晶体耦合腔波导的新型慢光结构研究

对二维介质柱光子晶体耦合腔波导慢光结构进行了研究,发现随着缺陷腔之间晶格个数增多,群速度减小很快,选用7×7超胞单元时耦合腔波导结构的导模最大群速度ν_g-max只有光子晶体线缺陷波导的1/251.然后对7×7超胞单元的缺陷腔周围四个介质柱半径进行调整,发现新型结构导模的ν_g-max进一步减小,最小可达到589×10^-4c,约为未调整之前的1/5.最后通过比较发现,当改变缺陷腔上下相邻两个介质柱半径时得到的结构具有更好的慢光特性.     

耦合腔光子晶体慢光波导结构

在单线缺陷结构中引入两个附加的相邻介质柱,构成一种新型的光子晶体耦合腔波导结构.通过平面波展开法对波导结构的的慢光特性进行了仿真分析,研究了平移线缺陷上下两侧介质柱,以及改变腔体的长度对器件色散特性和群速度的影响.结果表明:与平移缺陷上下两侧介质柱相比,通过改变腔体的长度,不仅可将光群速度低到0.03c(c为真空下的光速),而且器件的有效波长范围接近20nm.利用时域有限差分法得到波导结构的传输场分布图,研究波长的选取对入射激励光在光子晶体耦合腔波导中传输场的影响,发现结构参量优化后的光子晶体耦合腔波导仍然具有良好的传输特性.     

椭圆柱微腔光子晶体耦合腔波导的慢光特性研究

采用大介质柱和椭圆介质柱环绕微腔结构构成光子晶体耦合腔光波导(PC-CROW),在获得慢光的同时,其缓存特性也获得了提高。当普通介质柱半径为0.25a(a为光子晶体晶格常数),环绕微腔圆形大介质柱半径为0.35a时,得到小于2.37×10-4c(c为真空中的光速)的导模群速度,这比均匀介质柱微腔波导的最大群速度减小了一个数量级,存储容量也有所下降;考虑到缓存性能,为了进一步改善PC-CROW的慢光性能和缓存特性,将环绕微腔大介质柱椭圆化,在椭圆长轴为0.42a,短轴为0.20a时,获得导模群速度小于2.3053×10-4c,存储容量达到9.8214 bit,品质因子Q也达到了最大值3575.1。     

光子晶体耦合腔光波导慢光结构特性研究

研究了用于光缓存的光子晶体耦合腔光波导的结构对慢光传输特性的影响.详细讨论了微腔间距关于波导禁带、导模带宽、导模传输群速度的具体关系.计算发现,随着微腔之间距离的增加导模显著平坦化,群速度急剧减小.当相邻微腔之间距离为7个晶格常数时,获得了小于2×10~(-4)c的超小群速度.通过长度为13.23 μm的7×7超胞构成的光子晶体耦合腔光波导,产生的最大光延迟超过了400 ps,这比相同长度传统光波导产生光延迟大四个数量级.     

低群速度色散和低损耗的二维光子晶体慢光波导

利用平面波展开(PWE)法分析了慢光在由介质柱和空气背景构成的二维三角晶格光子晶体耦合微腔波导中的传播特性.数值模拟结果表明:随着缺陷腔之间距离的增大,导模的群速度减小很快;兼顾色散和损耗的影响,当相邻微腔间距两倍于晶格常数时,耦合微腔波导单位厚度(mm)透射比为47%,带宽为1.97 GHz,导模有效群折射率为22....     

Ku波段光子晶体加载曲折波导慢波结构

研究了Ku波段光子晶体加载曲折波导慢波结构的色散特性和耦合阻抗。用电磁仿真软件CST MWS进行了仿真, 讨论了慢波结构外光子晶体对慢波通道内电磁波的选择通过性。对具有相同结构尺寸慢波结构的研究结果表明:光子晶体加载慢波结构的色散比传统曲折波导慢波结构的色散低;和传统曲折波导慢波结构相比,光子晶体加载曲折波导慢波结构的耦合阻抗略高。     

高品质因子和高传输效率的二维光子晶体耦合腔波导研究

基于时域有限差分方法,通过仿真计算设计了一种具有较高品质因子和传输效率的二维光子晶体耦合腔波导结构。通过改变二维光子晶体波导微腔结构中隔绝波导与微腔的空气孔的半径和数量,在获得近似90%的传输效率的同时,使得品质因子达到了8.20×104。为了使品质因子在大幅度提高的同时,传输效率只有小幅度的降低,在波导微腔结构中引入了链式微腔。将链式微腔结构与传统的波导微腔结构相结合,使这种新形式的耦合腔结构的品质因子提高了1个数量级,传输效率仅下降了约40%。     

Ku波段光子晶体加载曲折波导慢波结构

研究了Ku波段光子晶体加载曲折波导慢波结构的色散特性和耦合阻抗。用电磁仿真软件CST MWS进行了仿真, 讨论了慢波结构外光子晶体对慢波通道内电磁波的选择通过性。对具有相同结构尺寸慢波结构的研究结果表明：光子晶体加载慢波结构的色散比传统曲折波导慢波结构的色散低;和传统曲折波导慢波结构相比,光子晶体加载曲折波导慢波结构的耦合阻抗略高。     

高透射率慢光速的光子晶体耦合腔波导的研究

将二维三角晶格光子晶体波导和微腔结构结合,优化设计了一种二维三角晶格光子晶体共振耦合腔波导,运用时域有限差分法(FDTD)模拟共振耦合腔波导TE偏振光的透射谱,通过透射谱得到传输光的透射率和群速度。结果表明,合适参数的二维三角晶格共振耦合腔波导在波长1.551μm处的群速度为c/130、透射率为20.1%,在波长1.502μm处的群速度为c/50、透射率为29.2%。运用平面波展开法(PWE)计算的该波导的能带结构对慢光特性进行了分析。这种慢光特性的光子晶体波导将在光存储、光延迟及光子集成等方面有潜在的应用价值。     

High efficiency filtering using two-dimensional photonic crystal coupled cavity structures

Transmission spectra of coupled cavity structures (CCSs) in two-dimensional (2D) photonic crystals (PCs) are investigated using a coupled mode theory, and an optical filter based on CCS is proposed. The performance of the filter is investigated using finite-difference time-domain (FDTD) method, and the results show that within a very short coupling distance of about 3λ, where λ is the wavelength of signal in vacuum, the incident signals with different frequencies are separated into different channels with a contrast ratio of 20 dB. The advantages of this kind of filter are small size and easily tunable operation frequencies.     

Slow wave phenomena in photonic crystals

Slow light in photonic crystals and other periodic structures is associated with stationary points of the photonic dispersion relation, where the group velocity of light vanishes. It is shown that in certain cases, the vanishing group velocity is accompanied by the so‐called frozen mode regime, when the incident light can be completely converted into the slow mode with huge diverging amplitude. The frozen mode regime is a qualitatively new wave phenomenon – it does not reduce to any known electromagnetic resonance. Formally, the frozen mode regime is not a resonance, in a sense that it is not particularly sensitive to the size and shape of the photonic crystal. The frozen mode regime is more robust and powerful, compared to any known slow‐wave resonance. It has much higher tolerance to absorption and structural imperfections.     

二维等离子体填充金属光子晶体腔体特性

设计了等离子体填充的二维金属光子晶体特殊开放腔体结构,并采用粒子模拟技术(PIC)建立了基于等离子体填充腔体结构物理模型,分析了等离子体填充下二维腔体的各模式场分布特性,以及等离子体的引入对腔体内各模式工作频率、电场幅值的影响。结果表明:腔体内各模式的电场强度随等离子体密度的增加而减弱,模式频率随背景等离子体归一化频率的提高而增加,工作模式的产生与激励方式密切相关。     

圆柱形光子晶体中电磁波的模式和带隙

利用电磁波在一维圆柱光子晶体中径向受限的条件,推导出电磁波在一维圆柱光子晶体中各个模式满足的关系式。研究了各个模式的特征。计算出TE波和TM波各模式的禁带随模式量子数、圆柱半径以及入射角的变化规律。得出了一些不同于一维非受限光子晶体带隙的新结构。     

Beaming effect in multimode photonic crystal by using coupled waveguides

Beaming effect of a multimode photonic crystal (PC) covered by a waveguide array on the exit plane is investigated theoretically. The simulation results show that the multimode PC can make the incident light split into two beams, which can be regarded as secondary sources radiating light into the waveguide array. As a result, many light beams can be generated in the array by the coupling among the waveguides, and the interference of these light beams after passing the system leads to directional emission. Additionally, the directional emission is greatly affected by the beam distribution on the exit plane of the system. Once the main light beams are formed on the exit plane of the system by modulating the system size, steady beaming effect can be obtained in the horizontal direction.     

Modes of coupled photonic crystal waveguides

We consider the modes of coupled photonic crystal waveguides. We find that the fundamental modes of these structures can be either even or odd, in contrast with the behavior in coupled conventional waveguides, in which the fundamental mode is always even. We explain this finding using an asymptotic model that is valid for long wavelengths.     

Ultrahigh-quality photonic crystal cavity in GaAs

Membrane-based photonic crystal GaAs cavities with a double-heterostructure design were investigated. They show the highest quality factors for GaAs photonic crystal cavities to date, exhibiting quality factors higher than 10(5). The resonances of these cavities were fine-tuned in steps smaller than 2 nm by digital etching.     

Vertically coupled photonic crystal optical filters

A novel design of optical filters, based on the vertical coupling between channel waveguides and photonic crystal microcavities, is proposed. The choice of channel waveguides can be arbitrary because of the flexibility of the device geometry, which makes it possible to utilize conventional low-loss waveguides. The separation between waveguides and microcavities, which determines filter bandwidths and drop efficiencies, can be accurately controlled by material growth (or deposition). The filters might also be switchable, e.g., by mechanical movements of microcavities. An example of a reflection-type optical filter is demonstrated in numerical experiments using the finite-difference time-domain method.