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。     

一种新型高透射率高品质因子光子晶体耦合腔波导结构

提出了一种在二维三角晶格光子晶体线缺陷波导中放置椭圆空气孔的耦合腔波导结构。基于平面波展开法,利用MPB对线缺陷波导的能带结构进行了计算并给出能带图。基于时域有限差分法（FDTD）,利用MEEP对椭圆空气孔在波导中的排列方式、数量、尺寸进行优化设计,并对频率位于微腔共振频率处的光波在耦合腔波导结构中的品质因子和传输特性进行研究与比较,给出了电场分布图。仿真结果表明,当椭圆空气孔的长轴方向纵向排列时,相应的微腔共振频率在光子禁带内可获得90%以上的透射率,对应的品质因子Q可达10⁴量级;选择合适的参数,获得的Q可高达10⁷量级,对应共振频率的透射率仍在60%以上。     

二维三角晶格光子晶体波导的出射光集束传播

为了解决光子晶体波导出射端光场控制, 同时解决二维三角晶格光子晶体波导出射光辐射困难的问题。利用二维三角晶格光子晶体设计了一种新型光子晶体波导出射口结构。在二维三角晶格光子晶体波导出射端引入两个微腔, 通过光波与微腔发生共振, 形成类似于三个点光源干涉的出射光, 同时进一步提出波导出射端喇叭口干涉出射光定向辐射的设计。通过这种微腔喇叭口设计, 利用时域有限差分法分析结果表明光波实现很好的定向辐射, 并且辐射距离显著提高。     

高下路空气孔型光子晶体环形谐振腔的设计

提出一种基于二维正方晶格光子晶体空气孔型高下路效率的环形谐振腔,通过压缩线缺陷波导的宽度实现单模有效控制,同时讨论内围光子晶体列数对传输场的影响,然后运用二维时域有限差分方法数值分析了耦合强度及环区局部折射率调制对下路效率、品质因子以及下路波长等参量的影响.结果表明:当波导宽度为0.7个晶格常量,耦合强度为0个晶格常量,在信道波长为1 528.1nm时,下路效率为99%,品质因子Q为379;当耦合强度提高到1个晶格常量,下路波长稍微漂移为1 524.3nm,品质因子显著提高到1 397,而下路效率下降为89%.同时,下路波长会随着环区折射率的增加呈线性红移.     

高下路空气孔型光子晶体环形谐振腔的设计

提出一种基于二维正方晶格光子晶体空气孔型高下路效率的环形谐振腔,通过压缩线缺陷波导的宽度实现单模有效控制,同时讨论内围光子晶体列数对传输场的影响,然后运用二维时域有限差分方法数值分析了耦合强度及环区局部折射率调制对下路效率、品质因子以及下路波长等参量的影响.结果表明:当波导宽度为0.7个晶格常量,耦合强度为0个晶格常量,在信道波长为1 528.1 nm时,下路效率为99%,品质因子Q为379;当耦合强度提高到1个晶格常量,下路波长稍微漂移为1 524.3 nm,品质因子显著提高到1 397,而下路效率下降为89%.同时,下路波长会随着环区折射率的增加呈线性红移.     

一种新型高效光子晶体多信道下载滤波器的设计

采用二维正方排列的光子晶体,根据微腔缺陷模和波导模共振耦合原理,设计了一种新型的多信道下载滤波器,该滤波器通过主波导、90°弯波导和共振微腔的组合,提高了各个信道下载波导的下载效率。利用二维时域有限差分法模拟了滤波器的传输特性,并理论分析了影响下载效率的因素,进一步对滤波器进行了优化,使得各信道下载波导的下载效率均在91%以上。模拟结果表明该滤波器能有效地实现光波的分波下载,传输谱信道波长间隔约为20nm,中心波长误差为±2nm,传输谱的最大半宽度为3.2nm,有良好的波长选择性,证实了增大下载波导和共振微腔的耦合区域可以有效地提高滤波器的下载效率。     

打破光子晶体非线性Fano腔结构对称性实现单向传输

设计了一种基于二维光子晶体波导旁侧Fano微腔的全光二极管结构,实现光的单向传输。其关键技术是在光子晶体波导中采用简单反射层打破Fano微腔结构上的空间对称性,使得反射层两侧波导与微腔耦合效率不对称。两侧波导入射光激发微腔非线性克尔材料所需的光强阈值不同,从而实现单向导通功能。通过有限时域差分(FDTD)方法对其传输特性和性能进行了数值仿真和分析,研究发现:该结构在较低的光强阈值下可以实现正向导通、反向截止的全光二极管效果;该结构具有超快的响应时间,达到皮秒量级;该结构具有较高的最大透射率(达到90%)和较高的正反透射比。基于光子晶体结构的设计使得该器件可以具有很好的工作波长可调特性,并易于在目前半导体工艺基础上进行制作以及与其他器件集成。     

波导基本结构对光子晶体耦合腔光波导慢光特性的影响

研究了二维光子晶体耦合腔波导的结构对慢光特性的影响,发现微腔间的距离n、填充因子r/a和缺陷柱的尺寸rd是影响光子晶体禁带中慢光导模传输特性的重要参数。随着缺陷微腔间距离的增加,导模群速度vg急剧减小;当填充因子和缺陷柱尺寸增加时,导模向低频方向移动,同时,导模群速度降低;填充因子和缺陷柱尺寸降到一定数值后,vg达到最小值,此后,当r和rd分别超出其特定值继续增大,导模群速度反而增大。取微腔之间介质柱个数为6,普通介质柱尺寸为r=0.22a,a为光子晶体晶格常数,缺陷柱尺寸为rd=0.12a,得到导模群速度最大值vgmax1.93×10-3c,带边处vg10-4c(c为光速)。这一结果显示,通过基本结构设计可以实现对光子晶体耦合腔光波导中慢光的有效控制,这将为基于光子晶体功能器件的设计和应用提供有效的支持。     

液晶调制光子晶体微腔光衰减器

设计了一种二维液晶调制光子晶体微腔光衰减器。两条二维三角晶格空气孔光子晶体波导由一个光子晶体微腔连接,在微腔的点缺陷中填充苯乙炔类液晶。通过施加不同电压,电场诱导液晶取向以改变液晶的折射率,从而改变光子晶体微腔的谐振波长,进而实现光传播强度调节。运用时域有限差分方法和平面波展开法分析了二维液晶调制光子晶体微腔光衰减器的光学特性。数值计算结果表明:对于1.55μm通信波段,通过外界电场控制所填充的向列相液晶的方向可以对这种二维液晶调制光子晶体微腔光衰减器实现3.40%～99.58%的可调谐光输出。     

光控液晶光子晶体微腔全光开关

设计了一种缺陷模迁移光子晶体微腔全光开关. 两条二维三角晶格空气孔光子晶体波导由一个光子晶体微腔连接, 在微腔的点缺陷中填充掺有少量偶氮聚合物的苯乙炔类液晶. 通过调节控制光的偏振态, 使偶氮聚合物发生顺-反异构化反应, 带动液晶分子重新取向, 从而改变光子晶体微腔的谐振波长, 进而实现光的通过与截止. 运用时域有限差分法和平面波展开法分析 了二维光控液晶光子晶体微腔全光开关的光学特性. 数值计算结果表明: 对于1.55 μ通信波段通过外界偏振光控制所填充的向列相液晶 的折射率可以实现对光波的导通与截止. 分析结果显示, 此开关具有阈值低, 消光比较大, 体积小等优点. 关键词： 二维光子晶体微腔 波导 时域有限差分(FDTD) 液晶     

Low group velocity in a photonic crystal coupled-cavity waveguide

A two-dimensional photonic crystal coupled-cavity waveguide is designed and optimized, the transmission spectrum is calculated by using the finite-difference time-domain method, and the group velocity of c/1856 is obtained. To our knowledge, this value of group velocity is the lowest group velocity in a photonic crystal waveguide calculated from its transmission spectrum so far. The result is confirmed by the photonic band structure calculated by using the plane wave expansion method, and it is found that the photonic crystal waveguide modes in a photonic band structure are in accordance with those in the transmission spectrum by using the finite-difference time-domain method. The mechanism of slow light in the coupled-cavity waveguide of photonic crystal is analysed.     

Photonic crystal optical switch using a new slow light waveguide and heterostructure Y-junctions

In this paper we propose a photonic crystal Mach-Zehnder interferometer (MZI) based on a new coupled-cavity waveguide, where its advantage over the previous type of photonic crystal coupled-cavity waveguide is discussed. A heterostructure Y-junction is comprised of square and hexagonal lattices of the new coupled-cavity waveguide. It is designed by applying the temporal coupled-mode theory and is optimized, where an overall throughput efficiency of more than 90% is achieved at the wavelength of 1.55 μm. The design of the Y-junction is performed using finite-difference time-domain method. The designed heterostructure Y-junction is used in the structure of a MZI, where its arms are approximately as short as 24 μm. Finally, the transient response of the proposed optical switch is investigated.     

慢光在光子晶体弯折波导中的高透射传播

研究了慢光模式在SOI(silicon-on-insulator)材料光子晶体线缺陷弯折波导中的传输特性. 通过优化波导弯折处的结构参数,慢光模式在光子晶体60°与120°弯折波导中的透射率提高10倍以上,归一化透射率分别达到80%和60%以上. 为了进一步减慢光速,设计了新颖的高Q值耦合腔弯折波导结构,在归一化透射率达到75%的基础上,光波群速度低至c/170(c为真空光速). 研究结果对于增强光子晶体的慢光效应,提高光子晶体慢光器件的微型化和集成化都有一定的积 关键词： 光子晶体 慢光 弯折波导 透射率     

基于六角格子光子晶体波导的高效全光二极管设计

提出了一种基于六角格子光子晶体波导微腔和Fabry-Perot(FP)腔非对称耦合的全光二极管结构, 它由一个包含非线性Kerr介质的高Q值微腔与一个光子晶体波导中的FP腔组成. 通过有限时域差分方法对其传输特性进行了仿真, 发现通过两腔的非对称耦合可以实现在特定光强度下的正向传输、反向截止的功能. 在靠近微腔方向光入射时, 特定强度的光可以激发非线性微腔的Kerr效应, 改变了Fano腔的共振频率, 从而变成透射状态. 而远离微腔方向光入射, 由于这个不对称的结构造成场局域的分布不对称, 激发微腔Kerr效应的光强还不够, 所以光不能透射. 所设计的全光二极管结构具有良好的性能参数: 最大透射率高和高透射比、光强阈值低和易于集成等.     

Design and optimization of photonic crystal based eight channel dense wavelength division multiplexing demultiplexer using conjugate radiant neural network

In this paper, two dimensional photonic crystal, based eight-channel demultiplexer is proposed and designed for DWDM applications. The performance parameters of the demultiplexer such as transmission efficiency, channel spacing, spectral line width, Q factor, and crosstalk have been evaluated. The proposed demultiplexer comprises of bus waveguide, drop waveguide and parellogram resonant cavity (PRC). The bus waveguide transmits light to the PRC and exits through respective drop waveguide. The PRC consists of a parellogram resonator with a nano ring cavity that is used for dropping eight specific wavelength for ITU-T G 694.1 standard with 50 GHz channel spacing. The circular ring resonator is placed above the PRC wherein a resonant air hole (Cr) is positioned for desired channel selection. The channel selection is done by altering the radius of the air hole. In addition, a conjugate radiant neural network is implemented for optimizing the radii of resonant air holes to select the required channel wavelength. The proposed device is very compact and it could be considered for implementing the photonic integrated circuits.     

Numerical characterization of nanopillar photonic crystal waveguides and directional couplers

We numerically characterize a novel type of a photonic crystal waveguide, which consists of several rows of periodically arranged dielectric cylinders. In such a nanopillar photonic crystal waveguide, light confinement is due to the total internal reflection. A nanopillar waveguide is a multimode waveguide, where the number of modes is equal to the number of rows building the waveguide. The strong coupling between individual waveguides leads to the proposal of an ultrashort directional coupler based on nanopillar waveguides. We present a systematic analysis of the dispersion and transmission efficiency of nanopillar photonic crystal waveguides and directional couplers. Plane wave expansion and finite difference time domain methods were used to characterize numerically nanopillar photonic crystal structures both in two- and three-dimensional spaces.     

Special control of the cutoff frequencies in a 2D photonic crystal coupled-cavity waveguide

We show theoretically that the upper and lower cutoff frequencies of the guided band in a 2D photonic crystal coupled-cavity waveguide can be controlled independently or synchronously by changing two configuration parameters of the waveguide simultaneously. The independent control range for the lower and upper cutoff frequencies can be as large as 68.6% and 67.9% of photonic band gap, respectively. The two cutoff frequencies can also be tuned in the same direction over equal distances up to 25.7% of photonic band gap. These results offer an efficient way for designing the various dispersion relations for photonic crystal waveguides.