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.     

可调谐光子晶体微环腔型光分叉复用器的设计

提出了一种基于二维光子晶体微环腔的新型光分叉复用器,并可以通过改变环区的硅介质柱的折射率实现波长调谐.运用经典的微环自由光谱范围FSR和微环半径R的关系,证实新型的光子晶体微环腔也满足该关系.利用二维时域有限差分法系统分析了下路信号波长及相应效率随折射率的变化关系.结果表明,只需改变环区折射率0.005,下路波长就可以漂移1 nm,而有效微环半径还不足1.4 μm.     

可调谐光子晶体微环腔型光分叉复用器的设计*

提出了一种基于二维光子晶体微环腔的新型光分叉复用器,并可以通过改变环区的硅介质柱的折射率实现波长调谐.运用经典的微环自由光谱范围FSR和微环半径R的关系,证实新型的光子晶体微环腔也满足该关系.利用二维时域有限差分法系统分析了下路信号波长及相应效率随折射率的变化关系.结果表明,只需改变环区折射率0.005,下路波长就可以漂移1 nm,而有效微环半径还不足1.4 μm.     

二维正方晶格光子晶体三光波导方向耦合器

光子晶体是以介电常数呈周期性排布且在光波长量级构建的人工微结构,利用其具有光子禁带这一特性可实现对光子的控制。引入线缺陷可形成光子晶体波导。以1.55μm的TE偏振光作为光源,用时域有限差分法计算并分析了二维正方晶格光子晶体三光波导方向耦合器在不同波导间距下的耦合长度及耦合效率分别与介质柱折射率和介质柱半径的变化关系。研究结果为1.55μm耦合器的结构设计及制备提供一定的理论指导。     

利用二维光子晶体提高波的耦合效率

通过多重散射方法数值模拟研究和实验测量表明利用二维光子晶体可以提高波的耦合效率.研究发现,高的波耦合效率通常发生在光子禁带的边沿和其它非禁带区的某些频率处.当光子晶体的晶格常数接近于所传输的波的波长时,会出现很高耦合效率的共振耦合现象.利用二维光子晶体的情况下的波耦合效率最高可以达到不利用二维光子晶体时的1.89倍.这种现象在光集成器件中尤其有用.     

基于光子晶体耦合波导的宽带慢光研究

提出了在完整三角晶格光子晶体中引入两线缺陷构成的耦合型波导结构。通过分析谱带形对不同结构参数的依赖关系,在最优化的光子晶体耦合波导中,找到了一种独特的、群速近似为零的谱带。通过对波导宽度的啁啾实现了不同频率光的色散补偿,最终得到了带宽为13.24nm、平均群折射率为28的宽带理想慢光,并进一步采用二维时域有限差分(FDTD)算法进行了验证。数值分析结果表明,高斯脉冲在耦合波导中传输后的相对时域展宽低于10%。     

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%。     

高效多信道光子晶体滤波器的设计与仿真

利用二维光子晶体仿真设计了四信道光滤波器.首先根据时域耦合模理论导出了实现100％信道耦合的条件;然后根据该条件设计了四信道滤波器,并利用时域有限差分法进行了仿真.仿真结果显示,四信道耦合效率均超过96％,当晶格常量取570 nm时,四信道的中心频率在1 520 nm到1 580 nm之间,信道间隔均小于20 nm,信道间窜扰很小.     

光子晶体波导慢光特性研究

基于二维三角晶格空气孔光子晶体,通过在光子晶体单线缺陷波导两侧引入不同的耦合腔,设计了慢光特性较好的波导结构.利用平面波展开法计算波导的色散曲线,并分析慢光模式的群速度和群速度色散特性.耦合腔采用单缺陷腔时,适当调节波导宽度可以获得在零色散点群速度为0.0128c的慢光模式,对应在1.55 μm波长处的带宽为409 G...     

二维蜂窝格子光子晶体的远场成像特性及界面对成像质量的影响

利用有限时域差分法研究了一种二维蜂窝格子光子晶体的远场亚波长成像特性，发现和折射率为-1时的负折射成像规律符合得很好.但是由于晶格结构本身的特性，入射光以大角度入射时，这种结构的耦合效率很低，影响了像的强度和质量.通过适当改变界面上介质柱的半径的方法可以提高耦合效率，进而有效提高成像的质量和强度.     

Characteristics of Add Drop Filter using single and dual PCRR in square lattice

A Photonic Crystal Ring Resonator (PCRR) based Add Drop Filter is designed using two dimensional (2D) square lattice PC silicon rods in air host. The normalized transmission spectra for a single-ring and dual-ring configurations have been investigated using 2D Finite Difference Time Domain (FDTD). The filter characteristics such as coupling efficiency, dropping efficiency, resonant wavelength and Q factor are numerically analyzed for single ring and dual ring PCRR. It is noted that the coupling efficiency, dropping efficiency and Q factor of single ring circular PCRR with scatterer rod are 100%, 100% and 186.75, respectively. The backward dropping is observed in single ring PCRR whereas forward dropping are noticed in dual ring PCRR based ADF. The Photonic Band Gap (PBG) with respect to structural parameters such as the radius of the rod, lattice constant and refractive index difference, and propagation modes in periodic and nonperiodic structure are calculated by Plane Wave Expansion (PWE) method.     

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.     

Analysis of directional emission in square resonator lasers with an output waveguide

Square microcavity laser with an output waveguide is proposed and analyzed by the finite-difference time-domain (FDTD) technique. For a square resonator with refractive index of 3.2, side length of 4 μm, and output waveguide of 0.4-μm width, we have got the quality factors (Q factors) of 6.7 × 102 and 7.3 × 103 for the fundamental and first-order transverse magnetic (TM) mode near the wavelength of 1.5 μm, respectively. The simulated intensity distribution for the first-order TM mode shows that the coupling efficiency in the waveguide reaches 53%. The numerical simulation shows that the first-order transverse modes have fairly high Q factor and high coupling efficiency to the output waveguide. Therefore the square resonator with an output waveguide is a promising candidate to realize single-mode directional emission microcavity lasers.     

Theoretical study on biosensing characteristics of heterostructure photonic crystal ring resonator

In this paper, we investigate the biosensing characteristics of two-dimensional heterostructure photonic crystals (PCs) ring resonator theoretically by using the finite difference time domain (FDTD). The coupling air holes and inner air holes of ring resonator are treated as coupled sensing area and internal sensing area. When both of the sensing areas are filled with the same biological samples solution, the resonant peak wavelength shift of the ring resonance is different. Both the resonant peak center wavelength and peak intensity are related to the positions of sensing holes. With the same refractive index change of the biological sample, the sensing sensitivity of the coupling sensing area is much higher than that of the inner sensing area. Meanwhile, through the analysis of resonant peak wavelength shift, the refractive index change of the sample filled in the sensor area can be derived, which can be monitored real-time.     

Two dimensional Photonic Crystal Ring Resonator based Add Drop Filter for CWDM systems

In this paper, two-dimensional circular Photonic Crystal Ring Resonator (2D PCRR) based Add Drop Filter (ADF) using circular rods is designed for ITU-T G.694.2 eight channel Coarse Wavelength Division Multiplexing (CWDM) systems to add/drop a channel centered at a resonant wavelength of 1491 nm. The Plane Wave Expansion (PWE) method and 2D Finite Difference Time Domain (FDTD) method are employed to obtain the Photonic Band Gap (PBG) range and output spectra of the ADF. Close to 100% of coupling and dropping efficiencies, 13 nm of passband width and 114.69 of quality factor are observed for the designed filter at 1491 nm which is highly sufficient and fulfill the requirement of ITU-T G.694.2 CWDM system. Further, the resonant wavelength tuning possibilities of ADF are theoretically studied to cover the lower channels of CWDM systems. The structural parameters such as refractive index, lattice constant and radius of the rod in the structure are considered for resonant wavelength tuning.     

Loss analysis and increasing of the fabrication tolerance of resonant coupling by tapering the mode beating section

The film mode matching method was used to analyze the inter waveguide coupling losses in a passive asymmetric twin waveguide caused by waveguide width and refractive index variation for both resonant and adiabatic coupling at a wavelength of 1,550 nm. The reasons for power losses are shown. It is demonstrated that tapering the mode beating section of the resonant coupler can increase the fabrication tolerance of resonant coupling without increasing the coupling length.     

基于LiNbO_3的长周期波导光栅可调谐耦合器的设计

设计了一种基于LiNbO_3的长周期波导光栅可调谐耦合器.该耦合器利用长周期光栅的独有特性将输入波导的导模经包层模耦合至输出波导导模.由于LiNbO_3的电光效应,波导光栅芯层与包层的有效折射率随外加电压变化,从而耦合器的谐振波长及耦合效率可由外加电压调谐.分析了光栅周期与耦合器的长度对耦合器带宽和耦合效率调谐范围的影响,以及波导尺寸对谐振波长调谐灵敏度的影响.结果表明光栅周期越短,耦合器长度越长,则耦合器的带宽越窄,耦合效率调谐范围也越大.此外,谐振波长调谐灵敏度随波导宽度的增加而减小,而波导厚度对谐振波长调谐灵敏度的影响可以忽略.对光栅周期为94μm、长度为3.52cm的耦合器进行仿真,结果表明,谐振波长灵敏度为26.2pm/V,3dB带宽可达4.5nm,当外加电压从0变化到200V时,谐振波长变化5.24nm,耦合效率可在1到0.15之间进行调谐.