空芯光子晶体光纤光子带隙的测量与数值模拟

用全矢量平面波法计算三角结构光子晶体光纤的带隙. 用透射法测量了自制的空芯光子晶体光纤的透射谱,得到了它在可见光波段透射强度与波长的关系,并在随后的实验中观测到了传光的模场图.通过理论模拟了实验所用的空芯光子晶体光纤的带隙图,与实验结果具有较好的一致性. 关键词： 空芯光子晶体光纤 光子带隙 全矢量平面波法 透射     

基于正方形格子的空芯光子带隙光纤的模式特性和泄漏损耗

利用全矢量有限元法计算和分析了基于正方形格子的空芯光子带隙光纤的模式特性和泄漏损耗.通过分析发现,圆正方形空气孔按正方形格子排列的空芯光子带隙光纤可以实现宽带和有效的单模运转.随后对正方形格子空芯光子带隙光纤的泄漏损耗进行了全面分析,通过分析发现纤芯直径和包层空气孔间距的变化对泄漏损耗的影响较小,但可以通过调节包层空气孔间距来实现给定的波长具有最小的泄露损耗;圆化直径对泄漏损耗的影响较前两个因素要大,且存在一个最佳的圆化直径即d_c/d=0.4;包层空气孔的 关键词： 空芯光子带隙光纤 全矢量有限元法 正方形格子 泄露损耗     

空芯光子晶体光纤表面模损耗控制的研究

本文研究了纤芯结构对空芯光子晶体光纤光子带隙和传输损耗的影响,得到了适合光纤制备工艺的纤芯结构．首先利用平面波展开法计算了一定占空比三角形结构的空芯光子晶体光纤的带隙结构,给出了在传输波长λ=1．55μm时光纤的结构参数值,并模拟了纤芯直径对带隙位置和大小的影响,得出纤芯直径的取值范围,通过分析泄露损耗特性得出纤芯壁厚的取值．然后根据分析结果设计出了光纤端面图,运用全矢量有限元法模拟出在不同纤芯直径的情况下的模场分布,通过对比分析得出光纤的最佳纤芯半径R为1．6以-1．75A．研究结果表明,选择合适的纤芯结构既能满足空芯光子晶体光纤的光子带隙和损耗特征,又可以适当降低光纤制备工艺的难度．     

空芯光子带隙光纤纤芯-包层交界面的设计

利用平面波展开法计算了圆六边形空气孔按三角形排列的光子晶体带隙,基于带隙图设计了移去7根玻璃毛细管形成纤芯、传输波长λ=1.55 μm的空芯光子带隙光纤的结构参量.随后利用全矢量有限元法计算了所设计的在纤芯-包层交界面处引入石英环的光纤,给出了在不同半径情况下沿z轴方向的光强分布、光强等高线分布图和损耗随引入石英环相对厚度的变化曲线.得出了光纤消除表面模、减小损耗的纤芯外半径取值范围为1.55Λ～1.7Λ,石英环的相对厚度取值范围为1.3～1.5或3.4～3.8.通过分析发现石英环的引入既可以抑制表面模也可以激发表面模,抑制还是激发有赖于纤芯外半径和石英环厚度的选择.     

光子带隙光纤的可调谐泄漏损耗特性的研究

通过向折射率引导型光子晶体光纤的空气孔中填充可调的高折射率的材料可以获得带隙可调的光子带隙光纤.本文采用矢量平面波展开法与矢量有限元法对可调光子带隙光纤的泄漏损耗特性进行了理论研究.研究表明，这种可调光子带隙光纤的光子带隙效应使其泄漏损耗与填充材料的折射率有很强的依赖关系，同时给出了光子带隙光纤的泄漏损耗和群速度色散与归一化波长的关系.     

4.3μm低损耗硫系空芯光子带隙光纤结构设计及性能研究

运用平面波展开法分析As2S3、Ge20Se65Sb15和As2Se3硫系玻璃光纤在不同空气填充率下的带隙分布图,分析结果表明三种材料在空气填充率提高到0.75时,光子带隙与空气线均出现交汇模式,且带隙宽度大,纤芯空气孔中适宜进行激光传输.运用有限元法分析不同纤芯孔直径的Ge20Se65Sb15硫系玻璃空芯光子带隙光纤的基模限制损耗和有效模场面积,结果表明纤芯直径9.2μm时限制损耗最低,模场面积较小.通过优化光纤的结构参量,适合于4.3μm波长处高功率中红外激光传输的空芯光子带隙光纤,其限制损耗为0.00472dB/m,有效模场面积为58.046μm2.     

基于高折射率断环结构的全固光子带隙光纤的设计

设计了基于断环结构的全固光子带隙光纤,其背景材料为熔石英而断环结构由若干掺杂的高折射率介质柱构成.基于平面波展开法计算得到的态密度图和Bloch模场分布表明,该种光纤中的一个高阶带隙可以得到调节并被极大展宽,带隙调节的基本原理是断环可以同时控制包层介质柱的线偏振模式的角向和径向模式阶数.研究表明,断环中的介质柱数目决定了受影响最小的一组线偏振模式的最高角向阶数,而带隙宽度受介质柱尺寸影响很大.这一宽的高阶带隙可以用来设计带隙中心分别在800和1550 nm、带宽分别为488和944 nm的全固光子带隙光纤 关键词： 全固光子带隙光纤 光子带隙 光纤设计 平面波展开法     

光子晶体光纤带隙及模场的一种综合模拟分析方法

提出直接由MATLAB读入光纤端面图实现复杂结构光子晶体光纤(PCF)模型的快速建立,并综合平面波法(PWM)和频域有限差分(FDFD)法,模拟分析带隙型光子晶体光纤(PBG-PCF)的带隙和模场分布.利用PWM计算得到了在PBG-PCF中传输的光波频率及模式有效折射率范围;基于FDFD法在给定波长及模式有效折射率范围情况下,模拟得到了PBG-PCF中可能存在的模场分布及其他特性.以市售的PBG-PCF为例,验证了数值模拟的正确性,随后系统地分析了结构参数(晶格结构、"原子"占有率、背景材料折射率及"原子 关键词： 光子晶体光纤(PCF) 光子带隙(PBG) 平面波法(PWM) 频域有限差分法(FDFD)     

混合导引型光子晶体光纤中纤芯折射率相关的导光特性研究

利用全矢量有限元法研究了一种混合导引型光子晶体光纤在纤芯折射率改变时,光纤导光机理和模式的演变特性.当纤芯折射率小于混合包层中空气孔包层的有效折射率时,芯模的导光机理为"双带隙导引型";当纤芯折射率位于空气孔和高折射率两套包层的有效折射率之间时,芯模的导光机理为"单带隙+全内反射导引型";当纤芯折射率大于高折射率棒包层的有效折射率时,芯模的导光机理为"全内反射导引型".并对该光纤在上述三种条件下的导光特性进行了比较和讨论.这些结果对设计特殊用途的光子晶体光纤具有指导意义. 关键词： 混合导引型光子晶体光纤 带隙 模式     

PBG-PCF基模特性全矢量平面波多极方法联合数值研究

用全矢量平面波方法与多极方法联合数值研究六重对称带隙型光子晶体光纤的基模特性.通过全矢量平面波方法可确定组成PBG-PCF的二维光子晶体的带隙,基模(束缚模)存在其频率要落在带隙内且须在k0a=βa的直线附近上部区域,在带隙外形成辐射(泄漏模).把频率作为输入变量用多极方法计算,数据导出用MATLAB数学软件作出模场分布图,结果发现,不是所有基模可能存在的区域都有基模存在,为带隙型光子晶体光纤的基模寻找提供一种可行的方法.     

Optical properties of high-order band gaps in one-dimensional photonic crystal

Plane wave expansion method and transfer matrix method have been used to study the optical properties of eighty ninth photonic band gaps (PBGs) in one dimensional photonic crystal (1DPCs) with a form of Si (air|Si)₈. The results show that high order PBGs (HR-PBGs) in normalize dispersion curves have slower convergence speed than low order PBGs (LR-PBGs) and appear periodic detergency phenomena with the increasing of Λ/λ values (where Λ is the constant of one dimensional lattice and λ is wavelength) and their band widths and central wavelengths are more sensitive to fabrication errors than that of LR-PBG. Finally, some special forms of Si (air|Si)₈ structure with input and output rib waveguides are fabricated on Silicon-on-Insulator (SOI) materials by semiconductor micromachining technology. By measuring and analyzing their insertion loss spectra, we demonstrate that the HR-PBGs of 1DPCs also have the potential application in integration optics.     

Propagation effects in a polymer-based photonic liquid crystal fiber

In this paper propagation effects induced by thermal tuning of photonic band gaps (PBGs) in a polymer photonic crystal fiber (Pol-PCF) infiltrated with a specially designed liquid crystal (LC) are observed. When temperature increases PBGs in the transmission spectrum are narrowing and moving towards shorter wavelengths. However, when the temperature approaches the nematic-isotropic phase transition, PBGs are getting wider and shift back towards longer wavelengths.     

Simulation and fabrication of THz waveguides with silicon wafer by using eye-shaped pillars as building blocks

Silicon-based photonic crystal is a promising material for terahertz (THz) waveguide due to its high refractive index contrast. In this work, we introduce eye-shaped pillars as the feature building blocks for two-dimensional (2D) photonic crystals. The simulation study shows that larger TE mode band gaps (PBGs) can be created by the arrangement of dielectric eye-shaped pillars in air. The reflective spectra demonstrate that there are complex PBGs, where the peak position and intensity can be changed by varying the parameter e. Moreover, the peak of reflective spectra exhibits an obvious blue shift with the increase of incidence angle of light. When the vacant space in the structure is filled by polystyrene (PS) microspheres of 2 μm in diameter, the peak intensity of reflective spectra reduces significantly compared with that without PS microspheres, which suggests that this design can act as a sensor in the fields of biology, agriculture or medicine.     

基元配置对二维光子晶体不同能带之间带隙的调节和优化

介绍一种方法来调节和优化二维光子晶体不同能带之间的带隙.在单胞中任意位置增加一个基元,可以调节不同能带之间的带隙.而且固定两个基元的最佳位置,调节两个基元柱体边长,可以找到一个合适的配置,使各自的带隙相对带宽达到更大值.同时结果也表明双基元情况下,不同能带之间带隙优化对系统对称性要求不同,频率越高处的带隙优化要求系统对称性越低. 关键词： 光子晶体 带隙 配置 对称性     

Absolute photonic band gaps of two-dimensional square-lattice photonic crystals with Taiji-shaped dielectric rods

A novel structure of two-dimensional (2D) square-lattice photonic crystal (SLPC) composed of Taiji-shaped dielectric rods imbedded in air is constructed and the properties of absolute photonic band gap (PBG) are theoretically analyzed in both the number and width by Plane Wave Expansion Method (PWM). By comparing the absolute PBGs in 2D SLPCs consisting of four shapes of rods with different symmetries (circle, button, semicircle and Taiji) at the same filling ratio, we find that both the number and width of absolute PBG significantly increase with the breaking of scatterer's symmetry, and the Taiji-shaped rods with the poorest symmetry can attain both the most number and the largest width of absolute PBGs. Additionally, we also study the influence of dielectric constant ε and three geometric parameters of Taiji-shaped scatterer on the absolute PBG and discover that the SLPC with Taiji-shaped rods can generate at most nine absolute PBGs and the largest absolute PBG with the width 0.0485 (ωa/2πc).     

Study on the anisotropic photonic band gaps in three-dimensional tunable photonic crystals containing the epsilon-negative materials and uniaxial materials

In this paper, the properties of anisotropic photonic band gaps (PBGs) for three-dimensional (3D) photonic crystals (PCs) composed of the anisotropic positive-index materials (the uniaxial materials) and the epsilon-negative (ENG) materials with body-centered-cubic (bcc) lattices are theoretically studied by a modified plane wave expansion (PWE) method, which are the uniaxial materials spheres inserted in the epsilon-negative materials background. The anisotropic photonic band gaps (PBGs) and one flatbands region can be achieved in first irreducible Brillouin zone. The influences of the ordinary-refractive index, extraordinary-refractive index, filling factor, the electronic plasma frequency, the dielectric constant of ENG materials and the damping factor on the properties of anisotropic PBGs for such 3D PCs are studied in detail, respectively, and some corresponding physical explanations are also given. The numerical results show that the anisotropy can open partial band gaps in such 3D PCs with bcc lattices composed of the ENG materials and uniaxial materials, and the complete PBGs can be obtained compared to the conventional 3D PCs containing the isotropic materials. The calculated results also show that the anisotropic PBGs can be manipulated by the parameters as mentioned above except for the damping factor. Introducing the uniaxial materials into 3D PCs containing the ENG materials can obtain the larger complete PBGs as such 3D PCs with high symmetry, and also provides a way to design the tunable devices.     

Applications of the expanded basis method to study the properties of photonic crystals with frequency-dependent dielectric functions and dielectric losses

Band structures of two-dimensional photonic crystals (PCs) made of polar material with frequency-dependent dielectric constant are calculated by using an expanded basis method. The effect of the polariton gap (PG) of polar material on the photonic band gaps (PBGs) is explored. It is found that the PBGs are significantly modified near the PG, where the abrupt change of the dielectric constant appears. The feature of electromagnetic (EM) field is revealed when the frequency is located in the flat band. We display the equifrequency-surface configuration of the localized field and the spacial distributions of field. We observe the existence of several equi-ω curves for a specified frequency and the localized field distribution exhibiting various different patterns, dependent of the mode index. We also study the influence of the dielectric losses of the polar material on dispersion and find that the change of the real part of the Bloch wave vector is crucially related to the real part of the dielectric constant and the attenuated length is determined by its imaginary part.     

Tunable photonic band-gaps in one-dimensional photonic crystals containing linear graded index material

We have demonstrated control of the photonic band gaps (PBGs) in 1-D photonic crystals using linear graded index material. The analysis of PBG has been done in THz region by considering photonic crystals in the form of ten periods of second, third and fourth generation of the Fibonacci sequence as unit cell. The unit cells are constituted of two kinds of layers; one is taken of linear graded index material and other of normal dielectric material. For this investigation, we used a theoretical model based on transfer matrix method. We have obtained a large number of PBGs and their bandwidths can be tuned by changing the grading profile and thicknesses of linear graded index layers. The number of PBGs increases with increase in the thicknesses of layers and their bandwidths can be controlled by the contrast of initial and final refractive index of the graded layers. In this way, we provide more design freedom for photonic devices such as reflectors, filters, optical sensors, couplers, etc.     

Bandgap properties of Kagomé photonic crystal fibers

Photonic crystal fibers (PCFs) can guide light by the photonic bandgap (PBG) effect created by the periodically arranged air holes in the cladding. In this paper, the bandgap properties of Kagomé photonic crystal fibers (KPCFs) are investigated in detail. First, the bandgap properties of PCFs based on the basic Kagomé lattice are analyzed and compared with the PBGs of PCFs based on honeycomb and triangular lattices. We highlight the similarities between KPCFs and honeycomb PCFs in their PBGs, both having air-guiding regions only at very large air filling fractions (AIFs), whereas the PBGs of triangular PCFs can have large air-guiding regions at smaller AIFs due to the difference in the gap structure. In the second half of this paper, we show how the PBGs of KPCFs can be modified by introducing an extra air hole into the vacant space of the original lattice. In particular, KPCFs with medium-sized air holes can be designed to guide air by introducing extra air holes of a larger size. The air-guiding regions of KPCFs with very large air holes can also be greatly extended by the extra air holes. These air-guiding regions occur at higher normalized frequencies, resulting in larger air hole pitches favorable for fabrication. PACS 42.70.Qs; 42.25.Bs; 42.81.Qb     

Large photonic band gaps and strong attenuations of two-segment-connected Peano derivative networks

In this Letter, based on ancient Peano curves we construct four kinds of interesting Peano derivative networks composed of one-dimensional (1D) waveguides and investigate the optical transmission spectra and photonic attenuation behavior of electromagnetic (EM) waves in one- and two-segment-connected networks. It is found that for some two-segment-connected networks large photonic band gaps (PBGs) can be created and the widths of large PBGs can be controlled by adjusting the matching ratio of waveguide length and are insensitive to generation number. Diamond- and hexagon-Peano networks are good selectable structures for the designing of optical devices with large PBG(s) and strong attenuation(s).