一维无序结构光子晶体的能带特性研究

通过引入结构参数a，深入研究了具有无序结构的一维二元光子晶体的能带特性。研究发现，无序结构有效拓宽了光子带隙，与均匀结构相比，拓宽率达到200％以上；无序一维光子晶体表现出从可见到红外很宽区域的高反射特性。本文还计算和分析了入射角和无序度D对光子晶体带隙的影响。     

无序一维三元光子晶体的带隙展宽

Bandgap properties of disordered one-dimensional (1D) ternary photonic crystals are investigated by optical transfer matrix method for the first time . The results show that disordered structure provides strikingly extended bandgap compared with the corresponding periodic structure. The more ingredient of disordered dielectric multilayers adopted in the calculation, the wider stop band will be obtained. The influence of degree of disorder D and contrast of high and low refractive indices to the photonic bandgap are also calculated and discussed.     

异质结构光子晶体的能带特性研究

运用光学传输矩阵理论,研究了异质结构光子晶体的能带特性。结果表明,与周期结构相比异质结构光子晶体可以显著地拓宽光子晶体的光子带隙;在该文提出的结构中引入缺陷,与(1H1L)m(1H)n(1L1H)m光子晶体相比,产生缺陷模式光子带隙范围明显拓宽,适当调整缺陷层的数目、位置和厚度可得到多通道滤波;并研究了实际操作中随机误差带来的影响,随无序度的增大,其带宽基本不变。     

两端有慢变结构的光子晶体的能带特性研究

研究了几种两端有慢变周期结构的光子晶体的能带特性，研究发现，通过在普能光子晶体两端添加适当的慢变周期结构，可以使光子晶体的光子禁带区向短波区或向长波区扩展，也可以同时向短波和长波两个区域扩展，与普通结构的光子晶体的光子禁带宽度相比，可以获得400％以上的禁带区宽度的拓展。     

Numerical study on characteristic of two-dimensional metal/dielectric photonic crystals

An improved plan-wave expansion method is adopted to theoretically study the photonic band diagrams of twodimensional(2D) metal/dielectric photonic crystals.Based on the photonic band structures,the dependence of flat bands and photonic bandgaps on two parameters(dielectric constant and filling factor) are investigated for two types of 2D metal/dielectric(M/D) photonic crystals,hole and cylinder photonic crystals.The simulation results show that band structures are affected greatly by these two parameters.Flat bands and bandgaps can be easily obtained by tuning these parameters and the bandgap width may reach to the maximum at certain parameters.It is worth noting that the hole-type photonic crystals show more bandgaps than the corresponding cylinder ones,and the frequency ranges of bandgaps also depend strongly on these parameters.Besides,the photonic crystals containing metallic medium can obtain more modulation of photonic bands,band gaps,and large effective refractive index,etc.than the dielectric/dielectric ones.According to the numerical results,the needs of optical devices for flat bands and bandgaps can be met by selecting the suitable geometry and material parameters.     

二维三维混杂及准三维嵌套复式光子晶体带隙研究

提出了由两套晶格嵌套组成的全新二维/三维混杂及准三维嵌套复式周期光子晶体结构,并通过理论计算获得了带隙位置主要取决于外周期晶格常量,内周期有助于获得超窄禁带的新型带隙特性.这种内外结构周期效应同时发挥带隙调制作用的性质是该类嵌套复式结构所特有.从理论上验证了嵌套结构利用小尺寸周期调制大波长禁带的可行性.     

二维光子晶体量子阱的光谱特性研究

研究了二维光子晶体量子阱的光谱特性,该量子阱结构由二维正方晶格圆柱晶胞光子晶体通过移去中间位置的介质圆柱层形成。由于光子晶体中的光子禁带充当了光子运动的势垒,类似于半导体量子阱中电子的行为,在光子晶体量子阱结构中会出现量子化的光子能态。文章利用平面波展开法计算了所用光子晶体的能带结构,利用传输矩阵方法计算了量子阱结构的透射光谱。计算结果表明,在光子禁带中出现了离散的透射峰,透射峰的强度随着势垒宽度的增加而减弱,个数随着势阱宽度的增加而增加,通过计算得到了其定量关系,并且讨论了透射峰频率与势阱宽度的关系。     

A new fabrication technique for photonic crystals: Nanolithography combined with alternating-layer deposition

We propose two photonic crystal structures that can be created by combining nanolithography with alternating-layer deposition. Photonic band calculations suggest that a drilled alternating-layer photonic crystal combining two-dimensional (2D) alternating multilayers and an array of vertically drilled holes may achieve a full photonic bandgap. In addition, a 3D/2D/3D cross-dimensional photonic crystal, which sandwiches a 2D photonic crystal slab between three-dimensional (3D) alternating-layer photonic crystals, should provide better vertical confinement of light than a conventional index guiding slab. Fabrication techniques based on existing technologies (electron beam lithography, bias sputtering, and low-pressure ECR etching) require very few process steps. Our preliminary fabrication suggests that, by refining these technologies, we will be able to realize photonic crystals.     

Terahertz demonstrations of effectively two-dimensional photonic bandgap structures

We demonstrate effectively two-dimensional (2D) terahertz (THz) photonic bandgap (PBG) structures for transverse electromagnetic (TEM) mode propagation within metal parallel plate waveguides (PPWG). The 2D-PBG structures consisting of square arrays of dielectric cylinders were characterized by THz time-domain spectroscopy (THz-TDS). THz photonic bandgaps were observed, as determined by the 160 mum lattice constant, the 65 mum diameter, and the dielectric constant of the cylinders. The experimental measurements were fitted with excellent agreement to 2D theory, confirming that for TEM mode propagation, effectively 2D propagation experiments can be achieved within the bounded space of the PPWG.     

3D-2D-3D photonic crystal heterostructures fabricated by direct laser writing

Using direct laser writing, we fabricate photoresist templates for 3D-2D-3D photonic crystal heterostructures for what we believe to be the first time. The optical properties of these structures are directly compared with the theoretical ideal, revealing good agreement and hence good sample quality. This provides an experimental starting point for the microfabrication and testing of broadband, 3D air-waveguide microcircuitry in photonic bandgap materials.     

一维和二维系统中电子禁带与光子禁带的数学等价特性

论证了在不针对特殊的结构和未做任何近似的情况下,一维和二维系统中的电子的Schrdinger方程和沿垂直方向传播的S极化光子的Maxwell方程具有完全相同的数学形式,即二者在数学上是完全等价的,这自然解释了到目前为止发现的存在于电子晶体的电子禁带和光子晶体的光子禁带之间的许多相似性.这种等价性还表明,在电子晶体中出现的许多现象可以推广到光子晶体中;研究电子晶体的理论和方法也可以应用于光子晶体的研究中去.     

Analysis of tunable bandgaps in liquid crystal-infiltrated 2D silicon photonic crystals

We present a theoretical study on two-dimensional photonic crystals composed of silicon and the E7 liquid crystal. We analyze how the optical axis orientation of the liquid crystal influences the photonic bands and bandgaps, for the case when the Maxwell equations can be decoupled into the TE and TM modes. We consider two different structures, a triangular lattice of E7 liquid crystal cylinders in a silicon background and a triangular lattice of silicon cylinders in an E7 liquid crystal background. The effect of the liquid crystal anisotropy on the geometry of the irreducible Brillouin zone allows us to propose a simplified way to calculate the photonic bandgaps. Results show that the bandgap width and center frequency have a 60° periodicity for both structures. Using the plane-wave expansion method, we determined the maximum bandgap and the optimal radius of the cylinders for each structure. Finally, for the second structure, we propose an optical switch with a 50% duty cycle. These structures can be applied to design tunable photonic devices.     

Photonic network laser

We demonstrated lasing in two-dimensional trivalent network structures with short-range order. Despite the lack of translational and rotational symmetries, such structures possess a large isotropic photonic bandgap. Different from those of a photonic crystal, the band-edge modes are spatially localized and have high quality factor.     

Modeling of realistic cladding structures for air-core photonic bandgap fibers

Cladding structures of photonic bandgap fibers often have airholes of noncircular shape, and, typically, close-to-hexagonal airholes with curved corners are observed. We study photonic bandgaps in such structures by aid of a two-parameter representation of the size and curvature. For the fundamental bandgap we find that the bandgap edges (the intersections with the air line) shift toward shorter wavelengths when the air-filling fraction f is increased. The bandgap also broadens, and the relative bandwidth increases exponentially with f2. Compared with recent experiments [Nature 424, 657 (2003)] we find very good agreement.     

异质镜像光子晶体的光子带隙研究

对异质镜像结构光子晶体(ABCCBA)^N进行了研究。首先,利用一维介电体系中处理光传播的方法--传输矩阵法,详细推导了异质镜像光子晶体透射率的计算公式;然后,采用Matlab软件编程仿真并分析了光子带隙形成与镜像周期数目、光子带隙数目与光子晶体薄层厚度、光子带隙位置与入射角大小等的关系。结果表明:光子带隙的形成及变化主要受光子晶体薄层厚度及入射角大小变化的影响。通过改变影响光子晶体光子带隙的参数,可得到不同频段的光子带隙,用来制作高质量反射镜、滤波器和发光二极管等。     

Eigenstate statistics and optical properties of one-dimensional disordered photonic crystals

Optical eigenstates in one-dimensional disordered photonic crystals were studied. The threshold disorder level was established below which the probability of appearance of an eigenstate at the photonic bandgap center is negligible. The threshold is reached when the relative fluctuation in the optical lengths of the structure periods becomes equal to the square root of one-third of the relative bandgap width. The dependence of the ensemble-averaged structure transmission coefficient on the fluctuation of the period optical length has a break corresponding to the threshold fluctuation.     

Temperature dependence of the photonic bandgap and the orientational order parameter for a cholesteric photonic crystal

The reflection spectra of a cholesteric photonic crystal have been measured. The experimental spectra are described by a theoretical expression that follows from the analytical solution of the Maxwell equations. The photonic bandgap width Δν has been determined. The photonic bandgap width changes abruptly as the position of the diffraction band changes. The temperature dependence of the relative bandgap width Δν/ν₀ and the order parameter for a photonic crystal are described by Landau’s theory of phase transitions.     

光子晶体在微波技术中的应用

文章以高方向性天线及光子晶体微带传输线为例，综述了光子晶体在微波技术中的研究进展．将光子晶体与传统的微波技术相结合，可以设计并制作许多小型、高效的新型微波器件．这类新型光子晶体材料在微波通讯中有着广阔的应用前景。     

Creation of tunable absolute bandgaps in a two-dimensional anisotropic photonic crystal modulated by a nematic liquid crystal

Photonic crystals (PCs) have many potential applications because of their ability to control light-wave propagation. We have investigated the tunable absolute bandgap in a two-dimensional anisotropic photonic crystal structures modulated by a nematic liquid crystal. The PC structure composed of an anisotropic-dielectric cylinder in the liquid crystal medium is studied by solving Maxwell's equations using the plane wave expansion method. The photonic band structures are found to exhibit absolute bandgaps for the square and triangular lattices. Numerical simulations show that the absolute bandgaps can be continuously tuned in the square and triangular lattices consisting of anisotropic-dielectric cylinders by infiltrating nematic liquid crystals. Such a mechanism of bandgap adjustment should open up a new application for designing components in photonic integrated circuits.     

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