含负折射率材料的一维光子晶体的光学传输特性

采用光学传输矩阵方法,模拟研究了由正折射率材料和负折射率材料交替组成的一维光子晶体的光学传输特性.计算了这种含负折射率材料的一维光子晶体的透射谱和色散关系.结果表明,在正入射时,含负折射率材料的光子晶体的带隙要比传统的光子晶体要大得多,并具有狭窄的透射带,从光学薄膜理论的色散关系出发解释了形成上述现象的原因.讨论了在不同的偏振模式下,光以中心波长入射时,反射率随着入射角度的变化关系.发现含负折射率材料的一维光子晶体具有更好的角度特性,可以用来实现对中心波长的全方位反射.     

Tuning the negative electromagnetic response in periodically perforated metal-dielectric-metal structures

We fabricate Ag-SU-8-Ag sandwich metamaterials perforated with a periodic array of dipoles. The transmittance spectra of both experiment and modeling have indicated the existence of low- and high-intensity transmission bands in midinfrared frequencies. The position of these transmission bands depend on the dipole length, and lattice structure. The high-intensity transmission bands are due to the excitation of the external surface plasmon plartion (SPP) modes and the localized modes, while the low-intensity transmission bands are from the excitation of the internal SPP modes. The transmittance of the low transmission bands can be increased by decreasing the relative position of the two transmission bands, and the negative electromagnetic response of the metamaterials is also increased. However, if we further decrease the relative position of the two bands, the low transmission band will be merged in the high transmission band, and no negative electromagnetic response can be retrieved.     

Ultrawide low frequency band gap of phononic crystal in nacreous composite material

The band structure of a nacreous composite material is studied by two proposed models, where an ultrawide low frequency band gap is observed. The first model (tension-shear chain model) with two phases including brick and mortar is investigated to describe the wave propagation in the nacreous composite material, and the dispersion relation is calculated by transfer matrix method and Bloch theorem. The results show that the frequency ranges of the pass bands are quite narrow, because a special tension-shear chain motion in the nacreous composite material is formed by some very slow modes. Furthermore, the second model (two-dimensional finite element model) is presented to investigate its band gap by a multi-level substructure scheme. Our findings will be of great value to the design and synthesis of vibration isolation materials in a wide and low frequency range. Finally, the transmission characteristics are calculated to verify the results.     

Investigation of one-dimensional photonic crystals composed of dispersive materials

One-dimensional photonic crystals (1DPCs) composed of dispersive materials (including negative refractive index materials, negative μ materials, and negative ? materials) are proposed. The dependence of the band gaps on the angle of incidence and thickness scale are investigated by using the transfer matrix method. Simulation results show that the band gaps of these dispersive material 1DPC are insensitive to the thickness scale. The defect modes of these doped 1DPCs behave specially when the thickness of the defect layer, the angle of incidence and the thickness scale of PC change.     

一维类梳状光子晶体中的缺陷模研究

本文研究了一种一维类梳状光子晶体的事结构及缺陷态对带隙的影响。发现这种结构的带隙来源于结构 周期性及所接分支所形成的共振态。通过移去或插入一定数目的缺陷分支在带隙中将形成局域态，通过对透射系数的研究，发现局域态以窄的尖峰形式出现在透射谱中，并且，局域态的性质与所接缺陷的数目、缺陷分支的长度及所接的位置有关。     

Metamaterial composed of wire pairs exhibiting dual band negative refraction

The design of the metamaterial that can exhibit negative refraction at two frequency bands is presented. The components of this metamaterial are cut wire pairs and continuous wires. The cut wire pairs structure in our sample can achieve the magnetic resonance at two frequency bands by appropriately designing the cut wire dimension. Through numerical simulation, the transmission property of the proposed dual band negative index metamaterial is investigated and its result shows that with the introduction of continuous wires, the stop bands for cut wire pairs (permeability μ<0) and the frequency band for continuous wires (permittivity ε<0) components would overlap and lead to the appearance of pass bands near the two magnetic resonance frequency bands. Its electromagnetic properties are then retrieved to demonstrate that the dual band left-hand behavior can be obtained in our sample structure. It is believed that our approach will be effective to make this kind of dual band negative refractive metamaterial based on the multiple magnetic resonances work at optical frequency.     

Arbitrary chirped fiber Bragg gratings on application of filtering for optical communications

This paper presents an analysis of how to obtain narrow transmission band in the centre of the spectrum of the arbitrary chirped fiber Bragg grating (ACFBG). Grating chirp coefficient and refractive index profile are the critical parameters in contributing to performance of fiber Bragg grating. The reflection spectra and transmission band were analyzed with different refractive index profile. Apodization techniques are used to get optimized reflection spectra. The simulations are based on solving coupled mode equations by transfer matrix method that describes the interaction of guided modes.     

Multiple narrow bandpass optical filters based on one-dimensional rugate photonic structures of two periodicities

A theoretical analysis of a design of multiple narrow bandpass filters based on one-dimensional (1D) rugate photonic structures with a period jump defect is presented. The optical properties, including transmittance and energy density distributions, are numerically calculated using the propagation matrix method. Our results show that multiple resonance transmission modes are produced when the period jump defect is introduced into the 1D rugate film. Both blueshift and redshift of the stop band of the rugate structure and wavelengths of resonant modes are observed, depending on the change of period jump. The number, the wavelengths, the band intervals, and the intensities of multiple resonance transmission modes are tunable by adjusting structure parameters of the rugate structure. Experimental feasibility of the proposed multiple narrow bandpass optical filters using the technique of glancing angle deposition is also discussed.     

Defect modes properties in periodic lossy multilayer containing negative index materials with symmetric and asymmetric geometric structures

In this paper, the characteristic matrix method is used to study the propagation of electromagnetic waves through one-dimensional lossy photonic crystals composed of negative and positive refractive index material layers with symmetric and asymmetric geometric structures with a defect layer at the center of the structure. First, the positive index material defect layer is considered, and the effects of the polarization and the angle of incidence on the defect mode in the transmission spectra of the both structures are investigated. The results show that the number of the defect modes in the transmission spectra depends on the geometry (symmetric or asymmetric) of the structure. In addition, it is shown that the defect mode frequency increases as the angle of incidence increases. This property is independent of the geometry of the structure. Then, for normal incidence, the negative index material defect layer is considered, and the properties of defect modes for both structures are investigated. The results can lead to designing new types of transmission narrow filters.     

Effects of electron-hole excitations in ion-surface collisions

We investigate effects related to electron-hole pair production and atomic level shift in atom scattering at surfaces by using a recently proposed exactly soluble model. We show that electron-hole pair production weakens Stückelberg oscillations and enhances loss of memory of the initial atomic charge state for narrow bands because of the diffusion of an electron or hole captured by the band. Wide band materials tend to display memory loss at lower velocities than do narrow band materials. Allowing the atomic energy level to shift above the Fermi energy tends to reduce memory loss.     

双周期厚度调制的一维光子晶体的电磁模

计算了厚度调制的双周期一维光子晶体的能带. 当一维光子晶体的厚度被周期性地调制时， 原来的能带分裂为许多子能带，其中一些很窄的子能带进入了原来的单周期光子晶体的带隙 内. 这些窄带内的电磁模的场强具有双周期性分布的特点，并有较强的局域性. 在较宽的子 能带中的电磁模是扩展的. 关键词： 光子晶体 双周期 电磁模     

含各向异性左手材料一维光子晶体的传输特性分析

采用光学传输矩阵方法,研究了由各向异性左、右手材料交替排列构成的一维人工周期结构的带隙结构和传输特性,讨论了反射率随入射角度的变化关系。结果表明,含各向异性左手材料的光子晶体比传统的光子晶体有更宽的禁带;含各向异性左手材料的一维光予晶体具有更好的角度特性,可以用来实现对某一低频波段的全方位反射;通过适当选取左手材料的参数,禁带中会出现狭窄的透射峰。     

色散负折射特异介质的1维光子晶体缺陷态

在1维光子晶体中引入色散负折射特异介质,分析了其介电常数和磁导率在微波区（1～10 GHz）与频率的关系。分别对以色散负折射介质为缺陷的正折射率介质光子晶体及以正折射率介质为缺陷的正负折射率介质光子晶体进行了数值仿真,得出了均匀平面电磁波在正入射和斜入射时的透射谱。结果表明:在介电常数和磁导率均为负值的不同禁带中,分别出现了单、双缺陷模。利用透射谱的这一特点,可实现单、双通道滤波。     

含负折射率缺陷的一维光子晶体的杂质带

利用传输矩阵方法研究了含负折射率缺陷的一维光子晶体的透射谱.以19个周期的1/4波堆存在3个负折射率缺陷的光子晶体为例进行了数值计算.结果表明:如果改变缺陷的折射率,缺陷模之间的耦合作用将发生改变,带隙中形成的杂质带也随之改变; 当这个折射率取适当值时,在禁带中出现多个尖锐的透射峰,与正折射率缺陷构成的杂质带不同.     

Band structure of two-dimensional square lattice photonic crystals of circular dispersive metamaterial rods

By virtue of the efficiency of the Dirichlet-to-Neumann map method, the details of the band structure of a two-dimensional square lattice photonic crystal composed of dispersive metamaterial circular rods in air background has been studied. We show that there are two flat bands at the band structure of the system for both H-polarization and E-polarization. These flat bands are created around the magnetic resonance frequency, surface plasmon frequency and magnetic surface plasmon frequency. We realized that the modes with frequencies lying above the resonance frequency behave like resonant cavity modes created in a single metallic cylindrical waveguide. While, due to the relatively large and imaginary refractive index of the metamaterial rods at the frequencies lying below the resonance frequency, the modes are localized modes with negligible penetration into the rods. Moreover, the modes are localized at the interface of the cylindrical metamaterial rods and the air background for the frequencies around the surface plasmon frequency and the magnetic surface plasmon frequency.     

High numerical aperture and low-loss negative refraction based on the fishnet rich anisotropy

In this paper we report both numerical and experimentally high numerical aperture on a mesostructure based on fishnet-like building blocks. Under the indefinite media framework, we are able to identify a negative refraction never cutoff band (3rd band of the extraordinary transmission metamaterial) with low-losses at millimeter-waves. We relate negative refraction with the diffraction modes of the periodic structure. The work is another step forward in the new but rapidly evolving subfield of negative refraction metamaterials by anisotropy. The breadth and utility of this approach suggests that metamaterials at their meso-scale may circumvent the problem associated to narrowness and losses exhibited by negative refractive index media at their subwavelength domain, while still being away from the wavelength scale of electromagnetic band-gap.     

纵模对光子晶体中类狄拉克点传输特性的影响

本文通过数值仿真分析了无序正方晶格光子晶体中类狄拉克点的光子传输特性. 结构中的无序是通过随机移动氧化铝介质柱的位置来实现. 研究发现, 由于纵模被激发出来, 在类狄拉克点及其附近无序对结构透射率的影响是不同的. 在类狄拉克点, 由于纵模的干扰, 透射率随着无序的增加而减小, 与通带的行为类似. 在不受纵模干扰的类狄拉克点附近, 透射率几乎不受无序的影响, 这主要是由于结构可以等效为近零折射率材料, 等效的波长非常大. 本文的研究结果有助于人们进一步理解光学纵模和零折射率材料.     

实现多共振模的一维异质结构光子晶体

用两种正折射率材料设计了一维光子晶体异质结构模型,并利用传输矩阵法对该光子晶体的透射谱进行了理论研究。结果发现:光通过光子晶体时,在较宽的禁带范围内出现透射率为100%的多条共振模,且共振模的数目与光子晶体结构周期数m相对应;当入射角一定时,共振模的位置可以通过介质的折射率、厚度来调制;当入射光入射角度增大时,多共振模出现整体蓝移,同时共振模宽度变窄。这些特性有望应用于多通道窄带滤波器的设计。     

Tunable narrow-band infrared emitters from hexagonal lattices

In this work, we present both the theoretical basis as well as supporting experimental measurements for development of a novel mid-infrared thermally stimulated narrow band emitter with a spectral bandwidth of less than 10%. To achieve this, we utilize a metallized-surface 2D photonic crystal of air voids in a silicon background with hexagonal structure symmetry. Our results are based on the generation of discrete surface plasmon (SP) modes in the thin metallized layer residing on the top surface. This yields a series of adequately spaced discrete peaks in the reflection spectrum, dominated by a single sharp feature corresponding to the lowest plasmon order, in an otherwise uniform highly reflective spectrum (>90%) over most of the IR spectrum. This, in turn, gives rise to a sharp absorption feature with a correspondingly narrow thermal emission peak in the emission spectrum. Transfer matrix calculations simulate well both the position and strengths of the absorption peaks. By altering the period of the surface photonic lattice, the SP peak and emissive band can be tuned to the desired wavelength. These devices promise a new class of tunable infrared emitters with high power in a narrow spectral bandwidth. Such narrow band sources are critical to achieving high efficiency gas sensors.