共查询到20条相似文献,搜索用时 15 毫秒
1.
Yun WangKe Deng Shengjun XuChunyin Qiu Hai YangZhengyou Liu 《Physics letters. A》2011,375(10):1348-1351
The unwanted reflection seriously baffles the practical applications of sonic crystals, such as for various acoustic lenses designed by utilizing the in-band properties of sonic crystals. Herein we introduce the concept of the antireflection coating into the sonic crystal-based devices. The efficiency of such accessorial structures is demonstrated well by an originally high reflection system. Promising perspectives can be anticipated in extending the antireflection coating layers into more general acoustic applications through a flexible design process. 相似文献
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Modified-DBR-based semi-omnidirectional multilayer anti-reflection coating for tandem solar cells 下载免费PDF全文
In this paper, multilayer antireflection coatings are designed by modifying the thickness of two and three paired layer distributed Bragg reflector (DBR) structure. Our proposed DBR-based structures show antireflection behaviors, in spite of the reflection treatment in traditional DBR structures. Firstly, the proposed structures are designed to be equivalent to the theoretical ideal triple-layer (TL) antireflection coating (ARC). Therefore, the problem of finding a suitable material for the middle layer of triple structure is solved. Simulation results show the significant equivalency for the reflectance of proposed structures to the ideal TL ARC at the same wavelengths and incident angles. Also, the design of the structure is changed in order to present the constant reflectance coefficient over a wide range of wavelengths. This structure enhances the omni-directionality of the multilayer ARC. 相似文献
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Elford DP Chalmers L Kusmartsev FV Swallowe GM 《The Journal of the Acoustical Society of America》2011,130(5):2746-2755
The results of numerical modeling of sonic crystals with resonant array elements are reported. The investigated resonant elements include plain slotted cylinders as well as their various combinations, in particular, Russian doll or Matryoshka configurations. The acoustic band structure and transmission characteristics of such systems have been computed with the use of finite element methods. The general concept of a locally resonant sonic crystal is proposed that utilizes acoustic resonances to form additional band gaps that are decoupled from Bragg gaps. An existence of a separate attenuation mechanism associated with the resonant elements that increases performance in the lower frequency regime has been identified. The results show a formation of broad band gaps positioned significantly below the first Bragg frequency. For low frequency broadband attenuation, a most optimal configuration is the Matryoshka sonic crystal, where each scattering unit is composed of multiple concentric slotted cylinders. This system forms numerous gaps in the lower frequency regime, below Bragg bands, while maintaining a reduced crystal size viable for noise barrier technology. The finding opens alternative perspectives for the construction of sound barriers in the low frequency range usually inaccessible by traditional means including conventional sonic crystals. 相似文献
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Modelling and simulation of acoustic wave propagation in locally resonant sonic materials 总被引:2,自引:0,他引:2
Sonic crystals are artificial structures consisting of a periodic array of acoustic scatterers embedded in a homogeneous matrix material, with a usually large impedance mismatch between the two materials. They exhibit strong sound attenuation at selective frequency bands due to the interference of multiply reflected waves. However, sound attenuation bands in the audible range are only achieved by unfunctionally large sonic crystals. If local resonators are used instead of simple scatterers, the frequencies of the attenuation bands can be reduced by about two orders of magnitude. In the present paper we perform numerical simulations of acoustic wave propagation through sonic crystals consisting of local resonators using the local interaction simulation approach (LISA). Three strong attenuation bands are found at frequencies between 0.3 and 6.0 kHz, which do not depend on the periodicity of the crystal. The results are in good qualitative agreement with experimental data. We analyze the dependence of the resonance frequencies on the structural parameters of the local resonators in order to create a tool for design and optimization of any kind of sonic crystal. 相似文献
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J. Cos J. Ferré-Borrull J. Pallarès L. F. Marsal 《Applied physics. B, Lasers and optics》2010,100(4):833-839
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. 相似文献
7.
Chen-Yang Liu 《Physics letters. A》2008,372(31):5198-5202
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. 相似文献
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Noise reduction through upward refraction can be achieved by artificial means, using a graded index sonic crystal. In addition to upward refraction, it will be shown that these periodically spaced cylinder formations can simultaneously benefit from band-gap phenomena. The aim of this paper is to present a method to optimise the broadband noise reducing performance of graded index sonic crystals, in a frequency range from well below to well above the lowest band-gap frequency. A design technique based on the creation of complex cylinder formations has been explored, in which the effective propagation speed is spatially varied using natural cubic splines. Sets of complex barrier shapes are compactly described by re-locating a number of control points in a two-dimensional cartesian plane and connecting the control points by (curved) line segments. In addition to the cluster shape, a complex graded index sonic crystal structure was formed by varying the lattice constant and the cylinder radius, where the cylinder radius was varied as a function of height. All these parameters were optimised with a multi-objective genetic algorithm, for structures based on horizontally oriented acoustically hard cylinders, located above a perfectly reflecting ground plane. A four-lane outdoor situation, with a traffic scenario consisting of 95% light and 5% heavy duty vehicles driving at 70 km/h has been studied in a two-dimensional domain. For such a configuration we obtained a spatially averaged mean reduction of 4.2–5.3 dBA, with structures covering an effective cross-sectional area of 1 m2. It was found that the insertion loss among the studied traffic lanes was reasonably constant. In addition, it was found that the low-frequency performance of the studied structures is enhanced by incrementing the barrier-height while increasing the number of scatterers as a function of height. 相似文献
11.
Acoustic wave propagation in a woodpile sonic crystal with a defect is studied theoretically and experimentally. The woodpile sonic crystal is composed of polymethyl methacrylate square rods which orthogonally stacked together, and it is embedded in air background. Defects are created by varying the width and positions of the middle rods in the periodic structure. Defect bands and transmission spectra are calculated by using the finite element method with the periodic boundary condition and the Bloch–Floquet theorem. Frequencies of defect bands are strongly dependent on the width and positions of the middle rods in the periodic structure. The experimental transmission spectra of the woodpile sonic crystals with a defect are also presented and compared with the numerical results. The defect mode properties of the woodpile sonic crystal with a defect can be applied to design novel acoustic devices for filtering sound and trapping sound in defects. 相似文献
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A detailed study of a platform of ultra-small photonic large-scale integrated circuits was conducted. Bandgap structure calculations of silicon-on-insulator (SOI) based photonic crystals have been investigated. The photonic crystal consists of dielectric cylinders in air. Using the band structure calculations we obtained design parameters for the proposed structures. The coupling between the photonic crystal and a waveguide fabricated from SOI system has been analysed. It is shown that the optical coupling is improved by interfacing different types of spot-size converters (SSCs) between the SOI waveguide and the photonic crystal. Also, the possibility and limitations of silicon doped germanium and SOI photonic crystals to analyse the light guiding in the third dimension is discussed. 相似文献
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In article a two-dimensional photonic crystal (PhC) is considered and modelled as a new generation antireflection coating for optoelectronic devices. Traditional antireflective coatings (ARCs) reduce the reflection of the radiation only – the new generation of antireflective coatings should affect the distribution of the radiation also. Such functionality can be provided by the two-dimensional PhC which reduce the reflection and scatter transmitted light. Prior to the fabrication, the PhCs should be designed and analysed. Results of the analysis should provide quantitative means for choice of materials and design solutions. In work, we analyse the electromagnetic field distribution as Poynting vectors inside the materials of optoelectronic devices, in order to investigate the possibility of improving the construction of future optoelectronic devices. Furthermore, we calculate the reflection and transmission of that ARC. It’s a complex optic analysis of new generation of ARC. The numerical analysis has been performed with the FDTD method in Lumerical Software. In work, we consider the two-dimensional photonic crystal on the top surface of optoelectronic structures. We compared the results with the traditional ARC from these same parameters as PhC: thickness and material. As an example, we presented the application of modelled, photonic crystal, thin-film, GaAs solar cells with PhC on top. The efficiency of this solar cell, using the photonic crystal, was improved by 6.3% over the efficiency of this same solar cell without PhC. Thus, our research strongly suggests that the unique properties of the photonic crystal could be used as a new generation of ARC. 相似文献
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In this paper we report a simple method to fabricate a novel subwavelength structure surface on fused silica substrate using one-step reactive ion etching with two-dimensional polystyrene colloidal crystals as masks. The etching process and the morphologies of the obtained structure are controlled. We show that the period of the obtained fused silica pillar-like arrays were determined by the initial polystyrene nanoparticle size. The height of pillar arrays can be adjusted by controlling the etching duration, which is proved to be of importance in tailoring the antireflection properties of subwavelength structures surface. The novel subwavelength structures surface exhibit excellent broadband antireflection properties, but the size of the pillar affects the antireflective properties in short wavelength region. We anticipate this method would offer a convenient and scalable way for inexpensive and high-efficiency high power laser field designs. 相似文献
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在二维三角光子晶体环形腔的周围增加六个散射介质柱,构成一个新的环形腔结构,该结构使光波的透射率达到90%,带宽也比较小。通过改变光子晶体介质柱的折射率,使环形腔的选择波长不断改变,能够明显地区分出两个不同波长,且分波波长在通信波长范围之内。将不同折射材料的光子晶体连接在一起,构成一种新的光子晶体波分复用器,相比同种材料,它具有高效率,多波长选择的优点。利用这种异质结构可以构建一个多波长的波分复用结构,它也为制作多通道波分复用器奠定了基础。 相似文献
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氮化铌(NbN)纳米线是超导纳米线单光子探测器(SNSPD)常用的光敏材料,其光学性质是影响SNSPD性能的关键因素.本文结合实验数据和仿真结果,系统研究了多种NbN超导纳米线探测器器件结构的光学特性,表征了以下四种器件结构下的反射光谱以及透射光谱:1)双面热氧化硅衬底背面对光结构;2)双面SiN硅衬底背面对光结构;3)硅衬底上以金层+SiN缓冲层为反射镜的正面对光结构;4)以分布式布拉格反射镜(DBR)为衬底的正面对光结构.并在上述四种器件结构基础上,生长了不同厚度的NbN薄膜,观察不同厚度NbN薄膜的吸收效率.经分析,发现在不同器件结构下的最佳NbN厚度与光吸收率的关系如下:双面热氧化硅衬底上的NbN层在1606 nm处最大吸收率为91.7%,其余结构在最佳NbN厚度条件下吸收率都能达到99%以上.其中双面SiN的硅衬底结构中最大吸收率为99.3%, Au+SiN为99.8%, DBR为99.9%.最后,将DBR器件实测结果与仿真结果进行了差异性分析.这些结果对高效率SNSPD设计与研制具有指导意义. 相似文献
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Sonic crystals can be used as acoustic lenses in certain frequencies and the design of such systems by creating vacancies and using genetic algorithms has been proven to be an effective method. So far, rigid cylinders have been used to create such acoustic lens designs. On the other hand, it has been proven that Helmholtz resonators can be used to construct acoustic lenses with higher refraction index as compared to rigid cylinders, especially in low frequencies by utilizing their local resonances. In this paper, these two concepts are combined to design acoustic lenses that are based on Helmholtz resonators. The Multi-Level Wave Based Method is used as the prediction method. The benefits of the method in the context of design procedure are demonstrated. In addition, symmetric boundary conditions are derived for more efficient calculations. The acoustic lens designs that use Helmholtz resonators are compared with the acoustic lens designs that use rigid cylinders. It is shown that using Helmholtz resonator based sonic crystals leads to better acoustic lens designs, especially at the low frequencies where the local resonances are pronounced. 相似文献
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光学减反膜是激光系统的重要组成部分,也是在激光照射下最容易发生损伤的部分,如何提高减反膜的激光损伤阈值是研究的热点之一。在保持目标透射光谱要求和膜系总光学厚度不变的前提下,研究了不同梯度化减反膜与激光损伤阈值之间的关系。首先采用混合渐变膜系设计方法设计了一种渐变减反膜系,G/H1→H/L/A;其次通过渐变折射率分层等效方法将渐变减反膜系进行不同的梯度化,并利用PECVD技术,在K9玻璃上沉积了满足光学性能指标要求的不同渐变减反膜系(多层梯度渐变膜系和相应的坡度渐变膜系);最后进行了激光损伤阈值(LIDT)测量。研究结果表明:在保持目标透射光谱要求和膜系总光学厚度不变的前提下,渐变减反膜系相比于传统减反膜系,抗激光损伤阈值有明显的提高;随着梯度化层数的增加,渐变减反膜系的激光损伤阈值呈减小的趋势;对于相同膜层的渐变折射率薄膜,采用坡度法制备的样片抗激光损伤阈值均优于采用梯度化制备的样片。 相似文献
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