共查询到20条相似文献,搜索用时 31 毫秒
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A. A. Greshnov M. A. Kaliteevskiĭ R. A. Abram S. Brand G. G. Zegrya 《Physics of the Solid State》2007,49(10):1999-2003
An analytic theory of the density of states in one-dimensional disordered photonic crystals is proposed. It is shown that the problem of the density of optical modes can be reduced in the small dielectric contrast approximation to solving a generalized Fokker-Planck equation for the distribution function of the logarithmic derivative of the electric field (the wave phase). The exact analytic solution and density-of-states asymptotics deep in the band gap of the photonic crystal and close to the band gap edge are derived. The results obtained agree well with the empirical relations derived earlier from numerical experiments. 相似文献
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Lanxiang Chen 《Physics letters. A》2018,382(18):1195-1201
As a new technique for authentication and key generation, physically unclonable function (PUF) has attracted considerable attentions, with extensive research results achieved already. To resist the popular machine learning modeling attacks, a framework to enhance the security of PUFs is proposed. The basic idea is to combine PUFs with a chaotic system of which the response is highly sensitive to initial conditions. For this framework, a specific construction which combines the common arbiter PUF circuit, a converter, and the Chua's circuit is given to implement a more secure PUF. Simulation experiments are presented to further validate the framework. Finally, some practical suggestions for the framework and specific construction are also discussed. 相似文献
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无序一维三元光子晶体的带隙展宽 总被引:11,自引:7,他引:4
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. 相似文献
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Zheng Yang Xiaowen Zhao Yuqiao Ding Qin Yang 《Journal of Macromolecular Science: Physics》2019,58(1):113-127
A series of phenolic epoxy resin (PEP) modified polyurethane foams (PUF) were prepared via an in-situ polymerization, one step process. It was found that the epoxy modified PUF foam exhibited a perforated network structure with larger cell size, higher open cell porosity and enhanced ovality compared with pure PUF. With increasing content of PEP, the tensile strength, elongation at break and low temperature modulus of PUF decreased. A single Tg was observed for PEP modified PUF, indicating that the two component phases of the polyurethane-epoxy were miscible. With increasing PEP content, the Tg of PUF shifted slightly to higher temperature, tan δmax dropped to lower values, and the retention value of the storage modulus at ?20 and ?10?°C increased. For pure PUF, the cell walls degraded and the structure became disordered after aging under heat and stress, while for PUF/20wt%PEP, the degradation degree was obviously reduced, and an orientation of the cells along the stress direction and a density increase was observed. During aging at 200?°C, the retention of the mechanical properties of PUF/20wt% PEP was much higher than that of pure PUF, and it showed superior stability under heat and stress, attributed to incorporation of the thermally resistant oxazolidone rings and benzene rings in the PU backbones, the highly cross-linked networks of the polyurethane-epoxy systems and the obvious orientation of the cells under stress. 相似文献
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《Waves in Random and Complex Media》2013,23(1):65-90
A new electromagnetic method is developed for the mean field analysis of discrete random media in which particles are distributed in disjoint regions in space. This type of distribution can be observed in organized vegetation canopies, photonic band gap materials and disordered crystals. The method is based on an ‘effective scatterer’ concept. As far as the mean field is concerned, the random problem is approximated by a deterministic one composed of effective scatterers. Application of the effective scatterer approach to two-dimensional mean field propagation through a cylinder distribution that is periodic on average is verified by Monte Carlo simulations. Comparisons with other known methods such as the Foldy approximation are also presented. 相似文献
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A new electromagnetic method is developed for the mean field analysis of discrete random media in which particles are distributed in disjoint regions in space. This type of distribution can be observed in organized vegetation canopies, photonic band gap materials and disordered crystals. The method is based on an 'effective scatterer' concept. As far as the mean field is concerned, the random problem is approximated by a deterministic one composed of effective scatterers. Application of the effective scatterer approach to two-dimensional mean field propagation through a cylinder distribution that is periodic on average is verified by Monte Carlo simulations. Comparisons with other known methods such as the Foldy approximation are also presented. 相似文献
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将石墨烯中赝磁场的产生机理运用于光子石墨烯,通过在光子石墨烯中引入晶格有规律单轴形变的方式,理论分析得到了谷依赖的均匀赝磁场,并通过数值模拟的方法观察到明显的谷霍尔效应.这种谷霍尔效应的显著程度随晶格形变度的增加而加强.在具有一定损耗的电介质材料构成的形变光子石墨烯中仍可观察到明显的谷霍尔效应.随着电介质材料损耗的增加,谷霍尔效应导致的波束转弯效果依然能够保持,只是强度逐渐变弱.类似于自旋电子学中的自旋霍尔效应,这种光子石墨烯中等效赝磁场作用下的谷霍尔效应在未来谷极化器件的设计和应用中具有重要意义. 相似文献
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We present an investigation of disordered photonic crystals (PhCs) based on the combination of photonic Wannier functions with the concept of the coherent potential approximation (CPA). In particular, we provide the theoretical foundation of a real-space cluster CPA that is causal, enforces the proper symmetries of the effective medium, and includes effects of multiple scattering of the same and nearby defects, which is essential for strong defects. Based on this, we present results for the density of states of disordered PhCs for different types of disorder. Our results are thus relevant to such diverse areas as random lasing and the analysis of fabricational imperfections in PhCs. 相似文献
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In order to study the design flexibility of photonic bandgap structures, we investigate different examples of 1D traditional
Bragg layers and 2D photonic crystals. We have also considered a simple case of 3D woodpile structures. It turns out that
in systems with large gaps, the evanescent waves penetrate into the bulk only distances comparable to one lattice constant.
Therefore confinement of light can also be achieved without long range order, which leads to the introduction of novel photonic bandgap designs. Adhering to some constraints, the changes
in the photonic bandgap in disordered structures are negligible. The important quantity to characterize the presence or absence
of modes is the local photonic density of states, however bandgap phenomena in size and position disordered arrangements can
also be verified with plane wave supercell calculations as well as finite difference time domain techniques. 相似文献
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Birefringence properties of a disordered two-dimensional photonic crystal are demonstrated experimentally for the first time. It is proposed to use porous anodic aluminum oxide, which has anisotropy on the scale of the wavelength of light, as a new birefringent material in the optical range. An original method for studying the birefringence properties of two-dimensional photonic crystals based on the use of monochromatic light is described. 相似文献
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X. Xu 《Applied physics. B, Lasers and optics》2007,86(3):467-471
The photon localization in disordered two-dimensional photonic crystal is studied theoretically. It is found that the mean
transmission coefficient in the photonic band decreases exponentially as the disorder degree increases, reflecting the occurrence
of Anderson localization. The strength of photon localization can be controlled by tuning the disorder degree in the photonic
crystal. We think the variation regular of the transmission coefficient in our disordered system is equivalent to that of
the scaling theory of localization.
PACS 42.70.Qs; 41.20.Jb; 42.25.Dd 相似文献
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Silvia Gentilini Mauro Missori Neda Ghofraniha Claudio Conti 《Annalen der Physik》2020,532(8):2000005
Multiple scattering of electromagnetic (EM) waves arises in disordered media with a refractive index varying on the scale of the wavelength. The diffusion approximation is a powerful tool to treat multiple scattering as a photon random walk, neglecting resonant phenomena. However, as the light intensity varies on a scale much smaller than the transport mean free path, resonances may occur in media formed by finite-size scatterers and break the diffusion approximation. The energy and phase velocity are very useful tools to reveal the onset of the resonant transport regime. In this paper the study of the propagation of terahertz (THz) waves through 3D random media by employing terahertz time-domain spectroscopy (THz-TDS) is addressed. Specifically, measurements of the electric field transmitted by samples of different thicknesses made of 1 mm diameter silica spheres dispersed in a paraffin matrix at different filling fractions are reported. This investigation has provided an accurate measurement of the EM field phase and, hence, information on the radiation propagation velocity that has enabled the first observation of a photonic glass at the THz range. 相似文献
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亚波长尺度光子晶体结构可有效提升发光二极管(LED)的光提取效率(LEE),然而在制造过程中会存在缺陷或无序.利用时域有限差分法对理想方形光子晶体结构进行了优化,在此基础上对三种无序光子晶体结构进行了仿真,研究了光子晶体结构参数的无序变化对GaN基蓝光LED LEE的影响.结果表明,光子晶体空气孔位置和半径的无序变化使优化的80 nm光子晶体LED的LEE下降,而可使非优化的60nm光子晶体LED的LEE增加;当光子晶体空气孔位置和半径的无序变化量从0到士20 nm之间变化时,LEE最大会产生53.8%的浮动;光子晶体刻蚀深度的无序变化对LEE影响较小,一般可以忽略,研究结果为高性能蓝光光子晶体LED的设计制作提供了重要的理论参考. 相似文献
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采用自组装法制备了聚苯乙烯(PS)微球三维光子晶体结构,通过在PS微球悬浮液中掺入不同浓度的二氧化硅大球,实现了光子晶体结构从有序向无序过程的转变。通过对这些样品的透射、反射进行测量和分析,发现无序效应对光子晶体的光子响应特性具有极大的影响,随着无序程度的增加,高频波段的透射率急剧下降,低频波段的法布里-珀罗振荡消失,光子带隙蓝移且逐渐消失;而在掺杂浓度为0.02%(质量分数)时,光子晶体带隙中心的最低透射率从10%下降到1%,且反射单峰随着探测角度的增大而分裂为双峰。这有助于基于介质球三维光子晶体沿Γ-L方向透射消光,促进其在新型光学器件领域的应用发展。 相似文献
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Dielectric microspheres can confine light in a three-dimensional (3D) region called photonic nanojet is shown when they are illuminated by different polarized beams. The influence of incident light polarization on photonic nanojet using the finite-difference time-domain (FDTD) method is demostrated. The axial field intensity profiles of photonic nanojets for both the linear and circular polarization incident beams are very similar. Azimuthal polarization incident beam induces a doughnut beam along the optical axis, while the radial polarization incident beam permits one to reach an effective volume as small as 0.7(λ/n) 3 . 相似文献
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A. M. Zheltikov S. A. Magnitskii A. V. Tarasishin 《Journal of Experimental and Theoretical Physics》2000,90(4):600-608
Properties of an electromagnetic field localized in the defect modes of two-dimensional photonic crystals are studied. The defect-mode spectrum of these structures is calculated, electromagnetic field localization and channeling effects are analyzed, and the properties of the field inside and beyond a photonic crystal with a lattice defect are also studied. The calculations show that the electromagnetic field is localized in the defect mode of a photonic crystal in a region smaller than the wavelength. The dependence of the defect-mode spectrum on the parameters of the photonic crystal is investigated and possibilities for controlling the spectrum of defect modes are indicated. It is shown that the optical field leaving a photonic crystal possesses the properties of a evanescent wave, which means that spatial resolution substantially greater than the wavelength of the radiation can be achieved in the near field and opens up possibilities for using photonic crystals with a lattice defect in near-field optical microscopy. The possibility of externally controlling an optical field localized in the defect modes of a photonic crystals is demonstrated. 相似文献
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Wentao Jin 《Optics Communications》2011,284(24):5814-5817
We fabricate three-dimensional nonlinear photonic lattices in iron-doped lithium niobate photorefractive crystal for the first time by a single amplitude mask. The experimental setup of this method is very simple and flexible. The period of the lattices can be dominated easily. We analyze the three-dimensional photonic lattices by plane wave guiding and far field diffraction pattern imaging. The induced photonic lattices can exist stably for a long time in the photorefractive crystal. 相似文献