一维周期性增益介质的临界长度

用传输矩阵方法研究了一维周期性增益介质的透射频谱随系统层数的变化规律.研究发现：对层数一定的介质,透射率在某些频率上有很大的峰值;增加层数,尖峰在频谱图上出现的位置会发生移动,且对不同的频段,其位置随介质层数的变化规律是不同的.考察了这种系统中每个频率的光所对应的临界长度,解释了不同频段激光出现位置随层数变化的规律.比较了周期系统和随机系统中临界长度与频率关系的异同,用群速度理论和能带理论对此做了解释.     

Photonic crystal with epsilon negative and double negative materials as an optical sensor

Two ternary photonic crystals are proposed for sensing applications. The first one is composed of an air layer as an analyte sandwiched between two double negative material (DNM) layers whereas the second one consists of an air layer sandwiched between two epsilon negative material (ENM) layers. The transmission spectrum is studied for two different values of the refractive index of the analyte layer with ?n = 0.01. A specific peak in the transmission spectrum is observed and the wavelength at which the peak occurs is determined. The wavelength shift due to any change in the index of the analyte layer is also determined. The effect of varying the parameters of the DNM and ENM on the sensitivity of the sensor is discussed. It is found that the sensitivity of the structure ENM/air/ENM is much greater than that of the structure DNM/air/DNM and it is estimated as 26 times of the sensitivity of the latter structure.     

Dispersion properties of cyclotron waves in periodic semiconductor-insulator structures

The band spectrum of cyclotron waves propagating in a periodic layered semiconductor-insulator structure at an angle to an external magnetic field that is applied perpendicularly to the layers is calculated for two relationships between the characteristic frequencies of the semiconductor: ω_H>ω_P and ω_H<ω_P. The wave field distributions across the layers and over the period of the structure are analyzed. In both spectra, transmission bands arise when the conditions for dimensional resonance across the semiconductor layer are fulfilled. The graphic solution of the dispersion relation demonstrates that the cyclotron wave spectrum can be subdivided into two spectra of normal waves according to the Bloch wavenumbers of the periodic structure. The cases where the band spectra complement each other or overlap are considered.     

Enhanced transmission of electromagnetic waves through metamaterials

This paper reviews our recent experimental and simulation results regarding the electromagnetic wave transmission through three configurations of sandwiching structures of metamaterials: a metallic mesh sandwiched between two identical layers composed of split rings, metallic fractals, and fractal slits, respectively. We observed the enhanced transmission of the waves through these three types of sandwiching composites with respect to the opaque metallic mesh. The locations of the transmission peaks in the spectrum are associated closely with the band characteristics of the sandwiching layer by appearing either on the left- or the right-hand side of its band. PACS 41.20.Jb; 42.70.Qs; 78.20.-e; 42.25.Bs; 47.53.+n     

Finite-difference time-domain studies of low-frequency stop band in superconductor-dielectric superlattice

<正>The transmission coefficients of electromagnetic(EM) waves due to a superconductor-dielectric superlattice are numerically calculated.Shift operator finite difference time domain(SO-FDTD) method is used in the analysis.By using the SO-FDTD method,the transmission spectrum is obtained and its characteristics are investigated for different thicknesses of superconductor layers and dielectric layers,from which a stop band starting from zero frequency can be apparently observed.The relation between this low-frequency stop band and relative temperature,and also the London penetration depth at a superconductor temperature of zero degree are discussed,separately.The low-frequency stop band properties of superconductor-dielectric superlattice thus are well disclosed.     

Optical transmission through double-layer metallic subwavelength slit arrays

We present measurements of transmission of infrared radiation through double-layer metallic grating structures. Each metal layer contains an array of subwavelength slits and supports transmission resonance in the absence of the other layer. The two metal layers are fabricated in close proximity to allow coupling of the evanescent field on individual layers. The transmission of the double layer is found to be surprisingly large at particular wavelengths, even when no direct line of sight exists through the structure as a result of the lateral shifts between the two layers. We perform numerical simulations using rigorous coupled wave analysis to explain the strong dependence of the peak transmission on the lateral shift between the metal layers.     

Antireflection film in one-dimensional metallo-dielectric photonic crystals

We calculated the transmittance of a one-dimensional (1D) metallo-dielectric photonic crystal (MDPC) in the optical region including the absorption losses in metal layers. The structure consists of five Ag and four GaN layers stacked alternately. When we add an antireflection coating to each end of the stack, the transmittance of the MDPC is increased twice as much and the oscillations in the transmission spectrum are also smoothed out compared with the case without them. The transmittance for oblique incident angles is also increased by the addition of two antireflection layers at the ends of the 1D MDPC.     

近红外“3R”法双谱自适应去噪

针对近红外透射和吸收双光谱提出一种自适应的去噪方法。同步采集样品的近红外透射谱和吸收谱,在相同分解原则下总体经验模态法分解两组光谱,得到单组分特征模态分量。计算特征模态分量与原透射谱、吸收谱之间相关性,以及两组特征模态分量之间相关性,相关性最小模态分量初判为噪声分量。分析该分量在光谱中点处自相关性,若中点处很大,其他点几乎为零或很小,可以判断该分量为噪声。这种基于模态分量相关性的噪声判别方法称为“3R”法则。剔除噪声分量,重构光谱信号,循环上述分解过程,直到不满足“3R”法则,降噪过程结束。构造理想光谱,叠加噪声,“3R”法降噪效果优于EMD和EEMD低通滤波器,略逊于小波分解。真实光谱实验中,经过上述方法降噪处理过的玉米叶片光谱采用3层BP神经网络建立与叶绿素之间预测模型,“3R”法处理模型具有最大校正相关系数和预测相关系数,最小校正标准差和预测标准差。在四种降噪方法中,“3R”法对光谱谱峰位置和峰高的影响最小。实验表明,“3R”双谱去噪方法无需预设迭代次数,不用考虑分解层数,没有基函数,是自适应的,该方法适合近红外光谱去噪。     

Interference of opposing longitudinal acoustic waves in an isotropic absorbing plate and a periodic structure with defects

Interference of longitudinal acoustic waves propagating in opposite directions in a homogeneous isotropic absorbing plate and a periodic structure with a defect is considered theoretically. The periodic structure consists of alternating absorbing solid and transparent liquid layers. The defect is modeled by replacing a solid layer by a liquid layer of the same thickness. The dependences of the transmission spectrum of the energy flux on the amplitude ratio and phase difference of the interacting waves are studied. It is shown that, by varying the parameters of the opposite pressure wave, it is possible to change the transmission spectrum of the direct wave in a wide frequency range. An expression is obtained to determine the extremums of the wave amplitude transmitted through an absorbing plate depending on the amplitude ratio of the interacting waves. The results of studying a one-dimensional periodic structure demonstrate the possibility to considerably change the transmission spectrum of the pressure wave leaving the structure and also to eliminate the invariance of this spectrum under the interchange of the kth and (n?k+1)th layers (where n is the total number of layers in the structure).     

一维液晶光子晶体透射谱的研究

一维液晶光子晶体在光滤波器、低阈值激光器和光开关等领域有着很好的应用前景。研究了一维液晶光子晶体的透射谱,电压范围在0～10V内,光谱调谐范围约为50nm,透射峰半高宽为18nm,禁带宽度近400nm。进一步提出了非偏振光型液晶光子晶体,设计了相互垂直0°扭曲取向的双液晶层一维液晶光子晶体器件。双液晶层起到了对各向偏振光光程的补偿作用,使得禁带中的两个透射峰合并为一个透射峰,加强了光强度,增强了滤波性能。     

Transport properties of graphene under periodic and quasiperiodic magnetic superlattices

We study the transmission of Dirac electrons through the one-dimensional periodic, Fibonacci, and Thue–Morse magnetic superlattices (MS), which can be realized by two different magnetic blocks arranged in certain sequences in graphene. The numerical results show that the transmission as a function of incident energy presents regular resonance splitting effect in periodic MS due to the split energy spectrum. For the quasiperiodic MS with more layers, they exhibit rich transmission patterns. In particular, the transmission in Fibonacci MS presents scaling property and fragmented behavior with self-similarity, while the transmission in Thue–Morse MS presents more perfect resonant peaks which are related to the completely transparent states. Furthermore, these interesting properties are robust against the profile of MS, but dependent on the magnetic structure parameters and the transverse wave vector.     

Dispersion properties of a periodic semiconductor structure in a magnetic field directed along the periodicity axis

The band spectrum of natural waves in a periodic structure formed by alternating dielectric and semiconductor layers is investigated for the propagation of waves at some angle with respect to a magnetic field applied along the periodicity axis. A method is presented for deriving a dispersion equation, and its properties are analyzed numerically. It is shown that, in the absence of dissipation, there are two independent spectra of natural waves in the structure being considered, and the regions of existence of various types of such waves are classified. It is established that the transmission bands of the two spectra may supplement one another or overlap. It is found that, for the chosen magnetic-field direction, there exist numerous bands of transmission of cyclotron waves.     

Passage of an ultrasound wave through a magnetic superlattice of finite length

The method and results of calculating the coefficient of transmission of a circular ultrasound wave through a multilayer ferromagnet/nonmagnet dielectric system with allowance for excitation of spin waves in magnetic layers are presented. The dependence of the resonance structure of the transmittance spectrum on the number of layers and the magnetic field strength has been studied.     

The extraordinary optical transmission through double-layer gold slit arrays

We present the numerical investigation of the optical transmission through a periodic gold nano-slit structure composed with two non-identical layers, and compare it with that of double-layer structure with two identical layers. The optical enhancement is attributed to the surface Plasmon resonance collaborated with the localized waveguide resonance. It is shown that the transmission behaviors are strongly dependent on the layer separation and lateral displacement between the two single metallic gratings. Especially, it is found that extraordinary transmission exists even if the slit of one layer shifts laterally over that of the other one to the situation that no light can propagate directly when layer separation D = 0. When the slit widths of two layers are not equal, the surface plasmon resonance peak alternately decreases and increases twice, and the localized waveguide resonance peak appears at a longer wavelength as the lateral displacement varies for a non-zero layer separation, which differs from the situation with two identical layers. These transmission properties of the structures show promise for applications in optical devices.     

Photoacoustic spectroscopy analysis of thin semiconductor samples

This paper is an analysis of determination possibility of the optical absorption coefficient spectra of thin semiconductor layers from their normalized photoacoustic amplitude spectra. Influence of multiple reflections of light in thin layers on their photoacoustic and optical absorption coefficient spectra is presented and discussed in detail. Practical formulae for the optical absorption coefficient spectrum as a function of the normalized photoacoustic amplitude spectrum are derived and presented. Next, they were applied for computations of the optical absorption coefficient spectra of thin In₂S₃ thin layers deposited on a glass substrate. This method was experimentally verified with the optical transmission method.     

Effect of diffusion layers and defect layer on acoustic phonons transport through the structure consisting of different films

By using the continuum elastic approximation model and the transfer matrix method, we investigate the effect of diffusion layers and defect layer on acoustic phonons transport through the structure consisting of different films. Our work show that most acoustic phonons can easily pass the structure, but some only have much less transmission probabilities and form corresponding dips in the transmission spectrum. With the change of the structure parameters such as the width of diffusion layers and defect layer, the number of unit cell and the density of containing Al in diffusion layers and defect layer, the magnitude of the frequencies of acoustic phonons corresponding to the dips almost remain unchanged, but the transmission coefficients corresponding to the dips change at different degree, and the transmission probabilities of some frequencies are very sensitive to the variation of the above-mentioned structure parameters. These results can provide some references in controlling the transmission coefficients of acoustic phonons, devising parts of acoustic apparatus and theoretical investigation related.     

Simultaneous excitation of cavity resonance and surface plasmon resonance in Ag/Al<Subscript>2</Subscript>O<Subscript>3</Subscript>/Ag layer structure

Simultaneous excitation of cavity resonance (CR) and surface plasmon resonance (SPR) was observed in the angular spectrum by substituting Ag/Al₂O₃/Ag layers for the metal film in a Kretschmann structure. Two reflective valleys, elicited respectively by CR and SPR, appeared at different positions in the angular spectrum. The former is the sum of enhanced transmission of CR and absorption of the metal, expressed in the reflection spectrum and extremely insensitive to the changes of the surface environment (refractive index). The latter behavior is like that when two metal films are stuck together: it has almost the same resonance depth and width, and is extremely sensitive to the changes of the surface environment. Moreover, two SPR peaks could be excited simultaneously at one angle but with different wavelengths in the frequency spectrum, which is not seen in traditional Kretschmann structures.     

ΓX-interaction effects in GaAs/AlAs-structures with a different number of layers

The energy dependencies of the transmission coefficients of electrons in GaAs/AlAs-structures with a different number of layers are obtained using the three-valley model developed earlier. It is shown that it is important to take into account the ΓX-mixing with GaAs/AlAs(001)-heterointerfaces in the electron wave functions for such structures. A relation is established between the form of the Γ- and X-resonances in the transmission spectrum, the thickness of the layers and their number. Some features in the behavior of the resonances are analyzed using the simple two-valley model. It is shown that to study ΓX-mixing, structures which include at least one electrode of AlAs are preferable. V. D. Kuznetsov Siberian Physico-Technical Institute, Tomsk State University. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 1, pp. 63–69, January, 1997.     

两端对称负折射率缺陷复合光子晶体:多通道滤波和光开关

采用传输矩阵法对两端对称负折射率缺陷复合光子晶体结构[D(AB)mD]N的透射特性进行了研究.结果表明:当N=2时,该结构透射谱的禁带出现两个完全共振透射峰,当N增加时,每个共振透射峰又分裂为N-1条；当复合光子晶体的层数m逐渐增加时,透射峰的品质因子逐渐提高,且分裂的共振透射峰距离逐渐减少；既为该结构实现高品质的多通...