等离子体填充盘荷波导高频特性分析

从麦克斯韦方程和流体理论出发，推导了填充磁化等离子体慢波结构的基本方程.在大磁场情况下，对等离子体填充盘荷波导的色散特性和耦合阻抗作了研究，结果表明填充等离子体使色散曲线上移，耦合阻抗提高.等离子体填充产生出模式谱非常丰富的周期性低频等离子体模式(TG模式).当等离子体密度增加到一定程度后，场模TM₀₁模的频率范围和TG₀₁模的频率范围相近，两个模式互相耦合产生出新的混合模G₁,G₂.如果相对论行波管工作在混合模上，将会产生新的工作机理. 关键词： 盘荷波导 等离子体填充 色散特性 相对论行波管     

Near-infrared tunable narrow filter properties in a 1D photonic crystal containing semiconductor metamaterial photonic quantum-well defect

The near-infrared (NIR) narrow filter properties in the transmission spectra of a one-dimensional photonic crystal doped with semiconductor metamaterial photonic quantum-well defect (PQW) were theoretically studied. The behavior of the defect mode as a function of the stack number of the PQW defect structure, the filling factor of semiconductor metamaterial layer, the polarization and the angle of incidence were investigated for Al-doped ZnO (AZO) and ZnO as the semiconductor metamaterial layer. It is found that the frequency of the defect mode can be tuned by variation of the period of the defect structure, polarization, incidence angle, and the filling factor of the semiconductor metamaterial layer. It is also shown that the number of the defect mode is independent of the period of the PQW defect structure and is in sharp contrast with the case where a common dielectric or metamaterial defect are used. The results also show that for both polarizations the defect mode is red-shifted as the number of the defect period and filling factor increase. An opposite trend is observed as the angle of incidence increases. The proposed structure could provide useful information for designing new types of tuneable narrowband filters at NIR region.     

长程表面等离子体的增强效应

研究了双层金属薄膜构型中构型参数对长程表面等离子体的影响,并发现了衰减全反射激发方法下长程表面等离子体的增强效应.以特征矩阵算法为基础,通过数值计算构型的反射谱,研究构型参数的变化对反射谱的影响.发现由于衰减全反射激发方法中耦合器的存在导致的非对称特性,会使双层金属薄膜构型中的长程表面等离子体拥有本征模式特性以外的有趣特性,如长程模式得到增强而另一支受到抑制,从而使能量更为集中在希望被激发的一支.研究结果对非对称激发构型中的长程表面等离子体研究具有启发意义.     

Effects of a bar on optical transmission through Z-shaped metallic slit arrays

We investigate the effects of a bar on optical transmission through Z-shaped metallic slit arrays by using the finite-difference time domain (FDTD) method. A new hybrid Fabry-Perot (FP) surface plasmon polariton (SPP) mode emerges when changing the geometric parameters of the bar, and this mode can be viewed as a coupling between FP mode and SPP mode. In addition, an obvious dip appears in a featured area when the bar deviates from the central line, and a small displacement of the bar leads to tremendous change of the dip. These behaviors can be attributed to the phase resonance. In short, the structure is very sensitive to the metal bar. Furthermore, it combines photonic device miniaturization with sensitivity, which is useful for making optical switches.     

新型柱孔式模式转换型纵-扭复合模态超声振动系统*

为了改善基于螺旋槽结构和斜槽结构的模式转换型纵-扭复合模态超声振动系统存在的结构复杂、扭转分量较小等问题,论文提出了基于新型柱孔式复合变幅杆的模式转换型纵-扭复合模态超声振动系统,并利用有限元法和数据分析对其进行了仿真分析,结果表明,引入新型柱孔式复合变幅杆的系统的输出端面的剪切应力、旋转角度得到了大幅提升,能够有效地提高纵、扭振动的转换效率。     

Guided-mode-leaky-mode-guided-mode fiber structure and its application to high refractive index sensing

We propose a fiber structure based on a single-mode-multimode-single-mode one. A theoretical analysis model based on leaky mode expansion along with a new concept of leaky mode interference is presented to facilitate and enlighten the analysis for the leaky structure. Then we focus on transmission characteristics of the structure in response to surrounding refractive indices (RI) that are higher than that of the silica fiber. In our simulation, output intensity of the structure increases monotonically for RI from 1.46 to 1.55, and changes over 2.0 dB for a change of 0.01 in RI range from 1.46 to 1.48, which is well verified by the following experiments.     

Design for beam splitting components employing silicon-on-insulator rib waveguide structures

We present a new design for beam splitting components employing a silicon-on-insulator rib waveguide structures. In the new design, a high-index thin-film layer is deposited in the rib section to reduce the wave field dispersive tails in the slab section and accordingly render the mode field a confined spot. This in turn improves the beam splitting performance of some conventional waveguide components such as y branches and multimode interference couplers (MMICs), in terms of the excess loss, fiber coupling loss, and compactness of these components. For a 1 x 2 y-branch beam splitter, the excess loss can be as small as 0.43 dB in the new design, which is much lower than that for a conventional rib waveguide structure (which is 1.28 dB). For a 1 x 2 MMIC in our example, the new rib waveguide structure presents an excess loss of 0.064 dB for the TE mode and 0.046 dB for the TM mode, with negligible nonuniformity in dimensions of 30 microm x 1040 microm, whereas its counterpart (i.e., the one with the same dimensions but without a thin-film layer) presents an excess loss of approximately 0.86 dB for both modes. A conventional MMIC must have dimensions larger than 70 microm x 5650 microm to maintain almost the same low excess loss.     

透明导电薄膜ITO对浅面浮雕VCSEL的影响

对于顶面出光的浅面浮雕VCSEL结构,有源区的电流密度分布的不均性制约着单模稳定性的提高。为此,提出了一种新型结构:氧化铟锡透明导电薄膜(ITO)浅面浮雕VCSEL。该结构不仅能够增大高阶模式的阈值增益,还能够提高基模的增益,实现基模对高阶模式的稳定抑制。研究了ITO的厚度对阈值增益的影响及ITO对VCSEL有源区电流密度分布的影响。研究结果表明:在ITO的厚度为半波长的整数倍时,基模对高阶模式的限制作用最强;ITO通过改善VCSEL有源区的电流密度分布,达到了增大基模的增益和降低高阶模式增益的目的,同时还降低了串联电阻和外电压。     

Relativistic backward wave oscillator using a selective mode converter

A new version of the relativistic backward wave oscillator (BWO) is proposed and investigated experimentally, where the cutoff (for the working mode mode) taper at the cathode end is replaced by a selective Bragg-type mode converter. In the experimental BWO model, which operates in the three-centimeter range and is equipped with a mode converter based on a slightly corrugated waveguide, a radiated power of 700 MW in pulses of duration up to 100 ns with an output spatial structure similar to a Gaussian wave beam is obtained at an accelerating potential of 0.8 MV and a focusing magnetic field of 7 kOe. Zh. Tekh. Fiz. 69, 102–105 (November 1999)     

Non resonant transmission modelling with statistical modal energy distribution analysis

Statistical modal Energy distribution Analysis (SmEdA) can be used as an alternative to Statistical Energy Analysis for describing subsystems with low modal overlap. In its original form, SmEdA predicts the power flow exchanged between the resonant modes of different subsystems. In the case of sound transmission through a thin structure, it is well-known that the non resonant response of the structure plays a significant role in transmission below the critical frequency. In this paper, we present an extension of SmEdA that takes into account the contributions of the non resonant modes of a thin structure. The dual modal formulation (DMF) is used to describe the behaviour of two acoustic cavities separated by a thin structure, with prior knowledge of the modal basis of each subsystem. Condensation in the DMF equations is achieved on the amplitudes of the non resonant modes and a new coupling scheme between the resonant modes of the three subsystems is obtained after several simplifications. We show that the contribution of the non resonant panel mode results in coupling the cavity modes of stiffness type, characterised by the mode shapes of both the cavities and the structure. Comparisons with reference results demonstrate that the present approach can take into account the non resonant contributions of the structure in the evaluation of the transmission loss.     

All-optical set-reset flip-flop based on frequency bistability in semiconductor microring lasers

The electric field of the modes of semiconductor microring lasers (SMRLs) in the presence of bus waveguide reflections are linear combinations of the clock wise (CW) and the counter clock wise (CCW) electric fields. The mode structures can be controlled by the waveguide reflection coefficients. The power ratio and phase difference of the CW and CCW fields of one mode is proportional to the ratio of the reflection coefficients of the left and right waveguides. It is shown that the degenerate CW and CCW modes in the presence of bus waveguide reflections are split into two modes with different frequencies. Employing these new modes, SMRL can be used as an element to design flip-flops used in photonic integrated circuits. For a symmetric structure, the inter-frequencies of CW and CCW waves relating to each mode can be considered as the output of the optical flip-flop. Output of asymmetric mode is zero while the symmetric mode has a nonzero output.     

Zone-folding effects on phonons and excitons in polytypic BiI3 single crystals

Resonant Raman scattering (RRS) of new mode phonons in BiI₃ crystals containing stacking faults is reported. Under excitation with laser light tuned to a characteristic sharp absorption line, new mode Raman lines show the resonance behavior. The new phonon modes and the origin of the sharp absorption line can be interpreted in terms of folding back effects of the Brillouin zone for phonons and excitons in a polytypic structure     

Symmetric and antisymmetric modes of electromagnetic resonators

In this paper, we numerically study a new type of infrared resonator structure, whose unit cell consists of paired split-ring resonators (SRRs). At different resonant frequencies, the magnetic dipoles induced from the two SRRs within one unit cell can be parallel or antiparallel, which are defined as symmetric and antisymmetic modes, respectively. Detailed simulation indicates that the symmetric mode is due to magnetic coupling to resonators, in which the effective permeability could be negative. However, the antisymmetric mode originating from strong electric coupling may contribute to negative effective permittivity. Our new electromagnetic resonators with pronounced magnetic as well as electric responses could provide a new pathway to design negative index materials (NIMs) in the optical region. PACS 78.20.Ci; 73.20.Mf; 42.25.Bs     

Realizing mode conversion and optical diode effect by coupling photonic crystal waveguides with cavity

We propose a novel two-dimensional photonic crystal structure consisting of two line defect waveguides and a cavity to realize mode conversion based on the coupling effect. The W1/cavity/W2 structure breaks the spatial symmetry and successfully converts the even(odd) mode to the odd(even) mode in the W2 waveguide during the forward(backward)transmission. When considering the incidence of only the even mode, the optical diode effect emerges and achieves approximate 35 d B unidirectionality at the resonant frequency. Moreover, owing to the narrow bandpass feature and the flexibility of the tuning cavity, utilization of the proposed structure as a wavelength filter is demonstrated in a device with a Y-branch splitter. Here, we provide a heuristic design for a mode converter, optical diode, and wavelength filter derived from the coupling effect between a cavity and adjacent waveguides, and expect that the proposed structure can be applied as a building block in future all-optical integrated circuits.     

Raman scattering from gas-evaporated silicon small particles

Raman scattering measurements are reported on silicon small particles prepared by gas-evaporation technique. The crystalline structure is also observed for the sample having 70 A particles in average size. Four resolved component modes with Gaussian distribution function are identified with the three usual modes (LA, TO and allowed-TO) and a new surface mode. The surface mode of silicon particle, whose relative integrated intensity decrease with an increase of the particle size, is presented for the first time.     

Coupling of the B1g phonon to the antinodal electronic states of Bi2Sr2Ca0.92Y0.08Cu2O8+delta

Angle-resolved photoemission spectroscopy on optimally doped Bi(2)Sr(2)Ca(0.92)Y(0.08)Cu(2)O(8+delta) uncovers a coupling of the electronic bands to a 40 meV mode in an extended k-space region away from the nodal direction, leading to a new interpretation of the strong renormalization of the electronic structure seen in Bi2212. Phenomenological agreements with neutron and Raman experiments suggest that this mode is the B(1g) oxygen bond-buckling phonon. A theoretical calculation based on this assignment reproduces the electronic renormalization seen in the data.     

On exact and approximated formulations for scaling-mode shapes in operational modal analysis by mass and stiffness change

When operational modal analysis (OMA) is used to estimate modal parameters, mode shapes cannot be mass normalized. In the past few years, some equations have been proposed to scale mode shapes using the mass-change method, which consists of repeating modal testing after changing the mass at different points of the structure where the mode shapes are known. In this paper, the structural-dynamic-modification theory is used to derive a set of equations, from which all the existing formulations can be derived. It is shown that the known equations can be divided into two types, the exact and the approximated equations, where the former type does in fact fulfill the equations derived from the theory of structural modification, whereas the remaining equations do not, mainly because the change of the mode shapes of the modified structure is not properly taken into account. By simulations, the paper illustrates the large difference in accuracy between the approximate and the exact formulations. The paper provides two new exact formulations for the scaling factors, one for the non-modified structure and – for the first time in the literature – one for the modified structure. The simulations indicate the influence of errors from the measured natural frequencies and mode shapes on the estimation of the scaling factors using the two exact formulations from the literature and the new exact formulation proposed in this paper. In addition, the paper illustrates statistics of the errors on mode-shape scaling. All simulations were carried out using a plate with closely spaced modes.     

Damage detection by mode shape squares extracted from a passing vehicle

The success of damage detection heavily depends on the quality of damage features, such as mode shapes and power mode shapes, etc. However, these features are usually difficult and inconvenient to be accurately obtained in practice. To solve this problem, this paper develops a simple method to approximately extract structural mode shape squares from the acceleration of a passing tapping “vehicle”, which serves as a “message carrier” of the dynamic properties of the structure. Based on the approximately obtained mode shape square, a new damage index is proposed to improve the sensitivity to damage. Numerical simulations and simple experiments demonstrate the validity of the proposed method. Compared with traditional methods, it is easier to be implemented and more accurate in noisy environment, because it requires neither pre-installing many sensors on the structure, nor solving eigenvector or singular value problems and uses only the information of point impedance. In addition, the density of measurement points can be flexibly adjusted since the tapping vehicle scans the structure continuously.     

基于错位和花生形结构的全光纤马赫-曾德干涉仪的研究

研究了一种基于错位和花生形结构的全光纤马赫-曾德干涉仪,进行了液位和曲率的测量实验,利用错位结构将纤芯模式激发到包层,包层模式经过花生形结构被耦合到纤芯与原有的纤芯模式发生干涉。包层模式对外界物理量如折射率、应力的变化敏感,导致透射光谱漂移。波谷波长的漂移量与液位和曲率的变化成线性关系,利用波谷的漂移实现液位和曲率的测量。在液位实验中,在水位变化范围为1.00～5.00 cm时,波谷向短波方向漂移,灵敏度最高为-0.68 nm·cm-1,线性拟合度为0.995 4。在曲率实验中,曲率的变化范围为0.3～1.2 m-1时,波谷向长波方向漂移,灵敏度最高为22.47 nm·m,线性拟合度为0.986 4,表现出较高的灵敏度。错位结构和花生形结构被用于组成马赫-曾德干涉仪,用普通的光纤熔接机和普通单模光纤即可熔接,结构和制作方法简单,灵敏度高,尤其在曲率的测量中表现出较高的灵敏度。