Optimization, bandwidth and the effect of loss on the characteristics of the coupled ring reflector

Reflection and group delay characteristics of the coupled ring reflector (CRR), consisting of two identical microrings coupled to each other and to a bus waveguide providing feedback, is analytically and numerically investigated under loss-free and lossy conditions and subject to arbitrary (asymmetric) positioning of the couplers. Allowing for a variable coupling strength, the spectral locations where the extreme values of the reflectivity occur as well as its bandwidth are determined and their sensitivity to loss evaluated. Critical coupling conditions that determine the shape and the turning points of the reflectance spectrum, and their sensitivity to loss are obtained. Attention is paid to the bandwidth maximization satisfying a prescribed ripple tolerance within the passband. Group delay in the presence of loss and circuit parameter variations is also treated.     

Peculiarities of propagation of electroinductive waves in magnetic metamaterials

The coupling of doubly split ring resonators in the GHz range has been experimentally, analytically, and numerically studied in order to design a metamaterial with dominant electrical coupling as a model of nanoscale metamaterials. An example of propagation of GHz electroinductive waves in a metamaterial is demonstrated.     

Experimental study and large Eddy simulation of a coaxial jet with perforated obstacles to control thermal mixing characteristics

Thermal mixing phenomena of a coaxial jet with perforated obstacles are analyzed both experimentally and numerically. Perforated obstacles are used in front of a coaxial jet that has different temperatures of the fluid to control the thermal mixing behavior. An experimental set-up was constructed to perform several cases and all cases are simulated by using large eddy simulation (LES) turbulence model. Results of the study presented that inserting perforated obstacle affects the mixing performance positively and the best mixing performance is obtained in the case that the obstacle has the highest permeability. Experimental and computational results were compared and a good agreement was obtained.     

Nonsymmetrical Electromagnetic Waves in Partially Plasma — Filled Waveguide

The dispersion of nonsymmetrical electromagnetic waves in waveguide, partially filled with plasma, is studied numerically and experimentally. An external d.c. coaxial magnetic field is applied to the waveguide. The dispersion equation of these waves is obtained, and it is solved numerically for the experimental conditions. Results are obtained, which show coupling of the waveguide HE_l1-modes with the family of the high-frequency plasma HE_ln-modes. The numerical dispersion curves are experimentally examined, and the influence of the magnetic field and the plasma density is studied.     

基于有源广义忆阻的无感混沌电路研究

采用常见元器件等效实现一个广义忆阻器, 进而制作出一个电路特性可靠的非线性电路, 有助于忆阻混沌电路的非线性现象的实验展示及其所产生的混沌信号的实际工程应用. 基于忆阻二极管桥电路, 构建了一种无接地限制的、易物理实现的一阶有源广义忆阻模拟器; 由该模拟器并联电容后与RC桥式振荡器线性耦合, 实现了一种无电感元件的忆阻混沌电路; 建立了无感忆阻混沌电路的动力学模型, 开展了相应的耗散性、平衡点、稳定性和动力学行为等分析. 结果表明, 无感忆阻混沌电路在相空间中存在分布2个不稳定非零鞍焦的耗散区和包含1个不稳定原点鞍点的非耗散区; 当元件参数改变时, 无感忆阻混沌电路有着共存分岔模式和共存吸引子等非线性行为. 研制了实验电路, 该电路结构简单、易实际制作, 实验测量和数值仿真两者结果一致, 验证了理论分析的有效性.     

Synchronized Chaos in a Modulated Bidirectional Ring Laser

Nonlinear dynamics of a pump-modulated bidirectional experimentally. Theoretical investigations are based on the pumped bidirectional ring laser that supports single mode in solid-state ring laser are studied theoretically and semiclassical equations of motion for an optically each direction. These equations include coupling of modes via their competition for gain as well as their coupling due to backscattering. Approximate analytical and numerical methods are used to study the dynamical behavior of the system when pump is square-wave modulated. It is found that depending on the depth and frequency of modulation, mode intensities exhibit a rich array of nonlinear dynamical behavior including synchronous and asynchronous chaos, and antiphase periodic and quasi-periodic oscillations.     

Tunable, narrow-band, grating-assisted microring reflectors

Tunable, grating-assisted ring resonator based optical mirrors are analyzed and their characteristics numerically evaluated. Mode number selection rules are presented to aid mirror optimization for high, narrow-band reflection and efficient sidelobe suppression. Data is presented on tuning sensitivity, on the effect of coupling on bandwidth and reflection coefficient, and on the influence of waveguide and grating loss on mirror performance. Group delay in the presence of loss and circuit parameter variations is also treated.     

Dual-band isotropic metamaterial absorber based on near-field interaction in the Ku band

We numerically and experimentally investigate single-band and dual-band isotropic metamaterial absorbers (IMAs) based on metallic disks. By optimizing the diameter of the metallic disks and the thickness of the dielectric substrate, the single-band IMA is observed at 16.2 GHz with absorptivity of 97%. When adding one disk-pair to the structure, the dual-band IMA is obtained at 12.8 and 15.5 GHz due to the symmetry breaking. The physical mechanics is explained by near-field coupling effect and equivalent LC circuit model. The measurement results performed in the range 12–18 GHz show a good agreement with simulation and theoretical analysis. Our findings demonstrate a new approach to achieve dual-band and multi-band IMAs.     

延迟变量反馈法控制离散混沌系统的电路实验

利用电子线路实验实现了一个具有混沌和超混沌特性的二维离散系统以及延迟变量反馈和它的增强型的方法用于混沌和超混沌的控制.实验结果，包括控制前实验电路出现的各种复杂行为和控制后从实验中观测到的许多被稳定住的周期状态，与理论分析和数值计算的结果几乎完全一致.也证实了增强型延迟变量反馈法控制混沌和超混沌的有效性.     

The dynamics of ring dark soliton in inhomogeneous Bose-Einstein condensates

The dynamics of the ring dark soliton in an inhomogeneous Bose-Einstein condensates (BEC) with thin disk-shaped potential trapping is investigated analytically and numerically. Analytical result shows that the ring dark soliton is governed by a variable coefficients Korteweg-de Vries (KdV) equation. The effect of the ring curvature (nonplanar geometry) and the inhomogeneous of the background on soliton amplitude and the emitted radiation profiles are obtained analytically. The theoretical results are confirmed by the direct numerical results.     

A metamaterial with multi-band left handed characteristic

A novel left handed (LH) metamaterial (LHM) with multi-band (MB) LH behavior is numerically and experimentally studied based on three split ring resonator pairs (SRRPs). The SRRPs are patterned on both sides of a single dielectric slab, featuring three magnetic resonances and two electric resonances. By cautiously designing the dimensions of each SRRP, the magnetic resonances and electric resonances can be individually controlled, and the resulting negative permeability and negative permittivity can be overlapped to engineer a MB LHM. The multiresonant mechanism has been studied from field distribution analysis and circuit model analysis. For demonstration, a prototype example was fabricated and measured. Good agreement between simulation and measurement is observed. Measurement results indicate two bands of negative refractive index (NRI) in 7.41–7.74 GHz and 9.8–10.4 GHz. The suggested novel LHM opens an alternative to prepare the cloaks, absorbers, antennas, and frequency selective surface (FSS) suitable for multifrequencies.     

Rotating spiral waves in a modified Fitz-Hugh-Nagumo model

A modified Fitz-Hugh-Nagumo model (a two-variable reaction-diffusion system with an excitable kinetics and a diffusing fast variable) was used to study numerically the rotating waves in a circular domain and in a two-dimensional ring. Large deviations from a Wiener type of behaviour of rotating spiral waves were revealed. We have shown that there are conditions under which: (i) vortices can appear in a medium with a hole but do not exist in a disk; (ii) two kinds of vortices with considerably differing periods can occur in the same ring; (iii) there is a non-monotonic dependence of vortex period on the hole size. These phenomena are believed to take place in myocardial tissue and in chemical active media. The conditions under which they could be observed experimentally are discussed.     

Study on the radial composite piezoelectric ceramic transducer in radial vibration

A new type of radial composite piezoelectric transducer in radial vibration is developed and analyzed. The radial composite transducer consists of a piezoelectric ceramic thin ring polarized in the thickness direction and a metal thin circular ring. They are connected together and excited to vibrate in the radial direction. The radial vibrations of a piezoelectric ceramic thin ring and a metal thin circular ring are analyzed, respectively. Their radial electro-mechanical equivalent circuits are obtained. Based on the electro-mechanical equivalent circuits and using the boundary conditions between the piezoelectric ceramic thin ring and the metal thin circular ring in the radial direction, the electro-mechanical equivalent circuit of the radial composite piezoelectric transducer is derived out and the resonance frequency equation is obtained. The relationship between the resonance frequency and the geometrical dimensions of the transducer is analyzed. Some radial composite piezoelectric transducers are designed and manufactured. The resonance frequencies and the anti-resonance frequencies, the electro-mechanical equivalent circuit parameters are measured. The effective electro-mechanical coupling coefficient and the mechanical quality factor are calculated. It is illustrated that the measured radial resonance frequencies are in good agreement with the theoretical results from the resonance frequency equation.     

基于软光刻的片间光学互连线路

设计并试制了由软光刻法转印,可敷设在印刷电路板上用于芯片间互连的光学互连线路。提出了一种新颖的端口耦合结构,并发现在耦合适配段长度与接收窗口的长度比值为12∶1时耦合效率最佳,且该耦合结构有效降低了对安装精度的要求;分析了该光学互连线路在交叉布线时的基本准则,获得对于不同横截面矩形波导结构在交叉布线时呈现的串扰与交叉角度的相关性,并发现在强束缚下交叉角度大于54°的交叉结构都能达到低串扰(小于-30 dB)。采用软光刻技术制作了上述高聚物波导光学互连线路元件,实验测量结果与设计数据符合较好。与传统的光刻或激光直写技术相比,软光刻转印具有制作简单,易于实现高聚物三维结构的大批量高精度复制。     

Vortex rings and plasma toroidal vortices in homogeneous unbounded media. II. The study of vortex formation process

The conditions of the formation of toroidal vortices (TVs), i.e., the plasma TV and air vortex ring at atmospheric pressure, are experimentally determined. The TV formation process is numerically simulated. Local characteristics of the pulsed jet, induced flow of ambient medium (air), and forming TV at various time points are obtained. It is shown that the results of the preliminary numerical calculation are in agreement with experimental data.     

A study of pulsatile jet discharged from pipe end

Noise is generated from a flow field upstream of a shock wave periodically discharged from a pipe end. A vortex ring and an underexpanded jet are periodically formed and diffused downstream. To clarify the mechanism of the noise generation, the flow field was experimentally and numerically studied. The flow field was visualized mainly by the schlieren method and the sound pressure of the noise was measured. The pulsatile flow through the pipe was numerically simulated by Random-Choice Method and using these results as the boundary condition, the pulsatile jet was simulated by TVD scheme. As a result, a good qualitative agreement was found between the flow field obtained by the calculations and that by the experiments. Furthermore, a relation between the behaviour of the vortex ring and the generation of the noise was discussed.     

Optical multistability in three-level atoms inside an optical ring cavity

Optical multistability in an optical ring cavity filled with a collection of three-level Lambda-type rubidium atoms has been experimentally demonstrated. The observed multistability is very sensitive to the induced atomic coherence in the system and can evolve from a normal bistable behavior with the change of the coupling field as well as the atomic number density. The underlying mechanism for the formation of such multistability is also discussed.     

Alternate oscillations in semiconductor ring lasers

We report on fabrication and characterization of single-longitudinal- and transverse-mode semiconductor ring lasers. A bifurcation from bidirectional stable operation to a regime with alternate oscillations of the counterpropagating modes was observed experimentally and is theoretically explained through a two-mode model. Analytical expressions for the onset and the frequency of the oscillations are derived, and L-I curves numerically evaluated. Good quantitative agreement between theory and measurements made over a large number of tested devices is obtained.     

Spatiotemporal stochastic resonance in a bistable FitzHugh-Nagumo ring with phase-repulsive coupling

In this paper, we numerically study a ring of bistable FitzHugh-Nagumo elements coupled in a phase-repulsive way, which are externally driven by a weak periodic signal and noises, and focus on the system’s response. A novel type of spatiotemporal stochastic resonance of antiphase state is uncovered, namely, for an intermediate strength of individual noise, the elements can form an “...-upper-lower-upper-lower-...” antiphase structure along the ring, and the global activation oscillates nearly synchronously with the weak periodic signal. Meanwhile, the system response undergoes a resonant behavior with the intensity of noise. It is shown that the combinative effects of the periodic signal, noise, and coupling are of importance for its appearance. The influences of common and individual noises are also investigated.     

The bit pattern effect on all-optical clock recovery using tank circuits and birefringent resonators

In this paper we discuss the bit pattern effect on optical clock signals recovered using tank circuits and using birefringent resonators. For the first time we compare the bit pattern dependence of the clock signals recovered from both schemes. We show that a birefringent resonator can recover the clock for the same number of consecutive zeros as the optical tank circuit. We also show quantitatively that the fluctuation of the clock signal amplitude is less for the birefringent resonator than the optical tank circuit. These results are obtained numerically and confirmed experimentally.