含色散介质的一维光子晶体微腔的透射谱

研究了含色散介质的一维光子晶体微腔的透射谱,对色散介质采用Lorentz振子模型,腔模的频率设置在光子晶体带隙中心。发现当吸收可以忽略时,色散效应将导致在腔模附近有很高的态密度,与此相应地在透射谱中出现一个较宽的透射带。当吸收存在时透射带中心的透射峰消失,但带尾的透射峰依然存在。     

Reflection from 1D quasi-periodical structures

A theoretical investigation of 1D stationary and transient quasi-periodical dielectric structures is presented. A new approach for solving the problem of field interaction with such structures common for both stationary and transient cases, based on integral equations for the fields in transient media, is proposed. Some special cases of quasi-periodical structures with doubled quasi-periodicity are investigated numerically, showing that an additional complexity of the structure allows to obtain good filtering properties with a small number of quasi-periods. Transient structures with the same spatial dependencies, but with a time-dependent permittivity were also investigated.     

Optical properties of 1D and 2D approximants of quasi-crystalline structures

The possibility of identifying 1D and 2D approximants of quasi-crystalline structures, based on recording local patterns and scaling parameters in probe-beam fields, is considered. The effect of structural defects on the shape of pattern formations is estimated.     

Relativistic surface-wave oscillators with 1D and 2D periodic structures

A nonlinear nonstationary theory of surface-wave oscillators with 1D and 2D periodic structures is constructed in terms of a quasi-optical approach. The radiation field is represented as a superposition of quasi-optical wave beams coupled on a corrugated surface and forming a self-consistent structure. Synchronous interaction with rectilinear relativistic ribbon and cylindrical electron beams is observed when the surface wave slows down. The results obtained in terms of the average approach are compared with those obtained by direct numerical particle-in-cell simulation. The feasibility of creating small-size millimeterwave gigawatt power supplies based on 2D planar and cylindrical surface-wave oscillators is demonstrated.     

Mode propagation in curved waveguides and scattering by inhomogeneities: application to the elastodynamics of helical structures

This paper reports on an investigation into the propagation of guided modes in curved waveguides and their scattering by inhomogeneities. In a general framework, the existence of propagation modes traveling in curved waveguides is discussed. The concept of translational invariance, intuitively used for the analysis of straight waveguides, is highlighted for curvilinear coordinate systems. Provided that the cross-section shape and medium properties do not vary along the waveguide axis, it is shown that a sufficient condition for invariance is the independence on the axial coordinate of the metric tensor. Such a condition is indeed checked by helical coordinate systems. This study then focuses on the elastodynamics of helical waveguides. Given the difficulty in achieving analytical solutions, a purely numerical approach is chosen based on the so-called semi-analytical finite element method. This method allows the computation of eigenmodes propagating in infinite waveguides. For the investigation of modal scattering by inhomogeneities, a hybrid finite element method is developed for curved waveguides. The technique consists in applying modal expansions at cross-section boundaries of the finite element model, yielding transparent boundary conditions. The final part of this paper deals with scattering results obtained in free-end helical waveguides. Two validation tests are also performed.     

On maximal eigenfrequency separation in two-material structures: the 1D and 2D scalar cases

We present a method to maximize the separation of two adjacent eigenfrequencies in structures with two material components. The method is based on finite element analysis and topology optimization in which an iterative algorithm is used to find the optimal distribution of the materials. Results are presented for eigenvalue problems based on the 1D and 2D scalar wave equations. Two different objectives are used in the optimization, the difference between two adjacent eigenfrequencies and the ratio between the squared eigenfrequencies. In the 1D case, we use simple interpolation of material parameters but in the 2D case the use of a more involved interpolation is needed, and results obtained with a new interpolation function are shown. In the 2D case, the objective is reformulated into a double-bound formulation due to the complication from multiple eigenfrequencies. It is shown that some general conclusions can be drawn that relate the material parameters to the obtainable objective values and the optimized designs.     

Crystallographic and magnetic order analysis of a banded limonite

Mössbauer and XRD studies of the light and dark brown parts of a banded limonite showed the presence of kaolinite in the light brown regions. Relaxation behaviour was very well described by a recently proposed model based on magnetic ordering of clusters. The difference in relaxation behaviour of the samples was attributed to different concentrations of non-magnetic impurities.     

Optical contrastivity of complicated materials: finite layered structures

We define the intrinsic optical contrastivity of a complicated layered structure as the relative total gap taken inside the total internal reflection region over a chosen range of frequencies. The notion introduced for ordered 1D systems retains its meaning for 2D and 3D ordered optical systems, as well as for disordered structures. The parametric maps of contrastivity and sensitivity are calculated for 1D comb matrices based on glass, silicon, and microporous silicon with various fillings, comb sizes, and densities of a gaseous filling. The existence of areas on a parametric map which are highly sensitive to deviations in the contrastivity is shown for different materials. In the case of a gaseous filling of voids between the matrix material layers, the areas of a very high sensitivity are also found.     

Low band gap frequencies and multiplexing properties in 1D and 2D mass spring structures

This study reports on the propagation of elastic waves in 1D and 2D mass spring structures.An analytical and computation model is presented for the 1D and 2D mass spring systems with different examples.An enhancement in the band gap values was obtained by modeling the structures to obtain low frequency band gaps at small dimensions.Additionally,the evolution of the band gap as a function of mass value is discussed.Special attention is devoted to the local resonance property in frequency ranges within the gaps in the band structure for the corresponding infinite periodic lattice in the 1D and 2D mass spring system.A linear defect formed of a row of specific masses produces an elastic waveguide that transmits at the narrow pass band frequency.The frequency of the waveguides can be selected by adjusting the mass and stiffness coefficients of the materials constituting the waveguide.Moreover,we pay more attention to analyze the wave multiplexer and DE-multiplexer in the 2D mass spring system.We show that two of these tunable waveguides with alternating materials can be employed to filter and separate specific frequencies from a broad band input signal.The presented simulation data is validated through comparison with the published research,and can be extended in the development of resonators and MEMS verification.     

Coherent and incoherent structures in systems described by the 1D CGLE: experiments and identification

Much of the nontrivial dynamics of the one-dimensional (1D) complex Ginzburg–Landau equation (CGLE) is dominated by propagating structures that are characterized by local “twists” of the phase-field. I give a brief overview of the most important properties of these various structures, formulate a number of experimental challenges and address the question how such structures may be identified in experimental space–time data sets.     

Design,nano-fabrication and analysis of near-infrared 2D photonic crystal air-bridge structures

Selective wet etching is a technique that allows fabrication of freely suspended thin slabs in epitaxial heterostructures. This technique, together with high-aspect ratio dry etching, is used to create two-dimensional (2D) photonic crystals for near-infrared wavelengths in thin suspended AlGaAs membranes. The active photonic crystal areas contain hexagonal arrays of cylindrical holes completely perforating the membrane. For an appropriate selection of the slab thickness and the lattice parameter, dispersion relations for the guided modes are explicitly computed by solving the Maxwell equations in a geometry containing a 2D photonic crystal defined in the core layer of a dielectric waveguide structure. Measurements of the spectral transmittance in air-bridge samples show a narrow 30-dB-deep stop band for TM polarized incident light. The spectral position of the stop band shows a good agreement with theoretical band structure calculations when also the quasi-guided resonant modes outside the light cone are taken into account.     

Entangling strings of neutral atoms in 1D atomic pipeline structures

We study a string of neutral atoms with nearest neighbor interaction in a 1D beam splitter configuration, where the longitudinal motion is controlled by a moving optical lattice potential. The dynamics of the atoms crossing the beam splitter maps to a 1D spin model with controllable time dependent parameters, which allows the creation of maximally entangled states of atoms by crossing a quantum phase transition. Furthermore, we show that this system realizes protected quantum memory, and we discuss the implementation of one- and two-qubit gates in this setup.     

Sensitivity improvement of broadband electro-optic polymer-based optical phase modulator using 1D and 2D photonic crystal structures

This Letter introduces the design and simulation of a microstrip-line-based electro-optic(EO) polymer optical phase modulator(PM) that is further enhanced by the addition of photonic crystal(PhC) structures that are in close proximity to the optical core. The slow-wave PhC structure is designed for two different material configurations and placed in the modulator as a superstrate to the optical core; simulation results are depicted for both1 D and 2D PhC structures. The PM characteristics are modeled using a combination of the finite element method and the optical beam propagation method in both the RF and optical domains, respectively.The phase-shift simulation results show a factor of 1.7 increase in an effective EO coefficient(120 pm/V) while maintaining a broadband bandwidth of 40 GHz.     

2D FDTD Algorithm for the Analysis of Lossy and Dispersive Millimeter-Wave Coplanar Waveguide

The dispersion and loss characteristics of millimeter-wave coplanar waveguides (CPWs) are analyzed by using an efficient two-dimensional finite-difference time-domain (2D FDTD) algorithm. Combined with graded mesh technique, alternating direction implicit technique and curve-fitting technique, this proposed algorithm verifies its accuracy and efficiency through an example of infinite-ground CPW. Moreover, the influence of ground-plane width on CPW's loss characteristics is analyzed. Bulk micromachined CPWs with low loss are also analyzed by the proposed algorithm.     

Light–matter interaction of 2D materials:Physics and device applications

In the last decade, the rise of two-dimensional(2D) materials has attracted a tremendous amount of interest for the entire field of photonics and opto-electronics. The mechanism of light–matter interaction in 2D materials challenges the knowledge of materials physics, which drives the rapid development of materials synthesis and device applications. 2D materials coupled with plasmonic effects show impressive optical characteristics, involving efficient charge transfer, plasmonic hot electrons doping, enhanced light-emitting, and ultrasensitive photodetection. Here, we briefly review the recent remarkable progress of 2D materials, mainly on graphene and transition metal dichalcogenides, focusing on their tunable optical properties and improved opto-electronic devices with plasmonic effects. The mechanism of plasmon enhanced light–matter interaction in 2D materials is elaborated in detail, and the state-of-the-art of device applications is comprehensively described. In the future, the field of 2D materials holds great promise as an important platform for materials science and opto-electronic engineering, enabling an emerging interdisciplinary research field spanning from clean energy to information technology.     

New fast and memory-sparing method for rigorous electromagnetic analysis of 2D periodic dielectric structures

A method is presented that performs the exact electromagnetic analysis of 2D periodic dielectric structures of arbitrary profile or index distribution and possibly large period. The generalized source method is used to formulate the problem of light diffraction in the form of a volume integral equation reduced to a linear equation system, which is solvable by known fast algorithms. The calculation time and required memory are linearly proportional to the total number N_o of considered diffraction orders instead of N_o³ typical for conventional methods. Numerical examples are provided to demonstrate the potential of the method for the analysis of complex periodic structures.     

Dispersive of propagation wave structures to the dullin-Gottwald-Holm dynamical equation in a shallow water waves

This article secures the new exact wave structures to Dullin-Gottwald-Holm (DGH) equation which is used as a governing model to explain the behaviour of waves in shallow water. The wave structures in the forms of solitary, shock, singular, shock-singular as well as hyperbolic, singular periodic and rational solutions are secured with the aid of computational strategy namely modified direct algebraic and ansatz approaches. The constraint conditions which ensure the validity of new wave structures are also reported. Moreover, the graphs of the solution attained are recorded in terms of 3D, 2D and contour plots by fixing parameters. The achieved outcomes show that the applied computational strategy is direct, efficient, concise and can be implemented in more complex phenomena with the assistant of symbolic computations.