Diffraction of an Electromagnetic Wave on a Dielectric Rod in a Rectangular Waveguide. A Method of Partial Waveguide Filling

Russian Physics Journal - A variant of the method of partial waveguide filling is considered in which a sample is put into a waveguide through holes in wide waveguide walls at the distance equal to...     

Transmission characteristics of wave modes in a rectangular waveguide filled with anisotropic metamaterial

In this paper, transmission characteristics of wave modes in a rectangular waveguide filled with lossless anisotropic metamaterial are theoretically investigated. The wave equation and dispersion relations for TE and TM modes in the waveguide are obtained and analyzed. It is shown that the negative constitutive parameters of the filling anisotropic metamaterial can be used to control the wave magnitude and the phase velocity direction in the waveguide over the entire frequency domain, both below and above the cutoff frequency. Particularly, not only backward waves, but also forward waves can propagate below the cutoff frequency in the waveguide. Furthermore, a typical example is calculated to demonstrate transmission characteristics of waves inside the waveguide. Numerical results are obtained in the paper and compared with theoretical predictions: a good agreement is found.     

Characteristics of slow light in a magnetized plasma hyperbolic metamaterial waveguide

The characteristics of slow light in a magnetized plasma hyperbolic metamaterial waveguide are analyzed in detail. Compared with a conventional waveguide filled with hyperbolic metamaterial cladded by dielectric or a dielectric waveguide cladded by hyperbolic metamaterial, the characteristics of slow light in a magnetized plasma hyperbolic metamaterial waveguide are actively tunable. The results show that plasma filling factor, dielectric constant of background materials, plasma density, and external magnetized field have significantly changed the characteristics of slow light. Parameter dependence of the effects is examined and discussed.     

Design of hybrid optical waveguide with a 90° bend structure for high density photonics integrated circuits

A hybrid optical waveguide having a 90° sharp bend structure, composed of a dielectric straight waveguide, tapered dielectric strip waveguide, and microscale metal gap waveguide, is proposed and simulated to improve the efficiency of light coupling between dielectric and plasmonic waveguides. Our simulation result is a critical step for the hybrid integration of plasmonic components with conventional dielectric components.     

Novel waveguide components based on complementary electrically small resonators

In this paper, we present a new class of waveguide components based on the use of complementary electrically small resonators etched on metallic sheets. We first show a rectangular-to-circular waveguide transition that allows to effectively match waveguides with different cross-sections and to transform the linearly polarized TE₁₀-mode of a rectangular waveguide into a circularly polarized TE₁₁-mode of a circular waveguide. Then, using similar structures, we present the design and the numerical results of two power dividers and of an orthomode transducer. All these components, employing only thin metallic sheets with properly shaped slits, can be integrated in waveguide transmission systems without increasing their space occupancy. A proper set of full-wave numerical simulations proves the validity of the proposed approach.     

基于Drude-FDTD算法的单负介质组合填充波导传播特性研究

提出了电单负介质和磁单负介质组合填充矩形波导结构,通过理论分析和修正的3D-Drude-FDTD算法进行数值仿真,分析了电磁波在其中的传播特性.仿真结果表明,新结构波导中存在异于传统介质填充波导的亚波长导模,且传播常数基本不随频率的变化而变化,可以用于宽带微波器件和天线的设计. 关键词： 单负介质 传播常数 截止频率 时域有限差分法     

Group index and dispersion properties of photonic crystal waveguides with circular and square air-holes

The slow light and group velocity dispersion properties of 2D triangular lattice photonic crystal line defect waveguide (PCW) with square and circular air-holes are numerically investigated with the plane-wave expansion method. The simulation results show that the guided mode is impacted slightly by the cross section’s shape of the air-holes of the same filling ratio. Adjusting two rows of the inner-hole adjacent to the waveguide and modifying the waveguide width can bring in low-group velocity and low-dispersion (LVLD) region, in which the group index of the square holes can reach 210 which is far better than the circular-holes. At the same air-hole size and waveguide width, the PCW with the square holes can support higher bit rate of the signal up to 35 Gb/s. These results provide important theoretical basis for realizing of optical buffering and optical logic devices in all-optical network.     

光子晶体波导对垂直腔面发射激光器光束远场形貌的调控

研究了光子晶体波导对垂直腔面发射激光器(VCSEL)光束远场形貌的调控.采用三层对称平板波导模型分析了影响光子晶体VCSEL(PC-VCSEL)远场发散角的参数.研究表明,PC-VCSEL中光子晶体的填充比(空气孔直径和光子晶体周期的比值)以及空气孔的刻蚀深度控制了光束的发散角,低填充比和浅刻蚀的PC-VCSEL有利于获得低发散角的光束.设计并制作了两种不同结构参数的PC-VCSEL,这两种器件中光子晶体的填充比和空气孔的刻蚀深度不同.实验结果表明,低填充比和浅刻蚀的PC-VCSEL的发散角更低,与理论分析符合得很好.     

Simulation investigation on waveguide properties of terahertz wave through subwavelength semiconductor gap

The waveguide propagation properties of terahertz wave through subwavelength semiconductor trench have been simulationally investigated. The effects of gap width, temperature, doping concentration and dielectric filling materials on waveguide property have been given and discussed. The results show that as temperature and doping concentration increases, the skin depth and the propagation constant decreases. In addition, the effective index increases and the propagation length decreases as the dielectric constant of filling materials increases.     

二维正方光子晶体波导中的慢光传输

采用平面波展开法分析了正方晶格光子晶体线缺陷波导中的慢光传输.数值模拟结果表明,介质柱光子晶体线缺陷波导中,缺陷模的群速度与填充比、缺陷处介质柱半径及与波导相邻介质柱半径有关,其中缺陷处介质柱半径对缺陷模的群速度影响最大|随着填充比和缺陷处介质柱半径的增大及与波导相邻介质柱半径的减小,缺陷模的群速度逐渐减小且最小减至0.015c.进而对比研究空气柱光子晶体线缺陷波导,发现缺陷模的群速度随着缺陷处空气柱半径的减小而减小,最小减至0.008c.     

Mode Structure and the Envelope of a High-Power Pulse in a Nonsymmetric Graded-Index Waveguide Layer

Radiophysics and Quantum Electronics - We consider a weakly nonlinear process of propagation of a modulated pulse with high-frequency filling in a plane graded-index waveguide layer. The transverse...     

Dielectric Cherenkov masers as powerful amplifiers with superwidebandwidth

Here, we explore an important feature of dielectric Cherenkov masers (DCM's) that distinguishes them from other relativistic microwave devices. Most previous DCM experiments were carried out with rather thin dielectric liners or films. In this paper we show, however, that when the coefficient of waveguide filling with dielectric is not small, the beam-wave coupling doesn't depend on frequency, and, hence, superwide bandwidth is possible. The value of bandwidth is also determined by the current and velocity of the electron beam. DCM dispersion relations are examined both analytically, in the simplest model of total waveguide filling, and numerically, for a hollow beam in a waveguide with a dielectric liner. We show that a maximum value of bandwidth is achieved at a certain optimal value of the beam current for fixed velocity (and vice versa). Numerical results demonstrate a -3 db bandwidth of 40-50% at a peak gain of 40 dB for electron energies of 300-600 keV and beam currents of 1-10 kA     

DIELECTRIC EFFECT ON THE RADIO-FREQUENCY CHARACTERISTICS OF A RECTANGULAR WAVEGUIDE GRATING TRAVELING WAVE TUBE

A new type of partial-dielectric-loaded rectangular waveguide grating slow-wave structure (SWS) for millimeter wave traveling wave tube (TWT) is presented in this paper. The radio-frequency characteristics including the dispersion properties, the longitudinal electric field distribution and the beam-wave coupling impedance of this structure are analyzed. The results show that the dispersion of the rectangular waveguide grating circuit is weakened, the phase velocity is reduced and the position of the maximum E _z is basically invariant after partially filling the dielectric materials in the rectangular waveguide grating SWS. Although the coupling impedance decreases a little, it still keeps above 40 Ω.     

Interference of co-and counterpropagating waveguide modes in a planar structure

Interference between inhomogeneous waves in a planar waveguide placed in a perfectly conducting environment is studied. It is shown that the interference flux of copropagating waveguide TM modes behaves like counterpropagating homogeneous volume waves. The longitudinal and transverse components of the interference fluxes of co-and counterpropagating waves in the general case result from interference between both the active and reactive components of the field. The interference flux of waveguide modes may also be observed when the partial fluxes of the modes equal zero.     

The Partial-Region Method for Electrodynamic Calculation of Cylindrical Structures with Metal Radial T-Ridges and Inhomogeneous Dielectric Filling

Radiophysics and Quantum Electronics - We solve the problem of electrodynamic analysis of the mode content in a circular waveguide with radial metal T-ridges and layered dielectric filling....     

Focusing and waveguiding of Lamb waves in micro-fabricated piezoelectric phononic plates

This paper presents results on the numerical and experimental studies of focusing and waveguiding of the lowest anti-symmetric Lamb wave in micro-fabricated piezoelectric phononic plates. The phononic structure was based on an AT-cut quartz plate and consisted of a gradient-index phononic crystal (GRIN PC) lens and a linear phononic plate waveguide. The band structures of the square-latticed AT-cut quartz phononic crystal plates with different filling ratios were analyzed using the finite element method. The design of a GRIN PC plate lens which is attached with a linear phononic plate waveguide is proposed. In designing the waveguide, propagation modes in square-latticed PC plates with different waveguide widths were studied and the results were served for the experimental design. In the micro-fabrication, deep reactive ion etching (Deep-RIE) process with a laboratory-made etcher was utilized to fabricate both the GRIN PC plate lens and the linear phononic waveguide on an 80 μm thick AT-cut quartz plate. Interdigital transducers were fabricated directly on the quartz plate to generate the lowest anti-symmetric Lamb waves. A vibro-meter was used to detect the wave fields and the measured results on the focusing and waveguiding of the piezoelectric GRIN PC lens and waveguide are in good accordance with the numerical predictions. The results of this study may serve as a basis for developing an active micro plate lens and related devices.     

同轴线-矩形波导结散射特性的数值分析

 提出了一种数值分析同轴线-矩形波导结散射特性的模式匹配方法。采用同轴线和矩形波导的本征模函数表示电磁场分量,通过同轴线-矩形波导结截面横向场分量匹配获得波导结的散射参数,引入电场模式匹配矩阵的解析形式提高了计算效率。给出了基于模式匹配法数值仿真的各种同轴线-矩形波导结散射特性及仿真结果分析,并与3维全电磁波分析软件HFSS的仿真结果进行了比较,二者非常吻合。模式匹配法计算效率高,能广泛应用于微波毫米波元器件及系统结构的设计与优化。     

各向异性超常媒质矩形波导的导波特性研究

研究中通过建立和求解填充各向异性超常媒质的矩形波导TE模式和TM模式的波动方程和场分布方程,讨论了各向异性超常媒质矩形波导的有效介电常数、有效磁导率、相位常数以及传输系数与所填充超常媒质本构参数之间的变化关系.研究发现,填充了各向异性超常媒质的矩形波导的导波特性在截止频率之上的频率区域,其导波特性由所填充超常媒质的横向本构参数决定,而与超常媒质的纵向本构参数无关.但是,在截止频率之下的频率区域,该矩形波导的导波特性则由所填充超常媒质的横向本构参数和纵向本构参数共同决定.研究中通过典型的计算实例对所得到的结 关键词： 各向异性 超常媒质 矩形波导 导波特性     

A continuous-wave and pulsed electron spin resonance spectrometer operating at 275 GHz

An electron paramagnetic resonance (EPR) spectrometer is described which allows for continuous-wave and pulsed EPR experiments at 275 GHz (wavelength 1.1 mm). The related magnetic field of 9.9 T for g approximately 2 is supplied by a superconducting solenoid. The microwave bridge employs quasi-optical as well as conventional waveguide components. A cylindrical, single-mode cavity provides a high filling factor and a high sensitivity for EPR detection. Even with the available microwave power of 1 mW incident at the cavity a high microwave magnetic field B1 is obtained of about 0.1 mT which permits pi/2-pulses as short as 100 ns. The performance of the spectrometer is illustrated with the help of spectra taken with several samples.     

Analytical model of a corrugated optical waveguide

An analytical model of the diffraction energy exchange between the radiative and the waveguide modes in a planar optical waveguide corrugated by a waveguide grating with an arbitrary form of teeth is developed on the basis of the coupled-wave method. It is shown that the mechanism of the energy exchange between the modes is determined by the partial interaction of all components of the spatial frequency spectrum of the waveguide modes with the corresponding components of the spatial frequency spectrum of the grating. It is established that gratings with an asymmetric tooth profile providing a shift of the peak of the spatial frequency spectrum toward matching are characterized by a higher diffraction efficiency α; however, at small thicknesses δ of the waveguide grating, the efficiency is almost independent of the tooth profile. It is shown that gratings with a symmetric profile give on average a decreasing dependence α(δ), while gratings with an optimized asymmetric profile yield a monotonically increasing saturating dependence α(δ).