Groove Waveguide Research Articles

Subwavelength guiding of channel plasmon polaritons by textured metallic grooves at telecom wavelengths

It is demonstrated that by texturing metallic grooves, the characteristics of channel plasmon polaritons (CPPs) can be remarkably improved and thus subwavelength localization becomes available for them at telecom wavelengths. Like visible CPPs in uniform grooves, these CPPs in the textured grooves can exhibit relatively low propagation losses under tight field confinements in the telecom range, while single-mode propagation is still available there. Moreover, gradually texturing the groove waveguide may introduce effective mechanisms to manipulate the transmission behaviors of CPPs, opening the way to interesting applications such as energy concentration.

Nanocircuit Loading of Plasmonic Waveguides

We apply the optical nanocircuit concepts to model and design optical nanofilters in realistic plasmonic waveguides of different nature, including strips and groove waveguides. The nanocircuit elements are designed to fit the waveguide geometry, and its equivalent impedance is analytically calculated by substituting the role of the conduction current with displacement current. The effect of plasmonic waveguide walls is rigorously modeled in terms of an extra nanocircuit loading that is included in our model. We show via numerical results that the nanocircuit approach may be effectively applied to the design of nanofilters, analogous to familiar concepts at radio-frequencies.

Highly-Confined Guiding of Terahertz Waves Along Subwavelength Grooves

We propose a scheme of guiding and manipulating terahertz waves that features tight confinement and large propagation length, even when the waveguide lateral dimensions are well in the subwavelength regime. In a tapered structure of the proposed groove waveguide, the guided mode can be stopped at different positions for different frequencies when it travels along the waveguide. Additionally, we demonstrate that nearly 100% transmission through a sharp 90° bend can be achieved in this groove waveguide.

V-Shape Folded Rectangular Groove Waveguide for Millimeter-Wave Traveling-Wave Tube

A novel slow-wave structure called V-shape folded rectangular groove waveguide is proposed to develop high-power, wide-bandwidth, and high-efficiency millimeter-wave traveling-wave tube. This structure evolves from a conventional rectangular groove waveguide bending the groove with V-shape along its longitudinal direction, which can operate with the sheet electron beam. In this paper, the electromagnetic characteristics and the beam-wave interaction of this structure operating in the V-band are obtained. From our calculations, this circuit structure possesses low transmission loss and can produce an output power of over 900 W ranging from 56 to 65 GHz when the cathode voltage and beam current are set to 12.8 kV and 500 mA, respectively. The corresponding gain and electron efficiency can reach over 36.5 dB and 14%, respectively.

Coupling of energy from quantum emitters to the plasmonic mode of V groove waveguides: A numerical study

This work is a theoretical investigation into the coupling of a single excited quantum emitter to the plasmon mode of a V groove waveguide. The V groove waveguide consists of a triangular channel milled in gold and the emitter is modeled as a dipole emitter, and could represent a quantum dot, nitrogen vacancy in diamond, or similar. In this work the dependence of coupling efficiency of emitter to plasmon mode is determined for various geometrical parameters of the emitter-waveguide system. Using the finite element method, the effect on coupling efficiency of the emitter position and orientation, groove angle, groove depth, and tip radius, is studied in detail. We demonstrate that all parameters, with the exception of groove depth, have a significant impact on the attainable coupling efficiency. Understanding the effect of various geometrical parameters on the coupling between emitters and the plasmonic mode of the waveguide is essential for the design and optimization of quantum dot–V groove devices.

A Novel Slow-Wave Structure—Folded Rectangular Groove Waveguide for Millimeter-Wave TWT

A novel slow-wave structure (SWS) called the folded rectangular groove guide, its electromagnetic characteristics, and the beam-wave interaction are presented. This structure, evolved from a conventional rectangular groove guide by bending the groove along its longitudinal direction, can operate with the sheet electron beam or the circular electron beam. From our calculations, this SWS possesses larger interaction impedance and lower ohmic loss than those of a folded rectangular waveguide with the same size. This circuit can produce output power of over 260 W with a sheet electron beam in the 3-dB bandwidth range of 88.5.5-98.5 GHz when the cathode voltage and beam current are set to 19.45 kV and 150 mA, respectively, whereas the folded rectangular waveguide can produce output power over 245 W in the 3-dB bandwidth range of 84-89 GHz.

Research on the V-shape folded rectangular groove slow-wave structure

A novel slow-wave structure called V-shape folded rectangular groove waveguide is proposed. This structure evolves from a conventional rectangular groove waveguide bending the groove with V-shape along its longitudinal direction, and the gap between metal plates forms a sheet electron beam channel naturally. Compared with the traditional U-shape structure, it can increase the interaction area without changing good high-frequency properties, which can adopt the sheet electron beam with a larger area to acquire more output power. In this paper, the high-frequency properties of this structure are analyzed, the interaction circuit for the V-band TWT is designed and the PIC simulation is performed to predict the operating characteristics. From our calculations, this tube can produce average saturation output power over 1000 Watts in a frequency range from 58 GHz to 64 GHz when the cathode voltage and beam current are set to be 12.8 kV and 600 mA respectively. The corresponding saturation gain and electron efficiency can reach over 33 dB and 13.2% respectively.

折叠矩形槽波导行波管输入输出过渡波导

折叠矩形槽波导行波管输入输出过渡波导

Efficient channel-plasmon excitation by nano-mirrors

We demonstrate a configuration for efficient channel-plasmon mode excitation using tapered terminations of V-shaped groove waveguides. The plasmon excitation is achieved by directly illuminating tapers of gold V-grooves with a focused laser beam, incident normally onto the sample surface. For near-infrared wavelengths, we find experimentally as well as numerically, by conducting three-dimensional finite-difference time-domain calculations, that the efficiency of channel-plasmon mode excitation exceeds 10% in the optimum configuration, which is the highest experimentally observed efficiency of coupling from free-propagation light into a nanoscale-size waveguide.

Guidance Properties of Plasmonic Nanogrooves: Comparison Between the Effective Index Method and the Finite Integration Technique

In this letter, we compare the effective index method (EIM), applied to derive an analytical model of the guidance properties of plasmonic groove waveguides, to full-wave simulations based on finite integration technique (FIT). We apply our results to different plasmonic groove geometries, with particular attention to the triangular (V-groove) waveguide. We first approximate the V-groove geometry with a multiple-sections rectangular-stepped waveguide, for which EIM may be applied in closed form. Explicit formulas for the dispersion properties are given in terms of a set of transcendental equations, which are then solved with standard numerical complex-zeros-searching routines. Our numerical results are then compared and validated with FIT full-wave simulations, showing the range of validity of EIM and providing an efficient analytical description and physical insights into the guided propagation in V-groove plasmonic waveguides.

Characteristics of Arbitrarily-Shaped Helical Groove Slow-Wave Structure Loaded with a Concentric Dielectric-Rod

The dielectric-rod is loaded on the central axis of the arbitrarily-shaped helical groove slow-wave structure. Meanwhile, the profile of the groove is replaced by a series of continuous rectangular steps. The unified dispersion equation of the arbitrarily-shaped helical groove waveguide loaded with a concentric dielectric-rod is obtained by means of a combination of filed-matching method and admittance-matching technique. Then, the effect of the change of groove shape and the dielectric-rod parameters on the dispersion and coupling impedance is approached by theory calculation. The results show that: loaded with dielectric-rod, the bandwidth of the helical groove traveling wave tube (TWT) is effectively broadened, but the coupling impedance is reduced. Among the five different groove shapes, the triangle-type groove has the widest bandwidth but the smallest coupling impedance, and the swallow-tailed-type groove has the narrowest bandwidth but the largest coupling impedance.

Realization of subwavelength guiding utilizing coupled wedge plasmon polaritons in splitted groove waveguides

A detailed numerical study of propagation characteristics of a coupled wedge plasmon polariton (CWPP) in splitted groove waveguide (SGW) formed with two metal wedges is performed by using the finite element method (FEM). It is shown that the SGW structure could confine CWPP modes tightly to the nano-gap region between the wedge tips, operating in a much broad bandwidth. The effect of the glass substrate, wedge roundness, gap width, groove wedge angle, and groove depth are also investigated. Particularly, our SGWs are found to be quite robust against groove depth reduction, which could be beneficial to minimize the waveguide structure dimensions. Feasibility of using such SGWs for the design of efficient subwavelength plasmonic elements is also discussed on the nanoscale whispering gallery resonators as an example.

Dispersion characteristics of channel plasmon polariton waveguides with step-trench-type grooves

We have studied the dispersion characteristics of single-mode channel plasmon polaritons (CPPs) with step-trench-type groove waveguides. From the numerical simulations using the finite-element method, the modal shapes and the complex propagation constants of the CPPs over a wide spectral range were obtained. It is shown that the dispersion characteristics of the step-trench-type CPP waveguide, which is composed of a step trench with a stacking nature, show an intermediate feature between the narrow and broad trenches. The results show that this configuration allows for a well-confined CPP with a moderate propagation loss at the wavelengths investigated.

Accurate analysis of arbitrarily-shaped helical groove waveguide

This paper presents a theory on accurately analysing the dispersion relation and the interaction impedance of electromagnetic waves propagating through a helical groove waveguide with arbitrary groove shape, in which the complex groove profile is synthesized by a series of rectangular steps. By introducing the influence of high-order evanescent modes on the connection of any two neighbouring steps by an equivalent susceptance under a modified admittance matching condition, the assumption of the neglecting discontinuity capacitance in previously published analysis is avoided, and the accurate dispersion equation is obtained by means of a combination of field-matching method and admittance-matching technique. The validity of this theory is proved by comparison between the measurements and the numerical calculations for two kinds of helical groove waveguides with different groove shapes.

Millimeter waveband semisymmetrical groove guide resonators

As an alternative to the classical waveguides, such as the H-waveguide and the rectangular waveguide, the groove waveguide has been used at millimetre wavelengths for the last couple of decades. Most of these properties are attributed to the open sides of the guide, which reduce the wall losses. This article describes a semisymmetrical groove guide resonator that is designed and analyzed analytically, numerically, and experimentally. The numerical simulations are performed via a powerful time-domain simulator based on the finite-difference, time-domain (FDTD) method. Both Cartesian- and cylindrical-coordinate FDTD packages are developed and used for the simulations. The purpose in using cylindrical-coordinate FDTD is to calibrate Cartesian-coordinate FDTD and to see the error introduced due to discretization. A measurement setup with an adjustable support platform in the frequency range of 20-40 GHz is used in the experiments.

Experimental demonstration of the effect of groove shape on the wave properties of the helical groove waveguide

This letter presents a simple and general fabrication method for helical groove waveguides (HGWs) with successful fabrication of a number of novel HGWs such as the hole-gap-shaped groove HGW, the swallow-tailed groove one, the trapezoid groove one and the ridge-loaded rectangular one. Also, measurements on these structures have been carried out to determine their dispersion properties. The experimental results agree well with the theoretical results and demonstrate the large influence of groove shape on the dispersion characteristics of the structures.

Rectangular-to-circular groove waveguide junction

Mode matching method is used to analyze the scattering characteristics of the rectangular-to-circular groove waveguide junction. Firstly, the scattering matrix equation is obtained by matching the electromagnetic fields at the boundary of the junction. The scattering coefficients can be obtained from the equation. Secondly the scattering characteristics of the iris with rectangular window positioned in circular groove waveguide are briefly analyzed. Thirdly, the convergent problem is discussed and the numerical results are given. At last experiment is made and good agreement is found between the calculated results and the measured results.

The Method of Lines: A Versatile Tool for the Analysis of Waveguide Structures

Algorithms for the determination of eigenmodes and for the analysis of longitudinally varying structures are presented. The media may be anisotropic and the devices may consist of an arbitrary number of layers or waveguide sections, respectively. Starting with generalized transmission line equations, suitable expressions are derived which are implemented in the method of lines, a semianalytical algorithm. To ensure the numerical stability, a transformation of the reflection coefficient is performed. Numerical results are presented for a Bragg-grating with a very high number of periods, for an electro-optical switch, and for an anisotropic groove waveguide. The results prove stability of the algorithm, and comparisons with other methods show the accuracy.

Linear Theory of the Coaxial Ridge-Loaded Helical Groove Waveguide

The coaxial ridge-loaded helical groove waveguide, an all-metal slow-wave circuit, has advantages of good heat dissipation and great size, and thus is suitable for use of millimeter TWTs. In this paper, the dispersion equation of the circuit with an annular electron beam is obtained according to self-consistent field theory. The influence of various electron beam parameters on the small signal gain is investigated and discussed by the numerical computation.

Analysis of the Coaxial Ridge-Loaded Helical Groove Waveguide

The coaxial ridge-loaded helical groove waveguide is proposed in this paper. As an all-metal slow-wave circuit, it has advantages of good heat dissipation and great size, and thus is suitable for use of millimeter TWT. By means of field theory, the expressions of the dispersion equation and the coupling impedance of the coaxial ridge-loaded helical groove waveguide are obtained. The influence of various circuit dimensions on the dispersion relation and the coupling impedance is investigated by the results of numerical computation.