Dispersion Characteristics Of Waveguides Research Articles

Dispersion characteristics of arc-axis waveguides

Ultrasonic single mode excitation methods, mode separation algorithms and damage detection applications all require the calculation of the dispersion characteristics of the waveguide. However, existing dispersion calculation methods are mainly applicable to straight-axis waveguides. Therefore, in this paper, a novel semi-analytical finite element method in cylindrical coordinates (SAFEM-CC) is established and we focus on the dispersion characteristics of arc-axis waveguides. The cross-section of the waveguide can have arbitrary complex shapes, and the correctness of this method is verified by the finite element eigenfrequency method. At the same time, this paper takes the example of an arc-axis structure with a square cross-section and investigates the convergence of SAFEM-CC under different numbers of elements, element types, and element orders. This paper also establishes a finite element simulation model to study the waveform transmission law over a wide frequency range and the wave amplitude distribution law within the cross-section of arc-axis waveguides. The dispersion characteristics of arc-axis waveguides at different radii are also investigated. Finally, the correctness of the proposed method and the dispersion characteristics of arc-axis waveguides are verified by a large number of experiments. The main conclusions are as follows: the waveform transmission laws of the guided wave in arc-axis waveguides at each frequency agree with the dispersion curve; the theoretical wavestructure gives the distribution law of the amplitude within the cross-section; when the axis is arc, the displacement of the wavestructure on the inner and outer sides does not have symmetry, and the difference between the left and right sides gradually increases as the radius decreases.

ANN-based estimation of dispersion characteristics of slotted photonic crystal waveguides

ANN-based estimation of dispersion characteristics of slotted photonic crystal waveguides

Self-calibration technique for characterization of integrated THz waveguides

Emerging high-frequency accelerator technology in the terahertz regime is promising for the development of compact high-brightness accelerators and high resolution-power beam diagnostics. One resounding challenge when scaling to higher frequencies and to smaller structures is the proportional scaling of tolerances which can hinder the overall performance of the structure. Consequently, characterizing these structures is essential for nominal operation. Here, we present a novel and simple self-calibration technique to characterize the dispersion relation of integrated hollow THz-waveguides. The developed model is verified in simulation by extracting dispersion characteristics of a standard waveguide a priori known by theory. The extracted phase velocity does not deviate from the true value by more than $ 9 \times 10^{-5} ~\%$. In experiments the method demonstrates its ability to measure dispersion characteristics of non-standard waveguides embedded with their couplers with an accuracy below $ \approx 0.5~\% $ and precision of $ \approx 0.05~\% $. Equipped with dielectric lining the metallic waveguides act as slow wave structures, and the dispersion curves are compared without and with dielectric. A phase synchronous mode, suitable for transverse deflection, is found at $ 275~\text{GHz} $.

Dispersion Optimization of Silicon Nitride Waveguides for Efficient Four-Wave Mixing

Silicon nitride waveguides have emerged as an excellent platform for photonic applications, including nonlinear optical signal processing, owing to their relatively high Kerr nonlinearity, negligible two photon absorption, and wide transparent bandwidth. In this paper, we propose an effective approach using 3D finite element method to optimize the dispersion characteristics of silicon nitride waveguides for four-wave mixing (FWM) applications. Numerical studies show that a flat and low dispersion profile can be achieved in a silicon nitride waveguide with the optimized dimensions. Near-zero dispersion of 1.16 ps/km/nm and 0.97 ps/km/nm at a wavelength of 1550 nm are obtained for plasma-enhanced chemical vapor deposition (PECVD) and low-pressure chemical vapor deposition (LPCVD) silicon nitride waveguides, respectively. The fabricated micro-ring resonator with the optimized dimensions exhibits near-zero dispersion of −0.04 to −0.1 ps/m/nm over a wavelength range of 130 nm which agrees with the numerical simulation results. FWM results show that near-zero phase mismatch and high conversion efficiencies larger than −12 dB using a low pump power of 0.5 W in a 13-cm long silicon nitride waveguide are achieved.

Wave Guide Structures in an Electromagnetic Crystal with a Triangular Grid

In this paper, we study EBG-waveguides in an electromagnetic crystal in the form of a two-dimensionally periodic lattice of metal cylinders with a triangular grid. The dispersion characteristics of waveguides formed by removing one, two, and three rows of cylinders along the orthogonal axes of the crystal are obtained. A parametric analysis of the critical frequencies of the waveguide modes and eigenwaves of a homogeneous crystal is performed. Electrodynamic modeling was performed in the ANSYS HFSS system using the eigenwave mode. The optimal parameters of the electromagnetic crystal, which provide the maximal operating frequency bands of waveguides with various orientations in the grid, are obtained. The characteristics of waveguides in crystals with triangular and square grids are compared.

Mechanics of 2D Elastic Stress Waves Propagation Impacted by Concentrated Point Source Disturbance in Composite Material Bars

Green’s function, an analytical approach in inhomogeneous linear differential equations, is the impulse response, which is applied for deriving the wave equation solution in composite materials mediums. This paper investigates the study of SH wave’s transmission influenced by concentrated point source disturbance in piezomagnetic material resting over heterogeneous half-space. Green function approach is used to solve differential equation and obtain the dispersion relation in determinant form and match with existing classical Love wave equation for the authenticity for the article. The properties of SH wave throughout the considered framework and their state of relying on varied geometrical and physical parameters are scrutinized. The simulated outcomes of disparate physical quantities viz., dimensionless phase velocity, elastic parameter, group velocity, initial stress, piezomagnetic/heterogeneity parameter and stress distribution of SH wave in the considered structure are investigated and used to regulate the behavior of dispersion characteristics of smart material waveguides.

Waves in Diagonally-Oriented EBG Waveguides in Electromagnetic Crystals with a Square Lattice

Abstract—EBG waveguides in an electromagnetic crystal are studied in the form of a two-dimensionally periodic array of metal cylinders located between conducting screens. The dispersion characteristics of waveguides formed by removing one, two, and three rows of cylinders along the diagonal of a square crystal lattice are obtained. As a result of analyzing the frequency dispersion of the fundamental waveguide modes and eigenmodes of a homogeneous crystal, the factors limiting the operating frequency bands of the waveguides are determined and the lattice parameters optimal from the aspect of the band properties are obtained. The characteristics of waveguides oriented along the diagonal of the crystal lattice are compared with similar characteristics of waveguides formed along the principal axes in crystals with a square lattice.

Numerical modeling of integrated electro-optic modulators based on mode-gap shifting in photonic crystal slab waveguides containing a phase change material

This paper presents novel designs and simulation results of electro-optic modulators in integrated silicon photonics platforms. The electro-optic modulators described in this paper are based on the modulation of the photonic bandgap in a silicon photonic crystal slab waveguide, consisting of a phase change material (germanium selenide) sandwiched in between silicon layers. Three-dimensional finite difference time domain (FDTD) modeling is employed to simulate two configurations of electro-optic modulators based on mode-gap shifting in photonic crystal slab waveguides—one that is designed for operation with the transverse electric (TE) polarization of light and the other for the transverse magnetic (TM) polarization. When the electric field is applied across the germanium selenide layer surrounded by doped silicon layers, there is a change of phase of the germanium selenide layer. A large refractive index contrast between the two phases of the germanium selenide layer—i.e., between the amorphous phase and the crystalline phase—on application of the electric field is responsible for shifting of the mode gap in the dispersion characteristics of the PhC slab waveguide. Our results show excellent performance of the electro-optic modulators in terms of the high On/Off extinction ratio ( > --> 37 d B in the TE configuration and > --> 28 d B in the TM configuration), broadband switching capability ( ∼ 100 n m ), low insertion loss in the On state ( < 2 d B ), high range of tunability (by changing the lattice constant and radius of air holes), and low operating voltage ( < 4 V ). The proposed devices can be used as electro-optic modulators in future nanoscale photonic integrated circuits.

Dispersion and attenuation characteristics of steady-state microwave plasma waveguide

Near the electrostatic plasma frequency, plasma exhibits a relative permittivity near zero, and this property has been used to make transient plasma waveguides at microwave and optical wavelengths by ionizing gases with pulsed electromagnetic fields and laser radiation. However, to our knowledge, no one has constructed a steady-state RF-excited plasma waveguide for the purpose of studying its microwave attenuation and dispersion characteristics. We report here the results of investigations at 2.8–3.7 GHz of a variable-length plasma waveguide up to 30 cm long in which the plasma’s relative permittivity was as low as 0.2. De-embedded S-parameter power loss is as low as 4.6 dB and the dispersion is largely consistent with theory, although further work remains to be done.

Stretching, Amplification, and Compression of Microwave Pulses Using Helically Corrugated Waveguides

We demonstrate the possible implementation of the chirped pulse amplification (CPA) method, which is widely used in optics, for the microwave frequency band. This method is based on the preliminary elongation of the incident pulse in the stretcher, sequential amplification of spectral components in a wideband amplifier, and final compression in a line with negative dispersion (compressor). A circuit is considered in which multifold, helically corrugated waveguides are used as an operating space in each section, including a stretcher, an amplifier, and a compressor. The dispersion characteristics of such waveguides can vary significantly when its geometrical parameters are changed, which makes it possible to ensure optimal dispersion characteristics in the stretcher and compressor, as well as the largest gain bandwidth in the amplifier. In addition, these dispersive elements allow us to avoid spurious reflection of the signal due to the absence of a stopband in the operating frequency range. Simulations within the framework of the coupledwave approach showed the prospects of the circuit proposed. In particular, using an experimentally realized 30-GHz gyro-TWT, the peak power of a 200-ns, 300-W incident pulse can be increased up to 4 MW, which is about six times higher than the power of the driving electron beam. With direct amplification (in the absence of a stretcher and a compressor) of the specified incident pulse in the same gyro-TWT, the output peak power does not exceed 250 kW.

Surface plasmonic bismuth ion-doped waveguide with black phosphorus cladding.

In this paper, a waveguide device with bismuth ion (Bi+)-doped glass as the core and black phosphorus acting as the cladding is theoretically proposed. Finite-difference time-domain and numerical methods are used to elucidate the waveguide dispersion characteristics, elaborate the transverse-electric mode profiles, solve the characteristic eigenvalue equations, and calculate the gain/noise figure characteristics of the guiding medium. The numerical results show that the mode confinement factor for the fundamental mode with h=5 μm can reach 99.8%. The analytical results also indicate that with pump power fixed at 100mW, the active ion concentration fixed at 2×1027 ion/m3, the gain and noise figure of a waveguide device with 0.10m length are 34dB and 3.38dB, respectively. The proposed waveguide device is a promising candidate as a building block for various integrated photonic circuits.

Detection of high energetic alpha particle radiation through metal clad planar waveguide based sensor

In present communication, the dispersion characteristic, electromagnetic field distribution and performance parameter of a metal clad planer waveguide sensor for detection of high energetic alpha particle radiation is simulate and studied. Using the boundary matching technique, the modal equation and other necessary formulae of proposed waveguide are derived. It is observed that the dispersion characteristics of waveguide have their usual shape in presence of alpha particle radiation. The cutoff film thickness of waveguide decreases with increase of the dose of alpha particle radiation. The TE mode analysis of proposed waveguide based sensor shows the sensitivity, detection accuracy and overall performance are 153.33°/RIU, 5.75 and 1916.67 RIU−1, respectively. Our analysis also shows that the obtained detection accuracy and overall performance of proposed waveguide for TE mode analysis are sufficiently large comparison to the TM mode analysis.

Plasmonic slow light waveguide with hyperbolic metamaterials claddings

Plasmonic waveguides with an insulator core sandwiched between hyperbolic metamaterials (HMMs) claddings, i.e. HIH waveguide, are investigated for achieving wide slow-light band with adjustable working wavelength. The transfer matrix method and the finite-difference-time-domain simulation are employed to study waveguide dispersion characteristics and pulse propagation. By selecting proper silver filling ratios for HMMs, the hetero-HIH waveguide presents a slow-light band with a zero group velocity dispersion wavelength of 1.55 μm and is capable of buffering pulses with pulse width as short as ∼20 fs. This type of waveguides might be applicable for ultrafast slow-light application.

Dispersion characteristics of dielectric tube waveguide loaded with plasma for leaky wave antenna application

The leaky mode dispersion characteristics (ω-β) of a Dielectric Tube Waveguide Loaded with Plasma (DTWLP) is analytically solved and numerically computed using Muller’s complex root search algorithm with an aim to define its complex propagation constant behaviour. Consequently, complex leaky mode characteristics and its classification as guided mode, reactive mode and antenna mode have been investigated. These modal characteristics reveal wide fundamental antenna mode (TM01) with the variation in plasma density, which can find prospective application in high resolution radar and communication system where “re-tuning” of the antenna to a new frequency or making it electrically invisible is required. A computational cum simulation study is also performed using CST Microwave Studio software, which confirms our analytical findings.

Efficient Integrated Graphene Photonics in the Visible and Near‐IR

AbstractGraphene photonics has emerged as a promising platform for providing desirable optical functionality. However, graphene's monolayer‐scale thickness fundamentally restricts the available light matter interaction, posing a critical design challenge for integrated devices, particularly in wavelength regimes where graphene plasmonics is untenable. While several plasmonic designs have been proposed to enhance graphene light interaction in these regimes, they suffer from substantial insertion loss due to metal absorption. Here we report a non‐resonant metamaterial‐based waveguide platform to overcome the design bottleneck associated with graphene device. Such metamaterial structure enables low insertion loss even though metal is being utilized. By examining waveguide dispersion characteristics via closed‐form analysis, it is demonstrated that the metamaterial approach can provide optimized optical field that overlaps with the graphene monolayer. This enables graphene‐based integrated components with superior optical performance. Specifically, the metamaterial‐assisted graphene modulator can provide 5‐fold improvement in extinction ratio compared to Si nanowire, while reducing insertion loss by one order magnitude compared to plasmonic structures. Such a waveguide configuration thus allows one to maximize the optical potential that graphene holds in the telecom and visible regimes.

Analysis of in-plane wave propagation in periodic structures with Sierpinski-carpet unit cells

In this study, the dispersion relationships and characteristics of directional periodic structure waveguides with Sierpinski carpet unit cells were investigated. Finite element method was used to analyze the Sierpinski-carpet periodic structures with square Pb cylinders inserted in the rubber background. The dispersion curves of unit cells with different stages were investigated first, then group velocities of periodic structures at given frequencies were calculated and used to analyze the directional waveguide characteristics in the Sierpinski-carpet periodic structures. The dynamic responses of finite periodic structures were investigated to observe the directional features, and the results were used to support the fact that Sierpinski carpet unit cells with different stages can control the propagation behavior of elastic waves in specific ways; the dispersion curves grew compressed as the stage increased. Multiple band characteristics were observed in the case of the second-stage fractal configuration. The directional propagation characteristics in Sierpinski carpet periodic structures can be utilized to further extend the range of vibration reduction zones. The results of this study have significant potential in terms of the application of Sierpinski-carpet periodic structures for vibration isolation.

Dispersion characteristics of nanometer-scaled silicon nitride suspended membrane waveguides**Project supported by the National Natural Science Foundation of China (Nos. 61435002, 61527823 61321063).

We investigate the dispersion properties of nanometer-scaled silicon nitride suspended membrane waveguides around the communication wavelength and systematically study their relationship with the key structural parameters of the waveguide. The simulation results show that a suspended membrane waveguide can realize anomalous dispersion with a relatively thinner silicon nitride thickness in the range of 400 to 600 nm, whereas, for the same membrane thickness, a conventional rib or strip silicon nitride waveguide cannot support anomalous dispersion. In particular, a waveguide with 400 nm silicon nitride thickness and deep etch depth (r = 0.05) exhibits anomalous dispersion around the communication wavelength when the waveguide width ranges from 990 to 1255 nm, and the maximum dispersion is 22.56 ps/(nm·km). This specially designed anomalous dispersion silicon nitride waveguide is highly desirable for micro-resonator based optical frequency combs due to its potential to meet the phase-matching condition required for cascaded four-wave-mixing.

Modeling of single mode optical fiber having a complicated refractive index profile by using modified scalar finite element method

A numerical method based on modified scalar finite element method (SC-FEM) is presented and programmed on MATLAB platform for optical fiber modeling purpose. We have estimated the dispersion graph, mode cut off condition, and group delay and waveguide dispersion for highly complicated chirped type refractive index profile fiber. The convergence study of our FEM formulation is carried out with respect to the number of division in core. It has been found that the numerical error becomes less than 2 % when the number of divisions in the core is more then 30. To predict the accurate waveguide dispersion characteristics, we need to compute expression $$\frac{{{\text{d}}^{2} \left( {\text{vb}} \right)}}{{{\text{dv}}^{2} }}$$ numerically by the FEM method. For that the normalized propagation constant b (in terms of $$\beta$$ ) should be an accurate enough up to around 6 decimal points. To achieve this target, we have used 1 million sampling points in our FEM simulations. Further to validate our results we have derived the higher order polynomial expression for each case. Comparison with other methods in calculation of normalized propagation constant is found to be satisfactory. In traditional FEM analysis a spurious solution is generated because the functional does not satisfy the boundary conditions in the original waveguide problem, However in our analysis a new term that compensate the missing boundary condition has been added in the functional to eliminate the spurious solutions. Our study will be useful for the analysis of optical fiber having varying refractive index profile.

Dispersion characteristics of optical waveguides based on ZnO nanorods

Using the method of separation of variables in the cylindrical coordinate system, the problem of propagation of electromagnetic waves in a 2D periodic lattice of ZnO nanwaveguides covered with a thin metal film is solved. Comparison of calculation results with results of simulation with the use of the COMSOL Multiphysics™ package based on the finite-element method is performed. The obtained results are used for forecasting the resonance wavelengths of a 2D periodic lattice of ZnO nanorods grown on a dielectric substrate.

A systematic asymptotic approach to determine the dispersion characteristics of structural-acoustic waveguides with arbitrary fluid loading

Structural-acoustic waveguides of two different geometries are considered: a 2-D rectangular and a circular cylindrical geometry. The objective is to obtain asymptotic expansions of the fluid–structure coupled wavenumbers. The required asymptotic parameters are derived in a systematic way, in contrast to the usual intuitive methods used in such problems. The systematic way involves analyzing the phase change of a wave incident on a single boundary of the waveguide. Then, the coupled wavenumber expansions are derived using these asymptotic parameters. The phase change is also used to qualitatively demarcate the dispersion diagram as dominantly structure-originated, fluid-originated or fully coupled. In contrast to intuitively obtained asymptotic parameters, this approach does not involve any restriction on the material and geometry of the structure. The derived closed-form solutions are compared with the numerical solutions and a good match is obtained.