Analysis Of Leaky Modes Research Articles

Solving leaky modes on a dielectric slab waveguide involving materials of arbitrary dielectric anisotropy with a finite-element formulation

A planar optical waveguide mode solver is established based on a finite-element (FE) formulation for determining the guided and leaky modes that exist on waveguides made of anisotropic materials with an arbitrary permittivity tensor, for example, with arbitrary optic-axis orientation in the uniaxially anisotropic material case. Correct numerical determination of the complex effective index, especially its imaginary part that gives the modal leakage, is particularly emphasized referring to available analytical solutions. For the situation when the optic axis changes its direction only in the plane parallel to the waveguide interface planes, analytical characteristic equations for solving purely guided and leaky modes are separately derived in a more systematic manner compared with prior analytical formulae reported more than three decades ago, with the obtained complex effective indices agreeing excellently with FE solutions. It is found that in the FE analysis of leaky modes, the thickness of the perfectly matched layer (PML) and the PML theoretical reflection coefficient should be properly chosen. The FE formulation is based on either the three electric-field components or the three magnetic-field components using quadratic nodal bases, resulting in a quadratic eigenvalue equation that is then solved by the shift-and-invert Arnoldi method.

Periodic Leaky-Wave Antenna for Millimeter Wave Applications Based on Substrate Integrated Waveguide

Substrate integrated waveguides (SIW) are built up of periodically arranged metallic via-holes or via-slots. The leakage loss of SIW structures increases with the distance between the via-holes or via-slots. An open periodic waveguide with a large via distance supports the propagation of leaky-wave modes and can thus be used for the design of a leaky-wave antenna. In this paper, this leakage loss is studied in detail and used to design a periodic leaky-wave antenna. The proposed concept represents an excellent choice for applications in the millimeter-wave band. Due to its versatility, the finite difference frequency domain method for periodic guided-wave or leaky-wave structures is used to analyze the characteristics of the proposed periodic leaky-wave antenna. Two modes (TE10 and TE20) are investigated and their different leaky-wave properties are analyzed. Based on the proposed leaky-mode analysis method, a novel periodic leaky-wave antenna at 28-34 GHz is designed and fabricated.

Analysis of leaky modes in deep-ridge waveguides using the compact 2D FDTD method

The compact 2D finite difference time domain method combined with the uniaxial anisotropic perfectly-matched-layer (UPML) absorption boundary condition and the Padé approximation transform has been employed in a novel method to analyse leaky modes in deep-ridge semiconductor waveguides. Compared with frequency-domain mode solvers based on complex root searching, this method is easy to implement and can calculate the mode loss and the propagation constant separately and reliably.

Analysis of leaky modes by a modified finite-element method

The finite-element method with integral boundary conditions is used to investigate leaky modes (quasi-eigenmodes) of open dielectric waveguides. Dispersion characteristics and field distributions in double-layer and multilayer circular waveguides are calculated. The influence of uniform deformations of the waveguide cross section on the properties of these modes is studied.

Analysis and design of periodic leaky-wave antennas for the millimeter waveband in hybrid waveguide-planar technology

This work presents a full-wave integral equation approach specifically conceived for the analysis and design of laterally-shielded rectangular dielectric waveguides, periodically loaded with planar perturbations of rectangular shape. This type of open periodic waveguide supports the propagation of leaky-wave modes, which can be used to build leaky-wave antennas which exhibit many desirable features for millimeter waveband applications. The particularities of the leaky-mode analysis theory are described in this paper, and comparisons with other methods are presented for validation purposes. Using this leaky-mode analysis method, a novel periodic leaky-wave antenna is presented and designed. This novel antenna shows some important improvements with respect to the features of previously proposed antennas. The results of the designed radiation patterns are validated with three-dimensional electromagnetic analysis using commercial software.

Analysis of leaky modes and Bragg fibers using transmission line equivalent T-circuits

In this letter, we have extended the transmission line (TL) technique to calculate the effective index of leaky modes and demonstrated it by using the model of Bragg fibers. From Maxwell's equations we derived a TL equivalent circuit for the Bragg fiber and we demonstrate how it can be used to determine the mode effective index. Transverse magnetic modes of Bragg fibers and mode bandgap structures can be analyzed using the TL method. Furthermore, we demonstrate that this model allows us to carry out the inverse problem and synthesize the exact refractive index profile if the desired Bragg fiber near field is available. The accuracy of the reconstructed waveguides is also examined numerically.

Accurate first-order leaky-wave analysis of antiresonant reflecting optical waveguides

We present a closed-form approximation for estimating both the field distribution and complex propagating constant of the antiresonant reflecting optical waveguide (ARROW) based on a first-order leaky-mode analysis. The formula was obtained from a novel coupled-electric-coupled-magnetic matrix method and provides six significant figures of the real part of the propagation constant beta of a SiO2/TiO2/SiO2/Si ARROW with an 8-microm core. The accuracy for the quantity of the imaginary part of beta is greater than 98.4% for the TE0 mode and 99.3% for TM0. The approximate values for field components are 96.1% accurate. In addition, a slight absorption by the substrate will result in modification of the initial improper leaky-mode behavior, which grows exponentially in the substrate, yielding a proper solution.

A novel leaky-wave antenna combining an image NRD guide and a strip circuit

This letter presents a novel leaky-wave antenna which combines an image NRD (nonradiative dielectric) guide and a printed strip circuit. The proposed structure allows for an easier, cheaper and more flexible tapering mechanism than all previous leaky-wave antennas in NRD technology. The working mechanism is explained, and two different tapering strip-circuit topologies are proposed. Cosine tapered illuminations are designed using a two-dimensional leaky-mode analysis technique. Simulations with high-frequency structure simulator (HFSS) three-dimensional analysis are presented for validation purposes. Also, the influence of the feeding transitions for each printed-circuit design is studied. Results show the feasibility of one of the proposed designs, leading to a tapered radiation pattern with sidelobes level below -20 dB.

Identifying hollow waveguide guidance in air-cored microstructured optical fibres

An analysis of leaky modes in real microstructured optical fibres fabricated specifically for photonic band gap guidance in an air core has been used to identify alternative guiding mechanisms. The supported leaky modes exhibit properties closely matching a simple hollow waveguide, uninfluenced by the surrounding microstructure. The analysis gives a quantitative determination of the wavelength dependent loss of these modes and illustrates a mechanism not photonic band gap in origin by which colouration can be observed in such fibres. These findings are demonstrated experimentally.

Introduction to the issue on integrated optics and optoelectronics

ELECTRONICS is devoted to Integrated Optics and Optoelectronics. A total of 64 submissions were received, and the referees suggested acceptance of 29. Special thanks are due to the referees who provided very rapid feedback on the papers, in most cases within a week, and in some within a day or two. The papers have been sorted into four sections: 1) modeling, simulation, and theory; 2) waveguides and passive devices; 3) active devices; and 4) detectors and receivers. The modeling section includes papers on analysis of optical structures in anisotropic media, vector integral equation methods for analyzing guides, analysis of leaky modes and bends in guides. It also includes modeling of photonic bandgap structures, modulators, wavelength-division-multiplexing (WDM) components, guide-to-fiber coupling and filters. The waveguide section has an invited paper on magnetically anisotropic devices, and papers on fabrication methods for guides and gratings and a technique for coupling fibers and guides. The active devices section has an invited paper on WDM sources, and papers on sampled grating lasers, lateral injection lasers, lasers with mode expansion techniques, rare-earth-doped dielectric waveguide lasers, semiconductor amplifiers, and potential sources in other materials. The final section on detectors includes papers on integrated detectors and photoreceivers.

Guided-mode and leaky-mode analysis by imaginary distance beam propagation method based on finite element scheme

As a simple analysis method to solve eigenmodes of optical waveguides, we present an imaginary distance beam propagation method (BPM) based on finite element scheme. The matrices used in the beam propagation analysis are essentially complex, so lossy optical waveguides can be easily treated. Moreover, employing the transparent boundary condition or perfectly matched layer boundary condition, the validity of a which has been already confirmed in the real distance BPM, we can easily treat not only guided modes but leaky ones. To show the validity and usefulness of this approach, eigenmodes of twoand three-dimensional leaky waveguides, and optical fibers are calculated.

Efficient β-formulation for the FEM analysis of leaky modes in general anisotropic channel waveguides

An efficient method to model guided and leaky modes of anisotropic dielectric waveguides with arbitratry dielectric tensor e¯¯ is presented. This method takes advantage of a particular β-formulation approach of the finite element method (FEM), leading to an optimized use of the computational resources.

Leaky Modes in Weakly Guiding Fiber Acoustic Waveguides

The analysis of leaky modes in a fiber acoustic waveguide with small differences between the acoustic parameters (Vr-, Vs, p) of its core and infinitely thick cladding is presented. These modes become ideally guided if both the shear-velocity and density differences vanish. The propagation constant of leaky modes is complex and has a small imaginary part that accounts for the attenuation of acoustic fields and power along the fiber. Aside from the attenuation coefficient, the trans- mission properties of leaky modes such as phase and group velocities, cutoff frequencies, and power flow are essentially the same as those of ideally guided modes that are independent of shear wave velocities. Furthermore, all modes are predominantly longitudinal if the differ- ence between the longitudinal velocities of the core and cladding is small. Their phase velocities lie between the two longitudinal velocities and they may not be of torsional or Stoneley wave types. The atten- uation coefficient, however, depends strongly on the shear velocity dif- ference t = lVSz - V~ssll/Vs, and is proven to be of U(t2) (subscripts 1 and 2 refer to the core and cladding regions, respectively). Waveguide materials and aspects of coupling techniques for longitudinal modes are also discussed.

Finite-element analysis of leaky waveguide antennas

A finite-element method is described for the analysis of leaky modes of open uniform waveguides with arbitrary cross-section. The field is represented by a hybrid element in the infinite exterior region, and by conventional triangular elements inside and near the waveguide. Results are presented for channel waveguide, slotted square guide and slotted circular waveguide.

Analysis of leaky modes in three‐layer nonreciprocal waveguides and its application to isolators

Analysis of leaky modes in three‐layer nonreciprocal waveguides and its application to isolators