Refractive index approximations from linear perturbation theory forplanar MQW waveguides

The mode powers and propagation constants for planar multilayer waveguides formed with multiple quantum well (MQW) materials and with the MQW layers replaced by a single uniform layer are compared. By considering linear perturbations of the solutions of the wave equation, the optimal choice of average for the dielectric constant of the substituted single layer is determined. For the case of TE modes, minimal error in the propagation constant is predicted if a weighted average of the dielectric constants of the MQW materials is used. For the case of TM modes, using a weighted average of the reciprocal of the dielectric constants is predicted to yield the minimum error. Numerical results confirm these predictions     

Optical propagation of the HE11 mode and Gaussian beams in hollow circular waveguides

The propagation of the HE₁₁ mode and Gaussian beams in hollow oversized circular waveguides is analyzed using optical theories. Different types of waveguides are considered : hollow dielectric or conducting waveguides, dielectric-lined waveguides, corrugated waveguides. General formulas are derived which give the power transmission through these different guides. The best wall materials and structures are determined from a comparison of the waveguide transmissions, at the infrared and millimeter wavelengths. The question of the coupling between the HE₁₁ mode and Gaussian beams is discussed and from a review of coupling coefficients derived before, an optimum value is pointed out. The problem of matching a Gaussian beam into circular waveguides in order to achieve the maximum power transmission is analyzed. These results are of interest for infrared lasers or waveguide applications and for Electron Cyclotron Wave (ECW) systems at the millimeter wavelength.     

Exact formulas for wave impedance and propagation constants ofhomogeneous, lossy dielectric and/or magnetic materials

Calculations of propagation constants for lossy materials are performed under the approximations of low loss (or high conductivity). To improve the understanding and better predict the analysis of such materials, exact formulation for wave impedance and propagation constants of homogeneous, lossy, dielectric/magnetic materials are proposed. Formulation is based on dielectric and/or magnetic loss tangent of the material     

Propagation Constant Below Cutoff Frequency in a Circular Waveguide with Conducting Medium

Exact and approximate propagation characteristics of normal modes in the cutoff region of a circular waveguide surrounded by a medium of finite conductivity are discussed. An exact solution is obtained by numerical analysis, and an approximate one is derived by expanding the characteristic equation considering the finite conductivity of the cylinder wall. The computed values are compared with experimental ones. It is shown that the attenuation of TM/sub 01/ mode at frequencies that are much lower than the cutoff frequency is constant, i.e., independent of frequency and the material constants of the external medium, and this mode is the most suitable one for realizing a precision circular piston attenuator.     

Analysis of bilateral coplanar waveguides printed on anisotropicsubstrates for use in monolithic MICs

The spectral-domain method is applied to the analysis of bilateral (double-sided) coplanar waveguides that are printed on electric and/or magnetic anisotropic substrates. A nondecoupling approach is used to solve the coupled differential equations for the transverse propagation constants inside the substrate. The dyadic admittance Green's function is derived for both open and shielded bilateral coplanar waveguides, taking into account the anisotropy of the material. Finally, numerical results, describing the propagation characteristics of these structures, are presented for both electric and magnetic wall symmetries     

Symmetric waves in a circular metal waveguide containing an anisotropically conducting coaxial cylindrical surface

Symmetric waves propagating in a hollow metallic waveguide that contains a coaxial cylindrical surface which conducts perfectly along helical lines with a small twist angle are investigated. It is found that, at certain ratios between the structure’s geometric parameters, there exist two modes with close propagation constants. It is shown that the superposition of these modes results in a field that, during propagation along the waveguide, periodically coincides either with the field of the E ₀₁ mode of the inner cylindrical channel (in this case, the field is zero in the coaxial area) or with the field of the H ₀₁ mode of the outer channel. A circular-waveguide E ₀₁ ? H ₀₁ mode converter has been developed and experimentally investigated. It is shown that the conversion loss does not exceed 0.8 dB.     

Propagation in a Dielectric-Loaded Parallel Plane Waveguide

A theoretical analysis of wave propagation in a parallel plane waveguide partially filled with a dielectric is performed. This transmission line is a symmetrical three-region structure consisting of two infinite parallel conducting planes with a dielectric slab of rectangular cross section between and contacting each of the planes. It has been found that TEM and TM modes cannot propagate on this structure. This investigation is concerned with TE modes, although hybrid modes can also propagate on this line. The lowest order TE mode, which is the dominant mode, has no cutoff and hence is inherently suited to extremely wide bandwidth operation. Equations have been presented for the field components, guide wavelength, cutoff criteria, power handling capabilities, wall losses, and dielectric losses as a function of the operating wavelength, waveguide dimensions, and material constants. In the case of the dominant mode, design curves covering a large range of wavelengths, dimensions, and dielectric constants are presented. For a loosely bound wave, the losses are comparable or less than those of conventional rectangular waveguide and the power handling capacity is an order of magnitude greater.     

Propagation and radiation characteristics of the circular electric,circular magnetic and hybrid waveguide modes

The field distributions and propagation constants of the circular electric, circular magnetic and hybrid modes of oversized waveguides are expressed, taking the effects of walls into account. These effects are described by wall functions which depend on surface impedances of the wall, and are determined for different types of guides. The near and far field patterns are derived in the case of real wall functions. It is shown that, for very oversized waveguides, the terms containing wall functions can be ignored in the calculations, and it results that the expressions of fields and propagation constants become independent of the types of waveguides. An application to corrugated waveguides for Electron Cyclotron Resonance Heating experiments shows the variations of the radiation characteristics versus geometric parameters of the corrugations and determines the ranges of interest for these parameters.     

Analysis of Guided Waves Along the Cladded Optical Fiber: Parabolic-Index Core and Homogeneous Cladding

This paper is concerned with the determination of the propagation characteristics of modes in the cladded optical fiber which consists of a parabolic-index core and a uniform cladding. The propagation constants of propagating modes are obtained analytically. The results are given in simple form. The asymptotic forms of the propagation constants are also given, which are valid for lower order mode propagation.     

A class of artificial materials isorefractive with free space

A new class of dispersion-free artificial material that is isorefractive with free space is presented. Materials can be fabricated by composing an array of conducting inclusions in a tenuous host medium that are symmetric with respect to the direction of propagation. Strategies are proposed for both longitudinal and radial propagation. In the presence of the transverse electromagnetic mode, the inclusions are transversely polarized and hence raise the effective relative dielectric constant of the material. The inclusions simultaneously constrict the magnetic field lines, lowering the effective permeability by the same factor. The net effect is to make an artificial material with the same speed of propagation as the host material, but with a lower effective impedance. Such a material can be used to improve aperture efficiency in impulse radiating antennas. Limitations of the materials including field enhancement due to the inclusions and skin losses due to finite conductivities are also discussed.     

Surface modes in slab waveguides with a left handed materials cover

The surface mode propagation along a dielectric slab waveguide which consists of the core and substrate of right handed materials (RHM) and the cover of left handed materials (LHM) is studied. The normalized frequency and normalized propagation constant are introduced to the left-handed material slab waveguides. The dispersion relations expressed by the normalized parameters are derived. Universal dispersion curves are obtained analytically. Based on that, the dispersion properties differ dramatically for d...     

Intrinsic modes of radiation in ferrite patch antennas

We have found two types of radiation modes for patch antennas loaded with ferrite materials. Each mode of radiation is a linear combination of normal modes of propagation in parallel plate waveguide separated by a slab of ferrite material. We have introduced new boundary conditions in which only TE modes of oscillation in the patch antenna cavity result. According to different propagation directions relative to the applied DC field these TE modes are distinguished as transverse modes and longitudinal modes, and they possess mutually perpendicular radiation polarizations. While the longitudinal TE modes are found to form discrete modes in the frequency domain, the radiation frequency of a transverse TE mode can be continuously tuned over a wide frequency range by varying the biasing magnetic field. Circularly polarized radiations may result from simultaneous excitations of these two modes. Ferrite patch antennas of square geometry have been fabricated and tested. The measured resonant frequencies compared very well with our theory     

Non-radiative phenomenon in couple dielectric guide

The solutions of electromagnetic field equations for non-radiative coupled dielectric guides are derived using mode matching technique. Dispersion curves are plotted for various dielectric materials and dimensional parameters. The non-radiative phenomenon in the coupled dielectric guide has been discussed in detail. The hybrid directional couplers in the above configuration have been theoretically designed by computing the normalized propagation constants. The superiority of such directional couplers is discussed.     

Properties of high-Tc superconducting circular waveguides with Meissner boundary

The propagation properties of the TE-modes in a high-temperature superconducting circular waveguide using the Mei\ner boundary conditions on the wall are presented for the first time. The results show that now the normalized cutoff parameterk _c R, (whereR is the radius of the superconducting circular waveguide andk _c the cutoff wavenumber,) is dependent on the radius unlike conventional metallic circular waveguide whose normalized cutoff parameterk _c R is a constant for a given mode and the filled dielectrics. Instead of TE₁₁-mode now TE₀₁ mode becomes the dominant mode and the normal component of magnetic field for the dominant mode is not equal to zero on the wall. Other unique results of high-T _c superconducting circular waveguides are illustrated, too.     

Coupled modes of multiwaveguide systems and phased arrays

A new theory describing coupled mode propagation in an array of arbitrary optical waveguides is developed. The formulation unambiguously accounts for real and/or imaginary index perturbations and its solutions yield supermode patterns and propagation constants. Several examples of coupled TE slab waveguides are evaluated and the results are shown to compare very favorably with exact solutions. The calculated propagation constants and mode patterns differ quantitatively and qualitatively from those derived from the prior theory. In particular, the supermode gains derived according to the new theory agree very well with exact solutions and predict different supermode ordering and splitting than those derived by the prior theory.     

Guided Waves in Inhomogeneous Focusing Media Part I: Formulation, Solution for Quadratic Inhomogeneity

This work is a theoretical study of waves in a circular-cylindrical radially inhomogeneous guiding medium. A vector theory based upon Maxwell's equatious is used to derive linear homogeneous fourth-order equations satisfied by the longitudinal electric and magnetic field components for a medium in which the permittivity decreases monotonically from the propagation axis. The percentage change of permittivity from the guide axis to some radius a is assumed small. For modes with propagation constants approximately equal to the wave number at guide center, all field components are shown to satisfy second-order differential equations. In particular, all transverse field components are proportional to a single scalar function. In a Iossless system with no containing boundary, a new class of polynomial-Gaussian solutions describes the longitudinal fields for the case of a quadratically decreasing permittivity, while the transverse fields are Gaussian-Laguerre. Mode patterns, propagation constants, and orthogonality relations are given. It is shown analytically that the modes tend to TE or TM as the mode order increases. Moreover, the transverse fields become dominant at large wave numbers, and the fields become tightly bound to the guide axis as the wave number and/or inhomogeneity increases. Studies of more general permittivity variations and wall effects will be reported shortly.     

Optimization of Prussian Blue Coated NaDyF4:x%Lu Nanocomposites for Multifunctional Imaging‐Guided Photothermal Therapy

Imaging‐guided photothermal therapy based on functional nanomaterials has recently received significant attention and the selection of functional materials with optimal imaging and therapy effect is extremely important. In this work, NaDyF₄‐based nanoparticles with varying size are synthesized by doping with different amounts of lutetium ions. To obtain an optimized material, the influence factor of magnetic resonance, X‐ray attenuation, and photothermal properties are discussed in detail. Then, NaDyF₄:50%Lu@Prussian blue (PB) nanocomposite is selected as the optimal functional material for T₁‐ and T₂‐weighted magnetic resonance imaging, X‐ray computed tomography, and photothermal imaging‐guided photothermal therapy of tumor on a small animal model, and the treatment is applied with good results. Studies also suggest that the NaDyF₄:50%Lu@PB nanocomposites are biocompatibile. The selection of an optimal material from a multi‐perspective study has provided an incentive for the development of an assortment of novel multifunctional materials for early cancer multifunctional diagnosis and imaging‐guided photothermal therapy.     

Resonance characteristics of whispering-gallery modes in anelliptic dielectric disk resonator

This paper presents a novel calculation method for resonance characteristics of an elliptic dielectric disk resonator. In the elliptic resonator, electromagnetic energy propagates as a whispering gallery (WG) mode along the edge region of the dielectric disk. In the novel analysis, a local propagation constant of the WG mode at each point of the elliptic disk edge is represented by a propagation constant of a WG mode in a circular disk whose radius of curvature, material constants, and thickness are equal to those of the elliptic disk. Therefore, we can easily calculate the resonance characteristics of the elliptic dielectric disk resonator by applying a conventional technique for the circular dielectric disk. The calculated results of the resonant frequencies and field distribution are well confirmed by experiments     

A Perturbation Method for the Analysis of Wave Propagation in Inhomogeneous Dielectric Waveguides with Perturbed Media

This paper presents a perturbation method for determining the modes and the propagation constants of TE and TM waves in inhomogeneous dielectric waveguides whose index distributions depart from well-known profiles; e.g., a parabolic profile for which exact solutions can be obtained. Applying the variable-transformation technique to the wave equations, the wave-equation problem is transformed into the related-equation problem. The approximate solutions of the wave equations are obtained solving the related equation. The method is applied to the analysis of lower order mode propagation in a near-parabolic-index medium. The first-order field functions and the second-order propagation constants are given.     

EM Wave Propagation in Ferrite-Filled Transversely Magnetized Circular Waveguide

This paper presents a rigorous method of solving Maxwell's equations for ferrite-filled transversely magnetized circular waveguide. Solutions for cylindrical coordinate system are derived by using power series expansion of the field's potentials. Complex propagation constants are obtained by applying boundary conditions and representing fields in partial cylindrical modes. Plane wave representation of propagation is also considered. Numerical calculations of the propagation constants as well as the dominant waveguide mode reflection and transmission from a ferrite-filled waveguide section are presented.