Analysis of coupling between two parallel dielectric waveguides

The coupling between two parallel dielectric waveguides with a finite coupling length is investigated. The ends of the waveguides are tapered in order to reduce the scattering losses. It is shown that the taper sections can be utilized to achieve an effective coupling which is insensitive to the coupling length, thus, providing a much greater tolerance for the design and manufacturing of coupling devices.     

Mode coupling between dielectric and semiconductor planar waveguides

Computer modeling studies on four-layer silicon-clad planar dielectric waveguides indicate that the attenuation and mode index behave as exponentially damped sinusoids when the silicon thickness is increased. This effect can be explained as a periodic coupling between the guided modes of the lossless structure and the lossy modes supported by the high refractive index silicon. Furthermore, the attenuation and mode index are significantly altered by conductivity changes in the silicon. An amplitude modulator and phase modulator have been proposed using these results. Predicted high attenuations in the device may be reduced significantly with a silicon dioxide buffer layer.     

Analysis of rib dielectric waveguides

An analysis of rib dielectric waveguides based on a mode matching technique is presented. When the constituent slab guides support only one guided mode, it is shown that the cutoff condition for the higher order modes is the same as the result of the effective dielectric constant method. However, when the rib region is thick enough to support two guided slab modes, the cutoff conditions are significantly different. For this case universal design curves are produced and plotted. The results are also compared with another theory that exists to analyze such structures.     

Mutual coupling between two circular waveguides

The problem of coupling between two circular waveguides is solved using the Wiener-Hopf technique. Expressions for the radiated, reflected, and the transmitted fields are obtained and are expressed by three terms. The first term in these expressions represents the solution for an open ended circular waveguide, while the other two are due to the interaction between the two waveguides. It is shown that, the radiated, reflected, and the transmitted fields can also be found from the reflection coefficient of an open ended circular waveguide and an evaluation of a semi-infinite integral involving the fourier transformed Green's function of the Weiner-Hopf equation. Exact solutions are used to generate the approximate solution of the ray theory of diffraction. This is achieved by expanding the exact solution and using the modified diffraction coefficient of Lee in conjunction with a spherical wave-factor.     

Condensed formula for coupling coefficients between parallel dielectric waveguides

A simple, condensed formulation for coupling coefficients between parallel dielectric waveguides is derived from a straightforward variational technique. Formulas are given for weak or strong guidance.     

Characteristics of coupling between parallel-plate waveguides with and without dielectric plugs

An analysis is presented of the coupling between parallel-plate waveguides excited in TE modes. Integro-differential equations are formulated for finite arrays of such waveguides with arbitrary widths and spacings. The waveguides, moreover, may be loaded with dielectric plugs having different dielectric constants and thicknesses. Solutions to these equations are effected by the method of moments. Extensive numerical data are obtained for the coupling between two waveguides, and their characteristics are examined in detail. The results show that in unloaded situations the coupling diminishes monotonically with increasings/lambda, wheresis the separation between the waveguides andlambdais the wavelength. At a given frequency, moreover, the coupling for largesdecreases asymptotically ass^{-3/2}. By contrast, an asymptotic dependence ofs^{-3/2}was uncovered earlier for TM-mode coupling. It is found that substantially different coupling behavior may result when the waveguides are loaded by dielectric plugs because of the excitation by the aperture discontinuity of higher order modes, which propagate inside the dielectric but are attenuated in the unloaded waveguide region. Of particular interest is the observation, under suitable conditions, of resonance characteristics in the coupling as functions of both the frequency and the thickness of the dielectric plug. These resonances are found to occur when the impedances of a certain higher order mode satisfy the transverse resonance condition, and thus are the manifestation of the resonances of such modes inside the cavity formed by the dielectric plug.     

Universal relations for coupling of optical power betweenmicroresonators and dielectric waveguides

The most basic and generic configuration, which consists of a unidirectional coupling between a ring resonator and a waveguide, is considered. The fundamental working equations required to describe the associated power transfer are derived and the application of this geometry to a variety of optical phenomena is discussed. These phenomena include `add/dropping' of optical beams, add/drop filtering and optical power switching     

Coupling of surface waves by two crossed dielectric waveguides

The coupling of surface waves by two crossed dielectric slab sections with curved transition waveguides is investigated by the method of staircase approximation. the coupling problem of the nonuniform structure is analyzed in terms of the scattering of incident surface wave by the crossed structure as a whole. The scattering characteristics of the crossed waveguides are calculated with a particular attention directed to the effect of radiation due to bending of the curved transition waveguides on coupling properties of the structure. Some useful guidelines for the design of the coupling structures are thereby suggested.     

Direct coupling between two dielectric resonators

The letter deals with a new method of calculation of direct coupling between two dielectric resonators. This method could be used for the design of microwave integrated filters. Comparison between calculated and measured values of this coupling shows good agreement.     

A transverse displacement at the junction of two planar dielectric waveguides

The guided-wave transmission and reflection coefficients, the pattern, and the energy of the radiated field are calculated as functions of the value of the displacement at the junction of two single-mode waveguides for various values of the permittivity of waveguiding layers. It is shown that the correction to the wave transmission coefficient calculated at the first and second iteration steps increases while the permittivity grows, and the way this correction increases is demonstrated.     

On the coupling characteristics of coplanar waveguides andmicrostrip lines to multilayer dielectric media

The spectral-domain technique is utilized to optimize the coupling of coplanar waveguides and microstrip lines to lossy dielectric media. It is shown that to enhance the coupling, higher frequencies should be used, the dielectric constant of the substrate should be small (∈=2.56), and the width of the center conductor and gaps should be as large as possible. The dielectric constant of the superstrate should be low if a leaky-wave type of coupling is desired or large if a strong coupling by the transverse-field components is desired. It is shown that the quasi-static TEM and TM₀ modes will be excited if a superstrate is present between a high dielectric lossy media and the coplanar waveguide     

Analysis of multilayered dielectric waveguides: variationaltreatment

A fast and near exact modal analysis is presented to obtain the propagation constants and electric field profiles for dielectric multilayered channel (rib) waveguides. Calculations are performed for a particular channel configuration and found to be in excellent agreement with those obtained using the finite difference method     

Electromagnetic coupling of coplanar waveguides and microstriplines to highly lossy dielectric media

The spectral-domain technique is utilized to analyze the coupling characteristics of coplanar waveguides and microstrip lines coupled with multilayer lossy dielectric media. Numerical results illustrating the dispersion characteristics of coplanar and microstrip lines, as well as the various electric field components coupled to highly lossy dielectric media, are presented. It is shown that the presence of a superstrate of lossless dielectric between the coplanar waveguide and the lossy medium plays a key role in setting up an axial electric field component that facilitates leaky-wave-type coupling to the lossy medium. The thickness of the superstrate relative to the gap width in the coplanar waveguide is important in controlling the magnitude of this axial electric field component. The coupling characteristics of the microstrip and coplanar lines are compared, and results generally show improved coupling if coplanar waveguides are utilized. Values of the attenuation constant α are higher for coplanar waveguide than for microstrip line, and for both structures α decreases with frequency     

Improved analysis for the coupling characteristics of tworectangular dielectric waveguides laid in different layers

A coupled-mode theory proposed by A. Hardy and W. Streifer (J. Lightwave Technol., vol.3, p.1135-46, 1985) and step-like approximation are used in this analysis. Comparison between the present result and the previous one indicates that the present approach is more useful, especially in case of strong coupling     

Radiation and near-field coupling between two collinear open-ended waveguides

An experimental and theoretical study of closely spaced collinear coupled waveguides radiating through a common perfectly conducting ground plane is described. The problem is formulated as a set of simultaneous integral equations and solved approximately by expanding the aperture field in a Fourier series. The special case of a single isolated waveguide is treated first, and the results are compared with experiment as well as with the approximate results of Lewin. Attention is given to the edge singularities. The more general case of two collinear coupled waveguide slots is solved by the same numerical method using the symmetrical properties of the geometry. Phase and amplitude of the mutual coupling are evaluated and compared with experiment. Agreement is excellent.     

Effects of high-order mode coupling in dielectric covered finitearray of dissimilar rectangular waveguides

Expressions are presented for the computation of mutual admittance between rectangular apertures of different size, in a finite planar array. The equations allow any orientation for any of the apertures, with any number of transverse electric (TE) and transverse magnetic (TM) waveguide modes. Furthermore, the expressions also include the effect of dielectric covering of these apertures. A versatile software package, useful for the design and analysis of finite phased arrays, is produced incorporating these features, and its extensive validation is provided     

Coupling characteristics of two rectangular dielectric waveguides laid in different layers

The coupling characteristic of rectangular dielectric waveguides which lay in different, parallel layers and one waveguide crossed over the other one are studied. Step-like approximation and the variational method are used for calculating the coupling coefficient which varies with axial distancez. Electromagnetic field expression for the dielectric waveguide mode of rectangular cross section is newly introduced and used. Calculated coupling characteristics are compared with experimental results carried on 50 GHz band. The principle of crossed waveguides leads us to the new design concept of "multilayered integrated circuit."     

Analysis of dielectric E-plane waveguides and design of filters

A small-size waveguide made of high-permittivity ceramic is analyzed. The propagation constants are calculated approximately by an approach where the electromagnetic fields outside the waveguide are fully taken into consideration. The analysis values agree well with the experimental values. The constants of equivalent circuit for the metallic strip section are obtained by using a separate model for the analysis of the structure. Based on these results, bandpass filters (BPF's) are designed and fabricated. The fabricated BPF's have better transmission and reflection characteristics than those designed on the basis of a trough-guide model