Attenuation in wall-impedance waveguides: a new approach

The Rayleigh-Schroedinger power expansion of perturbed eigenvalues is used to determine propagation constants in wall-impedance waveguides, the final objective being a design procedure for trunk-communication waveguides. Examples of applications, where corrections up to the fifth order are accounted for, include ideal helix waveguides and thickly dielectric-lined circular waveguides.     

Numerical modeling of second harmonic generation in opticalwaveguides using the finite element method

A numerical study of second harmonic generation (SHG) in optical waveguides is presented using the finite element method (FEM) and the Crank-Nicholson split-step procedure. Results are given for a Cherenkov radiation scheme in both planar and channel waveguides. Also presented are results obtained on frequency doubling for guided modes in both planar and channel waveguides, using the quasi-phase-matching scheme     

In situ measurement of absorption and emission cross sections in Er3+-doped waveguides for transitions involving thermalizedstates

An application to transitions involving thermalized states of a procedure based on the McCumber theory to determine emission and absorption cross sections in waveguides from transversal fluorescence spectra is presented. The procedure is tested in Er-doped Ti:LiNbO₃ waveguides to provide accurate cross-section values for the recently attractive 550-nm band. We also study the excited-state absorption transition around 860 nm and present, to our knowledge, the first published cross-section values for this transition     

Approximation Technique for Dielectric Loaded Waveguides

An algebraic procedure is described which yields approximate values for the cutoff frequencies and propagation constants of dielectric-loaded waveguides. The procedure is demonstrated for a waveguide completely filled with an anisotropic dielectric and for waveguides partially filled with isotropic dielectrics. For the latter case results are tabulated for five types of waveguide loading. The symmetrically loaded waveguide is used to show the accuracy which may be expected. This procedure is shown to be identical with the Rayleigh-Ritz variational method but with the advantage that it provides a systematic approach to improve the accuracy and to handle a multitude of waveguide geometries.     

Process and waveguide parameter relationships for the design of planar silver ion-exchanged glass waveguides

In this paper the experimental results of diffusion studies and modal characterization of Ag⁺-Na⁺exchanged glass waveguides are presented. Empirical relations between the process and the device parameters are derived and subsequently used to formulate a systematic procedure for fabricating single- and multimode waveguides.     

Theoretical S-bend profile for optimization of optical waveguideradiation losses

High-density optical integrated circuits require curved waveguides with low radiation losses. The optimization of S-bend profiles that produce a minimum of pure bending losses is considered. The analytical profile that optimizes these losses in low-slope S-bends is presented, assuming an exponential representation for the bending losses per unit length. On the other hand, a numerical optimization procedure has been developed for curved waveguides with an arbitrary representation of the unitary bending losses. Some results are provided for LiNbO₃ waveguides, including a comparison between the optimal profile and other usual S-bend profiles     

Buried ion-exchanged glass waveguides using field-assisted annealing

Theoretical and experimental studies on buried ion-exchanged waveguides using field-assisted annealing (FAA) in erbium-doped phosphate glasses are reported. The procedure for making buried waveguides with the use of a two-step process is demonstrated. An analytical model for the FAA process was developed to simulate the experimental conditions, and both the refractive index profiles and the effective buried depths of these waveguides are predicted. The mode intensity profiles as well as the buried depths are measured, and the measured data are in good agreement with the simulated results.     

A Design Procedure for High-Performance, Rib-Waveguide-Based Multimode Interference Couplers in Silicon-on-Insulator

Single mode silicon-on-insulator rib waveguides offer a weak lateral confinement, which makes it difficult to design high-performance multimode interference couplers (MMIs) based on these waveguides. Here, a complete design procedure for single etch step MMIs with tapered rib access waveguides is presented, which yields low excess loss (0.1 dB) and good imbalance (0.02 dB). Furthermore, polarization dependence is low, and high fabrication tolerances are achieved, especially with respect to etch depth.      

Equivalent network approach for multistep discontinuities inelectron waveguides

An analysis method is described for multistep discontinuities in electron waveguides composed of semiconductor heterostructures. The method is based on a rigorous mode-matching procedure that takes into account the effects of external finite potential and spatially varying effective mass. Stress is placed on network representations to establish physical pictures of the quantum effects and to yield insight; in addition, a systematic microwave network approach is employed. The equivalent network representation is given for the waveguide modes propagating normally to the step discontinuity, and the mode-matching procedure is described for the boundary-value problem of the step discontinuity. Combining the above two procedures, the super-cascade matrix formulation is carried out, from which the reflection and transmission characteristics of multistep discontinuities in electron waveguides can be estimated. In order to show the validity and usefulness of this approach, examples are computed for constriction structures composed of three-layered electron waveguides     

Scalar analysis of arbitrarily shaped optical waveguides by full guided mode expansion method and optimized sine method

This paper shows that the full guided mode expansion method and the optimized sine method, with a rather “rigorous” procedure of determing the dimensions of reference waveguides, provide simple, fast and accurate way for the scalar analysis of arbitrarily shaped optical waveguides. Use of a smaller matrix results in good agreement with previous works.     

Low-loss, single-mode, organic polymer waveguides utilizingrefractive index tailoring

Low-loss, single-mode optical waveguides have been fabricated from photopolymerizable acrylic monomers. The material system consists of a low-index cladding resin and a high-index core resin. The two resins are miscible so that precise control over the refractive index can be obtained. This allows the fabrication of single-mode waveguides with specific cross-sectional dimensions. One advantage of this is the ability to fabricate waveguides with high coupling efficiencies to other devices such as optical fiber or semiconductor lasers. The materials adhere to a wide variety of substrates and exhibit average waveguide losses of 0.56 dB/cm at 1300 nm for single-mode waveguides. Details of the fabrication procedure, index of refraction tailoring technique, and waveguide loss data are presented     

Accurate characterization of optical filters with two-dimensionalconfinement

A rigorous numerical procedure is presented for the accurate characterization of optical filters incorporating two nonidentical coupled waveguides. Numerically simulated results are shown for InGaAsP/InP-based design indicating narrow bandwidth is achievable, by using waveguides with two-dimensional confinement. The numerical solution presented here also suggests that by using the multiple quantum well (MQW) region for a waveguide core the polarization dependent properties of the device can be compensated     

Impedance boundary method of moments for accurate and efficientanalysis of planar graded-index optical waveguides

An impedance boundary method of moments (IBMOM) is proposed to accurately and efficiently compute the propagation characteristics including the number of guided modes of general graded-index dielectric slab waveguide structures. The method is based on Galerkin's procedure in the method of moments and employs the exact impedance boundary condition at the interfaces between the graded-index region and constant-index cladding. Legendre polynomials are utilized in the field expansion. Computational results are shown for waveguides with various inhomogeneous refractive index profiles. The results indicate that typically five Legendre polynomials are sufficient for accurate solutions of the dominant TE and TM modes in optical waveguides having a finite region of inhomogeneous refractive index. Diffused optical waveguides with untruncated index profiles as well as coupled dielectric waveguides can be accurately analyzed using ten Legendre polynomials     

Transverse scattering matrix formulation for a class of waveguideeigenvalue problems

Based on the mode-matching procedure, a unified transverse scattering matrix formulation is presented for the characterization of a class of waveguide eigenvalue problems, which include not only closed but also open structures. As examples, calculations are carried out on the dispersion characteristics of ridged waveguides and their variations, nonradiative dielectric (NRD) waveguides, groove guides, microstrip lines, finlines and coplanar waveguides. Comparisons with published data are made and verify the versatility and accuracy of the method. Besides its generality, this approach is also superior to some other techniques in simplicity and numerical efficiency     

Analysis of general lossy inhomogeneous and anisotropic waveguidesby the finite-element method (FEM) using edge elements

Several finite element formulations based on edge elements have been developed in recent years, avoiding the appearance of spurious modes in waveguides. However, no formulation of this kind dealing with general lossy inhomogeneous and anisotropic waveguides has been found in the literature. In this paper, a new finite element scheme for the most general linear waveguides has been derived from vector wave equations via a Galerkin procedure. In this formulation, triangular and quadrilateral edge elements have been used in order to avoid the spurious solutions. Furthermore, the final eigensystem involves only very sparse matrices, thus allowing important savings in time and memory     

Effect of transition waveguides on dielectric waveguide directionalcouplers

The coupling of energy between two curved dielectric waveguides is investigated by the staircase approximation method, which combines the building-block approach of multimode network theory with a rigorous mode-matching procedure. Particular attention is directed toward two major effects of transition waveguides on the performance of directional couplers composed of dielectric waveguides: one is the change in the coupling length, the other is the radiation loss. The coupling problem is analyzed in terms of the scattering of an incident guided mode by the coupler structure as a whole. Numerical results are given to illustrate the coupling characteristics of various structures and to establish useful guidelines for the design of directional couplers     

Matching and mutual coupling characteristics of the elements of a finite waveguide array with an impedance flange

Matching and mutual coupling characteristics of the elements of a waveguide antenna array consisting of a finite number of aperture radiators with a finite flange are analyzed. The radiators are formed by semi-infinite cylindrical waveguides of an arbitrary cross section. The array radiates into a plane-layered medium. The solution procedure is based on the single-mode variational approach. Numerical results are presented for an array consisting of nine apertures of rectangular waveguides.     

Exact multilayer waveguide design including absorbing or metal layers

Multilayered slab waveguides with absorbing or metal layers have complex propagation constants. A novel and exact numerical procedure is introduced for finding these. The procedure is validated on a model useful in device applications, with metal cladding and a buffer layer.<>     

Computation of cutoff wavenumbers of TE and TM modes in waveguidesof arbitrary cross sections using a surface integral formulation

A procedure is described for obtaining the cutoff wave numbers of transverse electric (TE) and transverse magnetic (TM) modes in waveguides of arbitrary cross section. A surface integral equation approach is used in which the E-field equation has been transformed into a matrix equation using the method of moments. An iterative technique is used to pick the eigenvalues of the solution matrix which corresponds to the waveguide cutoff wave numbers. The salient features of this technique are its speed, its simplicity, and the absence of any spurious modes when waveguides of arbitrary cross section are treated. The first four modes are tabulated for various waveguides, and the results are in very good agreement with published data     

Phase constants and scattering electromagnetic properties of circular dielectric waveguides

A variational method, based on the telegraphist's equations, is used to calculate the dispersion and scattering characteristics of circular dielectric waveguides which arc enclosed by perfectly conducting walls of rectangular cross-section. Our propagation solutions are compared with those obtained by other authors and the convergence of the method is evaluated. A procedure which combines this variational method with the modal matching technique was implemented in order to analyse multiple discontinuities in cyclindrical dielectric waveguides. To verify the usefulness and accuracy of the procedure, theoretical and experimental results were obtained for different dielectric guiding structures, connected by means of abrupt and gradual transitions. The experimental values show a good agreement with the theoretical ones.