The nonorthogonal finite-difference-time-domain method is applied to the analysis of structures is a square coaxial waveguide to demonstrate the influence of the mesh on the results. The analysis presented provides in...
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The nonorthogonal finite-difference-time-domain method is applied to the analysis of structures is a square coaxial waveguide to demonstrate the influence of the mesh on the results. The analysis presented provides insight on how best to discretize the computational domain when modelling discontinuities with this method. Three structures, described as 90-degrees, 120-degrees, and 170-degrees bends, are used as examples in our analysis. A comparison is made with results obtained using the FEM method for the 90-degrees bend. The comparison shows good agreement between these two techniques. (C) 1995 John Wiley & Sons, Inc.
In this letter, we combine the nonorthogonal FDTD method with a perfectly matched layer (PML) absorbing boundary condition to analyze waveguide structures. This combination provides a very useful numerical tool for mo...
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In this letter, we combine the nonorthogonal FDTD method with a perfectly matched layer (PML) absorbing boundary condition to analyze waveguide structures. This combination provides a very useful numerical tool for modeling complex waveguide structures. The PML absorbing boundary condition is tested by simulation of propagation in a WR-75 rectangular waveguide. It easily gives lower than -60-dB return loss in the frequency band of interest. An E-plane, U-bend waveguide transmission line is modeled to demonstrate the usefulness of this technique. (C) 1995 John Wiley & Sons, Inc.
Planar waveguides are built up (around 300 K) in lithium iodate by means of proton implantation. The waveguide properties are investigated by a prism coupling technique (m-lines spectroscopy). Both TE and TM modes are...
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Planar waveguides are built up (around 300 K) in lithium iodate by means of proton implantation. The waveguide properties are investigated by a prism coupling technique (m-lines spectroscopy). Both TE and TM modes are used to investigate the ordinary and extraordinary indices. The reconstructed index profiles obtained with inverse WKB method, are compared to the ion concentration profile as determined by simulation (TRIM). All the measured effective index values are smaller than these of the bulk indice. Moreover, the optical barrier is relevant to a maximum index change of about 0.03.
The system of the eigenmodes propagating along an anisotropic fibre is constructed by the S-operator method. The fields of the radiation modes are shown to be unbounded at infinity in cross-section. For these modes th...
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The system of the eigenmodes propagating along an anisotropic fibre is constructed by the S-operator method. The fields of the radiation modes are shown to be unbounded at infinity in cross-section. For these modes the orthogonality relations are derived with the help of regularisation of divergent integrals. The normalising factor is demonstrated to be expressed in terms of the eigenvectors of the S-operator. The results obtained are applied to an excitation problem. The structure of the far-zone fields is analysed.
A system of coupled scalar wave equations is derived for anisotropic inhomogeneous media. Conditions of small index gradients, paraxial propagation and moderate anisotropy are used. The equations obtained serve as a b...
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A system of coupled scalar wave equations is derived for anisotropic inhomogeneous media. Conditions of small index gradients, paraxial propagation and moderate anisotropy are used. The equations obtained serve as a basis for a beam propagation method (BPM) algorithm in anisotropic media. The anisotropy slightly modifies the dispersion characteristics of diffused channel waveguides. The BPM algorithm is tested by application to Ti indiffused waveguides in LiNbO3, the principal axes of which are declined against the laboratory coordinate system about an arbitrary angle. Very good agreement with results obtained from a plane wave analysis is confirmed. The method is applied to a combined collinear acoustooptical waveguide with transverse and longitudinal variation of one off-diagonal element of the permittivity tensor. Coupling to radiation modes occurs for sufficiently high off diagonal elements.
A method for the description of the fields in finlines on anisotropic substrates is presented. The method also allows the complex tensor character of all material parameters and the influence of second-order effects, ...
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A method for the description of the fields in finlines on anisotropic substrates is presented. The method also allows the complex tensor character of all material parameters and the influence of second-order effects, such as metallisation thickness, to be taken into account. The principal boundary value problem can be described with the help of a relatively small eigen-matrix and so the numerical treatment demands little work. Numerical and measurement results are presented, and discussed, for the transmission properties and for the field and power distributions. Furthermore, a suitable definition of the characteristic impedance is introduced, having in mind CAD applications. Design procedure and measurement characteristics for nonreciprocal elements are also included.
The necessity of using effective absorbing boundary conditions (ABCs) to terminate microstrip or other planar waveguides in the FDTD method has long been appreciated but, until recently, little attention has been give...
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The necessity of using effective absorbing boundary conditions (ABCs) to terminate microstrip or other planar waveguides in the FDTD method has long been appreciated but, until recently, little attention has been given in the literature to the best choice of ABC algorithm for this purpose. Although some comparisons of ABCs are now available they, unfortunately, differ in their conclusions. In the Letter the theoretical and numerical behaviour of some published ABCs are compared and the best ABC algorithm for this application is identified.
A planar waveguide containing a nonlinear film whose thickness varies in the transverse direction can be used to simulate propagation in a one (transverse)-dimensional medium with constant refractive index but a spati...
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A planar waveguide containing a nonlinear film whose thickness varies in the transverse direction can be used to simulate propagation in a one (transverse)-dimensional medium with constant refractive index but a spatially varying nonlinearity. This idea is illustrated by finding the steady-state solutions for several examples.
Planar optical waveguides were fabricated by proton implantation at 0.8 MeV in single crystal of lithium niobate (LiNbO3;Y-cut). Their thermal stability was investigated by measuring the evolution of the ordinary effe...
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Planar optical waveguides were fabricated by proton implantation at 0.8 MeV in single crystal of lithium niobate (LiNbO3;Y-cut). Their thermal stability was investigated by measuring the evolution of the ordinary effective indices (TE modes) on thermal annealing achieved in air and in the range of 250 to 350-degrees-C. This evolution is compared to that of the nuclear damage induced by implantation effects which is analysed by channeling Rutherford backscattering. It is shown that an optical barrier does exist and optical modes can be excited, although the lattice dammage is reduced by annealing to a value as low as the one of an unimplanted sample. Since the observed thermal stability of the waveguides is rather good, proton implantation in LiNbO3 offers high potentiality for the elaboration of optical integrated devices.
It is well known that in analysing symmetric directional coupler problems only half of the cross-section need be considered, thereby shortening CPU time and reducing the computer memory needed. This simplicity disappe...
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It is well known that in analysing symmetric directional coupler problems only half of the cross-section need be considered, thereby shortening CPU time and reducing the computer memory needed. This simplicity disappears in the case of important devices such as the asymmetric directional coupler. The paper proposes a new methodology which allows fine-mesh finite difference analysis for the modal indices and field profiles of the two lowest supermodes of such an asymmetric structure.
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